bluuebunny/crossref_metadata_2025 huggingface dataset:
Microstructural Developments and Dielectric Properties of Rapid Thermally Processed PZT Thin Films Derived by Metallo‐organic Decomposition
Authors: Mansour Said A. , Liedl Gerald L. , Vest Robert W.
Published: July 2005

Microstructural developments and dielectric properties of lead zirconate titanate thin films (0.22 4mUm) with the composition Pb(Zr0.53Ti0.47)O3 were studied. The films were prepared by metallo‐organic decomposition (MOD) and rapid thermal processing (RTP) in the temperature range 475–825°C for 2 min in an oxygen gas flow with and without post‐annealing. An amorphous–pyrochlore–perovskite phase transformation is indicated at or below 525°C RTF temperatures while a direct amorphous‐to‐perovskite phase transformation is indicated at higher RTP temperatures. A decrease in grain size with increasing temperature is correlated with an increase in and dominance of nucleation of perovskite sites. The best dielectric and fatigue properties were exhibited by films processed in the temperature range 725–775°C. Hysteresis loops tended toward squareness and polarization charges increased with increased temperature. Furthermore, 45% of the initial charge remained after 109switching reversals. A degradation, however, was observed in both properties at higher temperatures.
Formation of Reaction‐Bonded Silicon Nitride from Silane‐Derived Silicon Powders: Nucleation and Growth Mechanisms
Authors: Sheldon Brian W , Rankin Janet , Haggerty John S.
Published: July 2005

The nucleation and growth of Si3N4 on silane‐derived Si powders was investigated with transmission electron microscopy and FTIR spectroscopy. Thermogravimetric analysis (TGA) was also used to monitor the process through different stages of the reaction. The FTIR and TEM results provide clear evidence that the nucleation of crystalline Si3N4 coincides with the onset of rapid nitridation. Electron diffraction indicates that Si3N4 forms heteroepitaxially on the Si powder surfaces, with Si (111) || Si3N4(0001) and Si || Si3N4. Also, flat interfaces between the Si and Si3N4 (compared to the initial spherical surface of the Si powders) indicate that a significant rearrangement of the particle surface occurs during the initial stages of nitridation. The results reported here demonstrate that the rapid, low‐temperature nitridation observed with silane‐derived powders is possible because the Si/vapor surfaces are not covered with a continuous Si3N4 product layer. The measured nitridation rates are comparable to Si evaporation rates, which suggests that Si vaporization is rate limiting. This is significantly different from conventional RBSN, where nitridation is limited by solid‐state diffusion through a Si3N4 product layer.
Experimental Study of the Fracture Toughness of a Ceramic/Ceramic‐Matrix Composite Sandwich Structure
Authors: Li Zhiguang , Taya Minoru , Dunn Martin L. , Watanabe Ryuzo
Published: July 2005

A hybrid experimental–numerical approach has been used to measure the fracture resistance of a sandwich structure consisting of a 304 stainless steel/partially stabilized zirconia ceramic‐matrix composite crack‐arresting layer embedded in a partially stabilized zirconia ceramic specimen. The mode I fracture toughness increases significantly when the crack propagates from the ceramic into the ceramic‐matrix composite region. The increased toughening due to the stainless steel particles is explained reasonably well by a toughening model based on processing‐induced thermal residual stresses. In addition, several experimental modifications were made to the chevron‐notch wedge‐loaded double cantilever beam specimen to overcome numerous problems encountered in generating a precrack in the small, brittle specimens used in this study.
In Situ Fluorescence Probing of the Chemical Changes during Sol–Gel Thin Film Formation
Authors: Nishida Fumito , McKiernan John M. , Dunn Bruce , Zink Jeffrey I. , Brinker C. Jeffrey , Hurd Alan J.
Published: July 2005

Pyranine (8‐hydroxy‐l,3,6‐trisulfonated pyrene) was used as an in situ fluorescence probe to monitor the chemical evolution during sol‐gel thin film deposition of silica by the dip‐coating process. The sensitivity of pyranine luminescence to protonation/deprotonation effects was used to quantify changes in the water/alcohol ratio in real time as the substrate was withdrawn from the sol reservoir. The spatially resolved spectral results showed that preferential evaporation of alcohol occurred, and that the solvent composition in the vicinity of the drying line reached values in excess of 80 vol% water. Correlation of the luminescence results with the interference pattern of the depositing film allowed the solvent composition to be mapped as a function of film thickness.
Ultraviolet Patterning of Alkoxy‐Derived Lithium Niobate Film
Authors: Yogo Toshinobu , Takeichi Yoshikuni , Kikuta Koichi , Hirano Shin‐ichi
Published: July 2005

Patterned lithium niobate (LN) films were synthesized successfully from a precursor film containing 1‐phenyl‐1,3‐butanedione (PBD) by ultraviolet (UV) irradiation. A LN precursor solution composed of lithium ethoxide and niobium ethoxide was modified with PBD in ethanol to form LiNb(OEt)6‐n(PBD)n, which was designed to have a specific UV absorption at 330 nm. The precursor film began to crystallize at 400°C on sapphire C substrates. The UV absorption band at 330 nm in the precursor film decreased in intensity with increased exposure time to UV light. The patterned LN films crystallized at 550°C on sapphire C substrates showed a (006) preferred orientation.
Phase Diagram of Wollastonite—Tricalcium Phosphate
Authors: De Aza Piedad N. , Guitián Francisco , De Aza Salvador
Published: July 2005

A study of the system CaO·SiO2 (CS)‐3CaO·P2O5 (TCP) was conducted as a preliminary step toward obtaining polycrystalline wollastonite–tricalcium phosphate bioceramics. The results showed that the system is a true binary, with an invariant point at 1402 ± 3°C and a composition of 60 wt% CS/40 wt% TCP. These results are in disagreement with the reported data.
Preparation of CdS‐doped Glasses from Gels Containing Diethyldithiocarbamatocadmium
Authors: Iwami Tomoaki , Tadanaga Kiyoharu , Tatsumisago Masahiro , Minami Tsutomu , Tohge Noboru
Published: July 2005

CdS‐doped SiO2 glasses were prepared via silica gels containing diethyldithiocarbamatocadmium Cd(S2CN(C2H5)2)2. Heat treatment of the gels gave transparent yellow SiO2glasses doped with hexagonal CdS crystals. In optical absorption and fluorescence spectra, the optical absorption edge and the emission peak clearly exhibited a blue shift, which was attributed to the quantum size effect of the carrier confinement, as the CdS content was decreased. In the fluorescence spectra of the CdS‐doped silica glasses, the emission peak was observed only near 500 nm and not observed at longer wavelengths which were known to be present if there were sulfur vacancies.
Effect of Moisture Adsorption on the Electrical Properties of Hardened Portland Cement Compacts
Authors: Wilkosz Daniel E. , Young J. Francis
Published: July 2005

Dense bodies were formed by cold compaction of Portland cement, with and without silica fume additions, followed by autoclaving at temperatures up to 240°C. Samples were analyzed to determine crystalline phases and pore structures in the cementitious matrix, and their electrical properties (resistivity and complex permittivity) measured. The adsorption of moisture was monitored as a function of relative humidity and correlated to changes in electrical properties. These changes can be explained in terms of the formation of conducting paths as water is adsorbed into the connected pore system.
Possibility of Spinodal Decomposition in ZrO2‐Y2O3 Alloys: A Theoretical Investigation
Authors: Fan Danan , Chen Long‐Qing
Published: July 2005

The thermodynamics and kinetics of cubic → tetragonal phase transformations in ZrO2‐Y2O3 alloys were investigated by using thermodynamic stability analysis and kinetic computer simulations to explore the possibility of a spinodal mechanism during decomposition. Based on a simple free energy model, it is shown that, depending on the alloy composition, a cubic phase aged within the t + c two‐phase field may result in three different sequences of phase transformations: (1) direct nucleation and growth of the equilibrium t‐phase from the c‐phase matrix; (2) formation of a metastable t′‐phase followed by nucleation and growth of the equilibrium c‐ and t‐phases; and (3) formation of a transient t′‐phase followed by its spinodal decomposition into two tetragonal phases with one of the tetragonal phases eventually transforming to the equilibrium c‐phase. The temporal microstructure evolutions for different compositions were studied by using computer simulations based on the time‐dependent Ginzburg‐Landau (TDGL) model which incorporates the long‐range elastic interactions.
Reaction of SiCf/SiC Composites with a Zinc Borate Glass
Authors: Lemoine Patrick , Salvo Milena , Ferraris Monica , Montorsi Margherita , Scholz Harold
Published: July 2005

Two different types of SiCf/SiC composites were successfully joined using a zinc borate glass as a joining agent. The characterization of the joined specimens included XRD, DSC, DTA, SEM‐EDS, macroporosimetry, and shear testing measurements. For both composites, the interfaces were continuous and crack‐free, and a reaction occurred between the liquid glass and the composite's surface. The large porosity of the chemical vapor deposited (CVI) composite allowed the glass to infiltrate the sandwich structure, the driving force being gaseous product pressurization and capillary surface forces.
Surface Diffusivity under High‐Pressure Gas
Authors: Nanko Makoto , Ishizaki Kozo , Fujikawa Takao , Kondo Yoshihito
Published: July 2005

The sintering behavior of TiO2 under high‐pressure gas (100 MPa) was studied with respect to densification rate, decreasing rate of specific surface area, and narrowing rate of pore size distribution. At the low sintering temperature (800°C) used in this study, the densification rate under high‐ pressure gas was similar to that under low (i.e., 1 atm) pressure. The specific surface area decreased and the pore size distribution narrowed at a faster rate under high‐ pressure gas than under low‐pressure gas. These results imply that high‐pressure gas enhances surface diffusion.
Acoustic Emission during Indentation Fracture
Authors: Tanikella B. V. , Scattergood Ronald O.
Published: July 2005

Acoustic emission measurements were made during controlled indentation of soda‐lime glass. Pulses were detected at specific points during the loading or unloading cycles. The response and reproducibility were dependent upon the indenter shape. Comparison with earlier data reported in the literature showed that the acoustic activity was correlated with crack initiation events corresponding to median/ radial, lateral, or other fracture modes.
Effect of O2 Concentration in Firing Atmosphere on Resistance of RuO2‐Glass Thick‐Film Resistors
Authors: Nakano Takashi , Yamaguchi Takashi
Published: July 2005

The effect of oxygen concentration in the firing atmosphere on the resistance of RuO2‐glass thick‐film resistors (TFRs) has been studied using glasses with various compositions. The resistance decreased with increasing oxygen concentration for TFRs made from PbO‐containing glasses, but TFRs prepared from PbO‐free glasses exhibited no oxygen concentration dependence of resistance. Experimental results suggest that the RuO2‐PbO interaction is responsible for the oxygen concentration dependence of the resistance.
Glass/Substrate Interaction in Model RuO5‐Glass Double‐Layer Thick Films
Authors: Nakano Takashi , Iizuka Toshihiro , Takada Tomoyuki , Yamaguchi Takashi
Published: July 2005

Chemical interaction between RuO2‐glass thick‐film resistors and substrates was studied by observing microstructural changes in model double‐layer thick films, which were composed of a top glass layer and an RuO2 layer. The concentration profiles of Al, Pb, and Ru in the film were analyzed. A new glass layer formed on the alumina substrate during firing, the formation of which resulted from dissolution of A12O3 into glass. A mechanism of microstructural changes has been proposed based on the results of EPMA.
Effects of Heat Treatment in a Wet Hydrogen Atmosphere on the Reliability of Sintered α‐Silicon Carbide
Authors: Kim Hyoun‐Ee , Moorhead Arthur J. , Riu Doh‐Hyung , Lee Dong‐Han
Published: July 2005

Sintered α‐SiC was exposed, for times up to 2 h, to a flowing wet H2 atmosphere (PH2O= 1 × 10‐4 MPa) at temperatures of 1300°, 1400°, and 1500°C. The effect of such conditions on the reliability of the ceramic was estimated by comparing the Weibull modulus of the groups of specimens, tested in four‐point flexure, before and after exposure. The Weibull modulus of as‐polished specimens was 6.7, indicating a wide variation in room‐temperature flexural strength. The Weibull modulus was increased to 14.2 by the heat treatment for 2 h in wet H2 at 1400°C. The average strength was also improved from 347 to 446 MPa by such exposure. Heat treatment at 1300° and 1500°C also improved the reliability of the material, as indicated by increases in the Weibull modulus, but to less a degree than did exposure at 1400°C. The increases in reliability and average strength were attributed to the blunting of surface flaws by the formation of a thin SiO2 layer on the sample surface.
Detection of Failures around Main Cracks and Their Relation to the Fracture Toughness of Cement Pastes
Authors: Igarashi Shin‐ichi , Kawamura Mitsunori
Published: July 2005

Fluorescence microscopy examinations revealed the characteristics of crack path and the presence of local failures around the main cracks in hardened cement pastes. Reduction in the water: cement ratio and the addition of silica fume led to a decrease in locally damaged regions around the main cracks. However, the R‐ curve of the silica fume‐free cement paste with the water: cement ratio of 0.55 was much different from that of the silica fume‐bearing paste. The silica fume‐bearing cement paste exhibited a relatively flat R‐curve, whereas reduction in the water: cement ratio in the silica fume‐free paste led to a rising R‐curve. These results were related to the toughening mechanisms of cement pastes derived from the characteristics of the crack path and the areas of local failures around main cracks that were revealed by fluoresence microscopy. Presumably, these differences in fracture toughness resulted from the nature of hydration products and/or their inherent microstructure.
Notch Sensitivity and Stress Redistribution in Three Ceramic‐Matrix Composites
Authors: Mackin Thomas J. , Purcell Thomas E. , He Ming Y , Evans Anthony G.
Published: July 2005

Fiber‐reinforced ceramic‐matrix composites (CMCs) depend upon inelastic mechanisms to diffuse stress concentrations associated with holes, notches, and cracks. These mechanisms consist of fiber debonding and pullout, multiple matrix cracking, and shear band formation. In order to understand these effects, experiments have been conducted on several double‐edge‐notched CMCs that exhibit different stress redistribution mechanisms. Stresses have been measured and mechanisms identified by using a combination of methods including X‐ray imaging, edge replication, and thermoelastic analysis. Multiple matrix cracking was found to be the most effective stress redistribution mechanism.
Effect of Particle Packing on the Filtration and Rheology Behavior of Extended Size Distribution Alumina Suspensions
Authors: Smith Peter A. , Haber Richard A.
Published: July 2005

The effect of particle packing on the rheology and casting behavior and cast cake characteristics of aqueous alumina suspensions (5O vol%) was investigated using the Andreasen approach. Varied packing was produced by blending two starting materials that differed in average size by a factor of 10. Formulations closest to ideal packing lowered viscosity. Specifically, the lowest viscosity suspension, 196 mPa s, was produced with the distribution closest to the ideal packing distribution. Typically, a well‐dispersed suspension (characterized by low viscosity) casts slower than one of poorer dispersion given the same solids content. However, the suspension that provided the lowest viscosity cast at a rate of 0.41 mm2/s, which was the fastest rate of the compared formulations. Therefore, suspensions consisting of extended size distributions do not necessitate slow filtration rates. The colloidal properties of the individual starting materials, low shear rate rheology, and mercury porosimetry were used to explain the unexpected casting behavior. The dispersion and structure formation within the suspension were investigated using electrokinetic sonic amplitude measurements. Mercury porosimetry characterized the flow channels that developed in the casts. Low shear rate rheology confirmed the presence of flocculation that was first suggested by the porosimetry results.
Low‐Temperature Phase Equilibria in the Y‐Ba‐Cu‐O System
Authors: Brosha Eric L. , Garzon Fernando H. , Raistrick Ian D. , Davies Peter K.
Published: July 2005

Ultrasonically prepared freeze‐dried nitrate precursors and high‐precision solution calorimetry were used to investigate the low‐temperature thermodynamic stabilities of compounds in the Y‐Cu‐O, Ba‐Cu‐O, Y‐Ba‐O, and Y‐Ba‐Cu‐O pseudobinary and pseudoternary systems at 1 atm of oxygen. Y2Cu2O5, Y2BaCuOs, and BaCuO2 were found to be metastable below 682°, 728°, and 710°± 5°C, respectively. The only stable phases in the Y‐Ba‐Cu‐O system at 298 K and 1 atm of oxygen are Ba2Cu3O6, CuO, BaO2, and Y2O3. By compiling the calorimetric and phase equilibria data, a series of Y‐Ba‐Cu‐O isothermal phase diagrams were constructed between 25° and 900°C at 1 atm of oxygen.
Homogeneous Distribution of Sintering Additives in Liquid‐Phase Sintered Silicon Carbide
Authors: Lidén Eva , Carlstrom Elis , Eklund Lars , Nyberg Brita , Carlsson Roger
Published: July 2005

The addition of sintering additives to silicon carbide particles by electrostatic adsorption of colloidal A12O3 and Y2O3 sols has been studied as a way to achieve an optimum homogeneity in the microstructure. The adsorption behavior of the sol particles was examined by electrophoretic measurements and X‐ray fluorescence analysis. Both A12O3 and Y2O3 sols could simultaneously be adsorbed on the SiC particle surfaces. Viscosity measurements showed that the colloidal sol particles had a stabilizing effect on the slip, and hence slips with relatively high solid loadings could be prepared without adding extra dispersing agent. Liquid‐phase‐sintered silicon carbide materials (LPS‐SiC) with 2 wt% A12O3 and 1 wt% Y2O3 were prepared by freeze granulation/ pressing and sintering at 1880deg;C for 4 h. The homogeneity of the green compacts was quantified using a spot analysis technique in an electron probe microanalyzer. It was clearly shown that the addition of sols gave a more homogeneous microstructure than the reference sample with Y2O3 and A12O3 added as powders. The addition of sintering additives as sols also enhanced the sintering behavior.
Dependence of Apatite Formation on Silica Gel on Its Structure: Effect of Heat Treatment
Authors: Cho Sung‐Baek , Nakanishi Kazuki , Kokubo Tadashi , Soga Naohiro , Ohtsuki Chikara , Nakamura Takashi , Kitsugi Toshiaki , Yamamuro Takao
Published: July 2005

The prerequisite for glasses and glass‐ceramics to bond to living bone is the formation of biologically active bonelike apatite on their surfaces in the body. Our previous study showed that a silica gel prepared by hydrolysis and polycon‐ densation of tetraethoxysilane in aqueous solution containing poly(ethy1ene glycol) induces apatite nucleation on its surface in a simulated body fluid. In the present study, the effects of heat treatment of silica gel on its catalytic effects in apatite nucleation was investigated in a simulated body fluid. I t was found that apatite forms on the surfaces of silica gels heat‐treated below 8OO°C, but not on those heat‐treated above 900°C. The volume of nanometer‐range pores in the gel remarkably decreased by heat treatment above 900°C. The concentration of silanol groups in the silica gels gradually decreased with increasing heat treatment temperature. The rate of silica dissolution from the gel into the simulated body fluid decreased remarkably by heat treatment above 900°C. This suggested that a special type of silanol group which is formed by soaking the gel treated below 800°C into the simulated body fluid is respon sible for apatite nucleation.
Competitive Adsorption of Citric Acid and Poly(vinyl alcohol) onto Alumina and Its Influence on the Binder Migration during Drying
Authors: Hidber Pirmin C. , Graule Thomas J. , Gauckler Ludwig J.
Published: July 2005

Poly(viny1 alcohol) (PVA) and citric acid (CA) are a commonly used binder and dispersant, respectively, for aqueous Al2O3 slurries. The competitive adsorption of these additives on A12O3 from aqueous solution was studied, as was the influence of this competition on the binder migration in centrifugally cast compacts during the drying process. PVA did not influence the adsorption behavior of CA. However, the adsorption of PVA on α‐Al2O3 was strongly reduced by the presence of CA. This displacement of PVA by CA led to a drastically increased segregation of PVA during the drying process.
Supercritical Debinding of Injection Molded Ceramics
Authors: Chartier Thierry , Ferrato Marc , Baumard Jean F.
Published: July 2005

Extraction of organic additives from extrusion‐molded cylinders of alumina by a supercritical fluid is investigated. Hildebrand parameters alone are not adequate to predict conditions for optimal polymer extraction with supercritical CO2. The results obtained with two models developed for the kinetics of binder extraction suggest that polymer extraction from green samples is controlled by diffusion without development of a reaction front. The solubility and diffusivity of polymers both affect the extraction rate, with opposite pressure and temperature dependencies.
Ultrasonic Evaluation of Initiation and Development of Oxidation Damage in Ceramic‐Matrix Composites
Authors: Chu Ya‐Cherng , Lavrentyev Anton I. , Rokhlin Stanislav I. , Baaklini George Y. , Bhatt Ramakrishna T.
Published: July 2005

In this paper we report on the development of a method for ultrasonic nondestructive characterization of oxidation damage in ceramic‐matrix composites. The method is based on ultrasonic measurement of elastic moduli of the composite, which are then used to determine the elastic moduli of the fiber‐matrix interphase. Thus the interphasial damage may be estimated quantitatively. As a model system we used, to demonstrate applicability of the method, a unidirectional SiC‐fiber‐reinforced reaction‐bonded silicon nitride matrix composite (SiC/RBSN). The composite samples were oxidized in flowing oxygen for 0.1, 1, 10, and 100 h at 600°, 900°, 1200°, and 1400°C. The ultrasonic phase velocity in the composite was measured at room temperature before and after oxidation; the data were then used to find the composite moduli, which quantify the induced damage. Significant changes in ultrasonic velocities and composite moduli were found as a result of oxidation. Fiber‐matrix interphasial moduli were determined by multiphase micromechanical analysis. We found that oxidation of the carbon interphasial layer is the dominant mechanism in decreasing the elastic moduli of the composite. The critical exposure time for transition from the nondamaged to the damaged state at different oxidation temperatures has been determined.
Pyrolysis of Titanium‐Metal‐Filled Poly(siloxane) Preceramic Polymers: Effect of Atmosphere on Pyrolysis Product Chemistry
Authors: Yu Sung Hun , Riman Richard E. , Danforth Stephen C. , Leung Roger Y.
Published: July 2005

Pyrolysis of unfilled as well as Ti‐metal‐filled poly(siloxane) preceramic polymers, heated at 1350deg;C in N2, Ar, or NH3, was evaluated in terms of the effect of atmosphere on pyrolysis product chemistry. Pyrolysis of the unfilled poly(siloxane) in N2 or Ar resulted in the formation of a metastable, amorphous SiOxCy phase with a residual turbostratic carbon phase, with the evolution of CH4 and H2 as the main pyrolysis products. However, pyrolysis of the unfilled poly (siloxane) in NH3 resulted in a partial substitution of nitrogen from the atmosphere for network carbon to form a binary mixture of amorphous SiOxCy and SiOxNy phases. Pyrolysis of the Ti‐filled poly(siloxane) in NH3 resulted in the reaction of the Ti particles with the atmosphere to form nearly stoichiometric TiN. In Ar, the Ti particles react with either gaseous hydrocarbon, i.e., CH4, or the carbon pyrolysis products of the poly(siloxane), to form slightly nonstoichiometric TiC along with a partial reduction of the SiOxCy matrix. Finally, in N2, the Ti particles react with both carbon from the poly(siloxane) and nitrogen from the atmosphere to form a solid solution of TiC and TiN.
Structure‐Optical Property Correlation of Epitaxial Potassium Niobate Thin Films Deposited on Magnesium Oxide (100) Substrates Using a Strontium Titanate Transition Layer
Authors: Gopalan Venkatraman , Raj Rishi
Published: July 2005

Epitaxial thin films of orthorhombic KNbO3 (100)/(010) were deposited on MgO (100) single‐crystal substrates by pulsed laser ablation using an ε120 Å SrTiO3 (110) transition layer in between. From X‐ray diffraction, the orientation relationships were determined as (010) [100] or (100) [010] KNb03∥ (110) [110] SrTiO3∥ (100) [011] MgO and (010) [001] or (100) [001] KNbO3∥ (110) [001] SrTiO3∥ (100) [011] MgO. The measured film refractive indices at 632.8 nm were 2.213 ± 0.003, 2.278 ± 0.003, and 2.285 ± 0.003, respectively, along MgO [100], [011], and [011] directions. A model was developed to correlate the measured effective refractive indices of the film to area fractions of domain variants in the film. Using the model, the area fraction of domains with their polarization axis normal to the substrate was estimated to be 60.0 ± 2.7%.
Zinc Sulfide/Gallium Phosphide Composites by Chemical Vapor Transport
Authors: Han Yong , Akinc Mufit
Published: July 2005

Chemical vapor transport was employed to prepare ZnS/ GaP composite powders. Spherical, submicrometer, nano‐ porous ZnS powders were used as a substrate, where GaP was deposited via a transport reaction involving iodine. XRD examinations of the powders with various GaP contents indicated that the powders consisted mainly of solid solutions with small amounts of GaP and ZnS. The powders were then densified to greater than 98% relative densities by cold isostatic pressing followed by hot isostatic pressing at 900deg;C under 207 MPa. Vickers hardness improved from 1.38 GPa for pure ZnS to 2.82 GPa (13.7 wt% GaP) and fracture toughness increased from 0.50 MPa.m1/2for pure ZnS to 0.89 MPa.m1/2(21.0 wt% GaP).
High‐Strength and High‐Fracture‐Toughness Ceramics in the Al2O3/LaAl11O18 Systems
Authors: Yasuoka Masaki , Hirao Kiyoshi , Brito Manuel E. , Kanzaki Shuzo
Published: July 2005

Control of microstructure in the Al2O3/LaAl11O18 system was performed. Elongated alumina grains were formed by doping with small addition of silica, and 20 vol% lanthana‐ luminate was formed in situ by the reaction of LaAlO3‐ A12O3 in an alumina matrix. Strengths of over 600 MPa and a high fracture toughness (6 MPa.m1/2) were achieved in the material with both elongated A12O3 grains and LaAl11O18 platelets. Generally antagonistic properties such as strength and fracture toughness have been made compatible in the same ceramic system.
Phase Equilibria of the Calcium Oxide‐Copper Oxide System in Oxygen at 1 atm
Authors: Tsang Chi‐Fo , Meen James K. , Elthon Don
Published: July 2005

Phase equilibria in the CaO‐CuO system have been determined at 1 atm pressure in oxygen over the temperature range 800° to 1300deg;C. CaO is the stable phase at the calcium‐rich end of the system. Two intermediate crystalline phases, namely Ca2CuO3 and Ca3Cu7O10, form. CazCuO3 is stable up to 1085°± 3deg;C, where it melts incongruently to CaO + liquid (peritectic liquid has ε82% CuO). Ca3Cu7O10 becomes stable at 977°± 3deg;C by reaction between Ca2CuO3 and CuO. Ca3Cu7O10 melts incongruently at 1046°± 3deg;C to Ca2CuO3+ liquid (peritectic liquid has ε83% CuO). CuO is the stable copper oxide phase up to 1061°± 3deg;C at the copper‐rich end of the system; at higher temperatures, Cu2O is stable until the liquidus is reached at 1121deg;C. The binary eutectic is at 1045°± 5deg;C, in which a liquid with 83% CuO coexists with Ca3Cu7O10 and CuO.
Mechanical Properties of Magnesia‐Doped Lanthanum Chromite versus Temperature
Authors: Montross Charles S. , Yokokawa Harumi , Dokiya Masayuki , Bekessy Lambert
Published: July 2005

Magnesia‐doped lanthanum chromite is a potential material for use in solid oxide fuel cells as an interconnector due to its resistance to oxidation and reduction. The strength and toughness of La(Cr0.9Mg0.1)O3 were measured from 25° to 1000deg;C in the as‐fired reduced state and after oxidation. The as‐fired samples showed a peak in toughness of approximately 3.9 MPa.m1/2 at 125deg;C which decreased to approximately 1.4 MPa.m1/2 at 600deg;C and 2.8 MPa.m1/2 at room temperature. This peak in toughness is hypothesized to be due to the rhombohedral‐to‐orthorhombic phase transition by a toughening mechanism that is currently being investigated. The strength was also affected by the phase transition for both the as‐fired reduced and the oxidized samples.
Effects of Damage on Thermal Shock Strength Behavior of Ceramics
Authors: Jin Zhi‐He , Mai Yiu‐Wing
Published: July 2005

When subjected to severe thermal shock, ceramics suffer strength degradation due to the damage caused by the shock. A fracture‐damage analysis is presented to study the effects of damage on the thermal shock behavior of ceramics. It is assumed that a narrow strip damage zone is developed at the tip of a preexisting crack after a critical thermal shock and the damage behavior can be described by a linear strain‐softening constitutive relation. Damage growth and strength degradation are determined based on fracture and damage mechanics. Numerical calculations are carried out for two ceramic materials, and the strength degradation agrees quite well with experimental results. The effects of bridging/damage stress, the fracture energy of the bridging/damage zone, and specimen size on thermal shock strength behavior are studied. A higher fracture energy can enhance the residual strength of thermally shocked ceramics and, for a given fracture energy, a higher bridging stress is needed to reduce the strength degradation. It is also shown that the thermal shock strength behavior is size‐dependent, and a high value of (KIC/Ob)2, where KIC is the intrinsic fracture toughness and Ob is the bending strength, can improve significantly the residual strength.
Gibbs Energy of Formation of CuGd2O4 and Phase Relations in the Cu‐Gd‐O System
Authors: Kale G. M. , Fray D. J.
Published: July 2005

Oxygen potentials for the coexistence of Cu2O + Gd2O3+ CuGd2O4, Cu2O + CuO + CuGd2O4, and Cu + Cu2O + Gd2O3 three‐phase equilibrium have been measured by employing the solid‐state galvanic cells

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between 960 and 1290 K, respectively. The results obtained in this study indicate that the ternary phase, CuGd2O4, is nearly stoichiometric. The measured oxygen potentials for the coexistence of various three‐phase assemblages are given by the expressions

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between 960 and 1290 K, respectively. Combining the oxygen potentials for the coexistence of Cu2O + Gd2O3+ CuGd2O4 with that of Cu2O + CuO gives for the reaction

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The results obtained in the present investigation suggest that the formation of CuGd2O4 from component oxides is slightly endothermic and the phase CuGd2O4 is an entropystabilized compound. The enthalpy and entropy of formation of CuGd2O4 from component oxides obtained in this study are in excellent agreement with the recent calorimetric data. Phase relations and oxygen‐potential diagram for the Cu‐Gd‐O ternary system have been constructed at 1273 K by combining the results obtained in this study and the auxiliary thermodynamic data available in the literature.
Crack Propagation Behavior of Y‐TZP Ceramics
Authors: Chevalier Jérome , Olagnon Christian , Fantozzi Gilbert , Galès Bernard
Published: July 2005

Y‐TZP ceramics present the twofold advantage of a very fine grain size and a phase transformation leading to some reinforcement, making them useful in hip joint head prostheses. The subcritical crack growth of such a material that mainly drives the lifetime of the components has been evaluated for wide crack velocity ranges down to 10‐11 m/s by using both double torsion and static fatigue tests. It appeared that subcritical crack growth was activated by H2O. It is shown that two types of flaws should be considered: surface flaws caused by machining located in the compressive layer present at the surface, and so‐called volume flaws. The subcritical crack growth and the toughness of both types of defects are different. The relevance of subcritical crack growth analysis for such surface cracks is discussed. The compressive layer at the surface leads to a threshold value below which no crack growth occurs.
Use of Spodumene in the Processing of Alumina‐Matrix Ceramics—Influence on Microstructure and Mechanical Properties
Authors: Latella Bruno A. , Burton Graeme R. , O'Connor Brian H.
Published: July 2005

A study has been conducted on the microstructural character, phase assemblage, and selected physical properties of liquid‐phase‐sintered (LPS) aluminas processed from formulations containing β‐spodumene, Li2O·Al2O3·4SiO2. Assessments were made using density data, SEM imaging, XRD analysis, Vickers indentation testing, and Young's modulus measurements. The results indicate that using β‐spodumene to develop LPS alumina ceramics provides materials containing a mix of crystalline β‐spodumene and glassy material which are comparable in mechanical performance to currently available commercial debased alumina ceramics.
Development of Fine Scale PZT Ceramic Fiber/Polymer Shell Composite Transducers
Authors: Livneh Shai S. , Janas Victor F. , Safari Ahmad
Published: July 2005

The relic processing technique was used to fabricate fine‐scale piezoelectric lead zirconate titanate (PZT) ceramic fiber/polymer shell composites. In this technique sacrificial activated carbon fabrics were soaked in a PZT precursor solution, dried, and heat treated to form piezoceramic relics. Relics were embedded with polymer, which was allowed to cure, and the resulting composites were polished, electroded, and poled. Different facets of the composite‐ forming process were examined: structural modifications, soaking, firing, and polymer impregnation. The physical and electromechanical properties of the unique resulting composite were evaluated. Optimized PZT shell composites with 39 vol% ceramic exhibited the following property values:Kε200, tan δε5.5%,d33ε290 pC/N,dhε100 pC/N,dhghε6000 ± 10‐15m2N,kpε0.19, andktε0.28.
In Situ Annealing Studies of Sol‐Gel Ferroelectric Thin Films by Spectroscopic Ellipsometry
Authors: Trolier‐McKinstry Susan , Chen Jiayu , Vedam Kuppuswami , Newnham Robert E.
Published: July 2005

Spectroscopic ellipsometry was utilized to follow in situ the annealing of sol‐gel Pb(Zr,Ti)O3 films on sapphire and platinum‐coated silicon substrates. Low‐temperature processes, such as pyrolysis of organics and film densification, could be identified readily. Crystallization of the perovskite phase was initiated between 500° and 600deg;C for the film on sapphire. This was coincident with the roughening of the film surface. Identification of higher‐temperature processes in the film on platinum‐coated silicon was complicated by temperature‐dependent changes in the substrate. In situ annealing studies on the substrate alone confirmed that, for the lengthy annealing profiles utilized in these experiments, substantial and irreversible changes in the effective substrate dielectric function occurred at temperatures >550deg;C. In addition, the role of extended, high‐temperature annealing on the optical frequency dielectric properties of the films was investigated.
High‐Temperature Behavior of Indent and Creep‐Nucleated Cracks in Vitreous‐Bonded Alumina
Authors: Murphy Dawn , Jakus Karl , Ritter John E. , Hill Barry C.
Published: July 2005

Crack behavior was studied at elevated temperatures in a commercial vitreous‐bonded alumina for two types of cracks: one introduced by indentation at room temperature and the other by the creep process. Indentation cracks with relatively small initial size grew progressively longer during creep before they became blunt and arrested; however, they continued to widen throughout the creep process. Larger indentation cracks under high stress condition continued to grow until failure. The evolution of creep‐nucleated cracks was so fast that they were observed only in their arrested state. Once observed, their length remained essentially constant, but they did grow in width. The crack‐opening displacement rates of both types of cracks were linearly related to the creep rate as predicted by fracture mechanics for stationary cracks. All but the specimens with the largest indentation crack exhibited flaw tolerance in that they failed by the coalescence of creep‐nucleated cracks instead of the growth of a single crack. The results illustrate the crack behavior in the brittle‐to‐ductile transition regime for ceramics that deform by grain boundary sliding.
29Si and 27Al MASNMR Study of Stratlingite
Authors: Kwan Stephen , LaRosa Judith , Grutzeck Michael W.
Published: July 2005

Strätlingite (2CaO·Al2O3·SiO2·8H2O) is a complex calcium aluminosilicate hydrate commonly associated with the hydration of slag‐containing cements or other cements enriched in alumina. Strätlingite can coexist with the hydrogarnet solid solution [hydrogarnet (3CaO·Al2O3·6H2O)‐katoite (3CaO·Al2O3·SiO2·4H2O)] and calcium silicate hydrate (C‐S‐H). Since Strätlingite is present in many blended cements, the knowledge of strätlingite's characteristic silicate anion structure and how aluminum is accommodated by the structure is important. Phase pure Strätlingite samples have been synthesized from oxides in the presence of excess water and from metakaolinite, calcium aluminate cement, CaO, NaOH, and water. The samples were characterized using X‐ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA) and then further examined using 29Si, with and without cross‐polarization (CP), and 27Al solid‐state magic angle nuclear magnetic resonance spectroscopy (MASNMR). For the most part, NMR data for these strätlingites corroborate structural information available in the literature. The aluminum atoms are both tetrahedrally and octahedrally coordinated, and the silicon atoms exist predominantly as Q2, Q2(1Al), and Q2(2Al) species. The presence of alkali affects the structure of strätlingite in subtle ways, significantly reducing the AlIV/A1VI ratio.
Epitaxial Aluminum‐Doped Zinc Oxide Thin Films on Sapphire: II, Defect Equilibria and Electrical Properties
Authors: Srikant V , Sergo Valter , Clarke David R.
Published: July 2005

The electrical transport properties of epitaxial ZnO films grown on different orientations of sapphire substrates have been measured as a function of partial pressure of oxygen. After equilibration, the carrier concentration is found to change from a p‐1/4O2 to a p‐3/8O2 dependence with increasing oxygen partial pressure. The partial pressure dependence is shown to be consistent with zinc vacancies being the rate‐controlling diffusive species. In addition, the carrier concentration in ZnO films grown on A‐, C‐, and M‐plane sapphire are the same but that of R‐plane sapphire is systematically lower. Electron Hall mobility measurements as a function of carrier concentration for all the substrate orientations exhibit a transition from “single‐crystal” behavior at high carrier concentrations to “polycrystalline” behavior at low carrier concentrations. This behavior is attributed to the effective height of potential barriers formed at the low‐angle grain boundaries in the epitaxial ZnO films. The trap density at the grain boundaries is deduced to be 7 × 1012/cm2. The electron mobility, at constant carrier concentration, varies with the substrate orientation on which the ZnO films were grown. The difference is attributed to the difference in dislocation density in the films produced as a result of lattice mismatch with the different sapphire orientations.
Molten Glass Corrosion Resistance of Immersed Combustion‐Heating Tube Materials in E‐Glass
Authors: Sundaram S. Kamakshi , Hsu Jen‐Yen , Speyer Robert F.
Published: July 2005

The corrosion resistance of molybdenum, molybdenum disilicide, and a SiC(p)/Al2O3 composite to molten E‐glass at 1550deg;C was studied. Mo showed no tendency to oxidize as it was immersed in soda‐lime silicate glass in a parallel study. MoSi2 was corroded by soluble molecular oxygen, leaving a Mo5Si3 interface behind. The SiC(p)/Al2O3 composite was corroded at a more rapid rate wherein the SiC component was oxidized to form amorphous silica and CO bubbles. Based on these results, the activity of soluble molecular oxygen in E‐glass was determined to be in the range of 2.4 × 10‐14 to 2.0 × 10‐8.
Role of Defects in the Ferroelectric Relaxor Lead Scandium Tantalate
Authors: Chu Fan , Reaney Ian M. , Setter Nava
Published: July 2005

Unlike Pb(Mg1/3Nb2/3)O3 and similar ferroelectric relaxors which never truly become ferroelectric at zero‐field, disordered Pb(Sc1/2Ta1/2)O3 (PST) is a relaxor that spontaneously transforms into a ferroelectric phase. The control of the degree of order of the B‐site cations in PST by appropriate heat treatment has been often used to demonstrate the influence of chemical disorder on the dielectric properties of ferroelectrics. Here it is shown that, in PST, disorder itself is not sufficient to prevent a macroscopic ferroelectric transition, and that disordered stoichiometric PST exhibits a strong dielectric relaxation, but upon cooling it spontaneously becomes a macroscopic ferroelectric. Lead deficiency in disordered Pb(SC1/2Ta1/2)O3 prevents this spontaneous ferroelectric transformation, and the material shows more usual relaxor properties.
Processing Effects on Microstructure and Superconducting Properties of Sintered YBa2Cu3O6+x
Authors: Hill Michael D. , Blendell John E. , Vaudin Mark D. , Chiang C. K.
Published: July 2005

The relationships between the microstructure of sintered YBa2Cu3O6+x superconductors and processing variables (sintering time, sintering temperature, and oxygen partial pressure) were examined. Large‐grained microstructures were obtained in 100 kPa oxygen sintering atmospheres, while fine‐grained microstructures were obtained in 2 kPa oxygen. The formation of liquid phases below the peritectic decomposition temperature of YBa2Cu3O6+x was found to have an effect on both the microstructure (as observed by optical and transmission electron microscopy) and the transport critical current density (Jc). The critical current density was found to be highest for sintering below the lowest invariant point, which is a function of the oxygen partial pressure. However, over the range of conditions examined here, there does not appear to be any correlation between microstructural features, such as average grain size and aspect ratio, and the transport Jc.
Application of Magnetic Susceptibility to Study Low Iron Substitution in Tricalcium Aluminate
Authors: Ahmed Mohamed A. , Hassaan Mohamed Y. , Mahrous Salah , Mikhail Habib , El‐Desoky Mohamed M.
Published: July 2005

The magnetic susceptibilities of the tricalcium aluminate prepared containing 0.5, 1, or 2 wt% FeC2O4 or Fe2O3 before firing were measured at different temperatures and different magnetic field intensities. The Curie temperature of each compound is determined from the magnetic susceptibility temperature curves. The values of the effective magnetic moments were calculated from the experimental data for the different compounds. The variations in the magnetic properties and the magnetic constants with the type and concentration of iron added to C3A confirm that the magnetic susceptibility measurements could be considered a good tool to estimate the solubility limit of iron in different forms in C3A. Our data confirm also the previous data of IR measurements for such samples at low iron concentrations.
Effect of Carbon and Boron on the High‐Temperature Oxidation of Silicon Carbide
Authors: Fergus Jeffrey W. , Worrell Wayne L.
Published: July 2005

Silicon carbide has good oxidation resistance, due to the formation of a protective silica layer. Although amorphous silica is an excellent oxygen barrier, it is very sensitive to impurity elements, which affect its viscosity, oxygen diffusivity, and crystallization kinetics. This paper compares the oxidation rates of CVD SiC, sintered α‐SiC, and CVD SiC‐ coated graphite in 1 atm oxygen at 1500deg;C to determine the effects of small additions of boron and carbon. The formation of bubbles in the silica scale formed on sintered α‐SiC in oxygen between 1230° and 1550deg;C is also discussed.
Tensile Strength of SiC Fibers
Authors: Zok Frank W. , Chen Xiuyen , Weber Christian H.
Published: July 2005

An experimental investigation has been conducted on the effects of gauge length on the tensile strength of SiC fibers. The results show that the overall strength distribution cannot be described solely in terms of the two‐parameter Weibull function. The overall distribution is found to be consistent with two concurrent flaw populations, one of them being characteristic of the pristine fibers, and the other characteristic of the additional flaws introduced into the fiber during processing of the composite.
High‐Temperature Microwave Complex Permittivity of YBa2Cu3O7‐δ Superconductors
Authors: Aral Masayuki , Dinner Jon G. P. , Cross Tom E.
Published: July 2005

The high‐temperature microwave complex permittivity of YBa2Cu3O7‐δ superconductors was characterized using a coaxial probe system designed and built in our laboratory. An anomalous difference in complex permittivity between a green sample and a sintered sample was analyzed with respect to oxygen content being a possible key factor to affect the dielectric properties.
Thermal Expansion and Glass Transition Temperatures of Y‐Mg‐Si‐Al‐O‐N Glasses
Authors: Peterson Irene M. , Tien Tseng‐Ying
Published: July 2005

The thermal expansion coefficients and glass transition temperatures of Y‐Mg‐Si‐Al‐O‐N glasses were measured using dilatometry. The thermal expansion coefficients of these glasses could be calculated on the basis of composition, using experimentally determined thermal expansion prefactors

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Effects of Melt Chemistry and Platinum Doping in the Refinement of Y2 Ba1Cu1Oy Particles for the System Y‐Ba‐Cu‐O
Authors: Lee Hee‐Gyoun , Park Jong‐Hyun , Song Jin‐Tae
Published: July 2005

Effects of melt chemistry and platinum doping in the refinement of Y2Ba1Cu1Oy(211) particles were investigated for the system Y‐Ba‐Cu‐O. The shapes of the 211 particles in the present study changed from needlelike in a (CuO + BaCuO) melt to nearly spherical in a CuO melt. Platinum plays a small role in the growth inhibition of 211 particles. Barium atoms clearly had no effect on the role of Pt in refining 211 particles, and Pt was found to affect the refinement as an elementary atom rather than as part of a Pt‐related compound. The main role of Pt in the refinement process for the system Y‐Ba‐Cu‐O seems to lie in changing the interfacial energy of the 211 particles.
Growth of Hollow Cr3C2 Polycrystals with Cr2O3
Authors: Hashimoto Shinobu , Yamaguchi Akira
Published: July 2005

Hollow Cr3C2 polycrystals with Cr2O3 were grown by heating a powder compact of MgO and Cr2O3 in carbon powder at 1600° to 1700deg;C. They were classified into two types: a stick and a thick plate. After being heated at 1700deg;C for 2 h, the polycrystals grown as the thick‐plate type were several micrometers to about 3 mm in length, whereas the polycrystals grown as the stick type were several micrometers to about 1 mm in length. They were considered to be grown by a vapor‐solid mechanism.