bluuebunny/crossref_metadata_2025 huggingface dataset:
Impact Behavior of Fiber Reinforced Glass Matrix Composites
Authors: Hasson D. F. , Fishman S. G.
Published: March 2011

Ceramic matrix composites with continuous fibers in glass matrices were tested with instrumented impact apparatuses. The composite architectures were unidirectional (0°) and crossply (0/90°). For the 0/90° laminates, interlaminar and edge on orientation specimens were tested. An orientation dependence was observed. The CMC material with a weaker fiber/matrix interfacial bond had longer fiber pullout, and hence due to the frictional sliding mechanism higher dynamic work to fracture. In the fracture analysis discussion it is suggested that the use of the LEFM, K, parameter should be qualified in the fracture testing of CMC materials. These qualified toughness K values were found to be in the range of those reported for metal matrix composites.
The Influence of Heat Treatment upon Fiber Pull-Out in a Ceramic Composite
Authors: Thouless M. D. , Sbaizero O. , Bischoff E. , Luh E. Y.
Published: March 2011

The toughness of ceramic-matrix composites is strongly influenced by fiber pull-out. The extent of the pull-out depends upon the properties of the fiber and the fiber/matrix interface. Samples of a SiC/LAS composite were subjected to different heat treatments in order to systematically vary these properties. The predicted distribution of the fiber pull-out lengths was calculated by combining a shear lag analysis with Weibull statistics for the fiber strengths. Comparison of the analysis with experiments and microstructural observations contribute to an understanding of the role of the fiber/matrix interface upon the mechanical properties.
Novel Method for Constructing Tetrahedral Frames
Authors: Gilman John J.
Published: March 2011

This paper is concerned with the design and construction of a frame that makes optimal use of modern materials together with optimal structural design. It is modular in format and can be constructed using puckered rings which combine to make a frame with tetrahedral nodes and cubic symmetry; analogous with the crystal structure of diamond. This frame can be extended indefinitely in three dimensions by adding modules to its core. Such a frame has high capacity to bear loads relative to its weight. For some types of loading it has the highest possible specific-structural strength (for a frame of struts). It is a structural analog of a foam.
Effect of Temperature on the Mechanical Properties and Microstructures of In Situ Formed Cu-Nb and Cu-Ta Composites
Authors: Spitzig W. A. , Krotz P. D. , Chumbley L. S. , Downing H. L. , Verhoeven J. D.
Published: March 2011

The effect of temperature on the mechanical properties and microstructures has been evaluated for heavily cold drawn Cu-20% Nb and Cu-20% Ta composites. The strengths of the composites decrease with increasing temperature, with the decrease becoming most pronounced at temperatures above about 300°C and at larger draw ratios. Cu-20% Ta composites are stronger than Cu-20% Nb composites throughout the temperature range studied (22–600°C) with the improvement increasing with increasing temperature. Resistivity measurements and substructure analyses showed that at temperatures where softening accelerated, resistivity decreased indicating a substructural change which was observed to be coarsening of the Nb and Ta filaments in the composites.
Preliminary Investigations on Alumina-Fiber Reinforced Ni3Al Matrix Composites
Authors: Moore B. , Bose A. , German R. M. , Stoloff N. S.
Published: March 2011

Composites containing alumina fibers in Ni3Al+B or an Ni3Al, Cr+B alloy have been prepared by several powder metallurgical processes. Tensile tests reveal some ductility and a mixed fracture mode in both monolithic and composite alloys. Previous reports of inadequate bonding of fibers in Ni3 Al+B have been confirmed.
Toughening Mechanisms in Intermetallic γ-TiAl Alloys Containing Ductile Phases
Authors: Elliott C. K. , Odette G. R. , Lucas G. E. , Sheckherd J. W.
Published: March 2011

This work is aimed at developing understanding of ductile phase toughening in powder-processed intermetallic γ-TiAl alloys. The nominally ductile phases studied include Nb and Ti6Al4V, in the form of pancake shaped particles. Toughening is primarily due to the formation of crack face bridging zones. Toughness increases in the composites with a Ti6Al4V phase are limited due to particle embrittlement during processing. In this case, toughening is associated with the formation of short, low ductility/high strength bridge zones. Larger toughness increases and significant resistance curves are observed in composites containing Nb particles. In this case, long, high ductility/low strength bridge zones are observed. The behavior of the Nb composites is consistent with current understanding of constrained deformation of embedded particles and bridge zone toughening models. Additional toughening was observed in the Nb composites due to crack deflection and blunting in orientations where the crack intersects the broad pancake face.
Sol-To-Gel Transition in Reversed Micelles Microemulsions I. A New Route to Produce Monolithic Metal-Organic Derived Gels
Authors: Guizard C. , Stitou M. , Larbot A. , Cot L. , Rouviere J.
Published: March 2011

A new versatile method to prepare monolithic metal-organic derived gels is presented in which the sol-to-gel transition is achieved through hydrolysis and condensation reactions in a reversed micelles microemulsion. C7 to C10 alkanes were used as solvents for the reaction and water molecules were solubilized using a non ionic surfactant. The general rules governing the sol-to-gel transition for several alkoxides such as Ti (OPri)4, Ti(OBut)4 and Fe(OPri)3 have been laid down and the exchange of water between reversed micelles related to hydrolysis and condensation rates has been investigated. Hydrolysis and condensation kinetics were monitored for different water/surfactant ratio u-sing gas chromatography. At the sol state growing of colloidal particles is mainly affected by the structure of the water inside the reversed micelles. It has been demonstrated using light scattering measurements that gelation times depend on the particle size evolution into the sol.
Organometallic Approaches to Ceramic Materials
Authors: Hrncir Duane C.
Published: March 2011

Het erosiloxanes containing the Group IV metals, Ti, Zr, and Hf, are conveniently prepared by the facile silanol-induced cleavage of organometallic compounds. The isoleptic metallasiloxanes, M(OSiR3)4, vary from mobile liquids to insoluble non-melting powders depending upon the constituents bonded to the silicon. They can be fired into oxides at 650°C. The resulting materials have the formula MSi4o10. FT-IR and ESCA data suggest that the M-o-Si linkage remains intact during this process. Thus the MSi4O10 material can be considered a mixed oxide alloy rather than a simple mixture of the oxides MO2 and SiO2. Lower temperature treatments cures the liquid heterosiloxane, Hf(OSiE3),4 into a thin film which still contains some degree of organometallic character.

A similar silanol cleavage reaction involving Zr(CH2SiMe3)4 and (Ph)2(OH)SiOSi(OH)Ph2 affords (Me3SiCH2)2Zr[OSi(Ph)2OSi(Ph)2O], a cyclic metallasiloxane with a Zr:Si ratio of 1:2. This compound can be passivated and fired into an oxide material. It also reacts via the remaining organo groups with substrates containing reactive surface hydroxyls, e.g. silica, to form an organometallic coating which can In turn be fired into a refractory coating.
Investigation of the Effect of Dimethylformamide Addition on Alumina Sol-Gel Formation by 27Al NMR and Rheology Measurements
Authors: Nazar L. F. , Klein L. C. , Napier D.
Published: March 2011

The role of dimethylformamide (DMF) in the sol-gel processing of alumina at high acid/Al ratios was studied at different hydrolysis and aging temperatures by 27A1 NMR and rheology measurements. The composition of sols in which aluminum sec-butoxide was hydrolyzed in 50/50 mixtures of DMF and H2O was similar to those hydrolyzed without DMF, although the DMF sols contained a slightly lower concentration of mobile alumina species. The Al13O4 (OH)24(H2O)127+ cation predominated in both DMF and aqueous sols hydrolyzed at room temperatures at acid/Al ratios between 0.4 and 0.6. However, aging the room temperature DMF sols at 90°C for 24 hrs was found to cause rapid gelation whereas a similar treatment of the aqueous sols resulted in a decrease in viscosity. This gelation process was correlated with a more rapid decay of the Al13 and A1(H2O)63+ cations in the DMF sols. In contrast, DMF sols hydrolyzed at 90°C were found to be less viscous than their aqueous counterparts at high acid ratios.
Chemical and Physical Principles of Processing that affect Microstructure of Al2O3-ZrO2 Composites
Authors: Bleier Alan , Westmoreland Gary
Published: March 2011

Aqueous processing of 1- to 20-% v/v binary suspensions containing 0.50-μm α-Al2O3 and 0.71-μm m-ZrO2 was investigated in the presence and absence of AlCl3 from pH 2 to 12 using sedimentation, rheological, electrokinetic, and potentiometric techniques. Differential sedimentation of the oxide particulates leads to a nonuniform distribution of ZrO2 when colloidally stable slurries are used. However, processing under conditions that promote weak association of the oxides improves uniformity, with optimal conditions in the absence of AlCl3 being in the pH range 5 to 6. Thus, prefired microstructure depends on the pH at which processing occurs, behavior derived from the different, pH-dependent surface properties of the oxides. Pre-exposure of m-ZrO2 to AlCl3 in the pH range of 4 to 8 alters the final composite microstructure via adsorption of Al-species and renders the two solids more similar electrostatically, thereby reducing the forces responsible for the weak association and uniform distribution.
Ionic Properties of Vanadium Pentoxide Gels
Authors: Livage J. , Barboux P. , Badot J. C. , Baffier N.
Published: March 2011

Vanadium pentoxide gels V2O5·nH2O are actually hydrous oxides. Water adsorption and dissociation occurs at the surface of the oxide leading to negatively charged oxide particles surrounded by an acid aqueous medium. Ionic conductivity is observed, arising from proton diffusion through the water molecules. This process mainly depends on the nature of adsorbed water molecules. Proton conductivity is strongly related to the water adsorption isotherm.

Ion exchange readily occurs at the oxide-solution interface when the gel is dipped into an aqueous solution of a metal chloride. New vanadium bronzes have been obtained upon heating such gels around 300° C. They exhibit interesting properties as reversible cathodes.

Electrochemical insertion of Li* into the gel phase is quite easy. This is due to the very open structure of the gel and the mixed valence behavior of the vanadium oxide.

Transition metal oxide gels could then be used as thin films or pressed pellets for making micro-ionic devices.
Crystallization Behavior of Chemically Prepared and Rapidly Solidified PbTiO3
Authors: Schwartz Robert W. , Payne D. A.
Published: March 2011

The crystallization behavior of chemically prepared and rapidly solidified PbTiO3 was investigated. Chemical methods were (i) polymeric sol-gel processing and (ii) co-precipitation of fine particles. Rapid solidification was obtained by a twin-roller quencher. Details are reported for the processing methods and the characteristics of the materials. X-ray diffraction and electron microscopy confirmed the amorphous nature of the prepared materials. Crystallization was examined as a function of heat-treatment conditions. Non-isothermal DSC was used to determine the kinetics of crystallization. Activation energies and frequency factors were determined. Co-precipitated PbTiO3 crystallized at the lowest temperature of 375 C, followed by sol-gel at 425 C, and rapidly solidified at 475 C. The results are interpreted in terms of processing routes, structural free-energies, available surface areas and fractional free volumes.
Inorganic Gels with Nanometer-Sized Particles
Authors: Tarasevich B. J. , Liu J. , Sarikaya M. , Aksay I. A.
Published: March 2011

Fundamental issues involving interactions and packing of nanometer-sized particles are being investigated as an extension of previous experimental studies on larger submicron particles and in relationship to general theoretical work on colloidal systems. Relationships between particle interaction energies and packing indicate (1) dense gels can be formed in stable systems by minimization of the hydrodynamic radius and (2) dense clusters can be formed in flocculated systems by the use of weakly attractive particles where particle restructuring occurs. Novel techniques for the formation of nanostructures within polymeric matrices are also introduced to address gel cracking problems.
Controlled Horphology in Electronic Ceranic Powder Preparation
Authors: Legros R. , Metz R. , Caffin J. P. , Lagrange A. , Rousset A.
Published: March 2011

The oxalate precursor method appears as a new efficient route in order to control the shape and size of particles of various manganites. Thus electrical properties of electronic ceramics (NTC) are optimized through the proposed chemical process.
Spherical Zirconia Particles Via Electrostatic Atomization: Fabrication and Sintering Characteristics
Authors: Slamovich E. B. , Lange F. F.
Published: March 2011

From the first recorded investigations by Bosetti in 1745 through G.I. Taylor's[2] work on the “Disintegration of Water Droplets in an Electric Field” in 1964, electrostatic atomization of liquids has been put to use in a variety of applications ranging from crop spraying to the propulsion of space vehicles. Here, we have used electrostatic atomization to form micron size droplets of zirconium acetate which pyrolyze to spherical ZrO2 particles for use in sintering studies. Two ZrO2 powders were fabricated. Both are spherical and of similar size distribution, however, in one, the particles are single crystals, while in the other, the particles are polycrystalline. This work discusses the processing of these different particles, and the relative sintering behavior of powders that are composed of either monocrystalline or polycrystalline particles.
Energetics, Composition, and Structure of Alkoxide Derived Silica Gels
Authors: Maniar P. , Navrotsky A. , Rabinovich E. M. , Wood D. L. , Kopylov N. A.
Published: March 2011

Acid and base catalyzed alkoxide silica gels are studied by simultaneous DSC/DTGA under oxidizing and oxygen-free conditions and by intrared spectroscopy. The results are utilized to determine the composition of the dried gels and to estimate the extent of the net hydrolysis reaction. Our results suggest that, with sufficient water, condensation of partially hydrolyzed TEOS is the dominant reaction at high pH whereas, at low pH hydrolysis is rapid, relatively complete and precedes condensation. Thus the dry gels formed at high pH, with sufficient water, contain more alkoxy groups and fewer hydroxyl groups bound to Si than the dry gels formed at low pH.
Physico-Chemical Characterization of the Coprecipitated Y-Ba-Cu-O Fine Powders
Authors: Jang H. M. , Moon K. W. , Moon J. H. , Shin H. S. , Kwon S. J. , Baik S.
Published: March 2011

Y-Ba-Cu-o fine powders were prepared by coprecipitating in the oxalate form from metal nitrates solution. The stoichiometry of metals in the precipitate was adjusted by systematic change of copper nitrate (or yttrium nitrate) concentration for a fixed concentration of barium nitrate in the ruactant. Approximately one micron size powders, with a uniform size distribution, were obtained by this new approach. The optimum condition for calcination and sintering was studied by thermal gravimetric analysis(TGA), X-ray powder diffraction(XRD) and scanning electron microscopy(SEM).
Syntactic Intergrowth Problems with Bcsco and Fabrication Difficulties Therefrom
Authors: Morgan P.E.D. , Ratto J. J. , Housley R. M. , Porter J. R.
Published: March 2011

Bismuth containing oxide superconductors were first encountered in the BaPb1−xBxO3 perovskites [1]. In the the YBa2Cu3Ox family, bismuth was a possible substitute for yttrium and was attempted by us many months ago (and undoubtedly by many other groups) with the result that, under the necessary oxidizing conditions, BaBiO3 formed as a separate phase. Attempts to substitute bismuth into the La2−xSrxCuO4 family were reported [2], with the intriguing result of a 42K superconductor with Tc higher than the previous 38K high for the family. A second paper [3] discussed the new compound “Bi2Sr2Cu7+δ, a = 5.32Å, b = 26.6Å, C = 48.8Å”, with TC of 7K to 22K; this was confirmed, but C = 24.4Å was found [4], and it is now clear that this compound is ideally Bi2Sr2CuO6+δ. A higher Tc than in BaPb1−xBixO3 was next detected in the Ba-K-Bi-O system [5]. Work at the Japanese National Research Institute of Metals [6] then disclosed T_ of as high as ∼ 105K in the Bi-Ca-Sr-Cu-O (BCSCO) system; both Ca and Sr must be present to produce these higher values.
Microstructural Evidence of Interactions in Si3N4/Polysilazane Systems
Authors: Schwartz Kenneth B. , Blum Yigal D.
Published: March 2011

Compression molded bodies fabricated from commercial Si3N4 powder using a polysilazane precursor to Si3N4 as a preceramic binder have been characterized. The process has been partially optimized and can produce green bodies with densities approaching 75% theoretical and considerable mechanical strength. Microstructural development during binder pyrolysis and high-temperature treatment indicate significant interactions and bonding between the commercial powder and the polymer-derived material.
New Catalytic Routes to Preceramic Polymers: Ceramic Precursors to Silicon Nitride and Silicon-Carbide Nitride
Authors: Youngdahl Kay A. , Laine Richard M. , Kennish Richard A. , Cronin Terrence R. , Balavoine Gilbert G.A.
Published: March 2011

Pyrolyses of a set of silicon and nitrogen substituted polysilazancs arc conducted under a set of standard conditions (5°C/min to 900°C in a nitrogen atmosphere). The apparent ceramic compositions and ceramic yields for pyrolyzed samples of the polysilazancs -[Ph(H)SiNH]x-, -[C6H13(H)SiNH]x-, -[Me(H)SiNH]x-, and -[H2SiNMc]x- arc determined. Preliminary conclusions concerning structure/reactivity relationships are discussed based on the pyrolysis results.
The Preparation of Some Silicon (OXY)Nitrides
Authors: Lednor Peter W. , Ruiter René De
Published: March 2011

Various routes to silicon (oxy)nitrides are described, using both low-temperature solution chemistry and high temperature gas-solid reactions. The latter approach has led to a convenient synthesis of high-surface-area (e.g. 130 m g) silicon oxynitride, Si2N2O, from gaseous ammonia and commercially available, finely divided amorphous silica.
Sol-to-Gel and Gel-to-Glass Transitions in the As2S3-Amine system
Authors: Guiton T. A. , Pantano C. G.
Published: March 2011

It is proposed that solutions of arsenic trisulfide and ethylenediamine consist of arsenic-sulfur rings (As4S6) which are interlinked through sulfur-sulfur bridges. The Raman spectra of the solutions exhibit an intense band at 438 cm-1 which is attributed to the stretching resonances of these bridges. The bridges are not present in a-As2S3 glass, and thus, the intensity of the band has been used to characterize the molecular connectivity of sols and gels. This band is most intense in the highest viscosity gels, whereas the relative intensity of the band is diminished in the dry gels. The intensity of the band further decreases during vacuum heat-treatment of fibers drawn directly from the gel. TEM analysis of the fibers verify the creation of a dense amorphous structure, while SIMS depth profiles of the films further verify their composition. Altogether, these observations confirm the structural model proposed for the solution, and suggest a relaxation/ recombination process for the molecular gel-to-network glass transition.
Characterization of Newly Synthesized Novel Graphite Films
Authors: Krishnan Kannan M. , Kouvetakis John , Sasaki Takayoshi , Bartlett Neil
Published: March 2011

Reactions of C5H6 and BCl3 at 800°C yields a metallic graphite-like material of composition BCx (3.0 ≤ x ≤ 4.00) while reactions of BCl3, NH3 and C2 produces a B/C/N graphitic semiconductor of approximate stoichiometry B2CN2. Both materials were shown to be homogeneous using Auger electron spectroscopy and extensively characterized by electron energy-loss spectroscopy. Single loss profiles of the EELS data were obtained using the fourier-log deconvolution method. Compositions were determined using hydrogenic cross-sections. A careful study of the plasmon resonance energies and the fine structures of the core-loss edges of these materials has been invaluable in demonstrating that the boron, carbon and nitrogen atoms are all sp2 hybridized. Therefore, these new materials are in-sheet graphite hybrids and not intercalations.
The Control of Precipitation in Sol-Gel Solutions
Authors: Zheng Haixing , Colby Mary W. , Mackenzie J. D.
Published: March 2011

The preparation of homogeneous gels from liquid solutions necessitates the prevention of precipitation. This becomes increasingly difficult in multicomponent systems. Currently, there are no systematic considerations on precipitation in sol-gel solutions. This paper is concerned with the methods to control precipitation in alkoxide solutions. Each method is applied to specific systems, containing alkoxides of various metals, such as yttrium, lanthanum, barium, and titanium, in alcoholic solutions.
Oxidation Reduction of Sol-Gel Derived WO3 on Ni Substrates
Authors: Covino J. , McManis G. E.
Published: March 2011

The Sol-Gel process was used to deposit WO3 on Ni substrates. These materials as well as the synthetic methods used have application in electronic devices.

In an effort to quantify the oxidation/reduction chemistry of such materials, electrochemistry was performed in both aqueous and non-aqueous (CH3CN, DMF) solutions. Different intercalation cations such as protons, Li and Na, were used. This paper discusses the synthesis, characterization, and electrochemistry of these materials.
Surface Studies of Aluminum Mitride Thik Films
Authors: Hatwar T. K. , Pian T. R.
Published: March 2011

The nature and the composition of the surface and near surface region of A1N films plays a significant role in determining their chemical and thermal stability. A1N thin films were deposited by reactive RF magnetron sputtering of Al in argon and nitrogen atmosphere. Transmission and scanning electron microscopy indicated that these films have a dense columnar microstructure with columns oriented along the c-axis of the A1N crystallites. X-ray photo-electron spectroscopy (XPS) revealed a graded oxygen-rich surface layer about 5–10 nm thick which is formed when the film is exposed to the atmosphere. This oxide is limited to the surface and does not grow even when the film is annealed at 600°C for 10 hours in dry oxygen. It is expected that this passivating oxygen rich surface layer will, to a large extent, determine the oxidation resistance of the fresh underlying AIN. A surface chemistry model is proposed for this protection behavior.
Physical Properties of Dried Na2O-SiO2 Monoliths
Authors: Li Rounan , Hench L. L.
Published: March 2011

Dried monolithic gels of compositions XNa2O-(1-X)SiO2 (with X from 0 mol% to 7 mol%) were obtained by acid catalyzed sol-gel processing using tetramethylorthosilicate and NaNO3. Optically clear monoliths in the range of 20 to 90 mm diameter by 3 to 20 mm thickness were routinely produced by controlling the processing schedule. Complete drying in air without cracking was achieved at 180°C from 10–14 days. The bulk density and optical properties of the gels, characterized by UV/VIS/NIR transmission, IR reflection and index of refraction, showed a compositional dependence on Na2O similar to melt glasses of the same Na2O content. However, the true density and microhardness decreased with Na2O content in contrast to melt glasses.
Gel-Based Processing of Glass-Ceramic Particulate Composites
Authors: Walck James C.
Published: March 2011

Glass-ceramic composites were successfully fabricated by incorporating amorphous lithium aluminosi Iicate (LAS) particulates into a silica gel matrix. LAS volumes in the composites were varied from 50 to 75%, and all composites were easily cast, dried and fired without segregation or cracking. Elevated temperature processing resulted in crystallization of the LAS into a P-spodumene solid solution phase as well as densification of the gel-derived glass matrix. An inverse relationship was found between densification efficiency and LAS volume percent.
Sol-Gel Processing of Transparent MgAl2O4
Authors: Yu Yuan-Fu , Heng Sangvavann , Mah Tai-Il , Hermes Edward E.
Published: March 2011

High-purity, transparent monolithic spinel (MgAl2O4) was synthesized via the hydrolytic thermal decomposition of mixed alkoxide organo-metallic precursors. Several factors, such as the metal alkoxide concentration in various solvents, the water to solvent ratio, and the reaction temperatures affect the hydrolysis of the mixed alkoxides. These factors also influence the transparency of the resulting sols and gels. The degree of transparency of the sols and gels is also influenced by such factors as pH and drying control chemical additives. Variations in the processing conditions during drying, aging, and sintering of the gels produced ceramic materials with high degree of transparency.
Thermal Evolution and Electrical Properties of Rare-Earth Oxide Doped Zirconia
Authors: Chiou B. S. , Lee M. Y. , Duh J. G.
Published: March 2011

Synthesized 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

Continuous 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

Fluorite-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

Front-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

The 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

Positronium 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

The 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

Vanadium 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

SiCI4 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

The 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

ZrO2 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

Excavated 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.
Gleaning Processual Data from Materials Analysis of Museum Collections: The Harvard University Peabody Museulm's Mecklenburg Collection and Social Evolution in Late Rehistoric Europe
Authors: Geseilwitz Michael N.
Published: March 2011

In recent years the research potential of museum collections has come to be more widely recognized by anthropologists [1]. There are a number of factors that account for a turn from collecting “primary” data towards an approach based on reevaluating material remains collected by another. Prehistoric archaeologists have often led the way in artifactual analysis because the physical artifact is our only means of reconstructing past lifeways. Although sane have argued that this limitation in our range of data does not limit the possibilities of ultimate reconstruction [2], nevertheless it is with the artifact that we must begin.
Obsidian Hydration Rate Development
Authors: Ericson Jonathon E.
Published: March 2011

Since 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

The 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

The 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

Although 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

The 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

The 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

There 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

Carbon-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

Results 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

Reactions 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

The 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

Carbon/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.