bluuebunny/crossref_metadata_2025 huggingface dataset:
The System MgO─P2O5─H2O at 25°C
Authors: Brown Paul W. , Gulick Julie , Dumm John
Published: March 2005

The phase diagram for the ternary system MgO─P2O5─H2O at 25°C has been constructed. The magnesium phosphates represented are Mg(H2PO4)2·nH2O (n= 4, 2, 0), MgHPO4·3H2O, and Mg3(PO4)2·mH2O (m= 8, 22). Because of the large differences in the solubilities of these compounds, the technique which involves plotting the mole fractions of MgO and P2O5 as their 10th roots has been employed. With the exception of MgHPO4·3H2O, the magnesium phosphates are incongruently soluble. Because incongruency is associated with a peritectic‐like reaction, the phase Mg2(PO4)3· 8H2O persists metastably for an extended period.
Effect of Load on the Hardness of Hot Isostatically Pressed Silicon Nitride
Authors: Berriche Ridha , Holt Richard T.
Published: March 2005

The hardness values of five hot isostatic pressed silicon nitride materials, with varying densities, were measured at loads between 1 and 200 N. For the fully dense materials, the calculated hardness decreased from about 30 to 15 GPa as the load increased to about 10 N, and the hardness remained constant at higher loads. For the samples that showed indentation size effect (ISE), cracks formed at the corners of the indentation, starting at the lowest load of 1 N. Materials with lower densities had lower hardness values, displayed a very small or no ISE, and formed corner cracks only at high loads. For the samples that displayed an ISE at low loads, the formation of cracks was analyzed using the Niihara et al. criterion for Palmqvist cracks.
Dynamic Observation of Crack Propagation in Piezoelectric Multilayer Actuators
Authors: Furuta Atsushi , Uchino Kenji
Published: March 2005

Crack propagation in multilayer piezoelectric actuators made of Pb((Ni1/3Nb2/3), Ti, Zr)O3 ceramics with an interdigital electrode configuration was observed dynamically under an applied cyclic electric field using charge coupled device microscopy. The crack was observed only under a high electric field, and it healed under zero field. The crack was initiated at the internal electrode edge and propagated from the electrode edge in three directions. The electric‐field‐induced displacement was measured simultaneously with the propagation. The displacement of the multilayer actuator became gradually smaller and asymmetric with respect to the sign of the field with increased driving cycle.
Chemical Control of the Grain‐Boundary Migration of SrTiO3 in the SrTiO3─BaTiO3─CaTiO3 System
Authors: Yoon Kyung J. , Kang Suk‐Joong L.
Published: March 2005

The grain‐boundary migration induced by chemical instability has been studied in SrTiO3. Sintered SrTiO3 has been packed with various BaTiO3/CaTiO3 powder mixtures and annealed at 1400°C for various times. At the surface region of most SrTiO3 specimens, the grain boundary has migrated with the diffusion of Ba and Ca ions. The ratio of Ba and Ca ions present in the migrated region varies with the depth from the surface and the packing‐powder composition, and is not equal to the cation ratio of packing powder. When the Ba/Ca ratio of packing powder is 1, cessation of migration has been observed. The composition of the area without migration is estimated to be approximately equal to the composition for the matching of crystal lattices between the original grain (SrTiO3) and the layer formed by diffusion of Ba and Ca ions. The coherency strain energy induced by diffusion of solute atoms is believed to be the major driving force for the grain‐boundary migration of SrTO3 under the chemical instability. The grain‐boundary migration can be accordingly controlled by lattice parameter change and matching.
Analysis of Local Cation Arrangement in Mullite Using 29Si Magic‐Angle Spinning Nuclear Magnetic Resonance Spectra
Authors: Ban Takayuki , Okada Kiyoshi
Published: March 2005

Local cation arrangements for mullites with various chemical compositions were examined using 29Si magic‐angle spinning nuclear magnetic resonance (MAS NMR) spectra and the X‐ray Rietveld method. The structure of mullite was refined using the Rietveld method, and the relations between chemical composition and lattice constants were revised. 29Si NMR spectra of mullites showed a main resonance at −86 ppm accompanied by weak resonances at −94, −90, and −81 to −82 ppm. These resonances were assigned to each local cation arrangement of TO4 tetrahedra in mullite by calculating the chemical shift according to Sherriff and Grundy's method. The resonances at −81 to −82 ppm were assigned to the arrangement of the T(Si),T(Al)–O*c–T* (Al) cluster, which has been considered to be rather unusual, and their population was found to increase with increase in the Al2O3 content in mullite.
Slow Crack Growth in Sapphire Fibers at 800° to 1500°C
Authors: Newcomb Stephen A. , Tressler Richard E.
Published: March 2005

Sapphire fibers with (near) c‐axis orientation were tested in tension over a range of strain rates (10−5 to 0.5 min−1) at elevated temperatures (800° to 1500°C). The strength of the fibers was dependent on the strain rate. Slow crack growth was confirmed as the degradation process by direct inspection of the fracture surfaces and estimation of fracture stresses from measured flaw sizes. The slow crack growth parameter, N, decreased with increasing temperature. At 1400°C a threshold in strength was observed; the threshold stress intensity factor was estimated to be ≅ 1 MP·m1/2 at 1400°C. Thermally activated bond rupture (e.g., lattice trapping model) is postulated as the mechanism responsible for the slow crack growth.
Relationship between Water Desorption and Low‐Temperature Densification of Colloidal Anatase Thin Films
Authors: Keddie Joseph L. , Braun Paul V. , Giannelis Emmanuel P.
Published: March 2005

Films consisting of discrete anatase crystals with an average diameter of 8 nm were deposited from a colloidal sol synthesized from titanium(IV) isopropoxide. From ion‐beam analysis (FRES and RBS) and ellipsometry, we found that desorption of Type I water from the films is accompanied by a decrease in the refractive index but no densification. Conversely, desorption of Type II water or surface hydroxyls at higher temperatures leads to film densification but has no apparent effect on the refractive index. The densification involves progressive condensation of hydrogen‐bonded hydroxyls and finally isolated hydroxyls. The refractive index for films exposed to air for 6 months increases regardless of heat treatment because of surface rehydration which nearly recreates the original surface.
SiC‐Whisker‐Reinforced Al2O3 Composites by Free Sintering of Coated Powders
Authors: Hu Ching‐Li , Rahaman Mohamed N.
Published: March 2005

SiC whiskers were coated with a thick cladding of finegrained Al2O3 powder by controlled heterogeneous precipitation in a concentrated suspension of whiskers. After calcination, the coated whiskers were compacted by cold isostatic pressing and sintered at a constant heating rate of 5°C/min in a helium atmosphere. The parameters which control the coating process and the sintering characteristics of the consolidated powders are reported. Starting with an initial matrix density of 40–45% of the theoretical, composites containing up to ≅20 vol% whiskers (aspect ratio ≅15) were sintered freely to nearly theoretical density below 1800°C. By comparison, a similar composite formed by mechanical mixing of the whiskers and the precipitated Al2O3 powder reached a density of only 68% of the theoretical after sintering under identical conditions. For a fixed whisker content, the sinterability of the composites formed from the coated whiskers shows a fairly strong dependence on the whisker aspect ratio.
Atomic Force Microscopy and X‐ray Photoelectron Spectroscopy Investigation of the Onset of Reactions on Alkali Silicate Glass Surfaces
Authors: Rudd Gregory I. , Garofalini Stephen H. , Hensley David A. , Mate C. Mathew
Published: March 2005

Atomic force microscopy was used to measure forces acting on a sharp tungsten tip as it was brought into contact with silica and 30 mol% binary alkali silicate glasses. Experiments were performed in controlled atmospheres and under vacuum. Attractive forces and liquid‐layer thicknesses were found to vary markedly between the glasses, and heterogeneity was observed on the binary alkali silicates analyzed in vacuo. Air or wet carbon dioxide exposure resulted in the penetration of the tip into a soft surface layer on the alkali silicates. In addition, liquid layer formation on the alkali silicates was found to be promoted by exposure to water vapor in the order lithium < sodium < potassium. X‐ray photoelectron spectroscopy indicated that reaction between the potassium silicate surface and water vapor occurred on exposure to only 10−4 torr (1 torr = 1.33 × 102 Pa) water. Surface segregation and leaching of potassium occurred under the same conditions.
Subcritical Crack Growth in Y‐TZP and Al2O3‐Toughened Y‐TZP
Authors: Knechtel Mathias C. , Garcia Daniel E. , Rödel Jürgen , Claussen Nils
Published: March 2005

Crack velocity curves for Y‐TZP and Al2O3‐toughened Y‐TZP were determined for long cracks in compact tension specimens with an in situ fracture device on the stage of an optical microscope. Indications for a crack velocity threshold were found for both materials. Above this threshold, at 2.6 MPa·m1/2 for Y‐TZP and 3.6 MPa·m1/2 for Al2O3‐toughened Y‐TZP, chemically assisted subcritical crack growth occurs over an extended regime of applied stress intensity factors of width 2.1–2.8 MPa·m1/2. It is recognized that the dependence of the shielding term on the crack‐tip stress field renders transformation‐toughened materials particularly susceptible to stress‐corrosion cracking. This interrelation leads to the definition of a steady‐state velocity at constant applied stress intensity factor. This velocity is obtained in the situation where the shielding term is fully defined by the present crack‐tip stress field, not depending on prior loading history.
Hole Doping Mechanism in Bismuth Cuprates
Authors: Nomura Shunji , Yoshino Hisashi , Ando Ken
Published: March 2005

The role of oxygen for the hole doping has been investigated for single‐phased (Bi,Pb)2Sr2Ca2Cu3O.z Defects introduced by oxygen have been clarified to be interstitial atoms by pycnometric density measurements. The c axis decreases and the modulation periods along the b axis also decrease with increasing oxygen content in the crystal. It is likely that extra oxygen ions exist between the BiO double layers and those oxygen ions are responsible for the modulation. Samples with oxygen content ranging from 9.99 to 10.18 showed superconductivity. The critical temperature Tc, exhibited a maximum value (109 K) at 10.07 oxygen atoms in the formula unit, which coincided with the average Cu valence of 2.13. The data indicated that hole formation was governed by oxygenation reaction in this system.
Melt‐Infiltration Processing and Fracture Toughness of Alumina‐Glass Dental Composites
Authors: Wolf William D. , Francis Lorraine Falter , Lin Chun‐Pin , Douglas William H.
Published: March 2005

Alumina‐glass composites were prepared by a melt‐infiltration process that is similar to a fabrication method for dental crowns and bridges. Cylindrical alumina samples with green densities ranging from 62% to 72% of theoretical were formed by slip casting followed by sintering at 1100°C for 2 h. A borosilicate glass was infiltrated at 1200°C, resulting in a composite microstructure consisting of fused alumina particles and glass‐filled pores. Fracture toughness of the composites, measured by a chevron‐notch method with a short rod sample, was ∼3.8 MPa·m1/2 and was relatively insensitive to the volume fraction of alumina in the range of 0.62 to 0.72.
Evolution of Topology during Simulated Sintering of Powder Compacts
Authors: Zheng Jingmin , Johnson Paul E
Published: March 2005

Topological features were calculated for three‐dimensional microstructures simulated using a computer model. A method in which the material is divided into small volume elements (SVE method) was developed to measure topological features such as numbers of coordinating faces, edges, and corners on the computer‐generated microstructures. New relationships between different types of topological features of special interest in ceramics were derived based on the computer simulation statistics. These relationships enabled us to calculate the topological properties of a two‐phase system in which one phase has no internal boundaries, such as the pore, liquid, or glass phases in polyerystalline ceramics. Computer simulations allowed averaging those features statistically from large sample sizes, which can be difficult to do in practice. Dependence of topological features, such as the number of coordinating pores around a grain, on particle size distribution and sintered density of the system was studied. Results show that the number of coordinating faces is proportional to the square of particle size, and the number of edges per face is smaller for a wider particle size distribution. Equations are derived to describe the dependence of the number of coordinating faces and number of edges per face on grain size. The simulation shows that closed pores form at a lower sintered density for a wider particle size distribution.
Amorphous Intergranular Films in Silicon Nitride Ceramics Quenched from High Temperatures
Authors: Cinibulk Michael K. , Kleebe Hans‐Joachim , Schneider Gerold A. , Rühle Manfred
Published: March 2005

High‐temperature microstructures of an MgO‐hot‐pressed Si3N4 and a Yb2O3+ Al2O3‐sintered/annealed Si3N4 were obtained by quenching thin specimens from temperatures between 1350° and 1550°C. Quenching materials from 1350°C produced no observable changes in the secondary phases at triple‐grain junctions or along grain boundaries. Although quenching from temperatures of ∼ 1450°C also showed no significant changes in the general microstructure or morphology of the Si3N4 grains, the amorphous intergranular film thickness increased substantially from an initial ∼ 1 nm in the slowly cooled material to 1.5–9 nm in the quenched materials. The variability of film thickness in a given material suggests a nonequilibrium state. Specimens quenched from 1550°C revealed once again thin (1‐nm) intergranular films at all high‐angle grain boundaries, indicating an equilibrium condition. The changes observed in intergranular‐film thickness by high‐resolution electron microscopy can be related to the eutectic temperature of the system and to diffusional and viscous processes occurring in the amorphous intergranular film during the high‐temperature anneal prior to quenching.
Salt‐Occluded Zeolites as an Immobilization Matrix for Chloride Waste Salt
Authors: Lewis Michele A. , Fischer Donald F. , Smith Londa J.
Published: March 2005

The pyrometallurgical processing of spent fuel from the integral fast reactor (IFR), an advanced reactor under development at Argonne National Laboratory, will generate a chloride salt waste containing the alkali‐metal, alkaline‐earth, and some of the rare‐earth fission products. Salt‐occluded zeolite A, formed by equilibrating simulated molten waste salt and zeolite A, has been investigated as an immobilization matrix for this salt waste. In this concept, the chloride waste salt is loaded into the zeolite cavities, and cesium and strontium from the salt are preferentially sorbed by the zeolite. Experiments showed that the salt‐occluded zeolite powders are leach resistant and radiation stable. The conclusion is that the salt‐occluded zeolite is a promising immobilization matrix for the IFR waste salt.
Preparation of Magnesium Nitride Powder by Low‐Pressure Chemical Vapor Deposition
Authors: Murata Tsuyoshi , Itatani Kiyoshi , Howell F. Scott , Kishioka Akira , Kinoshita Makio
Published: March 2005

Submcrometer‐scale magnesium nitride (Mg3N2) powder was prepared by low‐pressure chemical vapor deposition, i.e., the reaction of Mg vapor with mixed NH3–N2 gases at 800°C under a pressure of ∼1 kPa. The mixing ratios of NH3–N2 gases were 0% NH3–100% N2 (pure N2), 20% NH3–80% N2, 40% NH3–60% N2, 60% NH3–40% N2, 80% NH3–20% N2, and 100% NH3–0% N2 (pure NH3). The reactions between Mg vapor and NH3–N2 gases produced platy Mg3N2 particles <0.2 μm and acicular particles with long‐axis length of ∼0.2 μm, whereas the reaction of Mg vapor with pure NH3 gas produced spherical Mg3N2 particles with diameters of ∼0.1 μm.
Statistics of Brittle Failure in Multiaxial Stress States
Authors: Andreasen Jens Henrik
Published: March 2005

Two methods for relating failure statistics for different stress states in brittle materials are compared. Despite the fact that the two methods are based on the same fundamental assumptions on crack distributions, they give apparently very different formulations. In this paper it is shown that the two methods are equivalent, and the apparent ambiguity resulting from having two seemingly different results from the same set of basic assumptions is removed.
Synthesis of 0.4Pb(Mg1/3Nb2/3)O3–0.3Pb(Mg1/2W1/2)O3–0.3PbTiO3 Ceramics by Metal Alkoxide Method, and Its Dielectric Properties
Authors: Aruga Atsushi , Nakamura Yoshikazu , Aoi Tsuneharu , Watanabe Yoshihisa , Hirayama Shigekazu , Fujimoto Shirou
Published: March 2005

0.4Pb(Mg1/3Nb2/3)O3–0.3Pb(Mg1/2W1/2)O3–0.3PbTiO3+xMgO (x= 0 to 0.04) were prepared by a metal alkoxide method. The percent of perovskite phase of the calcined powders increased with increased calcination temperatures. About 89% of perovskite phase was obtained at 1050°C. The dielectric constant of the pellets fired at 1100°C was increased by the addition of 10 wt% excess Mg(OC2H5)2 and had a maximum value of 7532 at 1 kHz.
Creep Damage Development in Structural Ceramics
Authors: Chan Kwai S. , Page Richard A.
Published: March 2005

Creep rupture of structural ceramics occurs by either the nucleation, growth, and coalescence of grain‐boundary cavities throughout the material or the growth of a dominant flaw. Recent experimental results obtained with small‐angle neutron scattering (SANS) and stereoimaging strain analysis are reviewed and used to answer a number of critical questions pertaining to both damage mechanisms. The nucleation and growth processes of grain‐boundary cavities are examined using the SANS results and pertinent results from other studies. The stochastic nature of cavitation is demonstrated and discussed. Creep‐crack growth is described as either a direct mass transport process or a damage zone growth process. New stereoimaging strain results pertinent to the damage zone growth process are presented and used to elucidate the crack growth process and the growth threshold.
Precipitate Morphology in Ternary MgO,CaO‐Partially‐Stabilized Zirconias
Authors: Dickerson Robert M. , Heuer Arthur H.
Published: March 2005

Precipitation in a series of MgO–CaO–ZrO2 ceramics containing variable MgO:CaO ratios (Mg,Ca–PSZs) aged at 1400°C was studied. Precipitate morphology varied systematically with composition, and “layering” of individual precipitates by variant, due to strain‐induced coarsening, was observed in some samples. Strain energy calculations to predict precipitate–matrix habit planes were performed and compared to experiment.
Ag2O‐Doped Bi2Sr2Ca1Cu2Ox Superconductors Prepared via Melt‐Quenching
Authors: Lee Won‐Hyuk , Abe Yoshihiro , Inukai Eikichi
Published: March 2005

Ag2O‐doped superconducting Bi2Sr2Ca1Cu2Ox ceramics were prepared by a melt‐quenching–reheating method. It is found that the Ag2O‐doped, as‐cast specimens exhibit superconductivity (Tc= around 80 K) by heat treatment at temperatures around 800°C even in an evacuated and sealed silica glass tube, while the undoped specimens do not and vaporize by the corresponding heat treatment. Conversion of the Ag2O‐doped, as‐cast specimens into superconducting ceramics when heated in an evacuated vessel is explained in terms of the oxygen donor of Ag2O in the specimen. This finding enables us to fabricate a desired shape of superconducting Bi2Sr2Ca1Cu2Ox ceramics sealed in metals or glasses. The addition of Ag2O to Bi2Sr2Ca1Cu2Ox melt, however, had deleterious influences on the superconducting properties (Tc and Jc) of the resultant ceramics when obtained by heat treatment in air.
Notch Strength and Fracture Behavior of 2‐D Carbon‐Carbon Composites
Authors: Griesheim Gary E. , Pollock Peter B. , Yen Shing‐Chung
Published: March 2005

This study examined Mode I in‐plane fracture in two‐directional carbon‐carbon composites. Linear elastic fracture mechanics (LEFM) provided good predictions for the failure loads of the compact tension specimens, and consistent values of KIC were calculated. However, values for the strain energy release rate GIC were inconsistent. Analysis of loading/unloading cycles applied to the specimens showed that significant inelastic behavior occurred prior to fracture. Hence the J‐integral method is not thought to be appropriate for fracture prediction. It was also found that the real crack tip stresses in carbon‐carbon composites are much lower than theoretical predictions. An interesting discovery is that cracks in carbon‐carbon composites appear to be naturally blunt. The lower limit on the crack tip diameter corresponds with the spacing of the woven fiber bundles. A significant conclusion from this study is that the material behavior can be modeled as the sum of two contributions: (i) a linear elastic solid, which fails according to LEFM, and (ii) an independent damage mechanism, which absorbs energy but does not alter the ultimate fracture load. Possible candidates for the damage mode are fiber pullout and inelastic deformations due to shear stresses.
Threshold Stress Intensity for Crack Growth in Silicon Carbide Ceramics
Authors: Yavuz Bulent O. , Tressler Richard E.
Published: March 2005

Measurements of threshold stress intensities for crack growth, Kh, of three polycrystalline SiC materials were attempted using interrupted static fatigue tests at 1200°–1400°C. Weibull statistics were used to calculate conservative Kth values from test results. The Kth of a chemically vapor deposited β‐SiC could not be determined, as a result of its wide variations in strength. The Kth≥ 3.3,2.2, and 1.7 MPa·m1/2 for an Al‐doped sintered α‐SiC; and Kth≥ 3.1, 2.7, and 2.2 MPa·m1/2 for a hot isostatically pressed α‐SiC, both at 1200°, 1300°, and 1400°C, respectively. A damage process concurrent with subcritical crack growth was apparent for the sintered SiC at 1400°C. The larger Kth's for the HIPed SiC (compared to the sintered SiC) may be a result of enhanced viscous stress relaxation caused by the higher silica content and smaller grain size of this material. Values measured at 1300° and 1400°C were in good agreement with the Kth's predicted by a diffusive crack growth model, while the measured Kth's were greater than the predicted ones at 1200°C.
Phase Diagram of Wollastonite‐Zirconia
Authors: De Aza Piedad N. , López Carmen M. , Guitián Francisco , De Aza Salvador
Published: March 2005

A reexamination of the system CaO·SiO2–ZrO2 has been conducted in order to use this system to obtain ZrO2‐toughened wollastonite materials. The results have shown that CaO·SiO2–ZrO2 is a pseudobinary system with an invariant peritectic point at 1467°± 2°C, which is in disagreement with previously reported results.
Rheological Behavior of Injection‐Moldable Silicon Powder–Silicon Carbide Whisker Formulations
Authors: Tsao Inlin , Danforth Stephen C. , Metzner Arthur B.
Published: March 2005

The rheological behavior of injection‐moldable formulations for reaction‐bonded Si3N4 toughened with silicon carbide whiskers was studied using capillary rheometry. The effects on rheology of the following parameters were examined: solids loading, powder/whisker volume ratio, particle size and type, and binder composition. Two important aspects of the flow behavior were delineated. First, corrections for end effects and slippage along the wall were made in order to interpret the experimental data properly. At high shearing rates (i.e., 103 s−1) slip may account for more than 50% of the total flow. Such slippage promotes flow into the smallest channels or corners of the mold and may appreciably facilitate molding. Consequently the careful study of slippage is an inherent requirement of the rheological characterization of these concentrated suspensions. Second, the suspension viscosities were delineated. An empirical equation for predicting relative viscosity was developed for formulations containing up to ∼30 vol% of silicon carbide whiskers (with more than 50 vol% total solids). Suspension viscosities generally increased with decreasing particle size and increasing whisker contents. Particle surface roughness appears to affect the shearing behavior. Binders of low molecular weight resulted in higher relative viscosities than higher molecular weight binders, indicating possibly better dispersion of solids when more viscous binders are employed.
Evaluation of Interfacial Properties of Fiber‐Reinforced Ceramic Composites Using a Mechanical Properties Microprobe
Authors: Hsueh Chun‐Hway
Published: March 2005

The application of a mechanical properties microprobe to evaluate the interfacial properties of fiber‐reinforced ceramic composites is addressed. The stress–displacement relation of the embedded fiber, which is subjected to an axial loading–unloading cycle, is analyzed. The interfacial bonding, Coulomb friction at the debonded interface, Poisson's effect of the loaded fiber, and residual stresses are included in the analysis, and closed‐form analytical solutions are obtained. Based on the analytical solutions, a methodology is established to extract the interfacial properties from experimental stress–displacement curves. The roles of interfacial bonding, Poisson's effect, and residual axial stresses on the residual fiber displacement after complete unloading are also addressed in the present study.
Tensile Creep and Creep Rupture Behavior of Monolithic and SiC‐Whisker‐Reinforced Silicon Nitride Ceramics
Authors: Ohji Tatsuki , Yamauchi Yukihiko
Published: March 2005

The tensile creep and creep rupture behavior of silicon nitride was investigated at 1200° to 1350°C using hotpressed materials with and without SiC whiskers. Stable steady‐state creep was observed under low applied stresses at 1200°C. Accelerated creep regimes, which were absent below 1300°C, were identified above that temperature. The appearance of accelerated creep at the higher temperatures is attributable to formation of microcracks throughout a specimen. The whisker‐reinforced material exhibited better creep resistance than the monolith at 1200°C; however, the superiority disappeared above 1300°C. Considerably high values, 3 to 5, were obtained for the creep exponent in the overall temperature range. The exponent tended to decrease with decreasing applied stress at 1200°C. The primary creep mechanism was considered cavitationenhanced creep. Specimen lifetimes followed the Monkman–Grant relationship except for fractures with large accelerated creep regimes. The creep rupture behavior is discussed in association with cavity formation and crack coalescence.
R‐Curve and Compliance Change upon Renotching
Authors: Lutz Ekkehard H. , Sakai Mototsugu
Published: March 2005

A novel approach is addressed in the application of the renotching technique to the consideration of toughening processes and mechanisms of ceramic materials. Crackbridging stresses and the contribution of other mechanisms which enhance crack‐face friction are stepwise removed during renotching. This technique enables one to determine the amount and distribution of bridging stresses behind the crack tip, as well as to separate the contributions of crack‐face, crack‐wake, and crack‐tip processes and mechanisms. Five ceramic materials with different microstructures are used for experimentally determining their conventional KR‐ and “renotched”K̃R‐ curves in addition to measuring the compliance changes during extending as well as renotching the crack. A simple theoretical approach is presented and applied to the experimental results, which enables one to easily determine the magnitude and the distribution of crack‐face bridging stresses. The contributions of various toughening processes to the conventional and the renotched R‐curve behavior are discussed.
Adsorption of Sulfonic Acid Doped Poly(vinyl chloride) on Barium Ferrite Particles
Authors: Sakai Hiroshi , Cima Michael J. , Rhine Wendell E.
Published: March 2005

Adsorption of sulfonic acid doped poly(vinyl chloride) (PVC–SO3H) and poly(vinyl chloride) (PVC) on barium ferrite particles is described. The maximum surface adsorption of PVC–SO3H on barium ferrite was twice that of PVC. Surface chemical interaction between the sulfonic acid groups and barium ferrite surfaces was examined by adsorption of toluene‐4‐sulfonic acid. Sulfonic acid groups were found to adsorb selectively on both Ba–OH and Fe–OH sites by an acid–base interaction. Increasing the hydroxyl content on the barium ferrite surface creates increased dispersion stability in the presence of sulfonic acid doped PVC.
Hot‐Grip Tensile Method for Alumina‐Fiber Testing
Authors: Unal Ozer , Lagerlof K. Peter D.
Published: March 2005

A new tensile test method has been developed for high‐temperature testing of Al2O3 fibers. The advantage of this technique is that it enables testing of ceramic fibers up to 1500°C while the entire sample, including the grips, is within the hot zone. The most critical stage in the entire testing procedure is the alignment of test specimen with respect to the loading axis. The success rate of this testing method is currently around 60%.
Residual Stresses in Ceramic–Interlayer–Metal Joints
Authors: Yu Hsiang‐Yung , Sanday Santiago Carlos , Rath Bhakta Bhusan
Published: March 2005

Thermal residual stresses due to the thermal expansion mismatch in a ceramic–interlayer–metal joint are calculated analytically. A qualitative estimate of the stress distribution is obtained by assuming the joint consists of one or two elastic slabs sandwiched between two semi‐infinite isotropic elastic solids. These elastic solids and the interlayer(s) are perfectly bonded to each other at the planar interfaces. The region where temperature change takes place is assumed to be a cylinder with its axis normal to the interface. A simple equation is obtained for the stress value at the center of the ceramic‐interlayer interface as a function of the thermal expansion coefficients, elastic constants of the constituent materials, and the thickness of the interlayer(s). The results obtained by this simple model agree well, qualitatively, with those obtained experimentally and numerically (finite element calculations). An appropriate interlayer material to reduce the residual stress in ceramic‐metal joints is suggested.
Comparison of Slow Crack Growth Behavior in Alumina and SiC‐Whisker‐Reinforced Alumina
Authors: Zeng Kaiyang , Breder Kristin , Rowcliffe David
Published: March 2005

Results of dynamic fatigue experiments in water at room temperature on an indented Al2O3/25 wt% SiC whisker composite material have shown that this composite has a high resistance to slow crack growth. Aging tests in water revealed that the residual stress due to the indentation does not play an important role, and interrupted fatigue tests showed that the crack starts to grow at very low stress intensities, but the velocity is very low. Detailed fractography indicated that the slow crack growth path is intergranular in the whisker composite. The slow crack growth behavior in the whisker composite is discussed in association with the indentation residual stress, the change of the crack shape during the bending test. These results are compared with a bio‐grade Al2O3 with lower resistance to slow crack growth, and important differences are pointed out.
Reaction Sintering of Zinc Ferrite during Constant Rates of Heating
Authors: Rahaman Mohamed N. , De Jonghe Lutgard C.
Published: March 2005

The reaction sintering of equimolar quantities of zinc oxide and ferric oxide was investigated under conditions of constant rates of heating (1–10°C/min from room temperature to 1350°C) and the data were compared with those for a calcined, single‐phase zinc ferrite powder. For the heating rate of 1°C/min, the densifications of the reaction‐sintered sample and the calcined sample were approximately the same. However, as the heating rate increased, the density at any temperature increased slightly for the reaction‐sintered sample but decreased slightly for the calcined powder. The factors responsible for this slight difference in sintering between the reaction‐sintered sample and the calcined sample are discussed. For the constant heating rates used, the reaction was completed prior to any significant densification. Relative densities of >95% were obtained for both the reaction‐sintered sample and the calcined sample under identical sintering conditions (1–10°C/min to 1350°C). Reaction sintering in a steep temperature gradient produced a nearly fully dense body prior to complete reaction; a composite microstructure consisting of fine zinc oxide grains in a matrix of zinc ferrite was obtained.
Kinetics of the α‐to‐α′H Polymorphic Phase Transition of Ca2SiO4 Solid Solutions
Authors: Fukuda Koichiro , Maki Iwao , Toyoda Kazuhiro , Ito Suketoshi
Published: March 2005

The α‐to‐α′H transition of Ca2SiO4 solid solutions (C2S(ss)) is a nucleation and growth process. This process was shown on time–temperature–transformation (TTT) diagrams for C2S(ss) with different concentrations of foreign oxides (Na2O, Al2O3, and Fe2O3). The kinetic cutoff temperature and the activation energy for growth of the α′H phase increase steadily with increasing concentration of impurities. The activation energy for nucleation also increases above 950°C. The α′H phase, which exists in equilibrium with the α phase at 1280°C, is formed at a maximum rate at around 1100°C regardless of the chemical composition. The TTT diagrams enable us to predict, as a function of cooling rate, the phase constitution of C2S(ss) at ambient temperature.
Crystallization Mechanism of MAS‐osumilite with Composition Mg2Al4Si11O30 from Glass
Authors: Winter Wolfgang , Berger Axel , Muller Gerd , Pannhorst Wolfgang
Published: March 2005

MAS‐osumilite is a metastable double‐ring silicate which is attractive for use in glass‐ceramics because of its low thermal expansion coefficient. The phase can be crystallized from glass powders of MAS‐osumilite composition containing small amounts of BaO. The nucleation and crystallization process has been investigated by means of TEM and SEM. Crystallization starts with the precipitation of β‐quartzss of composition MgAl2O4·nSiO2. BaO concentrates in a residual glass phase between the β‐quartzss crystals. In a second stage small amounts of Ba‐osumilite (BaMg2Al6‐Si9O30) nucleate and crystallize from this glass phase, In a third stage BaO‐free MAS‐osumilite crystals are formed by epitactic growth on the Ba‐osumilite surfaces and grow into adjacent β‐quartzss grains. Two factors are essential for the suppression of undesired further phases to develop a monophase (besides some Ba‐osumilite) MAS‐osumilite glassceramic: a residual glass phase with a composition close to Ba‐osumilite, and β‐quartzss crystals having a composition close to that of MAS‐osumite.
Adsorption as a Method of Doping 3‐mol%‐Yttria‐Stabilized Zirconia Powder with Copper Oxide
Authors: Seidensticker John R. , Mayo Merrilea J. , Osseo‐Asare K.
Published: March 2005

The adsorption behavior of Cu2+ on 3‐mol%‐yttria‐stabilized tetragonal zirconia polycrystalline (3Y‐TZP) powder was studied. There is a window of ph values (10 < pH < 11) where adsorption may be used as a method of doping 3Y‐TZP with Cu2+. The maximum mole percent of the CuO additions is determined by the specific surface area of the 3Y‐TZP powder; a powder with a specific surface area of 16.1 m2/g is limited to about 1 mol% CuO. Compacts made from powders doped with CuO using this method exhibited an enhancement in superplasticity comparable to that observed in other studies using samples doped with CuO by attrition milling.
Thermooptic Coefficients of Soda–Lime–Silica Glasses
Authors: Jewell John M.
Published: March 2005

The thermooptic coefficients, dn/dT, of two series of soda–lime–silica glasses, 25Na2O·xCaO·(75 –x)SiO2 and (25 –y)Na2O·yCaO·75SiO2, have been measured. When CaO is substituted for SiO2, the magnitude of dn/dT passes through a maximum negative value. When CaO is substituted for Na2O, there is a monotonic change from negative to positive dn/dT. These effects are accounted for by the changes in relative values of the coefficient of thermal expansion and the temperature coefficient of electronic polarizability, Θ. The effect of composition on Θ is explained by the changes in density of various nonbridging and bridging oxygens in the glass.
Novel Technique for Zirconia‐Coated Mullite
Authors: Sainz Maria A. , Torrecillas Ramón , Moya José S.
Published: March 2005

A novel, low‐cost, screen‐printing route to obtain zirconiacoated mullite starting from zircon powder has been proposed. A zirconia thick film of ∼30‐μm thickness with a strong adherence to the mullite substrate has been obtained. The role of zircon impurities in the coating characteristics as well as the effect of firing temperature are discussed.
Processing–Microstructure–Property Relationships of Al2O3‐Fiber‐Reinforced High‐Temperature Superconducting (Bi,Pb)2Sr2Ca2Cu3Oy Composite
Authors: Wong Ming‐Shih , Miyase Akira , Yuan Yu‐Sheng , Wang Su Su
Published: March 2005

Monolithic high‐temperature superconducting (HTS) materials are recognized to have inherently weak mechanical properties, such as low strength and fracture toughness. These drawbacks usually can be improved by introducing strong continuous fibers into the brittle ceramic materials. In this study, a systematic investigation on the relationships among processing variables, microstructure, and superconducting and mechanical properties of a continuous Al2O3‐fiber‐reinforced HTS (Bi,Pb)2Sr2Ca2Cu3Oy composite is presented. The Al2O3/BPSCCO composite is fabricated initially by a slurry method, followed by binder extraction up to 800°C in an 8% O2 atmosphere, and finally hot pressed at 800°C in air. Phases present in the HTS composite are identified by XRD, and the microstructure and microchemistry studied by SEM and EPMA. Of particular interest is the fiber/matrix interface; the interfacial reaction is studied for composite specimens which have undergone long heat treatment. The HTS composite is observed to have a good combination of superconducting properties and mechanical properties.
Growth of α‐AI2O3 Platelets in the HF‐γy‐AI2O3 System
Authors: Shaklee Charles A. , Messing Gary L.
Published: March 2005

In the presence of a fluorine mineralizer, highly aggregated, <5 μm α‐Al2O3 platelet particles form by vapor transport during the thermal transformation of γ‐alumina. Platelet aggregation was determined to occur by platelet inter‐growth and by edge nucleation on primary α‐Al203 platelets. The addition of 1010α‐alumina seed particles/cm3γ–Al2O3 resulted in the development of discrete particles during the initial stage of transformation. Impingement of the growing platelets during the latter stage of transformation, however, resulted in intergrowth, a process which was not changed by seeding. Particle size distribution broadening was observed to increase with increasing HF and H2O concentrations because vapor reactant supersaturation increases the degree of edge nucleation. When initially low HF and H2O concentrations were used in seeded systems, however, essentially aggregate‐free α‐Al2O3 platelets of 10–15 μm were obtained.
Effect of Moisture on the Structure and Fracture Strength of Ceramic Green Bodies
Authors: Tanaka Hiroshi , Fukai Seiki , Uchida Nozomu , Uematsu Keizo , Sakamoto Akira , Nagao Yoshihiko
Published: March 2005

To study independently the effects of moisture on the structure and the mechanical strength of the binder in green bodies, specimens of the system alumina/PVA were formed with spray‐dried granules of various moisture contents. The structure and fracture strength of these specimens then were examined after their moisture contents had been adjusted to specified values. As moisture content increased in the granules during compaction, the density and strength of the green body also increased. The accompanying change in the fracture mode, from intergranular to transgranular, showed that the strength of the green bodies was affected more significantly by bonding between granules than by bonding between powder particles.
Nd2O3‐Doped Sialons with ZrO2/ZrN Additions Formed by Sintering and Hot Isostatic Pressing
Authors: Ekström Thommy , Herbertsson Harald , James Matthew , Fleck Ian
Published: March 2005

β‐sialon and Nd2O3‐doped α‐sialon materials of varying composition were prepared by sintering at 1775° and 1825°C and by glass‐encapsulated hot isostatic pressing at 1700°C. Composites were also prepared by adding 2–20 wt% ZrO2 (3 mol% Nd2O3) or 2–20 wt% ZrN to the β‐sialon and α‐sialon matrix, respectively. Neodymium was found to be a fairly poor α‐sialon stabilizer even within the α‐phase solid solution area, and addition of ZrN further inhibited the formation of the α‐sialon phase. A decrease in Vickers hardness and an increase in toughness with increasing content of ZrO2(Nd2O3) or ZrN were seen in both the HIPed β‐sialon/ZrO2(Nd2O3) composites and the HIPed Nd2O3‐stabiIized α‐sialons with ZrN additions.
Seeding Effects on Crystallization of KAlSi3O8, RbAlSi3O8, and CsAlSi3O8 Gels and Glasses
Authors: Liu Chunling , Komarneni Sridhar , Roy Rustum
Published: March 2005

Crystallization of stoichiometric KAlSi3O8, RbAlSi3O8, and CsAlSi3O8 gels (single‐phase and multiphasic gels) and glasses with and without seeding has been investigated by X‐ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectrometry (EDS). The pure gels of K‐, Rb‐, and Cs‐feldspar compositions crystallized mainly to leucite (KAlSi2O6), a Rb analogue of leucite (RbAlSi2O3), and pollucite (CsAlSi2O6), respectively. The KAlSi3O8 glass also yielded leucite. No feldspar phases crystallized in the temperature region studied. The leucite crystallization temperature was lowered by using multiphasic gels. The crystallization sequence of the KAlSi3O8 glasses and single‐phase gels did not change upon seeding with isostructural feldspar crystals. No significant crystallization effects were detected with the use of RbAlSi3O8 and CsAlSi3O8 multiphasic gels. However, K‐feldspar (sanidine) was crystallized by using both compositionally and structurally different gels of KAlSi3O8, i.e., multiphasic gels seeded With feldspar crystals. The microstructure of oriented sanidine crystals around the seeds indicated an epitaxial crystallization mechanism.
Characterization of PLZT Films Deposited by Spray Pyrolysis
Authors: Delikouras Evangelos A. , Perlmutter Daniel D.
Published: March 2005

Spray pyrolysis was used to prepare films of PLZT ceramics, a class of electrooptic materials that find applications in integrated optics devices. The films were prepared by spraying an aqueous solution of mainly nitrate salts of the desired cations onto oriented silicon and magnesia substrates. After drying, the solid deposit was thermally decomposed to yield the mixture of the desired oxides. The surface morphology of the prepared thin films was examined by optical and scanning electron microscopy and the presence of crystalline phases was identified by X‐ray powder diffraction. Compositional homogeneity was determined by energy‐dispersive X‐ray microanalysis.
Corrosion Kinetics of Silicon Nitride in Dry Air Containing Sodium Nitrate Vapors
Authors: Sun Tawei , Pickrell Gary R. , Jr. Brown Jesse J.
Published: March 2005

The gaseous alkali corrosion kinetics of Si3N4 were systematically investigated from 950° to 1100°C in dry air containing 0.98 vol% sodium nitrate vapors. The linear reaction rates observed at all temperatures indicate that the alkali corrosion of Si3N4 is interface‐controlled with an activation energy of 199 kJ/mol. The overall reaction involves a complex absorption–dissolution–oxidation process and the rate‐controlling step appears to be the interfacial oxidation of Si3N4 to SiO2. A comparison of the reaction kinetics and mechanism between the oxidation of Si3N4 in pure oxygen and in the alkali‐containing atmosphere is presented.
Residual Stresses in Silicon Carbide–Zircon Composites from Thermal Expansion Measurements and Fiber Pushout Tests
Authors: Reddy Srinivas K. , Kumar Susmit , Singh Raj N.
Published: March 2005

Coefficients of thermal expansion (CTE) in the axial direction of two types of SiC fibers, monolithic zircon, monolithic SiC, and several SiCf‐zircon composites were measured in the temperature range of 50 to 1380C. The measured CTE values of composites were compared with values predicted by the rule‐of‐mixtures approach, and a small difference in measured and calculated values was ascribed to the nature of interfacial bonding and assumptions implicit in the rule‐of‐mixtures approach. Fiber pushout tests were performed on these composites and the residual stresses were extracted from the analysis of the load–displacement plots in terms of the shear‐lag and progressive debonding models. The radial and axial residual stresses arising from the mismatch in CTE were calculated and compared with values obtained from the fiber pushout tests. The fiber pushout tests in general produced lower values of the residual stresses, but the residual stresses obtained using shear‐lag analysis were in good agreement with the calculated values based on the CTE mismatch in composites with lower values of the interfacial shear stress. The influence of anisotropic fiber expansion in the radial and axial directions on the radial and axial residual stresses in composites were also examined.
TEM Examination of Heart‐Treated Nanocrystalline ZnS
Authors: Voiles E. Todd , Chumbley L. Scott , Han Yong , Akinc Mufit
Published: March 2005

Monodisperse, spherical, submicrometer‐size ZnS particles with nanocrystalline substructure were heated and examined in situ using a Gatan hot stage and a transmission electron microscope (TEM) at temperatures ranging from 500° to 900°C. The goal of this study was to observe the micro‐structural changes that occur in these particles during heat treatment. The particles, whose morphology consists of an agglomeration of nanocrystals, showed significant grain growth and sintering at temperatures as low as 600°C, much lower than expected for bulk ZnS crystals. In addition, the particles were seen to develop hollow cores during heat treatment. This hollowing effect appears to be related to the nanocrystalline/nanoporous nature of the particles.
Temperature–Time Texture Transition of Pb(Zr1−xTix)O3 Thin Films: II, Heat Treatment and Compositional Effects
Authors: Chen San‐Yuan , Chen I‐Wei
Published: March 2005

Texture transition of Pb(Zr1−xTix)O3 thin films grown from a metallo–organic solution onto Pt/Ti/SiO2/Si substrates has been studied. The orientation obtained depends on the crystallization temperature and time and can be drastically altered by modifying the heat treatment schedule. A [100] texture requires an initial seeding treatment in the intermediate temperature range. This is attributed to a nucieation advantage associated with the formation of an intermediate PbO[001] texture that tends to form at intermediate temperature over time. A [111] texture develops at higher temperature during rapid heating and can be rationalized by the formation of an epitaxial intermetallic phase Pt5–7Pb, at the PZT/Pt interface that provides lattice matching between PZT(lll), Pt5–7Pb(lll), and Pt(lll). Temperature–time transformation texture (TTT) diagrams of PZT texture have been constructed for seeding various orientations. The effect of composition (Pb excess and Zr/Ti ratio) and the possible manipulation of these texture selection relations by combining compositional tailoring and heat treatment schedules are illustrated.