bluuebunny/crossref_metadata_2025 huggingface dataset:
Damage to the Pore Structure of Hardened Portland Cement Paste by Mercury Intrusion
Authors: Olson Rudolph A. , Neubauer Christopher M. , Jennings Hamlin M.
Published: July 2010

Microstructural changes due to mercury intrusion porosimetry were documented in a 6‐month‐old sample of ordinary portland cement paste made with a water/cement ratio of 0.5. Specimens before and after mercury intrusion were viewed at 60% relative humidity using an environmental scanning electron microscope. Specimens were intruded to a pressure just below the critical threshold pressure, removed for observation, then intruded to a pressure well above the critical threshold pressure. Significant damage caused by relatively low pressures of 10–20 MPa was found in the interior of the sample. The connectivity of pores in the 10–1 μm size range was much higher after intrusion.
Preparation of Crystallized Sr1−XCaXMoO4 Solid‐Solution Films by an Electrochemical Method at Room Temperature and Their Luminescence
Authors: Yoshimura Masahiro , Ohmura Mitsuhiro , Cho Woo‐Seok , Yashima Masatomo , Kakihana Masato
Published: July 2010

A complete series of well‐crystallized solid‐solution Sr1–X‐CaXMoO4 films has been prepared on molybdenum substrates in an electrolytic solution containing Sr2+ and Ca2+ ions by an electrochemical method at room temperature (25°C). The peak positions of excitation and emission of the Sr1–XCaXMoO4 solid‐solution films were independent of the Ca content: 285 ± 2 nm for excitation and 536 ± 2 nm for emission at liquid‐nitrogen temperature (−196°C).
New Concept for Simulating Particle Packing in Colloidal Forming Processes
Authors: Hong Chu‐Wan
Published: July 2010

A new simulation concept based on the discrete element method (DEM) has been developed for studying particle‐packing dynamics during colloidal forming processes. Long‐range potential interactions, medium influences, solid‐body contact, and adhesion are considered. DEM regards each particle as an individual element and enables the observation of the spatially and temporally resolved microscopic details. The importance of different competitive interaction forces is compared. The electrostatic repulsion constrains the Brownian motion for all particle sizes. The simultaneous, competitive influences of the colloidal chemical and process parameters on the particle‐packing structure during pressure filtration and centrifugal casting have been simulated and analyzed. In the pressure filtration test, the well‐stabilized monomodal particles form a close‐packed hexagonal structure, and this regularity is strongly dependent on the filtration rate. The higher the filtration rate, the more packing defects are formed. Although well‐stabilized suspensions with high zeta‐potential tend to form particle chains, suspensions with low zeta‐potential form agglomerate structures. The limitations of the long‐range interaction functions derived from the Hamaker theory and from the electrostatic Poisson‐Boltzmann equation are discussed.
Patterning of Lithium Niobate Thin Films Derived from Aqueous Solution
Authors: Ono Satomi , Hirano Shin‐ichi
Published: July 2010

The micropatterning of lithium niobate (LiNbO3) thin films was conducted by applying a photolithographic technique to an aqueous precursor solution that was derived from a double alkoxide. The neutralization process of the alkaline lithium niobium hydroxide solution was essential to avoid the dissolution of the aluminum masking pattern on the sapphire substrate. The acetic acid was a suitable neutralizer to form the stoichiometric and transparent gel film. The gel film that was prepared from a neutralized precursor solution at pH 6.4 gave high‐quality crystalline LiNbO3 films after heat treatment at 500°C.
Formation of Mullite from Filled Siloxanes
Authors: Suttor Daniel , Kleebe Hans‐Joachim , Ziegler Gunter
Published: July 2010

Monolithic mullite with low sintering shrinkage was synthesized from polymer/filler blendsMthat is, siloxane/alumina (siloxane/Al2O3) (and siloxane/aluminum (siloxane/Al)) mixtures. The synthesis was based on a reaction‐bonding process of amorphous silica, which formed when the siloxane was oxidized, with Al2O3 (or oxidized aluminum filler) at temperatures >1250°C. Thermodynamic calculations were used to calculate the phase composition at equilibrium. Thermoanalytical, infrared‐spectroscopic, and microscopic techniques were applied to reveal the microstructural evolution. The corresponding volume changes were used to evaluate the linear shrinkage, based on the quantitative phase assemblage.
Synthesis, Densification, and Conductivity Characteristics of BICUVOX Oxygen‐Ion‐Conducting Ceramics
Authors: Simner Steven P. , Suarez‐Sandoval Donaji , Mackenzie John D. , Dunn Bruce
Published: July 2010

Copper‐substituted bismuth vanadate (Bi2V0.9Cu0.1O5.35), known as BICUVOX, possesses high oxygen ion conductivities at low temperatures. The ionic conductivity of this material at 300°C (∼1 × 10−3 S/cm) is 50 to 100 times greater than any other solid electrolyte in this temperature range. In this paper we report the preparation of sinterable BICUVOX powders by solid‐state reaction and conventional ceramic powder processing techniques. Densification studies indicate that optimum densities (>95% theoretical) can be obtained after 10‐20 h sintering at 800°C. Ionic conductivity characteristics were evaluated with respect to temperature, sample density, and prolonged isothermal heating.
Mechanical Behavior at 20° and 1200°C of Nicalon‐Silicon‐Carbide‐Fiber‐Reinforced Alumina‐Matrix Composites
Authors: Celemaín Jose Antonio , Pastor Jose Ygnacio , LLorca Javier , Elices Manuel
Published: July 2010

Tensile and fracture tests were conducted at 20° and 1200°C on a ceramic‐matrix composite that was composed of an alumina (Al2O3) matrix that was bidirectionally reinforced with 37 vol% silicon carbide (SiC) Nicalon fibers. The composite presented nonlinear behavior at both temperatures; however, the strength and toughness were significantly reduced at 1200°C. In accordance with this behavior, matrix cracks were usually stopped or deflected at the fiber/matrix interface, and fiber pullout was observed on the fracture surfaces at 20° and 1200°C. The interfacial sliding resistance at ambient and elevated temperatures was estimated from quantitative microscopy analyses of the saturation crack spacing in the matrix. The in situ fiber strength was determined both from the defect morphology on the fibers and from the size of the mirror region on the fiber fracture surfaces. It was shown that composite degradation at elevated temperature was due to the growth of defects on the fiber surface during high‐temperature exposure.
Structure and Properties of Silica Derived from Silicon Alkoxide Reacted with Tartaric Acid
Authors: Izutsu Hiroyuki , Mizukami Fujio , Kiyozumi Yoshimichi , Maeda Kazuyuki
Published: July 2010

The effects of tartaric acid that was used in sol–gel processing on specific surface area, pore‐size distribution, and gel structure of sol–gel‐derived silica gels were investigated. The specific surface area of silicas that were calcined at 450°C increased from ∼600 m2/g to ∼1200 m2/g as the amount of tartaric acid that was used increased. The pore‐size distribution changed as the surface area increased, and only the gels that had a surface area of 930‐990 m2/g showed a very sharp pore‐size distribution in the mesopore range. The difference in gel structure and properties was explained in terms of the acidity of tartaric acid and the inhibition of condensation among primary particles through the coordination or adsorption of tartaric acid on the particle surface. From the thermal behavior of the gels with different features, it was concluded that gel properties are determined not only by the structure of the precursor gel but also by the surface activity. The gel with uniform mesopores gave a high surface area over a wide range of calcination temperatures.
Shift of the Curie Point of Barium Titanate Ceramics with Sintering Temperature
Authors: Kuwabara Makoto , Matsuda Hirofumi , Kurata Natsuko , Matsuyama Eiji
Published: July 2010

Definite increases in the Curie point (TC) of undoped and lanthanum‐ (La‐) doped (<0.5 at.%) barium titanate (BaTiO3) ceramics sintered at elevated temperatures in the range of 1300°‐1450°C were observed. Both undoped and 0.3 at.% La‐doped BaTiO3 (chosen as a typical doping concentration to yield semiconducting materials) ceramics showed almost the same TC behavior; their TC values increased by ∼3.5°C as the sintering temperature was increased from 1300° to 1450°C. Semiconducting 0.3 at.% La‐doped materials increased in room‐temperature bulk resistivity and TC with increased sintering temperature. The bulk resistivity of the La‐doped materials, which was obtained from complex impedance analysis, increased from ∼2 omega cm for the material sintered at 1350°C to ∼6 ω cm at 1450°C. The phenomenon of bulk resistivity increase with sintering temperature was observed in the materials with a doping concentration of ≥ 0.2 at.% La, but was not observed in those doped with <0.2 at.% La. The mechanisms of TC and the bulk resistivity increase observed in the present materials with increased sintering temperature are discussed based on various models found in the literature, particularly in terms of the defect chemistry in semiconducting BaTiO3 ceramics and the influence of liquid phases present during sintering.
Oriented Lead Titanate Film Growth at Lower Temperatures by the Sol‐Gel Method on Particle‐Seeded Substrates
Authors: Moon Jooho , Kerchner Jeffrey A. , LeBleu James , Morrone Augusto A. , Adair James H.
Published: July 2010

An approach to fabricate lead titanate (PbTiO3) films with preferred orientation on arbitrary substrates by a sol‐gel method was developed. To ensure a preferred crystallographic orientation on the substrates with different crystal structure, well‐defined platelet PbTiO3 particles were used as seeds. Because the basal plane of the platelet‐shaped particles was the (001) plane, the particles aligned with the c‐axis perpendicular to the substrates. During crystallization of the sol‐gel PbTiO3 films on the particle‐seeded substrate, preferential nucleation occurred on seeded particles with the same crystallographic orientation as the particles at a much lower temperature. In the current study, (100) and (001) textured PbTiO3 films have been produced on various substrate materials such as silicon, silicate glass, indium tin oxide (ITO) glass, and titanium metal at temperatures as low as 275°C. The microstructure of the films was examined by scanning electron microscopy and atomic force microscopy. Limited ferroelectric properties also were determined, to underscore the preferred orientation that was produced in these materials.
Densification and Crystallization of Lead Titanate Aerogels
Authors: Löbmann Peer , Glaubitt Walther , Fricke Jochen
Published: July 2010

Crack‐free monolithic lead titanate (PbTiO3, or PT) aerogels were prepared via a sol‐gel process and drying in supercritical carbon dioxide. The material was characterized by thermogravimetric analysis, dilatometry, helium pycnometry, and X‐ray diffraction. Skeletal densification was the main reason for the observed shrinkage of the heat‐treated porous material at temperatures <450°C. The transition (at temperatures of 500°‐600°C) from an amorphous state to the crystalline (tetragonal) PT was accompanied by significant particle coarsening, as revealed by transmission electron microscopy. Nitrogen adsorption measurements confirmed that crystallization was preceded by the formation of interparticle necks.
Conversion of Diaspore to Corundum: A New α‐Alumina Transformation Sequence
Authors: Carim Altaf H. , Rohrer Gregory S. , Dando Neal R. , Tzeng Shih‐Ying , Rohrer Cathy L. , Perrotta Anthony J.
Published: July 2010

A new two‐step transformation sequence has been identified for the conversion of diaspore (α‐AlOOH) to corundum (alpha‐Al2O3). The powder X‐ray diffraction pattern of the intermediate phase, designated alpha'‐Al2O3, has been indexed to a monoclinic (P2) cell, with a = 9.566(5) Å, b = 5.124(2) Å, c = 9.156(4) Å, and ß= 91.76(3)°. Nuclear magnetic resonance of alpha'‐Al2O3 indicates that 15‐20% of the aluminum is on tetrahedral sites, with the remainder in octahedral coordination. Controlled‐atmosphere high‐temperature X‐ray diffraction shows that water accelerates the second transformation step, alpha'‐Al2O3→> alpha‐Al2O3, acting as a mineralizer for the conversion process.
R‐Curve Behavior of Silicon Nitride–Titanium Nitride Composites
Authors: Choi Heon‐Jin , Cho Kyeong‐Sik , Lee June‐Gunn , Kim Young‐Wook
Published: July 2010

The R–curve for Si3N4−40 wt% TiN composites was estimated by the indentation‐strength method and compared to that of monolithic Si3N4 with duplex microstructure. Both materials exhibited rising R‐curve behavior. The Si3N4‐TiN composites, however, displayed better damage tolerance and higher resistance to crack growth. From TEM observation, it was inferred that this superior performance of Si3N4‐TiN composites can be attributed mainly to stress‐induced microcracking at hete rophase (Si3N4/TiN) boundaries.
Relation between Mechanical Twinning and Cracking in Stoichiometric Lithium Niobate Single Crystals
Authors: Park Bong Mo , Kitamura Kenji , Furukawa Yasunori , Ji Yangyang
Published: July 2010

The relationships between cracking and mechanical twinning, and between ferroelectric polarization and mechanical twinning, in stoichiometric LiNbO3 were investigated in the present study. Three sets of mechanical twins crossed one another, and the crossed points of those twins provided preferred sites for the nucleation of cracks. Mechanical twins of LiNbO3 revealed a head‐to‐tail arrangement of ferroelectric polarization, and complicated polarization states were observed at the crossed points. Some possible mechanisms of crack nucleation and propagation are proposed in this paper.
Tetragonal‐to‐Cubic Structural Phase Transition in Pollucite by Low‐Temperature X‐ray Powder Diffraction
Authors: Yanase Ikuo , Kobayashi Hidehiko , Shibasaki Yoshio , Mitamura Takashi
Published: July 2010

The tetragonal‐to‐cubic structural phase transition in pollucite (CsAlSi2O6) was investigated using low‐temperature X‐ray powder diffraction in the temperature range of 93 to 298 K, and the lattice constants were refined with Rietveld analysis. It was found that CsAlSi2O6 had a tetragonal phase with a space group of I41/acd in the temperature range of 93 to 248 K, a = 1.36337(4) nm, c = 1.36988(6) nm at 248 K, and underwent a phase transition from tetragonal to cubic with a space group of Ia‐3 in the temperature range of 248 to 273 K, a = 1.36645(3) nm at 273 K.
Sol–Gel Synthesis of Perovskite‐Type Lanthanum Manganite Thin Films and Fine Powders Using Metal Acetylacetonate and Poly(vinyl alcohol)
Authors: Shimizu Youichi , Murata Tomohiko
Published: July 2010

A novel sol–gel process was developed for preparing thin films and fine powders of lanthanum manganite (LaMnO3) with perovskite‐type structure. Lanthanum and manganese acetylacetonate powders could be easily dissolved in a mixed solution of methyl alcohol and ethylene glycol (or methyl alcohol and propionic acid) to give a spinnable organic solution as a starting material. Pretreatment of a substrate by poly(vinyl alcohol) (PVA) aqueous solution, a gel former, made it possible to deposit a thin film as well as to lower the sintering temperature.
Preparation of Lead Zirconate by Homogeneous Precipitation and Calcination
Authors: Oren Ersin Emre , Taspinar Ercan , Tas A. Cuneyt
Published: July 2010

Antiferroelectric PbZrO3 has been synthesized by homogeneous precipitation from aqueous solutions in the presence of urea (NH2CONH2) and calcination for 6 h at 700°C. SEM studies displayed the presence of submicrometer powder, with a significant degree of agglomeration.
Forming Textured Microstructures via the Gelcasting Technique
Authors: Zimmerman Michael H. , Faber K. T. , Fuller Edwin R.
Published: July 2010

Crystallographically textured samples of iron titanate were produced by gelcasting in the presence of a strong magnetic field. Texture was assessed by measuring X‐ray pole figures on samples that were cast in different orientations relative to the applied field. Specimens in this study exhibit fiber‐type texture, with the b‐axes aligned parallel to the applied field. Peak texture strengths were on the order of 3 and 48 multiples of a random distribution (MRD) when processed in a 3.2 and 8.4 T magnetic field, respectively. This study shows that a combination of gelcasting with magnetic‐field‐assisted processing provides a convenient method for fabricating samples which can be used to study the role of crystallographic texture on the physical properties of polycrystalline ceramics, e.g., their elastic or fracture behavior.
Translucent Tin Dioxide Ceramics Obtained by Natural Sintering
Authors: Gouvea Douglas , Smith Agnès , Smith David Stanley , Bonnet Jean Pierre , Varela Jose Arena
Published: July 2010

Dense SnO2‐based ceramics (relative density >95%) have been obtained by natural sintering at a moderate temperature (≤ 1300°C) with the help of a small amount of manganese. Further thermal treatments above 1500°C result in grain growth and transport of manganese toward the sample surface. If the ceramic is embedded inside alumina powder, the diffusion of Mn out of the sample and into alumina during such heat treatments leads to a manganese‐free body (<40 ppm) which is translucent. The transmission in the visible region depends on sample thickness; 61% was achieved for a 0.05 mm thick sample.
Formation and Sintering of TiO2 (Anatase) Solid Solution in the System TiO2‐SiO2
Authors: Yoshinaka Masaru , Hirota Ken , Yamaguchi Osamu
Published: July 2010

In the TiO2‐SiO2 system, anatase solid solutions (ss) containing up to similar/congruent ∼15 mol% SiO2 are formed in the as‐prepared state by the hydrazine method. The lattice parameters a and c decrease linearly from 0.3785 to 0.3776 nm and from 0.9514 to 0.9494 nm, respectively, with increased SiO2 content. At high temperatures, the solid solutions by transformation decompose into rutile and amorphous SiO2. The anatase(ss) powders have been characterized for particle size and surface area. They consist of very fine particles (7‐25 nm). Surface areas at low temperatures are very high and do not drop below 60 m2/g at 1000°C. Nanostructured anatase(ss) ceramics, with greaterthan/equal to 99.5% of theoretical density and an average grain size of 72 nm, have been fabricated by hot isostatic pressing for 1 h at 850°C and 196 MPa. Their mechanical and electrical properties have been examined.
Control of Interfacial Properties through Fiber Coatings: Monazite Coatings in Oxide–Oxide Composites
Authors: Kuo Dong‐Hau , Kriven Waltraud M. , Mackin Thomas J.
Published: July 2010

Fiber pushout tests were used to quantify the effects of fiber coating thickness on the mechanical properties of two model composite systems: a monazite‐coated (LaPO4‐coated) alumina (Al2O3) fiber in an Al2O3 matrix and a LaPO4‐coated yttrium aluminum garnet (YAG) fiber in an Al2O3 matrix. Interface properties were quantified using the Liang and Hutchinson (LH) pushout model and mechanistically rationalized by considering the change in residual thermal stresses with changes in the coating thickness. Measures of the pure Mode II interfacial fracture energy, the coefficient of friction, and a radial clamping pressure are extracted by fitting the LH equations to the experimental results. Using the approach that has been developed herein, a methodology is available for measuring the interfacial properties, predicting the effect of coating thickness, and selecting the coating thickness to
Formation and Stability of β‐Quartz Solid‐Solution Phase in the Li‐Si‐Al‐O‐N System
Authors: Nordmann Astrid , Cheng Yi‐Bing
Published: July 2010

The development of crystalline phases in lithium oxynitride glass‐ceramics was examined, with particular emphasis placed on the effect of the nitrogen source (AlN or Si3N4) on the formation and stability of a β‐quartz solid‐solution (ss) phase. Oxynitride glasses derived from the Li‐Si‐Al‐O‐N system were heat‐treated at temperatures up to 1200°C to yield glass‐ceramics in which β‐quartz(ss) and β‐spodumene(ss) of approximate composition Li2OAl2O34SiO2 formed as major phases and in which X‐phase (Si3Al6O12N2) and silicon oxynitride (Si2N2O) were present as minor phases. The nitrogen‐containing β‐quartz(ss) phase that was prepared with AlN was stable at 1200°C; however, the use of Si3N4 as the nitrogen source was significantly less effective in promoting such thermal stabilization. Lattice parameter measurements revealed that AlN and Si3N4 had different effects on the crystalline structures, and it was proposed that the enhanced thermal stability of the β‐quartz(ss) phase that was prepared with AlN was due to both the replacement of oxygen by nitrogen and the positioning of excess Al3+ ions into interstitial sites within the β‐quartz(ss) crystal lattice.
Quantitative Microscopy of β‐Si3N4 Ceramics
Authors: Björklund Håkan , Wasén Jonas , Falk Lena K. L.
Published: July 2010

The three‐dimensional grain size distribution in an experimental β‐Si3N4 material has been determined using the hexagonal prism as a model of β‐Si3N4 grain shape. Results from quantitative microscopy of polished and etched sections were compared with computer‐generated two‐dimensional stereological parameters of hexagonal prisms with different aspect ratios in order to determine an average grain shape (i.e., aspect ratio) in the microstructure. Section parameter distributions for the average grain shape were obtained from the computer simulations and used in a three‐dimensional reconstruction of the microstructure. The results showed that this Si3N4 ceramic had the postulated fibrous microstructure and a broad grain size distribution.
Solid Solubility of Neodymium in BaCeO3
Authors: Makovec Darko , Samardzija Zoran , Kolar Drago
Published: July 2010

Incorporation of Nd into the BaCeO3 perovskite structure was studied by quantitative wavelength dispersive spectroscopy‐electron probe microanalysis (WDS/EPMA) in combination with scanning electron microscopy (SEM) and X‐ray powder diffractometry (XRPD). Highly Nd‐doped BaCeO3 specimens, synthesized by mixed oxide technology, were sintered at 1400°C in ambient air. Concentrations of cations obtained by microanalysis were calculated to the ABO3 perovskite formula, considering incorporation of Nd at Ba as well as at Ce sites. Nd‐BaCeO3 solid solutions may be represented by the general formula Ba1−XNdXCe1−YNdYO3−(Y‐X)/2(VO)(Y‐X)/2. The ratio between Nd incorporated at Ba sites and at Ce sites (X/Y) is a function of the starting composition, changing from 1 in the CeO2‐rich part of the BaO‐CeO2‐Nd2O3 system, to ~0.1 in the BaO‐rich part of the system.
Phase Stability of Graphitelike BC4N up to 2100 K and 7 GPa
Authors: Solozhenko Vladimir L. , Turkevich Vladimir Z. , Sato Tadao
Published: July 2010

Thermal phase stability of graphitelike BC4N (g‐BC4N) has been studied up to 7 GPa and 2100 K using in‐situ powder diffraction of synchrotron radiation. It has been shown that the process of g‐BC4N decomposition at ambient pressure starts at 2050 K and occurs to form highly ordered hexagonal graphitelike boron nitride (hBN) and disordered graphite. As the pressure increases up to 6.6 GPa, the temperature of the decomposition onset decreases to 1070 K. At this pressure in the 1070‐1400 K temperature range (decomposition degree of less than or equal to 0.1), the decomposition products remain the same, whereas at higher temperatures, the decomposition of g‐BC4N is accompanied by the formation of cubic boron nitride (cBN) and disordered graphite. Measurement of 298 K equation of state of g‐BC4N results in a zero‐pressure bulk modulus of 18.1 ± 0.2 GPa and its pressure derivative of 6.6 ± 0.1. Thermodynamic analysis has shown that the g‐BC4N decomposition is a nonequilibrium process and the phase itself is metastable.
Investigation of High‐Alumina Spinel: Effect of LiF and CaCO3 Addition
Authors: Huang Jow‐Lay , Sun Si‐Yau , Ko Yung‐Chao
Published: July 2010

This work examines the effects of LiF or LiF/CaCO3 additives on the phases, microstructure, sintering temperature, and activation energy of MgO‐Al2O3 spinel formation. According to these results, the spinel formation temperature decreases and the spinel phase content increases by incorporating sintering additives. Such an effect is due to the formation of liquid phases at sintering temperatures. The Al composition in spinel is substantially higher in samples containing LiF or LiF/CaCO3 than in samples without sintering additives. Results obtained from the Arrhenius equation and Jander's model indicate that the activation energy for forming spinel decreases by incorporating LiF or LiF/CaCO3.
Simplified Equation for Evaluating the Influence of Surface Residual Stresses on the Toughness of Zirconia Ceramics
Authors: de Portu Goffredo , Conoci Sabrina
Published: July 2010

A simplified theoretical equation was developed to estimate the influence of a thin surface layer with a nonuniform profile of residual compressive stress on indentation cracking. The model was used to evaluate the toughness of tetragonal zirconia polycrystals that had been doped with 3 mol% yttria (3Y‐TZP), which contained surface residual stresses due to phase transformation.
Processing of a Silicon‐Carbide‐Whisker‐Reinforced Glass‐Ceramic Composite by Microwave Heating
Authors: Chen Lifu , Leonelli Cristina , Manfredini Tiziano , Siligardi Cristina
Published: July 2010

A calcium magnesium aluminosilicate‐based glass that contained 10 wt% of silicon carbide whiskers (SiCw) as reinforcement was prepared by tape casting, followed by sintering either in a conventional furnace or in a microwave oven. The results were consistent with retardation of glass sintering through whisker bridging. The glass, by itself, was sintered to almost‐full density at 750°C for 4 h by conventional furnace sintering; the best sintered composite, with an estimated density of ∼90%, was obtained at 800°C with a dwell time of 4 h. Sintering at a temperature of >800°C did not improve the densification but rather resulted in severe whisker oxidation. A reduced densification rate was observed for the samples that were sintered in nitrogen. By contrast, in the microwave oven, almost‐full density for the glass and ∼95% of the theoretical density for the composite were obtainable at 850°C for 15 min, which represented a reduction of ∼10 h of the total processing time and a reduced SiCw oxidation.
Thermodynamic Analysis of Grain Aspect Ratio in Fibrous Microstructures of Silicon Nitride
Authors: Raj Rishi , Hoffmann Michael J.
Published: July 2010

Needlelike, free‐floating ß‐crystals of silicon nitride, precipitated within a supersaturated Y‐Si‐Al‐O‐N oxynitride glass, apparently approach an equilibrium value of the aspect ratio. An expression that relates this aspect ratio to the anisotropy in the interfacial energies of the longitudinal and transverse interfaces of the crystal is derived. The prediction agrees reasonably well with theoretical estimates of the interfacial energies. Kinetic and stearic effects that often lead to nonequilibrium values of the aspect ratio are discussed.
Transformation‐Toughened Ceramic Multilayers with Compositional Gradients
Authors: Yoo Jaedeok , Cho Kyung‐mox , Bae Won Sang , Cima Michael , Suresh Subra
Published: July 2010

The processing and the thermomechanical characteristics of zirconia‐toughened alumina (ZTA) ceramic multilayers, with through‐thickness gradients in the concentrations of the tetragonal and monoclinic zirconia phases, are studied both theoretically and experimentally. Analytical solutions for the evolution of thermal strains, internal stresses, and the overall curvature changes in response to various temperatures were derived using known plate theory formulations. Compositionally graded multilayer stacks and complex shapes of ZTA ceramics were fabricated by three‐dimensional printing (3DP). The relative fractions of the tetragonal to monoclinic ZrO2 phases were varied in a prescribed fashion. Phase transformation of ZrO2 in ZTA during cooling from the sintering temperature was controlled by doping different amounts of Y2O3 through the thickness of the ZTA multilayer plate. The local content of monoclinic ZrO2 through the thickness was characterized by X‐ray diffraction analysis. The microstructure, some basic mechanical properties, and thermal expansion behavior of the 3DP ZTA system were also characterized. Thermally induced curvature of the ZTA multilayer plate was measured, and the experimental results were compared with the predictions based on the analytical solutions. Symmetric ZTA multilayers with surface compression were also prepared by 3DP and tested for flexural strength. Results showed a significant increase in strength from the monolithic specimens to the compositionally controlled ones. Results from the compression tests of notched ZTA blocks demonstrated the role of m‐ZTA shield zones in enhancing the load‐bearing characteristics. This study also demonstrated the possibility that commonly available computational tools can be used to design and construct complex shapes with compositional variation to enhance and control mechanical properties.
Alumina/Silicon Carbide Nanocomposites by Hybrid Polymer/Powder Processing: Microstructures and Mechanical Properties
Authors: Sternitzke Martin , Derby Brian , Brook Richard J.
Published: July 2010

Nanocomposites with fine, coarse, and bimodal silicon carbide (SiC) particle‐size distributions were hot pressed and examined by transmission electron microscopy, scanning electron microscopy, and optical microscopy, as well as by four‐point‐bend and indentation tests. The finer SiC nanophase was introduced homogeneously by coating a silicon‐containing polymer onto the alumina (Al2O3) powder, followed by a pyrolysis procedure; for the coarser SiC, nanophase conventional powder processing was used. Powder‐ and polymer‐processed nanocomposites both had their maximum strengths at 5 vol% of SiC. High‐strength nanocomposites that contained a higher volume fraction of SiC could be fabricated when the two methods were combined in a hybrid processing route. The SiC phase in the resulting hybrid materials originated from both the polymer and the SiC powder. The mechanical properties of these materials could be correlated with the fabrication route. Processing‐flaw populations and calculated Griffith‐flaw sizes were not only smaller, but they were also significantly different in the nanocomposites, in comparison to those in Al2O3 ceramics; this may explain the strength increase in Al2O3/SiC nanocomposite materials.
Effect of Grain‐Boundary Phase on Dynamic Compression Fatigue in Hot‐Pressed Silicon Nitride
Authors: Sharma Vinod , Nemat‐Nasser Sia , Vecchio Kenneth S.
Published: July 2010

Two types of hot‐pressed silicon nitride, one having an amorphous grain‐boundary phase (6 wt% yttria, 3 wt% alumina) and the other having a predominantly crystalline grain‐boundary phase (8 wt% yttria, 1 wt% alumina), were tested on a split Hopkinson pressure bar with a momentum trap, such that, in each test, the sample was subjected to a single predefined stress pulse and then recovered without being subjected to any other loads. The specimens were loaded repeatedly with a triangular pulse of 3.2 GPa amplitude at a strain rate of approximately 400/s. The dynamic fatigue life of amorphous grain‐boundary‐phase silicon nitride was observed to be higher than that of the corresponding fatigue life of crystalline grain‐boundary‐phase silicon nitride. The difference in fatigue lives is correlated to the microstructural damage occurring in both materials.
Synthesis and Sintering of Cerium(III) Sulfide Powders
Authors: Hirai Shinji , Shimakage Kazuyoshi , Saitou Yasushi , Nishimura Toshiyuki , Uemura Yoichiro , Mitomo Mamoru , Brewer Leo
Published: July 2010

Cerium(III) sulfide (Ce2S3) powder was synthesized via the sulfurization of ceria (CeO2) powder using carbon disulfide gas. Single‐phase α‐Ce2S3 could be formed via sulfurization at 973 K for 28.8 ks. The preparation of α‐Ce2S3 became feasible at low temperature, in comparison to sulfurization using hydrogen sulfide gas. According to the fact that the formation of α‐Ce2S3 was accelerated by the addition of carbon black to the CeO2 powder, carbothermic reduction was considered to become a dominant reaction, as the temperature increased. To obtain the activation energy for the densification of β‐Ce2S3 powder, which was prepared by vacuum heating α‐Ce2S3, the data of densification by hot pressing was analyzed by a kinetic equation that was proposed by other researchers. As a result, the sintering behavior could be best explained by a grain‐boundary‐diffusion mechanism that had an apparent activation energy of 382 kJ/mol.
Impact Strength of Continuous‐Carbon‐Fiber‐Reinforced Silicon Nitride Measured by Using the Split Hopkinson Pressure Bar
Authors: Ogawa Kinya , Sugiyama Fumiko , Pezzotti Giuseppe , Nishida Toshihiko
Published: July 2010

Three‐point impact bending tests, using the split Hopkinson pressure bar method, were performed to evaluate the fracture resistance of monolithic silicon nitride (SN) and carbon‐fiber‐reinforced silicon nitride (CFRSN) ceramics. By applying ramped incident‐stress waves in the split Hopkinson pressure bar apparatus, relatively smooth stress‐time curves could be recorded without using any artificial filtering process. The maximum load in the load‐deflection curve of the CFRSN material increased, in comparison to its static value, when impact testing was applied. Such behavior was substantially different from that of the monolithic SN material, for which the maximum load values from impact and static testing were almost the same. The time dependence of strength in the CFRSN ceramic was then investigated by using relaxation tests, and the impact strength behavior could be explained by these results. Also, the shear strength was significantly dependent on the deformation rate, whereas the tensile strength was almost independent of it. The experimental results were compared with the numerical predictions of the stress distribution that were obtained by using finite‐element analysis.
Electrical Conductivity in Transparent ZnGa2O4: Reduction and Surface‐Layer Structure Transformation
Authors: Yan Zheng , Takei Humihiko , Kawazoe Hiroshi
Published: July 2010

An optically transparent and electrically conductive surface layer has been obtained by hydrogen annealing a bulk single crystal of ZnGa2O4, where a band gap as wide as 4.0 eV has been calculated from the results of optical transmittance. The carriers are mainly generated from oxygen vacancies. The conductivity is 10−1 S/cm at a temperature of 290 K, and the activation energy of donors, which is derived from the conductivity‐temperature relation, is 0.02 eV. Although various reduction conditions have been used to increase the thickness of the conductive layer, it is limited to ∼50 µm. Zinc depletion at the surface layer of all the annealed samples has been detected, and a two‐layer reduction process of the hydrogen annealing has been suggested. X‐ray precession photographs show a structural transformation from the normal spinel Fd3m space group to the rhombohedral R3m space group of the conductive layer, which seems to be related to the conversion of zinc atoms from a tetrahedral coordination to an octahedral coordination. The converted electronic configuration of the surface layer, which is caused by the position shift of zinc atoms, is thought to be beneficial to high conductivity.
Evolution of the Phase Content of Zirconia Powders Prepared by Sol‐Gel Acid Hydrolysis
Authors: Rivas Patricia C. , Martínez Jorge A. , Caracoche María C. , Rodríguez Agustín M. , García Alberto R. López , Pavlik Robert S. , Klein Lisa C.
Published: July 2010

The evolution of the phase content in zirconia powders that have been prepared by sol—;gel acid hydrolysis has been investigated using the perturbed‐angular‐correlation (PAC) technique and X‐ray diffractometry. As a consequence of performing annealing treatments at increasing temperatures between room temperature and 1000°C, the amorphous starting material transforms to the tetragonal form and then to the monoclinic form. The metastable tetragonal phase exhibits two hyperfine components, one of which describes very defective zirconium surroundings. The evolution of PAC relative fractions is in agreement with the diffraction results. The durability of the samples in sodium hydroxide seems to increase as the relative amount of the most‐defective zirconium surroundings of the tetragonal form increases.
Infiltration of Glass Melts into Fully Dense Al2O3 and MgO Ceramics
Authors: Kim Jeong‐Joo , Harmer Martin P.
Published: July 2010

The infiltration of glass melts into fully dense Al2O3 and MgO ceramics has been studied with emphasis on elucidating the penetration mechanism and the change in shape and size of the solid grains that accompany the penetration process. For Al2O3, penetrated by a Ca—Al—Si—O glass melt, the grains developed a prismatic shape consistent with interface‐reaction‐controlled grain growth. For MgO, penetrated by a Ca—Mg—Si—O glass melt, the grains maintained a spherical shape consistent with diffusion‐controlled grain growth. When glass penetrated into the dense polycrystalline alumina specimen, it resulted in a homogeneous distribution of liquid phase and a uniform grain size throughout the whole specimen. In contrast, when glass penetrated the magnesia specimen, the volume fraction of liquid phase at the surface region (which was in direct contact with the melt) was higher than that in the center region. Furthermore, the average grain size was larger in the center, where the volume fraction of glass was lower. This microstructural inhomogeneity stayed uncorrected even after prolonged annealing treatments. Reasons for this behavior are discussed.
Contact Damage Accumulation in Tic3SiC2
Authors: Low It Meng , Lee Seung Kun , Lawn Brian R. , Barsoum Michel W.
Published: July 2010

The evolution of deformation—;microfracture damage below Hertzian contacts in a coarse‐grain Ti3SiC2 is studied. The Hertzian indentation stress—;strain response deviates strongly from linearity beyond a well‐defined maximum, with pronounced strain—;softening, indicating exceptional deformability in this otherwise (elastically) stiff ceramic. Surface and subsurface ceramographic observations reveal extensive quasi‐plastic microdamage zones at the contact sites. These damage zones are made up of multiple intragrain slip and intergrain shear failures, with attendant microfracture at high strains. No ring cracks or other macroscopic cracks are observed on or below the indented surfaces. The results suggest that Ti3SiC2 may be ideally suited to contact applications where high strains and energy absorption prior to failure are required.
Oriented Structure and Crystallography of Directionally Solidified LaB6—ZrB2 Eutectic
Authors: Chen Chang‐Ming , Zhou Wang‐Cheng , Zhang Li‐Tong
Published: July 2010

Directional solidification of LaB6—ZrB2, by use of an electron beam heating technique, yielded oriented ZrB2 fibers in a LaB6 matrix. The average diameter of the ZrB2 fibers was ∼0.2–1.2 µm, with fiber lengths up to 100 µm. Primary platelike LaB6 dendrites formed upon the solidification of an ingot with a composition of LaB6—18 wt% ZrB2. LaB6 was the first phase to nucleate when eutectic growth occurred, and ZrB2 showed nonfaceted growth. For the ingot solidified with planar growth the orientation relations of the phases were as follows: growth direction, [001]LaB6∥[00.1]ZrB2; interfacial plane, (11.0)LaB6∥(11.0)ZrB2.
Oxygen Position and Bond Lengths from Lattice Parameters in Tetragonal Zirconias
Authors: Howard Christopher J. , Hunter Brett A. , Kim Dae‐Joon
Published: July 2010

A survey of the available data on the oxygen positions in various tetragonal zirconias reveals a simple, approximate relationship between the departure of the oxygen from the position it would have in the ideal fluorite structure, and the tetragonality (c/a) of the material. This relationship can be understood on the basis that the two oxygen—oxygen contact distances are very nearly equal. The relationship may be used to estimate the oxygen position from the lattice parameters, and from that all the bond lengths in the structure.
Effect of the Strontium:Barium Ratio and Atmosphere on the Sintering Behavior of Strontium Barium Niobate
Authors: Lee Wen Jiung , Fang Tsang‐Tse
Published: July 2010

The sintering behavior of SrxBa1−xNb2O6 (SBN) (x= 0.5, 0.6, and 0.7) was studied. The densification rate increased and the evaluated activation energy of SBN decreased as the Sr:Ba molar ratio increased. Also, when SBN50 (SBN where x= 0.5) was sintered at <1300°C, the densification rate decreased as the oxygen partial pressure increased, and, at 1300°C, the oxygen partial pressure had insignificant influence on the densification. The relationship of sintering behavior and structure of SBN has been discussed, and the niobium ion was suggested as being the rate‐limiting species when sintering SBN.
Grain‐Boundary Diffusion of Strontium in (La,Ca)CrO3 Perovskite‐Type Oxide by SIMS
Authors: Horita Teruhisa , Sakai Natsuko , Kawada Tatsuya , Yokokawa Harumi , Dokiya Masayuki
Published: July 2010

The grain‐boundary‐diffusion coefficient (Dgb) of strontium in La0.9Ca0.13CrO3‐δ was determined by secondary‐ion mass spectrometry (SIMS), using two different measurement modes: depth profiling from the surface and line scanning on the fracture surface. The depth profiles that were sputtered by an O2+‐primary‐ion beam gave two slopes of strontium concentration profiles, which corresponded to grain (bulk) and grain‐boundary diffusion. The depth profiles were fitted to an appropriate equation that gave the grain‐ (bulk‐) and grain‐boundary‐diffusion coefficients (Dbulk= 6.5 × 10‐20 m2/s and Dgb= 1.6 × 10‐15 m2/s in air at 1273 K, respectively). Initially, to obtain the Dgb value via the SIMS line‐scanning measurement, the fracture surface of La0.9Ca0.13CrO3‐delta was measured by a low‐energy O2+‐primary‐ion beam. The line‐scanning measurement enabled us to successfully determine the strontium concentration profiles around the grain boundary. However, the Dgb value that was obtained via the line‐scanning mode was 6.0 10−13 m2/s, which was a factor of 100 greater than that which was obtained by the depth‐profile mode. Comparison between the depth‐profile and line‐scanning modes will require additional careful examination.
Piezoresistivity in PTCR Barium Titanate Ceramics: I, Experimental Findings
Authors: Capurso Joseph S. , Schulze Walter A.
Published: July 2010

Positive temperature coefficient of resistance (PTCR) barium titanate is the active material in a ceramic sensor which employs piezoresistivity to detect changes in applied stress. High‐purity, chemically prepared barium titanate is donor‐doped with 0.30 at.% lanthanum, and <0.10 at.% of a transition‐metal counterdopant may be added to enhance the PTCR effect. Tape‐cast sheets of undoped and PTCR BaTiO3 are laminated to produce a three‐layer “trilaminate”—a sintered structure which has two semiconducting PTCR layers separated by an insulating layer. The trilaminate is stressed in a four‐point bend configuration (placing one semiconducting layer completely in tension, the other in compression), and the resistivities for both stress states are measured concurrently as functions of applied stress and temperature. Results are presented for various semiconducting layer compositions and sintering conditions.
Interface Nanostructure of Brazed Silicon Nitride
Authors: Iwamoto Chihiro , Tanaka Shun‐ichiro
Published: July 2010

Nanomorphologies and crystallographic orientations of the brazed interface of silicon nitride (Si3N4) were analyzed via high‐resolution transmission electron microscopy. When Si3N4 was brazed using an Ag‐Cu‐Ti alloy, titanium nitride (TiN) nanoparticles were formed adjacent to the ceramic as reaction products, and these nanoparticles were commonly accompanied by C‐phase material. The structure of Si3N4/TiN interface was wavy on an atomic scale, which was considered to provide anchoring points that offered high mechanical strength. The TiN nanoparticles extended along the [0001] axis of Si3N4. The orientation relationship between TiN and ß‐Si3N4 was, as determined from the observed lattice images, that the [110] direction of TiN was parallel to the [0001] direction of Si3N4. The nature of the crystallographic relationships and interface nanomorphologies were also discussed.
Low‐Temperature Synthesis, Characterization, and Properties of Lead‐Based Ferroelectric Niobates
Authors: Sekar Michael M. A. , Halliyal Arvind
Published: July 2010

Technologically important lead‐based ferroelectric niobates of the type A(B′B″)O3(where A is Pb, B′ is Fe, Ni, Mg, or Zn, and B″ is Nb), and their solid solutions with barium titanate and lead titanate, have been prepared via a solution combustion process that involves metal nitrates/oxalate and tetraformal trisazine (TFTA) at a temperature of 350°C. The thermal evolution of perovskite niobates has been investigated at different calcination temperatures. Particulate properties such as density, particle size, and surface area have been determined. Particles are fine (<1 µm) and are sinter active at low temperature (1050°C). Dielectric and piezoelectric properties of the lead‐based ferroelectrics that have been prepared via the low‐temperature method are reported in this paper.
Electrokinetic Behavior and Stability of Silicon Carbide Nanoparticulate Dispersions
Authors: Tartaj Pedro , Reece Michael , Moya José S.
Published: July 2010

The stability of aqueous suspensions containing SiC nanoparticles prepared by inductively coupled plasma has been studied. Physicochemical analyses indicated that the as‐prepared samples consisted of monocrystalline spherical particles of the 3C‐SiC polytype with a mean diameter of about 40 nm. HRTEM clearly showed that the particles were covered by an amorphous surface layer which according to XPS was mainly composed of carbon. DTA and TG analyses showed that the free carbon was eliminated by heating the sample at 650°C in air, but the resulting powder exhibited an excess of amorphous SiO2 on the particle surfaces. This silica coating was leached out by using a 5% HF solution. It has been determined, by evaluating an effective Hamaker constant, that the most stable aqueous suspensions are obtained by using the sample containing the amorphous SiO2 surface layer. Finally, evidence of the presence of a strong hydrophobic force was detected in the original sample and in the one prepared by heating at 650°C and further leaching with HF.
Study of Phase Relationships within the MgO‐CuO‐Cu2O‐P2O5 System
Authors: Bamberger Carlos E.
Published: July 2010

The formation of the known compound Cu+Cu2+Mg3(PO4)3 by alternate reactions and its thermal stability were studied. The formation of solid solutions of the types Mg2‐xCuxP2O7 and Mg3‐xCux(PO4)2 was reexamined, mainly to aid in the identification of the products of decomposition of Cu+Cu2+Mg3(PO4)3. X‐ray diffractometry patterns of Mg2‐xCuxP2O7 varied gradually in the range 0 lessthan equal to x lessthan equal to 2, which indicates complete miscibility.
Processing and Mechanical Properties of Pressureless‐Sintered Niobium‐Alumina‐Matrix Composites
Authors: García Daniel E. , Schicker Silvia , Bruhn Jörn , Janssen Rolf , Claussen Nils
Published: July 2010

Niobium‐alumina (Nb‐Al2O3) composites have been fabricated via the pressureless sintering of compacts of intensively milled Nb‐Al2O3 mixtures. Strength and fracture toughness of the composites increase as the niobium content increases. For a composite that contains 50 vol% niobium, strengths of up to 680 MPa, with a corresponding fracture toughness of 6.3 ± 0.3 MPam1/2 and hardness of 6.4 GPa, have been obtained.