bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of the Interparticle Pair Potential on the Rheological Behavior of Zirconia Powders: I, Electrostatic Double Layer Approach
Authors: Klein Sascha , Fisher Matthew , Franks George , Colic Miroslav , Lange Fred
Published: July 2010

Aqueous slurries containing 20 vol% ZrO2 powder doped with 3 mol% Y2O3 were prepared by first dispersing the powder at pH 11, then adding 0.1M to 1.0M tetramethylammonium chloride (TMACl), or 1.0M of TPACl, CsCl, and LiCl to produce different, weakly attractive particle networks. The particle pair potentials in the slurries were investigated by viscosity versus shear rate measurements. Slurries exhibited increasing viscosities (at a given shear rate) with increasing salt concentration and decreasing (unhydrated) counterion size. The viscosities for these weakly attractive networks were intermediate to dispersed (pH 11 without added salt) and flocced (isoelectric point, pH 7.5) slurries. Cylindrical bodies were consolidated from these slurries by pressure filtration at different applied pressures. The bodies consolidated from slurries formulated with TMACl had the highest packing densities relative to those consolidated from a flocculated slurry, but the relative densities were much lower than those achieved from bodies consolidated from a dispersed slurry. The plastic or brittle nature of these bodies was determined in uniaxial compression. Powder compacts consolidated from flocced slurries and slurries coagulated with 1M TMACl, CsCl, and LiCl showed plastic behavior for filtration pressures ≤7.5 MPa. Results for ZrO2 will be compared with those previously obtained for Al2O3, which produces plastic, consolidated bodies over a much broader range of slurry conditions.
Niobium Doping and Dielectric Anomalies in Bismuth Titanate
Authors: Shulman Holly S. , Damjanovic Dragan , Setter Nava
Published: July 2010

A study of the complex permittivity in bismuth titanate was conducted to reveal the nature of an anomaly in the real part of the permittivity, which occurs below the Curie temperature. This anomaly is frequency dependent and is caused by a combination of two relaxation phenomena that appear in the imaginary part of the permittivity. One of the relaxations showed classic characteristics of an ion‐jump process. Niobium doping suppressed this relaxation and eliminated the nonferroelectric anomaly in permittivity. Niobium is proposed to affect the ion‐jump relaxation through a decrease in the concentration and possibly the mobility of oxygen vacancies.
Thermal Conductance of Delamination Cracks in a Fiber‐Reinforced Ceramic Composite
Authors: McDonald Kathleen R. , Dryden John R. , Majumdar Arun , Zok Frank W.
Published: July 2010

The thermal conductance of delamination cracks in a unidirectionally reinforced ceramic composite is investigated. A phase‐sensitive photothermal technique is used to measure the crack conductance in situ under load. Special emphasis is given to the effects of the local crack opening displacement (δ). A crack conductance model that considers the contributions from both the air and the fibers within the crack is developed and compared with the measurements. Despite considerable scatter in the experimental data, the model adequately predicts the increased conductance that is associated with fiber bridging, as well as the overall trend that is observed with δ.
Apatite Formation in the CaO–PbO–P2O5–H2O System at 23°± 1°C
Authors: Bothe James V. , Brown Paul W.
Published: July 2010

Lead is a toxic heavy metal that is commonly used to manufacture products such as storage batteries and electroceramics. In an effort to minimize the health risks to humans, the low‐cost stabilization of lead via its incorporation into the apatite crystal structure has been explored. Therefore, apatite formation in the quaternary system CaO–PbO–P2O5–H2O at room temperature (23°± 1°C) and atmospheric pressure from PbO, CaHPO4, Ca4(PO4)2O, and H3PO4 was studied. Apatites were prepared via precipitation from aqueous‐based mixtures with a constant (Ca + Pb):P molar ratio of 1.67. Aqueous mixtures that contained up to 1 mol of PbO (massicot) per mole of apatite (Ca10−xPbx(PO4)6(OH)2) resulted in the precipitation of weakly crystalline Ca10(PO4)6(OH)2 as the predominant phase. Highly crystalline Pb10(PO4)6(OH)2 was formed from mixtures that contained 8–9 mol of PbO per mole of apatite. Intermediate proportions of lead oxide, which entailed 4.5–7 mol of PbO per mole of apatite, produced a stable quaternary apatite phase of moderate crystallinity, with an approximate composition of Ca5Pb5(PO4)6(OH)2. The lattice parameters of this quaternary apatite were calculated using a least‐squares refinement program and other existing X‐ray diffraction software. Experimental observation, along with computer modeling of the solution chemistry, enabled the mechanism of apatite formation to be established. Dissolution of lead oxide and calcium‐bearing minerals, such as monetite (CaHPO4), with the aid of H3PO4, resulted in the precipitation of lead‐rich apatites. This phenomenon was followed by their slow conversion to the stable quaternary apatite (Ca5Pb5(PO4)6(OH)2).
Monitoring of Hydration of White Cement Paste with Proton NMR Spin–Spin Relaxation
Authors: Greener Jessie , Peemoeller Hartwig , Choi Changho , Holly Rick , Reardon Eric J. , Hansson Carolyn M. , Pintar Mik M.
Published: July 2010

By monitoring the free induction decay and spin–echo envelope (acquired with the Meiboom–Gill modified Carr–Purcell pulse sequence), during hydration of white cement paste, information about growth patterns of various cements is obtained. In particular, the secondary hydration water is characterized through direct observation, and a relatively immobile, near solidlike water phase, observed for the first time in hydrating cement, is discussed.
ac Impedance Study of Zirconia Doped with Yttria and Calcia
Authors: Gong Jianghong , Li Ying , Zhang Zhongtai , Tang Zilong
Published: July 2010

The ionic conductivity in the system (1 − 0.08x− 0.12y)ZrO2–0.08xY2O3–0.12yCaO (where x+y= 1 and y= 0–1) has been investigated using the complex impedance technique at 523–973 K. Doping CaO in the ZrO2–Y2O3 system may result in an increase in the activation energy for lattice conduction and depress the grain‐boundary effect on conduction. Analysis of the temperature dependence of the lattice conductivity, according to the familiar Arrhenius equation, predicts that the examined ternary system may exhibit greater lattice conductivity than the ZrO2–Y2O3 binary system at higher temperatures. Preliminary explanations for these experimental phenomena and predictions also have been presented.
Electric‐Field‐Induced Crack Growth Behavior in PZT/Al2O3 Composites
Authors: Tajima Ken‐ichi , Hwang Hae Jin , Sando Mutsuo , Niihara Koichi
Published: July 2010

Hard lead zirconate titanate (PZT) and PZT/Al2O3 composites were prepared and the alternating‐electric‐field‐induced crack growth behavior of a precrack above the coercive field was evaluated via optical and scanning electron microscopy. The crack extension in the 1.0 vol% Al2O3 composite was significantly smaller than that in monolithic PZT and the 0.5 vol% Al2O3 composite. Secondary‐phase Al2O3 dispersoids were found both at grain boundaries and within grains in the composites. A large number of dispersoids were observed at the grain boundaries in the 1.0 vol% Al2O3 composite. It appears that the Al2O3 dispersoids reinforce the grain boundaries of the PZT matrix as well as act as effective pins against microcrack propagation.
Localized Densification during the Compaction of Alumina Granules: The Stage I—II Transition
Authors: Kong Consuelo Margarita , Lannutti John J.
Published: July 2010

Tungsten marker layers and X‐ray computed tomography were used to monitor the compaction of spray‐dried alumina. Local density changes and compaction curves show that the well‐known Stage I—II transition indicates an alteration in the direction of transmitted pressure through the uppermost layer. Stage I pressure is dispersed in local agglomerate contacts until “pockets” of low density are eliminated. In Stage II, these deformed/fragmented agglomerates behave as a continuous body and interact with wall friction to transmit pressure nonuniformly into the bulk. Discrete element simulations reproduced the compaction curves and provided clear explanation of the density distribution development.
Deposition of Nano‐Size Titania—Silica Particles in a Hot‐Wall CVD Process
Authors: Lu Shih‐Yuan , Chen Shan‐Wei
Published: July 2010

The deposition of nano‐size titania—silica particles is carried out in a hot‐wall CVD reactor by using two premixed precursors, titanium tetraisopropoxide (TTIP) and tetraethyl orthosilicate (TEOS). The deposition occurs mostly in two regions, one near the reactor entrance and the other near the reactor exit. Deposits collected near the reactor entrance are densely packed micrometer‐size aggregates/particles of good adhesion to the substrate, while those near the reactor exit are loosely packed nano‐size particles with a poor adhesion to the substrate. It is conjectured that the more reactive TTIP reacts first and produces TiO2 particles later covered by SiO2 formed via a catalytic surface reaction of the less reactive TEOS on TiO2 particle surfaces. The presence of surface SiO2 retards the growth of TiO2 particles, leading to deposits formed by micrometer‐size aggregates containing nano‐size primary particles of 30 to 40 nm in the first deposition region. With less or no SiO2 present on TiO2 particle surfaces, the deposits formed in the first deposition region are densely packed micrometer‐size particles. The Ti/Si ratio of the produced particles, for a furnace temperature of 750°C, increases with increasing TTIP/TEOS concentration ratio, and is lower than the Ti/Si ratio of the incoming reactant stream. The Ti/Si ratio of the particles is also found to decrease with increasing furnace temperature.
Comparison of Ion Irradiation Effects in Silicon‐Based Preceramic Thin Films
Authors: Pivin Jean C. , Colombo Paolo , Sorarù Gian D.
Published: July 2010

Thin films of polymers (polysiloxanes, polycarbosilanes, and polysilazanes) and alkoxide‐derived siloxane gels, precursors for SiC, SiCN, SiOC, and SiOBC ceramics, were irradiated with increasing fluences of C or Au ions to study the kinetics of their conversion into ceramics. Ion beam analyses showed that the main effect of irradiation on the composition of the films is the selective release of H2 by radiolysis. During subsequent high‐temperature annealing of films converted as much as possible by irradiation, COx, CHx, or silane molecules do not evolve, contrary to what is observed during the pyrolysis of unirradiated precursor films. According to Raman analyses, a large proportion of the carbon atoms segregate into clusters after irradiation and in films converted by direct pyrolysis (or combined treatments). However, carbon particles formed during irradiation are more diamond‐like, affording films with 2—3 times higher hardness, as shown by nanoindentation tests. In both types of ceramics (SiC or SiOC), the optimal properties (hardness, thermal stability, and photoluminescence) associated with C segregation are obtained for a C/Si ratio of the order of 1. Boron addition is detrimental to hardening of SiOC glasses, in contrast to nitrogen.
Oxidation of Hafnium Carbide and Titanium Carbide Single Crystals with the Formation of Carbon at High Temperatures and Low Oxygen Pressures
Authors: Shimada Shiro , Yunazar Fahmi , Otani Shigeki
Published: July 2010

The isothermal oxidation of the 200 face of HfC and TiC single crystals was performed at temperatures of 700°—1500°C and at oxygen pressures of 0.08—80 kPa for 4 h. The weight gain by oxidation of the two crystals was followed using an electromicrobalance. A polished cross section of the oxidized crystals was observed using backscattered electron imaging in a scanning electron microscope. Quantitative chemical analysis for Hf, Ti, O, and C was performed by wavelength‐dispersive X‐ray microanalysis. The early‐stage oxidation kinetics of HfC crystals were described by the contracting volume equation, followed by slowed reaction in the latter stage, whereas the same equation was applied to the oxidation of TiC over the entire oxidation time. The preferred {200} orientation of monoclinic HfO2 occurred on the oxidized surface of the HfC crystal. The oxide scale on the HfC crystal consisted of a compact and pore‐free black inner scale (zone 1) and a white/gray outer scale that contained many pores (zone 2). Zone 1 contained ∼25 at.% unoxidized carbon, and zone 2 contained 6—11 at.% carbon. The oxide scale of TiC was composed of an inner dense lamella subscale (zone 1) with a carbon content of 7—23 at.% and an outer region with laminations that was separated by pores and cracks (zone 2). The Ti3O5 phase, which exhibits a strong 020 line, was formed at depths of ≥40 μm in the scale obtained at 1500°C. Treatment with a concentrated HF solution allowed zone 1 to be separated from the HfC crystal in the form of carbon‐containing films, which were characterized using Raman spectroscopy and transmission electron microscopy.
Compaction and Sintering Behavior of Bimodal Alumina Powder Suspensions by Pressure Filtration
Authors: Shi Jian‐Lin , Zhang J. D.
Published: July 2010

The compaction behavior of fine alumina powders with different particle sizes or bimodal particle‐size distributions that are undergoing pressure filtration was investigated. Three alumina powders—average particle sizes of 0.2—0.86 μm—were compacted to a solids fraction of 62—65 vol% from suspensions at pH 3, which was the pH level at which the suspensions showed their lowest viscosity. When the powders of different average sizes were mixed, the suspensions showed better flowability, and the lowest viscosity was obtained when the fraction of fines was ∼30 vol% and pH = 3. The mixed‐sized powder suspensions were compacted to higher density than the suspensions of unmixed fine or coarse powders, and the maximum density was obtained for mixed suspensions that had the lowest viscosity, despite the different particle‐size ratio. Maximum densities of 72.5% and 75.0% were attained when the size ratios were 2 and 5, respectively. The compacts that were pressure‐filtered from mixed suspensions exhibited a single‐peaked pore‐size distribution and a homogeneous microstructure, whereas the pore‐size distributions of dry‐pressed compacts were double‐peaked. The sintering behavior of the compacts that were pressure‐filtrated from bimodal powders exhibited significantly better sinterability and much‐less linear shrinkage than the coarser powders and the dry‐pressed powder compacts.
Calculation of the Composition Profile of a Functionally Graded Material Produced by Centrifugal Casting
Authors: Biesheuvel P. Maarten , Verweij Henk
Published: July 2010

Functionally graded materials have designed inhomogeneous distributions of different components on the scale of the material. They can be made by suspension processing, in which particles are stacked in a controlled manner. Segregation effects can be used to obtain the required gradient if the particles in suspension have different velocities. A model is derived for the composition profiles that develop as a result of these effects. The model can be used to determine the most suitable process conditions. The outcome of the model shows fair agreement with experiments found in the literature in which an Al2O3/ZrO2 composite has been produced by uniaxial centrifugal casting.
Microstructural Characterization of ZrO2 Particles Prepared by Reaction of Gaseous ZrCl4 with Fe2O3
Authors: Bohé Ana E. , Andrade‐Gamboa Julio , Pasquevich Daniel M. , Tolley Alfredo J. , Pelegrina Jorge L.
Published: July 2010

The microstructure of ZrO2 fine particles produced by a novel synthesis method at 450° and 950°C has been studied. The fundamentals of the synthesis method, which involves both chemical and diffusion phenomena, are presented. The method is based on mass transport through the gaseous phase between metallic zirconium and Fe2O3 powder. The mass‐transporting chemical species are zirconium and iron chlorides. This article focuses on the microstructure and structure of ZrO2 particles formed by the reaction between gaseous ZrCl4 and solid Fe2O3, which is a relevant reaction step that occurs during the synthesis process. The resulting ZrO2 crystals grown on Fe2O3 particles have been analyzed using transmission electron microscopy. Microstructural characterization has been complemented by X‐ray diffractometry analysis. Tetragonal‐ZrO2 is produced at 450°C and monoclinic‐ZrO2 single crystals are produced at 950°C.
Chemical Diffusivity of BaTiO3−δ: IV, Acceptor‐Doped Case
Authors: Song Chang‐Rock , Yoo Han‐Ill
Published: July 2010

The chemical diffusivity of 1.8 mol% aluminum‐doped BaTiO3−δ was measured on single‐crystal specimens, as a function of ambient oxygen partial pressure, in the range 10−18 atm ≤PO2≤ 1 atm and at temperatures of 800°≤T≤ 1100°C, via a conductivity‐relaxation technique. As in the polycrystalline, undoped BaTiO3−δ described in Part II of this work, the chemical diffusivity exhibited a maximum, of thermodynamic origin, approximately at the stoichiometric composition (δ= 0). The measured diffusivity was analyzed, based on the defect structure proposed and Wagner's classic theory of chemical diffusion, and the mobilities of the electrons and holes, as well as all of the relevant defect‐equilibrium constants, then were evaluated with no prior assumptions. The evaluated parameters were compared with those for the undoped BaTiO3−δ.
2.0 μm Emission Properties and Energy Transfer between Ho3+ and Tm3+ in PbO—Bi2O3—Ga2O3 Glasses
Authors: Shin Yong Beom , Lim Hyung Tack , Choi Yong Gyu , Kim You Song , Heo Jong
Published: July 2010

Emission properties of 2.0 μm fluorescence and the energy transfer between Ho3+ and Tm3+ in 57PbO·25Bi2O3·18Ga2O3 (mol%) glass codoped with Ho3+ and Tm3+ were investigated. Cross‐relaxation rates in Tm3+ increased approximately 5 times when the Tm2O3 concentration was increased from 1.0 to 1.5 wt%. Coefficients of the forward Tm3+→ Ho3+ energy transfer were about 15 times larger than those of the Tm3+← Ho3+ backward transfer. Analysis of the energy transfer and gain spectra indicated that the highest gain at the 2.0 μm wavelength region could be achieved from the glass with 1.5 wt% of Tm2O3 and 0.3 wt% of Ho2O3.
New Method for Determining the Nucleation and Crystal‐Growth Rates in Glasses
Authors: Ray Chandra S. , Fang Xiangyu , Day Delbert E.
Published: July 2010

The rates for nucleation (I) and crystal growth (U) for a lithium disilicate (Li2O·2SiO2, LS2) glass were determined, as a function of temperature, using a new differential thermal analysis (DTA) technique. This technique requires in situ nucleation and crystal‐growth heat treatment of a small amount of powdered sample inside the DTA apparatus, which then are followed by a DTA scan at a constant heating rate. The I and U values that have been determined at selected temperatures for the LS2 glass are in excellent agreement with those reported in the literature. The technique also has been used to determine the concentration of quenched‐in nuclei in LS2 glasses prepared from melts that have been quenched at different rates, which are in reasonable agreement with those estimated from theoretical considerations. This new DTA technique is less tedious, requires a smaller amount of sample, and is at least 10 times faster than the conventional methods that have been used to measure I and U. Also, no special sample preparation, other than simply grinding and screening the glass to a particle size that is suitable for use, is required in this technique, whereas grinding, polishing, or etching is required in conventional methods. The excellent agreement in the I or U values that have been determined for the LS2 glass via the present and conventional methods demonstrates the accuracy, validity, and usefulness of this DTA method for rapid determination of the nucleation and crystal‐growth rates in glasses.
Role of Lamellae Morphology on the Microstructural Development and Mechanical Properties of Small‐Particle Plasma‐Sprayed Alumina
Authors: Trice Rodney W. , Faber K. T.
Published: July 2010

The influence of spray parameters on the microstructure and flexural strength of plasma‐sprayed alumina was investigated. Coatings were applied using a small‐particle plasma spray (SPPS) method, which is a recently patented process that allows submicrometer‐sized powders to be sprayed. Using identical starting powders, coatings that were produced using two distinctly different spray conditions exhibited significant differences in both microstructure and strength. Scanning electron microscopy investigations of single lamellae (or splats) revealed that, for one spray condition, melted alumina particles will splash when they contact the substrate. The morphology of the splats that comprised the subsequent layers of the coating also were highly fragmented and thinner than lamellae formed under “nonsplashing” spray conditions. The surface roughness was strongly dependent on the morphology of the lamellae; increased roughness was noted for fragmented splats. Thick coatings that were comprised of splashed splats developed a unique microstructural feature that was responsible for the observed increase in roughness. These microstructural differences greatly influenced the flexure strength, which varied from 75 ± 21 MPa for the nonsplashing spray condition to 17 ± 2.4 MPa for the “splashing” condition.
Phase Transformation in EB‐PVD Yttria Partially Stabilized Zirconia Thermal Barrier Coatings during Annealing
Authors: Schulz Uwe
Published: July 2010

Electron‐beam physical‐vapor‐deposited thermal barrier coatings consisting of ZrO2 stabilized by 7 wt% Y2O3 were investigated in regard to phase transformation after annealing. Free‐standing ceramic layers were heat‐treated in air, for up to 200 h, in the temperature range 1200°—1400°C and then analyzed by X‐ray diffractometry. Based on information obtained from the {111} and {400} peaks, the phase composition and the Y2O3 content in the phases were calculated. At the start of transformation, small grains of a low‐Y2O3t phase and a c phase formed. After >30 h at 1300°C and at 1400°C, a mixture of a t phase deficient in Y2O3, an m phase, and a c phase formed after cooling, with the Y2O3 contents in the phases roughly predicted by the phase diagrams. The results of the present study are discussed here in detail and compared with data for plasma‐sprayed coatings.
Effect of Divalent Cation Additives on the γ‐Al2O3‐to‐α‐Al2O3 Phase Transition
Authors: Okada Kiyoshi , Hattori Akiyoshi , Taniguchi Taketoshi , Nukui Akihiko , Das Rathindra Nath
Published: July 2010

The effect on the γ‐Al2O3‐to‐α‐Al2O3 phase transition of adding divalent cations was investigated by differential thermal analysis, X‐ray diffractometry, and surface‐area measurements. The cations, Cu2+, Mn2+, Co2+, Ni2+, Mg2+, Ca2+, Sr2+, and Ba2+, were added by impregnation, using the appropriate nitrate solution. These additives were classified into three groups, according to their effect: (1) those with an accelerating effect (Cu2+ and Mn2+), (2) those with little or no effect (Co2+, Ni2+, and Mg2+), and (3) those with a retarding effect (Ca2+, Sr2+, and Ba2+). The crystalline phase formed by reaction of the additive with γ‐Al2O3 at high temperature was a spinel‐type structure in groups (1) and (2) and a magnetoplumbite‐type structure in group (3). In groups (2) and (3), a clear relationship was found between the transition temperature and the difference in ionic radius of Al3+ and the additive (Δr): The transition temperature increased as Δr increased. This result indicates that additives with larger ionic radii are more effective in suppressing the diffusion of Al3+ and O2− in γ‐Al2O3, suppressing the grain growth of γ‐Al2O3, and retarding the transformation into α‐Al2O3.
Synthesis of Silicon Carbide through the Sol—Gel Process from Rayon Fibers
Authors: Raman Vasantha , Parashar Virendra Kumar , Dhakate Sanjay , Bahl Om Prakash , Dhawan Urmila
Published: July 2010

Silicon carbide whiskers (SiC(w)) are synthesized by the pyrolysis of rayon fibers impregnated with sol—gel‐derived SiO2. The influence of boric acid on whisker growth and the effect of varying the TEOS:rayon weight ratio are studied and reported. Evolution of SiC(w) from impregnated rayon fibers in the carbonized and in the carbothermal stages is investigated.
Alumina Sol‐Assisted Sintering of SiC—Al2O3 Composites
Authors: Yang Quanzu , Troczynski Tom
Published: July 2010

The composite sol—gel (CSG) technology has been utilized to process SiC—Al2O3 ceramic/ceramic particulate reinforced composites with a high content of SiC (up to 50 vol%). Alumina sol, resulting from hydrolysis of aluminum isopropoxide, has been utilized as a dispersant and sintering additive. Microstructures of the composites (investigated using TEM) show the sol‐originating phase present at grain boundaries, in particular at triple junctions, irrespective of the type of grain (i.e., SiC or Al2O3). It is hypothesized that the alumina film originating from the alumina sol reacts with SiO2 film on the surface of SiC grains to form mullite or alumina‐rich mullite‐glass mixed phase. Effectively, SiC particles interconnect through this phase, facilitating formation of a dense body even at very high SiC content. Comparative sinterability studies were performed on similar SiC—Al2O3 compositions free of alumina sol. It appears that in these systems the large fraction of directly contacting SiC—SiC grains prevents full densification of the composite. The microhardness of SiC—Al2O3 sol—gel composites has been measured as a function of the content of SiC and sintering temperature. The highest microhardness of 22.9 GPa has been obtained for the composition 50 vol% SiC—50 vol% Al2O3, sintered at 1850°C.
Simple Synthesis of Submicrometer Lead Titanate Powder by Precipitation of TiO2 Precursor on PbO Particulates
Authors: Han Kyoung R. , Koo Hee Jin , Hong Mee‐Jeong , Lim Chang Sup
Published: July 2010

A simple way to prepare phase‐pure, submicrometer PbTiO3 powder was tried by precipitation. Precipitation was carried out in an aqueous PbO slurry using aqueous TiCl4 and dilute NH4OH at pH 9.5 ± 0.1. The TG/DSC curves of the PT precursor show weight loss of ∼7% and two exotherms at 492° and 522°C. They are attributed to the crystallization of tetragonal PbTiO3. XRD shows that tetragonal PbTiO3 can be obtained by heat treatment around 500°C via a noncrystalline state. SEM shows that the PbTiO3 powder calcined at 600°C for 1 h is well crystallized and in the range of 100—300 nm.
Near‐Net‐Shaped Calcium Hydroxyapatite by the Oxidation of Machinable, Calcium‐Bearing Precursors (the Volume Identical Metal Oxidation, or VIMOX, Process)
Authors: Saw Eaden , Sandhage Ken H. , Gallagher Patrick K. , Litsky Alan S.
Published: July 2010

A novel VIMOX (volume identical metal oxidation) route to near‐net‐shaped calcium hydroxyapatite, Ca10(PO4)6(OH)2, is demonstrated: the oxidation of machinable Ca—Ca2P2O7 precursors. Mechanically alloyed mixtures of Ca and β‐Ca2P2O7 were compacted into disk‐ and bar‐shaped preforms. The latter preforms could be machined into cylinders using a metalworking lathe (200 rpm, hardened steel tooling). After oxidation at 600°C in O2, and then postoxidation annealing in H2O/O2 mixtures at 850°C and 1150°C, phase‐pure hydroxyapatite was obtained. Because of offsetting volume changes from calcium oxidation and hydroxyapatite formation, porous hydroxyapatite bodies were produced that retained the shapes and dimensions (within 1%) of the machined precursors.
Bulk Crystallization of Glasses Belonging to the Calcia—Zirconia—Silica System by Microwave Energy
Authors: Siligardi Cristina , D'Arrigo Maria Cristina , Leonelli Cristina , Pellacani Gian Carlo , Cross Tom E.
Published: July 2010

This paper reports results that show the effect of microwave absorption on the bulk crystallization of two glasses in the CaO—ZrO2—SiO2 system. The glass samples were devitrified using either microwave or conventional heating, to compare the results obtained from the two different techniques. Remarkably different crystallization paths were observed, depending mostly on the composition of the glass. This observation was especially true when microwave heating was used, where the dielectric losses observed in silicate glasses are related to the ZrO2 content. X‐ray diffraction analysis was performed on the powdered samples, to determine the crystalline phases present. The microstructure and microanalysis results of these glass‐ceramic compositions are presented and are related to the different ZrO2 contents.
Effect of Hydrogen Atmosphere on Pyrolysis of Cured Polycarbosilane Fibers
Authors: Takeda Michio , Saeki Akinori , Sakamoto Jun‐ichi , Imai Yoshikazu , Ichikawa Hiroshi
Published: July 2010

SiC‐based fibers with various chemical compositions were synthesized using an irradiation‐curing process. Polycarbosilane (PCS) fibers were cured by irradiation with an electron beam in a helium atmosphere. The cured PCS fibers were pyrolyzed at 1300°C under controlled hydrogen or argon atmospheres, and SiC fibers with C/Si of 0.84 to 1.56 were obtained. The fibers consisted of <1.0 wt% O, <0.2 wt% N, <0.1 wt% H, with the balance being Si and C. The mechanism of pyrolytic transformation of cured PCS to SiC‐based ceramics was investigated using TG/DTA analysis. Greater mass losses were observed during pyrolysis in a hydrogen atmosphere than in argon. This result suggests that the hydrogen atmosphere suppresses H2 evolution and helps to remove excess carbon as CH4 during pyrolysis. The microstructure and mechanical properties of the resulting SiC‐based fibers were found to be very dependent on their C/Si chemical compositions.
Extrusion of Metal–Ceramic Composite Pipes
Authors: Chen Zhongchun , Ikeda Keisuke , Murakami Tadasu , Takeda Takenobu
Published: July 2010

Metal–ceramic composite pipes were prepared through simultaneous extrusion of different pastes by a multi‐billet extrusion method. ZrO2 and stainless steel powders were chosen, and an aqueous solution of water‐soluble polymer, hydroxypropyl methylcellulose (HPMC), was used as binder. The maximum extrusion pressure and the minimum amount of binder required reached their lowest values when the mixing fraction of ZrO2 powder was 0.4. The minimum amount of binder for forming the outer layers was 4%–5% higher than that for inner layers, even for the same powder. It was possible to decrease the binder content and broaden the extrudable range of the binder content by means of mixing coarse and fine powders.
Reactive Synthesis and Phase Stability Investigations in the Aluminum Nitride–Silicon Carbide System
Authors: Carrillo‐Heian Ellen M. , Xue Hongyong , Ohyanagi Manshi , Munir Zuhair A.
Published: July 2010

The effect of AlN on the structure formation of SiC was investigated. SiC was synthesized in the presence of AlN under vacuum at 1500°C, and the result was cubic SiC. The synthesis of AlN–SiC composites through the reaction Si3N4+ 4Al + 3C = 3SiC + 4AlN was also investigated and compared with synthesis via field‐activated self‐propagating combustion (FASHS). Reactants were heated in a vacuum furnace at temperatures ranging from 1130° to 1650°C. Below 1650°C, the reaction is not complete and at this temperature the product phases are AlN and cubic SiC. At 1650°C, the product contained an outer layer which contained β‐SiC only and an inner region which contained AlN and cubic SiC. 2H‐SiC and AlN composites synthesized via field‐activated self‐propagating combustion were annealed at 1700°C under vacuum. The AlN dissociated and evaporated and the 2H‐SiC transformed to the cubic β phase. Reasons for the differences in products of furnace heating and FASHS are discussed.
Effects of B2O3 Addition on the Dielectric and Ferroelectric Properties of Ba0.7Sr0.3TiO3 Ceramics
Authors: Rhim Sung Min , Hong Seokmin , Bak Heungjin , Kim Ok Kyung
Published: July 2010

The effects of B2O3 addition on the sintering behavior and the dielectric and ferroelectric properties of Ba0.7Sr0.3TiO3 (BST) ceramics were investigated. The dielectric and ferroelectric properties of a BST sample with 0.5 wt% B2O3 sintered at <1150°C were as good as those of undoped BST sintered at 1350°C, and the dielectric loss was better. When >1.0 wt% B2O3 was added to BST, the overdoped B2O3 did not form a liquid phase or volatilize; it remained in the samples and formed a secondary phase that lowered the sintering behavior and the dielectric and ferroelectric properties of the BST.
Finite‐Element Analysis of Ceramic Multilayer Capacitors: Modeling and Electrical Impedance Spectroscopy for a Nondestructive Failure Test
Authors: Prume Klaus , Waser Rainer , Franken Klaus , Maier Horst R.
Published: July 2010

The opportunities are introduced to calculate the electrical, mechanical, and thermal couplings of ceramic multilayer capacitors (MLCs) with the finite‐element method. The results may lead to improvements in the production, integration, and operation of MLCs. In this paper, a comparison is given of calculations and measurements of electromechanical resonances in the impedance spectra of MLCs. The simulation of defective capacitors with three different types of assumed faults reveals the changes in the impedance spectra due to these defects. This allows the prediction of flaws in MLCs based on measurement of the impedance spectra.
Flexural Fracture Strength, Fracture Locations, and Monte Carlo Predictions for a Silicon Nitride by Ten U.S. Laboratories
Authors: Tennery Victor J. , Breder Kristin , Ferber Mattison K. , Jenkins Michael G.
Published: July 2010

The work reported was conducted to provide a basis for a number of structural ceramic mechanical property standardization activities in the United States, Germany, Japan, and Sweden. A comparison of key property values of a commercial silicon nitride determined in a number of laboratories was a major objective. The work reported was conducted by 10 U.S. laboratories on GN‐10 silicon nitride, and represented the U.S. work within an International Energy Agency program including the United States, Germany, Japan, and Sweden. Fracture location analyses showed that fracture location within the inner span often was not a linear function of location within the span. Some of this behavior was explained by random sampling effects based upon simulation predictions, but some was apparently dependent upon friction within the fixtures in spite of efforts to minimize it. Flexural strengths were measured at 25° and 1250°C in air and were analyzed using the two‐parameter Weibull model in terms of m and σΘ using both linear regression (LR) and maximum likelihood (ML) methods. Under the measurement conditions for the 10 room‐temperature strength sets, the value of the ML estimator for m varied by as much as 36%, while the value for the σΘ parameter estimator varied only 3.3%. The LR estimator for m varied by about 54%. For the high‐temperature specimens, the ML estimator for m varied by 48% while the LR estimator varied by 38%. Ranked fracture location analysis showed that the high‐temperature fracture locations were more random than those in the room‐temperature specimens, and was probably due to friction in the high‐temperature fixtures. There was little pin rolling ability in many of the high‐temperature fixtures used. Monte Carlo and one‐way analysis‐of‐variance (ANOVA) methods provided insight into the consistency of the strength values. Monte Carlo predictions showed that for room‐temperature strength, the maximum likelihood estimator m for all 10 laboratories fit within the 10% and 90% confidence bounds for 30 specimen sets. The dispersion of the high‐temperature data was such that the m estimator satisfied the model only at the 1% and 99% confidence levels for the 15 specimen sets. ANOVA results showed that for the room‐temperature flexural strength, data from all 10 laboratories were not distinguishable for this evaluator at the 95% confidence level and that scatter within individual data sets was a larger effect than was the variation between the data sets. For the high‐temperature data, the results from one laboratory were clearly outside the allowable range at this confidence level.
Kinetics of Enthalpy Relaxation at the Glass Transition in Ternary Tellurite Glasses
Authors: Aida Kazuya , Benino Yasuhiko , Dimitrov Vesselin , Komatsu Takayuki , Sato Ryuji
Published: July 2010

The kinetics of enthalpy relaxation (recovery) at the glass transition in xK2O·(20−x)MgO·80TeO2 glasses has been examined from heat capacity measurements using differential scanning calorimetry to clarify the features of the structural relaxation in ternary TeO2‐based glasses. Ternary glasses such as 10K2O·10MgO·80TeO2 show high thermal resistance against crystallization compared with binary glasses. The degree of fragility m estimated from the activation energy for viscous flow Eη and the glass transition temperature Tg is m= 55–62, indicating a fragile character in TeO2‐based glasses. Large heat capacity changes of 43.1–48.2 J·mol−1·K−1 are also observed at the glass transition. The activation energy for enthalpy relaxation ΔH is evaluated from the cooling rate dependence of the limiting fictive temperature, and values of ΔH= 897–1268 kJ·mol−1 are obtained. Negative deviation from additivity in ΔH is also observed. Values of the Kovacs–Aklonis–Huchinson–Ramos (KAHR) parameter θ estimated from ΔH and Tg are 0.33–0.42 K−1. It has been proposed that ternary glasses have more homogeneous and constrained glass structure compared with binary glasses.
Effect of Fiber Bridging Stress on the Fracture Resistance of Silicon‐Carbide‐Fiber/Zircon Composites
Authors: Wang Yu‐Lin , Anandakumar Umashankar , Singh Raj N.
Published: July 2010

The room‐temperature fracture‐resistance behavior (R‐curve) of unidirectional silicon‐carbide‐fiber‐reinforced zircon‐matrix composites has been studied experimentally and numerically. The composites showed strong rising R‐curve behavior from experimental results that used in situ crack‐length measurements taken via optical microscopy as well as the compliance method. A numerical calculation, based on the available models, then was performed to determine the bridging‐stress function from the experimental R‐curve. In addition, the effect of the residual stress and constituent properties on the bridging‐stress function also has been considered in the numerical calculations. These results have indicated that the bridging‐stress function, which controls the fracture resistance of ceramic composites, can be obtained from the carefully measured R‐curve.
Experimental Method for Determining Surface Energy Anisotropy and Its Application to Magnesia
Authors: Saylor David M. , Mason Darren E. , Rohrer Gregory S.
Published: July 2010

An experimental technique has been developed to determine the surface energy anisotropy of crystalline solids. The technique is based on atomic force microscopy measurements, which are used to quantify the geometry of thermal grooves, and electron backscattered diffraction pattern measurements, which are used to specify crystallographic orientations. Observations are made at circumferential thermal grooves, where it is assumed that Herring's local equilibrium condition for a triple junction holds and that the grain‐boundary energy is independent of its boundary plane. A truncated double Fourier series is used to approximate the surface energy, and the unknown coefficients of the series are determined by fitting the observations to the local equilibrium condition. The method, which should be applicable to most polycrystalline materials, has been tested on magnesia that has been thermally grooved at 1400°C in air. The maximum of the best‐fit surface energy function is at (111) and the minimum is at (100). The relative surface energies of the low‐index planes are γ110/γ100= 1.040 ± 0.008 and γ111/γ100= 1.072 ± 0.010.
Effect of Monovalent Cation Additives on the γ‐Al2O3‐to‐α‐Al2O3 Phase Transition
Authors: Okada Kiyoshi , Hattori Akiyoshi , Kameshima Yoshikazu , Yasumori Atsuo , Das Rathindra Nath
Published: July 2010

The effect of monovalent cation addition on the γ‐Al2O3‐to‐α‐Al2O3 phase transition was investigated by differential thermal analysis, powder X‐ray diffractometry, and specific‐surface‐area measurements. The cations Li+, Na+, Ag+, K+, Rb+, and Cs+ were added by an impregnation method, using the appropriate nitrate solution. β‐Al2O3 was the crystalline aluminate phase that formed by reaction between these additives and Al2O3 in the vicinity of the γ‐to‐α‐Al2O3 transition temperature, with the exception of Li+. The transition temperature increased as the ionic radii of the additive increased. The change in specific surface area of these samples after heat treatment showed a trend similar to that of the phase‐transition temperature. Thus, Cs+ was concluded to be the most effective of the present monovalent additives for enhancing the thermal stability of γ‐Al2O3. Because the order of the phase‐transition temperature coincided with that of the formation temperature of β‐Al2O3 in these samples, suppression of ionic diffusion in γ‐Al2O3 by the amorphous phase containing the added cations must have played an important role in retarding the transition to α‐Al2O3. Larger cations suppressed the diffusion reaction more effectively.
Characteristic Spherulitic Microstructure in Partial‐Melt‐Processed YBa2Cu3Ox/HfO2
Authors: Yan Yong , Evetts Jan E. , Zhang Jin‐li , Stobbs William M.
Published: July 2010

The microstructure of partial‐melt‐processed YBa2Cu3Ox/HfO2 has been studied by transmission electron microscopy. A characteristic spherulitic microstructure is formed in the system. A model for the growth mechanism has been proposed. The critical heterogeneous nucleation of the YBa2Cu3Ox phase appears to occur from the melt in an epitaxially controlled manner on CuO particles. Subsequent growth of YBa2Cu3Ox platelets from the nucleus region is repeatedly interrupted by the nucleation of hafnium‐rich phases in the liquid at the solid/liquid interface in a manner that again appears to be epitaxially controlled and that promotes the splay of the c orientation of the YBaCuO grain.
Field‐Assisted Sintering of Nanocrystalline Titanium Nitride
Authors: Groza Joanna R. , Curtis Justin D. , Krämer Martin
Published: July 2010

Nanosized TiN powder was densified via field‐assisted sintering at temperatures of 1150°–1350°C and a pressure of 66 MPa under vacuum. A maximum relative density of ∼97% and a maximum mean grain size of 150–200 nm were obtained. Densification and microstructural evolution have been discussed, in terms of superplasticity and electric‐field effects.
Pr3+/Er3+ Codoped Ge‐As‐Ga‐S Glasses as Dual‐Wavelength Fiber‐optic Amplifiers for 1.31 and 1.55 μm Windows
Authors: Park Se Ho , Lee Dong Chin , Heo Jong , Kim Hyoun Soo
Published: July 2010

Fluorescence emissions at both 1.31 and 1.55 μm communication windows were observed from Pr3+/Er3+ codoped Ge‐As‐Ga‐S glasses with a single wavelength pumping at 986 nm. The lifetime of the Er3+:4I11/2 level decreased as the Pr3+ concentration increased, and that of the Pr3+:1G4 level increased as the Er3+ concentration increased. Energy transfer from the Er3+:4I11/2 level to the Pr3+:1G4 level was responsible for emission of the 1.31 μm fluorescence from the Pr3+:1G4 level. Ge‐As‐Ga‐S glasses that have been doped with Pr3+ and Er3+ cations are promising amplifier materials for both 1.31 and 1.55 μm communication windows.
Formation of Nanometric TiB2 from TiO2
Authors: Welham Nicholas J.
Published: July 2010

Titanium diboride can be produced by ball‐milling a mixture of TiO2, B2O3, and Mg metal for between 10 and 15 h. The reaction was found to be completed during the milling with no evidence of residual Mg. The unwanted phase, MgO, was readily removed by leaching in acid. The leached powder obtained after 15 h milling had a particle size of <200 nm and was highly faceted. The particle size decreased to ∼50 nm after 100 h milling and seemed to be relatively monodisperse. Scherrer calculation of the crystallite size showed that the product particles were probably single crystal.
Infrared Spectroscopic Method for Determination of Thermal Properties of Fluorophosphate Glasses
Authors: Karmakar Basudeb , Kundu Paritosh , Dwivedi Ravindra Nath
Published: July 2010

Fluorophosphate glasses of the Ba(PO3)2–MgF2–CaF2–AlF3 system exhibit anomalous behavior, in regard to the glass‐transition temperature (Tg) and the coefficient of thermal expansion (αCTE), at a fluoride concentration of ∼36 mol%. A similar trend in the infrared band absorption coefficient (αIR) at 2170 cm−1 of the overtone of 2νss(OPO) and/or a combination of νas(OPO)+νas(POP) fundamental vibrations of PO4 tetrahedra also has been observed, relative to changes in the glass composition. Statistical analyses have shown that the Tg and αCTE values are correlated with αIR at 2170 cm−1 by linear equations. The thermal properties of some of the glasses have been calculated using these equations, to test their validity and utility. The experimental property values of the glasses present a very good fit of data within a 95% confidence interval of the calculated mean values.
Microscopic Study of SnO2 Crystals in the Gold Decoration Layer of Bone China
Authors: Chung Yong‐Chae , Im Dong Hyun , Kim Chang Kyung , Yoon Chong S.
Published: July 2010

The microstructure of the gold decoration layer of bone china was investigated to pinpoint the cause of the gold cracking occurring during the manufacture of high‐quality bone china. Using cross‐sectional TEM analysis, it was observed that SnO2 crystals from the matting agent underneath the gold underwent abnormal growth. When the few SnO2 crystals grew excessively, the matting oxide burst through the gold layer, resulting in the gold cracking. From this study, we conclude that control of the size distribution of SnO2 crystals is very important to keep a high‐quality gold layer.
Colloid Emulsion of Nanosized Strontium Bismuth Tantalate Powder
Authors: Lu Chung‐Hsin , Saha Susanta Kumar
Published: July 2010

A novel colloid‐emulsion process has been used to synthesize nanosized strontium bismuth tantalate (SrBi2Ta2O9) particles. During calcination, the desired bismuth‐layered structure phase develops at the expense of the pyrochlore phase. Calcining the precursor powder at 750°C for 2 h leads to the complete formation of single‐phase layered‐structured SrBi2Ta2O9. The powder that is formed consists of nanoparticles with a narrow size distribution and almost‐spherical morphology. The crystallinity of the calcined powder increases as the calcination temperature and heating time increases. The developed colloid‐emulsion process significantly reduces the SrBi2Ta2O9 particle size, in comparison to conventional process techniques, and results in a uniform microstructure of the obtained powder.
Yttrium Silicate Coatings for Oxidation Protection of Carbon–Silicon Carbide Composites
Authors: Aparicio Mario , Durán Alicia
Published: July 2010

Yttrium silicate (Y2SiO5) coatings complement SiC coatings for protecting ceramic multilayer composite materials based on carbon‐fiber‐reinforced SiC composites (C‐SiC). Thick (100 μm), dense Y2SiO5 coatings were prepared by dip coating, using concentrated aqueous slips. The resulting phases were studied by taking into account the simultaneous presence of oxide and non‐oxide materials, which affected the chemical stability of the coatings. Thick, mechanically stable coatings were obtained by sintering in carbon crucibles and a SiC bed in an argon‐flow furnace. Pure Y2SiO5 coatings completely separated from the SiC substrates. A high percentage of Y2Si2O7 was necessary to fit the thermal expansion coefficients and ensure the stability of the coatings. Oxidation resistance of the coated substrates was investigated by isothermal and stepwise oxidation tests.