bluuebunny/crossref_metadata_2025 huggingface dataset:
Time Evolution of Demixing in Oxides under an Oxygen Potential Gradient
Authors: ISHIKAWA TAKUMA , AKBAR SHEIKH A. , ZHU WEIGUANG , SATO HIROSHI
Published: March 2005

Time evolution of concentration profiles leading to steady‐state demixing in oxides under oxygen partial pressure gradient is treated based on a microscopic model by applying the path probability method of irreversible statistical mechanics. The redistribution of vacancies and cations toward the steady‐state distribution has essentially been reduced to the diffusion of vacancies and the interdiffusion of cations along the specimen. Atomistic features of the problem, such as a vast difference in the relaxation times for the redistribution of vacancies and cations, are emphasized. Time required for the system to reach the steady state is then estimated in terms of fundamental material properties.
Effect of Pore Distribution on Microstructure Development: II, First‐ and Second‐Generation Pores
Authors: ZHAO JUNHONG , HARMER MARTIN P.
Published: March 2005

A sintering model has been developed to predict the consequences of independently varying the grain growth rate in alumina during final‐stage sintering of a microstructure containing both small (first‐generation) and large (inter‐agglomerate second‐generation) pores. The model shows that although it may be thermodynamically favorable to increase the grain growth rate, the kinetics of densification are such that it almost always pays to inhibit grain growth. This conclusion was verified by experiments on undoped, MgO‐doped, and ZrO2‐doped alumina impregnated with model spherical large pores produced by the burnt‐out latex sphere method. A new type of ceramic processing map has also been developed to aid in the selection of the optimum processing conditions for the sintering of ceramics containing large pores.
Evaporation and Energy Transfer for a Partially Molten, Laser‐Heated Sapphire Filament
Authors: ABREVAYA HAYIM , NORDINE PAUL C.
Published: March 2005

Molten regions were formed on 0.025‐cm‐diameter sapphire filaments that were heated from one side with a continuouswave CO2 laser beam in a low‐pressure flow reactor. As the laser intensity was increased, the liquid/solid interface moved from the laser‐heated edge to the opposite edge of the filament, the apparent temperature measured in the molten region with an optical pyrometer increased from 1470 ± 25 to 2040 ± 30 K, and the filament evaporation rate increased by a factor of 1.6. This change in apparent temperature resulted from an increase in the spectral emittance with the liquid layer thickness. The change in evaporation rate resulted from a 1.09 times larger evaporating area, a 1.24 ± 0.09 times larger evaporation coefficient, and a 10 ± 5 K larger average temperature when the filament cross section was completely liquid than when liquid first formed on the solid filament. Optical and energy‐transfer properties of sapphire and liquid Al2O3 were calculated from optical pyrometry, energy‐balance measurements, and spectral absorption coefficient data for sapphire. At the melting temperature, the total emittance is approximately 0.051 and 0.31 ± 0.03 for the solid sapphire and liquid aluminum oxide filaments, respectively. The thermal accommodation coefficient for Ar atoms is 0.53 ± 0.07 on the solid and approximately unity on the liquid. The spectral absorption coefficient, kλ, at the optical pyrometer wavelength (0.665 μm) is 0.1 ± 0.04 cm−1 for the solid and 12 ± 12 cm−1 for the liquid. This value of kλ for solid sapphire at the melting point is 12 times that of pure, void‐free material and reflects the influence of impurities and small voids in the sapphire filaments that were used.
Effect of Devitrification on Creep Deformation in Glass‐Containing Ceramics
Authors: WILKINSON DAVID S.
Published: March 2005

Many commercial structural ceramics contain glass. This glass is often unstable and devitrifies during creep at elevated temperatures. Two models for this process have been developed, in order to understand how devitrification affects measured creep parameters. They indicate that when creep data are measured after a constant amount of creep strain, the effect of devitrification can be large. Moreover, if devitrification is stress‐state dependent, a different creep rate on the tensile and compressive sides of a bend bar is predicted. This can contribute to the redistribution of stress across a bend bar and complicate the analysis of creep data obtained in bending.
Formation of a Zinc Oxide/Yttria‐Stabilized Zirconia Interface
Authors: Schneider Susan C. , Seitz Martin A. , Choudhury Apurba
Published: March 2005

Zinc oxide was deposited on the (111) face of an yttria‐stabilized zirconia single crystal using the chemical vapor phase method. Zinc vapor was obtained by reducing polycrystalline ZnO in hydrogen at 1200°C. The deposition of the ZnO was accomplished by the reoxidation of zinc vapor at temperatures of 1300° to 1345°C.
Preparation of Silicon Carbide and Aluminum Silicon Carbide from a Montmorillonite–Polyacrylonitrile Intercalation Compound by Carbothermal Reduction
Authors: Sugahara Yoshiyuki , Sugimoto Ken‐Ichi , Kuroda Kazuyuki , Kato Chuzo
Published: March 2005

Both silicon carbide and aluminum silicon carbide have simultaneously been obtained directly from naturally occurring aluminosilicate by carbothermal reduction for the first time. A precursor of a montmorillonite–polyacrylonitrile (PAN) intercalation compound was heated at 1700°C in Ar. For comparison, montmorillonite–carbon mixtures were similarly heated. α‐SiC, β‐SiC, and Al4Si2C5 formed from the montmorillonite–PAN intercalation compound. Mainly α‐Al4SiC4 was obtained with ternary carbides from the montmorillonite–carbon mixtures in addition to a large amount of β‐SiC. Hence, aluminum silicon carbide formation was affected by the mixing condition of the starting materials.
Effect of Milling Medium on the Properties of Superconducting YBa2Cu3O7–x
Authors: Dou S. X. , Liu H. K. , Bourdillon A. J. , Zhou J. P. , Tan N. X. , Sun X. Y. , Sorrell C. C.
Published: March 2005

Ball milling can be used for preparing large quantities of dense YBa2Cu3O7. Studies of superconducting properties show that while a medium of alumina in hexane can be used to mix and to reduce particle size of the starting materials, it contaminates the reacted ceramic. Copper slugs produce an excess of Cu through wear, while balls made of partially stabilized zirconia produce the best results.
Sintering and Microstructure of Mullite Aerogels
Authors: Rahaman Mohamed N. , De Jonghe Lutgard C. , Shinde Subhash L. , Tewari Param H.
Published: March 2005

Mullite (3Al2O3·2SiO2) was prepared by a sol‐gel process and dried by supercritical extraction with CO2. The aerogel (<0.05 of the theoretical density of mullite) experienced a shrinkage of up to 0.6 and reached a density of only ∼0.5 of theoretical after 1 h at 1350°C Mechanically compacted aerogels, however, sintered to nearly theoretical density below 1200°C. This density is somewhat higher than those of gels prepared by conventional drying (i.e., exposure to the atmosphere) and is considerably higher than mullite prepared from mixed powders at higher temperatures. Although the X‐ray diffraction pattern of the sintered gels was almost identical to that of mullite, transmission electron microscopy and energy‐dispersive microanalysis showed two types of grain structure. Elongated grains with an Al/Si atomic ratio corresponding to that of stoichiometric mullite were surrounded by equiaxed grains with a lower Al/Si ratio.
Heats of Fusion of Fluorozirconate Systems
Authors: Gupta Prabhat K.
Published: March 2005

The heat of crystallization of a glass obtained by an isothermal DSC experiment does not represent the true value of the heat of fusion. A procedure is described to evaluate the heat of fusion from measured values of heats of crystallization. The correction term is estimated to be as important as the measured values of heats of crystallization in the case of fluorozirconate glasses.
Liquid‐Phase Sintering of MgO–Bi2O3
Authors: De Jonghe Lutgard C. , Srikanth Varanisa
Published: March 2005

Liquid‐phase sintering of MgO‐5 wt% Bi2O3 was studied by loading dilatometry. The ratio of the creep viscosity to the densification viscosity (∼1.8) and the sintering stress remained nearly constant in a wide density interval. These results, together with results on several other systems, indicate that the constancy of the sintering stress during densification may be a general phenomenon, regardless of densification mechanism.
Domain Switching as a Toughening Mechanism in Tetragonal Zirconia
Authors: Li Bao‐Shun , Cherng Jyh‐Shiarn , Bowman Keith J. , Chen I‐Wei
Published: March 2005

Evidence for a toughening contribution from domain switching, a deformation mode akin to twinning, has been sought in uniaxial tension and compression, biaxial compression, and on the fracture surfaces of several tetragonal zirconia polycrystalline (TZP) ceramics. Only in biaxial compression was domain switching found. In other cases, textures of both the tetragonal and monoclinic phases were due to stress coupling with transformation shear strain. The lower bound of the critical stress for domain switching is placed at the bend strength of TZP, which can exceed 1000 MPa. Although thermal activation may lower the critical stress sharply, at lower temperatures, domain switching is not likely to be an important toughening mechanism.
Role of Zinc Volatilization on the Microstructure Development of Manganese Zinc Ferrites
Authors: SAINAMTHIP PRINYA , AMARAKOON V.R.W.
Published: March 2005

The role of Zn atmosphere on the microstructure development of Mn‐Zn ferrite prepared by alcholic dehydration was investigated. Discontinuous grain growth and intragranular porosity were observed throughout the specimen when a low oxygen partial pressure was employed during sintering. The microstructure of Mn‐Zn ferrite sintered in air resembled a mixture between Mn ferrite (uniform grain size) and Zn ferrite (exaggerated grain growth). Exaggerated grain growth was also observed on the surface of Mn ferrite sintered in the presence of a Zn‐rich atmosphere. The presence of Zn vapor phase enhanced the grain growth kinetics. The overall results indicate that a strict control of atmosphere is required in order to achieve a uniform pore‐free microstructure.
In Situ Martensitic Transformation in a Ternary MgO‐Y2O3‐ZrO2 Alloy: I, Transformation in Tetragonal ZrO2 Grains
Authors: LEE RAN‐RONG , HEUER ARTHUR H.
Published: March 2005

The martensitic transformation in tetragonal ZrO2 grains in a ternary MgO‐Y2O3‐ZrO2 alloy has been studied using in situ observations in the transmission electron microscope. Transformation occurred by the nucleation and growth of monoclinic laths; thermoelastic equilibrium can be maintained at different extents of transformation by continuously varying the applied stress. The product phase was always twinned, but two twinning mechanisms were found‐sequential formation of twin‐related variants and posttransformation deformation twinning. In one example, a (401)/(410) pair of martensite habit planes led to a (100) conjunction twinning plane.
Detection of a Lithium‐Rich Skin on Lithium Niobate Single Crystals
Authors: Gallagher Patrick K. , Peterson George E.
Published: March 2005

Optical and DTA measurements of a single crystal of LiNbO3 pulled from the congruent melt indicate a radial composition gradient leading to a Li‐rich surface. From Tc measurements it is concluded that the surface is ≥0.15 mol% Li2O richer than the bulk composition. The skin thickness is ≤1 mm and is generally removed prior to device preparation; however, some possible sources of concern are discussed for subsequent high‐temperature processing.
Structural Changes by Mechanical and Thermal Stresses of 2.5‐mol%‐Y2O3‐Stabilized Tetragonal ZrO2 Polycrystals
Authors: Kitano Yukishige , Mori Yuuji , Ishitani Akira , Masaki Takaki
Published: March 2005

Structural changes of 2.5‐mol%‐Y2O3‐stabilized tetragonal ZrO2 polycrystal fractured surfaces, as well as ground, polished, and annealed surfaces, were studied by X‐ray diffraction. Much greater intensity of the (200) tetragonal peak than (002) was found on the thin surface layer of the ground specimen, but not on the fracture surface. The intensity changes were discussed in relation to the toughening mechanism.
Mixed Mode I—Mode III Fracture in Ceramic Single Crystals
Authors: Tossell David A. , Ashbee Kenneth H.G.
Published: March 2005

A recently reported method has been used to propagate stable mixed mode I‐mode III cracks in thin slices of single‐crystal α‐quartz (low quartz, SiO2) and single‐crystal rutile (TiO2). A bond‐counting technique has been developed and used to isolate planes of weakness in the crystalline structures of both crystals. Good correlation has been obtained with observed crack planes. Mode III component (KIII) versus crack velocity (v) relations for specified mode I contributions have thus been determined for m{1010} fracture in basal (0001) slabs and for {a+c} fracture in m{1010} slabs of α‐quartz and also for (110) fracture in basal (001) and (101) fracture in (010) slabs of rutile.
Computer Simulation Studies of Perfect and Defective Surfaces in Cr2O3
Authors: Lawrence P.J. , Parker S.C. , Tasker P.W.
Published: March 2005

This communication demonstrates an application for computer simulation techniques to determine the energies of perfect surfaces and of defects near those surfaces. The work presented here will concentrate on Cr2O3, determining the perfect surface energies of five low‐index planes and the vacancy formation energies as a function of distance from the two lowest‐energy planes.
Rapid Heating of a Glass Batch in an Advanced Glass Melter
Authors: TIWARY R. , STICKLER D. , WOODROFFE J.
Published: March 2005

In the advanced glass melter the glass batch is rapidly heated to glass melting temperature by convecting the batch in the combusting gas. Total heating time for the batch, which has particle sizes in the 10‐ to 150‐μm range, is of the order of 50 ms. A computer model has been developed to predict thermal history of the particles including temperature and other phenomena such as calcination and fusion. It also predicts particle velocity and acceleration in the gas and inertial separation of particles from the gas at the target. The model was developed to help in choosing particle sizes of different batch ingredients, defining the operating envelope and optimizing system performance. Experimental measurements of heated batch temperature show good agreement with numerical calculations.
Numerical Modeling of Glass Formation Process in an Advanced Glass Melter
Authors: TIWARY R. , STICKLER D. , WOODROFFE J.
Published: March 2005

In the advanced glass melter glass batch materials are entrained in gas and then rapidly heated to glass formation temperature by combusting the gas. The glass batch separates on a target where glass formation takes place. A numerical model has been developed to simulate this glass formation process, which differs from the conventional glass formation process because the batch materials are mixed at glass formation temperatures and because the calcination of Na2CO3, CaCO3, and MgCO3 occurs on the surface of the glass layer, not in the bulk material. The numerical model is based on diffusion‐controlled dissolution of sand particles in the liquid glass. Preliminary experimental data support the rapid glass formation rates predicted by the numerical model.
Numerical Modeling of Reacting Liquid Glass Layer in an Advanced Glass Melter
Authors: TIWARY R. , STICKLER D. , WOODROFFE J.
Published: March 2005

In the advanced glass melter small particles of batch materials are rapidly heated to glass formation temperatures while entrained in gas, and then deposited on a target surface. The resulting liquid slurry, consisting of sand, CaO, and MgO particles in the liquid formed by mixing of molten cullet and Na2CO3, flows down the center body. During this flow the solid particles dissolve in the liquid and diffuse to form glass. This paper describes a numerical model developed to describe the behavior of this liquid layer. The model is based on Navier‐Stokes equations reduced for the case of a low Reynolds number liquid layer flowing under the action of gravity and shear from gases flowing on top. Experimental results agree with model predictions.
Toughening by Stress‐Induced Microcracking in Two‐Phase Ceramics
Authors: Faber Katherine T. , Iwagoshi Thawi , Ghosh Asish
Published: March 2005

Two glass/alumina composites were examined as potential systems for stress‐induced microcrack toughening. A borosilicate glass/alumina material having a thermal mismatch strain of approximately 0.8% demonstrated toughness up to twice that of an aluminosilicate glass/alumina composite and other reported glass/alumina composites. High‐sensitivity density measurements confirmed a density reduction on application of a stress in the borosilicate glass/alumina system, providing indirect evidence for stress‐induced microcracking.
Method of Fabricating Ceria‐Stabilized Tetragonal Zirconia Polycrystals
Authors: Bhaduri Sarit B. , Chakraborty Amitavo , Rao R. Mohan
Published: March 2005

Most zirconia‐based toughened ceramics need specialized processes to achieve their desired properties. In this paper, we report the fabrication of toughened ceria‐stabilized tetragonal zirconia polycrystal by conventional processing, i.e., ball milling and cold‐pressing followed by sintering. We believe that ball milling works here because a somewhat coarser particle size is actually beneficial in this case. Although the samples were not fully dense (they need not be), a composition of ZrO2‐12 mol% CeO2 yielded a fracture toughness value of 14.1 MPa·m1/2. This is comparable to values reported for materials processed by specialized techniques and can be rationalized in terms of R‐curve behavior.
Viscous Sintering with a Pore‐Size Distribution and Rigid Inclusions
Authors: Scherer George W.
Published: March 2005

The model developed for sintering of a bimodal pore‐size distribution is generalized to describe an arbitrary distribution. The model is further extended to allow for the presence of nonsintering (i.e., rigid) inclusions. This analysis uses the self‐consistent approach that takes account of the local stresses created by differential sintering rates.
Elastic Properties of Polycrystalline Aluminum Oxynitride Spinel and Their Dependence on Pressure, Temperature, and Composition
Authors: GRAHAM EARL K. , MUNLY W.C. , McCAULEY JAMES W. , CORBIN NORMAN D.
Published: March 2005

The isotropic elastic moduli of four specimens of nitrogen‐stabilized cubic aluminum oxide (ALON) were measured using pulse superposition interferometry. Experiments were carried out as a function of both pressure (ambient to 1 GPa) and temperature (0° to 25°C) for specimens of 30.0 and 35.7 mol% AlN. The second‐order moduli results were corrected for porosity using the “self‐consistent‐scheme” approach. Pertinent ambient results for isotropic pore‐free ALON are K= 226.3 GPa and G= 132.0 GPa for the 30.0 mol% AlN material, and K= 229.8 GPa and G= 135.5 GPa for 35.7 mol% ALON (K and G denote the bulk and shear moduli, respectively). The estimated uncertainties in these values are about 2%. The second‐order elastic properties of ALON, as well as their pressure and temperature derivatives, fall midway between spinel (MgAl2O4) and corundum (Al2O3), indicating the excellent potential of this material for structural engineering purposes.
Thin‐Foil Phase Transformations of Tetragonal ZrO2 in a ZrO2‐8 wt% Y2O3 Alloy
Authors: BESTGEN HARRO , CHAIM RACHMAN , HEUER ARTHUR H.
Published: March 2005

Tetragonal zirconia (t‐ZrO2) grains in an annealed ZrO2 8 wt% Y2O3 alloy transformed to orthorhombic (o) or monoclinic (m) symmetry by stresses induced by localized electron beam heating in the transmission electron microscope. Different transformation mechanisms were observed, depending on foil thickness and orientation of individual grains. In thicker grains (≥150 nm), the transformation proceeded by a burst‐like growth of m laths, and this is believed to approximate bulk behavior. In thinner grains near the edge of the foil, usually those with a [100], orientation perpendicular to the thin‐foil surface, “continuous” growth of an o or m phase with an antiphase‐boundary‐containing microstructure was observed. The o phase is believed to be a high‐pressure poly‐morph of ZrO2, which forms (paradoxically) as a thin‐foil artifact because it is less dense than t‐ZrO2, but more dense than m‐ZrO2. In some very thin grains, the t→m transformation was thermoelastic. Furthermore, a mottled structure often occurred just before the t→m or t→o transformation, which is attributed to surface transformation. Aside from the lath formation, the observed transformation modes are a result of the reduced constraints in thin foils.
Incorporation of Mullite as a Second Phase into Alumina by an Infiltration Technique
Authors: Marple Basil R. , Green David J.
Published: March 2005

A process has been developed for incorporating mullite into alumina by infiltrating partially sintered (porous) alumina bodies with a prehydrolyzed ethyl silicate solution. The technique allows for the incorporation of mullite into only the surface (partial infiltration) or throughout the alumina body (complete infiltration). Sintering infiltrated bodies at 1600°C for 12 h yielded specimens with relative densities >98% in which only mullite and alumina were detected by X‐Ray diffraction analysis. The presence of mullite significantly limited grain growth in alumina.
Nonaqueous Spray‐Drying as a Route to Ultrafine Ceramic Powders
Authors: ARMOR JOHN N. , FANELLI ANTHONY J. , MARSH G.M. , ZAMBRI P.M.
Published: March 2005

Spray‐drying imparts unique powder handling features to a wide variety of dried products and is usually carried out in a heated airstream while feeding an aqueous suspension of some solid material. The present work, however, explores nonaqueous spray‐drying as a means of preparing fine powders of metal oxides. In this case an alcohol solvent was used in place of water and the slurry sprayed under an inert atmosphere. Using the nonaqueous technique, the product consists of distinct but loosely aggregated primary particles.
Study by Extended X‐ray Absorption Fine Structure Technique and Microscopy of the Amorphous State of Titanium Diboride Thin Films
Authors: KALOYEROS ALAIN E. , WILLIAMS WENDELL S. , RIZK RICHARD B. , BROWN FREDERICK C. , GREENE ALEX E.
Published: March 2005

The local atomic structure and the stability of amorphous titanium diboride (TiB2) thin films, prepared by electron beam vaporization (EBV) of the crystalline compound onto liquid‐nitrogen‐cooled substrates, are studied using extended X‐ray absorption fine structure (EXAFS) and extended energy‐loss fine structure (EXELFS). From a comparison of the extended fine structure spectra of the amorphous films with corresponding spectra of crystalline TiB2, accurate information is derived on the nature of local structure, or short‐range order, and on the type and degree of nanostructural atomic disorder σ2 in amorphous TiB2. Subsequent controlled heating experiments and observation and imaging by transmission electron microscopy to determine the crystallization temperature of the amorphous phase show that the crystallization temperature and, thus, the stability of the amorphous phase are strongly dependent on σ2. It is shown that minimizing σ2 is crucial in enhancing the amorphicity. Finally, EXAFS and EXELFS are employed to examine in detail the structural changes induced in amorphous TiB2 by variations in the EBV deposition parameters.
Low‐Temperature Sintering of Seeded Sol—Gel‐Derived, ZrO2‐Toughened Al2O3 Composites
Authors: Messing Gary L. , Kumagai Masato
Published: March 2005

Seeding a mixture of boehmite (AIOOH) and colloidal ZrO2 with α‐alumina particles and sintering at 1400°C for 100 min results in 98% density. The low sintering temperature, relative to conventional powder processing, is a result of the small alumina particle size (∼0.3 μm) obtained during the θ‐to α‐alumina transformation, homogeneous mixing, and the uniform structure of the sol‐gel system. Complete retention of pure ZrO2 in the tetragonal phase was obtained to 14 vol% ZTA because of the low‐temperature sintering. The critical grain size for tetragonal ZrO2 was determined to be ∼0.4 μm for the 14 vol% ZrO2—Al2O3 composite. From these results it is proposed that seeded boehmite gels offer significant advantages for process control and alumina matrix composite fabrication.
Temperature Dependence of Infrared Absorption Spectra of Hydroxyl Groups in Soda Germanate Glasses
Authors: Hosono Hideo , Abe Yoshihiro
Published: March 2005

Infrared absorption spectra of hydroxyl stretching vibrations in soda germanate glasses were measured over the range from ambient temperature up to about their softening point. The spectrum of 5Na2O · 95GeO2 glass was found to consist of two absorption bands through an analysis of the spectral changes with temperature. One is located around 3550 cm−1, similar to the band seen in GeO2 glass. Another is centered around 3300 cm−1, also seen in 28Na2O · 72GeO2 glass. From the OH band position and the negative charge on the acceptor oxygen, the bonding configuration responsible for the latter band is considered to be an OH group forming a hydrogen bond with an oxygen bridging a 4Ge and a 6Ge (superscript: coordination number). The equilibrium between the two types of hydroxyl groups giving the above two bands was almost frozen at a temperature far below the Tg of the host glass.
Effect of Creep Damage on the Tensile Creep Behavior of a Siliconized Silicon Carbide
Authors: Carroll Daniel F. , Tressler Richard E.
Published: March 2005

The tensile creep behavior of a siliconized silicon carbide was investigated in air, under applied stresses of 103 to 172 MPa for the temperature range of 1100° to 1200°C. At 1100°C, the steady‐state stress exponent for creep was approximately 4 under applied stresses less than the threshold for creep damage (132 MPa). At applied stresses greater than the threshold stress for creep damage, the stress exponent increased to approximately 10. The activation energy for steady‐state creep at 103 MPa was approximately 175 kJ/mol for the temperature range of 1100° to 1200°C. Under applied stresses of 137 and 172 MPa, the activation energy for creep increased to 210 and 350 kJ/mol, respectively, for the same temperature range. Creep deformation in the siliconized silicon carbide below the threshold stress for creep damage was determined to be controlled by dislocation processes in the silicon phase. At applied stresses above the threshold stress for creep damage, creep damage enhanced the rate of deformation, resulting in an increased stress exponent and activation energy for creep. The contribution of creep damage to the deformation process was shown to increase the stress exponent from 4 to 10.
Fracture Toughness of Polycrystalline Ceramics in Combined Mode I and Mode II Loading
Authors: Singh Dileep , Shetty Dinesh K.
Published: March 2005

Fracture of Polycrystalline alumina and zirconia ceramics in combined mode I and mode II loading was studied using precracked disk specimens in diametral compression. Fracture toughness was assessed in different stress states (including pure mode I, combined mode I and mode II, and pure mode II) by aligning the center crack at specific angles relative to the loading diameter. The resulting mixed‐mode fracture‐toughness envelope showed significant deviation to higher fracture toughness in mode II relative to the predictions of the linear elastic fracture mechanics theory. Critical comparison with corresponding results on soda–lime glass and fracture‐surface observations showed that crack‐surface resistances arising from grain interlocking and abrasion were the main sources of the increased fracture resistance in mode II loading of the polycrystalline ceramics. Quantitative fractography confirmed an increased percentage of transgranular fracture of the grains in mode II loading.
Effects of Particle Size Distribution on the Kinetics of Hydration of Tricalcium Silicate
Authors: Brown Paul Wencil
Published: March 2005

An analysis of the validity of approximating selected particle size distributions by small numbers of size classes was carried out. It was determined that the selection of a small number of particle size classes is not adequate to describe a particle size distribution. One consequence of this is that the particle size distribution, if not properly accounted for, can mask the kinetics of a hydration process. The hydration rates of two finnesses of tricalcium silicate, each with known particle size distributions, were measured by isothermal calorimetry for a period of 28 d. These data were integrated, normalized, and represented as α‐time curves as a basis for comparison with kinetic models of hydration. Agreement with kinetic models was found to be strongly influenced by the effect of particle size distribution. However, the rate‐limiting mechanisms appear to be independent of particle size distribution No single kinetic model was adequate to describe C3S hydration over the first 28 d. A kinetic model that assumes initial surface‐area control with diffusion control dominating subsequently provided an excellent fit to the experimental data.
Mechanism of Mechanical Strength Increase of Soda–Lime Glass by Aging
Authors: Han Won‐Taek , Tomozawa Minoru
Published: March 2005

Two models have been proposed to explain the mechanical strength increase of abraded or indented soda–lime glasses upon aging, namely, crack tip blunting and the release of residual tensile stress near the crack tip. To clarify the mechanism, the time dependence of the strengthening of an abraded soda–lime glass was investigated. Effects of aging media, such as moist air, distilled water, 1N HCI and 1N NaOH solutions, as well as the abrasion flaw depth, were determined. The strength increase rate in water of abraded soda–lime glass was compared with those of borosilicate and high‐silica glasses. The effect of stressing during aging was also investigated. It was found that the rate of strength increase was faster with decreasing abrasion flaw depth and with decreasing chemical durability. For a given flaw depth, an acidic solution produced the fastest strengthening. The strengthening rate was found to accelerate because of the “coaxing’effect of stressing during aging. From these observations, it was concluded that the strengthening rates relate to the diffusion process and chemical reactions, especially the alkali–hydrogen (or hydronium) ion‐exchange reaction, near the crack tip. The role of the residual tensile stress appears to be similar to that of the applied tensile stress, helping the diffusion process near the crack tip. The observed strength increase of soda–lime glass by aging was thus attributed to the effective blunting of the crack tip geometry by the glass–water reaction.
Factors Affecting the Preparation of Barium Titanyl Oxalate Tetrahydrate
Authors: Fang Tsang‐Tse , Lin Horng‐Bin
Published: March 2005

Several experiments have been conducted to investigate the preparation of barium titanyl oxalate tetrahydrate (BTO). Differential thermal analysis and thermogravimetric analysis were employed to investigate the thermal decomposition, and an X‐ray diffractometer and a transmission electron microscope were used to analyze the phases and crystalline states. It has been found that BTO is a nonstoichiometric compound, in which barium hydrogen oxalate hydrate was inserted by the titanium species. Moreover, it has been shown that a mixture would from rather than BTO, depending on pH, mixing order, and oxalate solution.
Interaction of Titanium with Silica After Rapid Thermal Annealing in Argon, Nitrogen, and Oxygen
Authors: Taylor J. Ashley , Desu Seshu B.
Published: March 2005

The interaction of Ti with SiO2 as a result of rapid thermal annealing in argon, nitrogen, and oxygen over a tempetature range of 600° to 1000° has been studied using the analytical techniques of Auger depth profiling, Rutherford backscattering, and X‐ray diffraction. After annealing in argon and nitrogen, Ti5Si3 (with some oxygen) was formed at the Ti/SiO2 interface at all temperatures in this range. For temperatures below 800° in Ar, an outer uniform layer of α‐Ti with randomly dissolved oxygen or Ti2O was formed. At temperatures above 800°, a Ti oxide (O/Ti ratio 1.6) was formed. Annealing in an oxygen ambient showed the formation of rutile with very little reaction of the Ti with SiO2. After annealing in nitrogen, a three‐layered structure of TiN/TiOx/Ti5Si3 (with x ≤ 1) was formed, with the relative thickness of each layer dependent upon the annealing temperature. Discussion of the effect of the ambient on the various reactions and diffusion mechanisms is also presented.
Equivalent Circuit Model in Grain‐Boundary Barrier Layer Capacitors
Authors: Chiou Bi‐Shiou , Lin Sin‐Tah , Duh Jenq‐Gong , Chang Peng‐Heng
Published: March 2005

Electrical properties of BaTiO3‐based capacitors are investigated. A new model is developed to explain the frequency response of the impedance of grain‐boundary barrier layer (GBBL) capacitors. This model takes into consideration the dipole polarization effect and provides a simple and effective approach to evaluate the performance of GBBL capacitors with various dopants and sintering in different atmospheres. When sintered in a reducing atmosphere, doped BaTiO3 exhibits a higher dielectric constant and a relatively stable dieletric constant with respect to the frequency response and temperature dependence. Also, smaller grain resistivity is obtained with addition of both Dy2O3 and Nb2O5.
Fluoride Glass Fibers with Improved Mechanical Strength
Authors: Pureza Pablo C. , Brower Daniel T. , Aggarwal Ishwar D.
Published: March 2005

The practical strength of ZrF4‐based optical fibers reported to date is still significantly lower than that of state‐of‐the‐art silica fibers. Longer length fluoride fibers with improved strength were, however, achieved after the preforms were polished to a mirrorlike finish prior to etching in acidic ZrOCl2 solution. Strength in the range of 430 to 820 MPa (62 to 119 ksi) was observed using the bend technique.
Effect of Powder Characteristics on Compounding and Green Microstructure in the Injection‐Molding Process
Authors: Pujari Vimal K.
Published: March 2005

Compounding characteristics of a ceramic powder in the injectionmolding process were studied. Powderdispersion uniformity and loading in the suspension were optimized by achieving critical powder volume concentration (CPVC). A temperature spike during compounding, defined as a mechanical exotherm, was correlated to CPVC. Based on theoretical and measured densities, a new approach for estimating CPVC was established.
Optical Basicity of Titanium(IV) Oxide and Zirconium(IV) Oxide
Authors: Duffy John A.
Published: March 2005

The relationship between electronic polarizability of oxide(—II), αO2−, and the electron donor power, expressed as the optical basicity, ∧, indicates that ∧(TiO2) is much greater than ∧(SiO2) and is approximately the same as ∧(CaO). Such a high basicity is supported by the trend in the Racah B parameter for the Ni2+ ion in crystalline hosts and is also indicated from αO2− values of glasses containing TiO2. Electronic polarizability and other data for zirconium(IV) media indicate that ZrO2 also has a high basicity, but that ∧(ZrO2) is somewhat less than ∧(TiO2).
Grain‐Boundary Phase Crystallization of Silicon Nitride with Material Loss During Heat Treatment
Authors: Tsuge Akihiko , Inoue Hiroshi , Komeya Katsutoshi
Published: March 2005

An analysis was made of the Si3N4· Y2O3 crystallization process from a compacted Si3N4 powder (composition: 5 wt% Y2O3 and 2 wt% Al2O3) during heat treatment in various powder beds. X‐ray diffraction was used to measure the degree of cyrstallization, which was correlated with weight loss. Crystallization and weight loss were affected significantly by the SiO2 content in the packing powder. Crystallization correlated strongly with the weight loss. The dominant loss was attributed to SiO volatilization from the Y‐Si‐Al‐O‐N liquid. The crystallization mechanism with the loss of material was interpreted using a solubility—supersolubility diagram at constant temperature.
Sintering of a Ceramic at Very Low Temperatures
Authors: Jain Himanshu , Parkash Om , Xu M. Y.
Published: March 2005

Surface area, linear shrinkage, and compressive strength measurements show that, with the help of neutron irradiation, sintering of high‐purity alumina can be initiated at temperatures lower than 150°C; such radiation sintering might be beneficial to many other ceramics.
Yttrium‐Silicon‐Aluminum Oxynitride Glass Fibers
Authors: Messier Donald R. , Gleisner Robert P. , Rich Ronald E.
Published: March 2005

Fibers were made from Y‐Si‐Al‐O‐N glasses previously shown to have excellent mechanical properties and outstanding water corrosion resistance. Fibers of glasses containing, respectively, 3.2 and 6.6 wt% N were pulled free‐hand in air and from glass rods in N2 Continuous fibers (up to several kilometers long) of the former glass were melt‐drawn in N2 while being wound in air outside of the glass‐melting furnace. The fibers, some as small as 10 μm in diameter, retained the desirable properties of the bulk glass.
Estimating the Viscosity of Viscoelastic Solids Based on a Three‐Parameter Model
Authors: Berg Gunnar , Grau Peter
Published: March 2005

A method is proposed for estimating the material parameters of a threeelement model. It has the advantage that all the information gained from the experimental curve can be utilized. In addition, this procedure yields criteria for the validity of the analysis. The curve calculated by using the parameters determined has a minimum deviation from the experimental values of the whole deformation curve.
Environmentally Enhanced Fracture of Gallium Arsenide
Authors: White Grady S. , Freiman Stephen W. , Wilson Anne M.
Published: March 2005

GaAs has been found to undergo environmentally enhanced crack growth in water, formamide, acetonitrile, and methanol. In contrast, no crack extension whatsoever was observed in ammonia gas, N2 gas at 50% relative humidity, or heptane. These results are consistent with a model of electrostatic, rather then chemical, interaction between the environment and the crack‐tip bonds, governing the rate of crack growth. The lack of any water‐impurity‐controlled crack growth further suggests that it is the dielectric constant of the liquid medium rather than the polarizability of an individual molecule that is important.
Thermal Behavior of Alumina—Silica Xerogels During Calcination
Authors: Hsi Chi‐Shiung , Lu Hong‐Yang , Yen Fu‐Su
Published: March 2005

Xerogels of 3Al2O3·2SiO2 mullite were prepared by hydrolyzing Al(NO3)3·9H2O and Si(OC2H5)4 solutions with pH values of 8.3, 9.4, 10.1, and 10.4; the xerogels were composed of a combination of singlephase and diphasic materials. A strong alkaline solution enhanced bayerite formation in the gels. Mullite from the diphasic xerogels was produced by reacting θ‐Al2O3 with amorphous SiO2, whereas mullite from the single‐phase xerogels was transformed from Al‐Si spinel. For the single‐phase xerogel, the DTA curve closely resembled the kaolinite‐to‐ mullite reaction. For the diphasic xerogels, the Al3+ ‐containing solution gelled to pseudoboehmite, which transformed to bayerite in solution. The bayerite then decomposed to η‐Al2O3 and to θ‐Al2O3 sequentially on heating.
SiC Crystals Derived from β‐SiC Powder Using a Conically Converging Shock‐Wave Technique
Authors: Yamada Kenjiro , Tobisawa Shotaro
Published: March 2005

α‐SiC and β‐SiC crystals are prepared from vapor by sublimation of β‐SiC powder subjected to a conically converging shock‐wave generated by detonating an explosive charge. α‐SiC crystals are mainly 6H modifications and their features are plates, pyramids, needles, and filaments grown in the [0001] direction; 4H‐SiC filaments are also obtained. α‐SiC rods having a triangular cross section develop parallel to the [111] direction.
Cracking of Surface Mount Capacitors: Crack Susceptibility by Vickers Indentation Techniques
Authors: Haynes Richard
Published: March 2005

Crack susceptibility of surface mount capacitors fabricated using NPO, Z5U, and X7R materials have been evaluated using Vickers indentation techniques. Capacitors from two sources using X7R have been compared. A relative quality scale between the four surface mount capacitors has been made using the calculated critical stress factor necessary to initiate a crack. It is shown the Vickers indentation technique can be used to determine positional dependence of crack susceptibility. Z5U and NPO materials are used as examples. The Vickers indentation technique has potential of being used to distinguish between acceptable and rejectable lots. It appears from this study that the technique can be an aid to incoming inspection of devices that use ceramic material in their construction, such as surface mount capacitors, electronic packaging devices, and superconductor devices.
Change in Oxygen Content of Y2O3‐Nd2O3‐Doped Silicon Nitride During Firing
Authors: Hirosaki Naoto , Okada Akira
Published: March 2005

The oxygen content of silicon nitride with 1 mol% Y2O3—Nd2O3 additive was measured after firing to determine the compositional change during gas‐pressure sintering. Oxygen content decreases from 2.5 to 0.94 wt% during firing for 4 h at 1900°C and 10‐MPa pressure in N2. This decrease in oxygen results from the release of SiO gas generated by a thermaldecomposition reaction between Si3N4 and SiO2. The resultant sintered silicon nitride material contains less than 1 wt% oxygen.
Coarsening Kinetics of the Tetragonal Phase in a Magnesia‐Partially‐Stabilized Zirconia
Authors: Bateman Charles A. , Notis Michael R. , Williams David B.
Published: March 2005

The coarsening kinetics of the tetragonal phase in a magnesia‐partiallystabilized zirconia at 1420°C was examined using transmission electron microscopy and found to be controlled by volume diffusion. The rate constant was larger and the particle‐size distribution was broader than predicted by the Lifshitz–Slyozov–Wagner theory of particle coarsening. A volume fraction modified coarsenng theory was found which better fits the experimental rate constant and particle‐size distribution.
Ferroelectric Properties of Tungsten Bronze Morphotropic Phase Bounary Systems
Authors: Oliver John R. , Neurgaonkar Ratnakar R. , Cross L. Eric
Published: March 2005

Tungsten bronze ferroelectrics which have a morphotropic phase boundary (MPB) can have a number of enhanced dielectric, piezoelectric, and electrooptic properties compared to more conventional ferroelectric materials. The structural and ferroelectric properties of several MPB bronze systems are presented, including data from sintered and hot‐pressed ceramics, epitaxial thin films, and bulk single crystals. Included among these are three systems which had not been previously identified as morphotropic. The potential advantages and limitations of these MPB systems are discussed, along with considerations of the appropriate growth methods for their possible utilization in optical, piezoelectric, or pyroelectric device applications.
Particle Orientation During Tape Casting in the Fabrication of Grain‐Oriented Bismuth Titanate
Authors: Watanabe Hidenori , Kimura Toshio , Yamaguchi Takashi
Published: March 2005

Slurries containing platelike Bi4Ti3O12 particles have been tape cast to prepare green sheets with aligned particles. The slurries contain well‐dispersed particles and show nearly Newtonian flow behavior. The effect of slurry composition and casting conditions on the particle orientation has been examined. The particle orientation in the green sheet is determined mainly by powder content; other parameters, such as binder content, casting speed, and blade opening, have little effect. The interaction between particles is a main cause for particle alingnment. The slurry with a large powder content is favorable for preparing dense grain‐oriented ceramics.
Dislocation‐Induced Softening of MgO·2.9Al2O3 Single Crystals
Authors: Suematsu Hisayuki , Suzuki Tetsuya , Iseki Takayoshi , Mori Tsutomu
Published: March 2005

Magnesium aluminate spinel (MgO·2.9Al2O3) single crystals were deformed in compression along the [001] direction at temperatures between 1100° and 1500°C. Dislocations introduced by plastic deformation were observed by transmission electron microscopy. These dislocations lead to plasticity at a temperature where undeformed spinel has no ductility. Further, room‐temperature Vickers hardness decreases after plastic deformation at 1500°C.
Adsorption of Dispersants on Zirconia Powder in Tape‐Casting Slip Compositions
Authors: Richards Von L.
Published: March 2005

This paper reports the extension of the more fundamental work of Tormey et al. on the effectiveness of a common dispersant (menhaden fish oil) and a model system (glycerol trioleate) to tape‐casting slip formulation. The adsorption isotherms of the two adsorbates on doped zirconia from methyl ethyl ketone—ethanol solutions were measured by thermogravimetric analysis of solutions equilibrated with the powder surface. Viscosity decreased while sintered density increased in tape‐cast samples prepared to dispersant concentrations corresponding to points along the adsorption isotherm in a way which follows the isotherm if binder competition for surface sites is considered.
Oxidation Behavior of Silver‐ and Copper‐Based Brazing Filler Metals for Silicon Nitride/Metal Joints
Authors: Kapoor Rakesh R. , Eagar Thomas W.
Published: March 2005

The oxidation behavior of reactive‐element‐containing brazing filler metals at 600°C was studied. Weight‐gain measurements coupled with scanning electron microscopy and energy dispersive X‐ray analysis indicated the formation of a nonprotective oxide on the following three ternary alloys: (i) Cu‐80%, Sn‐10%, Ti‐10%; (ii) Ag–Cu eutectic + 5% Ti; and (iii) Ag–Cu eutectic + 5% Zr. Additions of Ni and Si to these alloys failed to reduce spallation. However, a protective oxide was formed by adding Al. The resultant quaternary alloys possessed excellent flow properties on silicon nitride.
Preparation and Structural Characterization of Ultrafine Zirconia Powders
Authors: Benedetti Alvise , Fagherazzi Giuliano , Pinna Francesco
Published: March 2005

Factors concerning the stabilization of the tetragonal and cubic phases, metastable at room temperature, with respect to the monoclinic stable phase in ultrafine zirconia powders are studied. The importance of Na+ ions in the initial zirconia amorphous gel in obtaining a cubic phase has been confirmed. By an X‐ray diffraction study using a new peak profile fitting procedure, the amount of the crystalline phases and their microstructural properties (crystallite size and lattice distortions) have been obtained.
Microstructures of Mullite Sintered from Seeded Sol—Gels
Authors: Mroz Thomas J. , Laughner James W.
Published: March 2005

Mullite has been prepared by firing colloidal aluminosilicate gels seeded with crystalline mullite. The seeded gel samples exhibited a variety of microstructures which were dependent on seed concentration. In samples where the volume fraction of seeds was relatively high, an equiaxed grain microstructure was observed. Insamples with a low seed concentration, seed particles grew to form whiskerlike grains with a high aspect ratio within a fine grain matrix.
Formation of Titanium Nitride Whiskers by Reaction of Sodium Titanium Bronze with Molten Sodium Cyanide
Authors: Bamberger Carlos E. , Angelini Peter , Nolan Theodore A.
Published: March 2005

The production of titanium nitride, TiN, whiskers by reaction of sodium titanium bronze, NaxTiO2 (STB), with excess sodium cyanide, NaCN, at 1000°C is reported. The solubility of Ti from a STB in molten NaCN has been estimated experimentally. The TiN whiskers obtained under different experimental conditions have been examined by scanning electron microscopy and analyzed by analytical electron microscopy.