bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Heat Treatment on Crack‐Resistance Curves in a Liquid‐Phase‐Sintered Alumina
Authors: Bennison Stephen J. , Chan Helen M. , Lawn Brian R.
Published: March 2005

The effects of heat treatment on the Rcurve (crack‐resistance) behavior of a commercial liquid‐phase‐sintered (LPS) alumina have been studied using the indentation–strenght test. An enhancement of the R‐curve characteristic of this LPS alumina is obtained by a treatment that increases the scale of the microstructure. The enhanced R‐curve characteristic leads to the desirable property of flaw tolerance, albeit at the expense of a diminished strenght at small crack sizes. The implications of these findings are discussed with reference to processing and design strategy.
Small‐Specimen Double‐Cantilever‐Beam Test Applicable to Monoliths and Joints
Authors: de With Gijsbertus
Published: March 2005

A small‐specimen double‐cantilever‐beam test has been used to measure the tughness of monolithic ceramics and joined ceramics. The specimen was tested on several monolithic ceramics to evaluate its quality before it was used for joints. Despite the small dimensions of the specimen, the test appears to be reliable and to yield reproducible data. Two bonding processes were used for joining single‐crystal Mn‐Zn ferrite tiles. After optimization, toughness values were comparable to those of single crystals.
Diffusion of Sputtered Vanadium, Nickel, and Silver in Lead Magnesium Niobate Ceramic
Authors: Ling Hung C.
Published: March 2005

The sputtering of nickel‐vanadium (Ni‐V) and silver (Ag) to form thin films on lead magnesium niobate (PMN) ceramic substrates has been studied. An empirical equation was derived which correlated the average Ni‐V film thickness with three sputtering variables: input power, argon pressure, and sputtering time. The films were dense, smooth, and feature less. Upon annealing at 800°C in argon, both Ni and V diffused into PMN; but reverse diffusion from the ceramic into the metal film was not observed. Vanadium diffused at a faster rate than Ni, leaving pores in the film. The diffusion coefficient of Ni in PMN was determined to be 4.1 × 10−12 cm2/s, whereas the diffusion coefficient of V was determined to be between 3.5 × 10−9 and 2.9 × 10−11 cm2/s at 800°C. Sputtered Ag was also dense, smooth, and featureless. However, the diffusion of Ag at 800°C in PMN was much slower than that of either Ni or V.
Type II Magnetic Levitation on Sinter‐Forged YBa2Cu3Ox Superconductor
Authors: Wang Jenqdaw , Yanoviak Margaret M. , Raj Rishi
Published: March 2005

Submicrometer powder of singlephase YBa2Cu3Ox (YBC), prepared from nitrate salts, were free‐sintered and sinter‐forged at 1223 K. The levitation force on magnets exerted by the superconductor was found to depend on the thickness of the superconductor, the shear strain imposed during sinter‐forging, and the time and temperature of the high‐pressure oxygen anneal after sinter‐forging. The first result is direct proof of the type II nature of the YBC superconductor. In the second experiment a shear strain of 300% increased the levitation force by a factor of 3. The third result confirmed that YBC transforms to the tetragonal structure at 1223 K, which must be restored to the orthorhombic structure by annealing at lower temperature. Optimum results were obtained when the specimens were annealed in pressurized oxygen (3 MPa) for 50 h at 673 K.
Structural Changes by Compressive Stresses of 2.0‐mol%‐Yttria‐Stabilized Tetragonal Zirconia Polycrystals
Authors: Kitano Yukishige , Mori Yuuji , Ishitani Akira , Masaki Takaki
Published: March 2005

Reorientation of the tetragonal (002) peak in tetragonal ZrO2 polycrystals (TZP) (so‐called domain switching) was studied by XRD and residual stress measurement using TZP specimens containing 2.0 mol% Y2O3 that had undergone mechanical and thermal treatments and compressive stress. The observed domain switching was due to a preferred transformation of the tetragonal phase caused by compressive stress above 70 MPa leading to a remnant c‐axis orientation normal to the compressive direction. Domain switching did not depend on thermal stress but arose directly from the tetragonal phase with little relation to monoclinic phase.
Reaction of Zirconia with Silica at the Stoichiometry of Zircon
Authors: Trappen Karen M. , Eppler Richard A.
Published: March 2005

Zirconia was combined with silica and halide mineralizers and fired in a nitrogen atmosphere. X‐ray analysis showed zircon was formed, demonstrating that an oxygen atmosphere is not necessary for the formation of zircon. The reaction mechanism is the same as that forming zircon in air, involving transport of the silica as a volatile halide, followed by diffusion of silica and oxygen across the product layer to a reaction site on the zirconia.
Ferroelectric‐Domain Structure in Piezoelectric Ceramics
Authors: Lucuta Petru Grigorie
Published: March 2005

Twin‐related (tetragonal (T), rhombohedral (R)) adjacent ferroelectric domains, which require a smaller energy for the rotation of the polarization vector, have been found to occur in lead zirconate titanate type piezoceramics at the morphotropicphase boundary, explaining the triplet splitting observed in electron diffraction patterns. The values of elastically stored energy density in the walls of the twinning domains are estimated, and a packing model of the ferroelectric domain structure as a T1RT2RT1…succession is proposed to explain the coexistence of the two ferroelectric phases in the morphotropicphase boundary region. A crystallographic analysis of the transformation from the paraelectric to the ferroelectric phase is performed on the basis of martensite transformation theory. The calculated results are in good agreement with the observed transmission electron microscopy data. In particular, the crystallography and morphology of the “herringbone” domain structure, often observed in piezoelectrio ceramics, are well explained by this analysis.
Strengthening of Ceria‐Doped Tetragonal Zirconia Polycrystals by Reduction‐Induced Phase Transformation
Authors: Heussner Karl‐Heinz , Claussen Nils
Published: March 2005

Phase‐transformation‐induced compressive surface stresses were introduced into ceria‐doped tetragonal zirconia polycrystals by reduction of CeO2. Four‐point‐bending strength of sintered ZrO2 containing 12 mol% CeO2 increased from 240 to 545 MPa after it was annealed at 1400°C for 2 h in nitrogen. The strength of the same material hot isostatically pressed in oxygen increased after it was annealed in nitrogen for 2 h at 1500°C from 430 to 595 MPa.
Effect of Wear Damage on the Strength of Hot Isostatically Pressed Silicon Nitride
Authors: Wang Zhiping , Ruiz Carlos
Published: March 2005

Bending tests have been used to characterize the effect of wear damage of hot isostatically pressed silicon nitride in contact with waspaloy at 600°C. The problem arises at the junction between turbine blades and disks where wear may result in premature fatigue cracking of the blade root. The tests show that wear always results in a reduction of strength, whereas the Weibull modulus may decrease or remain unchanged, depending on the amount of surface damage.
MoO2 Diffusion in Aluminosilicate Glass
Authors: Samuel Edwin , Hrma Pavel
Published: March 2005

A diffusion couple of an oxidized molybdenum disk and a glass cylinder was used to measure the solubiiity and effective binary diffusion coefficient of MoO2 in a non‐alkali aluminosilicate glass. At 1400°C, the solubility limit was 8.4 mol%; the value of the diffusion coefficient (4.1 × 10−16 m2/s) was significantly lower than that estimated from the Stokes‐Einstein relation.
Synthesis and Characterization of Lead‐Titanium Complex Alkoxide
Authors: Kezuka Kayo , Hayashi Yoshihiro , Yamaguchi Takashi
Published: March 2005

Characterization of Pb‐Ti complex alkoxide has been made by molecular weight determination and viscosity measurement. Complex alkoxides were prepared by heating an equimolar mixture of lead acetate and tetrabutoxytitanium in different solvent species such as methoxyethanol, butoxyethanol and xylene under different time‐temperature conditions. Analysis by the Mark‐Houwink equation proposed that the early complex alkoxide molecules are spherical up to tetramers but change to an elongated structure on further polymerization. Thus, a sharp increase in viscosity observed after extended reaction time has been explained as due to the formation of polymers with high aspect ratios. The gelation time increased with increasing molecular weight in the spherical region but decreased in the high aspect ratio region.
Alumina Monolith Formation by Flocculation of Boehmite Sols
Authors: Horn Debra S. , Messing Gary L.
Published: March 2005

Flocculating a boehmite sol with ammonia results in drying and shrinkage uniformity which contributes to the formation of a dry monolithic gel. It is demonstrated that flocculation immobilizes the randomly dispersed platelet‐shaped boehmite particles, inducing uniform shrinkage and density in the gel structure. Flocculation also increases the rate of gelation and an increased gel integrity is attributed to the cumulative effects of both van der Waals attractive forces and increased hydrogen bond formation (gelation). Flocculation does not adversely effect either phase transformation or sintering of the seeded boehmite gels.
Spherical‐Impact Damage and Strength Degradation in Silicon Nitrides for Automobile Turbocharger Rotors
Authors: Akimune Yoshio , Katano Yasushi , Matoba Kazuo
Published: March 2005

Spherical‐impact damage to two silicon nitrides is investigated. Gas‐pressure‐sintered silicon nitride exhibits an elastic response to impact by spherical partially stabilized zirconia particles, resulting in Hertzian cone‐crack initiation in the sintered body. Pressureless‐sintered silicon nitride, on the other hand, demonstrated an elastic/plastic response, with median/radical‐crack initiation. These differences in behavior are due to their microstructural differences as well as to the different hardness values of the silicon nitrides in relation to those of the PSZ spheres. The postimpact bend strength of silicon nitrides is also degraded when crack length exceeds the inherent flaw size.
Electric Relaxation Studies of Defects and Defect Associates in Dilute Ceria‐Lanthanum Oxide Solid Solutions
Authors: Sarkar Partho , Nicholson Patrick S.
Published: March 2005

Electric modulus formalism was used to study relaxation processes in the 0.75‐mol%‐La2O3‐doped CeO2 system between 387 and 470 K in the frequency range 5 to 107 Hz. Two relaxation processes were observed in the isothermal studies: one at low frequencies due to long‐range migration of free oxygen vacancies (process A) and one at high frequencies due to charge reorientation relaxation of (LaCeVo’defect associates (process B). The relaxation processes were analyzed using a nonexponential decay function (φ(t) = exp[—(t/τoβ] for 0<β1) of the electric field. The activation enthalpy estimated for process A is 0.72 eV and for process B is 0.55 eV.
Thermomechanical Properties of β‐Sialon Synthesized from Kaolin
Authors: Lee Hong‐Lim , Lim Hun‐Jin , Kim Shin , Lee Hyung‐Bock
Published: March 2005

β‐Sialon powder was synthesized by the simultaneous reduction and nitridation of Hadong kaolin at 1350°C in an N2–H2 atmosphere, using graphite as a reducing agent. The average particle size of β‐sialon powder was about 4.5 μm. The synthesized β‐sialon powder was pressureless sintered from 1450° to 1850°C under a N2 atmosphere. The relative density, modulus of rupture, fracture toughness, and microhardness of β‐sialon ceramics sintered at 1800°C for 1 h were 92%, 248 MPa, 2.8 MN/m3/2, and 13.3 GN/m2, respectively. The critical temperature difference (ΔTc) in water‐quench thermal‐shock behavior was about 375°C for the synthesized β‐sialon ceramics.
Thermodynamic Properties of Nonstoichiometric Yttria‐Stabilized Zirconia at Low Oxygen Pressures
Authors: Park Jang‐Hee , Blumenthal Robert N.
Published: March 2005

Thermodynamic properties of 8‐mol%‐yttria‐stabilized zirconia have been determined in the 810° to 1040°C temperature range at low Po2. A high‐temperature solid‐state coulometric titration method was used. The mass action constant, Kma, can be represented at low Po2 as Kma=0.677 exp [(–3.98 ±0.03 eV)/kT].
Extension of Glass‐Forming Region in a ZrF4‐Based System by Rapid Melt Quenching
Authors: Ahlf Dierk , Frischat Guenther H.
Published: March 2005

It was shown that rapid melt quenching can extend the glass‐forming region of a ZrF4–BaF2–YF3–AlF3 composition considerably. Cooling at a rate of ∼102 K · s−1 prevented glass formation at compositions less than about 25 mol% BaF2, whereas quenching at a rate of ∼2×106 K · s−1 resulted in glasses with a BaF2 content as low as about 13 mol%. This high quenching rate was achieved by a specially designed twin‐roller apparatus.
Comparison of Sizes of Magnesia Crystals Calculated from X‐ray Diffraction Line‐Broadening and Transmission Electron Microscopy Observations
Authors: Kim Mun Gyu , Cima Michael J. , Searcy Alan W.
Published: March 2005

When MgO is formed by decomposition of MgCO3 under vacuum, crystal sizes calculated from XRD line breadths are in reasonable agreement with direct TEM observations, 4.4 ± 0.6 nm compared with 3.2 ± 0.8 nm. For aligned MgO crystallites from Mg(OH)2, the sizes calculated are discordant, 14.0 ± 3.0 nm and 2.6 ± 0.7 nm. The sizes calculated from XRD data are too large because the MgO crystallites form from Mg(OH)2 in near‐perfect alignment.
Molybdenum Oxycarbide and Tungsten Oxycarbide Coatings on Silicon Carbide Fibers
Authors: Kmetz Michael , Suib Steven L. , Galasso Francis S.
Published: March 2005

The strength and toughness of fibrous composites depend on the interface properties which control the bonding between the fibers and matrices. One method of controlling the interface involves coating the fiber with an appropriate material. In a previous study, it was found that there is a definite advantage in using low coating temperatures to prevent fibers from degrading. We therefore were interested in a report that Mo2C could be deposited from Mo(CO)6 at temperatures as low as 300° to 475°C. Our studies indicated that the material was not Mo2C, but an oxycarbide, which, with an analogous tungsten oxycarbide coating, was applied to SiC yarns. Both oxycarbides could be converted to the metals by heat‐treating in N2.
Fourier Transform Infrared Microspectroscopy Method to Determine Stress in Sapphire
Authors: Rydzak James W. , Cannon W. Roger
Published: March 2005

Fourier transform infrared microspectroscopy was used to nondestructively measure stress in ceramics, with sapphire being the model material. An infrared transmitting microscope was used to investigate, via external reflectance, spatial areas as small as 100 μm.
Microstructural Evolution in Near‐Eutectic Yttrium Silicate Compositions Fabricated from a Bulk Melt and as an Intergranular Phase in Silicon Nitride
Authors: Lee William E. , Drummond Charles H. , Hilmas Gregory E. , Kumar Suresh
Published: March 2005

Near‐eutectic composition Y2O3─SiO2 melts were formed as bulk samples or as an intergranular phase in Si3N4. Upon cooling to room temperature the bulk material partially crystallized to γ‐Y2‐Si2O7 whereas the intergranular phase was glass. On heat‐treating at 1500°C the bulk material transformed to γ‐Y2Si2O7 whereas the intergranular glass crystallized first to γ‐Y2Si2O7 and then to β‐Y2Si2O7. Possible reasons for the different behavior are discussed.
Oblique Impact of Spherical Particles onto Silicon Nitride
Authors: Akimune Yoshio
Published: March 2005

Oblique impact damage to gas‐pressure‐sintered silicon nitride is investigated by examining changes in the stress field beneath the impact site of the silicon nitride. Varying the impact angle changes the morphologies of the initiated cracks from Hertzian cone crack to surface ring crack as the impact angle decreases. Moreover, impact at greater angles (90° and 60°) creates Hertizian cone cracks that drastically decrease the strength of the target materials; impact at smaller angles (45° and 30°), on the other hand, creates surface ring cracks that cause only moderate strength degradation.
Strength and Toughness Degradation of Tungsten Carbide–Cobalt Due to Thermal Shock
Authors: Han Dongbin , Mecholsky John J.
Published: March 2005

WC–Co composites are widely used as cutting or drilling tools because of their high hardness, strength, and fracture toughness. The working temperature is generally in the range of 300° to 700°C, so thermal shock fracture of WC–Co can occur if the parts are suddenly cooled. In this study, changes in fracture strength and fracture toughness after thermal shock were observed.
Reaction‐Bonded Niobium Carbide on Graphite via a Novel Solution Impregnation Process
Authors: Maclnnes Andrew N. , Barron Andrew R. , Soman Rajiv S. , Gilbert Thomas R.
Published: March 2005

A simple and rapid process has been developed that allows the preparation of NbC‐C composite rods. Graphite rods are impregnated with an ethanolic solution of NbOCl2 and resistively fired (> 1900°C) under an argon atmosphere. The final composite product is found to contain residual carbon particles within a NbC‐C matrix.
Combustion Synthesis of Sialon Powders (Si6‐zAlzOzN8‐z, Z = 0.3, 0.6)
Authors: Zeng Jianren , Miyamoto Yoshinari , Yamada Osamu
Published: March 2005

Fine sialon powders (Si6‐zAlzOzN8‐z, Z = 0.3, 0.6) were prepared by nitriding combustion. Silicon powders was reacted with AlN and Si3N4 under 10 MPa of nitrogen gas. The reaction temperature reached above 2000°C and single‐phase sialon powders were synthesized within minutes. The obtained powders were fully densified without additives by hot isostatic pressing. The sintered body had a flexural strength of 600 MPa by 4‐point bending.
Quantification of Grain Boundary‐Pore Contact During Sintering
Authors: Patterson Burton R. , Liu Yixiong
Published: March 2005

A stereological method has been used to determine the degree of grain boundary‐pore contact during sintering of Al2O3. Al2O3 doped with 200 ppm MgO exhibits a degree of contact of 5.7 times that expected from random intersections with pores, while pure Al2O3 shows a pore contact factor of 4.8. These data are larger than the values of 2.8 for sintered or hot‐pressed UO2, computed from published data, and values of 1.7 and 1.8 for sintered W and Cu powders, respectively. The degree of grain boundary‐pore contact for each material remains constant throughout densification from pressed powder to near full density.
Microstructure and Dielectric Properties of Lead Magnesium Niobate‐Pyrochlore Diphasic Mixtures
Authors: Chen Jie , Harmer Martin P.
Published: March 2005

The microstructure and dielectric properties of lead magnesium niobate (PMN) ceramics containing the determental second phase, pyrochlore, have been studied. The pyrochlore phase within PMN was found to be present as isolated grains in the microstructure with a composition of Pb2(Mg0.25Nb1.75)O6.625 and a preferred octahedral morphology. The amount of pyrochlore second phase can be easily controlled by changing the Mg/Nb ratio on the B‐site of the perovskite structure, and a series of diphasic mixtures from near‐pure PMN to near‐pure pyrochlore were obtained. Its effect on the permittivity follows the isolated Wiener's mixture rule up to a pyrochlore content of 18 vol%.
Effect of Water Concentration on the Properties of Commercial Soda‐Lime‐Silica Glasses
Authors: Jewell John M. , Spess Marie S. , Shelby James E.
Published: March 2005

The effect of water concentration on the properties of three commercial soda‐lime‐silica glasses has been measured. Water (H2O) concentration varied from 50 to 550 ppm‐wt. Properties measured include glass transformation temperature, transformation range viscosity, thermal expansion coefficient, electrical conductivity, and refractive index. The viscosity, Tg, and electrical conductivity decreased with increasing water content, while the thermal expansion coefficient and refractive index were unaffected by changes in water concentration.
Effects of Annealing Conditions of Electrodes on the Photovoltaic Properties of Sintered Cadmium Sulfide/Cadmium Telluride Solar Cells
Authors: Kim Chul S. , Im Ho B.
Published: March 2005

Polycrystalline n‐CdS/p‐CdTe solar cells with a commerical carbon paint on the p‐CdTe layer and an In‐Ag paint on the n‐CdS layer were fabricated by a coating and sintering method. Electrical properties of the conducting paints and solar cell parameters of the heterojunction solar cells were investigated as a function of electrode annealing conditions. The sintered CdS/CdTe solar cells whose electrode contacts were annealed at 350°C for 10 min in nitrogen showed maximum values of short‐circuit current density, fill factor, and solar efficiency. Commercial carbon and silver paints can be used as electrodes to fabricate sintered CdS/CdTe solar cells with efficiency over 10%.
Stress Corrosion Cracking of Bioactive Glass Composites
Authors: Troczynski Thomas B. , Nicholson Patrick S.
Published: March 2005

Bioactive glass was reinforced with 20 vol% Ag particles and 20 vol% SiC whiskers. Fatigue parameters and lifetime data for the two composites were determined via the stressing rate dependence of the bend strength in a bio‐simulating buffered solution (pH of 7.4). A lifetime of 10 yr was estimated for the SiC‐reinforced composites under bend stresses of 34 MPa and for Ag composites under 23 MPa. Stresses for similar survival of pure bioactive glass are 17 MPa.
Preparation of Cobalt‐ and Fluorine‐Doped Barium Hexaferrite by the Glass Synthesis Method
Authors: Zagnazi Hassan , Malassis Marc , Chaumont Christian , Bernier Jean Claude
Published: March 2005

Doped barium hexaferrite (BaFe12‐xCoxO19‐xFx) was prepared by the glass synthesis method. The fluorine improves the pouring of the melt and the crystallization of the glass, while the cobalt decreases the coercive force. Addition of Al2O3 does not significantly alter the properties of barium hexaferrite, but it increases the crystallization. Doped products are attractive for high‐density vertical magnetic recording (1400 < Hc < 2300 Oe, 60 < σs < 68 (emu cgs)/g, and σr/σs≃ 0.5).
The Role of Excess Magnesium Oxide or Lead Oxide in Determining the Microstructure and Properties of Lead Magnesium Niobate
Authors: Wang Hui‐Chieh , Schulze Walter A.
Published: March 2005

Near‐phase pure perovskite lead magnesium niobate (PMN) with MgO or PbO additives was produced by reacting PbO with MgNb2O6 at 800°C and sintering at 1200°C. Dense ceramics were characterized by scanning electron microscopy, X‐ray diffraction, and dielectric measurements. The microstructural studies showed that excess MgO exists as micrometer spherical particles either in the grain boundary as a discrete particle or in the perovskite grain as an inclusion. The pyrochlore phase exists in large isolated grains in the microstructure. The 10 mol% MgO excess composition had a peak dielectric constant of 19 500 at 100 Hz, which suggests very “clean” or uninhibiting grain boundaries. The excess addition of PbO did not improve the yield of perovskite PMN phase and decreased the dielectric constant. PMN grain boundaries are the dominant path of fracture. This paper, to a certain degree, explores the chemistry and characteristics of these grain boundaries.
Genesis of the (111) Twin in Barium Titanate
Authors: Kraševec Viktor , Drofenik Miha , Kolar Drago
Published: March 2005

On the basis of the topotaxy between BaTiO3 and Ba6Ti17O40 found recently, a model of a nonconservative (111) twin in TiO2‐rich BaTiO3 was constructed. The model consists of several (001) layers of Ba6Ti17O40 intergrown between (111) layers of BaTiO3, the core of the twin being a slightly modified double layer of Ba6Ti17O40 containing face‐sharing octahedra. Using this model, anomalous grain growth below the eutectic temperature and preferential growth of (111) twins in a reducing atmosphere were explained, as well a nucleation of butterfly twins.
Electrical Behavior of Ceria‐Stabilized Zirconia with Rare‐Earth Oxide Additives
Authors: Chiou Bi‐Shiou , Dai Hsing‐Tao , Duh Jenq‐Gong
Published: March 2005

The electrical properties of rare‐earth oxide doped CeO2‐ZrO2 ceramics are evaluated by impedance spectroscopy. Doping of the trivalent metal oxide decreases both the grain and grain‐boundary resistivities of the CeO2‐ZrO2 system. The grain and grain‐boundary resistivities as well as the activation energy for conduction increase with the dopant cation radius. The grain conductivity is fairly constant for 2 mol% YO1.5‐10 mol% CeO2‐88 mol% ZrO2 samples sintered under different conditions, while lower grain‐boundary resistivity is obtained for samples sintered at higher temperature for longer times. Possible mechanisms for the electrical behavior of the rare‐earth oxide doped CeO2‐ZrO2 ceramics are proposed and discussed.
Alkoxide‐Hydroxide Route to Syntheltize BaTiO3‐Based Powders
Authors: Chaput Frédéric , Boilot Jean‐Pierre , Beauger Alain
Published: March 2005

When preparing homogeneous, fine barium titanate powders, the major difficulty is to avoid the spontaneous self‐condensation between the Ti‐OH groups. In the usual way of preparing fine barium titanate powders, chelating agents (citrate, oxalate) or simply unidentate ligands (alkoxy or carboxyl groups) are used to complex titanium atoms. Another way is to mix barium and titanium precursors in a strongly basic medium. The condensation between the Ti(OH)2‐6Ba2+ species directly gives the perovskite compound. Using an alkoxide‐hydroxide route, a homogeneous Ba‐Ti solution was prepared that completely advanced by condensation between the Ti(OH)2‐6Ba2+ species and led to a controlled‐stoichiometry powder. Concerning pure barium titanate, dried powders exhibited the cubic perovskite structure, and a direct sintering at 1150°C, without calcination, led to highly dense BaTiO3 bodies with fine‐grained uniform microstructure (1 μm) that exhibited a high permittivity value at room temperature (K= 5400). The alkoxide‐hydroxide method was also used to prepare dense alkaline‐earth perovskite ceramics with complex compositions.
Hydration and Strength Development of T and X Phase Pastes (T = Ca0.69Ba1.31SiO4, X = Ca1.52Ba0.48SiO4)
Authors: Halle Radcvan , Matković Boris
Published: March 2005

T and X phases were investigated with respect to strength development, hydration rate, and composition of hydrated products. Samples of X phase without gypsum addition develop strength more rapidly than corresponding samples of T phase but begin to lose strength after 3 months. The optimal addition of gypsum to X and T phases is 4 wt%. Larger addition of gypsum to T phase samples causes a decrease of sterngth after 3 months hydration.
Defect Equilibria and Transport in YBa2Cu3O7‐x at Elevated Temperatures: III, Defect Model and Conductivity Mechanism
Authors: Ncworthy Janusz , Rekas Mieczyslaw
Published: March 2005

Based on the measurements of electrical conductivity and thermopower (Seebeck coefficient) as a function of oxygen partial pressure, the defect structure and corresponding conduction mechanisms at elevated temperatures are considered for the Y‐Ba‐Cu‐O (1:2:3) system. It has been postulated that the simple hopping model is not applicable to YBa2Cu3O7‐x. A modified conduction hopping mechanism has been proposed and equations describing the mobility of charge carriers in the studied system are derived. The most important advantage of the present model, in comparison to previous models, involves considering interactions between both electrons and electron holes and the resulting effect on their mobility terms. The observed departure of experimental data from the Heikes formula is explained by a very high concentration of defects and resulting substantial interactions between the defects which must be taken into account. The proposed transport model exhibits good agreement with experimental data of nonstoichiometry and the presently determined electrical conductivity and thermopower. It has been argued that the charge transfer mechanism depends substantially on the oxygen partial pressure and resulting oxygen content in the oxide lattice.
Corrosion Resistance and Microstructure of High‐Alumina Refractories, Based on the Rotary Slag Test
Authors: Yang Houng‐Yi , Chan C. F.
Published: March 2005

The corrosion resistance and microstructure of four highalumina and two chromia‐containing high‐alumina refractories were evaluated. Analysis of the refractories after exposure in the rotary slag test showed that the chromia‐containing products had better slag resistance than the chromia‐free products. Three factors contributed to this conclusion, including formation of a Cr‐spinel layer at the slag/refractory interface, formation of an impermeable mullite layer just below the interface, and improved matrix bonding from chromia‐alumina solid‐solution formation.
Voltage‐Current Characteristics of a Simple Zinc Oxide Varistor Containing Magnesia
Authors: Smith Agnès , Gasgnier Gilles , Abélard Pierre
Published: March 2005

This paper examines the effect of MgO addition on the structural and electrical characteristics of a ZnO varistor composition with few dopants. MgO acts as a grain‐growth inhibitor. The electrical performances of the obtained varistors are improved.
Low‐Firing, Temperature‐Stable Dielectric Compositions Based on Bismuth Nickel Zinc Niobates
Authors: Yan Man F. , Ling Hung C. , Rhodes Warren W.
Published: March 2005

Low‐sintering dielectric materials with small temperature co‐efficients were developed. The newly developed materials are based on the Bi2(ZnNb2)O9 and Bi3(Ni2Nb)O9 system with a bismuth‐layered crystal structure. Preliminary results show that these materials have relatively large dielectric constants of 80 to 100, small temperature coefficients of ≤20 × 10−6/°C, and relatively large Q values of 2000 to 3000. Furthermore, these materials can be sintered at temperatures ranging from 850° to 950°C, and these low sintering temperatures might permit the use of a less expensive silver electrode. These materials compare favorably with the conventional NPO (small temperature coefficient) dielectric materials based on MgTiO3.
Transmission Electron Microscopy Study on the Annealing of YBa2Cu3O7‐δ
Authors: Monteiro Othon R. , Johnson Sylvia M.
Published: March 2005

Annealing in oxygen‐rich atmosphere at temperatures between 400° and 600°C is an important step in the manufacture of superconducting YBa2Cu3O7‐δ. The symmetry of the orthorhombic phase requires that if more than one type of twin plane is present within a grain, a distorted region should exist inside the multiple twinned grain. This distorted region hinders the tetragonal‐to‐orthorhombic transformation and may account for some retained tetragonal phase inside an otherwise orthorhombic grain. A physical model is presented describing the formation of such regions and their eventual transformation into low‐angle grain boundaries after long annealing. Extended annealing at intermediate temperatures apparently leads to the formation of planar faults in off‐stoichiometric samples. Transmission electron microscope image contrast and energy dispersive X‐ray analyses of highly defective regions suggest these defects are CuOx (x= 1, 2) extra layers. These extra layers tend to form near grain boundaries or free surfaces, where oxygen is readily available.
Liquid‐Phase Reaction‐Bonding of Silicon Carbide Using Alloyed Silicon‐Molybdenum Melts
Authors: Messner Robert P. , Chiang Yet‐Ming
Published: March 2005

We have investigated reaction‐forming of silicon carbide by the infiltration of carbonaceous preforms using alloyed silicon melts, in order to synthesize composite materials free of the residual silicon phase that has previously limited mechanical properties and upper use temperatures. In this approach, rejection of the alloying component(s) from the primary silicon carbide phase into the remaining melt results in the formation of a secondary refractory phase, such as a silicide, in place of residual free silicon. Experiments conducted in the Si‐Mo melt system show that relatively dense (>90%) silicon carbide‐molybdenum silicide materials free of residual silicon and residual carbon can be obtained. A model for reactive infiltration based on time‐dependent permeabilities is proposed. Processing variables important for control of the reaction rate relative to the infiltration rate, and associated processing flaws, are discussed.
Electron Microscopy of Defects in Epitaxical β‐SiC Thin Films Grown on Silicon and Carbon {0001} Faces of α‐SiC Substrates
Authors: More Karren L. , Kong† Hua Shuang , Glass Jeffrey T. , Davis Robert F.
Published: March 2005

Defects present in β‐SiC thin films epitaxically grown on hexagonal 6Hα‐SiC substrates via chemical vapor deposition have been characterized by transmission electron microscopy. These defects are different from those previously observed in β‐SiC films grown on (100) silicon, which were predominantly stacking faults and microtwins. The most common defects in the films grown on α‐SiC were large domains rotated 60° with respect to each other and were identified as double positioning boundaries. These boundaries are a special type of incoherent twin boundary. Differences observed in films grown on either the silicon or carbon face of the {0001}α‐SiC are characterized as a function of the mechanism of formation of the defects and type of substrate used for growth.
Admittance‐Curve‐Fitting Method for Semiconductive Piezoelectric Ceramics
Authors: Tsurumi Takaaki , Ichihara Takashi , Asaga Kiyoshi , Daimon Masaki
Published: March 2005

The admittance‐curve‐fitting method is proposed to determine material coefficients of semiconductive piezoelectric ceramics. In this method, the frequency dependence of admittance of a plate resonator is calculated around the resonance frequency, and the piezoelectric, elastic, and dielectric coefficients in the theoretical formula are refined to fit the observed data. The result of a simulation using four types of hypothetical ceramics with different conductivities and electromechanical coupling factors indicates that various constants determined by this method are more accurate than those by the conventional method. The fitting method is applied practically to the PZT ceramics and Bi,K‐doped PZT ceramics which show semiconductivity.
Electroceramics from Source Materials via Molecular Intermediates: BaTiO3 from TiO2 via (Ti(catecholate)3)2‐
Authors: Davies Julian A. , Dutremez Sylvain
Published: March 2005

Rutile or anatase may be depolymerized and complexed by sequential treatment with (i) H2SO4/(NH4)2SO4, (ii) H2O, and (iii) catechol/NH4OH to produce the intermediate (NH4)2(Ti(catecholate)3) · 2H2O. Treatment with Ba(OH)2· 8H2O leads to an acid‐base reaction generating Ba(Ti(catecholate)3) · 3H2O, in which the Ba:Ti ratio is held at 1:1 at the molecular level. Calcination produces BaTiO3 powder.
Microstructures and Dielectric Properties of Pure and Doped KNbO3 Ceramics
Authors: Ding Shengping , Shen Jiaqi
Published: March 2005

Regions consisting of grains of pronounced cubic develpment exist in pure KNbO3 ceramics which exhibit a temperature dependence of dielectric constant very similar to that of KNbO3 crystals. KNbO3 ceramics doped with GeO2‐K2O additives have small grains, semiconducting resistance, and a different curve of dielectric constant versus temperature. As the average grain size decreases, the shape of the curve differs increasingly from that of KNbO3 crystals.
Mechanism of Oxygen Diffusion in Glassmelts Containing Variable‐Valence Ions
Authors: Beerkens Ruud G.C. , de Waal Henk
Published: March 2005

A mechanism is proposed to describe the influence of redox reactions, which involve variable‐valence ions, on the diffusional mass transport of molecular dissolved oxygen in glassmelts. The concentration profile for molecular dissolved oxygen in a melt with diffusional transport in one direction in a Cartesian coordinate system is described by a differential equation: ∂(O2/∂t=Dc(∂2[O2]/∂x2), where Dc depends on the actual value of the diffusivity D of physically dissolved oxygen, the local molecular oxygen concentration, the concentration of variable‐valence ions, and the equilibrium constant for the relevant redox reaction. This equation is applicable for diffusion into or outwards from the melt from or into the furnace atmosphere. It is shown here that the value of Dc is always less than D. Concentration profiles for diffusing oxygen in glassmelts with refining agents (containing variable‐valence ions) are thus steeper than profiles in melts without refining agents. A decrease in temperature of a glassmelt with variable‐valence ions generally leads to diffusion of oxygen into the melt. The flux of oxygen gas into (oxidation) or out (reduction) of the melt is proportional to (D/Dc)1/2 and is enhanced by the effect of variable‐valence ions dissolved in the melt.
Pressureless Sintering of SiC‐Whisker‐Reinforced Al2O3 Composites: I, Effect of Matrix Powder Surface Area
Authors: Lee Hae‐Weon , Sacks Michael D.
Published: March 2005

Pressureless sintering of SiC‐whisker‐reinforced Al2O3 composites was investigated. In Part I of the study, the effect of the matrix (Al2O3) powder surface area on densification behavior and microstructure development is reported. Compacts prepared with higher surface area Al2O3 powder showed enhanced densification at lower whisker concentrations (5 and 15 vol%). Samples with 15 vol% whiskers could be pressureless sintered to ∼97% relative density with zero open porosity and ∼1.6‐μm matrix average grain intercept size.
Residual Displacement Effects During Crack Propagation in High‐Toughness Magnesia‐Partially‐Stabilized Zirconia
Authors: Steinbrech Rolf W. , Inghels Eric , Heuer Arthur H.
Published: March 2005

Fracture mechanics testing of high‐toughness MgO‐partially‐stabilized ZrO2 (Mg‐PSZ) using the double‐cantilever‐beam (DCB) geometry leads to large residual displacements in specimens unloaded after partial crack propagation. The residual displacements are due to transformation “plasticity” (the martensitic transformation of tetragonal precipitates within the PSZ) and increase linearly with increasing crack extension; the residual displacements can be eliminated by removing portions of the crack “wake” by machining (renotching). Surprisingly, some residual displacement survived after removal of more than 500 μm from the crack surfaces, implying that the transformation zone was >250 μm in extent. Furthermore, the results suggest subcritical transformation in the zone. Annealing eliminates the residual displacements, due to retransformation of transformed particles. Retransformation began at 500°C and was not completed until 900°C. The residual displacements depend on specimen and crack geometry; thus a geometry dependence is inherent in resistance (R) curves that are derived from load‐displacement‐crack extension data.
R‐Curve Behavior in a Silicon Carbide Whisker/Alumina Matrix Composite
Authors: Homeny Joseph , Vaughn Wallace L.
Published: March 2005

R‐curve measurements were performed on a SiC whisker/Al2O3 matrix composite. A controlled flaw/strength technique was utilized to determine fracture resistance as a function of crack extension. Rising R‐curve behavior with increasing crack extension was observed, confirming the operation of wake toughening effects on the crack growth resistance. Observations of crack/microstructure interactions revealed that bridging by intact whiskers in the crack wake was the mechanism responsible for the rising R‐curve behavior.
Crystal Growth of Tungsten Carbide Plates by Condensation of High‐Temperature Ultrasupersaturated Gas
Authors: Yamada Kenjiro
Published: March 2005

Fine plates of tungsten carbide with hexagonal structure were prepared by condensation of a high‐temperature ultrasupersaturated gas derived from tungsten carbide powder by means of a cylindrical shock wave method. The majority of the plates were equilateral trigonal shape in the basal face. Equilateral or scalene hexagonal, pentagonal, trapezoidal, and rhombic plates were also observed. Trigonal and hexagonal plates had growth directions 〈1010〉 and 〈1120〉 in the basal faces, respectively. It is inferred that the difference between the growth directions of trigonal plates and hexagonal plates is due to differences in the local environment during crystallization. Moreover, the thickning of the plates in a direction perpendicular to the basal face is discussed on the basis of the vapor–liquid–solid growth mechanism.
Self Diffusion in Na2O‐Rb2O‐SiO2 Glass Melts as Obtained by Microgravity Experiments
Authors: Meier Martin , Braetsch Volker , Frischat Günther H.
Published: March 2005

Sodium and rubidium self‐diffusion in several melts of the system (1 −x)Na2·xRb2O·3SiO2 were studied at temperatures greater than 1150°C under microgravity conditions. The diffusion coefficients (D*) may be considered as intrinsic data. At 1250°C, D*Na in this system is nearly independent of Rb2O concentration, whereas D*Rb is more impeded the higher the Na2O content. Furthermore, it can be confirmed that the Nernst‐Planck model, which relates selfdiffusion and interdiffusion coefficients, is also reasonably well fulfilled for this high‐temperature melt state.
Chemical‐Vapor‐Infiltrated Silicon Nitride, Boron Nitride, and Silicon Carbide Matrix Composites
Authors: Veltri Richard D. , Galasso Francis S.
Published: March 2005

Composites of carbon/chemical‐vapor‐deposited (CVD) Si3N4, carbon/CVD BN, mullite/CVD SiC, and SiC yarn/CVD SiC were prepared to determine if there were inherent toughness in these systems. The matrices were deposited at high enough temperatures to ensure that they were crystalline, which should make them more stable at high temperatures. The fiber‐matrix bonding in the C/Si3N4 composite appeared to be too strong; the layers of BN in the matrix of the C/BN were too weakly bonded; and the mullite/SiC composite was not as tough as the SiC/SiC composites. Only the SiC yarn/CVD SiC composite exhibited both strength and toughness.
Fabrication of Titanium Carbide‐Alumina Composites by Combustion Synthesis and Subsequent Dynamic Consolidation
Authors: Rabin Barry H. , Korth Gary E. , Williamson Richard L.
Published: March 2005

Dispersed‐phase composites of TiC‐Al2O3 were fabricated from low‐cost reactants by external ignition of powder compacts followed by dynamic consolidation of the hot products using explosives. Near full densification was achieved using shock pressures as low as 1 GPa. Care must be taken to allow for the escape of evoled gases during exothermic reaction, and rapid cooling of the consolidated composite must be avoided to prevent cracking.
Photoemission Studies of High‐Temperature Superconductivity
Authors: Margaritondo Giorgio
Published: March 2005

Photoemission spectroscopy has recently emerged as one of the leading techniques in the study of high‐temperature superconductors. Relevant successes include the direct detection of the superconductivity gap, tests for departure from Fermi‐liquid behavior, and many interface chemical studies with technological interest. We present a review of the fundamental and applied aspects of this technique; the review is written for readers who are not specialized in electron spectroscopy or surface science.
Atomistic Study of Polarons in YBa2Cu3O7
Authors: Baetzold Roger C.
Published: March 2005

Simulation techniques are applied to the orthorhombic YBa2Cu3O7 crystal in order to describe possible polaron and bipolaron species in the crystal. Perfect crystal properties are fitted well with a two‐ and three‐body potential model. The O− polaron state is significantly stabilized by the presence of holes in the CuO plane. A bipolaron O2−2 is slightly stable on the O4 and O2 or O3 lattice ion sites of oxygen. The oxidation reaction leading to O− and involving Cu+ and oxygen vacancies is exothermic.
Optical Properties of the Vanadium Oxides VO2 and V2O5
Authors: Parker John C. , Geiser Urs W. , Lam Daniel J. , Xu Yongnian , Ching Wai Yim
Published: March 2005

The optical properties of VO2 and V2O5 were determined using spectroscopic ellipsometry. The unique physical properties of these materials will be presented and discussed in conjunction with the materials electronic band structure determined by calculations using the orthogonalized linear combination of atomic orbitalsmethod.
Scanning Tunneling Microscopy of Cubic Silicon Carbide Surfaces
Authors: Chang Chia‐Seng , Zheng Nan‐Jiu , Tsong Ignatius S. T. , Wang Yu‐Cheng , Davis Robert F.
Published: March 2005

Scanning tunneling microscopy is used to study β‐SiC(001) surfaces. The β‐SiC(001) single crystals were epitaxially grown by a two‐steep chemical vapor deposition process on Si(001) wafer substrates. The overall surface topography of β‐SiC is generally much rougher than that of Si wafers. Atomically resolved images corresponding to 3 × 2 and c(2 × 2) geometries of the β‐SiC(001) surface are presented. Our results agree with models constructed from Si dimers for these structures. The larger‐scale images show that the surface is under compressive stress and exhibits high density of defects, e.g., antiphase boundaries (APB's), in some areas. Images with unusual superstructures are also shown.
Effect of Silicon Carbide Whisker and Titanium Carbide Particulate Additions on the Friction and Wear Behavior of Silicon Nitride
Authors: Blanchard Cheryl R. , Page Richard A.
Published: March 2005

A Si3N4/TiC composite was previously demonstrated to exhibit improved wear resistance compared to a monolithic Si3N4 because of the formation of a lubricious oxide film containing Ti and Si at 900°C. Further improvements of the composite have been made in this study through additions of SiC whiskers and improved processing. Four materials—Si3N4, Si3N4/TiC, Si3N4/SiCwh, and Si3N4/TiC/SiCwh— were processed to further optimize the wear resistance of Si3N4 through improvements in strength, hardness, fracture toughness, and the coefficient of friction. Oscillatory pin on flat wear tests showed a decrease in the coefficient of friction from ∼0.7 (Si3N4) to ∼0.4 with the addition of TiC at temperatures reaching 900°C. Wear track profiles illustrated the absence of appreciable wear on the TiC‐containing composites at temperatures above 700°C. Microscopic (SEM) and chemical (AES) characterization of the wear tracks is also included to deduce respective wear and lubricating mechanisms.
Residual Stress in a Soft‐Buffer‐Inserted Metal/Ceramic Joint
Authors: Xian Ai‐Ping , Si Zhong‐Yao
Published: March 2005

Residual stresses in a soft buffer layer developing during cooling of a metal/buffer/ceramic joint were analyzed. It is shown that there is a parabolic distribution for normal stress and a cubic parabola for shear stress in the buffer. The maximum shear stress, τ12 or τ13, is approximately proportional to the ratio of length to thickness of the buffer, and it is far more than the normal stress σ1, σ2 or σ3. With increasing thickness of the soft buffer, the maximum shear stress will decrease, but the normal stress will change little. A new physics parameter m is suggested in this paper to describe the beneficial role of the buffer, and the influence factors of m are also discussed.