bluuebunny/crossref_metadata_2025 huggingface dataset:
Water Sorption‐Desorption Characteristics of Proton‐Conducting Antimonic Acids with Cubic and Monoclinic Structures
Authors: Sakka Y. , Sodeyama K. , Uchikoshi T. , Ozawa K. , Amano M.
Published: September 2005

Protonic conductivities of cubic and monoclinic antimonic acids are known to depend on water vapor pressure. Their water sorption‐desorption characteristics are compared and discussed with the water sorption isotherms and the desorption spectra of H216O, D2O, and H218O. The cubic antimonic acid contains more water than the monoclinic acid, which can be attributed to the existence of micropores in the cubic (pyrochlore type) structure.
Mechanical and Thermal Properties of β′‐Sialon Prepared by a Slip Casting Method
Authors: Suzuki Suguru , Nasu Takakuni , Hayama Seiji , Ozawa Masakuni
Published: September 2005

Various mechanical and thermal properties of β′‐sialon ceramics, Si6–zAlzOzN8–z, prepared from aqueous slurries by a slip casting method were investigated as a function of Z values from 0 to 4. In the present study, Si6–zAlzOzN8–z occurred in the β′‐sialon crystalline phase only near Z = 1. The maximum values for bending strength and fracture toughness, 660 MPa and 5.7 MPa·m1/2, respectively, were obtained at Z = 0.5. The thermal expansion coefficient exhibited its lowest value, 3.4 × 10−6·T−1, at Z = 0.5. In view of the present results, β′‐sialon, Si6–zAlzOzN8–z (Z = 0.5–1), prepared by a slip casting method using aqueous slurries could be adopted, with no problem, for refractory parts.
Relic Processing of Fine‐Scale, Large‐Area Piezoelectric Ceramic Fiber/Polymer Composites
Authors: Ting Steven M. , Janas Victor F. , Safari Ahmad
Published: September 2005

Fine‐scale, large‐area lead zirconate titanate (PZT) ceramic fiber/polymer composites were developed using the relic method. Carbon fabrics were used as a starting template material. These fabrics were soaked in PZT stock solution, stacked, and fired, removing the carbon and resulting in a relic structure identical to that of the original template. The relics were then sintered, backfilled with polymer, polished, and poled, resulting in a piezoelectric ceramic/polymer composite. The processing of the larger‐area composites involved scaling up the procedure utilized in the fabrication of the smaller composites. The application of an optimum uniaxial pressure of 580 Pa to the stacks during firing was found to improve the piezoelectric properties and facilitate the increase in sample area. Scale‐up to large area was achieved using two approaches: (1) the use of a larger template material, and (2) tiling smaller area relics together in an array configuration. The dielectric and piezoelectric properties of relic composites of 2.5 × 2.5 cm2 area with ∼37 vol% PZT were K= 150 ± 8, d33= 180 ± 11 pC/N, dh= 85 ± 7 pC/N, and dhgh= 5525 × 10−15m2/N. The properties of large‐area composites were comparable with those of small area.
Effects of Temperature and Atmosphere on the Formation Mechanism of Barium Titanate Using the Citrate Process
Authors: Tsay Jenq‐Dar , Fang Tsang‐Tse
Published: September 2005

In this investigation, several experiments have been conducted to study the effects of temperature and atmosphere on the formation of BaTiO3 using the citrate process. It was found that BaTiO3 could be completely formed when the precursor powder was heated at 300°C in O2 for 24 h and then heated in situ at 475°C for 1 h, during which no intermediate phase was observed throughout the process. Moreover, BaTiO3 could be formed at 400°C in O2 via the combustion of organic materials, in which the amount of the residual BaCO3 depended on the partial pressure of O2. The development of BaCO3 and oxycarbonate intermediate was found to be dependent on the temperature, the atmosphere, and the organic materials, and their formation mechanisms are discussed.
Liquid‐Channel Grain‐Boundary Structures
Authors: Belousov Valery V.
Published: September 2005

A combination of independent methods was used for studying the formation, structure, and conductivity of liquid‐channel grain‐boundary structures (LGBS) with Bi2CuO4and CuO as examples. It was shown that LGBS can be formed by partial thermal decomposition or liquid oxide permeation along boundaries of ceramic materials. It was found that the high ionic conductivity of ceramic LGBS originates from the fact that they are matrix‐type distributed structures.
Characteristics and Formation Mechanism of BaTiO3 Powders Prepared by Twin‐Fluid and Ultrasonic Spray‐Pyrolysis Methods
Authors: Milošević Olivera B. , Mirković Mirjana K. , Uskoković Dragan P.
Published: September 2005

Spherical fine (micrometer and submicrometer in size) homogeneous BaTiO3 powders were synthesized from ethanol: water solutions of BaCl2 and TiCl4 using the spray‐pyrolysis technique. Two different atomizers—twin‐fluid and ultrasonic, with a resonant frequency of 2.5 × 106 Hz—were used for mist generation. Hollow spherical particles containing a certain amount of unreacted BaCl2 phase and having a mean particle diameter of 2.5 μm were obtained at 1173 K using a twin‐fluid atomizing system. Decomposition of precursors and their transition to the cubic BaTiO3 phase occurred, even at 973 K in the case of the ultrasonic atomizing system. For the initial droplet size of 2.2 μm and residence time of ∼60 s, spherical BaTiO3 particles with the mean particle diameter of 0.53 μm were obtained. A BaTiO3 formation mechanism has been proposed as a reaction between TiO2 and BaCl2 rather than a reaction of oxides.
Electrophoretic Deposition (EPD): Mechanisms, Kinetics, and Application to Ceramics
Authors: Sarkar Partho , Nicholson Patrick S.
Published: September 2005

The mechanisms of electrophoretic deposition (EPD) are discussed and their shortcomings identified. The kinetics of the processes involved are analyzed for constant‐current and constant‐voltage conditions. A method of determining the Hamaker constant of suspended particles is developed by modeling the relationship between the particle inter‐action energy and the suspension stability. A three‐probe dc technique is used to map the voltage profile around the depositing electrode, and the results are used to explain discrepancies between the calculated and experimentally observed voltage drops during deposition. A mechanism of deposition is proposed based on DLVO theory and particle double‐layer distortion/thinning on application of a dc field to the suspension. Kinetic equations are developed for constant‐current and constant‐voltage EPD using mass balance conditions; these are verified by experiments. After the phenomenon is introduced and discussed, a critique of the application of EPD to the synthesis of ceramic shapes and coatings is given.
Formation and Control of Agglomerates in Alumina Powder
Authors: Kitayama Mikito , Pask Joseph A.
Published: September 2005

High‐purity alumina powder with submicrometer particle size was colloidally dispersed and classified in either water or ethanol to remove agglomerates from as‐received powder. After the slurries were dried, fine alumina particles cohered to form agglomerates, which were “hard” when formed in a water slurry, and “soft” in an ethanol slurry. Firing of the powder compacts with “hard” agglomerates resulted in inhomogeneous microstructures, and homogeneous microstructures were formed with “soft” agglomerates. The reasons for their formation are discussed and experimentally confirmed. In the case of water slurry, a small amount of transition alumina reacted with water at low pH. After drying, alumina gels were formed and acted as a strong binder between α‐alumina particles to form “hard” agglomerates.
Preparation of Silica from Rice Husks
Authors: Real Concha , Alcalá María D. , Criado José M.
Published: September 2005

Preliminary leaching of rice husks with a solution of hydrochloric acid before their combustion at 600°C is shown to be required to obtain relatively pure silica (∼99.5%) with a high specific surface area (∼260 m2/g) that is maintained even after heating at 800°C. Transmission electron microscopy observations indicate that this material has a homogeneous size distribution of nanometric particles. However, if the leaching with HCl is performed on the white ashes obtained by combustion of the rice husks at 600°C, an amorphous silica with the same purity also is obtained, but its specific surface area decreases to 1 m2/g. This behavior is due to a strong interaction between the silica and the potassium contained in the rice husks, which leads to a dramatic decrease of the specific surface area if K+ cations are not removed prior to the heat treatment at 600°C. This finding leads to a better understanding of the effect of potassium on the morphology of silica.
Chemical Instability of Silicon Carbide in the Presence of Transition Metals
Authors: Pan Yi , Baptista João L.
Published: September 2005

SiC has been proved chemically unstable at temperatures >1073 K (800°C) in the presence of cobalt, nickel, or iron. The instability results from reactions of cobalt, nickel, or iron with SiC to produce silicides and free carbon. A method of calculation is proposed for thermodynamic analyses of these reactions. The results show that the silicides of cobalt, nickel, and iron are thermodynamically more stable than SiC. The metal–silicon eutectic may provide kinetic condition to the reactions. Calculations also are performed for reactions of SiC with other transition metals. Instabilities of SiC in the presence of those metals are predicted.
Microstructure of (Fe0.2Co0.8)0.8(Fe2.38Co0.62O4): A Magnetic Oxidation Resistant Composite Formed by Coprecipitation
Authors: Yamegni‐Noubeyo Jean‐Celestin , Pourroy Genevieve , Werckmann Jacques , Malatsi Riera Antoni , Ehret Gabrielle , Poix Paul
Published: September 2005

The metal–ferrite composite (Fe0.2Co0.8)0.8(Fe2.38Co0.62O4) has been studied by X‐ray diffractometry measurements and high‐resolution transmission electron microscopy. Spinel ferrite occurs in highly crystalline domains 100–150 nm in size, and the iron–cobalt alloy occurs in smaller and less‐crystalline domains (10–20 nm). Both phases are heterogeneous in composition. The metal is embedded in the spinel phase, located near the edges, and overlaid by a poorly crystallized layer or misshapen regions containing small spinel crystals and amorphous phases. By annealing under vacuum up to 800°C, the misshapen regions disappear and the size of the metallic regions increases. The concentration of iron in the metallic regions decreases and their structure changes to face‐centered cubic, while the spinel becomes enriched in iron.
A Model to Compute Phase Diagrams in Oxides with Empirical or First‐Principles Energy Methods and Application to the Solubility Limits in the CaO–MgO System
Authors: Tepesch Patrick D. , Kohan Adrian F. , Garbulsky Gerardo D. , Ceder Gerbrand , Coley Crystal , Stokes Harold T. , Boyer Larry L. , Mehl Michael J. , Burton Benjamin P. , Cho Kyeongjae , Joannopoulos John
Published: September 2005

The CaO–MgO system is used as a prototype system to evaluate the accuracy of several energy and entropy approximations for predicting solid‐state phase diagrams in ionic materials. Configurational disorder between the cations is parameterized with the cluster expansion technique. The vibrational contribution to the free energy is incorporated with a harmonic model that accounts for the dependence of the vibrational density of states on the cation configuration. The CaO–MgO phase diagram can be predicted very accurately with quantum mechanical energy methods, without the use of any adjustable parameters. Published empirical potential parameters for the CaO–MgO system reproduce the qualitative features of the phase diagram but significantly underestimate the solubility limits. Parameters that reasonably reproduce the quantum mechanical results are presented.
Mechanical Characterization of Sol–Gel‐Derived Silicon Oxycarbide Glasses
Authors: Sorarù Gian Domenico , Dallapiccola Elisabetta , D'Andrea Gennaro
Published: September 2005

Silicon oxycarbide glasses have been fabricated, in the shape of thin rods suitable for flexural test experiments, by pyrolysis in an inert atmosphere at 1000° and 1200°C of solgel precursors containing Si–CH3 and Si–H bonds. The amount of carbon in the silicon oxycarbide network has been controlled by varying the carbon load in the precursor gel. Density and surface area analysis revealed that all of the samples pyrolyzed at 1200°C were well‐densified silicon oxycarbide glasses whereas for the glasses treated at 1000°C, compositions with low carbon loads showed the presence of a residual fine porous phase. The elastic modulus (E), flexural strength (MOR), and Vickers hardness (Hv) increase markedly with the amount of carbon in the oxycarbide glasses reaching the maximum values (E∼ 115 GPa, MOR ∼ 550 MPa, and Hv∼ 9 GPa) for samples with the highest carbon content. The experimental elastic modulus values of the silicon oxycarbide glasses compare well with the theoretical estimations obtained using the Voigt and Reuss models assuming the disordered network formed by the corresponding thermodynamic compositions.
Rare‐Earth Melilite Solid Solution and Its Phase Relations with Neighboring Phases
Authors: Huang Zhen‐Kun , Chen I‐Wei
Published: September 2005

Rare‐earth (R) melilite M(R) and its solid solution M'(R) are investigated. Starting with compositions of R2Si3O3N4 and R2Si2AlO4N3, the formation conditions for M(R), M'(R), and their neighboring phases have been delineated, and their lattice parameters and stoichiometry have been determined. Systematic trends in the solubility of M'(R), the unit‐cell dimensions, and the competition with neighboring phases with different rare‐earth ions have been identified and rationalized in terms of size effects and acid–base reactions. The compatibility between melilite and neighboring phases, including α′‐ and β′‐SiAlON and polytypoids, is summarized in a series of tentative phase diagrams to elucidate the various phase relations for R‐Si‐(Al/O)‐N systems.
Reaction Sintering and Mechanical Behavior of Cordierite Containing Sapphirine Dispersoids
Authors: Genevrier Marc , Mocellin Alain
Published: September 2005

The preparation of cordierite–sapphirine composites through additions of magnesia–alumina mixtures to a cordierite powder has been studied. Kinetic experiments have shown that the reaction sequence varies little with composition, always involving the transient presence of spinel before sapphirine forms. The appearance of a liquid phase, that can be accounted for by phase‐diagram considerations, leads to some differences in the reaction‐sintering paths and microstructures. The reaction–densification range remains narrow in most composites. However, the addition of 1 wt% titania has proved efficient in improving both densification and reaction behaviors. Relative fracture energy and strength increases up to 30% and 100%, respectively, have been obtained. The results are qualitatively rationalized with reference to differences in the modes of testing. Cracks propagate at moderate velocities (work of fracture) entirely within the matrix, whereas they may reach particle–matrix interfaces at higher rates (strength tests), thus allowing other energy‐dissipating processes to occur.
Effects of Addition of Na2O, Sb2O3, CaO, and ZrO2 on the Properties of Lithium Zinc Ferrite
Authors: Rezlescu Nicolae , Rezlescu Elena
Published: September 2005

Some effects of CaO, Na2O, Sb2O3, and ZrO2 additions on Li0.3Zn0.4Fe2.3O4 ferrite were studied to improve its density and other material properties. The densification behavior of the ferrite depended on the amount and type of additive. A relative density of ∼98.5% was achieved with the addition of CaO. The grain size decreased with the addition of Na2O, CaO, and Sb2O3. The permeability and electrical resistivity increased with additives. CaO remarkably increased resistvity, whereas, ZrO2 increased permeability. Na2O and Sb2O3 increased the Curie temperature, whereas CaO and ZrO2 decreased it. These effects were attributed to mainly additive segregation on the grain boundaries, which suppressed grain‐size development during the sintering of lithium zinc ferrite.
Cracking of Laminates Subjected to Biaxial Tensile Stresses
Authors: Hillman Craig , Suo Zhigang , Lange Fred F.
Published: September 2005

During the processing of laminar ceramic, biaxial residual stresses can arise due to differential thermal contraction between unlike layers. A tensile stress can cause preexisting flaws to extend across the layer and into the adjacent layers and then tunnel until they meet either another crack or a free surface. A previous analysis has shown that for a given residual stress there is a critical layer thickness, below which no tunnel cracks will exist, regardless of initial flaw size. Here, the previous analysis was modified to take into account the crack extension into adjacent layers. To determine the validity of the analysis, laminates composed of alternating layers of zirconia and alumina/zirconia were fabricated by a sequential centrifugation technique. The composition of the alumina/zirconia layer was varied to change the biaxial, tensile stresses in the zirconia layer. Observations were then made to determine the critical layer thickness for tunnel cracks and their extension into the adjacent layers. These observations were compared to the theoretical predictions.
Calculations of Internal Stresses during Sintering in Two Dimensions
Authors: Zhang Wen , Schneibel Joachim H.
Published: September 2005

The internal stresses which may arise during sintering are modeled by calculating the behavior of coupled strings of circular particles. Strings consisting of large and small particles are connected in parallel and are allowed to sinter by surface and grain boundary diffusion. The strings consisting of the smaller particles experience tensile stresses, since their shrinkage is inhibited by the slower sintering of the larger particles. These internal stresses are followed as a function of time. The calculations provide a first‐order estimate of the internal stresses which may arise during the sintering of irregular arrays of particles.
High‐Temperature lonic Conduction in Multicomponent Solid Oxide Solutions Based on HfO2
Authors: Weyl Axel , Janke Dieter
Published: September 2005

The parameter pe' of HfO2–CaO, HfO2–Y2O3, and HfO2–RE2O3 (where RE is a rare‐earth element) solid solutions with high dopant concentrations was measured at 1200°–1600°C. In the oxide systems, the cubic phase was identified using X‐ray diffractometry. All dopant oxides formed wide cubic solid‐solution regions with HfO2. In the HfO2–Y2O3 system, the 15 mol% Y2O3 composition featured the lowest parameter pe' and, thus, represented the optimum composition for a solid electrolyte. For the investigated RE2O3‐doped HfO2 solid solutions, the parameter pe' decreased as the dopant radius decreased. The lowest parameter pe' values among the RE2O3‐doped systems were obtained for HfO2–Dy2O3 or HfO2–Yb2O3 at1600°C. Furthermore, parameter pe' values were determined for the fluorite‐ and pyrochlore‐type structures in the HfO2–Gd2O3 system and ternary oxide solutions based on HfO2. Additional investigations confirmed the good reproducibility of the parameter pe' values using two different measuring methods and different sintering conditions for the HfO2–30 mol% Y2O3 composition. A comparison between the parameter pe' values of doped HfO2 and ZrO2 systems revealed that the parameter pe' values of HfO2 systems were one to three orders of magnitude lower than those of ZrO2 systems in the 1200°–1600°C temperature range.
Yttria Doping and Sintering of Submicrometer‐Grained α‐Alumina
Authors: Sato Eiichi , Carry Claude
Published: September 2005

The sintering behavior of α‐alumina powders doped with magnesia (500 or 1500 ppm) and yttria (0, 500, or 1500 ppm) was investigated using constant‐heating‐rate dilato‐metric experiments. The apparent activation energies for the intermediate stage of sintering were 740, 800, and 870 kJ/mol for 0, 500, and 1500 ppm yttria doping levels, respectively; these were independent of magnesia doping. Yttria‐doped powder compacts exhibited systematic anomalous second peaks in the densification rate curves at certain grain sizes which were determined only by yttria doping levels. Before the anomalous peak, with lower yttrium contents at grain boundaries, yttrium in an atomic state delays densification and raises the apparent activation energy. Beyond the peak, with higher yttrium contents at grain boundaries, yttria‐rich precipitation delays the densification. Within the peak, yttrium segregation near the saturation level enhances densification.
Interdiffusion in SiC–AlN and AlN–Al2OC Systems
Authors: Tian Qiang , Virkar Anil V.
Published: September 2005

AlN, Al2OC, and the 2H form of SiC are isostructural. Both SiC–AlN and AlN–Al2OC form homogeneous solid solutions above 2000° and 1950°C, respectively. The kinetics of phase separation in the two systems, however, are quite different. Interdiffusion in both SiC–AlN and AlN‐Al2OC systems was examined in the solid‐solution regime in an attempt to elucidate differences in the kinetics of phase separation that occur in the two systems when annealed at lower temperatures. Diffusion couples of (SiC)0.3(AlN)0.7/(SiC)0.7(AlN)0.3 and (AlN)0.7(Al2OC)0.3/(AlN)0.3(Al2OC)0.7 were fabricated by hot pressing and were annealed at high temperatures by encapsulating them in sealed SiC crucibles to suppress loss due to evaporation. Interdiffusion coefficients in (SiC)0.3‐(AlN)0.7/(SiC)0.7(AlN)0.3 diffusion couples were measured at 2373, 2473, and 2573 K, and the corresponding activation energy was determined to be 632 kJ/mol. (AlN)0.7(Al2OC)0.3/ (AlN)0.3(Al2OC)0.7 samples were annealed at 2273 K. The interdiffusion coefficient measured in the AlN–Al2OC system was much larger than that in the SiC–AlN system.
Morphological Forms of Tobermorite in Hydrothermally Treated Calcium Silicate Hydrate Gels
Authors: Bell Nelson S. , Venigalla Sridhar , Gill Petra M. , Adair James H.
Published: September 2005

The morphology of the calcium silicate hydrate phase, tobermorite, generally thought to be the bonding phase in ordinary portland cement, was studied. Tobermorite was hydrothermally synthesized at pH 12.6 at 150°C. The powder was characterized by XRD and SEM analysis. Modeling of the morphology was performed using the SHAPE and ATOMS programs. Two morphologies were produced: fibers and platelets. Computer calculations of equilibrium particle shape suggest that growth occurs on the (110)‐type planes for both morphologies.
Processing of a Novel Multilayered Silicon Nitride
Authors: Shigegaki Yasuhiro , Brito Manuel E. , Hirao Kiyoshi , Toriyama Motohiro , Kanzaki Shuzo
Published: September 2005

A new type of silicon nitride with a layered structure of alternating dense and porous layers was obtained by addition of β‐Si3N4 whiskers to the porous layers. The materials consisted of dense layers 60 μm thick and porous layers 40 μm thick with a final porosity of about 30%. Highly anisotropic shrinkage behavior was observed during sintering. A large addition of whiskers to the porous layers resulted in layers with well‐oriented and tightly tangled elongated grains, where porosity is represented by anisotropic shaped pores.
Properties of CeO2–Al2O3–SiO2 Glasses Prepared in Air
Authors: Hwang Chii‐Shyang , Ji Shi‐Dong , Lin Sin‐Lung
Published: September 2005

Properties of 15–30 mol% CeO2/23 mol% Al2O3/62–47 mol% SiO2 glasses prepared in air have been investigated in this study. Experimental results show that the glass transformation temperature, the dilatometric softening temperature, and the transmittance in the visible region decrease with increasing ceria content; but the thermal expansion coefficient, the bulk density, and the microhardness increase with increasing ceria content.
Influence of Powder Composition and Milling Media on the Formation of Molybdenum Disilicide by a Mechanically Induced Self‐Propagating Reaction
Authors: Yen Bing K. , Aizawa Tatsuhiko , Kihara Junji
Published: September 2005

The spontaneous formation of molybdenum disilicide (α‐MoSi2) during the mechanical alloying of a stoichiometric Mo‐Si powder mixture occurred by a mechanically induced self‐propagating reaction (MSR)—a mechanism similar to that of the thermally ignited self‐propagating high‐temperature synthesis (SHS). The bulk of α‐MoSi2 formation occurred in less than 15 min once the reaction commenced after 14 h, 15 min of milling. When the milling media was switched from zirconia to steel, however, the reaction rate became sluggish as both the α and β phases were formed. The mechanical alloying of the Si‐rich and Si‐poor compositions was also characterized by the gradual formation of α and β phases.
Influence of Viscous Deformation at the Contact Point of Primary Particles on Compaction of Alkoxide‐Derived Fine SiO2 Granules under Ultrahigh Isostatic Pressure
Authors: Kamiya Hidehiro , Suzuki Hisao , Kato Daisuke , Jimbo Genji
Published: September 2005

Viscous deformation and the adhesion force at the contact point between amorphous silica particles under ultrahigh isostatic pressure (up to 1 GPa) are important in the densification of powder compacts. The amount of viscous deformation and the strength of adhesion force have been changed in the present study by altering the calcination temperature and particle diameter, and the new values have been determined successfully using a diametral compression test. The diameter of spherical and monosized alkoxide‐derived silica powders has been controlled within the range of 10–400 nm. Close‐packed granules of these powders have been produced by spray drying. Because of viscous deformation, as‐spray‐dried ultrafine silica powders without calcination could be consolidated into highly dense compacts (>74% of theoretical density) by applying ultrahigh isostatic pressure (1 GPa). Relatively high temperature in the calcined particles (400°C) causes viscous deformation at the contact point to disappear almost completely and clearly increases the adhesion force, because of neck growth that has resulted from viscous sintering. At temperatures >200°C, the green density of the calcined powders decreases to 65% of theoretical density, even under 1 Gpa pressure. The relationship between green density and viscous deformation in silica particles at the point of contact has been analyzed quantitatively by the Hertz and Rumpf model. On the other hand, if relatively low isostatic pressure (Pc < 100 MPa) is applied, the green density and intergranular pore volume depend on the strength of the spray‐dried granules. The relationship between granule strength and neck growth at the contact point with calcination has been estimated quantitatively.
Crack Stability and Its Effect on Fracture Toughness of Hot‐Pressed Silicon Nitride Beam Specimens
Authors: Bar‐On Isa , Baratta Francis I. , Cho Kyu
Published: September 2005

The effect of stable crack extension on fracture toughness test results was determined using single‐edge precracked beam specimens. Crack growth stability was examined theoretically for bars loaded in three‐point bending under displacement control. The calculations took into account the stiffness of both the specimen and the loading system. The results indicated that the stiffness of the testing system played a major role in crack growth stability. Accordingly, a test system and specimen dimensions were selected which would result in unstable or stable crack extension during the fracture toughness test, depending on the exact test conditions. Hot‐pressed silicon nitride bend bars (NC132) were prepared with precracks of different lengths, resulting in specimens with different stiffnesses. The specimens with the shorter precracks and thus higher stiffness broke without stable crack extension, while those with longer cracks, and lower stiffness, broke after some stable crack extension. The fracture toughness values from the unstable tests were 10% higher than those from the stable tests. This difference, albeit small, is systematic and is not considered to be due to material or specimen‐to‐specimen variation. It is concluded that instability due to the stiffness of test system and specimen must be minimized to ensure some stable crack extension in a fracture toughness test of brittle materials in order to avoid inflated fracture toughness values.
Grain‐Boundary Microstructure and Chemistry of a Hot Isostatically Pressed High‐Purity Silicon Nitride
Authors: Pan Xiaoqing , Gu Hui , van Weeren Remco , Danforth Stephen C. , Cannon Rowland M. , Rühle Manfred
Published: September 2005

Two high‐purity Si3N4 materials were fabricated by hot isostatic pressing without the presence of sintering additives, using an amorphous laser‐derived Si3N4 powder with different oxygen contents. High‐resolution transmission electron microscopy and electron energy‐loss spectroscopy (EELS) analysis of the Si3N4 materials showed the presence of an amorphous SiO2 grain‐boundary phase in the three‐grain junctions. Spatially resolved EELS analysis indicated the presence of a chemistry similar to silicon oxynitride at the two‐grain junctions, which may be due to partial dissolution of nitrogen in the grain‐boundary film. The chemical composition of the grain‐boundary film was SiNxOy, (x ∼ 0.53 and y ∼ 1.23), and the triple pocket corresponded to the amorphous SiO2 containing ∼2 wt% nitrogen. The equilibrium grain‐boundary‐film thickness was measured and found to be smaller for the material with the lower oxygen content. This difference in thickness has been explained by the presence of the relatively larger calcium concentration in the material with the lower amount of SiO2 grain‐boundary phase, because the concentration of foreign ions has been shown to affect the grain‐boundary thickness.
Models of High‐Temperature, Environmentally Assisted Embrittlement in Ceramic‐Matrix Composites
Authors: Evans Anthony G. , Zok Frank W. , McMeeking Robert M. , Du Zheng Z.
Published: September 2005

The intermediate‐temperature oxidation embrittlement, or ‘pest,’ effect found in ceramic‐matrix composites (CMCs) is shown to have features analogous to stress corrosion cracking. The behavior involves crack growth upon oxidation of the fibers or the fiber coatings to form an oxide that weakens the fibers. It has reaction‐ and diffusion‐controlled regimes. The former occurs at low stresses. The latter occurs at higher stresses. It is controlled by oxygen ingress through the matrix cracks. There is also a crack growth threshold. Expressions for the crack velocity above the threshold are derived as well as the stress dependence of the rupture life.
Effect of Oxidation Heat Treatments on the Mechanical Behavior of a Si‐C‐O‐Fiber‐Reinforced Magnesium Aluminosilicate
Authors: Kumar Atul , Knowles Kevin M.
Published: September 2005

Oxidized magnesium aluminosilicate composites reinforced with Si‐C‐O (Nicalon) fiber have been found to retain their as‐received flexural strength. The elastic moduli of the oxidized composites exhibited an increase for samples oxidized at 1000°C and a decrease at higher temperatures. Densification of the matrix may increase the elastic modulus of composites oxidized at 1000°C, whereas cracks in the matrix and at the fiber‐matrix interfaces may be responsible for the low elastic moduli of composites oxidized at higher temperatures. The interfacial friction stresses were high at or near the edges and low in the interior of the oxidized samples. As a result, the oxidized composites failed by fiber fracture on the surface, followed by delamination and fiber pullout in the interior.
Experimental Evaluation of a New Flocculation‐Filtration Model for Ceramic Shape Forming Processes
Authors: Haerle Andrew G. , Haber Richard A.
Published: September 2005

The effect of suspension rheology on the casting mechanics of 37 vol% aqueous silicon carbide slips was examined. Slip viscosities of 180, 120, 90, and 58 mPa.s were evaluated. The 58 mPa.s slip was considered to be fully deflocculated; the others were underdeflocculated to varying degrees. The fully deflocculated slip cast according to parabolic rate behavior, while the others cast at a faster than parabolic rate. Deviations from parabolic rate behavior were correlated with a nonuniform cake structure observed through ultrasound and mercury porosimetry measurements. The observed casting behavior was explained on the basis of a suspension flocculation‐filtration model. From rheological measurements, it was found that flocculation of the SiC particles during casting in the underdeflocculated suspensions caused the local void volume within the forming cake to increase as a function of cake thickness. The fully deflocculated slip was rheologically stable, and therefore cast with a uniform microstructure.
Controlled Crystallization and Properties of Zirconium Fluoride‐Based Glass‐Ceramics
Authors: Jewell John M. , Friebele E. Joseph , Aggarwal Ishwar D.
Published: September 2005

51ZrF416BaF2, 5LaF3.3AlF2,.20Li.F5PbF2, glasses were pre‐pared with CdF, additions of 0, 2, 5, and 7.5 mol%. The glasses with 2 and 5 mol% exhibited controllable nucleation upon heat treatment above the glass transformation tem‐perature. The nucleation and crystallization of glasses with 5 mol% CdF, were characterized using bulk heat treat‐ments, differential scanning calorimetry, and scanning elec‐tron microscopy. The isothermal crystallization of nucleated glasses resulted in the formation of a glass‐ceramic that was transparent in the infrared (>70% transmission) and more resistant to fracture than typical fluoride glasses.
Raman and11B Nuclear Magnetic Resonance Spectroscopic Studies of Alkaline‐Earth Lanthanoborate Glasses
Authors: Brow Richard K. , Tallant David R. , Turner Gary L.
Published: September 2005

Glasses from the RO.La2O3.B2O3(R = Mg, Ca, and Ba) systems have been examined. Glass formation is centered along the metaborate tie line, from La(BO2)3to R(BO2)2. Glasses generally have transition temperatures >60°C and expansion coefficients between 60 × 10‐7/°C and 100 × 10‐7/°C. Raman and solid‐state nuclear magnetic resonance spectroscopies reveal changes in the metaborate network that depend on both the [R]:[La] ratio and the type of alkaline‐earth ion. The fraction of tetrahedral sites is generally reduced in alkaline‐earth‐rich glasses, with magnesium glasses possessing the lowest concentration of B[4]. Raman spectra indicate that, with increasing [R]:[La] ratio, the preferred metaborate anion changes from a double‐chain structure associated with crystalline La(BO2)3to the singlechain and ring metaborate anions found in crystalline R(BO2)2phases. In addition, disproportionation of the metaborate anions leads to the formation of a variety of other species, including pyroborates with terminal oxygens and more‐polymerized species, such as diborates, with tetrahedral borons. Such structural changes are related to the ease of glass formation and some of the glass properties.
Chemical Preparation of Lead‐Containing Niobate Powders
Authors: Yoshikawa Yoshio , Uchino Kenji
Published: September 2005

A chemical precipitation method was developed for synthesis of typical relaxor compounds—Pb(Mg1/3Nb2/3)O3 (PMN), Pb(Fe1/2Nb1/2)O3 (PFN), and Pb(Sc1/2Nb1/2)O3 (PSN)—from nitrate solutions. To obtain a niobium precursor compatible with the aqueous chemical routes, peroxo‐niobium complex solutions were prepared by dissolving hydrated niobia precipitates in a dilute nitric acid solution with hydrogen peroxide. Powders that consisted of small particles ranging from 20 to 40 nm were successfully precipitated from the mixed nitrate solutions by hydrolysis with aqueous ammonia solutions. On calcination, these powders were highly reactive. For example, PMN precursor powder began to crystallize simultaneously to cubic pyrochlore and perovskite phases at ∼400°C and yielded ∼95% of the perovskite phase after calcination at 800°C for 1 h. PFN and PSN precursor powders calcined under similar conditions formed single perovskite phases.
Electrical Conductivity in Mixed‐Alkali Aluminosilicate Melts
Authors: Kim Ki‐Dong
Published: September 2005

The mixed‐alkali effect in ac electrical conductivity has been investigated in 25R2O(Na2O+K2O)‐yAl2O3‐(75‐y)SiO2 melts, with y= 0, 5, 7.5, and 10 mol%, at temperatures of 1000°‐1400°C. The results for the molten state show a typical mixed‐alkali effect, similar to that exhibited below the transformation temperature. These results imply that the interaction between two different alkali ions is maintained in the molten state. However, the mixed‐alkali effect increases as the Al2O3 content increases (in other words, with decreasing nonbridging oxygen content). Such results can be explained in terms of the binding state of AlO4‐R+ and ‐O‐‐R+, based on the conductivity behavior of alkali aluminosilicate melts.
Precipitation of Hydroxyapatite under Stearic Acid Monolayers
Authors: Unuma Hidero , Ito Kazutoshi , Ota Toshitaka , Takahashi Minoru
Published: September 2005

The nucleation and growth of hydroxyapatite (HAp) crystals from solutions with and without Langmuir monolayers of stearic acid (SA) were investigated. The monolayers apparently enhanced the nucleation of HAp. Monolithic, filmlike polycrystalline HAp with preferred orientation of (00l) planes parallel to the monolayer interface was precipitated, while colloidal and powdery precipitation in the bulk solution was predominant in the absence of the monolayer. Geometrical similarity was found between the hexagonal packing conformation of the SA headgroups in the monolayers and the alignment of calcium ions in the (001) plane of HAp. It was suggested that HAp crystals nucleated and grew epitaxially on the monolayer interface.
Preparation of Thin Sections of Coated Fibers for Characterization by Transmission Electron Microscopy
Authors: Cinibulk Michael K. , Welch John R. , Hay Randall S.
Published: September 2005

A method of preparing transmission electron microscopy (TEM) specimens of coated ceramic fibers has been developed, which produces large electron transparent areas due to the minimal preferential milling of the fiber, coating, or epoxy matrix. Multiple individual fibers or tows are impregnated with a high‐temperature epoxy and contained to assure a high fiber‐to‐epoxy volume ratio. The samples are then sectioned and mechanically thinned either parallel or normal to the fiber axes using a wedge polisher on diamond lapping films to achieve a thickness of less than 5 μ.m. The thinned sample is then ion‐milled to electron transparency in less than 30 min, giving representative specimens of the coating, fiber, and coating‐fiber interface. This technique is also well suited to preparing extremely flat specimens for scanning electron microscopy analysis of thin coatings. Examples of TEM sections of coated fibers prepared using this technique are presented.
Improved Endurance Limit of Zirconia Ceramics by Overloading
Authors: Møller Carsten V. , Andreasen Jens H. , Karihaloo Bhushan L.
Published: September 2005

The influence of initial overloads upon the subsequent fatigue crack growth in transformation‐toughened ceramics (TTCs) is investigated. It is revealed that initial overloading can be beneficial to these ceramics. In particular, it is shown that an overload will facilitate crack arrest in a low transformation strength material which would otherwise be prone to cyclic fatigue degradation and eventual failure. Based on the results of this investigation, a proof test may be designed to screen out TTC components which do not attain a prescribed endurance limit.
Preparation of Porous Cr3C2 Grains with Cr2O3
Authors: Hashimoto Shinobu , Yamaguchi Akira
Published: September 2005

Porous Cr3C2 grains (∼300 to 500 μm) with ∼10 wt% of Cr2O3 were prepared by heating a mixture of MgCr2O4 grains and graphite powder at 1450° to 1650°C for 2 h in an Al2O3 crucible covered by an Al2O3 lid with a hole in the center. The porous Cr3C2 grains exhibited a three‐dimensional network skeleton structure. The mean open pore diameter and the specific surface area of the porous grains formed at 1600°C for 2 h were ∼3.5 (μm and ∼6.7 m2/g, respectively. The present work investigated the morphology and the formation conditions of the porous Cr3C2 grains, and this paper will discuss the formation mechanism of those grains in terms of chemical thermodynamics.
Effect of Refractory Oxides on the Oxidation of Graphite and Amorphous Carbon
Authors: Yamaguchi Akira , Zhang Shaowei , Yu Jingkun
Published: September 2005

The effect of refractory oxides on the oxidation of graphite and amorphous carbon was investigated. Al2O3 accelerated the oxidation of graphite greatly. TiO2, ZrO2, and MgO inhibited the oxidation of graphite, while SiO2 inhibited the oxidation of graphite slightly. The above oxides had no effect on the oxidation of amorphous carbon.
Review article: hepatitis C virus and calcineurin inhibition after renal transplantation
Authors: FABRIZI F. , BROMBERG J. , ELLI A. , DIXIT V. , MARTIN P.
Published: September 2005

The impact of hepatitis C virus on patient and graft survival after renal transplantation remains controversial. However, recent studies have given emphasis on the detrimental role of hepatitis C on long‐term patient and graft survival after renal transplantation. Various mechanisms can promote the lower survival in hepatitis C virus‐positive recipients, i.e. post‐transplant diabetes mellitus, liver disease and infections.

Novel evidence has been accumulated showing the inhibitory activity of ciclosporin on the hepatitis C virus replication rate in human hepatocytes; ciclosporin has been shown in vitro to suppress hepatitis C virus replication as effectively as interferon alpha. This effect has not been seen with tacrolimus and is separate from its immunosuppressive activity. Data from patients with normal kidney function or after bone marrow transplantation show that ciclosporin inhibits hepatitis C virus replication. It appears that the progression of liver fibrosis is slower in hepatitis C virus‐positive liver transplant recipients treated with ciclosporin than tacrolimus. In contrast, the clinical outcome of hepatitis C in hepatitis C virus‐positive patients after liver transplantation treated with ciclosporin vs. tacrolimus has given mixed results. No information after renal transplantation is available.

Various parameters can promote the worsening of hepatitis C after renal transplantation but choice of calcineurin inhibition is one of the few risk factors that can potentially be modified by the physician. Prospective, comparative trials of ciclosporin and tacrolimus with large size and adequate follow‐up after renal transplantation are in progress.
Coeliac disease case finding and diet monitoring by point‐of‐care testing
Authors: KORPONAY‐SZABÓ I. R. , RAIVIO T. , LAURILA K. , OPRE J. , KIRÁLY R. , KOVÁCS J. B. , KAUKINEN K. , FÉSÜS L. , MÄKI M.
Published: September 2005

Background : Immunoglobulin A class transglutaminase autoantibodies are highly predictive markers of active coeliac disease, a disorder difficult to recognize solely on clinical grounds.

Aims : To develop and evaluate a simple rapid test for point‐of‐care detection of coeliac autoantibodies.

Methods : The novel whole blood test utilizes the patient's endogenous transglutaminase in red blood cells for detection of transglutaminase‐specific immunoglobulin A antibodies present in the blood sample, with normal plasma immunoglobulin A detection as positive test control. We evaluated 284 patients under suspicion of coeliac disease and undergoing jejunal biopsy, and 263 coeliac patients on a gluten‐free diet, 383 being tested prospectively in a point‐of‐care setting. Results were compared with histology, conventional serum autoantibody results and dietary adherence.

Results : The rapid test showed 97% sensitivity and 97% specificity for untreated coeliac disease, and identified all immunoglobulin A‐deficient samples. Point‐of‐care testing found new coeliac cases as efficiently as antibody tests in laboratory. Coeliac autoantibodies were detected onsite in 21% of treated patients, while endomysial and transglutaminase antibodies were positive in 20% and 19%, respectively. The positivity rate correlated with dietary lapses and decreased on intensified dietary advice given upon positive point‐of‐care test results.

Conclusions : Point‐of‐care testing was accurate in finding new coeliac cases and helped to identify and decrease dietary non‐compliance.
Distribution of larval fishes among water masses in Onslow Bay, North Carolina: implications for cross‐shelf exchange
Authors: QUATTRINI A. M. , LINDQUIST D. G. , BINGHAM F. M. , LANKFORD T. E. , GOVONI J. J.
Published: September 2005

The Gulf Stream (GS) is a major oceanographic feature with potential to influence the recruitment of larval fishes to continental shelf habitats in the southeastern United States. To test the hypothesis that the GS is a source of certain larval fishes to Onslow Bay, North Carolina, we (i) classified water masses as shelf, GS, GS front (GSF), or GS/shelf mixture (GS/S); (ii) compared larval fish assemblages and concentrations among these water masses; and (iii) compared length–frequency distributions and length–concentration relationships of indicator and commercially important taxa among water masses. A total of 21,222 larvae were collected with bongo and neuston nets from April 2000 to December 2001. Non‐metric multidimensional scaling analyses revealed distinct larval assemblages associated with different water masses. For bongo catches, bothids were abundant in all water masses, gobiids, callionymids, and labrids were abundant in shelf waters, and myctophids and scombrids were abundant in the GS. For neuston catches, carangids dominated in GS/S, GSF, and GS waters, whereas triglids were abundant in shelf water. Larval concentrations in neuston catches were lower in shelf waters and higher in GS and GSF waters. Concentrations of most taxa in bongo catches were low in the GS and higher in shelf waters. We used trends in myctophid (offshore/GS) and gobiid (shelf) length–concentration data as indicators of the sources of commercially important serranids. Length distributions and concentrations of larval indicator taxa suggested local, shelf spawning, and transport of larvae from offshore.
Rep helicase suppresses short‐homology‐dependent illegitimate recombination in Escherichia coli
Authors: Shiraishi Kouya , Imai Yukiho , Yoshizaki Shinji , Ikeda Hideo
Published: September 2005

To study roles of Rep helicase in short‐homology‐dependent illegitimate recombination, we examined the effect of a rep mutation on illegitimate recombination and found that the frequency of spontaneous illegitimate recombination is enhanced by the rep mutation. In addition, illegitimate recombination was synergistically enhanced by the rep mutation and UV irradiation, showing that Rep helicase plays a role in suppression of spontaneous as well as UV‐induced illegitimate recombination. The defect in RecQ helicase also has a synergistic effect on the increased illegitimate recombination in the rep mutant. It was also found that the illegitimate recombination induced by the rep mutation is independent of the RecA function with or without UV irradiation. Nucleotide sequence analyses of the recombination junctions showed that the illegitimate recombination induced by the rep mutation mostly takes place between short homologous sequences. Based on the fact that the defect of Rep helicase induces replication arrest during replication, resulting in the formation of DNA double‐strand breaks, we propose a model for illegitimate recombination, in which double‐strand breaks caused by defect of Rep helicase promotes illegitimate recombination via short‐homology‐dependent‐end‐joining. In addition, the mechanism of synergistic action between the rep mutation and UV irradiation on illegitimate recombination is discussed.