Donald R Uhlmann

Interests

No activities entered.

Courses

Scholarly Contributions

Journals/Publications

• Silvestry-Rodriguez, N., Bright, K. R., Slack, D. C., Uhlmann, D. R., & Gerba, C. P. (2008). Silver as a residual disinfectant to prevent biofilm formation in water distribution systems. Applied and Environmental Microbiology, 74(5), 1639-1641.
  More info

  PMID: 18192431;PMCID: PMC2258619;Abstract: Biofilms can have deleterious effects on drinking water quality and may harbor pathogens. Experiments were conducted using 100 μg/liter silver to prevent biofilm formation in modified Robbins devices with polyvinyl chloride and stainless steel surfaces. No significant difference was observed on either surface between the silver treatment and the control. Copyright © 2008, American Society for Microbiology. All Rights Reserved.
• Silvestry-Rodriguez, N., Bright, K. R., Uhlmann, D. R., Slack, D. C., & Gerba, C. P. (2007). Inactivation of Pseudomonas aeruginosa and Aeromonas hydrophila by silver in tap water. Journal of Environmental Science and Health - Part A Toxic/Hazardous Substances and Environmental Engineering, 42(11), 1579-1584.
  More info

  PMID: 17849299;Abstract: This study was conducted to assess the efficacy of silver as a secondary disinfectant to replace or reduce the level of chlorine utilized in water distribution systems. Pseudomonas aeruginosa and Aeromonas hydrophila are opportunistic pathogens present in drinking water and have been associated with waterborne disease. After 8 hours of exposure to 100 μg/L of silver, there was a >6-log10 reduction in P. aeruginosa in tap water at room temperature at pH7 and a 5.55-log10 reduction in the presence of 3 mg/L humic acid. Similar reductions were observed at pH9. At 4°C, reductions greater than 4-log10 were observed after 24 hours. For A. hydrophila, a >6-log10 reduction occurred at both pH7 and pH9 within nine hours. The World Health Organization has determined that this amount of silver could be used for water disinfection without health risks. Furthermore, silver shows promise as a secondary disinfectant, even in the presence of organic matter in concentrations that would reduce the effectiveness of free chlorine. Copyright © Taylor & Francis Group, LLC.
• Uhlmann, D. R. (2005). Michael C. Weinberg, a personal reminiscence. Journal of Non-Crystalline Solids, 351(18), xi-xii.
• Uhlmann, A. T., Uhlmann, D. R., & Workman, S. (2004). Distress of clinicians with decisions to withhold or withdraw life-support measures (multiple letters). Journal of Critical Care, 19(2), 118-120.
  More info

  PMID: 15236145;
• Dawley, J. T., Radspinner, R., Zelinski, B. J., & Uhlmann, D. R. (2001). Sol-gel derived bismuth titanate thin films with c-axis orientation. Journal of Sol-Gel Science and Technology, 20(1), 85-93.
  More info

  Abstract: Bismuth titanate (Bi4Ti3O12), a member of the layered perovskite family, has a unique set of ferroelectric properties, which include a high remanent polarization, low coercive field, and high Curie temperature, that make it a possible candidate for data storage applications. For this investigation, bismuth titanate, or BiT, films were fabricated via sol-gel method to examine the effect of processing on phase development and orientation. Solutions were deposited onto platinized silicon, and then heat treated for one hour at temperatures ranging from 550°C to 700°C in 100% O2. It was found that c-axis oriented BiT films could be formed at temperatures as low as 550°C by using bismuth oxide template layers, while films without bismuth oxide templating possessed a random orientation over the same temperature range.
• Denesuk, M., & Uhlmann, D. R. (2000). Influence of the intercalate species on the quasi-static electrochromic behavior of tungsten-oxide-based devices. Solar Energy Materials and Solar Cells, 62(4), 335-355.
  More info

  Abstract: The influence of the intercalate species on the quasi-static electrochromic behavior of tungsten-oxide-based devices is investigated. Two different electrolytes are used in the devices: an aqueous sulfuric acid solution, from which it is assumed that intercalation of hydrogen occurs; and a solution of lithium perchlorate in propylene carbonate, from which it is assumed that intercalation of lithium occurs. Experiments are performed in which a step-current of small magnitude is imposed through the device, and the corresponding time-dependence of the electrical potential and optical transmission are measured simultaneously. The behavior of the optical efficiency is relatively insensitive to the nature of the intercalate species, but the device potential is appreciably more sensitive to lithium intercalation than to hydrogen intercalation. The disparity in electrical behavior is likely due to increased strain effects and/or a diminished availability of sites associated with the larger lithium intercalate. It is shown that the electrical and optical behavior of the two types of devices may be related by a single linear scaling relation, indicating that the fundamental processes involved in the operation of the devices are similar.
• Uhlmann, D. R., Dawley, J. T., Poisl, W. H., Zelinski, B. J., & Teowee, G. (2000). Ferroelectric films. Journal of Sol-Gel Science and Technology, 19(1-3), 53-64.
  More info

  Abstract: The preparation and properties of ferroelectric films are reviewed. Specific attention is directed to ferroelectric films prepared by wet chemical methods. Emphasis is placed on the microstructure and properties of SBT films for memory applications, and their dependence on chemistry and processing, as well as on the effects of chemistry and processing on the properties of piezoelectric and pyroelectric films. Emphasis is placed on recent results obtained in our laboratories, including modeling of the ferroelectric behavior of films and experimental results in each of these areas. Also considered is the use of ferroelectric films in memory, piezoelectric and pyro-electric devices of various types, with specific note made of the recently-announced use of pyroelectric sensors in automobiles.
• Denesuk, M., & Uhlmann, D. R. (1999). Resistance-limited kinetics and use of equivalent circuits for electrochromic intercalation devices. Proceedings of SPIE - The International Society for Optical Engineering, 3788, 132-140.
  More info

  Abstract: The hypothesis of resistance-limited device behavior and the efficacy of equivalent circuits in modeling the behavior of electrochromic devices are considered. Two types of electrochromic systems, both based on tungsten oxide, are investigated. One is an all-solid-state-stack device, and the other is an aqueous, three-electrode cell system. The general appropriateness of the resistance-limited hypothesis is well-demonstrated, implying that diffusive processes are not important kinetically. The results suggest that development of useful equivalent circuits for electrochromic devices, which would prove invaluable for systems integration, should be pursued aggressively.
• Gudgel, T. J., Cronin, J. P., Kennedy, S. R., & Uhlmann, D. R. (1999). TiO₂ films for user-controlled photochromic applications. Proceedings of SPIE - The International Society for Optical Engineering, 3788, 50-58.
  More info

  Abstract: User-controlled photochromic devices are currently under investigation due to their unique ability to harness solar energy for coloration while retaining user control over the depth of coloration. Such devices utilize both a chromogenic electrode and a photosensitive layer. One highly active photosensitive layer of interest for this application is titania, and this paper focuses on a highly porous titania film with low scattering loss and good uniformity that is deposited from a stable colloidal suspension. The stability of the suspension along with the low temperature heat treatment and ease of coating by dip-coating provide an attractive method for the deposition of these films. The performance of a user-controlled photochromic device containing such films is described.
• Shneidman, V. A., & Uhlmann, D. R. (1999). Quenching of a Brownian oscillator. Physical Review E - Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics, 59(4), 3954-3957.
  More info

  Abstract: The thermodynamic behavior of a Brownian oscillator is a fluid with diverging viscosity is asymptotically analyzed. Its kinetics in a cooled and reheated systems with the viscosity is analyzed. An explicit expression is derived for the temperature-dependent specific heat in a quench-heating cycle.
• Suratwala, T., Davidson, K., Gardlund, Z., Collins, D., & Uhlmann, D. R. (1999). Reversing Gels and Water Soluble Colloids from Aminosiloxanes. Journal of Sol-Gel Science and Technology, 13(1-3), 553-558.
  More info

  Abstract: The unique sol/gel behavior of an organic/inorganic hybrid material synthesized from 3-aminopropyltriethoxysilane (3AS) and tetramethoxysilane (TMOS) is discussed and examined. The addition of H2O to a mixture of a basic (3AS) and an acidic (TMOS) alkoxide leads to rapid gel formation. This wet gel reverses to a sol upon heating which is attributed to the dissolution of siloxane bonds between the surfaces of colloidal particles in the gel. The reversed sol dries to an optically transparent solid which is water soluble. The water solubility and the stability of these colloidal particles are described by their aminopropyl/silanol surface and the electrostatic interactions between them using DLVO theory.
• Teowee, G., McCarthy, K. C., McCarthy, F. S., Bukowski, T. J., Davis Jr., D. G., & Uhlmann, D. R. (1999). Dielectric and Ferroelectric Properties of Sol-Gel Derived YMnO₃ Films. Journal of Sol-Gel Science and Technology, 13(1-3), 899-902.
  More info

  Abstract: There has been considerable interest in ferroelectric (FE) films especially for non-volatile memories and ultra high density DRAM applications. Such FE films typically consist of lead zirconate titanate (PZT) with novel oxide contacts, or layered perovskite such as Sr2Bi2TaO9. Recently, there have been reports of sputtered YMnO3 films which exhibit a single polarization axis and do not contain any volatile species of Pb or Bi. Single crystal YMnO3 exhibits satisfactory polarization (6 γC/cm2) and low coercive field (
• Teowee, G., McCarthy, K. C., McCarthy, F. S., Bukowski, T. J., Davis Jr., D. G., & Uhlmann, D. R. (1999). Preparation and Characterization of Sol-Gel Derived Y₂O₃ Thin Films. Journal of Sol-Gel Science and Technology, 13(1-3), 895-898.
  More info

  Abstract: Sol-gel derived Y2O3 thin films have been prepared on platinum coated silicon wafers and fired to temperatures ranging from 400°C to 750°C. Multiple coats were used to obtain films up to 0.5 μm thick with an intermediate firing of 400°C between coatings. Top Pt electrodes were sputtered to form monolithic capacitors. These films exhibited a dielectric constant of 18 and a leakage current of 1011-107 A/cm2, making them attractive candidates for high dielectric constant dielectric films in high density DRAMs.
• Uhlmann, D. R., & Teowee, G. (1999). Sol-gel science and technology: Current state and future prospects. Journal of Sol-Gel Science and Technology, 13(1-3), 153-162.
  More info

  Abstract: This paper addresses the current state and future prospects of sol-gel processing. It summarizes responses to a questionnaire received from more than four dozen leaders of the sol-gel community. Overall, the respondents remain quite sanguine about the future prospects for the field, and with numerous areas where sol-gel processing can provide unique capabilities and novel materials. The present authors acknowledge this potential, but argue that its achievement will depend upon greatly increased involvement of the sol-gel community with applications, and carrying out a much larger fraction of sol-gel research in the context of applications.
• Denesuk, M., & Uhlmann, D. R. (1998). Phenomenological analysis of the optoelectrochemical behavior of electrochromic intercalation devices. Journal of Solid State Electrochemistry, 2(3), 181-190.
  More info

  Abstract: A set of phenomenological analysis tools have been developed for the characterization of the optoelectrochemical behavior of electrochromic intercalation devices. Both step current and step potential excitations are considered. Great simplification is afforded by working with the passed charge as the primary independent variable; consideration is also given, however, to the transmission or built-in device potential as independent variables. It is shown that quasi-static intercalation efficiency curves, generated from step current measurements, can elucidate the intercalation site-energy distribution; these curves are also compared to dynamic intercalation efficiency curves obtained from step potential measurements. Quasi-static and dynamic optical efficiencies are also considered and compared. The scaling properties of some of the phenomenological parameters may be used to generate master curves which unify sets of data obtained under a variety of conditions (applied voltages, imposed currents, film thicknesses, etc.). Quantitative predictions can be made of device behavior under conditions not probed experimentally.
• Hemry, J. D., Weinberg, M. C., & Uhlmann, D. R. (1998). Lithium borate gel films prepared from aqueous solution. Journal of Materials Science, 33(15), 3853-3858.
  More info

  Abstract: Transparent, durable films of lithium diborate gel can easily be prepared on a variety of substrates from supersaturated aqueous solutions of lithium hydroxide monohydrate and boric acid by spin-coating. The gel to dried gel to glass to crystalline lithium tetraborate (Li2B4O7) transformation has been studied by infrared spectroscopy of thin films cast on potassium bromide windows. Examination by scanning electron microscopy disclosed that distinctly different crystal morphology was associated with a difference in the transformation rate observed between gel and dried gel films. Films of 250 nm to 30 μm in thickness have been produced. © 1998 Kluwer Academic Publishers.
• Shneidman, V. A., & Uhlmann, D. R. (1998). Crystallization kinetics in a glass-forming melt with retarded viscosity. Journal of Non-Crystalline Solids, 223(1-2), 48-52.
  More info

  Abstract: In conventional descriptions of nucleation and crystallization kinetics, it is usually assumed that the kinetic parameters related to the viscosity of the melt depend exclusively on the current temperature of the system. On the other hand, after a rapid quench to a low temperature, T, the viscosity, η, requires a time (τη) to reach its equilibrium value, η∝(T). Since the transient viscosity, η(t), can be much smaller than η∝ and isothermal crystallization kinetics are inversely proportional to the fourth power of the viscosity, a substantial increase in the crystallized volume fraction can be anticipated compared to what is predicted using η∝. An analytical study of this effect is presented, together with estimations of experimental observability. Typically, the latter is associated with temperatures below the glass transformation region. © 1998 Elsevier Science B.V.
• Shneidman, V. A., & Uhlmann, D. R. (1998). Does a Lennard-Jones glass exist?. Journal of Non-Crystalline Solids, 224(1), 86-88.
  More info

  Abstract: Even at large undercoolings the viscosity of a one-component Lennard-Jones fluid may be not high enough to form a glass which would be stable on a laboratory time scale. Results of molecular dynamics simulations support this view. © 1998 Elsevier Science B.V.
• Shneidman, V. A., & Uhlmann, D. R. (1998). The fast cooling/heating rate effects in devitrification of glasses. I. Number of nucleated particles. Journal of Chemical Physics, 108(3), 1094-1102.
  More info

  Abstract: We consider nucleation of crystalline phase in a glass-forming melt which is quenched at some arbitrary rate, S, and then reheated at some other (typically smaller) rate, H. In conventional (steady-state) approaches it is assumed that the nucleation rate is a function of temperature only, so that the number of nucleated crystallites is proportional to 1/S+ 1/7H. We demonstrate, however, that in general the nucleation rate depends on the quench/heating rate and that there exists an S- and H-dependent temperature region which effectively does not contribute to nucleation, so that the aforementioned scaling does not hold. An expression for the non-steady-state nucleation rate is derived analytically. In certain cases, the number of nucleated crystallites can be reduced by orders of magnitude compared to the steady-state predictions. The results are tested against numerically exact data obtained from the Turnbull-Fisher nucleation model. ©1998 American Institute of Physics.
• Shneidman, V. A., & Uhlmann, D. R. (1998). The fast cooling/heating rate effects in devitrification of glasses. II. Crystallization kinetics. Journal of Chemical Physics, 109(1), 186-195.
  More info

  Abstract: An analytical description of devitrification kinetics induced by time-dependent nucleation and growth of crystallites during a quench-heating cycle is proposed. Relevant experimental situations include differential thermal analysis (DTA) or differential scanning calorimetry (DSC). The proposed description involves very few assumptions regarding the temperature dependence of various kinetic parameters, but rather employs measured values of growth rates. It is shown that the conventional description of nucleation based on the steady-state approximation, as a rule, is inapplicable for the description of the DTA/DSC experiment for experimentally reasonable quench/heating rates. The latter is confirmed by the analysis of available experimental data on o-terphenyl and lithium disilicate. © 1998 American Institute of Physics.
• Suratwala, T., Gardlund, Z., Davidson, K., Uhlmann, D. R., Watson, J., & Peyghambarian, N. (1998). Silylated Coumarin Dyes in Sol-Gel Hosts. 1. Structure and Environmental Factors on Fluorescent Properties. Chemistry of Materials, 10(1), 190-198.
  More info

  Abstract: Several silylated coumarin dyes with different linkages and degrees of functionality have been synthesized and incorporated in both SiO2 xerogels and various solvent hosts. The absorption and fluorescence spectra were examined to explore selected structural and environmental effects on the optical properties of these dyes. Silylated dyes (also referred to as grafted or functionalized dyes) are dye molecules that have been chemically altered to provide alkoxysilane functionality allowing the active molecule to be covalently bonded to the host. Silylation of dye molecules had little effect on the absorption and fluorescence spectra in neutral solvent environments. The optical spectra of silylated dyes compared to those of their conventional counterpart were less influenced by the local chemical environment (e.g., pH) and thus allow for greater control and stability of the fluorescent properties of the dyes in different host environments. Spectroscopy during the drying/gelling of a derCoum xerogel film containing a silylated coumarin dye illustrate changes in the chemical forms of the dye molecules associated with changes in the local chemical environment of the dye.
• Suratwala, T., Gardlund, Z., Davidson, K., Uhlmann, D. R., Watson, J., Bonilla, S., & Peyghambarian, N. (1998). Silylated Coumarin Dyes in Sol-Gel Hosts. 2. Photostability and Sol-Gel Processing. Chemistry of Materials, 10(1), 199-209.
  More info

  Abstract: The photostability characteristics of numerous silylated coumarin dyes within SiO2 xerogels and SiO2:PDMS Polyceram films, and of neat silylated coumarin dye films have been determined and related to the sol-gel processing conditions and host composition. FTIR spectroscopy was used to monitor the hydrolysis reaction rates of the silylated dyes and other Si-alkoxide precursors. The silylated dyes had varying reaction rates depending on the degree of functionality and the linkage between the alkoxide and the dye. Matching the reaction rates between TMOS and the silylated dye was accomplished by prehydrolysis of the silylated dye. The photostability of the dyes in the xerogels was measured by monitoring the drop in fluorescence intensity upon pumping with a N2 laser and also by monitoring the drop in dye absorption upon irradiating the films with a UV lamp. At optimized prehydrolysis times, a silylated coumarin dye (derCoum) within a SiO2 xerogel host demonstrated a 3-fold improvement in long-term photostability compared to its unsilylated counterpart. The use of a silylated dye results in covalently bonding the dye to the host matrix, increasing the probability that the dye will be caged and inhibiting dynamic processes which can lead to photodegradation. CP-MAS 29Si NMR data for a derCoum xerogel confirmed that a large degree of dye bonding occurred. The addition of PDMS to the basic SiO2 xerogel host composition had little effect on the photostability of the dye. The neat dye films showed improved fluorescence photostability with increase in hydrolysis time. These films showed poor photostability upon exposure to UV lamp degradation due to lower thermal degradation resistance and/or thermal conductivity compared to the SiO2 xerogel films.
• Teowee, G., & Uhlmann, D. R. (1998). Modeling of a thin film pyroelectric pixel: Steady state results. Integrated Ferroelectrics, 22(1-4), 411-419.
  More info

  Abstract: Pyroelectric thin films are receiving increasing attention for the next generation of integrated room temperature uncooled IR arrays. In this study, steady state modeling of a pixel consisting of black absorber, pyroelectric, Pt, TiO2, SiO2 and Si are performed. Thermal conduction and radiative transfer are assumed to take place across this stack and at the Si substrate-air interface respectively. The effects of individual film thickness, IR chopping frequency, thermal conductivity of the thermal barrier layer and substrate thickness on pyroelectric responsivity are evaluated. At low chopping frequencies, large thermal isolation is crucial to obtain optimal pyroelectric responsivity but at high frequencies, the pyroelectric response is independent of thermal isolation. Large responsivities are also obtained by using thin Si substrates. The modeling also considers air bridge structures, typically used in microelectromechanical devices.
• Teowee, G., & Uhlmann, D. R. (1998). Modeling of a thin film pyroelectric pixel: Transient results. Integrated Ferroelectrics, 22(1-4), 421-429.
  More info

  Abstract: Pyroelectric thin films are receiving increasing attention for the next generation of integrated room temperature uncooled IR arrays. Pixel size and NETD (net equivalent temperature difference) of 50 μm and 0.005K are projected respectively. In this study, the 1-D transient response of a pixel consisting of black absorber, pyroelectric, Pt, TiO2, SiO2 and Si are performed. Thermal conduction and radiative transfer are assumed to take place across this stack and at the Si substrate-air interface, respectively. The effects of individual film thickness, IR chopping frequency, thermal conductivity of the thermal barrier layer and substrate thickness on the pyroelectric response are investigated.
• Teowee, G., Boulton, J. M., & Uhlmann, D. R. (1998). Optical and electro-optical properties of sol-gel derived ferroelectric thin films. Integrated Ferroelectrics, 20(1-4), 39-54.
  More info

  Abstract: Ferroelectric (FE) thin films have been widely studied, especially for their electrical and ferroelectric properties, such as nonvolatile FE memory and ultrahigh density DRAMs. FE films also give rise to a variety of interesting and unique optical applications, such as electro-optic switches, passive and active waveguides, second harmonic generation, optical data storage, optical diodes and photovoltaic devices. Their dielectric properties have been extensively optimized but the optical and electro-optical aspects have not been satisfactorily explored. This paper will review the latest advances in the optical and electro-optical properties of FE films, highlighted by data obtained from our laboratories. Optical (refractive index and waveguiding loss) and electro-optical (linear (r33) and quadratic (R33) electro-optic coefficients) properties will be presented. Optimization of these properties by precise tailoring of chemistry, processing conditions and microstructure is discussed. Low optical loss, i.e., < 2 dB/cm and an exceptionally high r33 value of 315pm/V from PLZT films were obtained.
• Teowee, G., Boulton, J. M., Hassan, S., McCarthy, K., McCarthy, F., Bukowski, T. J., Alexander, T. P., & Uhlmann, D. R. (1998). Sol-gel derived RuO₂-PZT-RuO₂ ferroelectric capacitors. Integrated Ferroelectrics, 18(1-4), 287-295.
  More info

  Abstract: There has been a lot of attention on novel oxide electrodes, e.g., RuO2, LaSrCoO3, YBCO, for contacts to ferroelectric capacitors. Such devices were reported to yield fatigue-free behaviors which are crucial for implementation in ferroelectric memory technology. Typical Pt/PZT/Pt capacitors fatigue as fast as after 104 cycles. In this study, sol-gel techniques are used to prepare both conducting RuO2 and PZT 53/47 thin films. Conductivity of the RuO2 films ranged was measured as 5 × 10-4 Ω-cm. Oxidized Si and platinized Si wafers were used as the substrates; Si/ SiO2/RuO2/PZT/RuO2 and Si/SiO2/Pt/RuO2/PZT/RuO2/Pt and Si/SiO2/Pt/PZT/Pt capacitors were obtained. The effect of RuO2 electrode on microstructure, ferroelectric properties and leakage characteristics will be discussed.
• Teowee, G., McCarthy, F. S., McCarthy, K. C., Dietz, B. H., & Uhlmann, D. R. (1998). Pyroelectric properties of sol-gel derived PZT thin films with various Zr/Ti ratios. Integrated Ferroelectrics, 22(1-4), 431-438.
  More info

  Abstract: Integrated pyroelectric arrays are receiving serious attention for the next generation of room temperature uncooled IR cameras. Such pyroelectric arrays are based on monolithic ferroelectric(FE) thin films. FE films with large values of reported pyroelectric coefficients include PbTiO3, Ca-doped PbTiO3, La-doped PbTiO3, PZT 53/47 and Pb(Sc0.5Ta0.5)O3. The present paper reports a systematic study of the compositional dependence of PZT thin films on their pyroelectric properties. A series of sol-gel derived PZT (lead zirconate titanate) thin films with various Zr/Ti ratios, namely, PbTiO3, PZT 20/80, PZT 35/65, PZT 53/47, PZT 65/35, PZT 92/8 and PbZrO3, were prepared on platinized Si substrates. The films were fired to 650-700°C to crystallize them into single-phase perovskite. The degree of preferred orientation, grain size and firing temperature affect the pyroelectric responses. Pyroelectric coefficients as large as 2.5 × 10-8 C/cm2-K were obtained, making such PZT thin films attractive in pyroelectric arrays.
• Teowee, G., McCarthy, K. C., McCarthy, F. S., Davis, D. G., Dawley, J. T., Zelinski, B. J., & Uhlmann, D. R. (1998). Piezoelectric properties of sol-gel derived PZT thin films with various Zr/Ti ratios. Materials Research Society Symposium - Proceedings, 493, 439-444.
  More info

  Abstract: Piezoelectric thin films are useful for application in microelectromechanical devices. A series of sol-gel derived PZT (lead zirconate titanate) thin films with various Zr/Ti ratios were prepared on platinized substrates. These films were fired to 650C - 700C to crystallize them into single-phase perovskite films, and their piezoelectric properties were measured using optical lever-based instrumentation. Large d33 piezoelectric coefficients up to 400 pm/V were obtained at the morphotropic phase boundary (PZT 53/47), making such films attractive in applications such as thin film transducers, microcantilevers and surface acoustic wave devices.
• Teowee, G., McCarthy, K. C., McCarthy, F. S., Davis, D. G., Dawley, J. T., Zelinski, B. J., & Uhlmann, D. R. (1998). Sol-gel derived Pb(Zn_1/3Nb_2/3)O₃-PbTiO₃ thin films. Materials Research Society Symposium - Proceedings, 493, 445-450.
  More info

  Abstract: A series of sol-gel derived Pb(Zn1/3Nb2/3)O3-PbTiO3 (PZN-PT) films, with various PbTiO3 contents, have been prepared on platinized Si wafers. The (1-x)PZN - xPT films fired to 700C became single phase perovskite for x ≥ 0.7. In the PZN-0.1PT films, the films still contain pyrochlore phase at a firing temperature of 850C; the perovskite phase appeared at a firing temperature of 800C. The dielectric constant increased with increasing PT content, with a peak in dielectric constant at x = 0.8. PZN-PT films with x = 0.8 exhibited dielectric constant, dissipation factor, remanent polarization and coercive field values of 600, 0.10,6 and 45 kV/cm respectively.
• Teowee, G., McCarthy, K. C., McCarthy, F. S., Dietz, B. H., Davis Jr., D. G., & Uhlmann, D. R. (1998). Sol-gel derived ferroelectric YMnO₃ films. Materials Research Society Symposium - Proceedings, 495, 327-332.
  More info

  Abstract: Sol-gel derived YMnO3 films have been prepared on platinized Si wafers. Crystallization took place at firing temperatures above about 750 C. The crystallized films were very conductive. YMnO3 films exhibited a dielectric constant of 23, a remanent polarization of 1.0 μC/cm2 and a coercive field of 12 kV/cm, all measured at -33 C. The FE loop was lossy and elliptical at room temperature but became more distinct at lower measuring temperatures or at higher measuring frequencies.
• Teowee, G., McCarthy, K., McCarthy, F., Bukowski, T. J., Alexander, T. P., & Uhlmann, D. R. (1998). Dielectric and ferroelectric properties of sol-gel derived BiFeO₃ films. Integrated Ferroelectrics, 18(1-4), 329-337.
  More info

  Abstract: There has been a lot of interest on ferroelectric (FE) films especially for non-volatile memories and ultra high density DRAM applications. These films such as PZT and (Ba,Sr)TiO3 are crystalline perovskite. BiFeO3 is an interesting antiferromagnetic material which belongs to the perovskite crystal structure. Sol-gel derived BiFeO3 films have been prepared on platinized Si substrates and their electrical and magnetic properties were obtained. XRD indicated that the films were crystalline perovskite when fired at 400°C and above. Dielectric constant of up to 100 was also obtained; however, the films tend to exhibit low resistivities especially in films fired to higher temperatures. The hysteretic loops obtained indicated a remanent polarization and coercive field of 5.5 μC/cm2 and 180 kV/cm respectively.
• Alexander, T. P., Uhlmann, D. R., Teowee, G., McCarthy, K., McCarthy, F., & Bukowski, T. J. (1997). Dielectric characterization of sol-gel derived Sn doped ZrTiO₄ thin films. Integrated Ferroelectrics, 17(1-4), 221-230.
  More info

  Abstract: High-quality thin film dielectric materials are critical for the next generation of integrated microwave devices. Much recent attention has been focused on ZrTiO4 and Sn doped ZrTiO4 films for applications in these devices. Sol-gel derived Sn doped ZrTiO4 thin films were prepared on Si and platinized Si wafers and fired to temperatures ranging from 550°C to 700°C. Multiple spincoating was performed to obtain films up to 0.5μm thick, with intermediate firings at 400°C between coatings. The ZrTiO4 films exhibited a dielectric constant of about 32 with low leakage currents of 2×10-9 A. These films were crystalline when fired to 700°C or above. The addition of Sn lowered the dielectric constant but also improved the dissipation factor.
• Bukowski, T. J., McCarthy, K., McCarthy, F., Teowee, G., Alexander, T. P., Uhlmann, D. R., Dawley, J. T., & Zelinski, B. J. (1997). Piezoelectric properties of sol-gel derived ZnO thin films. Integrated Ferroelectrics, 17(1-4), 339-347.
  More info

  Abstract: ZnO films exhibit a wide range of interesting material properties. Recently, ZnO films have been studied for sensing applications based . on their piezoelectric and pyroelectric behaviors. Reported literature values of piezoelectric and pyroelectric coefficients of ZnO films are in the range of 11-12 pm/V and 1.0-1.4 nC/cm2-K respectively. In this study, the piezoelectric properties of sol-gel derived ZnO thin films were measured. These films were prepared on platinized Si wafers and fired to temperatures ranging from 550°C to 750°C. Multiple spincoating was performed with an intermediate/king at 400°C between coatings to obtain films up to 6000 A thick. Top Pt electrodes were sputtered to form monolithic capacitors. XRD indicated that the films consisted of crystalline wurtzite at firing temperatures as low as 400°C, and that the c-axis orientation increased with increasing firing temperature. A dielectric constant of 10 was obtained, while piezoelectric characterization indicated d33 values as large as 12 pm/V i.e., values similar to those of bulk ZnO.
• Denesuk, M., Cronin, J. P., Kennedy, S. R., & Uhlmann, D. R. (1997). Step-current analysis of the built-in potential of tungsten oxide-based electrochromic devices and the effects of spontaneous hydrogen deintercalation. Journal of the Electrochemical Society, 144(3), 888-897.
  More info

  Abstract: General methods for the analysis of step-current measurements on intercalation devices are applied to an aqueous, protonic, tungsten oxide-based device. Plots of the built-in potential as a function of the passed charge, V bi(ΔQ), are generated. Methods are demonstrated for extracting a useful indicator of the intercalation level from ΔQ and for relating V bi to the applied potential. An intercalation efficiency, ζ, is defined, and ζ(V bi) plots are generated. With proper accounting for extraneous contributions, ζ(V bi) provides a measure of the effective site energy distribution and of the instantaneous efficiency (or capacity) of the intercalation process. A nonfaradaic spontaneous deintercalation process has been observed which acts to deintercalate the film without contributing to the measured current. Methods for including this effect in the analysis are presented in terms of a virtual current.
• Denesuk, M., Cronin, J. P., Kennedy, S. R., & Uhlmann, D. R. (1997). The relation between coloring and bleaching with hydrogen in tungsten oxide-based electrochromic devices: Step current analysis. Journal of the Electrochemical Society, 144(6), 2154-2158.
  More info

  Abstract: The relationshin between hydrogen intercalation and deintercalation (coloring and bleaching) in an aqueous tungsten oxide-based electrochromic device is presented. The built-in potential and optical transmission of the device are measured under step-current conditions; both display a hysteresis which can be explained by a two-phase model in which intercalation occurs as the parallel, equipotential filling of the two phases, but where a deintercalation barrier associated with one of the phases imposes an asymmetry. The observed data are well explained by a corresponding equivalent circuit which allows for the prediction of deintercalation behavior from intercalation behavior with a single adjustable parameter, which represents the barrier to deintercalation.
• Denesuk, M., Cronin, J. P., Kennedy, S. R., & Uhlmann, D. R. (1997). The relation between coloring and bleaching with lithium in tungsten oxide based electrochromic devices: Step current analysis. Journal of the Electrochemical Society, 144(6), 1971-1979.
  More info

  Abstract: An analysis of Li-intercalation and deintercalation in a tungsten-oxide based electrochromic device is presented. An hysteresis between intercalation and deintercalation has been separately observed in both the built-in potential and the optical efficiency of the devices. This hysteresis is explained by a two-phase model in which intercalation occurs as the parallel equipotential filling of the two phases, but where a deintercalation barrier associated with one of the phases imposes the observed asymmetry. An equivalent circuit model is given, allowing for the prediction of the deintercalation behavior from the intercalation behavior with a single adjustable parameter (representing the deintercalation barrier). The observed data are well-explained by the circuit model; using a single adjustable parameter, an accurate description of the deintercalation behavior may be obtained from the data on intercalation.
• McCarthy, F., McCarthy, K., Teowee, G., Bukowski, T., Alexander, T., & Uhlmann, D. R. (1997). Effect of measurement temperature on the dielectric and ferroelectric properties of various sol-gel derived PLZT thin films. Integrated Ferroelectrics, 17(1-4), 213-220.
  More info

  Abstract: Sol-gel derived PLZT, including PbTiO3, PbLaTiO3 28, PLZT 9/65/35 and PZT 53/47 films were prepared on platinized substrates. The dielectric and ferroelectric properties of the films were measured at 260K-580K. The values of polarization, coercive field, dielectric constant and dissipation factor in these films typically increased with increasing temperature. The changes in dielectric properties of the films with temperature were not sharp unlike the transitions in single crystals or bulk ceramics. The pyroelectric coefficients, on the other hand, decreased monotonically with increasing temperature in all these films.
• Mccarthy, K. C., Mccarthy, F. S., Teowee, G., Bukowski, T. J., Alexander, T. P., & Uhlmann, D. R. (1997). Pyroelectric properties of various sol-gel derived PLZT thin films. Integrated Ferroelectrics, 17(1-4), 377-385.
  More info

  Abstract: Pyroelectric IR imaging, especially based on monolithic technology integrated with semiconductors, is receiving increased attention for the next generation of room temperature uncooled IR cameras. In the present work, sol-gel derived PZT, including PbTiO3, PLT 28, PLZT 9/65/35, and PZT 53/47, films were prepared on platinized Si substrates. Their pyroelectric properties were determined, and are discussed with respect to film microstructures, processing, and chemistries. Pyroelectric coefficients as large as 7.7×10-8 C/cm2-K, were obtained for PZT 53/47 films.
• Suratwala, T., Davidson, K., Gardlund, Z., & Uhlmann, D. R. (1997). Control of porosity in SiO₂:PDMS Polycerams through variations in sol-gel processing and polymer content. Proceedings of SPIE - The International Society for Optical Engineering, 3136, 36-47.
  More info

  Abstract: A series of optically transparent SiO2: Polydimethylsiloxane (PDMS) Polyceram monoliths have been synthesized by two-step acid/base sol-gel processes. Two different processing routes are discussed and compared; one synthetic route (Route 1) utilizes lower water content, shorter reflux times, and faster drying conditions compared to the other synthetic route (Route 2). The Route 1 Polycerams were all essentially non-porous at all PDMS contents examined (20-80 volume % PDMS). In contrast, the porosity of the Route 2 Polycerams varied dramatically as a function of PDMS content. The surface area and pore volume for a 0% PDMS Route 2 Polyceram were 573 m2/gm and 0.59 cm3/gm, respectively; the surface area and pore volume decreased with increasing PDMS content. The amount of porosity within the Polycerams is proposed to be controlled by the relative rates of condensation and evaporation during processing and by the amount of PDMS trapped in the pores. This ideas supported by the differences in the drying behavior with processing and by the structural information obtained by magic angle spinning solid-state 29Si NMR of the Polyceram monoliths. Quantitative evaluation of the 29Si NMR and porosity data are utilized to formulate structural models of these Polycerams. The structural models are then specifically used to describe the effect of porosity on the photostabilization of a laser dye doped within these Polyceram monoliths.
• Suratwala, T., Davidson, K., Gardlund, Z., Uhlmann, D. R., Bonilla, S., & Peyghambarian, N. (1997). Molecular engineering and photostability of laser dyes within sol-gel hosts. Proceedings of SPIE - The International Society for Optical Engineering, 2986, 141-152.
  More info

  Abstract: The use of a solid-state dye laser for commercial applications has been limited largely by the poor photostability of the gain medium. Techniques are examined to improve the photostability of Coumarin and Pyrromethene-BF2 567 (PM-567) laser dyes within xerogel and Polyceram hosts synthesized by sol-gel processing. The photochemical mechanisms by which laser dyes degrade are discussed and determined specifically for PM-567. PM-567 was determined to degrade both by photo-oxidation and acid degradation. Techniques for improving photostability are described from a molecular engineering perspective. These techniques include: covalently attaching the laser dye to the host; controlling the chemical environment of the dye; increasing dye caging by increasing the SiO2 content; removing porosity from the host; and incorporating additives such as hindered amine light stabilizers to minimize photodegradation.
• Suratwala, T., Gardlund, Z., Davidson, K., Uhlmann, D. R., Bonilla, S., & Peyghambarian, N. (1997). Photostability of Silylated Coumarin Dyes in Polyceram Hosts. Journal of Sol-Gel Science and Technology, 8(1-3), 973-978.
  More info

  Abstract: Numerous silylated coumarin dyes have been incorporated within silica : polydimethylsiloxane Polyceram hosts using the sol-gel process to form crack-free, polishable monoliths. The use of silylated laser dyes allows for covalently bonding the laser dyes to their hosts. Photostability of the samples was evaluated by measuring the decrease in the dye absorption in the Polyceram upon ultraviolet lamp exposure and by monitoring the fluorescence intensity as function of pump pulses from a N2 laser at 337 nm. Both methods showed a significant improvement in photo- and thermal-stability of the silylated dye Polyceram compared to that of the unsilylated dye Polyceram at a dye : Si mole ratio of 10-4: 1. The improved stability is attributed to the immobilization and higher degree of caging of the silylated dye Polyceram with respect to the unsilylated dye Polyceram.
• Suratwala, T., Gardlund, Z., Davidson, K., Uhlmann, D. R., Bonilla, S., & Peyghambarian, N. (1997). Processing and Photostability of Pyrromethene 567 Polycerams. Journal of Sol-Gel Science and Technology, 8(1-3), 953-958.
  More info

  Abstract: Polyceram materials are attractive hosts for laser dyes because they can have high optical transparencies, high laser damage thresholds, and the ability to tailor optical properties by varying the composition and synthetic routes. Pyrromethene 567 has been successfully incorporated within silica : polydimethylsiloxane (PDMS) Polycerams to obtain polishable, crack-free, transparent monoliths using the sol-gel process. Fluorescence photostability was measured by pumping with a Q-switched, frequency doubled Nd : YAG laser (532 nm) at a pulse rate of 10 Hz. Fluorescence intensity dropped to 50% after approximately 50,000 pulses at a fluence of 0.10 J/cm2. UV degradation studies were performed on Polycerams with different polymer contents, and the absorption photostability is related to the solubility and type of caging of the dye.
• Teowee, G., Boulton, J. M., Franke, E. K., Motakef, S., Alexander, T. P., Bukowski, T. J., & Uhlmann, D. R. (1997). Optical waveguide losses of PZT thin films with various Zr/Ti stoichiometries. Integrated Ferroelectrics, 15(1-4), 281-288.
  More info

  Abstract: Sol-gel derived PZT thin films were spincoated on Corning 7059 glass substrates and fired to temperatures ranging from 500C to 600C for 30 min. The PZT compositions consisted of PZT x/y where x/y = 0/100, 20/80, 35/65, 53/47, 65/35, 80/20 and 100/0. Only single coated films were used since multiple coatings led to higher losses. XRD was used to characterize the phase assembly of the fired films and indicated that films with higher Zr contents contained proportionally more pyrochlore; while films with higher Ti contents have higher perovskite contents. UV-VIS spectroscopy was utilized to obtain the transmission and optical properties(refractive index and extinction coefficient) via the envelope method. Waveguide losses were measured using prism coupling at the 633 nm HeNe laser wavelength. The waveguide losses in the PZT films ranged from 1. 3 to 2. 0 dB/cm. The surface texture or morphology of the films significantly affected the optical losses as striated films gave losses of 2. 7 to 3. 3 dB/cm. The relatively low losses of the PZT films, together with their high values of refractive indices (2. 1 to 2. 7) make them highly attractive as waveguides in integrated optics.
• Teowee, G., Boulton, J. M., McCarthy, K., Franke, E. K., Alexander, T. P., Bukowski, T. J., & Uhlmann, D. R. (1997). Effect of PbO content on the properties of sol-gel derived PZT films. Integrated Ferroelectrics, 14(1-4), 265-273.
  More info

  Abstract: The PbO content of lead zirconate titanate(PZT) films has been widely recognized as affecting not only the phase assembly and microstructure but also the dielectric and ferroelectric properties. Excess PbO has often been incorporated in PbO-based films to optimize the film properties by compensating for PbO loss either through volatilization or diffusion into the substrates. Sol-gel derived PZT 53/47 films with various PbO contents, i.e., Pbx Zr0.53 Ti0.47O3 (x = 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.05, 1.10, 1.25 and 1.5) were prepared on platinized Si wafers and fired to temperatures ranging from 550C to 700C under oxygen. Multiple spincoating with an intermediate firing of 400C between coatings was performed to obtain films up to 0.5 urn thick. After the final crystallization firing, top Pt electrodes were sputtered to form monolithic capacitors. These capacitors were subjected to dielectric and ferroelectric characterization using an impedance analyzer and a Radiant Technologies RT66A Ferroelectric Test System. XRD was used to study the phase development and phase assembly of the fired films. The dielectric and ferroelectric properties of the films are discussed with respect to the effects of PbO content on the phase assembly, microstructure and processing conditions.
• Uhlmann, D. R., & Teowee, G. (1997). Ferroelectric thin films by sol-gel processing. Proceedings of SPIE - The International Society for Optical Engineering, 3136, 384-396.
  More info

  Abstract: A wide range of ferroelectric and pyroelectric films have been synthesized using wet chemical processing techniques. With appropriate selection of composition and precursors, and with appropriate use of processing methods to develop desired microstructures, films with exceptional combinations of properties have been prepared. The present paper will provide an overview of recent results obtained in our laboratories on ferroelectric and ZnO films, and on the integration of such films into device structures. Specific discussion will be directed to the effects of chemistry and important processing variables on the structure and properties of the resulting films. Also discussed will be the important aspects of device structures utilizing such films.
• Uhlmann, D. R., Suratwala, T., Davidson, K., Boulton, J. M., & Teowee, G. (1997). Sol-gel derived coatings on glass. Journal of Non-Crystalline Solids, 218, 113-122.
  More info

  Abstract: Sol-gel processing is a versatile method for depositing oxide based coatings on a variety of substrates in an economical manner. The present review will consider coatings deposited on glass, and will discuss a number of representative applications for such coatings, namely anti-reflection coatings, transparent conducting coatings, anti-static coatings, fluorinated coatings, coatings incorporating active dye molecules and ferroelectric coatings. © 1997 Published by Elsevier Science B.V.
• Uhlmann, D. R., Teowee, G., & Boulton, J. (1997). Future of sol-gel science and technology. Journal of Sol-Gel Science and Technology, 8(1-3), 1083-1091.
  More info

  Abstract: This paper addresses the future prospects for sol-gel processing. It includes responses from nearly two dozen leading practitioners of the sol-gel art, who were kind enough to answer a questionnaire about the present state and future directions of the field. Overall, the prospects appear quite bright; but achievement of anything like the full potential of the method will require greatly increased interaction between sol-gel specialists and device technologists.
• Alexander, T. P., Bukowski, T. J., Teowee, G., Uhlmann, D. R., McCarthy, K. C., Dawley, J., & Zelinski, B. J. (1996). Dielectric properties of sol-gel derived ZnO thin films. IEEE International Symposium on Applications of Ferroelectrics, 2, 585-588.
  More info

  Abstract: Sol-gel derived ZnO thin films were prepared on platinized Si wafers and fired to temperatures ranging from 550C to 700C. Multiple spincoating was performed with an intermediate firing at 400C between coatings to obtain films up to 6000 A thick. Top Pt electrodes were sputtered to form monolithic capacitors. Dielectric characterization indicated dielectric constants as large as 24, twice the highest value reported previously. The leakage currents decreased with increasing firing temperature. XRD indicated that the films consisted of crystalline wurtzite films at firing temperatures as low as 400C and that the c-axis orientation increased with increasing firing temperature. Piezoelectric characterization indicated d33 values as large as 17 pm/V, which is larger than any previously reported value for ZnO films.
• Bukowski, T. J., Alexander, T. P., Uhlmann, D. R., Teowee, G., & McCarthy, K. C. (1996). Preparation and characterization of sol-gel derived Bi₄Ti₃O₁₂ thin films. IEEE International Symposium on Applications of Ferroelectrics, 2, 589-592.
  More info

  Abstract: Sol-gel derived Bi4Ti3O12 thin films have been prepared on platinized Si wafers and fired to temperatures ranging from 550 °C to 700 °C. Excess Bi was incorporated in the precursor solutions to determine its effects on dielectric and ferroelectric properties. Multiple spincoating with an intermediate firing of 400 °C between coatings was performed to obtain films up to 0.5 μm thick. Single phase Bi4Ti3O12 films were obtained when fired at 600 °C which exhibited a dielectric constant of 225.
• Dawley, J. T., Teowee, G., Zelinski, B. J., & Uhlmann, D. R. (1996). Piezoelectric characterization of bulk and thin film ferroelectric materials using fiber optics. Materials Research Society Symposium - Proceedings, 433, 317-323.
  More info

  Abstract: In this study, the use of a fiber optic technique for the measurement of the piezoelectric properties of ferroelectric bulk and thin film samples was investigated. The strain and piezoelectric properties (namely the d33 coefficients) were measured using the MTI-2000 Fotonic Sensor, which uses the principle of the optical lever to resolve very small changes in sample displacement (1 angstrom). Using this technique, we were able to detect the very small strains associated with the converse piezoelectric effect for PVDF films and bulk PZT samples, and correlate the results with data acquired from direct piezoelectric effect measurement. Comparison of the data sets prove that the optical lever would be a useful optical technique for measuring of the d33 values of ceramic thin films, such as BaTiO3, ZnO, and PZT.
• Teowee, G. T., McCarthy, K., & Uhlmann, D. R. (1996). Sol-gel-derived ferroelectric films as pyroelectric detectors in imaging applications. Proceedings of SPIE - The International Society for Optical Engineering, 2746, 38-50.
  More info

  Abstract: This paper reviews the latest developments in pyroelectric devices for IR detection based on sol-gel derived ferroelectric thin films, highlighted by recent results from our laboratories. The optimization of sol-gel processing has led to ferroelectric films with pyroelectric coefficients as high as 200 nC/cm 2-K. Some modeling results of the thin film devices, which aid in device design, are also discussed. At the film level, various factors such as chemistries, microstructures and processing conditions all affect the final pyroelectric properties of the films. At the device level, processing compatibility and device layout need to be taken into account to optimize fully the device performance.
• Teowee, G., McCarthy, K. C., Alexander, T. P., Bukowski, T. J., & Uhlmann, D. R. (1996). Sol-gel derived Pb_1-xCa_xTiO₃ thin films. IEEE International Symposium on Applications of Ferroelectrics, 1, 487-490.
  More info

  Abstract: A series of sol-gel derived CaTiO3 - PbTiO3 thin films were prepared on platinized Si substrates and fired to temperatures ranging from 550C to 650C. Multiple spincoating, with an intermediate firing of 400C between coatings, was performed to obtain films up to 0.5 μm thick. All the films were single phase perovskite after firing to 600C. The dielectric constant ranged from 100-300 depending on the amount of Ca. Leakage currents as low as 2*10-9 A/cm2 were obtained in these films.
• Teowee, G., McCarthy, K. C., Baertlein, C. D., Boulton, J. M., Motakef, S., Bukowski, T. J., Alexander, T. P., & Uhlmann, D. R. (1996). Dielectric properties of organic-inorganic hybrids: PDMS-based systems. Materials Research Society Symposium - Proceedings, 435, 559-564.
  More info

  Abstract: Organic-inorganic hybrids, with tailorable properties via control of their chemistries, offer great potential for many optical, electrical and mechanical applications. PDMS-based materials have been fabricated, having low optical losses of
• Teowee, G., McCarthy, K. C., Bukowski, T. J., Alexander, T. P., Motakef, S., & Uhlmann, D. R. (1996). Optical properties of Au and Pt-doped PLT 28 films. IEEE International Symposium on Applications of Ferroelectrics, 2, 671-674.
  More info

  Abstract: Metal colloid-doped oxides yield potentially interesting non-linear optical properties especially third order non-linearity which is expected to be enhanced in oxide matrices with high values of dielectric constant or refractive index. La-doped PbTiO3 (i.e. PLT 28) films, incorporated with 0.05 to 2 mole % Au and Pt, were obtained using sol-gel deposition techniques. The films were spincoated on Corning 7059 glass substrates and fired at 400 °C - 600 °C. The films were then subjected to optical characterization, namely transmission and absorbance spectroscopy. PLT films dolled with Au appeared bluish which turned deeper with higher Au concentration or higher firing temperatures. Additionally, the absorbance peak (near 650 nm) shifted to shorter wavelengths with higher metal colloid contents but shifted to longer wavelengths at higher firing temperatures. The waveguiding loss in the Pt-doped films ranged from 2 - 3 dB/cm.
• Teowee, G., McCarthy, K. C., Franke, E. K., Boulton, J. M., Alexander, T. P., Bukowski, T. J., & Uhlmann, D. R. (1996). Dielectric and ferroelectric characterization of sol-gel derived Ca-doped PbTiO₃ thin films. Materials Research Society Symposium - Proceedings, 433, 431-436.
  More info

  Abstract: A series of sol-gel derived CaTiO3-PbTiO3 thin films (i.e. Pb1-xCaxTiO3 with x = 0-1) was prepared on platinized Si substrates and fired to temperatures ranging from 550 °C to 650 °C. Multiple spincoating was performed to obtain films up to 0.5 μm thick with an intermediate firing of 400 °C between coatings. After the final crystallization firing, top Pt electrodes were sputtered to form monolithic capacitors. These capacitors were subjected to dielectric and ferroelectric characterization using an impedance analyzer and Radiant Technology RT66A Ferroelectric Test System. XRD was used to study the phase development and phase assembly of the fired films. All compositions were single perovskite phase after firing to 600 °C. The effects of Ca content on the crystallization behavior and ferroelectric properties are discussed.
• Uhlmann, D. R., Boulton, J. M., & Teowee, G. (1996). New optical materials by wet chemical processing. Journal of Non-Crystalline Solids, 196, 26-36.
  More info

  Abstract: Wet chemical processing of ceramics, glasses and inorganic-organic hybrids for optical applications is rapidly developing. The present review focuses on optical films obtained by wet chemical processing, with emphasis on recent developments in ferroelectric and magneto-optic films, rare earth lasers and surface patterned films. Where appropriate, the subject matter is illustrated with recent results from our laboratories.
• Kim, S. J., III, D. B., Zelinski, B. J., & Uhlmann, D. R. (1995). Practical limits on up-gradient crystallization. Journal of Non-Crystalline Solids, 181(3), 291-300.
  More info

  Abstract: The kinetic processes relevant to up-gradient crystallization are analyzed in detail. Crystallization occurs upon moving an amorphous sample up through a temperature gradient which is the reverse of traditional crystallization from the melt. Both nucleation and growth processes are important to the present technique. To obtain a highly oriented microstructure, bulk nucleation must be prevented. Generally, a liquid with small nucleation rate and large crystal growth rate is favorable for the present route. The model was tested for the lithium diborate glass system, which yielded a highly oriented microstructure with only isolated additional nucleation events. © 1995.
• Motakef, S., Boulton, J. M., Roncone, R. L., Neilson, G., Teowee, G., & Uhlmann, D. R. (1995). Optical loss study of MPEOU-based polyceram planar waveguides. Applied Optics, 34(4), 721-728.
  More info

  Abstract: Sol-gel derived polyceram planar planar waveguides are investigated for their passive optical properties. Emphasis is on the attenuation of the waveguides as a function of chemistry and composition. The inorganic component's effect on the optical properties is studied in detail.
• Teowee, G., Motakef, S., Bukowski, T. J., Boulton, J. M., III, D. B., & Uhlmann, D. R. (1995). Optical losses in sol-gel derived lead lanthanum titanate waveguides. Microelectronic Engineering, 29(1-4), 323-326.
  More info

  Abstract: A series of solgel derived lead lanthanum titanate films were prepared on Corning 7059 glass substrates. Waveguiding properties of these films were studied as a function of La content and film thickness. 0.5M precursor solutions based on lead acetate, La nitrate and Ti Zr alkoxides were refluxed for 1 hour and later spincoated at various speeds on the substrates under clean room condition. Films were fired to 400C for 1 hr to burn off the organics and to consolidate the coatings. They were then fired at temperatures ranging from 500C to 600C. XRD was used to determine the phase assembly present in these films; the presence of La seemed to aid in the formation of the perovskite phase. Transmission spectra were gathered using a UV-Vis spectrometer; and the spectra were then used to calculate the refractive indices based on the envelope method. The waveguiding properties and optical attenuation were studied via prism coupling using a rutile prism. The optical losses in these films decrease with La content and also in thicker single-coated films. On the other hand, thicker films achieved by multiple coating appeared to exhibit higher losses. Crystalline PLZT 28/0/100 yielded loss of < 2 dB/cm, the lowest among reported literature values for any sol-gel or sputtered PLZT films. © 1995.
• Teowee, G., Quackenbush, E. L., Baertlein, C. D., Boulton, J. M., Kneer, E. A., & Uhlmann, D. R. (1995). Dielectric and ferroelectric properties of sol-gel derived PLZT films. Materials Research Society Symposium - Proceedings, 361, 433-438.
  More info

  Abstract: There has not been much exploration of PLZT film properties as a function of composition reported in the literature. A survey of numerous PLZT films covering a wide spectrum of the PLZT phase diagram was undertaken to explore the dependence of film properties on composition. A series of sol-gel derived PLZT films were prepared on platinized Si wafers and fired to 700 C to obtain the perovskite phase. The film compositions include PLZT x/65/35, x/20/80, x/53/47 for x = 0, 2, 4, 6, 8, 10 and 12 and 7.5/x/y where x/y = 70/30, 53/47, 20/80 and 0/100. These films were characterized for their dielectric and ferroelectric properties. The films definitely showed a strong dependence of final film properties on composition, providing a valuable tool for the material engineering of ferroelectric film properties.
• Teowee, G., Simpson, J. T., Zhao, T., Mansuripur, M., Boulton, J. M., & Uhlmann, D. R. (1995). Electro-optic properties of sol-gel derived PZT and PLZT thin films. Microelectronic Engineering, 29(1-4), 327-330.
  More info

  Abstract: Ferroelectric(FE) films exhibit interesting electro-optic (EO) properties and are utilized in devices used for second harmonic generation, spatial light modulators and optical switches. These films typically yield large values of linear and quadratic electro-optic coefficients. Solgel derived FE films namely PZT 53 47 and PLZT 28/0/100 were prepared on conductive glass substrates. 0.5M precursor solutions based on the appropriate stoichiometric amounts of lead acetate, La nitrate and Ti Zr alkoxides were refluxed for 1 hour and later spincoated on the substrates. They were the fired to 600C to crystallize them into single phase perovskite films. Top Au Pd electrodes were deposited to form the top contacts for the capacitors. The refractive indices, extinction coefficients, linear and quadratic coefficients of the films were obtained using multiangle reflection ellipsometry. These parameters were then used to calculate the linear and quadratic electro-optic coefficients of the films. The quadratic EO coefficients of PLZT 28/0/100 and PZT 53 47 films were measured to be 0.07 and 0.38 × 10-16 m2/V2 respectively while the linear electrooptic coefficients of PLZT 28/0/100 and PZT 53 47 were found to be 59 and 315 pm/V respectively, with the reff value for PZT 53 47 the highest among reported ferroelectric films in literature. © 1995.
• Denesuk, M., Cronin, J. P., Kennedy, S. R., Law, K. J., Nielson, G. F., & Uhlmann, D. R. (1994). Coloration behavior of hybrid electrochromic films. Proceedings of SPIE - The International Society for Optical Engineering, 2255, 52-61.
  More info

  Abstract: A novel synthesis of a sol-gel precursor for WO3 thin films is presented. Through addition of oxalic acid dihydrate to the precursor solution, films with different microstructures may be obtained; and these microstructures are characterized using TEM, FESEM, and SAXS. Without the additive, the films are relatively homogeneous and amorphous; with the additive, the films are multiphase, containing amorphous and crystalline regions. In addition, the latter films contain numerous small regions of apparently much higher electron density, which likely correspond to a dispersed W-rich phase. Optoelectrochemical analysis of the films under galvanostatic conditions demonstrates that the homogeneous, amorphous films display a pronounced cycling effect in both the response of the electrode potential and the optical efficiency. In contrast, the multiphase films show no significant cycling effect.
• Denesuk, M., Zelinski, B. J., Kreidl, N. J., & Uhlmann, D. R. (1994). Dynamics of incomplete wetting on porous materials. Journal of Colloid and Interface Science, 168(1), 142-151.
  More info

  Abstract: The spreading kinetics of incompletely wetting liquids on porous substrates, highlighting the competition between composite interface spreading and liquid infiltration into the porous substrate are considered. The energetic impact of the surface porosity on the advancing of the contact line is modeled by using three idealized microtopologies associated with the kinetic behavior of the liquid in the pores. The results are used to modify a previously developed hydrodynamic spreading model to include the effects of substrate porosity. The results of a previously developed model for the depletion of a liquid droplet on a porous substrate are then used to consider the interaction between the spreading and depletion processes. It is predicted that, for a wide class of situations, a major portion of the spreading process will generally be completed before liquid drainage becomes significant. A contact angle hysteresis associated with spreading on a porous substrate is predicted to occur, with the advancing angle being larger than the receding angle; and an analogy is made with spreading on a rough or pitted substrate which provides a mechanism for contact angle hysteresis on such surfaces.
• Lee, S. C., Teowee, G., Schrimpf, R. D., III, D. B., Uhlmann, D. R., & Galloway, K. F. (1994). I-V measurement method and its application for characterizing ferroelectric PZT thin films. Integrated Ferroelectrics, 4(1), 31-43.
  More info

  Abstract: A static I-V measurement method for ferroelectric thin films is developed to distinguish the leakage current from the switching current. The initial polarization state and the exponential decay behavior of the switching current are considered in this method. The feasibility of this I-V measurement method is investigated by examining fatigue effects on sol-gel derived PZT thin films. Changes in polarization due to fatigue are correlated with the changes in the switching current and the leakage current.
• Motakef, S., Boulton, J. M., & Uhlmann, D. R. (1994). Organic-inorganic optical materials. Optics Letters, 19(15), 1125-1127.
  More info

  Abstract: This paper presents the synthesis and optical characterization of class of hybrid materials called polycerams which offer the advantages of processability by techniques such as spin coating, high refractive indices by simple chemical reactions, patternability by techniques such as embossing, combined with low optical attenuations in fabricated films, making it suitable for optical applications e.g. passive waveguides. Active waveguides can be easily obtained by incorporation of lasing elements or dyes. Also gratings of different depths can be developed in the surfaces.
• Motakef, S., Suratwala, T., Roncome, R. L., Boulton, J. M., Teowee, G., & Uhlmann, D. R. (1994). Processing and optical properties of inorganic-organic hybrids (polycerams). II. PDMS-based waveguides. Journal of Non-Crystalline Solids, 178(C), 37-43.
  More info

  Abstract: Polydimethylsiloxane and the oxides of silicon, titanium and germanium have been incorporated using sol-gel chemistry to yield new polyceram planar waveguides. The waveguides exhibit superior optical properties such as losses as low as
• Motakef, S., Suratwala, T., Roncone, R. L., Boulton, J. M., Teowee, G., Neilson, G. F., & Uhlmann, D. R. (1994). Processing and optical properties of inorganic-organic hybrids (polycerams). I. MPEOU-based waveguides. Journal of Non-Crystalline Solids, 178(C), 31-36.
  More info

  Abstract: Sol-gel techniques have been employed to synthesize a number of organic-modified hybrid materials (polycerams) using a functionalized organic polymer (N-triethoxysilypropyl O-polyethylene oxide urethane) together with a range of metal alkoxides and acetates. Despite the disparate nature of the constituents, the chemistry and processing have been successfully controlled to achieve a high level of homogeneity down to the molecular level. The opticla properties (index of refraction, loss, dispersion and transmittance) of the polycerams are reported as functions of various metal oxides. These properties are then correlated to the homogeneity of the network. Polycerams of differing compositions can be easily designed and synthesized to yield low-loss ( < 1 dB / cm) optical waveguides with the desired refractive index and dispersion. © 1994.
• Teowee, G., Baertlein, C. D., Schlegel, S. A., Boulton, J. M., & Uhlmann, D. R. (1994). Effects of rare earth incorporation on the ferroelectric and dielectric properties of sol-gel derived PbTiO₃ films. Materials Research Society Symposium - Proceedings, 346, 291-296.
  More info

  Abstract: Ferroelectric (FE) films, especially PZT films, have received increasing attention for microelectronics applications such as FE memory and in high density DRAM's. While rare earth doped PbTiO3 ceramics has been studied for SAW and piezoelectric applications, rare earth-doped films seldom have been systematically explored. A series of sol-gel derived PbTiO3 films with varying amounts (5-15 mole %) of rare earths (such as, Nd, Sm, Tb, Dy, Er, Yb and La) have been prepared using acetates and alkoxides as precursors. The solutions were spin coated onto platinized Si wafers. The effects of the type and amount of rare incorporation on the phase assembly and microstructure have been quantified. The results of dielectric characterization (e.g., dielectric constant, dissipation factor and leakage currents) and FE behaviors (viz.remanent polarization, and coercive field) are presented; these films exhibited low leakage currents (3E-10 A/cm2) and much higher dielectric constant (up to 525) compared to undopeal PbTiO3 films.
• Teowee, G., Boulton, J. M., Baertlein, C. D., Wade, R. K., & Uhlmann, D. R. (1994). Effect of post-metallization annealing on the ferroelectric properties of sol-gel derived PZT thin films - Code: EP34. Journal of Sol-Gel Science and Technology, 2(1-3), 623-626.
  More info

  Abstract: A series of monolithic Pt-PZT-Pt capacitors was prepared based on sol-gel derived PZT 53/47 films fired to 700 C. After deposition of top Pt electrodes, the capacitors were subjected to post-metallization annealing (PMA) temperatures of 100 C to 700 C. Dielectric and ferroelectric (FE) characterizations were performed. Increasing the PMA temperature produced lower values of spontaneous and remanent polarizations, dielectric constant and leakage currents. The observations are correlated with a proposed FE capacitor model. © 1994 Kluwer Academic Publishers.
• Teowee, G., Boulton, J. M., Baertlein, C. D., Wade, R. K., & Uhlmann, D. R. (1994). Electrical properties of sol-gel derived La-doped PbTiO₃-containing films. Integrated Ferroelectrics, 4(3 pt 2), 231-238.
  More info

  Abstract: A series of sol-gel derived La-doped PbTiO3-containing films was prepared on platinized Si wafers. The compositions investigated include PLT (0-28 mole % La) and PLZT (e.g., 9/65/35 and 12/80/20) films. These films were fired at temperatures ranging from 500 to 750 °C. While most of the films were single-phase perovskite when fired at 700 °C, lower firing temperatures (approximately 500 °C) are sufficient to obtain crystalline PLT films, especially when the La content is more than 15 mole %. The paraelectric or ferroelectric character of the films as a function of La content is also addressed. In PLZT films, the Zr/Ti ratio affects the crystallization behavior and also the perovskite structure, i.e., either tetragonal or rhombohedral. Ferroelectric PLZT films exhibit high values of both dielectric constant (>700) and leakage current. The values of dielectric constant in the relaxor PLZT films are low, especially when compared to their bulk ceramic values (5000-10000). Paraelectric PLT films exhibit high values of dielectric constant (>500) and low leakage currents.
• Teowee, G., Quackenbush, E. L., Baertlein, C. D., Boulton, J. M., & Uhlmann, D. R. (1994). Fatigue and retention behaviors of Pt-PZT-metal capacitors with various top metallization. IEEE International Symposium on Applications of Ferroelectrics, 523-526.
  More info

  Abstract: The PZT-substrate or PZT-electrode interface can affect the FE properties and specifically the fatigue behaviour. Typical Pt-PZT-Pt capacitors exhibited fatigue resistance up to 10x - 109 cycles, while RuO2, La0.5Sr0.5CoO3 and YBa2Cu3O7 electrodes have been reported in literature to yield fatigue-free devices up to 1011 - 1012 cycles. In an early study which compared the fatigue behaviour of bulk PLZT ceramics with various metal electrodes, it was found that in offered the best fatigue performance (up to 109 cycles). A series of sol-gel derived PZT 53/47 films were fired to 700C to achieve single-phase FE perovskite films. Bottom electrode (or the substrate) consisted of sputtered Pt on oxidized Si wafers. Monolithic capacitors were obtained by depositing top electrodes of Ag, Au, Au-Pd, Pd and Pt. All the capacitors exhibited fatigue, manifested by lower values of Pr, Ec and εr but higher leakage currents after cycling.
• Uhlmann, D. R., Motakef, S., Suratwala, T., Wade, R., Teowee, G., & Boulton, J. M. (1994). Ceramic films for optical applications - Code: D7. Journal of Sol-Gel Science and Technology, 2(1-3), 335-340.
  More info

  Abstract: Recent progress is reviewed on the wet chemical synthesis of films for optical applications. Specific attention is directed to planar waveguides and to electrooptic, non-linear optical and electrochromic films, including recent results obtained in our laboratories. © 1994 Kluwer Academic Publishers.
• Aruchamy, A., Kim, S. J., III, D. B., & Uhlmann, D. R. (1993). Glass microstructure and initial crystallization of Pb_0.32Bi_1.68Sr_1.75Ca₂Cu₃O_x. Journal of Non-Crystalline Solids, 160(1-2), 60-67.
  More info

  Abstract: Microstructure and phase development of as-quenched and annealed samples of the glass of composition Pb0.32Bi1.68Sr1.75Ca2Cu3Ox have been studied. Evidence for liquid-liquid phase separation during quenching was found The microstructure of this glass during the early stage of crystallization is similar to that found for Bi2Sr2CaCu2Ox (2212) glass. The first phase that crystallizes on annealing at low temperatures appears to be Cu2O. In further heat treatments the sequential crystallization of the R-phase of (PbyBi2-y)Sr2CuOx ('2201') composition and the PbyBi2-ySr2CaCu2Ox ('2212') phase was found, in agreement with other studies. Phase separation determines the initial crystal phase and the development of the superconducting phases. Phase separation observed in this glass points to the possibility that immiscibility may be a common feature of a wide range of Bi(or PbBi)SrCaCuO compositions. © 1993.
• Denesuk, M., Cronin, J. P., Zelinski, B. J., Kreidl, N. J., & Uhlmann, D. R. (1993). Predictive modelling of liquids spreading on solid surfaces. Physics and Chemistry of Glasses, 34(5), 203-211.
  More info

  Abstract: A liquid spreading model is developed in which surface and gravitational driving energies are balanced against the energy lost through bulk viscous dissipation. Behavior is described in terms only of independently measurable quantities, with no adjustable parameters. Additionally, the model can be used to predict liquid viscosity as a function of spreading behavior. Two different liquid velocity fields are considered, one appropriate for bulk droplet spreading, and the other for thin liquid.
• Denesuk, M., Smith, G. L., Zelinski, B. J., Kreidl, N. J., & Uhlmann, D. R. (1993). Capillary Penetration of Liquid Droplets into Porous Materials. Journal of Colloid And Interface Science, 158(1), 114-120.
  More info

  Abstract: The behavior of a liquid droplet placed on a porous solid is considered. A model is developed for the infiltration of finitesize liquid droplets into porous materials, including the effects of the instantaneous droplet size on the number of pores in contact with the droplet. Simple analytical solutions are developed for the time dependence of the droplet radius under two limiting case assumptions concerning the kinetic behavior of the droplet as its volume is depleted. The two limiting cases are seen to represent upper and lower limits on the liquid depletion time. Liquid depletion data of silicone liquids on a soda-lime-silicate porous solid are presented and compared with predictions of the models. © 1993 Academic Press. All rights reserved.
• Denesuk, M., Zelinski, B. J., & Uhlmann, D. R. (1993). Dispersion Energy of a Spherical Cap on a Semi-infinite Solid. Journal of Colloid And Interface Science, 155(2), 520-521.
  More info

  Abstract: A calculation is performed to quantify the dispersion interactions associated with a spherical cap on a semi-infinite solid. Expressions are derived for the difference between the actual value of the interfacial energy of the spherical cap/semi-infinite solid interface and the value which assumes the phases to be of infinite extent. Applying these considerations to macroscopic, noncompletely wetting liquids on flat solids indicates that neglect of the finite extent of the liquid is normally appropriate. © 1993 Academic Press. All rights reserved.
• Kim, S., P., D., & Uhlmann, D. R. (1993). Early-stage microstructure development in Bi-Sr-Ca-Cu-O glasses. Journal of the American Ceramic Society, 76(12), 3087-3092.
  More info

  Abstract: Amorphous samples of Bi2Sr2Ca1Cu2Ox were produced by quenching from the melt. The early-stage microstructure development in these samples was monitored using XRD, DTA, and hot-stage TEM. It was observed that the molten glass undergoes phase separation during initial quenching and that subsequent refinement of these features generates the initial DTA exotherm during heating. This exotherm has been found for many related compositions, and has been shown not to correspond to crystallization. This initial phase separation strongly impacts the final microstructure by providing copious nucleation sites for the R-phase that ultimately crystallizes first.
• Seraphin, S., Zhou, D., Teowee, G., Boulton, J. M., & Uhlmann, D. R. (1993). Transmission electron microscopy of PZT thin-films prepared by a sol-gel technique. Materials Research Society Symposium - Proceedings, 310, 369-374.
  More info

  Abstract: The microstructures of lead zirconate titanate (PZT) thin films prepared by a sol-gel technique was investigated using transmission electron microscopy (TEM) and transmission electron diffraction. We investigated the microstructure of three sets of thin films with different chemical compositions: PZT 53/47 films with no excess PbO; with excess PbO; and PZT 65/35 with no excess PbO. All samples were fired for 30 minutes at temperatures ranging from 400C to 700C. Incorporation of excess PbO in the 53/47 film fired at 450C resulted in polycrystalline perovskite grains with an average grain size of less than 0.1 μm. Grain boundaries are decorated by 5-10 nm diameter precipitates possibly caused by the segregation of remnant pyrochlore or excess PbO. The films have high values of dielectric constant (up to 2500) when fired at 700C. PZT 65/35 fired at 700C consists of two distinct phases: a fine-grained matrix of pyrochlore, and 10-μm diameter rosettes of perovskite. The correlations between the compositions, the microstructures of the films, and their processing conditions on the one hand, and ferroelectric properties on the others are discussed.
• Teowee, G., & Uhlmann, D. R. (1993). Model of the metal-ferroelectric-metal capacitor. Materials Research Society Symposium - Proceedings, 310, 415-422.
  More info

  Abstract: Ferroelectric (FE) films especially PZT films, have received increasing attention for microelectric applications such as ferroelectric memory and high density DRAM. There has been significant progress in the preparation of high quality PZT films involving wet chemical land physical vapor deposition techniques. Metal-FE-metal structures, typified by Pt-PZT-Pt capacitors, are the basic building blocks for the ferroelectric devices. The leakage currents of the capacitors are known to be non-ohmic and exhibit an exponential dependence on applied voltage.
• Teowee, G., Boulton, M., Orr, M. N., Baertlein, C. D., Wade, R. K., Birnie, D. P., & Uhlmann, D. R. (1993). Effect of Zr/Ti ratio on the fatigue and retention behavior of sol-gel derived PZT films. Materials Research Society Symposium - Proceedings, 310, 423-428.
  More info

  Abstract: A series of sol-gel derived PZT films with various Zr/Ti ratios-namely PT, 0/100 -20/80, 35/65, 53/47, 65/35 80/20, 94/6 and PZ, 100/0 -were prepared on platinized Si wafers. Excess PbO was added to the precursor chemistries to compensate for eventual PbO loss and also to aid in obtaining the desired perovskite phase. It was found that the phase assembly, namely the presence of tetragonal or rhombohedral perovskite phases, plays an important role in determining the fatigue and retention behavioral. PT-rich (or tetragonal) films offer better retention characteristics than those observed in PZ-rich (or rhombohedral) or PZT 53/47 films. Films with PZ-rich compositions tend to exhibit superior fatigue behavior compared with PT-rich films.
• Boulton, J. M., Teowee, G. T., Bommersbach, W. M., & Uhlmann, D. R. (1992). Second-harmonic generation from sol-gel-derived ferroelectric and piezoelectric thin films. Proceedings of SPIE - The International Society for Optical Engineering, 1758, 292-303.
  More info

  Abstract: Sol-gel routes were developed to Ba2NaNb5O15, BaTiO3, Ba0.8Pb 0.2TiO3, Ba0.8Sr0.2TiO3, Bi4Ti3O12, LiNbO3, LiTaO 3, Pb5Ge3O11, PbTiO3, Pb0.85La0.15Ti0.96O3, PbZr 0.2Ti0.8O3, WO3 and ZnO thin films. Second harmonic generation (SHG) from these films deposited on fused SiO2 was investigated as a function of processing temperature. The SHG values were found to be related to the second-order nonlinear optical susceptibilities of the bulk materials, and dependent on the crystal size and crystalline orientation of the film. The highest SHG observed was from PbTiO3 films which is consistent with the fact that the d-coefficient of PbTiO3 is the highest among that of any room temperature ferroelectric. The poor SHG activity of BaTiO3-based films was due to the very small grain size of the sol-gel derived material.
• Kim, S. J., III, D. B., Aruchmay, A., Uhlmann, D. R., El-Bayoumi, O., & Suscavage, M. J. (1992). Phase separation in BiSrCaCuO melts during quenching. Physica C: Superconductivity and its applications, 191(3-4), 316-320.
  More info

  Abstract: Phase separation is found for the first time in quenched samples of amorphous Bi2Sr2Ca1Cu2Ox (often called "2212" composition). Clear evidemce for metastable phase separation is found using X-ray diffraction (XRD), transmission electron microscopy (TEM), and differential thermal analysis (DTA). This has serious implications for possible fabrication of high current density devices from these compositions, especially via glass-ceramic processing routes. © 1992.
• Motakef, S., Boulton, J. M., Teowee, G. T., Uhlmann, D. R., Zelinski, B. J., & Zanoni, R. (1992). Polyceram planar waveguides and optical properties of polyceram films. Proceedings of SPIE - The International Society for Optical Engineering, 1758, 432-445.
  More info

  Abstract: Low loss sol-gel derived polyceram optical waveguides have been prepared for the first time. Polyceram films were obtained by reacting (N-triethoxysilyl propyl) o-polyethylene oxide urethane with silicon and titanium alkoxides. The optical properties of the films were investigated using ellipsometry, UV-VIS transmission spectroscopy and waveguide loss measurements. Refractive index and attenuation loss measurements were carried out as a function of organic/inorganic content, different processing conditions and aging of solutions. Refractive indices as high as 1.685 and attenuation losses as low as 1.4 dB/cm were obtained. In addition, surface morphology, mechanical properties and thermal stability of the polyceram films were studied.
• Teowee, G. T., Boulton, J. M., Motakef, S., Uhlmann, D. R., Zelinski, B. J., Zanoni, R., & Moon, M. (1992). Optical properties of sol-gel-derived PZT thin films. Proceedings of SPIE - The International Society for Optical Engineering, 1758, 236-248.
  More info

  Abstract: A series of sol-gel derived PT-based films, including PT, PZ, PZT, PLT, PLZ and PLZT, was prepared on platinized Si, fused SiO2 and Corning 7059 substrates. These films were fired at 400 - 700 C for 30 mins. The phase assembly and development were dependent on the precursor chemistries, processing and choice of substrates. The presence of Zr impacted significantly on the crystallization behavior, PbO loss and cracking behavior of the films. Crystallization was severely retarded, especially in Zr-containing PZT films when deposited on amorphous substrates compared to crystalline Pt substrates. Amorphous and crystalline PZT films can be utilized for passive and active optical applications. Waveguiding was achieved in an amorphous PZT 53/47 and a crystalline PLT 28 films and gave attenuation losses of 1.0 and 1.4 dB/cm respectively which represent the lowest values reported to date. The optical properties of the films were investigated using ellipsometry, UV-VIS transmission spectroscopy and waveguide loss measurements. Depending on composition and processing conditions, PZT films (2500 A thick) with refractive indices of 1.60 to 2.33 and absorption edges of 2900 - 3100 A can be obtained. It was ascertained that the resulting interfacial reaction layers between the films and substrates affected considerably the optical properties of thinner films (< 2000 A).
• Teowee, G., Boulton, J. M., Bommersbach, W. M., & Uhlmann, D. R. (1992). Second harmonic generation from PbTiO₃-based ferroelectric thin films. Journal of Non-Crystalline Solids, 147-148(C), 799-802.
  More info

  Abstract: Sol-gel-derived lead titanate, lead lanthanum titanate, lead zirconate titanate and lead lanthanum zirconate titanate films were prepared. Second harmonic generation (SHG) activity from these films was explored as a function of composition, processing, phase assemblage, microstructure and orientation. Undoped PbTiO3 films exhibited strong, angular-dependent SHG signals. Incorporation of La and Zr resulted in a decrease in the signal magnitude. © 1992 Elsevier Science Publishers B.V. All rights reserved.
• Uhlmann, D. R., Teowee, G., Boulton, J. M., Motakef, S., & Lee, S. C. (1992). Electrical and optical properties of chemically derived ferroelectric films. Journal of Non-Crystalline Solids, 147-148(C), 409-423.
  More info

  Abstract: Wet chemical (sol-gel) methods have been used to synthesize a variety of ferroelectric (FE) thin films, most notably lead zirconate titanate. Ferroelectric films have a wide variety of applications ranging from non-volatile memory devices to pyroelectric detectors. Recent progress in this area of sol-gel processing is surveyed, and examples are illustrated by results from the authors' laboratory. It is concluded that impressive results have been achieved in the chemical processing of FE films, but that more effective collaboration needs to be established between chemists/ceramists knowledgeable about wet chemical processing, and device technologists knowledgeable about the characteristics of coatings. © 1992 Elsevier Science Publishers B.V. All rights reserved.
• Agrawal, A., & Uhlmann, D. R. (1991). Modelling of condensation reactions in an amine-cured epoxy system with groups of unequal reactivity. Polymer, 32(2), 290-296.
  More info

  Abstract: A simple model is presented to simulate the process of network formation involving bifunctional epoxies and amines. This model takes account of different reaction rates of the primary and the secondary amines. At the start of the reaction, the amine could either be a mixture of primary and secondary amines or only primary amine, but as a hydrogen of a primary amine is consumed during the reaction, the other hydrogen becomes secondary. The principal effects of the higher reactivity of the primary amines are: (a) increased extents of reaction are required to reach the gel point, with this extent being dependent on the initial stoichiometry; and (b) increased number of less branched species are generated during the reaction. © 1991.
• Uhlmann, D. R., Teowee, G., & Boulton, J. M. (1991). Dielectric relaxation in ferroelectrics. Journal of Non-Crystalline Solids, 131-133(PART 2), 1194-1201.
  More info

  Abstract: Ferroelectrics are important multifunctional materials with applications ranging from high Er capacitors to non-volatile memory devices. Dielectric relaxation studies of ferroelectrics help elucidate the various mechanisms responsible for polarization. These insights are beneficial for materials engineering and tailoring of specific properties. In the present review, a comparison among the paraelectric, ferroelectric and physical states of the material are made. Compositional and dopant effects are also addressed. In ferroelectrics, the domain structure is shown to play a crucial role in determining both the nature and mechanism of the dielectric relaxation in the microwave region. At lower frequencies interfacial polarization dominates, especially for polycrystalline samples. © 1991.
• Uhlmann, D. R., Zelinski, B. J., Teowee, G., Boulton, J. M., & Koussa, A. (1991). Wet chemical synthesis of bulk optical materials. Journal of Non-Crystalline Solids, 129(1-3), 76-92.
  More info

  Abstract: Wet chemical processing has a large number of both proven and potential applications in different areas of glasses and ceramics. In optics where homogeneity and high purity are of utmost importance, the inherent advantages of sol-gel methods can be fully exploited. The optical applications of wet chemical methods are widespread and range from direct casting of SiO2 lenses to semiconductor-doped glasses. The most notable benefits of wet chemical approaches and progress achieved to date in a number of the most attractive representative areas are surveyed. © 1991.
• Fabes, B. D., & Uhlmann, D. R. (1990). Strengthening of glass by sol-gel coatings. Journal of the American Ceramic Society, 73(4), 978-988.
  More info

  Abstract: The affects of alkoxide-derived coatings on the bending strength of silica glass were investigated. For densified coatings, increases in strength of 120% to 130% were found. A model of the strengthening process, based on the filling-in and partial healing of surface flaws, is proposed. The model accounts for the temperature dependence of strengthening, the insensitivity of strengthening to the size of oligomers in the coating solution, and the insensitivity of strengthening to the thickness of the coating. The presence of a significant residual tensile stress in sol-gel-strengthened material is also indicated.
• Uhlmann, D. R., Boulton, J. M., Teowee, G., Weisenbach, L., & Zelinski, B. J. (1990). Sol gel synthesis of optical thin films and coatings. Proceedings of SPIE - The International Society for Optical Engineering, 1328, 270-295.
  More info

  Abstract: Sol-gel methods offer a number of notable advantages for the synthesis of optical films and coatings. Areas of potential or actual application of this technology range from single layer and multilayer antireflection coatings to embossed planar waveguides and organic-modified oxide materials. The most notable advantages of these wet chemical methods will be surveyed, as will progress achieved to date in a number of the most attractive representative areas. The technical bases for the success/failure in each case will be considered. Also to be discussed will be the prospects - in both the near-term and long-term - of future developments in the sol-gel synthesis of optical films, as well as the principal technical hurdles which must be overcome in order that such synthesis methods may achieve more widespread use in the future. Finally, a comparison will be made between the microstructures and characteristics of films and coatings deposited using sol-gel methods with those deposited from the vapor phase. In all cases, use will be made of recent advances in our laboratory in the subject area.
• Weinberg, M. C., Zelinski, B. J., Uhlmann, D. R., & Zanotto, E. D. (1990). Critical cooling rate calculations for glass formation. Journal of Non-Crystalline Solids, 123(1-3), 90-96.
  More info

  Abstract: An assessment is made of the various factors which are involved in the calculation of critical cooling rates for glass formation. In particular, attention is focused upon the sensitivity of computed critical cooling rates Rc to various approximations and uncertainties in physical parameter data. SiO2 and GeO2 are chosen as model systems to illustrate the major features. It is shown that Rc is rather insensitive to the mode of computation of the volume fraction crystallized, but is quite dddependent upon the material parameters which enter into the nucleation and crystal growth expressions. © 1990.
• Kitipichai, P., LaPeruta Jr., R., Korenowski, G. M., Wnek, G. E., Gorodisher, I., & Uhlmann, D. R. (1989). New polymers for second harmonic generation. American Chemical Society, Polymer Preprints, Division of Polymer Chemistry, 30(2), 176-.
  More info

  Abstract: Most of the authors preliminary work has employed the diol N,N-Di-(2-hydroxyethyl)-p-nitroaniline (R1 = p-nitrophenyl). The synthesis of this material and polyurethane films derived from it as well as second harmonic generation efficiencies are discussed. It is shown that the SHG maximum near 55° corresponds to a value roughly twice that of the first Maker fringe of quartz. This is a respectable value obtained from a poled polymer film which took only a few minutes to fabricate from the corresponding monomers.
• Weinberg, M. C., Uhlmann, D. R., & Zanotto, E. D. (1989). "Nose method" of calculating critical cooling rates for glass formation. Journal of the American Ceramic Society, 72(11), 2054-2058.
  More info

  Abstract: In the past, it has been shown that reasonably good estimates of critical cooling rates for glass formation could be obtained by computing the cooling curve which just passes through the nose of a T-T-T (time-temperature- transformation) diagram. Also, it has been noted that critical cooling rates found by this procedure are generally greater than those obtained by other methods. Herein, we provide an explanation of these observations. The nose method of computing critical cooling rates is compared with others, and specific illustrations are given for the glass-forming systems SiO 2, GeO 2, and P 2O 5.
• Filippo, G. D., Sande, J. V., & Uhlmann, D. R. (1988). ON THE STRUCTURE OF GLASSY POLYMERS. VIII. USE OF Z CONTRAST TO ELUCIDATE THE MICROSTRUCTURE OF EPOXY AND POLYIMID RESINS.. Journal of Applied Polymer Science, 35(2), 485-505.
  More info

  Abstract: The technique of ultramicrotomy of polymers, followed by staining of the resulting thin sections with heavy metal ions and viewing with Z enhancement in the scanning transmission electron microscope is described. When applied to anhydride-cured epoxy resins, the structure is found to be heterogeneously crosslinked on a scale of a few hundred angstrom. When the technique is applied to amine-cured epoxy resins, the microstructure is found to change from homogeneous to inhomogeneously crosslinked, depending on stoichiometries and cure cycles. For amine-cured resins whose cure conditions are within the range of microstructural change, the bright field of the stained specimens alone does not detect heterogeneities, and the Z contrast becomes crucial to discern the kind of microstructure. A commercial polyimide film examined in the same way is found to exhibit systematic variations in structure through the thickness of the film.
• Uhlmann, D. R., Weinberg, M. C., & Teowee, G. (1988). Crystallization of gel-derived glasses. Journal of Non-Crystalline Solids, 100(1-3), 154-161.
  More info

  Abstract: The crystallization behaviors of gels, gel-derived glasses and melted glasses are reviewed, and comparisons are effected among the observed behaviors. These comparisons are related to the behavior expected on the basis of models for the nucleation frequency and crystal growth rate, as well as the anticipated differences in material characteristics among gels and the two types of glasses. Different temperature regimes are identified where different comparisons between melted and gel-derived materials are expected. It is concluded that a need exists for more definitive, detailed data on the crystallization behavior of gel-derived materials. © 1988.
• Yang, X., Pierre, A. C., & Uhlmann, D. R. (1988). TEM study of boehmite gels and their transformation to α-alumina. Journal of Non-Crystalline Solids, 100(1-3), 371-377.
  More info

  Abstract: The transformations of boehmite gels during heat treatments at temperatures up to 1150°C have been studied using transmission electron microscopy. Specific attention is directed to the evolution of porosity during the transformations, with isolated small pores seen in λ-Al2O3, aligned small pores in θ-Al2O3, and large cylindrical pores in α-Al2O3. The results are compared with the previous observations of Wilson and Stacey of the transformations which occur on heating boehmite monocrystals. The observed evolution of porosity is related to the results of Kumagai and Messing on the effects of seeding alumina gels with small α-Al2O3 particles, where dense α-Al2O3 structures were obtained at 1200°C. It is suggested that such seeding avoids the formation of wormy crystalline structures with large intragranular pores. Also discussed is the approach of developing alumina sols which will form smectic structures on approaching the leatherhard point during drying of the gels. © 1988.
• Alexander, M. N., Onorato, P. I., Struck, C. W., Tasker, G. W., & Uhlmann, D. R. (1987). Structure of alkali (alumino) silicate glasses. II. Luminescence of thallium doped sodium aluminosilicates, and implications for optical basicity theories. Journal of Non-Crystalline Solids, 91(1), 63-82.
  More info

  Abstract: Optical excitation and emission spectra are reported for Na aluminosilicate glassed doped with 0.001-0.005 M Tl+ ions, whose spectra probe Na+ environments in the glasses. The experimental data buttress earlier work by the authors, which showed that Al/Na = 1 is the condition for (dis)appearance of nonbridging oxygens in Na aluminosilicate glasses. The Tl+ spectra are in qualitative disagreement with theories of average optical basicity propounded by Jørgensen and by Duffy and Ingram (glass compositions were chosen so samples had theoretical optical basicities of Λth = 0.55, 0.57, or 0.60). In contrast to the single absorption band predicted by average basicity theories, two absorption bands were found for Tl+ in Na aluminosilicate glasses. The two bands arise from Tl+ acting as network modifiers and from Tl+ acting as charge compensators for network Al. The principal features of these spectra are shown to be consistent with XPS results. The assumptions underlying average and group optical basicity theories are critically reviewed and are found to be deficient in that: (1) they direct attention to a network atom (Si or Al) and the oxygen bonded to it, rather than to the luminescent probe ion and its neighboring oxygens; (2) they neglect lattice relaxation (Franck-Condon shift) effects. Important special circumstances are nevertheless identified in which average optical basicity theories may be useful guides to the peak energies of probe ion spectra. © 1987 Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division).
• Hishinuma, A., & Uhlmann, D. R. (1987). Nucleation kinetics in some silicate glass-forming melts. Journal of Non-Crystalline Solids, 95-96(PART 1), 449-455.
  More info

  Abstract: Nucleation phenomena in several congruently melting silicate glasses were studied previously. Classical nucleation theory was found to provide a good description of the results in some silicate melts and not in others. In this study, crystal nucleation in several silicate melts has been re-investigated. The kinetics of nucleation were determined trom the measured number of crystals as a function of time, evaluated from the optical microscopy of the thin sections, for crystals formed internal to the samples. The crystalline phases produced in such volume crystallization were identified by x-ray diffraction. The results obtained are compared with previous reports of nucleation kinetics in the materials, and with predictions of classical nucleation theory. © 1987 Elsevier Science Publishers B.V.
• Makous, J. L., Maritato, L., Falco, C. M., Cronin, J. P., Rajendran, G. P., Uhlmann, E. V., & Uhlmann, D. R. (1987). Superconducting and structural properties of sputtered thin films of YBa₂Cu₃O_7-x. Applied Physics Letters, 51(25), 2164-2166.
  More info

  Abstract: We have fabricated thin films of YBa2Cu3Ox by dc triode sputtering from two metallic targets. Post-annealing in pure O2 after sputtering resulted in superconducting films with a T c onset as high as 89 K and a midpoint Tc of 75 K. We report preliminary results of films deposited on sapphire, MgO and sol-gel coatings of ZrO2 on sapphire, with and without buffer layers of Ag. The chemical and physical structures of these films were analyzed by using several x-ray diffraction techniques and Rutherford backscattering spectroscopy.
• Pierre, A. C., & Uhlmann, D. R. (1987). GELATION OF ALUMINUM HYDROXIDE SOLS.. Journal of the American Ceramic Society, 70(1), 28-32.
  More info

  Abstract: The gelation of aluminum hydroxide sols obtained from aluminum sec-butoxide has been studied as a function of the conditions of preparation, including pH, temperature, and time of aging. It has been found that stable sols can easily be obtained by processing at any temperature between 20 degree C and 90 degree C beyond a molar proportion of 0. 28 HNO//3. The corresponding gels are suggested to have a boehmite-like structure.
• Tesoro, G. C., Rajendran, G. P., Park, C., & Uhlmann, D. R. (1987). IMIDE SILANES: ADHESION PROMOTERS FOR POLYIMIDES.. Journal of Adhesion Science and Technology, 1(1), 39-51.
  More info

  Abstract: The investigation of adhesion promoters prepared by the reaction of amino-functional silanes with dianhydrides (or diester-diacid chlorides) of tetracarboxylic aromatic acids is reported. The new coupling agents, designed to exhibit superior thermo-oxidative stability were applied under conditions determined from kinetic studies of hydrolysis and condensation reactions, and their coupling effectiveness for polyimides was evaluated by peel tests. For a wholly aromatic imide silane (CA-25), adhesion retention after prolonged exposure to elevated temperature was far greater than obtained with adhesion promoters previously evaluated in polyimide systems.
• Tesoro, G. C., Rajendran, G. P., Uhlmann, D. R., & Park, C. (1987). TOUGHNESS OF SILICONE BLOCK COPOLYIMIDES.. Industrial and Engineering Chemistry Research, 26(8), 1672-1678.
  More info

  Abstract: Block copolyimides were synthesized from 3,3 prime ,4,4 prime benzophenonetetracarboxylic dianhydride by reaction with 4,4 prime -methylenedianiline and poly(dimethylsiloxane) diamines. Aromatic diamineterminated poly(dimethylsiloxanes) were prepared by the base-catalyzed equilibration of octamethylcyclotetrasiloxane with 1,3-bis(4-aminophenoxypropyl) tetramethyldisiloxane. The amount of poly(dimethylsiloxane) incorporated in the copolyimides was 5-15 wt %. The selected molecular weight of poly(dimethylsiloxane) diamine was 4500.
• Uhlmann, D. R., & Weinberg, M. C. (1987). NUCLEATION AND GLASS FORMATION.. Materials Research Society Symposia Proceedings, 57, 99-114.
  More info

  Abstract: The role of nucleation kinetics in affecting glass formation behavior is discussed. Also considered are measurements of homogeneous crystal nucleation in a variety of liquids. For a number of oxide glass-forming liquids, available data indicate pre-exponential factors which are larger than those predicted from classical nucleation theory by factors of 10**1**7 to 10**4**9. Possible sources of this discrepancy are discussed.
• Agrawal, A., Yinnon, H., Uhlmann, D. R., Pepper, R. T., & Despar, C. R. (1986). Boron modification of carbon fibres. Array.
  More info

  Abstract: Carbon fibres based on polyacrylonitrile were graphitized with varying concentrations of boron in the atmosphere of the graphitization furnace. A variety of techniques was used to characterize the structures of the fibres, including small- and wide-angle X-ray scattering. It was found that the presence of boron does not affect the important structural features of the fibre bulk.
• Agrawal, A., Yinnon, H., Uhlmann, D. R., Pepper, R. T., & Desper, C. R. (1986). Boron modification of carbon fibres. Journal of Materials Science, 21(10), 3455-3466.
  More info

  Abstract: An investigation is reported of the effect of boron modification on the mechanical properties of carbon fibres. It was found that the presence of boron in the furnace atmosphere does not affect the important structural features of the bulk of the fibres, that in many fibres the added boron is largely confined to the near-surface regions of the fibres, and that a large fraction of the boron is present as boron carbide. The largest improvements in strength were obtained when both carbon and boron were present in the furnace atmosphere. © 1986 Chapman and Hall Ltd.
• Alexander, M., Onorato, P., Struck, C., Rozen, J., Tasker, G., & Uhlmann, D. (1986). Structure of alkali (alumino)silicate glasses. I. Tl⁺ luminescence and the nonbridging oxygen issue. Journal of Non-Crystalline Solids, 79(1-2), 137-154.
  More info

  Abstract: Optical excitation spectra of Tl+ ions, corresponding to emission at 350 nm, have been measured in Na aluminosilicate glasses. These excitation spectra were found to be good representations of absorption spectra. The excitation spectra are shown to be superpositions of two primary spectra, which are identified with Tl+ acting as network modifiers or as charge compensators for network aluminums. When A1/Na ≥ 1, only the charge compensator spectrum can be observed. As A1/Na decreases below unity, the fraction of the charge compensator spectrum decreases rapidly, and the fraction of the network modifier spectrum increases correspondingly. No other discontinuous behavior in the characteristics of the excitation spectra as a function of composition was found. These results strongly support the traditional model of alkali aluminosilicate structure, in which the critical compositions for (dis)appearance of nonbridging oxygens are given by A1/Na = 1; they contradict reports of XPS measurements from which it had been concluded that the critical compositions are given by A1/Na ≅ 0.7. Measurements of Tg also contradict the conclusions drawn from those XPS measurements. The rapid appearance of the network modifier spectrum immediately below A1/Na = 1 is attributed to Tl+ ions being more likely to occupy network modifier sites than charge compensator sites. A statistical mechanical calculation, used in conjunction with the excitation spectra, shows that the preference energy favoring Tl+ occupation of n network modifier sites is ≅ 750 cm-1. © 1986.
• Cornie, J. A., Chiang, Y., Uhlmann, D. R., Mortensen, A., & Collins, J. M. (1986). PROCESSING OF METAL AND CERAMIC MATRIX COMPOSITE.. American Ceramic Society Bulletin, 65(2), 293-304.
  More info

  Abstract: This paper is directed toward surveying the current state and future course of developments in this technology, with respect to both metal and ceramic matrix composites. The intent of this paper was to review the open literature on the fundamentals of processing of metal and ceramic matrix composites and to draw attention to areas relating to the problems or limitations in these newly emerging technology.
• Fabes, B. D., Doyle, W. F., Zelinski, B. J., Silverman, L. A., & Uhlmann, D. R. (1986). Strengthening of silica glass by gel-derived coatings. Journal of Non-Crystalline Solids, 82(1-3), 349-355.
  More info

  Abstract: The use of sol-gel coatings to strengthen oxide glasses has been demonstrated for the case of fused silica. Increases in strength to as much as 2.2 tiimes the strength of uncoated glass have been obtained. The strengthening does not involve the annealing of surface microcracks, but rather the filling-in of such flaws. The strengthening does not depend on coating thickness over the range 2000-10000 Å, but does depend significantly upon the state of hydrolysis of the substrate surface. © 1986.
• Parkhurst, C. S., Doyle, W. F., Silverman, L. A., Singh, S., Andersen, M. P., McClurg, D., Wnek, G. E., & Uhlmann, D. R. (1986). SILOXANE MODIFIED SiO//2-TiO//2 GLASSES VIA SOL-GEL.. Materials Research Society Symposia Proceedings, 73, 769-773.
  More info

  Abstract: Polydimethylsiloxane left bracket PDMS right bracket -modified SiO//2-TiO//2 glasses have been prepared via the sol-gel route. Polymer compositions varied between 17 and 67 wt% PDMS of molecular weights 1,700 and 36,000. Also varied was the Si/Ti ratio for a given polymer content and the nature of the Ti alkoxide. A general synthetic procedure made optically clear samples. Dense monolithic structures were obtained at room temperature for all compositions. The room temperature densification is attributed to relaxation and flow due to the presence of the polymer. The effects on properties of the overall composition and molecular weight of the polymer are reported implications in terms of structural models are considered.
• Pierre, A. C., & Uhlmann, D. R. (1986). Amorphous aluminum hydroxide gels. Journal of Non-Crystalline Solids, 82(1-3), 271-276.
  More info

  Abstract: The gelation of aluminum hydroxide sols obtained from aluminum-sec-butoxide in acidic media leads, depending on the conditions of preparation, to gels with a structure ranging from crystalline to amorphous to super-amorphous. A model for the structure of "super-amorphous" gels is presented to explain the observations. This model suggests the presence of swollen and folded boehmite planes as essential structural features. © 1986.
• Pierre, A. C., & Uhlmann, D. R. (1986). COMPARISON OF CLAY-WATER SYSTEMS WITH ALUMINUM HYDROXIDE GELS PREPARED IN ACIDIC MEDIA.. Materials Research Society Symposia Proceedings, 73, 481-487.
  More info

  Abstract: Alumina sols made by the hydrolysis of aluminum sec-butoxide in an acidic medium show behavior during drying and aging which appears similar to that reported for gels in a number of clay-water systems. Structural and phenomeological characteristics of these two classes of materials are compared. The extension to aluminum hydroxide systems of the models proposed to explain the gelation of clay sols are discussed. A model is presented to describe the gelation behavior of aluminum hydroxide sols which is based on electrostatic linking.
• Pierre, A. C., Uhlmann, D. R., & Hordonneau, A. (1986). CERAMIC COMPOSITES MADE BY SOL-GEL PROCESSING.. Revue internationale des hautes temperatures et des refractaires, 23(1), 29-35.
  More info

  Abstract: The applications of hydrous metal oxides in ceramics are discussed. One application is in ceramic composites with the oxide as the matrix. The results of an experimental study of undirectional fiber composites with alumina or zirconia matrix made by sol-gel processing are presented.
• Silverman, L. A., Teowee, G., & Uhlmann, D. R. (1986). CHARACTERIZATION OF SOL-GEL DERIVED TANTALUM OXIDE FILMS.. Materials Research Society Symposia Proceedings, 73, 725-730.
  More info

  Abstract: The authors studied the densification and dielectric properties of sol-gel derived tantalum oxide thin films as insulators in MIS capacitors. Hydrolysis of tantalum ethoxide is rapid and goes to completion in ethanol. Condensation is also rapid and goes to completion in toluene. Multiple layers were applied by spin-coating up to thicknesses of 3000 Angstrom before cracking of the coating during drying ensured. Densification occurs from room temperature to 450 C, with the original film thickness decreasing by about half in one hour at 450 C. No additional densification occurs upon heating to 750 C. The dielectric constant decreases from unfired samples to those fired at 450 C, and then increases on firing from 600 to 750 C. The value of the dielectric constant at 1 MHz for samples fired at 750 C for one hour is 20. Leakage currents as low as 2 multiplied by 10** minus **7 amp cm** minus **2 have been measured for applied fields of 200,000 v cm** minus **1.
• Zelinski, B. J., Fabes, B. D., & Uhlmann, D. R. (1986). Crystallization behavior of sol-gel derived glasses. Journal of Non-Crystalline Solids, 82(1-3), 307-313.
  More info

  Abstract: The synthesis of cordierite and anorthite by an all-alkoxide route has been demonstrated. Amorphous gel-derived anorthite powders are shown to exhibit crystallization behavior similar to that of melt-derived glasses. Crystallization of amorphous gel-derived cordierite powders takes place by the formation of a transient, metastable stuffed β-quartz phase, which converts to cordierite at higher temperatures - similar to the sequence of phase development in melt-derived glasses which are close to cordierite in composition. © 1986.
• El-Bayoumi, O., & Uhlmann, D. R. (1985). Preface. Journal of Non-Crystalline Solids, 73(1-3), vii-viii.
• Hodgins, O. C., Dresselhaus, M. S., Uhlmann, D., & Aliotta, C. F. (1985). CONTACT ANGLE MEASUREMENTS OF WETTING IN PRISTINE AND ION IMPLANTED HIGH MODULUS BENZENE DERIVED GRAPHITE FIBERS.. Materials Research Society Symposia Proceedings, 40, 111-116.
  More info

  Abstract: Measurements are reported of the contact angles of benzene-derived carbon fibers with de-ionized water, aminopropyltriethoxy silane and du Pont 5878 polyimide solutions. Both pristine fibers and fibers implanted with 5 multiplied by 10**1**2 cm** minus **2 and 1 multiplied by 10**1**5 cm** minus **2 fluences of **3**1P ions were investigated. Such implantation was observed to decrease the contact angle in all three solutions. The ion implantation had no significant effect on tensile strength, but did result in increased structural disorder (as reflected in the width of the main wide angle X-ray diffraction peak) and increased surface roughness. The increased disorder and roughness are believed to be principally responsible for the observed change in wetting angle. This study is relevant to graphite-fiber-reinforced materials for microelectronics.
• Jang, B. Z., Uhlmann, D. R., & Sande, J. V. (1985). CRAZING IN POLYPROPYLENE.. Polymer Engineering and Science, 25(2), 98-104.
  More info

  Abstract: The subject of crazing in crystalline polymers is reviewed and specific consideration given to crazing in polypropylene (PP). Tensile tests conducted over a wide spectrum of temperatures and strain rates indicate that, for a given test temperature, there exists a critical strain rate above which crazing is the dominant deformation mode of PP. Similarly, for a given strain rate, there exists a critical temperature which demarcates crazing from shear yielding as the characteristic process of deformation.
• Jang, B. Z., Uhlmann, D. R., & Sande, J. V. (1985). RUBBER PARTICLE SIZE DEPENDENCE OF CRAZING IN POLYPROPYLENE.. Polymer Engineering and Science, 25(10), 643-651.
  More info

  Abstract: The tensile crazing and Charpy impact behavior of polypropylene modified with styrene-butadiene copolymer (SBR) and ethylene-propylene-diene monomer (EPDM) was studied. Various rubber particle size distributions were obtained by varying the relative viscosities between rubbery phase and PP matrix. Transmission electron microscopy and computer-aided image analysis were used to provide particle size information. In general, PP blends with smaller rubber particles are tougher and more ductile than those with larger particles, probably because the former represents a more efficient use of rubbery phase in promoting crazing and/or shear yielding. Small particles, inducing smaller stress-enhanced zones, are therefore not effective in initiating crazes.
• Jang, B. Z., Uhlmann, D. R., & Sande, J. V. (1985). RUBBER-ROUGHENING IN POLYPROPYLENE.. Journal of Applied Polymer Science, 30(6), 2485-2504.
  More info

  Abstract: The deformation and fracture behavior of several polypropylene (PP) and rubber-modified PP materials have been investigated. Plastic deformation mechanisms of these systems depend upon the test rate and temperature with high rates and low temperatures being in favor of crazing. The second phase morphology with smaller average rubber particle diameter D appears to be more efficient than that with large D in toughening PP. Theoretical calculations indicate that the stresses imposed upon the rubber particles due to volume shrinkage of PP during crystallization are sufficient to compensate for the stresses due to differential thermal contraction in cooling from solidification temperature to end-use temperature. The difference between these two is small, and therefore they provide very little contribution to interfacial adhesion between rubber particle and PP matrix, the adhesion being insufficient for the rubber particles to be effective in controlling craze propagation.
• Onorato, P. I., Alexander, M. N., Struck, C. W., Tasker, G. W., & Uhlmann, D. R. (1985). STRUCTURE OF ALKALI ALUMINOSILICATE GLASSES.. Electrochemical Society Extended Abstracts, 85-1, 625-626.
  More info

  Abstract: The authors performed new XPS measurements on these glasses, using a Physical Electronics 548 spectrometer using a Mg K alpha x-ray source. The Au-dot calibration method of Stephenson and Binkowski was adapted to the analysis of fracture surfaces formed in high vacuum. The binding energies are thus measured relative to the Fermi level of the insulator through the Fermi level of the Au calibrant. Moreover, the method avoids spurious spectral features caused by uncontrolled charging of the insulating sample. All data were digitized, fed to a mini-computer, signal averaged, deconvoluted to remove the Mg K alpha //2 contribution to the raw width, and smoothed.
• Onorato, P. I., Alexander, M. N., Struck, C. W., Tasker, G., & Uhlmann, D. R. (1985). BRIDGING AND NONBRIDGING OXYGEN ATOMS IN ALKALI ALUMINOSILICATE GLASSES.. Journal of the American Ceramic Society, 68(6), 148-150.
  More info

  Abstract: Thallium-probe ion luminescence spectroscopy and X-ray photoelectron spectroscopy were used to study the structure of sodium aluminosilicate glasses. It was demonstrated that the O1s spectral envelope for these glasses is comprised of three energetically distinct peaks, two attributed to bridging oxygen atoms (Si-O-Si and Al-O-Si) and one to nonbridging oxygen atoms (Si-O-Na). Both techniques indicate that nonbridging oxygen atoms are present in all sodium aluminosilicate glasses.
• Uhlmann, D. R. (1985). Crystallization and glass formation. Journal of Non-Crystalline Solids, 73(1-3), 585-592.
  More info

  Abstract: The principal outstanding problems in the areas of glass formation, crystal nucleation and crystal growth are discussed. Each of these areas is seen to provide notable opportunity for improvements in our understanding. Also discussed are anticipated future directions in crystallization and glass formation. These include an expanded range of materials obtained and used as glasses, increasing utilization of rapid quench techniques, and wider use of sol-gel methods and forming glasses by viscous sintering. © 1985.
• Barsoum, M. W., Tuller, H. L., & Uhlmann, D. R. (1984). REACTION KINETICS AND ELECTROCHEMICAL STABILITY DOMAINS OF AMORPHOUS Li-BORATE BASED SOLID ELECTROLYTES.. Electrochemical Society Extended Abstracts, 84-2, 238-.
  More info

  Abstract: A novel electrochemical technique was developed to measure the chemical and electrochemical domain boundaries of some Li-ion conducting glasses. The activity of the Li in the working Sn electrode was slowly increased coulometrically by passing a current through one electrolyte and simultaneously measuring the open cell EMF across the other identical electrolyte.
• Fang, C. -., & Uhlmann, D. R. (1984). The process of crystal melting II. Melting kinetics of sodium disilicate. Journal of Non-Crystalline Solids, 64(1-2), 225-228.
  More info

  Abstract: The kinetics of crystal melting for sodium disilicate have been determined over the temperature range 875-884°C. When compared with previous data on crystallization kinetics, melting is found to take place much more rapidly than crystallization. The reduced melting rate is found to be independent of superheat, and the interface morphology in melting is non-faceted. It is suggested that the crystal-liquid interface in melting is rough on an atomic scale. © 1984.
• Jang, B. Z., Uhlmann, D. R., & Sande, J. (1984). CRYSTALLINE MORPHOLOGY OF POLYPROPYLENE AND RUBBER-MODIFIED POLYPROPYLENE.. Journal of Applied Polymer Science, 29(12 pt 2), 4377-4393.
  More info

  Abstract: The crystalline morphology of injection-molded polypropylene (PP), its relationship with crazing, and the effects of various impact modifiers on the morphology, crystallization, and fusion of PP have been studied. The highly oriented skin layer of an injection-molded tensile bar after deformation was found to be free from crazing in contrast to the heavy craze density in the randomly oriented spherulitic core zone. Reasons for the difficulty in craze nucleation in a preoriented zone are given in light of Argon's theory of craze initiation. Addition of a rubbery phase results in an irregular texture of spherulite, smaller spherulitic diameter, and decrease in the degree of undercooling, but no appreciable change in heats of fusion and crystallization other than a trivial volume effect. The rubbery phase is not pushed by the melt-solid interface to relocate to the interspherulitic boundaries. Rather, it is engulfed by the growing melt-solid interface, leaving behind a random spatial distribution of rubber particles in the PP matrix.
• Jang, B. Z., Uhlmann, D. R., & Sande, J. V. (1984). CRAZING IN POLYPROPYLENE.. Annual Technical Conference - Society of Plastics Engineers, 523-525.
• Jang, B. Z., Uhlmann, D. R., & Sande, J. V. (1984). DUCTILE-BRITTLE TRANSITION IN POLYMERS.. Journal of Applied Polymer Science, 29(11), 3409-3420.
  More info

  Abstract: Tensile experiments on polypropylene and various rubber-modified polypropylenes, conducted over a wide range of temperatures and strain rates, have shown that ductile-brittle transition in these highly crystalline polymers is strongly affected by both temperature and strain rate. Such polymers can either craze or shear yield, depending on the temperature and rate of test. High temperatures and low strain rates favor shear yielding, while low temperatures and high strain rates promote crazing. The ductile-brittle transition of these polymers may be understood as due to an alteration in deformation mode. The competition between crazing and shear yielding dictates the subsequent failure mode. The dependence of the ductile-brittle transition on the test and material parameters (such as temperature, strain rate, pressure, orientation, notching, and plasticizer) may be ascribed to the respective influences of these parameters on crazing relative to shear yielding.
• Jang, B. Z., Uhlmann, D. R., & Sande, J. V. (1984). POSTDISPERSION COALESCENCE PHENOMENON IN POLYMER-POLYMER BLENDS.. Rubber Chemistry and Technology, 57(2), 291-306.
  More info

  Abstract: Three novel experimental techniques have been developed to study the phase separation dynamics and morphology of polymer-polymer blends. Samples prepared from different materials by different methods appear to follow the same phase transformation behavior. The particle size distribution is more or less random and tends to broaden with time. The volume fraction of the second phase has a substantial effect on its growth rate. It has been demonstrated that a combination of hot-staged optical microscopy, transmission electron microscopy, high-speed cinematography, and the three novel sample preparation techniques facilitate a detailed study on the late-stage mechanisms of phase separation of polymeric blends.
• Jang, B. Z., Uhlmann, D. R., & Sande, J. V. (1984). RUBBER PARTICLE SIZE DEPENDENCE OF CRAZING IN POLYPROPYLENE.. Annual Technical Conference - Society of Plastics Engineers, 549-551.
• Weinberg, M. C., Neilson, G. F., & Uhlmann, D. (1984). Homogeneous versus heterogeneous crystal nucleation in Li₂O · 2SiO₂ glass. Journal of Non-Crystalline Solids, 68(1), 115-122.
  More info

  Abstract: When crystal nucleation occurs in glasses, it is difficult to ascertain whether the crystallization has initiated homogeneously or by a heterogeneous mechanism. Here we suggest a method which might enable one to make this choice, and it is applied to the bulk crystal nucleation observed in Li2O · 2SiO2. It is concluded that crystal nucleation in the latter system most probably occurs homogeneously. © 1984.
• Zelinski, B. J., & Uhlmann, D. R. (1984). Gel technology in ceramics. Journal of Physics and Chemistry of Solids, 45(10), 1069-1090.
  More info

  Abstract: The use of sol-gel techniques to prepare ceramic materials ranks high among those areas in ceramic science and technology which are changing most rapidly and which offer the greatest promise for outstanding improvements in both understanding and applications. This paper reviews the important theoretical considerations, processing techniques and applications related to sol-gel derived ceramics. The gelation behavior of colloidal and polymeric gels, in general, and the influence of such variables as solvent type and concentration, pH, catalyst concentration, temperature, etc. on several oxide systems including silica are considered. The importance of capillary stresses and the various techniques used to minimize them during drying are discussed as are the relevant theories which describe the sintering and firing behavior of the dried gels. To produce ceramics containing more than one oxide, appropriate chemical techniques must be employed to obtain the desired homogeneity. The addition of salts, partial hydrolysis, and alkoxide complexation are among the more widely employed techniques reviewed. A review of current and potential applications of sol-gel derived ceramics, which includes specific examples from the areas of novel glasses, fibers, abrasives, thin films and coatings, is included as well. The paper closes with recommendations and suggestions for future work especially in areas which would benefit from the expertise of physicists and chemists. © 1985.
• Button, D. P., Mason, L. S., Tuller, H. L., & Uhlmann, D. R. (1983). Structural disorder and enhanced ion transport in amorphous conductors. Solid State Ionics, 9-10(PART 1), 585-592.
  More info

  Abstract: Conductivity (σ) data are reported for Li2B4O7 and LiBO2 crystals. While the σ behavior of boracite glass has been suggested to be comparable to its fast ion conducting (FIC) crystalline form, diborate and metaborate glasses are observed to be substantially better conductors than their crystalline counterparts. Both here and in the literature, framework disorder can be associated with enhanced σ's. Data on density and lithium vibration spectra are considered in a critical analysis of the borate structures. The distribution of anionic species about the framework, and in turn, about interstices in the carrier sublattice, is shown to influence critically the transport behavior. Paradigms for FIC are reevaluated in light of a closer inspection of structure-transport relationships in polymorphic materials. © 1983.
• Cranmer, J. H., Plotzker, I. G., Peebles Jr., L. H., & Uhlmann, D. R. (1983). Carbon mesophase-substrate interactions. Carbon, 21(3), 201-207.
  More info

  Abstract: The formation, growth and coalescence of mesophase materials have been followed by hot stage microscopy and by room temperature examination of polished surfaces for various mesophase-forming materials and in the presence of various substrates. The appearance of mesophase particles should be preceded by polymerization of isotropic material into sheet-like molecules, followed by orientation of the sheet-like molecules into ordered regions. Precipitation, growth and coalescence should require ordering of small molecules in a viscous medium. Our results indicate that dynamic motion in the fluid, rather than the presence of nucleating particles, is the controlling factor, very likely reflecting a small mesophase-isotropic liquid interfacial energy. Where dynamic motion is restricted, as in the interstices of a yarn, mesophase formation and growth are also restricted. Alignment of mesophase material with a substrate is primarily controlled by the motion of the mesophase droplets as they flow across the substrate. In general, substrates are not wetted by mesophase in the presence of isotropic material. Certain surfaces are wetted by the mesophase droplets but alignment appears to be controlled more by flow orientation than by surface energy interaction. © 1983.
• Fang, C. Y., Yinnon, H., & Uhlmann, D. R. (1983). Cooling rates for glass containing lunar compositions.. Journal of Geophysical Research, 88(Supplement), A907-A911.
  More info

  Abstract: Cooling rates required to form glassy or partly crystalline bodies of 14 lunar compositions were estimated using a previously introduced, simplified model. The calculated rates were found to be in good agreement with cooling rates measured for the same compositions. Measurements are also reported of the liquidus T and glass transition T for each composition. Inferred cooling rates are combined with heat-flow analyses to obtain insight into the thermal histories of samples 15422, 14162, 15025, 74220, 74241, 10084, 15425 and 15427. The critical cooling rates required to form glasses of 24 lunar compositions, including the 14 compositions of the present study, are suggested to increase systematically with increasing ratio of total network modifiers/total network formers in the compositions. This reflects the importance of melt viscosity in affecting glass formation.-P.Br.
• Fang, C., Yinnon, H., & Uhlmann, D. R. (1983). A kinetic treatment of glass formation. VIII: Critical cooling rates for Na₂OSiO₂ and K₂OSiO₂ glasses. Journal of Non-Crystalline Solids, 57(3), 465-471.
  More info

  Abstract: The critical cooling rates required to form glass have been measured for Na2OSiO2 compositions containing 15.4, 20.6, 29.9 and 34.0 wt% Na2O and for K2OSiO2 compositions containing 15.3, 21.7, 34.3, 41.8 and 43.9 wt% K2O. Pronounced minima in critical cooling rate are observed in the ranges about 25 wt% Na2O and 33 wt% K2O. The locations of these minima correlate with regions of low liquidus temperatures (near eutectics) in the phase diagrams. Calculations of critical cooling rates have been carried out using the analysis of crystallization statistics and the simplified model of glass formation. In both cases, the models predict well the measured critical cooling rates and their variation with composition. © 1983.
• Herms, J., Peebles Jr., L. H., & Uhlmann, D. R. (1983). Chemical stress cracking of acrylic fibres. Journal of Materials Science, 18(8), 2517-2530.
  More info

  Abstract: The generation of periodic microscopic transverse cracks in oriented acrylic fibres immersed in hot alkaline hypochlorite solution is described in detail and shown to be a variety of chemical stress cracking. It is greatly accelerated by external tensile stress, high fibre permeability, moderate fibre orientation, and water-plasticization. The proposed mechanism for bond cleavage involves cyclization of nitrile groups (similar to the "prefatory reaction" in pyrolysis of acrylic fibres), followed immediately by N-chlorination and chain scission. Mechanical retractile forces (internal or external) then cause chain retraction and crack growth. Despite the remarkable regularity of the crack pattern, which typically resembles a series of stacked lamellae, the process is independent of any such underlying fibre morphology. The cracking process does, however, appear to be a sensitive indicator of residual latent strain in the fibre, which may persist even after high-temperature annealing. © 1983 Chapman and Hall Ltd.
• Jang, B. Z., Uhlmann, D. R., & Sande, J. V. (1983). CRYSTALLINE MORPHOLOGY OF POLYPROPYLENE AND RUBBER-MODIFIED POLYPROPYLENE.. Polymeric Materials Science and Engineering, Proceedings of the ACS Division of Polymeric Material, 49, 645-649.
• Jang, B. Z., Uhlmann, D. R., & Sande, J. V. (1983). MECHANISM OF DUCTILE-TO-BRITTLE TRANSITION IN POLYMERS.. Polymeric Materials Science and Engineering, Proceedings of the ACS Division of Polymeric Material, 49, 129-132.
• Uhlmann, D. R. (1983). GLASS FORMATION, A CONTEMPORARY VIEW.. Journal of the American Ceramic Society, 66(2), 95-100.
  More info

  Abstract: The process of glass formation is discussed from several perspectives. Particular attention is directed to kinetic treatments of glass formation and to the question of how fast a given liquid must be cooled in order to form a glass. Specific consideration is paid to the calculation of critical cooling rates for glass formation.
• Uhlmann, D. R. (1983). GLASS PROCESSING IN A MICROGRAVITY ENVIRONMENT.. Advances in Ceramics, 5, 118-127.
• Yinnon, H., & Uhlmann, D. R. (1983). Applications of thermoanalytical techniques to the study of crystallization kinetics in glass-forming liquids, part I: Theory. Journal of Non-Crystalline Solids, 54(3), 253-275.
  More info

  Abstract: A critical review is presented of mathematical methods advanced over the last 20 years for the analysis of data obtained from non-isothermal thermoanalytical studies of crystallization of glass-forming liquids. Methods proposed by Ozawa, Piloyan and Borchardt, Coats, Redfern and Sestak, Ozawa and Chen, Takhor, Kissinger, and Augis and Bennett are examined in detail. All these methods are based on the Avrami treatment of transformation kinetics and define an effective crystallization rate coefficient having an Arrhenian temperature dependence. Several different ways of mathematically treating the data have been proposed. Most are shown to be based on an incorrect neglect of the temperature dependence of the rate coefficient. By taking proper account of the temperature dependence of the crystallization rate coefficient, all the methods are shown to lead to similar conclusions. In detail, it is shown that the effective activation energy of the overall crystallization process can be calculated from the slope of the line obtained by plotting 1n[Q/(TP - T0)] versus 1/TP is the temperature of maximum crystallization rate, TO is an initial temperature and Q is the heating rate employed in the experiment. It is further argued that in general the overall crystallization rate coefficient is not Arrhenian in character. Thus, in general, non-isothermal transformation cannot be treated analytically. A detailed description of nonisothermal transformation can, however, be obtained by numerical methods. Such a method is described and its uses in obtaining kinetic data from thermoanalytical studies are demonstrated. © 1983.
• Button, D., Tandon, R., King, C., Veléz, M., Tuller, H., & Uhlmann, D. (1982). Insights into the structure of alkali borate glasses. Journal of Non-Crystalline Solids, 49(1-3), 129-142.
  More info

  Abstract: In the light of extensive new glass transition temperature (Tg) and density (ρ{variant}) data obtained for the ternary glass system Li2O(LiCl)2B2O3 we have re-examined the well accepted structural models developed for borate glasses by Krogh-Moe and co-workers. We find that, in contrast to the conclusions of NMR, Raman and IR spectroscopy, glasses in the binary and in the ternary systems with common O/B ratios do not exhibit identical boron-oxygen networks. Rather, we find that as LiCl in the ternary is increased the network is systematically weakened and expanded to accommodate the large Cl- anion. On the basis of these observations we question the ability of spectroscopic techniques such as Raman and NMR to confirm the uniqueness of structural models based on combinations of intermediate-range units. We propose a tentative model which is qualitatively in agreement with the observed changes in Tg and ρ{variant} upon addition of LiCl, and explains how the large Cl- ions can be accommodated without large increases in energy due to strain and electrostatic effects while maintaining BO4/BO3 constant. Recent transport results on some fast ion conducting glasses in this system are also discussed in terms of the proposed model. © 1982.
• Cranmer, J. H., Tesoro, G. C., & Uhlmann, D. R. (1982). CHEMICAL MODIFICATION OF CARBON FIBER SURFACES WITH ORGANIC POLYMER COATINGS.. Industrial & Engineering Chemistry, Product Research and Development, 21(2), 185-190.
  More info

  Abstract: Modifications of the carbon fiber-matrix interface for the purpose of improving the performance of composites require consideration of the microstructure, chemistry and geometry of fiber surfaces, as well as of molecular interactions at the interphase. Several approaches to tailoring of the interphase by coating carbon fibers with organic polymers have been reported. This study concerns one such approach, namely, the coating of carbon fibers by interfacial polycondensation. The conditions required for the formation of uniform adherent films on the fiber surfaces have been investigated for selected substrates and monomer pairs, and the feasibility of the approach has been demonstrated. Further research is in progress to establish correlations between the chemical structure and properties of the organic polymer coating and its effectiveness in improving the properties of composites in which the modified fibers are used.
• Herms, J., Peebles, L. H., & Uhlmann, D. R. (1982). Chemical stress cracking of acrylic fibres. Array.
  More info

  Abstract: The generation of periodic microscopic transverse cracks in oriented acrylic fibres immersed in hot alkaline hypochlorite solution is described. A variety of chemical stress cracking was observed. It was found that cracking was accelerated by external tensile stress, high fibre permeability, moderate fibre orientation, and water-plasticization. It was also found that the cracking process was a sensitive indicator of residual latent strain in the fibre, which may persist after high-temperature annealing.
• Kwizera, P., Dresselhaus, M. S., Uhlmann, D. R., Perkins, J. S., & Desper, C. R. (1982). Microstructure of intercalated graphite fibres. Array.
  More info

  Abstract: The structures of graphite fibres derived from polyacrylonitrile and pitch were studied by means of scanning and transmission electron microscopy and small- and wide-angle X-ray diffraction. A higher degree of crystalline order was observed in pitch-based carbon fibres.
• Kwizera, P., Dresselhaus, M. S., Uhlmann, D. R., Perkins, J. S., & Desper, C. R. (1982). The microstructure of intercalated graphite fibers. Carbon, 20(5), 387-394.
  More info

  Abstract: A study of the microstructure of two types of graphite fibers GY70, a polyacrylotrinitrile (PAN) based fiber and UC4104B a pitch based fiber, is reported. These high modulus fibers were modified by intercalation with the donors K, Rb, Cs and the acceptors FeCl3, AlCl3. Several experimental techniques were used, to elucidate the effects of intercalation on the microstructure of the graphite fibers. These include scanning and transmission electron microscopy and small and wide angle X-ray diffraction. © 1982.
• Neiman, T. S., Yinnon, H., & Uhlmann, D. R. (1982). Crystallization kinetics of lead metasilicate. Journal of Non-Crystalline Solids, 48(2-3), 393-403.
  More info

  Abstract: The crystallization kinetics of PbO·SiO2 have been determined from 500°C. The thickness of the crystal layer was found to increase linearly with time; and the interface morphology was faceted at all temperatures. The heat of fusion of PbO·SiO2 was estimated in two ways: (1) from DSC measurements of heat capacities of glassy and crystalline PbO·SiO2 combined with tabulated ΔS0(298) values; and (2) from direct mesurements using heat-flux DSC. The average value of ΔHf obtained is 8.1 × 103 cal mol-, corresponding to an entropy of fusion of 3.9R. The growth process of PbO·SiO2 is interface-controlled, with an interface site factor which increases with increasing undercooling. The plot of log (growth rate × viscosity) versus (T ΔT-1 can be described by two straight lines with different slopes. The slopes correspond to edge surface energies of 113 and 51 erg cm-2, leading to values of 0.35 and 0.16 respectively for the ratio σM/ΔHfM (were σM is the molar surface energy and ΔHfM is the molar heat of fusion). It is shown that the crystal growth data on PbO·SiO2 are within an order of magnitude of the theoretically-predicted values based on the standard model of surface-nucleation controlled crystal growth, at least at small undercoolings. The data seem, however, at variance with predictions based on computer simulations of crystal growth using the measured heat of fusion. The excellent glass-formability of PbO·SiO2, in spite of its high fluidity, may be explained by this deviation from expected behavior and by the absence of effective nucleating heterogeneities. © 1982.
• Uhlmann, D. R. (1982). CRYSTAL GROWTH IN GLASS-FORMING SYSTEMS: A TEN-YEAR PERSPECTIVE.. Advances in Ceramics, 4, 80-124.
• Uhlmann, D. R. (1982). GLASS PROCESSING IN A MICROGRAVITY ENVIRONMENT.. Materials Research Society Symposia Proceedings, 9, 269-278.
• Uhlmann, D. R. (1982). KINETICS OF GLASS FORMATION AND DEVITRIFICATION BEHAVIOR.. Journal de Physique (Paris), Colloque, 43(12), 175-190.
• Uhlmann, D. R. (1982). Microstructure of glasses: Does it really matter?. Journal of Non-Crystalline Solids, 49(1-3), 439-460.
  More info

  Abstract: The important microstructural features of glasses - phase separation structures, stones, cord, striae, knot, ream and seed - are discussed from the perspective of their effects on the processing and properties of glasses. Also considered are the effects of melt history on the properties of glasses and a number of applications involving the control of two-phase structures in glasses. It is suggested that further attention be directed to applying our present knowledge of phase separation phenomena to the development of novel products and processes, and also to the development of improved models for the glassy state. © 1982.
• Veléz, M., Tuller, H., & Uhlmann, D. (1982). Chemical durability of lithium borate glasses. Journal of Non-Crystalline Solids, 49(1-3), 351-362.
  More info

  Abstract: A series of lithium borate and lithium chloroborate glasses, some of which exhibit fast ion conduction, have been tested for their corrosion resistance to molten lithium at temperatures of 180 to 250°C. In all cases, the mechanism of corosion involved formation of crystalline reaction layers. The thickness of these layers increased parabolically with time, supporting a model involving diffusion-controlled chemical attack. The rate of growth of the reaction layer was found to decrease significantly with increasing Li2O content in the binary B2O3Li2O system, and to depend on the Li2X/B2O3 (X = Cl, O) in the ternary B2O3Li2O(LiCl))2 system. For glasses with high B2O3 contents (>70 m/o), the durability decreases with increasing chlorine concentration; while for low B2O3 contents (>50 m/o), the addition of LiCl increases the durability of the glasses at modest temperatures. The apparent activation energies for the corrosion process depend on initial glass composition, and vary from ∼0.5 eV for pure B2O3 to ∼2.0 eV for high (LiCl)2/B2O3 ratios. The results suggest that a glass with minimum B2O3 content, consistent with glass formability, will result in optimum resistance to molten Li attack. The same glasses have been tested for their durability in water, both buffered (pH=7) and unbuffered solutions at various temperatures. All glasses dissolved at a constant rate, suggesting a reaction-controlled mechanism of attack. A minimum in dissolution rate was found at about 25-30 m/o Li2O in the binary B2O3Li2O system, and at O/B∼1.7 for glasses in the B2O3Li2O(LiCl)2 system. For a constant O/B ratio, addition of chlorine results in a decrease of the durability of the glasses. The combined results are discussed with reference to current views of the structure of borate and chloroborate glasses with insights obtained from NMR studies and measurements of densities and glass transition temperatures. © 1982.
• Yinnon, H., & Uhlmann, D. R. (1982). A kinetic treatment of glass formation VII: Transient nucleation in non-isothermal crystallization during cooling. Journal of Non-Crystalline Solids, 50(2), 189-202.
  More info

  Abstract: The analysis of crystallization statistics has been modified to allow for time-dependent (transient) nucleation. To establish its accuracy, the numerical analysis has been applied to isothermal crystallization kinetics and shown to yield crystallization versus time curves which compare very closely with curves calculated analytically with or without the inclusion of transient nucleation. The numerical analysis including transient has been used to calculate the critical cooling rates for glass formation in anorthite and o-terphenyl considering (1) only homogeneous nucleation and (2) homogeneous nucleation + heterogeneous nucleation for 107 heterogeneities cm-3 with contact angles between 40° and 100°. It has been shown that inclusion of time-dependent nucleation in the calculations does not change the critical cooling rates for glass formation calculated assuming steady-state homogeneous nucleation in both materials. The critical cooling rate in anorthite calculated including steady-state heterogeneous nucleation was found to be decreased only slightly by the inclusion of time-dependent nucleation; while the critical cooling rates calculated for o-terphenyl were not change at all by the inclusion of time-dependent nncleation. The lack of an effect of time-dependent nucleation on the critical cooling rates calculated assuming only homogeneous nucleation is explained by the relatively small transient times on the high temperature side of the nucleation peak (a temperature range which has an overwhelming effect on the overall crystallization process because of the relatively high crystal growth rates in this range). Although the critical cooling rates associated with heterogeneous nucleation are large, the nucleation here takes place at relatively small undercooling where the transient times are relatively small. Thus, transient nucleation causes only a temporary delay in the over all crystallization, and its effect on the critical cooling rate is small. © 1982.
• Barsoum, M., Velez, M., Tuller, H. L., & Uhlmann, D. R. (1981). REACTIONS AT ALKALI METAL-GLASS INTERFACES.. Materials Science Research, 14, 567-577.
• Button, D. P., Tandon, R. P., Tuller, H. L., & Uhlmann, D. R. (1981). Fast Li+ ion conductance in chloroborate glasses II-diborates and metaborates. Solid State Ionics, 5(C), 655-658.
  More info

  Abstract: The understanding of FIC in amorphous materials is limited in part due to a lack of reliable structural models. Alkali oxide additions to B2O3 are known to modify the glass network initially by the formation of BO4-tetrahedral units at the expense of trigonal BO3 units. Our recent studies on the system 36.4 mol%Li2Z(Z=0,Cl2)-63.6 mol% B2O3 demonstrate that major structural changes in the network also accompany the large increases in ion conductivity upon the replacement of oxygen with chlorine. In the present study, the scope of our investigation has been extended to glasses of composition Li2Z.2B2O3 (diborate) and Li2Z.B2O3 (metaborate). This enables us to study glasses at several different total Li contents lying in different regimes of network structure, as a function of Cl additions. Results of extensive measurements of electrical conductivity, glass transition and density as a function of glass composition and temperature are used to emphasize the importance of considering structural changes along with ion transport variations upon modification of glass composition. Suggestions for the cause of observed structure-transport relations are presented. © 1981.
• Chen, S. S., Herms, J., Peebles Jr., L. H., & Uhlmann, D. R. (1981). Oxidative stabilization of acrylic fibres - Part 5 The decolouration reaction. Journal of Materials Science, 16(6), 1490-1510.
  More info

  Abstract: When acrylic fibres are heat treated for various times at 220 to 250° C, they form dark, insoluble structures of uncertain chemical character which are inert to many strong oxidizing and reducing agents. The heat-treated fibres are, however, rapidly decoloured by warm alkaline hypochlorite solutions. When fibres which have undergone short-time heat treatment are subjected to the hypochlorite, incubation periods are observed before decolouration is noted; and a swollen acrylic network remains after decolouration is complete. The acrylic network is primarily unreacted precursor units save for a small amount of hydrolyzed material. The decoloured reaction is zero order, indicating a reaction at the surface. The rate of the decolouration reaction also increases with increasing duration of the stabilization heat treatment. In fibres which have undergone partial diffusion-controlled stabilization, a dark mantle surrounds a lightly coloured core. The rate of decolouration is unaffected as the decolouration interface passes from the mantle to the core, indicating that the decolouration reaction is not influenced by the occurance of any sequent reactions. The existence of the acrylic residue indicates that the prefatory reactions are continuing in both mantle and core during the course of stabilization.13C-NMR spectra of the acrylic residue show the same triad methine peak areas as those obtained on the untreated fibre; hence the stereoregularity of the nitrile groups has no influence on the rate of nitrile polymerization. The mechanisms of nitrile initiation and of decolouration are discussed. The residue obtained by sulphuric acid etch is different from that obtained by hypochlorite treatment. These results suggest that during the early-to-intermediate stages of stabilization, the fibre consists of interpenetrating networks of original material, i.e., fibre which has undergone only the prefatory reactions and fibre which has undergone the sequent reactions. © 1981 Chapman and Hall Ltd.
• Chen, S. S., Herms, J., Peebles, L. H., & Uhlmann, D. R. (1981). Oxidative stabilization of acrylic fibres. V. Decoloration reaction. Array.
• Cranmer, D., & Uhlmann, D. R. (1981). Viscosities in the system albite - anorthite.. Journal of Geophysical Research, 86(B9), 7951-7956.
  More info

  Abstract: The viscosities of several compositions were measured from 800o to 1600oC. The logeta vs 1/T show continuous curvature for all compositions. The viscosity-T relations have a crossover so that at approx 750oC, viscosity increases with An content.-K.A.R.
• Cranmer, D., & Uhlmann, D. R. (1981). Viscosity of liquid albite, a network material. Journal of Non-Crystalline Solids, 45(2), 283-288.
  More info

  Abstract: The viscosity of liquid albite (NaAlSi3O8) has been determined over the temperature range 800-1000°C. The results are combined with data obtained at higher temperatures to obtain the overall log η versus 1 T relation. The relation indicates Arrhenian behavior, with an apparent activation energy of ∼95 kcal mol-1. By comparing the viscous flow behavior of albite with that of the other materials, including SiO2, GeO2 and B2O3, it is suggested that liquid albite is a random network of SiO4 and AlO4 tetrahedra. © 1981.
• Cranmer, D., Salomaa, R., Yinnon, H., & Uhlmann, D. R. (1981). Barrier to crystal nucleation in anorthite. Journal of Non-Crystalline Solids, 45(1), 127-136.
  More info

  Abstract: The kinetics of crystal nucleation in anorthite (CaAl2Si2O8) have been determined over the range of undercooling between 475 and 600°C. The plot of In(Ivη) versus (ΔT|staggered|r2T|staggered|r3)-1 is a straight line of negative slope over the temperature range investigated. The slope of this relation indicates a free energy barrier to crystal nucleation of about 82 kT* (where T* = 0.8TE). The intercept at (ΔT|staggered|r2Tstaggered|r3)-1 = 0 is approximately 1027 cm-3 s-1P. Samples of anorthite glass were also analyzed by differential thermal analysis, with the temperature of maximum crystallization rate being determined as a function of heating rate. From this variation, a nucleation barrier of about 80 kT* was estimated. The combined results are in good agreement with predictions of the classical theory of homogeneous nucleation. © 1981.
• Onorato, P. I., Hopper, R. W., Yinnon, H., Uhlmann, D. R., Taylor, L. A., Garrison, J. R., & Hunter, R. (1981). Solute partitioning under continuous cooling conditions as a cooling rate indicator.. Journal of Geophysical Research, 86(B10), 9511-9518.
  More info

  Abstract: A mathematical model is given for the concentration profile as a function of time, including a T-dependent partitioning of the solute between the two phases. It is illustrated by the partitioning of zirconia between ilmenite and ulvospinel. The cooling rates of a suite of Apollo 15 Elbow Crater gabbros are calculated and the implications are discussed. -K.A.R.
• Yinnon, H., & Uhlmann, D. R. (1981). A kinetic treatment of glass formation V: Surface and bulk heterogeneous nucleation. Journal of Non-Crystalline Solids, 44(1), 37-55.
  More info

  Abstract: An analytical method is described for calculating the detailed distribution of crystallite sizes in a supercooled liquid, and the changes in this distribution as a function of temperature (time) while the liquid is cooled from above the melting point. This method, termed the analysis of crystallization statistics, is applied to the calculation of continuous cooling curves for anorthite and o-terphenyl as representative of inorganic and organic systems. In addition to homogeneous nucleation, bulk as well as surface heterogeneous nucleation are considered. The effects of distributions of heterogeneities with contact angles between 40 and 100° as well as overall concentrations of heterogeneities between 103 and 109 cm-3 are considered. Heterogeneities with contact angles higher than about 100° are shown not to have an effect on the critical cooling rate for typical concentrations of heterogeneities. For liquids containing distributions of heterogeneities, the nucleation behavior is dominated by small concentrations of heterogeneities having small contact angles. Theoretical log (Ivη) versus (Tr3ΔTr2)-1 curves have been constructed for homogeneous nucleation + heterogeneous nucleation with a single type of heterogeneity and for homogeneous nucleation + heterogeneous nucleation with the heterogeneities distributed with regard to contact angle. In the former case, the curve is composed of two linear portions; and in the latter case, the curve shows pronounced curvature. The curvature reflects a continous change in the frequency of heterogeneous nucleation. Surface heterogeneous nucleation was assumed to originate at discrete surface heterogeneities and was shown to give rise to continuous cooling curves similar to those calculated for bulk heterogeneous nucleation. © 1981.
• Button, D. P., Tandon, R. P., Tuller, H. L., & Uhlmann, D. R. (1980). FAST Li** plus ION CONDUCTION IN CHLORO-BORATE GLASSES.. Journal of Non-Crystalline Solids, 42(1-3), 297-306.
  More info

  Abstract: Substitutions of Cl for O in lithium borate glasses of the type Li//2O-(LiCl)//2-B//2O//3 (Li//2Z equals 36. 4 m/o) were found to result in systematically increasing Li ion conductivity, and decreasing Tg and density. In contrast to earlier studies which implied no B-O network modification upon Cl addition, substantial changes were found as exemplified in Tg and density variations. The effect of Cl substitution was traced to a change in O/B ratio. Liquid-liquid immiscibility limited the vitreous domain of glasses formed with LiCl. This resulted in a leveling off of various physical parameters with composition in the two-phase domain.
• Chen, S. S., Herms, J., Peebles, L. H., & Uhlmann, D. R. (1980). Oxidative stabilization of acrylic fibres. V. The decoloration reaction. Array.
• Matyi, R. J., Uhlmann, D. R., & Koutsky, J. A. (1980). STRUCTURE OF GLASSY POLYMERS - 7. SMALL-ANGLE X-RAY SCATTERING FROM EPOXY RESINS.. Journal of polymer science. Part A-2, Polymer physics, 18(5), 1053-1063.
  More info

  Abstract: In the reported experiments, the small-angle x-ray scattering (SAXS) from an Epon 812 and two Epon 828 (one amine-cured and one anhydride-cured) epoxy resins has been measured using a Bonse-Hart system. The data cover the angular range (2 theta ) between 20 sec and 60 min. After correction for absorption, background and vertical beam divergence, they have been placed on an absolute basis by comparison with the scattering from a previously studied polycarbonate sample. The magnitude of the intensity in the constant-intensity region is close to the value predicted by thermodynamic fluctuation theory for fluids applied at the glass transition temperature. The increase in intensity at angles smaller than 20-30 min is associated with heterogeneities in the cured resins. These heterogeneities cover a range of sizes in all samples, from less than 100 A to more than 1000 A, with the most frequently occurring size in the range 100-200 A.
• Onorato, P. I., Uhlmann, D. R., & Hopper, R. W. (1980). KINETIC TREATMENT OF GLASS FORMAWTION - 4. CRYSTALLIZATION ON REHEATING A GLASS.. Journal of Non-Crystalline Solids, 41(2), 189-200.
  More info

  Abstract: An analysis, based on the approach of crystallization statistics, is presented to describe crystallization on reheating a glass. The analysis treats heating carried out at the same or different rate relative to the cooling rate used to form the glass. The analysis takes account of the finite size of the critical nucleus and provides a description of the state of crystallinity in a body for both short and long times. The temperature of crystallization on reheating a glass is shown to depend strongly on the heating rate and on the barrier to crystal nucleation and less strongly on the cooling rate used to form the glass.
• Tuller, H., Button, D., & Uhlmann, D. (1980). Fast ion transport in oxide glasses. Journal of Non-Crystalline Solids, 40(1-3), 93-118.
  More info

  Abstract: The discovery of fast ion transport in solids has in recent years stimulated much interest in the scientific community both with regard to obtaining improved understanding of the phenomenon and applying such materials in advanced battery systems. More recently the phenomenon of fast ion transport has also been observed to occur in increasing numbers of amorphous systems. In this paper we review recent transport data obtained in over 100 glasses which appear to exhibit exceptionally high Ag, Li, Na and F ion conductivities at temperatures far from the melting points. We also include results recently obtained in our laboratory for glasses in the lithium borate system. Common characteristics of these glasses are summarized and are compared with predictions of classical diffusion theory. Relatively low and composition-independent values of σ0 indicate poor agreement with a simple isolated-ion diffusion model, while composition-dependent activation energies are related to structural changes. Some glasses share similar properties with their crystalline counterparts while others do not. This is discussed in terms of the relative disorder already existing within the crystals. The need for improved characterization of glasses is also discussed. © 1980.
• Uhlmann, D. R. (1980). Nucleation, crystallization and glass formation. Journal of Non-Crystalline Solids, 38-39(PART 2), 693-698.
  More info

  Abstract: The kinetic treatment of glass formation has been extended to describe crystallization on reheating a glass and to estimate critical cooling rates for glass formation from three measurable quantities, Tg, TL and the heat of fusion. The crystallization temperature on reheating a glass is found to depend strongly on the heating rate and on the barrier to crystal nucleation, and only weakly on the cooling rate used to form the glass. The analysis indicates that simple DTA analyses can be used to estimate the magnitudes of the nucleation barriers of various materials. The simplified treatment of glass formation gives predictions which agree within about an order of magnitude with those obtained using the full detailed kinetic analysis. © 1980.
• Uhlmann, D. R. (1980). On the internal nucleation of melting. Journal of Non-Crystalline Solids, 41(3), 347-357.
  More info

  Abstract: Crystals of quartz have been superheated by some 450°C and crystals of albite by some 185°C above their respective melting points. In all cases, melting took place by the nucleation of liquid at the external surfaces (and internal boundaries as well in the case of albite). No evidence for the internal nucleation of liquid was found at any superheat for either material. The results of quartz indicate an exceptionallu large barrier to the internal nucleation of liquid. It is suggested that this large nucleation barrier is associated with the strain energy of forming a liquid nucleus within the crystalline phase. It is also indicated that the nucleation of liquid at the external surfaces of crystals at negligible superheats suggests that the free surfaces of liquids do not per se serve as preferred nucleating sites for crystallization - and that the crystal nucleation often observed at external surfaces or internal surfaces is in fact associated with condensed second-phase impurities. © 1980.
• Uhlmann, D. R. (1980). POLYMER GLASSES AND OXIDE GLASSES.. Journal of Non-Crystalline Solids, 42(1-3), 119-142.
  More info

  Abstract: The similarities and differences in the structure of polymer glasses and oxide glasses are reviewed, together with models suggested to describe structure on various scales. It is suggested that random array models seem to provide the best description of structure for most glasses of both types of materials. also considered are the crystallization and viscous flow behavior of both classes of materials, together with the implications of the observed behavior for their formation as amorphous solids. The role of the chain character of polymer liquids in affecting their kinetic behavior is considered, as are recent controversies concerning the microstructure of partly-crystallized polymer.
• Weinberg, M. C., Onorato, P. I., & Uhlmann, D. R. (1980). BEHAVIOR OF BUBBLES IN GLASSMELTS - 1. DISSOLUTION OF A STATIONARY BUBBLE CONTAINING A SINGLE GAS.. Journal of the American Ceramic Society, 63(3-4), 175-180.
  More info

  Abstract: Various methods applied to eliminate bubbles from glassmelts are reviewed. This paper reports in some details the dissolution rates of carbondixode bubbles in a soda-lime melt. An analytic expression for the bubble radius as a function of time, was obtained. The effects of surface tension on the dissolution process are included, a factor ignored by many previous investigators.
• Dill, K. A., Frank, F. C., Dill, A. K., Sadler, D. M., DiMarzio, E. A., Guttman, C. M., Hoffman, J. D., Flory, P. J., Yoon, D. Y., Dowell, F., Stein, R. S., Samulski, E. T., Windle, A. H., Everett, D. H., Rigby, D., Stepto, R. F., Pechhold, W., Fischer, E. W., Lovell, R., , Mitchell, G. R., et al. (1979). General discussion. Faraday Discussions of the Chemical Society, 68, 104-140.
• Kolbeck, A. G., & Uhlmann, D. R. (1979). CHARACTERISTICS OF SOLID-STATE EXTRUDED POLYETHYLENE.. J Polym Sci Polym Phys Ed, 17(3), 421-436.
  More info

  Abstract: This paper describes the properties of solid-state extruded polyethylene as a function of two primary processing variables, extrusion temperature, and area reduction. The polymer was extruded in sheet form, giving a material having an orthotropic mode of orientation. Property data are presented for melting temperature and heat of fusion; sonic modulus, yield stress, and elongation at fracture; small-angle x-ray scattering; optical absorption coefficient; and morphology for material etched by ion bombardment at liquid nitrogen temperature. It is found that over the temperature range of about 90-120 degree C, where polyethylene can be successfully extruded to large area reductions, many properties of the extrudates show a surprisingly small dependence on extrusion temperature. A notable exception to this behavior is the elastic modulus, which increases significantly with increasing extrusion temperatures. In contrast to extrusion temperature, area reduction is found to have a major effect on nearly all properties of solid-state extruded polyethylene.
• Point, J. -., Rault, J., Hoffman, J. D., Kovacs, A. J., Mandelkern, L., Wunderlich, B., DiMarzio, E. A., Gennes, P. D., Klein, J., Ball, R. C., Flory, P. J., Yoon, D. Y., Guttman, C. M., Khoury, F., Voigt-Martin, I., Bassett, D. C., Frank, W. F., Atkins, E. D., Booth, C., , Uhlmann, D. R., et al. (1979). General discussion. Faraday Discussions of the Chemical Society, 68, 365-490.
• Uhlmann, D. R. (1979). Electron microscopy and SAXS studies of amorphous polymers. Faraday Discussions of the Chemical Society, 68, 87-95.
  More info

  Abstract: Small angle X-ray scattering (SAXS) and high resolution electron microscopy have been used to characterize the structure of glassy polymers. The SAXS from polycarbonate, poly(methyl methacrylate), poly(ethylene terephthalate), poly(vinyl chloride) and polystyrene is inconsistent, both in the form and magnitude of the scattered intensity, with the presence of nodules as representative of the bulk structure. The electron microscope results provide no evidence for heterogeneities on a scale and volume fraction of the reported nodules. Only the pepper and salt features characteristic of microscope operation near the resolution limit are seen. It is suggested that the structures of these amorphous thermoplastics be regarded as random arrays.
• Warner, S. B., Peebles Jr., L. H., & Uhlmann, D. R. (1979). Oxidative stabilization of acrylic fibres - Part 1 Oxygen uptake and general model. Journal of Materials Science, 14(3), 556-564.
  More info

  Abstract: The mechanism of oxidative stabilization of acrylic fibres is characterized by two limiting cases which are determined by the fibre chemistry, the reaction conditions, and the diameter of the filament. These limiting cases correspond to diffusion-limited and reaction-limited kinetic processes. Although the chemistry of stabilization is too complex to specify, the various reactions are separated into two categories: those which occur prior to or concurrently with polymerization of the nitrile groups, called "prefatory reactions"; and those which occur subsequent to nitrile polymerization, called "sequent reactions". Under conditions which allow the prefatory reactions to occur significantly before the sequent reactions, the diffusion of oxygen to reactive sites is limited by previously oxidized material; and the fibre shows a typical two-zone morphology. Under conditions where the prefatory and sequent reactions occur sequentially, the overall stabilization process is limited by the rate of the prefatory reactions; but a skin is established at the fibre surface which acts as an oxygen barrier. Data from a variety of sources, including oxygen analysis, microscopic examination, fibre residue after etching, tension developed in fibres held at constant length, and small-angle X-ray patterns, are cited as evidence for the two limiting cases. © 1979 Chapman and Hall Ltd.
• Warner, S. B., Peebles Jr., L. H., & Uhlmann, D. R. (1979). Oxidative stabilization of acrylic fibres - Part 2 Stabilization dynamics. Journal of Materials Science, 14(3), 565-572.
  More info

  Abstract: As acrylic fibres are heated in air to induce the stabilization reactions, the tension developed when stabilized at constant length and the instantaneous velocity of stabilizing fibres undergoing continuous processing both depend on the chemical composition, diameter, and orientation of the precursor fibre. An orientated fibre will tend to shrink when heated in the range 130 to 160° C, and hence will develop tension if restrained at constant length. Although this process has no direct relation to the stabilization process, it will influence the instantaneous velocity of the fibre during the later stages of continuous processing. As a fibre held at constant length is heated above 160° C the tension developed by entropic relaxation decreases and the fibre starts to undergo the prefatory and sequent reactions of stabilization described in a previous paper. If the prefatory reactions are rapid, a rigid structure is quickly established in the fibre and tension again increases rapidly. However, if the prefatory reactions are slow, select portions of the fibre react preferentially and the unreacted portions tend to relax to maintain a temporary quasi-equilibrium tension level. In both cases the fibres shrink at the later stages of stabilization because of chemical reactions. The shape of the tension-time curve is similar to the oxygen-uptake curves: The diffusion-limited mechanism of stabilization produces parabolic curves whereas the reaction-limited mechanism produces linear curves. Because each element of a fibre undergoing processing is subjected to the same tension at all times, previously orientated fibres first shrink, then stretch, and finally shrink again. These competing processes give rise to a changing instantaneous velocity. Data are presented for fibres of varying chemical composition, diameter, and initial orientation as well as for different conditions of stabilization. © 1979 Chapman and Hall Ltd.
• Warner, S. B., Peebles Jr., L. H., & Uhlmann, D. R. (1979). Oxidative stabilization of acrylic fibres: Part 4 Moisture sensitivity. Journal of Materials Science, 14(11), 2764-2765.
• Warner, S. B., Peebles, L. H., & Uhlmann, D. R. (1979). Oxidative stabilization of acrylic fibres. I. Oxygen uptake and general model. Array.
• Warner, S. B., Peebles, L. H., & Uhlmann, D. R. (1979). Oxidative stabilization of acrylic fibres. I. Oxygen uptake and general model. II. Stabilization dynamics. Array.
• Warner, S. B., Peebles, L. H., & Uhlmann, D. R. (1979). Oxidative stabilization of acrylic fibres. II. Stabilization dynamics. Array.
• Warner, S. B., Peebles, L. H., & Uhlmann, D. R. (1979). Oxidative stabilization of acrylic fibres. IV. Moisture sensitivity. Array.
• Warner, S. B., Uhlmann, D. R., & Peebles Jr., L. H. (1979). Oxidative stabilization of acrylic fibres - Part 3 Morphology of polyacrylonitrile. Journal of Materials Science, 14(8), 1893-1900.
  More info

  Abstract: A new model for the structure of oriented acrylic fibres is presented. The polyacrylonitrile molecules (or the acrylic sequences in a co-polymer) are suggested to form two distinct regions within a fibril: amorphous (disordered) and partially ordered. In the partially ordered regions, the polymer molecules assume a contorted helical shape to form rods with a diameter averaging about 6.0 Å in which the nitrile units are oriented at various angles to the rod axis, but are spaced irregularly on or near the surface of the rod. The nitrile groups of adjacent rods can interpenetrate to form dipole pairs. The rods are ordered into a liquid crystal-type array, giving in some cases a lamellar-like texture oriented perpendicular to the fibril axis, with the ordered lamellae regions interspersed with amorphous regions. Evidence for the structure is obtained from transmission electron microscopy observations, a transient peak observed in small-angle X-ray scattering when fibres are thermally treated, as well as wide-angle X-ray diffraction patterns. The proposed model is consistent with the absence of a periodic repeat unit along the chain direction, with the h k 0 reflections seen in wide-angle X-ray and electron diffraction, with the spherulitic morphology reported in some studies, and with the platelike morphologies obtained under some conditions of precipitation from dilute solution. © 1979 Chapman and Hall Ltd.
• Warner, S. B., Uhlmann, D. R., & Peebles, L. H. (1979). Oxidative stabilization of acrylic fibres. III. Morphology of polyacrylonitrile. Array.
• Meyer, M., Sande, J. V., & Uhlmann, D. R. (1978). ON THE STRUCTURE OF GLASSY POLYMERS - 6. ELECTRON MICROSCOPY OF POLYCARBONATE, POLY(EHTYLENE TEREPHTHALATE), POLY(VINYL CHLORIDE), AND POLYSTYRENE.. J Polym Sci Polym Phys Ed, 16(11), 2005-2014.
  More info

  Abstract: In the reported experiments, high-resolution electron microscopy studies have been carried out on four glassy polymers examined in previous small-angle x-ray scattering (SAXS) investigations. The polymers include polycarbonate, poly(ethylene terephthalate), poly(vinyl chloride), and polystyrene. For all four polymers, both bright-field and dark-field observations indicate the general absence of microstructural features of a size down to the resolution limit of the electron microscope. Only ″pepper and salt″ features on a scale ca. 5A are seen as characteristic of the structures. These features reflect simple interferences as the resolution limit is approached, and are seen for single crystals and oxide glasses as well as for the polymers. The present results, taken together with structural information from light scattering, SAXS and small-angle neutron scattering, indicate that glassy polymers should be regarded as having random structures. The combined results are inconsistent with heterogeneous microstructures having regions of locally high order present in large volume fractions.
• Meyer, M., Sande, J. V., & Uhlmann, D. R. (1978). On the structure of glassy polymers. VI. Electron microscopy of polycarbonate, poly(ethylene terephthalate), poly(vinyl chloride), and polystyrene. Array.
• Renninger, A. L., & Uhlmann, D. R. (1978). STRUCTURE OF GLASSY POLYMERS. V. SMALL-ANGLE X-RAY SCATTERING FROM POLYSTYRENE.. J Polym Sci Polym Phys Ed, 16(12), 2237-2244.
  More info

  Abstract: In the reported experiments, small-angle x-ray scattering (SAXS) from glassy atactic polystyrene has been measured using a Bonse-Hart system. After correcting for absorption, background, and beam divergence, the scattering has been placed on an absolute basis using a standard silica suspension as a reference. The desmeared absolute intensity decreases strongly with increasing scattering angle over the range between 20 sec and 20 min. At larger angles, the intensity decreases much more slowly with increasing angle and approaches the value expected for density fluctuations frozen-in at the glass transition. The angular variation of intensity is well described by the scattering from heterogeneities of various sizes and concentrations superimposed on the scattering from thermal density fluctuations. These heterogeneities range in radius from 10 to 4000 A. The present SAXS results on glassy polystyrene seem inconsistent with the presence of nodular features as representative of the bulk polymer.
• Warner, S. B., Peebles, L. H., & Uhlmann, D. R. (1978). Oxidative stabilization of acrylic fibres. I. Oxygen uptake and general model. Array.
• Warner, S. B., Peebles, L. H., & Uhlmann, D. R. (1978). Oxidative stabilization of acrylic fibres. II. Morphology of polyacrylonitrile. Array.
• Warner, S. B., Peebles, L. H., & Uhlmann, D. R. (1978). Oxidative stabilization of acrylic fibres. III. Stabilization dynamics. Array.
• Klein, L. C., Handwerker, C. A., & Uhlmann, D. R. (1977). Nucleation kinetics of sodium disilicate. Journal of Crystal Growth, 42(C), 47-51.
  More info

  Abstract: The kinetics of crystal nucleation in Na2O · 2SiO2 have been determined over the range of undercoolings between 173 and 373°C. The plot of log(Ivn{long right leg}) versus 1 ΔT2rT3r is a straight line of negative slope over some 13 orders of magnitude in Iv. The slope of this relation indicates a nucleation barrier of about 45 kT at ΔTr = 0.2, and the intercept at 1 ΔT2rT3r = 0 is 1026 cm-3 sec-1. poise. The results are in good agreement with predictions of the theory of homogeneous nucleation, even in the pre-exponential factor. © 1977.
• Kolbeck, A. G., & Uhlmann, D. R. (1977). PROCESSING OF SEMICRYSTALLINE POLYMERS BY HIGH-STRESS EXTRUSION.. J Polym Sci Polym Phys Ed, 15(1), 27-42.
  More info

  Abstract: In the reported experiments, a study has been conducted on the solid-state extrusion of three semicrystalline polymers: PP, poly(vinylidene fluoride) (PVDF), and HDPE. HDPE has been extruded in continuous lengths with area reductions up to 25 multiplied by at temperatures substantially below the melting region. Such extrusion has been identified as a solid-state process, since measurements of the temperature of the polymer during extrusion indicate the absence of significant heating due to the deformation. In contrast, continuous lengths of PP and PVDF could not be obtained substantially below their melting temperatures, indicating that crystallization during extrusion is an important process for these polymers. Under severe extrusion conditions (low temperatures, high area reductions, etc. ), all three polymers failed within the tapered region of the extrusion die. Two modes of failure have been identified, brittle fracture and, surprisingly, necking. Grid-line distortion patterns and a highly simplified upper-bound plasticity analysis both indicate that shear deformations are a major factor during high-stress extrusion.
• Scherer, G. W., & Uhlmann, D. R. (1977). Diffusion-controlled crystal growth in K₂OSiO₂ compositions. Journal of Non-Crystalline Solids, 23(1), 59-80.
  More info

  Abstract: The growth of cristobalite dendrites in two K2OSiO2 glasses containing 10.3 and 15.0 mol% K2O has been studied over a wide range of temperature. The kinetics of crystallization were linear; i.e. the growth rates were independent of time. The observed crystallization rates were consistent with a diffusion-controlled mechanism. Measurements of the tip radii of curvature of the dendrites are consistent, at low undercoolings, with the predictions of Horvay and Cahn for the growth of an isolated dendrite. However, at lower temperatures at which the dendrites are closely spaced, the predicted radii are seriously in error. A model is described which takes account of the overlapping diffusion fields of neighboring dendrites and gives improved agreement with the observed growth rates. The presence of a maximum in each of the crystal growth rate versus temperature curves has not been explained. This phenomenon is apparently related to changes in the size, shape and spacing of the dendrites, which occur in the same temperature range. © 1977.
• Uhlmann, D. R. (1977). Glass formation. Journal of Non-Crystalline Solids, 25(1-3), 42-85.
• Weinberg, M. C., Glen, G. L., Eich, E. D., Williams, J. A., Uhlmann, D. R., & Straff, R. (1977). GLASS AS A DIELECTRIC FOR HIGH VOLTAGE CABLE SYSTEMS.. Array, 327-330.
  More info

  Abstract: A review of previous studies on the electrical breakdown characteristics of glass is presented along with a discussion of the additional research required. The use of thick wall glass tubing as the dielectric in high voltage (230 kv and higher) underground cable systems is being evaluated. The present paper discusses the dielectric requirements of such an insulation system, and gives an outline of the electrical testing portion of the development program.
• Kolbeck, A. G., & Uhlmann, D. R. (1976). DEFORMATION STRUCTURES IN SOLID-STATE EXTRUDED POLYETHYLENE.. J Polym Sci Part A-2 Polym Phys, 14(7), 1257-1270.
  More info

  Abstract: Deformation structures resembling kink bands have previously been reported in a number of oriented semicrystalline polymers which have undergone various modes of deformation. In the present work, such structures have been observed and studied in solid-state extruded PE which has been processed to give a biaxial, ″single-crystal″ texture. Deformation of this material by bending followed by unbending has been observed to lead to shear during the bending stage and to void formation during the unbending stage. The kink bands which form during this treatment exhibit a single morphology regardless of the axis of bending so long as the direction of compression during bending is parallel to the original extrusion direction. Besides intracrystalline slip, which is known to contribute at least in part to the process of kink band formation, mechanisms involving interlamellar slip and interfibrillar slip are also considered.
• Onorato, P. I., & Uhlmann, D. R. (1976). Nucleating heterogeneities and glass formation. Journal of Non-Crystalline Solids, 22(2), 367-378.
  More info

  Abstract: The kinetic treatment of glass formation is extended by the introduction of continuous cooling (CT) curves to estimate the cooling rates required to form glasses of various materials. The CT curves may be constructed from isothermal time-temperature-transformation curves following the approach originally suggested by Grange and Kiefer. The modified analysis is used to evaluate the effects of nucleating heterogeneities on glass formation. It is found that for the concentrations of such heterogeneities found in most liquids, those characterized by contact angles greater than about 100° have a negligible effect on the cooling rate required to form glasses. Heterogeneities with smaller contact angles, can, however, have a significant effect on glass formation, with the critical cooling rate increasing with decreasing contact angle. The effects on glass formation of changes in the contact angle of nucleating heterogeneities are also compared with the effects of changes in the thermodynamic barrier to nucleation (in the crystal-liquid surface energy). © 1976.
• Renninger, A. L., & Uhlmann, D. R. (1976). ON THE STRUCTURE OF GLASSY POLYMERS - 3. SMALL-ANGLE X-RAY SCATTERING FROM AMORPHOUS POLYETHYLENE TEREPHTHALATE.. J Polym Sci Part A-2 Polym Phys, 14(3), 415-425.
  More info

  Abstract: Experimental data are presented which show that the small-angle x-ray scattering (SAXS) from glassy polyethylene terephthalate (PET), varies with scattering angle in a manner generally similar to that observed previously for glassy polycarbonate and PMMA. The SAXS intensity from PET decreases sharply with increasing angle in the very small angle region (2 theta less than 10 min), followed by a more gradual decrease over the angular range between 10 min and 45 min; this is followed by a nearly constant intensity over a sizable range of angle which gradually merges with the tail of the main wide-angle diffraction maximum. As with polycarbonate and PMMA, the measured SAXS in the constant intensity region corresponds closely with that expected for thermal density fluctuations frozen-in at the glass transition. The present results are inconsistent, both in magnitude and form of the SAXS intensity, with the presence of nodular features as representative of the bulk polymer. It is suggested that the nodular structures seen in this polymer be associated with surface effects. It is also suggested that the structure of glassy PET be regarded as that of a random amorphous polymer, with a small concentration of heterogeneities - some perhaps crystallites - superimposed on thermal density fluctuations frozen-in at the glass transition.
• Renninger, A. L., & Uhlmann, D. R. (1976). On the structure of glassy polymers. III. Small-angle X-ray scattering from amorphous polyethylene terephthalate. Array.
• Scherer, G. W., & Uhlmann, D. R. (1976). Effects of phase separation on crystallization behavior. Journal of Non-Crystalline Solids, 21(2), 199-213.
  More info

  Abstract: The effects of phase separation on the kinetics of crystal growth have been investigated for three compositions in the Na2OSiO2 system, containing about 1.5, 10 and 15 mol% Na2O. In the two cases for which reliable data could be obtained over the full range of temperature (10 and 15% Na2O), the measured growth rates are independent of time, for crystallization temperatures within as well as outside the miscibility gap. In both cases, the growth rate versus temperature relations are continuous through the region of the immiscible boundary. These results are related to previous data on the effects of phase separation on viscosity in the Na2OSiO2 system and on nucleation and crystallization in the Li2OSiO2 system. It is suggested that transport at the crystal-liquid interface in a phase-separating system involves different types of atomic rearrangements than those involved in viscous flow. © 1976.
• Straff, R. S., & Uhlmann, D. R. (1976). ON THE STRUCTURE OF GLASSY POLYMERS - 4. SMALL-ANGLE X-RAY SCATTERING FROM RIGID POLYVINYL CHLORIDE.. J Polym Sci Part A-2 Polym Phys, 14(2), 353-365.
  More info

  Abstract: In the reported experiments, the small-angle x-ray scattering (SAXS) from quenched and annealed rigid PVC has been measured using a Bonse-Hart system. The scattering from annealed (6 days at75 degree C) and unannealed PVC was identical within experimental error, varying with scattering angle in a manner similar to the SAXS from other amorphous polymers. The intensity decreases rapidly with increasing scattering angle over the ranges from 20 sec to 20 min. The angular variation of intensity is well described by the scattering from heterogeneities of various sizes and concentrations superimposed on the scattering from thermal density fluctuations. It is pointed out that the results obtained are inconsistent with the presence of nodular features as representative of the bulk polymer. Rather, it is suggested that they are associated with surface effects. It is further suggested that previously indicated volume fractions of crystallinity in rigid PVC are incorrect, and that the model of a three-dimensional network of crystallites should be re-examined.
• Straff, R., & Uhlmann, D. R. (1976). ENTHALPY RELAXATION OF RIGID POLY(VINYL CHLORIDE).. J Polym Sci Part A-2 Polym Phys, 14(6), 1087-1095.
  More info

  Abstract: In the reported experimental study, the changes which take place on annealing rigid PVC in the vicinity of the glass transition have been followed by differential scanning calorimetry. The changes appear as an increase in the glass-transition temperature and a decrease in the enthalpy with time of annealing. For annealing at 75 degree C, the enthalpy after 50-100 hr approaches the value characteristic of the equilibrium liquid state. The results obtained for annealing at 65 degree C and 75 degree C are in accord with those expected for the relaxation of an amorphous material, and are at variance with those expected on the basis of crystallization taking place on annealing. The enthalpy relaxation process is characterized by a distribution of activation energies centered about 18. 8 kcal mole** minus **1, and seems to reflect a multiplicity of molecular processes. 10 refs.
• Uhlmann, D. R., & Kolbeck, A. G. (1976). PHASE SEPARATION AND THE REVOLUTION IN CONCEPT OF GLASS STRUCTURE.. Physics and Chemistry of Glasses, 17(5), 146-158.
  More info

  Abstract: The present paper reviews the current understanding of liquid-liquid immiscibility in oxide systems. The mechanism of phase separation in most oxide systems under most conditions has not yet been established. Both discrete particle and interconnected structures can be produced by either nucleation-growth-coalescence or spinodal decomposition; and the general form as well as the detailed characteristics of the phase separation structures seen in glasses depend strongly upon their composition and thermal mechanical history. Coarsening has been shown to be an important process in phase separation, and can involve changes in the morphology as well as the scale of the structure.
• Hopper, R. W., & Uhlmann, D. R. (1975). Dependence of interfacial tension on separation for two regular solution interfaces. Journal of Non-Crystalline Solids, 19(C), 149-165.
• Scherer, G. W., & Uhlmann, D. R. (1975). Diffusion-controlled growth of dendrite arrays. Journal of Crystal Growth, 30(3), 304-310.
  More info

  Abstract: The diffusion-controlled growth of dendrite arrays is analyzed using an approach similar to that of Jackson and Hunt for rod eutectic growth. The growth rate is found to be determined by the diffusion coefficient, the size and spacing of the dendrites, and the differences of the interface concentration from that in bulk liquid and in the crystal. Relative to the model of an isolated dendrite, the results of the present analysis provide an improved description of the crystallization of a 0.10 K2O-0.90 SiO2 composition. © 1975.
• Uhlmann, D. R. (1975). AMORPHOUS SOLIDS.. Sagamore Army Mater Res Conf (Charact of Mater in Res, Ceram and Polym), 20th, Proc, Raquette Lake, 43-72.
  More info

  Abstract: The structure of amorphous solids on various scales, including atomic structure, submicrostructure, microstructure, and macrostructure, is discussed. In the area of the atomic structure of oxide glasses, attention is directed to the relation between experimental data (and distribution functions derived therefrom) and the predictions of various structural models. In the area of submicrostructure, attention is focused on the widespread occurrence of phase separation, as well as on the relation between the multiphase structures observed and the mechanism of phase separation.
• Uhlmann, D. R., & Scherer, G. W. (1975). Crystallization kinetics of Na₂O · 3SiO₂. Journal of Crystal Growth, 29(1), 12-18.
  More info

  Abstract: The crystallization kinetics of Na2O · 3SiO2 have been determined over the temperature range between 600°C and 800°C. The (metastable) melting point of this material has been determined as 811 ± 3°C. The growth rate vs. temperature relation exhibits the maximum generally found for glass-forming systems, with the maximum growth rate (3.3 x 10-6 cm sec-1) observed at 735 °C. Under all conditions of growth, the crystal-liquid interfaces are faceted. This is indicative of significant growth rate anisotropy, and suggests that the entropy of fusion is large in Jackson's sense (ΔSfM &62- 4R, where ΔSfM is the molar entropy of fusion). Assuming ΔSfM = 4R, by analogy with the characteristics of Na2O · 2SiO2, the reduced growth rate versus undercooling relation has been constructed. The form of this relation - a straight line of positive slope passing through the origin - is suggestive of growth by a screw dislocation mechanism. The magnitudes of the growth rates are in close accord with the predictions of the standard model for such growth. © 1975.
• Uhlmann, D. R., Klein, L., & Hopper, R. W. (1975). Sintering, crystallization, and breccia formation. The Moon, 13(1-3), 277-284.
  More info

  Abstract: The process of breccia formation by viscous sintering in the absence of pressure, advanced forcefully by Simonds (1973), is examined in detail. The limitations on the standard model for such sintering are considered. The competing process of crystallization is analyzed kinetically in terms of time-temperature-transformation curves corresponding to various degrees of crystallinity. The analysis is applied to Lunar Composition 15418 to illustrate the approach. The results indicate that close constraints can be placed on the thermal histories of lunar breccias, particularly breccias with modest degrees of crystallinity, from microstructural observations and kinetic measurements. © 1975 D. Reidel Publishing Company.
• Uhlmann, D. R., Kritchevsky, G., Straff, R., & Scherer, G. (1975). Crystal nucleation in normal alkane liquids. The Journal of Chemical Physics, 62(12), 4896-4903.
  More info

  Abstract: The homogeneous nucleation of crystals in normal alkane liquids has been studied using a droplet technique for a range of alkanes between C 16H34 and C5H12. The critical undercooling for nucleation, ΔTN, relative to the melting point TE, increases significantly with decreasing length of the alkane chain n:ΔTN/TE increases from 0.05 for C 16H34 to 0.20 for C5H12, with separate variations noted for the odd-n and even-n alkanes. Use of a spherical nucleus model gives molar surface energies σM relative to the molar heat of fusion, ΔHM, which also increase significantly with decreasing n but show little odd-even variation: σM/ ΔHM increases from 0.07 for C16H34 to 0.28 for C5H12. Because of the pronounced increase in surface energy with decreasing chain length, the model of a spherical nucleus is suggested to be inappropriate for the alkane liquids (at least for the high-n alkanes). Using a preferred cylindrical nucleus model with separate side- and end-surface energies, a side-surface energy of about 6 erg cm-2 is estimated from the present data, at least for the high-n alkanes. Using this model, the end-surface energies are found to increase with decreasing chain length. This increase is taken to reflect the increasing importance of chain localization and chain end effects with decreasing chain length. For the small-n alkanes, the side-surface energy is also suggested to increase with decreasing chain length, again associated with chain localization effects in the liquid adjacent to the crystal (nucleus) surface. Copyright © 1975 American Institute of Physics.
• Warner, S. B., Uhlmann, D. R., & Peebles Jr., L. H. (1975). Heterogeneities in carbon fibers. Carbon, 13(5), 433-436.
  More info

  Abstract: Acrylic fibers, stabilized acrylic fibers, and graphite fibers have been selectively etched by ion bombardment. After ion etching, the fibers are characterized by structures oriented transverse to the fiber axis with an average spacing ranging from 500 to 3000 Å. These transverse structures are considered to be representative of structural inhomogeneities in the fibers, which are transmitted from the precursor fiber through the stabilization treatment to the final carbon fibers. The relation between these heterogeneities and the standard microstructura! models of carbon fibers remains to be elucidated satisfactorily. © 1975.
• Warner, S. B., Uhlmann, D. R., & Peebles Jr., L. H. (1975). Ion etching of amorphous and semicrystalline fibres. Journal of Materials Science, 10(5), 758-764.
  More info

  Abstract: Ion etching of amorphous and semicrystalline fibres produces structures which can be observed in either the transmission electron microscope or the scanning electron microscope. The structures so produced have previously been identified as resulting from the etching process (artifacts), or as representing characteristics of the material, or both. The artifacts can be eliminated or minimized by rotating the sample during irradiation, using a low angle of incidence, and ensuring that the temperature of the sample surface remains low. When such precautions are used, amorphous fibres and semicrystalline fibres which are not oriented remain featureless after ion etching. Oriented semicrystalline fibres, however, develop a striated structure which is oriented perpendicular to the stretch direction. The spacing between the striations is in the range of 500 to 5000 å, an order of magnitude larger than the characteristic lamellar spacing in the materials. These transverse structural features reflect characteristic features of drawn fibres; but the relation between these features and the lamellar spacing is unclear. © 1975 Chapman and Hall Ltd.
• Warner, S. B., Uhlmann, D. R., Peebles, L. H., Warner, S. B., Uhlmann, D. R., & Peebles, L. H. (1975). Ion etching of amorphous and semicrystalline fibres. Array.
• Warner, S. B., Uhlmann, D. R., Peebles, L. H., Warner, S. B., Uhlmann, D. R., Peebles, L. H., Warner, S. B., Uhlmann, D. R., Peebles, L. H., Warner, S. B., Uhlmann, D. R., & Peebles, L. H. (1975). Heterogeneities in carbon fibres. Array.
• Gamberg, E., Uhlmann, D., & Chung, D. (1974). Pressure dependence of the elastic moduli of glasses in the K₂OSiO₂ system. Journal of Non-Crystalline Solids, 13(3), 399-408.
  More info

  Abstract: The elastic moduli and their variation with pressure have been determined for three glass compositions in the K2OSiO2 glass system. The results may be summarized: {A table is presented}. Additionally, the heat capacities of the three compositions were determined over the temperature range of 320 to 700 K, and were used together with the other data to evaluate the thermal Grüneisen ratios. This parameter was found to increase with increasing K2O concentration, with values of 0.48, 0.63 and 0.69 for the three compositions indicated above. For comparison, the acoustic Grüneisen ratios evaluated from the variation of the moduli with pressure were found to be negative and also to increase with increasing K2O concentration. © 1973.
• Goodof, R., & Uhlmann, D. R. (1974). THERMAL SHOCK RESISTANCE OF AIR PREHEATER MATERIALS.. Array.
  More info

  Abstract: Research has been carried out on Al//2O//3-MgO, Al//2O//3-TiO//2, and TiO//2-SiO//2 refractories which indicates that the development of microstructures having a large number of short, stable, blunt flaws in the as-fired material can impart greatly improved resistance to thermal shock. Such flaws can be introduced by second-phase particles having thermal expansion coefficients differing significantly from those of the matrix or by the selection of materials which exhibit highly anisotropic thermal expansion behavior. Of immediate concern in the present paper is their use in air preheaters, particularly in cases where the thermal cycles involve large temperature differences and short cycle times.
• Hopper, R. W., & Uhlmann, D. R. (1974). On diffusive creep and viscous flow. Materials Science and Engineering, 15(2-3), 137-144.
  More info

  Abstract: The relation between viscous and diffusive deformations is discussed, and their nonequivalence is emphasized. Molecular theories relating self diffusivity to viscosity, as well as the macroscopic behavior of materials deforming by diffusive creep and by viscous flow, are reviewed. It is concluded that while molecular theories can properly relate viscosity to diffusivity, viscous flow and diffusive creep are not macroscopically equivalent. A "viscosity" obtained by equating a diffusive creep flow to a viscous flow will in general depend upon the state of stress and will therefore not be a material property. The differences between the flow types are illustrated with two examples, the spheroidization of a nearly spherical particle, and the effective viscosity of a suspension of particles in viscous liquid. © 1974.
• Hopper, R. W., & Uhlmann, D. R. (1974). Solute redistribution during crystallization at constant velocity and constant temperature. Journal of Crystal Growth, 21(2), 203-213.
  More info

  Abstract: An analysis is presented for the time-dependent solute redistribution which occurs during crystallization at constant velocity and constant temperature. The analysis is suggested to be applicable to many studies of crystallization in glass-forming systems, where solidification takes place at temperatures well above the solidus and where the solubility in the crystalline phase is quite limited. Appropriate for these situations, the usual condition of Cs = kCL is replaced by the approximate condition of Cs = Csolidus. The results indicate a concentration of the liquid at the interface which is limited only by the liquidus composition, and not by a steady-state composition of CO/k. Limitations of the present analysis for cases where the growth rate becomes concentration-dependent are discussed. © 1974.
• Hopper, R. W., Scherer, G., & Uhlmann, D. R. (1974). Crystallization statistics, thermal history and glass formation. Journal of Non-Crystalline Solids, 15(1), 45-62.
  More info

  Abstract: The formal theory of transformation kinetics describes the volume fraction of a phase transformed in a given time at a given temperature. The basic concepts are extended for isotropic crystal growth in a material having a known thermal history T(r, t). A crystal distribution function ψ(r, t, R) is defined such that the number of crystallites in a volume dυ at r having radii between R and R + dR at time t is ψ(r, t, R) dυ dR. The function ψ contains essentially complete statistical information about the state of crystallinity of a material. Formal expressions for ψ are obtained. Applications are discussed, including predictions of crystallinity when T(r, t) is known; predictions of glass-forming tendencies; experimental determination of nucleation rates; and the determination of the thermal history of a sample from post mortem crystallinity measurements. As an example, ψ(r, t, R) is calculated for a lunar glass composition subjected to a typical laboratory heat treatment. © 1974.
• Hopper, R., & Uhlmann, D. (1974). Diffuse interfaces and the general minimization of the mean field free energy. Journal of Colloid And Interface Science, 47(1), 77-85.
  More info

  Abstract: A mean field pair interaction theory of interfaces is presented. The theory is related to diffuse interface theories based on gradient energy expansions, but avoids certain mathematical approximations. The theory consists of obtaining a general expression for the mean field pair interaction free energy of the system and obtaining that composition profile which minimizes this free energy. A condition for the minimization is obtained from variational principles and solved numerically. The interface profiles are compared with those of standard diffuse interface theory and are found to be similar. The theory is a mean field theory because the local configurational entropy is taken as ideal. © 1974.
• Renninger, A. L., & Uhlmann, D. R. (1974). Small angle X-ray scattering from glassy SiO₂. Journal of Non-Crystalline Solids, 16(2), 325-327.
• Scherer, G., Uhlmann, D. R., Miller, C. E., & Jackson, K. A. (1974). Crystallization behavior of high purity o-terphenyl. Journal of Crystal Growth, 23(4), 323-330.
  More info

  Abstract: The crystallization behavior of high purity o-terphenyl has been investigated over a range of undercooling up to 70 °C. The material was prepared by multiple pass zone refining (153 passes). The growth rate reaches a maximum in the range of 10-3 cm sec-1 at an undercooling of about 20 °C, and decreases to about 10-7 cm sec-1 at the lowest temperature of study. The reduced growth rate versus undercooling relation has been constructed, and indicates an interface site factor which increases continuously with increasing undercooling. The logarithm of (growth rate × viscosity) does not decrease linearly with increasing 1/TΔT. The variation of the growth rate with temperature cannot be described in satisfactory detail by the standard theoretical models for surface nucleation growth, but exhibits a form predicted by recent computer simulations of crystal growth. The high purity of the present material, combined with the similar logarithm of (growth rate × viscosity) versus 1/TΔT curves observed with other materials, suggest that such relations are characteristic of the crystallization process. In all materials investigated, the increase of the interface site factors with increasing undercooling as well as the faceted interface morphologies are in agreement with the predictions of Jackson for materials characterized by large entropies of fusion. © 1974.
• Uhlmann, D. R. (1974). CRYSTAL GROWTH AND GLASS FORMATION.. Mater Sci Res, 9, 465-478.
  More info

  Abstract: The effects of nucleating heterogeneities on glass formation have been explored using the spherical cap model of the heterogeneous nucleus. In accord with experimental results on many materials, a total density of heterogeneities of 10**9 cm** minus **3 is assumed. The results indicate that heterogeneities characterized by contact angles smaller than 90-100 degree can have a sizable effect on glass formation, with the critical cooling rates increasing with decreasing contact angle.
• Uhlmann, D. R., & Renninger, A. L. (1974). ELECTRON MICROSCOPY AND SMALL ANGLE X-RAY STUDIES OF AMORPHOUS POLYMERS.. American Chemical Society, Polymer Preprints, Division of Polymer Chemistry, 15(2), 28-34.
  More info

  Abstract: General considerations of heterogeneity and nodular structure of amorphous polymers and their studies by using small angle x-ray scattering (SAXS) techniques are followed by presentation of results of an investigation in which polycarbonate polymer was tested. The investigation was carried out using a Bonse-Hart small angle scattering system. The measured intensities were corrected for absorption and residual background; and sufficiently long counting times were used so that the scattering at any angle attributable to the polycarbonate was accurate to better than 10 pct. THe data, suitably scaled, are in substantial agreement with those of W. Lin and E. J. Kramer. Results obtained are analyzed by using mathematical techniques. It is suggested that the SAXS from glassy polycarbonate, and other glassy polymers as well, be taken as representative of a generally random structure, with a small concentration (in the range of 0. 04 volume pct. or less) of heterogeneities such as crystallites, second-phase particles or surface defects. It is further suggested that the nodular structures seen in glassy polymers be associated with surface effects rather than structural features of the bulk material.
• Warner, S. B., Peebles, L. H., & Uhlmann, D. R. (1974). PLASTICIZATION OF CARBON FIBRES.. Array.
  More info

  Abstract: A technique for temporarily plasticizing high-modulus carbon fibers which offers promise for permitting familiar textile operations to be carried out on them without mechanical damage, consists in exposing the carbon fibers to a suitable material, such as bromine or iodine monochloride. These materials have the effect of plasticizing the fibers, perhaps temporarily lowering their modulus values. In the plasticized state, the yarns can be made to take various shapes including sharp bends. On removal of the plasticizer, the yarns will retain a portion of the shape imparted to them. Tensile properties of the yarn and flexural properties of composites obtained on yarn that has undergone bromination and debromination show no changes relative to the untreated samples.
• Warner, S. B., Peebles, L. H., & Uhlmann, D. R. (1974). Plasticization of carbon fibres. Array.
• Calvert, P. D., & Uhlmann, D. R. (1973). SURFACE STRESSES AND CRYSTAL TWISTING IN HIPPURIC ACID AND IN POLYMERS.. J Polym Sci Part A-2 Polym Phys, 11(3), 457-465.
  More info

  Abstract: An approximate model is developed which relates the twisting seen in the spherulitic crystallization of many materials to surface stresses. Expressions are presented for the twist period as a function of the surface stress. These are compared with previous experimental data on polyethylene and data on hippuric acid obtained in the present investigation. In both cases the experimental data are in accord with the predictions of the model.
• Cohen, B. M., Uhlmann, D. R., & Shaw, R. R. (1973). Optical and electrical properties of lead silicate glasses. Journal of Non-Crystalline Solids, 12(2), 177-188.
  More info

  Abstract: The optical and electrical properties of PbO-SiO2 glasses containing 24.6 to 65 mole % PbO have been determined. While the short-wavelength cutoff increases continuously in wavelength with increasing PbO concentration, an abrupt lightening in color is observed in the vicinity of 38-40% PbO. The darker color of glasses containing 30-38% PbO has been associated with a scattering process. The origin of this scattering is discussed and is tentatively identified with the formation of microcrystals of SiO2 in the glasses. The alternative process of liquid-liquid phase separation seems less likely, but cannot be ruled out with certainty. The electrical conductivity of all glasses investigated exhibits an Arrhenian temperature dependence. The activation energy decreases from about 1.23 eV for the 30% PbO composition to about 1.11 eV for the 50% PbO composition, and remains about constant for glasses containing higher concentrations of PbO. Addition of NH4Cl or Sb2O3 to the batch or use of Pb(NO3)2 or Pb3O4 instead of PbO as a raw material does not affect the electrical properties. The dielectric constant at 1kHz increases continuously with increasing PbO concentration, from a value in excess of 20 for the 55% PbO composition. The implications of these results for the conduction mechanism in PbO-SiO2 glasses are discussed. © 1973.
• Cukierman, M., & Uhlmann, D. R. (1973). Viscous flow behavior of selenium. Journal of Non-Crystalline Solids, 12(2), 199-206.
  More info

  Abstract: The viscosity of 99.99% pure selenium has been determined over the available range of temperature where crystallization could be avoided. A bending beam viscosimeter was used to obtain data in the high viscosity region, and a rotating cylinder instrument was employed for the low viscosity range. Also determined was the stress dependence of the viscosity at temperatures of 31.5 and 29.6°C. The critical stress for non-Newtonian flow was found to lie in the range of hundreds of psi, which is appreciably smaller than that for oxide liquids in a similar range of viscosity. © 1973.
• Cukierman, M., Lane, J. W., & Uhlmann, D. R. (1973). High-temperature flow behavior of glass-forming liquids: A free-volume interpretation. The Journal of Chemical Physics, 3639-3644.
  More info

  Abstract: High-temperature viscous flow data are reported for three relatively simple organic liquids: o-terphenyl, salol, and α-phenyl-o-cresol. The results are combined with previous flow data on the same liquids to obtain viscosity-temperature relations over some 15 orders of magnitude. For each liquid, as well as for tri-α-naphthylbenzene, the free-volume theory of Turnbull and Cohen is found to provide a close representation of the data for viscosities between 10-2 P (the high-temperature limit of the data) and about 104 P. Over this range, even the pre-exponential factors derived from fitting the experimental results are in close agreement with those predicted by the theory. At lower temperatures, the free-volume expression overestimates the difficulty of flow. For all four organic liquids, the fractional free volumes at the points of departure, T, of the experimental data from the free volume predictions are close to 0.015. An empirical high-temperature flow relation of the free-volume form is suggested as η≈s[(MkT)1/2/a20] exp{0.25/[0.015 + Δα(T - TB)]}, where M is the mass of the molecule, a 0 is its diameter, and Δα is the difference in thermal expansion coefficient between liquid and glass. It is suggested again that free-volume theories be used to represent flow behavior in the fluid range rather than in the high-viscosity region as the glass transition is approached.
• Hakim, R. M., & Uhlmann, D. R. (1973). DIELECTRIC RELAXATION IN Cs//2O-SiO//2 AND Na//2O-SiO//2 GLASSES.. Physics and Chemistry of Glasses, 14(5), 81-89.
  More info

  Abstract: Dielectric loss curves have been determined for a number of Cs//2O-SiO//2 and Na//2O-SiO//2 glasses. The forms of these curves, as well as those of the distributions of relaxation times derived therefrom, are similar for all glasses studied. The G( tau )- tau curves are all asymmetric to the small tau side, and may be super-imposed by shifting along the relaxation time axis. It is suggested that the observed distributions of relaxation times may not reflect corresponding distributions of molecular processes. 17 refs.
• Hopper, R. W., & Uhlmann, D. R. (1973). Comments on the stability of dispersed particles. Scripta Metallurgica, 7(5), 467-470.
• Hopper, R. W., & Uhlmann, D. R. (1973). EFFECTS OF ELECTRIC FIELDS ON SPINODAL DECOMPOSITION.. Physics and Chemistry of Glasses, 14(2), 37-44.
  More info

  Abstract: An analysis is presented of the effects of electric fields on spinodal decomposition in a perfect dielectric material. The appropriate diffusion equation is derived for fields which oscillate slowly with time, and is solved for the early stages of decomposition. The theory is phenomenological and takes account of effects due to free energy changes with polarization and to field dependent mobilities. The results indicate that electric fields should generally act to inhibit spinodal decomposition at least in systems exhibiting positive curvature in the relation between dielectric constant and composition.
• Hopper, R. W., & Uhlmann, D. R. (1973). Higher derivative terms in spinodal decomposition. Acta Metallurgica, 21(3), 267-272.
  More info

  Abstract: The effects of higher order terms on the kinetics of spinodal decomposition are evaluated. The terms considered are the higher derivative terms in the diffuse interface free energy expansion. It is shown that the next approximation to the local free energy results in a kinetic amplification factor of the form: R(β) = Nv-1 M ̃(-f{hook}″β2 - 2κβ4 + 2μβ6), where μ can be related to coefficients in the free energy expansio Problems associated with a continuation of the expansion to evaluate further effects on spinodal decomposition kinetics are noted. © 1973.
• Hopper, R. W., & Uhlmann, D. R. (1973). Temperature distributions during crystallization at constant velocity. Journal of Crystal Growth, 19(3), 177-186.
  More info

  Abstract: The temperature distribution in a crystal-melt system solidifying with a planar interface is examined. The case of an infinite system, initially at a uniform temperature, solidifying at a constant (interface controlled) velocity is solved explicity. The limiting interface heating is found to be the latent heat divided by the specific heat, which can be quite large. Estimates of the effect of finite sample size are given. Interface attachment kinetics and heat flow control mechanisms are discussed. The results of the analysis are compared with experiments on three representative materials: sodium disilicate (an oxide glass-former), α-phenol o-cresol (an organic glass-former) and tin (a metal). © 1973.
• Hopper, R., & Uhlmann, D. (1973). Spinodal decomposition without diffuse interface theory, II: K(β) and comparisons. Acta Metallurgica, 21(4), 377-384.
  More info

  Abstract: A recent mean field pair interaction (MFPI) formulation of the theory of spinodal decomposition is extended with quantitative calculations based on representative pair potentials. These include a nearneighbor potential, a screened impurity potential, and various inverse power law potentials. For the nearneighbor potential, as well as for power law potentials with exponents n ≥ 5, results in accord with the standard theory are obtained. For power law exponents n < 5 (for systems in which long-range intermolecular potentials are important), the amplification factor, R(β), is expected to decrease less rapidly with increasing wavenumber at large β than predicted by the standard theory, and R(β) should not be quadratic in β for small β. The predictions of the MFPI formulation are compared with experimental data on the kinetics of phase separation. A qualitative preference for the MFPI formulation seems indicated: but in quantitative detail, the agreement between theory and experiment still leaves much to be desired. The needs for further extensions of the theory, and most importantly for reliable experimental data on initially homogeneous specimens, are emphasized. © 1973.
• Hopper, R., & Uhlmann, D. (1973). Spinodal decomposition without diffuse interface theory-I. Theory. Acta Metallurgica, 21(1), 35-42.
  More info

  Abstract: It has been shown that when higher derivative tenns of the diffuse interface expansion are included in the theory of spinodal decomposition, exceptional results are obtained. Within a mean field pair interaction (MFPI) interpretation, the coefficients of terms ▽2nc in the extended diffuse interface expansion eventually become infinite in magnitude. These anomalies are discussed and circumvented in a new analysis of spinodal decomposition. Within the MFPI interpretation a Fourier analysis of the composition is made at an earlier stage in the analysis. The result is a diffusion equation which can be related to the usual diffusion equation of spinodal decomposition. In the early stages, the only change encountered is that the factor κβ2 in the amplification factor is replaced by a function K(β). When κ is defined, K(β) approaches κβ2 in the limit of small β. When, because of long-range intermolecular potentials, the standard definition of κ does not converge, K(β) remains well defined but no longer increases as β2 in the small β limit. This can result in amplification factors which are qualitatively different from those predicted by the standard theory. © 1973.
• Park, J. B., & Uhlmann, D. R. (1973). RECOVERY OF DEFORMED POLYMERS - 3. THERMAL PROPERTIES.. Journal of Applied Physics, 44(1), 201-206.
  More info

  Abstract: Measurements of heat capacity as a function of temperature are used to evaluate the changes in heat content of three deformed polymers during isothermal annealing treatments. The polymers investigated are amorphous polycarbonate (PC) and semicrystalline polyethylene (PE), and polypropylene (PP). In all cases, the differences between the original and drawn states are of the order of a few cal gm** minus **1. These differences are observed to anneal out completely in the case of PC heat treated in the vicinity of its glass transition, while only incomplete recovery is observed in the case of PE and PP. The spectra characterizing enthalpy recovery are similar to those derived previously from retraction kinetics, and indicate the similarity of relaxation processes involved in the two recovery phenomena.
• Uhlmann, D. R. (1973). Densification of alkali silicate glasses at high pressure. Journal of Non-Crystalline Solids, 13(1), 89-99.
  More info

  Abstract: The densification behavior of a number of alkali silicate glasses has been investigated using a Bridgman anvil high pressure device. The pressure range of the investigation was 10 to 60 kilobars; the temperature range was 100 to 400°C. In all cases, the densification was found to increase with increasing temperature and pressure. In the two systems where compositional variations were explored, Na2OSiO2 and K2OSiO2, a pronounced maximum in densification in the vicinity of 10 mole % alkali oxide was observed (for a given temperature and pressure). These maxima are taken to reflect a competition between two processes, one of which - the variation of molecular mobility with composition - should lead to increasing densification with increasing alkali concentration. Several possibilities are discussed for the decrease in densification with alkali oxide concentrations greater than about 10% (to values smaller than that of SiO2 in some cases). The present results are related to those obtained in previous investigations of the densification of oxide and polymeric glasses. © 1973.
• Warner, S. B., Peebles, L. H., & Uhlmann, D. R. (1973). Plasticization of carbon fibres. Array.
• Calvert, P. D., & Uhlmann, D. R. (1972). CRYSTALLIZATION OF POLYETHYLENE AT HIGH PRESSURE: A KINETIC VIEW.. J Polym Sci Part A-2 Polym Phys, 10(9), 1811-1836.
  More info

  Abstract: A model for the crystallization kinetics of polymers is outlined and is used to interpret observations of the crystallization of PE at high pressures. This model introduces a distinction between sigma //e the lamellar surface energy which controls the lamellar thickness, and sigma //e', the surface nucleus surface energy which controls the growth rate. Differential scanning calorimetry and electron microscopy data for several polyethylenes crystallized at pressures of up to 8 kb are preseinted. It is found that sigma //e increases markedly with pressure leading to the formation of very thick crystals at high pressures. Fractionation effects and the differences in behavior between different polyethylenes are also discussed.
• Calvert, P. D., & Uhlmann, D. R. (1972). Surface nucleation growth theory for the large and small crystal cases and the significance of transient nucleation. Journal of Crystal Growth, 12(4), 291-296.
  More info

  Abstract: Models for surface nucleation controlled crystal growth are analyzed. It is shown that in general the large-crystal model rather then the small-crystal model should be used to describe growth kinetics. Consideration of the effects on calculated crystal growth rates of time dependent nucleation processes shows that these effects should not be significant in the growth of most typical materials from the melt. © 1972.
• Calvert, P. D., & Uhlmann, D. R. (1972). Theory of polymer crystallization without chain folding. Journal of Applied Physics, 43(3), 944-949.
  More info

  Abstract: A theoretical treatment of nucleation-controlled polymer crystal growth is developed. A distinction is made between the end-surface energy of the crystal lamella and that of the nucleus for growth. The growth rate is related to the nucleation frequency using a thick-crystal treatment, and the lamellar thickness is viewed as limited by diffusion of the crystallizing chain in the liquid. Exponential growth kinetics are predicted by the model, and when compared with available experimental data on polyethylene, a reasonable value for the end-surface energy of the nucleus is obtained. The lamellae formed at a given under-cooling are expected to be distributed over a range of thicknesses, with a most probable value of about twice the minimum thickness stable at the undercooling. © 1972 The American Institute of Physics.
• Das, G. C., Bever, M. B., Uhlmann, D. R., & Moss, S. C. (1972). Relaxation phenomena in amorphous selenium-tellurium alloys. Journal of Non-Crystalline Solids, 7(3), 251-270.
  More info

  Abstract: Amorphous specimens of selenium-tellurium alloys containing 0-35 at% Te were held for various times at temperatures ranging from room temperature to 318°K. Changes with time in the microhardness, density, small-angle X-ray scattering and heat capacity were determined. The hardness of crystalline specimens containing 0-100 at% Te and the density of crystalline specimens containing 0-30 at% Te were also measured. The microhardness and density of the amorphous specimens increased with time at room temperature to approximately constant values. With increasing time of annealing, the intensity of small-angle scattering decreased. Peaks developed in the heat capacity versus temperature curves; their height increased with time and decreased with temperature of annealing. The peaks moved to higher temperatures with increasing tellurium concentration. Changes in the enthalpy were determined from the heat capacities. The increases in microhardness, density and height of the heat capacity peaks reflect relaxation towards a more stable structure of smaller molecular mobility. The decrease in small-angle X-ray scattering indicates the disappearance of inhomogeneities in the density during the early stages of annealing. At a later stage, the enthalpy decreased with the most rapid change occurring over a narrow time interval. A spectrum of activation energies centered around 23 kcal (gram-atom)-1 was derived. The effects of composition, temperature and time of annealing on the various properties are explained in terms of structural changes and relaxation kinetics. © 1972.
• Hopper, R. W., & Uhlmann, D. R. (1972). Higher derivatives in the thermodynamics of nonuniform solutions. I. Basic interface theory. The Journal of Chemical Physics, 56(8), 4036-4042.
  More info

  Abstract: The thermodynamics of nonuniform solutions usually employs a gradient energy term in the expression for the local free energy. This arises from retaining the first nonvanishing terms of a MacLaurin expansion of the free energy in the composition and its derivatives. The nature of this expansion is discussed, and the formulation is extended to include derivatives higher than the second. General, a priori arguments suggest that a reasonable next approximation is f*=f(c) +κ1∇2C+κ2(∇c) 2+κ3∇4c+κ4(∇ 2c)2+κ5∇c·∇ 3c+κ6(∇c)2∇ 2c+κ7(∇c)4, for an isotropic solution. The results for a cubic system are also presented. The significance of the coefficients are discussed using a simple mean field pair interaction analysis. This interpretation provides physical insight into the nature of the terms and suggests that in the absence of specific knowledge about a particular situation, the derivative terms may be ordered in the following sequence of decreasing importance: κ1∇2c, κ3∇4c, [k2(∇c)2, κ5∇c·∇3c], [κ 4(∇2c)2, κ6(∇c) 2∇2c, κ7(∇c)4]. The effect on the profile and interfacial tension of a flat diffuse interface of the K3V*c and the -4(Vc)*terms are determined. The pair interaction analysis indicates that the κ3∇4c term sharpens the interface profile and decreases the interface tension. When K? is positive, the κ7(∇c)4 term increases the interfacial tension and makes the interface more diffuse.
• Hopper, R. W., & Uhlmann, D. R. (1972). Size stability of dispersed particles in the diffuse interface limit. Scripta Metallurgica, 6(4), 327-331.
• Laughlin, W. T., & Uhlmann, D. R. (1972). Viscous flow in simple organic liquids. Journal of Physical Chemistry, 76(16), 2317-2325.
  More info

  Abstract: The viscosities of three organic liquids, salol, α-phenyl-o-cresol, and o-terphenyl, have been measured over a wide range of temperature using falling-sphere and bending-beam viscosimeters. The heat capacity vs. temperature relations for each of these materials have also been determined for the glass, liquid, and crystalline states, as have the thermal expansion coefficients of glassy and liquid α-phenyl-o-cresol. For none of the liquids investigated can the flow behavior over the full range of measured viscosity be adequately represented by any of the standard theoretical models. The agreement between molecular dynamics calculations and a modified free volume theory is combined with the close description of flow at high temperature by a free volume model to suggest that free volume theories are most appropriately used to describe flow in the high-temperature region rather than in the region around the glass transition. It is also suggested that a second, easier flow process becomes dominant in the low-temperature region. Flow data on several classes of liquids may be correlated by means of a corresponding-states parameter. Although limitations are recognized for the use of any such normalization factor, the most satisfactory corresponding-states parameter for liquid viscosity seems to be the glass-transition temperature.
• Park, J. B., & Uhlmann, D. R. (1972). Densification behavior of an aluminate glass. Journal of Non-Crystalline Solids, 7(4), 438-440.
• Scherer, G., & Uhlmann, D. R. (1972). Crystallization behavior of α-phenyl o-cresol. Journal of Crystal Growth, 15(1), 1-10.
  More info

  Abstract: The crystallization behavior of α-phenyl o-cresol (o-benzyl phenol) has been investigated over the range of undercooling up to 90 °C. The growth rate reaches a maximum value of about 10-3cm sec-1 at an undercooling of about 30 °C and decreases to about 10-7 cm sec-1 at the lowest temperature of study. The reduced growth rate versus undercooling relation has been constructed, and indicates an interface site factor which increases continuously with increasing undercooling. The logarithm of growth rate × viscosity does not decrease linearly with increasing 1 TδT. The variation of the growth rate with temperature, as well as the corresponding variation of the interface morphology, cannot be described in satisfactory detail by any standard theoretical model. The forms of these variations are in agreement with the predictions of Jackson for materials characterized by large entropies of fusion. © 1972.
• Uhlmann, D. R. (1972). A kinetic treatment of glass formation. Journal of Non-Crystalline Solids, 7(4), 337-348.
  More info

  Abstract: A kinetic treatment of glass formation is presented. This treatment is based on the construction of time-temperature-transformation curves corresponding to some barely detectable degree of crystallinity. From such curves, the minimum cooling rates required to form glasses of various materials are estimated. The most important factors determining the glass-forming abilities of different materials are suggested to be the magnitude of the viscosity at the melting point and the rate of increase in viscosity with falling temperature below the melting point. © 1972.
• HAKIM, R. M., & UHLMANN, D. R. (1971). Electrical conductivity of alkali silicate glasses. Physics and Chemistry of Glasses, 12(5), 132-138.
  More info

  Abstract: A modification of the model of Anderson & Stuart has been used to describe the variation of the activation energy with alkali concentration in homogeneous glasses, while a two- phase model is used to calculate the activation energy of phase separated compositions.
• Kimmel, R. M., & Uhlmann, D. R. (1971). Activation-energy spectra for retraction of hot-stretched polystyrene and shear creep in polymethyl methacrylate. Journal of Applied Physics, 42(12), 4926-4930.
  More info

  Abstract: The data of Andrews for the retraction kinetics of hot-stretched polystyrene and the data of Thompson for shear creep in polymethyl methacrylate in the glassy state have been analyzed to obtain activation-energy spectra characterizing the kinetic processes. For the retraction data, singly peaked spectra covering the range between 15 and 35 kcal/mole were found. These were virtually independent of widely varying sample history, and the range of activation energies was somewhat higher than that found for volume relaxation in unoriented samples of the same polymer. The energy spectrum for the creep data is similar in shape to the retardation-time spectrum derived by Thompson, and covers the range 6-43 kcal/ mole. This range includes the three energy values previously calculated from the temperature dependence of the shift factor, log10aT. Changes in structure with temperature are easily inferred from the temperature dependence of the shift factor used to derive the energy spectrum. © 1971 The American Institute of Physics.
• Kimmel, R. M., & Uhlmann, D. R. (1971). Effects of high pressure on amorphous polymers. II. Annealing of densified polymethyl methacrylate. Journal of Applied Physics, 42(5), 1892-1896.
  More info

  Abstract: The annealing at atmospheric pressure of polymethyl methacrylate (PMMA) densified in various pressure-temperature-time cycles has been examined in the temperature range 25°-90°C. PMMA densified in the glassy state was found to be less stable than that densified by cooling through the glass transition under pressure, in agreement with previous results on inorganic glasses. Moreover, the relative stability of densified PMMA depended on the sample residence time in the glass transition region at pressure. In the one case where an energy spectrum for annealing could be calculated, the data indicated a multiplicity of molecular processes with activation energies in the range 14-19 kcal/mole. © 1971 The American Institute of Physics.
• Kimmel, R. M., & Uhlmann, D. R. (1971). Effects of pressure on amorphous polymers. III. Thermodynamic properties of densified polymethyl methacrylate. Journal of Applied Physics, 42(12), 4917-4925.
  More info

  Abstract: Measurements of the temperature dependence of specific heat are presented for polymethyl methacrylate densified in various pressure-temperature-time cycles. It is found that treatment in the glass transition region produces samples with higher glassy specific heat (0. 38 vs 0. 35 cal/g°C) and lower heat content (difference in enthalpy of 2 to 5 cal/g) than the original material. The change in thermal properties is directly correlated with increased density and increased resistance to annealing. High-pressure treatment in the glassy state is found to produce little change in the thermodynamic properties. Samples vitrified by rapid application of high pressure show complex specific-heat-temperature curves. The results are related to previously reported data on densification and annealing and are discussed in terms of theories of the glassy state and the glass transition. © 1971 The American Institute of Physics.
• Shaw, R., & Uhlmann, D. (1971). Effect of phase separation on the properties of simple glasses II. Elastic properties. Journal of Non-Crystalline Solids, 5(3), 237-263.
  More info

  Abstract: Available theories for the variation of elastic moduli in two-phase materials are reviewed. It appears that only three rigorous independent solutions currently exist: the upper Voigt limit, the lower Reuss limit, and the interdependent boundaries obtained by Hashin and Shtrikman. The lower Hashin-Shrikman boundary appears to best describe the behavior of elastic properties over the complete range between the end-members. This boundary was previously derived by Kerner for the case of spherical particles. Plots of moduli against volume fraction always have positive (concave-upward) curvature, with the exception of the linear behavior of the Voigt model. In terms of weight percent, the curvatures may be positive, negative, or zero, according to the relative values of the densities and moduli of the end-members. Sonic velocities and adiabatic moduli are reported for PbOB2O3, Li2OSiO2, and PbOSiO2 glasses. The Hashin-Shtrikman/Kerner relations describe the moduli fairly well over known or suspected two-phase composition regions. Maxima and minima previously reported for certain properties in the LiOSiO2 and the PbOSiO2 systems were not verified in this investigation. The Hashin-Shtrikman/Kerner relations fit the experimental data fairly well over the two-phase regions in the sodium silicate system and in the alkali borate glass systems, with the fit being poorest for the potassium borates. No immiscibility is expected near 12 wt % (24 mole %) Na2O in the Na2OP2O2O5 system, or over the range 0-10 wt% Na2O(O-16 mole % Na2O) in the Na2OGeO2 system. © 1971.
• Uhlmann, D. R., & Hakim, R. M. (1971). Derivation of distribution functions from relaxation data. Journal of Physics and Chemistry of Solids, 32(11), 2652-2655.
• Uhlmann, D. R., & Park, J. B. (1971). Recovery of deformed polymers. II. Repeated cold drawing of polycarbonate, polyethylene, and polypropylene. Journal of Applied Physics, 42(10), 3800-3805.
  More info

  Abstract: Studies of repeated cold drawing with intermediate annealing have been carried out on three polymers: polycarbonate, polyethylene, and polypropylene. In the case of polycarbonate, samples recovered to their original lengths in the anneals. On testing, necking and yielding behavior were observed on all draws, with the modulus and yield stress dropping most significantly between the first and second draws, and by a smaller amount between the second and subsequent draws. The recovery kinetics are complex; activation energy spectra derived from these kinetics are centered about 22.5-24.5 kcal/mole, and do not vary significantly with the initial strain or number of the draw. In the case of polypropylene, yielding and necking were observed on all draws after annealing at 160°C; with annealing at lower temperatures, yielding was noted on only the first draw. For both polyethylene (PE) and polypropylene (PP) incomplete recovery was observed on the intermediate anneals; the elastic modulus and drawing stress were significantly smaller on the second draw than on the first draw, and were effectively unchanged between the second and subsequent draws. This softening effect decreased with increased extent of recovery in the intermediate anneal. Activation energy spectra derived from the recovery kinetics were centered about 14.5-15.5 kcal/mole for PP and 22-23 kcal/mole for PE; the occurrence of recovery processes having significantly lower activation energies is also indicated. © 1971 The American Institute of Physics.
• Uhlmann, D. R., Kolbeck, A. G., & Witte, D. D. (1971). Heat capacities and thermal behavior of alkali borate glasses. Journal of Non-Crystalline Solids, 5(5), 426-443.
  More info

  Abstract: The heat capacities of selected glasses in the five alkali borate systems have been measured over a range of high temperatures which includes the respective glass transition regions. The heat capacities per gram atom at 350°K show little variation with composition while those at the low temperature ends of the glass transition, Tg-, show some systematic variations. When compared with the respective 3R values, the heat capacities at Tg- range from about 0.75 for B2O3 to values in excess of unity for various alkali borate compositions. The present data on heat capacity have been combined with previous data on the elastic moduli, densities and thermal expansion coefficients to evaluate the Grüneisen constant, γ, for each composition for temperatures around ambient. For B2O3, γ has a low value of about 0.25. It decreases with additions of Li2O and increases with additions of the other alkali oxides. © 1971.
• CALVERT, P. D., & UHLMANN, D. R. (1970). Direct crystallization of extended- chain crystals of polyethylene from the melt at high pressure. J Polym Sci Part B Polym Lett, 8(3), 165-172.
  More info

  Abstract: Samples have been crystallized both isothermally and in a temperature gradient. It is found that extended- chain crystals, once nucleated, can form directly and rapidly from the melt. Extended- chain crystals form directly from the melt at high pressure. It is suggested that at temperatures close to the extended chain crystals melting point, the primary nucleation of these crystals is slow but their growth is rapid. At lower temperatures, the growth of folded chain crystals is kinetically preferred. 10 refs.
• Goldstein, M., Scholes, S., Barry, T. I., Zarzycki, J., Tomozawa, M., MacCrone, R. K., Porai-Koshits, E., Andreev, N. S., Mazurin, O. V., Simmons, J. H., Angell, C. A., Uhlmann, D. R., West, A. R., Glasser, F. P., Gutzow, I., Robson, M. J., & Herman, H. (1970). General discussion. Discussions of the Faraday Society, 50, 222-240.
• HOPPER, R. W., & UHLMANN, D. R. (1970). MECHANISM OF INCLUSION DAMAGE IN LASER GLASS. Journal of Applied Physics, 41(10), 4023-4037.
  More info

  Abstract: The use of glass lasers in high-power applications is frequently limited by breakdown of the host glass at certain discrete points. This type of breakdown, known as inclusion damage, has generally been associated with the presence in the glass of second-phase particles. The present paper is concerned with-elucidating the origin of inclusion damage; specifying the effects of particle size; shape, and absorptivity upon the likelihood of damage; describing observations of damage on different scales in a Nd-doped barium crown glass; and considering the possible effects of phase separation in the glass on inclusionbreakdown. It is suggested that inclusion damage is associated with particles, most likely metallic, absorbing energy from the laser beam and heating to temperatures well above the range of vaporization under standard conditions. This heating of particles relative to the surrounding glass produces stresses in the glass which can exceed its theoretical strength and results in failure.
• HOPPER, R. W., LEE, C., & UHLMANN, D. R. (1970). The inclusion problem in laser glass. Array, 55-66.
  More info

  Abstract: The problem of inclusion damage in laser glass is considered with attention directed to an improved treatment of the stress around a hot inclusion particle. The existence of a layer of molten glass surrounding such particles is suggested; and the new analysis indicates a maximum tensile stress in the nearby cooler glass, rather than at the solid- liquid glass boundary. The magnitude of this tensile stress can exceed the expected strength of the glass for a range of particle sizes under high power laser operation, and failure is then expected to occur. Thereakdown condition is shown to depend upon the flux level and pulse time of the laser beam, as well as the size and shape of the inclusion particles and various material properties of the inclusion and glass. Under most conditions of laser operation, nonmetallic inclusions - even those containing large concentrations of highly absorbing ions - are expected to be safe; and under all conditions they should be appreciable less dangerous than similar metal particles.
• Hopper, R. W., & Uhlmann, D. R. (1970). Coalescence of second phase particles in phase separation. Discussions of the Faraday Society, 50, 166-174.
  More info

  Abstract: A model has been suggested by Haller and others for the development of interconnected submicrostructures in glasses which involves the nucleation, growth and coalescence of discrete second-phase particles. A theoretical objection has been raised to this model - viz., that interparticle interference effects limit diffusion controlled growth and prevent coalescence. The present paper discusses three mechanisms whereby coalescence may occur despite interference effects. These include heterogeneous nucleation between two particles; capillarity-induced volume diffusion; and diffusion driven by the variation with separation of the interfacial energy of two interfaces. Two theories of the latter variation are presented, a diffuse interface theory based on the variational method of Cahn and Hilliard, and a pair interaction, sharp-interface model. Both models predict a monotonic decrease in the interfacial energy as the separation decreases. Other aspects of coalescence as well as the alternative model of spinodal decomposition are briefly discussed. The results of various experiments attempting to distinguish between spinodal decomposition and nucleation-growth-coalescence are reviewed. It is concluded that the operative mechanism for the formation of interconnected submicrostructures in nearly all glass systems remains to be established.
• Hopper, R. W., & Uhlmann, D. R. (1970). Vaporization of inclusions during laser operation. Journal of Applied Physics, 41(13), 5356-5357.
• KIMMEL, R. M., & UHLMANN, D. R. (1970). EFFECTS OF HIGH PRESSURE ON AMORPHOUS POLYMERS. DENSIFICATION OF POLYMETHYL METHACRYLATE. Journal of Applied Physics, 41(7), 2917-2927.
  More info

  Abstract: The densification of polymethyl methacrylate resulting from pressure and temperature treatment in a Bridgman anvil device has been studied at temperatures to 245 C and pressures to 50 kbar. Effects of treatment in the glass transition region, in the glassy state, and on samples held in the transition region under pressure and then vitrified by rapid application of a high pressure, are studied. The results are compared with thermodynamic theories of the glass transition and with similar data on other polymers and inorganic glasses.
• Kimmel, R. M., & Uhlmann, D. R. (1970). Activation energy spectra for nonlinear relaxation processes. Journal of Applied Physics, 41(2), 592-596.
  More info

  Abstract: The first approximation analysis for deriving activation energy spectra from relaxation data, originally derived for linear distributed relaxation processes, is shown to be valid as well for nonlinear distributed processes. The analysis is also applied to nonlinear, undistributed processes and found to indicate a spectrum of activation energies with a maximum at the characteristic energy of the single process. The characteristics of spectra resulting from nonlinearities are considered, and a procedure for evaluating the possible physical significance of derived activation energy spectra is considered. © 1970 The American Institute of Physics.
• Li, J. H., & Uhlmann, D. R. (1970). The flow of glass at high stress levels. I. Non-Newtonian behavior of homogeneous 0.08 Rb₂O·0.92 SiO₂ glasses. Journal of Non-Crystalline Solids, 3(1), 127-147.
  More info

  Abstract: A homogeneous 0.08 Rb2O·0.92 SiO2 glass has been tested at temperatures between 480 and 555°C (low-stress viscosities between 1017.1 and 1013.5 poise) and at stress levels up to 109.5 dyne/cm2 or more. At low stress levels, Newtonian behavior was observed; at stress levels above some critical stress, the viscosity was observed to decrease with increasing stress. This critical stress for non-Newtonian flow was found to be about 109.1 dyne/cm2, approximately independent of temperature. The variation of the viscosity with stress in the high-stress region can be described by absolute rate theory only by assuming a flow volume which increases with increasing stress. © 1970.
• Li, J. H., & Uhlmann, D. R. (1970). The flow of glass at high stress levels. II. The effect of phase separation on viscosity. Journal of Non-Crystalline Solids, 3(2), 205-224.
  More info

  Abstract: The effects of phase separation on the viscosity of glass-forming liquids has been investigated using a fiber-elongation technique. The materials studied were a borosilicate glass and a 0.14 Na2O·0.86 SiO2 glass. In the latter case, the viscosity has been measured at temperatures of 501 and 555 °C, and found to depend strongly on the extent, scale, and morphology of the phase separation. The faster development of a large-scale interconnected submicrostructure at 555 °C has been associated with the viscosity of samples tested at this temperature being higher than those at 501 °C, for tests up to about one mouth in duration. The borosilicate glass was tested at temperatures of 536, 482, 460, and 448 °C. In contrast with the results obtained previously on a homogeneous rubidium silicate glass, no evidence for non-Newtonian behavior was found on this phase-separated glass, even for tensile stresses as large as 2.3 × 1010 dyne/cm2. © 1970.
• Park, J. B., & Uhlmann, D. R. (1970). Recovery of deformed polymers. I. Retraction of cold-drawn polycarbonate, polyethylene, and polypropylene. Journal of Applied Physics, 41(7), 2928-2935.
  More info

  Abstract: A study is reported of the similarities and differences in the cold drawing and annealing behavior of amorphous polycarbonate (PC) and semicrystalline polyethylene (PE) and polypropylene (PP). The recovery data for all three polymers cover a range of temperature and initial strains. From these kinetic data, activation-energy spectra characterizing the recovery process are derived using an analysis for processes distributed in activation energy. These spectra are centered about 22-24 kcal/mole for PC, 22 kcal/mole for PE, and 15 kcal/mole for PP, treating recovery in the temperature ranges 170°-150°C for PC, 70°-60°C for PE, and 90°-80°C for PP. The mean activation energies do not vary with the initial strain but seen to decrease with increasing recovery temperature. © 1970 The American Institute of Physics.
• Kimmel, R. M., & Uhlmann, D. R. (1969). Activation energy spectra for relaxation in amorphous materials. I. Volume relaxation in polystyrene and polyvinyl acetate. Journal of Applied Physics, 40(11), 4254-4260.
  More info

  Abstract: A modification of the Primak analysis for activation energy distributions is presented and compared with the well-known analysis for relaxation time distributions. Mathematical and physical interrelationships between the two analyses are discussed. Activation energy spectra are derived from the data of Kovacs for volume relaxation in polystyrene and polyvinyl acetate. The energy spectra are bell shaped and cover the range from 5 to 20 kcal/mole. The concept of a shift factor is introduced to account for changing structure in the glass transition region. The shapes and locations of the spectra are discussed and compared with previous interpretations of volume relaxation data. © 1969 The American Institute of Physics.
• Li, J. H., & Uhlmann, D. R. (1969). A note on the largest viscosity measurable in finite experimental times. Journal of Non-Crystalline Solids, 1(4), 339-343.
• Shaw, R. R., & Uhlmann, D. R. (1969). Effect of phase separation on the properties of simple glasses I. Density and molar volume. Journal of Non-Crystalline Solids, 1(6), 474-498.
  More info

  Abstract: The variation of bulk density with composition across a miscibility gap is adequately described by a simple model in which volume additivity of the two phases is assumed. The density-weight percent composition function must always have positive (concave-upward) curvature across a two-phase region. The density-mole percent composition function can have either positive or negative curvature, depending upon the location of the miscibility gap in the binary diagram and upon the molecular weights of the end-member oxides. Immiscible composition regions are generally signalled more clearly by simple density-weight percent composition plots than by density-mole percent plots or molar volume or partial molar volume analyses. The model is used to predict possible immiscible regions in the system K2OSiO2, PbOSiO2, B2O3GeO2, SiO2GeO2, PbOGeO2, and PbOP2O5. Immiscibility is probably not present on the GeO2-rich side of the alkali germanate series of glasses. The LiF-rich limit of the miscibility gap in the LiF-BeF2 system is estimated. © 1970.
• Uhlmann, D. R., & Shaw, R. R. (1969). The thermal expansion of alkali borate glasses and the boric oxide anomaly. Journal of Non-Crystalline Solids, 1(5), 347-359.
  More info

  Abstract: A brief review is presented of the major theories for the so-called "boric-oxide anomaly" in alkali borate glasses, and a comparison is effected with recent published information on the structure of B2O3 and alkali borate glasses. These indicate serious shortcomings in current theories. An experimental study is reported of the mean linear thermal expansion coefficients between 25°C and -196°C of a series of glasses, prepared at composition intervals of 2 mole% alkali oxide, in all five alkali borate systems. The thermal expansion versus composition relations are characterized by broad, flat minima, with no single composition being uniquely identifiable with the minimum. It is concluded that the compositional variation of the thermal expansion coefficient of alkali borate glasses is not truly anomalous, but rather seems to vary with structural variations in a generally predictable manner. It is suggested that the term "anomaly" be reserved for the more serious problem of explaining the change in boron coordination with composition. © 1969.
• Jackson, K. A., Uhlmann, D. R., & Hunt, J. D. (1967). On the nature of crystal growth from the melt. Journal of Crystal Growth, 1(1), 1-36.
  More info

  Abstract: The theory of interface motion as applied to crystal growth by Cahn and his coworkers is examined in detail. This theory, as derived, applied to systems which can have a second order phase transformation but not to liquid-solid or vapor-solid phase transformations which are first order. In this paper, the formalism of the theory is applied to these first order phase transformations. Reasonable agreement with experiment still cannot be obtained. This is because the molecular configuration of the interface is averaged out in the theory by considering a diffuse interface, rather than taking it into account properly in calculating the growth rate. Experimental data on crystal growth have been accumulated and analyzed. It is concluded from this analysis that the theory of Jackson on interface roughness qualitatively predicts crystal growth morphology. Most of the quantitative data on crystal growth are, however, of questionable reliability or are not sufficiently complete for detailed comparison with theory. None of the existent theories of crystal growth can account for these data. © 1967.
• Jackson, K. A., & Uhlmann, D. R. (1966). Particle sorting and stone migration due to frost heave. Science, 152(3721), 545-546.
• Jackson, K. A., Uhlmann, D. R., & Chalmers, B. (1966). Frost heave in soils. Journal of Applied Physics, 37(2), 848-852.
  More info

  Abstract: The Jackson-Chalmers model of frost heave is extended with a more detailed treatment of the heat flow and water transport problems in soils. Concepts derived from a study of the interaction between particles and a solid-liquid interface are combined with the previous model and applied to the formation and growth of ice lenses. Quantitative predictions relating heave rate with various soil parameters are found to agree well with available experimental data. © 1966 The American Institute of Physics.
• Scholz, J. T., Uhlmann, D. R., & Chalmers, B. (1965). Elutriation particle separator. Review of Scientific Instruments, 36(12), 1813-1816.
  More info

  Abstract: An elutriation particle separator is described which provides an inexpensive, efficient, and accurate method of obtaining from an original mixed sample sizable fractions of particles with diameters within preselected size ranges. Preliminary results for three size ranges between 10 and 100 μ are presented, together with proposed modifications (including a connected series of separators) for more efficient operation. © 1965 The American Institute of Physics.
• Seward, T. P., Molea, F. N., & Uhlmann, D. R. (1965). Hot stage for x-ray diffraction of ceramic systems. Review of Scientific Instruments, 36(12), 1851-1852.
  More info

  Abstract: A resistance type heating device is described which adapts a standard high temperature x-ray camera for use in diffraction studies where uniformity of temperature is required. With this device, a volume 6×6×3 mm can be maintained within ±6°C at a temperature of 550°C. © 1965 The American Institute of Physics.
• Wanser, R., & Uhlmann, D. R. (1965). Evacuate-back fill glove box. Review of Scientific Instruments, 36(9), 1365-1366.
  More info

  Abstract: A glove box is described whose chamber may be evacuated into the range of 10-6 mm Hg and subsequently back-filled with a dry gas. Essential features include caps for evacuating simultaneously both sides of the gloves and quick disconnecting fittings for ready accessibility to the box. Slight modification of design permits wide variation in box geometry. © 1965 The American Institute of Physics.
• Uhlmann, D. R., Chalmers, B., & Jackson, K. A. (1964). Interaction between particles and a solid-liquid interface. Journal of Applied Physics, 35(10), 2986-2993.
  More info

  Abstract: The interaction between particles and an advancing solid-liquid interface has been investigated both experimentally and theoretically. For each particular type of particle, a "critical velocity" was observed, below which the particles are rejected by the interface, and above which they are trapped in the solid. The dependence of the critical velocity on various properties of matrix and particle was investigated. A theory has been developed, based on the assumption that a very short-range repulsion exists between the particle and the solid. This repulsion occurs when the particle-solid interfacial free energy is greater than the sum of the particle-liquid and liquid-solid interfacial free energies. The particle is pushed along ahead of the advancing interface and becomes incorporated into the solid if liquid cannot diffuse sufficiently rapidly to the growing solid behind the particle. Reasonable agreement was obtained between the calculated and experimentally observed critical velocities. © 1964 The American Institute of Physics.
• Uhlmann, D., & Chadwick, G. (1961). Unidirectional solidification of melts producing the peritectic reaction. Acta Metallurgica, 9(9), 835-840.
  More info

  Abstract: The unidirectional solidification of liquid alloys that undergo a peritectic reaction is discussed and a prediction of the micro-morphology resulting from the solidification process is given. Experimental results substantiate the prediction. Dendrites of the higher melting point phase are found in a matrix of the lower melting point phase in all alloys within the range of compositions of the peritectic horizontal. © 1961.