bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of Ceramic Foams through Fourier Analysis of Digital Images
Authors: Hall Matthew J. , Bracchini Miguel
Published: July 2010

There is an industrial need to accurately characterize the structure of complex materials. Current techniques often rely on a subjective visual examination of the material surface. In this study, a digital camera was used to image ceramic foams having similar structure, but different pore sizes. The structures of the foams were quantified by taking one‐dimensional Fourier transforms of digital images of the surfaces of each sample. The Fourier analysis was used to determine the distribution of spatial frequencies representative of the materials. The goal was to develop a technique to quantify the average pore size and pore spacing of complex porous materials.
Formation of Anatase Porous Ceramics by Hydrothermal Hot‐Pressing of Amorphous Titania Spheres
Authors: Yanagisawa Kazumichi , Ioku Koji , Yamasaki Nakamichi
Published: July 2010

Anatase porous ceramics were produced at low temperatures below 350°C by hydrothermal hot‐pressing of amorphous titania consisting of spherical particles prepared by hydrolysis of titanium tetraethoxide. After fine anatase crystals were formed in the original amorphous spheres by hydrothermal hot‐pressing, the spherical particles were deformed and the fine anatase crystals flowed into the interstices among the original spheres by compression from outside the autoclave to form a compact with homogeneous distribution of fine pores. The fine anatase crystals in the compacts were bonded together by dissolution and deposition to form a compact with high mechanical strength. The porous anatase ceramics with open pores were prepared by drying in air after removing water which had occupied the pores in the compacts during hydrothermal hot‐pressing.
Grain‐Oriented Microstructure of Alumina Ceramics Made through the Injection Molding Process
Authors: Uematsu Keizo , Ohsaka Shigeru , Shinohara Nobuhiro , Okumiya Masataro
Published: July 2010

The relevance of powder packing structure and microstructure in alumina ceramics made through the injection molding process was investigated in the present study. The packing structure of oriented powder particles was retained in the present ceramics after sintering. Even after significant growth, the orientation of the grains was similar to that of the particles in the green body. Anisotropic shrinkage during sintering was attributed to the packing structure. A density distribution also was found, but its origin remains to be clarified.
Microwave Dielectrics in the (La1/2Na1/2)TiO3–Ca(Fe1/2Nb1/2)O3 System
Authors: Kim Hyun‐Jai , Kucheiko Sergey , Yoon Seok‐Jin , Jung Hyung‐Jin
Published: July 2010

Dielectric properties of the system (1 − x)(La1/2Na1/2)TiO3–xCa(Fe1/2Nb1/2)O3, where 0.4 #x# 0.6, have been investigated at microwave frequencies. The temperature coefficient of resonant frequency (τf), nearly 0 ppm/°C, was realized at x= 0.58. These ceramics had perovskite structure and showed relatively low dielectric losses. A new dielectric material applicable to microwave devices having Q·f of 12000–14000 GHz and a dielectric constant (εr) of 59–60 has been obtained at 1300–1350°C for 5–15 h sintering.
Analysis of Size Dependence of Ceramic Fiber and Whisker Strength
Authors: Zhu Yuntian T. , Blumenthal William R. , Taylor Seth T. , Lowe Terry C. , Zhou Benlian
Published: July 2010

The strengths of ceramic fibers and whiskers have been observed to increase with decreasing fiber diameter and length. Typically, both surface flaws and volume flaws exist in ceramic fibers and whiskers, which makes it impossible to characterize the strength dependence of both the diameter and the length with a single‐modal Weibull distribution function. Our data also show that the single‐modal Weibull distribution is inadequate to characterize the strength of fibers with varying diameters even in the case of a constant fiber length. In addition, experimental data also show that, for sapphire whiskers whose surface flaws were removed by chemical polishing, the whisker strength has a much stronger size dependence on diameter than predicted by the single‐modal Weibull function, which indicates that factors other than those characterized by the Weibull function also play a role in the strength of sapphire whiskers. In this paper, the factors affecting the strengths of ceramic fibers and whiskers are analyzed in terms of Weibull statistics, fracture mechanics, and flaw size density variation with varying fiber diameters. A three‐parameter modified Weibull distribution, which combines the above strength‐affecting factors, is proposed to characterize both the diameter and the length dependence for ceramic fibers and whiskers with or without surface flaws. Characterization of the strength data of sapphire whiskers and Nicalon SiC fibers with varying diameters shows the validity of the modified Weibull distribution function.
Effect of Tetravalent Dopants on Raman Spectra of Tetragonal Zirconia
Authors: Kim Dae‐Joon , Jang Joo‐Wung , Lee Hong‐Lim
Published: July 2010

Tetragonal zirconia solid solutions were prepared by the additions of ceria, titania, germania, and cassiterite into 2‐mol%‐Y2O3‐stabilized t‐ZrO2 (2Y‐TZP), and the effect of the dopant size on the changes in the Raman spectra of t‐ZrO2 was investigated. The frequencies of the Raman modes that were associated with Zr‐O bond stretching decreased as doping with the oversized cation (Ce4+) increased and increased linearly as doping with the undersized dopants (Ti4+, Ge4+, Sn4+) increased within the solubility limits of the dopants in 2Y‐TZP. The frequency of the 640 cm−1 Raman band decreased as the square root of the unit‐cell volume increased, suggesting that the ionic size of dopants governs the Raman mode that is related to the short ZrO bond between two ZrO bonds in t‐ZrO2 solid solutions. Although there was no consistent relationship between the change in the tetragonality of t‐ZrO2 solid solutions and the tetravalent cation size, the intensity ratio of the Raman modes at 609 and 640 cm−1 (I609/I640) decreased as the ionic size decreased.
Mechanism of the Blue Up‐Conversion in Tm3+/Nd3+‐doped Calcium Aluminate Glasses
Authors: Chung Woon Jin , Yoo Jae Ryoung , Kim You Song , Heo Jong
Published: July 2010

Blue up‐conversion fluorescence from the Tm3+:1G4→3H6 (480 nm) transition has been observed from calcium aluminate glass codoped with Tm3+/Nd3+. The mechanism for the up‐conversion process consists of a two‐photon process. An excitation beam with a wavelength of 791 nm first excites Tm3+ to the 3H4 level, where Tm3+ again absorbs the 1060 nm emission from Nd3+:4F3/2→4I11/2 to attain the Tm3+:1G4 level. Lifetime and intensity variations with compositions suggest the presence of an efficient energy transfer from Nd3+ to Tm3+. The highest 480 nm emission intensity has been obtained from the glass with 0.1 mol% of Nd2O3 and 0.2 mol% of Tm2O3.
Optical Scattering Centers in Polycrystalline Nd:YAG Laser
Authors: Ikesue Akio , Yoshida Kunio , Yamamoto Takahisa , Yamaga Isao
Published: July 2010

For the present study, 1.1‐at.%‐Nd‐doped YAG ceramics with controlled amounts of grain‐boundary phase were fabricated by a solid‐state reaction method using high‐purity powders. The optical scattering loss of the Nd:YAG ceramics, obtained from Fresnels equation, increased simply with increased amounts of grain‐boundary phase. The continuouswave laser output power of the Nd:YAG ceramics clearly was related to the scattering loss coefficients of the specimens that, in turn, were affected by the amount of grain‐boundary phase. Although the scattering loss coefficients of Nd:YAG ceramics with grain‐boundary‐free structure and a lower pore volume (}150 vol ppm) were almost equivalent to those of a 0.9‐at.%‐Nd‐doped YAG single crystal grown by the Czochralski method, the laser output power of the Nd:YAG ceramics exceeded that of the Nd:YAG single crystal with increased exciting power under excitation with an 808 nm diode laser because of the large amount of neodymium additives. Lasing performance was not affected by the existence of grain boundaries in the polycrystalline specimen.
Crystallographic Properties of Hydrothermal Barium Titanate Crystallites
Authors: Shi Er‐Wei , Xia Chang‐Tai , Zhong Wei‐Zhou , Wang Bu‐Guo , Feng Chu‐De
Published: July 2010

The crystallographic properties and defects of hydrothermally grown barium titanate crystallites are reported. When a precursor with a Ba:Ti molar ratio of 1.0 was used, cubic barium titanate crystallites were formed. However, when the precursor Ba:Ti molar ratio was 3.0, the product was tetragonal. The defect concentration (including OH defects and barium vacancies) was higher in cubic crystallites than in tetragonal crystallites. Because of the defects in the crystallites, the displacement of Ba2+ cations and the deformation of the Ti‐O6 octahedrons was suppressed; thus, no phase transition from cubic to tetragonal occurred at the Curie point. When the defects were eliminated by thermal treatment, the normal crystallographic properties were obtained. A high reaction temperature and a high Ba:Ti molar ratio in the precursor were beneficial to limiting defect dormation in the crystallites; thus, tetragonal crystallites were obtained.
Reaction‐Forming of Mullite Ceramics Using an Aqueous Milling Medium
Authors: Wu Suxing , Chan Helen M. , Harmer Martin P.
Published: July 2010

Mullite and mullite/ZrO2 ceramics were fabricated starting from Si/Al2O3 and Si/Al2O3/ZrO2 powder mixtures, which were mixed and attrition milled with TZP balls in water. Isopressed powder compacts were subjected to a heat treatment in air, during which the Si was oxidized to SiO2. At } 1410°C, reaction between Al2O3 and SiO2 occurred, resulting in mullite (3Al2O3·2SiO2). Depending on the composition of the starting powders, the end product was either single‐phase mullite or a mullite composite. The reaction process was monitored by thermogravimetry and dilatometry. It was found that the microstructure and mechanical properties of the reaction‐formed mullite ceramics were significantly improved by ZrO2 additions.
Interaction between Alumina and Binary Glasses
Authors: Kuromitsu Yoshirou , Yoshida Hideaki , Takebe Hiromichi , Morinaga Kenji
Published: July 2010

Interaction between 96% alumina and three binary glasses used as frits in thick‐film technology is studied. A possible interfacial reaction mechanism where a melt glass penetrates into the alumina through the grain boundaries dissolving SiO2, one of the grain boundary components, is suggested. The formulation expressing the glass penetration rate into the alumina based on Poiseuilles law, assuming the driving force for the glass penetration is the capillary force, is consistent with the experimental growth rate of the reaction layer in the alumina. The formulation also clearly explains the relationship of the degree of glass penetration to the viscosity and the surface tension of the melt glass. The extraordinary difference in K, designated as the coefficient of penetration, between the calculated result and the experimental result suggests that the process of dissolving SiO2 into a melt glass at the alumina grain boundaries retards the glass penetration.
Colloidal Stability of Zirconia‐Doped Yttria–Silica Binary Aqueous Suspensions
Authors: Yasrebi Mehrdad , Springgate Mark E. , Nikolas Douglas G. , Kemp William , Sturgis David H. , McCarthy John M.
Published: July 2010

Minor amounts of zirconia (up to 5 wt%) were fused with yttria and their effect on water solubility of yttria, and colloidal stability of yttria–silica aqueous binary suspensions, was examined. It is shown that incorporated zirconia reduces the water sensitivity of yttria while maintaining the hydrophilic nature of the surface. This fusion procedure makes yttria particles suitable for production of longlasting yttria–silica aqueous suspensions.
Nanostructuring of Laser‐Deposited Ti Films by Self‐Limited Oxidation
Authors: Gorbunov Andre A. , Pompe Wolfgang , Eichler Horst , Huey Bryan , Bonnell Dawn A.
Published: July 2010

Local laser‐induced oxidation of thin titanium films on glass is shown to be self‐limiting due to a decrease in the absorptivity during the reaction. Taking advantage of this confinement, stable writing of transparent oxide line structures narrower than the diffraction‐limited focused spot of a continuous wave Ar ion laser (500 nm) has been accomplished. The greatest optical contrast (1:10) with the highest resolution down to 165 nm was observed if the film thickness is of the order of the light absorption length in the metal.
Debonding in Multilayered Composites of Zirconia and LaPO4
Authors: Marshall David B. , Morgan Peter E. D. , Housley Robert M.
Published: July 2010

Multilayered composites consisting of LaPO4 (La‐monazite) layers alternating with various ZrO2‐based materials were fabricated to investigate whether LaPO4 provides a weakly bonded interface suitable for promoting toughening, as previously observed in the system LaPO4/Al2O3. The following ZrO2‐based materials were assessed: Y‐ZrO2, Y‐ZrO2/Al2O3, Ce‐ZrO2, and Ce‐ZrO2/Al2O3. Debonding was observed in all cases. The composites containing Y‐ZrO2 and Y‐ZrO2/Al2O3 were stable, with no reactions, at temperatures up to at least 1600°3C. However, in the composites containing Ce‐ZrO2, interdiffusion of Ce and La occurred, resulting in formation of a pyrochlore‐like phase and, in the case of the Ce‐ZrO2/Al2O3 composite, a (Ce,La)Al11O18 magnetoplumbite phase.
Ferroelasticity of t‘‐Zirconia: I, High‐Voltage Electron Microscopy Studies of the Microstructure in Polydomain Tetragonal Zirconia
Authors: Baither Dietmar , Baufeld Bernd , Messerschmidt Ulrich , Foitzik Andreas H. , Rühle Manfred
Published: July 2010

The microstructure of polydomain tetragonal zirconia (t‐ZrO2), i.e., a ZrO2 modification exhibiting ferroelastic behavior, is studied by high‐voltage electron microscopy. This material consists of three domain variants of the tetragonal phase with their c‐axes nearly orthogonal to each other. Always two variants of these platelike domains are alternately arranged, forming elongated regular colonies. Hence, in both variants the common habit plane of the domains is a {110} twin plane. The colonies are of columnar shape with a longitudinal axis. They are bound by {110} planes, too, which are twin planes for the domains in the contiguous colonies. Owing to their particular structure and the helical arrangement of the adjoining colonies, the material remains coherent and pseudocubic over large macroscopic regions, although it is formed by different tetragonal domains.
Compression Test and Plastic Strain of α‐Al2O3 Single Crystals
Authors: Rivière Jean Pierre , Castaing Jacques
Published: July 2010

Compression tests of single crystals are analyzed with respect to shear due to the friction at the loaded ends. This simple approach permits an explanation of the features associated with prism plane slip in sapphire (α‐Al2O3), i.e., the shape changes of the specimens and the curvature of the glide planes.
Origin of the Positive Temperature Coefficient of Resistivity Anomaly in the ZnO‐NiO System
Authors: Drofenik M. , Lisjak D. , Zajc I.
Published: July 2010

An anomalous positive temperature coefficient of resistivity (PTCR) was investigated in the ZnO‐NiO system. It was found that the ZnOSS (Zn0.97Ni0.03O) and NiOSS (Ni0.6Zn0.4O) constituent phases of that system exhibit negative temperature coefficient of resistivity (NTCR) character, while their combination shows a PTCR effect with a maximum at 400°3C, which coincides with a large difference in the coefficient of linear thermal expansion between the ZnOSS and NiOSS phases at that temperature. On the basis of the brick wall model microstructure, the PTCR anomaly of this system can be explained. The magnitude of the PTCR effect is governed by the difference in resistivity of the two constituent phases at the temperature where the maximum of the PTCR anomaly occurs. The predicted temperature dependence of the resistance, R(T), of a model microstructure consisting of constituent phases with different grain sizes agrees well with the experimental R(T) of the prepared composite ceramics.
Oxidation of Single Crystals of Hafnium Carbide in a Temperature Range of 600° to 900°3C
Authors: Shimada Shiro , Nakajima Kenichiro , Inagaki Michio
Published: July 2010

The isothermal oxidation of HfC single crystals with (100) orientation was carried out using an electromicrobalance at temperatures of 600° to 900°3C at an oxygen pressure of 2 to 8 kPa. Nonisothermal oxidation was performed by a simultaneous thermogravimetry—differential thermal analysis—mass spectrometry analysis. A polished cross section of the oxidized crystal was observed by backscattered electron imaging in a scanning electron microscope. Quantitative chemical analysis for Hf, O, and C and their elemental profiles in the HfC and oxide scale was carried out by wavelength dispersive X‐ray microanalysis. It was found that the oxide scale consists of two regions, zones 1 and 2, both of which showed the existence of carbon. The carbon content at the middle point of zone 1 was about twice that in zone 2, which contained 7 to 14 at.% carbon. Zone 1 showed an almost compact and pore‐free phase; its thickness remained constant (1 to 2 μm) after a prolonged time. The thickness of zone 2 increased linearly with time. The oxidation mechanism including interfacial reaction responsible for the deposition of carbon is discussed.
Thermally Induced Reversible Coagulation in Ceramic Powder‐Polymer Liquid Suspensions
Authors: Horn Jeffrey A. , Patterson Burton R.
Published: July 2010

It was observed that slurries of oxide powders in oxidized polybutene fluids can be caused to change reversibly between fluid, nearly Newtonian behavior and plastic behavior by modest changes in temperature. This phenomenon was believed to result from changes in the dispersion vs association among the particles. The rheological effects of temperature, polymer oxidation, and particle size were observed for 30 vol% slurries of TiO2, Al2O3, and ZrO2 powders in polybutene fluids. Elasticity (in oscillation) and low‐shear‐rate viscosity (in steady shear) were observed to increase with increasing temperature for TiO2 and Al2O3 particles in oxidized polybutene fluids. This behavior was attributed to the creation of interparticle structures. The attainment of this structure on heating was observed to be inhibited by increased oxidation of the polymer and increased particle size. It was concluded that the adsorption of oxidized molecules from the polymer liquid, along with the high viscosity of the bulk polymer, resulted in suspensions that were metastable against coagulation. Increased temperature resulted in lower viscosities of the liquid, allowing coagulation on a short time scale. The presence of the adsorbed polymer, however, prevented intimate contact among the particles so that the coagulated structure was easily destroyed upon subsequent cooling and shearing.
Influence of the Oxide Precursors on the Reaction Sequencing and Kinetics in the Yttrium—Barium—Copper—Oxygen System
Authors: Licci Francesca G. , Wang Longmei , Besagni Tullo
Published: July 2010

The reactions of stoichiometric Y2O3, CuO, and different barium salts (BaCO3, Ba(NO3)2, BaO2, BaCuO2) for forming various compounds in the yttrium—barium—copper—oxygen system (i.e., YBa2Cu3O7–8, BaCuO2, Y2BaCuO5, and Y2Cu2O5) were systematically investigated by thermal analysis and X‐ray diffractometry. In a few cases, the relevant activation energies were calculated. The reaction pathway and kinetics were significantly dependent on the physicochemical and thermal stability of the barium precursors, as well as on the crystalline size of the reagent. Binary BaO‐CuO phases formed at low temperature (650°‐700°3C) when in the presence of easy‐to‐decompose barium precursors, and then slowly transformed to ternary compounds; in contrast, when barium ions were released at temperatures of >900°3C, ternary phases formed directly from the components.
Strengthening of Alumina by Formation of a Mullite/Glass Layer on the Surface
Authors: Kim Hyoun‐Ee , Moorhead A. J. , Kim Sang‐Hak
Published: July 2010

A layer composed of mullite and silicate glass was caused to form on the surface of a high‐purity alumina ceramic in order to enhance the strength of the material. The layer was formed by exposing the specimens above a bed of SiC platelets at 1400°3C to a flowing H2 atmosphere containing ∼0.1% H2O. A reaction between the SiC platelets and the H2O in the environment resulted in the generation of SiO gas. Some of the SiO gas subsequently reacted with ambient H2O in the atmosphere, forming SiO2“smoke” which was deposited on, and reacted with, the alumina substrate. The strength of the ceramic was significantly improved by the reaction layer, which was found to be comprised of mullite and silicate glass. The increases in strength (about 60% above that of the material in the “as‐polished” condition) was attributed to the blunting of surface cracks. A similar strengthening effect was observed in samples of the material which had been ground with a 220‐grit diamond abrasive wheel (as had all of the samples) but not polished.
Fast Li+ Ion Conduction in Li2O‐Al2O3‐TiO2‐SiO2‐P2O2 Glass‐Ceramics
Authors: Fu Jie
Published: July 2010

Fast lithium ion conducting glass‐ceramics have been successfully prepared from the pseudobinary system 2[Li1+xTi2SixP3‐xO2]‐AlPO4. The major phase present in the glass‐ceramics was LiTi2P3O12 in which Ti4+ ions and P5+ ions were partially replaced by Al3+ ions and Si4+ ions, respectively. Increasing x resulted in a considerable enhancement in conductivity, and in a wide composition range extremely high conductivity over 10‐3 S/cm was obtained at room temperature.
Dielectric Depression and Dispersion in Electrophoretically Fabricated BaTiO3 Ceramic Films
Authors: Yamashita Kimihiro , Matsuda Motohide , Inda Yasushi , Umegaki Takao , Ito Masayuki , Okura Toshinori
Published: July 2010

Dielectric depression and dispersion were observed in BaTiO3 ceramic films fabricated by electrophoretic deposition followed by sintering. The dielectric constants were depressed down to 6800‐4600 around the Curie point (TC). The dielectric dispersion occurred above TC. These dielectric properties are attributable to a surface layer formed during sintering. XRD analysis indicated that the surface layer was a hexagonal‐like BaTiO3 phase. A mixed solvent of acetylacetone and alcohol employed in the present work may have been responsible for the formation of the surface layer.
Characterization of the Cotunnite‐Type Phases of Zirconia and Hafnia by Neutron Diffraction and Raman Spectroscopy
Authors: Haines Julian , Léger Jean Michel , Hull Steve , Petitet Jean Pierre , Pereira Altair S. , Perottoni Claudio A. , da Jornada Joäo A. H.
Published: July 2010

The crystal structures of the cotunnite‐type phases (space group, Pnam, Z= 4) of pure zirconia and hafnia prepared under high‐temperature, high‐pressure conditions in a multianvil device were refined by time‐of‐flight neutron powder diffraction. The structures of both compounds are very similar and the nine polyhedral metal‐oxygen distances range from 2.133(1) to 2.546(1) Å in ZrO2 and from 2.121(1) to 2.535(2) Å in HfO2. The Raman spectra of both phases resemble one another strongly and are consistent with the cotunnite‐type structure. These results confirm that ZrO2 and HfO2 undergo transitions to the same phase at high pressure.
Evaluated Material Properties for a Sintered alpha‐Alumina
Authors: Munro Ronald G.
Published: July 2010

Results of a data evaluation exercise are presented for a particular specification of sintered alpha‐alumina (mass fraction of Al2O3, ≥0.995; relative density (rho/rhotheoretical), ≥0.98; and nominal grain size, 5 μm). A comprehensive set of material property data is established based on published physical, mechanical, and thermal properties of alumina specimens that conform to the constraints of the material specification. The criteria imposed on the properties are that the values should be derived from independent experimental studies, that the values for physically related properties should be mutually self‐consistent, and that the sets of values should be compatible with established material property relations. The properties assessed in this manner include crystallography, thermal expansion, density, sound velocity, elastic modulus, shear modulus, Poisson's ratio, bulk modulus, compressive strength, flexural strength, Weibull characteristic strength, Weibull modulus, tensile strength, hardness, fracture toughness, creep rate, creep rate stress exponent, creep activation energy, friction coefficient, wear coefficient, melting point, specific heat, thermal conductivity, and thermal diffusivity.
Constrained Densification of Alumina/Zirconia Hybrid Laminates, I: Experimental Observations of Processing Defects
Authors: Cai Peter Z. , Green David J. , Messing Gary L.
Published: July 2010

Various forms of damage were observed in pressure‐less‐sintered Al2O3/ZrO2symmetric laminates and asymmetric laminates (bilayers) fabricated by tape casting and lamination. These defects included channel cracks in the ZrO2 layers, Al2O3 edge‐effect cracks parallel to the layers, delamination in the Al2O3layers, and debonding between the Al2O3and ZrO2layers. Based on detailed microscopic observations, the defects were attributed to sintering rate and thermal expansion mismatch between the layers. Cracks or cracklike defects were formed in the early stages of densification, and these cracks either opened during sintering or acted as preexisting flaws for thermal expansion mismatch cracks. Consequently, the extent of cracking could be reduced or even eliminated by decreasing mismatch stresses during the sintering and cooling stages. This can be accomplished by reducing the heating and/or cooling rates or by adding Al2O3in the ZrO2layers. The sintering mismatch stresses were estimated from the degree of curling in asymmetric laminates and from layer viscosities that were obtained by cyclic loading dilatometry. The measured curvature was an indication of the mismatch in sintering strain between Al2O3and ZrO2and were consistent with the dilatometric data that were obtained for the component layers.
Constrained Densification of Alumina/Zirconia Hybrid Laminates, II: Viscoelastic Stress Computation
Authors: Cai Peter Z. , Green David J. , Messing Gary L.
Published: July 2010

To analyze the inhibited densification during sintering and differential shrinkage during cooling of Al2O3/ZrO2symmetric and asymmetric laminates, viscoelastic formulations, in which the viscosity and elastic modulus vary with time, have been developed. The viscoelastic mismatch stresses have been numerically computed over the entire processing cycle, including the heating period, the isothermal period, and the cooling period. The viscosity and free sintering rates that are needed for stress computation have been obtained by modifying the parameters that are measured for a normal isotropic densifying compact using cyclic loading dilatometry. The modification is based on the available sintering models to account for the effect of strain history on compact viscosity and sintering rates. The stress calculation shows that, with the exception of the initial heating period, the viscoelastic stress is identical to the viscous stress that is calculated solely from the strain rate mismatch. Sintering damage in the laminates is shown to occur during densification under conditions where the differential sintering stress is smaller than the intrinsic sintering pressure. The magnitude of residual stress in hybrid laminates on cooling is dependent on the cooling rate, and slower cooling rates are capable of almost completely relaxing the expansion mismatch stress at temperatures of >1200°C.
Formation Mechanism of Hydrous‐Zirconia Particles Produced by Hydrolysis of ZrOCl2 Solutions
Authors: Matsui Koji , Ohgai Michiharu
Published: July 2010

The secondary particle size of hydrous‐zirconia fine particles that have been produced by the hydrolysis of various ZrOCl2 solutions, with and without the addition of NH4OH or HCl, was measured using transmission electron microscopy to investigate the effects of the H+ and Cl−ion concentrations on the formation of secondary particles. The average secondary particle size of hydrous zirconia increased as the H+ion concentration increased, attaining a maximum of 200 nm at an H−ion concentration of 0.44 moldm‐3. Further increases in the H+ion concentration then caused a decrease in the average particle size. The present experimental results revealed that the secondary particle size of hydrous zirconia is controlled primarily by the concentration of H+ ions that are produced during hydrolysis. The formation mechanism for the secondary particles in hydrous zirconia was determined on the basis of the present experimental results.
Tensile Stress Rupture of SiCf/SiCmMinicomposites with Carbon and Boron Nitride Interphases at Elevated Temperatures in Air
Authors: Morscher Gregory N.
Published: July 2010

The stress‐rupture properties of precracked minicomposites were determined in air at temperatures in the range of 700°‐1200°C. The minicomposite systems consisted of a single tow of Nicalon or Hi‐Nicalon fibers with carbon or boron nitride (BN) interphases and a chemical‐vapor‐infiltrated silicon carbide (CVI‐SiC) matrix. The stress‐rupture results were compared to single‐fiber stress‐rupture data and composite data in the literature. Severe embrittlement occurred for carbon interphase minicomposites. However, BN interphase minicomposites showed only mild degradation in the rupture properties. This was true even though the BN interphase reacted and vaporized because of water vapor in the atmosphere at intermediate temperatures (700°‐950°C) and glass formation occurred at higher temperatures (950°‐1200°C). The severe degradation in rupture properties that occurred for carbon interphase composites at intermediate temperatures was due to degradation of the Nicalon‐fiber properties from the environment. The rupture properties of the BN‐interphase minicomposites were controlled by the fiber rupture properties at temperatures of less than ˜900°C and greater than ~1100°C. In the range of ˜900°‐1100°C, most fibers fused to the matrix because of a glass layer that formed between the fiber and matrix, resulting in fiber stress concentrations that led to the mild embrittlement of the BN‐interphase minicomposites.
Transformation Toughening in Sol–Gel‐Derived Alumina‐Zirconia Composites
Authors: Srdi Vladimir V. , Radonji Ljiljana
Published: July 2010

The microstructures of α‐Al2O3 seeded sol–gel‐derived alumina‐zirconia composites containing 20 wt% unstabilized zirconia (processed from zirconium n‐propoxide) were very fine, with submicrometer alumina grains and small, mainly intergranular zirconia particles, the latter having a critical size for the tetragonal‐to‐monoclinic phase transformation of 0.45 μm. The corresponding ratios of the toughening contribution to the matrix toughness are relatively low (δKc/K0<1). This finding is confirmed by an analysis of the tetragonal zirconia particle size dependence of the stress‐induced transformation toughening.
Elastic Response of Thermal Spray Deposits under Indentation Tests
Authors: Leigh Sang‐Ha , Lin Chung‐Kwei , Berndt Christopher C.
Published: July 2010

The elastic response behavior of thermal spray deposits at Knoop indentations has been investigated using indentation techniques. The ratio of hardness to elastic modulus, which is an important prerequisite for the evaluation of indentation fracture toughness, is determined by measuring the elastic recovery of the in‐surface dimensions of Knoop indentations. The elastic moduli of thermal spray deposits are in the range of 12%‐78% of the comparable bulk materials and reveal the anisotropic behavior of thermal spray deposits. A variety of thermal spray deposits has been examined, including Al2O3, yttria‐stabilized ZrO2(YSZ), and NiAl. Statistical tools have been used to evaluate the error estimates of the data.
Phase Transitions and Transient Liquid‐Phase Sintering in Calcium‐Substituted Lanthanum Chromite
Authors: Chick Larry A. , Liu Jun , Stevenson Jeffry W. , Armstrong Timothy R. , McCready David E. , Maupin Gary D. , Coffey Gregory W. , Coyle Chris A.
Published: July 2010

This paper investigates sintering and phase transitions of La0.7CaxCrO3(0.25≥x≥0.35), a material useful as electrical interconnections in solid oxide fuel cells. Heating of the quenched, metastable single‐phase chromite resulted in exsolution of CaCrO4 due to Ca solubility limitations below 1200°C. A transient liquid phase formed between 850° and 1000°C as the CaCrO4 melted, causing partial densification in materials having 0.25 < x < 0.30. A slight increase in Ca content induced an additional liquid‐phase sintering event, likely due to melting of Ca3(CrO4)2, which facilitated near‐complete densification by 1250°C. After enhancing sintering, the secondary phases redissolved into the chromite.
Flow Characteristics of a Vertical Spinning Disk, Low‐Pressure Vapor Deposition Apparatus
Authors: Zhang Rui‐Chao , Duke John D. , Xu Ren , Virkar Anil V.
Published: July 2010

The flow characteristics of a new vertical spinning disk, low‐pressure vapor deposition apparatus were studied. The nominal boundary‐layer thickness dependence on the reactor pressure, substrate rotation rate, and substrate temperature were examined with the aid of a smoke that was generated from hydrolyzed TiCl4 vapor. The measured nominal boundary layer thickness was found to have a strong dependence on the reactor pressure and the substrate rotation rate, whereas the temperature dependence was not easily resolved by the present method. The experimental data and the theoretical prediction were found to agree within the accuracy of the measurements.
Shrinkage‐Free, Alumina–Glass Dental Composites via Aluminum Oxidation
Authors: Lee Sang‐Jin , Waltraud M. Kriven , Kim Hyun‐Min
Published: July 2010

Alumina–glass composites that contain oxidized aluminum were investigated to make shrinkage‐free, all‐ceramic dental porcelain. This was achieved by control of the volume expansion and shrinkage that occur during the aluminum oxidation and densification processes. The dimensional change and strength of the alumina‐glass composites were dependent on the aluminum content and particle size. A shrinkage‐free sample with a strength of 330 MPa and transmittance of 1.21 was fabricated by using 4‐5 vol% of aluminum powder with an average particle size of 6 μ m in the alumina‐glass composite made by the In‐Ceram method.
High‐Temperature Hall Measurements on BaSnO3Ceramics
Authors: Ostrick Bernhard , Fleischer Maximilian , Meixner Hans
Published: July 2010

Simultaneous Hall and conductivity measurements were performed in situ between 650° and 1050°C on n‐type semiconducting BaSnO3ceramics. The variation of the Hall mobility and the Hall carrier density as a function of oxygen partial pressure between 102 and 105 Pa and of temperature was investigated. At temperatures below 900°C the conductivity exhibits a dependence on temperature and oxygen partial pressure which is mainly determined by variations of the Hall mobility. Above 900°C most of the significant dependence is due to a variation in carrier density. Furthermore, a simple defect model assuming doubly ionized oxygen vacancies and acceptor impurities is discussed for BaSnO3.
Nitridation Effect on Properties of Stannous‐Lead Phosphate Glasses
Authors: Yung Hsiwen , Shih P. Y. , Liu H. S. , Chin T. S.
Published: July 2010

Stannous‐lead phosphorus oxynitride (Sn‐Pb‐P‐O‐N) glasses were prepared by remelting under an anhydrous ammonia atmosphere. Glasses that contained up to ∼4.2 wt% (9 at.%) of nitrogen were obtained. The rate of nitrogen dissolution was studied as a function of remelting time (3–66 h) and temperature (400°–600°C). The onset nitridation temperature was extrapolated to be 315°C; higher nitridation temperatures accelerated nitrogen dissolution. Nitridation of the stannous‐lead oxyphosphate (Sn‐Pb‐P‐O) glasses decreased the dissolution rate in water and the thermal expansion coefficient; however, it increased the dilatometric softening temperature, the glass‐transition temperature, the microhardness, and the density. The chemical durability of the nitrided glasses increased more than four orders of magnitude with 3.0 wt% of nitrogen content. An increase in the lead oxide content in the stannous phosphate glasses also improved the chemical durability. Fourier transform infrared spectroscopy and X‐ray photoelectron spectroscopy suggested that nitrogen replaces the terminating hydroxyl ion and the bridging and nonbridging oxygen atoms in the PO4 tetrahedra to form the functional groups –NH<, –N<, and –N=, which leads to enhanced crosslinking of the glass network. Quantitative results regarding these bondings have been given.
Synthesis of Novel Niobium Aluminide‐Based Composites
Authors: Garcia Daniel E. , Schicker Silvia , Bruhn Jorn , Janssen Rolf , Claussen Nils
Published: July 2010

A reactive sintering process has been used to produce almost fully dense composites with interpenetrating networks of NbAl3 and Al2O3. The process involves the reaction synthesis of niobium aluminides and Al2O3 from compacts of intensively milled aluminum and Nb2O5 powder mixtures. During carefully controlled heating under an inert atmosphere, the oxide reduction by aluminum to form niobium aluminides and Al2O3 proceeds at temperatures below the melting point of aluminum. At temperatures of >1000°C, the reaction‐formed niobium aluminides and Al2O3 sinter. The present paper discusses processing parameters, such as attrition milling, the heating cycle, and the metal:ceramic ratio in the starting mixture, that control microstructure development and mechanical properties.
Phase Stability and Electrical Conductivity in Gd2Ti2O7‐Gd2Mo2O7 Solid Solutions
Authors: Porat Ofer , Heremans Catherine , Tuller Harry L.
Published: July 2010

Solid solutions in the Gd2(Ti1‐yMoy)2O7 pyrochlore system, with y = 0.1, 0.3, 0.5, and 0.7, have been investigated as potential candidates for the anode material of solid‐oxide fuel cells. The electrical conductivity, stability range, and optimal synthesis conditions of the pyrochlore phase have been explored by electrical, coulometric titration, and X‐ray diffractometry techniques. As the molybdenum content increases, the maximum conductivity increases to a value of 70 S/cm for y = 0.7 at 1000°C, whereas the stability range in the oxygen partial pressure (pO2) decreases to just over two orders of magnitude in pO2 in the temperature range of 600°‐1000°C. A decomposition reaction that leads to decreased conductivity in oxidizing atmospheres is proposed.
Thermal Behavior of Silver in Ion‐Exchanged Soda‐Lime Glasses
Authors: Wang Paul W. , Zhang Lipeng , Tao Ying , Wang Chengyu
Published: July 2010

The refractive index and the nonlinear optical properties of sodium silicate glass can be easily tailored by replacing the sodium with silver. However, the thermal responses of silver and the corresponding modifications of the silica (SiO2) network in ion‐exchanged glass under heating are still not clear. X‐ray photoelectron spectroscopy has been used to study the in‐situ behavior of silver and SiO2networks on the surfaces of silver‐ion‐exchanged‐content soda‐lime glasses during heating and cooling processes under ultrahigh vacuum. Temperature‐dependent concentration changes and oxidation states have been monitored. The results show that silver diffuses toward the surface, precipitates, and crystallizes during heating, and the total silver surface concentration is slowly increased during cooling. The concentration changes and binding‐energy shifts of oxidized and neutral silver atoms, a new nonbridging oxygen species (NBO*), and a new silicon species (Si[a]) have been applied to deduce a disappropriation reaction mechanism of the Ag+ ion on the surface during annealing. The SiO2 network is modified at temperatures of <350°C to accommodate more silver on the surface and to balance the extra charge that is carried by the Ag+ ion. The fact that the SiO2 network polymerizes during annealing has been deduced from the results of the higher binding energies of Si 2p and O 1s after annealing. This observation is of importance in optimizing the distribution of the ion‐exchanged silver and in the formation of silver‐metal colloids in glass networks.
Carbon‐Coated‐Glass‐Fiber‐Reinforced Cement Composites: I, Fiber Pushout and Interfacial Properties
Authors: Huang Chao M. , Zhu Dong , Cong Xiang‐Dong , Kriven Waltraud M. , Loh Roland R. , Huang Jianzhong
Published: July 2010

Interfacial mechanical properties of carbon‐coated‐S‐glass‐fiber‐reinforced cement were characterized by a fiber pushout technique. The pushout experiments were conducted on model composites, where the S‐glass monofilaments with and without carbon coating were unidirectionally embedded in ordinary portland cement. Interfacial properties, including bonding strength, frictional stress, residual stress, and fracture energy, were extracted from the previously developed progressive debonding model. The composite with a carbon interface exhibited a weaker interfacial bonding strength and frictional stress than did the composite without a carbon interface. The interfacial fracture energy of the composite with a carbon interface was 7.9 J/m2, as compared to 47.6 J/m2 for the composite without a carbon interface. The composite with the carbon interface exhibited a smaller residual clamping stress (18 MPa), in comparison to that for the composite without a carbon interface (69 MPa). Scanning electron microscopy observations indicated that the filament without a carbon coating was significantly attacked by the alkaline environment and was strongly bonded onto the matrix, whereas the filament with a carbon coating remained intact under the same curing conditions. These studies suggest that carbon coating provides the glass fiber with significantly improved corrosion resistance to alkali in the cement environment.
Ferroelectric Polarization Fatigue in PZT‐Based RAINBOWs and Bulk Ceramics
Authors: Dausch David E.
Published: July 2010

The ferroelectric fatigue behavior of high‐displacement reduced and internally biased oxide wafer (RAINBOW) actuators was investigated and compared with that of conventional bulk ceramics. Piezoelectric lead zirconate titanates (PZT‐5H and PZT‐5A) as well as electrostrictive lead lanthanum zirconate titanate (PLZT 9/65/35) materials were studied. Piezoelectric bulk ceramics experienced a 25% decrease in remanent polarization over 10–8 switching cycles, whereas RAINBOW polarization degraded by 33%–53%. Bulk ceramic and RAINBOW electrostrictors both fatigued only 8%. Bulk ceramics fatigued as a result of reorientation of the polar axes away from the electric‐field direction. RAINBOW fatigue was believed to have been caused by degradation at the interface between the oxide and chemically reduced layers.
Effect of Densification Mismatch on Camber Development during Cofiring of Nickel‐Based Multilayer Ceramic Capacitors
Authors: Jean Jau‐Ho , Chang Chia‐Ruey , Chen Zhien‐Chi
Published: July 2010

The development of camber during the cofiring of a two‐layered structure of Ni‐electrode/BaTiO3‐dielectric as a function of temperature has been investigated. At a given thickness of Ni electrode, less camber and camber rate with increasing thickness of BaTiO3 dielectric have been observed. This phenomenon is attributed to the densification mismatch between the Ni electrode and the BaTiO3 dielectric during cofiring. The mathematical analysis of camber development, based on a viscous model, shows significant agreement with experimental observations.
Formation of AlN‐Polytypoid Phases during α‐SiAlON Decomposition
Authors: Zhao Rupeng , Swenser Steven P. , Cheng Yi‐Bing
Published: July 2010

Phase transformations from α– to ß–SiAlONs (i.e., from α′ to ß′) have been recently reported in a number of rare‐earth SiAlON systems during postsintering heat treatment. In the present work, this transformation process in a Sm (α+ß)‐SiAlON material is studied by using XRD, TEM, and EDS X‐ray mapping techniques. It is observed that in addition to the formation of ß′ and M′ phases, the α′‐to‐ß′ transformation is accompanied by a significant increase in the amount of an AlN‐polytypoid phase. The results suggest that some α′ phases are thermodynamically unstable at temperatures lower than the material sintering temperature and will decompose when conditions allow. For the composition studied in this work, the α‐SiAlON decomposition can be described in general as α′→ß′+ M′+ AlN polytypoid.
Effect of Hydrogen Fluoride Gas Treatment on High‐Strength Fluoride‐Fiber Fabrication
Authors: Nishida Yoshiki , Ohishi Yasutake , Fujiura Kazuo , Kanamori Terutoshi , Sudo Shoichi
Published: July 2010

The effect of treating a ZrF4‐based fluoride‐glass surface with hydrogen fluoride gas is investigated using secondary‐ion mass spectroscopy. The analysis reveals that this treatment is effective in reducing the oxygen concentration at the surface. A strong fiber with a mean tensile strength of 550 MPa and maximum strength of 600 MPa is successfully fabricated by using this technique.
Reaction Pathways in the Synthesis of Photorefractive gamma‐Bi12MO20 (M = Si, Ge, or Ti)
Authors: Fu Senlin , Ozoe Hiroyuki
Published: July 2010

Reaction pathways in the synthesis of three photorefractive silicates—γ‐Bi12 SiO20 (BSO), γ‐Bi12 GeO20 (BGO), and gamma‐Bi12 TiO20 (BTO)—were systematically investigated. The main results were as follows: (i) all the reactions of the form 6Bi2O3+ MO2→> γ‐Bi12 MO20 (SR1 for M = Si, SR2 for M = Ge, SR3 for M = Ti) in the solid state seemed to be diffusion‐controlled processes and were affected by both temperature and time, where the reaction temperature increases in the order SR1 < SR2 < SR3; (ii) the metastable phases Bi2 SiO5 (tetragonal) in reaction SR1, Bi2 GeO5 (orthorhombic) in reaction SR2, Bi4 Ti3 O12 (orthorhombic) in reaction SR3 may be formed and seemed to greatly accelerate the above‐mentioned solid‐state reaction processes; and (iii) for a continuous heating process, pure γ‐Bi12 SiO20 and γ‐Bi12 GeO20 could be produced before melting, whereas pure γ‐Bi12 TiO20 could not be produced, even if all the mixed phases had melted.
Local Chemical Bonding around Rare‐Earth Ions in α‐ and ß‐Si3N4
Authors: Nakayasu Tetsuo , Yamada Tetsuo , Tanaka Isao , Adachi Hirohiko , Goto Seishi
Published: July 2010

First‐principles molecular‐orbital calculations of α‐ and ß‐Si3N4 with a trivalent lanthanide (Ln3+) ion at the interstitial site are conducted using model clusters that are composed of 41‐43 atoms, neglecting lattice relaxation effects. When an interstitial Ln3+ ion is present, strong antibonding between the Ln3+ ion and Si3N4 is found. The magnitude of the antibonding is almost the same between the alpha‐ and ß‐Si3N4 matrices. On the other hand, the Si‐N bond around the Ln3+ ion is notably reinforced in alpha‐Si3N4 but not so much in ß‐Si3N4. The different electronic response to the presence of the Ln3+ ion for the Si‐N bond is concluded to be the origin of the different solubilities of interstitial Ln3+ ions between alpha‐ and ß‐SiAlONs that are reported experimentally. The contribution of the electric field that is induced by the presence of a trivalent charge at the interstitial site is examined in detail; we have found that the Si‐N bond strength is not simply determined by the electric field but rather in a more complex manner.