bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis and Dielectric Properties of Solution Sol‐Gel‐Derived 0.9Pb(Mg1/3Nb2/3)O3–0.1PbTiO3 Ceramics
Authors: Ravindranathan Palaniappan , Komarneni Sridhar , Bhalla Amar S. , Roy Rustum
Published: March 2005

A solution sol‐gel method has been developed to prepare 0.9Pb(Mg1/3Nb2/3)O3‐0.1PbTiO3 (0.9PMN‐0.1PT) ceramics. During the processing the gel first converted to cubic pyrochlore phase at a calcination temperature of 600°C followed by the formation of pure perovskite phase at 775°C. The ceramics sintered at 1250°C for 4 h showed ≈98% of the theoretical density. The room‐temperature dielectric constant of the pellets sintered at 1250°C showed a maximum value of 25035 at 1 kHz. Sintering studies at different temperatures revealed that the dielectric constant increased with increasing grain size in these ceramics.
Effective Thermal Conductivity of a Packed Bed of Hollow Zirconia Microspheres, under Vacuum and under 100 kPa of Argon
Authors: Londry Frank A. , Slavin Alan J.
Published: March 2005

Measurements have been made of the effective thermal conductivity of a packed bed of hollow, yttria‐stabilized zirconia microspheres, under vacuum and under 100 kPa of argon gas. Above 1400 K the spheres begin to sinter together. Before this occurs, the conductivity is given under vacuum by A1T3+A2 with A1= 2 × 10−11 W · m−1· K−4 and A2= 0.01 W · m−1· K−1. The thermal conductivity increases strongly with both the gas pressure and the degree of sintering of the spheres. The measured values can be fitted reasonably well by a model developed by Takegoshi et al. These results may have some applicability to the development of high‐temperature thermal insulation.
High‐Strength Mica‐Containing Glass‐Ceramics
Authors: Uno Tomoko , Kasuga Toshihiro , Nakajima Kiichi
Published: March 2005

Glass‐ceramics containing barium–mica in the system Ba0.5 Mg3 (Si3AIO10)F2–2MgO · 2Al2O3· 5SiO2–Ca3 (PO4)2 are two to three times stronger than conventional mica‐containing glass‐ceramics. Moreover, the barium‐mica glass‐ceramics are easier to machine, as confirmed by a drilling test using conventional steel tools. Such mechanical properties are attributable to the microstructure of the barium–mica glass‐ceramics. Very fine, interlocking mica crystals are precipitated in the glass, and a crack‐deflection mechanism is observed by scanning electron microscopy.
Effect of Pore–Grain‐Boundary Interactions on Discontinuous Grain Growth
Authors: Sone Takanori , Akagi Hirokazu , Watarai Hisao
Published: March 2005

Pore behavior as influenced by migration of an abnormal grain boundary was studied. The pore behavior during the discontinuous growth of hot‐pressed spinel (MgAl2O4) — whether the pore can move attached to the grain boundary — is particularly governed by the pore size and the matrix grain size. These phenomena can be understood from the interaction between the pore and the abnormal grain boundary.
Li2O─SiO2─Al2O3─MeIIO Glass‐Ceramic Systems for Tile Glaze Applications
Authors: Leonelli Cristina , Manfredini Tiziano , Paganelli Mariano , Pellacani Gian Carlo , Albaro Jose Luis Amoros , Navarro Jose Emilio Enrique , Orts Maria Jose , Bruni Silvia , Cariati Franco
Published: March 2005

In order to verify the possibility of using glass‐ceramic materials as tile coatings, the devitrification processes of three industrial formulations belonging to the Li2O─Al2O3─SiO2 glass‐ceramic system were investigated by differential thermal analysis, X‐ray diffractometry, scanning electron microscopy, and IR spectroscopy. Compositional variations were made by addition of large amounts of MgO or CaO or PbO (ZnO) oxides as well as through smaller additions of other oxides. In these systems the surface crystallization contributes appreciably to the bulk crystallization mechanism. All the systems investigated show a high tendency toward crystallization even at very high heating rates, developing a very close network of interlocked crystals of synthetic β‐spodumene‐silica solid solutions (LiAlSi4O10). The results of this research are expected to establish the conditions under which these glass‐ceramic systems can be practically used as tile glazes.
Influence of BaCuO2 on the Sintering and the Properties of YBa2Cu3O7−δ‐Based Ceramics
Authors: Heintz Jean‐Marc , Sanz Mariano , Marquestaut Emile , Etourneau Jean , Bonnet Jean‐Pierre
Published: March 2005

The preparation of YBa2Cu3O7 ‐ δ‐based ceramics was made from a mixture of oxides taken in the molar proportions α:1:2 BaCuO2:Y2BaCuO5:CuO(0.95 α 3). The densification of the ceramics is strongly dependent on the initial amount of BaCuO2. The highest density is obtained when α= 1. All the ceramics present a superconducting transition. A sintering mechanism is proposed in which the densification is mainly governed by the appearance of a metastable BaCuO2‐based liquid at around 900°C.
Nucleation in Lithium Disilicate Glass: A Test of Classical Theory by Quantitative Modeling
Authors: Greer A. Lindsay , Kelton Kenneth F.
Published: March 2005

Published data on the kinetics of crystal nucleation in lithium disilicate glass are analyzed using a numerical simulation based on classical nucleation theory. With a reasonable set of materials parameters, a quantitative fit is possible to all measured data, including those showing transient behavior in single‐stage or multistage anneals. The fitting constitutes a comprehensive test of classical nucleation theory, which, even in the simple form used here, is found to be capable of quantitative prediction. The numerical simulation will be of use in developing heat treatments for glassceramics.
Effects of Impurities and Manufacturing Methods on the Devitrification of Silica Fibers
Authors: Zhou Wancheng , Fu Hengzhi , Zhang Litong , Sun Xiaomei , She Shengyang , Ma Junzhang
Published: March 2005

Devitrification resistance is one of the most important properties of silica fibers. The devitrification behavior of silica fibers made by the acid leaching method, the sol‐gel method, and the high‐purity silica fusing method, and the effects of small amounts of Al2O3 and B2O3, were studied by using X‐ray diffraction. The results indicated that the devitrification tendency of silica fibers made by the high‐purity silica fusing method is apparently greater than that of the fibers made by the other two methods. A small amount of B2O3 has the effect of retarding devitrification, while Al2O3 promotes devitrification of the fibers. The combined effect of Al2O3 and B2O3 is to strongly enhance the devitrification of silica fibers. The results are discussed in the context of structural analysis.
Ionic Conductivity of the Fluorite‐Type Hafnia–R2O3 Solid Solutions
Authors: Trubelja Mladen F. , Stubican Vladimir S.
Published: March 2005

The ionic conductivity of the hafnia‐scandia, hafnia‐yttria, and hafnia‐rare earth solid solutions with high dopant concentrations of 8, 10, and 14 mol% was measured in air at 600° to 1050°C. Impedance spectroscopy was used to obtain lattice conductivity. A majority of the investigated samples exhibited linear Arrhenius plots of the lattice conductivity as a function of temperature. For all investigated dopant concentrations the ionic conductivity was shown to decrease as the dopant radius increased. The activation enthalpy for conduction was found to increase with dopant ionic radius. The fact that the highest ionic conductivity among 14‐mol%‐doped systems was obtained with HfO2─Sc2O3 suggested that the radius ratio approach should be used to predict the electrical conductivity behavior of HfO2─R2O3 systems. A qualitative model based on the Kilner's lattice parameter map does not seem to apply to these systems. For the three systems HfO2─Yb2O3, HfO2─Y2O3, and Hf2O3─Sm2O3 a conductivity maximum was observed near the dopant concentration of 10 mol%. Deep vacancy trapping is responsible for the decrease in the ionic conductivity at high dopant concentrations. Formation of microdomains of an ordered compound cannot explain the obtained results. A comparison between the ionic conductivities of doped HfO2 and ZrO2 systems indicated that the ionic conductivities of HfO2 systems are 1.5 to 2.2 times lower than the ionic conductivities of ZrO2 systems.
Sintering of Lithium Zinc Ferrites with Alkoxide‐Derived Borosilicate Liquid Phase
Authors: Brooks Keith G. , Amarakoon Vasantha R. W.
Published: March 2005

Lithium zinc ferrites (Li0.3Zn0.4Mn0.05Fe2.25O4) of > 97% theoretical density were prepared with alkoxide‐derived borosilicate sintering additive. A sol‐gel technique was used to incorporate the borosilicate phase prior to sintering. The effects of borosilicate composition and additive quantity on microstructural development and densification are reported. Direct current resistivity, dynamic hysteresis, and microwave property data are discussed in terms of processing parameters and resultant microstructures. The microstructure of the sintered ferrites was analyzed using SEM and TEM. Heterogeneities including regions of liquid‐phase coalescence and intragranularly included glass phase were observed in some cases. These microstructural features were shown to have deleterious effects on microwave magnetic properties when compared to those of commercial ferrites of the same nominal composition sintered with Bi2O3 additive.
Evolution of the Pore Size Distribution in Final‐Stage Sintering of Alumina Measured by Small‐Angle X‐ray Scattering
Authors: Krueger Susan , Long Gabrielle G. , Black David R. , Minor Dennis , Jemian Pete R. , Nieman G. William , Page Richard A.
Published: March 2005

Small‐angle X‐ray scattering was used to follow the evolution of the pore size distribution during final‐stage sintering of alumina and of alumina doped with 0.25 wt% magnesia. The volume‐weighted (Guinier) results indicate that the effective size of the largest pores increases as the body goes from 97% to more than 99% dense. The surface‐area‐weighted (Porod) results show that the median size of the smallest pores decreases slightly over the same density range. Taken together, these data indicate that the pore size distribution becomes broader as final‐stage densification proceeds. This was confirmed by a maximum entropy analysis, which was used to derive pore size distributions directly from the data. Finally, the evolution of the pore size distributions in alumina, with and without sintering aid, were compared.
Hydrothermal Crystallization of Zirconia and Zirconia Solid Solutions
Authors: Pyda Waldemar , Haberko Krzysztof , Bułko Miroslaw M.
Published: March 2005

Zirconia as well as yttria‐zirconia and calcia‐zirconia solid‐solution powders were crystallized under hydrothermal conditions from (co)precipitated hydroxides. The morphology of the powder particles is strongly dependent on the crystallization conditions. The powders crystallized in a water solution of Na, K, and Li hydroxides show elongated particles of much larger sizes than those which result from the process carried out in pure water or a water solution of Na, K, or Li chlorides. The shapes of the latter particles are isometric. The growth mechanism of the elongated particles is suggested.
Normal‐Pressure Hot‐Pressing of α‐Alumina‐Diamond Composites
Authors: Liu Jenq , Ownby P. Darrell
Published: March 2005

α‐Alumina‐diamond composites have been developed by normal hot‐pressing procedures using a conventional pressure of 32 MPa and 1250°C. Heretofore this type of composite has required a pressure of 6 GPa (60 kbar) to prevent the transformation of diamond to graphite. The mechanical properties, density, and thermal expansion coefficient of these composites have been characterized. The fracture toughness (KIc) of alumina shows a considerable increase with the addition of diamond particles. Diamond additions tend to decrease the thermal expansion coefficient of these composites. The composite properties are dependent on the volume fraction of diamond particles.
Small‐Angle X‐ray Scattering Study of the Thermal Decomposition of Magnesium Hydroxide
Authors: Vollet Dimas Roberto , Varela José Arana
Published: March 2005

The submicroscopic porous structure developed in the isothermal decomposition of Mg(OH)2 was studied in situ by means of small‐angle X‐ray scattering (SAXS). The scattering intensity in the 100% decomposed system has a good fit with an exponential correlation function, g(r)= exp(‐r/a) (where a is the correlation distance), according to the Debye, Anderson, and Brumberger (DAB) model which holds for a random distribution of pore shape and size in the solid. The DAB correlation distance is about 3.2 nm for systems decomposing at 583 and 623 K. According to the available pore volume fraction, such a correlation distance would imply a porous structure built up by pores of 7‐nm mean size randomly distributed in a solid skeleton of 6‐nm mean particle size.
Texture from Domain Switching of Tetragonal Zirconias
Authors: Bowman Keith J.
Published: March 2005

Although crystallographic textures are most often attributed to slip or twinning, textures from compression, tension, or grinding of tetragonal zirconias have been ascribed to ferroelastic domain switching. If consideration of this phenomenon is limited to the effect of switching, each deformation mode should have a particular textural result. In this paper a simple geometric model for texture from domain switching is proposed.
Microstructure and Crystallography of Titanium Nitride Whiskers Grown by a Vapor–Liquid–Solid Process
Authors: Nolan Theodore A. , Allard Lawrence F. , Coffey Dorothy W. , Hubbard Camden R. , Padgett Raymond A. , Rawlins Mary H. , Nixdorf Richard W.
Published: March 2005

Titanium nitride whiskers having diameters of 0.5 to 1.5 μm and aspect ratios in the range of 20 to 50 have been produced by a new commercially scalable vapor–liquid–solid process. Electron microscopy studies have shown that most of the whiskers can be classified into two types based upon structure and morphology. The whiskers of one type are single crystals and have a growth direction of (100). Whiskers of the second type are comprised of two crystals having a common (110) growth direction. Both types have smooth surfaces and relatively few internal defects. Additionally, a small percentage of whiskers have considerable internal structure related to significant magnesium impurities.
Metastable Crystallization, Phase Partitioning, and Grain Growth of ZrO2─Gd2O3 Materials Processed from Liquid Precursors
Authors: Leung Dominic K. , Chan Chin‐Jong , Rühle Manfred , Lange Fred F.
Published: March 2005

Aqueous mixtures of Zr(C2H3O2)4 and Gd(NO3)3 were used to prepare chemically homogeneous ZrO2—Gd2O3 solid solutions containing 0 to 9 mol% Gd2O3. The application of kinetically limited equilibria concepts explains why a metastable tetragonal phase crystallized subsequent to precursor pyrolysis from compositions containing <6.5 mol% Gd2O3 and a metastable cubic phase crystallized from precursors with >6.5 mol% Gd2O3. Partitioning experiments for a composition containing 3 mol% Gd2O3 showed that the maximum equilibrium solid‐solubility of Gd2O3 in tetragonal ZrO2 is 1.0 ± 0.1 mol% and the minimum equilibrium solid‐solubility in cubic ZrO2 is 8.0 ± 0.2 mol% at 1400°C. Although phase partitioning appeared to initiate during heating, complete partitioning at 1400°C required ∼ 200 h. Large compositional variations (≤±1 mol% Gd2O3) were observed within tetragonal grains and from grain to grain during the first 50 h at 1400°C, whereas the composition of cubic grains produced during partitioning were relatively invariant. Experiments showed that this compositional variability was not present in material rapidly heated to 800°C, but was a result of partitioning. At 1400°C, growth of the tetragonal grains was very sluggish; it increased only to 3 μm after 500 h, whereas the number of larger cubic grains increased during this same period. The implications of these observations are related to the processing of rare‐earth‐stabilized ZrO2 transformation‐toughened materials.
Effect of Interfacial Roughness on the Frictional Stress Measured Using Pushout Tests
Authors: Jero Paul D. , Kerans Ronald J. , Parthasarathy Triplicane A.
Published: March 2005

A fiber which is partially pushed out of a surrounding matrix and subsequently pushed in the opposite direction exhibits a substantial decrease in sliding friction as it passes through its original position (its “origin”). This is manifest by a decrease in the load required to push the fiber. It is suggested that interfacial roughness causes this phenomenon and that the decrease in load (friction) is associated with the fiber seating back into its original position. The period of the drop has been correlated with the spatial extent of the interfacial surface roughness, and the magnitude of the drop (referred to hereafter as the seating drop) has been correlated with the amplitude of the interfacial roughness. Observation of the seating drop allows separation of the friction associated with interfacial irregularities from that resulting primarily from residual stresses at the interface. Implications for composite design and use are discussed. The effect of abrasion at the sliding interface is also addressed.
Preparation of Calcium Lanthanum Sulfide Powders via Alkoxide Sulfurization
Authors: Han Yong , Akinc Mufit
Published: March 2005

Calcium lanthanum sulfide powders were prepared by reacting methoxides of calcium and lanthanum with H2S. Alkoxide mixtures of various La/Ca ratios dispersed in methanol were reacted with H2S at 25° to 85°C and the amorphous gels obtained after the removal of methanol were heat‐treated in H2S for full sulfurization at various temperatures. Up to 500°C, cubic LaS2 was the only crystalline phase present. Calcium lanthanum sulfide phase started to form at 550°C. In the temperature range of 650° to 750°C, single‐phase calcium lanthanum sulfide powders were obtained for La/Ca = 2.41 and 2.68.
Direct Measurement of Crack Tip Stresses
Authors: Haerle Andrew G. , Cannon W. Roger , Denda Mitsunori
Published: March 2005

Raman microprobe spectroscopy was used to measure the crack tip stress distribution in single‐crystalline silicon using a wedge‐loaded double cantilever beam (dcb) specimen. The wedge was advanced until the crack just propagated. After the crack arrested, the stresses were measured between 3 and 20 μm directly ahead of the crack. An average value of –0.43 was obtained for the slope of log stress vs log distance from the crack tip, rather than the theoretical value of –0.5. The value of KI was determined from (1) the intercept of this curve and (2) the slope of stress against
.
The values were in good agreement. The average experimental value of KI was determined to be 0.71 MPa · m1/2, compared to literature values for the KIC ranging from silicon of 0.8 to 0.94 MPa · m1/2. The value measured with the Raman is the arrest value of KI and is expected to be lower from kinetic energy considerations associated with wedge‐loaded dcb specimens.
Effect of Nitridation Rate on the Composition and Conductivity of Titanium Nitride Films Prepared from Sol–Gel Titania
Authors: Keddie Joseph L. , Li Jian , Mayer James W. , Giannelis Emmanuel P.
Published: March 2005

Nitridation of TiO2 films in NH3 was studied as a function of heating rate by 14N(α, α)14N and 16O(α, α)16O nuclear resonance, Auger depth profiling, X‐ray diffraction, and electrical conductivity measurements. TiN films containing minimal amount of oxygen and exhibiting the lowest resistivity were obtained when the fastest nitridation rate (70°C/min) was used. Nitridation at slower rates not only increased the film‐oxygen content and electrical resistivity but also produced an oxygen concentration gradient across the film.
Polymorphs of Cobalt Oxide
Authors: Grimes Robin W. , Lagerlöf K. Peter D.
Published: March 2005

Through controlled thermal decomposition of cobalt acetate tetrahydrate, cobalt monoxide can be synthesized with three different crystal structures: rock salt, zinc blende, and wurtzite. Using electron microscopy techniques, it is shown that the polymorphs exhibit characteristic crystallite morphologies; “tetrahedral” for the zinc blende type and “lathlike” for the wurtzite form. Atomistic simulation calculations predict the lattice energies of the three polymorphs to be relatively close, with the rock salt polymorph being most stable, followed by the wurtzite form and lastly zinc blende.
Aging Behavior of xPb(Fe2/3W1/3)O3· (1 –x)Pb(Fe1/2Nb1/2)O3 Ceramic
Authors: Ling Hung C. , Yan Man F. , Rhodes Warren W.
Published: March 2005

The aging behavior of a series of lead perovskite dielectrics with the compositions xPb(Fe2/3W1/3)O3·(1 –x)Pb(Fe1/2‐Nb1/2)O3, where 0 ≤x≤ 1, and the effect of dopants were studied. Below the Curie temperature (Tc), the capacitance and the dissipation factor (tan δ) decrease approximately linearly with logarithmic time. The aging rate depends on the temperature difference, ΔT, between the aging temperature and Tc, and on the dopant concentration, but is independent of the measurement frequency between 1 and 1000 kHz. The maximum aging rate is about 3% per decade of time for capacitance and 5% per decade for tan δ at 1 mol% dopant concentration, and increases to 6.3% for capacitance and 8.5% for tan δ at 0.7 mol% dopant concentration. These results are consistent with an aging mechanism caused by changing ferroelectric domain structure with time, as proposed for BaTiO3.
Mechanical Properties of Si2N2O/SiC‐Whisker Composites
Authors: Lio Satoshi , Yokoi Hitoshi , Watanabe Masakazu , Matsuo Yasushi
Published: March 2005

The mechanical and thermal properties of Si2N2O/SiC‐whisker composites were studied with emphasis on the effect of matrix composition and of whisker content. The fracture toughness of Si2N2O was remarkably improved by 90% with a concomitant 70% strength improvement by addition of SiC whiskers of only 10 vol%. Optimum mechanical and thermal properties of Si2N2O/SiC‐whisker composites were obtained at an equimolar ratio of Si3N4/SiO2, which is the stoichiometric composition for Si2N2O. Additional investigation concerning the Si2N2O‐matrix/SiC‐whisker interface by controlling sintering additives is necessary for further improvement of mechanical and thermal properties of Si2N2O/SiC‐whisker composites.
EXAFS Study of Cation Distribution in Nickel Aluminate Ferrites
Authors: Yao Takeshi , Imafuji Osamu , Jinno Hiroshi
Published: March 2005

A new method for analyzing the cation distribution of spinel crystals by extended X‐ray absorption fine‐structure spectroscopy has been developed to overcome the disadvantage of X‐ray diffraction, which cannot readily distinguish among different transition‐metal ions. EXAFS analysis was conducted on Ni2+ and Fe3+ ions in nickel aluminate ferrites, and the cation distributions obtained were in good agreement with values obtained by other methods. The ratio of tetrahedral sites occupied by Ni2+ ions decreases with increasing iron content. Fe3+ ions distribute nearly equally to both tetrahedral and octahedral sites. Apparently, not only crystal‐field stabilization energy but also ion size affects cation distribution.
Diffusion‐Induced Grain‐Boundary Migration in Ceria‐Stabilized Tetragonal Zirconia Polycrystals
Authors: Schmid Herbert K.
Published: March 2005

The microstructure and microchemistry of grain‐boundary regions in (CeO2+ La2O3)‐stabilized tetragonal ZrO2 polycrystals (Ce(La)‐TZP) were studied by means of transmission electron microscopy (TEM). Evidence was found for the existence of crystalline and vitreous intergranular phases situated in small pockets at multiple grain junctions and in thin films along grain boundaries. In this ceramic system grain‐boundary migration was observed in situ in the TEM in sample areas subjected to electron irradiation. Interfaces migrated away from their centers of curvature. Evidence was found for Ce de‐alloying in the volume swept by the advancing boundaries. It is suggested that the coherency lattice strain brought about by a partial reduction of Ce, resulting in the diffusion of Ce3+ along grain boundaries to free surfaces, is the driving force for this phenomenon.
Indentation Determination of Crack Growth Parameters in Gallium Arsenide
Authors: White Grady S. , Freiman Stephen W. , Wilson Anne M.
Published: March 2005

Indentation measurements of the environmentally enhanced crack growth parameter, n, in GaAs have been made in water, acetonitrile, and methanol. Reasonable agreement with n values obtained from double‐cantilever‐beam tests was obtained. It is concluded that the range of n values which can be measured by the indentation technique is much wider than previously observed, and is strongly dependent upon the experimental configuration employed.
Scanning Tunneling Microscopy of Optical Fiber Corrosion: Surface Roughness Contribution to Zero‐Stress Aging
Authors: Robinson R. S. , Yuce Hakan H.
Published: March 2005

Strength, fatigue resistance, and zero‐stress aging behavior control the long‐term mechanical reliability of optical fibers. Zero‐stress aging refers to the loss of strength of high‐strength glass fibers after exposure to some corrosive environments in the absence of stress. Understanding the effect of the chemical environment under zero stress on the subsequent fracture strength of optical fibers is important because optical fibers in service will probably encounter water and other chemical species while exposed to zero‐ or low‐stress conditions. In this work, the strength of fibers aged under zero‐stress conditions at 80°C in deionized water has been measured. Scanning tunneling microscopy was also used to measure the roughening of the fibers from corrosion at intervals during the aging. The product of the median inert strength of fibers aged for various times and the square root of the roughness depth of fibers was constant within experimental error. The results show that surface roughening contributes to zero‐stress aging in silica fibers.
Iron and Spinel Precipitation in Iron‐Doped Sapphire
Authors: Moon Anthony R. , Phillips Matthew R.
Published: March 2005

Single crystals of Al2O3 containing 0.5 wt% Fe were exposed to low po2 atmospheres at 1500°C to produce precipitate phases. Analytical TEM identified the precipitate phases as spinel (hercynite) and iron, with the following orientation relationships: 〈001〉Fe‖〈2201〉s with {110}Fe‖{1120}s, 〈111〉Fe‖〈1010〉s with {011}Fe‖ (0001)s, and 〈110〉H‖〈0110〉s with {111}H‖ (0001)s. The three phase fields observed — (Fe, Al)2O3, spinel +α‐Al2O3, and iron +αAl2O3— are in accordance with phase stability diagrams. Precipitation kinetics indicate that oxygen is mobile in the reduced region of the crystal.
Effect of Vapor—Liquid—Solid and Vapor—solid Silicon Carbide Whiskers on the Effective Thermal Diffusivity/Conductivity of Silicon Nitride Matrix Composites
Authors: Russell Laura M. , Donaldson Kimberly Y. , Hasselman D. P. H. , Corbin Normand D. , Petrovic John J. , Rhodes James F.
Published: March 2005

A study was conducted of the relative effect of vapor—liquid—solid (VLS) and vapor—solid (VS) SiC whiskers on the effective thermal diffusivity and conductivity of pressed‐densified silicon nitride. It was found that VLS whiskers cause an increase in the thermal diffusivity/conductivity, whereas the opposite effect was found for the VS‐SiC whiskers. Comparison with composite theory suggests that the VS‐SiC whiskers have a thermal conductivity as low as 25 to 30 W/(m·K). In contrast the VLS‐SiC whiskers appear to have a value for the thermal conductivity of at least about 100 W/(m·K) to as high as 250 W/(m·K). These large differences in thermal conductivity for these two types of SiC whiskers are attributed to the much larger density of structural defects in the VS‐SiC whiskers, which act as phonon scatterers, thereby lowering the thermal conductivity.
Synthesis and Characterization of Barium Lanthanum Titanates
Authors: Guha J. P.
Published: March 2005

Ternary compounds in the system BaO—TiO2—La2O3 were prepared by the solid‐state reaction technique at temperatures between 1300° and 1400°C using precursor oxides as the starting materials. In an alternative processing technique, BaTiO3 was reacted with appropriate proportions of prefabricated lanthanum titanates at 1350°C to obtain the compounds. Two compounds were identified in the TiO2‐rich region of the system. The X‐ray powder diffraction pattern of a compound with a chemical composition BaLa2Ti3O10 (BaO·La2O3·3TiO2) is indexed on the basis of an orthorhombic unit cell with a= 7.665 × 10−1 nm, b= 28.524 × 10−1 nm, and c= 3.876 × 10−1 nm. The other compound, which has a chemical composition Ba4La8Ti17O50 (BaO·La2O3·4.25TiO2) occurs in a narrow homogeneity range within the system. The X‐ray powder diffraction pattern of the compound is indexed on the basis of an orthorhombic unit cell with a= 12.317 × 10−1 nm, b= 22.394 × 10−1 nm, and c= 3.881 × 10−1 nm. Both the compounds are compatible with BaTiO3 and form pseudobinary joins with BaTiO3 in the system BaO—TiO2—La2O3.
Bioceramics: From Concept to Clinic
Authors: Hench Larry L.
Published: March 2005

Ceramics used for the repair and reconstruction of diseased or damaged parts of the musculo‐skeletal system, termed bioceramics, may be bioinert (alumina, zirconia), resorbable (tricalcium phosphate), bioactive (hydroxyapatite, bioactive glasses, and glass‐ceramics), or porous for tissue ingrowth (hydroxyapatite‐coated metals, alumina). Applications include replacements for hips, knees, teeth, tendons, and ligaments and repair for periodontal disease, maxillofacial reconstruction, augmentation and stabilization of the jaw bone, spinal fusion, and bone fillers after tumor surgery. Carbon coatings are thromboresistant and are used for prosthetic heart valves. The mechanisms of tissue bonding to bioactive ceramics are beginning to be understood, which can result in the molecular design of bioceramics for interfacial bonding with hard and soft tissues. Composites are being developed with high toughness and elastic modulus match with bone. Therapeutic treatment of cancer has been achieved by localized delivery of radioactive isotopes via glass beads. Development of standard test methods for prediction of long‐term (20‐year) mechanical reliability under load is still needed.
Rapid Hot‐Pressing of Ultrafine PSZ Powders
Authors: Matthews M. Dean , Pechenik Alexander
Published: March 2005

The process of compaction and densification of ultrafine (40‐ to 60‐nm grain size) powder of partially stabilized zirconia with 3 mol% of Y2O3 (Y3‐PSZ) during rapid hot‐pressing was investigated. A special apparatus was designed to allow rapid application of 1.6 GPa of quasi‐isostatic pressure at temperatures of 1100° to 1300°C to powder compacts encapsulated in glass under vacuum. Pressure was applied for 10 s, then the samples were rapidly cooled to room temperature, removed from the encapsulating glass, and characterized using SEM, TEM, and X‐ray diffraction. Density and mechanical properties of the prepared materials were measured and compared with those of similar materials fabricated using conventional hot‐pressing. SEM and TEM observations revealed that the ultrafine grains of the starting powder coarsened rapidly during the initial heating, and the compacts developed large (> 10 μm) and small (< 1 μm) pores. The process of densification under pressure consisted of closing of the large pores, whereas the small pores were relatively unaffected by the application of pressure at all investigated temperatures. The major mechanism of densification during the rapid pressing appears to be rearrangement and sliding of grains around the large pores. The material prepared by rapid pressing at 1300°C had higher hardness (Hv= 1400 versus 1300 kg/mm2) but somewhat lower fracture toughness (KIC= 5.5 versus 6.0 MPa · m1/2) compared with the conventionally hot‐pressed Y3‐PSZ. Density of the material pressed at 1300°C was 97% of theoretical density.
Chemical Vapor Deposition of CuOx Films by Cul and O2: Role of Cluster Formation on Film Morphology
Authors: Hong Lu‐Sheng , Komiyama Hiroshi
Published: March 2005

CuOx films were deposited on silica substrates by the chemical vapor deposition (CVD) method, using CuI and O2 as source gases at low pressure in a tubular reactor. The growth mechanism to obtain a dense and uniformly distributed (in the axial direction in a tubular reactor) film was investigated. It was found that the occurrence of homogenous nucleation caused an abrupt increase of deposition rate and made the film porous. Homogeneous nucleation can be prevented by properly selecting reactant concentration, reactor temperature, and reactor diameter. Based on an aerosol diffusion theory from laminar pipe flow, a method of predicting cluster size in this CVD reaction system was proposed. The result showed that the clusters formed by homogeneous nucleation had an average size of about 1 nm in diameter.
Some Considerations of Determination of Residual Stresses and Young's Moduli in Ceramic Coatings
Authors: Hsueh Chun‐Hway
Published: March 2005

Residual stresses that develop during cooling of a ceramic coating/substrate strip are considered. Bending occurs because of an asymmetric stress distribution in the strip. In the presence of residual stresses, strains induced on the surfaces of the coating and the substrate are analyzed when (1) the coating‐substrate interface exhibits a transition from a bonded to a debonded state, and (2) a bending moment is applied to straighten the strip. The result shows that both the residual stress and Young's modulus in the ceramic coating can be determined from the surface strains due to either interfacial debonding or strip straightening, Young's modulus of the substrate, and the thicknesses of the coating and the substrate.
Crystal Growth of Mg2SiO4 and MgSiO3 Single Crystals by the Flux Method
Authors: Ushio Masumi , Kobayashi Nobuo , Suzuki Miyoko , Sumiyoshi Yoshihiro
Published: March 2005

Single crystals of Mg2SiO4 and MgSiO3 have been synthesized by the evaporation‐aided slow‐cooling flux method. Acidic oxides such as V2O5, MoO3, and WO3 were used as the flux, and alkali metallic oxides or calcium oxides were added to the MoO3 and WO3 as flux modifiers. The starting mixture was first held at 1400°C and then slow cooled to 1000°C at a rate of 10 C/h. The temperature difference between the upper and lower limits of the melt was ∼25°C. Using an Li2O─MoO3 system flux with an Li2O:MoO3 ratio of 1:2 produces a polycrystalline clinoenstatite with a 9‐mm crystal size; a 1:1 ratio, however, results in forsterite crystals of 90‐μm size. The metallic oxides (Na2O and K2O) as flux modifiers produce forsterite with a crystal size of 65 and 40 μm, respectively. Similar results are observed when a Li2O─WO3 flux is used. Enstatite (10‐mm size) and forsterite (1.6‐mm size) are produced when the Li2O:WO3 ratios are 1:2 and 1:1, respectively. A V2O5 or CaO·WO3 flux produces no forsterite. The V2O5 flux results in tridymite as a primary phase, whereas calcium and magnesium tungstate were grown from a CaO·WO3 flux. The forsterite single crystals are tabular in form, generally bounded by the planes (001), (100), (010), (110), and (021), and are transparent. The enstatite consists of an aggregation of individual single crystals. The refractive indexes of the forsterite are α= 1.636 ± 0.001, β= 1.653 ± 0.001, and γ= 1.671 ± 0.001 (20°C).
Control of the Microstructure of Alumina–Zirconia Alloys Starting from Inorganic Salts
Authors: Wang Jenqdaw , Raj Rishi
Published: March 2005

Coprecipitated powders of alumina—zirconia, prepared from inorganic salts, crystallized differently than either of the constituents by themselves. Whereas alumina or zirconia, prepared in a similar way, began to crystallize at 370°C, the crystallization of the alloy was delayed until 800°C. When hot‐pressed under 40 MPa at 1400°C, the coprecipitated powders developed crystallographic texture in the α‐alumina phase. Preferred crystal growth under a uniaxial stress is offered as a possible explanation for the crystallographic texture.
Sol–Gel Alumina‐Coated Carbon Film
Authors: Pope Edward J. A. , Almazan Alex , Kratsch Kenneth
Published: March 2005

A simple method for dipcoating porous reticular carbon foam with aluminum oxide thin‐film coatings is presented. Weight gain versus temperature and number of dipcoatings is presented along with scanning electron micrographs of uniform, adherent alumina thin films. Composite foam structures of up to 57% alumina have been prepared.
Hot Isostatic Pressing of Sintered Silicon Nitride
Authors: Kim Sang S. , Baik Sunggi
Published: March 2005

Pressureless‐sintered silicon nitride with varying additives was hot isostatic pressed under 150 MPa of nitrogen at 1800°C. Moderate increases in densities were observed when sintered densities exceeded 90% of theoretical. However, density changes became insignificant as the amount of additives exceeded 12 wt%; moreover, density reduction was occasionally observed. Microstructural analysis, after the silicon nitride was reannealed at 1650°C under 0.1 MPa of nitrogen, revealed that intergranular glass was supersaturated with nitrogen and “bloated” as a result of nitrogen evolution. This result suggested that the effectiveness of container‐free hot isostatic pressing of silicon nitride was severely limited by enhanced solubility of nitrogen gas in the glassy phase under high pressure.
Processing, Mechanical Properties, and Oxidation Behavior of Silicon Oxynitride Ceramics
Authors: Ohashi Masayoshi , Kanzaki Shuzo , Tabata Hideyo
Published: March 2005

Silicon oxynitride ceramics were prepared by hot‐pressing an equimolar Si3N4+ SiO2 mixture with 3 mol% CeO2. The Ce2O3/SiO2 ratio of intergranular phase (liquid phase) increased as the formation of Si2N2O proceeded. The intergranular liquid remained as a glass on cooling until the Ce2O3/SiO2 ratio exceeded a certain value, at which point the liquid crystallized. There were great differences in thermal and mechanical properties and oxideation behavior between the specimen containing intergranular glassy phase and the one containing intergranular crystalline phase (Ce5(SiO4)3N–Ce4.67(SiO4)3O). The specimen containing the intergranular glassy phase showed excellent hightemperature strength and oxidation resistance.
Tape Casting and Sintering of Strontium‐Doped Lanthanum Chromite for a Planar Solid Oxide Fuel Cell Bipolar Plate
Authors: Tai Lone‐Wen , Lessing Paul A.
Published: March 2005

Nonagglomerated strontium‐doped lanthanum chromite powders were prepared by a modified Pechini resinintermediate process and tape cast to form bipolar plates for a planar solid oxide fuel cell. An air‐sintering technique for the strontium‐doped lanthanum chromite was developed, which involved placing the green tape between Cr2O3‐fired plates. The sintering process was found to be diffusion controlled, with densification beginning at the surface and proceeding to the interior. A bipolar plate of 2‐mm thickness was fired to more than 93.5% theoretical density when fired at 1670°C for 7 h.
Kinking and Cracking Caused by Slip in Single Crystals of Silicon Carbide
Authors: Suematsu Hisayuki , Suzuki Tetsuya , Iseki Takayoshi , Mori Tsutomu
Published: March 2005

α‐SiC single crystals were compressed parallel to the basal plane, (0001), at temperatures between 900° and 1500°C. Plastic deformation by slip on the basal planes which accompanied kinking occurred above 1000°C. At kink boundaries, two kinds of cracks were observed. One was the cracks elongated parallel to the basal plane. This kind of crack was initiated by the tensile stress produced by piled‐up dislocations on the basal planes against a kink boundary. The other was on a kink boundary, and was induced by the stress of dislocations, heterogeneously distributed on the kink boundary. The initiation of cracks produced by dislocations was considered to be a possible cause of fracture in polycrystalline SiC at high temperatures.
The Calcia–Zirconia Phase Diagram Revisited: Stability of the Ordered Phases φ1 and φ2
Authors: Dickerson Robert M. , Heuer Arthur H.
Published: March 2005

Single crystals of CaO‐stabilized ZrO2 containing between 15.3 and 18.9 mol% CaO were heat‐treated for 5000 h at 1200°C to study the stability of the ordered defect‐fluorite phase, CaZr4O9 (φ1). Subsequent TEM analysis of the equiaxed φ1 domains in samples richer than approximately 18 mol% in CaO showed a random distribution of φ1 variants, with no preferred interfacial habit planes. A critical review of the literature, combined with the new data, supports the Stubican‐Hellmann‐Hannon version of the phase diagram in the region 15 to 26 mol% CaO and 1000° to 1400°C and strongly suggests that φ1 is a stable phase in the ZrO2‐CaO systems.
Prebreakdown Conduction in ZnO Varistors
Authors: Castro Miriam S. , Nuñez Guillermo M. , Resasco Daniel E. , Aldao Celso M.
Published: March 2005

A model which quantitatively accounts for the important features of prebreakdown conduction in ZnO‐based metal oxide varistors in presented. The prebreakdown current dependence with applied voltage and temperature enables us to extract several features for the grain boundary. Estimations have been made for the local electron concentration in polycrystalline ZnO near the grain boundary and for the grain boundary potential barrier height.
Pressure‐Induced Phase Transformation of HfO2
Authors: Arashi Haruo
Published: March 2005

The pressure dependence of the Raman spectra of HfO2 was measured by a micro‐Raman technique using a singlecrystal specimen in the pressure range from 0 to 10 GPa at room temperature. The symmetry assignment of Raman bands of the monoclinic phase was experimentally accomplished from the polarization measurements for the single crystal. With increased pressure, a phase transformation for the monoclinic phase took place at 4.3 ± 0.3 GPa. Nineteen Raman bands were observed for the high‐pressure phase. The spectral structure of the Raman bands for the high‐pressure phase was similar with those reported previously for ZrO2. The space group for the high‐pressure phase of HfO2 was determined as Pbcm, which was the same as that of the high‐pressure phase for ZrO2 on the basis of the number and the spectral structure of the Raman bands.
Phase and Property Studies of Boron Carbide–Boron Nitride Composites
Authors: Ruh Robert , Kearns Michael , Zangvil Avigdor , Xu Youren
Published: March 2005

Boron carbide–boron nitride particulate composites were fabricated by vacuum hot‐pressing. Near‐theoretical densities of B4C were obtained, but percent theoretical densities decreased with increasing amounts of BN. The grain size of B4C and BN was not affected by composition, but the amount of twinning in B4C decreased with increasing BN content. No third phase was found at the B4C–BN interface by analytical STEM analysis. Lattice parameter measurements indicated slight solubility of B4C in BN, but no solubility of BN in B4C for samples hot‐pressed at 2250°C. Room‐temperature flexural strength measurements revealed a sharply decreasing strength with increasing BN content up to 40% BN, and then relatively constant values with greater amounts of BN.
Effects of Water Content on the Properties of Sodium Aluminosilicate Glasses
Authors: Jewell John M. , Shelby James E.
Published: March 2005

Sodium aluminosilicate glasses of the general formula 25Na2O.xAl2O3.(75 –x)SiO2 were prepared with a range of hydroxyl contents. Both the glass transformation and isokom temperatures decrease as the hydroxyl content increases. The magnitude of the decrease in each property is a function of the alumina content of the glass, with the largest effects occurring for the glass containing 25 mol% Al2O3. The magnitude of the effect of water as a function of alumina content reflects the decrease in the concentration of nonbridging oxygens in the glass with increasing Al2O3 content, since the effect of the terminal hydroxyl species on the connectivity of the glass is enhanced by the elimination of nonbridging oxygens. The results indicate that the large effect of water content on the properties of these glasses must be considered when discussing the role of alumina in glasses.
Structural Instability and Microstructural Change of La3+‐Doped M‐Type Calcium Ferrite
Authors: Fang Tsang‐Tse , Hwang Jiung‐Bin
Published: March 2005

Several compositions were selected to investigate the formation of M phase. It was found that by reducing Fe2O3 or increasing La2O3, we were able to obtain pure M phase, as deduced from X‐ray patterns, but CaO.2Fe2O3 was always observed in micrographs of the polished surfaces. The instability of the M phases might be due to the distortion of the lattice structure. The development of humps in the microstructures was related to the distribution of La3+. Retardation in the formation of M phase when sintered in O2 could be interpreted by the defect equation.
Thermodynamics of Vapor Synthesis of AlN by Nitridation of Aluminum and Its Halides
Authors: Hashman Thomas W. , Pratsinis Sotiris E.
Published: March 2005

A thermodynamic analysis for the vapor synthesis of AlN is presented. A thermodynamic equilibrium computer code and recent thermochemical tables are used to evaluate various reactant gases for their potential to produce high‐purity AlN at high yields. The Al/N/H/X/Y systems are examined, where X is any halide atom and Y is an inert gas. The effects of reactant ratio, temperature, and pressure on reactant conversion and product purity are estimated. Results from two systems are presented in the form of design diagrams, which represent the phases formed and the conversion achieved at various process conditions.
Diffusional Creep and Cavitational Strains in High‐Purity Alumina under Tension and Subsequent Hydrostatic Compression
Authors: Xu Antai , Solomon Alvin A.
Published: March 2005

Diffusional creep and cavitation in pure alumina prepared with three different fabrication processes are compared under tension and subsequent hydrostatic compression. The deformation rates are separated into a volume‐conserving creep rate and cavitational rate by measuring the longitudinal and transverse strains intermittently during deformation. Concurrent grain growth causes the volume‐conserving strain rate to decrease in a manner consistent with Nabarro‐Herring creep. The creep stress index of n= 1.3 and the average activation energy of Q= 480 kJ/mol are also consistent with Nabarro‐Herring creep controlled by aluminum lattice diffusion. Anelastic loading and unloading transients are also identified and separated from the creep strains. High‐voltage electron microscopy indicates that cavities nucleate at grain edges early and continuously in the creep process. The surfaces of these cavities tend after some growth to exhibit negligible curvature and various dihedral angles. The activation energy of Q= 450 kJ/mol and stress dependence of the cavitation rate of n= 1.3 are consistent with a grain boundary diffusional growth mechanism. The loading mode is found to have no significant effect on the cavitation rate during tensile creep and the subsequent decavitation rate during hydrostatic compression. The cavitation and decavitation rates are in good agreement with the model proposed by Speight and Beere when the effects of grain growth on cavity accumulation on grain boundaries are included. Exaggerated grain growth in high‐density specimens can lead to early cavity coalescence and failure.
Hydration of Germanium Oxide Carnotite
Authors: Martin Roger I. , Brown Paul W.
Published: March 2005

The quaternary invariant point was reached in the CaO–GeO2–P2O5–H2O system by the hydration of germanium oxide carnotite. Complete reaction was achieved although the kinetics were very slow. Three products were identified by X‐ray diffraction: calcium germanate hydrate, hydroxyapatite, and calcium hydroxide. Energy dispersive X‐ray analyses established the compositions of the three phases present in the heterogeneous microstructure. Calcium germanate hydrate exhibited a fibrous habit and was present as large individual fibers as well as small thin fibers. The small fibers were intermixed with hydroxyapatite. The latter was observed to form feltlike assemblages. Stacked calcium hydroxide plates were unequivocally observed.