bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fracture Mechanisms in SiC-Whisker Reinforced Alumina
Authors: Boulanger Christophe H. , Chiang Yih-Cherng , Majidi Azar P. , Chou Tsu-Wei 
Published: March 2011

AbstractThe fracture mechanisms involved in the toughening of alumina by whisker reinforcement are studied at room temperature. The fracture toughness of a hot pressed SiC-whisker/alumina composite is measured and good agreement is found between the experimental data and a model that takes into account the effects of crack deflection and whisker pullout mechanisms. From the model, it is seen that the role of whisker pullout is negligible compared to that of crack deflection.
Impact Behavior of Fiber Reinforced Glass Matrix Composites
Authors: Hasson D. F. , Fishman S. G. 
Published: March 2011

AbstractCeramic 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

AbstractThe 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.
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

AbstractThe 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

AbstractComposites 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

AbstractThis 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

ABSTRACTA 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

ABSTRACTHet 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

ABSTRACTThe 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

ABSTRACTAqueous 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

ABSTRACTVanadium 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

ABSTRACTThe 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

ABSTRACTFundamental 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

ABSTRACTThe 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.
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

ABSTRACTAcid 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

ABSTRACTY-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).
Microstructural Evidence of Interactions in Si3N4/Polysilazane Systems
Authors: Schwartz Kenneth B. , Blum Yigal D. 
Published: March 2011

ABSTRACTCompression 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

ABSTRACTPyrolyses 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

ABSTRACTVarious 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

ABSTRACTIt 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

ABSTRACTReactions 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

ABSTRACTThe 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

ABSTRACTThe 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

ABSTRACTThe 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

ABSTRACTDried 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

ABSTRACTGlass-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

ABSTRACTHigh-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.