bluuebunny/crossref_metadata_2025 huggingface dataset:
Secular Trends of Hospitalization With Vancomycin-Resistant Enterococcus Infection in the United States, 2000–2006
Authors: Ramsey Andrew M. , Zilberberg Marya D.
Published: January 2009

Although the incidence of hospitalizations with infection due to vancomycin-resistant pathogens in the United States remained stable during 2000–2003, it increased from 4.60 to 9.48 hospitalizations per 100,000 population during 2003–2006. Hospitalizations with infection due to vancomycin-resistant pathogens also increased as a proportion of all US hospitalizations, from 3.16 to 6.51 hospitalizations with VRE infection per 10,000 total hospitalizations during 2003–2006. The number of hospitalizations with infection due to vancomycin-resistant pathogens is increasing in the United States. Because infection due to vancomycin-resistant organisms is associated with poor outcomes, the epidemiology of this trend needs further exploration.
Measurement Equivalence of Nationalism and Constructive Patriotism in the ISSP: 34 Countries in a Comparative Perspective
Authors: Davidov Eldad
Published: January 2009

Studies on national identity differentiate between nationalistic attitudes and constructive patriotism (CP) as two more specific expressions of national identity and as theoretically two distinct concepts. After a brief discussion of the theoretical literature, the following questions are examined: (1) Can nationalism and CP be empirically identified as two distinct concepts?; (2) Is their meaning fully or partially invariant across countries?; and (3) Is it possible to compare their means across countries? Data from the International Social Survey Program (ISSP) 2003 National Identity Module are utilized to answer these questions in a sample of 34 countries. Items to measure nationalism and CP are chosen based on the literature, and a series of confirmatory factor analyses to test for configural, measurement (metric), and scalar invariance are performed. Full or partial metric invariance is a necessary condition for equivalence of meaning across cultures and for a meaningful comparison of associations with other theoretical constructs. Scalar invariance is a necessary condition for comparison of means across countries. Findings reveal that nationalism and CP emerge as two distinct constructs. However, in some countries, some items that were intended to measure one construct also measure the other construct. Furthermore, configural and metric invariance are found across the full set of 34 countries. Consequently, researchers may now use the ISSP data to study relationships among nationalism, CP, and other theoretical constructs across these nations. However, the analysis did not support scalar invariance, making it problematic for comparing the means of nationalism and CP across countries.
Microengineering of Ceramics by Direct Ink‐Jet Printing
Authors: Mott Matthew , Song Jin‐Hua , Evans Julian R. G.
Published: January 2009

A modified piezoelectric drop‐on‐demand ink‐jet printer was used to build 3‐D ceramic structures with cavities and overhangs by direct ceramic deposition. Inks in the form of zirconia and carbon suspensions were prepared with suitable viscosities and surface tensions. The multinozzle printer was used to microengineer small components in which support structures were created from the carbon ink and the carbon was removed after pyrolysis of the organic vehicle but before sintering the zirconia. The viability of this process is discussed in terms of machine limitations and ink drying problems.
Mechanochemical Synthesis of Lead Zirconate Titanate from Mixed Oxides
Authors: Xue Junmin , Wan Dongmei , Lee See‐Ee , Wang John
Published: January 2009

High‐density lead zirconate titanate (PZT) ceramics have been successfully prepared by using a novel mechanochemical fabrication technique, which skips the phase‐forming calcination at an intermediate temperature that is always required in the industrial processes currently in use. The fabrication technique starts with mixing of the low‐cost industrial oxide powders, and the designed PZT perovskite phase is formed by reacting the oxide constituents in a mechanochemical chamber that consists of a cylindrical alumina vial and one stainless‐steel ball inside it. The solid‐state reaction among constituent oxides is activated via mechanical energy instead of high temperature. When mechanochemically activated for 20 h, an ultrafine PZT powder of perovskite structure with a minimized degree of particle agglomeration is obtained. The resulting PZT powder sinters to 99.0% of theoretical density at 1100°C for 1 h. The sintered PZT ceramic exhibits a dielectric constant of 1340 and a dielectric loss of 0.6% at a frequency of 1 kHz at room temperature.
Engineered Porosity via Tape Casting, Lamination and the Percolation of Pyrolyzable Particulates
Authors: Corbin Stephen F. , Apté Prasad S.
Published: January 2009

Sintered ceramic preforms with open pore volumes from 20% to 80% (with no alteration in sintering shrinkage) were developed by adding pyrolyzable pore‐forming agents (PFAs) to a tape‐casting colloidal suspension. Sintered porous characteristics were directly controlled by the amount, size, and distribution of the PFA added to the green tape as well as adjustments made to the tape formulation. A conceptual model of the green tape microstructure was used to explain the influence of PFA and tape formulation on retained porosity and sintering shrinkage. The creation of a connected, open, porous network within the preform was the result of PFA particle percolation within the green body.
Effect of Processing Parameters on the Morphology of Hydrothermally Derived PbTiO3 Powders
Authors: Peterson Chad R. , Slamovich Elliott B.
Published: January 2009

The influence of processing parameters on the growth and morphology of hydrothermally derived lead titanate (PbTiO3) powders was investigated. PbTiO3 powder was synthesized by suspending nanocrystalline powders of TiO2 in aqueous solutions of KOH and Pb(CH3COO)2·3H2O at temperatures ranging from 120° to 200°C. PbTiO3 growth initiated in the <100> exposing the (001) surfaces and resulting in a faceted platelet morphology. Particle growth proceeded by further nucleation and growth on existing (001) surfaces. Through repeated dissolution and precipitation, the platelet clusters coarsened into larger cuboidal particles. PbTiO3 particle size was controlled by either inhibiting or promoting dissolution‐precipitation. Dissolution‐precipitation was inhibited by lowering the KOH concentration or the reaction temperature, or maintaining an excess of lead ions in solution, while it was promoted by increasing the KOH concentration and temperature. Coarsening of PbTiO3 particles coincided with decreases in the X‐ray diffraction (XRD) peak breadth, the asymmetry of lcomponent XRD reflections, and the c‐axis length.
A Finite‐Element Approach for the Shape Prediction of Ceramic Compacts during Sintering
Authors: Sanliturk Kenan Y. , Aydin Ismail , Briscoe Brian J.
Published: January 2009

This paper describes and demonstrates the effectiveness of a finite‐element procedure to predict the shape changes of “green powder compacts” during sintering processes. The approach is based on the conservation‐of‐mass principle and requires for its implementation (i) descriptions of the finite‐element meshes of the original form (powder bed) and the green bodies when ejected from the die (thus, de‐scriptions of the geometries of the compact before and after the compaction process) and (ii) the densities of the com‐pacts before the compaction and after the sintering pro‐cesses. Numerical shape predictions have been compared with experimental data, for all the external surfaces that are obtained from sintered, cylindrical alumina specimens. The overall predicted diametric dimensional‐variation changes correlate with the corresponding measured data; both indicate a “barrel” shape. The comparisons reveal that the quantitative predictions in regard to the height and diameter range correlate closely with the measured values; the differences are <1.6% and 0.4%–0.08%, respectively. The overall predicted deviation changes of the end surfaces of the sintered compacts correlate with the corresponding measured data; both indicate a “concave” shape, with ref‐erence to the horizontal plane, as viewed from the compac‐tion direction. The quantitative shape comparisons for the top and bottom surfaces are <18.9% and <65.84%, respec‐tively. The qualitative predictions at the top and bottom surfaces are considered to be in good agreement, for most practical purposes.
Enhancing Effect of Iron Chlorides on the Anatase‐Rutile Transition in Titanium Dioxide
Authors: Gennari Fabiana C. , Pasquevich Daniel M.
Published: January 2009

The effect of solid Fe2O3 and gaseous iron chlorides on the anatase‐rutile phase transition was investigated in the temperature range of 750°‐950°C via X‐ray diffractometry and scanning electron microscopy. In both cases, iron diffusion in the anatase lattice decreased the transition temperature and increased the anatase‐rutile transformation rate, in comparison with that in TiO2 fired in air. The enhancement effect of iron on the anatase‐rutile transition is understood on the basis of oxygen‐vacancy formation, which favors rutile nucleation. Solid‐state iron diffusion between the contact points of TiO2 and Fe2O3 particles and vapor mass transport through gaseous chlorides were the primary mechanisms of iron mass transport to the TiO2 surface in the presence of both Fe2O3 and gaseous iron chlorides, respectively. The transformation rate at a given reaction temperature increased in the following order of reaction conditions: pure TiO2 in air, TiO2 in the presence of Fe2O3 in air, TiO2 in the presence of Fe2O3 in chlorine, and TiO2 in the presence of gaseous iron chlorides.
Dispersion of Alumina and Silicon Carbide Powders in Alumina Sol
Authors: Yang Quanzu , Troczynski Tom
Published: January 2009

Dispersion of Al2O3 and SiC particles in an alumina sol has been investigated through determination of particle‐size distribution, zeta potential, and agglomerate morphology. The particle size of Al2O3 and SiC (as determined by the particle‐size analyzer) is strongly affected by the presence of alumina sol in the solution. The average agglomerate size is decreased by at least 50%. The zeta potential of Al2O3 in 1Malumina sol increases slightly, whereas that of SiC reverses its sign over a wide range of pH values. It is proposed that these effects are caused by AlO4Al12(OH)24(H2O)7+12 sol clusters (1‐2 nm in size) that are absorbed on the surface of the large (1‐5 µm) ceramic particles. The electrostatic and steric effects of the cluster absorption help to control the dispersion and stabilize the suspension of ceramic particles in the alumina sol during wet processing. It is expected that the alumina‐sol clusters can be used as an efficient, clean dispersant for single‐phase and composite ceramic powders.
Relation of Pore Size to Green Density: The Kozeny Equation
Authors: Sweeney Sean M. , Mayo Merrilea J.
Published: January 2009

A relation between nitrogen desorption/mercury intrusion porosimetry‐measured pore size and green density of a powder compact is examined with respect to data from the literature, as well as data from the current study on three ceramic oxides. In almost all cases, the relationship is well obeyed. Deviations from the relation (originally developed by Kozeny) in the current study are shown to be due to the presence of large, interagglomerate pores which persist during low‐pressure pressing. Thus, a powder compact's adherence to the Kozeny relation can be used to gauge its degree of packing homogeneity.
Raman Study of the Interface between Hot‐Pressed Silica Parts
Authors: Chmel Alexandre E. , Smirnov Andrej N. , Shashkin Victor S.
Published: January 2009

We present a Raman spectroscopy study of silica glasses prepared by hot‐pressing of gels. Our particular interest is the structure at the interfaces formed during hot‐pressing of small parts to obtain large pieces, such as silica tubes for optical‐fiber preforms. A specific feature of the interface that distinguishes this layer from the bulk is its fractal structure. The parameters of the fractal units, including their maximum dimensions in real space, are determined by the pre‐hot‐pressing mechanical processing. We attribute this structure to residual microcracks inherent in the surface layer of polished plates. There are no fractals at the interfaces sintered at temperatures higher than the glass transition temperature.
Aqueous Gel‐Forming of Silicon Nitride Using Carrageenans
Authors: Millán Arnaldo J. , Nieto M. Isabel , Moreno Rodrigo
Published: January 2009

Much effort has been devoted recently to the development of near‐net‐shaping processes in water. Agarose has been demonstrated to be a suitable gelling agent for aqueous forming. However, its high cost and the difficulties in controlling the rheological properties have restricted large‐scale applications. In this work a novel gelling binder, namely carrageenan, is proposed as a low‐cost and high‐gel‐strength additive for gel‐forming ceramic powders. The capability to obtain silicon nitride parts by carrageenan gelation is described. Aqueous silicon nitride slips are prepared at pH >11 to a solids content of 70 wt% using tetramethylammonium hydroxide as a dispersant. Dissolution and gelation of carrageenan are studied by continuous measurements of viscosity with temperature for solutions prepared at different pH values. The final injection slips prepared by mixing at <60°C the previously heated suspension and the carrageenan solution are rheologically characterized also. After the blend is injected into cooled nonporous molds, gelling occurs in a few seconds and samples can be dried in air for 24–48 h. Green densities of 52% of theoretical are obtained.
Determination of Individual Fiber Failure in Fiber Bundles
Authors: Toffoli Samuel M. , Lehman Richard L.
Published: January 2009

The onset of fiber failure signals the commencement of catastrophic structural failure in fiber bundle systems, a process that is important in standalone bundles and in other material structures. In this work, we have demonstrated a technique by which the onset of fiber failure can accurately be identified by monitoring the electrical continuity and resistance of filaments and bundles during loading. The dual sensor/loading functionality of the fibers differs from most prior approaches wherein separate sensors were added to the load‐bearing fiber array. Individual fiber failure and bundle onset failures in 50 fiber bundles were reliably and reproducibly detected.
Preparation and Properties of Hydrothermally Stable γ‐Alumina Membranes
Authors: Nijmeijer Arian , Kruidhof Henk , Bredesen Rune , Verweij Henk
Published: January 2009

Supported mesoporous γ‐Al2O3 membranes deteriorate and blister in steam‐containing environments at high temperatures. This deterioration led us to the development of a new type of supported γ‐Al2O3 membrane with significantly improved stability under hostile conditions. Two measures were taken to achieve this result. First, the γ‐Al2O3 itself was stabilized by an addition of 6 mol% La2O3 to suppress pore growth of the mesoporous structure. Second, the adherence of the γ‐Al2O3 membrane to the α‐Al2O3 support was significantly improved by application of phosphate bonding between the membrane layer and the support, using an Al(H2PO4)3 precursor solution. Membranes applied without phosphate bonding were separated from the α‐Al2O3 support during high‐temperature steam treatment, resulting in complete loss of separative properties. The newly developed membranes could be operated for 100 h at 600°C in H2O/CH4= 3/1 (by volume) at 2.5 MPa total pressure with no delamination or cracking in the membrane–support interface and with no significant pore growth in the γ‐Al2O3 membrane.
Spectroscopic Properties and Thermal Stability of Er3+‐Doped Germanotellurite Glasses for Broadband Fiber Amplifiers
Authors: Feng Xian , Tanabe Setsuhisa , Hanada Teiichi
Published: January 2009

The thermal stability and spectroscopic properties of Er2O3‐doped TeO2–GeO2–ZnO–Na2O–Y2O3 glasses for 1.5 μm fiber amplifiers were investigated. The thermal stability of the 75TeO2·20ZnO· 5Na2O glass was improved by introducing GeO2 and Y2O3. The radiative transition and the nonradiative transition have a dominant influence on the 4I13/2 level lifetime of Er3+ in high‐ and low‐GeO2 regions, respectively. Adding Y2O3 increases the 4I13/2 level lifetime of Er3+ significantly. The Judd–Ofelt (J‐O) parameter Ω6 shows a strong correlation with the 1.5 μm emission bandwidth; and the larger the Ω6, the wider the bandwidth.
Effect of the Pb/Ti Source Ratio on the Crystallization of PbTiO3 Thin Films Grown by Metalorganic Chemical Vapor Deposition at Low Temperature of 400oC
Authors: Wang Chae Hyun , Choi Doo Jin
Published: January 2009

Crystalline PbTiO3 thin films were successfully deposited on (111)‐oriented Pt/Ti/SiO2/Si and on (200)‐oriented Pt/SiO2/Si by metalorganic chemical vapor deposition at a substrate temperature of 400°C, using a β‐diketonate complex of Pb(tmhd)2 (tmhd = 2,2,6,6‐tetramethyl‐3,5‐heptanedionate) and titanium isopropoxide as source precursors. The dependence of the formation of crystalline PbTiO3 phase on the Pb/Ti input precursor ratio is qualitatively described. The structure of the films deposited at 400°C changed from amorphous to polycrystalline with an increase of the Pb/Ti ratio from 1.1 to 5.0, including a partially crystallized structure at some intermediate ratio. Partial crystallization of as‐grown PbTiO3 film was analyzed by scanning electron microscopy, micro‐Raman, and Auger electron spectroscopy measurements. It was found that the control of excess Pb precursor through a change in the Pb/Ti ratio is the key process parameter for the formation of crystalline PbTiO3 phase in the low‐temperature MOCVD process.
Mechanochemical Synthesis and Electrochemical Properties of LiMn2O4
Authors: Choi Heon‐Jin , Lee Ki‐Min , Kim Gyeung‐Ho , Lee June‐Gunn
Published: January 2009

Spinel LiMn2O4 as a cathode material for lithium secondary batteries has been synthesized by a mechanochemical process, and its electrochemical properties have been characterized. Highly disordered nanocrystalline LiMn2O4 powders have been prepared by the mechanochemical processing of Li2O and MnO2 powder mixtures for 24 h. Electrochemical characterization of mechanochemically processed powder has shown that the intercalation of Li+ takes place with an initial capacity of 167 mA·h/g in the 2.5–4.3 V range and has better capacity retention as compared to the well‐ordered crystalline LiMn2O4 powders. The better capacity retention of the mechanochemically processed LiMn2O4 powder may be attributed to the highly disordered structure that could accommodate the Jahn–Teller distortion of the spinel structure during Li+ intercalation around the 3 V region.
Infrared Microscopy for Examination of Structure in Spray‐Dried Granules and Compacts
Authors: Uematsu Keizo , Uchida Nozomu , Kato Zenji , Tanaka Satoshi , Hotta Tadashi , Naito Makio
Published: January 2009

Novel infrared microscopy has been developed to improve the liquid‐immersion method, which is a technique that has been developed by the authors to study the packing structures of powder particles in ceramic green bodies. This paper demonstrates the high potential of the novel technique by presenting clear structures of Si3N4 powder granules and their compacts.
Energetics of Substituted Pollucites Along the CsAlSi2O6–CsTiSi2O6.5 Join: A High‐Temperature Calorimetric Study
Authors: Xu Hongwu , Navrotsky Alexandra , Balmer Mari Lou , Su Yali , Bitten Eric R.
Published: January 2009

Enthalpies of drop solution for a suite of substituted pollucites with the compositions CsTixAl1−xSi2O6+0.5x, 0 ≤x≤ 1, which are synthesized using the sol–gel method, have been measured in molten lead borate (2PbO·B2O3) at 701°C. As Ti4+ substitutes for Al3+, the enthalpies of drop solution become less endothermic and show exothermic heats of mixing within the composition range from x= 0.3 to 1. This nonideal mixing behavior is consistent with the trend seen in variation of lattice parameters, and we interpret it to be a result of the short‐range order associated with the framework cations Al3+, Si4+, and Ti4+ in the structure. Using enthalpies of drop solution of SiO2, Al2O3, TiO2, and Cs2O, standard molar enthalpies of formation of these phases from their constituent oxides and from the elements are derived for the first time.
Rheological Behavior of Dilute SiAlON with or without Intergranular X‐Phase
Authors: Pezzotti Giuseppe , Okamoto Kazuhiro , Ota Ken'ichi
Published: January 2009

Dense nearly single‐phase β′‐SiAlON materials (with substitutional level z∼ 1) have been prepared by hot isostatic pressing and their high‐temperature deformation behavior has been investigated using low‐frequency damping and torsional creep experiments. Addition of a small fraction of AlN (∼0.5 wt%) to the starting (nominally z= 1) SiAlON powder enabled us to “balance” the excess SiO2 which likely arises from surface contamination of the starting SiAlON powder upon exposure to atmosphere. As a result, a fine‐grained β′‐SiAlON polycrystal free of residual (glassy) X‐phase segregated to grain boundaries could be prepared. This microstructure is in contrast with that found for an “unbalanced” composition prepared from the same raw β′‐SiAlON powder but without the corrective AlN addition. In this latter case, residual glass (X‐phase), consisting of Al‐rich SiO2, was entrapped at multiple grain junctions. The presence of such a low‐melting intergranular glass dominates the high‐temperature deformation behavior of the dilute SiAlON material, involving marked degradation of creep resistance and significant damping relaxation due to grain‐boundary sliding. “Balancing” the SiAlON microstructure with a small addition of AlN enabled us to suppress anelastic relaxation by grain‐boundary sliding and to increase the creep resistance of the material by more than 1 order of magnitude.
Permeability of Refractory Castables at High Temperatures
Authors: Innocentini Murilo D. M. , Silva Maurícioi G. , Menegazzo Bruno A. , Pandolfelli Victor C.
Published: January 2009

Temperature is an important factor affectng the permeation of fluids in refractory castables. Because of experimental difficulties, however, permeability parameters are usually obtained at room temperature and then extrapolated to the temperature of interest, with no concern regarding porous structure modification (thermal expansion, etc.). In this work, an apparatus has been developed to evaluate the air‐flow permeability of refractory castables at temperatures up to 800°C. The objective is to investigate modifications in the permeability constants obtained by Forchheimer's equation to provide a more realistic relationship with castable processing and molten‐metal corrosion parameters.
Ethene/Ethane (C2H4/C2H6) Separation through an Inorganic–Organic Hybrid Membrane Containing Silver(I) Ions as Olefin Carriers, Using Poly(N‐vinylpyrrolidone) as a Mediation Agent
Authors: Su Caili , Kuraoka Koji , Yazawa Tetsuo
Published: January 2009

Novel inorganic–organic membranes that contained Ag+ ions as olefin carriers were prepared using sol–gel and dip‐coating processes. The permeance of the membranes for nitrogen, helium, ethane (C2H6), and ethene (C2H4) were evaluated using the single‐gas permeation method at temperatures of 298, 373, and 423 K. The results showed that the selectivity of the membranes to C2H4 against C2H6 increased as the measurement temperature increased, because the decomplexation rate of C2H4 molecules from Ag+ sites is enhanced by increases in the temperature. Fourier transform infrared spectrophotometry of the hybrid membranes and the performance of the membranes at 373 and 423 K indicated that poly(N‐vinylpyrrolidone) (PVP) had a role in increasing the flexibility of the inorganic network and also served as a mediation agent to fix Ag+ ions in the polymer segments, because of the coordination interaction between the Ag+ ions and the PVP.
Effect of β‐to‐α Phase Transformation on the Microstructural Development and Mechanical Properties of Fine‐Grained Silicon Carbide Ceramics
Authors: Zhan Guo‐Dong , Xie Rong‐Jun , Mitomo Mamoru , Kim Young‐Wook
Published: January 2009

Ultrafine β‐SiC powders mixed with 7 wt% Al2O3, 2 wt% Y2O3, and 1.785 wt% CaCO3 were hot‐pressed and subsequently annealed in either the absence or the presence of applied pressure. Because the β‐SiC to α‐SiC phase transformation is dependent on annealing conditions, the novel processing technique of annealing under pressure can control this phase transformation, and, hence, the microstructures and mechanical properties of fine‐grained liquid‐phase‐sintered SiC ceramics. In comparison to annealing without pressure, the application of pressure during annealing greatly suppressed the phase transformation from β‐SiC to α‐SiC. Materials annealed with pressure exhibited a fine microstructure with equiaxed grains when the phase transformation from β‐SiC to α‐SiC was <30 vol%, whereas materials annealed without pressure developed microstructures with elongated grains when phase transformation was >30 vol%. These results suggested that the precise control of phase transformation in SiC ceramics and their mechanical properties could be achieved through annealing with or without pressure.
Dense Layered Molybdenum Disilicide–Silicon Carbide Functionally Graded Composites Formed by Field‐Activated Synthesis
Authors: Carrillo‐Heian Ellen M. , Carpenter R. Douglas , Paulino Glaucio H. , Gibeling Jeffery C. , Munir Zuhair A.
Published: January 2009

Dense, layered, single‐ and graded‐composition composites of MoSi2 and SiC were formed from elemental powders in one step, using the field‐activated pressure‐assisted combustion method. Compositions ranging from 100% MoSi2 to 100% SiC were synthesized, with relative densities ranging from 99% to 76%, respectively. X‐ray diffractometry results indicated the formation of pure phases when the concentration of MoSi2 was high and the appearance of a ternary phase, Mo4.8Si3C0.6, when the concentration of SiC was high. Electron microprobe analysis results showed the formation of stoichiometric and uniformly distributed phases. A layer‐to‐layer variation in composition of 10 mol% was sufficient to prevent thermal cracking during formation of the layered functionally graded materials.
Preparation of Nanosized Perovskite‐Type LaMnO3 Powders Using the Thermal Decomposition of a Heteronuclear Complex, LaMn(dhbaen)(OH)(NO3)(H2O)4
Authors: Aono Hiromichi , Tsuzaki Mioko , Kawaura Akihiro , Sakamoto Masatomi , Traversa Enrico , Sadaoka Yoshihiko
Published: January 2009

The heteronuclear LaMn(dhbaen)(OH)(NO3)(H2O)4 complex was synthesized and perovskite‐type hexagonal LaMnO3 was obtained by its thermal decomposition at approximately 700°C. The complex and its decomposition products were analyzed using simultaneous thermogravimetric and differential thermal analysis (TG/DTA), X‐ray diffraction (XRD) analysis, Fourier‐transform infrared (FTIR) spectroscopy, Auger electron spectroscopy (AES), transmission electron microscopy (TEM) characterization, and specific surface area measurements. Although XRD analysis did not show the peaks of LaMnO3 for the sample sintered at 600°C, the presence of polycrystalline LaMnO3 together with an amorphous phase was confirmed by TEM‐selected area diffraction. Particle sizes of the samples decomposed at 600° and 700°C were 20 and 50 nm, respectively. For the conventional solid‐state reaction method, XRD results showed the formation of a LaMnO3 single phase for the samples fired above 1000°C. However, AES showed that the elemental distributions of La, Mn, and O on the surface were not homogeneous even for the sample sintered at 1200°C. The thermal decomposition of the heteronuclear complex at low temperatures allows the synthesis of single‐phase hexagonal LaMnO3 powders having nanosized particles, homogeneous and free of intragranular pores, which are suitable for electroceramics applications.
Behavior of Paramagnetic Iron during the Thermal Transformations of Kaolinite
Authors: Djemai Amédée , Balan Etienne , Morin Guillaume , Hernandez Giancarlo , Labbe Jean Claude , Muller Jean Pierre
Published: January 2009

Kaolinites with various degrees of structural order and iron content were heated and subsequently analyzed via electron paramagnetic resonance. Iron was present in two different states in the heated materials, either as dilute structural Fe3+ ions or in concentrated Fe3+ phases. During metakaolinization, the environment of dilute Fe3+ ions changed, following modifications of the Al3+ coordination, and the Fe3+ concentration increased. With the breakdown of metakaolinite, the diffusion of Fe3+ ions induced their exsolution in superparamagnetic iron‐rich domains (Fe3+ clusters in γ‐Al2O3 and/or Fe3+ oxide nanophases), which produced a decrease in the dilute Fe3+ concentration. The subsequent breakdown of γ‐Al2O3 and the formation of mullite made the dilute Fe3+ concentration increase again, because of the incorporation of Fe3+ ions in the mullite structure.
Mechanical Properties of Two Plain‐Woven Chemical Vapor Infiltrated Silicon Carbide‐Matrix Composites
Authors: Jacobsen Torben K. , Brøndsted Povl
Published: January 2009

The elastic and inelastic properties of a chemical vapor infiltrated (CVI) SiC matrix reinforced with either plain‐woven carbon fibers (C/SiC) or SiC fibers (SiC/SiC) have been investigated. It has been investigated whether the mechanics of a plain weave can be described using the theory of a cross‐ply laminate, because it enables a simple mechanics approach to the nonlinear mechanical behavior. The influences of interphase, fiber anisotropy, and porosity are included. The approach results in a reduction of the composite system to a fiber/matrix system with an interface. The tensile behavior is described by five damage stages. C/SiC can be modeled using one damage stage and a constant damage parameter. The tensile behavior of SiC/SiC undergoes four damage stages. Stiffness reduction due to transverse cracks in the transverse bundles is very different from cross‐ply behavior. Compressive failure is initiated by interlaminar cracks between the fiber bundles. The crack path is dictated by the bundle waviness. For SiC/SiC, the compressive behavior is mostly linear to failure. C/SiC exhibits initial nonlinear behavior because of residual crack openings. Above the point where the cracks close, the compressive behavior is linear. Global compressive failure is characterized by a major crack oriented at a certain angle to the axial loading. In shear, the matrix cracks orientate in the principal tensile stress direction (i.e., 45° to the fiber direction) with very high crack densities before failure, but only SiC/SiC shows significant degradation in shear modulus. Hysteresis is observed during unloading/reloading sequences and increasing permanent strain.
Phase Diagram Studies in the Systems La2O3–SrO–Ga2O3, La2O3–MgO–Ga2O3, and SrO–MgO–Ga2O3 at 1400°C in Air
Authors: Majewski Peter J. , Rozumek Michael , Schluckwerder Heike , Aldinger Fritz
Published: January 2009

The ternary systems La2O3–SrO–Ga2O3, La2O3–MgO–Ga2O3, and SrO–MgO–Ga2O3 were studied at 1400°C in air, with emphasis on LaGaO3. The compound exhibited a small solid solubility of strontium substituting for lanthanum and also of magnesium substituting for gallium. In the system La2O3–SrO–Ga2O3, LaGaO3 existed only within a very narrow concentration region, whereas in the system La2O3–MgO–Ga2O3, LaGaO3 was in equilibrium with most of the phases of the system. The system SrO–MgO–Ga2O3 at 1400°C in air was characterized by an extended liquid phase at ∼1185°C.
Effect of Composition on Microstructural Development in MgO–Al2O3–SiO2 Glass‐Ceramics
Authors: Hwang Shiang‐Po , Wu Jenn‐Ming
Published: January 2009

The transformation kinetics and microstructures of glass‐ceramics, which deviate from those of a stoichiometric cordierite compound, are greatly dependent on the compositions of the starting glasses. Compositions richer in (MgO,SiO2) than the stoichiometric cordierite compound suppress the formation of μ‐cordierite, yet enhance the crystallization of α‐cordierite, resulting in a higher content of α‐cordierite. In contrast, compositions richer in Al2O3 than the stoichiometric cordierite compound have no effect on the crystallization of α‐cordierite. Thus, most of the glass crystallizes to μ‐cordierite in the initial stage, followed by the slow transformation of μ‐cordierite into an α‐phase, which results in a low content of α‐cordierite.
Effect of Coarse‐Powder Portion on Abnormal Grain Growth during Hot Pressing of Commercial‐Purity Alumina Powder
Authors: Cho Seong‐Jai , Lee Yun‐Cheol , Yoon Kyung‐Jin , Kim Jong‐Jip , Hahn Jun‐Hee , Park Hyun‐Min , Yanagisawa Masaaki
Published: January 2009

By classification, two powder portions, one consisting of coarse particles and the other consisting of fine particles, were separated from a MgO‐doped (1000 ppm) commercial‐purity Al2O3 powder. Examinations of microstructure evolution during hot pressing showed that extensive abnormal grain growth occurred for the coarse portion. For the fine portion, although there was an indication that grain‐size distribution deviated from normal distribution on prolonged hot pressing, such extensive abnormal grain growth did not occur. Extensive abnormal grain growth also occurred when the coarse portion was mixed into a high‐purity powder that exhibited no abnormal grain growth alone. Chemical analyses revealed that the coarse portion contained the higher concentration of impurities but lower concentration of magnesium than the fine portion. It was discussed that particle aggregates in the coarse portion might have been responsible for the higher concentration of impurities but lower concentration of magnesium and, thus, for the extensive abnormal grain growth.
Crystal Structure of Metastable Tetragonal Zirconia up to 1473 K
Authors: Igawa Naoki , Ishii Yoshinobu
Published: January 2009

The crystal structure of metastable tetragonal zirconia prepared via the alkoxide method has been investigated at temperatures up to 1473 K, to clarify the similarity between this metastable phase and the tetragonal phase at high temperature. The lattice constants, tetragonality, oxygen shift parameter, and equivalent isotropic thermal parameter of the metastable tetragonal phase are proportional to the temperature. These parameters, when extrapolated to the high‐temperature range, are very similar to those of the high‐temperature tetragonal phase. Present results indicate that the structure of the metastable tetragonal phase is the same as that of the high‐temperature tetragonal phase.
Investigation of Magnetic Force for Barium and Strontium Ferrites
Authors: Hosseinpour Ardeshir , Zakery Abdolnaser
Published: January 2009

A new method is presented for calculation of the maximum magnetic force of magnetic ceramics, based on their crystalline structure. The results of this model for the magnetic forces of barium and strontium ferrites are compared with experimental values. In this comparison, the experimental values are less than the values determined by the theoretical model for various magnet cross‐sectional areas. This difference is due to the presence of crystal imperfections and incomplete alignment of the magnetic domains. In addition, the magnetic forces of barium and strontium ferrites are a sensitive function of their heat treatments.
Effective Medium Theory of the Porosity Dependence of Bulk Moduli
Authors: Munro Ronald G.
Published: January 2009

Effective medium theory is used to obtain a closed‐ form expression for the porosity dependence of the bulk moduli of ceramics. The theory is illustrated with an application to data for high‐purity alumina that spans a volume fraction of porosity ranging from 0.5% to 90%.
Effect of pH on the Chemistry of the Barium Titanium Citrate Gel and Its Thermal Decomposition Behavior
Authors: Fang Tsang‐Tse , Tsay Jenq‐Dar
Published: January 2009

In this investigation, X‐ray diffractometry and 13C NMR spectroscopy were used to characterize the effect of pH on the formation of gel and its thermal decomposition by the Pechini process. It was found that the major effect of pH was to destroy the esterification between citric acid (CA) and ethylene glycol, which in turn could influence Ba species and the formation of a mixed‐metal CA complex. It was also found that barium carbonate was derived from the Ba species and was not related to the instability of Ba2Ti2O5CO3, but Ba2Ti2O5CO3 was formed by the thermal decomposition of a mixed‐metal CA complex. Moreover, BaTiO3 formed via two routes, the reaction of BaCO3 with Ti species and thermal decomposition of Ba2Ti2O5CO3.
Kinetics of Templated Grain Growth of 0.65Pb(Mg1/3Nb2/3)O3·0.35PbTiO3
Authors: Sabolsky Edward M. , Messing Gary L. , Trolier‐McKinstry Susan
Published: January 2009

Single‐crystal layers of 0.65Pb(Mg1/3Nb2/3)O3·0.35PbTiO3 (PMN‐35PT) were grown heteroepitaxially on {001}‐BaTiO3 template crystals. A {001}‐BaTiO3 crystal was embedded in a fine‐grained matrix of PMN‐35PT containing excess PbO and heated between 950° and 1150°C for 0–5 h. The initial growth of the PMN‐35PT on the {001} surface and the growth of the matrix grains both displayed a t1/3 dependence which is characteristic of diffusion‐controlled growth. Growth was limited to ∼100–150 μm due to the significantly reduced driving force at longer times because of matrix coarsening and porosity evolution.
Effect of Silica Surface Dopants on the Formation of Alumina/Aluminum Composites by the Directed Metal Oxidation of an Aluminum Alloy
Authors: Park Hong Sik , Kim Do Kyung
Published: January 2009

This study focused on clarifying the effect of SiO2 surface dopants on the formation of Al2O3/aluminum composites, especially on oxidation phenomena during the incubation period. The present results showed that a surface dopant decreased the incubation period of an Al‐Mg‐Si alloy, as well as that of an Al‐Mg alloy, and that addition of an external surface dopant decreased the incubation period more effectively than did an internal alloying of silicon. A two‐step oxidation process was also conducted. In the first step of the process, an aluminum alloy was oxidized without a surface dopant and cooled to room temperature during the incubation stage. In the second step, the same specimen was surface‐doped with SiO2 powder and reoxidized. The incubation time for the specimen subjected to the two‐step oxidation process was the same as that for the single‐step specimen oxidized with a surface dopant. The substantial decrease in the incubation period, especially for the Al‐Mg alloy, is ascribed to interaction between the SiO2 surface dopant and the MgO layer. This interaction made the MgO layer thinner and increased the number of magnesium vacancies in the MgO layer, thus providing an appropriate microstructure in the MgO layer for bulk‐growth initiation.
Hydrothermal Synthesis and Formation Mechanisms of Lanthanum Tin Pyrochlore Oxide
Authors: Moon Jooho , Awano Masanobu , Maeda Kunihiro
Published: January 2009

Well‐defined La2Sn2O7 with a phase‐pure pyrochlore structure was produced by hydrothermal synthesis at temperatures as low as 200°C. Production of phase‐pure La2Sn2O7 requires a pH above 10, and higher pH accelerates the crystallization process. The synthesis produced spherical particles of average particle size ∼0.59 μm (±0.12) and surface area ∼14.1 m2/g. SEM and TEM observation for morphologic evolution and kinetic analysis during crystallization indicated that La2Sn2O7 formation probably proceeds via a two‐step reaction. First a transient dissolution–precipitation occurs. Then the primary crystallites aggregate because of their colloidal instability, and heterocoagulation with the lanthanum hydrous oxide precursor particles also occurs. The sluggish reaction rate at the later stage of reaction is characterized by an insitu transformation, where the soluble tin species is diffused through the porous La2Sn2O7 aggregates to react with entrapped lanthanum precursors.
Effect of Phosphorus Ions on the Proton Conductivity in the Sol–Gel‐Derived Porous Glasses
Authors: Nogami Masayuki , Goto Yoichi , Tsurita Yasushi , Kasuga Toshihiro
Published: January 2009

The effect of phosphorus ions on the proton conductivity was examined for the sol–gel‐derived glasses. The porous glasses were prepared through hydrolysis of PO(OCH3)3 and Si(OC2H5)4, in which the phosphorus ions consisted of the POH bonds and were dissolved into the silica matrix without any P‐O‐Si bond. The electrical conductivity increased in a humid atmosphere and reached ∼30 mS/cm at 50°C under 70% RH. High conductivity is achieved by both the POH bonds and the molecular water bonded to the POH bonds. The conductivity increased with a change in humidity from 40% to 80% RH. The phosphorus ions were selectively dissolved in water, resulting in a lower conductivity.
Phase Relations and Dielectric Properties in the Bi2O3–ZnO–Ta2O5 System
Authors: Youn Hyuk‐Joon , Sogabe Tomohiro , Randall Clive A. , Shrout Tom R. , Lanagan Michael T.
Published: January 2009

Dielectric properties and phase formation of Bi‐based pyrochlore ceramics were evaluated for the Bi2O3–ZnO–Ta2O5 system. The compositional range rBi2(Zn1/3Ta2/3)2O7· (1−r)(Bi3/2Zn1/2)(Zn1/2Ta3/2)O7 (0 ≤r≤ 1) in Bi2O3–ZnO–Ta2O5 was investigated to determine the relative solubility of BZT cubic (α‐BZT, r= 0) and the pseudo‐orthorhombic (β‐BZT, r= 1) end members. It was found that extrinsic factors, such as kinetically limited phase formation and bismuth loss, contribute to apparent phase boundaries in addition to thermodynamic stability of each phase. Considering this, the locations of true phase boundaries were r < 0.30 and r≥ 0.74 for α and β phases, respectively. Dielectric constants between 58 and 80 and low dielectric loss (tan δ < 0.003) were measured for the complete compositional range. The temperature coefficient of capacitance was controlled by composition, which was found to be <30 ppm/°C at the edge of β‐phase solid solution. In addition to the excellent dielectric properties these materials can be sintered at low temperatures, which make Bi‐based pyrochlores promising candidates for high‐frequency electronic applications.
Measurement of Very Slow Crack Growth in Glass
Authors: Kocer Cenk , Collins Richard E.
Published: January 2009

The rate of very slow crack growth in glass is measured by inducing small, controllable changes in the direction of propagation of Hertzian cone cracks at known times. After completion of a growth sequence, the sample is sectioned to reveal the fracture surface. The stress intensity factor at each stage of crack growth is calculated by using finite‐element modeling of the stresses near the crack tip. Data are presented for crack growth velocities as low as 10−14 m/s in soda–lime glass. These data provide strong evidence for the existence of a subcritical limit for crack growth in this material.
Compression Creep Characteristics of 8‐mol%‐Yttria‐Stabilized Cubic‐Zirconia
Authors: Sudhir B. , Chokshi Atul H.
Published: January 2009

Constant stress compression creep tests were conducted on 8‐mol%‐yttria‐stabilized cubic‐zirconia (8YCZ) over stress (ς), temperature, and grain‐size ranges from ∼20 to 300 MPa, 1673 to 1773 K, and 4 to 8 μm, respectively. Creep data were analyzed in terms of the relationship [epsivdot] ∝ςn, where [epsivdot] is the strain rate and n the stress exponent. Although the experimental data yielded a stress exponent of n & 2, analysis of the results with compensation of significant concurrent grain growth revealed that the true stress exponent was n∼ 1. The results were consistent with deformation by the Coble creep mechanism. Experiments at stresses greater than ∼100 MPa revealed a transition from grain‐size‐dependent Coble diffusion creep to grain‐size‐independent intragranular dislocation creep.
Oxide–Oxide Interfaces: Atomistic and Density Functional Study of Cubic‐ZrO2 (100) ‖ NiO (111)
Authors: Guo Chang‐Xin , Warschkow Oliver , Ellis Donald E. , Dravid Vinayak P. , Dickey Elizabeth C.
Published: January 2009

The cubic‐ZrO2 (100) ‖ NiO (111) interface provides an opportunity for comparison between atomic‐scale measurements, atomistic simulations, and theoretical electronic structures. High‐resolution electron microscopy indicates that the oxides share a common oxygen layer and that the small lattice strain is largely taken up by NiO near the interface. Using simple Coulomb plus Buckingham‐type interatomic potentials, we are able to provide a more focused picture, revealing two types of boundary. The lowest energy interface is highly planar, almost ideal in structure; there is a second interface, of higher energy, that shows a rumpled structure with strain taken up by deformation of nickel chains. Depth profiling of atomic site energies permits calculation of interface versus bulk and surface energies, and it shows that the interface effects penetrate only two to three atomic layers. Embedded cluster density functional studies of bulk and interface‐region sites permit the characterization of perturbations of electronic density around the boundaries.
Fluid Dynamics and Thermal Aspects of the Dewatering of High‐Alumina Refractory Castables: Removal of Physically Absorbed Water
Authors: Innocentini Murilo D. M. , Ribeiro Caue , Bittencourt Luis R. M. , Pandolfelli Victor C.
Published: January 2009

This article reports on an experimental investigation of the dewatering process of cement‐free high‐alumina refractory castables. Simultaneous fluid dynamic, thermal, and mass loss effects were investigated during the removal of physically absorbed water at temperatures of 25° to 700°C. The release of steam was decisively affected by the castable's permeability level and the heating rate applied. The analysis of fluid dynamics revealed that at 1°C/min, the main bulk of physical water was released as steam under saturated conditions at 100°C. However, at 5°C/min, steam was trapped within the pores, and water loss was chaotically released and shifted to higher temperatures. Thermal analysis showed that the endothermic boiling of water may result in a critical thermal shock in the castable's structure. Both steam entrapment and thermal shock were more severe with the reduction in the castable's permeability level.