bluuebunny/crossref_metadata_2025 huggingface dataset:
Production of TiB2–TiN Composites by Combustion Synthesis and Their Properties
Authors: Tomoshige Ryuichi , Murayama Akio , Matsushita Toru
Published: July 2010

The self‐propagating high‐temperature synthesis (SHS) process has been applied to formation of composites consisting of TiB2 and TiN ceramics synthesized simultaneously. Ti, B, and BN powders were used as raw materials. The SHS reaction was initiated by a tungsten heating coil. XRD experiments confirmed that the reaction was complete, and that only TiB2 and TiN phases were detected. Microstructural observations revealed that both TiN and TiB2 crystal grains had small sizes of less than 1 μm in the composites with high TiN content. Inhibition of grain growth can be attributed to the pinning effect of TiN grains. Excellent corrosion resistance was obtained for HCl reagent.
Formation of Lead Magnesium Niobate Perovskite from Niobate Precursors Having Varying Magnesium Content
Authors: Joy Pattayil Alias , Sreedhar Krishnan
Published: July 2010

Formation of lead magnesium niobate (PMN) perovskite phase using a columbite type of precursor together with the addition of excess MgO has been investigated. When MgO and Nb2O5 are reacted with 1:1 stoichiometry, a minor amount (}2%) of Mg4Nb2O9 is formed along with the columbite‐type phase which in turn could lead to the formation of a minor amount of “free Nb2O5” in the precursor. This may be the reason for the formation of small amounts of pyrochlore phase during the synthesis of PMN perovskite from the stoichiometric 1:1 precursor. However, it has been found that the perovskite phase can easily be stabilized by the addition of a large excess of MgO in the precursor, although this leads to additional Mg‐Nb‐O phase Mg4Nb2O9, besides the columbite‐type phase MgNb2O6. It has been shown that, after this precursor reacts with PbO to form the PMN perovskite, the excess Mg present in the Mg‐rich niobate precursor separates out as MgO, as evidenced by X‐ray diffraction, which can be removed by leaching with dilute nitric acid, thus forming pure PMN.
Analysis of (Cr,Mo) Oxycarbide Films Grown on Stainless Steel via Metalloorganic Chemical Vapor Deposition
Authors: Lo Ming‐Hung , Wei Wen‐Cheng J.
Published: July 2010

A mixture of hexacarbonyl of chromium and molybdenum ((Cr,Mo)(CO)6) was used to deposit oxycarbide films on stainless steel at temperatures of 175°–450°C. Through the analysis of deposition kinetics in various temperature regions, the controlling mechanism was determined to be exothermic surface reactions. Activation energies of the low‐ and medium‐temperature regions were determined to be 71.2 and −60.1 kJ/mol, respectively. Some properties including densities, composition, and crystalline phases of the films were investigated. Results revealed that the chromium content of coating products increased as the temperature increased. The dominating surface reactions switched as temperature increased, because of the increase of chromium content in the precursor gas. Hence, the coating rate and density increased to a maximum, then decreased as the coating temperature was increased to 275°C. Deposited phases were determined by X‐ray diffractometry, and the relationship with film density phases has been discussed, using their microstructural textures from scanning electron microscopy micrographs. Corrosion resistance was measured by an electrochemical method. The films obtained in the low‐ and medium‐temperature regions improved the corrosion resistance of stainless‐steel substrates by a factor of 24. In addition, the latter case showed the effect of passive protection and was an optimized selection for corrosive protection. The relationship of the improvement of corrosion resistance, physical properties, and the contribution of composed phases was discussed.
Stable and Metastable Phase Relations in the System Alumina–Zirconia–Yttria
Authors: Lakiza Sergij M. , Lopato Lidia M.
Published: July 2010

The Al2O3ZrO2Y2O3 system was studied in the range of temperatures 1600°–2800°C by methods of X‐ray analysis at 20°C, petrography, DTA in He at temperatures to 2500°C, thermal analysis in air using a solar furnace at temperatures to 3000°C, and electron microprobe X‐ray analysis. The stable and metastable phase diagrams were constructed. The liquidus and solidus projections, crystallization paths for the alloys, and polythermal sections are presented in the article. The structure of the restricting systems defines the phase equilibria in the ternary system. No ternary compounds were found. The metastable phase relations were caused by the ambivalent behavior of Y3Al5O12 during crystallization.
Fracture Resistance Behavior of Multilayered Silicon Nitride
Authors: Ohji Tatsuki , Shigegaki Yasuhiro , Miyajima Tatsuya , Kanzaki Shuzo
Published: July 2010

This paper investigates the fracture resistance behavior of a novel silicon nitride with a unique laminated structure consisting of alternate dense and porous layers, in the latter of which β‐silicon nitride whiskers were aligned parallel to the layer. The R‐curve was determined by using a chevron–notched–beam technique when a crack propagated in the direction normal to the whisker axis. The resistance markedly increased whenever a crack passed the porous layer, resulting in stepwise rising R–curve behavior. Microscopic study revealed that the aligned whiskers were almost completely pulled out in the porous layer.
Homogeneity Ranges of Phases Sr4−xLn2x/3Ti4O12 (Ln = Sm to Lu) and Sr1−yEuy∥TiO3
Authors: Bamberger Carlos E.
Published: July 2010

The homogeneity ranges of phases Sr4−xLn2x/3Ti4O12, in which Ln = Sm to Lu, have been established using X‐ray diffraction (XRD) analysis. It was found that the maximum value of x is dependent on the ionic radius of the lanthanide element. The effect of hydrogen reduction on single‐phase and multiphasic preparations containing Sr‐Eu(III) titan‐ ates has been studied. The replacement of the lanthanide element in such Sr‐Ln compounds by a mixture of two lanthanides that have an average ionic radius similar to the single lanthanide was examined.
Super‐Water‐Repellent Al2O3 Coating Films with High Transparency
Authors: Tadanaga Kiyoharu , Katata Noriko , Minami Tsutomu
Published: July 2010

We have prepared transparent, super‐water‐repellent coating films of alumina on glass plates by a combination of geometric and chemical approaches. The contact angle for water in the films was 165° and the transmittance for visible light was higher than 92%. A roughness of 20 to 50 nm was obtained, which is too small to scatter visible light, while the degree of roughness was great enough to enhance the water‐repellent properties together with the chemical effect of a fluorine‐containing agent and gave a super‐water‐repellent surface. The coatings have great potential for practical applications such as eyeglasses, cover glasses for solar cells, windshields of automobiles, and so on.
Microscopic Origin of the PTC Effect in Niobium‐Doped Barium Titanate
Authors: Gillot Cristophe , Michenaud Jean‐Pierre , Baukens Isabelle , Duvigneaud Paul‐Henri
Published: July 2010

The influence of bulk conductivity on the PTC effect of Nb‐doped barium titanate is investigated. Both macroscopic and microscopic resistance measurements are performed as a function of temperature. The macroscopic measurement refers to the whole sample while the microscopic one, obtained by photolithography techniques, concerns only several grains. The results show that the increase of resistivity occurs in two steps: first, an abrupt variation at the Curie temperature Tc which is ascribed to the phase transition in the bulk; second, a continuous increase above Tc which is usually explained from grain boundary potential barriers only. However, our results suggest that a nonnegligible contribution of the bulk is also involved in this increase above Tc.
Decomposition of Ruthenium Oxides in Lead Borosilicate Glass
Authors: Adachi Kenji , Kuno Hiroko
Published: July 2010

Behaviors of apparent phase changes of Ru‐containing oxides in lead borosilicate glass at high temperature have been investigated using X‐ray diffraction and transmission electron microscopy in application to thick‐film resistors. During firing of thick films containing Ru oxide powder and lead borosilicate glass frits, apparent phase changes of Ru oxides have been found to occur both ways between ruthenium dioxide and lead ruthenate pyrochlore via decomposition of one phase in glass and subsequent formation of the other. The formation of pyrochlore occurs in a lead‐rich form, Pb2(Ru2−xPbx)O6.5, whereas the formation of RuO2 is characterized by a platelike morphology instead of initial globular morphology. A general tendency is observed that RuO2 is stable in low‐PbO glass compositions and at high temperatures, while Pb2(Ru2−xPbx)O6.5 is stable in high‐PbO glass compositions and at low temperatures, with the implication that the stability of these phases is dictated by the chemical activity of PbO in the glass melt.
Influence of Crystal Structure on the Fatigue Properties of Pb1−xLax(Zry′, Tiz)O3 Thin Films Prepared by Pulsed‐Laser Deposition Technique
Authors: Lin Wen‐Jen , Tseng Tseung‐Yuen , Lin Sheuan‐Perng , Tu Shun‐Lih , Chang Hong , Yang Sheng‐Jenn , Lin I‐Nan
Published: July 2010

Lead lanthanum zirconate titanate (Pb1−xLax(Zry,Tiz)O3, PLZT) films containing [00l] preferentially oriented grains were produced successfully on YBa2Cu3O7−x‐coated (YBCOcoated) SrTiO3 (STO) or YBCO/CeO2‐coated silicon substrates; films containing randomly oriented grains were created on platinum‐coated silicon substrates. The latter possessed significantly inferior ferroelectric properties, a fact ascribed to the presence of a paraelectric phase (TiO2) at the PLZT/platinum interface. On the other hand, the PLZT/YBCO/STO films exhibited better electrical properties than did the PLZT/YBCO/CeO2/Si films, and this phenomenon was attributed to better alignment of the grains in normal and in‐plane orientations. In terms of fatigue properties, the [00l] textured films that were deposited on YBCO/CeO2/Si substrates possessed substantially superior polarization‐switching‐cycle endurance versus the randomly oriented films grown on Pt(Ti)/Si substrates. Moreover, the tetragonal films behaved much more satisfactorily than did the rhombohedral PLZT films. The ferroelectric parameters of tetragonal PLZT films showed no significant degradation up to 109 polarization switching cycles, whereas the remnant polarization and coercive force of the rhombohedral PLZT films had already degraded to 80% of their initial values after 108 cycles.
Time–Temperature–Transformation Diagrams for Borosilicate Glasses and Preparation of Chemically Durable Porous Glasses
Authors: Nakashima Kunihiko , Noda Kenji , Mori Katsumi
Published: July 2010

To clarify the effects of glass composition and heat‐treatment conditions on phase separation and crystallization, time–temperature–transformation (TTT) diagrams for the system (65 −x)SiO2·25B2O3·(10 −y)Na2O·yCaO·xZrO2, which is used for fabricating alkali‐durable porous glasses, were determined. The microstructures and properties, such as resistance to alkaline attack as a function of ZrO2 content, of the porous glasses fabricated on the basis of the developed TTT diagrams were examined. CaO and ZrO2 additions were shown to affect the locations of the noses in the TTT curves for phase separation and crystallization. The substituting of CaO for Na2O was effective for retaining ZrO2 in the skeleton of the porous glasses. The alkali resistance of ZrO2‐containing porous glasses was 8–10 times superior to that of the porous glass without ZrO2. The results demonstrate that TTT diagrams can be used as guides for heat‐treatment scheduling in processing or predicting of glass‐forming ability and the onset of phase separation and crystallization in glass‐forming systems.
Abnormal Grain Growth of Alumina
Authors: Bae Il‐Joon , Baik Sunggi
Published: July 2010

Abnormal grain growth (AGG) is not one of the intrinsic properties of alumina but rather is an extrinsic property that is controlled by certain impurities that are introduced during powder synthesis, processing, or sintering. When small amounts of glass‐forming impurities are introduced, some portion beyond their solubility limits will accumulate at grain boundaries at the final stage of densification, form thin intergranular glass films of thermodynamically stable thickness, and induce the sudden appearance of abnormal grains by increasing the rate of grain‐boundary migration abruptly. The proposition has been tested experimentally with small, but varying, amounts of silica in ultrapure alumina (99.999%) that has been sintered in a contamination‐free condition. Average grain sizes for the appearance of AGG are inversely related to the doping concentration of silica. The thickness of intergranular silicate glass films at the onset of AGG in alumina is constant and estimated to be }3.7 nm.
Texture and Formation Mechanism of Fibrous Calcium Hydroxyapatite Particles Prepared by Decomposition of Calcium–EDTA Chelates
Authors: Kandori Kazuhiko , Horigami Naoto , Yasukawa Akemi , Ishikawa Tatsuo
Published: July 2010

The texture of fibrous calcium hydroxyapatite (Ca10‐(PO4)6(OH)2, CaHAP) particles that were prepared by the decomposition of calcium–ethylenediaminetetraacetic acid (calcium–EDTA) chelates at 100°C under various pH conditions (pH values of 5–10) was investigated by various means. Well‐crystallized fibrous CaHAPs were produced at pH .6. The stoichiometry of the CaHAPs with a chemical formula of Ca10−x(HPO4)x(PO4)6−x(OH)2−x(H2O)x was improved by increasing the decomposition pH. All the CaHAPs had unit‐cell dimensions of a= 0.9436 ± 0.0003 nm and c= 0.6881 ± 0.0006 nm, exhibiting an enlarged a value. The finding of mesoporosity of CaHAPs by nitrogen gas (N2) adsorption measurement indicated that the CaHAPs were produced by an agglomeration of primary particles. Furthermore, the nonstoichiometric CaHAPs that formed at pH 6 developed ultramicropores, which were accessible to water (H2O) molecules but not to N2 molecules, by the elimination of H2O molecules that were adsorbed in interstices of primary particles in less‐orderly crystallized CaHAPs and/or by dehydration of HPO42− groups. These findings by gas adsorption techniques could give evidence for the agglomeration mechanism to attain a polycrystalline CaHAP, although they exhibited good crystallinity with large size.
Electronic and Structural Properties of Bulk γ‐Al2O3
Authors: Mo Shang‐Di , Xu Yong‐Nian , Ching Wai‐Yim
Published: July 2010

γ‐Al2O3 is a defective spinel phase of alumina with cation site vacancies randomly distributed. Its structure and properties are not well understood. There has been long‐standing controversy as to whether the cation vacancies are located at the tetrahedral sites or the octahedral sites. Based on an empirical pair potential calculation and first‐principles electronic structure studies, we have concluded that cation vacancies are preferentially located at the octahedral sites in bulk γ‐Al2O3. Our calculation shows that the electronic structure of γ‐Al2O3 differs from that of α‐Al2O3 in fine details. γ‐Al2O3 has a smaller band gap and wider valence bandwidths. The calculated density of states (DOS) of γ‐Al2O3 is in good agreement with recent experimental XPS and XES data. Site‐ and orbital‐resolved partial DOS (PDOS) of Al atoms shows significant dependence on the local coordinations. The PDOS of an oxygen adjacent to a vacancy differs substantially from that of a fully coordinated anion.
Experimental Design Applied to the Chemical Durability of Sol–Gel‐Derived Zirconias
Authors: Pavlik Robert S. , Klein Lisa C. , McCauley Ronald A.
Published: July 2010

A statistical design was used to investigate the effects of various processing conditions on the chemical durability of sol–gel‐derived zirconias. Eight processing variables were investigated: water:alkoxide molar ratio, alcohol:alkoxide molar ratio, nitric acid:alkoxide molar ratio, mixing temperature during hydrolysis, firing temperature, heating rate, soak at firing temperature, and firing atmosphere. Processing variables were set at high and low limits in a main‐effects statistical design. The design identified four critical processing variables (listed in descending order of significance): firing temperature, firing atmosphere, water:alkoxide ratio, and nitric acid:alkoxide ratio. Sol–gel‐derived zirconias were characterized by differential scanning calorimetry, X‐ray diffractometry, and mercury intrusion. Suggestions are offered that may help to explain why these particular processing conditions influenced the chemical durability of sol–gel‐derived zirconias.
Transmission Electron Microscopy Investigation of the Oxidation of Hot Isostatically Pressed Silicon Nitride with and without Sintering Aids
Authors: O'Meara Colette , Sjöberg Jörgan
Published: July 2010

Analytical transmission electron microscopy of thin‐foil cross sections has been used to examine the oxidation behavior of hot isostatically pressed silicon nitride (Si3N4) materials. The transmission electron microscopy (TEM) cross sections are prepared by a special technique that provides electron transparency through the entire oxide, interfacial, subscalar, and matrix regions simultaneously. The materials are oxidized in an alumina furnace at 1250°C for 100 h. TEM investigation indicates that oxidation of Si3N4 occurs in an oxidation reaction zone that is comprised of the scale, oxide/matrix interface, and subscalar regions; therefore, the silica (SiO2)/Si3N4 interfacial surface area that is available for oxidation is very large. The oxidative attack on the Si3N4 grains is not uniform or sequential, and oxygen diffuses into the matrix before the surface grains are consumed. Gas bubbles, probably nitrogen gas, accumulate at all levels of the scale, and no evidence is found for the existence of an “oxynitride” layer. Disintegration of the secondary phase, Y2Si2O7, in the subscalar region is observed to occur, indicating that secondary, oxidation‐related phenomena are occurring.
Ferroelasticity of t‘‐Zirconia: II, In situ Straining in a High‐Voltage Electron Microscope
Authors: Baufeld Bernd , Baither Dietmar , Messerschmidt Ulrich , Bartsch Martin , Foitzik Andreas H. , Rühle Manfred
Published: July 2010

The ferroelastic deformation of t‐ZrO2, the microstructure of which was described in detail in Part I, was investigated by in situ deformation experiments in the high‐voltage electron microscope at 1150°3C. During the experiments those two domain variants with their c‐axes perpendicular to the [010] tensile direction were transformed into the third one with its c‐axis parallel to the tensile direction. The subsequent ‘switching’ of the domains inside the colonies proceeds much faster than the penetration of the transformation front into a neighboring colony. Therefore, the transformed region, exhibiting a unique tetragonal structure and containing residual defects, preferentially expands into the longitudinal directions of the colonies. The transformation of single domains proceeds instantaneously within the time resolution of the video tape recording.
Computer Simulation of Grain Growth and Ostwald Ripening in Alumina—Zirconia Two‐Phase Composites
Authors: Fan Danan , Chen Long‐Qing
Published: July 2010

The kinetics of grain growth and Ostwald ripening in Al2O3‐ZrO2 two‐phase composites was systematically investigated using two‐dimensional (2‐D) computer simulations, based on a diffuse‐interface field model. Using average values for the experimentally measured ratios of the grain boundary energies to the interphase boundary energy as the input, the predicted 2‐D microstructural features and their evolution are in excellent qualitative agreement with experimental observations on 2‐D cross sections of 3‐D Al2O3‐ZrO2 two‐phase composite microstructures. It was found that the coupled grain growth in Al2O3‐ZrO2 composites is controlled by long‐range diffusion and the average size (Rt) as a function of time (t) follows the power‐growth law, Rmt ‐ Rm0=kt with m= 3, which is independent of the initial microstructures and volume fractions of the two phases. The predicted variation of the kinetic coefficient (k) on the volume fraction follows a trend similar to that experimentally measured through the entire range of volume fractions. The scaling of grain size distributions is observed at a given volume fraction, i.e., they are time‐invariant in the steady state. However, the characteristics of size distributions vary with the initial microstructures and the volume fractions. The relationship between matrix grain size and second‐phase grain size is discussed.
Minimizing Infiltration Times during Isothermal Chemical Vapor Infiltration with Methyltrichlorosilane
Authors: Chang Han‐Chieh , Morse Theodore F. , Sheldon Brian W.
Published: July 2010

Minimum infiltration times during isothermal chemical vapor infiltration were calculated for the formation of a silicon carbide matrix composite from methyltrichlorosilane (MTS). Several different reaction models were used to describe the SiC deposition kinetics. The results show that the nature of the reaction model has a significant effect on process optimization considerations. It is clear that a simple first‐order deposition reaction does not accurately describe the infiltration process, while rate expressions that treat the effect of chlorine‐containing byproduct gases provide much more accurate predictions. In theory, much shorter infiltration times can be obtained with precursor chemistries that do not produce Cl‐containing gases. The results also provide guidelines for minimizing infiltration times with MTS.
High‐Temperature Transverse Fracture Toughness of Nicalon‐Fiber‐Reinforced CAS‐II Glass‐Ceramic Matrix Composite
Authors: Kahramany Ramazan , Mandell John F. , Deibert Max C.
Published: July 2010

Cracking parallel to the fibers in off‐axis plies is usually the initial form of damage in composite laminates. This cracking process has been associated with the (transverse) fracture toughness, defined by the critical strain energy release rate, GIc. The measurement of GIc provides basic information about the transverse crack resistance. In this study, the utility of the double torsion (DT) test technique to determine GIc in a glass‐ceramic matrix composite (Nicalon/CAS‐II) at temperatures up to 1000°3C has been demonstrated. GIc did decrease moderately with increasing temperature (as does the bulk matrix); however, no evidence of an interphase oxidizing effect on crack growth (parallel to the fibers) could be found. The inevitable misalignment of fibers in the material was not very efficient at bridging the crack in the DT specimens, in contrast to the significant matrix crack interactions with the fibers reported for other geometries such as double cantilever beam and flexure specimens.
Fiber‐Reinforced Ceramic‐Matrix Composites with a Polysiloxane/Boron‐Derived Matrix
Authors: Suttor Daniel , Erny Tobias , Greil Peter , Goedecke Holger , Haug Tilman
Published: July 2010

A ceramic matrix for carbon‐fiber‐reinforced ceramic‐matrix composites (CMCs) has been developed from poly‐siloxane/boron mixtures. Complex geometries can be realized by using standard technologies of fiber‐reinforced polymer composites. On pyrolysis, the polymer—filler mixture is converted to a ceramic matrix, consisting of silicon carbide, boron carbide, boron nitride, and a silicon oxycarbide (SiOC) glass, without reacting with the carbon fiber. Because of the large volume increase of the boron filler on nitridation (142 vol%), no multiple reinfiltration of the structure is necessary to achieve a dense matrix. Tensile strength and interlaminar shear strength exhibit maxima at a pyrolysis temperature of 1300°3C, where extensive fiber pullout is observed. Thermodynamic calculations have been used to evaluate the theoretical qualitative and quantitative phase compositions at equilibrium. Thermoanalytical (thermogravimetry—mass spectroscopy) and structural analysis (X‐ray diffractometry) have shown a satisfying coherence with respect to the condensed phases, whereas deviations have been noted with respect to the composition of the gas phase.
Quantitative Characterization of Indentation Crack Path in a Cubic Zirconia—10 vol% Alumina Composite
Authors: Bhargava Parag , Patterson Burton R.
Published: July 2010

Stereological measurements were performed to characterize the indentation crack path in a cubic zirconia—10 vol% alumina (c‐ZrO2‐10 vol% Al2O3) composite. Cracks were generated using Vickers indentation, and the crack propagation behavior was characterized as a function of the indentation loading/unloading rates. Cracks that were produced by Vickers indentation formed at higher crack velocities as the loading/unloading rates increased. The amount of contact between the crack and the Al2O3 particles increased as the indentation rate decreased. The total number of crack—particle interactions per unit crack length also increased as the indentation rate decreased, because of an increase in the number of particles that were fractured per unit crack length, whereas the number of particles that were debonded remained relatively constant as the indentation rate changed. These results suggest that residual thermal mismatch stresses have predominant control of the crack path at lower crack velocities (low indentation loading/unloading rate), whereas elastic mismatch stresses predominate at higher crack velocities (high indentation loading/unloading rate).
X‐ray Photoemission and Energy Dispersive Spectroscopy of Hydroxyapatite‐Coated Titanium
Authors: Drummond James L. , Steinberg Arnold D. , Krauss Alan R.
Published: July 2010

The purpose of this study was to determine the chemical composition changes of hydroxyapatite (HA) coated titanium using surface analysis (X‐ray photoemission) and bulk analysis (energy dispersive spectroscopy). The specimens examined were controls and specimens aged 30 min and 3 h at room temperature in distilled water and 0.2M sodium phosphate buffer (pH 7.2). Each X‐ray photoemission cycle consisted of three scans followed by argon sputtering for 10 min for usually 20 cycles, corresponding to a sampling depth of ∼1500 Å. The energy dispersive spectroscopy analysis was on a 110 by 90 μm area for 500 s. The X‐ray photoemission results indicated the oxidation effect of water on the titanium (as TiO2) and the effect of the buffer to increase the surface concentration of phosphorus. No differences in the chemical composition were observed by energy dispersive spectroscopy analysis.
Thermal Conductivity of Packed Beds of Refractory Particles: Experimental Results
Authors: Fedina Irina , Litovsky Efim , Shapiro Michael , Shavit Arthur
Published: July 2010

Experimental data on thermal conductivity of packed beds composed from various refractory particles (corundum, silica, magnesia, baddeleyite, yttrium oxide, spinel) obtained in the temperature range 400‐2000 K in various gases are presented. It is found that thermal conductivity of a bed composed from crushed refractory particles may change after the first and subsequent heatings. This occurs as a result of smoothing of particle surfaces and decreasing of contact heat barrier resistances between the granules. The influence of smoothing is most significant for beds composed from particles with sizes below 2 mm. In polydisperse beds, containing micrometer‐size particles, sintering processes were found to occur at temperatures above 1600 K. This led to a sharp increase of the bed thermal conductivity. In regimes where sintering did not take place, decreasing of particle size resulted in a decrease of the effective thermal conductivity. This is attributed to the increased number of contacts between the particles and the scattering of thermal radiation.
A New Model for the Pollucite Thermal Expansion Mechanism
Authors: Kobayashi Hidehiko , Yanase Ikuo , Mitamura Takashi
Published: July 2010

The thermal expansion behavior of cubic pollucite (CsAlSi2O6) in the temperature range 298 to 1473 K was investigated from the viewpoint of crystal structure, based on the model proposed in this study, with Rietveld analysis and high‐temperature X‐ray powder diffraction. Consequently, it has been found that the CsAlSi2O6 structure provides an enlargement‐contraction mechanism for two kinds of rings, each composed of six (Si,Al)O4 tetrahedra in a three‐dimensional aluminosilicate framework, in the temperature range 298 to 673 K.
Effect of Green Density on the Subsequent Densification and Grain Growth of Ultrafine SnO2 Powder during Isochronal Sintering
Authors: Ahn Jae‐Pyoung , Park Jong‐Ku , Huh Moo‐Young
Published: July 2010

An ultrafine powder of SnO2 has been synthesized by a gas flow condensation method. The average particle size of the powder was about 40 nm. The effect of the green density on the subsequent densification and grain growth of the ultrafine SnO2 during sintering has been studied. A loose green compact consolidated under 500 MPa (green MC) showed rapid densification as well as rapid grain growth at relatively low sintering temperatures. A dense green compact fabricated under 4.5 GPa (green GC) exhibited a slow increase in the density and almost no grain growth even at high sintering temperatures.
Thermodynamics and Transport of Ionic and Electronic Defects in Crystalline Oxides
Authors: Lankhorst Martijn H. R. , Bouwmeester Henny J. M. , Verweij Henk
Published: July 2010

The first part of this article concerns the thermodynamics of point defects. In the traditional analysis of reactions in which point defects are involved, point defects are assumed to be ideally diluted, which leads to familiar mass‐action‐type equations. In this article, situations in which deviations from ideal mass‐action‐type behavior occur are investigated by evaluating the influence of defect interactions on the chemical potentials of point defects. Expressions for chemical potentials are derived for the case of weak interactions between neighboring defects. Strong repelling interactions between neighboring defects are discussed using the concept of excluded configurations, and strong attractive interactions are analyzed by introducing clusters. The chemical potential of electrons occupying energy states in an electron band also is analyzed as a function of bandwidth and electron occupation number. An expression for the chemical potential of electrons in partially filled bands is derived, which incorporates the average density of states at the Fermi level. Also discussed is the relationship between formation energies and entropies of defects in oxides and the measurable energy and entropy part of the oxygen chemical potential. The second part of this article concerns the transport of ionic and electronic defects in oxides. Within the framework of irreversible thermodynamics, a formalism is presented that allows the description of the general case in which ambipolar diffusion of ions and electrons in oxides is governed by contributions of several ionic and electronic point defects. The formalism allows the handling of defect association, defect interactions, and coupling of the overall ionic and electronic fluxes. The origin of the coupling and its influence on the net oxygen transport and electric current density is investigated.
Wetting Behavior between Fayalite‐Type Slags and Solid Magnesia
Authors: Fukuyama Hiroyuki , Donald Jeffrey R. , Toguri James M.
Published: July 2010

The wetting behavior of single‐crystalline magnesia (MgO) by fayalite‐type slag melts has been studied by the sessile‐drop technique, which incorporates high‐temperature X‐ray radiography. The experiments have been performed under oxygen partial pressures of 106 and 104 Pa at a temperature of 1473 K. The mass ratios of iron to silica, Fe/SiO2, in the slag that has been used are 1.44 and 2.05. Infiltration behavior of a fayalite‐type slag into MgO are discussed, based on the experimental results that involve wettability and surface tension. Two phases—magnesio‐wustite and olivine—are observed at the interface. Interdiffusivity in the magnesiowustite solid solution has been determined as a function of the iron oxide content. To investigate the interfacial reaction, experiments that use high‐density MgO crucibles also have been conducted. Phase relations between the magnesiowustite and the olivine, and the rate of growth of the phases, are discussed.
Crack‐Growth Resistance‐Curve Behavior in Silicon Carbide: Small versus Long Cracks
Authors: Gilbert C. J. , Cao J. J. , de Jonghe L. C. , Ritchie R. O.
Published: July 2010

Crack‐growth resistance‐curve (R‐curve) behavior for small (<400 μm) surface cracks and long (>3 mm) through‐thickness cracks is examined in two silicon carbide (SiC) ceramics that have sharply contrasting fracture properties. The first, an in‐situ toughened material designated ABC‐SiC, fails by intergranular fracture, whereas the second, a commercial SiC (Hexoloy SA), fails by transgranular cleavage. In the former microstructure, hot pressing with aluminum, boron, and carbon additives yields a network of plate‐shaped grains, and the presence of an amorphous grain‐boundary film that is ∼1 nm thick promotes debonding and crack deflection. The resultant grain bridging generates R‐curve toughening; in contrast, no evidence of crack‐tip shielding is observed in Hexoloy SA. R‐curve behavior has been evaluated using two techniques for the different crack‐length regimes: a small‐crack R‐curve has been deconvoluted from indentation‐strength data and a long‐crack R‐curve has been directly measured using fatigue‐precracked, disk‐shaped compact‐tension specimens. Although Hexoloy SA fails catastrophically at <3 MPa.m1/2, ABC‐SiC exhibits much‐improved flaw tolerance with significant rising R‐curve behavior and a steady‐state fracture toughness of ∼9 MPa.m1/2 after crack extension of ∼600 μm. In ABC‐SiC, however, differences in the behavior of long and small cracks exist for crack sizes of less than ∼120 μm, with the small‐crack measurements demonstrating much‐reduced crack‐growth resistance; this effect is not observed in Hexoloy SA. Microstructural sources of this behavior are discussed.
Degradation of Magnesite–Chrome Refractory Brick by Hydration
Authors: Malarria Jorge A. , Tinivella Ricardo
Published: July 2010

Magnesite‐chrome refractory brick that is heated to temperatures as low as 500°C undergoes premature degradation, with a significant decrease in mechanical properties. Results that are obtained by dilatometry, differential thermal analysis, thermogravimetry, differential scanning calorimetry, X‐ray diffractometry, and water absorption indicate that superficial hydration of the periclase grains during storage causes such degradation.
Suppression of Viscous Grain‐Boundary Sliding in a Dilute SiAION Ceramic
Authors: Pezzotti Giuseppe , Kleebe Hans‐Joachim , Ota Ken'ichi , Yabuta Kazuya
Published: July 2010

Aluminum nitride (AIN) and alumina (Al2O3) additives were blended into a high‐purity silicon nitride (Si3N4) powder, and optimized processing conditions were applied for promoting a sintering process, which was shown to partly remove the amorphous silica‐rich (SiO2‐rich) remains from grain boundaries. Such an approach led to the formation of a dilute SiAlON structure. The microstructure of the obtained SiAlON material consisted of two distinct types of matrix phases, namely, a main network of equiaxed (dilute) ß‐SiAlON grains, with a minor fraction of (oxygen‐rich) acicular O'‐SiAlON grains. As a consequence of the resulting solid solution of aluminum plus oxygen in the Si3N4 lattice, many grain boundaries were free from any amorphous interlayer, as revealed by high‐resolution electron microscopy (HREM) observation. Other than some boundaries that were still wetted, small amounts of residual glass were noted at some triple‐grain pockets. However, the average size of such glass pockets was only a few nanometers. The observed microstructural characteristics were critical for the anelastic response of the present SiAlON material, as compared with undoped Si3N4, whose grains were continuously encompassed by an amorphous SiO2 film. Internal‐friction data that were collected up to very high temperatures showed that, in the present SiAlON material, no anelastic relaxation peak was monitored. Thus, viscous sliding along grain boundaries was inhibited. In addition, the partial elimination of the amorphous SiO2 film also implied that no continuous path for oxygen diffusion was available along grain boundaries. Because of this important circumstance and despite the possible softening effect due to solid solution, the viscoelastic (background) component of the internal‐friction data shifted toward higher temperatures and the creep resistance of the material was improved.
Microstructural Development during Sintering of Lithium Fluoride
Authors: Bullard Jeffrey W. , Searcy Alan W.
Published: July 2010

Measurements are reported of the influences of temperature, green density, and pore network breakup on the densification, grain growth, and pore volume distribution in LiF compacts. As long as most of the pore volume remained open to the compact perimeter, the ratio of the rate of densification to the rate of grain growth was higher than that sometimes reported for copper or typical oxides. Plots of the logarithm of densification rates versus sintered density for LiF are approximately linear during intermediate‐stage sintering, like those for some oxides. But the plots for LiF are unlike those of the oxides in that, for LiF, densification rates measured at different temperatures converge near the density at which half the pore volume is isolated from Hg intrusion. Calculations suggest that further densification of the LiF compacts is blocked because air trapped in isolated pores becomes sufficiently compressed to balance the sintering stress.
Formation of Metastable Fluorite Phase by Rapid Quenching of Melts in the Y2O3‐Ta2O5 System
Authors: Yokota Osamu , Yashima Masatomo , Yamamoto Naoki , Yoshimura Masahiro
Published: July 2010

Melts of x mol% Ta2O5–Y2O3 (x = 0–32.5) were rapidly quenched to investigate the formation of metastable fluorite solid solutions. C‐type Y2O3, fluorite, and fergusonite phases existed in the compositional regions of 0 x 16, 8 x 32.5, and 27.5 x 32.5, respectively. Their lattice parameters were precisely measured through either Rietveld analysis or a least‐squares fit of the individual X‐ray diffraction peak positions. The lattice parameter of the fluorite phase decreased linearly with increasing Ta2O5 content, strongly suggesting the formation of compositionally homogeneous metastable solid solutions. Ta2O5 was almost insoluble into Y2O3 at 1700°C in the equilibrium state.
Synthesis of LaMeO3 (Me = Cr, Mn, Fe, Co) Perovskite Oxides from Aqueous Solutions
Authors: Yao Takeshi , Ariyoshi Akira , Inui Takashi
Published: July 2010

LaMeO3 (Me = Cr, Mn, Fe, Co) perovskite oxides have many functional uses, and methods for forming films from aqueous solutions are advantageous compared with CVD, sputtering, sol‐gel methods, etc., because of lower cost, no requirement for a vacuum or high temperature, and applicability to films with wide areas and/or complicated shapes. A novel method for synthesizing LaMeO3 from aqueous solutions at ordinary temperature and pressure has been discovered. LaMeO powder produced by solid‐state reaction was dissolved in hydrofluoric acid. Boric acid was added to shift the chemical equilibrium, then LaMeO3 was synthesized. This method promises to lead to applications for preparing perovskite films for various uses.
Zeolites Synthesized from Class F Fly Ash and Sodium Aluminate Slurry
Authors: Grutzeck Michael W. , Siemer Darryl D.
Published: July 2010

A Class F fly ash was combined with a sodium aluminate slurry (3:1 Na:Al) in an attempt to synthesize zeolites from a highly alkaline waste stream. The reaction was studied as a function of composition (3:2, 1:1, and 1:2 fly ash:slurry), time (1, 3, and 7 days), and temperature (80°, 130°, and 180°C). X‐ray diffraction analyses of the products indicated that the fly ash and sodium aluminate had combined to form Zeolite A at 80°C, and NaP1 (a gismondene‐type) and an unnamed hydroxysodalite‐type at 130° and 180°C. The fact that the pH of the reactants decreased from initial values in excess of 13 to near neutral (7–9) after reaction signifies that the bulk of the sodium had been incorporated into zeolitic phases. Because of the unique adsorptive and cation exchange capabilities of zeolites and the fact that some samples formed reasonably hard monoliths, zeolitic materials formed in this way might make excellent waste forms for “mixed wastes” which contain both radioactive and hazardous chemical species.
Fibrous Monolithic Ceramics
Authors: Kovar Desiderio , King Bruce H. , Trice Rodney W. , Halloran John W.
Published: July 2010

Fibrous monolithic ceramics are an example of a laminate in which a controlled, three‐dimensional structure has been introduced on a submillimeter scale. This unique structure allows this all‐ceramic material to fail in a nonbrittle manner. Materials have been fabricated and tested with a variety of architectures. The influence on mechanical properties at room temperature and at high temperature of the structure of the constituent phases and the architecture in which they are arranged are discussed. The elastic properties of these materials can be effectively predicted using existing models. These models also can be extended to predict the strength of fibrous monoliths with an arbitrary orientation and architecture. However, the mechanisms that govern the energy absorption capacity of fibrous monoliths are unique, and experimental results do not follow existing models. Energy dissipation occurs through two dominant mechanisms—delamination of the weak interphases and then frictional sliding after cracking occurs. The properties of the constituent phases that maximize energy absorption are discussed.
Microstructure and Phase Stability of Yttria‐Doped Tetragonal Zirconia Polycrystals Heat Treated in Nitrogen Atmosphere
Authors: Chung Tai‐Joo , Song Huesup , Kim Gyeung‐Ho , Kim Doh‐Yeon
Published: July 2010

The low‐temperature degradation of zirconia (ZrO2) that was doped with 3 mol% yttria (Y2O3) (3Y‐TZP) was prevented by the heat treatment of sintered specimens in nitrogen. The heat treatment of sintered specimens resulted in a surface layer that was stabilized by nitrogen ions, whereas the interior was only slightly affected by the heat treatment. X‐ray diffractometry and transmission electron microscopy analyses revealed that the stabilized surface layer consisted of cubic grains with tetragonal precipitates. Although the presence of the surface layer decreased the strength of the sintered 3Y‐TZP, the strength of nitrified specimens was maintained when low‐temperature annealing was applied.
Thermodynamic Assessment of the Bismuth–Calcium–Oxygen Oxide System
Authors: Hallstedt Bengt , Risold Daniel , Gauckler Ludwig J.
Published: July 2010

The experimental data on the oxide part of the Bi‐Ca‐O system have been reviewed, and an optimized thermodynamic description is presented. There are six known stable ternary oxide phases, two of which show considerable solid‐solution ranges. At least two phases—delta–Bi2O3 and the rhombohedral ß‐phase–are good oxygen‐ion conductors. Because all oxide phases are found on the Bi2O3–CaO line, the Bi2O3‐CaO system can be treated as a true binary system. Most experimental data are in reasonable agreement with each other; however, there are fairly large uncertainties on the extension of the solid‐solution phases and on the thermodynamic properties.
Crack Initiation by Indentation Fatigue in Lead Alkali and Soda–Lime Glass
Authors: Banerjee Rajat , Sarkar Bijit Kumar
Published: July 2010

An indentation technique using a conventional Vickers microhardness tester was used to evaluate fatigue properties of lead‐alkali and soda‐lime silica glasses. The specimens were indented repeatedly at the same point with subcritical loads until radial cracks were initiated. The number of cycles to initiate the cracks at different subcritical loads demonstrated typical fatigue curves for both glasses. The uniqueness of the experiment was that the diagonal lengths of the deformed cavity were observed to increase with the number of cycles. This increase of the deformed cavity for a certain number of cycles prior to the visibility of crack initiation was analyzed, correlating the elastic‐plastic phenomenon and the accumulation of the residual stress in each cycle.
Microstructural Evolution of Gas‐Pressure‐Sintered Si3N4 with Yb2O3 as a Sintering Aid
Authors: Lee Won‐Ho , Kim Hyoun‐Ee , Cho Seong‐Jai
Published: July 2010

Microstructural evolution of gas‐pressure‐sintered Si3N4 with Yb2O3 as a sintering aid was observed. Microstructures typical for in situ toughened Si3N4, i.e., large elongated grains randomly distributed in a fine matrix, were observed. However, the size of the elongated grains near the surface was much larger than that at the center, resulting in two distinct regions: an inner region and an outer region. The smaller the amount of Yb2O3 added, the larger the difference in the size of the elongated grains between the outer and inner regions. The difference between microstructures was diminished when 16 wt% Yb2O3 was added. The microstructural change with Yb2O3 content was attributed to the evaporation of Yb‐containing liquid phase from the surface.
Structures, Phase Transformations, and Dielectric Properties of Pyrochlores Containing Bismuth
Authors: Wang Xiaoli , Wang Hong , Yao Xi
Published: July 2010

The structures, phase transformations, and dielectric properties of pyrochlore ceramics containing bismuth were studied. The relation between the orthorhombic and cubic pyrochlores in the Bi2O3‐ZnO‐Nb2O5 (BZN) system has been investigated. The effect of bismuth in distorted cubic pyrochlore structures is discussed. BZN compositions with pyrochlore structures have excellent dielectric properties, very low dielectric loss, and high dielectric constants with stable frequency and temperature dependence.
Structural Studies of Jennite and 1.4 nm Tobermorite: Disordered Layering along the [100] of Jennite
Authors: Viehland Dwight , Yuan Lijian J. , Xu Z. , Cong Xian‐Dong , Kirkpatrick R. James
Published: July 2010

Transmission electron microscopy of synthetic jennite reveals strong streaking in the electron diffraction patterns along the [100], along which dark‐field imaging and lattice fringing confirm the presence of a layering with a striation‐like morphology. The average periodicity between the layers is ∼35 Å; however, there is significant variation around this value in the range of 20‐40 Å, which is in agreement with the range of periodicities that are associated with the streaking in the diffraction patterns. These results clearly demonstrate the presence of a layering along the [100] with a periodicity that varies spatially throughout the specimen, which results in the presence of a disordered modulated structure. We believe that the disorder is induced by frozen‐in fluctuations in the local calcium:silicon ratio, which correspondingly results in fluctuations in the local structural order and periodicity of the modulated structure. Similar studies of 1.4‐nm tobermorite have revealed streaking along the [100]; however, it was weak and diffuse.
Mixture Experiment Techniques for Reducing the Number of Components Applied for Modeling Waste Glass Sodium Release
Authors: Piepel Greg , Redgate Trish
Published: July 2010

Statistical mixture experiment techniques were applied to a waste glass data set to investigate the effects of the glass components on Product Consistency Test (PCT) sodium release (NR) and to develop a model for PCT NR as a function of the component proportions. The mixture experiment techniques indicate that the waste glass system can be reduced from nine to four components for purposes of modeling PCT NR. Empirical mixture models containing four first‐order terms and one or two second‐order terms fit the data quite well, and can be used to predict the NR of any glass composition in the model domain. The mixture experiment techniques produce a better model in less time than required by another approach.