bluuebunny/crossref_metadata_2025 huggingface dataset:
Glass‐Forming Region and Structure of Oxyhalide Glasses in the System LiCl‐Li2O‐TeO2
Authors: Yoko Toshinobu , Kamiya Kanichi , Yamada Hiroyuki , Tanaka Katsuhisa
Published: March 2005

The glass‐forming region for oxyhalide glasses in the system LiCl‐Li2O‐TeO2 has been established. It extends to the LiCl‐rich side, ranging from 15 to 60 mol% LiCl, whereas it is limited to only about 30 mol% Li2O on the lithia‐rich side. The reason for such an extended glass‐forming region on addition of LiCl to TeO2 is discussed on the basis of the results of infrared spectroscopic measurements.
Liquid Corrosion and High‐Temperature Oxidation Effects on Silicon Carbide/Titanium Diboride Composites
Authors: Seshadri S.G. , Srinivasan M.
Published: March 2005

A silicon carbide composite containing titanium diboride particulate reinforcement was subjected to room‐temperature acidic corrosion in aqua regia solutions for 200 h, and 50% NaOH+50% H2O and 10% HF+57% HNO3+33% H2O solutions for up to 500 h. A small increase in room‐temperature strength was observed after the aqua regia exposure. Separately, this ceramic was oxidized at 1400°C for 24 h and then tested for strength retention at room temperature. Contrary to the observations reported in the literature on similar material, there was no significant room‐temperature strength decrease in this particular composite.
Synthesis and Defect Structure of Two Types of Cadmium Antimony Oxide Semiconducting Ceramics
Authors: Biao‐Rong Li
Published: March 2005

The synthesizing process and mass transport mechanism of CdO‐Sb2O5 ceramics are discussed. Two compounds with stable structure have been obtained and the crystal structures and microstructures are examined by XRD and SEM. A differential scanning calorimeter is used to determine the phase transformation and latent heat. The defect structure of these semiconducting ceramics are investigated by varying the atmosphere, trivalent ion doping, and Seebeck effect experiments.
Preparation of SiO2 Glass from Model Powder Compacts: III, Enhanced Densification by Sol Infiltration
Authors: SACKS MICHAEL D. , VORA SHAILESH D.
Published: March 2005

Highly ordered powder compacts were formed using spherical, nearly monosized, amorphous SiO2 particles. Some of these compacts were subsequently infiltrated with a “silica’sol. After drying, the powder compact interstices contained small, porous xerogel particles, thereby increasing the green relative density of the compact. Sintering studies showed a significant enhancement in densification for the sol‐infiltrated samples.
Measurement of the Sintering Pressure in Ceramic Films
Authors: CHENG TSUNGNAN , RAJ RISHI
Published: March 2005

An experimental technique is described to estimate the intrinsic sintering pressure in ceramic films. It involves measuring the time‐dependent axial strain of the film during isothermal sintering under a varying tensile load. The applied stress when the axial strain rate goes to zero gives the measurement of the sintering pressure. Such experiments with titania tapes fabricated by tape casting showed the intrinsic sintering pressure to lie in the range of 200 to 130 kPa for densities in the range of 85% to 95% of the theoretical density. The sintering pressure decreased with increasing density. These results are in agreement with measurements of sintering pressure in alumina and titania obtained from sinter‐forging experiments.
High‐Temperature Behavior of Chemically Treated Silicon Nitride Powders
Authors: Hermansson Leif A.G. , Burströ Martin , Johansson Thomas , Hatcher Michael E.
Published: March 2005

The mechanical properties of chemically treated, then sintered, Si3N4 was studied. Raw materials consisted of two types of Si3N4 produced by the nitridation of silicon. The chemical treatment involved leaching in different acids (HCl, HNO3, HF, and combinations thereof). The powders were sintered by hot isostatic pressing with 2.5% yttria, and the high‐temperature properties of the resultant materials were evaluated by the stepped‐temperature stress rupture (STSR) method (24‐h hold time at 150‐MPa stress at 1000°, 1100°, 1200°, 1300°, and 1400°C). A significant decrease in high‐temperature performance was observed for acidleached powders, especially when HF‐containing acids were used.
Effects of Thermal Pretreatment on Coarsening of Nominally Monodispersed Titania
Authors: Edelson Lawrence H. , Glaeser Andreas M.
Published: March 2005

The coarsening of nominally nwnodisperscd, ∼0.35‐μm‐diameter titania powders produced by controlled hydrolysis of titanium tetraethoxide was studied. Thermal treatments prior to coarsening experiments had a minimal effect on the apparent particle size distribution, but significantly modified the coarsening behavior and microstructural characteristics. Explanations attributing these differences to the effects of preannealing on the microstructure (grain size and phase composition) within particles are proposed.
Microstructure of Glass‐Ceramics in the System B‐Na‐Si‐Ta Oxides
Authors: SCHMID H.K.
Published: March 2005

A phase‐separable glass composed of 61 wt% sodium borate and 39 wt% (SiO2+ Ta2O5) was prepared by melting a powder mixture. The phase separation process was activated by heat treatment, and porous skeleton structures were produced by subsequently leaching the glass bodies in boiling water. The microstructure and composition of the glass were analyzed by transmission electron microscopy, energy‐dispersive X‐ray spectroscopy, electron energy‐loss spectroscopy, and X‐ray diffraction. Lattice images and electron diffraction experiments indicate the existence of a one‐dimensionally ordered paracrystalline phase in the phase‐separated glass. Spinodal decomposition is assumed to be the leading mechanism in the phase separation process. Annealing at temperatures T > 1000°C transforms the paracrystalline phase into a glass‐ceramic with tetragonal crystal symmetry; a relationship between this final structure and compositional fluctuations during the phase separation process is suggested.
Preparation and Characterization of Li‐Si‐Al‐O‐N Glasses
Authors: MESSIER DONALD R. , GLEISNER ROBERT P.
Published: March 2005

The glass‐forming region in the AIN‐Li2O–SiO2 ternary was defined, and glass batches up to 15 g were prepared and characterized. Thermogravimetric data on thermal decomposition were interpreted in terms of probable decomposition reactions. Crystalline phases identified in partly crystalline and devitrified glasses include α′‐ and β′‐sialons, eucryptite, and τ‐LiAlO2, all of which may contain some substituted N. Micro‐hardness and elastic modulus of a glass of approximate composition Li2Si2AlO5N are both considerably higher than values for similar oxide glasses.
Effect of Contact Residual Stress on Proof Testing
Authors: RITTER JOHN E. , JAKUS KARL , SHI PING
Published: March 2005

Theoretical predictions are made of strength distributions after proof testing accounting for the possibility of a contact residual stress. Assuming a simple power‐law relationship between subcritical crack velocity and the stress intensity factor, the amount of crack growth, hence strength degradation, that occurs during a proof stress cycle is determined. The results clearly show that the contact residual stress can strongly influence the after‐proof strength distribution so that after‐proof strengths can become weaker than the initial. The results are consistent with experimental observations with soda–lime glass; thus, the importance of accounting for the contact residual stress is emphasized.
Crystal Structure and Defects of Ordered (Pb1‐xCax)TiO3
Authors: KING GRACE , GOO EDWARD , YAMAMOTO TAKASHI , OKAZAKI KIYOSHI
Published: March 2005

Crystal structure and defects of ordered ((Pb1‐xCax)TiO3 ceramics have been investigated by transmission electron microscopy. The structure is determined to be tetragonal, belonging to point group 4mm. Pb and Ca are in an ordered fcc arrangement on the A sites. In addition to the chemical ordering, there is ordering due to atomic shuffling or what has been referred to as electrical ordering. Two distinct sets of planar defects are observed in the same region. One set of planar defects are identified as antiphase boundaries that are the results of chemical ordering and the other set are displacement boundaries that are the results of electrical ordering.
Formation Reaction of ZrO2 Scatterers in ZrF4‐Based Fluoride Fibers
Authors: FUJIURA KAZUO , SAKAGUCHI SHIGEKI , OHISHI YASUTAKE , TERUNUMA YUKIO
Published: March 2005

This paper clarifies the formation reaction of ZrO2 crystals which appear as extrinsic scatterers in fluoride fibers. EPMA analysis indicates that BaO exists at grain boundaries of BaF2 purified by sublimation. BaO reacts with ZrF4 to form ZrO2 at 600°C during a glass‐melting process. The ZrO2 formation reaction is influenced by H2O. Ba(OH)2, which is formed by the reaction between BaO and water vapor, melts at 370° to 420°C and reacts with ZrF4 to form ZrO2 at 450° to 520°C. When low‐oxide‐content BaF2 is used for fiber preparation, scatterers significantly decrease.
Accumulation of Creep Damage in a Siliconized Silicon Carbide
Authors: CARROLL DANIEL F. , TRESSLER RICHARD E.
Published: March 2005

The accumulation of creep damage in a siliconized silicon carbide was investigated as a function of applied stress, creep strain, and microstructure. At 1100°C, creep damage was observed to accompany deformation in specimens tested to creep strains greater than 0.10%, under applied stresses greater than 137 MPa. At low creep strains, creep damage occurred in regions of the microstructure of high silicon carbide content. As deformation progressed, creep damage extended into regions of the microstructure of lower silicon carbide content. The area density and area fraction of cavities were found to increase linearly with creep strain. From these results, a threshold stress for the formation of creep damage was determined to be 132 MPa at 1100°C. It was suggested that the formation of creep damage was controlled by the heterogeneous nucleation of cavities at the silicon‐silicon carbide interface, with the aid of high localized stresses and iron impurities in the silicon phase.
Some Considerations of Nonideal Transformation‐Zone Profile
Authors: HSUEH CHUN‐HWAY , BECHER PAUL F.
Published: March 2005

The nonideal transformation‐zone profile, in which the volume fraction of transformed particles decreases with the increase in the lateral distance from crack surfaces, is considered for the stress‐induced phase transformation in ceramics containing zirconia. It is shown that one source of this nonideal transformation‐zone profile can be the size distribution of the transforming particles/grains. Then, an equation for toughening due to the existence of such a nonideal transformationzone profile is derived. In calculating the toughness, it is shown that the uncertainty in determining the transformationzone size, which can occur by attempts to fit it to an ideal zone profile, can be avoided by using the present approach.
New Cubic Structure in the Ca‐Si‐O‐N System
Authors: Pugar Eloise A. , Kennedy John H. , Morgan Peter E. D. , Porter John R.
Published: March 2005

Subsolidus‐phase studies in the calcium‐silicon‐oxygen‐nitrogen system have been conducted using the reactive precursors calcium nitride, calcium oxide, and silicon nitride. A new structure has been isolated with a large, face‐centered cubic lattice, a=1.4864 nm, which coexists with several new CaSiON phases as well as Ca3Si2O4N2 and the unknown “D’ phase, reported previously by other workers. The new structure is not isotypic with any known mineral oxide. The highest degree of phase purity has been obtained using a 1.1 calcium nitride:silicon nitride starting mixture. Structural and approximate compositional analyses were conducted by X‐ray diffraction and TEM energy dispersive spectroscopy.
Microstructural Evidence for Diffusion‐Driven Tetragonal‐to‐Orthorhombic Phase Transformation in Y‐Ba‐Cu‐O Superconductor
Authors: Park Yong K. , Lee Ho K. , Hwang Nong M. , Kwon Houk C. , Park Jong C. , Yoon Duk N.
Published: March 2005

Microstructures of Y‐Ba‐Cu‐O superconductor were observed using a polarized microscope. Orthorhombic and tetragonal phases were easily distinguished by the optical etching with cross‐polarized light. In the specimen cooled rapidly in oxygen, it was possible to see the path of oxygen diffusion by observing the variation of the twin concentration. At the boundary between transformed and untransformed materials, evidence for diffusion‐driven transformation could be clearly seen.
Identification of Intergranular Cu2O in Polycrystalline YBa2Cu3O7‐x Superconductors
Authors: Sarikaya Mehmet , Thiel B.L.
Published: March 2005

The presence of intergranular Cu2O has been identified in polycrystalline YBa2Cu3O7‐x superconducting samples (Tc∼90 K) which are prepared by dry‐powder processing techniques. Transmission electron microscopy was employed to determine the crystal structure of the phase while energy‐dispersive analysis provided the composition. The intergranular Cu2O, as indicated by XRD and shown by optical microscopy, is concentrated around pores and extends back along grain boundaries adjacent to these pores. Analysis performed on samples sintered in a furnace atmosphere at 950°C, with and without a post‐oxygen anneal at 450°C, gave similar results.
Fracture Toughness Measurement of Glass and Ceramic Materials Using Chevron‐Notched Specimens
Authors: Reddy K. Pattabhi Rami , Fontana Eugene H. , Helfinstine Jchn D.
Published: March 2005

Fracture toughness of several different materials was measured using chevronnotched short bar and four‐point bend specimens For glass‐ceramic and ceramic samples both specimens gave valid results. Fracture toughness values measured with bend specimens are 5% to 10% higher compared to those of the short bar. Consistent results for glass could be obtained only with short bar specimens. The notch width of the bend specimen affected the stability of crack growth in glass samples. Fracture toughness values measured in the present study are in good agreement with those of the previous studies.
Role of Intergranular Damage‐Induced Decrease in Young's Modulus in the Nonlinear Deformation and Fracture of an Alumina at Elevated Temperatures
Authors: VENKATESWARAN ANURADHA , DONALDSON KJMBERLY Y. , HASSELMAN D.P.H.
Published: March 2005

The effect of the time‐dependent decrease in Young's modulus due to damage accumulation by pore growth and intergranular cracking on the stress‐strain behavior of a coarse‐grained polycrystalline alumina deformed under conditions of displacement control at elevated temperatures was investigated. Considerable nonlinearity in stress‐strain behavior, which increased with decreasing strain rate, was noted. At the higher strain rates, the failure stress was found to be independent of strain rate, thought to be due to a strain‐rate‐dependent fracture toughness due to the growth of microcracks at the tip of the failure‐initiating macrocrack, which offsets the expected strain‐rate sensitivity due to the growth of a single macrocrack only. Pore growth and intergranular cracking, accompanied by major reduction in Young's modulus by as much as a factor of 5, was most pronounced at the intermediate values of strain rate. This decrease in Young's modulus, under conditions of displacement‐controlled loading, results in a decrease in stress, referred to as strain softening, which contributed to the observed nonlinear deformation. This conclusion was confirmed by a theoretical analysis, which showed that in addition to diffusional creep, time‐dependent decreases in Young's modulus (elastic creep) by crack growth can make significant contributions to nonlinear deformation.
Contact Damage in Single‐Crystalline Silicon Investigated by Cross‐Sectional Transmission Electron Microscopy
Authors: JOHANSSON STEFAN , SCHWEITZ JAN‐AKE
Published: March 2005

Cross‐sectional transmission electron microscopy (TEM) is demonstrated as a powerful tool for investigating subsurface damage in the micrometer and submicrometer ranges in brittle materials, and applications to a wide variety of contact damage in silicon are discussed and illustrated with TEM images. Regions of plasticity and different types of cracking are identified and characterized for various contact situations: indentation, scribing, solid‐particle impacts, and polishing/grinding. Most single‐point contact situations result in similar types of damage in silicon, although transitions between different damage mechanisms occur between different load levels. Normally, the crack geometry is governed by the principal stress directions and is only weakly influenced by the lattice orientation. Grinding with metal‐bonded abrasives results in fairly deep subsurface damage zones, but the main mode of material removal is superficial lateral cracking. Polishing with small‐size free abrasives results in very superficial damage zones and mirror‐like surface finish.
Phase Relations at Liquidus Temperatures in the System MgO‐NiO‐SiO2
Authors: GRUTZECK MICHAEL W. , MUAN ARNULF
Published: March 2005

The well‐known “quenching technique” has been used to determine liquidus and solidus phase relations in the system MgO‐NiO‐SiO2. Oxide mixtures were heated at selected temperatures for sufficient lengths of time for attainment of equilibrium, followed by quenching to room temperature, and phase identification by optical microscopy (transmitted‐and reflected‐light examination) and X‐ray diffraction. Two ternary liquidus invariant points are present in the system. One is characterized by the coexistence of pyroxene (Mg‐SiO3‐NiSiO3 solid solution), olivine (Mg2SiO4‐Ni2SiO4 solid solution), silica (cristobalite), and liquid at 1547°C. The other eutectic is at 1633°C and is characterized by the coexistence of olivine, oxide (MgO‐NiO solid solution), silica, and liquid. There is a temperature maximum on the olivine‐silica liquidus boundary curve at 1639°C. Reversals in the distribution ratios of magnesium and nickel between solid and liquid phases coexisting in equilibrium during crystallization of melts in this system may occur, depending on the compositions of the mixtures.
In Situ Martensitic Transformation in a Ternary MgO‐Y2O3‐ZrO2 Alloy: II, Transformation in Tetragonal ZrO2 Precipitates
Authors: LEE RAN‐RONG , HEUER ARTHUR H.
Published: March 2005

The stress‐induced martensitic transformation of t‐ZrO2 precipitates in a ternary MgO‐Y2O3‐ZrO2 alloy has been studied in situ in the transmission electron microscope. The transformation occurs autocatalytically and takes place by piecewise growth of two twin‐related m‐ZrO2 variants. Unloading causes retransformation of partially transformed precipitates, but this reverse (m→t) transformation of fully transformed precipitates only occurs on heating. The martensitic transformation in this system is clearly thermoelastic.
Shelyubskii Method of Studying Phase Separation in the System Li2O‐SiO2
Authors: Braetsch Volker , Frischat Guenther H.
Published: March 2005

The experimental performance of the Shelyubskii method has been improved and applied to studying the change in glass homogeneity of the system Li2O‐SiO2 caused by phase separation. Binodal temperatures obtained by this method are in good agreement with literature data obtained by an alternative method. The Shelyubskii method is capable of monitoring changes in glass homogeneity from a change in refractive index of the material with an accuracy of Δn×10−5.
Formation, Transformation, and Decomposition of Y2TeO6
Authors: Yamaguchi Osamu , Uegaki Tatsuji , Shimizu Kiyoshi
Published: March 2005

A metastable modification of Y2TeO6 crystallizes at 770°C to 870°C at a heating rate of 10°C·min−1 in air from an amorphous material prepared by the simultaneous hydrolysis of yttrium and tellurium alkoxides. It has a tetragonal unit cell with a=1.0428 nm and c=1.7524 nm. The tetragonal‐to‐hexagonal phase transformation occurs at 920° to 960°C. Hexagonal Y2TeO6 decomposes into Y6TeO12 and TeO3↑ at 1220° to 1320°C; only Y6TeO12 is obtained as the decomposition product. Both modifications of Y2TeO6 are built up by octahedral TeO6 groups.
Hydrogen Surface Etching of Molten Silica
Authors: Mattox Douglas M. , Smith Harry D.
Published: March 2005

Melting experiments with quartz sand were carried out under H2 atmospheres at temperatures between 1700° and 1850°C. Upon quenching, fine‐scale, hemispherical, pitted morphologies were noted at the surface of the melts. The degree of uniformity of the resulting features was observed to depend on the temperature of melting. The results are compared with similar reported observations at lower temperatures that are attributed to impurity‐based instabilities in the surface tension and evaporation.
Erosion Damage and Strength Degradation of Zirconia‐Toughened Alumina
Authors: BREDER KRISTIN , DE PORTU GOFFREDO , RITTER JOHN E. , FABBRICHE D. DALLE
Published: March 2005

The erosion wear and posterosion strength properties of Al2O3 containing 10 vol% ZrO2 were determined as a function of the kinetic energy of the impacting sharp particles. Samples were prepared with three different surface treatments to obtain different amounts of tetragonal zirconia on the surface. With all three surface treatments a transformation from tetragonal to monoclinic phase due to the impacting particles was observed. The erosive wear was independent of the initial amount of tetragonal phase at the surface and was not statistically different from that found for commercial alumina. The posterosion strength was relatively insensitive to increasing kineticenergy of the eroding particles, indicating a rising fracture resistance behavior for this zirconia‐toughened alumina.
Influence of Stoichiometry on the Electrical and Mechanical Behavior of Yttrium Oxide Ceramics
Authors: Jollet Françlois , Maire Philippe , Gautier Martine , Duraud Jean‐Paul , Gressus Claude Le
Published: March 2005

Because of their method of preparation, ceramics contain point defects, the concentration of which may vary from the center to the boundary of the grains, which may change the bulk properties of the material. The electronic structure of the oxygen‐related defects has been studied by electron spectroscopy in yttria ceramics submitted to various heating conditions under controlled atmospheres. The differences in the mechanical and electrical behaviors are observed to correlate with the defect content.
Influence of Surface Structure on the Fracture Toughness of Tempered Glass
Authors: Chao Chen , Zongzhe Jin , Jingyi Chang
Published: March 2005

A nondestructive measurement of the surface stress and an indentation technique were used to determine the relationship between the fracture toughness and the surface compressive stress of a tempered glass plate. Ignoring the effect of surface compression, one can determine the fracture toughness concerned only with a change in the glass structure. It is found that the fracture toughness is lower for tempered glass than for annealed glass. It is indicated that the decrease is due to structural changes in the surface layer during the heat treatment in tempering; this is confirmed by infrared reflection spectroscopy.
Factors Affecting the Formation of Ba2Ti9O20
Authors: WU JENN‐MING , WANG HONG‐WEN
Published: March 2005

The phase development sequence based on a composition equivalent to Ba2Ti9O20 during heating is found to be in the following order: BaTi5O11 > BaTi4O9 > Ba2Ti9O20. The lowest rate of formation of Ba2Ti9O20 is caused by its high surface energy and interface energy, which result in a low nucleation rate. The existence of BaTi5O11 in calcined powder helps to form Ba2Ti9O20 in sintered compacts. The effect of BaTi5O11 on Ba2Ti9O20 formation can be explained by their similar oxygen packing and by reduced volume change during transformation. The amount of BaTi5O11 formed during heating depends greatly on the compositional homogeneity of powders. The addition of SnO2 aids the formation of Ba2Ti9O20 by reduced strain energy at transformation and reduced surface energy.
Microstructure and Properties of Sprayed Ceramic Coating
Authors: SHI KE‐SHUN , QIAN ZENG‐YING , ZHUANG MING‐SIE
Published: March 2005

The potential benefits of a thermal barrier coating on the heated side of diesel or turbine components are well documented, and this as well as other applications of ceramics in heat engines are being actively pursued. The ceramic coatings used in heat engines must be able to withstand severe thermal stress. The microstructure and properties of several sprayed coatings are described, including flame‐sprayed alumina coatings, plasma‐sprayed alumina coatings, and plasma‐sprayed zirconia coatings. The results show that the modulus (E) of the coatings depends mainly on porosity and phase composition, and nonlinear stress‐strain behavior is caused by the laminar grain structure of the coatings. The fracture strain of a coating is a major factor in the thermal shock resistance of that coating.
Microstructural and Microchemical Characterization of Silicon Carbide and Silicon Carbonitride Ceramic Fibers Produced from Polymer Precursors
Authors: CHAIM RACHMAN , HEUER ARTHUR H. , CHEN R.T.
Published: March 2005

Several continuous SiC and SiC/N‐based ceramic fibers prepared from different polymer precursors have been characterized using X‐ray diffraction (XRD), transmission electron microscopy (TEM), electron energy loss spectroscopy (EELS), and high‐resolution electron microscopy (HREM). Methods to prepare longitudinal as well as cross‐sectional thin specimens from brittle ceramic fibers were developed to facilitate HREM and EELS studies. Lattice images clearly showed nanometer‐sized crystallites, as well as amorphous regions. Microchemical analysis using EELS permitted study of the form and distribution of the various chemical species within the fibers.
Synthesis and 980°C Phase Development of Some Mullite Gels
Authors: CHAKRAVORTY AKSHOY KUMAR , GHOSH DILIP KUMAR
Published: March 2005

Earlier works of mullitization through the gel route have been reviewed and the results show 980°C DTA and crystalline phases. Some Al2O3‐SiO2 gels have been synthesized by using different precursors and by varying pH and water content during the gelification process. Thermal changes of these coherent gels were studied by DTA and X‐ray powder diffractometry. The results demonstrate that two types of aluminosilicate gels form. The first type produces orthorhombic mullite directly on heating at 980°C, whereas the second type forms cubic mullite first at 980°C and then transforms to the orthorhombic variety on further heating. Lastly, the cause of the 980°C exotherm is explained with reference to kaolinite.
Predicting the Grain‐Size Distributions in High‐Density, High‐Purity Alumina Ceramics
Authors: Venkataraman Kollengode S. , DiMilia Robert A.
Published: March 2005

This paper discusses the image‐analyzer‐based grain‐size distributions (GSDs) of fully densified ceramics obtained from pressure casting a high‐purity alumina powder, develops an algorithm for predicting the GSDs as a function of sintering time and temperature, and compares of the GSDs thus predicted with those experimentally observed. The GSD data for all sintered specimens, when nondimensionalized in terms of the median grain size, reduced to a single self‐preserving GSD curve. The median grain was predicted as a function of sintering time and temperature using the classical kinetics equation. The GSDs predicted using the algorithm developed tallied well with those that were experimentally obtained.
Sodium Diffusion in the Nuclear Waste Glass GP 98/12
Authors: Thomas Michael P. , Matzke Hj.
Published: March 2005

The diffusion of22 Na was measured in the nuclear waste borosilicate glass GP 98/12 in the temperature range of 350° to 450°C. The boundary condition of a thin initial tracer layer and serial sectioning were employed to measure the diffusion profiles. The activation enthalpy was found to be 1.08 eV. A parallel experiment with the base glass VG 98/12 not containing added (chemically simulated, inactive) waste showed that Na diffusion does not vary significantly when adding the waste.
Diffusion of Water into Silica Glass at Low Temperature
Authors: Wakabayashi Hajimu , Tomozawa Minoru
Published: March 2005

Diffusion of water into silica glass was measured in the temperature range of 200° to 750° by treating the glass in air containing a constant water vapor pressure and analyzing the concentration profile using a Fourier transform infrared spectrometer. In the short‐time diffusion heat treatments, the surface concentration was lower and the apparent diffusion coefficient was higher than the corresponding steady‐state values. The temperature dependence of the steady‐state diffusion coefficient showed two different activation energies. Above ∼550° the diffusion coefficients were similar to the published results with an activation energy of ∼80 kJ/mol, while below ∼550°, the diffusion coefficient was higher than the value obtained by extrapolation from higher temperatures, and the activation energy was ∼40 kJ/mol. Correspondingly, the water solubility–temperature relation showed a sudden change at around the same temperature: at temperatures above this temperature the solubility increased with decreasing temperature, while at lower temperatures the trend was reversed. It was suggested that this observed peculiarity was caused by the initial nonequilibrium reaction between water and SiO2 glass and a change in enthalpy of the glass–water reaction.
Calculations of Solution Energies of Fission Products in Uranium Dioxide
Authors: Grimes Robin W. , Catlow C. Richard A. , Stoneham A. Marshall
Published: March 2005

Both lattice simulation and quantum‐mechanical techniques are applied to the study of the sites and solution energies of fission products in UO2. We consider noble gas atoms, alkali metal, alkaline‐earth, and halide species. It is shown that the charge state of the dissolved fission product may depend on the fuel stoichiometry. In particular, iodine may be stable as either I+ at U sites or I– at O sites in UO2+x, but should be present only as I– at O sites in UO2–x.
Microstructural Changes in β‐Silicon Nitride Grains upon Crystallizing the Grain‐Boundary Glass
Authors: Lee William E. , Hilmas Gregory E.
Published: March 2005

Crystallizing the grain‐boundary glass of a liquid‐phase‐sintered Si3N4 ceramic for 2 h or less at 1500° led to formation of δ‐Y2Si2O7. After 5 h at 1500°, the δ‐Y2Si2O7 had transformed to β‐Y2Si2O7 with a concurrent dramatic increase in dislocation density within β‐Si3N4 grains. Reasons for the increased dislocation density are discussed. Annealing for 20 h at 1500° reduced dislocation densities to the levels found in as‐sintered material.
Preparation of the High‐Quality Superconductor La1Ba2Cu3Oy
Authors: Wada Takahiro , Suzuki Nobuo , Yamauchi Hisao , Tanaka Shoji , Maeda Atsutaka , Uchinokura Kunimitsu
Published: March 2005

The relationship between the preparation procedure and superconducting properties of La1Ba2Cu3Oy was studied. A series of samples was sintered in an N2‐gas atmosphere for various lengths of time ranging from 1 to 40 h, followed by a fixed annealing procedure in O2. It was found that the shorter the sintering period, the higher was the oxygen content. The samples sintered for a period of less than 15 h contained excess oxygen compared with La1Ba2Cu3O7 and exhibited poor superconducting properties. The sample sintered for 40 h had an oxygen content y equal to 6.95, and had excellent superconducting properties. The mechanism for preparing high‐quality La1Ba2Cu3Oy is discussed.
Anomalous Birefringence in Discretely Phase‐Separated Glasses
Authors: Varshneya Arun K. , Hosmer Kevin
Published: March 2005

Rods of Corning code 7070 alkali borosilicate glass were stretched or compressed at 600° to 700°C before or after discrete phase separation and given a postpulling heat treatment at around 500°C. As expected, sections of the rods displayed anomalous birefringence which has been identified by Takamori to originate from anisotropy in the form and the distribution of the second‐phase particles. Specimens so obtained were reheated, and the birefringence measured as a function of temperature to separate the contributions of form, distribution, and the thermal expansion mismatch (if any) between the separated phases. It is clear that the form birefringence in 7070 glass is positive for stretched rods and negative for compressed rods and decays at lower temperatures than does the distribution birefringence which has an opposite sign. TEM replica micrographs show that the distribution birefringence decays as a function of temperature mostly because of phase dissolution and the reappearance of yet another phase randomly.
Internal Structure of Porous Silica: A Model System for Characterization by Nuclear Magnetic Resonance
Authors: Bhattacharja Sankar , D'Orazio F. , Tarczon J. C. , Halperin W. P. , Gerhardt Rosario
Published: March 2005

Nuclear magnetic resonance (NMR) relaxation methods have been used to investigate the internal structure of porous silica gelled from colloidal silica and potassium silicate mixtures. These materials possess a narrow pore size distribution with average pore diameter ranging from 470 to 2400 Å (47 to 240 nm) as determined from mercury intrusion porosimetry. NMR relaxation measurements were performed on deionized water impregnated into the pore space. These results determine the distribution of local surface‐to‐volume ratios and show that all of the silica samples are very uniform on a length scale greater than 5 μ. NMR relaxation measurements performed on silica samples partially filled with water provide a precise confirmation of the theoretical model upon which the NMR pore structure analysis is based. Measurements of the relaxation strength at the water—silica interface were found to depend systematically on the initial composition of the material. The self‐diffusion coefficient of water, saturated in the pore space, is reduced by 14% from its bulk value.
Microstructure and Optical Properties of Cd1−x ZnxS Films Sintered with Cadmium Chloride
Authors: Seol Yeo Song , Im Ho Bin
Published: March 2005

Polycrystalline Cd1−xZnxS films were prepared by coating (1 ‐ x) CdS + xZnS slurry which contained various amounts of CdCl2 on amorphous glass substrate and sintering in nitrogen to produce films with properties suitable for fabricating all‐polycrystalline Cd1−xZnxS/CdTe heterojunction solar cells. Optical properties of these films have been correlated with composition and microstructure. The sintered film has undulating grain boundaries due to the occurrence of chemically induced grain‐boundary migration. By optimizing the amount of CdCl2 in the slurry and sintering conditions, it is possible to produce sintered Cd1−xZnxS films on glass substrates with high optical transmission and to produce Cd1−xZnxS/CdTe solar cells with efficiency higher than 11%.
Fabrication and Microstructure of Composite Metal‐Clad Ceramic Superconducting Wire
Authors: Oh Min‐Seok , Liu Qin Fang , Misiolek Wojciech , Rodrigues Alex , Avitzur Betzalel , Notis Michael R.
Published: March 2005

Sheathed high‐Tc superconducting ceramic wire composites have been fabricated by wire drawing. Superconducting powders of YBa2Cu3O7‐x (Y‐123) and Bi4(Sr, Ca)6Cu4O16+x (Bi‐464) have both been prepared and successfully fabricated into continuous wire form. Under certain circumstances, a displacement reaction occurs at the interface between the ceramic superconductor and the containment tube; the nature of this displacement reaction and its prevention are discussed. Microcracking of the ceramic core is attributable predominantly to relative shrinkage effects during sintering. Failure of the metal wall during wire fabrication is attributed to drawing conditions and the mechanical properties of core and cladding.
Attenuated Toatal Reflectance Fourier‐Transform Infrared Spectra of a Hydrated Sodium Soilicate Glass
Authors: Uchino Takashi , Sakka Tetsuo , Hotta Koukichi , Iwasaki Matae
Published: March 2005

Attenuated total reflectance Fouriertransform infrared (ATR‐FTIR) spectra were measured in the region from 4300 to 400 cm−1 for a hydrated Na2O–SiO2 glass containing 35 wt% water. The Si–OH bending vibration mode was observed. It was found that the incorporated water, molecular water as well as hydroxyls, affected the Si–O vibrations. The effect of incorporated water upon the glass structure is discussed.
Transitional Phase of Ca2SiO4 Solid Solution with Incommensurate Superstructure
Authors: Fukuda Koichiro , Maki Iwao
Published: March 2005

Crystals of Ca2SiO4 doped with K, P, Al, and Fe were grown and examined by means of both X‐ray and electronbeam diffraction. They are made up of domains 120° different in orientation around the c axis of the previous α phase. Each of the domains gives an orthorhombic superstructure whose cell is incommensurate with the underlying orthorhombic subcell with a=0.540, b=0.936, and c=0.681 nm. This orthorhombic phase, characterized by the cell edge length of 3.8a, is termed 3.8aC2S(ss). Both the domain and the incommensurate structure strongly suggest that this is the precursor to a phase thermodynamically more advantageous at lower temperatures.
Anomalously Low Surface Area and Density in the Silica—Alumina Gel System
Authors: Hietala Susan L. , Smith Douglas M. , Golden Johnny L. , Brinker C. Jeffrey
Published: March 2005

A range of composition/processing conditions that yield xerogel surface areas 2 orders of magnitude lower than expected along with low skeletal densities has been discovered. For xerogel compositions in the vicinity of 50 wt% Al2O3, surface areas are 1 to 5 m2/g and skeletal densities are 2.1 to 2.2 g/cm3, as compared to the expected values of ∼300 m2/g and ∼2.6 g / cm3, respectively. This behavior is observed over a wide range of heat treatment temperatures (373 to 1073 K) and appears to be the result of closed porosity which evolves during gel drying.
Sol—Gel Processing of SiC‐Whisker‐Reinforced Silica‐Based Ceramic Composites
Authors: Lee Burtrand I. , Park Seung‐Yong
Published: March 2005

SiC whiskers were added to reinforce a gel‐derived SiO2–Al2O3–Cr2O3 matrix. Alumina and chromia were added to induce reaction sintering of the composites. A maximum of ∼90% of theoretical density was achieved after firing in argon for 2 h at 1400°C. The optimum amounts of alumina, chromia, and SiC were 26.5, 1.6, and 4.1 vol%, respectively. It was shown that the chromium acetate hydroxide, used as a precursor for chromia, acted as a gelling agent and as a sintering additive. The effect of producing gaseous products such as SiO, CO and/or CrO3 became significant above 1400°C where mullite formation also occurred. However, the measured mechanical properties were remarkable, considering the experimental conditions applied.
Influence of Fracture Toughness on the Wear Resistance of Yttria‐Doped Zirconium Oxide
Authors: Fischer Travgott E. , Anderson Michael P. , Jahanmir Said
Published: March 2005

Yttria‐doped zirconium oxide was prepared in the fully tetragonal, mixed tetragonal and cubic, and the fully cubic phases by varying the yttria conent. The fracture toughnesses of the materials were 11.6, 8.7, and 2.5 Mpa · m½, respectively. The wear resistance, measured in air at room temperature in slow sliding (1 mm/s speed and 9.8 N load), increases by a factor of 1200 from the brittle to the toughest material; it is proportional to the fourth power of toughness. Wear occurs predominantly by fracture in the brittle (cubic) material; plastic deformation is observed in the tougher zirconium oxide.
Calculation of Phase Diagrams for the YO1.5—BaO—CuOx System
Authors: Lee Byeong‐Joo , Lee Dong Nyung
Published: March 2005

The thermodynamic data for the YO1.5–BaO, BaO‐CuOx, and YO1.5–CuOx quasi‐binary systems were optimized from experimental phase diagrams. They were used to calculate tentative phase diagrams for the YO1.5–BaO—CuOx quasi‐ternary system. The equilibrim liquidus surface and the isothermal sections of the ternary system at 900°, 925°, 950°, 975°, and 1000°C were calculated. The isopleths containing YBa2Cu3O7‐δ were also calculated.
Formation of Microcrystalline α‐Alumina by Glycothermal Treatment of Gibbsite
Authors: Inoue Masashi , Tanino Hirokazu , Kondo Yasuhiko , Inui Tomoyuki
Published: March 2005

Microcrystalline α‐aluminas (hexagonal plates, ∼0.1 μm wide and ∼0.025 μm thick) were prepared by treating fineparticle gibbsite in glycol at 300°C under the spontaneous vapor pressure of glycol (glycothermal treatment). The α‐alumina was formed by the collapse of the glycol derivative of boehmite.
Thermoelastic Micromechanical Stresses Associated with a Large α‐Silicon Carbide Grain in a Polycrystalline β‐Silicon Carbide Matrix
Authors: Li Zhuang , Bradt Richard C.
Published: March 2005

The thermoelastic micromechanical stresses associated with a single large hexagonal α‐SiC grain within a fine‐grain‐size cubic (3C) β‐SiC matrix were calculated. The naturally occurring residual stresses which are created during cooling from the processing temperatures and the effects of superimposed applied external stresses are both considered. A significant effect of the shape or geometry of the α‐SiC grain is revealed, with the largest residual stresses associated with the naturally occurring tabular or platelet structure. The stresses are compared with the published strength results for these materials, which suggests that the residual stresses assume a significant role in the strength reduction that is observed.
Effects of CaO on the Strength and Toughness of AIN
Authors: Witek Stefan R. , Miller Gary A. , Harmer Martin P.
Published: March 2005

Fully dense, undoped AIN is found to have the following average mechanical properties: hardness, 12.2 GPa; strength, 377 MPa; and fracture toughness (based on the fracture load sustained by indented disks), 3.6 MPa·m½. The addition of 2 wt% CaO to AIN changes the fracture mode from transgranular to intergranular while concurrently decreasing the hardness, strenght, and toughness. Increasing the grain size of CaO‐doped AlN decreases strength and increases toughness. Toughness estimates based on the fracture load sustained by indented disks are about twice the value determined for crack extension after indentation.
Structural Control of Phase Formation in Low‐Tem perature AIPO4—Sio2 Reactions
Authors: Takahashi Tatsuhito , Agrawal D. K. , Roy R.
Published: March 2005

The phase relation along the binary join of AIPO4‐SiO2 were investigated up to 400°C using starting materials made by a solution route. Precursor structures used were boehmite (AIOOH), H3PO4, noncrystalline silica, and quartz. The silica precursors acted as structural seeds for the epitaxial growth of AIPO4. Studies showed that SiO2 and AIPO4 were the only crystalline and noncrystalline phases present along the binary join, and no substantial crystalline solution or any ternary phase was observed. Three polymorphic forms of AIPO4, i.e., berlinite, tridymite, and cristobalite, coexisted as low as 200°C. The nature of the silica precursor greatly influenced the development of the polymorphic phases of AIPO4. The low‐quartz precursor suppressed the formation of the cristobalite form of AIPO4 and favored berlinite (AIPO4 quartz) production. On the other hand, noncrystallin silica with a cristobalite‐like broad XRD peak suppressed the formation of berlinite and enhaned that of the cristobalite form of AIPO4. These precursor effects indicate that heteroepitaxy is very significant during the nucleation and growth of AIPO4 phases on the surface of SiO2 particles even in these low‐temperature reactions.
Tensile Strength Degradation of Ceramics from Prior Compression
Authors: Sines George , Taira Tomoyuki
Published: March 2005

Both theory and studies on models predict that cracks extend stably form flaws in brittle materials subjected to compression. Once cracks have originated and extended, the tensile strength transverse to the cracks should be reduced. Tests on siliconized carbide verify this prediction; however, tests on hot‐pressed silicon nitride refute it. Possible morphologies of the inherent flaws are speculated.
Anisometric Shape Factors for Ceramic Microstructures
Authors: Kibbel Bardley W. , Heuer Arthur H.
Published: March 2005

The weighted average of grain aspect ratios, as given by ellipses of equal moments of inertia, is proposed as a measure of the anisometry of a microstructure. Examples of anisometric α‐SiC microstructures are used to test this parameter.
Effect of Interface Mechanical Properties on Pullout in a SiC‐Fiber‐Reinforced Lithium Aluminum Silicate Glass‐Ceramic
Authors: Thouiess Michael D. , Sbaizero Orfeo , Sigl Lorenz S. , Evans Anthony G.
Published: March 2005

The pullout of fibers in the crack wake makes an important contribution to the toughness of ceramic‐matrix composites. The pullout is, in turn, influenced by the properties of the fibers and by the sliding resistance of the interface. Basic relationships governing the pullout are developed analytically and investigated experimentally using a lithium aluminum silicate/silicon carbide (LAS/SIC) composite subjected to various heat treatments. The experiments involve determining the strengths of single fibers and then measuring the pullout distributions. The results are used to provide a consistent view of the pullout process and related changes in mechanical properties.
Crystallization of Titanosilicate Glasses for Nuclear Waste Immobilization
Authors: Hayward Peter J. , Vance Eric R. , Cann C. Dennis , Doern Diane C.
Published: March 2005

The effects of different cooling and reheating rates on the phase constitutions of Na2O–Al2O3–TiO2–SiO2 glass‐ceramics containing up to 20 wt% of simulated nuclear fuel recycle waste have been studied using X‐ray diffraction, differential thermal analysis, and scanning and transmission electron microscopy. The metastable formation of a perovskite‐structured phase (nominally CaTiO3, but containing ionic substituents) was observed in samples with up to 15 wt% of simulated waste after cooling from the melt at rates between 0.25 and 50°C/min. When the partially devitrified glass was reheated to 1050°C, incomplete conversion of this phase to sphene (nominally CaTiSiO5) occurred by reaction with the silica‐rich glass matrix. The conversion was completed by heating further to 1150°C. Waste loadings ⋝10 wt% produced crystallization of powellite (nominally CaMoO4) in addition to sphene and perovskite, whereas metastable perrierite (a rare‐earth titanosilicate) was also crystallized at waste loadings ⋝15 wt%. New data on elemental partitioning between the crystalline and vitreous phases confirmed earlier results obtained in different atmospheres and with simplified waste compositions and were largely in accord with crystal‐chemical predictions.
Effects of Zirconia on Microstructure and Dielectric Properties of Barium Titanate Ceramics
Authors: Armstrong Timothy R. , Morgens Laurie E. , Maurice Alena K. , Buchanan Relva C.
Published: March 2005

Dielectric properties and structural characteristics of BaTiO3 ceramics are significantly influenced by small addition (2 wt%) of ZrO2. SEM and TEM observations revealed enhanced microstructural uniformity and retarded grain growth depending on sintering temperature. Above 1320°C, Zr diffusion into the BaTiO3 lattice resulted in a chemical modification of the tetragonal structure and the development of core–shell grains. Below 1320°C, TEM analysis showed ZrO2 at the grain boundaries as discrete particles (∼0.03μm). X‐ray diffraction analysis revealed a decrease in the axial (c/a) ratio with decreasing grain size. A corresponding decrease in the spontaneous polarization, and twinned domain structures, were also observed in the fine‐grained ceramics. These samples also showed a flattened permittivity response with temperature and significantly lower losses.