bluuebunny/crossref_metadata_2025 huggingface dataset:
Intermediate Phase Development in Phosphorus‐Doped Barium Titanate
Authors: Caballero Amador C. , Fernández José F. , Villegas Marina , Moure Carlos , Durán Pedro , Florian Pierre , Coutures Jean‐Pierre
Published: July 2010

In the present work, the phase formation and thermal evolution in phosphorus‐doped BaTiO3 have been studied using differential thermal analysis, X‐ray diffractometry, scanning electron microscopy coupled with energy‐dispersive spectroscopy, transmission electron microscopy, and high‐temperature nuclear magnetic resonance. Phosphorus cations that are incorporated from ester phosphate form a surface layer that covers the BaTiO3 particles. This layer acts as a reactive coating during sintering. Phosphorus‐doped BaTiO3 samples that have been treated at temperatures of 650°–900°C show the presence of crystalline Ba2TiP2O9 and/or Ba3(PO4)2 phases. The appearance of secondary phases is dependent on the cooling rate. Higher temperatures (900°–1200°C) result in the presence of a phosphorus–BaO‐rich phase that covers the BaTiO3 particles. As a consequence, the remaining titanium‐rich BaTiO3 drives the formation of a liquid phase at temperatures >1200°C. In regard to the reported sintering behavior of P5+‐doped BaTiO3, the formation of a phosphorus–BaO‐rich phase that covers the BaTiO3 particles could be the origin of the improved porosity coalescence and removal that is observed at the earlier stages of sintering.
Effect of Hot‐Pressing Temperature on Densification and Mechanical Properties of Titanium Diboride with Silicon Nitride as a Sintering Aid
Authors: Park June‐Ho , Lee Yong‐Ho , Koh Young‐Hag , Kim Hyoun‐Ee , Su Baek Seung
Published: July 2010

The effect of hot‐pressing temperature on the densification behavior and mechanical properties of titanium diboride (TiB2) was investigated. TiB2 specimens were hot‐pressed for 1 h at temperatures in the range of 1500°–1800°C, with an addition of 2.5 wt% of silicon nitride (Si3N4) as a sintering aid. The density increased markedly at temperatures in the range of 1500°–1600°C and remained constant thereafter. The formation of a eutectic liquid at 1550°C was attributed to the steep increase in density. The hot‐pressing temperature also improved the mechanical properties, such as the flexural strength, Vickers hardness, and fracture toughness of the specimens. Similar to the density, the mechanical properties improved remarkably at ∼1550°C, so that optimum properties were obtainable at temperatures as low as 1600°C.
Dispersion and Consolidation of Alumina Using a Bis‐Hydrophilic Diblock Copolymer
Authors: Palmqvist Lisa M. , Lange F. F. , Sigmund Wolfgang , Sindel Jürgen
Published: July 2010

A water‐soluble diblock copolymer, poly[(methacrylic acid)‐b‐(ethylene oxide)], has been used to formulate alumina slurries that are dispersed over a wide range of pH through a combination of electrostatic and steric repulsion. The anionic poly(methacrylic acid) block, a short chain (MW∼700 g/mol), interacts with the amphoteric alumina surface at pH 3 and acts as an anchor block. The nonionic poly(ethylene oxide) (PEO) block (MW= 3000 g/mol) only appears to have a steric functionality. At high pH, the polymer coated surface has a net negative charge due to the excess negative sites associated with the highly dissociated methacrylic acid (MAA) units; this provides electrostatic repulsion at, for example, pH 9, which is the isoelectric point for pure alumina. The PEO chains extend from the surface and stabilize the alumina particles between pH 5 to 9 via an entropy‐driven, steric repulsion. The PEO chains provide the dominating dispersive force at low pH, where very little electrostatic repulsion is possible because the positive surface charge of alumina has been neutralized by the negative sites of the adsorbed polyacid. On consolidation through pressure filtration at low pressures (2 to 5 MPa), the saturated, consolidated bodies formulated at pH 5 have a relative density of ∼0.56. These consolidated bodies initially exhibit a flow stress, but then fluidize after an extended strain (up to 0.5). The fluidization phenomenon is believed to be due to the unraveling of the PEO chains that appear to entangle between adjacent particles during consolidation. The unraveling was directly observed with an atomic force microscope between two BaTiO3 surfaces coated with the same diblock copolymer used for the alumina powder.
Forming and Sintering of in Situ Alumina Composite with Hydraulic Inorganic Binder
Authors: Nagaoka Takaaki , Iwamoto Yuji , Kikuta Koichi , Hirano Shin‐ichi
Published: July 2010

Two types of barium aluminate binders were prepared by heat treatment of barium aluminate precursors, synthesized by using solution processes, at low temperatures (T < 500°C). One was barium monoaluminate (BaAl2O4), and the other was barium aluminate binder (BAH binder) composed of amorphous phase, barium aluminate monohydrate (BaAl2O4·H2O), and BaAl2O4. The setting time of the BAH binder was controlled by adjusting the heat‐treatment temperature of the BAH binder precursor. The addition of the synthesized BaAl2O4 powders to Al2O3 powders improved the bending strength of Al2O3 matrix green bodies. The synthesized BaAl2O4 powders led to the in situ forming of barium hexaaluminate (BaO·xAl2O3, x= 6.9: BA6) platelets in the matrix by reacting with Al2O3 during sintering. The formed BA6 platelets inhibited the grain growth of the matrix Al2O3 grains.
Performance of Four Ceramic‐Matrix Composite Divergent Flap Inserts Following Ground Testing on an F110 Turbofan Engine
Authors: Staehler James M. , Zawada Larry P.
Published: July 2010

Four ceramic‐matrix composite flap inserts were evaluated following ground testing on a General Electric F110 turbofan engine. Three of the composites accumulated ∼117 h of engine time. The fourth composite, a NextelTM 720 material with aluminosilicate matrix, accumulated ∼40 h. Large through‐thickness cracks developed along the longitudinal edges of a Nicalon™/Al2O3 insert and the Nextel 720/aluminosilicate insert. The cracks developed because of high tensile stresses caused by the steep in‐plane thermal gradients induced across the flap width during afterburner lights. The Nextel 720/aluminosilicate insert also exhibited severe surface wear associated with the acoustic environment and contact with the adjacent divergent seals. Neither a Nicalon/silicon nitrocarbide insert nor a Nicalon/C insert exhibited significant signs of distress.
Paralinear Oxidation of CVD SiC in Simulated Fuel‐Rich Combustion
Authors: Fox Dennis S. , Opila Elizabeth J. , Hann Raiford E.
Published: July 2010

The oxidation kinetics of CVD SiC were measured by thermogravimetric analysis (TGA) in a 4H2·12H2O·10CO·7CO2·67N2 gas mixture flowing at 0.44 cm/s at temperatures between 1300° and 1450°C in fused quartz furnace tubes at 1 atm total pressure. The SiC was oxidized to form solid SiO2. At ≥1350°C, the SiO2 was in turn volatilized. Volatilization kinetics were consistent with the thermodynamic predictions based on SiO formation. These two simultaneous reactions resulted in overall paralinear kinetics. A curve fitting technique was used to determine the linear and parabolic rate constants from the paralinear kinetic data. Volatilization of the protective SiO2 scale resulted in accelerated consumption of SiC. Recession rates under conditions more representative of actual combustors were estimated from the furnace data.
Abnormal Grain Growth at the Interface of Centrifugally Cast Alumina Bilayer during Sintering
Authors: Cho Seong‐Jai , Kim Kyung‐Hee , Kim Dong‐Jin , Yoon Kyung‐Jin
Published: July 2010

Extensive abnormal grain growth occurs locally at the interface of centrifugally cast bilayers of MgO‐doped (1000 ppm) Al2O3 (99.8% purity) during sintering. Results of systematic experiments indicate that the abnormal grain growth is attributable to particle aggregates segregated at the interface during centrifugal casting. Apparently, the particle aggregates contain a higher concentration of impurities than do the fine primary particles, causing local abnormal grain growth at the interface.
Influence of Reaction Parameters on the Microstructure of the Germanium Disulfide Gel
Authors: Stanić Vesna , Pierre Alain C. , Etsell Thomas H. , Mikula Randy J.
Published: July 2010

A GeS2 gel was prepared by sol–gel processing of Ge(OEt)4 and H2S in toluene solution. The effects of H2S and germanium ethoxide concentrations, concentration ratio, and temperature on the microstructure of the prepared GeS2 gels were studied. It was found that the concentrations of the reactants had the most significant influence on primary particle size and gel morphology. The microstructure of the dried gels was characterized by nitrogen BET analysis, SEM, powder XRD analysis, and infrared spectroscopy. Results indicate that the GeS2 gels are amorphous colloidal xerogels regardless of the reaction conditions and length of aging.
Microstructure Control of In‐Situ‐Toughened α‐SiAlON Ceramics
Authors: Kim Joosun , Rosenflanz Anatoly , Chen I‐Wei
Published: July 2010

Single‐phase α‐SiAlON with elongated grains is obtained from α‐Si3N4 powder for a broad range of compositions of practical interest. Following the concept of nucleation and growth, two‐step firing is used for microstructure control. This method takes advantage of the slow transformation reaction from α‐Si3N4 to α‐SiAlON at low temperature when the composition is near the α‐SiAlON phase boundary and, hence, is marginally stable. For more‐stable compositions, the seeding of α‐SiAlON crystals is more effective, because it allows elongated grains to grow onto the seed crystals. The fracture toughness is strongly correlated with the microstructure and is enhanced greatly in the optimized materials.
Bismuth/Samarium Cosubstituted Ba6−3xNd8+2xTi18O54 Microwave Dielectric Ceramics
Authors: Wu Yong Jun , Chen Xiang Ming
Published: July 2010

Modification of the microwave dielectric properties in Ba6−3xNd8+2xTi18O54 (x= 0.5) solid solutions by Bi/Sm cosubstitution for Nd was investigated. A large increase in the dielectric constant and near‐zero temperature coefficient combined with high Qf values were obtained in modified Ba6−3xNd8+2xTi18O54 solid solutions where an enlarged solid solution limit of Bi in Ba6−3xNd8+2xTi18O54 was observed. Excellent microwave dielectric characteristics (ɛ= 105, Qf= 4110 GHz, and very low τf) were achieved in the composition Ba6−3x(Nd0.7Bi0.18Sm0.12)8+2xTi18O54.
Sintering Behavior of Nanocrystalline Zirconia Doped with Alumina Prepared by Chemical Vapor Synthesis
Authors: Srdić Vladimir V. , Winterer Markus , Hahn Horst
Published: July 2010

Powders of nanocrystalline zirconia doped with 3–30 mol% alumina have been synthesized using chemical vapor synthesis (CVS). Dense or mesoporous ceramics of small and narrowly distributed grain and pore sizes in the nanometer range are obtained via pressureless vacuum sintering. The microstructural development of the doped samples is strongly dependent on the alumina content. Sintering of zirconia samples with 3 and 5 mol% alumina at temperatures of 1000°C for 1 h results in fully dense, transparent ceramics with grain sizes of 40–45 nm and homogeneous microstructures.
Glass Formation and Polyamorphism in Rare‐Earth Oxide–Aluminum Oxide Compositions
Authors: Weber J. K. Richard , Abadie Johan G. , Hixson April D. , Nordine Paul C. , Jerman Gregory A.
Published: July 2010

We report formation of single‐ and two‐phase glasses from rare‐earth oxide–alumina materials. Liquids with the Y3Al5O12 and Er3Al5O12 compositions underwent a liquid–liquid phase transition which resulted in glasses with a cloudy appearance due to spheroids of one glass in a matrix of a second glass. The two glasses were isocompositional within the limits of experimental error. Clear, brilliant, single‐phase glasses were obtained from La3Al5O12, ErLaYAl5O12, and compositions containing ≥5 mol% La2O3 substituted for the other rare‐earth oxides. Formation of two glasses is attributed to nucleation and growth of the second liquid at a temperature below the equilibrium liquid–liquid transition temperature. Addition of lanthanum depresses the phase transition temperature below the glass transition temperature and the liquid–liquid phase transition is not observed. The results are discussed in the context of first‐order liquid–liquid phase transitions (polyamorphism) and formation of single‐phase glass from liquids that contain a high proportion of 4‐coordinate aluminum ions.
Disorder in Pyrochlore Oxides
Authors: Minervini Licia , Grimes Robin W. , Sickafus Kurt E.
Published: July 2010

Contour plots of disorder reaction energies across a wide variety of A2B2O7 pyrochlore oxides have been produced, using atomistic simulation calculations based on energy‐minimization techniques. The cations studied range from Lu3+ to La3+ on the A site and from Ti4+ to Ce4+ on the B site. The present results relate the experimentally observed stability range of the pyrochlore structure to A and B cation size and disorder. Disorder enthalpies decrease dramatically with increasing B cation size, while the rate of increase with A cation size depends markedly on the particular B cation. The association of anion Frenkel and cation antisite disorders is found to be of importance.
Electrophoretic Deposition Forming of Nickel‐Coated‐Carbon‐Fiber‐Reinforced Borosilicate‐Glass‐Matrix Composites
Authors: Kaya Cengiz , Boccaccini Aldo R. , Chawla Krishan K.
Published: July 2010

The present paper introduces a novel processing technique that involves in situ electrophoretic deposition (EPD), followed by pressureless sintering, to produce dense, defect‐minimized, carbon‐fiber‐reinforced borosilicate‐glass‐matrix composites with a nickel interface. The process relies on the deposition of submicrometer‐sized, colloidal charged particles onto unidirectionally aligned nickel‐coated carbon fibers. The preparation and characterization of a kinetically stable nanosized borosilicate sol suitable for EPD are described. The most‐important EPD processing parameters in the formation of dense, fully infiltrated, green‐body compacts are described, and issues that concern the infiltration of very tight carbon fiber preforms are discussed and effectively solved. Using the crack‐path‐propagation test, the metallic nickel interface is determined to be very effective to improve the composite mechanical performance, in terms of the nonbrittle fracture behavior. Catastrophic crack growth is prevented by such mechanisms as constrained plastic deformation of the interface and fiber debonding and pullout. The proposed processing technique has great potential to fabricate defect‐minimized and damage‐tolerant fiber‐reinforced brittle‐matrix composites with a ductile interface. Overall, this new approach offers a cost‐effective and short‐time processing route for the fabrication of continuous‐fiber‐reinforced ceramic‐matrix composites.
Evolution of Microstructures and Nitrogen Sorption during High‐Energy Milling of Silicon in Ammonia
Authors: Yang Zhenguo , Ren Ruiming , Shaw Leon L.
Published: July 2010

The structural transformation, microstructural changes, and nitrogen sorption of crystalline Si induced by high‐energy ball milling in ammonia have been investigated. It is found that significant refinement of particles and crystallites occurs at the early stage of milling (within ∼10 h of milling), after which the average particle size and crystallite size decrease gradually and approach a lower limit of ∼100 and 6.0 nm, respectively. It is proposed that refinement of particle sizes is dominated by the fragmentation process, whereas refinement of crystallite sizes is dictated by plastic deformation. Substantial amorphization does not occur until most of the crystallites have reached the average size of 6.5–6.0 nm. The crystallite‐refinement‐induced amorphization has been identified as the major mechanism for the nanocrystalline‐to‐amorphous transformation. A substantial amount of nitrogen is sorbed by Si powders and primarily dissolved in the amorphous Si phase.
Determination of the Degree of Mixing in Multicomponent Ceramic Powder Compacts by Micro‐Raman Spectroscopy
Authors: Dobal Pramod S. , Das Rasmi R. , Katiyar Ram S. , Agrawal Dinesh C.
Published: July 2010

Powder compacts of TiO2 and ZrO2 were prepared from their suspensions in water at different pH values, and micro‐Raman spectroscopy was used to reveal the degree of mixing in each of them, with different sizes of the focused laser spot. The change in laser intensity and particle‐size distributions led to a slight variation in the average composition, as determined using three different probe sizes. The Raman‐estimated volume fractions of each constituent indicated that the aqueous suspensions in which the powders were well dispersed produced the most‐uniform mixing. Powders that were flocculated in suspensions before mixing also resulted in a good mixture. The most‐nonuniform mixing was observed when, in the individual suspensions, one of the constituents was dispersed and the other was flocculated. These results indicated that Raman spectroscopy can be useful for the rapid determination of the degree of mixing in powder mixtures.
Instrumented Micro‐indentation of Zirconia Ceramics
Authors: Alcalá Jorge
Published: July 2010

Instrumented micro‐indentation experiments are conducted with Vickers and spherical indenters in Y‐TZP and two different Mg‐PSZ ceramics. The load (P)–depth of penetration (h) curves from Vickers indentation can be fitted to P=Chn with n∼ 1.8. It is shown that within the micro‐indentation range, measurements of Young's modulus (E) can be conducted in zirconia ceramics using sharp indenters, and that the results are consistent with those from spherical indentation. Quantification of piling‐up and sinking‐in is accomplished from P–h curves. Results from finite element computations are used to assess pressure‐sensitivity and plastic‐hardening coefficient from indentation experiments.
Reaction Mechanism in Alumina/Chromia (Al2O3–Cr2O3) Solid Solutions Obtained by Coprecipitation
Authors: Bondioli Federica , Ferrari Anna Maria , Leonelli Cristina , Manfredini Tiziano , Linati Laura , Mustarelli Piercarlo
Published: July 2010

The aim of this work is to study the structural characteristics and properties of the solid solution (Al,Cr)2O3. XRD analysis, 27Al MAS‐NMR measurements, and microstructural characterization were used to determine the relationship between color and crystallochemical properties of the compounds formed. In particular, to determine more accurately the mechanism of solid solution formation above the miscibility gap of the system, the marker technique was used. In order to define the behavior of the system for temperatures below the miscibility gap at 1 bar pressure, the composition Al2O3:Cr2O3 1:1 was studied with high‐temperature XRD.
Comparison of Texture Analysis Techniques for Highly Oriented α‐Al2O3
Authors: Seabaugh Matthew M. , Vaudin Mark D. , Cline James P. , Messing Gary L.
Published: July 2010

Texture measurements were performed on liquid‐phase‐sintered alumina textured by a templated grain growth process from 1250° to 1650°C. Texture distributions were measured using X‐ray pole figures, rocking curves, Rietveld refinement, and stereology. The March–Dollase equation fitted the measured distributions very well and gave quantitative values of the degree of texture and the texture fraction. The fitting parameters of the X‐ray diffraction measurements were comparable to those measured by stereology. Rocking curve analysis was found to be straightforward and to give accurate characterization of texture in the alumina system of this study in a relatively short time.
Processing, Microstructure, and Strength of Alumina–YAG Eutectic Polycrystals
Authors: Mah Tai‐Il , Parthasarathy Triplicane A. , Kerans Ronald J.
Published: July 2010

Dense polycrystalline eutectics of alumina and yttrium aluminum garnet (YAG) were fabricated by hot‐pressing powders of pulverized arc‐melted buttons at homologous temperatures of 0.9Teu–0.93Teu (where Teu is the eutectic temperature). The eutectic microstructure of the arc‐melted buttons was retained after densification, although the grain boundaries were decorated with equiaxed grains of alumina and YAG ∼1–5 μm in size; possible causes for their formation have been discussed. A comparison of the measured strength of the polycrystalline eutectics (274 ± 61 MPa) with grain size and fracture toughness suggests that the strength‐limiting flaws are significantly smaller than the mean grain size and larger than the mean eutectic spacing.
New Uniformly Porous CaZrO3/MgO Composites with Three‐Dimensional Network Structure from Natural Dolomite
Authors: Suzuki Yoshikazu , Morgan Peter E. D. , Ohji Tatsuki
Published: July 2010

Porous CaZrO3/MgO composites with a uniform three‐dimensional (3‐D) network structure have been successfully synthesized using reactive sintering of highly pure mixtures of natural dolomite (CaMg(CO3)2) and synthesized zirconia powders with LiF additive. Equimolar dolomite and zirconia powders doped with 0.5 wt% LiF were cold isostatically pressed at 200 MPa and sintered at 1100–1400°C for 2 h in air. Through the liquid formation via LiF doping, strong necks were formed between constituent particles before completion of the pyrolysis of dolomite, resulting in the formation of a 3‐D network structure. During and after the formation of the network structure, CO2 was given off to form a homogeneous open‐pore structure. The pore‐size distribution was very narrow (with pore size ∼ 1 μm), and the porosity was controllable (e.g., ∼30%–50%) by changing the sintering temperature. The porous composites can be applied as filter materials with good structural stability at high temperatures.
Surface Relief Induced by Martensitic Transformation in Phosphorus‐Bearing Dicalcium Silicate
Authors: Fukuda Koichiro , Taguchi Hiroyuki , Nomura Yasuteru , Ota Toshitaka
Published: July 2010

Crystals of (Ca1.955□0.045)(Si0.91P0.09)O4, where □ denotes a vacancy, have been prepared and examined by XRD, optical microscopy, SEM, and AFM. At 20°C, the crystals are composed of 38%α′L and 62%β phases. Upon cooling to −185°C, the α′L‐ to β‐phase transformation occurs, which increases the β‐phase composition to 72%. The transformation is also accompanied by the formation of platelike surface reliefs. The surface relief angles have been determined from observations (7.9°± 0.2°) and calculations based on a phenomenological analysis (7.84°). The fair agreement of these values indicates that the transformation is martensitic and mainly governed by a shear mechanism.
Fabrication of Graded Nickel–Alumina Composites with a Thermal‐Behavior‐Matching Process
Authors: Winter Andrew N. , Corff Brian A. , Reimanis Ivar E. , Rabin Barry H.
Published: July 2010

Composites of nickel and Al2O3 with compositionally graded microstructures were fabricated from powders through an empirically determined thermal‐behavior‐matching process that was designed to minimize processing‐induced stresses. Compositions ranged from pure Al2O3 to pure nickel. Specimen geometries included round disks 25 mm in diameter and 5–25 mm thick, as well as rectangular bars 25 mm × 25 mm in cross section and 75 mm long. Several different gradients were produced, including samples with single interlayers. Compacts were formed by cold uniaxial pressing in a die, followed by consolidation through sintering at 1 atm or hot isostatic pressing. Several different particle sizes of nickel and Al2O3 comprised the composite interlayers. The compaction behavior, sintering start temperature, sintering rate, and total linear shrinkage of each composition were evaluated. Careful data analysis, coupled with sintering theory, led to a layer configuration with matched green density and sintering behavior. Thermomechanically matched layers allowed large, crack‐free, graded composites to be produced.
Grain‐Growth Inhibition in Na2O‐Doped TiO2‐Excess Barium Titanate Ceramic
Authors: Lin Ming‐Hong , Chou Jung‐Fang , Lu Hong‐Yang
Published: July 2010

Pressureless‐sintered TiO2‐excess BaTiO3 (BT) ceramic doped with Na2O (as an acceptor oxide) has been investigated for the inhibition of platelike (111) twin grains and the associated microstructure development. Solid‐state reaction between the Na2O dopant and the excess TiO2 of the nonstoichiometric BaTiO3 powder during sintering has resulted in the formation of orthorhombic Na4TiO4(N4T) at temperatures of ≤1215°C. Enhanced densification is due to a liquid‐phase sintering mechanism, where the liquid eutectic is generated by reacting the excess TiO2 and the trace impurities of SiO2 and Al2O3 with the Na2O dopant. Suppression of the abnormally large, platelike grains occurs at a critical acceptor concentration of ∼0.50 mol% Na2O when sintering is conducted at 1215°C. The inhibition mechanism is associated with the secondary phases, whose formation gradually modifies the initially TiO2‐excess powder toward the stoichiometric composition. The corresponding sintered microstructure is analyzed using both scanning and transmission electron microscopy. The second‐phase precipitates of Na4TiO4, which are located intragranularly and intergranularly in the tetragonal BaTiO3 matrix grains, exhibit the following crystallographic orientation relationships: [110]BT// [100]N4T, (11)BT// (010)N4T, and (112)BT// (001)N4T.
Effects of Selected Processing Variables on Color Formation in Praseodymium‐Doped Zircon Pigments
Authors: Hill Kimberly , Lehman Richard , Swiler Dan
Published: July 2010

Although praseodymium yellow pigments have been used in industry for many years, a quantitative description of the effects of the processing parameters does not exist in the literature. A full factorial design has been used to investigate the effects of the particle size of the raw material, the mineralizer content, and the processing temperature on color formation. Results show that strong yellow colors are developed at temperatures of ∼900°C, and little benefit is realized at higher temperatures. The amount of fluoride mineralizer is a critical variable, especially at lower processing temperatures. Overall, color formation correlates strongly with the processing temperature, mineralizer content, and, to a lesser extent, particle size of the zirconia raw material.
Effect of Agglomerate Size Distribution on Loose Packing Fraction
Authors: Kong Consuelo Margarita , Lannutti John J.
Published: July 2010

Discrete element modeling was used to establish the effects of size distribution on loose packing fraction during the fall of 5000 to 10 000 agglomerates. Monosized distributions exhibited slightly lower packing fraction than “narrow” distributions. However, broad distributions always produced the lowest packing fraction. The application of radius ratio rules had an effect opposite to that intended. Smaller fines had a disproportionately large effect on packing fraction, an effect attributed to gaslike behavior. Gravity‐driven random packing in ceramic agglomerates was governed by a combination of “bridge” formation and kinetic agglomerate–agglomerate interactions, not by geometric constraints.
Novel Route to Lead‐Based Ferroelectric Compounds via Tetragonal Lead(II) Oxide Intermediates
Authors: Han Kyoung R. , Koo Hee Jin , Lim Chang Sup
Published: July 2010

Single‐phase perovskite lead‐based ferroelectric powders—Pb(Mg1/3Nb2/3)O3(PMN) or 0.9Pb(Mg1/3Nb2/3)O3–0.1PbTiO3(0.9PMN–0.1PT)—were prepared using Mg(NO3)2, instead of MgO or MgCO3, via a mixed‐oxide method and one‐step calcination. The reaction proceeded via the formation of 3Pb(NO3)2·7PbO, Pb(OH)2, tetragonal PbO, and then 2PbO–Nb2O5(P2N) for PMN or 3PbO–Nb2O5(P3N) for PMN–PT; a mixture of PMN and Pb2(MgxNb1.33)O5.33+x then formed, followed finally by the formation of single‐phase PMN or 0.9PMN–0.1PT. Such prepared powder showed excellent room‐temperature dielectric constants—13800 for PMN or 22600 for 0.9PMN–0.1PT—by sintering at a temperature of 900°C for 2 h.
Measuring Permeability of Rigid Materials by a Beam‐Bending Method: I, Theory
Authors: Scherer George W.
Published: July 2010

When a saturated porous material is deformed, pressure gradients are created in the liquid, and the liquid flows within the pores to equilibrate the pressure. This phenomenon can be exploited to measure permeability: A rod of saturated porous material is instantaneously bent by a fixed amount, and the force required to sustain the deflection is measured as a function of time. The force decreases as the liquid flows through the pore network, and the rate of decrease depends on the permeability. This technique has been applied successfully to determine the permeability of gels, as well as their viscoelastic properties; in this paper the method is extended to ceramic materials, such as porous glass and cement paste. The theory has been modified to take account of the compressibility of the solid and liquid phases (whereas, those factors are negligible for gels). Analyses are presented for constant deflection, constant rate of deflection, and sinusoidal oscillation, where the solid phase is either purely elastic or viscoelastic, and the beam is either cylindrical or square. Experimental tests on Vycor® glass and cement paste will be presented in companion papers.
Measuring Permeability of Rigid Materials by a Beam‐Bending Method: II, Porous Glass
Authors: Vichit‐Vadakan Wilasa , Scherer George W.
Published: July 2010

It has been shown in a companion paper that the permeability of a porous body can be found from a three‐point bending experiment. When the sample is bent, a pressure gradient is created in the liquid within the pores; as the liquid flows in response to the gradient, the force that must be applied to the rod to sustain a fixed deflection decreases with time. By fitting the force decay curve to the predicted shape, the permeability is obtained, along with the elastic modulus. In this paper, that theory is tested using porous Vycor® glass saturated with various solvents, including several normal alcohols, water, and glycerol. The shape of the measured decay is in excellent agreement with the prediction. Consistent with observations of previous workers, we find that the permeability is influenced by the size of the solvent molecule; by assuming that the pore surfaces are covered with a monolayer of immobile solvent, the observed variation can be explained. The advantage of the beam‐bending method is that the results are obtained in a few minutes; moreover, there is no problem with leaks or need for high pressures, as there is in conventional measurements of low permeabilities.
Elastic Constants of Erbia Single Crystals
Authors: Sharif Adel A. , Chu Fuming , Misra Amit , Mitchell Terence E. , Petrovic John J.
Published: July 2010

The elastic properties of single‐crystalline erbia (Er2O3) at room temperature have been investigated using resonant ultrasound spectroscopy. The three independent stiffness constants of anisotropic Er2O3 cubic type‐C crystals have been measured. The values of the stiffness constants were c11= 256.4 GPa, c12= 146.8 GPa, and c44= 75.2 GPa. From the stiffness constants, the estimated values for dense polycrystalline erbia for Young's modulus, the shear modulus, the bulk modulus, and Poisson's ratio at room temperature were 179 GPa, 67 GPa, 183.3 GPa, and 0.337, respectively. The value of Young's modulus is a minimum along [001] and a maximum along [111]. The value of the shear modulus is independent of the direction in the (001) and (111) planes, whereas it decreases in (11¯0) from 75 GPa along [001] to 55 GPa along [110].
Alumina Particle Degradation during Solid Particle Impact on Glass
Authors: Slikkerveer Peter J. , Veld Henri in't , Verspui Mariëtte , de With Bert , Reefman Derk
Published: July 2010

Particle degradation limits the reuse of powders in industrial powder‐blast processes. In this paper the degradation behavior of Al2O3 powder is studied during erosion of glass substrates. Three techniques were used on original and multiply used powders: particle size measurements, single particle crushing tests, and microstrain analysis by X‐ray diffraction. Combination of the three techniques shows that the degradation is dominated by flaws present in the original particles. Fracture at repeated use decreases the particle size, but by removing flaws also increases the degradation resistance of the particles.
Microstructural Observations in Barium Calcium Magnesium Niobate
Authors: Lee Hwack Joo , Park Hyun Min , Cho Yang Koo , Ryu Hyun , Song Yong Won , Paik Jong Hoo , Nahm Sahn , Byun Jae‐Dong
Published: July 2010

Microstructural studies on (1 −x)Ba(Mg1/3Nb2/3)O3–xCa(Mg1/3Nb2/3)O3 (BCMN) complex perovskite compounds, which are mixtures of Ba(Mg1/3Nb2/3)O3 (BMN) and Ca(Mg1/3Nb2/3)O3 (CMN), were conducted using scanning electron microscopy, transmission electron microscopy, and X‐ray diffractometry. Pure BMN and CMN both have a 1:2 ordered structure, via the chemical ordering of B‐site cations; however, the tilting of oxygen octahedra is involved in pure CMN, whose structure has a 1:2 ordered monoclinic unit cell that is characterized by (±1/6,±1/6,±1/6)‐type superlattice reflections in electron diffraction patterns along the [110] zone axis that is based on a simple cubic perovskite. Studies of the morphologic differences have indicated two types of inhomogeneities in a mixture of the BCMN system: (i) a rather large‐scale segregation (i.e., grain sizes of several micrometers), where the grains are separated compositionally as being barium‐rich or calcium‐rich, and (ii) fine‐scale lamellar‐type segregations 20 nm wide and 200 nm long. The segregation that is caused by Ba and Ca ions can be identified by the difference of superlattice modulations from high‐resolution transmission electron microscopy lattice images.
Molecular Dynamics Simulations of Calcium Aluminosilicate Intergranular Films on (0001) Al2O3 Facets
Authors: Litton David A. , Garofalini Stephen H.
Published: July 2010

Molecular dynamics simulations of intergranular films (IGF) containing SiO2, Al2O3, and CaO in contact with two surface terminations of the basal plane of Al2O3 were performed to model faceted grain boundaries in sintered Al2O3. In both the aluminum‐terminated and the oxygen‐terminated crystal surfaces, cage structures were observed in the intergranular film at the interface. Complete epitaxy of aluminum and silicon cations from the IGF was observed on the oxygen termination of the crystal surface. Calcium segregated to specific sites at the interface in all systems studied. Segregation of aluminum ions to the interface was observed from IGFs with high Al2O3 content. High‐SiO2 IGFs impeded the growth of the first of the two aluminum layers parallel to the basal plane, whereas CaO promoted the growth of this layer. However, CaO impeded the growth of the second aluminum layer parallel to the basal plane.
Quantitative Phase‐Composition Analysis of Liquid‐Phase‐Sintered Silicon Carbide Using the Rietveld Method
Authors: Ortiz Angel L. , Cumbrera Francisco L. , Sánchez‐Bajo Florentino , Guiberteau Fernando , Xu Huiwen , Padture Nitin P.
Published: July 2010

Accurate quantitative X‐ray diffraction analysis of SiC‐based ceramics is difficult because of the significant overlap of the Bragg reflections from the different SiC polytypes. In this regard, the Rietveld method is a powerful tool for the accurate and precise analysis of the phase/polytype compositions in these materials. In this study, we have used two different types of Rietveld codes for the quantitative phase/polytype analysis of a liquid‐phase‐sintered SiC specimen: FULLPROF, which is based on the classical Rietveld approach, and BGMN, which is based on the new fundamental parameter approach. In both cases, the effect of texture corrections on the precision of the analysis also was studied. The accuracy of the analysis, in terms of the weight percentage of SiC (all polytypes) and yttrium aluminum garnet liquid phase, as determined from the starting powder composition, is within the standard deviation of the analysis in both cases (FULLPROF and BGMN), with and without the texture corrections. In addition, in the case of the classical code (FULLPROF), inclusion of the texture corrections has been shown to improve the precision. In contrast, the precision of the analysis using the BGMN code without the texture corrections is better. However, inclusion of the texture corrections is expected to improve the accuracy of the analysis.
Microstructure of a Complex Oxide, Ho2MnxTa2−xO7(x≅ 1.0), with a Pyrochlore‐Related Structure
Authors: Nakano Hiromi , Kamegashira Naoki , Urabe Kazuyori
Published: July 2010

The ternary compound Ho2MnxTa2−xO7 was synthesized in air at 1523 K. Structural characterization of the compound was taken by X‐ray diffractometry (XRD) and transmission electron microscopy (TEM). The compound possessed a trigonal super cell derived from a rhombohedral basic cell with the a/2 of the trigonal super cell. The super cell was caused by the ordering of Mn and Ta ions and the derived structure model was in agreement with that of the zirkelite structure with the space group P3121. The compound had stacking disorder with different stacking sequences along the c‐axis. An orientation anomaly in the super cell reflections revealed that the super cell had an incommensurate nature.
Microwave Dielectric Properties and Far‐Infrared Reflectivity Characteristics of the CaTiO3–Li(1/2)−3xSm(1/2)+xTiO3Ceramics
Authors: Kim Woo Sup , Yoon Ki Hyun , Kim Eung Soo
Published: July 2010

Microwave dielectric properties and far‐infrared reflectivity spectra of the 0.3CaTiO3–0.7Li(1/2)−3xSm(1/2)+xTiO3 ceramics were investigated as a function of Sm3+ substitution (0.0 ≤x≤ 0.12). The dielectric constant decreased as the Sm3+ substitution increased. The Q×fvalue increased, up to a solid‐solution limit at x= 0.11, because of the change of vibration modes between the A‐site cation and the TiO6 octahedron, and then decreased because of the formation of a secondary phase (Sm2Ti2O7). On the analysis of the far‐infrared reflectivity spectra, in the 50–4000 cm−1 range, the change of the dielectric loss and dielectric constant could be explained by the intrinsic factor.
Influence of the Characteristics of Spinels on the Slag Resistance of Al2O3–MgO and Al2O3–Spinel Castables
Authors: Ko Yung‐Chao
Published: July 2010

The XRD patterns at ambient temperature and at 1500°C showed that the spinel in the Al2O3–MgO castables fired at 1500°C for 3 h has the higher peak intensity, compared to those in Al2O3–spinel castables; the interplanar distance in the set (311) is 2.43 Å for the spinel in Al2O3–MgO castables as well as the spinels in Al2O3–spinel castables using spinels containing 73, 90, and 94 wt% Al2O3, respectively. The corresponding alumina contents of the spinels in these castables were estimated to be around 75 wt%. The smaller grain size of the spinel in Al2O3–MgO castables compared to that in Al2O3–spinel castables is evidenced by the recrystallization of thein situspinel only occurring in Al2O3–MgO castables as revealed by the XRD patterns at ambient temperature and at 1500°C. The larger amount and smaller grain size of thein situ spinel in the matrix mostly account for the better slag resistance of Al2O3–MgO castables, compared to Al2O3–spinel castables.
Colloidal Processing of Ceramics
Authors: Lewis Jennifer A.
Published: July 2010

Colloidal processing of ceramics is reviewed with an emphasis on interparticle forces, suspension rheology, consolidation techniques, and drying behavior. Particular attention is given to the scientific concepts that underpin the fabrication of particulate‐derived ceramic components. The complex interplay between suspension stability and its structural evolution during colloidal processing is highlighted.
Electrophoretic Deposition and Characterization of Micrometer‐Scale BaTiO3 Based X7R Dielectric Thick Films
Authors: Zhang Jianping , Lee Burtrand I.
Published: July 2010

Uniform and relatively dense BaTiO3 thick films of 1–5 μm were prepared by an electrophoretic deposition process using submicrometer BaTiO3 powders (mean particle size: ∼0.2 μm). Two different BaTiO3 powders and solvent media were used to investigate the film quality and thickness control. The surface charge mechanism of BaTiO3 particles was explained according to the observed results. The microstructures were examined by means of SEM. The experimental results show that the thickness could be controlled independently of suspension concentration by keeping a constant applied voltage and a constant current drop in a given suspension. BaTiO3 thick films have good insulation resistance and dielectric properties such as a dielectric constant and a dissipation factor that are compatible with the data from conventional tape‐cast BaTiO3 thin layers.
Coal Slag Protection of Silicon Carbide with Chemically Vapor Deposited Mullite Coatings
Authors: Auger Michael L. , Sengupta Anita , Sarin Vinod K.
Published: July 2010

The corrosion characteristics of bulk alumina, SiC, mullite, and CVD mullite coatings on SiC in contact with coal slag were investigated. Uncoated SiC corroded in the presence of coal slag, forming mixed FeSi phases and carbon. Bulk Al2O3 and slag formed a diffusional phase believed to be the spinel hercynite (Fe,Mg)O·(Al,Fe)2O3. After exposure to coal slag, a compositional difference was observed at bulk mullite/coal slag interfaces, yet this diffusional phase did not appreciably degrade the mullite samples and no cracking was observed. CVD mullite coatings offered protection to SiC in a simulated coal gasification atmosphere with corrosion protection dependent on the uniformity of the coating. Microprobe analysis of the CVD mullite coating/slag interface showed the formation of a Fe(Mg)Al.
Effect of Acceptors on the Segregation of Donors in Niobium‐Doped Barium Titanate Positive Temperature Coefficient Resistors
Authors: Yoon Seok Hyun , Lee Kwang Ho , Kim Hwan
Published: July 2010

Small amounts of niobium (donor) doping in barium titanate (BaTiO3) cause semiconductivity in this material. When the amount of niobium is increased slightly, the BaTiO3 is converted back to an insulator. This phenomenon is attributed to donor segregation. Such an insulating material can recover its semiconductivity when specific amounts of acceptors are introduced. The space‐charge segregation theory explains that such acceptors can prevent the segregation of donors. Impedance/modulus analysis of BaTiO3 with a slightly increased niobium content and with no or a minimal amount of magnesium (acceptor) show a response of a third resistance–capacitance (RC) network, in addition to the two that have been thought to be caused by the grains and grain boundaries. The response of the third RC network is not observed at greater magnesium concentrations that give a recovery of the semiconductivity. This study suggests that acceptors can inhibit the donor segregation.
Dielectric and Electromechanical Properties of Chemically Modified PMN‐PT‐BT Ceramics
Authors: Cho Yong S. , Pilgrim Steven M. , Giesche Herbert , Bridger Keith
Published: July 2010

A particulate coating process incorporating small amounts of several additives such as titanium, zinc, barium, strontium and iron was used to modify the composition and resultant dielectric and electromechanical properties of a commercially available 0.96(0.91Pb(Mg1/3Nb2/3)O3·0.09PbTiO3)·0.04BaTiO3. This method led to intimate mixing of the additives at the nanoscale without an additional ball‐mixing process. Low‐ and high‐field characteristics including dielectric properties, induced strain and polarization, and associated hystereses were evaluated for the samples sintered at 1200°C for 4 h. All properties were found to depend on the chemical additives and temperature. Specifically, the addition of small quantities of titanium and barium tended to increase strain and Qeff while maintaining a low dielectric constant which is a promising result for room temperature transducer applications. The addition of titanium with zinc or iron raised dielectric constant, strain, and polarization with significant increases in the temperature of maximum permittivity. On the other hand, the electromechanical properties of the samples containing barium or zinc with titanium did not exhibit a transition to piezoelectric behavior at the temperature expected from the dielectric measurements.
Superplasticity of Liquid‐Phase‐Sintered β‐SiC with Al2O3–Y2O3–AlN Additions in an N2 Atmosphere
Authors: Nagano Takayuki , Kaneko Kenji , Zhan Guo‐Dong , Mitomo Mamoru
Published: July 2010

Compression and tension tests were performed on liquid‐phase‐sintered β‐SiC fabricated by hot‐pressing, using ultrafine powders, at 1973–2048 K in an N2 atmosphere. Amorphous phases were observed at the grain boundaries and at multigrain junctions in the as‐sintered material. Strain hardening was observed under all experimental conditions. Stress exponents in the compression test were 1.7–2.1 in the temperature range 1973–2023 K. A maximum tensile elongation of 170% was achieved at the initial strain rate of 2 × 10−5 s−1 at 2048 K.
Crystallization of (Na2O–MgO)–CaO–Al2O3–SiO2 Glassy Systems Formulated from Waste Products
Authors: Barbieri Luisa , Ferrari Anna Maria , Lancellotti Isabella , Leonelli Cristina , Rincòn Jesus Maria , Romero Maximina
Published: July 2010

Aluminosilicate and silicate glass‐ceramics were obtained from controlled devitrification of CaO–Al2O3–SiO2 glassy systems starting from Spanish and Italian coal fly ash or Italian municipal incinerator slag mixed with other byproducts, such as glass cullet and dolomite. The nucleation mechanism and the crystallization kinetics were investigated by thermal, diffractometric, and microstructural measurements. Moreover, the experimentally observed devitrification and the identification of the crystalline phases formed were compared with the indications derived from Ginsberg, Raschin‐Tschetveritkov, and Lebedeva diagrams used for petrological glass‐ceramics. All the glasses showed a good crystallization tendency with the formation of dendritic pyroxene and acicular wollastonite together with feldspar and iron spinels starting from the surface. The activation energy values for crystallization ranging from 472 to 832 kJ ·mol−1 were found to be close to those typical for aluminosilicate glasses; moreover, the possibility to vitrify and devitrify up to 100 wt% of slag and up to 40–50 wt% of ash mixed with glass cullet and dolomite makes the vitrification treatment a suitable disposal procedure.
Tensile Transformation‐Mismatch Plasticity of Bismuth Sesquioxide
Authors: Dunand David C. , Grabowski Jeffrey L.
Published: July 2010

This study reports on experiments where bismuth sesquioxide (Bi2O3) was cycled between its high‐temperature δ‐phase and one or more of its low‐temperature phases (α‐, β‐, or γ‐Bi2O3) while being subjected to uniaxial tensile stresses in the range of 0.11–0.55 MPa. Reproducible strain increments of 0.4%–3.9% have been measured after each thermal cycle, and total tensile fracture strains of 10%–28% have been obtained using a combination of isothermal creep and transformation‐mismatch plasticity. The strain due to transformation mismatch plasticity has been determined by two different methods and is proportional to the applied stress, which is quantitatively consistent with theoretical predictions for transformation superplasticity.
Nanostructure of Calcium Silicate Hydrate Gels in Cement Paste
Authors: Zhang Xiaozhong , Chang Wenyi , Zhang Tiejun , Ong Cong K.
Published: July 2010

High‐resolution electron microscopy study of calcium silicate hydrate (C‐S‐H) gels in ordinary portland cement (OPC) and a slag/OPC blend has been performed. Nanocrystalline regions on the scale of ∼5 nm or less in C‐S‐H are found in both cement pastes, and they are formed after a curing time as brief as 7 d. A change in the d‐spacing of the nanocrystalline regions with time is observed for the first time, which is believed to correspond to the development of C‐S‐H with time. The nanoheterogeneous nature of C‐S‐H is demonstrated and correlated to the strong Ca:Si ratio fluctuations that are observed.