bluuebunny/crossref_metadata_2025 huggingface dataset:
Properties of Nitrogen‐Containing Yttria—Alumina—Silica Melts and Glasses
Authors: Saito Noritaka , Kai Kentaro , Furusho Shingo , Nakashima Kunihiko , Mori Katsumi , Shimizu Fumiyuki
Published: July 2009

The viscosity and solubility of nitrogen in Y2O3–Al2O3–SiO2 melts have been systematically examined. The effects of nitrogen content on viscosity for Y‐Al‐Si‐O‐N melts and on Vickers hardness of oxynitride glasses also have been examined. Although the viscosity of Y2O3–Al2O3–SiO2 melts was decreased, the solubility of nitrogen into the melts was increased with increased Y2O3 content. These results indicated that the yttrium ion behaved as a network modifier. Therefore, the structural units for viscous flow became small, and the amount of nonbridging oxygen increased in the melts when the Y2O3 content increased. The viscosity of Y‐Al‐Si‐O‐N melts and Vickers hardness of oxynitride glasses remarkably increased with increased nitrogen content. These results suggested that the substitution of nitrogen for oxygen in the melts may have led to a high average coordination of nonmetal atoms and that the increased cross‐linking produced a more rigid glass network.
Structures of Filled α‐Si3N4‐Type Ca0.27La0.03Si11.38Al0.62N16 and LiSi9Al3O2N14
Authors: Grins Jekabs , Esmaeilzadeh Saeid , Shen Zhijian
Published: July 2009

Single crystals of the nitridosilicate Ca0.27La0.03Si11.38Al0.62N16 with a filled α‐Si3N4‐type structure were obtained when preparing lanthanum nitridosilicates in a graphite furnace accidentally containing calcium residues. The lithium α‐SiAlON LiSi9Al3O2N14 was prepared using spark plasma sintering, with the sample containing in addition a β‐SiAlON, LiAlSiO4, and a glass phase. The structure of Ca0.27La0.03Si11.38Al0.62N16 was refined using MoKα single‐crystal data, in space group P31c with a= 7.838(1), c= 5.703(1) Å, V= 303.4 Å3, to a weighted R(Fobs2) = 6.0% for 475 unique reflections. The isotypic structure of LiSi9Al3O2N14 was refined with anisotropic thermal parameters and a= 7.8277(2), c= 5.6909(2) Å to RF= 0.63% for 849 reflections for d≥ 0.5 Å using time‐of‐flight (TOF) neutron powder diffraction (NPD) data. The SiX4 (X = N or N/O) tetrahedra are regular in both structures, with Si‐N distances of 1.745(1) − 1.785(3) Å for the calcium‐lanthanum compound and 1.741(1) − 1.765(1) Å for the lithium compound. The Ca/La and lithium atoms are located on the 2b position, (1/3, 2/3, z), coordinated by seven anions with the shortest metal‐anion distances of 2.38(1) and 2.05(2) Å, respectively. The lithium atoms are displaced ∼0.28 Å relative to the position of the Ca/La atoms, and the lithium atoms can alternatively be described as tetrahedrally coordinated.
Effect of Addition of Oxides on Low‐Temperature Oxidation of Molybdenum Disilicide
Authors: Wang Gang , Jiang Wan , Bai Guangzhao , Wu Libin
Published: July 2009

A type of aluminosilicate that has a good wetting property for molybdenum disilicide (MoSi2) was added to a MoSi2 matrix to study the effects on the microstructure and low‐temperature oxidation. It was found that the composites had not only good low‐temperature oxidation resistance but also high thermal shock resistance when the added oxides formed a network microstructure in the matrix. There was no appreciable oxidation gain for MoSi2/oxide composites with a network microstructure at 773 K for 2500 h. The results indicate that microstructure design is a simple and effective solution to preventing the low‐temperature oxidation of MoSi2.
Barium Carbonate Phase on the Surfaces of Barium Titanate Particles and in Situ Transmission Electron Microscopy Observation of Its Decomposition
Authors: Nakano Hiromi , Urabe Kazuyori , Ikawa Hiroyuki
Published: July 2009

A BaCO3 phase is found on the surfaces of hydrothermally synthesized BaTiO3 particles; it occurs as aggregates or small protuberances. A small proportion of the phase decomposes to BaO crystallites when heated by a convergent electron beam in a transmission electron microscope. The BaO and BaCO3 crystallites disappear when they are irradiated successively by the convergent electron beam. The BaO crystallites and the BaCO3 phase sublimate and/or react with BaTiO3 crystals whose surface layers are deficient in Ba2+ ions.
Effect of Oligosaccharide Alcohol Addition to Alumina Slurry and Translucent Alumina Produced by Slip Casting
Authors: Hotta Yuji , Tsugoshi Takahisa , Nagaoka Takaaki , Yasuoka Masaki , Nakamura Kanzou , Watari Koji
Published: July 2009

A slurry used to produce dense green compacts by slip casting should exhibit low viscosity, high solids content, and good dispersion. Slurries with good characteristics were produced in the present study by adding oligosaccharide alcohol to an Al2O3 slurry with an NH4+ salt of poly(methacrylic acid) (NH4+‐PMA). The role of NH4+‐PMA and oligosaccharide alcohol in the Al2O3 slurry was examined by DTA, ζ‐potential measurement, high‐pressure liquid chromatography, and viscometry. The viscosity of the slurry with NH4+‐PMA and oligosaccharide alcohol was lower than that of the slurry with NH4+‐PMA at a high solids content. Oligosaccharide alcohol did not interact with the Al2O3 surface. However, the Al2O3 slurry with NH4+‐PMA was influenced by the addition of oligosaccharide alcohol. We found that the dispersibility of the slurry was greatly improved by adding oligosaccharide alcohol. The transmittance of the Al2O3 ceramics produced by slip casting using the slurry with both NH4+‐PMA and oligosaccharide alcohol was higher than that of ceramics produced by slip casting using the slurry with NH4+‐PMA alone. The increased optical property resulted from low viscosity, which was attributed to the addition of oligosaccharide alcohol, at a high solids content.
Quantitative Analysis of Zinc Vaporization from Manganese Zinc Ferrites
Authors: Suh Jung Ju , Han Young Ho
Published: July 2009

Zinc vaporization of Mn‐Zn ferrites was quantitatively characterized in terms of oxygen partial pressure PO2, temperature, grain size and sample geometry. The amount of zinc loss was measured as a function of time at various temperatures by a thermogravimetric method. The weight loss due to irreversible zinc vaporization showed a linear behavior with time and increased exponentially with temperature. The observed weight loss due to zinc evaporation at 1100°C was small, whereas a significant weight change was detected at 1200°C. The weight loss was even greater in a reducing atmosphere (PO2= 5 × 10−5). Below 1300°C, the diffusion of elemental zinc was sufficiently fast to compensate the zinc loss at the interface region, resulting in a linear dependence on time. At temperatures ≥1400°C, the weight change no longer followed the linear dependence and showed a rather parabolic behavior with a concave upward slope. The core shape and the gas flow around ferrite cores were important factors that affected the rate of zinc vaporization, but not the grain size.
Investigation of Apatite Deposition onto Charged Surfaces in Aqueous Solutions Using a Quartz‐Crystal Microbalance
Authors: Zhu Peixin , Masuda Yoshitake , Yonezawa Tetsu , Koumoto Kunihito
Published: July 2009

Hydroxyapatite (HAp) deposition onto positively charged surfaces (i.e., self‐assembled monolayers (SAMs) terminated with NH2 head groups) and negatively charged surfaces (i.e., OH‐SAMs (weak) and COOH‐SAMs (strong)) soaked at 50°C in aqueous supersaturated solutions (1.5 SBF, pH 7.0–7.6; SBF = simulated body fluid) was investigated using a quartz‐crystal microbalance. The results revealed that the solution conditions greatly influenced the formation of HAp on the charged surfaces. In a stable supersaturated solution of simulated body fluid (1.5 SBF, pH <7.4), more strongly negative surfaces had a more powerful induction capability for the heterogeneous nucleation of HAp (COOH > OH), whereas nucleation was obviously prohibited on a positive surface (NH2‐SAM). On the other hand, after the calcium phosphate particles had nucleated homogeneously in an unstable soaking solution (1.5 SBF, pH ≧7.4), adhesion of the HAp microparticles to the NH2‐SAM was observed. A two‐step interaction is conceivable to describe the formation of HAp on the positive NH2‐SAM: At the first stage, electrostatic interaction dominates the adhesion of HAp microparticles; at the second stage, hydrogen bonds possibly form between the HAp microparticles and the amino head groups of the NH2‐SAM, for a firm bonding with the substrate, and the microparticles grow progressively into a thin film. The electrophoretic behaviors of the HAp microparticles confirmed this hypothesis.
Unique Dielectric Behavior of 0.6Pb(Ni1/2W1/2)O3·0.4PbTiO3 Derived from Mechanical Activation
Authors: Gao Xingsen , Xue Junmin , Wang John , Yu Ting , Shen Ze Xiang
Published: July 2009

0.6Pb(Ni1/2W1/2)O3·0.4PbTiO3(0.6PNW·0.4PT) of complex perovskite structure is successfully synthesized by mechanical activation of mixed oxide composition, followed by sintering at 950°C. It exhibits a considerably stable temperature dependence of dielectric constant over the wide temperature range of −120° to 20°C, although there occurs a dielectric peak at around 74°C. Raman spectroscopic studies show the coexistence of tetragonal and pseudocubic perovskite phases on sintering at 950°C, which are attributed to the inhomogeneous distribution of PbTiO3 arising from mechanical activation. The dielectric behavior can be fine tuned by thermal annealing at 750°C, leading to phase redistribution in PNW‐PT.
Atmospheric Dependence on Dielectric Loss of 1/6Ba5Nb4O15· 5/6BaNb2O6 Ceramics
Authors: Kim Dong‐Wan , Kwon Do‐Kyun , Hong Kug Sun , Kim Deug Joong
Published: July 2009

Samples of 1/6Ba5Nb4O15·5/6BaNb2O6 along with the pure end members, Ba5Nb4O15 and BaNb2O6, were sintered under low oxygen partial pressure. The degradation mechanisms of dielectric loss in this reducing atmosphere have been studied. We found that the degradation occurred primarily due to the formation of oxygen vacancies caused by the reduction of Nb5+. This was determined by measuring the electrical conductivity, and through X‐ray photoelectron spectroscopy. More importantly, the dielectric loss of 1/6Ba5Nb4O15·5/6BaNb2O6 samples with higher temperature stability was further decreased on sintering in a reducing atmosphere. This observation has been explained by considering the increased porosity and formation of a reduced second phase, Ba0.65NbO3.
Detection of Drying‐Induced Microcracking in Cementitious Materials with Space‐Resolved 1H Nuclear Magnetic Resonance Relaxometry
Authors: Beyea Steven D. , Balcom Bruce J. , Bremner Theodore W. , Armstrong Robin L. , Grattan‐Bellew Patrick E.
Published: July 2009

Nuclear magnetic resonance (NMR) relaxation time mapping in partially dried mortar is presented. Relaxation times in concrete are typically multi‐exponential, and exhibit highly effective relaxation mechanisms (T1L∼ 3 ms, Δν1/2∼ 2500 Hz). One‐dimensional mapping of the spin–lattice relaxation time is used to study relative changes in the water‐occupied surface‐to‐volume ratio, as a function of mixture conditions, initial hydration period, and drying time. These results provide evidence for a penetrating microcracking phenomenon, due to local drying‐induced tensile stresses. This conclusion was further supported by a relaxation time study of samples which were preconditioned so as to be at equilibrium with various relative humidities.
Bioactivity and Mechanical Properties of Poly(dimethylsiloxane)‐Modified Calcia–Silica Hybrids with Added Titania
Authors: Chen Qi , Miyata Noboru , Kokubo Tadashi , Nakamura Takashi
Published: July 2009

Hydrolysis and polycondensation of poly(dimethylsiloxane) (PDMS), tetraethoxysilane (TEOS), and calcium nitrate, added with tetraisopropyltitanate (TiPT) at a TiPT/(TiPT + TEOS) molar ratio of 0.15, gave a pore‐ and crack‐free transparent monolithic organic‐inorganic hybrid material. It was speculated to be composed of a Si–O–Ti–O− network modified with methyl groups, and a Ca2+ ion ionically bonded to the network. The hybrid obtained showed a high apatite‐forming ability on its surface in a simulated body fluid that is indicative of high bioactivity, as well as mechanical properties such as bending strength, Young's modulus, and strain at failure, analogous to those of the human cancellous bone. This hybrid material is expected to be useful as a new type of bioactive bone‐repairing material.
Ultrasonic Velocity Technique for Nondestructive Quantification of Elastic Moduli Degradation during Creep in Silicon Nitride
Authors: Lofaj František , Blessing Gerald V. , Wiederhorn Sheldon M.
Published: July 2009

The ultrasonic velocity technique was used for nondestructive quantification of creep damage during interrupted tensile creep tests at 1400°C in an advanced silicon nitride to investigate the possibilities of this technique for creep damage monitoring in ceramic components. The longitudinal and shear wave velocities, Poisson's ratio, and Young's, shear, and bulk moduli linearly decreased with strain. Precise density change measurements indicated a linear relationship with a coefficient of proportionality of 0.69 between the volume fraction of cavities and tensile strain. Cavitation was identified as the main creep mechanism in the studied silicon nitride and the reason for ultrasonic velocity and elastic moduli degradation. The measurement of just the longitudinal wave velocity changes was found to be sufficient for quantification of cavitation during creep. The capability of the ultrasonic velocity technique for simple, sensitive, and reliable nondestructive monitoring of creep damage during intermittent creep was demonstrated in silicon nitride.
Raman Scattering Characterization of Polytype in Silicon Carbide Ceramics: Comparison with X‐ray Diffraction
Authors: Nakashima Shin‐ichi , Higashihira Makoto , Maeda Kouji , Tanaka Hidehiko
Published: July 2009

Raman scattering measurements have been made on SiC ceramics prepared from two powdered by sintering at different temperatures. The Raman spectra of starting powders have also been measured. The volume contents of the 4H and 15R polytype phases relative to that of the 6H phase in the ceramics are inferred from the Raman intensity of folded modes of the acoustic branches and compared with those determined from X‐ray diffraction (XRD) analysis. A strong correlation is found between the results obtained from the two analyses. The 4H polytype contents estimated by Raman measurement for specimens prepared from one powder show a good agreement with those obtained by the XRD analysis. For the 15R polytype component there is a correlation between the contents inferred by the two techniques when the content is not very small. The results obtained by the two techniques demonstrate that the Raman spectroscopy as well as the XRD analysis is useful to study the natures and preparation conditions of SiC ceramics.
Thermal Response and Oxidation of Tyranno™‐Fiber‐Reinforced Si‐Ti‐C‐O Matrix Composites for a Thermal Protection System in High‐Enthalpy Dissociated Air
Authors: Ogasawara Toshio , Ishikawa Takashi , Matsuzaki Takashi
Published: July 2009

The thermal response and oxidation of Tyranno™ Lox‐M fiber‐reinforced Si‐Ti‐C‐O matrix composites in high‐enthalpy dissociated air was investigated in an arc jet facility (an arc wind tunnel). The maximum surface temperature reached 1310–1670°C. Catalytic recombination of oxygen and nitrogen on the composite surface under dissociated air was not significant. Surface recession was insignificant below 1600°C surface temperatures and above 5 kPa of oxygen partial pressure at the stagnation point. Passive‐to‐active oxidation transition of the composite agreed with Balat's theory for monolithic silicon carbide. A glass sealant prevented active oxidation of the composite for short‐time exposures.
Suppression of Active Oxidation of Polycarbosilane‐Derived Silicon Carbide Fibers by Preoxidation at High Oxygen Pressure
Authors: Shimoo Toshio , Morisada Yoshiaki , Okamura Kiyohito
Published: July 2009

Three types of polycarbosilane‐derived SiC fibers (Nicalon, Hi‐Nicalon, and Hi‐Nicalon S) with different SiO2 film thicknesses (b) were subjected to exposure tests at 1773 K in an argon‐oxygen gas mixture with an oxygen partial pressure of 1 Pa. The suppression effect of a SiO2 coating on active oxidation was examined through TG, XRD analysis, SEM observation, and tensile tests. All the as‐received fibers were oxidized in the active‐oxidation regime. The mass gain and the SiO2 film development showed a suppression of active oxidation at b values of ≧0.070 μm for Nicalon, ≧0.013 μm for Hi‐Nicalon, and ≧0.010 μm for Hi‐Nicalon S fibers. Considerable strength was retained in the SiO2‐coated fibers. For Hi‐Nicalon fibers, the retained strength was 71%–90% of the strength in the as‐received state (2.14–2.69 GPa).
Comparison of Various Solvent Media Efficiency in the Grinding of a Frit Containing Zirconium Oxide
Authors: Andreola Fernanda , D'Arrigo Maria Cristina , Leonelli Cristina , Siligardi Cristina , Pellacani Gian Carlo
Published: July 2009

In the present work thermal and chemical properties of a glass‐ceramic frit containing zirconium oxide are evaluated after milling in various polar and nonpolar solvents. Particle‐size distribution is one of the main variables investigated to evaluate the efficiency of several solvents. Milling in various solvents does not affect the thermal properties of the glass while the presence of polar groups in the solvent molecule increases the cation release from the glass.
Grain Boundary Grooving Studies of Yttrium Aluminum Garnet (YAG) Bicrystals
Authors: Peters M. I. , Reimanis I. E.
Published: July 2009

Grain boundary grooving experiments were conducted with Σ5 (210) twist boundaries in Y3Al5O12 (YAG) with the goal of extracting information on diffusion in YAG. Planar boundaries oriented 90° to the surface were annealed in air at various times and temperatures. Atomic force microscopy was used to characterize the subsequent grooves. The Mullins approach leads to the following expression for the diffusion coefficient: D (m2/s) = 3.9 × 10−10 exp[−330 ± 75 (kJ/mol)/RT]. The relatively low activation energy agrees well with earlier oxygen tracer diffusion measurements on YAG, suggesting that oxygen is the limiting diffusing species in boundary grooving of YAG.
Bending Creep Test to Measure the Viscosity of Porous Materials during Sintering
Authors: Lee Sang‐Ho , Messing Gary L. , Green David J.
Published: July 2009

A bending creep test is proposed for measuring the change in viscosity of a porous material during densification. Equations, based on simple beam deflection theory, were derived to obtain the viscosity from a series of loading experiments using rectangular samples of different densities. By measuring the deflection in the center of the specimen between the spans, the viscosity of a porous material during densification can be measured. Experiments with porous Y2O3‐stabilized ZrO2 beams were used to illustrate the bending creep test. Consistent with theory the viscosity increased from 50 to 400 GPa·s as the sample densified from 87% to 98% density. The rapid increase in viscosity was considered to be a result of both densification and grain growth.
Enhanced Properties of Tin(IV) Oxide Based Materials by Field‐Activated Sintering
Authors: Scarlat Oana , Mihaiu Susana , Aldica Gh. , Zaharescu Maria , Groza Joanna R.
Published: July 2009

The densification of SnO2 (0.9 mol)–Sb2O3 (0.1 mol) solid solution without any additives was studied by conventional and field‐activated sintering technique (FAST). FAST sintering achieved a relative density value of 92.4% at 1163 K for 10 min versus 61.3% in conventional sintering at 1273 K for 3 h. An abnormal reduction of the IR transmittance and a semiconductor defect structure with only one donor level in the SnO2 energy gap were noticed in the FAST‐sintered as compared with the conventionally sintered Sn0.82Sb0.18O2 solid solution. A high charge carrier concentration (i.e., electronic conduction) was shown in the FAST‐sintered sample by conductivity measurements and the negative values of the Seebeck coefficient.
Electrodeposition Method for Terminals of Multilayer Ceramic Capacitors
Authors: Van Trinh Hung , Talbot Jan B.
Published: July 2009

A method using a combination of electroless and electrolytic plating was developed to provide an alternative method for forming the end terminals of multilayer ceramic capacitors. Electrodeposited terminals were formed by using electroless copper followed by electrolytic nickel plating. The electrical characteristics of the electrodeposited terminal capacitors were compared with standard capacitors and found to be identical.
Porous 2H‐Silicon Carbide Ceramics Fabricated by Carbothermal Reaction between Silicon Nitride and Carbon
Authors: Yang Jian‐Feng , Zhang Guo‐Jun , Kondo Naoki , She Ji‐Hong , Jin Zhi‐Hao , Ohji Tatsuki , Kanzaki Shuzo
Published: July 2009

Porous SiC ceramics were synthesized by sintering pressed and pressed/CIPed powder compacts of α‐Si3N4, carbon (Si3N4:C = 1:3 mol as ratio), and sintering aids, at 1600°C for few hours to achieve a reaction, and subsequently sintering at a temperature range of 1750°–1900°C, in an argon atmosphere. High porosities from 45%–65% were achieved by low shrinkage with large weight loss. Formation of pure 2H‐SiC phase via a reaction between Si3N4 and carbon can be demonstrated by X‐ray diffractometry. The resultant porous SiC samples were characterized by SiC grain microstructures, pore‐size distribution, and flexural strength. This method has the advantage of fabricating high‐porous SiC ceramics with fine microstructure and good properties at a relatively low temperature.
Electrical and Structural Characterization of a Low‐Angle Tilt Grain Boundary in Iron‐Doped Strontium Titanate
Authors: De Souza Roger A. , Fleig Jürgen , Maier Joachim , Kienzle Oliver , Zhang Zaoli , Sigle Wilfried , Rühle Manfred
Published: July 2009

The atomistic structure and electrical properties of a symmetrical 5.4° [001] tilt grain boundary in Fe‐doped SrTiO3 have been investigated, respectively, by means of various transmission electron microscopy (TEM) techniques and impedance spectroscopy. In weak‐beam dark‐field images, the grain boundary is revealed to consist of a periodic array of dislocations; high‐resolution TEM images show that the dislocation cores are separated by regions of strained lattice. The impedance response of the bicrystal has been measured in the frequency range 20 Hz ≤f≤ 106 Hz as a function of temperature and oxygen partial pressure. The transport of charge across the array of dislocations that form the grain boundary is strongly hindered. Analysis of the impedance data in terms of a double‐Schottky‐barrier model yields a space‐charge potential that exhibits a weak dependence on temperature and oxygen partial pressure and is ∼0.55 V in the investigated regime.
Flextensional Barium Strontium Titanate Actuators
Authors: Meyer Richard J. , Newnham Robert E. , Amin Ahmed , Kulwicki Bernard M.
Published: July 2009

This paper describes the performance of the cymbal flextensional transducer using Dy‐doped barium strontium titanate (BST) as the driver material. BST was first characterized for its dielectric and loss behavior as a function of temperature and electrical bias field. With no electrical bias, the transition temperature was measured to be near 20°C and have a dielectric constant >20 000. The strain of a BST disk was then measured and compared with other ceramics. At room temperature the strain and average effective piezoelectric d33 of this non‐lead composition was slightly larger than Navy type I lead zirconate titanate (PZT‐4) ceramic. The strain/field behavior was also measured as a function of temperature. Cymbal capped BST ceramic was found to have an amplified displacement of 28×, also very similar to type I ceramic. The stiffness of BST was found to be tunable by dc voltage and 2 to 3 times larger than that of PZT. This material has promise for applications in actuators and transducers with large generative force.
Dielectric Properties of the Fluorite‐like Bi2O3–Nb2O5 Solid Solution and the Tetragonal Bi3NbO7
Authors: Valant Matjaz , Suvorov Danilo
Published: July 2009

Our analysis of the microwave dielectric properties of the δ‐Bi2O3–Nb2O5 solid solution (δ‐BNss) showed a continuous increase in permittivity and dielectric losses with an increasing concentration of Nb2O5. The only discontinuity was found for the temperature coefficient of resonant frequency, which is negative throughout the entire homogeneity range but reaches a minimum value for the sample with 20 mol% Nb2O5. At the same composition there is a discontinuity in the grain size of the δ‐BNss ceramics. For the sample containing 25 mol% Nb2O5 two structural modifications were observed. A single‐phase tetragonal Bi3NbO7, in the literature referred to as a Type‐III phase, is formed in a very narrow temperature range from 850° to 880°C. A synthesis performed below or above this temperature range resulted in the formation of the end member of the δ‐BNss homogeneity range. Compared with the δ‐BNss the Bi3NbO7 ceramics exhibit lower microwave dielectric losses, an increased conductivity, and a positive temperature coefficient of resonant frequency.
Kinetic Study of Black Fe2O3‐Cr2O3 Pigment Synthesis: I, Influence of Synthesis Time and Temperature
Authors: Escardino A. , Mestre S. , Barba A. , Beltran V. , Blasco A.
Published: July 2009

A study was undertaken of the kinetics of the black Fe‐Cr oxide pigment synthesis process based on the oxide constituents (Fe2O3 and Cr2O3). A kinetic model is proposed which enables correlating the degree of transformation advance, expressed as the mass fraction of the arising solid solution (of the same composition as the starting oxide mixture), with synthesis time and temperature. The model is valid for raw materials, range of starting compositions, and operating conditions similar to those used in black Fe‐Cr oxide pigment processing in industry.
Influence of Moisture on Ultra‐High‐Temperature Tensile Creep Behavior of in Situ Single‐Crystal Oxide Ceramic Alumina/Yttrium Aluminum Garnet Eutectic Composite
Authors: Harada Yoshihisa , Suzuki Takayuki , Hirano Kazumi , Waku Yoshiharu
Published: July 2009

Tensile creep tests were conducted for an in situ single‐crystal alumina/yttrium aluminum garnet (Al2O3/Y3Al5O12 (YAG)) binary system eutectic composite at temperatures between 1773 and 1873 K in air and in a moist environment having a water‐vapor pressure range of 0.06–0.6 MPa, under a constant tensile stress range of 100–160 MPa. The Al2O3/YAG eutectic composite exhibited a stress exponent of 8–13, indicative of tensile creep behavior characterized by a dislocation back‐stress mechanism. Water‐vapor pressures ≤0.4 MPa led to a significant acceleration of creep rates as a result of enhanced dislocation mobility in the Al2O3 and YAG phases.
Aluminum Silicate Films Obtained by Low‐Pressure Metal‐Organic Chemical Vapor Deposition
Authors: Kuo Dong‐Hau , Chuang Po‐Yo
Published: July 2009

Amorphous alumina‐silica films with film thickness of 0.41–2.69 μm were prepared on glass and silicon substrates by metal‐organic chemical vapor deposition using a mixture of aluminum tri‐sec‐butoxide (ATSB), hexamethyldisilazane (HMDSN), and argon. By controlling the inputs of ATSB and HMDSN, alumina‐silica thin films could contain varied compositions and adjustable properties. Basically, the codeposition of alumina and silica to form alumina‐silica using ATSB and HMDSN had a faster growth rate than their individual components. The internal stress could be adjusted by deposition temperature and reactant inputs. Adhesion could be improved by having a silicon‐rich thin film, whereas an aluminum‐rich film could have slightly higher hardness. Optical properties, e.g., refractive index and optical transmittance, were also measured.
Tribological Properties of Silicon Carbide and Silicon Carbide–Graphite Composite Ceramics in Sliding Contact
Authors: Zhou You , Hirao Kiyoshi , Yamauchi Yukihiko , Kanzaki Shuzo
Published: July 2009

A monolithic SiC ceramic and two SiC–C composite ceramics containing 10 and 20 vol% graphite were fully densified with Al4C3 and B4C as additives. The tribological properties of these materials were evaluated by sliding against sintered silicon carbide under dry conditions using two tribometers, block‐on‐ring and pin‐on‐disk, where wear occurred under low and high contact stresses, respectively. For all three materials, under low stress, worn surfaces were smooth and wear processes were dominated by tribochemical reaction; under high stress, worn surfaces were rough and wear processes were dominated by fracture and three‐body abrasion. A lubricating effect of the graphite particles in the SiC–C composites was observed in all sliding tests. However, while the addition of graphite could concurrently result in a reduction in friction and an increase in wear resistance in the block‐on‐ring tests, the addition of graphite led to sharply enhanced wear rates despite the lowered coefficients of friction in the pin‐on‐disk tests. The cause for that difference was attributed to the effect of both the hardness of the materials and the contact stresses.
Crystallographic‐Orientation‐Dependent Dissolution Behavior of Sapphire in Anorthite Liquid Containing Chromia
Authors: Park Jong‐Keuk , Kim Doh‐Yeon , Lee Ho‐Yong , Blendell John , Handwerker Carol
Published: July 2009

A sapphire single crystal was put into anorthite powders containing Cr2O3 and then heat‐treated at 1600°C. The resultant morphologies of the sapphire—anorthite‐liquid interfaces were corrugated and quite different depending on the crystallographic orientation of the sapphire; all the planes perpendicular to the C>‐plane showed fingerlike morphologies, while long parallel segments were detached from the basal C‐plane. The results were interpreted in terms of coherency‐strain‐induced instability of the solid–liquid interface (ISLI) caused by the alloying of Cr2O3 into sapphire. The difference in microstructural evolution depending on crystallographic orientation was explained in terms of strong anisotropy of the solid–liquid interface characteristics.
Flaw Size Distribution in High‐Quality Alumina
Authors: Abe Hiroya , Naito Makio , Hotta Tadashi , Shinohara Nobuhiro , Uematsu Keizo
Published: July 2009

A difference in fracture strength was noted among commercial alumina ceramics. The origin of this difference was examined using optical microscopy in the transmission mode. Large defects measuring several tens of micrometers or more were clearly observed, and a direct correlation was found between the size of the large defects and the strength of the ceramics. The results indicated that a low concentration of large defects controlled the strength distribution of the ceramics studied.
Effect of Silver Addition on the Dielectric Properties of Barium Titanate‐Based X7R Ceramics
Authors: Chen RenZheng , Wang Xiaohui , Gui ZhiLun , Li LongTu
Published: July 2009

Different amounts of silver (0.5–10 wt%) have been mixed with EIA X7R‐type ceramic powders based on barium titanate. The XRD analysis indicated that no phases other than BaTiO3 and silver were present in the doped ceramics; it further suggested that no reaction took place between BaTiO3 and silver during calcination and sintering. SEM observation showed that the silver particles presented island distribution in the BaTiO3 ceramic matrix. The densification and dielectric properties of the silver‐doped ceramics in disk form were investigated. A large amount of silver addition (>1 wt%) was found to improve the sintered density and dielectric properties. The temperature coefficient of capacitors of the ceramics doped with 10 wt% silver still met the X7R characteristics, and the dielectric constant of the ceramics at room temperature was >6000, which is the highest dielectric constant in the BaTiO3‐based X7R system.
Crack‐Growth‐Velocity‐Dependent R‐Curve Behavior in Lead Zirconate Titanate
Authors: Dos Santos e Lucato Sergio L.
Published: July 2009

Crack‐velocity (v–K) curves and crack‐resistance (R) curves for unpoled ferroelectric and ferroelastic lead zirconate titanate (PZT) were determined for long cracks in compact‐tension (CT) geometry using an in situ fracture device on the stage of an optical microscope. The steady‐state crack length and the plateau value of R‐curves measured at controlled constant velocities increased with increased velocity. The plateau value for 10−6 m/s was 1.2 MPa·m1/2 after 1.3 mm of crack extension and for 10−4 m/s was 1.4 MPa·m1/2 after 2.2 mm.
Ductile‐Mode Material Removal of a Mica–Glass‐Ceramic
Authors: Ma Xin‐Pei , Li Guang‐Xin , Shen Lian , Jin Zhi‐Hao
Published: July 2009

The influence of crystal volume fraction on machining behavior was investigated for modified mica–glass‐ceramic materials that contained B2O3, Na2O, Li2O, and ZnO and had low melting temperatures. The machining behavior was characterized by drilling rate under a constant drilling force and chip morphology in a cutting test. To achieve the greatest drilling rate, an optimization volume fraction of crystalline mica (40%) had to be used; a further increase in the fraction of crystalline mica resulted in a corresponding decrease in the drilling rate. For this type of mica–glass‐ceramic, a continuous band of chips and a highly smooth cut surface could be formed during the cutting test at a high cutting velocity of 60 m/min and a depth of 1 mm. The results demonstrated that an outstanding machining behavior for glass‐ceramics can be achieved and that it can be comparable with metallic materials.
Fracture Toughness of a Toughened Silicon Nitride by ASTM C 1421
Authors: Quinn George D. , Swab Jeffrey J. , Motyka Matthew J.
Published: July 2009

The fracture toughness of a sintered reaction‐bonded silicon nitride was measured by the single‐edge precracked beam and surface crack in flexure methods, which are two of the three complementary test methods in ASTM C 1421. Results were compared with chevron‐notched beam results that were available from another source. Precracks ranged from tiny artificial flaws introduced by Knoop indentation to millimeter‐long precracks in single‐edge precracked beams. The fracture toughness values from the three methods were in good agreement at 5.6 MPa·m1/2.
Synthesis of Aluminum Nitride Nanopowder by Gas‐Reduction–Nitridation Method
Authors: Suehiro Takayuki , Hirosaki Naoto , Terao Ryo , Tatami Junichi , Meguro Takeshi , Komeya Katsutoshi
Published: July 2009

Aluminum nitride (AlN) nanopowder was successfully synthesized from transition alumina nanopowder using an NH3–C3H8 gas mixture as a reduction–nitridation agent. Phase‐pure, nanocrystalline AlN powder with a specific surface area of 36.4 m2/g and a mean particle size of 51 nm was prepared under typical reaction conditions. The resulting AlN nanopowders possessed excellent sinterability, allowing full densification in conventional processing, even without the addition of sintering aids.
Topotaxial Formation of Mg4Nb2O9 and MgNb2O6 Thin Films on MgO (001) Single Crystals by Vapor–Solid Reaction
Authors: Sun Duochun , Senz Stephan , Hesse Dietrich
Published: July 2009

Thin‐film solid‐state reactions in the system MgO–Nb2O5 are experimentally investigated. MgO (001) substrates are subjected to Nb‐O vapor at different temperatures in high vacuum. Thin films containing the phases Mg4Nb2O9 and MgNb2O6 are formed by a vapor–solid reaction between the Nb‐O vapor and the substrate. The crystallographic orientations of these phases are studied by X‐ray diffractometry including pole figure analysis. Mg4Nb2O9 grows (11.4)‐, (11.6)‐, and (11.9)‐oriented, whereas MgNb2O6 grows with a preferential (241) orientation. The crystallographic relationships and their origins are discussed.
Hydrothermal Synthesis of Nanosized CoAl2O4 on ZnAl2O4 Seed Crystallites
Authors: Chen Zhi‐Zhan , Shi Er‐Wei , Zheng Yan‐Qing , Xiao Bing , Zhuang Ji‐Yong
Published: July 2009

ZnAl2O4‐seeded CoAl2O4, with a core‐shell structure, has been prepared under hydrothermal conditions when the Co2+ salt solution is substituted by 10% Zn2+ as a precursor. The ZnAl2O4 seed is generated during the synthesis process. The seeding process can decrease the synthesis temperature from 245° to 230°C and the particle size from 67 to 20 nm. The process can economize the consumption of Co2+ and control the particle size effectively.
Formation of a Highly Protective Amorphous Aluminum Silicate Layer on Steel during Granite–Dry Steam Interaction
Authors: Yamasaki Nakamichi , Korablova Inna R. , Korablov Sergiy F.
Published: July 2009

Formation of an amorphous Al2Si2O5 layer on a steel pipe surface, after granite–dry steam interaction in the presence of copper, has been determined by XRD analysis and SEM (with energy dispersive X‐ray microanalysis). Kinetic data indicate high‐protective properties of the Al2Si2O5 layer, which formed a three‐dimension substrate ∼5 μm thick, after 100 h exposure.
Oxidation and Volatilization of Silica Formers in Water Vapor
Authors: Opila Elizabeth J.
Published: July 2009

At high temperatures, SiC and Si3N4 react with water vapor to form a SiO2 scale. SiO2 scales also react with water vapor to form a volatile Si(OH)4 species. These simultaneous reactions, one forming SiO2 and the other removing SiO2, are described by paralinear kinetics. A steady state, in which these reactions occur at the same rate, is eventually achieved. After steady state is achieved, the oxide found on the surface is a constant thickness, and recession of the underlying material occurs at a linear rate. The steady‐state oxide thickness, the time to achieve steady state, and the steady‐state recession rate can be described in terms of the rate constants for the oxidation and volatilization reactions. In addition, the oxide thickness, the time to achieve steady state, and the recession rate also can be determined from parameters that describe a water‐vapor‐containing environment. Accordingly, maps have been developed to show these steady‐state conditions as a function of reaction rate constants, pressure, and gas velocity. These maps can be used to predict the behavior of SiO2 formers in water‐vapor‐containing environments, such as combustion environments. Finally, these maps are used to explore the limits of the paralinear oxidation model for SiC and Si3N4.
Effects of High Water‐Vapor Pressure on Oxidation of Silicon Carbide at 1200°C
Authors: Tortorelli Peter F. , More Karren L.
Published: July 2009

The oxidation of SiC at 1200°C in a slowly flowing gas mixture of either air or air + 15 vol% H2O at 10 atm (1 MPa) was studied for extended times to examine the effects of elevated water‐vapor pressure on oxidation rates and microstructural development. At a water‐vapor pressure of 1.5 atm (150 kPa), distinct SiO2scale structures were observed on the SiC; thick, porous, nonprotective cristobalite scales formed above a thin, nearly dense vitreous SiO2layer, which remained constant in thickness with time as the crystalline SiO2continued to grow. The pore morphology of the cristobalite layer differed depending on the type of SiC on which it was grown. The crystallization and growth rates of the cristobalite layer were significantly accelerated in the presence of the high water‐vapor pressure and resulted in rapid rates of SiC surface recession that were on the order of what is observed when SiO2volatility is rate controlling at high gas‐flow velocities (30 m/s). The recession process can be described by a paralinear kinetic model controlled by the conversion of dense vitreous SiO2to porous, nonprotective SiO2.
Consequence of Intermittent Exposure to Moisture and Salt Fog on the High‐Temperature Fatigue Durability of Several Ceramic‐Matrix Composites
Authors: Zawada Larry P. , Staehler James , Steel Steve
Published: July 2009

Fatigue behavior of four ceramic‐matrix composites (CMCs) was documented at 1000°C, and a fifth composite was documented at 1200°C. Additional fatigue specimens were cycled for set blocks of cycles, removed from the fatigue machine, and exposed in a cyclic corrosion tester for 24 h with a fog of deionized water and a fog of deionized water containing 0.05 wt% NaCl. BN‐fiber‐coated Nicalon™/SiNC and Nicalon/Al2O3 experienced a pronounced decrease in fatigue life (∼86%) with salt fog exposure. Nicalon/C experienced rapid loss of the SiC exterior seal coat and a 30% decrease in life with salt fog exposure. Nextel610/AS and Nextel720/Al2O3 demonstrated no loss in fatigue performance or retained strength with water or salt fog exposure. Changes to the constituents of Nicalon/SiNC were evaluated to determine if they influenced moisture sensitivity. BN fiber coatings, BN or BN/SiC, alternate matrix prepreg, and matrix filler type had no influence on improving moisture resistance. Direct exposure to moisture fog produced accelerated rates of degradation in the BN fiber coating and greatly decreased fatigue durability.
Synergistic Effects of Water Vapor and Alkali Chloride Vapors on the High‐Temperature Corrosion of SiC‐Based Ceramics
Authors: Lee Soo Y. , Park Young S. , Hsu Pei Pei , McNallan Michael J.
Published: July 2009

The high‐temperature oxidation of SiC‐based structural ceramics is accelerated in the presence of KCl vapors. The corrosion products are primarily alkali silicates and the rate of attack is approximately proportional to the vapor pressure of KCl in the atmosphere. When both KCl and H2O are present in the oxidizing atmosphere, the rate of attack is further accelerated. The accelerated attack is related to the more negative free energy change of the fluxing reaction when the Cl can be removed as the more stable HCl molecule. Addition of Cl2 to the environment reduces the rate of attack by keeping the alkali bound to the chlorine rather than forming alkali silicates.
Radiation Characteristics of Glass Containing Gas Bubbles
Authors: Pilon* Laurent , Viskanta Raymond
Published: July 2009

In many materials processing and manufacturing situations such as steel, aluminum, ceramics, and glass, gas bubbles can form in liquid and solid phases. The presence of such bubbles affects the thermophysical properties and radiation characteristics of the two‐phase system and hence the transport phenomena. This paper presents a general formulation of the radiation characteristics of semitransparent media containing large gas bubbles (bubble radius is much larger than the wavelength of radiation). Sample calculations for the spectral absorption and extinction coefficients and single scattering albedo of soda–lime silicate glass containing bubbles are discussed. Particular attention is paid to the effect of the volumetric void fraction and the bubble size distribution. Results clearly show that the presence of bubbles strongly affects the radiation characteristics of the semitransparent media containing entrapped gas bubbles, particularly if bubbles, void fractions, and the spectral absorption coefficient of the continuous phase are small.
Fully Dense, Fine‐Grained, Doped Zinc Oxide Varistors with Improved Nonlinear Properties by Thermal Processing Optimization
Authors: Durán Pedro , Tartaj Jesus , Moure Carlos
Published: July 2009

Fully dense, doped ZnO varistors were prepared using an easy two‐stage pressureless‐sintering method at temperatures as low as 825°C, with a grain size of ∼0.5 μm. After the highly nonohmic ZnO varistors were sintered, their fine microstructure consisted of uniformly sized grains, small spinel grains with partially dissolved manganese and cobalt oxides discontinuously distributed in the fairly wide grain boundaries, and an intergranular layer of bismuth‐rich crystalline phase mainly detected at three or four ZnO grain junctions. There were twins near the middle of almost all the ZnO grains. The abnormally high nonlinear properties of the almost nanostructured varistors (FB≈ 6–8 kV/mm and α= 270) were attributed to a uniform and very fine microstructure, a high ZnO–ZnO grain direct contacts concentration, and a uniform hybrid layer substructure (grain boundaries and twin boundaries) with different (but probably accumulative) potential barriers.
Correlation between Arrangement of Dielectric Layers and Microwave Dielectric Properties of Mg0.93Ca0.07TiO3−(Ca0.3Li0.14Sm0.42)TiO3 Ceramics
Authors: Cho Joon Yeob , Yoon Ki Hyun , Kim Eung Soo
Published: July 2009

Effect of geometrical shape and induced thermal strain on the microwave dielectric properties of the layered structure ceramics of Mg0.93Ca0.07TiO3 with (Ca0.3Li0.14Sm0.42)TiO3 was investigated as a function of the number of dielectric layers. The dielectric constant and the temperature coefficient of resonant frequency (TCF) were not changed significantly with the number of dielectric layers but only depended on the net compositional ratio. However, the dielectric loss quality was affected by the number of interfaces between dielectric layers, which had a partial composition inhomogeneity due to the diffusion of Mg2+ and Ti4+ ions. The dielectric loss quality also decreased with an increase of thermal strain induced to each dielectric layer.
Structural, Dielectric, and Thermal Properties of Strontium Barium Niobate‐Doped Fused Silica Nanocomposites
Authors: Lu Sheng‐Guo , Mak Chee‐Leung , Wong Kin‐Hung
Published: July 2009

Ferroelectric strontium barium niobate (SBN)‐doped Na2O–B2O3–SiO2 (NBS) glass nanocomposites were prepared by dispersing sol–gel‐derived SBN powder into fused NBS glass. Their structures were characterized by X‐ray diffractometry and Raman spectroscopy. The dielectric constants were measured as functions of frequency and temperature using an impedance analyzer. The ferroelectric‐to‐paraelectric‐phase transition was studied by differential scanning calorimetric analysis. Our results revealed that the embedded SBN has lower phase transition temperature and phase transition heat than those of SBN bulk materials. Their activation energy, however, is larger than that of SBN ultra‐fine powders. Pure tetragonal‐phase SBN nanocomposites can be obtained at annealing temperatures of 750°–1000°C. Their dielectric constants are ∼32–46 and ∼20–25 at low frequencies and radio frequencies, respectively, and the loss tangent is <0.1 at room temperature in the radio frequencies range. Our studies suggested that additional reduction in the loss properties must be made before these systems can be considered for application as microwave dielectric materials.
Thermal Conductivity and Thermal Expansion Coefficients of the Lanthanum Rare‐Earth‐Element Zirconate System
Authors: Lehmann Henry , Pitzer Dieter , Pracht Gerhard , Vassen Robert , Stöver Detlef
Published: July 2009

To enhance the insulating properties of a thermal barrier coating, one has to focus on new materials with lower intrinsic thermal conductivity than established yttria‐stabilized zirconia. Substances with pyrochlore structure were investigated. Starting from lanthanum zirconate, substitutions of the lanthanum by other trivalent rare‐earth elements were made, and the thermal conductivity and the thermal expansion coefficient of the manufactured materials were measured. A complete substitution of the lanthanum led to increased thermal expansion coefficients, whereas the partial substitution did not show an appreciable effect. The thermal conductivities of the modified materials were lower than that of the pure lanthanum zirconate for temperatures <1000°C for all amounts and elements of substitution. A comparison of the observed values with calculated values of the thermal conductivities showed a relatively good agreement.