bluuebunny/crossref_metadata_2025 huggingface dataset:
Strong and Tough Hi‐Nicalon‐Fiber‐Reinforced Celsian‐Matrix Composites
Authors: Bansal Narottam P.
Published: July 2010

Strong, tough, and almost fully dense BN/SiC‐coated Hi‐Nicalon‐fiber‐reinforced celsian‐matrix composites have been fabricated by impregnation of the fiber tows with the matrix slurry, winding on a drum, stacking the prepreg tapes in the desired orientation, and hot pressing. The monoclinic celsian phase in the matrix was produced in situ, during hot pressing, from a mixed oxide precursor. The unidirectional composites having ˜42 vol% of fibers exhibited graceful failure with extensive fiber pullout in three‐point bend tests at room temperature. Values of stress and strain at the proportional limit were 435 ± 35 MPa and 0.27 ± 0.01%, respectively, and an apparent ultimate strength of 900 ± 60 MPa was observed. Young's modulus of the composites was 165 ± 5 GPa.
In Situ Observation of Phase Separation of a Barium Borate Melt in a Stable Immiscibility Region under Microgravity
Authors: Inoue Satoru , Makishima Akio , Inoue Hiroyuki , Soga Kohei , Konishi Tomoya , Asano Tomoyoshi , Ishii Yuu , Koyama Masato
Published: July 2010

The precipitation of droplets was directly observed on a BaO–B2O3 melt in a drop shaft experiment. This is the first time that precipitation of droplets has been observed in a 4.5 s drop test. The melt film of 4BaOz96B2O3 (mol%) held on a platinum wire loop was heated above the critical tem‐perature to produce uniformity and was cooled down to the phase separation temperature range. Phase separation of the melt was observed directly with a video camera. The IR image of the melt was simultaneously detected with a CCD array and was converted into a two‐dimensional thermograph.
Preparation of Al2O3–AlN–Ni Composites
Authors: Tuan Wei‐Hsing , Chou Wen‐Bing
Published: July 2010

A method is proposed to prepare Al2O3‐AlN‐Ni composites. The composites are prepared by sintering Al2O3/NiAl powder mixtures at 1600°C in a mixture of nitrogen and carbon monoxide. The presence of NiAl particles raises the green density of Al2O3/NiAl powder compacts. During sintering, NiAl reacts with nitrogen to form AlN and Ni inclusions. A volume expansion accompanies the reaction. Because of the high green density and the reaction, the volume shrinkage of the Al2O3‐AlN‐Ni composite decreases with the increase of added NiAl content.
Stress Intensity Factor for a Peripherally Cracked Spherical Cap
Authors: Zhu Gao‐Qiu , Ritter John E. , Jakus Karl , Bhattacharya Sandeepan
Published: July 2010

Stress intensity factors are estimated for a spherical cap surrounded by a peripheral crack in a semi‐infinite body. Using finite element analysis, the stress concentration of a spherical cap was determined as a function of the radius and depth of the cap. This stress concentration was then taken into account in developing the appropriate stress intensity factor for the peripheral crack around the spherical cap.
Phase Formation in the System CaO‐SeO2‐H2O
Authors: Dumm John Q. , Brown Paul W.
Published: July 2010

The chemistry of the system CaO‐SeO2‐H2O has been investigated at 23° and 80°C. The existence of four major phases in this system—CaSeO3H2O, Ca(HSeO3)2H2O, Ca2(SeO3)(Se2O5), and Ca2(HSeO3)2(Se2O5)—has been confirmed, and the equilibria among them determined. At 23°C, CaSeO3H2O and Ca(HSeO3)2H2O are the stable calcium selenites. CaSeO3H2O exists over the pH range 12.5‐3.7, making it the most important phase for natural systems as well as most technological applications. Ca(HSeO3)2H2O is the more acidic phase; it exists over the pH range 3.7‐0.4. Incongruent dissolution of Ca(HSeO3)2H2O forms CaSeO3H2O. These results indicate Ca2(HSeO3)2(Se2O5) is not a stable phase at 23°C. At 80°C, CaSeO3H2O, Ca2(SeO3)(Se2O5), and Ca2(HSeO3)2(Se2O5) are the stable calcium selenite phases. Ca(HSeO3) 2H2O has not been observed. Again, CaSeO 3H2O exists over the broadest pH range, 11.0‐3.9. Ca2(SeO3)(Se2O5) and Ca2(HSeO3)2(Se2O5) dissolve incongruently. The formation of Ca2(SeO3)(Se2O5) and Ca2(HSeO3)2(Se2O5) at 80°C demonstrates the increasing stability of the Se2O2‐ 5 ion and the decreasing stability of the HSeO‐3 ion with increasing temperature.
PbTiO3–PbO–SiO2 Glass‐Ceramic Thin Film by a Sol–Gel Process
Authors: Saegusa Kunio
Published: July 2010

PbTiO3(PT)‐PbO‐SiO2 glass‐ceramic thin films were pro‐duced by a sol‐gel process. The crystallization of PT oc‐curred at ∼700°C and was higher than that in PT‐PbO‐B2 O3 sol‐gel glass‐ceramics. A pinhole‐free thin film was obtained by a rapid thermal annealing process when the designed glass‐forming phase content in the thin film was >24 vol%. The measured dielectric constants of the films fairly agreed with the predicted values, based on a parallel mixing model. The dielectric constant was 219 and the di‐electric loss was 0.04 in the 0.6PT‐0.4(PbO‐SiO2) film that was fired at 700°C.
Mechanism of Biaxial Alignment of Oxide Thin Films during Ion‐Beam‐Assisted Deposition
Authors: Ressler Kevin G. , Sonnenberg Neville , Cima Michael J.
Published: July 2010

The mechanism of biaxial alignment was examined for yttria‐stabilized zirconia (YSZ) and La1−xCaxMnO3 (LCMO) films that were fabricated by ion‐beam‐assisted deposition (IBAD). Films that were deposited with both dual‐ion‐beam deposition and ion‐assisted electron‐beam evaporation were studied. The film texture formation was mostly dependent on the ratio of ion bombardment to molecule arrival and on the angle of the incident ions with respect to the substrate. Results were not dependent on the deposition technique. The observed IBAD YSZ and IBAD LCMO biaxial alignment did not occur because of ion channeling. It has been shown that the preferred film orientation develops because of anisotropy of ion‐induced damage on various crystal surfaces.
Preparation and Faraday Effect of Fluoroaluminate Glasses Containing Divalent Europium Ions
Authors: Qiu Jianrong , Tanaka Katsuhisa , Hirao Kazuyuki
Published: July 2010

Fluoroaluminate glasses containing various concentrations of Eu2+ were prepared under a reducing atmosphere for the present study, and the wavelength dependence of the Faraday rotation angle was examined. The magnitude of the Verdet constant (Vc) increased as the concentration of Eu2+ increased. In addition, the Verdet constant of glasses containing 5 cat.% Eu2+ was larger than that of fluoroaluminate glasses containing the same concentration of Tb3+ in the wavelength region from 400 to 600 nm. The effective transition wavelength, λt, for glasses containing Eu2+ as well as those containing Tb3+ was evaluated based on the Van Vleck and Hebb theory. Factors dominating the Verdet constant of those glasses are discussed in this report.
Metal Propionate Synthesis of Magnetoresistive La1−x(Ca,Sr)xMnO3 Thin Films
Authors: Hasenkox Ulrich , Mitze Carsten , Waser Rainer
Published: July 2010

A flexible chemical solution deposition (CSD) method for the preparation of magnetoresistive La1−x (Ca,Sr)x MnO3thin films based completely on metal propionates is pre‐sented.A number of polycrystalline thin films with varying stoichiometries were deposited on different substrate ma‐terials at temperatures between 550° and 850°C. The crys‐tallization behavior on selected substrates was found to de‐pend on the thin film stoichiometry. Magnetoresistivity and magnetization were measured as a function of temperature. For the selected samples, a magnetic Curie temperature TC, a metal–semiconductor transition, and magnetoresistive behavior were observed. These measurements demon‐strated that La1−x(Ca,Sr)x MnO3 thin films with properties well known from films deposited by PLD or sputtering can be prepared by a simple, propionate‐based CSD method.
Synthesis and Properties of Lead Magnesium Niobate Zirconate Relaxor Materials
Authors: Nijmeijer Arian , Kruidhof Henk , Hennings Detlev
Published: July 2010

Two materials were prepared with composition PbMg0.3‐Nb0.6Zr0.1O3 (PMNZ/10) and PbMg0.32Nb0.65Zr0.03O3 (PMNZ/3). Slight modifications in lead oxide content of these materials were made to study its influence on the sintering properties. The stoichiometric PMNZ/3 gave the best results. It has a sintering temperature as low as 900°C and a relative dielectric constant of 10 000 at room temperature.
Synthesis of ZrO2 and Y2O3‐Doped ZrO2 Thin Films Using Self‐Assembled Monolayers
Authors: Agarwal Monika , de Guire Mark R. , Heuer Arthur H.
Published: July 2010

Undoped or Y2O3‐doped ZrO2 thin films were deposited on self‐assembled monolayers (SAMs) with either sulfonate or methyl terminal functionalities on single‐crystal silicon substrates. The undoped films were formed by enhanced hydrolysis of zirconium sulfate (Zr(SO4)·4H4O) solutions in the presence of HCl at 70°C. Typically, these films were a mixture of two phases: nanocrystalline tetragonal‐ (t‐) ZrO2 and an amorphous basic zirconium sulfate. However, films with little or no amorphous material could be produced. The mechanism of film formation and the growth kinetics have been explained through a coagulation model involving homogeneous nucleation, particle adhesion, and aggregation onto the substrate. Annealing of these films at 500°C led to complete crystallization to t‐ZrO2. Amorphous Y2O3‐containing ZrO2 films were prepared from a precursor solution containing zirconium sulfate, yttrium sulfate (Y2(SO4)38·H2O), and urea (NH2CONH2) at pH 2.2–3.0 at 80°C. These films also were fully crystalline after annealing at 500°C.
Viscous Sintering and Mechanical Properties of 3Y‐TZP‐Reinforced LAS Glass‐Ceramic Composites
Authors: Choi Se Y. , Ahn Joon M.
Published: July 2010

The densification of lithium aluminosilicate glass‐ceramic composites strongly depended on dispersed 3‐mol%‐Y2O3‐tetragonal‐ZrO2‐polycrystal (3Y‐TZP) content, rather than the crystallization of a parent glass phase. Because of the reaction between 3Y‐TZP and the glass phase, tetragonal‐ZrO2 transformed to monoclinic‐ZrO2 with twinned structure because of the dissolution of Y2O3, and ZrSiO4 formed. Composites containing >50 wt% 3Y‐TZP were characterized by fully densified microstructures and decreased tetragonal‐to‐monoclinic transformation. Fracture toughness increased by almost a factor of 3, which was attributed mainly to stress‐induced phase transformation of tetragonal‐ZrO2 particles.
Preparation, Microstructure, and Mechanical Properties of Silicon Carbide–Dysprosia Composites
Authors: Kim Shin , Kriven Waltraud M.
Published: July 2010

Composites of silicon carbide (SiC) with up to 30 vol% of dysprosia (Dy2O3) were fabricated by hot pressing and hot isostatic pressing. The effects of Dy2O3 dispersions on the microstructure and on selected mechanical properties of the composites were investigated. When 10‐15 vol% of Dy2O3 was dispersed in the SiC matrix, the fracture toughness increased by ∼40%, whereas the flexural strength was comparable to that of unreinforced SiC. The increased fracture toughness was due to crack deflection, in conjunction with crack‐interface grain bridging, and was not related to a phase transformation of Dy2O3 in the matrix.
Crystalline Copper Phosphates: Synthesis and Thermal Stability
Authors: Bamberger Carlos E. , Specht E. D. , Anovitz Lawrence M.
Published: July 2010

The syntheses of Cu(PO3)2, Cu2P2O7, Cu4P2O9, Cu5P2O10, Cu3(PO4)2, and Cu2PO4 were accomplished by several new solid‐state routes. Attempts to synthesize CuPO3 were unsuccessful, and it is suspected that this compound, which is reported in the literature, may not exist. The thermal stabilities of Cu(PO3)2, Cu2P2O7 and Cu3(PO4)2 were examined, and their decomposition was concluded to be strongly dependent on slow kinetics.
Application of the Carreau Model to Tape‐Casting Fluid Mechanics
Authors: Terrones Guillermo , Smith Peter A. , Armstrong Timothy R. , Soltesz Tamara J.
Published: July 2010

Tape‐casting experiments were conducted with 30 different aqueous suspensions whose viscosities were functions of strain rate. Tape thickness measurements of the resulting casts varied from 180 to 310 μ m. The three‐parameter Carreau model accurately conformed to the rheological data of the suspensions between 0.46 and 581 s−1. With this model, the zero‐shear‐rate viscosities of the various suspensions ranged from 20 to 2 × 105 mPa·s. Within the framework of the Carreau model, the equations of motion for the flow of the suspension through the doctor blade were solved numerically. Calculated thicknesses were in very good agreement with experimental measurements.
Effect of Substrate Orientation, Roughness, and Film Deposition Mode on the Tensile Strength and Toughness of Niobium–Sapphire Interfaces
Authors: Gupta Vijay , Wu Jianxin , Pronin Alexander N.
Published: July 2010

The strength and toughness of interfaces between sputter‐deposited polycrystalline niobium films and sapphire substrates with basal and prismatic orientations were measured. The effect of deposition parameters and substrate roughness on these interface properties also was investigated. Substrates of polycrystalline alumina with two different surface morphologies were chosen for studying the effect of interface roughness. The interface strength was measured using a previously developed laser spallation experiment in which a laser‐generated compressive stress pulse in the substrate, upon reflection into a tensile stress pulse from the coating's free surface, pulls the interface apart. The interface toughness was obtained using a controlled delamination technique, in which a residually stressed loading layer was used to buckle the underlying test layer from its substrate. The energy balance in the prebuckeled and postbuckled states provided a direct measure of the interface toughness. These values were independently obtained by another experiment in which well‐characterized, artificially generated, interfacial flaws were loaded using a stress pulse in the laser spallation assembly. The coating's free surface velocity upon crack initiation was related to the critical energy release rate via a numerical simulation. The results of the two toughness experiments conformed to each other and related fairly well to the independently obtained strength measurements.
Effect of Heat Treatment on Rapidly Quenched AgI‐Based Silver Orthoborate Glasses Containing Large Amounts of AgI
Authors: Itakura Nobuyuki , Tatsumisago Masahiro , Minami Tsutomu
Published: July 2010

The effect of heat treatment on the twin‐roller rapidly quenched 75AgI·18.7Ag2O6.3B2O3 glass was investigated by differential scanning calorimetry (DSC), high‐temperature X‐ray diffraction (XRD), and field‐emission‐type scanning electron microscopy. The glass had an inhomogeneous microstructure with dispersed particles 40‐60 nm in diameter at room temperature. On the other hand, island regions of several hundred nanometers with fine dispersed particles about 20‐30 nm in diameter were observed in the glass after heating to 120°C. DSC and high‐temperature XRD measurements revealed that crystallization occurred at around 120°C, which is lower than the α‐β phase transformation temperature (147°C), to form α‐AgI in the glass. The crystallization of α‐AgI from the glass below the α‐ß phase transformation temperature strongly supports the possibility of the existence of α‐AgI nuclei in AgI‐based silver orthoborate glasses. Validating the existence of AgI microcrystals supports the microdomain model for superionic AgI‐based glasses.
Formation Process of Super‐Water‐Repellent Al2O3 Coating Films with High Transparency by the Sol–Gel Method
Authors: Tadanaga Kiyoharu , Katata Noriko , Minami Tsutomu
Published: July 2010

Alumina thin films with a roughness of 20 to 50 nm were formed by immersing porous alumina gel films prepared by the sol‐gel method in boiling water. When hydrolyzed fluoroalkyltrimethoxysilane was coated on the alumina films, the contact angle for water was increased with an increase of immersion time, and immersion for 30 s was long enough to give super‐water‐repellency and high transparency; the contact angle for water of the film was 165° and the transmittance for the visible light was higher than 92%. It was found that the surface of the alumina gel films immersed in boiling water consisted of boehmite crystals. It was shown that the existence of air in the hydrophobic pores on the surface caused the super‐water‐repellency.
Characterization and Sintering of Reactive Cerium(IV) Oxide Powders Prepared by the Hydrazine Method
Authors: Nakane Singo , Tachi Toshiaki , Yoshinaka Masaru , Hirota Ken , Yamaguchi Osamu
Published: July 2010

Nanocrystalline cerium(IV) oxide (CeO2) powders have been prepared by adding hydrazine monohydrate to an aqueous solution of hydrous cerium nitrate (Ce(NO3)3·6H2O), followed by washing and drying. The lattice parameter of the as‐prepared powder is a= 0.5415 nm. The powder characteristics and sinterability of reactive CeO2 have been studied. The surface areas of powders that have been heated at low temperatures are high, and these surface areas do not decrease to 10 m2/g until the temperature is >1200°C. Crystallite size and particle size are strongly dependent on the heating temperature. Optimum sintered densities are obtained by calcining in the temperature range of 700°–800°C. Ceramics with almost‐full density can be fabricated at a temperature as low as 1150°C.
Mullite Coatings on SiC and C/C–Si–SiC Substrates Characterized by Infrared Spectroscopy
Authors: Rüscher Claus H. , Fritze Holger , Borchardt Günter , Witke Thomas , Schultrich Bernd
Published: July 2010

Mullite (3Al2O3·2SiO2) coatings on SiC substrates and SiC precoated carbon/carbon composite (C/C‐Si‐SiC) substrates were produced by pulsed laser deposition (PLD) using pressed mullite powder targets. The layers can be characterized efficiently by IR reflection spectroscopy in the spectral range between 650 and 5000 cm−1. The deposited coatings turn into mullite upon oxidation in air at temperatures between 1400° and 1600°C. Fabry‐Perot interferences indicate a high quality and homogeneity of the mullite coating/SiC substrate interface. Amorphous SiO2 gradually forms during prolonged heating or at higher temperatures.
Effect of Alkali Ions on the Crystallization of 3BaO·5SiO2 Glass
Authors: Freiman Stephen W. , Onoda George Y.
Published: July 2010

In this study we have investigated the effects of alkali additions on the spherulitic crystallization process in 3BaO·5SiO2 glass. Both Li+ and Na+ increased the growth rate of the spherulites and reduced the crystallization temperature from that in the base glass. Li+ and Na+ also reduced the temperature at which the microstructural transformation from spherulites to laths took place. Dielectric loss measurements suggest that the effect of the alkali additions on crystallization temperature is due to their concentration in grain boundaries, thereby lowering the viscosity of the remaining glass, and increasing mobility rates.
Densification and Phase Development of Spodumene–Cordierite Glass Powder Mixtures
Authors: Shyu Jiin‐Jyh , Chuang Feng‐Ru
Published: July 2010

The sintering and crystallization of spodumene‐cordierite glass‐ceramics that are made from mixtures of Li2O‐Al2O3‐SiO2 (LAS) and MgO‐Al2O3‐SiO2(MAS) glass powders were investigated. Pure LAS and MAS powders have good sinterability. However, the densification of LAS was drastically reduced when small amounts of MAS were added. When larger amounts of MAS were added, the amount of densification further increased. The decrease in the Li2O content in the LAS glass promoted the densification of the mixed glass samples. The above‐mentioned results can be explained by examining the crystallization temperature, which is influenced by the interactions between the LAS and MAS glass particles. The lower the temperature of crystallization, the less sintering occurred. For the sintered samples, the phase that crystallized from the MAS glass was alpha‐cordierite, and that which crystallized from the LAS glass was ß‐spodumene or high‐quartz solid solution, depending on the Li2O content in the LAS glass.
Heavy‐Water (D2O) Take‐Up‐Induced Lattice Expansion in the High‐Temperature Proton Conductor Ba3Ca1.18Nb1.82O9−δ
Authors: Papathanassopoulos Konstantinos , Wenzl Helmut , Schober Tilman
Published: July 2010

Dimensional changes of the high‐temperature proton conductor Ba3Ca1.18Nb1.82O9−δ, when exposed to D2O vapor, were investigated using length‐change and precision density measurements. Such information is essential for possible applications of proton conductors in solid oxide fuel cells and humidity and hydrogen sensors. A linear increase of the sample lengths with increases in the deuterium content was observed. Comparison of the present D2O data with those that were previously obtained for H2O showed that there was a small isotope effect in the lattice expansion. The fact that the length‐change‐versus‐hydrogen‐isotope‐concentration curves were almost isotope independent supported the validity of the take‐up reaction H2O(g) + VOö+ OxO is an ⇄ 2OHO. In regard to the latter equation, it was found that small islands of silver, palladium, nickel, and platinum act as catalytic promoters of the reaction and lead, for given heavy‐water‐steam exposure conditions, to an increase of water absorption of up to 100%, when compared with samples without the catalytic surface layers.
Cyclic‐Fatigue Crack Initiation and Propagation in Smooth Alumina Specimens
Authors: Kishimoto Hidehiro , Ueno Akira , Matsunaga Atsushi , Kondo Takuya
Published: July 2010

Crack‐initiation sites and crack‐propagation rates of small cracks in smooth specimens of alumina with two grain sizes have been studied. The principal results that have been obtained are as follows: (i) in most cases, the crack‐initiation life comprises a large portion of the fatigue life, (ii) small cracks that are initiated in smooth specimens propagate with stress intensity factors that are much lower than the apparent threshold stress intensity factors (KImax) of artificial cracks that are 200 µm in length, and (iii) the critical crack lengths beyond which the crack‐propagation rate is described uniquely by KImax are 120 µm for fine‐grained alumina and 250 µm for coarse‐grained alumina.
Nanomaterial Deposits Formed by DC Plasma Spraying of Liquid Feedstocks
Authors: Karthikeyan Jeganathan , Berndt Christopher C. , Reddy Sri , Wang Jenn‐Yue , King Alexander H. , Herman Herbert
Published: July 2010

An experimental system consisting of an axial feed plasma gun, a variable‐rate liquid delivery system, a liquid atomizer‐feeder, and a substrate movement and control system was designed and assembled for preparing nanograined ceramic deposits. Sprayed deposits were produced with different spray and sol feed parameters and investigated in both the as‐sprayed and heat‐treated conditions. As‐sprayed deposits were predominately hydroxide phases and were strongly adherent to the substrates. Postspray heat treatment at 873 K led to conversion of the alumina and zirconia deposits to γ‐alumina and tetragonal zirconia phases, respectively. Subsequent heat treatment at 1273 K resulted in densification of the deposits and formation of high‐temperature phases. A small increase in the grain size was observed with heat treatment, but the specimens still retained nanosized grains.
Silicon Carbide Membranes Modified by Chemical Vapor Deposition Using Species of Low Sticking Coefficients in a Silane/Acetylene Reaction System
Authors: Lee Lang‐Luen , Tsai Dah‐Shyang
Published: July 2010

Asymmetric SiC membranes are modified by a SiH4/C2H2/Ar low‐pressure chemical vapor deposition (LPCVD) system at a temperature of 800°C. The pore size of the membrane is reduced to increase its selectivity at the expense of its permeance. The chemical vapor deposition (CVD) modification, using a chamber to minimize the gas‐phase reaction, is superior to that without a chamber, because the film‐forming species of low sticking coefficients can improve the pore size at a lower cost of permeance reduction. With the knowledge of pore structure and CVD kinetics, the alteration of membrane properties can be properly predicted.
Densification of Sol‐Gel‐Derived Mullite Ceramics after Cold Isostatic Pressing up to 1 GPa
Authors: Kamiya Hidehiro , Suzuki Hisao , Ichikawa Takahiro , Cho Yong Ick , Horio Masayuki
Published: July 2010

Molecular‐designed ultrafine mullite precursor powders with a stoichiometric composition were prepared by copolymerization of alkoxides. The precursor powders were calcined in the range from 800° to 1200°C and consolidated by ultra‐high‐pressure cold isostatic pressing up to 1 GPa. Ultrahigh isostatic pressure of 1 GPa led to a closed packing structure in the green compacts. Interaggregate pores in the green compacts were collapsed by the ultrahigh cold isostatic pressure to reduce the pore size below 6 nm. As a result, the maximum density of the green compacts reached 70% of theoretical. These closely packed green compacts of precursor powders with a stoichiometric composition and calcined at relatively low temperatures could be sintered to >95% of theoretical at 1500°C. Relatively low‐temperature sintering below the liquid formation temperature resulted in fine microstructure of the resultant mullite ceramic with a grain size below 300 nm.
Single Crystals of Pb(Mg1/3Nb2/3)O3—35 mol% PbTiO3 from Polycrystalline Precursors
Authors: Li Tao , Scotch Adam M. , Chan Helen M. , Harmer Martin P. , Park Seung‐Eek , Shrout Thomas R. , Michael Joseph R.
Published: July 2010

A potentially more cost‐efficient method of growing single‐crystal relaxor‐based ferroelectric materials has been investigated. Seed single crystals of Pb(Mg1/3Nb2/3)O3(PMN)—;35 mol% PbTiO3(PT) were embedded within polycrystalline powders and annealed at temperatures from 900° to 1200°C. The boundary of the single crystal migrated through the polycrystal matrix under the influence of grain boundary curvature; growth distances of several millimeters were observed, verifying the feasibility of the approach. The grown single crystals exhibited macroscopic cubic growth morphologies with (100) faces. Strain levels as high as 0.68% under an electric field of 30 kV/cm were observed in initial measurements.
Compositional Dependence of Infrared‐to‐Visible Upconversion in Yb3+‐ and Er3+‐Codoped Germanate, Gallate, and Tellurite Glasses
Authors: Murata Takahiro , Takebe Hiromichi , Morinaga Kenji
Published: July 2010

Upconversion fluorescences of the green 4S3/2→4I15/2 and red 4F9/2→4I15/2 transitions of the Er3+ ion are studied for Yb3+‐ and Er3+‐codoped sodium germanate, potassium tantalum gallate, and barium tellurite glasses by InGaAs laser‐diode pumping. The phonon energies of the host glasses are determined by infrared‐reflection measurements. Compositional effects on the Judd—;Ofelt parameters for the Er3+ ion, the spontaneous emission probability (SPE) of the 2F5/2→2F7/2 transition for the Yb3+ ion, and the phonon energy of the glass network are discussed in terms of glass structure. The factors that affect the upconversion fluorescence intensities of the Er3+ ion are discussed, using the phonon energy of the host glass and the SPE for the Yb3+ ion in the germanate, gallate, and tellurite glasses.
Elevated‐Temperature Toughness and Hardness of a Hot‐Pressed Al2O3—WC—Co Composite
Authors: Tai Weon‐Pil , Watanabe Tadahiko
Published: July 2010

The fracture toughness and hardness of an Al2O380WC10Co composite were investigated in air at elevated temperatures. The primary phases in the composite were WC, α‐Al2O3, and Co3W3C, but small amounts of Co and C (graphite) appeared at elevated temperatures, related to decomposition of the Co3W3C phase. The fracture toughness of the composite was constant with increasing temperature up to 330°C and then increased in the range 400° to 550°C. A transition of brittle to ductile behavior occurred at about 700°C. The enhancement of fracture toughness at elevated temperature is attributed to the decomposition of Co3W3C to Co and C, and enhanced crack deflection and bridging. Decreases in hardness with increasing temperature are attributed to the softening of WC matrix and decomposition of Co3W3C.
X‐ray Photoemission Spectroscopy (XPS) and Thermally Stimulated Current (TSC) Studies on the Resistance Degradation of Iron‐Doped Titania Ceramics
Authors: Sheng Jianxin , Fukami Tatsuo , Karasawa Junichi
Published: July 2010

An anomalous increase of current with time has been found in iron‐doped titania ceramics that have been subjected to a constant field. The result of thermally stimulated current analysis shows a peak at a temperature of 170°–180°C, which increases because of the depolarization of oxygen vacancies. X‐ray photoemission spectroscopy indicates that an electrical stress results in an electrochemical reduction inside the specimen, particularly on the cathodic side. These results reinforce the viewpoint that the space charge that is responsible for the anomalous current results from a blockage of the O2(g)/O2−(s) ion transfer at the cathode.
Eutectic Precipitation of the Spinel Solid Solution‐Yttrium Aluminum Garnet (YAG) System
Authors: Wang Shuqiang , Akatsu Takashi , Tanabe Yasuhiro , Nakagawa Zenbe‐e , Yasuda Eiichi
Published: July 2010

Isothermally solidified microstructures of the alumina‐rich spinel solid solution—yttrium aluminum garnet (YAG) composite was investigated. It was identified that the eutectic phase relation of the YAG—spinel system could be maintained with the formation of an alumina‐rich spinel solid solution, despite the significant change in eutectic compositions. In addition, divorced eutectic precipitates that have a spinel‐rich composition were observed surrounding the YAG dendrites.
Early‐Stage Thermal Oxidation of Carbothermal β‐Sialon Powder
Authors: Shimada Shiro , Aoki Takenori , Kiyono Hajime , MacKenzie Kenneth J. D.
Published: July 2010

Early‐stage thermal oxidation (below 1100°C) of carbothermally synthesized β‐sialon powder was monitored by X‐ray powder diffraction, solid‐state 29Si and 27Al MAS NMR spectroscopy, and thermogravimetry. No crystalline oxidation products were detected by XRD but 29Si and 27Al MAS NMR indicated the early formation of amorphous silica, followed by the formation of an amorphous aluminosilicate with an atomic environment similar to that of mullite. The initial oxidation was described by a linear kinetic law with an activation energy of 170 kJmol−1, suggesting the rate‐limiting step to be due to dissolution of O2 in an amorphous silica surface layer on the β‐sialon particles.
Creep Mechanisms in Multiphase Ceramic Materials
Authors: Wilkinson David S.
Published: July 2010

Hard, refractory particles long have been added to ceramic materials to impart creep resistance. The nature of such particles and the volume fraction added may vary widely between different systems. As a result, a rich variety of creep behavior and of attendant mechanisms is found. A critical survey is presented of the experimental data and of the models developed to rationalize them. Particular attention is paid to three materials systems: whisker‐reinforced ceramics (e.g., SiC‐whisker‐reinforced Al2O3); infiltrated powder compacts (e.g., siliconized SiC); and glass‐bonded ceramics (e.g., sintered Si3N4). A microstructural classification system is presented based on the nature of the network developed by the hard particles. This is useful as a guideline in developing mechanistic models. The current state of such models is reviewed critically. Although models for the high‐ and low‐volume‐fraction regions are well advanced, those applicable at intermediate volume fractions—relevant to whisker reinforcement for example—remain at an early stage. Finally, the experimental data on a range of materials are reviewed and classified. These data are compared with the models.
Microstructure and Chemistry of Intergranular Glassy Films in Liquid‐Phase‐Sintered Alumina
Authors: Brydson Rik , Chen Shih‐Chieh , Riley Frank L. , Milne Steve J. , Pan Xiaoqing , Rühle Manfred
Published: July 2010

Analytical and high‐resolution transmission electron microscopies were used to study the structure and chemistry of two‐grain boundaries and three‐grain junctions in polycrystalline alumina sintered with additions of between 0 and 10 wt% calcium silicate. Addition of calcium silicate greatly aided full densification and resulted in the presence of a continuous, amorphous grain‐boundary film at the majority of the two‐grain boundaries, the thickness of which was independent of the bulk level of additive. The chemistry of the glass at the grain boundaries and the three‐grain junctions was notably different. The grain boundaries showed strong segregation of calcium, whereas both silicon and calcium appeared to favor triple pockets and larger‐volume facets at the grain boundaries. Grain‐triple‐pocket interfaces also showed segregation of calcium. The overall extent of segregation appeared to be independent of the additive level. The amorphous grain‐boundary film was of nominal composition CaO6Al2O3 and contained predominantly octahedrally coordinated aluminum within the glass. The triple pockets were generally of a composition within the primary‐phase field of anorthite and contained tetrahedrally coordinated aluminum and silicon.
Spectroscopic Studies on the Localization of Vanadium(IV) in Vanadium‐Doped Zircon Pigments
Authors: Ocaña Manuel , González‐Elipe Agustín R. , Orera Victor M. , Tartaj Pedro , Serna Carlos J.
Published: July 2010

The origin of the blue color observed for vanadium‐doped zircon powders that have been prepared either in the presence or the absence of fluxes (NaF) has been investigated by analyzing the localization and distribution of the vanadium species in the zircon matrix. In both cases, the unit‐cell parameters determined from the X‐ray diffraction patterns of the samples and the results obtained from X‐ray absorption (X‐ray absorption near‐edge structure and extended X‐ray absorption fine structure), infrared, and electron spin resonance spectroscopies indicated that V4+ cations form a solid solution with the zircon lattice, substituting for both Si4+ and Zr4+ cations, although to a greater extent for the former. These vanadium cations are heterogeneously distributed in the zircon matrix, being mainly located in the outer layers of the particles in two different situations: “aggregated” in nearby lattice positions with V4+‐V4+ distances (dV‐V) of <8 Å (0.8 nm), and isolated with respect to other V4+ cations (dV‐V > 8 Å). The strongest blue color that is observed for samples prepared in the presence of NaF seems to be due to the higher amount of V4+ cations incorporated to the zircon lattice, because this flux agent does not have any structural role.
Preparation of a Barium Titanate‐Dispersed‐Magnesia Nanocomposite
Authors: Nagai Toru , Hwang Hae Jin , Yasuoka Masaki , Sando Mutsuo , Niihara Koichi
Published: July 2010

Ceramic nanocomposites with a perovskite‐type ferroelectric dispersoid were studied, to introduce ferroelectricity into structural ceramics. Barium titanate (BaTiO3) was found to be phase compatible with magnesia (MgO) during sintering, and a MgO matrix/BaTiO3 nanocomposite was successfully fabricated by a conventional powder mixing and sintering method. The mechanical strength of the nanocomposite was not degraded, although weak BaTiO3 was incorporated into the composite. The BaTiO3 dispersoid was tetragonal or possibly orthorhombic, although the tetragonality, c/a, was decreased from the starting powder.
Hydrothermal Synthesis of Interstratified Lizardite/Saponite
Authors: Torii Kazuo , Onodera Yoshio , Hayashi Hiromichi , Nagase Takako , Iwasaki Takashi
Published: July 2010

A novel interstratified lizardite/saponite which has never been found in nature is hydrothermally synthesized from uniform Si‐Al‐Mg gels at 300°C. The stacking ratios of lizardite layer to saponite layer in the structure are designed between 3/1 and 1/3. These materials give partially ordered X‐ray diffraction patterns depending on the layer composition. The lattice‐fringe image of the L/S= 1/1 sample shows that platelet particles have a thickness of 17.5 Å consisting of a lizardite layer (7.5 Å) and a dehydrated saponite layer (10.0 Å). They can disperse in water like smectite.
Three‐Dimensional Computer Simulation of Ferroelectric Domain Formation
Authors: Hu Hong‐Liang , Chen Long‐Qing
Published: July 2010

Three‐dimensional (3‐D) computer simulations of ferroelectric domain formation and evolution were performed, using a computer simulation model based on the time‐dependent Ginsburg‐Landau equations. A cubic‐to‐tetragonal ferroelectric phase transition is considered. It is shown that the initial stage of the transition during the annealing of a quenched cubic paraelectric phase involves the nucleation and growth of the ferroelectric domains, followed by the domain coarsening leading to the formation of 90° and 180° domain structures. Part of the 3‐D results reported here confirm our conclusions made earlier for the two‐dimensional (2‐D) case, namely, the nonlocal elastic interactions are critical to the formation of twin structure and the dipole‐dipole interactions are responsible for the head‐to‐tail arrangements of dipoles at twin boundaries. In contrast to our previous work, and others; the effect of the depolarization energy was explicitly incorporated into the simulation model. It is found that when there are no surface charges to compensate the Lorentz field due to the polarization charges, and if the system is mechanically clamped, both 90° and 180° domains are thermodynamically stable.
Thermodynamics of Oxides with Substitutional Disorder: A Microscopic Model and Evaluation of Important Energy Contributions
Authors: Ceder Gerbrand , Kohan Adrian F. , Aydinol Mehmet K. , Tepesch Patrick D. , van der Ven Anton
Published: July 2010

The first‐principles calculation of finite‐temperature phase stability and thermodynamic properties of multicomponent oxides presents a significant challenge. The time scale on which substitutional disorder occurs prevents the use of standard simulation methods, and a correct description of entropic effects requires that excitation energies can be calculated accurately on the scale of kBT. A model is presented in which substitutional disorder is parameterized with a cluster expansion. The thermodynamics of this model can be easily obtained with lattice model statistical mechanics. The only input required to the procedure is a description of bonding in the system, which is used to calculate the energy of ordered ionic configurations. This method is applied to the CaO‐MgO, Gd2O3‐ZrO2, CaO‐ZrO2 systems, and to LixCoO2 (x between 0 and 1) electrodes for rechargeable lithium batteries. In almost all cases, a correct description of the charge state of the ions is essential to obtain the proper mixing behavior. Only for a highly ionic material such as CaO‐MgO does the charge state of the ions remain unvaried upon mixing. We find that approximate energy models that employ fixed charges will tend to overestimate the energy required for mixing, hence the order‐disorder transition temperature.
Coexistence of Relaxor and Normal Ferroelectric Phases in Morphotropic Phase Boundary Compositions of Lanthanum‐Modified Lead Zirconate Titanate
Authors: Gupta Surya M. , Li Jie‐Fang , Viehland Dwight
Published: July 2010

Hot‐stage transmission electron microscopy studies of lanthanum‐modified lead zirconate titanate (Pb1‐xLax‐(Zr0.53Ti0.47)1‐x/4O3 (PLZT 100x/53/47) have been performed for compositions close to the morphotropic phase boundary (MPB). These studies have revealed the coexistence of relaxor and normal ferroelectric phases. Lanthanum substitution disrupts long‐range ferroelectric order, resulting in short‐range polar ordering. Investigations also have been performed using dielectric spectroscopy, electrically induced polarization, and strain methods. Three phases have been found for 10/53/47: a low‐temperature tetragonal phase, a high‐temperature cubic phase, and an intermediate‐temperature pseudocubic phase that exhibits relaxor ferroelectric behavior. Induced strain studies of 10/53/47 show a gradual change from butterfly‐shaped to slim‐quadratic loops with increasing temperature. In addition, the remanent strain decreases with increasing temperature, and reversible strain shows a peak at 80°C that corresponds to the appearance of intermediate phase.
Calculation of Grain‐Boundary Bonding in Rare‐Earth‐Doped β‐Si3N4
Authors: Nakayasu Tetsuo , Yamada Tetsuo , Tanaka Isao , Adachi Hirohiko , Goto Seishi
Published: July 2010

First‐principles molecular orbital calculations are performed by the discrete variational Xalpha method using model clusters of rare‐earth‐doped β‐Si3N4 and the interface between prismatic planes of β‐Si3N4 and intergranular glassy films. On the basis of the total overlap population of each cluster, the rare‐earth ions are implied to be stable in the grain‐boundary model, while they are not stable in the bulk model. These results are consistent with experimental observations showing significant segregation of Ln3+ ions at the grain boundary and no solubility of Ln3+ into bulk β‐Si3N4. Grain‐boundary bonding is weakened with an increase of the ionic radius of the rare‐earth ions, which provides a reasonable explanation for the ionic size dependence of the crack propagation behaviors as well as the growth rate of the prismatic plane in the rare‐earth‐doped β‐Si3N4 during liquid‐phase sintering.
Microstructural Study of the Hot Corrosion of a Calcium Aluminosilicate Glass‐Ceramic and a Si‐C‐O‐Fiber‐Reinforced Calcium Aluminosilicate Matrix Composite via Sodium Sulfate in Air and Argon at 900°C
Authors: Kumar Atul , Fox Alan G.
Published: July 2010

The hot corrosion of a calcium aluminosilicate (CAS) glass‐ceramic and a composite of CAS matrix that has been reinforced with Si‐C‐O (Nicalon) fiber has been investigated by X‐ray diffractometry, scanning electron microscopy, and transmission electron microscopy. Samples of the monolithic CAS and the Si‐C‐O‐CAS composite were subjected to corrosion using liquid sodium sulfate at 900°C for 50 h in air and argon environments. The monolithic and composite samples both were corroded by sodium sulfate, and corrosion damage in the composites was more severe than in the monolithic CAS, irrespective of the gaseous environment. The increased corrosion damage in the composites was due to the presence of Si‐C‐O fibers, which changes the mechanism of corrosion. The corrosion products in monolithic CAS were different from those in the composites; this disparity was also due to the presence of the fibers in the composite. The corrosion zones in all the samples were severely cracked, and the cracks extended into the unaffected regions of the samples. Mechanisms of hot corrosion have been proposed and discussed for both the monolithic and composite samples.
Characteristics of PbO–BiO1.5–GaO1.5 Glasses Melted in SnO2 Crucibles
Authors: Cerri José A. , Santos Iêda M. G. , Longo Elson , Leite Edson R. , Lebullenger Ronan M. , Hernandes Antonio Carlos , Varela José A.
Published: July 2010

PbO‐BiO1.5‐GaO1.5‐based glasses are good candidates for optical applications, because of some of their interesting characteristics, such as high refraction indices and high transmission in the ultraviolet (UV), visible (VIS), and infrared (IR) regions. A limited stage in the processing of these glasses is the corrosion that is caused by the melt in all currently used conventional crucibles, such as noble metals (platinum or gold) and Al2O3. The absorption of crucible material by the glass composition may reduce the transmission level, the cutoff in the UV‐VIS, and IR regions, and the thermal stability. In this study, a SnO2 crucible has been tested for PbO‐BiO1.5‐GaO1.5 molten glass. Optical and thermal analyses show, in some cases, advantages over the use of platinum and Al2O3 crucibles. A visible cutoff value of 474 nm has been measured, and a longer melting time (850°C for 4 h) results in a significant reduction of the O‐H absorption band at 3.2 μm.
Curie Temperature Anomaly in Lead Zirconate Titanate/Silver Composites
Authors: Hwang Hae Jin , Nagai Toru , Ohji Tatsuki , Sando Mutsuo , Toriyama Motohiro , Niihara Koichi
Published: July 2010

The Curie temperatures of lead zirconate titanate‐based (PZT‐based) composites that were incorporated with silver particles were evaluated as a function of the silver content. Although the substitution of the silver ion has been considered to decrease the Curie temperature, PZT/silver composites exhibited higher Curie temperatures than those of monolithic PZT ceramics. It was found that the Curie temperature gradually increased as the silver content increased. It was suggested that the observed Curie temperature anomaly resulted from the relaxation of transformation‐induced internal stress by intergranular silver particles.
Influence of Hydrostatic Pressure on the t→o Transformation in Mg‐PSZ Studied by In Situ Neutron Diffraction
Authors: Kisi Erich H.
Published: July 2010

The influence of hydrostatic pressure on the t→o transformation in Mg‐PSZ has been studied using a series of neutron diffraction measurements on samples cooled to cryogenic temperatures. A hydrostatic pressure of 400 MPa led to the t→o onset temperature being depressed by 75 K, and the yield of o phase at the base temperature (40 K) being halved. This lends support to the notion that the t particles in this system are predisposed to undergo the t→o transformation by thermal expansion mismatch stresses. It is estimated from thermal expansion data that the mismatch stresses could be as high as 760 MPa along the c‐axis of the tetragonal precipitates and that the mismatch strains are qualitatively very similar to the transformation strains for the t→o transformation. It is proposed that the critical factor in determining the transformation path (t→o vs t→m) is the presence, in multiphase systems, of a coherent interface between the t phase and the surrounding phases.
Preparation of Fibrous, Porous Hydroxyapatite Ceramics from Hydroxyapatite Whiskers
Authors: Suchanek Wojciech L. , Yoshimura Masahiro
Published: July 2010

Hydroxyapatite (HAp) whiskers have been used to prepare fibrous, porous HAp ceramics. The fibrous microstructure was retained in all cases after hot‐pressing the HAp whiskers at 800‐900°C (1 h, 30 MPa). The fracture path in the fibrous, porous HAp ceramics was partially intergranular, indicating the occurrence of crack deflection, bridging, and pull‐out effects. When the whiskers were hot‐pressed at 1000‐1100°C (1 h, 30 MPa), only large equiaxed grains were present in the HAp ceramics; thus no toughening occurred. When nonstoichiometric HAp whiskers were used to fabricate a porous body, β‐TCP precipitated on the whisker surface without destroying the fibrous microstructure. Sintering the HAp whiskers is thus an easy way for in situ fabrication of HAp/β‐TCP fibrous, porous materials with a controlled biodegradation rate.
Effects of Plasma Bombardment on the Initial Growth of (Ba,Sr)TiO3 Films and Their Properties
Authors: Tsai Wen‐Chou , Tseng Tseung‐Yuen
Published: July 2010

Magnetron‐sputtered (Ba,Sr)TiO3 films were grown on Pt/SiO2/Si and MgO substrates that were located inside and outside the plasma region. The effects of plasma bombardment on the properties of the grown films were observed. The films that were grown outside the plasma region exhibited better crystallinity, higher dielectric constants, higher electrical conductivity, and rougher surfaces than those that were grown inside the plasma region. However, plasma bombardment did not affect the initial growth of the films on Pt/SiO2/Si or MgO substrates, as explored by atomic force microscopy. The films that were grown on Pt/SiO2/Si showed island growth characteristics, whereas those that were grown on MgO substrates revealed layer‐by‐layer growth characteristics. Possible explanations for the different growth mechanisms are provided.