bluuebunny/crossref_metadata_2025 huggingface dataset:
Nitridation of Zirconia
Authors: Lerch Martin
Published: July 2010

ZrO2 can be nitrided partially by nitrogen at temperatures >1400°C. It is possible to describe all the synthesized phases with the general formula ZrO2‐2χN4χ/3 (system ZrO2‐Zr3N4). Parameters–such as nitridation time, temperature, nitrogen pressure, and particle size–have a strong effect on the amount of incorporated nitrogen. Variation of these parameters allows the synthesis of Zr‐O‐N ceramics within a wide range of possible compositions. ZrO2‐2χcN4χ/3 phases synthesized by reaction of ZrO2 with nitrogen show ordered anion vacancies (β‐type structures). β‐type phases are non‐transformable under mechanical stress at ambient temperature. Nitrogen‐containing ZrO2 shows very poor oxidation resistance. At temperatures >600°C, stability is found only in the presence of an oxygen getter.
Influence of Interfacial Sliding Stress on Fatigue Behavior of Oxidized Nicalon/Calcium Aluminosilicate Composites
Authors: Thomas Warren A. , Sanchez J. M.
Published: July 2010

The influence of the interfacial sliding stress on the steady‐state tensile fatigue behavior of a Nicalon/calcium aluminosilicate composite has been characterized experimentally. Characterization occurred in an experiment where the microstructure and properties of the carbon interface were altered by oxidation at increasingly greater temperatures. After each oxidation step, the steady‐state energy dissipation was quantified. Using a model, changes in the interfacial sliding stress were determined after each oxidation step. The results revealed a minimum in the sliding stress after oxidation in the temperature range of 100°‐300°C that corresponded to a maximum in the amount of energy dissipated by frictional sliding.
Raman Study of the Relationship between Room‐Temperature Tetragonality and the Curie Point of Barium Titanate
Authors: Begg Bruce D. , Finnie Kim S. , Vance Eric R.
Published: July 2010

Variable‐temperature Raman spectroscopy showed that, in progressively finer BaTiO3 powders, the Curie point increased as the room temperature tetragonality decreased. The influence of crystallite size distribution on the range of tetragonalities present in a powder was clearly evident in both phase transitions, as observed by Raman spectroscopy and room‐temperature X‐ray diffraction patterns. Titanium K‐edge X‐ray absorption spectroscopy could not distinguish between the cubic and tetragonal structures of BaTiO3, at 300°C and room temperature, respectively.
Microstructural Stability and Creep Behavior of Si‐C‐O (Nicalon) Fibers in Carbon Monoxide and Argon Environments
Authors: Bodet Raphael , Lamon Jacques , Jia Nanying , Tressler Richard E.
Published: July 2010

Constant‐load creep‐rupture tests were performed on single Si‐C‐O fibers (Nicalon). Test environments included pure carbon monoxide (CO), pure argon gas, and a mixture of CO and argon gas with a CO partial pressure of 40 kPa. Fibers were tested at temperatures of 1200°‐1400°C and at nominal applied stresses of 0.15–0.7 GPa. The as‐received and crept specimens were characterized by means of scanning electron microscopy, transmission electron microscopy, X‐ray photoemission spectroscopy, electron‐probe microanalysis, Auger electron spectroscopy, and thermo‐gravimetric analysis. In pure argon, the microstructure of the Nicalon fiber was unstable, which was attributed to the decomposition of the silicon oxycarbide phase, which resulted in CO and silicon monoxide gas evolution and silicon carbide grain growth. Fiber shrinkage was observed at temperatures <1300°C at low applied stresses. At high stresses, fibers exhibited only primary creep. In the CO/ argon‐gas environment, very limited grain growth and a smooth carbon coating were observed at the fiber surface at temperatures <1350°C. At all applied stresses, fibers exhibited steady‐state creep whose rates, strains, and times to failure were higher than those observed in argon. The apparent activation energy for creep of Nicalon fibers in the CO/argon‐gas environment was 435 kj/mol. At temperatures >1350°C in the CO/argon‐gas environment, however, the fiber behaved as in pure argon. Tests in pure CO only resulted in lower strains to failure and thicker carbon layers on the fiber surface. A rheological model based on the viscous flow of a concentrated suspension was proposed to describe the fiber deformation. The continuously decreasing creep rate in argon was suggested to be related to the continuous increase of the total solid volume fraction, which affects the fiber viscosity. On the other hand, the steady‐state creep of Nicalon with a stable microstructure in the CO/ argon‐gas environment was characterized by a Newtonian‐type viscous flow, which supports the predictions of the model.
Electron‐Beam‐Induced Loop Formation on Dislocations in Yttria‐Fully‐Stabilized Zirconia
Authors: Gómez‐García Diego , Martínez‐Fernández Julián , Domínguez‐Rodriguez Arturo , Westmacott Kenneth H.
Published: July 2010

The nature of the strain lobes and loops that form on edge dislocations in yttria‐stabilized zirconia during exposure in an electron microscope has been investigated. By changing the operating conditions, such as acceleration voltage, cycling the beam intensity, heating or cooling the specimen prior to observation, or heat treatment prior to the deformation, it has been shown that the effects result from beam heating. During specimen heating ZrN precipitates which have a large misfit with the ZrO2‐Y2O3 matrix form in the compressed regions of the dislocation core.
Microwave Dielectric Properties of CaTiO3‐Ca(Al1/2Ta1/2)O3 Ceramics
Authors: Kucheiko Sergey , Choi Ji‐Won , Kim Hyun‐Jai , Jung Hyung‐Jin
Published: July 2010

The microwave dielectric properties of CaTi1‐χ(Al1/2Ta1/2)cHO3 solid solutions (0.3 ≤χ≤ 0.5) have been investigated. The ceramic samples had perovskite structures similar to CaTiO3. The partial substitution of Ti4+ by a coupled Al3+/Tas+ permitted improvement of the quality factor Q. The dielectric constant (τr) and temperature coefficient of resonant frequency (τr) decrease rapidly with an increase of χ. A new high‐quality microwave dielectric material was found at χ= 0.46 with σr= 46.5, Qf= 27300 GHz, and πf= 0 ppm/°C. The relationship between microstructures and dielectric properties is presented.
Phase Equilibria in the Na2O‐Cs2O‐SiO2 System
Authors: Bennour Fatima , Rogez Jacques , Mathieu Jean Claude
Published: July 2010

The Na2O‐Cs2O‐SiO2 system has been investigated by means of a new differential thermal analysis apparatus. Two compounds have been observed for the first time in the metasilicate and disilicate joins. The CsNaSi2O5 disilicate melts congruently at 1217 K and the peritectic fusion of the CsNaSiO3 metasilicate occurs at 1120 K.
Nanoscale Coating of Silicon and Manganese on Ferrimagnetic Yttrium Iron Garnets
Authors: Cho Yong S. , Amarakoon Vasantha R. W.
Published: July 2010

A uniform microstructure of Gd‐substituted yttrium iron garnet (Y2Gd1Fe5O12) was obtained with additives of Si and Mn using a sol‐gel coating process. Tetraethyl orthosilicate (TEOS) and manganese acetate were used as Si and Mn sources for the sol‐gel coating procedure, respectively. TEM/EDS analysis confirmed the presence of a relatively uniform nanoscale coating of Si and Mn around each particle. High density and uniform microstructure were obtained after sintering at 1400°C in O2 atmosphere. The density and grain size of the specimens depended on Mn content. The results were compared with materials fabricated without additives incorporated by the sol‐gel coating procedure.
Isothermal Oxidation Behavior of Mo‐Si‐B Intermetallics at 1450°C
Authors: Meyer Mitchell K. , Akinc Mufit
Published: July 2010

Five Mo‐Si‐B multiphase intermetallic compositions were synthesized and oxidized isothermally at 1450°C in flowing air. Average mass change rates were strongly dependent on sample composition, particularly boron content. An Mo5Si3 matrix material containing 1.6 wt% boron exhibited parabolic mass gain with a rate of 5.3 × 10‐4 mg2(cm4.h), while a similar material with 0.14 wt% boron oxidized rapidly in a linear manner at a rate of ‐3.3 mg/(cm2.h). Oxidation rates of the Mo‐Si‐B intermetallics were compared to that of MoSi2 oxidized at 1450°C under identical conditions.
New Processing Technique for Hydroxyapatite Ceramics by the Hydrothermal Hot‐Pressing Method
Authors: Hosoi Kazuyuki , Hashida Toshiyuki , Takahashi Hideaki , Yamasaki Nakamichi , Korenaga Takashi
Published: July 2010

A new processing technique for preparing hyroxyapatite (HAp) ceramics has been developed using the hydrothermal hot‐pressing (HHP) method. Powder mixed dibasic calcium phosphate dihydrate and calcium hydroxide mixed with a Ca/P ratio of 1.67 was treated at 150°C and 40 MPa. The HHP method with the selection of the powder enabled the HAp to be solidified at the low temperature. The resulting HAp ceramics had a tensile strength of approximately 10 MPa. Furthermore, the HAp ceramics possessed a lamellar microstructure and high porosity.
Stress Rupture in Tension and Flexure of a SiC‐Whisker‐Reinforced Silicon Nitride Composite at Elevated Temperatures
Authors: Zhu Shijie , Mizuno Mineo , Nagano Yasuo , Kagawa Yutaka , Watanabe Makoto
Published: July 2010

Stress rupture of a 20 vol% SiC whisker‐reinforced Si3N4 composite processed by gas pressure sintering was investigated by both tension and flexure methods. The stress exponents for the stress rupture decrease with increasing temperature. The fracture surfaces of both tensile and flexural stress rupture at 1000°C consist of mirror, mist, and hackle regions. The size of the mirror region increases with decreasing stress. Crack propagation is a mixture of intergranular and transgranular modes at 1000°C. Both tensile and flexural fracture surfaces under constant stress at 1200°C were characterized by a rough zone and a mirror zone; the size of the rough zone increased with decreasing stress. Creep crack growth occurred at 1200°C, which is a process of cavity nucleation, growth, and interlinkage in front of a crack. The transition of fracture mechanisms with temperature is discussed.
In situ Profiles of Oxygen Diffusion in SrTiO3: Bulk Behavior and Boundary Effects
Authors: Denk Ingrid , Noll Frank , Maier Joachim
Published: July 2010

Diffusion profiles have been recorded in situ and evaluated using an optical technique. In this way, bulk diffusion coefficients have been reliably and quantitatively measured. It is shown that the values agree with calculations without using adjustable parameters if the coupling of the diffusing species to internal redox changes of the dopants is accounted for. Measurements on single crystals and on bicrystals with and without crack formation provide worthwhile information on the influence of free relaxed surfaces, freshly produced (crack) surfaces, and grain boundaries on the surface reaction rate and diffusional process. The inward diffusion of oxygen via crack surfaces is characterized by enhanced diffusion coefficients.
Shear Damage Mechanisms in a Woven, Nicalon‐Reinforced Ceramic‐Matrix Composite
Authors: Keith William P. , Kedward Keith T.
Published: July 2010

The shear response of a Nicalon‐reinforced ceramic‐matrix composite was investigated using Iosipescu tests. Damage was characterized by X‐ray, optical, and SEM techniques. The large inelastic strains which were observed were attributed to rigid body sliding of longitudinal blocks of material. These blocks are created by the development and extension of intralaminar cracks and ply delaminations. This research reveals that the debonding and sliding characteristics of the fiber—matrix interface control the shear strength, strain softening, and cyclic degradation of the material.
Influence of Porosity on Friction and Wear of Tetragonal Zirconia Polycrystal
Authors: He Yingjie , Winnubst Louis , Burggraaf Anthonie J. , Verweij Henk , Van der Varst Paul G. Th. , de With Bert
Published: July 2010

Sliding wear properties of ultra‐fine‐grained (180 nm) yttria‐doped tetragonal zirconia (Y‐TZP) ceramics were examined with porosities from 1.5% to 7%. On a pin‐on‐plate tribometer under dry‐N2 conditions, e.g., wear rates of the material increase by a factor of 5 by increasing porosity with a factor of 5 (from 1.5 to 7.0 vol%). In all cases no (irreversible) phase transformation to monoclinic zirconia took place during wear tests. The results for the relatively dense nanostructured materials showed significant evidence of plastic deformation and less microcrack formation. The morphology of the wear tracks in these ceramics indicate that the degree and amount of microcracks on the contact surface increased with porosity. A change in wear mechanism is observed.
Deposition of Oxide Coatings on Fiber Cloths by Electrostatic Attraction
Authors: Cinibulk Michael K.
Published: July 2010

Electrostatic attraction has been used to deposit alumina and mullite coatings onto woven cloths of Nicalon fiber. This approach produced uniformly coated cloths while minimizing the dependence on the wetting relationship between the fiber and the coating precursor. The use of low sol concentrations (#1 g/L) facilitated the removal of excess sol from the cloth. Water was used to further displace excess aqueous sol from the cloth to give minimal fiberfiber bridging while maintaining uniform fiber coatings. The use of a polyelectrolyte enabled multiple deposition of coatings onto the fibers in the cloth. Multiple coating steps resulted in completely coated fiber surfaces; coverage was limited to 50% with only a single coating step. Vacuum infiltration was necessary to remove entrapped air from the cloths during coating. A discussion of wetting and infiltration of fiber cloths has been presented, which highlights issues that are critical for obtaining uniformly coated fibers and minimal fiber bridging in a woven‐fiber cloth or preform.
Strain Tolerant Porous Silicon Nitride
Authors: Shigegaki Yasuhiro , Brito Manuel E. , Hirao Kiyoshi , Toriyama Motohiro , Kanzaki Shuzo
Published: July 2010

An approach to material strain tolerance, which basically makes it possible to lower the elastic modulus while retaining strength, was experimentally confirmed using as an example a porous silicon nitride composed of oriented anisotropic grains and pores. The porous structure consisting of tightly tangled rodlike grains and anisotropic pores was obtained by using β‐Si3N4 whiskers. This material exhibited a low Youngs modulus while retaining a relatively high fracture stress, even though it contained 14.4% porosity. Consequently, the strain to failure of silicon nitride was appreciably increased.
Damage Mechanisms around Hardness Indentations in Ti3SiC2
Authors: El‐Raghy Tamer , Zavaliangos Antonios , Barsoum Michel W. , Kalidindi Surya R.
Published: July 2010

Microstructural observations of damage around indentations in Ti3SiC2 are presented. The Vickers hardness decreased with increasing load and asymptotically approached 4 GPa at the highest loads. No indentation cracks were observed even at loads as high as 300 N. Preliminary strength versus indentation plots indicate that, at least for the large‐grained material (is approximately100 μm) studied here, Ti3SiC2 is a damage‐tolerant material able to contain the extent of microdamage to a small area around the indent. The following multiple energy‐absorbing mechanisms have been identified from scanning electron micrographs of areas in the vicinity of the indentation: diffuse microcracking, delamination, crack deflection, grain push‐out, grain pull‐out, and the buckling of individual grains.
Low‐Temperature ac Conductivity of Mixed Mobile Ion Germanate Glasses
Authors: Jain Himanshu , Lu Xiangdong
Published: July 2010

The conductivity of alternating current in the xAg2O: (1 ‐ x)Rb2O:4Geo2 glass series has been measured between 5.0 K and room temperature where x is varied from 0.0 to 1.0. The typical low‐temperature conductivity region is observed below 200 K. The temperature and frequency dependence of conductivity in this region can be explained by the thermal excitation of asymmetric double well potential configurations. Further, the classical mixed mobile ion effect is essentially absent, which shows that the effect is associated with the independent movement of the mobile ions.
In Situ Synthesis of TiCp/Ni3Al Composites under High Pressure
Authors: Liu Haozhe , Wang Aimin , Wang Luhong , Ding Bingzhe , Hu Zhuangqi
Published: July 2010

In this paper, TiCp/Ni3Al composites are synthesized in situ at near theoretical density under high‐pressure (1.56.5 GPa), high‐temperature (1073–1473 K) conditions. The grain size of TiC‐reinforced particles is nanometer scale, which influences the Vickers microhardness of the composites. The effect of pressure on the grain size of TiC is discussed.
Influence of Aluminum Titanate Formation on Sintering of Bimodal Size‐Distributed Alumina Powder Mixtures
Authors: Taruta Seiichi , Itou Yousuke , Takusagawa Nobuo , Okada Kiyoshi , otsuka Nozomu
Published: July 2010

The sintering behavior of green compacts, in which coarse alumina particles formed a skeletal structure and fine alumina and/or fine titania particles filled the voids of the skeletal structure, was investigated. Sinterability of the green compacts changed according to the titania content in the fine powder. The titania content of 33 mol% was the most effective for the densification. The volume expansion due to the aluminum titanate formation occurred in the voids of the skeletal structure, and the densification of the skeletal structure progressed more because the grain growth between the fine and coarse alumina particles did not proceed. As the titania content decreased, the densification did not progress more than that of the compact with 33 mol% titania content because the grain growth proceeded more. As the titania content increased, the expansion of the compacts was larger, and large grains were formed by the reaction between the titania and coarse alumina particles. Therefore, densification became difficult.
Influence of Particle Contact on the Estimation of Powder Reaction Kinetics of Binary Mixtures
Authors: Shimizu Akira , Hao Yu‐Jun
Published: July 2010

To develop a quantitative representation of the interparticle reaction rate of binary powder, an investigation of several models has been undertaken, and their fit to experimental data for the Fe2O3V2O5 system has been performed by the present authors, as well as for the Al2O3CuO, Al2O3ZnO, MgOAl2O3, MgOFe2O3, and Fe2O3ZnO systems published previously. A concentric spherical model proposed recently shows a quantitative correlation between the reaction rate and the number of contact points between particles in unidirectional diffusion and counterdiffusion systems. The model is consistent with experimental data for the above systems. It is potentially useful for reaction‐rate analysis of a wide range of powder systems in which particle sizes and the mixing ratio are varied independently. This is an improvement over previous unreacted core analyses such as the Jander and Ginstling–Brounshtein models.
Plasma Spraying of Lanthanum Chromite Films for Solid Oxide Fuel Cell Interconnection Application
Authors: Kuo Lewis J. H. , Vora Shailesh D. , Singhal Subhash C.
Published: July 2010

This paper discusses a novel plasma‐spraying process for depositing dense LaCrO3‐based interconnection for solid oxide fuel cells (SOFCs). Calcium aluminate was mixed with LaCrO3 in a slurry containing PVA binder and spray dried to form free‐flowing agglomerates. These free‐flowing agglomerates were plasma sprayed onto a porous substrate of doped LaMnO3 and then heat‐treated to form a gas‐tight and electrically conducting interconnection. Samples of the plasma‐sprayed interconnection were characterized for morphology, phase constituents, and coefficient of thermal expansion, as well as electrical resistivity and oxygen nonstoichiometry at 1000°C in the PO2 range from 1 to} 1× 10‐16 atm. The calcium aluminate additive was found to facilitate densification of the interconnection, most likely through the formation of low‐temperature melting phase(s) in the system Ca–Cr–Al–O. A SOFC with such a plasma‐sprayed interconnection was fabricated and electrically tested. This cell exhibited good electrical performance, and the interconnection was stable under fuel cell operation conditions.
New Ternary Nitride in the Ti‐Al‐N System
Authors: Lee Hee Dong , Petuskey William T.
Published: July 2010

The ternary compound Ti3Al1−xN2 was found to be stable between} 1523 and 1673 K and tended to be deficient in aluminum where 0.0 × 0.3. X‐ray diffraction indicated that the ternary compound possessed a hexagonal structure with unit‐cell dimensions of a0= 2.990 and c0= 23.3854. The existence of the compound “Ti3Al2N2” that had been reported previously could not be confirmed for any experimental conditions at 1 atm pressure.
Packing of Cylindrical Particles with a Length Distribution
Authors: Zou Rui‐Ping , Lin Xin‐Yu , Yu Ai‐Bing , Wong Patrick
Published: July 2010

The packing of cylindrical particles with log‐normal and modified power‐law length distributions has been experimentally studied. The results indicate that the packing density is heavily dependent on the parameters in the two distributions. However, this dependence cannot be predicted by the direct analogy to that for the packing of spherical particles. It is postulated that the packing of nonspherical particles be governed by two factors: the shape effect and the size effect, which respectively correspond to the unmixing and mixing states of a particle mixture and are quantified from the specific volumes of the two states. Analysis of the results suggests that the shape effect is dominant for the packing of cylindrical particles with a wide length distribution.
Simple Method for Determining Frictional Sliding Resistance and Frictional Energy Dissipation in Layered Ceramics
Authors: Kovar Desiderio , Thouless Michael
Published: July 2010

A method is presented for measuring the frictional sliding resistance between cracked laminae in a layered ceramic. The first step in the test involves using a wedge to completely crack a weak interface along the length of the specimen. The cracked specimen is then loaded in three‐point bending, and the loaddeflection response is monitored. A deviation from linearity is observed when the load is sufficiently high for sliding to occur between the upper and lower halves of the specimen. The load at which this nonlinearity is first observed can be related to the interfacial sliding resistance. A model is then developed to relate the energy absorbed during a loadunload cycle to the frictional sliding resistance. The analysis is verified using a model system made from steel, and a ceramic composite made from silicon nitride and boron nitride.
Elastic Properties and Microcracking Behavior of Particulate Titanium Diboride–Silicon Carbide Composites
Authors: Pan Ming‐Jen , Hoffman Patricia A. , Green David J. , Hellmann John R.
Published: July 2010

The spontaneous microcracking of particulate TiB2–SiC composites is studied as a function of TiB2 volume fraction. The degree of microcracking was examined by measuring elastic properties from room temperature to 1300°C. The results showed that only one composition contains microcracks. All other compositions did not microcrack regardless of TiB2 volume fraction. This was attributed to the difference in the sintering aids. In particular, the Al2O3 sintering aid needed in these compositions had reacted with SiO2 to form an amorphous grain boundary phase that allowed residual stresses to relax by viscous flow at moderate to high temperatures. The existence of this amorphous grain boundary phase was directly observed by transmission electron microscopy.
Thermal Diffusivity/Conductivity of Magnesium Oxide/Silicon Carbide Composites
Authors: Luo Jie , Stevens Ron , Taylor Roy
Published: July 2010

SiC‐particle‐reinforced MgO composites have been fabricated by hot pressing, and the thermal diffusivities of the composites measured in the temperature range 200–1000°C using a laser flash technique. The thermal conductivity of the composites was calculated by multiplying the diffusivity with density and with heat capacity. The Eshelby inclusion model has been examined, and an equation suitable for particulate composites with porosity has been derived using the multiphase Eshelby model. The model also considers the interfacial thermal condition. Good agreement was obtained between the predictions and the experimental results of the thermal conductivity of the composites, even for various levels of porosity in the composites. Crystal defects, observed in the composites, influenced the thermal conductivity, resulting in a deviation from isothermal interfacial condition. This was reflected in the interfacial thermal parameter,β used in the modeling, and the predicted value of β was in the range of 3–10, depending on the thermal conductivity of SiC used for the calculations.
On the Thermodynamic Stability of Amorphous Intergranular Films in Covalent Materials
Authors: Keblinski Pawel , Phillpot Simon R. , Wolf Dieter , Gleiter Herbert
Published: July 2010

The thermodynamic origin, structure, and stability of the thin amorphous films commonly found in grain boundaries in covalent ceramics are investigated by molecular‐dynamics simulation. To focus on the purely thermodynamic aspects, any kinetic effects associated with impurity‐controlled interface chemistry are excluded by investigating pure silicon (described by the Stillinger–Weber three‐body potential). For this single‐component covalent model material, we demonstrate that all high‐energy boundaries exhibit a universal amorphous structure, with a width of }0.25 nm, whereas low‐energy boundaries are crystalline and much sharper. We also demonstrate that introduction of an amorphous film into a crystalline interface lowers the excess energy to a level similar to the energy of two bulk crystalamorphous interfaces. The competition between a narrow crystalline boundary structure and a wider amorphous boundary structure is shown to be governed by the relative excess energies of the atoms in the grain boundaries and in the bulk amorphous phase. These observations suggest that, in principle, amorphous grain‐boundary films do not require impurities for their stabilization and that, as first proposed by Clarke, an equilibrium grain‐boundary phase of uniform thickness can be the result of purely thermodynamic rather than kinetic factors.
Effect of Solvent on Titania Particle Formation and Morphology in Thermal Hydrolysis of TiCl4
Authors: Park Hong Kyu , Kim Do Kyung , Kim Chong Hee
Published: July 2010

Titania powders were synthesized by the thermal hydrolysis of titanium tetrachloride with the yield of above 85% in a mixed solvent of n‐propanol and water. The morphology of the precipitates was controlled by adjusting the volume ratio of n‐propanol to water (RH ratio) of the mixed solvent. Precipitates obtained with an RH ratio of 0 were fine, and highly agglomerated. In contrast, an RH ratio of 3 resulted in precipitates consisting of uniform and discrete particles. According to observations of the zeta potentials of precipitates and the dielectric constants of solvents, the discrete particles obtained with an RH ratio of 3 resulted from the low zeta potential and dielectric constant. The result of Fourier transform infrared (FTIR) spectroscopy showed the chemical interaction of particle surface with the solvent alcohol, which decreased the zeta potential of precipitates with an increase of RH ratio. Adding hydroxypropyl cellulose (HPC) as a steric dispersant made it possible to reduce the size of particles to the submicrometer range. Effects of the solvent on the formation and morphology of the resulting particles were investigated.
Active Electrochemical Dissolution of Molybdenum and Application for Room‐Temperature Synthesis of Crystallized Luminescent Calcium Molybdate Film
Authors: Cho Woo‐Seok , Yashima Masatomo , Kakihana Masato , Kudo Akihiko , Sakata Tadayoshi , Yoshimura Masahiro
Published: July 2010

Crystallized luminescent calcium molybdate (CaMoO4) film has been prepared on a molybdenum substrate in an alkaline solution containing calcium ions by active electrochemical dissolution of molybdenum at room temperature (25°C). The dissolution rate became faster with an increase of pH value. A high concentration of calcium (0.02M) and a high pH value (13) favored the reaction of film formation. The film showed only a single green emission at 536 nm with the excitation of 285 nm at liquid‐nitrogen temperature (‐196°C), strongly suggesting that it consisted of well‐crystallized defect‐free crystals.
The High‐Temperature Proton Conductor Strontium Zirconate: Thermogravimetry of Water Uptake
Authors: Krug Frank , Schober Tilman
Published: July 2010

The water uptake of nominally 5%‐Yb‐doped strontium zirconate (SrZr0.95Yb0.05O3−α) was studied in situ by thermogravimetry at different temperatures and water vapor pressures. The process could be described in terms of an ideal solution behavior, showing a lower effective vacancy concentration than that expected from the nominal dopant content. The solution reaction was found to have ΔS°=−127 J/(mol·K) and ΔH°=−106 kJ/mol.
Melilite Formation in a Samarium‐Stabilized α‐Sialon Ceramic during Postsintering Heat Treatments
Authors: Shen Zhijian , Ashkin Daniel , Babushkin Oleg , Ekstrm Thommy
Published: July 2010

The formation of the melilite solid solution phase (M'), Sm2Si3−xAlxO3+xN4−x, in an α‐sialon sample of overall composition Sm0.6Si9.28Al2.69O1.36N14.76, was studied as a function of time in the temperature interval 1375–1525°C. The alpha‐sialon ceramic contained only minor amounts of the 21R sialon polytype and some residual grain‐boundary glass before heat treatment. In situ studies by high‐temperature X‐ray diffraction were combined with postsintering heat treatment followed by quenching. The M'‐phase was found to be formed by two different mechanisms: either crystallization of the residual grain‐boundary liquid or a direct decomposition of the α‐sialon phase. The liquid crystallized during the first 10–15 min of heat treatment, yielding a rapid M'‐phase formation, and further formation of M'‐phase continued at a much slower rate, related to the decomposition of α‐sialon.
High‐Temperature Environmental Stability of the Compounds in the Al2O3–Y2O3 System
Authors: Mah Tai‐Il , Keller Kristin A. , Sambasivan Sankar , Kerans Ronald J.
Published: July 2010

Heat treatments in several environments were performed on a series of compounds in the Al2O3 and Y2O3 system: Al2O3Y3Al5O12 eutectic, Y3Al5O12, YAlO3, Y4Al2O9, and Y2O3. The yttrium aluminates were found to be stable at high temperatures under vacuum and in air. However, when they were heat‐treated under vacuum in proximity to SiC, degradation was observed. This was found to be primarily a result of carbothermal reduction. In a similarly reducing environment without Si, the yttrium aluminates, and Al2O3 and Y2O3, all exhibited degradation by carbothermal reduction. Based upon the experimental results, a degradation mechanism for yttrium aluminates was proposed.
Synthesis of Nickel Sulfide Powders by Thioacetamide in the Presence of Urea
Authors: Grau Jason , Akinc Mufit
Published: July 2010

Additions of urea were found to increase the yield of nickel sulfide formation from acidic solutions of thioacetamide. Two precipitation mechanisms were identified: hydrolysis and direct reaction between nickel and thioacetamide. Hydrolysis‐controlled precipitation is evident with low initial pH. The direct reaction is dominant at high initial pH. Nucleation proceeds by a direct reaction between nickel and thioacetamide. The role of urea in precipitation of nickel was found to be twofold. Urea increases the rate of thioacetamide decomposition, thus increasing the concentration of H2S form. Secondly, decomposition increases the pH of the solution, which in turn increases the relative concentration of S= ions. Agglomeration of particles was more evident in the powders obtained in the presence of urea.
Mass Spectrometric Identification of Si–O–H(g) Species from the Reaction of Silica with Water Vapor at Atmospheric Pressure
Authors: Opila Elizabeth J. , Fox Dennis S. , Jacobson Nathan S.
Published: July 2010

A high‐pressure sampling mass spectrometer was used to detect the volatile species formed from SiO2 at temperatures between 1200° and 1400°C in a flowing water vapor/oxygen gas mixture at 1 bar total pressure. The primary vapor species identified was Si(OH)4. The fragment ion Si(OH)3+was observed in quantities 3 to 5 times larger than the parent ion Si(OH)4+. The Si(OH)3+ intensity was found to have a small temperature dependence and to increase with the water vapor partial pressure as expected. In addition, SiO(OH)+, believed to be a fragment of SiO(OH)2, was observed. These mass spectral results were compared to the behavior of silicon halides.
Effect of Yttrium and Lanthanum on the Tensile Creep Behavior of Aluminum Oxide
Authors: Cho Junghyun , Harmer Martin P. , Chan Helen M. , Rickman Jeffrey M. , Thompson A. Mark
Published: July 2010

The tensile creep behavior of two rare‐earth dopant systems, lanthanum‐ and yttrium‐doped alumina, are compared and contrasted in order to better understand the role of oversized, isovalent cation dopants in determining creep behavior. It was found that, despite some microstructural differences, these systems displayed qualitatively a similar improvement in creep resistance, supporting the hypothesis that creep is strongly influenced by segregation. Differences in primary creep behavior and activation energy for steady‐state creep were, however, observed for these systems. Given these results, it is expected that creep behavior can be further optimized by adjusting the dopant level and by controlling the microstructure.
Low Thermal Conductivity in Garnets
Authors: Padture Nitin P. , Klemens Paul G.
Published: July 2010

The thermal conductivity of dense, polycrystalline garnet ceramics with compositions of Y3AlxFe(5−x)O12(x = 0.0, 0.7, 1.4, and 5.0) was measured in the temperature range 23° to 1000°C. The high‐temperature thermal conductivity of some of these garnets was found to be as low as 2.4 W·m‐1K‐1. The effects of temperature and composition on the observed thermal conductivity are discussed with reference to established theories of thermal conduction. The potential use of yttrium aluminum garnet or YAG (Y3Al5O12), in particular, for a specific application of advanced thermal barrier coatings (TBCs) with improved durability is considered.
Vacuum Ultraviolet Spectra of Silver in a Borosilicate Glass
Authors: Yata Kunio , Yamaguchi Takashi
Published: July 2010

Vacuum ultraviolet absorption spectra of silver dissolved in 60 mol% B2O3‐40 mol% SiO2 glass in oxygen, nitrogen, and oxygen–nitrogen atmospheres at 1000°, 1100°, and 1200°C were measured. Strong absorption which may be attributed to Ag+‐complex was observed around 5.5 and 6.5 eV. It is suggested that an Ag+‐complex/Ag0 redox pair exists in the glass and that this pair shows O‐type redox behavior.
Hertzian Contact Damage in Porous Alumina Ceramics
Authors: Latella Bruno A. , OConnor Brian H. , Padture Nitin P. , Lawn Brian R.
Published: July 2010

A study has been made of Hertzian contact damage in porous and dense liquid‐phase‐sintered aluminas. Indentation stressstrain curves show increasing nonlinearity as the materials become more porous, illustrating an increasing component of “quasi‐plasticity” in the contact damage. Observations of the surface and subsurface damage patterns using a bonded‐interface sectioning technique reveal a transition in the Hertzian damage process, from classical tension‐driven cone cracks in the high‐density material, to distributed shear‐ and compression‐driven subsurface damage and deformation in the porous materials. Strength tests on specimens subjected to cyclic indentations reveal a substantially higher susceptibility to fatigue in the most porous structure.
Chemical Durability of Lead‐Oxide‐Based, Thick‐Film Binder Glasses
Authors: Mattox Douglas M. , Robinson Joshua H.
Published: July 2010

Lead‐oxide‐bearing glasses are incompatible with aluminum nitride metallizations, and federal legislation is recommending their replacement in thick‐film electronics and labeling. To evaluate alternatives, the benchmark chemical durabilities of the lead borosilicate and lead aluminate thick‐film binder glasses have been determined. Aluminum oxide (Al2O3) benefits water durability moderately, acid durability substantially, and basic durability indistinguishably. The rate of attack in water is approximately two orders of magnitude greater than for soda–lime glass. The thermal contractions of the glasses are compatible. An apparent, spontaneous phase separation in the Al2O3‐free glass is suppressed by Al2O3 that is included as a batch component.
Hopping and Ionic Conduction in Tin Oxide‐Based Thick‐Film Resistor Compositions
Authors: Rahman K. M. Anisur , Schneider Susan C. , Seitz Martin A.
Published: July 2010

Conduction mechanisms in tin oxide‐based thick‐film resistors have been investigated using impedance spectroscopic measurements. The sheet resistance, obtained by analyzing these impedance spectra, exhibits two regions of temperature dependence. The behavior in region I (room temperature to } 200°C) can be explained satisfactorily in terms of variable‐range hopping conduction and in region II (200° to }350C) by a diffusion model. It is assumed that ionic tin dissolved in glass serves as the hopping sites in region I. At higher temperatures, these tin ions may participate in an ion‐exchange‐type diffusion that results in region II behavior.
Polyhedral Arrangements in Lanthanum Aluminoborate Glasses
Authors: Brow Richard K. , Tallant David R. , Turner Gary L.
Published: July 2010

We have used magic‐angle spinning nuclear magnetic resonance (MAS NMR) and Raman spectroscopy to examine the polyhedral arrangements in ternary lanthanum aluminoborate glasses. We have characterized two glass‐forming series: xAl2O3·(1−x)LaB3O6 and 0.25La2O3·yAl2O3(1−y)‐B2O3. 11B MAS NMR reveals a decrease in the fraction of four‐coordinated boron atoms with increases in the Al2O3 content in both series. 27Al MAS NMR has detected four‐, five‐ and six‐coordinated aluminum atoms in complex aluminoborate networks similar to those reported elsewhere for alkaline‐earth aluminoborate glasses. Raman spectroscopy reveals a variety of borate and aluminoborate moieties, including isolated groups as well as methaborate chains and rings. These results indicate that the La3+ ion acts as a modifier to the aluminoborate network.
Pressureless Sintering of Si3N4 Ceramic Using AlN and Rare‐Earth Oxides
Authors: Huang Zhen‐Kun , Rosenflanz Anatoly , Chen I‐Wei
Published: July 2010

Using intermediate, liquid‐forming compositions in the (Y,La)2O3‐AlN system as additives, fully dense Si3N4 ceramics with high strength at high temperature have been obtained by pressureless sintering. The ceramics contain rod‐shaped β‐Si3N4 with M′ or K′ solid solutions as grain‐boundary phases. The strength of these ceramics is 1150 MPa at 1200°C, and the room‐temperature toughness is maintained at }7 MPa·m1/2. Phase relations that are pertinent to the new additive compositions are delineated to rationalize their beneficial effects on sinterability and mechanical properties.
Metal–Oxide Interactions on Copper‐Segregated and Copper‐Deposited TiO2 Rutile (001) Surfaces
Authors: Thibado Paul M. , Bonnell Dawn A.
Published: July 2010

Scanning tunneling microscopy and spectroscopy are used to study local electronic variations across a surface containing one monolayer of copper on TiO2 rutile (001). The interactions that occur at the metal–oxide interface when the sources of the copper are segregation from the bulk and ultra‐high‐vacuum deposition are compared by characterizing the associated surface morphologies and electronic properties. The morphologies of these surfaces are similar in that the copper forms clusters; they are dissimilar in that copper features exist on two size scales on the segregated surface, whereas the deposited copper clusters are uniform in size and are aggregated. The electronic properties of the two surfaces also are found to differ: the copper‐segregated surface is insulating, whereas the copper‐deposited surface is conductive. The electronic properties are discussed in terms of the effects of surface‐charge and ionic‐charge concentration gradients.
Effect of Quasi‐Static Loading Rate on Damage Formation in Silicon Carbide Reinforced Calcium Aluminosilicate Unidirectional Composites
Authors: Walter Mark E. , Ravichandran Guruswami
Published: July 2010

For experiments at higher and lower loading rates, significant differences in the mechanical responses of unidirectional silicon carbide reinforced calcium aluminosilicate composites were observed. Axial and transverse stress–strain measurements, acoustic emission measurements, and post‐test microstructural observations all indicated that there are changes in the sequence and extent of the formation of damage. The differences are attributed to rate‐dependent matrix cracking due to environmental effects and rate dependencies associated with the fiber–matrix interface.
Effect of Milling Conditions on the Strength of Alumina–Silicon Carbide Nanocomposites
Authors: Jeong Young‐Keun , Nakahira Atsushi , Morgan Peter E. D. , Niihara Koichi
Published: July 2010

Processing effects of wet ball‐milling on the microstructure and fracture strength of Al2O3/5 vol% SiC nanocomposites were investigated. Homogeneous microstructure and a high fracture strength of 1200 MPa could be achieved under the milling condition of relatively low wear contents of Al2O3 grinding media, maintaining the homogeneity of the ball‐milled powders. The fracture strength decreased with increasing wear content. Degradation of fracture strength was caused by abnormal grain growth related to wear particles from the Al2O3 balls.
Heat Capacity Changes at the Glass Transition in Mixed‐Alkali Tellurite Glasses
Authors: Komatsu Takayuki , Noguchi Tsutomu , Sato Ryuji
Published: July 2010

The heat capacity changes (ΔCp) at the glass transition in mixed‐alkali tellurite glasses of (20‐x)Li2O‐xNa2O‐80TeO2 that show different fragilities, depending on the Na2O/Li2O ratio, have been measured to obtain more‐detailed information on the structure of tellurite glasses or supercooled liquids with a fragile character. A large increase in Cp is clearly observed at the glass transition in all the samples. The values of the heat capacity of glasses and supercooled liquids (Cpg and Cpe, respectively) and ΔCp (equal to Cpe‐Cpg) at the glass transition temperature, Tg, are almost the same, irrespective of the Na2O/(Na2O+Li2O) ratio, indicating the absence of a clear, mixed‐alkali effect on Cp at Tg. The values of Cpg at 200°C, Cpe at 300°C, and ΔCp at Tg are } 75, 120, and 45 J·(mol·K)−1, respectively. The ratio of the heat capacity of the glassy state to the heat capacity of the supercooled liquid state, i.e., Cpe/Cpg, is 1.6; this large value indicates that the (20‐x)Li2OxNa2O80TeO2 system should be included in the category of fragile liquids. It has been suggested that the structural units of TeO4 trigonal bipyramid and TeO3 trigonal pyramid are weakly connected to each other and, thus, the intermediate structure varies largely as the temperature increases, which leads to a fragile character. The change in the fragility that is caused by the mixing of dissimilar alkali ions is not detected through ΔCp (i.e., there is no mixed‐alkali effect on thermodynamic fragility); however, it is observed from the viscosity behavior at } }Tg (i.e., the presence of the mixed‐alkali effect on kinetic fragility).
Effective Properties of Ferroelectric and/or Ferromagnetic Composites: A Unified Approach and Its Application
Authors: Nan Ce‐Wen , Clarke David R.
Published: July 2010

A recently developed multiple‐scattering approach for calculating the coupled electrical–mechanical response of composites is generalized to treat more‐complicated coupling between the constituent phases. This provides a unified theoretical framework for determining the effective properties of ferroelectric and/or ferromagnetic composites with any multifield coupled interaction between electrical, magnetic, mechanical, and thermal effects. Among the advantages of the theory is its simplicity of formulation, which is suited to computation. The common non‐self‐consistent approximation (NSCA) and self‐consistent effective medium approximation (SCEMA) of the theory are discussed through application to a number of piezoelectric, pyroelectricpyromagnetic, and magnetoelectric composites.
Stress‐Enhanced Displacements in PLZT Rainbow Actuators
Authors: Li Guang , Furman Eugene , Haertling Gene H.
Published: July 2010

The newly developed Rainbow actuator features high displacement and good load‐bearing capability, which are considered to be associated with Rainbow's unique dome‐shaped configuration and high internal stress created during processing. The effects of the internal stress on the field‐induced displacements of a series of PLZT Rainbow samples were investigated. It was found that the displacements were significantly enhanced for the samples having a reduced/total thickness ratio around 0.3 due to the interaction of the internal stress with ferroelectric domains. Finite element modeling was used to analyze the internal stress of the Rainbow actuators. The stress distribution revealed by the X‐ray diffraction (XRD) technique agreed well with the modeling. Enhancement of domain reorientation by the internal stress was observed from the behavior of the XRD peaks in the presence of applied electric fields. The Rainbow samples with maximum stress‐enhanced domain reorientation were found to exhibit maximum field‐induced displacements. A finite element model incorporating the stress‐enhancing mechanism with the displacement calculation was developed. This model yielded displacement values which were in good agreement with the experimental data.
Electroplastic Effect in Cast Polycrystalline NaCl with Various Orientations of the Electric Field
Authors: Yang Di , Conrad Hans
Published: July 2010

The influence of various orientations and configurations of an electric field on the flow and fracture stresses in compression of cast polycrystalline NaCl was determined at room temperature. An electric field of }0.1 MV/m reduced the flow and fracture stresses by }50%, relatively independent of the orientation of the field. This field is one to two orders of magnitude lower than those previously reported to enhance {110} (110) dislocation motion in NaCl single crystals. It is concluded that in the present tests on polycrystals the electric field enhanced cross slip. Several mechanisms by which this might occur are proposed.
Transient Growth Bands in Silicon Nitride Cooled in Rare‐Earth‐Based Glass
Authors: Wang Chong‐Min , Pan Xiaoqing , Gu Hui , Duscher Gerd , Hoffmann Michael J. , Cannon Rowland M. , Ruhle Manfred
Published: July 2010

Silicon nitride (Si3N4) particles embedded in various R‐SiAl‐O‐N glasses (R = La, Nd, Gd, Yb) have been systematically studied by high‐resolution transmission electron microscopy and by analytical electron microscopy. The particles typically show an internal growth band, which is attributed to the enhanced growth of the particles in the supersaturated silicate liquid during cooling and reheating. The electron energy‐loss spectroscopy and energy‐dispersive X‐ray spectroscopy analysis reveal that the growth band typically contains lanthanide elements. This trapping, especially of the lighter lanthanide elements, within the lattice of the β‐SiAlON is obviously beyond the general expectation that the lighter lanthanide ions hardly form solid solutions with either α‐ or β‐Si3N4. This ultimately provides some clues regarding the mobility of the lanthanide ions in the liquids and also revives interest in the general question of the possible effect of a cooling stage on the structures and compositions of the intergranular film and of the grain/glass interface in the Si3N4‐based polycrystalline ceramics.