bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermomechanical Behavior of High‐Alumina Refractory Castables with Synthetic Spinel Additions
Authors: Simonin Fabien , Olagnon Christian , Maximilien Sandrine , Fantozzi Gilbert , Diaz Luiz Antonio , Torrecillas Ramon
Published: July 2010

The thermomechanical behavior of a high‐alumina refractory that contains 10 wt% of synthetic spinel has been studied. Results have been correlated with the microstructural and mineralogical evolutions using X‐ray diffraction and scanning electron microscopy, as function of the firing temperature. Dry, castable, raw‐material mixtures were sieved to <125 μm, to separate the fraction that is considered as the matrix of this castable. Matrix samples were obtained for thermomechanical characterization, and the results were compared with those corresponding to the entire refractory. The thermal expansion mismatch between coarse grains and the matrix was observed to be responsible for the degradation in mechanical strength that was observed at low firing temperatures. From room temperature to ∼1000°C, the material exhibited a quasi‐brittle behavior, with diffuse and localized damage. The diffuse damage was analyzed by comparison of the load–strain bend curves to a smeared crack model that was calculated using a finite‐element method. A good fit was obtained, thereby allowing the parameters of the model to be determined. The localized damage regime was evaluated by recording the strain‐energy release rate. Because of the specimen size, an increase in energy was observed, relative to increasing crack size. At temperatures of >1000°C, viscoelasticity–plasticity dominated the mechanical behavior. In this case, the description was initiated by conducting load–relaxation tests, which allowed the behavior to be related to the viscous‐phase content.
Microstructure and Abrasive Wear of Binderless Carbides
Authors: Engqvist Håkan , Botton Gianluigi A. , Axén Niklas , Hogmark Sture
Published: July 2010

The microstructure and the abrasive wear characteristics of two binderless carbides (WC–Mo2C and WC–TiC–TaC) have been studied. The microstructural analysis identified differences in the amount of mixing between the γ‐phase and WC. Mo2C and WC showed a large tendency to form mixed carbides, whereas WC and TiC did not. In both materials grain boundary segregation of metallic species was found. Compared with alumina ceramics and WC–6 wt% Co the WC–Mo2C material showed the lowest abrasion rate and WC–TiC–TaC an intermediate. The wear mechanism was surprisingly ductile for WC–Mo2C, whereas WC–TiC–TaC suffered from grain pullout of TiC.
Layered Silicon Nitride‐Based Composites with Discontinuous Boron Nitride Interlayers
Authors: Lenčéš Zoltán , Hirao Kiyoshi , Brito Manuel E. , Toriyama Motohiro , Kanzaki Shuzo
Published: July 2010

The influence of a strong/weak interface ratio on the mechanical properties of Si3N4/BN‐based layered composites was studied. The ratio was controlled by the number of BN spots between the adjacent Si3N4 layers. By increasing the BN interface area from 0% to 72%, fracture toughness increased from 7.7 to 10.9 MPa·m1/2, and bending strength decreased from 1275 to 982 MPa. Fracture toughness was improved from 8.6 to 10.1 MPa·m1/2 by additional heat treatment of samples containing 2 vol%β‐Si3N4 seed particles. The bending strength of samples with 35% weak BN interfaces, measured perpendicular and parallel to layer alignment, was 1260 and 1240 MPa, respectively. This confirmed the two‐directional isotropy of layered samples.
Superplastic Deformation in Silicon Nitride–Silicon Oxynitride In Situ Composites
Authors: Xie Rong‐Jun , Mitomo Mamoru , Zhan Guo‐Dong , Emoto Hideyuki
Published: July 2010

Starting with a mixture of ultrafine β‐Si3N4 and a SiO2‐containing additive, a superplastic Si3N4‐based composite was developed, using the concept of a transient liquid phase. Significant deformation‐induced phase and microstructure evolutions occurred in the nonequilibrium, fine‐grained Si3N4 material, which led to the in situ development of a Si3N4–22‐vol%‐Si2N2O composite and strong texture formation. The unusual ductility of the composites with elongated Si2N2O grains was attributed to the fine‐grained microstructure, the presence of a transient liquid phase, and the alignment of the elongated Si2N2O grains. The mechanical properties of the resultant composite were enhanced rather than impaired by superplastic deformation and subsequent heat treatment; the resultant composite exhibited both high strength (957 MPa) and high fracture toughness (4.8 MPa·m1/2).
Structural Study of PbO–B2O3 Glasses by X‐ray Diffraction and 11B MAS NMR Techniques
Authors: Takaishi Taigo , Jin Jisun , Uchino Takashi , Yoko Toshinobu
Published: July 2010

The structure of PbO–B2O3 glasses has been investigated in the composition range of 25–80 mol% PbO by using X‐ray diffraction and 11B NMR techniques. The well‐separated peaks due to Pb–O and Pb–Pb pairs were first observed in the radial distribution function, and peak deconvolution was performed by using a pair function method. The average coordination number of lead atoms was determined to be about 6 in the low‐PbO‐content region and about 3 in the high‐PbO‐content region. With an increase of PbO content, the peaks at 0.24 and 0.40 nm shifted to shorter distances, and especially the latter peak drastically increased in intensity in the composition range >50 mol% PbO. It was suggested that PbO is a main glass former in the high‐PbO‐content region. Based on the results obtained, we propose structural models of lead borate glasses.
Structure and Viscosity of Grain Boundary in High‐Purity SiAlON Ceramics
Authors: Pezzotti Giuseppe , Kleebe Hans‐Joachim , Okamoto Kazuhiro , Ota Ken'ichi
Published: July 2010

Three high‐purity SiAlON materials (Si6−zAlzOzN8−z, z= 1, 2, 3) were characterized with respect to both structure and viscous behavior of internal grain boundaries. Internal friction experiments provided a direct measure of the intrinsic viscosity of grain boundaries and concurrently revealed the occurrence of a grain‐boundary interlocking mechanism that suppressed sliding. A residual glass phase (consisting of aluminum‐rich SiO2) and nanometer‐sized mullite residues were found at glassy triple‐grain junctions of the z= 1 SiAlON. A low‐melting intergranular phase dominated the high‐temperature behavior of this material and caused grain‐boundary sliding at temperatures as low as 1100°C. A quantitative analysis of the grain‐boundary internal friction peak as a function of oscillation frequency indicated an intergranular film viscosity of log η∼ 7.5 Pa · s at 1100°C. Glass‐free grain boundaries were a characteristic of SiAlON materials with z≥ 2, which yielded a significant improvement in refractoriness as compared to the z= 1 SiAlON material. In these materials, relaxation resulting from grain‐boundary sliding was suppressed, and the internal friction curve simply experienced an exponential‐like increase.
The Wulff Shape of Alumina: I, Modeling the Kinetics of Morphological Evolution
Authors: Kitayama Mikito , Narushima Takayuki , Carter W. Craig , Cannon Rowland M. , Glaeser Andreas M.
Published: July 2010

The rate at which fully facetted nonequilibrium shaped particles and pores approach their equilibrium (Wulff) shape via surface diffusion was modeled, and calculations relevant to alumina were performed to guide experimental studies. The modeling focuses on 2‐D features, and considers initial particle/pore shape, size, surface energy anisotropy, and temperature (surface diffusivity) as variables. The chemical potential differences driving the shape change are expressed in terms of facet‐to‐facet differences in weighted mean curvature. Two approaches to modeling the surface flux are taken. One linearizes the difference in the mean chemical potential of adjacent facets, and assumes the flux is proportional to this difference. The other approach treats the surface chemical potential as a continuous function of position, and relates the displacement rate of the surface to the divergence of the surface flux. When consistent values for the relevant materials parameters are used, the predictions of these two modeling approaches agree to within a factor of 1.5. As expected, the most important parameters affecting the evolution times are the cross‐sectional area (volume in 3‐D) and the temperature through its effect on the surface diffusivity. Pores of micrometer size are predicted to reach near‐equilibrium shapes in reasonable times at temperatures as low as 1600°C. The detailed geometry of the initial nonequilibrium shape and the Wulff shape appear to have relatively minor effects on the times required to reach a near‐equilibrium shape.
Effects of Individual Layer Thickness on the Structure and Electrical Properties of Sol–Gel‐Derived Ba0.8Sr0.2TiO3 Thin Films
Authors: Cheng Jian‐Gong , Meng Xiang‐Jian , Tang Jun , Guo Shao‐Ling , Chu Jun‐Hao , Wang Min , Wang Hong , Wang Zhuo
Published: July 2010

Ba0.8Sr0.2TiO3 thin films were prepared with various individual layer thicknesses using a sol–gel process. The individual layer thickness strongly affected the structure, ferroelectricity, and dielectric properties of the films. The films prepared with an individual layer thickness of 60 nm showed small equiaxed grains, cubic structure, temperature‐independent dielectric constant, and no ferroelectricity. The films prepared with an individual layer thickness of 8 nm showed columnar grains, tetragonal structure, good ferroelectricity, and two dielectric peaks in the dielectric constant–temperature curve. The individual layer thickness for layer‐by‐layer homoepitaxy growth that resulted in columnar grains was <20 nm.
Improvement of Mechanical and Electrical Properties of Scandia‐Doped Zirconia Ceramics by Post‐Sintering with Hot Isostatic Pressing
Authors: Hirano Masanori , Inagaki Michio , Mizutani Yasunobu , Nomura Kazuhiro , Kawai Masayuki , Nakamura Yasuhisa
Published: July 2010

Significant improvement in the fracture strength, accompanied by an enhancement in the electrical conductivity, of zirconia polycrystals that were doped with 3–7 mol% Sc2O3 was obtained by sintering at 1300°C for 1 h in air, followed by hot isostatic pressing (HIP) at 196 MPa at 1300° and 1450°C for 1.5 h in an argon‐gas atmosphere. Dense bodies (with an average grain size of <0.5 μm) that were doped with 3.5 mol% of Sc2O3 showed the highest average fracture strength up to 1770 MPa and an electrical conductivity of 0.08 S/cm at 1000°C. The present zirconia ceramics, which consisted of submicrometer‐sized grains of tetragonal phases and were stabilized with 5 and 6 mol% of Sc2O3, exhibited high strength (1330 and 1140 MPa, respectively) and good conductivity (0.15 and 0.18 S/cm, respectively); values for both properties were greater than those previously reported. The present HIPed zirconia ceramics, which have excellent properties, are candidates for an electrolyte of planar‐type solid oxide fuel cells.
Synthesis and Characterization of Nanocrystalline Lanthanide Oxysulfide via a La(OH)3 Gel Solvothermal Route
Authors: Jiang Yang , Wu Yue , Xie Yi , Qian Yi‐Tai
Published: July 2010

A La(OH)3 gel solvothermal process has been developed for the preparation of nanocrystalline lanthanide oxysulfide (La2O2S) in polar solvents at 300°C through a reaction between a La(OH)3 gel and K2S. X‐ray powder diffraction (XRD) indicated that the product was hexagonal La2O2S with cell parameters a= 4.046 Å and c= 6.951 Å. Transmission electronic microscopy (TEM) showed that different morphology nanocrystallites were formed, including particles with diameters of about 10 nm and nanorods about 10 nm in diameter and 300 nm in length, depending on the solvent.
Effect of Ba2+ Substitution on Dielectric and Electric‐Field‐Induced Strain Properties of PMN–PZ–PT Ceramics
Authors: Yoon Ki Hyun , Lee Hong Ryul
Published: July 2010

Effect of Ba2+ substitution for Pb2+ on the dielectric and electric‐field‐induced strain characteristics of the PMN–PZ–PT ceramics has been investigated in the compositions of the tetragonal‐rich 0.2PMN–0.36PZ–0.44PT and rhombohedral‐rich 0.2PMN–0.4PZ–0.4PT ceramics. The phase approached cubic structure from the tetragonal and rhombohedral, and grain size was reduced when the Ba2+ cation was substituted. As Ba2+ content increased, frequency‐dependent relaxor‐like behavior of the dielectric constant was observed at temperatures below the dielectric maximum (Tmax) for compositions with 20 and 25 mol% Ba2+. Electric‐field‐induced strain was maximized in the 12 mol% Ba2+‐substituted 0.2PMN–0.4PZ–0.4PT specimen (Smax= 0.15%), and maximum piezoelectric, d31, was 300 in the 14 mol% Ba2+‐substituted 0.2PMN–0.4PZ–0.4PT specimen.
Electrical Properties of a Bismuth Layer‐Structured Ba2Bi4Ti5O18 Single Crystal
Authors: Irie Hiroshi , Miyayama Masaru , Kudo Tetsuichi
Published: July 2010

Ba2Bi4Ti5O18 single crystals were grown, and their dielectric permittivity, conductivity, and ferroelectricity were investigated along the a‐(or b‐)axis and the c‐axis separately. The dielectric permittivity at 1 MHz along the a‐(or b‐)axis was 2000 at the Curie temperature (360°C); this value was 8 times greater than that along the c‐axis. The dc conductivity was greater along the a‐(or b‐)axis than that along the c‐axis, by one order of magnitude. In regard to the ferroelectricity, the saturated remanent polarization was 120 mC/m2 and the saturated coercive field was 3 MV/m along the a‐(or b‐)axis; values of 8.5 mC/m2 and 0.81 MV/m, respectively, were observed along the c‐axis. The Ba2Bi4Ti5O18 single crystals had large electrical anisotropies, which were due to the layered structure.
Realistic Finite‐Element Model for the Double‐Torsion Loading Configuration
Authors: Ciccotti Matteo
Published: July 2010

The analytical approach to the double‐torsion, constant‐displacement‐configuration technique has forced a strong oversimplification of the specimen model, and, therefore, of the strain field in classical applications. For the present study, accurate three‐dimensional finite‐element analysis was performed on a realistic specimen; that is, one with finite thickness, a groove, and an initial notch. The influence on the strain‐energy release rate of the specimen width and length, the fracture length, the presence and shape of the side groove, the presence of an initial notch, and the curved shape of the fracture front was estimated from this analysis. Significant deviations from the classical analytical solution were found. The present results should reduce the discrepancies found among measurements made in various laboratories and that traditionally have prevented the development of effectively applicable fracture models.
Radiation Characteristics of Glass Foams
Authors: Fedorov Andrei G. , Viskanta Raymond
Published: July 2010

This paper is concerned with the analysis of the radiative heat transfer in glass foams. The closed‐form analytical model for the reflectance, transmittance, and absorptance of radiation by a foam layer has been utilized to assess the resistance of radiation heat transfer from the hot combustion gases and refractories to the molten glass in the glassmelting furnace due to glass foaming. The size (radius) and shape (void fraction) of foam bubbles, their size distribution function, the scattering anisotropy, and the reflectance of the foam/glass interface have been identified as major physical parameters governing the problem. Detailed parametric calculations have been performed, and the results are reported and critically discussed with the aim of quantifying the radiation characteristics of glass foams. The findings lead to a fundamental understanding of the radiative transport in the foams, and can be used to improve the design and operation of modern glassmelting furnaces.
Sol–Gel Route to Porous Lanthanum Cobaltite (LaCoO3) Thin Films
Authors: Hwang Hae Jin , Moon Jooho , Awano Masanobu , Maeda Kunihiko
Published: July 2010

Sol–gel‐derived LaCoO3 thin films were deposited on yttria‐stabilized zirconia (YSZ) substrates from a lanthanum isopropoxide–cobalt acetate (with 2‐methoxyethanol) precursor solution. A chelating agent (2‐ethylacetoacetate) and polyethylene glycol (PEG) were used to modify the above‐mentioned precursor solution. The La‐Co precursor solution was sufficiently viscous, and transparent LaCoO3 gel films were prepared successfully using a spin‐coating technique. Crystallization behavior and microstructure evolution were investigated using X‐ray diffractometry (XRD) and scanning electron microscopy (SEM). A single‐phase perovskite thin film with the grain size of ∼50 nm was obtained by heat‐treating the spin‐coated gel film at a temperature of 600°C. SEM observations revealed that the microstructure of LaCoO3 thin films that were prepared from the precursor solution with PEG was porous, and the LaCoO3 thin film maintained its porous microstructure to a temperature of 800°C.
Ultrarapid Phase Conversion in β″‐Alumina Tubes
Authors: Henrichsen Matthew , Hwang Jinha , Dravid Vinayak P. , Johnson D. Lynn
Published: July 2010

β″‐Alumina, the electrolyte of choice of sodium/sulfur and sodium/metal chloride batteries and alkali‐metal thermal‐electric converters, was sintered from precursor phases to high β″‐phase purity in less than 15 s from the onset of densification by rapid pass‐through rf induction coupled plasma sintering. The maximum instantaneous shrinkage rate was 1.8%/s. The resistivity was measured to be 13.8 ± 1.4 Ω·cm. The rapid conversion found is a significant improvement over conventional processing of β″‐alumina, which requires extended postsintering annealing times to obtain high β″‐phase purity.
Densification and Mechanical Properties of B4C with Al2O3 as a Sintering Aid
Authors: Kim Hae‐Won , Koh Young‐Hag , Kim Hyoun‐Ee
Published: July 2010

The densification behavior and mechanical properties of B4C hot‐pressed at 2000°C for 1 h with additions of Al2O3 up to 10 vol% were investigated. Sinterability was greatly improved by the addition of a small amount of Al2O3. The improvement was attributed to the enhanced mobility of elements through the Al2O3 near the melting temperature or a reaction product formed at the grain boundaries. As a result of this improvement in the density, mechanical properties, such as hardness, elastic modulus, strength, and fracture toughness, increased remarkably. However, when the amount of Al2O3 exceeded 5 vol%, the level of improvement in the mechanical properties, except for fracture toughness, was reduced presumably because of the high thermal mismatch between B4C and Al2O3.
Effect of Milling Media on the Reaction Kinetics of the Mechanochemical Synthesis of Pentatitanium Trisilicide
Authors: Kudaka Katsuya , Iizumi Kiyokata , Sasaki Takeshi , Izumi Hiraomi
Published: July 2010

The mechanochemical synthesis of pentatitanium trisilicide (Ti5Si3) by the ball‐milling of elemental mixed powders using zirconia, stainless steel, and tungsten carbide milling media was performed. These reactions were mechanically induced self‐propagating reactions. The induction period during the reaction using zirconia milling media was the shortest among these reactions. Because the thermal conductivity of zirconia is the lowest, it is assumed that the heat produced during milling using the zirconia milling media was effectively stored, and the ignition temperature was attained within the shortest time. The ignition temperature was estimated to be ∼500°C. The particle size of the Ti5Si3 obtained using the tungsten carbide milling media was the finest because of the induction time and specific gravity.
Using Nanoscaled Powder as an Additive in Coarse‐Grained Powder
Authors: Hellmig Ralph Jörg , Ferkel Hans
Published: July 2010

Nanoscaled Al2O3 powder is used as additive in coarse‐grained Al2O3 green bodies. Its influence on the green density is investigated. The potential effect of powder mixing on the green density is described by a model for multimodal powder mixtures that predicts the powder composition for maximum green body density. The model is applied to bimodal and trimodal mixtures with one of the components being nano‐powder. The calculated relative densities are compared with experimental results. Furthermore, sintering experiments are conducted to investigate the influence of the amount of nanoscaled powder on the sintered densities of bimodal bodies.
Determination of Calcium/Phosphorus Atomic Ratio of Calcium Phosphate Apatites Using X‐ray Diffractometry
Authors: Raynaud Sylvie , Champion Eric , Bernache‐Assollant Didier , Laval Jean‐Paul
Published: July 2010

The properties of calcium phosphates of biological interest depend strongly on their calcium/phosphorus atomic ratios (Ca/P). Therefore, the precision for the determination of this ratio is crucial. We have investigated the accuracy of quantitative X‐ray diffractometry (QXRD) analysis for the determination of Ca/P in compounds with Ca/P ranging from 1.5 to 2. For 1.5 < Ca/P < 1.667, a high accuracy is obtained with relative uncertainties on Ca/P values between 0.1% and 0.4%. In this domain of composition, QXRD is more accurate than classical wet methods. For 1.667 < Ca/P < 2, the precision is lower and wet chemical methods appear to be superior.
Microstructure and Mechanical Properties of Sinter–Post‐HIPed Si3N4–SiC Composites
Authors: Yang Jian‐Feng , Sekino Tohro , Choa Yong‐Ho , Niihara Koichi , Ohji Tatsuki
Published: July 2010

The microstructural evolution and mechanical properties of Si3N4–SiC composites obtained by the sinter–post‐HIP process were investigated. SiC addition prohibited β‐Si3N4 grain growth; however, the grain growth followed the empirical growth law, with exponents of 3 and 5 for the c‐ and the a‐axis directions, respectively. Mechanical properties were strongly influenced by SiC addition and sintering conditions. Short‐crack propagation behavior was measured and analyzed by the indentation‐strength in‐bending (ISB) method. The present composites had high short‐crack toughness, compared with the values for monolithic Si3N4. The enhanced short‐crack toughness was attributed to crack‐tip bridging by the SiC particles.
Influence of Grain Phase on Slag Corrosion of Low‐Cement Castable Refractories
Authors: Sarpoolaky Hossain , Zhang Shaowei , Argent Bernard Barry , Lee William Edward
Published: July 2010

The grain phase has a significant influence on the extent and mechanism of attack of low‐cement castables with similar bond systems in a crucible corrosion test. The general corrosion mechanism, as determined by post mortem scanning electron microscopic examination of corroded samples and thermodynamic calculations for all four grain types examined (white‐fused alumina (WFA), tabular alumina (TA), brown‐fused alumina (BFA), and alumina‐rich spinel (S)), involves initial reaction of the most penetrating slag (enriched in calcium, manganese, and iron, because these elements diffuse rapidly) with the fine alumina and calcium aluminates of the matrix. This reaction gives a CaO‐rich local liquid, which can then react with each grain predominantly to form calcium hexaluminate (CA6) and hercynitic spinel. In the WFA system, a complete CA6 layer forms around the grain, whereas in the TA system, this layer is incomplete. In both systems, extensive penetration occurs, although corrosion is low. In the BFA system, titanates are released from the grain into the bond, leading to increased densification of the refractory, via liquid‐phase sintering, and consequent low penetration. However, the resulting fluid liquid dissolves easily in the slag, so that corrosive wear is high, even though a CA6 layer forms around the grain. In the S grain system, uptake of the rapidly diffusing cations into the spinel crystal structure leads to silica‐rich and viscous local liquid, which leads to low penetration and corrosion.
Zinc Vanadates in Vanadium Oxide‐Doped Zinc Oxide Varistors
Authors: Hng Huey‐Hoon , Knowles Kevin M. , Midgley Paul A.
Published: July 2010

Convergent‐beam electron diffraction has been used to determine the space groups of β‐ and γ‐Zn3(VO4)2 particles in vanadium oxide‐doped zinc oxide varistors. The crystal structure of β‐Zn3(VO4)2 has been determined to be monoclinic with space group P21 and lattice parameters of a= 9.80 Å, b= 8.34 Å, c= 10.27 Å, and β= 115.8°, whereas that of γ‐Zn3(VO4)2 is monoclinic with space group Cm and a= 10.40 Å, b= 8.59 Å, c= 9.44 Å, and β= 98.8°. Energy‐dispersive X‐ray microanalysis of these two phases shows significant deviations from their expected stoichiometry. It is apparent that the β‐phase is, in fact, the metastable Zn4V2O9 phase, whereas the γ‐phase either is a new oxide that consists of zinc, vanadium, and manganese or, more likely, is a zinc vanadate phase with a Zn:V atomic ratio of 1:1 that has the ability to go into solid solution with manganese.
Diffusion Bonding of Silicon Nitride Using a Superplastic β‐SiAlON Interlayer
Authors: Xie Rong‐Jun , Mitomo Mamoru , Zhan Gou‐Dong , Huang Li‐Ping , Fu Xi‐Ren
Published: July 2010

A superplastic β‐SiAlON was used as an interlayer to diffusionally bond a hot‐pressed silicon nitride to itself. The bonding was conducted in a graphite furnace under a constant uniaxial load of 5 MPa at temperatures varying from 1500° to 1650°C for 2 h, followed by annealing at temperatures in the range of 1600° to 1750oC for 2 h. The bonds were evaluated using the four‐point‐bend method at both room temperature and high temperatures. The results indicate that strong, void‐free joints can be produced with the superplastic β‐SiAlON interlayer, with bond strengths ranging from 438 to 682 MPa, and that the Si3N4 joints are heat resistant, being able to retain their strength up to 1000°C (635 MPa), and therefore have potential for high‐temperature applications.
Preparation of Li2S–P2S5 Amorphous Solid Electrolytes by Mechanical Milling
Authors: Hayashi Akitoshi , Hama Shigenori , Morimoto Hideyuki , Tatsumisago Masahiro , Minami Tsutomu
Published: July 2010

Amorphous solid electrolytes in the Li2S–P2S5 system were prepared successfully from a mixture of crystalline Li2S and P2S5, using a mechanical milling technique. The amorphous‐forming region was extended to higher Li2S compositions by mechanical milling, compared with melt quenching. The pelletized samples of the 75Li2S·25P2S5 (on a mole‐percent basis) amorphous powders obtained by mechanical milling for 20 h exhibited high conductivity (2 × 10−4 S/cm at room temperature) and an activation energy for conduction of 34 kJ/mol. The lithium‐ion transport number of the amorphous powders was almost unity.
Microwave Effects in Lead Zirconium Titanate Synthesis: Enhanced Kinetics and Changed Mechanisms
Authors: Vaidhyanathan Balasubramaniam , Singh Anirudh P. , Agrawal Dinesh K. , Shrout Thomas R. , Roy Rustum , Ganguly Suman
Published: July 2010

A novel, simple, and fast solid‐state procedure has been demonstrated for the synthesis of Pb(Zr,Ti)O3 (PZT), using microwave radiation. The process consists of starting with the respective oxides mixed in the required proportions and exposing the charge to the microwaves. By making one or more of the constituent oxides slightly nonstoichiometric, enormous enhancement in reaction rates has been achieved, and single‐phase PZT can be synthesized at temperatures as low as 600°C. Moreover, it has been shown that the combined use of nonstoichiometric precursors and microwave irradiation leads to different reaction pathways for the formation of PZT. Further, the microwave method diminishes PbO loss.
Synthesis of Dense TiB2‐TiN Nanocrystalline Composites through Mechanical and Field Activation
Authors: Lee Jae Won , Munir Zuhair A. , Shibuya Masachika , Ohyanagi Manshi
Published: July 2010

The synthesis of dense nanometric composites of TiN‐TiB2 by mechanical and field activation was investigated. Powder mixtures of Ti, BN, and B were mechanically activated through ball milling. Some powders were milled to reduce crystallite size but to avoid initiating a reaction. In other cases powders were milled and allowed to partially react. All these were subsequently reacted in a spark plasma synthesis (SPS) apparatus. The products were composites with equimolar nitride and boride components with relative densities ranging from 90.1% to 97.2%. Crystallite size analyses using the XRD treatments of Williamson‐Hall and Halder‐Wagner gave crystallite sizes for the TiN and TiB2 components in the range 38.5–62.5 and 31.2–58.8 nm, respectively. Vickers microhardness measurements (at 2 N force) on the dense samples gave values ranging from 14.8 to 21.8 GPa and fracture toughness determinations (at 20 N) resulted in values ranging from 3.32 to 6.50 MPa·m1/2.
Mechanical‐Activation‐Triggered Gibbsite‐to‐Boehmite Transition and Activation‐Derived Alumina Powders
Authors: Yong Chiang Chye , Wang John
Published: July 2010

Mechanical activation of monoclinic gibbsite (Al(OH)3) in nitrogen led to the formation of nanocrystalline orthorhombic boehmite (AlOOH) at room temperature. The boehmite phase formed after merely 3 h of mechanical activation and developed steadily as the mechanical‐activation time increased. Forty hours of mechanical activation resulted in essentially single‐phase boehmite, together with α‐alumina (α‐Al2O3) nanocrystallites 2–3 nm in size. The sequence of phase transitions in the activation‐derived boehmite was as follows: boehmite to γ‐Al2O3 and then to α‐Al2O3 when flash‐calcined at a heating rate of 10°C/min in air. γ‐Al2O3 formed at 520°C, and flash calcination to 1100°C led to the formation of an α‐Al2O3 phase, which exhibited a refined particle size in the range of 100–200 nm. In contrast, the gibbsite‐to‐boehmite transition in the unactivated gibbsite occurred over the temperature range of 220°–330°C. A flash‐calcination temperature of 1400°C was required to complete the conversion to α‐Al2O3 phase, with both δ‐Al2O3 and θ‐Al2O3 as the transitional phases. The resulting alumina powder consisted of irregularly shaped particles 0.4–0.8 μm in size, together with an extensive degree of particle agglomeration.
Positive Temperature Coefficient of Resistivity Effect in Highly Donor–Doped Barium Titanate
Authors: Makovec Darko , Ule Nina , Drofenik Miha
Published: July 2010

BaTiO3 ceramics doped with different La concentrations (0–12 mol%) were prepared by sintering under the reducing conditions of a nitrogen atmosphere containing 1% hydrogen. The critical donor concentration that causes blocking of the exaggerated grain growth was observed to be ∼10 mol% La. The samples, which were semiconducting after sintering under reducing conditions, were subsequently reoxidized by annealing in air to induce the positive temperature coefficient of resistivity (PTCR) effect. After reoxidation at 1150°C a noticeable PTCR effect was observed in the samples doped with La concentrations as high as 2.5 mol%. The room‐temperature resistivity after reoxidation was found to increase with increasing donor concentration due to an increase in the thickness of the insulating layers at the grain boundaries. TEM analysis showed that reoxidation of the samples caused precipitation of the Ti‐rich compound Ba6Ti17O40 inside the doped BaTiO3‐matrix grains.
Devitrification Kinetics and Mechanism of K2O–CaO–SrO–BaO–B2O3–SiO2 Glass‐Ceramic
Authors: Jean Jau‐Ho , Fang Yu‐Ching , Dai Steve X. , Wilcox David L.
Published: July 2010

The devitrification kinetics and mechanism of a low‐dielectric, low‐temperature, cofirable K2O–CaO–SrO–BaO–B2O3–SiO2 glass‐ceramic have been investigated. Crystalline phases including cristobalite (SiO2) and pseudowollastonite ((Ca,Ba,Sr) SiO3) are formed during firing. Activation energy analysis shows that the nucleation of the crystalline phases is controlled by phase separation of the glass. The crystallization kinetics of both cristobalite and pseudowollastonite obey Avrami‐like behavior, and the results show an apparent activation energy close to that of the diffusion of alkaline and alkali ions in the glass, suggesting that diffusion is rate limiting. The above conclusion is further supported by analysis of measured growth rates.
Fabrication of Porous Ceramics with Unidirectionally Aligned Continuous Pores
Authors: Zhang Guo‐Jun , Yang Jian‐Feng , Ohji Tatsuki
Published: July 2010

Porous alumina ceramics with unidirectionally aligned continuous pores were fabricated via the slurry coating of fugitive fiber. Cotton thread was coated with ceramic slurry by pulling it through the slurry, and specimens were produced by spooling the coated thread. The obtained porous alumina ceramics had an average pore diameter of 165 μm, 35% open porosity, and a bending strength of 160 MPa. It was suggested that the pore size and the porosity could be adjusted using the diameter of the cotton thread and the solids concentration of the slurry, respectively.
Fabrication and Characterization of Pyroelectric Ba0.8Sr0.2TiO3 Thin Films by a Sol‐Gel Process
Authors: Cheng Jian‐Gong , Tang Jun , Meng Xiang‐Jian , Guo Shao‐Ling , Chu Jun‐Hao , Wang Min , Wang Hong , Wang Zhuo
Published: July 2010

A sol‐gel process was used to prepare pyroelectric Ba0.8Sr0.2TiO3 thin films with large columnar grains (100–200 nm in diameter) on Pt/Ti/SiO2/Si substrates, via using a 0.05M solution precursor. The relationship between dielectric constant and temperature (ɛr‐T) showed two distinctive phase transitions in the Ba0.8Sr0.2TiO3 thin films. Both the remnant polarization and the coercive field decreased as the temperature increased from −73°C to 40°C. Its low dissipation factor (tan δ= 2.6%) and high pyroelectric coefficient (p= 4.6 × 10−4 C·(m2·K)−1 at 33°C), together with its good insulating properties, made the prepared Ba0.8Sr0.2TiO3 thin films promising for use in uncooled infrared detectors and thermal imaging applications.
Vaporization and Corrosion of Refractories in the Presence of Pressurized Pulverized Coal Combustion Slag
Authors: Biedenkopf Peter , Karwath Thomas , Kobertz Dietmar , Rane Manisha , Wessel Egbert , Hilpert Klaus , Singheiser Lorenz
Published: July 2010

The corrosion and vaporization behavior of eight commercial refractories containing Cr2O3 were investigated under simulated pressurized pulverized coal combustion (PPCC) conditions at 1723 K in the presence of liquid slag. The corrosion resistance of the refractory materials decreased with increased content of free Cr2O3, because bursting (reaction of Fe3O4 with Cr2O3) occurred. Refractories containing MgCr2O4 with dissolved Al2O3 showed the highest corrosion resistance. Thermodynamic calculations showed that CrO3 and CrO2(OH)2 were the most volatile species in air and in PPCC flue gas, whereas additions of A2O (A = Na and K, minor slag component) increased the chromium vaporization significantly because of A2CrO4 formation. Knudsen effusion mass spectrometry measurements showed that the chromium vaporization of refractories was directly correlated to the Cr2O3 content of the material. In contrast, refractories containing MgCr2O4 showed a significant decrease in chromium vaporization.
Microstructural Evolution of Transparent PLZT Ceramics Sintered in Air and Oxygen Atmospheres
Authors: Choi Jong‐Jin , Ryu Jungho , Kim Hyoun‐Ee
Published: July 2010

Transparent lanthanum‐doped lead zirconate titanate (PLZT) ceramics were fabricated by air‐pressure sintering. When the PLZT (9/65/35) specimens were sintered in air, the microstructure was not uniform throughout the body; the outer region near the surface was completely dense, while the inner region of the body was porous. The thickness of the outer dense layer increased parabolically with sintering time. When the specimen was sintered in air at 1200°C for 8 h, the thickness of the dense layer was ∼0.25 mm. Therefore, when the specimen had a thickness of <0.5 mm, it was dense and transparent. This difference in microstructure was attributed to the formation of lattice vacancies as a result of PbO evaporation from the surface. The sintering atmosphere also was important in determining the thickness of the dense layer. The thickness was strongly dependent on the oxygen partial pressure of the atmosphere. The oxygen‐gas trapped in pores was deemed to migrate easily through the lattice vacancies. By sintering in an oxygen‐gas atmosphere at 1200°C for 8 h, a transparent PLZT with thickness up to 2 mm was fabricated.
Preparation, Characterization, and Microwave Properties of RETiNbO6 (RE = Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Y, and Yb) Dielectric Ceramics
Authors: Sebastian Mailadil T. , Solomon Sam , Ratheesh Ravindran , George Jacob , Mohanan Pezholil
Published: July 2010

Microwave ceramic dielectric resonators (DRs) based on RETiNbO6 (RE = Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Y, and Yb) have been prepared using the conventional solid‐state ceramic route. The DR samples are characterized using XRD and SEM methods. The microwave dielectric properties are measured using resonant methods and a net work analyzer. The ceramics based on Ce, Pr, Nd, and Sm have dielectric constants in the range 32–54 and positive coefficient of thermal variation of resonant frequency (τf). The ceramics based on Gd, Tb, Dy, Y, and Yb have dielectric constants in the range 19–22 and negative τf.
Electrical Properties of Boron Nitride Matrix Composites: I, Analysis of McLachlan Equation and Modeling of the Conductivity of Boron Nitride–Boron Carbide and Boron Nitride–Silicon Carbide Composites
Authors: Runyan Julie , Gerhardt Rosario A. , Ruh Robert
Published: July 2010

The McLachlan equation, which incorporates both effective medium models and percolation, was used to predict the volume fraction–conductivity relationships of insulator–conductor composites, and results were compared with experimental data. Two composite systems were investigated (BN–B4C and BN–SiC). Both systems are anisotropic, because of the orientation of BN platelets perpendicular to the hot‐pressing direction. For BN–B4C composites, with increasing B4C content, the ac and dc conductivities are relatively constant to ∼40% B4C (the critical volume fraction). At this composition, the conductivity suddenly increases to a value closer to that of B4C and then resumes a gradual increase. Little difference is seen for measurements made perpendicular or parallel to the hot‐pressing direction, i.e., perpendicular or parallel to the BN platelets. Similar results are found for the BN–SiC composites, except that the critical volume fraction is ∼20% SiC in this case. The experimental curves are in good agreement with those predicted by the McLachlan equation. The parameters s and t of the McLachlan equation relate to the morphology of the phases present in the microstructure. The critical volume fraction relates to the connectivity of the phases in the composites.
Fracture Resistance of Highly Textured Alumina
Authors: Hall Peyton W. , Swinnea J. Steven , Kovar Desiderio
Published: July 2010

Textured alumina has been fabricated previously by either hot‐deformation processing, to produce moderate texture, or templating with aligned platelets, to produce stronger texture. Fracture‐toughness measurements on ceramics fabricated by hot deformation have indicated only a modest improvement in toughness compared with that of untextured ceramics, while measurements on more strongly textured ceramics have been very limited. In this work, a simplified process for fabricating highly textured alumina was developed, using a solvent‐based slurry, tape casting, and liquid‐phase sintering. Grain size was tailored to maximize the likelihood of grain bridging and crack deflection. Image analysis was used to characterize morphologic texture, and X‐ray pole‐figure analysis was used to measure crystallographic texture. Fracture tests revealed significant changes to the crack path as a result of the texture. However, the apparent fracture resistances measured using single‐edge notched‐beam samples were similar for textured and untextured ceramics. The lack of apparent toughening resulting from texturing is discussed in light of previous results.
Measurement of High‐Temperature Elastic Properties of Ceramics Using a Laser Ultrasonic Method
Authors: Matsumoto Takahiro , Nose Tetsuro , Nagata Yasuaki , Kawashima Katsuhiro , Yamada Tastuya , Nakano Hidetoshi , Nagai Satoshi
Published: July 2010

Young’s modulus and Poisson’s ratio of SiC ceramics at temperatures >1400°C were obtained using a laser ultrasonics method that included a Fabry‐Pérot interferometer (LUFP). At temperatures <1000°C, Young’s modulus and Poisson’s ratio measured using the LUFP method agreed well with those measured using standard contact methods, such as the resonance method and the ultrasonic pulse method. These results showed that the LUFP method is a powerful tool for measuring high‐temperature elastic properties of advanced ceramics in a noncontact manner.
Evaluation of Porous ZrO2‐SiO2 and Monazite Coatings Using NextelTM 720‐Fiber‐Reinforced Blackglas™ Minicomposites
Authors: Parthasarathy Triplicane A. , Boakye Emmanuel E. , Keller Kristin A. , Hay Randall S.
Published: July 2010

A procedure was developed to fabricate oxide‐fiber‐reinforced minicomposites with a dense matrix and evaluate two oxidation‐resistant interface coatings, porous oxide (zirconia‐silica mixture) and monazite. The coatings were evaluated using NextelTM 720‐fiber‐reinforced BlackglasTM‐matrix minicomposites. Boron nitride (BN) coated and uncoated fibers were used as controls for comparison. The evaluation was based on ultimate failure strengths, fractography, and fiber pushin tests. All the composites that used fiber coatings had ultimate strengths significantly better than the control that used uncoated fibers. In addition, porous‐oxide‐coated fibers were found to be similar to BN‐coated fibers in strength, fractography, and fiber pushin behavior. Monazite‐coated fibers resulted in similar ultimate strengths but showed no appreciable fiber pullout. Fiber pushin tests showed that monazite debonds readily but frictional resistance is higher than for BN or porous oxide fiber coatings.
Electrochemical Stability of Strontium‐Doped Ceria Electrolyte in Solid‐Oxide Fuel Cell Applications
Authors: Milliken Christopher E. , Guruswamy Sivaraman , Khandkar Ashok C.
Published: July 2010

SrO‐doped CeO2 electrolyte has been evaluated in single‐cell configuration under solid‐oxide fuel cell operating conditions. Because of oxygen loss from the crystal lattice, the material experiences a macroscopic expansion of several percent at 1000°C. On extended cell operation, strontium precipitates‐out at/near the anode, resulting in irreversible cell degradation in the case of SrO‐doped CeO2. Precipitation and diffusion of SrO causes decreased ionic conductivity and may result in anode delamination. SrO precipitation is attributed to insolubility of the dopant in the reduced CeO2 phase. The diffusion of strontium seems to be related to the flux of oxygen through the sample, but an exact mechanism is unknown.
Preparation of Synthetic Cordierite by Solid‐State Reaction via Bismuth Oxide Flux
Authors: Malachevsky Maria Teresa , Fiscina Jorge Eduardo , Esparza Daniel Antonio
Published: July 2010

A comparative study of the solid‐state reaction synthesis of cordierite with and without the use of a flux was performed, varying the sintering temperatures between 900° and 1400°C. Bi2O3 proved to be a useful additive for lowering the temperature needed for the reaction to take place. The deviation from the ordered β‐cordierite phase was analyzed using the distortion index Δ as a factor of merit. The values obtained for Δ in all compositions showed that cordierite tended to a much‐ordered structure with increased sintering temperatures.
Effect of Silica Additive on the Anatase‐to‐Rutile Phase Transition
Authors: Okada Kiyoshi , Yamamoto Nobuo , Kameshima Yoshikazu , Yasumori Atsuo , MacKenzie Kenneth J. D.
Published: July 2010

The effect of SiO2 addition on the anatase‐to‐rutile phase transition was investigated by DTA, XRD, FTIR, and XPS. TiO2 xerogels containing SiO2 up to 20 mol% were prepared by mixing and hydrolyzing titanium tetraisopropoxide (TTIP) and tetraethylorthosilicate (TEOS) with HNO3 as a catalyst. With increased amounts of SiO2 in the xerogels, the following results were obtained: (1) the crystallization temperature of anatase increased from 415°C in pure TiO2 to 609°C in 20‐mol%‐SiO2‐containing xerogel in the DTA curves; (2) the formation temperature of rutile, according to quantitative XRD analysis, increased with increased SiO2 content up to 5 mol% SiO2 but became constant at higher SiO2 contents; (3) the crystallinity of anatase became lower; and (4) the lattice parameter a of the anatase decreased slightly, but the parameter c decreased greatly up to 20 mol% SiO2. Although the added silicon atoms were considered from these results to be incorporated into the amorphous TiO2 and anatase structures, the 29Si MAS NMR spectra of the xerogels containing 10 mol% SiO2 showed only tetrahedral silicon, with no indication of silicon in octahedral coordination. When calcined at higher temperatures, the xerogel showed polymerization of the SiO4 tetrahedra in the NMR spectra and the Si–O–Si vibration in the FTIR spectra. The chemical composition of the xerogel surfaces, measured using XPS, showed increased SiO2 content with increased calcining temperature, indicating the expulsion of silicon from inside the particles to form an amorphous SiO2 surface layer. The formation of this amorphous SiO2 surface layer was considered to be important in retarding the anatase‐to‐rutile phase transition by suppressing diffusion between anatase particles in direct contact and limiting their ability to act as surface nucleation sites for rutile. These effects of silicon additions were similar to those observed in the γ‐Al2O3‐ to‐α‐Al2O3 transition.
Impurity‐Dependent Morphology and Grain Growth in Liquid‐Phase‐Sintered Alumina
Authors: Goswami Amiya P. , Roy Sukumar , Mitra Manoj K. , Das Gopes C.
Published: July 2010

The alumina grains in liquid‐phase‐sintered (LPS) materials prepared from different commercial sources have a predominantly platelet morphology. Generally, the MgO:(CaO + BaO + Na2O + K2O) ratio in the chemical composition controls the morphology in LPS alumina that is 91–94 wt% pure. Within a given range of SiO2 content (i.e., 4.3–5.2 wt% in the chemical composition), a low MgO:(CaO + BaO + Na2O + K2O) ratio (i.e., <1.0) in the LPS compositions favors the formation of elongated grains, whereas ratios of >1.0 result in equiaxed grains. SiO2 contents outside the 4.3–5.2 wt% range favor the formation of elongated grains. A tendency to form platelike grains is observed for LPS alumina with a purity of 91–94 wt% when both the MgO:(CaO + BaO + Na2O + K2O) ratio and the SiO2 content are relatively low. The sintered density generally increases as the SiO2 content in the chemical composition decreases.
Microstructure Characterizations in Calcium Magnesium Niobate
Authors: Lee Hwack Joo , Park Hyun Min , Cho Yang Koo , Song Yong Won , Nahm Sahn , Byun Jae‐Dong
Published: July 2010

Microstructural studies on the domain boundaries in Ca(Mg1/3CNb2/3)O3 (CMN) complex perovskite compound were conducted using X‐ray diffractometry and transmission electron microscopy. The 1:2 chemical ordering of B‐site cations and the tilting of oxygen octahedra were involved in the CMN microstructure, as inferred from the presence of two types of domain boundaries. One type was the antiphase boundaries (APBs), which did not lie on a specific set of crystallographic planes. These boundaries were caused by the chemical 1:2 ordering of B‐site cations, magnesium and niobium. The other type was the ferroelastic domain boundaries, which were parallel to a certain crystallographic plane. Therefore, CMN had the 1:2 ordered monoclinic unit cell distorted by the antiphase or in‐phase tilting of oxygen octahedra. CMN had the mixed phases rather than the homogeneous phase.