bluuebunny/crossref_metadata_2025 huggingface dataset:
Sintering and Properties of β′‐Sialon with a Nitrogen‐Rich Y2O3 Sintering Aid
Authors: Bandyopadhyay Siddhartha , Mukerji Joydeb , Roychoudhury Kalpana
Published: March 2005

The synthesis of dense sintered sialon with external additives selected from the system Y2O3–AIN–SiO2 is reported. The highest density (3.21 g/cm3) was achieved at 1750°C at 90 min of sintering with 5 wt% additive. The degree of sialon substitution increased with the amount of liquid; the YSiO2N crystalline phase formed concurrently. Strength degradation occurred above 1000°C. The fracture toughness of the material sintered with a lower amount of sintering aid remained relatively unchanged to 1200°C. The material with more additive exhibited decreased toughness above 1000°C.
Direct Determination of Grain Growth Behavior in Zinc Oxide with Added Barium Oxide
Authors: Uematsu Keizo , Terada Akihiko , Morimoto Tadahiko , Uchida Nozomu , Saito Katsuichi
Published: March 2005

Grain growth behavior in ZnO with 4 to 12 wt% BaCO3 (3.12 to 9.59 wt% BaO) added was studied by a new method, in which the sintered specimen was treated with boiling water to separate the grains by dissolving the grain‐boundary phase. The separated grains were examined with SEM to obtain quasi‐three‐dimensional information on the grain shape, size, and size distribution. The grains had a rounded shape, and the size distribution was found to be lognormal.
Hot‐Stage Study of Bubble Formation During Binder Burnout
Authors: Dong Chun , Bowen H. Kent
Published: March 2005

A technique for observing bubble formation during binder burnout in ceramics processing has been developed using the hot‐stage microscope. Four sets of samples were designed to meet different objectives of the study. Bubble nucleation, growth, and shrinkage were observed. Influencing factors, such as initially trapped gas bubbles, amount of residual solvent, ceramic powder surface, and heating rate were studied.
Thermal Expansion Behavior of the Si3N4‐Whisker‐Reinforced Soda‐Borosilicate Glass Matrix Composite
Authors: Kagawa Yutaka , Kogo Yasuo , Hatta Hiroshi
Published: March 2005

Thermal expansion behaviors of a Si3N4‐whisker‐reinforced sodaborosilicate glass matrix composite are studied. An abrupt increase of the coefficient of thermal expansion is observed and is attributed to formation of crystobalite in the sodaborosilicate glass matrix. This thermal expansion behavior is discussed with special reference to the phase transformation of the crystobalite.
Segregation Isotherms at the Surfaces of Oxides
Authors: Mackrodt William C. , Tasker Phillip W.
Published: March 2005

A non‐Arrhenius segregation isotherm is derived which includes the change in the heat of segregation with surface coverage due to impurity—impurity interactions. It is shown that a linear dependence of log (Xs) on the reciprocal temperature, where Xs is the surface atomic ratio, can derive either from a constant heat of segregation, i.e., Arrhenius behavior, or from a heat of segregation that varies as X−1s. This isotherm is then used to calculate the equilibrium surface coverages of Ca at the {001} surface of MgO1 Mg at the {0001} surface of α‐Al2O3, γ at the {1012} and {1120} surfaces of α‐Al2O3, and Na at the {111} and {110} surfaces of Li2O from the calculated heats of segregation. Where possible, comparisons are made with experiment. The more useful operational definition of the heat of segregation, namely, that derived from the measured coverage or that defined atomistically and obtained by calculation, is discussed.
Preparation and Properties of Oxynitride Glasses Made from Potassium Metaphosphate
Authors: Lei Xingye , Day Delbert E.
Published: March 2005

Potassium phosphate oxynitride (KPON) glasses were made by heating crystalline KPO3 at 702° to 775°C in dry ammonia. The softening temperature, thermal expansion coefficient, refractive index, and dissolution rate in water were measured as a function of nitrogen content and compared with the properties of oxynitride glasses made from LiPO3 and NaPO3.
Effects of Sodium Silicate Exposure at High Temperature on Sintered α‐Silicon Carbide and Siliconized Silicon Carbide
Authors: Butt Darryl P. , Mecholsky J. J. , Goldfarb Victor
Published: March 2005

Sintered α‐silicon carbide and siliconized silicon carbide were exposed to combustion off‐gas containing sodium silicate vapors and particulates in a combustion test facility for 24 to 373 h at 900° to 1050°C. Degradation was evaluated by measuring dimensional changes, by measuring loss in strength due to changes in flaw population, and by evaluating surface corrosion morphology. It is suggested that passive oxidation and dissolution of the silica oxidation scale play an important role in the corrosion process. These mechanisms were enhanced by the continuous removal and replenishment of corrosive material by the high‐velocity gas. These degradation phenomena caused surface pitting and an approximately 50% reduction in strength for both materials after long‐term exposure (>100 h). Morphological evaluation suggested that the grain boundaries in the α‐silicon carbide were oxidized more rapidly than the grains, while for the case of the siliconized silicon carbide the silicon phase was oxidized rapidly along with preferential oxidation of the silicon carbide grains parallel to the {0001} plains.
Intrinsic Disorder in Aluminum Nitride
Authors: Cormack Alastair N.
Published: March 2005

An interatomic potential model is developed for aluminum nitride and is used in conjunction with atomistic computer simulation methods to obtain the energies of intrinsic point defects. These energies are found to be very high, indicating no significant intrinsic disorder, even close to the melting point. Interstitial formation is particularly unfavorable, suggesting that these species will play no part in defect‐controlled processes in AlN.
Fiber–Matrix Interfacial Characteristics in a Fiber‐Reinforced Ceramic‐Matrix Composite
Authors: Singh Raj N.
Published: March 2005

Fiber—matrix interfacial shear stress and mechanical properties in zirconmatrix composites uniaxially re‐inforced with either uncoated or BN‐coated silicon carbide filaments were measured in the as‐fabricated state and after a thermal treatment at 1300°C for 100 h. All the tested composites showed higher fiber—matrix interfacial debond stress than frictional stress and toughened‐composite behavior. Mechanical properties of composites reinforced with uncoated filaments were unaffected by an annealing treatment at 1300°C for 100 h. In contrast, an identical annealing treatment given to a composite reinforced with BN‐coated filaments led to a decrease in first matrix cracking stress and ultimate strength. These observations were related to the changes in the measured interfacial shear stress values as a result of the annealing treatment.
Waveguides in Lithium Niobate
Authors: Abouellell Mahmoud M. , Leonberger Fred J.
Published: March 2005

Lithium niobate (LiNbO3 is considered to be the leading electrooptical material for fabrication of active waveguides, modulators, and switches for application in integrated optical circuits. LiNbO3 is a ferroelectric material with a high Curie temperature of 1210°C. This is essential to permit rapid diffusion at high temperature, e.g., >1000°C, without domain reversal. Its high electrooptic coefficient allows modulation at relatively low voltages. Waveguides are fabricated in LiNbO3 by Ti indiffusion around 1000°C, by Li2O outdiffusion, and, more recently, by Li+/H+ ion exchange. We report results of a study on diluted Li+/H+ ion exchange. This process is attractive because it allows control of the index change between 0.003 and 0.1 Furthermore, the fabricated waveguides are polarization selective, have high optical damage resistance, and do not exhibit index instability as is the case with complete Li+/H+ exchange. The variation in both the index of refraction and the diffusion coefficient with composition is very nonlinear. Mechanisms contributing to these nonlinear properties are discussed.
Microstructural Study of Phase Equilibria in the Fe‐Ca‐O System Involving CaFe5O7
Authors: Bergman Bill , Song Chengyi
Published: March 2005

By microscopic studies it is found that CaFe5O7 (often represented by CW3F) does not disappear by decomposition to three solid phases at about 1050°C, as suggested by previous phase diagrams. Instead it disappears by melting at about 1100°C. On cooling, part of the liquid solidifies to a eutectic structure, wustite + Ca2Fe2O5 (often represented by C2F). A revision of Turkdogan's oxygen potential–temperature diagram is proposed in order to account for the new information.
Synthesis of Sinterable β‐SiC Powders by a Solid Combustion Method
Authors: Pampuch Roman , Stobierski Ludoslaw , Lis Jerzy
Published: March 2005

A solid combustion method for obtaining sinterable β‐SiC powders from Si and C mixtures is described. The method is similar to the thermal explosion method in which a proper preheating of the reactive mixture enables a substantial increase in the temperature of the mixture, due to the heat of reaction, in a short time. The characteristics of the powders obtained by the method are given. Both a high chemical purity of the powders, which is due to the high temperature of synthesis, and an adequate BET surface area of the powders, obtained after vibratory milling, enable these powders to be used for producing sintered SiC materials.
Analytical Electron Microscopy Investigation of the AlN‐ZrO2 System: Identification of a Quaternary Zr‐Al‐O‐N Phase
Authors: Stoto Tiziana , Doukhan Jean‐Claude , Mocellin Alain
Published: March 2005

A combinastion of electron microscopy, diffraction, and spectroscopic techniques were used to identify and characterize the quaternary Zr‐Al‐O‐N phase, which forms during reaction sintering of AlN+ZrO2 mixtures. It is proposed that this phase has a space group Fd3m; several compositions are suggested.
Processing and Mechanical Properties of Dense Si3N4‐SiC‐Whisker Composites without Sintering Aids
Authors: Pezzotti Gluseppe , Tanaka Isao , Okamoto Taira , Koizumi Mitsue , Miyamoto Yoshinari
Published: March 2005

Si3N4 with 20 vol% SiC whisker was fabricated without sintering aids by hot isostatic pressing. Density higher than 99.5% was attained after sintering at 2000°C and 170 MPa for 1 h. Careful mixing procedures and the use of an appropriate amount of a dispersant was found to be effective in avoiding whisker segregation and inhomogeneity. Mechanical properties of the composite were investigated by measurements of flexural strength, microhardness, frature toughness, and Young's modulus as a function of temperature. At room temerature, Vickers microhardness and Young's modulus increased from the matrix value about 20% and 5%, respectively. Toughness was about 30% higher, without reduction in flexural strength, up to 1400Deg;C.
Synthesis and Microstructure of Highly Oriented Lead Titanate Thin Films Prepared by a Sol‐Gel Method
Authors: Chen Chiahong , Ryder Daniel F. , Spurgeon William A.
Published: March 2005

Thin films of PbTiO3 were deposited on fused silica, resistor‐grade alumina, and single‐crystal (100) MgO by a sol–gel processing method. Whereas the films deposited on silica and alumina substrates were randomly oriented and polycrystalline, highly {100} oriented PbTiO3 films were grown on the MgO single crystals. The perovskite‐type structure was observed with films deposited on the single‐crystal MgO and annealed at temperatures as low as 470°C, whereas a pyrochlore‐type strcuture was observed with films on fused silica and alumina processed in a similar manner. All films heat‐treated at temperatures in excess of 570°C showed significant formation of a second PbTi3O7 phase. The films were characterized by electron microscopy and glancing‐incidence‐angle X‐ray diffraction.
Preparation, Structure, and Dielectric Properties of the System Ba1−xLaxTi1−xNixO3
Authors: Parkash Om , Tewari Hari Shanker , Pandey Lakshman , Kumar Ravindra , Kumar Devendra
Published: March 2005

Attempts have been made to synthesize the compositions with x = 0.01, 0.05, 0.10, 0.20, 0.30, 0.40, and 0.50 in the valence‐compensated solid‐solution Ba1–xLaxTi1–xNixO3 by ceramic methods. Solid solutions formed in the compositions with x0.10. The structure of the composition with x = 0.01 is tetragonal, whereas samples with x = 0.05 and 0.10 are cubic. A ferroelectric‐paraelectric transition is observed only in the composition with x = 0.01 at ∼ 350 K.
Effect of Lead Zirconate on Positive‐Temperature‐Coefficient Materials
Authors: Smith James W.
Published: March 2005

The addition of small amounts of PbZrO3 to (Pb,Ba) TiO3 suitably doped to give positive‐temperature‐coefficient behavior resulted in a aramatic change in the resistivity‐temperature properties of the material. The results are explained on the basis of a synergy between Zr content and Pb volatilization in titanate‐based perovskites which favors partial compensation of the Pb vacancies with holes. A secondary result explains the pronounced grain growth which occurs at doping levels where semiconduction begins as being due to a minimum in the vacancy content which results in secondary recrystallization.
Effect of Manganese Oxide Additive on the Dielectric Properties of Mixed‐Sintering Ceramics
Authors: Takahara Hideyuki
Published: March 2005

The influence of internal electrode material on the sintering of mixed‐sintering ceramics and the effect of MnO2 additive on improving their dielectric properties were investigated for their application as multilayer ceramic capacitors. The resistivities of mixed‐sintering ceramic pellets sintered with Ag‐Pd electrode material decreased remarkably because of the expulsion of component elements during sintering. A small amount of MnO2 additive improved the resistivities. Extended X‐ray absorption fine‐structure analysis showed that MnO2 exists in the grain boundaries and compensates for the electrical valence of the expelled elements.
Phase Equilibria of the System SrO‐CaO‐CuO
Authors: Roth Robert S. , Rawn Claudia J. , Ritter Joseph J. , Burton Benjamin P.
Published: March 2005

A new phase, probably CaCuO2, is stable only below ∼740°C and has an orthorhombic average subcell: Cmca, a = 10.588 (1) × 10−1 nm, b = 2.8122(4) × 10−1 nm, and c= 6.3245(6)×10−1 nm. Very weak superstructure reflections indicate two distinct supercells: an orthorhombic cell with the b axis multiplied by 10, and a monoclinic cell, C2/c or equivalent, with amon= 10.946 × 10−1 nm∼ao−rh, bmon= 6.345 × 10−1 nm∼co−rh, cmon= 2.8100 × 12 × 10−1 nm = 33.72 × 10−1 nm∼12[120]o−rh, and β= 105.5°. At 950°C, the ternary system SrO‐CaO‐CuO has extensive regions of solid solution. Complete solution is observed for the 2:1 series (Sr,Ca)2/CuO3; the 1:1 series (Sr,Ca)CuO2 accepts Ca up to ∼Sr0.25Ca0.75O2; and the 14:24 series “Sr14Cu24O41’extends to at least “Sr7Ca7Cu24O41.” A new ternary phase with a very narrow homogeneity range is reported: (SrxCa1−x)CuO2, where x∼0.15 ± 0.02. The composition (Sr0.16Ca0.84)/CuO2 has a primitive tetragonal unit cell with a =3.867(2)×10−1 nm and c =3.2195(2)×10−1 nm.
Superconducting Coupling Nature at Grain Boundaries in Bi2Sr2CaCu2Ox Glass‐Ceramics
Authors: Komatsu Takayuki , Hirose Chisai , Ohki Tomohiro , Matusita Kazumasa
Published: March 2005

Superconducting coupling nature at grain boundaries in Bi2Sr2CaCu2Ox glass‐ceramics consisting mainly of the low‐Tc phase was first examined by measuring superconducting properties and temperature or ac field dependence of ac complex susceptibility. It was found from the ac loss peaks that superconducting coupling at grain boundaries was basically characterized by three types of weak links. The weak‐link behaviors at grain boundaries depended strongly on cooling conditions after annealing and annealing time and temperature. Particularly, it was found that the weak links at grain boundaries were improved by prolonged annealing at 840°C. The furnace‐cooled glass‐ceramics obtained by annealing at 820° or 840°C for about 200 h exhibited a critical transport current density (77 K, zero magnetic field) of about 200 A/cm2.
Sintering and Properties of Monazite‐Type CePO4
Authors: Hikichi Yasuo , Nomura Tsuyoshi , Tanimura Yoshiya , Suzuki Suguru , Miyamoto Masaaki
Published: March 2005

Monazite‐type CePO4 powder (average grain size 0.3 μm) was dry‐pressed to disks or bars. The green compacts began to sinter above 950°C. Relative density ≧ 99% and apparent porosity <1% were achieved when the specimens were sintered at 1500°C for 1 h in air. The linear thermal expansion coefficient and thermal conductivity of the CePO4 ceramics were 9 × 10−6/°C to 11 × 10−6/°C (200° to 1300°C) and 1.81 W/(m · K) (500°C), respectively. Bending strength of the ceramics (average grain size 4 μm) was 174 ± 28 MPa (room temperature). The CePO4 ceramics were cracked or decomposed by acidic or alkaline aqueous solutions at high temperatures.
Subcritical Crack Growth in Soda‐Lime Glass in Combined Mode I and Mode II Loading
Authors: Singh Dileep , Shelty Dinesh K.
Published: March 2005

Subcritical crack growth under mixed‐mode loading was studied in soda‐lime glass. Pure mode I, combined mode I and mode II, and pure mode II loadings were achieved in precracked disk specimens by loading in diametral compression at selected angles with respect to the symmetric radial crack. Crack growth was monitored by measuring the resistance changes in a microcircuit grid consisting of parallel, electrically conducting grid lines deposited on the surface of the disk specimens by photolithography. Subcritical crack growth rates in pure mode I, pure mode II, and combined mode I and mode II loading could be described by an exponential relationship between crack growth rate and an effective crack driving force derived from a mode I‐mode II fracture toughness envelope. The effective crack driving force was based on an empirical representation of the non‐coplanar strain energy release rate. Stress intensities for kinked cracks were assessed using the method of caustics and an initial decrease and a subsequent increase in the subcritical crack growth rates of kinked cracks were shown to correlate with the variations of the mode I and the mode II stress intensities.
Synthesis of Glass‐like Cordierite from Metal Alkoxides and Characterization by 27Al and 29Si MASNMR
Authors: Selvaraj Ulagaraj , Komarneni Sridhar , Roy Rustum
Published: March 2005

A sol‐gel process for the preparation of glass‐like cordierite and ceramic oxide powder is described. Metal alkoxide precursors were dissolved in 2‐methoxyethanol and the metal cations were complexed using 2,4‐pentanedione to overcome different hydrolysis rates of metal alkoxides which lead to microscopic inhomogeneities during gelation. Heating the gel in an aerated furnace resulted in ultrafine cordierite powder of stoichiometric composition at a relatively low temperature. Cordierite gel and glass were also prepared by other methods and compared with the above gel. The environments of aluminum and silicon in the glass and gels heated at various temperatures were studied using 27Al and 29Si magic angle spinning nuclear magnetic resonance (MASNMR) spectroscopy. Most of the heated gels and the glass showed resonances due to pentacoordinated aluminum along with 4‐ and 6‐coordinated aluminum. The homogeneities of the resulting gels and glass are compared using the MASNMR data.
Kinetics of Phase Change in Explosively Shock‐Treated Alumina
Authors: Beauchamp E. K. , Carr M. J.
Published: March 2005

The effect of shock treatment on the kinetics of transformation of transition‐phase alumina has been examined. Alumina powder, consisting of spherical particles produced by melting and quenching, was shock‐treated at 13‐ to 26‐GPa maximum pressure and subsequently heat‐treated at 1000° and 1050°C for various times. At 1050°C, the transformation of unshocked powder was typical of other aluminas with an incubation period of 60 min before significant conversion occurred. In contrast, in the shock‐treated material, no incubation period was observed and the α‐phase content increased exponentially with time. The growth kinetics of the shocked powder corresponded to a linear growth process with an activation energy of 482 kJ/mol. TEM examination revealed α‐phase morphologies consistent with linear growth.
Sintering with Rigid Inclusions: Pair Interactions
Authors: Sundaresan S. , Aksay Ilhan A.
Published: March 2005

The interaction between two spherical, rigid inclusions in an infinite, linearly viscous, densifying medium has been studied. The stresses in the vicinity of the two spheres are highly anisotropic, with significantly enhanced rates of densification in the gap between these particles. A pairwise‐additive approximation for the densification rate of the composite is presented and compared with the composite‐sphere and self‐consistent models described by Scherer.
Synthesis of Solid, Spherical Zirconia Particles by Spray Pyrolysis
Authors: Zhang Shi‐Chang , Messing Gary L. , Borden Michael
Published: March 2005

A model is used to predict solid particle formation during spray pyrolysis by correlating droplet shrinkage before salt precipitation with its relative solution saturation. For the rapid drying conditions and droplet size of ∼ 10 μm, which are characteristic of conventional spray pyrolysis, solid salt particles are formed when a droplet's initial relative solution saturation is ∼ 10−2 and the precipitated salt is sufficiently permeable to permit evolution of the remaining solvent after precipitation. It is proposed that this concentration allows the drying droplet more time and a shorter diffusion distance in which to maintain chemical homogeneity before precipitation. Using these concepts it is demonstrated that zirconyl chloride (ZrOCI2· 8H2O) and zirconyl hydroxychloride (ZrO(OH)CI) are excellent zirconium salts for solid zirconia particle synthesis by spray pyrolysis.
Characterization Studies of Goethite Samples of Varying Crystallinity Obtained by the Homogeneous Precipitation Method
Authors: Goñi‐Elizalde Sara , Garcia‐Clavel Maria E.
Published: March 2005

X‐ray diffraction, infrared spectroscopy, transmission electron microscopy, and thermogravimetry were used to study the solid phase obtained from sulfuric acid solutions of Fe(III) hydrolyzed with urea. The influence of solution factors (temperature, pH, hydrolysis rate, urea and iron concentration, and aging time) on the solid phase was discussed. Hematite (α‐Fe2O3), with impurities of goethite (α‐FeOOH), was obtained at a very rapid hydrolysis rate, whereas goethite was formed at a slow hydrolysis rate. As the pH and aging time increased, so did the crystallinity of goethite. This goethite contained adsorbed SO2‐4 ions which ranged from 1.3% to 9.6% in weight, depending on its crystallinity. In no cases were sulfated compounds detected.
Transformation Plasticity at High Strain Rate in Magnesia‐Partially‐Stabilized Zirconia
Authors: Rogers Wayne P. , Nemat‐Nasser S.
Published: March 2005

Transformation plasticity in magnesia‐partially‐stabilized zirconia (Mg‐PSZ) is studied using a split Hopkinson pressure bar modified for ceramic materials. Axial and transverse strains are measured under uniaxial compressive loading at a strain rate of 250/s. The transformation yield stress is found to increase from 900 MPa under quasi‐static loading to 1.2 GPa at high strain rate. Post‐yield deformation is characterized by shear and volumetric plastic strains up to 1.2%. During unloading, the axial and transverse plastic strains are partially recovered while the volume is conserved. Axially oriented microcracks are observed but they do no contribute significantly to plastic deformation in Mg‐PSZ.
Inversion Twin Boundaries in Zinc Oxide
Authors: Kim Jong Choul , Goo Edward
Published: March 2005

The crystallography and atomic structure of inversion twin boundaries were studied in polycrystalline ZnO using conventional transmission electron microscopy and high‐resolution electron microscopy. Inversion twin boundaries. In order to determine the atomic structure of the inversion twin boundary, high‐resolution transmission electron images were compared with simulated images. The atomic structure of the inversion boundary was determined to have a head‐to‐head configuration and its stacking sequence is AαBβAα‐ATCαA, where A, B, and C are Zn atomic planes and α, β, and T are O planes. A slight contraction of the planes in the boundary region is detected.
Strengthening of Glass by Sol‐Gel Coatings
Authors: Fabes B. D. , Uhlmann D. R.
Published: March 2005

The affects of alkoxide‐derived coatings on the bending strength of silica glass were investigated. For densified coatings, increases in strength of 120% to 130% were found. A model of the strengthening process, based on the filling‐in and partial healing of surface flaws, is proposed. The model accounts for the temperature dependence of strengthening, the inensitivity of strengthening to the size of oligomers in the coating solution, and the insensitivity of strengthening to the thickness of the coating. The presence of a significant residual tensile stress in sol‐gel‐strengthened material is also indicated.
Defect Equilibria and Transport in YBa2Cu3O7‐x at Elevated Temperatures: I, Thermopower, Electrical Conductivity, and Galvanic Cell Studies
Authors: Nowotny Janusz , Rekas Mieczyslaw , Weppner W.
Published: March 2005

Studies of the Y‐Ba‐Cu‐O system at elevated temperatures (300 to 1173 K) and under controlled oxygen activity (102 to 105 Pa) were performed by using electrical methods such as thermopower, electrical methods such as thermopower, electrical conductivity, and emf of solid‐state galvanic cell measurements. The discontinuities of measured electrical parameters demarcate regions of different properties and phenomena: (a) the transition between the range when the oxide sample is quenched on one side and the equilibrium range on the other side and (b) the transition between the quasi‐metallic and semiconducting (m/s) regimes. The temperature of the m/s transition increases from 950 K at po2= 102 Pa to 1150 K at 104 Pa. These data have served to derive a T‐po2 diagram for YBa2Cu3O7‐x. NO discontinuity of the measured electrical parameters has been observed under conditions accompanying the phase transition between the tetragonal and orthorhombic structures. A p‐n type transition has been observed within the semiconducting regime. Electrochemical oxygen titration has led to the determination of the relationship between the lattice oxygen content and the oxygen activity in the ambient gas atmosphere.
Defect Equilibria and Transport in YBa2Cu3O7‐x at Elevated Temperatures: II, Nonstoichiometry
Authors: Nowotny Janusz , Rekas Mieczyslaw
Published: March 2005

Aspects of nonstoichiometry for the Y‐Ba‐Cu (1: 2: 3) system are considered. The general formula YBa2Cu3O7‐x has been assumed for considerations of nonstoichiometry in 1: 2:3 oxide cuprates. Assuming that copper ions may occupy different lattice positions (independently of their valency), the equilibrium constants for oxygen intercalation were determined:
Joining of Yttria‐Tetragonal Zirconia Polycrystal with an Aluminum‐Zirconium Alloy
Authors: Rathner Roland C. , Green David J.
Published: March 2005

Specimens of yttria‐tetragonal zirconia polycrystal (Y‐TZP) have been joined with an Al‐5.8 wt% Zr alloy at temperatures of 900°C and above. The braze alloy contained large needlelike precipitates of the intermetallic phase Al3Zr. It is shown that these large precipitates can aid in strengthening of the joint, especially if they are close to the interface. With decreasing layer thickness, the strengths increased with values as high as 420 MPa.
Ordering Behavior of Lead Magnesium Niobate Ceramics with A‐Site Substitution
Authors: Lin Li‐Jiaun , Wu Tai‐Bor
Published: March 2005

The ordering behavior of lanthanum‐modified lead magnesium niobate ceramics was investigated over a wide range of lanthanum content (from 0 to 50 at.%). The ordering of magnesium and niobium ions in the B site was examined by X‐ray diffraction, and the superlattice reflection was associated with the A(B′1/2B″1/2)O3‐type partial ordering structure. Moreover, the ordering degree increased pronouncedly with respect to lanthanum content of the sample and almost reached unity at [La] = 50 at.%. Finally, a comparison of the ordering behavior was performed among several lead magnesium niobate (PMN) samples with different A‐site substitutional ions. The mechanism used to enhance the ordering of PMN by A‐site substitution is then described by the effect of high valence.
Effect of Substrate Orientation on Interfacial and Bulk Character of Chemically Vapor Deposited Monocrystalline Silicon Carbide Thin Films
Authors: Wang Yu Cheng , Kong Hua Shuang , Glass Jeffrey T. , Davis Robert F. , More Karren L.
Published: March 2005

The high breakdown electric field, saturated electron drift velocity, and melting (decomposition) point of SiC have given continual impetus to research concerned with the development of thin films having minimum concentrations of line and planar defects and electronic devices for severe environments. To this end, epitaxial growth via chemical vapor deposition of monocrystalline films of β‐SiC on Si (100) and 6H‐SiC {0001} substrates and 6H‐SiC on vicinal 6H‐SiC {0001} substrates have been conducted. High concentrations of stacking faults, microtwins, and inversion domain boundaries were produced in films grown directly on Si (100) as a result of a lattice parameter difference of ∼ 20% and the presence of single (or odd number) atomic steps on the substrate surface. Growth on Si (100) oriented 3° to 4° toward [011] completely eliminated the IDBs (but not the other defects) due to the preferential formation of double steps with dimerization axes on the upper terraces parallel to the step edges. Growth of β‐SiC films on 6H{0001} lowered the density of all defects but resulted in the formation of a new defect, namely, double positioning boundaries. The latter were eliminated by using 6H{0001} oriented 3° toward [1120]. The defect density in these last films, relative to those grown on on‐axis Si (100), was reduced substantially (to ∼105 cm/cm3). However, the resulting film was 6H‐SiC. Significant improvements in electrical properties of simple devices were obtained as the defect density was progressively decreased.
Residual‐Stress–Defect‐Severity Relationships in Ceramics
Authors: Sung Jason , Nicholson Patrick S.
Published: March 2005

Equivalent‐sized fracture‐origin defects in partially stabilized zirconia ceramics show dissimilar behavior in initiating fracture. It is suggested that the difference of relative defect severity is related to local residual stresses which develop during sintering and cooling and to elastic modulus differences in the case of solid inclusions on external loading. The existence of residual stresses associated with various defect types is demonstrated, and their variation with temperature is explored. The relative severity of α‐alumina defects in tetragonal zirconia varies with temperature, and it is suggested that this is associated with matrix compressive stress relaxation. The residual stress associated with agglomerate defects is temperature independent, and no residual stress is associated with pores.
Glass–Crystal Transition in II‐IV‐V2 Semiconducting Compounds
Authors: Hong Kug Sun , Berta Yolande , Speyer Robert F.
Published: March 2005

The crystallization behavior of amorphous CdGexAs2, where the x values were varied from 0 to 1.2, was studied in order to document the effect of germanium on the amorphous structure. The glass‐forming tendency of amorphous CdGexAs2 was evaluated by Hruby's criterion. The crystallization mechanism of each group was proposed, interpreting DSC, XRD, EDS, and TEM data, interactively. The crystallization behavior appeared as two distinct groups: those based on the CdAs2 structure and those on the CdGeAs2 structure (chalcopyrite), depending on Ge content. Ge atoms were found to suppress a glass‐to‐glass exothermic transformation to higher temperatures in the CdAs2 group, and crystallization in both groups. Proposed models of amorphous structure from previous investigators, measuring the radial distribution function, magnetic susceptibility, and macroscopic density, were correlated to the crystallization studies herein. A model of the transformation of glass structure with increasing Ge content from a CdAs2 to a CdGeAs2‐like structure was established by extrapolation of experimental results indicating this behavior in crystalline CdGexAs2 compounds with varying x.
Chemical Reactions During the Thermal Processing of Borazene Polymers
Authors: Rye Robert R. , Borek Theodore T. , Lindquist David A. , Paine Robert T.
Published: March 2005

A class of borazene polymers was developed which consists of a two‐dimensional array of six‐membered borazene rings with the borons of adjacent borazene rings separated by ‐NH‐ groups. Pyrolysis of these polymers above ∼1000°C leads to crystalline graphite‐like boron nitride (h‐BN). The thermal chemistry of thin films of one polymer deposited on KOH‐eched aluminum was examined by thermal decomposition mass spectroscopy (TDMS) and thermal gravimetric analysis (TGA), and the gas evolution chemistry was found to be essentially complete at temperatures less than 400°C. All products desorb with the same temperature profile and the major desorbing species are NH3 and N2, consistent with a loss of excess nitrogen and hydrogen in the polymer, and HCl from decomposition of byproducts of the synthesis step. Since the formation of ordered crystalline h‐BN films requires heating to temperatures of the order of 1000°C, whereas the gas evolution chemistry is complete by roughly 400°C, it is concluded that gas evolution chemical processes are not rate limiting in BN ceramic production.
Oxidation of Mullite‐Zirconia‐Alumina‐Silicon Carbide Composites
Authors: Baudín Carmen , Moya José S.
Published: March 2005

The isothermal oxidation of mullite‐alumina‐zirconia‐silicon carbide composites obtained by reaction sintering was studied in the temperature interval 800° to 1400°C. The kinetics of the oxidation process was related to the viscosity of the surface glassy layer as well as to the crystallization of the surface film. The oxidation kinetics was halted for T ≤ 1300°C, presumably because of crystallization.
Low‐Temperature Treatment of Transformation‐Toughened Partially Stabilized Magnesia‐Doped Zirconia–A Solid Particle Erosion Study
Authors: Srinivasan Sreeram , Scattergood Ronald O. , Pfeiffer Gerrard , Sparks Ronald G. , Paesler Michael A.
Published: March 2005

It is now well established that the mechanical behavior of transformation‐toughened partially stabilized zirconias (PSZs) is controlled by R‐curve effects arising from the martensitic transformations. Recent studies have induced the martensitic transformation via a liquid‐nitrogen‐cooling treatment. The result has been the transformation of the tetragonal phase to an orthorhombic phase. The effect of this treatment on solid particle erosion properties is investigated here for a set of commercial partially stabilized magnesiadoped zirconia (Mg‐PSZ) samples.
Redox‐Controlled Solubility of Palladium in a Borosilicate Glass Melt
Authors: Schreiber Henry D. , Harville Tina R. , Damron Gerald N.
Published: March 2005

Palladium establishes the Pd2+–Pd0 redox equilibrium in a reference alkali borosilicate melt. Most of the palladium exists as the insoluble metal, with only a small fraction of the palladium present as the divalent palladium ion dissolved in the melt. The relative reduction potential of this Pd2+–Pd0 redox couple in the reference glass melt is greater than such easily reduced couples as Ni3+–Ni2+ and Mn3+–Mn2+. Palladium metal in glass melts containing appropriate amounts of nickel and sulfur readily partitions into an immiscible nickel sulfide phase; palladium also tends to associate with tellurium in insoluble particulates.
Lead Titanate Ceramics with Positive Temperature Coefficients of Resistivity
Authors: Kuwabara Makoto
Published: March 2005

Lead titanate ceramics were successfully made into semiconductors exhibiting anomalous positive temperature coefficients of resistivity (PTCR) about 3 orders of magnitude above the Curie point (480° to 490°C). The PTCR characteristics of the materials prepared were found to be unstable and to show a significant degradation in both room‐temperature resistivity and magnitude of the PTCR effect with time. The instability of the PTCR characteristics observed in the present materials is considered to be related to the morphologies of their grain structures.
Strength of Hot Isostatically Pressed Si3N4 After Heat Treatment in Ar‐O2 and H2‐H2O
Authors: Kim Hyoun‐Ee , Moorhead Arthur J.
Published: March 2005

The effects of heat treatment in Ar‐O2 and H2‐H2O atmospheres on the flexural strength of hot isostatically pressed Si3N4 were investigated. Increases in room‐temperature strength, to values significantly above that of the aspolished material, were observed when the Si3N4 was exposed at 1400°C to (1) H2 with water vapor pressure (PH2O) greater than 1 × 10−4 MPa or (2) Ar with oxygen partial pressure (PO2) of between 7 × 10−6 and 1.5 × 10−5 MPa. However, the strength of the material was degraded when the PH2O in H2 was lower than 1 × 10−4 MPa, and essentially unaffected when the PO2 in Ar was higher than 1.5 × 10−5 MPa. We suggest that the observed strength increases are the result of strength‐limiting surface flaws being healed by a Y2Si2O7 layer formed during exposure.
Effect of Water Content on the Electrical Conductivity of Sodium Trisilicate Glasses
Authors: Jewell John M. , Shelby James E.
Published: March 2005

The effect of variations in water content on the direct‐current electrical conductivity of Na2O · 3SiO2 glass was measured. Increasing the water content of this glass from 10 to 500 wt ppm of H2O results in an increase in the resistivity of a factor of 2 to 3. The increase in resistivity is accompanied by an increase in the activation energy for conduction. Increasing resistivity with increasing water content is attributed to decreasing molar volume. Under identical annealing conditions, “wetter” glasses relax to a smaller molar volume (greater density) because of the presence of a larger number of “terminal” hydroxyl species that allow structural relaxation to continue to lower temperatures.
Polyphase Ceramic for Consolidating Nuclear Waste Compositions with High Zr‐Cd‐Na Content
Authors: Harker Alan B. , Flintoff John F.
Published: March 2005

The development of dense polyphase tailored ceramic forms for the immobilization of high‐level nuclear wastes has been extended to an Idaho Chemical Processing Plant Fluorinel composition. The ceramic was designed to maximize waste loading and subsequent waste volume reduction without sacrificing chemical durability in aqueous environments. The ceramic, fabricated by hot isostatic pressing, consists of four main crystalline phases, calcium fluoride, zirconia, an apatite‐structured solid‐solution phase, and sphene. The form also contains a designed borosilicate glass phase, a Ni‐Cd alloy, and a minor amount of crystalline zircon. The crystalline apatite solid‐solution phase is the major host for incorporating the actinide simulants U, Ce, and Y, while the glass phase contains Cs and Sr. The calcium fluoride and sphene phases provide microstructural isolation of the radionuclide‐containing phases. Since the glass and crystalline components of the ceramic are not phase compatible at all temperatures, the exact phase content is determined by the tailoring additives, consolidation temperature, and oxidation state control during processing. The simulated HLW ceramic has a density of 3.3 g/cm3 at a waste loading of 73 wt%.
Equivalence of Physically Based Statistical Fracture Theories for Reliability Analysis of Ceramics in Multiaxial Loading
Authors: Chao Luen‐Yuan , Shetty Dinesh K.
Published: March 2005

Two weakest‐link fracture statistics formulations for multiaxial loading, Batdorf's flaw density and orientation distribution approach and Evans' elemental strength approach, are compared for identical fracture criteria and distribution functions. It is demonstrated that despite some fundamental differences in the methodology used in calculating fracture probabilities for multiaxial loading the two approaches give identical predictions. A recent contradictory conclusion reported in the literature is shown to be incorrect.
Delamination Cracking in a Laminated Ceramic‐Matrix Composite
Authors: Sbaizero Orfeo , Charalambides Panos G. , Evans Anthony G.
Published: March 2005

Delamination crack propagation has been investigated in a laminated fiber‐reinforced ceramic‐matrix composite. The crack growth initiation resistance has been shown to be dominated by the critical strain energy release rate for the matrix. However, the resistance increases with crack extension because of bridging effects associated with intact fibers and, in some cases, intact segments of matrix. The delamination cracks also assume a steady‐state trajectory within a 0° layer close to the 0°/90° interface.
Microstructure Development in RuO2‐Glass Thick‐Film Resistors and Its Effect on the Electrical Resistivity
Authors: Yamaguchi Takashi , Iizuka Kazuhiko
Published: March 2005

Microstructure development in RuO2‐glass thick‐film resistors has been studied by optical microscopy with special emphasis on the effect of glass particle size and mixing and firing conditions. The microstructure development has been characterized by the coalescence of glass grains, infiltration of glass into RuO2 particle aggregates, and agglomeration of RuO2 particles. The resistivity‐firing temperature relationship has been correlated with the microstructure development.
Determination of the Elastic Modulus and Residual Stresses in Ceramic Coatings Using a Strain Gage
Authors: Chiu Chin‐Chen
Published: March 2005

Formulas based on the beam theory are derived for calculating the in‐plane elastic modulus and residual stresses in ceramic coatings. In addition to theoretical derivation, experimental data for SiC coating/graphite substrate composites are proposed. The results indicate that the modulus of SiC coatings is 359 GPa. The residual stresses are in compression and are functions of the ratio of substrate thickness to coating thickness.
Fracture Mechanics of High‐Toughness Magnesia‐Partially‐Stabilized Zirconia
Authors: Inghels Eric , Heuer Arthur H. , Steinbrech Rolf W.
Published: March 2005

Crack growth resistance in MgO‐partially‐stabilized ZrO2 (Mg‐PSZ) has been studied using notched double‐cantilever beams (DCB's). High‐toughness Mg‐PSZ exhibited nonlinear mechanical behavior in the form of residual displacements, related to the transformation of tetragonal (t) ZrO2 precipitates to monoclinic (m) symmetry. The influence of this residual displacement on crack resistance behavior (“R‐curve” behavior) was analyzed using several different fracture mechanics approaches. Specifically, the “global” resistance WR(Δa), a J‐integral type parameter WJ(Δa), were determined as a function of crack extension (Δa). Some of these parameters displayed a geometry dependence; their form depended on the initial notch depth and the size of the unbroken ligament. The early stages of crack growth were best described by WJ(δa). The residual strains building up in the wake during crack growth and their effect on specimen displacement made the WR curves (and to some extent the WJ curves) dependent on the ratio between initial notch depth and crack extension. The only curves independent of geometry were the G(δa) curves, but only in a restricted range of geometry. However, the material resistance of Mg‐PSZ is clearly under‐estimated with such a linear elastic approach.
Electron Spin Resonance of High‐Spin Co2+ in Alkali Borate and Alkali Germanate Glasses
Authors: Kojima Kazuo , Yano Hirotsugu , Matsuda Jiro
Published: March 2005

Electron spin resonance spectra of high‐spin Co2+ doped in alkali borate and alkali germanate glasses have been measured at 4.2 K. For comparison, the corresponding spectrum in a 33K2O·67SiO2 glass has also been measured. On the basis of the spectral line shape, the observed spectra, together with those in the literature, seem to be classified into four spectral types that represent Co2+ ions in octahedral coordination, a mixture of some types of coordination, tetrahedral coordination with nearly axial symmetry, and distorted tetrahedral coordination.
1000°C Phase Relations and Superconductivity in the (Nd‐Ce‐Cu)‐O Ternary System
Authors: Pieczulewski Charles N. , Kirkpatrick Kelly S. , Mason Thomas O.
Published: March 2005

The phase relations involving the 24 K n‐type Nd2‐xCexCuO4 superconductor were investigated at 1000°C in air. The terminal solid solubility was confirmed to be x= 0.2. This solid solution is the only ternary phase in the Nd2O3–CeO2–CuO diagram. A binary (1 −y)CeO2–yNdO1.5 solid solution exists out to y= 0.4. Phase diagrams for NdO1.5–CeO2–CuO (1000°C) and NdO1.5–CeO2 (900° to 1500°C) are presented.
Etching Alumina with Molten Vanadium Pentoxide
Authors: Katz Joel D. , Hurley George
Published: March 2005

A method for etching alumina using molten vanadium pentoxide at 750°C for up to 1 min is discussed. Microstructures of 95% dense alumina etched by this technique, boiling phosphoric acid, and ion and thermal etching are compared.
Theoretical Studies of the Electronic Properties of Ceramic Materials
Authors: Ching W. Y.
Published: March 2005

The first‐principles orthogonalized linear combination of atomic orbitals (OLCAO) method for electronic structure studies has been applied to a variety of complex inorganic crystals. The theory and the practice of the OLCAO method in the local density approximation are discussed in detail. Recent progress in the study of electronic and optical properties of a large list of ceramic systems are summarized. Eight selected topics on different ceramic crystals focusing on specific points of interest are presented as examples. The materials discussed are AIN, Cu2O, β‐Si3N4, Y2O3, LiB3O5, ferroelectric crystals, Fe‐B compounds, and the YBa2Cu3O7 superconductor. The results include the band structure, density of states, charge density distribution, spin density distribution, effective charges, total energy and totalenergy‐derived results, optical absorption, positron annihilation spectra, and more. Extension of the band theoretical approach to the study of other areas of fundamental ceramic science is also discussed.
Band Structure Calculations of the High‐Temperature Electronic Structure of Magnesium Oxide
Authors: French Roger H. , Kasowski Robert V. , Ohuchi Fumio S. , Jones David J. , Song Huesup , Coble Robert L.
Published: March 2005

The effects of high temperature on the electronic structure of a material consist of two major contributions, thermal lattice expansion and the electron‐phonon interaction. These can produce dramatic changes in the electronic structure and play a critical role in the high‐temperature properties and behavior of ceramics. We have used ab initio pseudofunction band structure methods to calculate the temperature dependence of the electronic structure of MgO from 300 to 1300 K modeling the independent effects of thermal lattice expansion and the electron‐phonon interaction. The band structure calculations were performed self‐consistently on a (MgO)4 supercell using experimental values obtained from high‐temperature X‐ray diffraction to determine the lattice constants up to 1300 K and the root mean square amplitude of phonon displacements. Lattice thermal expansion contributed ‐0.15 meV/K to the band gap temperature dependence. Individual phonon modes, with displacements in the 〈111〉, 〈110〉, and 〈100〉 directions, were modeled using distorted lattice calculations. The electron‐phonon coupling was found to be strongest for the 〈100〉 mode modeled, with strong coupling seen for modes which lead to the smallest decrease in the Mg‐O bond length. The overall magnitude of the electron‐phonon contribution to the band gap temperature dependence for the phonon modes modeled was −0.95 meV/K. The theoretical results account for a band gap temperature dependence in MgO of −1.1 meV/K, which compares well with the temperature dependence of approximately −1 meV/K determined experimentally using vacuum ultraviolet spectroscopy.