bluuebunny/crossref_metadata_2025 huggingface dataset:
Microstructures and Properties of Mo5Si3‐Particle‐Reinforced Si3N4‐Matrix Composites
Authors: Iizuka Tateoki , Murao Toshihiro , Yamamoto Hiroyuki , Kita Hideki
Published: July 2010

Mo5Si3‐particle‐reinforced Si3N4‐matrix composites were fabricated by sintering molybdenum‐solution‐infiltrated porous Si3N4. Fine Mo5Si3 particles, with an average diameter of ∼0.13–0.17 μm, grew in situ from the reaction between MoO3 and Si3N4 in the grain boundary of the Si3N4. The Mo5Si3 particles resided in the grain‐boundary glassy phase and reinforced the grain boundaries. The four‐point flexural strength and fracture toughness of a 2.8 wt% Mo5Si3‐Si3N4 composite were 1060 MPa and 7.7 MPa·m1/2, respectively. This was higher than those for normally sintered Si3N4 by ∼17% and ∼18%, respectively. The fracture toughness of the Mo5Si3‐Si3N4 composite increased as the content of Mo5Si3 particles increased, but the flexural strength decreased. Improvement in fracture toughness was attributed to a thermal expansion mismatch among the Mo5Si3, the Si3N4, and the grain‐boundary amorphous phases in the Mo5Si3‐Si3N4 composites. Another reason for the improved fracture toughness was the pullout of elongated Si2N2O grains that formed as a result of oxygen gas released from the reaction between the molybdenum‐solution‐obtained MoO3 and the Si3N4. The infiltration method for incorporating desired elements or compounds into a ceramic matrix holds promise as a process for fabricating submicrometer‐ or nanometer‐sized composites with high strength and high fracture toughness.
Atomic Resolution Analysis of the Defect Chemistry and Microdomain Structure of Brownmillerite‐Type Strontium Cobaltite
Authors: Ito Yasuo , Klie Robert F. , Browning Nigel D. , Mazanec Terry J.
Published: July 2010

To investigate the fundamental aspects of vacancy ordering in oxygen‐transporting ceramic membranes, we have performed atomic resolution analysis of individual domains in brownmillerite‐type SrCoO3−δ. Electron energy loss spectroscopy indicates that the Co valence state in adjacent planes can be 2+ and 4+. This charge localization is accompanied by oxygen deficiency and the formation of ordered octahedral and tetrahedral coordinated Co sites. At microdomain boundaries, Z‐contrast images reveal a structural relaxation of the octahedral site with the reduction of the Co valence state from 4+ to 3+ and the incorporation of extra oxygen vacancies.
Oxidation Behavior from Room Temperature to 1500°C of 3D‐C/SiC Composites with Different Coatings
Authors: Cheng Laifei , Xu Yongdong , Zhang Litong , Yin Xiaowei
Published: July 2010

A carbon‐fiber‐reinforced silicon carbide composite (3D‐C/SiC) was prepared by chemical vapor infiltration. A SiC and SiC/Si‐Zr coating were deposited on the composite to investigate the effect of different coatings on the oxidation behavior of 3D‐C/SiC composites. The 3D‐C/SiC(SiC/Si‐Zr) composite decreased in weight below 1000°C and increased in weight above 1000°C. With an increasing oxidation time, the weight loss increased greatly and the weight gain increased little. The 3D‐C/SiC(SiC) composite always decreased in weight over the full temperature range. With an increasing oxidation time, the weight loss increased rapidly below 1000°C and reached its minimum value at 1400°C. The 3D‐C/SiC(SiC/Si‐Zr) composite had a higher oxidation resistance above 1000°C, and the 3D‐C/SiC(SiC) composite had a higher oxidation resistance below 1000°C. The wider the coating cracks, the larger the maximum weight loss and the lower the temperature corresponding to the maximum weight loss. With an increasing oxidation time, the activation energy of the 3D‐C/SiC(SiC/Si‐Zr) composite increased from 96 to 138 kJ/mol, and the 3D‐C/SiC(SiC) composite increased from 130 to 180 kJ/mol.
(100)‐Orientation of Pseudocubic Perovskite‐Type LaNiO3 Thin Films on Glass Substrates via the Sol–Gel Process
Authors: Miyake Shinichi , Yamamoto Keisuke , Fujihara Shinobu , Kimura Toshio
Published: July 2010

(100)‐oriented, perovskite‐type LaNiO3 thin films were prepared on SiO2 glass substrates by the sol–gel method. Effects of thermal processing on the orientation, surface morphology, and electrical properties of the films were investigated. The nearly complete (100)‐orientation was achieved by drying the films at temperatures above 350°C before a final heat treatment at 700°C. It was the key to heat the substrate from the other side to obtain the oriented films. A possible mechanism of the orientation is proposed on the basis of surface energies of the films and the substrates and the interfacial energy between them.
Mechanical‐Alloying‐Assisted Synthesis of Ti3SiC2 Powder
Authors: Li Jing‐Feng , Matsuki Toshiro , Watanabe Ryuzo
Published: July 2010

Mechanical alloying (MA) has been used to synthesize Ti3SiC2 powder from the elemental Ti, Si, and C powders. The MA formation conditions of Ti3SiC2 were strongly affected by the ball size for the conditions used. MA using large balls (20.6 mm in diameter) enhanced the formation of Ti3SiC2, probably via an MA‐triggered combustion reaction, but the Ti3SiC2 phase was not synthesized only by the MA process using small balls (12.7 mm in diameter). Fine powders containing 95.8 vol% Ti3SiC2 can be obtained by annealing the mechanically alloyed powder at relatively low temperatures.
Effect of Reaction Parameters on γ‐AlON Formation from Al2O3 and AlN
Authors: Bandyopadhyay Siddhartha , Rixecker Georg , Aldinger Fritz , Pal Sushanta , Mukherjee Keka , Maiti Himadri Sekhar
Published: July 2010

The formation of γ‐AlON from Al2O3 and AlN was investigated as a function of some of the reaction parameters, that is, temperature and time. The appearance of phases was followed in conjunction with the change in lattice parameter to reveal the reaction sequences of formation. An oxygen‐rich γ‐AlON phase formed first, which reacted further with AlN. Nitrogen diffusion through the γ‐AlON lattice seemed to be rate controlling.
Fluorescence Spectroscopy of Color Centers Generated in Phosphate Glasses after Exposure to Femtosecond Laser Pulses
Authors: Chan James W. , Huser Thomas , Hayden Joseph S. , Risbud Subhash H. , Krol Denise M.
Published: July 2010

A confocal fluorescence microscopy setup was used to observe, in situ, spectral changes in phosphate glasses which were modified using 0.3 μJ of tightly focused 800 nm, 130 fs laser pulses. On 488 nm excitation, the modified glass shows a broad fluorescence centered at roughly 600 nm, which decays with prolonged exposure to the 488 nm light. The decay behavior is dependent on the 488 nm power, with a faster decay rate for higher powers. A mechanism whereby color centers, formed by the femtosecond pulses, fluoresce when excited by the 488 nm light and are simultaneously photobleached is proposed to explain the observed behavior.
Modeling and Optimization of Solar‐Control Glasses
Authors: Blume Russell , Drummond Charles
Published: July 2010

Computer‐assisted design of experiments based on the D‐optimal design methodology and multiple linear regression analysis has been applied to the control and optimization of solar‐control properties of a sulfate‐fined soda–lime–silicate glass (72.7% SiO2, 14.2% Na2O, 10.0% CaO, 2.5% MgO, 0.6% Al2O3) which has been modified with Fe2O3 (0.0 to 0.8 wt%), NiO (0.0 to 0.15 wt%), CoO (0.0 to 0.15 wt%), V2O5 (0.0 to 0.225 wt%), TiO2 (0.0 to 1.5 wt%), SnO (0.0 to 3.0 wt%), ZnS (0.0 to 0.09 wt%), ZnO (0.0 to 2.0 wt.), CaF2 (0.0 to 2.0 wt%), and P2O5 (0.0 to 2.0 wt%) additions. The experimental design consisted of 64 initial glass compositions which were fired as 500 g batches under ambient conditions in platinum crucibles at 1500°C for 3 h. The samples were then measured for total solar transmittance in accordance with the specifications of ASTM E903–96 (weighted ordinate method) using a Cary‐500 UV/vis/near‐IR spectrophotometer equipped with an integrating sphere. CIE‐LAB color and visible transmittance (illuminant‐A) was measured in accordance with the specification of ASTM E308. The total metal content, calculated as of V2O5, CoO, NiO, Fe2O3, FeO, P2O5, TiO2, SnO, ZnO, F, and SO3, was measured for each glass sample. A modified Lambert–Beer absorption law was utilized to correlate the apparent optical density at 210 discrete wavelengths necessary for the calculation of solar and visible transmittances to the glass batch composition. The developed model was then validated and was shown to exhibit excellent agreement with the measured optical transmission data. Innovative solar‐control glasses with exceptional performance characteristics have been realized in the current investigation by application of novel computer‐assisted design and multiple correlation methodologies.
Factors Determining Grain Orientation in Bismuth Sodium Potassium Titanate–Lead Zirconate Titanate Solid Solutions Made by the Reactive Templated Grain Growth Method
Authors: Abe Yuichi , Kimura Toshio
Published: July 2010

Grain‐oriented Bi0.5(Na0.85K0.15)0.5TiO3‐Pb(Zr1−xTix)O3 (BNKT‐PZT) ceramics were prepared via the reactive templated grain growth method, using platelike Bi4Ti3O12 particles. Factors that determine the degree of orientation were examined. Prereacted PZT gave a larger degree of orientation than PZT raw materials (PbO, ZrO2, and TiO2) in the 75BNKT‐25PZT (x= 0.5) system. Increases in the titanium concentration in the PZT of the 75BNKT‐25PZT system and in the BNKT concentration in the yBNKT‐(100 −y)PZT (x= 0.5) system increased the degree of orientation. The direction of material transport between BNKT and PZT was important to obtain ceramics with a large degree of orientation.
Morphological Control of Zirconia Nanoparticles through Combustion Aerosol Synthesis
Authors: Limaye Amit U. , Helble Joseph J.
Published: July 2010

Ceramic oxide nanoparticles produced by flame‐based processes are typically agglomerated, which can limit their use in some applications. In this paper, a novel combustion synthesis method that utilizes the spraying of combustible droplets into a premixed flame to produce nanoscale crystalline particles of agglomerated and unagglomerated morphologies is described. Although the same flame‐based experimental setup is used in both cases, variation in peak flame temperatures results in a corresponding variation between fractallike agglomerates and single isolated spherical particles. TEM/ED analysis shows that both classes of particles are the tetragonal crystal phase of zirconia. In the case of the unagglomerated spherical particles, results indicate that each precursor solution droplet, which acts as the feed, produces multiple spherical ceramic nanoparticles with a number mean diameter of 90 nm. The use of an inertial impaction stage in the precursor feed line to eliminate large feed droplets leads to a decrease in the number mean diameter to 60 nm, suggesting that crystalline spherical nanoparticles can be produced in a continuous flame‐based process through control of the feed droplet size.
Synthesis and Properties of Glassy Microcavities for Morphology‐Dependent Resonances through Liquid–Liquid Phase Separation
Authors: Konishi Tomoya , Soga Kohei , Inoue Hiroyuki , Makishima Akio , Inoue Satoru , Nakano Satoshi
Published: July 2010

Glassy microspheres containing a rare earth are attractive for practical use as microcavities for morphology‐dependent resonances (MDRs). However, no efficient and low‐cost mass‐production process has been established for such microcavities. In the present study, we have synthesized glassy microcavities through liquid–liquid phase separation of alkaline‐earth borate glass. Glassy microspheres have been prepared by the liquid–liquid phase separation of BaO‐B2O3 glasses, by controlling the particle size within the range 1–45 μm and the size distribution within 1%. The microspheres show periodic, sharp peaks, indicative of MDRs, in their Raman‐scattering spectra and in the fluorescence spectra of the internal rare earth. These microspheres act as high‐quality microcavities, with Q factors comparable to those calculated using the Lorenz–Mie theory.
Characterization and Mechanical Properties of Flexible Dimethylsiloxane‐Based Inorganic/Organic Hybrid Sheets
Authors: Katayama Shingo , Kubo Yuji , Yamada Noriko
Published: July 2010

Flexible large sheets of dimethylsiloxane‐based inorganic/organic hybrids with sizes of ∼200 mm × 290 mm and ∼1.5 mm thickness have been fabricated from poly(dimethylsiloxane) (PDMS) and metal alkoxides of Zr and Ta. The hybrid sheets were characterized by XPS, EXAFS, FT‐IR, HRTEM, and SAXS. The inorganic components derived from metal alkoxides in the dimethylsiloxane‐based hybrid sheets were found to be present as oxide‐like clusters with sizes of 2–3 nm or below, which were chemically attached to PDMS via M–O–Si bonds. The hybrid sheets showed high elongation, strength, and thermal stability. A high elongation of about 100% was observed in the hybrid sheets fabricated in Zr(OBun)4/PDMS = 2 at 180°C and a high tensile strength of about 3.0 MPa was observed in those fabricated in Zr(OBun)4/PDMS = 4 at 180°C. The flexibility of the hybrid sheets was kept at least to 200°C for 100 h in N2. These features are thought to come from the inorganic components derived from metal alkoxides, which are close to the molecular‐level size and behave as a strong cross‐linking agent of PDMS chains.
Microstructure and Mechanical Properties of Three‐Dimensional Textile Hi‐Nicalon SiC/SiC Composites by Chemical Vapor Infiltration
Authors: Xu Yongdong , Cheng Laifei , Zhang Litong , Yin Hongfeng , Yin Xiaowei
Published: July 2010

Three‐dimensional textile Hi‐Nicalon SiC‐fiber‐reinforced SiC composites were fabricated using chemical vapor infiltration. The microstructure and mechanical properties of the composite materials were investigated under bending, shear, and impact loading. The density of the composites was 2.5 g·cm−3 after the three‐dimensional SiC perform was infiltrated for 30 h. The values of flexural strength were 860 MPa at room temperature and 1010 MPa at 1300°C under vacuum. Above the infiltration temperature, the failure behavior of the composites became brittle because of the strong interfacial bonding and the mismatch of thermal expansion coefficients between fiber and matrix. The fracture toughness was 30.2 MPa·m1/2. The obtained value of shear strength was 67.5 MPa. The composites exhibited excellent impact resistance, and the dynamic fracture toughness of 36.0 kJ·m−2 was measured using Charpy impact tests.
Factors Affecting Threshold Strength in Laminar Ceramics Containing Thin Compressive Layers
Authors: Rao Masa P. , Lange Fred F.
Published: July 2010

Compressive layers placed within a laminate can arrest cracks. With increasing applied stress, the arrested crack can propagate through the compressive layer. These phenomena produce a material with threshold strength, i.e., failure cannot occur below a critical applied stress. A previously reported stress intensity function describes different variables, e.g., magnitude of compressive stress, thickness of compressive layer, and distance between compressive layers, which govern threshold strength. Laminar composites composed of thicker Al2O3 layers separated by thinner Al2O3/mullite layers were fabricated to test the different variables that are predicted to govern threshold strength. The data agreed well with the predicted values only when the magnitude of compressive stress and/or the thickness of the compressive layer were low. For these conditions, the crack extended straight through the compressive layers, as assumed by the model used to predict threshold strength. On the other hand, when the compressive stress and/or layer thickness were large, threshold strength was larger than the predicted value. In addition, for these conditions, the crack bifurcated through the compressive layer. The angle between the bifurcated cracks increased with increasing compressive stress.
Crystal Chemistry and Phase Transitions in Substituted Pollucites along the CsAlSi2O6‐CsTiSi2O6.5 Join: A Powder Synchrotron X‐ray Diffractometry Study
Authors: Xu Hongwu , Navrotsky Alexandra , Balmer M. Lou , Su Yali
Published: July 2010

The crystal structures for a suite of substituted pollucites with the compositions CsTixAl1–xSi2O6+0.5x, 0 ≤x≤ 1, have been determined from Rietveld analysis of powder synchrotron XRD data. Our results indicate that the pollucite end member (CsAlSi2O6) has a tetragonal structure (space group I41/a), whereas all other compositions are cubic (space group Ia3d). The increased symmetry for the titanium‐substituted structures is presumably due to the incorporation of additional O2− anions (needed for compensating the charge imbalance between Ti4+ and Al3+), which effectively holds open the expanded cubic framework. In situ cooling experiments of the substituted phase CsTi0.1Al0.9Si2O6.05 reveal a displacive transformation to the tetragonal structure at ∼230 K. This transformation is tricritical in nature and is analogous to the tetragonal‐to‐cubic transition in pollucite on heating.
Thermal Conductivity of Zinc Oxide: From Green to Sintered State
Authors: Olorunyolemi Tayo , Birnboim Amikam , Carmel Yuval , Wilson Otto Carl , Lloyd Isabel Knowlton , Smith Stephen , Campbell Rob
Published: July 2010

The thermal conductivity of ZnO with different particle sizes (micrometer, submicrometer, and nanometer) was measured using the laser flash technique. As the “green” samples were heated from room temperature to 600°C (and 1000°C) and then cooled down to room temperature, the thermal conductivity was measured in situ. A model for interparticle neck growth was developed based on mass transfer to the neck region of a powder as a result of known temperature. By combining this model with a three‐dimensional numerical code, the thermal conductivity of ZnO was calculated. Excellent agreement between the theoretical calculation and experimental data was found.
Effect of Sintering Atmosphere on Grain Shape and Grain Growth in Liquid‐Phase‐Sintered Silicon Carbide
Authors: Jang Cheol‐Woo , Kim Joosun , Kang Suk‐Joong L.
Published: July 2010

We investigated the effects of the sintering atmosphere on the interface structure and grain‐growth behavior in 10‐vol%‐YAG‐added SiC. When α‐SiC was liquid‐phase‐sintered in an Ar atmosphere, the grain/matrix interface was faceted, and abnormal grain growth occurred, regardless of the presence of α‐seed grains. In contrast, when the same sample was sintered in N2, the grain interface was defaceted (rough), and no abnormal grain growth occurred, even with an addition of α‐seed grains. X‐ray diffraction analysis of this sample showed the formation of a 3C (β‐SiC) phase, together with a 6H (α‐SiC) phase. These results suggest that the nitrogen dissolved in the liquid matrix made the grain interface rough and induced normal grain growth by an α→β reverse phase transformation. Apparently, the growth behavior of SiC grains in a liquid matrix depends on the structure of the grain interface: abnormal growth for a faceted interface and normal growth for a rough interface.
Hardness and Fracture Toughness of Pressureless‐Sintered Boron Carbide (B4C)
Authors: Lee Hyukjae , Speyer Robert F.
Published: July 2010

This is a companion work to our previous study on the pressureless sintering of boron carbide (B4C). The Vickers hardness and indentation fracture toughness of B4C compacts were measured after various sintering heat treatments. Increases in hardness and decreases in indentation fracture toughness as the grain size decreased in sintered B4C were attributed to the effects of more rapid strain hardening associated with dislocation pileups at grain boundaries.
Effects of Heat Treatment on the Surface Microstructure and Mechanical Properties of MoSi2‐TiC0.7N0.3 Composites
Authors: Zeng Yu‐Ping , Xu Chao‐Nan , Watanabe Tadahiko
Published: July 2010

MoSi2‐TiC0.7N0.3 composites were prepared by hot‐pressing under vacuum, and MoSi2–TiC0.7N0.3 composites were heat‐treated in air at various temperatures. SEM analysis showed that the surface microstructure of the MoSi2‐TiC0.7N0.3 composite changed because of the oxidation of MoSi2 and TiC0.7N0.3 and that many TiO2 whiskers appeared on the surfaces of the composites. Compared with the non‐heat‐treated MoSi2‐TiC0.7N0.3, the bending strength of the heat‐treated MoSi2‐TiC0.7N0.3 was significantly improved.
Direct Formation of Zirconia‐Doped Titania with Stable Anatase‐Type Structure by Thermal Hydrolysis
Authors: Hirano Masanori , Nakahara Chiaki , Ota Keisuke , Inagaki Michio
Published: July 2010

Nanoparticles of anatase‐type titania (TiO2) doped with zirconia (ZrO2) were directly synthesized from acidic precursor solutions of TiOSO4 and Zr(SO4)2 by simultaneous hydrolysis, under mild hydrothermal conditions, at 200° and 240°C. Doping ZrO2 into TiO2 suppressed the crystal growth of anatase and shifted the phase transformation from anatase‐type to rutile‐type structure to a high temperature. The presence of an anatase‐type structure with high crystallinity and high phase stability, even after annealing at 1000°C for 1 h, was fully achieved by both the doping of ZrO2 into TiO2 through direct precipitation and the simultaneous hydrolysis of the sulfate solutions.
Solid‐State Ionics: Roots, Status, and Future Prospects
Authors: Knauth Philippe , Tuller Harry L.
Published: July 2010

This review represents the authors' view of the evolution of solid‐state ionics over approximately the past 100 years. A brief history, introducing milestones of the development of this discipline, is followed by a short summary of the theory of ionic conduction in the bulk and the more recently developed theory of ionic conduction at interfaces. The central part of the article gives examples of ionic‐conducting materials systems with structures ranging from one‐ to three‐dimensional disorder. Important experimental techniques for analyzing ionic conduction, including alternating‐current impedance spectroscopy, direct‐current coulometry, and direct‐current current‐voltage measurements with blocking electrodes, are also summarized. The main technological applications, that is, batteries, solid‐oxide fuel cells, electrochemical sensors, electrochromic windows, and oxygen‐separation membranes, are reviewed. Finally, new concepts in solid‐state ionics are presented, including the investigation of new materials (such as nanostructured phases), the study of boundaries (for example, using microelectrodes), the development of computational techniques, and the connections with other classes of materials (notably magnetic and semiconducting materials).
Nonaqueous Aluminum Nitride Extrusion: I, Die‐Entry Flow Behavior
Authors: Jr. Wight John F. , Reed James S.
Published: July 2010

Simultaneous orifice and capillary rheometry at 160°C was used to determine flow parameters of aluminum nitride extrudates plasticized with a polyethylene–mineral‐oil binder. Data were analyzed using the Benbow model for square‐entry ram extrusion. Variables included the powder concentration, polymer molecular weight and concentration, and lubricant concentration. Die‐entry rheology was explained in terms of the mean interparticle separation, polymer spatial requirements, and lubricant adsorption. Particles and polymer were observed to not pack independently. The yield stress of the body increased rapidly as the solids loading approached the critical volume limit of extrudability. An increase in polymer molecular weight or partial decrease of adsorbed lubricant increased the yield stress of the body and produced a satisfactory extrudate.
Nonaqueous Aluminum Nitride Extrusion: II, Die‐Land Flow and Tribology
Authors: Jr. Wight John F. , Reed James S.
Published: July 2010

Die‐land flow on extruding a nonaqueous aluminum nitride plastic body was analyzed using simultaneous orifice and capillary rheometry. Extrudate slip on the wall of the die‐land was observed and concluded to involve frictional slip of extrudate particles against the die‐wall and the viscous flow of an annular liquid. Results supported a model of a hydroplaning mechanism for the radial consolidation of the particle and binder network with complementary syneresis of liquid. The thickness of the apparent annular slip film was calculated to be submicrometer and to increase with an increase in the extrudate velocity and a decrease in the bulk yield stress and diameter of the die‐land. The flow stress on approaching the critical volume concentration of particles terminating plastic flow increased abruptly for shear of the body in the die‐entry but more gradually for slip in the die‐land. Shear resistance in the die‐land was significantly decreased on adding a lubricant and was very dependent on the contact stress between the particle network and the die‐wall, controlled by the degree of pore saturation for an unsaturated body and the volume of particles and binder for the saturated extrudate.
Rheology of Cross‐Linked Chitosan–Alumina Suspensions Used for a New Gelcasting Process
Authors: Johnson Stephen B. , Dunstan David E. , Franks George V.
Published: July 2010

The rheological behavior of a low‐toxicity, aqueous, Al2O3–chitosan–2,5‐dimethoxy‐2,5‐dihydrofuran (DHF) system was examined over a temperature range of 20°–98°C. At room temperature, a high‐volume‐fraction solids, shear‐thinning suspension was produced. The suspension remained in a liquidlike state for ∼24 h. By contrast, at elevated temperatures, DHF became active as a cross‐linking agent for chitosan, and a rapid transition from liquidlike to solidlike suspension behavior was apparent. The rate of gelation and the gel strength increased with increased temperature and increased DHF concentration. Gelation occurred at pH 1.4–4.5, which is a complex function of pH. At pH above ∼4, rapid gelation was not possible because of the low‐pH solution conditions required for the cross‐linking reaction. An examination of the strength and shape‐forming properties of several Al2O3–chitosan–DHF systems showed them to be suitable for production of strong, reliable, complex‐shaped ceramic components. In particular, small, dense Al2O3 pseudorotors were formed and found to be of sufficient strength for mold removal and subsequent handling. In all formulations examined, chitosan concentrations of <0.5 wt% (by weight of ceramic) were required; therefore, the need for a discrete binder burnout process was eliminated.
Fabrication of Transparent Yttria Ceramics by the Low‐Temperature Synthesis of Yttrium Hydroxide
Authors: Ikegami Takayasu , Li Ji‐Guang , Mori Toshiyuki , Moriyoshi Yusuke
Published: July 2010

Thin flakes of yttrium hydroxide agglomerated in a manner resembling houses of cards with aging at 10°C. The agglomerate then dissociated into fine yttria particles with calcination at >800°C. The particle size of the calcined powder increased appreciably as the calcination temperature increased. The shrinkage curve indicated similar densification behavior among undoped yttria powders calcined at 800°–1000°C, despite considerable particle growth as the calcination temperature increased. Increasing the calcination temperature to >1000°C shifted the shrinkage curve appreciably to the high‐temperature region. Sulfate‐ion‐doped yttria particles had round edges, irrespective of calcination temperature, in contrast to the sharp edges of the undoped yttria particles. A calcination temperature of <1000°C resulted in skeleton yttria particles, which exhibited poor sinterability. At a calcination temperature >1000°C, the skeleton particles dissociated into monodispersed particles that densified easily. When the calcination temperature was >1000°C and the average particle sizes were similar, the undoped and sulfate‐ion‐doped yttria showed similar densification rates. The transparency of the sintered yttria ceramics was dependent on both the calcination temperature and sulfate‐ion doping: that is, sulfate‐ion doping and calcining at 1100°C were both necessary conditions for the fabrication of a transparent body.
Use of Mixed‐Rare‐Earth Oxide in the Preparation of Reaction‐Bonded Mullite at ≤1300°C
Authors: Kim Han Soo , Nicholson Patrick S.
Published: July 2010

A process for production of near‐net‐shape mullite‐matrix ceramic composites at ≤1300°C has been achieved by reaction‐bonding Al2O3, silicon, mullite seeds, and eutectics of Al2O3–SiO2–mixed‐rare‐earth oxide. The fusion temperature of the eutectic composition utilized is 1175°C. This liquid phase facilitates silicon oxidation, mullitization, and sintering. Mullite phase develops with low residual Al2O3 when 7.5 wt% mixed‐rare‐earth oxide and 5 wt% mullite seeds are used. The final sinter is >90% of theoretical density, >90% mullite (by quantitative XRD), and suffers 2.2% sintering shrinkage.
Comparative Lattice‐Dynamical Study of the Raman Spectra of Monoclinic and Tetragonal Phases of Zirconia and Hafnia
Authors: Quintard Pierre E. , Barbéris Pierre , Mirgorodsky Andrei P. , Merle‐Méjean Thérèse
Published: July 2010

An interpretation of the Raman spectra of monoclinic ZrO2and monoclinic HfO2is made by analyzing the results of the zirconia–hafnia substitution jointly with a lattice dynamical treatment of both structures. The Raman spectra of tetragonal ZrO2and tetragonal HfO2are also interpreted. Emphasis is put on their relations to the spectrum of the parent cubic structure and on the position of the soft mode. The band assignment proposed earlier by other researchers is critically reconsidered.
Raman Spectroscopic Study of Gallium‐Doped Ba(Zn1/3Ta2/3)O3
Authors: Webb Stephen J. , Breeze Jonathan , Scott Robert I. , Cannell David S. , Iddles David M. , Alford Neil McN.
Published: July 2010

Resonators of Ba(Zn1/3Ta2/3)O3, sintered between 1450° and 1600°C, are characterized by Raman spectroscopy, X‐ray diffraction, and scanning electron microscopy. The quality factors of the resonators are found to depend on sintering temperature, and at 1600°C there is evidence of Zn loss from the surface. The frequency of the A1gRaman mode changes from 800.9 cm−1for a sample withQ= 80000 (2 GHz), to 794.5 cm−1whenQ= 44000 (2 GHz). Changes in the position of this and other Raman modes are thought to be due to distortions of the oxygen octahedra, brought about by Zn loss. The presence of a BaTa2O6phase at the surface is confirmed by XRD and SEM.
Developing Interfacial Carbon‐Boron‐Silicon Coatings for Silicon Nitride‐Fiber‐Reinforced Composites for Improved Oxidation Resistance
Authors: Sato Kiyoshi , Morozumi Hiroki , Funayama Osamu , Kaya Hiroshi , Isoda Takeshi
Published: July 2010

C‐B‐Si coatings were formed on a Si3N4 fiber using chemical vapor deposition and embedded in a Si‐N‐C matrix using polymer impregnation and pyrolysis. The boron‐containing layer was anticipated to form borosilicate glass and seal oxygen‐diffusion passes. Two types of C‐B‐Si coatings were tested on the fiber–matrix interface, and they improved the oxidation resistance of the composite. The first coating was multilayered: a crystalline sublayer composed of B‐Si‐C was sandwiched between two graphitelike carbon sublayers. The second coating was a graphitelike carbon layer containing a small amount of boron and silicon. The carbon (sub)layer of both coatings weakened the fiber–matrix bonding, giving the composites a high flexural strength (1.1 GPa). The composites retained 60%–70% of their initial strength, even after oxidation at 1523 K for 100 h. The mechanism for improved oxidation resistance was discussed through the microstructure of the interface, morphology of the fracture surface, and oxygen distribution on a cross section of the oxidized composite.
Incorporation of Uranium in Zirconolite (CaZrTi2O7)
Authors: Vance Eric R. , Lumpkin Gregory R. , Carter Melody L. , Cassidy David J. , Ball Cliff J. , Day R. Arthur , Begg Bruce D.
Published: July 2010

Up to 0.15 formula unit (f.u.) of U4+ incorporated in the Zr site of zirconolite by firing CaUxZr(1−x)Ti2O7 compositions in argon at 1400°C allows retention of the 2M polytype. Further U4+ substitution for Zr, up to 0.4 f.u., produces the 4M polytype (containing ∼0.4 f.u. of U) plus the 2M polytype containing 0.15 f.u. of U. The pyrochlore structure (containing 0.6 f.u. of U) forms in conjunction with the 4M polytype at U contents of 0.4 f.u. up to 0.7 f.u. Higher U contents give the pyrochlore structure, but the solid‐state reactivity of even alkoxide‐based preparations becomes increasingly poor for x > ∼0.7 and hot pressing in graphite dies at ∼1250°C is necessary to achieve near single‐phase pyrochlore structures for x= 1. When samples of CaUxZr1−xTi2O7 stoichiometry (x= 0.1 and 0.2) are oxidized at 1400°C in air, diffuse reflectance spectroscopy (DRS) shows evidence for U5+ formation at the expense of U4+ via enhanced absorption bands, ∼50 nm in half‐width, near 970 and 1500 nm and correspondingly weakened absorption at 1150 and 1660 nm. Weight gains consistent with complete oxidation of U4+ to U5+ are observed when finely powdered argon‐fired samples with x= 0.1 and 0.4 are heated in air to 1200°C. Evidence for U valence states higher than +4 in both argon‐ and air‐heated materials containing charge compensators to encourage U5+ or U6+ formation was also derived from DRS (showing U5+ in particular), and XANES. DRS shows weak absorption bands attributable to U4+ in zirconolites containing ∼0.2 f.u. of U incorporated in the Ca site via Mg or Al substitutions in the Ti sites, with the spectrum being closely but not exactly similar to that attributed to U4+ in the Zr site. Zirconolite and pyrochlore compositions which are melted at 1500° or 1550°C in argon and furnace‐cooled yield broadly similar phase assemblages to the corresponding sintered materials, but there is evidence of incongruent melting in all materials.
Oxidation of a Silicon Nitride‐Titanium Nitride Composite: Microstructural Investigations and Phenomenological Modeling
Authors: Deschaux‐Beaume Frédéric , Cutard Thierry , Fréty Nicole , Levaillant Christophe
Published: July 2010

The high‐temperature oxidation of a silicon nitride‐titanium nitride (Si3N4–TiN) composite has been investigated via scanning electron microscopy and energy‐dispersive and wavelength‐dispersive spectrometry. At 1150°C, the oxidation of both the silicon nitride and titanium nitride phases takes place. Several oxidation processes act simultaneously and/or successively. First, the oxidation of the titanium nitride occurs and leads to the formation of a continuous titanium oxide (TiO2) crystal layer at the surface. Next, the TiO2formation takes place in the sublayer at the same time as the Si3N4oxidation. The oxidation of this last phase leads to the formation of vitreous silica (SiO2). For long a duration of oxidation (>50 h), a continuous layer of SiO2is formed under the outer TiO2scale. Large pores grow in this layer and deform the outer oxide layers, whereas the oxidation occurs in the material. Based on these results and bibliographical data, a phenomenological model is proposed to describe the stages of the high‐temperature oxidation of Si3N4–TiN materials.
Resource Recovery of Waste Incineration Fly Ash: Synthesis of Zeolites A and P
Authors: Miyake Michihiro , Tamura Chikashi , Matsuda Motohide
Published: July 2010

The conversion of waste incineration fly ash to zeolitic compounds by hydrothermal treatment in the presence of NaOH solution has been investigated. An acid pretreatment of fly ash in addition to water washing and heating at 800°C was found to be an important process to prepare reproducible zeolitic compounds. Treatment with a low‐concentration NaOH solution at 60°C and 100°–120°C successfully produced zeolites A and P, respectively, as major products. At increased concentrations of NaOH, sodalite was generated. The hydrothermal products showed uptake behavior for NH4+ ions.
Micropatterned Ceramics by Casting into Polymer Molds
Authors: Schönholzer Urs P. , Stutzmann Natalie , Tervoort Theo A. , Smith Paul , Gauckler Ludwig J.
Published: July 2010

Patterned ceramic surfaces with a feature resolution in the micrometer range are generated by casting aqueous suspensions of high solids loadings onto nonporous polymer molds. The suspensions are solidified by evaporation of the solvent. High‐quality line patterns with an aspect ratio of 1 and a pitch of 3 μm were fabricated for alumina, zirconia, cerium gadolinium oxide, and tin oxide powders using molds of poly(dimethylsiloxane). In addition, alumina parts were also created with molds made of a polyolefin (high‐density polyethylene), a fluoropolymer (poly(tetrafluoroethylene‐co‐hexafluoropropylene)), and an epoxy system.
Effect of 1600°C Heat Treatment on C/SiC Composites Fabricated by Polymer Infiltration and Pyrolysis with Allylhydridopolycarbosilane
Authors: Berbon Min , Calabrese Mike
Published: July 2010

Fiber‐coating debonding observed by transmission electron microscopy is suggested as the cause for an ∼60% reduction in strength after one cycle of 1600°C heat treatment in a carbon/silicon carbide (C/SiC) composite fabricated by polymer infiltration and pyrolysis with pure allylhydridopolycarbosilane polymer as the matrix precursor. Infiltration with a slurry of SiC powder and the polymer precursor was effective in preserving the coating integrity and composite strength. This study demonstrates that the addition of powder in polymer infiltration and pyrolysis process may impact composite mechanical properties significantly by altering the fiber‐matrix interface characteristics.
Interface Design for Oxidation‐Resistant Ceramic Composites
Authors: Kerans Ronald J. , Hay Randall S. , Parthasarathy Triplicane A. , Cinibulk Michael K.
Published: July 2010

Fiber‐reinforced ceramic composites achieve high toughness through distributed damage mechanisms. These mechanisms are dependent on matrix cracks deflecting into fiber/matrix interfacial debonding cracks. Oxidation resistance of the fiber coatings often used to enable crack deflection is an important limitation for long‐term use in many applications. Research on alternative, mostly oxide, coatings for oxide and non‐oxide composites is reviewed. Processing issues, such as fiber coatings and fiber strength degradation, are discussed. Mechanics work related to design of crack deflecting coatings is also reviewed, and implications on the design of coatings and of composite systems using alternative coatings are discussed. Potential topics for further research are identified.
Proton Conductivity Measurements in Yttrium Barium Cerate by Impedance Spectroscopy
Authors: Coors W. Grover , Readey Dennis W.
Published: July 2010

Proton‐conducting solid‐electrolyte perovskite ceramics based on acceptor‐doped barium and strontium cerates have become the focus of extensive investigations as candidate materials for fuel cells that operate at moderate temperatures. To assess the suitability of a material for this application, it is necessary that bulk electrolyte conductivity be measured at the operating temperature. However, very little reliable published conductivity data exist above 600°C. Protonic conductivity in yttrium‐doped barium cerate has been observed to be less at high temperatures than would be expected, based on the activation energy and preexponential for hydrogen transport at temperatures <300°C. Conductivity data obtained from impedance spectroscopy on BaCe0.9Y0.1O3–α over the extended temperature range of 100°–900°C are presented. An Arrhenius plot of the data shows two distinct linear regions, suggesting that two different rate‐limiting processes occur in series with a break‐over transition at ∼250°C. The decrease in conductivity is apparently not due to dehydration. An activation energy for protonic transport of 0.26 eV, about one‐half of the low‐temperature value, is proposed, based on curve fitting of the high‐temperature data.
Ceramic Oxygen Generators with Thin‐Film Zirconia Electrolytes
Authors: Guan Jie , Doshi Rajiv , Lear Gregory , Montgomery Kurtis , Ong Estela , Minh Nguyen
Published: July 2010

Ceramic oxygen generators (COGs) based on stabilized zirconia electrolytes are being developed for oxygen generation from air and other gases, e.g., carbon dioxide. In zirconia‐based COG cells, it is desirable to use thin‐film electrolytes to minimize ohmic resistance losses, thus permitting reduced operating temperatures (600°–800°C vs 900°–1000°C). The tape calendering process developed by Honeywell is a simple, cost‐effective process for fabrication of thin‐film electrolytes supported on a substrate electrode. In combination with optimized electrodes, thin‐film electrolytes allow significantly high performance in COG cells. Performance characteristics of COG cells and stacks made by tape calendering for oxygen generation from air and CO2 are discussed.
(Mg,Co)O Solid‐Solution Precursors for the Large‐Scale Synthesis of Carbon Nanotubes by Catalytic Chemical Vapor Deposition
Authors: Bacsa Revathi R. , Laurent Christophe , Peigney Alain , Vaugien Thibaud , Flahaut Emmanuel , Bacsa Wolfgang S. , Rousset Abel
Published: July 2010

Single‐ and double‐walled carbon nanotubes were produced in high yield using the selective reduction of solid solutions of Mg1–xCoxO in a methane and hydrogen atmosphere at 1000°C. The solid solutions were prepared using combustion synthesis with urea as the fuel. The BET surface areas ranged from 10 to 65 m2/g depending on the fuel content. A single crystalline phase was obtained only for fuel‐rich compositions. Increased fuel content increased the surface area by a factor of 6. However, very high fuel contents (>4 times the stoichiometric amount) caused a demixed solid solution. Surface‐area measurements and Raman spectra showed that the quantity of nanotubes formed depended on the surface area and composition of the precursor oxide.
Machinability of Silicon Nitride/Boron Nitride Nanocomposites
Authors: Kusunose Takafumi , Sekino Tohru , Choa Yong‐Ho , Niihara Koichi
Published: July 2010

The machinability and deformation mechanism of Si3N4/BN nanocomposites were investigated in the present work. The fracture strength of Si3N4/BN microcomposites remarkably decreased with increased hexagonal graphitic boron nitride (h‐BN) content, although machinability was somewhat improved. However, the nanocomposites fabricated using the chemical method simultaneously had high fracture strength and good machinability. Hertzian contact tests were performed to clarify the deformation behavior by mechanical shock. As a result of this test, the damage of the monolithic Si3N4and Si3N4/BN microcomposites indicated a classical Hertzian cone fracture and many large cracks, whereas the damage observed in the nanocomposites appeared to be quasi‐plastic deformation.
Influence of the Metal Particle Size on the Crack Growth Resistance in Mullite–Molybdenum Composites
Authors: Bartolomé José F. , Díaz Marcos , Moya José S.
Published: July 2010

The R‐curve for mullite–molybdenum (32 vol%) composites, which were obtained at 1650°C under reducing conditions with three different Mo average grain sizes (1.5, 3, and 9 μm), was estimated by the indentation‐strength method and compared with that monolithic mullite obtained under similar conditions. The composites material exhibited rising R‐curve behavior. The composite with larger grain size, however, displayed better damage tolerance and higher resistance to crack growth. Microscopic observation of the crack path revealed, in the composites, the systematic presence of dispersoids acting as bridging sites in the crack wake. Therefore, the increased fracture toughness of these ceramic‐matrix composites with adherent ductile phase can be attributed to clamping forces applied by metal ligaments that bridge the crack faces behind the crack front. These clamping forces retard the crack from opening as an external stress is applied. It was inferred that this superior performance of the larger Mo particle size composite can be attributed mainly to more effective bridging of the metal grains. Because of this, a higher applied stress intensity will be required to propagate the crack tip. These results suggest that the rising R‐curve should be proportional to the metal grain size, since the grain bridging area is proportional to the metal grain size.
Wear Simulation of Alumina‐on‐Alumina Prosthetic Hip Joints Using a Multidirectional Motion Pin‐on‐Disk Device
Authors: Saikko Vesa , Keränen Jaakko
Published: July 2010

The wear of a state‐of‐the‐art implant alumina against itself was studied with a circularly translating pin‐on‐disk (CTPOD) device, a wear simulator for prosthetic hip joint materials. The direction of sliding changed continually relative to the pin, preventing erroneous uniaxial grooving typical of ordinary pin‐on‐disk devices. The dominating wear mechanism was mild abrasion manifested as a relieflike surface, which agreed with clinical findings. The wear factor ranged from 1 × 10−8 to 6 × 10−8 mm3/(N·m). The CTPOD device, validated earlier for ultrahigh molecular weight polyethylene, was shown to be the first simple wear test device to produce wear similar to that known to occur clinically in alumina‐on‐alumina total hip prostheses.
Effect of Sintering Atmosphere on Grain Boundary Segregation and Grain Growth in Niobium‐Doped SrTiO3
Authors: Chung Sung‐Yoon , Kang Suk‐Joong L. , Dravid Vinayak P.
Published: July 2010

To investigate the donor segregation in grain boundary regions and its effect on grain growth in SrTiO3, SrTiO3 powder compacts were doped with Nb2O5 and sintered in air or in hydrogen. The Nb‐doped SrTiO3 sintered in air did not show any detectable Nb segregation at the grain boundary region while an appreciable segregation was observed in the space‐charge region of the sample sintered in H2. The observed donor segregation in H2 suggests a negative grain boundary charge and compensating positive space charge, which are the opposite to those in air. The negative grain boundary core was attributed to the segregation of inherently present acceptor impurities and the trapping of electrons at grain boundaries. In the H2‐sintered sample, where the added Nb ions were segregated in the space‐charge region, the grain growth was suppressed. This result may indicate that the grain growth suppression in H2 is due to the Nb solute drag of the boundary motion and the reduction in Ti vacancies.
Surface Breakaway Decomposition of Perovskite 0.91PZN–0.09PT during High‐Temperature Annealing
Authors: Lim Leong‐Chew , Liu Rongmin , Kumar Francis J.
Published: July 2010

The thermal stability of crystallite powder and bulk single crystals of relaxor 0.91Pb(Zn1/3Nb2/3)O3–0.09PbTiO3 (0.91PZN–0.09PT) solid solution in air and an PbO‐rich environment has been investigated. At 700°C, perovskite PZN–PT decomposes only slightly to the pyrochlore phase. At 800°C, the rate of decomposition is accelerated, promoted by a surface breakaway decomposition process. This process occurs via the inward growth of faceted pyrochlore grains from the particle surface. At a certain point of the growth process, they will break away and detach themselves from the perovskite phase. The transformation stress also causes the adjacent perovskite phase to fracture concurrently, contributing to the breakaway event. At higher annealing temperatures (i.e., 900°–1000°C) and/or in the PbO‐rich environment, a layer of PbO‐rich liquid phase is formed on the surface of the particle. Because of limited wetting between the PbO‐rich liquid phase and the earlier‐formed pyrochlore grains, the latter detach themselves from the perovskite substrate. This action frees the substrate from the pyrochlore nuclei to initiate the breakaway decomposition event, which causes the rate of decomposition to slow substantially. At 1100°C both in air and the PbO‐rich environment, the PbO‐rich liquid formed vaporizes readily, which causes the decomposition rate to accelerate again. The present work shows that (i) the decomposition of perovskite PZN–PT to the pyrochlore phase during high‐temperature annealing is a surface phenomenon and (ii) its rate is controlled by the relative rate of formation and vaporization of the protective liquid layer that is present under the annealing conditions.