bluuebunny/crossref_metadata_2025 huggingface dataset:
Double‐Shear Geometry for the Deformation and Flow of Ceramics at Elevated Temperatures
Authors: Sakai Mototsugu , Muto Hiroyuki , Haga Mikichika
Published: May 2005

Simple‐shear deformation is essential to the study of the time‐dependent rheological behavior of materials in atomistic and/or molecular terms, for the change in shape under simple shear is not accompanied by any change in volume. A novel test specimen with double‐shear geometry is proposed for the study of viscoelastic and elastoplastic deformation and flow of ceramic materials at elevated temperatures. The external load is applied to the specimen in compressive mode, which overcomes several difficulties in high‐temperature testing. In order to scrutinize the reliability, reproducibility, and the self‐consistency of experimental results obtained in the double‐shear geometry, the linear viscoelastic deformation and flow of soda‐lime glass are examined at temperatures greater than the glass transition point. It is concluded on the basis of experimental observation that the double‐shear geometry proposed in the present study produces ideal simple‐shear deformation at elevated temperatures in a relatively easy way and will provide an important tool for characterizing the high‐temperature deformation and flow of ceramic materials.
In Situ Toughened Silicon Carbide with Al‐B‐C Additions
Authors: Cao Joe J. , MoberlyChan Warren J. , De Jonghe Lutgard C. , Gilbert Christopher J. , Ritchie Robert O.
Published: May 2005

“In situ toughened” silicon carbides, containing Al, B, and C additives, were prepared by hot pressing. Densification, phase transformations, and microstructural development were described. The microstructures, secondary phases, and grain boundaries were characterized using a range of analytical techniques including TEM, SEM, AES, and XRD. The modulus of rupture was determined from fourpoint bend tests, while the fracture toughness was derived either from bend tests of beam‐shaped samples with a controlled surface flaw, or from standard disk‐shaped compact‐tension specimens precracked in cyclic fatigue. The R‐curve behavior of an in situ toughened SiC was also examined. A steady‐state toughness over 9 MPa·m1/2 was recorded for the silicon carbide prepared with minimal additives under optimum processing conditions. This increase in fracture toughness, more than a factor of three compared to that of a commercial SiC, was achieved while maintaining a bend strength of 650 MPa. The mechanical properties were found to be related to a microstructure in which platelike grain development had been promoted and where crack bridging by intact grains was a principal source of toughening.
Effect of Fly Ashes with High Total Alkali Content on the Alkalinity of the Pore Solution of Hydrated Portland Cement Paste
Authors: Lorenzo P. , Gñoni S. , Hernández S. , Guerrero A.
Published: May 2005

The influence of two Spanish fly ashes (ASTM class F) with high total alkali content (equivalent to 2.0% and 2.6% Na2O) on the alkalinity levels of the pore solutions expressed from hydrated portland cement pastes was studied during a period of 90 days from mixing. Mixtures with 0%, 15%, and 35% replacement of cement by fly ash were prepared with a water/mixture ratio of 0. 4. The effect of the fly ash on the pore solution depended mainly on the age and fineness of the fly ash.
High‐Temperature Deformation of SiC‐Whisker‐Reinforced MgO‐PSZ/Mullite Composites
Authors: Parthasarathy Triplicane A. , Hay Randall S. , Ruh Robert
Published: May 2005

The effect of 33.5 vol% SiC whisker loading on high‐temperature deformation of 1 wt% MgO‐38.5 wt% zirconia‐mullite composites was studied between 1300° and 1400°C. At strain rates of 10−6 to 5 × 10−4/s the creep resistance of zirconia‐mullite composites without SiC reinforcement was inferior to monolithic mullite of similar grain size. Analysis of the results suggested that the decreased creep resistance of mullite‐zirconia composites compared to pure mullite could be at least partially explained by mechanical effects of the weaker zirconia phase, increased effective diffusivity of mullite by zirconia addition, and to the differences in mullite grain morphology. With SiC whisker reinforcement, the deformation rate at high stress was nearly the same as that of the unrein‐forced material, but at low stress the creep rates of the SiC‐reinforced material were significantly lowered. The stress dependence of the creep rate of unreinforced material suggested that diffusional creep was the operative mechanism, while the reinforced material behaved as if a threshold stress for creep existed. The threshold stress could be rationalized based on a whisker network model. This was supported by data on other whisker‐containing materials; however, the threshold stress had a temperature dependence that was orders of magnitude higher than the elastic constants, leaving the physical model incomplete. The effects of residual stresses and amorphous phases at whisker/matrix interfaces are invoked to help complete the physical model for creep threshold stress.
Interaction of Low‐Expansion NZP Ceramics with Na2SO4 at 1000°C
Authors: Lee Woo Y. , Stinton David P. , Joslin Debra L.
Published: May 2005

The interaction between several low‐expansion NZP materials and Na2SO4 at 1000°C in pure O2 was studied. Ba1.25Zr4P5.5Si0.5O24 experienced extensive cracking and delamination upon reaction with Na2SO4. On the other hand, Ca0.5Sr0.5Zr4P6O24 remained intact in terms of visual appearance and had no significant weight loss or gain. However, the ion exchange between Na+ ions and Ca+2 ions was observed to be sufficiently rapid to allow the penetration of the Na+ ions into the test specimens in 100 h. The segregation of Ca to the specimen surface was observed due to the ion exchange. Ca0.6Mg0.4Zr4P6O24 was also tested, but its stability could not be properly assessed because the as‐received specimens contained a significant amount of MgZr4P6O24 as an impurity phase.
Zirconium Nitride Precipitation in Nominally Pure Yttria‐Stabilized Zirconia
Authors: Gómez‐García Diego , Martínez‐Fernández Julián , Domínguez‐Rodríguez Arturo , Westmacott Kenneth H.
Published: May 2005

Nominally pure yttria‐stabilized zirconia alloys are shown to contain unexpectedly large amounts of dissolved nitrogen. Its presence in the lattice was detected through the observation of large precipitates in alloys with three different concentrations of yttria deformed in compression in argon in the temperature range 1600°–1800°C. Electron diffraction, EDS and PEELS analyses, and Moiré imaging were used to identify the precipitates as ZrN. The possible origin of the nitrogen, its likely effects on properties, and the role of annealing atmosphere are briefly discussed.
Nucleation‐ or Growth‐Controlled Orientation Development in Chemically Derived Ferroelectric Lead Zirconate Titanate (Pb(ZrxTi1−x)O3, x= 0.4) Thin Films
Authors: Liu Yimin , Phulé Pradeep P.
Published: May 2005

The profound influence of low‐temperature processing steps, hitherto assumed benign from the viewpoint of texture development, is reported. On inclusion of a 400°C step and further heat treatment at 700°C, PZT (40/60) sol‐gel thin films with a strong (111) texture were obtained. When the 400°C step was excluded, the films exhibited a strong (100) texture. The (111) PZT texture development is nucleation‐controlled and is attributed to the solid‐phase epitaxial effect. The (100) texture is considered growth‐controlled in that (100) oriented grains grow preferentially so as to minimize surface energy.
Tensile Ductility in Zirconia‐Dispersed Alumina at High Temperatures
Authors: Okada Kazuki , Sakuma Taketo
Published: May 2005

High‐temperature plastic flow in Al2O3‐10 wt% ZrO2 (2.5 mol% Y2O3) has been examined at temperatures between 1400° and 1500°C. Al2O3‐10 wt% ZrO2 (2.5 mol% Y2O3) exhibits much higher flow stress and smaller tensile elongation below about 1450°C than 0.1 wt% MgO‐doped single‐phase Al2O3. The suppression of grain growth with ZrO2 dispersion into Al2O3 is not effective for improving the tensile ductility. The limited ductility in Al2O3‐10 wt% ZrO2 (2.5 mol% Y2O3) is associated with the increment of flow stress caused by ZrO2. The ZrO2 dispersion or segregation in Al2O3/Al2O3 boundaries suppresses the grain boundary sliding and hence results in the increased flow stress at high temperatures.
Solid‐State 29Si NMR Analysis of Amorphous Silicon Nitride Powder
Authors: Leone Edgar A. , Curran Sean , Kotun Margaret E. , Carrasquillo Gilbert , van Weeren Remco , Danforth Stephen C.
Published: May 2005

Solid‐state 29Si NMR techniques were used to characterize laser‐synthesized silicon nitride powder prepared from the reaction of silane with ammonia. When the powder is exposed to water vapor, a hydrated layer rapidly forms at the surface. A comparison of 29Si cross polarization (CP) and Bloch decay (BD)‐MAS‐NMR spectra revealed differences between surface and bulk compositions. CP‐NMR identified Si‐NHx (x = 1, 2) species with a chemical shift of −45 ppm in the as‐synthesized (unexposed) powder. In BD‐NMR spectra, the nitride resonance is observed at −48 ppm. For the hydrated powder, CP‐NMR identified additional =Si‐OH (Q3), =Si‐(OH)2 (Q2), and SiO2 (Q4) species present at the surface. The CP‐NMR spectra were corrected for TlpH relaxation effects and deconvoluted into individual components in order to extract quantitative measurements of the various species present.
Thermodynamic Assessment of the Zirconia‐Urania System
Authors: Yashima Masatomo , Koura Toshiaki , Du Yong , Yoshimura Masahiro
Published: May 2005

An optimal thermodynamic data set for the zirconia‐urania system is evaluated by the CALPHAD (CALcula‐tion of PHAse Diagrams) method. A regular solution model is applied to all phases of the cubic, tetragonal, and mono‐clinic solid solutions and the liquid. Comparisons between calculated and measured phase diagrams show that most of the experimental information is satisfactorily accounted for by thermodynamic calculations.
Synthesis of Ruthenium Dioxide Thin Films by a Solution Chemistry Technique
Authors: Tressler James F. , Watanabe Koji , Sony Masahiro Tanaka
Published: May 2005

Smooth, fine‐grained RuO2 thin films have been synthesized and deposited onto 〈100〉 silicon substrates via a solution chemistry technique. Ruthenium(III) chloride n‐hydrate dissolved in ethanol was used as the precursor solution. Thin films from a 0. 38M solution were spun at 4000 rpm for 20 s onto the substrates and fired at temperatures between 400° and 800°C. XRD analysis shows that RuO2 forms over this entire temperature range. Using an appropriate firing schedule, the grain growth can be controlled and reproduced to provide for a uniform grain size distribution consisting of equiaxed, submicrometer diameter grains. The electrical resistance of the films has been measured at 300 K using the conventional four‐point probe technique. The resistivity values range from 1. 8 μΩ·m for the films with an average grain size of 250 nm to 3.1 μΩ·m for the films with 30 nm grains. The presence of residual carbon and hydrogen is not believed to have a significant effect on the resistivity.
Effects of Gadolinia and Alumina Addition on the Densification and Toughening of Silicon Carbide
Authors: Chen Zhao
Published: May 2005

SiC with mixtures of A12O3 and Gd2O3 additions were effective in densifying SiC. The density of 98% of theoretical density was achieved with the Gd2O3 and A12O3 eutectic composition. It is suggested that the improvement in density is due to liquid phase formed between A12O3 and Gd2O3. The sintered bodies have an improved fracture toughness due to the crack deflection mechanism.
10 kbar Phase Equilibria in the Y‐Ba‐Cu Oxide System at 950°C
Authors: Lawanier Jean‐Pierre , Meen James K. , Elthon Don
Published: May 2005

Phase equilibria in the YO1.5BaO‐CuO system have been determined at 950°C at 10 kbar using a piston‐cylinder apparatus. The oxide phases stable under these conditions are Y2O3, Y2Cu2O5, CuO, Y2BaCuO5, YBa2Cu3O6.5, BaCuO2, Y2BaO4, Y2Ba3O6, and YBa4Cu2O7.5. The phase stabilities observed at 950°C at 10 kbar are identical to those observed at 950°C in air or oxygen at 1 atm for compositions with <40% Ba of the cations. In more Ba‐rich portions of the phase diagram, carbonates and oxycarbonates are stabilized and a systematic determination of the phase equilibria has not been successful.
Oxidation of BN‐Coated SiC Fibers in Ceramic Matrix Composites
Authors: Sheldon Brian W. , Sun Ellen Y. , Nutt Steven R. , Brennan John J.
Published: May 2005

Thermodynamic calculations were performed to analyze the simultaneous oxidation of BN and SiC. The results show that, with limited amounts of oxygen present, the formation of SiO2 should occur prior to the formation of B2O3. This agrees with experimental observations of oxidation in glassceramic matrix composites with BN‐coated SiC fibers, where a solid SiO2 reaction product containing little or no boron has been observed. The thermodynamic calculations suggest that this will occur when the amount of oxygen available is restricted. One possible explanation for this behavior is that SiO2 formation near the external surfaces of the composite closes off cracks or pores, such that vapor phase O2 diffusion into the composite occurs only for a limited time. This indicates that BN‐coated SiC fibers will not always oxidize to form significant amounts of a lowmelting, borosilicate glass.
High‐Temperature Strength of Melt‐Infiltrated SiC‐Mo(Al,Si)2 Composites
Authors: Shobu Kazuhisa , Tani Eiji , Akiyama Morito , Watanabe Tadahiko
Published: May 2005

High‐temperature fracture behavior of melt‐infiltrated SiC‐Mo(AI,Si)2 composites was studied. The composites exhibited moderate strength up to ∼1600°C under a fast loading rate. The softening of the Mo(Al,Si)2 phase determined dominantly the temperature over which the strength decreased. The composite with finer microstructure revealed a higher level of strength over the whole temperature range. At 1580°C, however, the composites revealed distinct strength degradation at a reduced loading rate.
Mechanical Properties of Polycrystalline Translucent Cubic Boron Nitride as Characterized by the Vickers Indentation Method
Authors: Taniguchi Takashi , Akaishi Minoru , Yamaoka Shinobu
Published: May 2005

Mechanical properties of polycrystalline translucent cubic boron nitride (cBN) were characterized by Vickers indentation measurement. The calculated hardness decreased from 54 to 49 GPa as the load increased to 39 N, and then remained constant for values above this load. According to the relationship between crack length and applied indentation load, the formation of the median/radial type of cracks seems to take place at an applied load above 29 N. Assuming that the ratio of hardness and Young's modulus is constant in the polycrystalline cBN, the fracture toughness, KIC, of cBN was estimated to be 5.0 ± 0.5 MPa·m1/2.
Tensile Specimens from Ceramic Components
Authors: French Jonathan D. , Wiederhorn Sheldon M.
Published: May 2005

Three sizes of flat tensile specimens, 76.2 mm, 50.8 mm, and 30 mm long, were developed for tensile testing of experimental lots of material and material taken from ceramic components. Five replicate measurements on each specimen type, at each of two test conditions, yielded statistically indistinguishable creep and creep rupture results. Additional studies indicate that creep testing at 400 MPa on the 76.2 mm and 50.8 mm specimens and 350 MPa on the 30 mm specimen is feasible, limited only by the strength or slow crack growth resistance of the loading pins.
Coating of Fine‐Grained Silicon Nitride Whiskers on Fiber‐like Silicon Nitride
Authors: Kawai Chihiro , Yamakawa Akira
Published: May 2005

Fine‐grained silicon nitride (Si3N4) whiskers were coated on Si3N4 fibers through a vapor‐liquid‐solid mechanism under the following process. After the oxide glass of a Si‐Al‐Y‐O system was coated on seed Si3N4 fibers, the coated fibers were heated at 1490°C and 700° in the vapor of the Si‐N system which was generated by decomposition of amorphous Si3N4. The resulting specimens looked just like rose twigs. The Si3N4 whiskers were precipitated by nucleation in a liquid phase generated by melting of the oxide glass layers on the Si3N4 fibers.
Phase Transformation of ZrO2 in MnZn‐Ferrite under Magnetic Field
Authors: Lin Ying‐Chun , Gan Dershin , Shen Pouyan
Published: May 2005

This letter reports the effect of an applied magnetic field on the phase transformation of ZrO2 particles in MnZn‐Ferrite. Of the 10 wt% ZrO2 in the as‐sintered composite, 64% is retained as tetragonal (t‐) particles with a critical size of about 2.5 μ. The t‐ZrO2 particles with size between 1.5 and 2.5 μ are induced to transform to m‐ZrO2 under a critical magnetic field (between 40 and 60 kOe), due to the stress induced by the magnetostriction of the ferrite matrix.
Influence of Particle Size Distribution on Ductile‐Phase Toughening in Brittle Materials
Authors: Sun Xudong , Yeomans Julie A.
Published: May 2005

In ductile‐phase‐toughened brittle materials the size distribution of the ductile phase sometimes has a remarkable effect on toughening. An equation for predicting the toughness increment due to crack bridging, taking into account a ductile‐phase particle size distribution, has been deduced. Comparison between the toughness value predicted by the equation and that obtained from a double cantilever beam (DCB) method on a Al2O3–20 vol% Ni composite material has shown that the equation gives a more reasonable estimate of the toughness than previous equations.
Effect of Sintering Atmosphere on the Densification and Abnormal Grain Growth of ZnO
Authors: Shin Seung‐Doh , Sone Cheol‐Soo , Han Joo‐Hwan , Kim Doh‐Yeon
Published: May 2005

When a ZnO powder compact is sintered at 1450°C in air, the grains at the surface region of the specimen are observed to grow abnormally. Such abnormal grain growth does not occur when the specimen is sealed in a small cylindrical quartz tube and sintered at the same temperature. The higher rate of densification at the near‐surface region than in the interior is suggested to trigger the abnormal grain growth observed.
Journal YBCO Thin Film Formation near the Stability Line by Resistive Evaporation of BaF2, Cu, and Y
Authors: Azoulay Jacob
Published: May 2005

A single resistively heated source was used to deposit a mixture of BaF2, Cu, and Y to form precursor films onto MgO substrates held at room temperature. Different heat treatment conditions were applied to study the stability diagram of YBa2Cu3O7−x. It was found that the stability line is shifted toward the higher oxygen partial pressure and lower temperature side of the pure YBCO line in the presence of fluorine and fluorides in the precursor. Films of good quality were obtained when the annealing conditions were in close proximity to this line.
Activation Energy for Mullitization of α‐Alumina/Silica Microcomposite Particles
Authors: Sacks Michael D. , Wang Keyun , Scheiffele Gary W , Bozkurt Nazim
Published: May 2005

The formation of mullite in silica‐coated α‐alumina microcomposite powders was investigated using differential thermal analysis. An apparent activation energy of 1042 ± 32 kj/mol was determined for the mullitization reaction. This result suggests that mullite formation in microcomposite powders occurs by the same mechanism as in diphasic gels.
Barium Holmium Zirconate, A New Complex Perovskite Oxide: I, Synthesis, Characterization, and Potential Use as a Substrate for High‐Critical‐Temperature Superconductors
Authors: Jose Rajan , John Asha Mary , Koshy Jacob
Published: May 2005

Barium holmium zirconate, a new complex perovskite ceramic oxide, has been synthesized through liquid‐phase sintering for the first time. The conventional solid‐state reaction method using constituent oxides and carbonates was found to be inadequate for the synthesis of Ba2HoZrO5.5 material. During high‐temperature annealing, the development of stable BaZrO3 and BaHoO2.5 phases prevented the formation of Ba2HoZrO5.5 as a single‐phase material, even at 1650°C. However, an addition of a small amount of CuO (1 wt%) in the reaction mixture has resulted in the formation of an ordered complex perovskite Ba2HoZrO5.5 phase during the heating process. The structure of Ba2HoZrO5.5 was studied by X‐ray diffraction and found to have a cubic perovskite structure with a lattice constant of a= 8.482 Å. Dielectric constant and loss factor values of Ba2HoZrO5.5 are also in the range suitable for use as a substrate for microwave applications. The X‐ray diffraction and resistivity measurements have shown that there is no detectable chemical reaction in YBa2Cu3O7−δ–Ba2HoZrO5.5 and Bi(2212)–Ba2HoZrO5.5 composites, even under extreme processing conditions. Dip‐coated and melt‐textured YBa2Cu3O7−δ and Bi(2212) thick films developed on polycrystalline Ba2HoZrO5.5 gave zero‐resistivity transition temperatures of Tc(0) = 92 and 85 K, respectively.
Primary Crystallization Behavior of ZrO2–Y2O3 Powders: In Situ Hot‐Stage XRD Technique
Authors: Ghosh Abhijit , Upadhyaya Dharni D. , Prasad Ram
Published: May 2005

A major component of the driving force for crystallization of hydrous zirconia–yttria powders comes from their noncrystallinity. Subsequent to dehydration of coprecipitated gels, the amorphous‐to‐crystalline phase transformation is the regime of primary crystallization. For the present study of 3.0‐, 5.0‐, and 9.0‐mol%‐yttria‐stabilized zirconia, the powders were produced as fine aggregates of ∼300 nm median diameter. The activation energy in all three cases was determined by the hot‐stage X‐ray diffraction technique where the powders were heated isothermally in the temperature range of 500°–600°C. The Avrami equation was used to calculate the rate constant value and the Arrhenius relationship was utilized to determine the value of the activation energy for primary crystallization.
Rheological, Structural, and Stress Evolution of Aqueous Al2O3:Latex Tape‐Cast Layers
Authors: Martinez Carlos J. , Lewis Jennifer A.
Published: May 2005

The rheological, structural, and stress evolution of aqueous alumina (Al2O3):latex tape‐cast layers of varying composition were studied by shear rheology, direct visualization, and a controlled environment stress measurement device. Their low shear viscosity was nearly independent of the alumina:latex ratio for binary mixtures whose particle size ratio (λ=D̄alumina:D̄latex) approached unity, but varied over an order of magnitude for systems with particle size asymmetry. Direct visualization of these mixtures revealed that particle flocculation occurred as their total solids loading increased. Their structure was characterized at intermittent points during the drying process by imaging freeze‐dried samples using scanning electron microscopy (SEM). Their corresponding stress histories exhibited three distinct regions: an initial period of stress rise, followed by a stress maximum, and, finally, a period of stress decay. Pure alumina layers exhibited a maximum stress of ∼1 MPa and a residual stress below 0.01 MPa. Pure latex films exhibited a maximum stress of ∼0.1 MPa and only a slight stress decay. The ceramic phase dominated the initial period of stress rise, while the latex phase strongly influenced the residual stress of composite layers cast from alumina:latex suspensions. Their maximum drying stress increased with decreasing Al2O3 particle size, whereas their residual stress increased with increasing latex Tg.
Self‐Propagating High‐Temperature Synthesis of Ti3SiC2: I, Ultra‐High‐Speed Neutron Diffraction Study of the Reaction Mechanism
Authors: Riley Daniel P. , Kisi Erich H. , Hansen Thomas C. , Hewat Alan W.
Published: May 2005

In situneutron diffraction at 0.9 s time resolution was used to reveal the reaction mechanism during the self‐propagating high‐temperature synthesis (SHS) of Ti3SiC2from furnace‐ignited stoichiometric 3Ti + SiC + C mixtures. The diffraction patterns indicate that the SHS proceeded in five stages: (i) preheating of the reactants, (ii) the α→β phase transformation in Ti, (iii) preignition reactions, (iv) the formation of a single solid intermediate phase in <0.9 s, and (v) the rapid nucleation and growth of the product phase Ti3SiC2. No amorphous contribution to the diffraction patterns from a liquid phase was detected and, as such, it is unlikely that a liquid phase plays a major role in this SHS reaction. The intermediate phase is believed to be a solid solution of Si in TiC such that the overall stoichiometry is ∼3Ti:1Si:2C. Lattice parameters and known thermal expansion data were used to estimate the ignition temperature at 923 ± 10°C (supported by the α→β phase transformation in Ti) and the combustion temperature at 2320 ± 50°C.
Rheological Characterization of Synergistic Mixtures of Carrageenan and Locust Bean Gum for Aqueous Gelcasting of Alumina
Authors: Santacruz Isabel , Nieto M. Isabel , Moreno Rodrigo
Published: May 2005

Previous works have shown that carrageenan can be successfully used in the aqueous gelforming of powders, because carrageenan forms a firm gel, similar to that formed by agarose, but at a much lower cost. In this work, the synergistic effect of carrageenan with locust bean gum is studied. The rheological behavior of 2 wt% solutions of these polysaccharides and their mixtures are measured under mixing conditions (60°C) and by recording the viscosity and elastic modulus on cooling. The effect of the addition of these solutions to 50 vol% alumina slurries up to a concentration of 0.5 wt% is studied. Although gelling time increases, the resulting gels are stronger than for carrageenan alone. Gelcast alumina bodies with green and sintered densities of 57% and 97.6% of theoretical have been obtained.
Shock‐Induced Transformations in Hexagonal Boron Nitride by High‐Velocity Thermal Spray
Authors: Goswami Ramasis , Herman Herbert , Sampath Sanjay , Parise John , Zhu Yimei , Welch David
Published: May 2005

Shock synthesis of cubic BN (c‐BN) was accomplished using high‐velocity thermal spray. Al‐8Si‐20BN (hexagonal BN, h‐BN) composite powders were injected into a high‐energy flame where the particles partially melted and accelerated to impact on steel substrates. The shock wave generated by the sudden impact of the droplets propagated through the underlying deposit, which experienced a polymorphic transition to high‐pressure forms. Transmission electron microscopy revealed that the deposits contained platelike c‐BN embedded in h‐BN. The c‐BN formed with a specific orientation relation, with (0001) h‐BN parallel to (111) c‐BN and [11–20] h‐BN nearly parallel to [2–20] c‐BN. As a result of shock propagation, a number of half‐Frank loops with Burgers vector ½[0001] were introduced and thin (∼3 nm) layers of amorphous BN (a‐BN), parallel to the (0002) plane, were formed. Significant shearing of the (10–10) plane with respect to the c‐axis, delamination, and kink bands were also observed in most of the h‐BN grains. The Hugoniot pressure calculation suggested that the impact pressure was sufficient to trigger the nucleation of c‐BN.
Direct Electroplating of Lithium Cobalt Oxide Film on Platinum Substrate in 100°–200°C Aqueous Solution
Authors: Han Kyoo‐Seung , Song Seung‐Wan , Fujita Hirofumi , Yoshimura Masahiro , Cairns Elton J. , Chang Soon‐Ho
Published: May 2005

Well crystallized, shape‐formed, and electrochemically active lithium cobalt oxide (LiCoO2) films are electroplated directly on an electron‐conducting substrate in an aqueous solution using a soft solution processing that is economical, consumes less energy consuming, and is environmentally friendly. Although LiCoO2 films are easily and economically prepared without any post‐synthesis heat treatment, the estimated film properties show a possibility of using the deposited films as a cathode film for lithium rechargeable microbatteries. In addition, the soft solution processing reveals that an exact understanding of chemical reactions and the proper combination of the chemical reactions can create an advanced synthetic procedure.
Control of Composition and Structure in Laminated Silicon Nitride/Boron Nitride Composites
Authors: Wang Chang‐an , Huang Yong , Zan Qingfeng , Zou Linhua , Cai Shengyou
Published: May 2005

Based on a biomimetic design, Si3N4/BN composites with laminated structures have been prepared and investigated through composition control and structure design. To further improve the mechanical properties of the composites, Si3N4 matrix layers were reinforced by SiC whiskers and BN separating layers were modified by adding Si3N4 or Al2O3. The results showed that the addition of SiC whiskers in the Si3N4 matrix layers could greatly improve the apparent fracture toughness (reaching 28.1 MPa·m1/2), at the same time keeping the higher bending strength (reaching 651.5 MPa) of the composites. Additions of 50 wt% Al2O3 or 10 wt% Si3N4 to BN interfacial layers had a beneficial effect on the strength and toughness of the laminated Si3N4/BN composites. Through observation of microstructure by SEM, multilevel toughening mechanisms contributing to high toughness of the laminated Si3N4/BN composites were present as the first‐level toughening mechanisms from BN interfacial layers as crack deflection, bifurcation, and pull‐out of matrix sheets, and the secondary toughening mechanism from whiskers in matrix layers.
Effect of pH of Medium on Hydrothermal Synthesis of Nanocrystalline Cerium(IV) Oxide Powders
Authors: Wu Nan‐Chun , Shi Er‐Wei , Zheng Yan‐Qing , Li Wen‐Jun
Published: May 2005

Well‐crystallized cerium(IV) oxide (CeO2) powders with nanosizes without agglomeration have been synthesized by a hydrothermal method in an acidic medium by using cerium hydroxide gel as a precursor. The relationship between the grain size, the morphology of the CeO2 crystallites, and the reaction conditions such as temperature, time, and acidity of the medium was studied. The experiments showed that with increasing reaction temperature and time, the CeO2 crystallites grew larger. The crystallites synthesized in an acidic hydrothermal medium were larger and had a more regular morphology than the ones synthesized in a neutral or alkaline medium when the reaction temperature and time were fixed. The CeO2 crystallites synthesized in an acidic medium were monodispersed; however, there was vigorous agglomeration among the grains synthesized in a neutral or alkaline medium. It was demonstrated that the hydrothermal treatment was an Ostwald ripening process and the acidity (pH) of the used hydrothermal medium played a key role in the dissolution of smaller grains. It is proposed that the dissolution process can control the kinetics of the growth of larger grains.
Microwave‐Assisted Synthesis of Fine Particle Oxides Employing Wet Redox Mixtures
Authors: Manoharan Solomon Sundar , Swati  , Prasanna Sigamani John , Rao Manju Lata , Sahu Ranjan Kumar
Published: May 2005

Interaction of electromagnetic radiation with a physical mixture of metal nitrates and amides/hydrazides is observed to initiate high‐temperature reactions, useful for realizing several high‐temperature ceramic materials. A judicious choice of such redox mixtures undergoes exothermic reactions when they couple with microwave radiation. The coupling of electromagnetic radiation with metal salts and amides/hydrazides depends on the dielectric properties of the individual components in the reaction mixture. The approach has been used to prepare γ‐Fe2O3, Fe3O4, MgCr2O4, α‐CaCr2O4, and La0.7Ba0.3MnO3.
Structure and Dielectric Properties of Lead Pyrochlores
Authors: Ubic Rick , Reaney Ian M.
Published: May 2005

This work investigates the structure and stability of the pyrochlore solid solution PbnNb2O5+n using a combination of high‐resolution electron microscopy and electron diffraction. The microwave dielectric properties of the series 1.5 ≤n≤3.0 have been established, and the effect of the substitution of Ta5+ for Nb5+ on dielectric properties has also been investigated for n= 1.5 and 2.0. Single‐phase cubic pyrochlore was obtained for n= 1.5. Compositions for which n > 1.5 showed discreet PbO‐rich layers on {111}cubic planes between alternating slabs of pyrochlore, similar in appearance to Ruddlesden–Popper phases. The occurrence of these layers results in a lowering of the overall symmetry to trigonal, and their presence was found to have a profound effect on the microwave dielectric properties.
Properties and Performance of Cation‐Doped Ceria Electrolyte Materials in Solid Oxide Fuel Cell Applications
Authors: Milliken Christopher , Guruswamy Sivaraman , Khandkar Ashok
Published: May 2005

Cation‐doped CeO2 electrolyte has been evaluated in single‐cell and short‐stack tests in solid oxide fuel cell environments and applications. These results, along with conductivity measurements, indicate that an ionic transference number of ∼0.75 can be expected at 800°C. Single cells have shown a power density >350 mW/cm2. Multicell stacks have demonstrated a peak performance of >100 mW/cm2 at 700°C using metallic separators.
Synthesis and Dielectric Properties of Li1−x+yTa1−x−3yTix+4yO3M‐Phase Solid Solutions
Authors: Borisevich Albina Y. , Davies Peter K.
Published: May 2005

The synthesis, structure, and dielectric properties of the so‐called M‐phase solid solutions in the Li2O–Ta2O5–TiO2 system were investigated. Although the range of stability of the tantalate phases is more limited compared with their niobate counterparts, they have identical structures based on intergrowths of LiTaO3‐type blocks separated by corundum type layers. The dielectric constants of the tantalate M‐phases range from 68 to 52 and they all exhibit a negative temperature coefficient of capacitance. The temperature coefficient of the resonant frequency measured in the microwave region can be tuned to zero, and the system shows quite good quality factors with the highest value reaching a Q×f= 10500 at 6.7 GHz.
X‐ray Absorption Near‐Edge Structure of Grain‐Boundary‐Segregated Y and Zr in Creep‐Resistant Alumina
Authors: Wang C. M. , Cargill G. Slade , Chan Helen M. , Harmer Martin P.
Published: May 2005

X‐ray absorption near‐edge structure (XANES) depends on stereochemical features of coordination polyhedra around probe atoms. K‐edge XANES of Y and Zr segregated in alumina grain boundaries has been obtained and analyzed using metallic Y and Zr, Y2O3, YAG, and monoclinic ZrO2 as standards. Grain‐boundary‐segregated Y and Zr show a positive chemical shift, and the magnitude of the shift, as compared with that of Y2O3 and ZrO2, respectively, is different for Y and Zr, indicating that, relative to Y2O3 and ZrO2, charge transfers for the grain‐boundary‐segregated Y and Zr are different. This result is also supported by the strength of the threshold resonance. A pre‐edge shoulder is seen in K‐edge XANES for grain‐boundary‐segregated Y and Zr but not for Y2O3 and ZrO2. This shoulder is attributed to the 1s→ 4d transition, which is normally forbidden, but can occur because of d–p mixing, which is favored by a tetrahedral coordination configuration. These results suggest that some of the grain‐boundary‐segregated Y and Zr have coordination configurations with a well‐defined tetrahedral symmetry. The XANES results are compared with those obtained from EXAFS. Implications of these results for understanding of the enhanced creep resistance in alumina are also discussed.
Influence of Composition on Fatigue Behavior and Threshold Stress Intensity Factor of Borosilicate Glasses
Authors: Bertoldi Massimo , Sglavo Vincenzo M.
Published: May 2005

Fatigue behavior of borosilicate glasses was studied using the analysis of subcritical propagation of Vickers indentation cracks. Glasses containing various amounts of glass‐network modifiers, mainly soda, were considered. Cone and median/radial crack systems were observed, depending on glass composition, indenter geometry, and test environment. Indentation tests were performed in water, holding the maximum load for durations ranging from 15 s to 6 d. The analysis of the crack length as a function of dwell time allowed evaluation of the subcritical growth parameters and fatigue limit at crack arrest. The influence of composition on fatigue parameters and fatigue limit was discussed in terms of fourfold‐coordinated boron atoms fraction compared with the content of glass‐network modifier ions.
Effect of Enameling on the Strength and Dynamic Fatigue of Soda–Lime–Silica Float Glass
Authors: Krohn Matthew H. , Hellmann John R. , Shelleman David L. , Pantano Carlo G. , Sakoske George E.
Published: May 2005

The effect of a glass enamel coating on the strength and fatigue behavior of float glass was investigated. Commercially available enamel that was comprised of Cu2Cr2O4 pigment particles in a bismuth‐zinc borosilicate glass matrix was applied to a soda–lime–silica float glass via screen printing, followed by fusion at elevated temperature. Strengths of the enameled specimens were evaluated in biaxial flexure using a ring‐on‐ring (ROR) test geometry, and the data were analyzed using a conventional two‐parameter Weibull distribution. Enameling was found to significantly degrade the strength of the float glass. There was no statistical difference in the characteristic strengths of samples enameled on the air side (66 MPa) compared with samples enameled on the tin side (61 MPa) of the float glass. Fractographic analysis revealed that the failures in the enameled float glass samples initiated at pores and pigment aggregates in the enamel, whereas failures in float glass samples initiated solely from surface flaws. Dynamic fatigue tests were performed on enameled float glass and indented float glass samples to determine the effect of the enamel on the stress corrosion behavior of the enameled components. There was no statistically significant difference between the stress corrosion exponents for the float glass and enameled float glass specimens.
Liquid‐Film‐Assisted Formation of Alumina/Niobium Interfaces
Authors: Sugar Joshua D. , McKeown Joseph T. , Marks Robert A. , Glaeser Andreas M.
Published: May 2005

Alumina has been joined at 1400°C using niobium‐based interlayers. Two different joining approaches were compared: solid‐state diffusion bonding using a niobium foil as an interlayer, and liquid‐film‐assisted bonding using a multilayer copper/niobium/copper interlayer. In both cases, a 127‐μm‐thick niobium foil was used; ∼1.4‐μm‐ or ∼3‐μm‐thick copper films flanked the niobium. Room‐temperature four‐point bend tests showed that the introduction of a copper film had a significant beneficial effect on the average strength and the strength distribution. Experiments using sapphire substrates indicated that during bonding the initially continuous copper film evolved into isolated copper‐rich droplets/particles at the sapphire/interlayer interface, and extensive regions of direct bonding between sapphire and niobium. Film breakup appeared to initiate either at niobium grain boundary ridges or at asperities or irregularities on the niobium surface that caused localized contact with the sapphire.
Fracture and Fatigue Behavior at Ambient and Elevated Temperatures of Alumina Bonded with Copper/Niobium/Copper Interlayers
Authors: Kruzic J. J. , Marks R. A. , Yoshiya M. , Glaeser A. M. , Cannon R. M. , Ritchie R. O.
Published: May 2005

Interfacial fracture toughness and cyclic fatigue‐crack growth properties of joints made from 99.5% pure alumina partially transient liquid‐phase bonded using copper/niobium/copper interlayers have been investigated at both room and elevated temperatures, and assessed in terms of interfacial chemistry and microstructure. The mean interfacial fracture toughness, Gc, was found to decrease from 39 to 21 J/m2 as temperature was raised from 25° to 1000°C, with failure primarily at the alumina/niobium interfaces. At room temperature, cyclic fatigue‐crack propagation occurred both at the niobium/alumina interface and in the alumina adjacent to the interface, with the fatigue threshold, ΔGTH, ranging from 20 to 30 J/m2; the higher threshold values in that range resulted from a predominantly near‐interfacial (alumina) crack path. During both fracture and fatigue failure, residual copper at the interface deformed and remained adhered to both sides of the fracture surface, acting as a ductile second phase, while separation of the niobium/alumina interface appeared relatively brittle in both cases. The observed fracture and fatigue behavior is considered in terms of the respective roles of the presence of ductile copper regions at the interface which provide toughening, extrinsic toughening due to grain bridging during crack propagation in the alumina, and the relative crack propagation resistance of each crack path, including the effects of segregation at the interfaces found by Auger spectroscopy.
Grain Growth of α‐SiAlON in the Calcium‐Doped System
Authors: Li Ya‐Wen , Wang Pei‐Ling , Chen Wei‐Wu , Cheng Yi‐Bing , Yan Dong‐Sheng
Published: May 2005

Two calcium‐doped α‐SiAlON compositions (Ca0.6Si10.2Al1.8−O0.6N15.4and Ca1.8Si6.6Al5.4O1.8N14.2) were prepared by hot pressing at 1600° and 1500°C, respectively, for complete phase transformation from α‐Si3N4to α‐SiAlON. Both samples were subsequently fired at different temperatures for different periods of time to study the grain growth of α‐SiAlON. Elongated α‐SiAlON grains were developed in both samples at high temperatures. The kinetics of grain growth was investigated based on the variations in length and width of the α‐SiAlON grains under different sintering conditions. Different growth rates were found between the length and width directions of the α‐SiAlON crystals, resulting in anisotropic grain growth in the microstructural development.
Metastable Phase Formation from an Undercooled Rare‐Earth Orthoferrite Melt
Authors: Nagashio Kosuke , Kuribayashi Kazuhiko
Published: May 2005

High‐speed digital imaging was conducted during the containerless solidification of rare‐earth orthoferrites (RE = La, Sm, Dy, Y, Yb, and Lu) with the perovskite structure to determine the metastable phase and elucidate its growth behavior. Observation using a high‐speed video camera revealed that the formation of the metastable phase became pronounced, and double recalescence from the metastable phase to a stable phase occurred, as the ionic radius of the rare‐earth element decreased. In the present paper, the formation of the metastable phase is discussed systematically in view of the stability of the perovskite structure and the activation energy of nucleation.
Influence of Interaction between Neighboring Oxygen Ions on Phase Stability in Cubic Zirconia
Authors: Kuwabara Akihide , Katamura Junji , Ikuhara Yuichi , Sakuma Taketo
Published: May 2005

The electronic structures of undoped c‐ and t‐ZrO2 were calculated by a first‐principles molecular orbital method. A preliminary analysis revealed that experimental energy‐loss near‐edge structure profiles obtained in ZrO2–8 mol% Y2O3 could be satisfactorily explained from the present theoretical calculation. The calculation suggests that the stability of t‐ZrO2 could be described by the interaction between neighboring oxygen ions rather than the covalency of Zr—O bonds. The effect of dopant cations on the stability of cubic‐zirconia solid solutions can be estimated semiquantitatively in terms of the repulsive Coulomb force between neighboring oxygen ions.
Formation of Silicalite‐1 in Channels of Novel SiO2–ZrO2 Porous Glass Tubes Used as Both a Silica Source and a Substrate
Authors: Jin Tetsuro , Kuraoka Koji , Matsumura Yasuyuki , Onishi Takaaki , Yazawa Tetsuo
Published: May 2005

Silicalite‐1 has been prepared using a novel SiO2–ZrO2 porous glass tube as both a silica source and a substrate. The SiO2–ZrO2 glass tube was found to possess sufficient physical strength to enable practical use as a separation and catalytic membrane after silicate‐1 deposition within its channel. This is in contrast to porous SiO2 glass which cannot be used to synthesize a silicalite‐1 deposited membrane with enough physical strength to perform gas permeance measurements.
Effect of Tween‐80 on the Control of Particle Size and Shrinkage Properties of Nanoscale α‐Alumina Synthesized by Sol–Gel Processing
Authors: Sharma Pramod K. , Varadan Vasundara V. , Varadan Vijay K.
Published: May 2005

The concept of tailored interfaces has been applied to the synthesis of nanoscale α‐Al2O3. Tween‐80 (poly‐oxyethylene(20) sorbitan monooleate, T‐80) was used as a surface modifier in the sol–gel process for this purpose. High‐resolution transmission electron microscopy study of the powder obtained with T‐80 confirmed the particle size of α‐Al2O3 (∼55 nm) and morphology (spherical). The exothermic peak temperature in the differential thermal analysis was shifted to a lower temperature (∼917°C) when the powder was derived from a T‐80 modifier content of 10 wt%. X‐ray diffraction showed that the α‐Al2O3 phase was the major phase that existed in modifier‐derived powder that was sintered at 1000°C. The experiments, based on linear shrinkage, indicated that the powder with T‐80 (10 wt%) could be densified at a low temperature.
Size Effects on Silica Polymorphism
Authors: Wu Sheng‐Wei , Wong David Shan Hill , Lu Shih‐Yuan
Published: May 2005

In this study, we found that the polymorphism and sintering behavior of silica can be affected by the size of starting particles. The formation of the stable tridymite phase, which is metastable unless a flux or mineralizer is present, is achieved with sintering of very fine silica particles of about 10 nm without the presence of a flux or mineralizer. Cristobalite phase is obtained as an intermediate as the amorphous phase transforms into the stable tridymite phase.
Fermentation patterns of small‐bale silage and haylage produced as a feed for horses
Authors: Müller C. E.
Published: May 2005

The fermentation quality of small‐bale silage and haylage for feeding to horses in Sweden, and using a conventional high‐density hay baler, was investigated in two experiments. Treatments studied were use of additives (inoculants containing lactic acid bacteria and a chemical additive consisting of hexamethylenetetramine, sodium nitrate, sodium benzoate and sodium propionate), the influence of dry‐matter (DM) content of wilted herbage and the effect of number of stretch film layers on fermentation pattern and aerobic stability. All silages and haylages were made from predominantly Timothy swards and were well fermented as indicated by low levels of ammonia and butyric acid. Values of pH were higher and concentrations of organic acids were lower in haylages than in the silages. This was not considered to be indicative of a poor fermentation in the haylage but of a restricted fermentation due to the high DM content of the herbage. The additives enhanced aerobic storage stability because of inhibition of mould growth. The only statistically significant effect of varying the number of stretch film layers was a higher content of CO2inside the bales when ten layers of stretch film were applied compared with six layers.
Competition between Artemisia frigida and Cleistogenes squarrosa under different clipping intensities in replacement series mixtures at different nitrogen levels
Authors: Gao Y. Z. , Wang S. P. , Han X. G. , Patton B. D. , Nyren P. E.
Published: May 2005

The relative competitive ability of Artemisia frigida Willd. (C3, semi‐shrub) and Cleistogenes squarrosa (Trin.) Keng (C4, perennial bunchgrass), grown in a greenhouse, was studied under three nitrogen fertilizer levels, three defoliation intensities and five competitive replacement series in a factorial arrangement. Relative yield total and the respective crowding coefficients for each species were calculated with reference to aboveground, below‐ground and total biomass. The index of aggressivity was also determined relative to total biomass.

Cleistogenes squarrosa was a consistently weak competitor at all nitrogen fertilizer and clipping levels compared with A. frigida. Artemesia frigida had a higher relative yield when grown in mixtures with C. squarrosa than in monocultures, whereas the yield of C. squarrosa was lower in mixtures with A. frigida than in monocultures. The relative competitive ability of A. frigida over C. squarrosa declined significantly at different clipping intensities with increasing nitrogen fertilizer. The interaction of nitrogen fertilizer with clipping was significant, although the clipping effect on aggressivity was not significant.