bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermal Evolution and Electrical Properties of Rare-Earth Oxide Doped Zirconia
Authors: Chiou B. S. , Lee M. Y. , Duh J. G. 
Published: March 2011

ABSTRACTSynthesized zirconia ceramics are prepared through the coprecipita-tion process. Application of the wet chemical approach is aimed at the achievement of highly sintered ceramics at lower temperature. The thermal evolution of the synthesized CeO2-ZrO2 powder is investigated with the aid of DTA and TGA measurement. The exothermic peaks on the DTA thermogram are futher identified by the IR analysis. The effect of CeO on the occurrence of the peaks is probed. For other rare-earth oxiae doped ceramics, such as Nd2O3. and Dy2O3. containing zirconia, the bulk and grain boundary resistances are evaluated by the impedance spectroscopy. The dependence of the associated activation energy in the rare-earth oxide doped zirconia is discussed with respect to the variation of the ionic radius of the rare earth constituent.
Continuous Spinning of Zirconia Fibers: Relations Between Processing and Strength
Authors: Khavari Mehrgan E. , Lange F. F. , Smith Paul , Marshall D. B. 
Published: March 2011

ABSTRACTContinuous ZrO2 precursor fibers were produced by dry spinning an aqueous zirconium acetate solution containing a soluble yttrium salt and a high molecular weight (MW = 5 × 106) polymer (PEO) to control rheology. A ZrO2-Y2O3 binary composition containing 3 mole % Y2O3 was chosen to control grain growth and to produce tetragonal ZrO2 subsequent to pyrolysis and heat treatment. Fine grained (< 0.3 μm), poly crystalline Zr(Y)O2fibers with diameters between 2 to 12 μm were produced by pyrolysis and heat treatment up to 1400 °C. Fiber tensile strength was measured as a function of processing variables. The objective was to relate flaw populations encountered during strength measurements to processing variables with the goal of controlling and increasing fiber strength.
High Resolution Electron Microscopy of Mixed Uranium Oxides
Authors: Pienkowski M. C. , Jenkins M. L. , Hutchison J. L. , Moseley P. T. 
Published: March 2011

ABSTRACTFluorite-related structures of mixed uranium oxides (Uy,M1-y)O2−x, where M = Ce, Sc, Y, have been studied using High Resolution Electron Microscopy (HREM). Ordered domains have, been observed directly in crystallites of urania-ceria solid solution. Preliminary investigations of urania-yttria also show evidence for the presence of ordered domains. A possible model for the structure of these regions is suggested.
Sol-Gel Protective Films for Metal Solar Mirrors
Authors: Reed Scott , Ashley Carol 
Published: March 2011

ABSTRACTFront-surface metal mirrors were coated with a variety of sol-gel derived glass films for preliminary evaluation as protective coatings for silver. Optical measurements (hemispherical, diffuse and specular reflectance) were used to characterize changes in the mirror resulting from the application of the sol, subsequent processing, or environmental testing. The abrasion resistance of the films was determined on sol-gel coated silicon wafers per ASTM procedures. The mirrors were exposed to outdoor environments in Albuquerque, N.M., as well as accelerated testing in H2SO4, with periodic monitoring of optical properties. A two layer coating scheme, consisting of a thin primary protective layer of sputter deposited SiO2 followed by a thicker sol-gel overcoat, was also evaluated.
Examination of YBa2Cu3O6+x precursor sol using 13C NMR Spectroscopy and Quasielastic Laser Light Scattering
Authors: Kramer S. , Moore G. , Kordas G. , Keifer P. A. , Knight C. T.G. 
Published: March 2011

ABSTRACTThe structural evolution of YBa2Cu3O6+x precursor sol was investigated using 13C NMR and quasielastic light scattering. A polydisperse colloidal suspension of yttrium, barium and copper alkoxides was characterized as hydrolysis and complexation reactions occurred. Light scattering data showed that the average particle size of a copper(II) alkoxide suspension decreased by a factor of 5 (1100 nm to 220nm) with the addition of the yttrium and barium alkoxides over a period of 24 hours. The acquired particle size data correlated well with 13C NMR spectra, which showed initial peak broadening and the copper complexing to the yttrium and barium as a function of hydrolysis time.
Positronium Decay Study of Pore Sizes in Silica Sol-Gels
Authors: Zerda T. W. , Hoang G. , Miller B. , Quarles C. A. , Orcel G. 
Published: March 2011

ABSTRACTPositronium annihilation has been used to measure pore diameters in silica sol-gels. The results have been compared to those obtained from the BET technique. Pore development in the presence of chemical additives and during the thermal treatment has been studied. A model relating positronium lifetime to the pore size has been proposed.
The Synthesis of Aluminum Nitride from Aluminum Hydride
Authors: Ochi Atsushi , KENT BOWEN H. , Rhine Wendell E. 
Published: March 2011

ABSTRACTThe reaction between ammonia and aluminum hydride (AIH3) was investigated as a possible synthetic route to aluminum nitride (AIN), using tetrahydromran (THF) as the solvent. When an excess of ammonia was employed, a white powder was obtained which was converted to AIN by calcination. However, when a stoichiometric amount of ammonia was used, a soluble intermediate was obtained. This intermediate polymerized slowly at room temperature via a condensation reaction involving the elimination of hydrogen to give a gel that could be converted to AIN.
Vanadium Dioxide Films Grown from Vanadium Tetrakis(t-Butoxide) by the Sol-Gel Process
Authors: Speck K. R. , Hu H. S-W. , Murphy R. A. , Potember R. S. 
Published: March 2011

ABSTRACTVanadium dioxide thin films have been grown from vanadium tetrakis (t-butoxide) by the sol-gel process. A new method for the synthesis of the vanadium precursor was developed. Films were deposited by dipcoating glass slides from an isopropanol solution, followed by post-deposition annealing of the films at 600 °C under nitrogen. The properties of these films, to a high degree, were a function of the preparation conditions. These gel-derived VO2 films undergo a reversible semiconductor-to-metal phase transition near 72 °C, exhibiting characteristic resistive and spectral switching comparable with near stoichiometric VO2 films prepared on non-crystalline substrates by other techniques. Paralleling the investigation of pure VO2, films were doped with hexavalent transition metal oxides to demonstrate lowering of the transition temperature.
Vapogel-A new Glass Formation Technique
Authors: Fleming James W. , Fleming Sandra A. 
Published: March 2011

ABSTRACTSiCI4 was tested in both the liquid and vapor state for its suitability as a monolithic gel precursor. Samples with molar ratios of H2O/SiCl4 ranging from 4 to 400 were investigated. Several advantages of using SiCl4 over the classic organometallics such as tetraethylorthosilicate and tetramethylorthosilicate were observed. Gelation of the SiCl4-H2O sol is more rapid. Also, greater purity is achieved with SiCl4 vapor as the starting material. In addition to the SiCl4 experiments, GeCl4 was also investigated as both a dopant and in the pure state for its gelation characteristics. Higher dopant concentrations were achieved using this technique than are possible with other monolithic gel methods, but pure GeO2 gels were not formed. The gel made by the vapor phase method has been named vapogel.
Parameters Affecting Elastic Properties of Silica Aerogels
Authors: Woignier T. , Phalippou J. , Vacher R. 
Published: March 2011

ABSTRACTThe Young's modulus of silica aerogels is measured using the three points flexural technique. Various parameters have been investigated such as the catalyting conditions used to elaborate the initial alcogel and the heat treatment performed to density the material. In a given sample porosity the elastic behaviour of aerogels depends on the conditions of gel preparation. This different elastic behaviour is related to the different spatial arrangement of the particles pointed out by fractal features.
Metal Oxide Films from Carboxylate Precursors
Authors: Davison W. W. , Shyu S. G. , Roseman R. D. , Buchanan R. C. 
Published: March 2011

ABSTRACTZrO2 and Ba2YCU3O7−x metal oxide films were prepared from carboxylate precursors. The zirconia films were prepared from Zr octoate and the Ba-Y-Cu-0 compound synthesized from a mixture of the metal neodeca-noates. Dense, adherent ZrO2 films were obtained on Si. Dense, superconducting Ba-Y-Cu-0 films were also fabricated utilizing the octoate-derived ZrO2 as a bonding surface and diffusion buffer
Technical Studies-Early Use of Metals
Authors: Maddin R. 
Published: March 2011

AbstractExcavated metals, some with secure dates as early as the eighth millennium BC, have been analyzed using a variety of scientific methods in order to provide insight into early metallurgical technology. The results are often used to reconstruct the role of technology in the social structure of the community. This lecture will review many of these methods giving examples from the examination of excavated objects.
Obsidian Hydration Rate Development
Authors: Ericson Jonathon E. 
Published: March 2011

AbstractSince the seminal work of Friedman and Smith [1] obsidian hydration dating (OHD) has undergone several important stages of development and refinement. This paper will summarize the history of research and developments as to elucidate some areas for future research.Archaeologists have taken a pragmatic and empirical approach towards OHD and hydration rate determination. They would like OHD to become an absolute chronometric technique. Geochemists and material scientists have sought to understand the hydration process from an environmental, chemical and thermodynamic perspective. As suggested by the literature, obsidian hydration appears to be a diffusion, reaction and dissolution process dependent on the chemical and thermal history of the hydration environment. Although there appear to be certain central tendencies, however, there are discrepancies between empirical archaeologically-derived data and theoretical models.California offers a rich data base for synthesis and testing of hydration models. There are over 25 natural obsidian sources many of whose chemical and physical properties have been measured by Ericson [2]. Obsidians have been distributed aboriginally as artifacts into diverse environments. Intensive excavations, underwritten by extensive land development, have contributed to development of a number of source-specific hydration rates for single sources. Reanalysis of the California data warrants future examination to advance our understanding of obsidian hydration dating on a world wide basis.
Experimental Hydration Studies of Natural and Synthetic Glasses
Authors: Bates John K. , Abrajano Teofilo A. , Ebert William L. , Mazer James J. , Gerding Thomas J. 
Published: March 2011

AbstractThe results of a series of hydration experiments on natural glasses (Hawaiian basalt, obsidian) and the nuclear waste glass WV-44 done to examine laboratory methods of accelerating reaction processes are summarized. The glasses were reacted in hydrothermal solution and in saturated vapor water. It was found that different reaction rates and processes were found using the differing conditions, and that laboratory efforts to accelerate and duplicate natural processes must account for the physical processes that occur naturally.
Diffusion Cells for Integrating Temperature and Humidity Over Long Periods of Time
Authors: Trembour Fred , Smith Franklin L. , Friedman Irving 
Published: March 2011

AbstractThe rate of many processes, including the diffusion of water into rhyolitic volcanic glass (obsidian), as well as the racemization of amino acids is temperature dependent, and a knowledge of temperatures integrated over time periods of at least a year is necessary to quantify these processes. The construction and properties of simple devices consisting of small plastic containers that change weight at a rate that is a function of temperature and the activity of water will be described. The cells function because water diffuses through the plastic across a constant vapor-pressure gradient. This vapor-pressure gradient is maintained constant between the substances within the cell and the materials outside the cell. The plastic cells are usually filled with water and surrounded by a dehydrating agent, such as silica gel. A better arrangement is to fill the cell with a mixture of solid sodium chloride (NaCl) and a saturated solution of NaCl, and to surround the cell with pure water. A number of plastics have been investigated, including polycarbonate, polystyrene, tefzel, polyallomer, and methacrylate. The cells have been sealed by various methods including screw caps, room-temperature vulcanizingsilicone rubber sealant, and rubber stoppers. The final design consists of a small cell made of a polycarbonate plastic centrifuge tube containing solid NaCl plus NaCl-saturated solution sealed with a rubber stopper and placed in a polypropylene tube containing pure water. Our aim has been to develop cells that are sufficiently sensitive to yield a precision of ±0.2° C when exposed for one year at temperatures that range from 0° to 40°, and that will fit into metal fittings that can be screwed into standard 3/4-inch plastic water pipe (approximately 1 inch outside diameter).
Recent Salinization of Ancient Egyptian Temples
Authors: Billard T. C. , Burns George 
Published: March 2011

AbstractAlthough an extensive type of salinization of ancient Egyptian temples has been recognized as early as 1977, and although the general mechanism of salinization has been proposed and verified by computer modelling in 1980 at least for the Karnak area near Luxor, the extent of salinization was not documented and its corollaries were not sufficiently elucidated. In this manuscript direct and indirect damage due to salinization of the Karnak Temples complex is identified and illustrated. Recent desalinization efforts are described and future necessary salinization studies are outlined.
Physicochemistry of the Tomb of Nefertari, Egypt.
Authors: Smeaton J. E. , Burns George 
Published: March 2011

AbstractThe Tomb of Nefertari, no. 66, Valley of the Queens, is an internationally known monument of historic and artistic importance; it is considere d one of the most beautiful of the Royal Egyptian tombs. The fragility of its plaster along with its ubiquitous sodium chloride crystals and microcrystals have complicated its conservation and restoration. In order to determine the optimum pathway for its conservation, the physicochemical processes which occur now in this Tomb must be well understood. To improve this understanding, samples of plaster taken from the Tomb have been analyzed using Differential Scanning Calorimetry and X-ray Diffraction and have been shown to be fully dehydrated; previous findings suggest that this is not the case in all contemporary Royal tombs. Although we are not aware of any kinetic study of gypsum dehydration in the solid state, the presence of anhydrite in the Tomb of Nefertari suggests that the CaSO4 ·2H2O → CaSO4 + 2H2O reaction is catalyzed. It is reasoned that finely-dispersed sodium chloride crystals act as effective catalysts in this reaction.
Glass Structure and Glass Durability
Authors: White William B. 
Published: March 2011

ABSTRACTThe vibrational spectra of silicate glasses provide some clues on the structure and stability of the glass-forming network. Wavenumbers of Raman bands are related to the types of linkages within the network and Raman intensities to the “speciation” within the network. Absolute infrared intensities which can be obtained from deconvolution of specular reflectance spectra can be used to obtain dipole derivatives which in turn can be correlated with effective charges on bridging and non-bridging oxygens. IR and Raman spectra measured on a variety of silicate glasses are used to extract network polymerization and bond effective charges which in turn are related to the durability of the glasses.
Glass Corrosion Theories a Tool for Understanding the Past, Designing for the Present and Predicting the Future
Authors: Adams P. B. 
Published: March 2011

ABSTRACTThere is renewed appreciation for understanding glass corrosion mechanisms due in large part to the urgency of nuclear waste management. Although the ultimate goal - to predict specific corrosion performance - has not yet been reached, theories continue to be fine tuned so that this objective now appears attainable.However, even at our present level of understanding, chemical durability theory is a vital tool in reading the secrets of the past as contained in both ancient and natural glasses, designing products such as optical waveguides for a new technological age and predicting how those products, such as nuclear waste glass, will perform - far into the future.
Response of Carbon-Carbon Composites to Challenging Environments
Authors: Maahs Howard G. , Ohlhorst Craig W. , Barrett David M. , Ransone Philip O. , Sawyer J. Wayne 
Published: March 2011

ABSTRACTCarbon-carbon composites are an emerging class of composite materials having a unique combination of high-temperature properties and low densities. These properties are attractive for hot structure and thermal protection system applications in future aerospace vehicles. Aerospace service environments of particular interest are cyclic temperature, oxidizing environments to 3000°F. For carbon-carbon composites to serve as practical engineering materials in such challenging environments, their long-term mechanical and chemical stability is essential.Many aspects of proposed service environments for these composites pose significant challenges to their satisfactory performance. Among these aspects are the oxidizing nature of the environments (including both high and low oxygen partial pressures), high temperatures, moisture, cyclic temperature service, and foreign-object impact. This paper presents results from materials performance evaluations which cover each of these parameters. The focus is on oxidation-resistant carbon-carbon composites intended specifically for multi-use aerospace applications. Results are presented for the carbon-carbon material currently in use on Space Shuttle and for newer, more advanced structural forms of these composites.
Role of Surface Layers in the Leaching Behavior of Glass
Authors: Zoitos B.K. , Clark D.E. 
Published: March 2011

ABSTRACTResults are presented from a two-year dynamic leach test of nuclear waste glass under conditions designed to simulate those of the Stripa granite repository. Solution and surface analytical techniques were used to assess the glass leach rate as well as surface composition and morphology. Glass leach rates were observed to decrease by a factor of two during the first six months. This effect is attributed to the formation of a protective surface layer. Analysis of this layer shows it to be rich in silicon and iron and depleted in lithium, sodium and boron. It was also found that the layer is subject to dissolution.
Reactions of Glasses with Aqueous and Nonaqueous Environments
Authors: Doremus R. H. 
Published: March 2011

ABSTRACTReactions of glasses with the environment occur directly on the glass surface and inside the glass after diffusion of molecules into it. Water, either vapor or liquid, is the most important reactant, but other gases can react with surface and internal silicon-hydroxyl and silicon-oxygen groups. Substantial amounts of water can be introduced into glasses at high temperatures and pressures; the resultant hydrosilicates have unusual properties.In multicomponent alkali silicate glasses water preferentially leaches components; the mobile alkali ions are leached over a wide pH range. Analysis of alkali profiles is straightforward, but measurement of hydrogen profiles requires special care because of outgassing of water. Hydration transforms the surface structure of less durable silicate glasses, leading to rapid outgassing and rapid ionic transport in the transformed layer.The rate of dissolution of the silicon-oxygen network depends on temperature, glass composition, and solution components, especially pH.Heavy metal fluoride glasses dissolve in water, and glass components precipitate on the glass surface. These glasses are quite durable in humid air, with a slow reaction with water to form HF vapor.
Radiation Effects in Silicate Glasses - A Review
Authors: Bibler Ned E. , Howitt David G. 
Published: March 2011

ABSTRACTThe study of radiation effects in complex silicate glasses has received renewed attention because of their use in special applications such as high level nuclear waste immobilization and fiber optics. Radiation changes the properties of these glasses by altering their electronic and atomic configurations. These alterations or defects may cause dilatations or microscopic phase changes along with absorption centers that limit the optical application of the glasses. Atomic displacements induced in the already disordered structure of the glasses may affect their use where heavy irradiating particles such as alpha particles, alpha recoils, fission fragments, or accelerated ions are present. Large changes (up to 1%) in density may result. In some cases the radiation damage may be severe enough to affect the durability of the glass in aqueous solutions.In this paper, we review the literature concerning radiation effects on density, durability, stored energy, microstructure and optical properties of silicate glasses. Both simple glasses and complex glasses used for immobilization of nuclear waste are considered.
Carbon/Carbon Composites: Fabrication and Properties and Selected Experiences
Authors: Dickinson Richard C. 
Published: March 2011

ABSTRACTCarbon/Carbon is a highly desirable material for use at elevated temperatures in structural applications due to its high strength-to-weight ratio and increasing strength with increasing temperatures.This presentation will survey the general methods used to fabricate and apply oxidation protection systems to these composites. This will be followed by an overview of typical physical and mechanical properties and selected results from oxidation rate studies.
Obsidian Hydration Rate Development
Authors: Ericson Jonathon E. 
Published: March 2011

ABSTRACTSince the seminal work of Friedman and Smith [1] obsidian hydration dating (OHD) has undergone several important stages of development and refinement. This paper will summarize the history of research and developments as to elucidate some areas for future research.Archaeologists have taken a pragmatic and empirical approach towards OHD and hydration rate determination. They would like OHD to become an absolute chronometric technique. Geochemists and material scientists have sought to understand the hydration process from an environmental, chemical and thermodynamic perspective. As suggested by the literature, obsidian hydration appears to be a diffusion, reaction and dissolution process dependent on the chemical and thermal history of the hydration environment. Although there appear to be certain central tendencies, however, there are discrepancies between empirical archaeologically-derived data and theoretical models.California offers a rich data base for synthesis and testing of hydration models. There are over 25 natural obsidian sources many of whose chemical and physical properties have been measured by Ericson [2]. Obsidians have been distributed aboriginally as artifacts into diverse environments. Intensive excavations, underwritten by extensive land development, have contributed to development of a number of source-specific hydration rates for single sources. Reanalysis of the California data warrants future examination to advance our understanding of obsidian hydration dating on a world wide basis.