bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of Rheological Behavior of Ceramic Mixes on Injection Molding of Ceramic Compacts
Authors: Zhang Tao , Jiang Zuozhao , Wu Jianguang , Chen Zhengang
Published: March 2005

The relation between the shear stress and viscosity of ceramic injection‐molding mixes and the dynamic and static losses of pressure in the cavity during injection molding is studied. The temperature distribution in the cavity is calculated. The relation between shear stress τ and shear rate γ is expressed by the equation . The change of pressure in the cavity is consistent with the change in temperature distribution. The density of the injection‐molded bodies is not affected by the injection pressure under usual injectionmolding conditions.
Anisotropy of Grain Growth in Alumina
Authors: Rödel Jürgen , Glaeser Andreas M.
Published: March 2005

Grain growth in theoretically dense undoped and MgO‐doped polycrystalline Al2O3 was studied, and average grain‐boundary migration rates were compared with those of a‐plane and c‐plane sapphire during migration into the same undoped and MgO‐doped materials. The results are discussed in terms of a grain‐size‐dependent grain‐boundary mobility‐grain‐boundary energy product, Mbγb. The grainsize dependencies of the Mbγb products for seed and matrix grains differ. Seed orientation appears to affect the nature of solute‐boundary interactions. The importance of grain‐boundary structure on migration characteristics is also indicated by a demonstration of twin‐formation‐enhanced grain growth.
Grain Size Control in Low‐Voltage Varistors
Authors: Hennings Detlev F. K. , Hartung Ruediger , Reijnen Piet J. L.
Published: March 2005

Low‐voltage ZnO varistors often suffer from a large spread in the current/voltage characteristics, due to discontinuously grown, inhomogeneous microstructures. Addition of seed grains to the ceramic powder is an effective means of preventing the growth of single large grains, thus making the control of final grain size and electrical properties much easier. Seed grains are generally single‐crystalline particles of the same composition with a grain size which is considerably larger than the average grain size of the starting ZnO powder.
Chemical Potential Diagrams for Rare Earth‐Transition Metal‐Oxygen Systems: I, Ln‐V‐O and Ln‐Mn‐O System
Authors: Yokokawa Harumi , Sakai Natsuko , Kawada Tatsuya , Dokiy Masayuki
Published: March 2005

The thermodynamic properties of double oxides in rare earth‐transition metal (V and Mn)‐oxygen ternary systems have been collected and evaluated to examine their stability using chemical potential diagrams plotted as log (αA/αB) vs log (P(O2)). The thermodynamic regularities of perovskites, pyrochlores, and other compounds have been discussed in terms of the effective ionic radii across a series of rare earths. The obtained regularities have been used to estimate tentatively the thermodynamic properties of some rare‐earth vanadium and manganese oxides.
Effect of Hydrogen‐Water Atmospheres on Corrosion and Flexural Strength of Sintered α‐Silicon Carbide
Authors: Kim Hyoun‐Ee , Moorhead Arthur J.
Published: March 2005

Sintered α‐SiC was exposed for 10 h to H2 containing various partial pressures of H2O (PH2O from 5×10−6 to 2×10−2 atm; 1 atm≅105 Pa) at 1300° and 1400°C. Weight loss, surface morphology, and room‐temperature flexural strength were strongly dependent on PH2O. The strength of the SiC was not significantly affected by exposure to dry H2 at a PH2O of 5×10−6 atm; and following exposure at PH2O >5×10−3 atm, the strength was even higher than that of the as‐received material. The increase in strength is thought to be the result of crack blunting associated with SiO2 formation at crack tips. However, after exposure in an intermediate range of water vapor pressures (1×10−5<PH2O <1×10−3 atm), significant decreases in strength were observed. At a PH2O of about 1×10−4 atm, the flexural strength decreased approximately 30% and 50% after exposure at 1300° and 1400°C, respectively. The decrease in strength is attributed to surface defects caused by corrosion in the form of grain‐boundary attack and the formation of pits. The rates of weight loss and microstructural changes on the exposed surfaces correlated well with the observed strength changes.
Mechanical Properties, Thermal Shock Resistance, and Thermal Stability of Zirconia‐Toughened Alumina‐10 vol% Silicon Carbide Whisker Ceramic Matrix Composite
Authors: Solomah Ahmad C. , Reichert Wolfgang , Rondinella Vincenzo , Esposito Leonardo , Toscano Enrique
Published: March 2005

Zirconia‐toughened alumina (Al2O3–15 vol% Y‐PSZ (3 mol% Y2O3)) reinforced with 10 vol% silicon carbide whiskers (ZTA‐10SiCw) ceramic matrix composite has been characterized with respect to its room‐temperature mechanical properties, thermal shock resistance, and thermal stability at temperatures above 1073 K. The current ceramic composite has a flexural strength of ∽550 to 610 MPa and a fracture toughness, KIC, of ∽5.6 to 5.9 MPa·m1/2 at room temperature. Increases in surface fracture toughness, ∽30%, of thermally shocked samples were observed because of thermal‐stress‐induced tetragonal‐to‐monoclinic phase transformation of tetragonal ZrO2 grains dispersed in the matrix. The residual flexural strength of ZTA–10 SiCw ceramic composite, after single thermal shock quenches from 1373–1573 to 373 K, was ∽10% higher than that of the unshocked material. The composite retained ∽80% of its original flexural strength after 10 thermal shock quenches from 1373–1573 to 373K. Surface degradation was observed after thermal shock and isothermal heat treatments as a result of SiC whisker oxidation and surface blistering and swelling due to the release of CO gas bubbles. The oxidation rate of SiC whiskers in ZTA‐10SiCw composite was found to increase with temperature, with calculated rates of ∽8.3×10−8 and ∽3.3×10−7 kg/(m2·s) at 1373 and 1573 K, respectively. It is concluded that this ZTA‐10SiCw composite is not suitable for high‐temperature applications above 1300 K in oxidizing atmosphere because of severe surface degradation.
Strength Analysis of Yttria‐Stabilized Tetragonal Zirconia Polycrystals
Authors: Noguchi Kenichi , Matsuda Yukihisa , Oishi Manabu , Masaki Takaki , Nakayama Sadao , Mizushina Masahiro
Published: March 2005

Tensile strength of Y2O3‐stabilized ZrO2 polycrystals (Y‐TZP) was measured by a newly developed tensile testing method with a rectangular bar. The tensile strength of Y‐TZP was lower than that of the three‐point bend strength, and the shape of the tensile strength distribution was quite different from that of the three‐point bend strength distribution. It was difficult to predict the distribution curve of the tensile strength using the data of the three‐point bend strength by one‐modal Weibull distribution. The distribution of the tensile strength was analyzed by two‐ or three‐model Weibull distribution coupled with an analysis of fracture origins. The distribution curve of the three‐point bend strength which was estimated by multimodal Weibull distribution agreed favorably with that of the measured three‐point bend strength values. A two‐modal Weibull distribution function was formulated approximately from the distributions of the tensile and three‐point bend strengths, and the estimated two‐modal Weibull distribution function for the four‐point bend strength agreed well with the measured four‐point bend strength.
Effect of Aluminum Fluoride on the Physical Properties and Stability of Fluorozirconate and Fluorozirco‐Hafnate Glasses
Authors: Sanghera Jasbinder S. , Hart Patricia , Sachon Maria G. , Busse Lynda , Aggarwal Ishwar
Published: March 2005

The glass quality, physical properties, and thermal stability of fluorozirconate and fluorozirco‐hafnate glasses were investigated as a function of the AIF3 content. The AlF3 concentration varied from 2 to 3.25 mol%. The ratio of the other components was constant, except for 50% substitution of ZrF4 by HfF4 in the fluorozirco‐hafnate glasses. The physical properties of all the glasses were not affected strongly by the AlF3 content. However, the fluorozirco‐hafnate glasses were prone to precipitate out AlF3 microcrystals for AlF3 contents greater than 3 mol%. The thermal stability of the glasses revealed a compositional dependence only in the case of the fluorozirco‐hafnate glasses. The thermal stability decreased as the AlF3 content increased above 3 mol%. The authors concluded that the AlF3 microcrystals nucleated other fluoride phases such as zirconium‐barium fluoride crystals.
Ceramics Reliability: Statistical Analysis of Multiaxial Failure Using the Weibull Approach and the Multiaxial Elemental Strength Model
Authors: Lamon Jacques
Published: March 2005

Methodology for designing reliable ceramic components requires a precise evaluation and correlation of strengths in different stress states. The present paper compares the merits of the Weibull approach and the multiaxial elemental strength model on an experimental case involving mixed‐mode failure in the presence of bimodal flaw populations (surface and volume flaws). The experimental data were obtained using flexure specimens of Si3N4 tested at various spans, with the purpose of enhancing shearing effects. The analysis of data was refined by developing an advanced postprocessor program to finite‐element codes for failure probability determination based upon the Barnett‐Freudenthal approximation of the Weibull approach and the multiaxial elemental strength model. In a second step, the strengths of the specimens exhibiting failures from the two concurrent populations of flaws (intermediate span) were predicted using both approaches from data obtained with different span lengths (long and short spans). Comparison with experimental data showed that the multiaxial elemental strength model is an improvement over the Weibull approach. It also allowed the short‐span bending test to be assessed. Finally, important implications for structural design with ceramics are discussed.
Preparation and Mechanism of Formation of Spherical Submicrometer Zinc Sulfide Powders
Authors: Celikkaya Ahmet , Akinc Mufit
Published: March 2005

Spherical, submicrometer particles of zinc sulfide were homogeneously precipitated by thermal decomposition of thioacetamide in acidic aqueous solutions. The rate of sulfide ion generation, determined by various combinations of temperature, PH, and initial concentrations of zinc ions and of thioacetamide, as related to particle growth rate, had the paramount effect on the particle size distribution. Monosized, bimodal, or narrow size distribution powders were obtained under certain combinations of experimental variables. Particles were porous agglomerates of ∼13‐nm sphalerite crystallites. Particle growth proceeded through diffusion‐controlled aggregation of crystallites.
Essential Factors for Shock Compaction of Diamond Composites
Authors: Sawai Sumiichi , Kondo Ken‐ichi
Published: March 2005

Shock compaction experiments for some diamond composites were carried out, and the best consolidated compacts of diamond/SiC and diamond/TiC had relative densities of 95% and 96%, and microhardnesses of 51 ± 2.9 and 48.6 ± 4.8 GPa, respectively. For obtaining better compacts on the shock compaction of mixtures, the ratio of the constituent particle sizes and the properties of the constituent materials are considered, and then the starting conditions of the mixtures must be decided. Here, a simple model concerned with the influence of both the ratio of the constituent particle sizes and the thermal properties of the constituent materials on the shock compaction of mixtures is also presented.
A Model for Power Consolidation
Authors: Kuhn Liisa T. , McMeeking Robert M. , Lange Fred F.
Published: March 2005

During pressure consolidation of powder compacts, particle rearrangement leading to nonrecoverable strain can be observed. In this study rearrangement is identified as a buckling mechanism that occurs in particle arches. The mechanism is initiated when the applied pressure generates a critical contact force at an arch within the powder compact. The consequence of the buckling is localized consolidation. The contact forces required to initiate this mechanism on a particle scale are evaluated. It is shown that this snap‐through‐buckle mechanism could play a significant role in powder consolidation.
Epitactic Nucleation of Spinel in Aluminosilicate Gels and Its Effect on Mullite Crystallization
Authors: Huling Jeffrey C. , Messing Gary L.
Published: March 2005

Control over the structure of hybrid (colloidal + molecular) aluminosilicate gels was utilized to demonstrate that precursor chemistry has a direct and controllable effect on the ∼1000°C crystallization of spinel and mullite in molecular precursor systems. Synthesis or preparation conditions leading to the development of a cubic, transition alumina result in the epitactic nucleation of spinel at ∼1000°C in gels that otherwise crystallize directly to mullite at ∼1000°C. Thus, the preference for spinel nucleation in gels derived from solution precursor systems whose chemistries promote formation of transition alumina readily explains the reported inability to obtain substantial mullite yields at ∼1000°C. Isothermal transformation kinetics of colloidal and hybrid gels show that in the absence of direct mullite formation at ∼1000°C, the release of alumina from the spinel‐type crystal structure becomes the rate‐controlling step in the transformation. This necessitates higher temperatures for mullite formation and limits the kinetic enhancement possible with extrinsic increases in mullite nucleation frequency.
Synthesis of Mullite Whiskers and Their Application in Composites
Authors: Okada Kiyoshi , Ōtuska Nozomu
Published: March 2005

Mullite whiskers were synthesized by a vapor‐solid reaction. Mullite composition xerogels were fired at 900° to 1600°C with AlF3 in an airtight container. An average whisker increased in length from 7 μm at 1100°C to 10 μm at 1600°C, whereas an average whisker decreased in aspect ratio from 25 to 10 with increased firing temperature. The whiskers elongated to the c‐axis and the side planes were the {110}. A clear lattice image corresponding to (110) lattice spacing up to the edges of the whiskers was observed with high‐resolution electron microscopy, and no droplet was observed on the tips of the whiskers. The chemical composition of the whiskers synthesized below 1100°C showed an apparent Al2O3‐rich composition of about 72 mol%. Composites reinforced by 15 vol% of mullite whiskers in the matrix of 75 vol% mullite/25 vol% Y‐TZP enhanced the fracture toughness compared with those materials without mullite whiskers.
Laser Synthesis of Low‐Agglomerated Submicrometer Silicon Nitride Powders from Chlorinated Silanes
Authors: Bauer Robert A. , Becht Johanna G. M. , Kruis F. Einar , Scarlett Brian , Schoonman Joop
Published: March 2005

The laser chemical vapor precipitation of Si3N4 powder from mixtures of SiH2Cl2 and NH3 has been studied. The reactant gases were mixed at different heights with respect to the laser beam, thus preventing low‐temperature reactions and agglomeration of the produced particles. The morphology and the size of the particles formed are dependent on the injection height of NH3 into the silicon reactant gas stream. Particle diameters are typically between 15 and 110 nm.
Study of the Order‐Disorder Transition in A(B′B″)O3 Perovskite Type Ceramics
Authors: Zhang Xiao‐wen , Wang Qiang , Gu Bing‐lin
Published: March 2005

Based on an order–disorder transition model and the calculation of coulombic electrostatic interaction of B‐site ions, an “ordering structure factor”F0 is introduced. Consequently, an available criterion and diagram to predict the order–disorder transition of A(B′B″)O3 is presented quantitatively. The theoretical results compare satisfactorily with experimental data collected from the literature for different kinds of A(B′B″)O3 ferroelectrics and antiferroelectrics. Permittivity ɛ′ is a sensitive parameter and plays an important role in order–disorder transition. The reason for conflicting arguments from different references for the ordering of some compounds is discussed.
IR Absorption and Raman Spectra of As‐Deposited and Annealed Hydrogenated Amorphous Carbon Films by Plasma Decomposition of Toluene
Authors: Nakamura Yoshikazu , Yamaguchi Yoshimasa , Hirayama Shigekazu , Watanabe Yoshihisa
Published: March 2005

Hydrogenated amorphous carbon (a‐C:H) films, prepared by the rf plasma decomposition of toluene, have been deposited at substrate temperatures of 35° to 60°C. Sharp C─H stretch absorption bands occur around 3000 cm−1, which suggest the microstructure of the films. A weak band at 3304 cm−1, which gives evidence for C─C triple bonds in a‐C:H films, diminishes in intensity at increasing annealing temperatures and disappears after annealing at 200°C.
Texture in Hot‐Pressed or Forged Alumina
Authors: Ma Yuechu , Bowman Keith J.
Published: March 2005

Quantitative texture analysis, including calculation of the orientation distribution function, is used to demonstrate textures in alumina hot‐forged at 1800°C. As suggested by earlier investigations, strong basal textures can be produced by pressing and forging alumina. Experiments in plane strain support arguments for slip‐based texture development. Since the earlier investigations provided incomplete information on preferred orientation, a comparison is made of current and past procedures used to report textures in alumina.
Metastable Alumina Structures in Melt‐Extracted Alumina–25 wt% Zirconia and Alumina–42 wt% Zirconia Ceramics
Authors: Ando Teiichi , Shiohara Yuh
Published: March 2005

Microstructures are examined of rapidly solidified hypoeutectic Al2O3–25 wt% ZrO2 and eutectic Al2O3–42 wt% ZrO2 ceramic alloys by using transmission electron microscopy and scanning transmission electron microscopy. Structures observed in the hypoeutectic alloy were dendritic. Three different types of dendrite morphologies were observed. These are believed to be the stable α‐ and metastable γ‐ and δ‐ modifications of alumina. The cores of the γ‐alumina dendrites were somewhat richer in ZrO2 than those of α‐alumina dendrites; δ‐alumina dendrites were substantially enriched in ZrO2. The lamellar structure of the eutectic in the Al2O3–42 wt% ZrO2 alloy became increasingly finer with increasing cooling rate and at the highest cooling rates was replaced by a fully amorphous structure (except in some instances a ZrO2‐rich needlelike phase identifiable as δ‐alumina was found in the amorphous matrix). An interpretation is given of the results obtained, based on assumed metastable free energy curves and dendrite growth theory.
Sintering of Ceramic Particulate Composites: Effect of Matrix Density
Authors: Rahaman Mohamed N. , De Jonghe Lutgard C.
Published: March 2005

Composites consisting of a fine‐grained, polycrystalline zinc oxide matrix and <10 vol% coarse, rigid silicon carbide inclusions were prepared by the same mixing procedure and then compacted to produce samples with matrix densities of 0.45 and 0.68 of the theoretical. The samples were sintered under identical temperature profiles in separate experiments that employed either a constant rate of heating of 4°C/min or near isothermal heating at 735°C. The ratio of the densification rate of the composite matrix to the densification rate of the unreinforced zinc oxide was found to be independent of the initial matrix density. This ratio increased significantly with temperature in the constant‐heating‐rate experiments but was relatively constant in the isothermal experiments. The results indicate that microstructural coarsening may be an important mechanism for explaining the reduced sinterability of polycrystalline matrix composites.
Nuclear Magnetic Resonance Studies of Silicon Carbide Polytypes
Authors: Apperley David C. , Harris Robin K. , Marshall Gregory L. , Thompson Derek P.
Published: March 2005

The 29Si MAS NMR spectra of the 2H, 4H, 6H, and 3C polytypes of silicon carbide are presented. An attempt is made to correlate differences in the chemical shifts with local atomic environment. The results of the analysis of the spectra of pure polytypes are used as a basic for the interpretation of the spectra of mixed polytypes and a discussion of the crystallinity and impurity levels of different samples. Carbon‐13 chemical shifts obtained from spectra of the same polytypes are also tabulated.
Ferroelastic Domain Switching in Tetragonal Zirconia Single Crystals—Microstructural Aspects
Authors: Chan Chin‐Jong , Lange Fred F. , Rühle Manfred , Jue Jan‐Fong , Virkar Anil V.
Published: March 2005

Ferroelastic domain switching is one of the possible toughening mechanisms in ceramic materials. Microstructural evidence of domain reorientation (switching) in polydomain tetragonal zirconia single crystals is observed upon the application of a unidirectional compressive stress at 1000° and 1400°C. Dark‐field imaging of the three {112{ tetragonal twin variants in a [111] zone indicates that two sets of twin variants grow at the expense of the third set upon application of uniaxial compression. The diminishing variant is the one with its c axis parallel to the compression axis. Inducing cracks into polydomain tetragonal zirconia single crystals provides further evidence of domain reorientation near the crack surface. It is noted again that two sets of twin variants grow at the expense of the third set. A construction for the orientation relationship of domains and their twin boundaries is presented, and a relation between shear stress and reorientation is proposed.
Spherulitic Growth of Apatite in a MgO─CaO─SiO2─P2O5 Glass
Authors: Shyu Jiin‐Jyh , Wu Jenn‐Ming
Published: March 2005

Differential thermal analysis, X‐ray diffraction, scanning electron microscopy with energy dispersive X‐ray analysis, and transmission electron microscopy were used to study the crystallization of a glass with a composition of 11.2 wt% MgO, 40.5 wt% CaO, 33.3 wt% SiO2, and 15 wt% P2O5. A two‐phase “composite,” which was composed of apatite and an intermediate phase (H‐phase), was formed under appropriate heat‐treatment conditions. The spherulitic morphology of apatite phase transformed from “open sheaf” into ellipsoidal as samples were heated to a higher temperature. These phenomena were due to the intermediate H‐phase becoming unstable at this temperature so that the retardation effect on the apatite dendritic growth disappeared.
Colloidal Processing for Improved Piezoelectric Properties of Flexible 0–3 Ceramic–Polymer Composites
Authors: Han Kwonhoon , Safari Ahmad , Riman Richard E.
Published: March 2005

Ceramic‐polymer composites with 0–3 connectivity were prepared from (Pb0.5, Bi0.5) (Ti0.5, (Fe1‐xMnx)0.5)O3 (x= 0.00 to 0.02) ceramic powder and epoxy polymer. Epoxy was dissolved in a methanol solution and the ceramic powder was added to form a suspension. Powder‐polymer coacervates were precipitated from the suspension by the addition of water. Colloidal filtration followed by cold‐pressing consolidated the coacervates to form composites with uniform microstructure. Composites fabricated in this manner could be poled with higher electric fields than could be sustained by the conventionally prepared composites. The values of piezoelectric coefficients, d33, dh, and gh were as high as 65, 41 pC/N, and 145 mV · m/N, respectively.
Sintering of Platelike Bismuth Titanate Powder Compacts with Preferred Orientation
Authors: Watanabe Hidenori , Kimura Toshio , Yamaguchi Takashi
Published: March 2005

The sintering of platelike Bi4Ti3O12 powder particles was investigated. Special emphasis was given to the role of particle orientation in the green sheet on densification and microstructure development. Compacts were made by tape‐casting and dry‐pressing. During the initial stage of sintering, the particles rearranged and formed colonies with the development of face‐to‐face contacts. Pores between particles in a colony disappeared during colony formation, and the volume of pores between colonies decreased on further heating. Grain growth started when the sintered density reached about 90% of theoretical density. The growth of well‐oriented grains increased the degree of orientation. Thus, highly oriented sintered bodies with high densities were prepared by heating at 1150°C.
Preparation and Nonlinear Optical Properties of Quantum‐Sized CuCl‐Doped Silica Glass by the Sol–Gel Process
Authors: Nogami Masayuki , Zhu Yi‐Qing , Tohyama Yoshihide , Nagasaka Katsumi , Tokizaki Takashi , Nakamura Arao
Published: March 2005

The sol–gel process has been applied successfully to the preparation of small‐sized CuCl‐doped silica glass with a significant quantum‐sized effect. Gel synthesized by the hydrolysis of a complex solution of Si(OC2H5)4 and CuCl with an HCl catalyst is heated to 900°C to form fine, cubic CuCl crystals. Above 700°C, absorption peaks observed at ∼370 and ∼380 nm are attributed to the excitation of confined Z1,2 and Z3 excitons, respectively, in the CuCl microcrystals. As the size of the CuCl crystals decreases, exciton energy shifts to the higher‐energy side. The resonant third‐order nonlinear susceptibility at 77 K is 1.1 × 10−8 esu, which originates from the enhancement by the quantum‐sized effect of the exciton.
Phase Equilibria in the System Barium Titanate—Strontium Titanate
Authors: Wechsler Barry A. , Kirby Kevin W.
Published: March 2005

Phase equilibria in the system BaTiO3–SrTiO3 (with 0 to 7 mol% SrTiO3) were studied at temperatures above 1600°C in air. Quenching experiments were performed using high‐purity starting materials, and run products were examined by X‐ray diffraction and differential scanning calorimetry to determine phase composition and Sr concentration. Melting involves a binary loop intersected by the invariant reaction hexagonal (Ba, Sr)TiO3(ss) ⇌ cubic (Ba, Sr)TiO3(ss) + liquid. In contrast with earlier work, these results indicate that there is no depression of the melting point with Sr addition and no congruent melting point in this compositional range.
Pseudobinary Phase Relations of Cuprates and Their Possible Use as Oxygen Concentration Cells
Authors: Hauck Jürgen
Published: March 2005

The pseudobinary phase diagrams MOx, where M is La4BaCu5, La4SrCu5, Pb2Sr2Y0.5Ca0.5Cu3, and YBa2Cu3, are useful in the preparation of compounds with homogeneous oxygen content, for single‐crystal growth, and in investigations, of physical properties which are dependent on oxygen content. The high mobility of oxygen and the coexistence of metallic and nonmetallic oxides suggest the use of the cuprates in oxygen concentration cells with a nonmetallic O2− electrolyte and metallic cathode or anode materials.
Density of Ga2O3 Liquid
Authors: Dingwell Donald B.
Published: March 2005

The density of Ga2O3 liquid in equilibrium with air has been measured at 18000 to 19000C using an Ir double‐bob Archimedean method. The data yield the following description of the density of Ga2O3 liquid: ρ= 4.8374(84)–0.00065(12)(T −18500C). This density‐temperature relationship is compared with the partial molar volume of Ga2O3 in glasses in the systems CaO–Ga2O3–SiO2 and Na2O–Ga2O3–SiO2, corrected to the glass transition temperature using thermal expansivities. The comparison illustrates that a positive excess volume term is required in these systems at low temperature. This observation is similar to those deduced from studies of the partial molar volumes of Fe2O3 and Al2O3 in silicate melts.
Transformation Zone Shape Effects on Crack Shielding in Ceria‐Partially‐Stabilized Zirconia (Ce‐TZP)–Alumina Composites
Authors: Yu Cheng‐Sheng , Shetty Dinesh K. , Shaw Michael C. , Marshall David B.
Published: March 2005

Crack tip shielding is evaluated for observed transformation zones in Ce‐TZP/Al2O3 composites, in which the transformation zone sizes were changed significantly by varying the sintering temperature to control the transformation yield stress. The calculated shielding effects are consistent with an observed insensitivity of crack resistance curves to transformation zone size; smaller zones in materials with higher yield stress were associated with larger ratios of wake length to zone width and correspondingly higher normalized shielding stress intensity factors. Shielding due to the dilatational component of the transformation strain accounted for most of the toughening observed in these materials.
Glass Formation, Properties and Structure of Soda–Yttria–Silica Glasses
Authors: Angel Paul W. , Hann Raiford E.
Published: March 2005

The glass‐formation region of the soda–yttria–silica system was determined. The glasses within this region were measured to have a density of 2.4 to 3.1 g/cm3, a refractive index of 1.50 to 1.60, Vickers hardness values of 3.7 to 5.8 GPa, softening temperature between 500° and 780°C, and a coefficient of thermal expansion of 7 × 10‐6/oC to 19 × 10‐6/o C. Aqueous chemical durability measurements were made on select glass compositions while infrared transmission spectra were used to investigate the glass structure and its effect on glass properties. A compositional region was identified which exhibited high thermal expansion, high softening temperatures, and good chemical durability.
Preparation of Aluminum‐Doped Zinc Oxide Films by a Normal‐Pressure CVD Method
Authors: Nishino Junichi , Ohshio Shigeo , Kamata Kiichiro
Published: March 2005

Aluminum‐doped zinc oxide films prepared using a normal‐pressure CVD (NP‐CVD) method were studied as a transparent electrode material. The films were prepared on fused quartz substrates at 500°C using bis(2,4‐pentanedionato)zinc and tris(2,4‐pentanedionato)aluminum as source material. The transparent films, ∼0.3 μm in thickness, with a transmittance above 80% at a wavelength between 400 and 820 nm, were easily obtained. The optical band gap of the films increased from 3.3 to 3.6 eV with increasing amounts of aluminum dopant. The minimum resistivity of the film was about 4.9 × 10−5Ω·m.
Al2TiO5 Formation in Alumina/Titania Multilayer Composites
Authors: Wohlfromm Hans , Pena Pilar , Moya José S. , Requena Joaquín
Published: March 2005

Al2TiO5 formation in Al2O3/TiO2 multilayer composites obtained by slip casting has been studied in the temperature interval ranging from 1200° to 1450°C. It has been found that nucleation plays a fundamental role in Al2TiO5 formation. Furthermore, it has been observed that initial growth of Al2TiO5 is substantially enhanced when in contact with TiO2.
Constitutive Equations for the Creep of a Silicon Carbide Whisker‐Reinforced Polycrystalline Alumina Composite Material
Authors: Lewis Gladius , Ostvoll Arnfinn
Published: March 2005

The θ‐projection parametric method is used to analyze the creep strain‐versus‐time data, obtained in four‐point flexure, for a 25 wt% silicon whisker‐reinforced polycrystalline alumina composite material. The results, used in conjunction with a suggested value of the activation energy for the creep‐rate‐controlling process for this material of about 620 kJ/mol, led to a postulate that grain‐boundary sliding is the rate‐determining mechanism. In addition, the use of the results in obtaining the values of relevant design creep parameters (namely, life or strain) is illustrated.
Factors Controlling the Sintering of Ceramic Particulate Composites: II, Coated Inclusion Particles
Authors: Hu Ching‐Li , Rahaman Mohamed N.
Published: March 2005

Composite powders were synthesized by coating coarse ZrO2 inclusion particles with a cladding of fine‐grained, crystalline ZnO powder using a chemical precipitation technique. Three different inclusion sizes (1, 3, and 14 μm) were used by selecting the size of the starting ZrO2 powder, and the volume fraction of the inclusions was controlled by the amount of ZnO precipitated. The powders were compacted by uniaxial pressing in a die and then sintered at a constant heating rate of 4°C/min to 1500°C. The sintering kinetics were almost independent of the inclusion volume fraction, and of the inclusion size, for inclusion contents up to ∼40 vol%. Furthermore, composites containing up to ∼40 vol% inclusions were sintered to almost full density under the same conditions used for the unreinforced matrix. This is considerably better than the densities obtained for conventionally mixed powders, where a modest inclusion content (< ∼ 10 vol%) has been observed to cause a severe reduction in the sintered density of the composite matrix. The kinetic data and microstructural observations are a further indication that the main factors which oppose the free sintering of ceramic particulate composites are processing‐related; these factors are (i) inclusion‐inclusion interactions which constrain the matrix and (ii) the packing of the matrix phase in regions immediately surrounding the inclusions.
Phase Relationships in the Ternary System CaO─P2O5─H2O at 25°C
Authors: Brown Paul Wencil
Published: March 2005

The portion of the stable phase diagram for the ternary system CaO‐P2O5‐H2O involving calcium phosphate phases more basic than Ca(H2PO4)2 has been constructed. Construction involves plotting concentrations as their fifth roots to allow phases having very different solubilities to be represented on a single diagram. Hydroxyapatite is shown to be congruently soluble. The stability region for hydroxyapatite includes compositions having Ca/P ratios extending between 1.5 and 1.67. Calcium‐deficient hydroxyapatite forms a stable invariant point with CaHPO4 and a metastable invariant point with CaHPO4. 2H2O. Inspection of the diagram indicates that the compounds CaHPO4 and CaPHO4.2H2O dissolve incongruently. Incongruent dissolution of either CaHPO4 or CaHPO4.2H2O results in the formation of hydroxyapatite during the dissolution process. Such incongruency between these compounds and hydroxyapatite influences their microstructural relationships.
Microstructural Development During Gas‐Pressure Sintering of α‐Silicon Nitride
Authors: Mitomo Mamoru , Uenosono Satoshi
Published: March 2005

Gas‐pressure sintering of α‐Si3N4 was carried out at 1850 ° to 2000°C in 980‐kPa N2. The diameters and aspect ratios of hexagonal grains in the sintered materials were measured on polished and etched surfaces. The materials have a bimodal distribution of grain diameters. The average aspect ratio in the materials from α‐Si3N4 powder was similar to that in the materials from β‐Si3N4 powder. The aspect ratio of large and elongated grains was larger than that of the average for all grains. The development of elongated grains was related to the formation of large nuclei during the α‐to‐β phase transformation. The fracture toughness of gaspressure‐sintered materials was not related to the α content in the starting powder or the aspect ratio of the grains, but to the diameter of the large grains. Crack bridging was the main toughening mechanism in gas‐pressure‐sintered Si3N4 ceramics.
A Simple Test for Thermomechanical Evaluation of Ceramic Fibers
Authors: Morscher Gregory N. , DiCarlo James A.
Published: March 2005

A simple bend stress relaxation (BSR) test has been developed to measure the creep‐related deformation properties of ceramic fibers and whiskers. The test was applied to a variety of commercial and developmental Si‐based fibers to demonstrate test capabilities and to qualitatively evaluate the relative creep resistance of the fibers at 1200° and 1400°C. The implications of these results and the advantages of the BSR test over typical tensile creep tests are dicussed.
Characterization of C─B─N Solid Solutions Deposited from a Gaseous Phase between 900° and 1050°C
Authors: Saugnac Frédéric , Teyssandier Francis , Marchand André
Published: March 2005

The composition, the structure, and some physical properties of boron–carbon–nitrogen solid solutions prepared by chemical vapor deposition (CVD) have been investigated. Both crystalline films and amorphous granular materials resulting respectively from heterogeneous and homogeneous nucleation were characterized by X‐ray diffraction, XPS, RBS, and TEM. The compositions of these single‐phase materials are gathered in two main domains located in the B/N > 1 part of the C─B─N composition diagram. It is stated that the carbon‐rich domain results from structural disorder of an ideal C5B2N composition. The thermal behavior of these films indicates that no mass loss can be detected after 1 h at 1700°C but a graphitization and a formation of small amounts of B13C2 are observed. Density and preliminary electrical conductivity measurements were also performed.
Mechanochemical Polishing of Silicon Carbide Single Crystal with Chromium(III) Oxide Abrasive
Authors: Kikuchi Masao , Takahashi Yutaka , Suga Tadatomo , Suzuki Shigenobu , Bando Yoshio
Published: March 2005

In order to clarify the mechanism of mechanochemical polishing of SiC with Cr2O3 abrasive, 6H‐wurtzite single‐crystal specimens were dry‐polished. A significant anisotropic polishing rate difference was found between Si(0001) and C(0001) surfaces. The C(0001) surface was removed 10 times as fast. Polished surfaces were observed from cross‐sectional and plan‐view directions by high‐voltage TEM. There was no trace of mechanical effects such as residual strain or scratches. The polishing debris was analyzed by X‐ray diffraction, high‐resolution TEM, and analytical TEM. No crystalline phases were identified from X‐ray diffraction patterns except for Cr2O3, while it was found from TEM observation that a large amount of an amorphous phase consisting of Si, C, and O was contained in the debris. These results indicated that the surface of SiC was removed mechanochemically by the aid of a catalytic oxidation effect of Cr2O3.
Rate Processes during Anodic Bonding
Authors: Albaugh Kevin B. , Rasmussen Don H.
Published: March 2005

The rate processes which occur during anodic bonding are modeled using data from various studies. For a given materials system, the process occurs at constant total charge transfer. The observed activation energies are consistent with dc conduction in the glass. The charge transfer required for bonding to aluminum anodes decreases with increasing alkali content of the glass, which is probably due to increasing solubility and mobility of aluminum in depletion layers with higher vacancy contents. The voltage required for bonding at constant time and varying temperature is also consistent with constant charge transfer. The kinetic data are consistent with an electrochemical oxidation model where the rate of bonding is limited by the rate of establishment of the depletion layer.
Microstructure of an Extruded β‐Silicon Nitride Whisker‐Reinforced Silicon Nitride Composite
Authors: Muscat Daniel , Pugh Martin D. , Drew Robin A. L. , Pickup Helen , Steele Don
Published: March 2005

β‐Si3N4 whisker‐reinforced β′SiAlON composites were fabricated by extrusion and densified, using pressureless sintering. Whisker alignment was observed in both the green and sintered microstructures. SEM analysis of polished, sintered samples showed a microstructure consisting of the original β‐Si3N4 whiskers in a matrix of fine SiAlON grains. SEM of plasma‐etched samples and TEM analysis showed that the whiskers, as a result of grain growth, consisted of two phases, a core and a sheath layer. X‐ray mapping and EDS analysis revealed that the core material contained no trace of Al, confirming the presence of original β‐Si3N4 whiskers. The composition of the sheath was qualitatively identical to that of the fine β′ SiAlON grains in the matrix. The sheath was thus formed by the precipitation of the β′SiAlON during liquid‐phase sintering and led to substantial growth of the whiskers. Microdiffraction showed that the β′SiAlON grew epitaxially on the β‐Si3N4 whiskers, resulting in a heavily faulted SiAlON layer.
Remelting Reaction within Belite Crystals during Cooling
Authors: Fukuda Koichiro , Maki Iwao , Ito Suketoshi
Published: March 2005

Belite crystals give six sets of twinned αH′l‐phase lamellae upon transition from α to αH′. During further cooling a remelting reaction occurs within the crystals with heterogeneous nucleation and growth of a liquid phase on the lamella boundaries. The liquid, spherical in shape (∼0.1 μm in diameter), is made up of 70 wt% Fe2O3, 20 wt% CaO, and 10 wt% SiO2 at 1100°C and vitrified on rapid cooling.
Analysis of Recent Measurements of the Viscosity of Glasses
Authors: Fulcher Gordon S.
Published: March 2005

Viscosity of Simple Soda‐Silicate Glasses, 500° to 1400°C

Comparison of the results given by English with those of Washburn, Shelton and Libman, indicates a discrepancy in the absolute values of log10 viscosity amounting to 0.6, those of Washburn et al., being relatively too high. If correction for this is made, the isothermal curves of log10 viscosity as a function of soda content are smooth up to 50% Na2O, showing no inflection. The observations as a function of temperature T are all represented within accidental error by an equation of the type log10η=−A+B× 103/ (T−T0) where all three constants vary regularly with the composition.

Change of Viscosity of Glass (6SiO2, 2Na2O) due to Molecular Substitution of CaO, MgO and Al2O3 for Na2O

The effect is clearly brought out by plotting (from the results of English) the change of log10n due to the substitution as a function of temperature. The curves each show a sharp bend at a temperature between 840° and 1050°C, which is designated the aggregation temperature Ta. If we divide these curves by the corresponding percentage substituted, we get curves for each oxide which are straight and parallel below the aggregation temperatures, the slopes (increase of change of log10n per 100°C) being −0.056 (CaO), −0.055 (MgO), −0.018 (Al2O3) per per cent oxide substituted. For substitution of 1/2 molecule the slopes are −0.325 (CaO), −0.23 (MgO) and −0.18 (Al2O3) per 100°. At the aggregation temperature the change of log10n per per cent is a minimum, 0.03 to 0.06 for CaO, 0.12 for MgO, 0.07 for Al2O3.

Evidence of Aggregation in Glasses, from Viscosity Measurements

. The sharp bends in the plots of change of log10n due to substitution of an oxide for Na2O, suggest the beginning of molecular aggregation at these temperatures. These aggregation temperatures are close to the devitrification temperatures, but the effect on the viscosity curves cannot be due to actual devitrification since it does not change with time. Taking the aggregation temperatures as equal to devitrification temperatures, additional isotherms are roughly sketched into the equilibrium triangle of the system Na2O─CaO─SiO2.

Change of Viscosity of Glass (4SiO2, 2Na2O) due to Substitution of B2O3 for SiO2

The change of log10n (from the results of English) is plotted as a function of temperature, and also the change of log10n per per cent B2O3. The curves are more complex than for the substitution for Na2O.
Effects of Yttrium Doping on the Grain and Grain‐Boundary Resistivities of BaTiO3 for Positive Temperature Coefficient Thermistors
Authors: Blanchart Philippe , Baumard Jean François , Abelard Pierre
Published: March 2005

Several positive temperature coefficient (PTC) thermistors made of barium titanate with an excess of titania and containing additives such as yttria, and eventually silica, have been prepared following two different routes. The electrical properties of the ceramic samples have been studied at room temperature, i.e., below the transition temperature, using complex impedance spectroscopy. The latter proved to be very useful to measure separately the grain and grain‐boundary resistivities which have been followed as a function of the yttrium concentration. They behave very similarly and go through a minimum for the same composition. From both electrical resistivity measurements and local chemical analysis, it is inferred that the average dopant concentration in the grains is lower than the nominal content in the starting powders. An overall interpretation is given, emphasizing the importance of liquid‐phase sintering.
Hot Extrusion of Ceramics
Authors: Wu Xin , Chen I‐Wei
Published: March 2005

Two dense ceramics, Bi2Sr2CaCu2O8+X and 2Y‐TZP: 10 wt% Al2O3, were hot‐extruded through conical dies under a wide range of conditions. Extrusion of Bi2Sr2CaCu2O8+X was performed at 775° to 825°C and speeds of 0.0005 to 0.2 mm/s, with the die semi‐angles from 30° to 60° and extrusion ratios from 4 to 9. Extrusion of 2Y‐TZP:10 wt% Al2O3 was performed at 1650°C and 0.017 mm/s. During hot extrusion of Bi2Sr2CaCu2O8+X, a strong texture was developed with the basal plane aligned along the extrusion direction, whereas the zirconia/alumina composite underwent grain growth which resulted in strain hardening. A simple analytical extrusion model for strain‐rate‐sensitive materials has been developed using a combined slab method and upper‐bound method and a power‐law material flow equation. The model predictions are in good agreement with the experimental results and they further serve to delineate the limitation of the extrusion technique for ceramic applications.
Assessment of Oxide Debond Coatings for Metal‐Toughene Intermetallics
Authors: Emiliani Mario L. , Déve Hervé E.
Published: March 2005

The interfacial debond characteristics of sputtered Al2O3 and Y2O3, coating were assessed in a γ‐TiAl/Nb composite. The preferred debond coating identified for this composite system was Y2O3, which also protected the ductile reinforcing phase from reaction with the matrix. Tension tests on a model laminate specimen were performed to characterize the toughening behavior and showed that interfacial debonding promoted extensive plastic deformation of the ductile phase over a large volume. The coatings were characterized to understand the debonding behavior. Comparison is made with other metal/oxide system.
Reexamination of the Basic Theoretical Model for the Kinetics of Solid–State Reactions
Authors: Frade Jorge R. , Cable Michael
Published: March 2005

The equations properly describing the diffusion–controlled reaction of a spherical particle to form a concentric spherical shell of product are set up then solved numerically and their predictions compared with those of the commonly used approximate models due to jander, Ginstling and Brounshtein, and Valensi or Carter. It is shown that the quasi‐steady‐state Ginstling and Brounshtein model correctly describes the kinetics of the process when the solute is of low solubility but becomes increasingly inaccurate as solubility increases; the Jander model gives almost identical predictions up to about 60% degree of converison. There is thus a range of problems of practical interst for which either the Jander or Ginstling and Brounshtein model gives an acceptable description of the shape of at least the early stages of the degree of reaction versus time curve, but these simple models do not then give the correct values of, for example, diffusivity from such curve fitting. The simple models are nevertheless suitable for determining whether a reaction is controlled by diffusion through the product layer or by reaction at the interface, provided that some important assumptions are satisfied.
Synthesis of Magnesium Dititanate
Authors: Baura‐Peña M. P. , Martínez‐Lope M. J. , García‐Clavel M. E.
Published: March 2005

A very pure magnesium dititanate, MgTi2O5, is obtained from a precipitate calcined at 480° to 500°C for 2 h in a dynamic atmosphere. This precipitate is prepared at room temperature by the coprecipitation of a sulfuric solution, Ti(IV)–Mg(II), in a molar ratio of 2:1, with an aqueous solution of sodium hydroxide at pH ≃ 12.
Fractal Dimension of Alumina Aggregates Grown in Two Dimensions
Authors: LaRosa Judith L. , Cawley James D.
Published: March 2005

The concepts of fractal geometry are applied to the analysis of 0.4‐μm alumina constrained to agglomerate in two dimensions. Particles were trapped at the bottom surface of a drop of a dilute suspension, and the agglomeration process was directly observed, using an inverted optical microscope. Photographs were digitized and analyzed, using three distinct approaches. The results indicate that the agglomerates are fractal, having a dimension of approximately 1.5, which agrees well with the predictions of the diffusion‐limited cluster–cluster aggregation model.