bluuebunny/crossref_metadata_2025 huggingface dataset:
Joining of Ceramics of Different Biofunction by Hot Isostatic Pressing
Authors: Li Jianguo , Hermansson Leif , Söremark Rune
Published: March 2005

Monolithic zirconia (Z) and zirconia‐hydroxyapatite (Z/HA) composites were joined by cold isostatic pressing (CIP at 300 MPa) and subsequently by glass‐encapsulated hot isostatic pressing (HIP at 1225°C, 1 h and 200 MPa). The physical and mechanical properties of the materials were measured. The fracture surface was studied using a light microscope. The results indicate a strength level of the joint similar to that of the corresponding composite material (Z/HA), 845 and 860 MPa, respectively. Similar experiments with monolithic alumina (A) and alumina‐hydroxyapatite (A/HA) were carried out without success. Cracking occurred in the joint area during the cold isostatic pressing process. It seems that ceramics with high green strength and similar green density are essential when joining ceramics by combined CIP and HIP processes.
Grain Alignment in Bulk YBa2Cu3Ox Superconductors by Isothermal Peritectic Reaction Process
Authors: Jee Young A. , Kang Suk‐Joong L. , Suh Jeong‐Hun , Yoon Duk Yong
Published: March 2005

An isothermal peritectic reaction (IPR) process has been developed to fabricate YBa2Cu3Ox (123) superconductors with aligned grain structure in a relatively short time without a temperature gradient. The process consists of the preparation of Y2BaCuO5 (211) powder compact in wire form and infiltration of a Ba‐Cu‐O glass melt into the 211 compact below the peritectic temperature of ∼ 1010°C. During the infiltration at 965°C the 123 phase forms at the surface of the compact by the reaction between 211 grains and the glass, and the newly formed 123 grains grow directionally towards the center of the compact. The result of the infiltration is an aligned grain structure with a preferred orientation of {100} planes in the axial direction of wire‐type compacts. These 123 superconductor specimens show the zero resistance (Tc) at 92 K and transport critical current density (Jc) of up to 1500 A/cm2. By this process, superconductor wires can be produced at shorter times and lower temperatures than the melt‐texturing methods.
Improvement of Creep Resistance of Sintered Silicon Nitride by Hot Isostatic Exudation of Intergranular Glass
Authors: Rouxel Tanguy , Besson Jean‐Louis , Goursat Paul
Published: March 2005

Postsintering treatment of pressureless‐sintered silicon nitride at 1250°C (i.e., above the glass transition temperature of the amorphous phase) by hot isostatic pressing was performed to diminish the quantity of residual intergranular amorphous phase that results from densification aids. The samples were first embedded in a powder (SiC or Al2O3), which worked as a diffusion barrier and a pressure transmitter; then, both sample and surrounding powder were encapsulated in evacuated tubes of borosilicate glass or stainless steel. Energy dispersive X‐ray spectrometry proved that, during the treatment, a noticeable amount of intergranular vitreous phase exuded out of the sample into powder pores. As a consequence, the creep resistance was enhanced by a factor of 3. When the HIP treatment was associated with a subsequent crystallization treatment, a further improvement in creep resistance was obtained.
Kinetics of Nonisothermal Crystallization of Bi2Sr2CaCu2Ox Glasses with Different Copper Valence States
Authors: Komatsu Takayuki , Sato Ryuji , Kuken Yusuke , Matusita Kazumasa
Published: March 2005

The kinetics of the nonisothermal crystallization process in Bi2Sr2CaCu2Ox glasses with different copper valance states, R(Cu+) = Cu+/(Cu++ Cu2+) = 0.79–0.99, were examined by using differential scanning calorimetry. Four different kinetic equations were used for the data analyses. It was found that the values of activation energy for crystal growth, Ea, decreased with increasing Cu+ content. The value of Ea, which was estimated from the modified Ozawa equation, for the glass with R(Cu+) = 0.79 was 483 kJ·mol‐1 and for the glass with R(Cu+) = 0.99 was 353 kJ·mol‐1. In the former glass, the number of crystal nuclei was almost independent of the heating rate. But, in the latter glass, the number of crystal nuclei varied significantly with the heating rate. The crystallization mechanism in the glasses was closely related to the thermal stability and viscosity of glasses: the glass with R(Cu+) = 0.99 showing a high thermal stability and a low activation energy for viscous flow had a small value of Ea. The plot of In (Tp2/α) against 1/Tp, where Tp and α are crystallization peak temperature and heating rate, respectively, gave a reasonable value of Ea for the glass with R(Cu+) = 0.79 but was unsuitable for the evaluation of Ea for crystal growth of the glass with R(Cu+) = 0.99.
Chemical State of Vanadium in Tin‐Based Yellow Pigment
Authors: Fujiyoshi Kaichi , Yokoyama Hisanori , Ren Feng , Ishida Shingo
Published: March 2005

Physicochemical states of vanadium in V‐doped SnO2 were studied to clarify the origin of the color of vanadium‐tin yellow pigment and its color instability when fired with glaze material. Precision measurements of lattice parameters of V‐doped SnO2 revealed that vanadium was dissolved as V4+ and its solubility limit was 0.9 wt% as V2O5. It was found that the color of vanadium–tin yellow was produced by two types of undissolved vanadium on SnO2 grains. One is poorly crystallized vandium oxide (v), (V2O5)′, having a yellow color, and the other is orange‐colored crystalline V2O5. The structure of (V2O5)′ was discussed in connection with its color.
Hot Deformation of YBa2Cu3O7‐δ and Composite YBa2Cu3O7‐δ/Ag
Authors: Hendrix Bryan C. , Abe Teruyoshi , Borofka Janine C. , Wang Pin‐Chin , Tien John K.
Published: March 2005

The response of ceramic superconductors and ceramic composites to compressive stresses at high temperatures has been examined. Monolithic YBa2Cu3O7‐δ and composite YBa2Cu3O7‐δ6/Ag were tested at constant true strain rates from 10‐6 to 10‐3 s‐1 at temperatures from 800° to 950°C. Fine‐grained monolithic YBa2Cu3O7‐δ appears to have a regime of superplastic deformation between temperatures of 850° and 950°C at strain rates from 10‐6 to 10‐4 S‐1. The addition of 20 vol% Ag to a coarser‐grained material enhances the ductility of the ceramic and lowers the flow stress by a factor of 3 to 10. However, there is no evidence of superplasticity in the composite material in the range of temperature and strain rate where it was tested.
Hot Isostatic Pressing of YBa2Cu3O7‐δ and YBa2Cu3O7–δ/Ag Composites
Authors: Borofka Janine C. , Hendrix Bryan C. , Attarwala Abbas I. , Tien John K.
Published: March 2005

Hot isostatic pressing (HIP) can be used to produce fully dense shapes of high‐temperature ceramic superconductors. Densification modeling of monolithic YBa2Cu3O7‐δ and the composite YBa2Cu3O7‐δ/Ag systems allows an understanding of the HIP process and has led to the development of successful protocols for HIP of these materials. Ag metal is the best encapsulation material found for both systems. HIP of monolithic YBa2Cu3O7‐δ requires a slow ramp of pressure in order to prevent decomposition into more basic oxides such as Y2BaCuO5 and CuO. HIP of composite YBa2Cu3O7‐δ/Ag requires careful powder processing to obtain dense material with a fine dispersion of Ag.
On the Isothermal Martensitic Transformation in 3Y‐TZP
Authors: Behrens Gesa , Dransmann Gerd W. , Heuer Arthur H.
Published: March 2005

The martensitic tetragonal (t) → monoclinic (m) transformation in 3Y‐TZP displays both athermal and isothermal kinetics; both are stress‐assisted. Room‐temperature transformation was induced with Vickers indentations; the isothermal, or thermally activated, component was induced by annealing indented samples at temperatures up to ∼ 900 K. The reverse m → t transformation occurred on annealing at still higher temperatures. The extent of transformation in the indented region was quantified with Raman microprobe spectroscopy, while the deformation associated with the transformed regions was evident as surface displacements around the indent. The spatial distribution of the transformation product(s) around the indents is complex and not yet entirely understood.
Oxidation of Chemically Vapor‐Deposited Silicon Nitride in Dry Oxygen at 1923 to 2003 K
Authors: Narushima Takayuki , Lin Ray Y. , Iguchi Yasutaka , Hirai Toshio
Published: March 2005

Oxidation of chemically vapor‐deposited Si3N4 was studied in dry oxygen between 1923 and 2003 K under a total pressure of 0.1 MPa using a thermogravimetric technique. At 1923 to 1953 K, a parabolic rate mechanism prevailed for the oxidation reaction. From 1973 K, the oxidation reaction exhibited a mixed linear‐parabolic rate mechanism. At 2003 K, on the other hand, the oxidation of Si3N4 showed a linear behavior. Both amorphous silica and cristobalite were identified as reaction products on the oxidized Si3N4 surface using X‐ray diffraction analysis. The percentage of cristobalite in the surface oxide scale was determined from the X‐ray diffraction pattern. It was found that, at 2003 K, only amorphous silica was formed. The parabolic rate constants (Kp) obtained from this study were close to those obtained in the literature.
Coalescence of Two Viscous Cylinders by Capillarity: Part I, Theory
Authors: Hopper Robert W.
Published: March 2005

The creeping plane flow of two viscous cylinders coalescing under the influence of surface tension is described theoretically in a series of three articles. Part I is a theoretical overview. The physical assumptions affecting applicability of the theory are discussed. The shape as a function of time and of the initial diameter ratio D≥ 1 is given in parametric form. For D= 1 and D∞, the shape sequences are known exactly; for finite D > 1, a first‐order differential equation is solved numerically. The time requires a quadrature. This is accurate, and easier than solving the fluid‐dynamical field equations. The theory encompasses time‐dependent liquid properties.
Effect of Substrate Texture on Orientations of rf‐Sputtered Ba2Si2TiO8 Thin Films
Authors: Li Yi , Youdelis William V. , Chao Benjamin S. , Yamauchi Hisao
Published: March 2005

Radio‐frequency‐sputtered barium silicon titanate, Ba2Si2TiO8 (BST), thin films were grown on various substrates at substrate temperatures ranging from 750° to 955°C. The asdeposited films were characterized using X‐ray diffraction, optical microscopy, and scanning electron microscopy (SEM). The results of the morphology analysis and X‐ray diffraction analysis show no crystalline structure for films deposited on the fused quartz and unetched Si (100) substrates at temperatures lower than 865°C. At a substrate temperature of 900°C, tiny tetragon‐like grains were observed for the film grown on the fused quartz, and the grains grew at a rate of 0.18 μm/min in the initial deposition stage. Optical and SEM micrographs reveal (001)‐oriented, tetragon‐like grains grown on HF‐etched Si (100) wafers in the initial deposition stage and in later stages at substrate temperatures from 822° to 865°C. The results of X‐ray diffraction analysis show a high (001) orientation for the thicker films, which corresponds to the tetragon‐like configuration of the grains in the initial stage. Triangle‐like grains were observed on the films deposited on etched Si (111) substrates in a temperature range from 822° to 899°C, but the grain configuration changed from the initial triangle shape to a tetragon shape as the films grew thick. The X‐ray diffraction spectra show a high (001) orientation for the thicker films, which indicates an orientation transformation during the deposition due to a very low interfacial energy between the (001)‐oriented BST overgrowth and the BST substrates in the later stage of deposition. Both the tetragon‐like and the triangle‐like grains have quasi‐two‐dimensional polygon shapes and have nonliquid‐like characteristics in coalescence, which suggests a strong interaction between the BST deposits and the Si substrates.
Effect of Hot Extrusion, Other Constituents, and Temperature on the Strength and Fracture of Polycrystalline MgO
Authors: Rice Roy W.
Published: March 2005

Improved agreement was confirmed between the Petch intercept and single‐crystal yield stresses at 22°C. Hot‐extruded MgO crystal specimens (recrystallized with no obvious grain boundary phases or residual porosity), stressed parallel with the resultant (100) axial texture (1) gave the highest and least‐scattered strength–grain size results at 22°C, (2) showed direct fractographic evidence of microplastic initiated fracture at 22°C and showed macroscopic yield at 1315° and especially 1540°C, and (3) fractured entirely via transgranular cleavage, except for intergranular failure initiation from one or a few grain boundary surfaces exposed on the subsequent fracture surface, mainly at 1540°C. Hot‐extruded, hot‐pressed MgO billets gave comparable strength when fracture initiated transgranularly, but lower strength when fracture initiated from one or especially a few grain boundary surfaces exposed on the fracture (with residual pores). The extent and frequency of such boundary fracture increased with test temperature. While oxide additions of ≤5% or impurities in hot‐pressed or hot‐extruded MgO can make limited strength increases at larger grain sizes, those having limited solubility can limit strength at finer grain sizes, as can coarser surface finish (the latter especially at 22°C). Overall, MgO strength is seen as a balance between flaw and microplastic controlled failure, with several parameters shifting the balance.
Effects of Microstructural Instability on the Creep Behavior of Si‐C‐O (Nicalon) Fibers in Argon
Authors: Jia Nanying , Bodet Raphael , Tressler Richard E.
Published: March 2005

Tensile creep tests of single Si‐C‐O fibers (Nicalon, Nippon Carbon Co., Tokyo, Japan) were conducted in argon at 1300°C and 300 to 700 MPa. Fibers exhibited only primary creep, where the creep strain ɛ and creep time t could be empirically fitted by ɛ= (1/β) ln (1 +βɛ0t). The fiber deformation was described by a rheological model for the viscous flow of a concentrated suspension. Under the test conditions, the microstructure of Nicalon was unstable, resulting in weight loss and SiC grain growth. This instability was attributed to the decomposition of the amorphous SiCxOy phase in the fiber, forming SiC and CO as products. As a result, the viscosity of the fiber increased because of an increase in the SiC volume fraction. The continuous increase in viscosity caused a continuously decreasing creep rate, which made steady‐state creep impossible under these conditions. Because of the instability in the microstructure, the chemical environment was found to have a profound influence on the mechanical properties of Nicalon at elevated temperatures.
Early‐Stage Microstructure Development in Bi‐Sr‐Ca‐Cu‐O Glasses
Authors: Kim Seong‐Jin , Birnie Dunbar P. , Uhlmann Donald R.
Published: March 2005

Amorphous samples of Bi2Sr2Ca1Cu2Ox were produced by quenching from the melt. The early‐stage microstructure development in these samples was monitored using XRD, DTA, and hot‐stage TEM. It was observed that the molten glass undergoes phase separation during initial quenching and that subsequent refinement of these features generates the initial DTA exotherm during heating. This exotherm has been found for many related compositions, and has been shown not to correspond to crystallization. This initial phase separation strongly impacts the final microstructure by providing copious nucleation sites for the R‐phase that ultimately crystallizes first.
Transverse Strength of SCS‐6 Silicon Carbide Fibers
Authors: Eldridge Jeffrey I. , Wiening Jonathan P. , Davison Terry S. , Pindera Marek‐Jerzy
Published: March 2005

A diametral compression test was used to measure the transverse strength of SCS‐6 SiC fibers before and after heat treatment. Subjecting fibers to diametral compression successfully produced transverse tensile failure in the form of fiber cracking along the same diametral plane in which the compressive load was applied. An analysis of the hoop stress along the diametral plane, in which the effects of the C core were included, showed that there is a large tensile hoop stress concentration in the SiC sheath at the interface between the C core and the SiC sheath, where the stress is 6.3 times greater than the stress present in a solid SiC fiber under identical loading. This high tensile hoop stress concentration promotes crack initiation near the core and significantly limits the capability of these fibers to withstand transverse compressive loading. The maximum tensile hoop stresses, located at the interface between the C core and SiC sheath, at the measured failure loads were 850 MPa for the as‐received SCS‐6 fiber and 1210 MPa for fibers exposed to a 1‐h heat treatment at 1850°C in 138 MPa of Ar.
Correlations between Strength and Acoustic Properties in Yttria‐Stabilized Zirconia Polycrystals
Authors: Oishi Manabu , Matsuda Yukihisa , Noguchi Kenichi , Masaki Takaki
Published: March 2005

The strength, bulk density, and acoustic properties of nine Y2O3‐stabilized ZrO2 polycrystals (Y‐TZPs) were evaluated in the present study. The samples showed a strong correlation between strength and acoustic properties, a phenomenon that reflects the internal bulk structure, especially the Pore size distribution. Strength increased with a decrease in the attenuation coefficient and with an increase in the transverse wave velocity of the samples. On the other hand, the bulk density of the samples showed no clear relationship with strength. Bulk density reflects only the amount of pore volume in the test piece, whereas the acoustic properties are sensitive to defects or inhomogeneities in the microstructure. The attenuation coefficient and transverse wave velocity thus seem to be good parameters for estimating the strength of Y‐TZPs.
Superplastic Gas‐Pressure Deformiation of YTZ Sheet
Authors: Wittenauer Jerry , Nieh Tai Gang , Wadsworth Jeffrey
Published: March 2005

The superplastic deformation behavior of fine‐grained, yttria‐stabilized tetragonal zirconia under conditions of biaxial gas‐pressure deformation is described. Sheet specimens were deformed into hemispherical caps at temperatures ranging from 1450° to 1600°C and at imposed gas pressures ranging from 345 to 2760 kPa. For the forming conditions examined, hemispherical caps were formed at times ranging from 2 to 476 min. A gas‐pressure‐forming apparatus used to conduct the experiments is described and a mechanical analysis of the deformation process is presented. Also discussed is the role of grain growth and the relationship between data obtained in uniaxial testing and the behavior observed during the biaxial deformation experiments of this study. A comparison is made between the observed thickness distribution in the hemispherical caps with predictions from an analytical model.
Evaluating Porosity Parameters for Porosity–Property Relations
Authors: Rice Roy W.
Published: March 2005

Porosity parameters are considered from the standpoint of a map of the volume fraction porosity (P) and the ratio of normalized radii of the pore (rp) and the solid particles, webs, or ligaments (rs) defining the pores. For pore structures derived from uniform stacking of identical spherical particles or bubbles, this “map” turns out to be a single S‐shaped curve showing (1) very significant constraints on porosity variations achievable, and (2) rp/rs contains no information not already given by P, but (3) P or rp/rs do not fully characterize the porosity. Of other interrelated porosity factors, i.e, open vs closed or inter‐ vs intragranular nature, coordination number of the pores or particles, the shape (e.g., curvature) of the pores, and the minimal solid area (i.e., minimum web cross sections or the bond area between particles) representing some porosity characteristics independent of P or rp/rs, it is concluded that the minitics solid area is the most appropriate one. For more complex ideal and real pore structures, (1) the above map starts from the ideal P vs rp/rs curve at the two extremes of P (0 and 1), but becomes a moderate band in‐between, with the ideal P vs rp/rs curve at, or near, the mean of this band, and (2) a second parameter is still needed, and the minimum solid area is still the most appropriate one.
Grain‐Bridging Mechanisms in Monolithic Alumina and Spinel
Authors: Hay Jack C. , White Kenneth W.
Published: March 2005

The postfracture tensile (PFT) test procedure is implemented to study wake zone stresses in monolithic alumina, which contribute toward the cumulative component of toughening. This novel procedure allows for the direct evaluation of the critical wake zone stress and stress distribution as a function of crack face separation. These PFT results for the current alumina yield a maximum wake zone stress which compares favorably with the theoretical and experimental citations in the literature. We present the controlling relationship between the grain size distribution and fracture mode, and the PFT curve character as a means which may lead to microstructural design. Finally, the grain interlocking mechanism is quantitatively shown to be more effective in this noncubic material than in cubic magnesium aluminate spinel microstructures.
Preparation of Unsupported Metal Organic and Ceramic Thin Film Specimens for TEM Observation
Authors: Kumar Suresh , Messing Gary L. , Randall Clive A.
Published: March 2005

A method for preparing TEM specimens from fragile metal organic resin and metal‐organic‐derived ceramic films is described. Unsupported films can be easily prepared by spin coating a metal organic solution onto a camphor substrate followed by separating the film by subliming the substrate. The method involves encapsulating the fragile film fragments in a low‐viscosity, thermosetting, epoxy‐hardener solution to obtain mechanical integrity. The encapsulated film can be easily hand polished to approximately 20‐μm thickness in less than 1 h. Electron‐transparent TEM specimens can then be prepared by ion‐beam thinning the encapsulated film, after mounting it on a slotted copper grid.
Chemical Etching of Silicon (100) by Hydrogen
Authors: Gallois Bernard M. , Besmann Theodore M. , Stott Michael W.
Published: March 2005

The reactive etching of silicon (100) by hydrogen was studied in the temperature range 1325–1600 K. Rectangular etch pits formed from inverted pyramids were predominant, although more complex shapes revealing (111) planes were noted. The observed etch rates were found to lie near the thermodynamic limit, of one accepts the most positive reported enthalpy of formation of silylene. An activation energy of 314 ± 42 kj/mol for the etching reaction was determined from the rates at 1325–1550 K. At temperatures >1550 K, the etch rated decreased with increasing temperature, indicating a possible transfer of material from the silicon carbide‐coated reaction chamber.
Effect of a Silicon Carbide “Nano‐Dispersion” on the Mechanical Properties of Silicon Nitride
Authors: Pezzotti Giuseppe , Sakai Mototsugu
Published: March 2005

The hypothesis that a synergistic effect by fine SiC dispersoids operating on the submicrometer scale is capable of enhancing the deformation and fracture properties of Si3N4 ceramics has been examined. In order to single out the effect of the SiC dispersion from other microstructural factors affecting the material properties, experiments were conducted on a highly pure and dense Si3N4 material, suitable for basic investigations. Fracture mechanics and creep characterizations were performed at room temperature and at 1400°C on composites containing 25 vol% submicrometer SiC particles, for which the intragranular fraction was varied by changing the sintering conditions. Despite the obtained difference in composite microstructure, almost no improvement in either the fracture toughness or strength, as compared with the monolithic material, was found. Similarly, the slow crack growth and creep resistance at 1400°C were still dictated by the inherent properties of the matrix. This study emphasizes the need for scientific rather than empirical approaches on simple systems, before deducing general rules for the microstructural design of structural ceramics.
Synthesis of Nanoparticulate Silica Composite Membranes by the Pressurized Sol–Gel Technique
Authors: Hyun Sang H. , Kang Beom S.
Published: March 2005

A crack‐free silica composite membrane has been synthesized from a nanoparticulate silica sol (particle diameter <10 nm) by a pressurized sol–gel coating technique developed in this study. The microporous silica layers with an estimated pore radius of 0.78 nm were deposited inside the pores (average pore size of 0.1 μm) of slip cast a‐alumina support tubes. The microstructure of the coated layer was controlled by adjusting sol properties and pressurizing conditions. The room‐temperature intrinsic permeability of N2 through the silica membrane layer after heat treatment at 200°C is about 4.9 × 10−12 mol·m/m2·s· Pa, and the mechanism of gas transport is Knudsen flow. The thermal stability of the silica composite membrane is excellent up to 500°C.
Electrochemical Chromium(III) Oxide Coatings on Non‐oxide Ceramic Substrates
Authors: Chaim Rachman , Almaleh‐Rockman Sylvie , Gal‐Or Leah , Bestgen Harro
Published: March 2005

SiC and TiB2 were electrochemically coated with Cr2O3 from a 0.1M aqueous solution of chromium nitrate hydrate with ethanol additives. On both substrate materials poly‐crystalline Cr2O3 was formed at current densities from 5 to 50 mA/cm2 and deposition durations of 5 to 30 min. The coating weight increased with current density and with deposition time. The as‐deposited coatings contained microcracks due to drying shrinkage. Microstructural observations indicate that sintering of the Cr2O3 coatings on TiB2 at 1100°C for 1 n in a reducing atmosphere in a closed graphite crucible causes the densification of the coating via a liquid phase, which forms by oxidation of TiB2. Under similar conditions, the Cr2O3 coatings on SiC may be sintered via an evaporation–condensation mechanism.
Self‐Combustion Reactions Induced by Mechanical Activation: Formation of Aluminum Nitride from Aluminum–Graphite Powder Mixture
Authors: Tsuchida Takeshi , Hasegawa Takeshi , Inagaki Michio
Published: March 2005

The powders of aluminum metal and natural graphite mixed in various molar ratios (Al/C = 7/0–0/7) were ground in a planetary ball mill. When the mixtures thus activated mechanically were exposed to air, exothermic reactions spontaneously occurred in two successive steps, evolving red heat initially and then white heat. The main product was aluminum carbide in the first step and aluminum nitride as well as carbide in the second step. From the measurements of XPS spectra and the lattice constants, it was concluded that the aluminum nitride obtained is solid solution with the composition of (Al2OC)1–x(AlN)x. The effects of mixing ratio of Al to C, grinding time, and gas atmosphere on the formation of aluminum nitride are discussed.
Effect of Heating Rate on the Dielectric Properties of the PMN‐PT Relaxor Ceramics
Authors: Liou Yi‐Cheng , Wu Long
Published: March 2005

The effect of heating rate (2 to 30°C/min) during sintering on the perovskite phase content, density, microstructure, and dielectric properties of 0.9PbMg1/3Nb2/3O3–0.1PbTiO3 relaxor ferroelectric ceramics has been studied. Increasing the heating rate reduced the level of PbO evaporation and resulted in high perovskite content and dense ceramics. With slow heating rate (2–10°C/min), excess MgO segregated as isolated submicrometer particles in the perovskite grains; these precipitates were absent in ceramics sintered with a heating rate of 30°C/min. The maximum dielectric constant was optimized with a heating rate of 10°C/min. The temperature of maximum dielectric constant shifted downward as the heating rate was increased.
Oxygen Displacement through the Ferroelectric Phase Transition of Barium Titanate—High‐Temperature 17O NMR
Authors: Spearing Dane R. , Stebbins Jonathan F.
Published: March 2005

Perovskite‐structured BaTiO3 undergoes a ferroelectric tetragonal‐to‐cubic phase transition at 130°C. High‐temperature 17O MAS and static NMR line shapes and relaxation times were examined to elucidate the nature of the anion motions associated with the transition. 17O MAS spectra show a gradual shift of the two oxygen peaks toward one another with increasing temperature, and a sudden collapse to one peak at the transition, which is consistent with its first‐order character. 17O TI data are relatively imprecise below the transition, but appear to decrease above it, indicating an increase in low‐frequency motions, suggesting a dynamically averaged high‐temperature phase.
Determination of Bridging Stresses in Reinforced Al2O3
Authors: Fett Theo , Munz Dietrich , Yu Chang‐Te , Kobayashi Albert S.
Published: March 2005

The determination of bridging stresses by evaluation of crack opening profiles is outlined for a whisker‐reinforced alumina. The application of the fracture mechanics weight function procedure results in an integral equation between bridging stresses and crack opening displacements. Its solution provides the bridging stress relation.
Thermal Decomposition of Tricalcium Silicate Hydrate
Authors: Okada Yoshihiko , Ishida Hideki , Mitsuda Takeshi
Published: March 2005

C3SH1.5 can be prepared in stirred suspensions using lime and silicic acid with Ca/Si = 3.0 for 14 days at 270°C under saturated steam pressure. The C3SH1.5 which forms consists of long, fibrous or prismatic aggregates having a specific surface area of 14.0 m2/g. The specimen gives an average Ca/Si ratio of 2.98 (29 crystals) and lattice parameters of a= 1.00291(8) nm and c= 0.74842(11) nm by ATEM and XRD examinations, respectively. NMR examination confirms the existence of dimer silicate anions in C3SH1.5, suggesting the possible composition Ca6(Si2O7)(OH)4. Upon being heated, C3SH1.5 dehydrates at 520–550°C with a sharp endothermy and decomposes to CaO plus a calciochondrodite‐like phase, which on further heating dissociates, with a gradual weight loss, to α′L‐C2S with CaO at 800°C. The intermediate calciochondrodite‐like phase has low crystallinity, but 29Si MAS NMR and infrared spectra identical for highly crystalline calciochondrodite. CPMAS measurements indicate the possibility that the calciochondrodite‐Iike phase contains both protonated and unprotonated monosilicate anions. The amount of CaO which forms through the two‐step process agrees with the calculated values from the stoichiometry of decomposition: [Ca6(Si2O7)(OH)6] → [Ca5(SiO4)2] + CaO + 2H2O →αL‐(Ca2(SiO4) + 2CaO + H2O.
High‐Temperature Active Oxidation and Active‐to‐Passive Transition of Chemically Vapor‐Deposited Silicon Nitride in N2–O2 and Ar–O2 Atmospheres
Authors: Narushima Takayuki , Goto Takashi , Yokoyama Yoshio , Hagiwara Jun , Iguchi Yasutaka , Hirai Toshio
Published: March 2005

The oxidation behavior of chemically vapor‐deposited silicon nitride in N2–O2 and Ar–O2 atmospheres was studied using a thermogravimetric technique at temperatures 1823 to 1923 K. Active oxidation was observed at low oxygen partial pressures. The active oxidation rates increased with increasing oxygen partial pressure (PO2) up to a certain PO2, and then passive oxidation occurred. The transition oxygen partial pressures from active to passive oxidation were determined. The rate‐controlling step for the active oxidation could be oxygen diffusion through a gaseous boundary layer near the Si3N4 surface. Decomposition of Si3N4 does not seem to be associated with the mass loss behavior. The Wagner model was employed to explain the oxidation behavior.
Influence of Oxygen Content on Formation of Yttrium α‐SiAlON Ceramics
Authors: Haviar Miroslav
Published: March 2005

Low porosity α‐ and β‐SiAION composite material was prepared when the powder mixture intended for preparation of yttrium α‐SiAlON, with the formula Y0.4Si12–m+n Alm+nOnN16–n, was attritor milled in isopropyl alcohol or contained excess oxygen (n > 0.6). The region of stability of single‐phase yttrium α‐SiAlON was smaller at lower temperatures. Wet milling (in isopropyl alcohol) of AIN powder was found to introduce excess oxygen into the milled powder.
Preferred Orientation of β‐Lead Fluoride Grains Formed within Micropores of Porous Alumina
Authors: Nagai Masayuki , Ogawa Kenji , Nishino Tadashi
Published: March 2005

A PbF2–Al2O3 composite was obtained by reaction between Pb(NO3)2 and NH4F solutions within micropores of a porous alumina pellet. The reaction resulted in the formation of a PbF2 deposit layer in the interior region of the pellet close to the surface at the Pb(NO3)2 solution side, toward which the deposit grew preferentially with time. It suggested that the diffusion of Fusions in the deposit would play an important role in this method because β‐PbF2 is known as a moderate F‐ ion conductor at room temperature. The deposit was identified to be †‐PbF2 with the fluorite structure, using both XRD and EPMA, although a small amount of α‐PbF2 with the rutile structure also existed. The β‐PbF2 grains in the initially formed deposit showed essentially no preferred orientation, while the subsequently formed part showed significant preferred orientation with the [hhO] direction parallel to the growing direction. The degree of preferred orientation increased with distance from the initially formed position and reached a saturated value. The orientation was presumed to be associated with the faster growth rate of the deposited grains along the [hhO] direction than the others.
Stress‐Induced Phase Transformation in the Systems (Ho1−xLax)4Al2O9 and (Y1−xLax)4Al2O9
Authors: Takizawa Hirotsugu , Shimad Masahiko , Shimoyashiki Kazuo , Endo Tadashi
Published: March 2005

New orthorhombic phases in (Ho1−xLax)4Al2O9 and (Y1−xLax)4Al2O9 systems have been synthesized by reaction sintering at 1600°C for 30 h in air and have been metastably retained to room temperature. Stress‐induced phase transformation from the orthorhombic phase to the monoclinic phase occurred in both systems. This phase transformation was accompanied by a 0.5% volume increase.
Growth of Alumina/Metal Composites into Porous Ceramics by the Oxidation of Aluminum
Authors: Watari Takanori , Mori Koichiro , Torikai Toshio , Matsuda Ohsaku
Published: March 2005

Alumina/metal composites were grown into the pores of porous alumina, porous aluminosilicate, and porous silicon carbide substrates through the oxidation of Al–Si (5 wt%) powder compacts coated with magnesia powder (11 mg/ cm2). The thickness of the resulting composite increased with oxidation time and temperature, and was proportional to (pore size)0.5 on using porous alumina. The composite thickness was more than 2 times larger in the silicon carbide and about 4 times larger in the aluminosilicate than in the alumina at 1523 K for 1 h. The products using these three types of substrates consisted of alumina, aluminum, and silicon, except that a silicon carbide phase occurred when using the silicon carbide substrate. Silica and mullite in the aluminosilicate substrate changed to silicon and alumina, and silica in the silicon carbide substrate changed to silicon because of the reduction by aluminum.
Fracture Behavior of Cyclically Loaded PZT
Authors: White Grady S. , Raynes Alan S. , Vaudin Mark D. , Freiman Stephen W.
Published: March 2005

The fracture behavior of PZT specimens driven at their resonant frequency by the application of an ac voltage was investigated and compared with fracture behavior of monotonically loaded PZT. Microcracking was observed in the cyclically loaded specimens; above 150°C, the micro‐cracks were dispersed in small clusters, while at T≤ 86°C, microcracks were generated in a densely populated region near the failure site (indentation). Macrocrack growth also demonstrated a temperature dependence, with crack growth occurring at T > 150°C but not at T≤ 86°C.
Structure and Microtexture Changes in Phosphorous‐Bearing Ca2SiO4 Solid Solutions
Authors: Fukuda Koichiro , Maki Iwao , Ito Suketoshi , Yoshida Hideto , Aoki Katsumi
Published: March 2005

The crystal structure and microtexture of P‐bearing Ca2SiO4solid solutions (C2S(ss)) were studied as a function of x= P/(Si + P) ranging from 0.085 to 0.398. All the samples were prepared at the stable‐temperature region of the α′l‐phase and quenched in air. The structures were described in terms of the orthohexagonal or hexagonal cell of the former α‐phase. The crystal with x= 0.085 was composed entirely of the orthorhombic α′l‐phase, the modulation wavelength of which was N= 3 along the c‐axis. With x= 0.118 and 0.156, the crystal grains were made up of both α′l and incommensurate orthorhombic phases. The volume fraction of the α′l‐phase decreased with increasing x. With x= 0.197, the crystal was made up exclusively of the incommensurate phase, with the modulation wave vector k given by (1/N) a*+ c*. A good correlation N= 4.370 – 2.50x was observed between N (3.75 ≤ N ≤ 4.09) and x (0.118 ≤x≤ 0.250). The crystal with x= 0.3.98 consisted of a single hexagonal phase. The modulation wavelength was N= 2 along the a‐axis and N= 3 along the c‐axis.
Characterization of Grain Boundaries in Superplastically Deformed Y‐TZP Ceramics
Authors: Boutz Michel M. R. , Chen Chu Sheng , Winnubst Louis , Burggraaf Anthonie J.
Published: March 2005

The effects of compressive deformation on the grain boundary characteristics of fine‐grained Y‐TZP have been investigated using surface spectroscopy, impedance analysis, and transmission electron microscopy. After sintering at low temperature (1150°C), the grain boundaries are covered by an ultrathin (1nm) yttrium‐rich amorphous film. After deformation at 1200°–1300°C under low stress, some grain boundaries are no longer covered by the amorphous film. Yttrium segregation seems to occur only at wetted grain boundaries. Evidence has been found that the extent of dewetting increases with increasing applied stress.
Solid‐Liquid Reactions in the System Si3N4–β‐SiAlON–Y3Al5O12
Authors: Wisnudel Michele , Tien Tseng‐Ying
Published: March 2005

Solid‐liquid equilibria in the system Si,Al,Y/N,0 were determined for the compatibility triangle bounded by the β‐SiAlON solid‐solution line and the compound Y3Al5O12. X‐ray diffraction was used to determine the crystalline phases present in the equilibrated, rapidly cooled specimens. The liquid phase was quantified with volume fraction measurements performed on scanning electron micrographs. The solid‐liquid tie lines at 1650° and 1750°C were established from lattice parameters of the β‐SiAlON phase and from the amount of liquid phase in equilibrium with the crystalline solid. The liquid phase was crystallized to verify the location of the starting composition.
Precipitate Coarsening by Liquid Film Migration in (Mg,Ca)‐PSZ's
Authors: Dickerson Robert M. , Laraia Vincent J. , Heuer Arthur H.
Published: March 2005

Precipitate coarsening involving preferential growth of solute‐poor tetragonal ZrO2 precipitates along grain boundaries, combined with migration of grain boundaries containing a liquid silicate phase to form solute‐rich precipitate‐free cubic ZrO2, has been observed in grain boundary regions of MgO–CaO–ZrO2 and CaO–ZrO2 alloys during isothermal aging at 1400°C. Studies of alloys with 9.5 mol% total solute, but with varying MgO/CaO ratios, demonstrated a marked composition dependence of the phase separation process, in that such phase separation was rare in MgO‐rich materials. The migration process is analyzed using models developed for migration in less complex materials, and a mechanism incorporating orientation‐dependent precipitate strain energies is proposed.
Deep Level Transient Spectroscopy of Zinc Oxide Varistors Doped with Aluminum Oxide and/or Silver Oxide
Authors: Fan Jiwei , Freer Robert
Published: March 2005

Deep level transient spectroscopy was employed to investigate the effect of two different dopants (aluminum and silver) on the electronic states of ZnO varistors. The base composition was a typical commercial formulation, and specimens were prepared by the mixed oxide route. Two electron traps were detected: trap L1, (Ec− 0.15 ± 0.01 eV) and trap L2 (Ec− 0.25 ± 0.01 eV). Doping specimens with trivalent Al increased the densities of both traps; such varistors have improved nonlinearity characteristics, but lower stability. In contrast, doping with monovalent Ag decreased the trap densities, reduced the nonlinearity exponents, but increased stability. Specimens containing an optimum combination of Al and Ag doping had a high L1, trap density, a low L2 trap density, and exhibited good nonlinearity and stability characteristics. The L1, trap appears to be associated with extrinsic donor defects, reflecting varistor non‐linearity; L1, trap density increased with nonlinearity exponents. The L2 trap appears to be associated with varistor stability. As the L2 trap density decreased, the sample stability increased; this may reflect the concentration of zinc interstitial defects.
Effect of Carbon Addition on Elevated Temperature Crack Growth Resistance in (Mo,W)Si2–SiCp Composite
Authors: Ramamurty Upadrasta , Suresh Subra , Petrovic John J.
Published: March 2005

Experimental results on subcritical crack growth behavior of hot‐pressed MoSi2–50 mol% Wsi2 alloy reinforced with 30 vol% SiC particles in the temperature range 1200°‐1300°C are presented. The effect of 2 wt% C addition on the stable crack growth resistance of this composite was investigated under both static and cyclic loading conditions. The results indicate that the addition of carbon to the composite improves the subcritical crack growth resistance under both static and cyclic loads and increases the elevated temperature capabilities of the (Mo,W)Si2 composite. Increasing the temperature from 1200° to 1300°C is found to increase the crack growth velocities with a concomitant decrease in the crack growth initiation thresholds. Electron microscopy of the crack‐tip region indicates that the stable crack growth process is influenced primarily by interfacial cavitation. At 1300°C, deformation processes such as twinning of the SiC particles and dislocation motion within the matrix grains appear to play an active role in determining the crack growth kinetics. The role of glassy phase in influencing the high‐temperature fracture behavior and its implications for design of the microstructures of the brittle materials are discussed.
Synthesis and Characterization of Amorphous Si2N2O
Authors: van Weeren Remco , Leone Edgar A. , Curran Sean , Klein Lisa C. , Danforth Stephen C.
Published: March 2005

Amorphous silicon oxynitride powder was synthesized by nitridation of high‐purity silica in ammonia at 1120°C. The resulting material was X‐ray amorphous, and its chemical characteristics were determined by X‐ray photoelectron spectroscopy (XPS) and 29Si nuclear magnetic resonance (NMR). The XPS analysis showed a shift to lower binding energies for the Si2p peak with increasing nitrogen content. Upon initial nitridation, the full width at half maximum (FWHM) of the Si2p peak increased, but decreased again at higher nitrogen contents, thus showing the formation of a silicon oxynitride phase with a single or small range of composition. The 29Si NMR analysis showed the formation of (amorphous) Si3N4 (Si–N4) and possibly two oxynitride phases (Si–N3O, Si–N2O2). It is concluded that while XPS, FT‐IR, and nitrogen analysis may show the formation of an homogeneous, amorphous silicon oxynitride (Si2N2O) phase, the formation of phase–pure, amorphous Si2N2O is extremely difficult via this route.
Elevated‐Temperature Fracture Characterization of Advanced Fibrous Ceramic Thermal Insulators
Authors: Ortiz‐Longo Carlos R. , White Kenneth W.
Published: March 2005

The elevated‐temperature mechanical behavior of two low‐density fibrous ceramic thermal insulators is discussed. Fracture toughness and R‐curve behavior are obtained from chevron notched bend bar and short double cantilever beam specimens, respectively. The fracture behavior is related to the bulk microstructures, the properties of the fibers, and the various fiber‐to‐fiber bond chemistries. A strong behavioral change at elevated temperatures is linked to the glass‐softening temperature of the multiphase structure characteristic of each material.
Influence of Oxygen Ion Conduction on Nitric Oxide Decomposition
Authors: Mori Toshiyuki , Yamamura Hiroshi , Ogino Hiroyuki , Kobayashi Hidehiko , Mitamura Takashi
Published: March 2005

Ba2In2O5, Ba2Y4O9, and BaLa2O4 having brownmillerite‐related structures were synthesized. Ionic conductivity and catalytic activity following the reduction of NO to N2 were also investigated, both of which increased at the order‐disorder transition temperature for oxygen vacancies of these compounds. It was made clear that the catalytic activity of NO decomposition reaction increased with a decrease in the order–disorder transition temperature. Moreover, it was found that ionic conductivity contributed to the catalytic activity of NO reduction to N2.
Interaction of CaO–FeO–SiO2 Slags with Partially Stabilized Zirconia
Authors: Chung Yau‐Don , Schlesinger Mark E.
Published: March 2005

Calcia‐ and magnesia‐partially‐stabilized zirconia samples were corroded under static and dynamic conditions in three slags from the CaO–FeO–SiO2 system. Low–basicity and high–FeO slags corroded tht samples by leaching magnesia from the cubic phase in the specimen, causing its destabilization and ultimate dissolution. However, a higher–basicity slag which proved the most corrosive of the three promoted bulk dissolution of the cubic phase instead, the rate of which was controlled by the thickness of the adjacent slag boundary layer. The levels of sample corrosion both at and below the slag line are used to illustrate the effects of experimental variables, including slag composition, specimen density, and slag motion.
Creep of Mg‐PSZ at Room Temperature
Authors: Finlayson Trevor R. , Gross Anita K. , Griffiths John R. , Kisi Erich H.
Published: March 2005

Transient β, or Andrade, creep occurs when magnesia‐partially‐stabilized zirconia is loaded in tension at room temperature. The equation relating the longitudinal or tensile creep strain, εcℓ to the tensile stress, σ, and to the time, t, has been determined to be εcℓ=Aσmtn in which the constants A, m, and n depend on the phase content of the zirconia. Observations are reported of the tetragonal‐to‐monoclinic and tetragonal‐to‐orthorhombic phase transformations which occur during creep: there is also a progressive development of microcracking. It is shown that a combination of these phenomena can account for the observed creep behavior.