bluuebunny/crossref_metadata_2025 huggingface dataset:
Cation Distribution and Defect Chemistry of Iron‐Aluminate Spinels
Authors: MASON T. O. , BOWEN H. K.
Published: June 2006

A model describing cation distribution and defect concentrations in iron‐aluminate spinels is presented. Cation distribution equilibrium constants are derived from phase‐boundary data at 1500° and 1280°C. Estimations of the defect concentrations for the entire solid solution are possible using defect equilibrium constants for Fe3O4.
Sintering of Acicular Fe2O3 Powder
Authors: Yamaguchi Takashi , Kosha Hideaki
Published: June 2006

The sintering of acicular Fe2O3 powder has been studied in comparison with an ordinary equiaxed powder. The acicular powder gave a dense material more than 99 % theoretical even from the relatively low green density. Oriented granular structures were observed in the 1200°C compacts. The observed densification behavior has been attributed to the pore configuration in the green compact.
Dielectric Loss of Microstructurally Anisotropic Borosilicate Glass
Authors: TAKATA MASASUKE , TOMOZAWA MINORU , TAKAMORI TAKESHI
Published: June 2006

Dhdelectric characteristics were determined for a microstructurally anisotropic borosilicate glass prepared by uniaxiallhd stretching phase‐separated glass rods. The specimen showed a dielectric loss peak caused by the inhomogeneous microstructure; its magnitude varied with the orientation of the specimen with respect to the electric field direction. The results are in agreement with Sillars’ theory.
Analysis of Effect of Crack Interaction on Nature of Strength Loss in Thermally Shocked Brittle Ceramics
Authors: Singh J. P. , Shih C. , Hasselman D. P. H.
Published: June 2006

A fracture mechanics analysis is presented to study the effect of collinear crack interaction on the crack stability and propagation behavior in a brittle material subjected to thermal stress failure. It is shown that collinear crack interaction may result in crack coalescence and complete failure.
Effects of Preparation History on TiO2· SiO2 Glasses
Authors: Bihuniak P. P. , Condrate R. A.
Published: June 2006

Differences in the Raman spectra of various heat‐treated TiO2· SiO2 glasses could be related to their thermal and chemical histories. For instance, while rutile could be detected in batch‐prepared glasses heated at 1100°C, only α‐cristobalite could be detected in heat‐treated devitrified flame‐prepared glasses with comparative TiO2‐concentrations. Thermal expansion coefficients increased for batch‐prepared glasses upon heat treatment due to exsolution of rutile from the glasses. Earlier work had noted similar behavior at lower temperatures due to exsolution of anatase.
Anomalous Grain Growth in PLZT Ceramics
Authors: Jyomura Shigeru , Matsuyama Iwao , Toda Gyozo
Published: June 2006

The isothermal grain growth of PLZT ceramics with various La concentrations from 0 to 10 at. % is studied. For all La concentrations, the sintering time (t) dependence of grain size (D) is expressed in the normal grain growth formula, Dn= Kt. The constants n and K greatly depend on the La contents. These facts indicate that there are several grain growth mechanisms related to the La concentrations in PLZT ceramics.
Correlation of Experimental Erosion Data with Elastic‐Plastic Impact Models
Authors: Gulden Mary Ellen
Published: June 2006

Five target materials of varying mechanical properties were eroded with natural quartz sand and SiC particles. The targets were four commercially available Si3N4 materials and MgF2. Several particle size ranges between 10 and 1000 μm, accelerated to several velocities between 61 and 275 m/s, were used for erosion testing. The erosion results are presented in terms of two models which have been developed for elastic‐plastic impact damage.
Measurement of Low‐Temperature Thermoelectric Power for Quenched Wustite
Authors: HODGE J. D. , BOWEN H. K.
Published: June 2006

Thermoelectric power was measured at low temperatures (90 to 370 K) on wustite single crystals that had been quenched from a high‐temperature equilibrium state into liquid nitrogen. Above 120 K, these measured results are consistent with the model proposed elsewhere by the authors to explain the high‐temperature thermoelectric effects observed in wustite if a significant aggregation of defects occurs during the quench. Below 120 K, the measured thermoelectric power drops sharply and changes sign from positive to negative. Similar behavior has been observed in magnetite. These results are explained in terms of the ordering of Fe2plus; and Fe3plus; cations near aggregated defect clusters. This ordering creates narrow 3d6 and 3d5 bands in which both electrons and electron holes are mobile.
Estimation of Fracture Toughness by Intrinsic Flaw Fractography for Sintered Alpha Silicon Carbide
Authors: Seshadri S. G. , Srinivasan M.
Published: June 2006

An attempt to apply three‐dimensional flaw models to characterize fracture origins in sintered alpha silicon carbide is made. Some general improvements in the intrinsic flaw fractography results are obtained by using three‐dimensional void models instead of two‐dimensional crack models.
A Proposed Definition for the Thermal Efficiency of Glass‐Melting Furnaces
Authors: COOPER A. R.
Published: June 2006

An unambiguous definition is proposed for the thermal efficiency of a fuel‐fired, ohmically heated, or combination furnace melting a glass of any com‐ position.
Liquid‐Liquid Immiscibility in BaO‐B2O3
Authors: Clemens K. , Yoshiyagawa M. , Tomozawa M.
Published: June 2006

A simple method to determine the liquid‐in‐liquid immiscibility boundary is applied to a BaO‐B2O3 glass. The method is based on the scanning electron microscope observation of the heat‐treated and quenched specimens and differentiation of the microstructure.
Phase Relations in the Systems A2O‐Metal Oxide‐WO3 (A=Li, Na; Metal=Fe, Cr, Sn, Zr, Th, V)
Authors: SPINNLER GERARD E. , CHANG LUKE L. Y.
Published: June 2006

Phase relations, with special emphasis on the formation of wolframite‐type phases, were determined in 12 ternary systems, each containing an alkali oxide (Li2O, Na2O), a polyvalent oxide (Fe2O3, Cr2O3, SnO2, ThO2, ZrO2, V2O5), and WO3. Among 12 ternary phases characterized, 5 have the wolframite‐type structure. They are LiFe(WO4)2, LiCr(WO4)2, NaFe(WO4)2, NaCr(WO4)2, and Li2Zr(WO4)3. Complete series of solid solutions exist along Li(Fe,Cr) (WO4)2 and Na(Fe,Cr)(WO4)2 joins but not along other wolframite joins. Both LiFe(WO4)2 and LiCr(WO4)2 were also found to form complete solid solution series with MgWO4, a compound used hi this study to represent the simple wolframite‐type phase.
Anisotropy Effects in the Thermal Diffusivity of Si3N4‐BN Composites
Authors: Niihara K. , Bentsen L. D. , Hasselman D. P. H. , Mazdiyasni K. S.
Published: June 2006

The thermal diffusivity of silicon nitride‐boron nitride composites is shown to exhibit considerable anisotropy with respect to the hot‐pressing direction due to the preferred orientation of the boron nitride inclusions.
Effect of Organic Acids on E‐Glass Fabric
Authors: Ramachandran B. E. , Balasubramanian N. , Rao G. V. Subba , Aravamudan G.
Published: June 2006

E‐glass fabric was treated with organic acids. Acid treatment leaches nonsiliceous ions from the glass structure via ion exchange. The degree of removal is determined by the strength of the acid and leaching time. The results, which are compared with those for mineral acids, show that the acid anion is involved in the leaching process.
The Thermodynamic Properties of Silicon Oxynitride
Authors: Fegley M. Bruce
Published: June 2006

A critical assessment of thermal and equilibrium data for silicon oxynitride (Si2N2O) is presented. Selected values for the heat of formation of Si2N2O from the elements and the absolute entropy of Si2N2O at 298.15 K are ΔH0f,298=−947.7 ± 5.4 kJ/mol and S0298= 45.35 ± 0.4 J/mol·K, respectively. A table of thermodynamic functions for Si2N2Ofrom 298 to 2500 K, which has been calculated from the analysis of the literature data, is also presented.
Aluminum Penetration and Fracture of Titanium Diboride
Authors: Dorward R. C.
Published: June 2006

Relatively porous titanium diboride (=96% dense) is penetrated with aluminum metal when used as a cathode in aluminum reduction cells operating at 970°C. Metal penetration changes the predominant fracture mode from trans‐granular to inter granular, and has potentially important ramifications on mechanical properties.
EPR and Kinetic Studies of Hydrogen Centers in Aluminoborate Glasses
Authors: PONTUSCHKA W. M. , ISOTANI S. , PICCINI A. , VUGMAN N. V.
Published: June 2006

Barium aluminoborate glasses containing hydrogen as an impurity, irradiated at 77 K with X rays, show the characteristic doublet of atomic hydrogen in the EPR spectra when measured at T<200 K. The hfs constant of the Hoi center is smaller than that of free atomic hydrogen, indicating that the attractive van der Waals interaction is more important than the repulsive Pauli exclusion forces in that glassy matrix. It is suggested on the basis of isochronal and isothermal annealing experiments that there are at least three different sites for hydrogen, each one contributing with Ist‐order decay kinetics. The activation energies found in 30 mol% BaO, 60 B2O3, 10 Al2O3 glass are, respectively, equal to E1=(0.5±0.1), E2=(0.24±0.03), and E3=(0.16±0.03)×lO−19 J.
A Ce‐Nb‐(Al) Oxide Porous Glass‐Ceramic
Authors: RES M. A. , FOURIE J. T. , WHITE R. W. , BEDNARIK J.
Published: June 2006

Substitution of the end‐member oxides in the ternary sodium borosilicate system diagram was studied. Replacing SiO2 in this ternary system with a combination of CeO2 and Nb2O5 was found to produce glasses which, after heat treatment, decomposed into two immiscible microphases of which one is water‐soluble. The mode of phase decomposition is sensitive to impurities. The importance of crucible selection, e.g. Al2O3 or Pt/Rh, is demonstrated by differences in pore size, surface area, heat resistance, and structure of the insoluble phase for a series of Ce2O3‐Nb2O5 and Ce2O3−Nb2O5−Al2O3 glass‐ceramics. These new materials have a specific surface area of up to 217 m2/g and a pore radius of between 1.1 and 54.5 nm.
Zircon‐Zirconia Ceramics Prepared from Plasma Dissociated Zircon
Authors: Mcpherson R. , Shafer B. V. , Wong Ai Ming
Published: June 2006

A ceramic consisting of a dispersion of ZrO2 particles (∼25%) in zircon was prepared by sintering partially leached plasma dissociated zircon. ZrO2 particles smaller than ∼150 nm were tetragonal inform; larger particles were monoclinic. The large increase in proportions of tetragonal ZrO2 after sintering may be ascribed partly to a reduction in particle size by reaction to form zircon, and partly to a matrix effect on the tetragonal to monoclinic transformation.
Crack Origins and Microcracking in Delayed Fracture of Alumina
Authors: Okada Tatsuo , Sines George , Green David
Published: June 2006

A fluorescent dye penetrant technique is used to study the onset of slow crack growth in a dense alumina. Interaction and coalescence of nearby flaws, after a very small amount of crack extension from individual flaws, appears to be the dominant mode of failure.
Preparation of Fine Monoclinic Hafnia Powders by Hydrothermal Oxidation
Authors: Toraya Hideo , Yoshimura Masahiro , Somiya Shigeyuki
Published: June 2006

Fine single‐phase monoclinic HfO2 powders were prepared from Hf metal chips and high‐temperature high‐pressure water by hydrothermal oxidation in closed and open systems. In the closed system, Hf metal was converted to HfO2 by treatment at ≥600°C under 100 MPa for 3 h. At 500°C half the Hf reacted to produce Hf hydride and a small amount of HfO2. In the open system, Hf metal scarcely reacted at 500°C, but at 600°C the reaction was more rapid than the corresponding run in the closed system.
Swelling of Microporous High‐Silica Glasses
Authors: Takamori Takeshi , Tomozawa Minoru
Published: June 2006

The swelling of microporous glasses in water was found to change as a function of the heat–treatment time and temperature required for phase separation in the original borosilicate glass (70SiO2‐23B2O3‐7Na2O (wt%)). The swelling appears to be determined primarily by the quantity of silica gel remaining in the micropores, which in turn is determined by the composition of the alkali‐borate‐rich phase of the phase‐separated glass.
Effect of Proof‐Testing Soda‐Lime Glass in Heptane
Authors: Ritter J. E. , Jakus K. , Young G. M. , Service T. H.
Published: June 2006

Soda‐lime glass was proof‐tested in heptane using three unloading rates. Observed after‐proof strength distributions shifted toward weaker strengths as the rate of unloading decreased. The theoretical implications of the results are discussed.
Effet of Billet Difference on the High–Temperature Strength of Hot–Pressed Silicon Nitride
Authors: Jakus K. , Ritter J. E. , Fahey J. P.
Published: June 2006

The strength and fatigue resistance of silicon nitride was determined from specimens machined from two hot–pressed billets. The results indicate that although fatigue resistance is not affected up to 1100°C, differences in chemical composition between the two billets result in different high–temperature strengths. Billet acceptance criteria include both high–temperature strength and oxidation resistance specifications.
Slow Growth of Microcracks: Evidence for One Type of ZrO2 Toughening
Authors: Claussen Nils , Cox Raymond L. , Wallace Jay S.
Published: June 2006

Alumina containing 15 vol% monoclinic ZrO2 dispersed at the grain boundaries exhibited very high room‐temperature fracture toughness (∼11 MPa·m1/2) on cooling from 1275°C when microcrack precursors nucleated at T<Ms. With increasing time (up to ∼12 h) at room temperature, KIc and Young's modulus decreased when dilational and thermal‐expansion strains subcritically propagated inter granular microcracks. Thus, transformation toughening of ceramics with inter crystalline ZrO2 dispersions is to a great extent caused by microcrack nucleation and extension.
Structural Rearrangement During the Sintering of MgO
Authors: VARELA J. A. , WHITTEMORE O. J.
Published: June 2006

MgO compacts were sintered from 900° to 1395°C in dry argon and in argon with 2.3 kPa of water vapor. The surface area and pore size distributions measured by mercury porosimetry showed large changes during the first minute of sintering, indicating that rearrangement instead of coalescence of small particles is the controlling process in the early stage. Rearrangement was found to be temperature‐dependent and to extend through the initial stage of sintering.
Application of the J Concept to Alumina at High Temperatures
Authors: KROMP K. , PABST R. F.
Published: June 2006

Conventional KIC measurements exhibit a dependence of KIC values on loading rate for material containing a second phase. An especially strong dependence had been observed at 900°C at which a maximum in KIC also occurred. In an attempt to determine if this effect is caused by the measurement method and/or reflects a true material property associated with the second phase, an energy concept like the J integral was applied. J‐calculation methods for a single load‐displacement curve and for J‐resistance curves (JR analyses) were applied to this alumina and the results compared to those for a pure alumina. The JR analysis, in the form of the single specimen compliance method with partial and total unloading and the multiple specimen method, points out both the influence of the second phase and the problems of describing material constants for specific ceramic materials at high temperatures.
Effect of Doping Simultaneously with Iron and Titanium on the Diffusional Creep of Polycrystalline A12O3
Authors: IKUMA YASURO , GORDON RONALD S.
Published: June 2006

The effect of doping simultaneously with iron and titanium was studied in dense, polycrystalline alumina over a range of grain sizes (10 to 100 μm) and temperatures (1250° to 1550°C). In the double‐doped system, the titanium concentration was varied between 0.05 and 0.15 cation %, whereas the iron‐dopant level was varied between 0.05 and 6 cation %. For iron concentrations below about 2 to 3%, the aluminum vacancy concentration was dominated by the presence of quadrivalent titanium in substitutional solid solution and Nabarro‐Herring diffusional creep at 1450°C was rate‐limited by aluminum lattice diffusion. As the iron‐dopant level was increased, the concentration of divalent iron became comparable to that of quadrivalent titanium, leading to a suppression in the cation lattice diffusivity at an iron‐to‐titanium ratio of ∼60. These results suggested that, at the dopant levels and temperatures studied, more than 98% of the iron was in the trivalent state. The diffusional creep of polycrystalline alumina doped with a single iron impurity (0.2 to 2%) was reinterpreted in terms of simultaneous contributions of aluminum lattice and grain‐boundary diffusion, consistent with a grain‐size dependence corresponding to a mixture of Nabarro‐Herring and Coble creep. Aluminum grain‐boundary diffusion was found to be significantly enhanced by the presence of iron in solid solution. Evidence is presented to suggest that the diffusional creep of polycrystalline Al2O3 doped with a single titanium dopant is interface‐controlled. Interfacial kinetics can be promoted by several factors, including (1) a small grain size, (2) a high cation lattice diffusivity, (3) slow cation grain‐boundary diffusion, and (4) the presence of a grain‐boundary second phase.
Microstructure and Deterioration in Steatite Ceramics
Authors: Nandi Prasanta , Prasad Vemuri C. S.
Published: June 2006

Pitting in steatite ceramics was found to occur as a result of (1) deterioration with time, the familiar aging phenomenon, and (2) secondary recrystallization, which takes place immediately after fabrication. Differences in microstructural and other features observed in the two cases are pointed out.
Efficiency Improvement in Thermophoretic Deposition
Authors: Weinberg Michael C.
Published: June 2006

Methods of improving the thermophoretic particle collection efficiency in optical‐fiber‐preform preparation are considered. One‐hundred percent collection efficiency may be effected by maintaining the temperature gradient in the gas or by suitably tailoring the initial particle concentration. The deposition efficiency is calculated for a simple nonuniform inlet concentration to illustrate the latter case.
Diffusion‐Controlled Redox Kinetics in a Glassmelt
Authors: GOLDMAN DON S. , GUPTA PRABHAT K.
Published: June 2006

A diffusion model was developed to analyze the rate at which Fe2+/Fe3+ equilibration occurs in a Ca‐Al‐borosilicate melt in an air atmosphere at 1260°C. The resulting diffusion coefficient of oxygen determined from the model of 3.7 × 10−7 cm2/s is in agreement with the range of values reported for other glass‐melts at this temperature and with the value determined from the viscosity of the melt using the Eyring model. The results support the general interpretation of the multivalent ion oxidation equilibrium as a diffusion‐controlled process. The model thus provides a means to determine the diffusivity of oxygen in glassmelts from the kinetics of the oxidation reaction for a variety of redox ions.
Transmission Electron Microscopy of Annealed ZrO2+8 Mol% Sc2O3
Authors: MOGHADAM FARHAD K. , YAMASHITA TOM , SINCLAIR ROBERT , STEVENSON DAVID A.
Published: June 2006

The influence of heat treatment (800°C for 200 h) on the micro‐structure of 8 mol% Sc2O3‐ZrO2 was investigated by XRD and TEM. The starting material was initially characterized and found to contain predominantly cubic‐fluorite phase grains, with <5% of the grain containing the rhombohedral β phase. The β phase was positively identified by the analysis of electron diffraction pattern and by quantitative energy dispersive X‐ray analysis. On aging, the relative amount of β phase was found to increase to about 15 to 20% by XRD measurement; this was confirmed by TEM observation. The orientation relation between the different variants of the β phase within a grain was determined to be (100)r||(010)r, and the geometrical arrangement of these variants within the grain was deduced using a 21/2D imaging electron microscopy technique.
Flaws Responsible for Slow Cracking in the Delayed Fracture of Alumina
Authors: SINES GEORGE , OKADA TATSUO
Published: June 2006

The early stages of crack extension from inherent flaws were observed directly in order to identify flaws responsible for crack initiation. The specimen surface was immersed in fluorescent dye penetrant while cracks were forming; this procedure allowed the dye to penetrate into the fine cracks. Once the cracking sites were located, scanning electron microscopy was used to identify the flaws. An eccentrically loaded column testing system was used to produce a number of crack initiations on a surface of a specimen without causing catastrophic failure of the specimen. There were many inherent flaws which, either by themselves or as an assembly, became potential crack origins. The initial stage of delayed fracture was shown to involve the interaction and coalescence of nearby flaws with intergranular cracking. It was also found that the crack origins were multiple in delayed fracture.
Effect of Cavities on Creep
Authors: Haselman D. P. H. , Venkateswaran Anuradha
Published: June 2006

The formation of cavities during creep increases the creep rate as a result of the combined effects of the decrease in elastic modulus, which results in elastic creep, and the enhanced rate of the basic creep process caused by stress transfer. Analyses of these effects are presented for the special case of cavities in the form of cracks. The net rate of creep can be described by a total of four terms. Permanent crack‐opening displacement resulting from creep deformation of material adjacent to the cracks results in a permanent pore phase following unloading.
Shear Moduli of Composites with Elliptical Inclusions
Authors: Stiffler Richard C. , Haselman D. P. H.
Published: June 2006

Equations for the shear modulus of a two‐dimensional model with preferentially oriented microcracks were derived from a tentative equation for the shear modulus of a corresponding model with elliptical inclusions obtained from solutions of stress concentration factors. Exact agreement found with literature solutions based on energy und dislocation methods suggests that the elastic behavior of ceramic matrix composites and microcracked ceramics can be predicted from the same equation.
Effect of High‐Temperature Exposure in Air on Strength of Hot‐Pressed Silicon Nitride
Authors: Ritter John E. , Jakus Karl , Strazdis Lucius A. , Rogers Wayne P.
Published: June 2006

Short‐term exposure of hot‐pressed Sl3N4 to high temperature (800°C) eradi cates the truncated strength distribution produced by room‐temperature proof‐testing, indicating that strengths after high‐temperature exposure are determined by jaws different from preexisting flaws. Since acid polishing of proof‐tested samples cycled to high temperature restored the truncated after‐proof strength distribution, it is believed that short‐term high‐temperature exposure causes amor phous SiO2 to form on the surface, thus blunting the surface flaws.
Relations Between Normal Boiling Point and Melting Point for Simple Halides and Oxides
Authors: VAN UITERT L. G.
Published: June 2006

For most halides the normal boiling point (Tb in kelvin units) is given by the relation: Tb= 440nc(ip·ea·d2)−1, where nc is the coordination number of the cation, ip the first ionization potential of the metal (in electron volts), ea the electron affinity of the anion former (in electron volts), and d the bond length in the crystal (in nanometers). Similar relations are found for oxides. For both classes the following relation applies: Tb/Tf= 1 + 0.67 /Va, where TI is the melting point of the crystal and Va is the valence of the anion. Exceptions occur when inert (s2) electron pairs form the outer shield of the cation or anion core, when electron spin pairing occurs between halogen or oxygen atoms, when there are direct interactions between metal atoms, or when nc is not the same in the molten and crystalline states. Further, it is shown that covalency related to the asymmetric polarization of anions by cations with partially filled valence shells can markedly increase cohesion in the melt. This relates to plasticity in the solid as well.
Spinodal Decomposition in Ionic Compounds
Authors: VIRKAR ANIL V. , PLICHTA MARK R.
Published: June 2006

Spinodal decomposition in ionic solid solutions of the form AX‐BX where A and B are cations and X is the anion is examined along similar lines as proposed by Cahn. Assuming anions to be immobile, electrostatic energy arising due to the differences in cationic mobilities is determined. This electrostatic energy is shown to retard the kinetics of spinodal decomposition. The role of aliovalent dopants on the kinetics of decomposition is also examined. Subsequently, the probable role of aluminum on spinodal decomposition in the system TiO2‐SnO2 is assessed.
Microstructure of Sintered Mullite‐Zirconia Composites
Authors: Prochazaka Svante , Wallace Jay S. , Claussen Nils
Published: June 2006

Fused mullite, pure and with 10 to 25 vol% ZrO2 added, was milled in an attritor and sintered in air at temperatures near 1600°C to a dense fine‐grained ceramic. The ZrO2 promoted densification and retarded grain growth of the mullite phase. Transmission electron microscopy showed that compositions containing ZrO2 were substantially free of glass, whereas pure mullite bodies contained a glassy phase. The ZrO2 formed inter granular, isolated particles.
Characterization of Insoluble Layers Formed by NaOH Attack on the Surface of a ZrO2‐Containing Silicate Glass
Authors: Makishima Akio , Tsutsumi Masayuki , Shimohira Takajiro , Nagata Tatsuya
Published: June 2006

The durability of an alkali‐resistant glass containing ZrO2 in NaOH solution was studied by scanning electron microscopy. Insoluble Zrrich reaction‐product layers ∼1 to 3 μm thick were observed on the surface of glass which had been soaked for 25 d in 2N NaOH at 95°C. In some cases the layer seems to be an adherent film, but in others it adheres loosely to the glass surface and does not seem to effectively block alkali attack.
Characterization of Creep Cavitation in Sintered Alumina by Small‐Angle Neutron Scattering
Authors: Page Richard A. , Lankford James
Published: June 2006

Small‐angle neutron scattering experiments were performed on compression‐crept alumina. The results suggest that grain‐boundary cavities, on the order of 100 nm in diameter, probably are present initially. For compression strains up to 8%, the average cavity size changes very little. However, the cavity density approximately triples, and it appears that the cavities become elongated in the direction of the compression axis.
Effect of Decomposition on the Densification and Properties of Nasicon Ceramic Electrolytes
Authors: McENTIRE B. J. , BARTLETT R. A. , MILLER G. R. , GORDON R. S.
Published: June 2006

Nasicon ceramic electrolytes were processed and characterized using a number of different techniques. The materials were sintered at T = 1100°C to 1375°C. Results of this work demonstrate that Nasicon ceramics with compositions around x =2 (i.e. Na3Zr2Si2POt2), are not monophase, possess poor mechanical strength and an anomalous thermal expansion behavior, and are subject to chemical and phase instability during densification at high temperatures. Wet‐chemical techniques, X‐ray diffraction, and SEM analyses were used to observe the phase and chemical decomposition of these materials. The products of this decomposition process are correlated with the poor physical properties.
A Technique for Introducing Surface Compression into Zirconia Ceramics
Authors: Green David J.
Published: June 2006

A technique is presented whereby compressive surface stresses are introduced into transformation‐toughened ZrO2 ceramics by removing the stabilizing oxides, such as Y2O3, from the surface. The advantages of this approach over other techniques are discussed, and experimental data confirming the presence of compressive surface stresses and subsequent improved resistance to indentation cracking are described.
Static Fatigue Limit for Sintered Silicon Carbide at Elevated Temperatures
Authors: MINFORD E.J. , KUPP D.M. , TRESSLER R.E.
Published: June 2006

The modified static loading technique for estimating static fatigue limits was used to study the effects of oxidation and temperature on the static fatigue limit, K10 for crack growth in sintered silicon carbide. For as‐machined, unoxidized sintered silicon carbide with a static load time of 4 h, K10× 2.25 MPa * m1/2 at 1200° and ∼1.75 at 1400°C. On oxidation for 10 h at 1200°C, K10 drops to ∼1.75 MPam1/2 at 1200° and ∼1.25 at 1400°C when tested in a nonoxidizing ambient. Similar results were obtained at 1200°C for tests performed in air. A tendency for strengthening below the static fatigue limit appears to result from plastic relaxation of stress in the crack‐tip region by viscous deformation involving an oxide grain‐boundary phase for oxidized material and, possibly, diffusive creep deformation in the case of unoxidized material.
Assessment of the Thermodynamic Values for PuO1.5 and High‐Temperature Determination of the Values for PuC1.5
Authors: BESMANN THEODORE M. , LINDEMER TERRENCE B.
Published: June 2006

Thermodynamic values for PUO1.5 were assessed using an improved method for estimating fef° <PuO1.5 and new data for S°298 <PuO1.5. Based on the assessment, a value of ΔH°298, <PuO1.5=–828 kJ/mol is recommended. Measurements of (CO) pressure over the nominal equilibrium <PuO1.5+ <PuO1.5+ C were performed between 1348 and 1923 K, yielding pressures between 0.644 and 11600 Pa. Second‐ and third‐law analyses were used to obtain a value for ΔH°298 <PuO1.5=–93.3°3.3 kJ/mol.
Removal of Oxide Contamination from TiB2 Powders
Authors: Brynestad Jorulf , Bamberger Carlos E. , Land J. Fred , Finch Cabell B.
Published: June 2006

Surface oxide contamination, which commonly occurs in fine TiB2 powders and afects their properties, can be removed by treatment with BCl3(g) at 650°C.
Surface Morphologies of Magnesium Vanadium Oxide, Mg2‐xV1+xO4
Authors: OSHIMA HIROTOSHI
Published: June 2006

The microscopic appearance of the particle surfaces of magnesium vanadium oxide, Mg2‐xV1+xO4, loose powders prepared in various atmospheres at 1200°C was studied. The surface morphology, observed by SEM, was dependent on the V4+ content, and three typical features were distinguished at the following x values:

0.75≤x<1.00; rounded crystals with smooth surfaces

0.55≤x≤0.75; edged crystals with stepped surfaces

x≤0.55; coarse crystals with rough surfaces
Precipitation of Mg2Zr5O12 in MgO‐Partially‐Stabilized ZrO2
Authors: Farmer Serene C. , Schoenlein Larry H. , Heuer A. H.
Published: June 2006

Decomposition of cubic, MgO‐stabilized ZrO2 solid solutions has been studied. Precipitates of the ordered compound, Mg2Zr5O12, form, but only when a two‐stage heat treatment involving nucleation at a low temperature followed by growth at a higher temperature is used. Other decomposition products are also present after such a heat treatment.
Spinodal Decomposition in a K2O‐Al2O3‐CaO‐SiO2 Glass
Authors: Chiang Yet‐Ming , Kingery W. David
Published: June 2006

Diffuse interfaces are observed in the interconnected structure of a phase‐separated K2O‐Al2O3‐CaO‐SiO2 glass. With continued electron irradiation in the scanning transmission electron microscope, the interfaces are observed to sharpen with little attendant change in phase morphology, indicating that the as‐cooled microstructure is formed through spinodal decomposition.
Characteristics of Si3N4‐SiO2‐Ce2O3 Compositions Sintered in High‐pressure Nitrogen
Authors: SANDERS WILLIAM A. , HERBELL THOMAS P.
Published: June 2006

Full‐density Si3N4‐SiO2‐Ce2O3 compositions were prepared by sintering with 2.5 MPa nitrogen pressure at temperatures of 1900° and 2090°C. Room‐temperature flexural strengths near 700 MPa for sintered material compared favorably with the strength of hot‐pressed material. At 1370°C, where flexural strengths as high as 363 MPa were obtained, it was observed that the coarsest structure was the strongest and the finest structure was the weakest. One of the compositions tested, Si3N4‐8.7 wt% SiO2‐8.3 wt%‐Ce2O3, was found to have excellent 200‐h oxidation resistance at 700°, 1000°, and 1370°C, without incidence of 700° to 1000°C phase instability and cracking.
Behavior of Glass Fibers in Strong Acidic and Alkaline Media
Authors: WOJNAROVITS ILONA
Published: June 2006

The properties of basaltic, glass wool, quartz, and E‐glass fibers were investigated under strong acid (HF:H2O=l:3, HF:H2O=1:1, 10% H2SO4+3% HF:H2O=1:1) and alkaline (1N NaOH + 1N Na2CO3) treatment. The multiple‐oxide fibers were found to be composed of several layers which exhibit different morphology and composition. These findings are in accordance with some proposals in the literature.
Densification in Irradiated UO2 Fuel
Authors: Hastings Ian J. , Fehrenbach Paul J. , Hosbons Robert R.
Published: June 2006

A densifcation algorithm for irradiated UO2 fuel, modified to reflect a rapid densification rate from 0 to 10 MW.h/kg U, is presented. Included in a fuel performance code, the algorithm gives improved agreement between measured and calculated sheath strains.
The Al2O3‐Nd2O3 Phase Diagram
Authors: COUTURES J. P.
Published: June 2006

A tentative phase diagram for the system Al203‐Nd2O3 is presented. Three compounds were obtained: a β‐A12O3‐type compound, the perovskite NdAlO3, and Nd4Al2O9. The perovskite melts congruently (mp 2090°C), and the two other compounds exhibit incongruent melting behavior: β‐Nd/Al2O3, mp 1900°C; Nd4Al2O9, mp 1905°C. Two eutectics exist with the following compositions and melting points: 80 mol% Al2O3, 1750°C; 23 mol% Al2O3,1800°C. Nd4Al2O9 decomposes in the solid state at 1780°C.
Critical Review of the Thermophysical Properties of Fast‐Reactor Fuel
Authors: FINK J. K.
Published: June 2006

This paper identifies the fuel properties for which more data are needed for fast‐reactor safety analysis. In addition, a brief review is given of current research on the vapor pressure over liquid UO2 and (U, Pu)O2‐x the solid‐solid phase transition in actinide oxides, and the thermal conductivity of molten urania.
Characterization of LiNbO3 by Dilatometry and DTA
Authors: GALLAGHER P. K. , O'BRYAN H. M.
Published: June 2006

DTA can successfully measure Tc and hence the lithium oxide content for samples over most of the single‐phase range of LiNbO3. Above 7sim;1190°C, however, the enthalpy associated with the decomposition and melting of the near stoichiometric material masks the weak thermal change associated with Tc. Fortunately, dilatometry can be also used to detect Tc. The values of Tc determined by these thermoanalytical techniques are 1130° and 1198°C for the congruent and stoichiometric compositions, respectively. Careful dilatometric measurement of the thermal expansion in the temperature range from 350 to 1300 K indicates that, while the a axis expands continuously, the c axis passes through a maximum at 640°C for the congruent material and 700°C for the stoichiometric material. Thermal expansion for the stoichiometric compared to the congruent composition is slightly greater along the c axis and somewhat smaller along the a axis. These expansions compensate to make the volume expansion of the two materials virtually identical.
Defects and Charge Transport in β‐Ta2O5: I, Analysis of the Conductivity Observed in Nominally Pure β‐Ta2O5
Authors: McHale A.E. , Filler H.L.
Published: June 2006

Simple ionic defect theory has not been successful in describing the observed defect and transport behavior in β‐Ta2O5. The available data were reviewed, and a revised model is proposed which more adequately describes the defect behavior of nominally pure or lightly doped β‐Ta2O5.
Synthesis of the Orthorhombic Phase of ZrO2
Authors: Suyama Ryuji , Ashida Toshifumi , Kume Shoichi
Published: June 2006

Single‐phase orthorhombic ZrO2 was prepared by quenching from high temperature and high pressure. The lattice parameters are a0=0.5042, b0=0.5092, and c0=0.5257 nm; the calculated density is 6.09 Mg·m−3. This phase is metastable under atmospheric pressure and reverts to the monoclinic phase either on heating above 300°C or when it is ground in a mortar.
Evaluation of α‐SiC Sintering Using Statistical Methods
Authors: HURST JANET B. , MILLARD MICHAEL L.
Published: June 2006

The effect of time and temperature on the density and strength of α‐Sic was studied and mathematically modeled using a central composite experimental design. A sintering temperature of 2150°C for 1.7 h maximized the flexural strength and densification values. However, temperatures above 2200°C promoted abnormal grain growth, with resulting appreciable decreases in strength. Flexural strength increased exponentially with increasing density for specimens with densities <92% of theoretical.
Hot Corrosion of Sintered α‐Sic at 1000°C
Authors: JACOBSON NATHAN S. , SMIALEK JAMES L.
Published: June 2006

The hot corrosion of sintered α‐Sic by thin films of Na2SO4 and Na2CO3 was studied at 1000°C in controlled gas atmospheres. Under all conditions corrosion led to 10 to 20 times the amount of SiO2 formed in pure oxidation after a 48‐h exposure. In addition, small amounts of sodium silicate formed. Melts of Na2SO4/SO3 caused uniform pitting of the Sic substrate; Na2CO3/CO2 melts caused localized pitting and grain‐boundary attack. In all cases the protective SiO2 layer dissolved to form silicate, leading to corrosion. In the sulfate case, free carbon in the Sic promotes this process. In all cases the presence of liquid films is responsible for rapid transport rates and the subsequent rapid reaction.
Strength Recovery in Degraded Yttria‐Doped Tetragonal Zirconia Polycrystals
Authors: MATSUMOTO ROGER L. K.
Published: June 2006

The low‐temperature tetragonal‐monoclinic phase transformation in yttria‐doped tetragonal zirconia polycrystalline ceramics which results in strength degradation was found to be reversible. The retransformed ceramic has properties equivalent to those of the as‐sintered ceramic.
Densification and Properties of α‐Silicon Carbide
Authors: Dutta Sunil
Published: June 2006

Densification of a‐Sic powders with no premixed sintering aids (type 1) and with premixed B and C (type 2) was investigated by sintering them at 2150° to 2200°C for 30 min. Flexure strengths, Weibull moduli, and fracture flaws were characterized for type 2 α‐SiC only. The results were compared with those for a state‐of‐the‐art sintered a‐Sic material.
Role of Acid Concentration in Leaching of Cordierite and Alkali Borosilicate Glass
Authors: ELMER THOMAS H.
Published: June 2006

The leaching rates of both cordierite and heat‐treated alkali borosilicate glass were studied in hot nitric acid solutions ranging from ∼0.1 to ∼16N. Weight loss and penetration measurements of the specimens showed that the reaction rates go through a maximum with acid concentration. The data indicate that the rate of leaching, which involves ion‐exchange and hydration reactions, is controlled not only by acid strength, but also by water activity.
Suppression of Insulator Charging During Secondary‐Ion Mass Spectroscopy and Scanning Electron Microscopy
Authors: Giraldez Emilio , Dolhert Leonard , David Kingery W. , Petuskey William T.
Published: June 2006

Work with a hot stage capable of temperatures of up to 1200°C has shown that charging of insulating materials in a scanning electron microscope can be completely eliminated by heating the sample to several hundred degrees centigrade. A similar scheme was devised to eliminate charging in a secondary‐ion mass spectrometer in order to study oxygen‐18 concentration profiles in MgO. Before and during analysis the sample surface was exposed to a high‐energy electron beam. The mechanism responsible for the elimination of spurious charging is related to surface heating by the electron beam.
Classification of Ferrospinel Structures and Textures
Authors: Bozadgiev Ljudmil , Dimova Todoka , Mitev Todor
Published: June 2006

The nomenclature and classification of ferrospinel structures and textures are presented. Conditions for their formation are described. In this respect, the classification suggested may be used both as a basis for closer investigation and as a means of obtaining ferrites with the desired structure.
7Li Nuclear Magnetic Resonance in (7Li,6Li) and (Li, Na) Triborate Glasses
Authors: Jain Himanshu , Balzer‐Jöllenbeck Gert , Kanert Otmar
Published: June 2006

Spin‐lattice relaxation times for 7Li were measured as a function of temperature in two mixed‐isotope (7Li,6Li) triborate glasses and one mixed‐alkali (Li, Na) triborate glass. The rapid increase in relaxation rate above 400 K is believed to result from localized alkali motion. A mixed‐alkali effect was observed for such a motion, but it is shown not to be a mass effect.
Spalling of Flat Plates by Thermal Shock
Authors: Thouless Michael D.
Published: June 2006

A model is presented for the thermal shock damage in plates subjected to a sudden rise in temperature. Spalling is assumed to follow localized buckling caused by the thermally induced compressive stresses above subsurface flaws. The minimum size o flaw required to cause spalling is determined as a function of the material properties of the plate, the temperature rise, the position of the paw, and the time after the thermal shock.
Surface‐Tension‐Driven Flow in a Glass Melt
Authors: McNEIL THOMAS J. , COLE ROBERT , SUBRAMANIAN R. SHANKAR
Published: June 2006

Motion driven by surface tension gradients was observed in a vertical capillary liquid bridge geometry in a sodium borate melt. The surface tension gradients were introduced by maintaining a temperature gradient on the free melt surface. The flow velocities at the free surface of the melt, which were measured using a tracer technique, were found to be proportional to the applied temperature difference and inversely proportional to the melt viscosity. The experimentally observed velocities were in reasonable accord with predictions from a theoretical model of the system.
Particle Size Distributions in Calcined Powders
Authors: Chou Kan‐Sen , Tien Gee‐Yang , Wu Wen‐Long
Published: June 2006

The changes in particle size distributions in bayerite and magnesium hydroxide on calcination are reported. In general, size distributions in calcined powders very closely resemble those obtained before calcination. Theoretical changes in particle volume, and hence in volume equivalent diameter, can be calculated from weight‐loss data and corresponding densities. Possible reasons for deviation from the theoretical size reduction ratio are also discussed.
Free Volume of Metaphosphate Glasses at the Transition Temperature
Authors: Suzuki Suguru , Takahashi Minoru
Published: June 2006

The free volume fraction (vf) defined by Simha and Boyer was measured for metaphosphate and mixed metaphosphate glasses (MO · P2O5; M=Ca, Sr, Ba, Mg, Zn). The glasses were classified into groups (1) in which M =Ca, Sr, Ba (Vf≠0.1) and (2) in which M =Mg, Zn (vf∼ 0.l). The Vf values of mixed glasses containing cations from both groups varied. Thus, these glasses are not in an iso‐free‐volume state at the glass transition temperature.
Effect of Silicon Activity on Liquid‐Phase Sintering of Nitrogen Ceramics
Authors: BAIK Sunggi , Raj Rishi
Published: June 2006

Volatilization resulting from the thermal decomposition of Si3N4 causes the large weight loss and desintering phenomenon observed during pressureless sintering of Si3N4‐5% MgO and sialon (z =2)‐5% MgO. The addition of a few weight percent of Si to the powder suppresses this volatilazation and helps to achieve fully dense Si3N4 components.
Interpretation of Analyses of Silicate Glasses and Minerals Obtained by Secondary‐Ion Mass Spectrometry
Authors: Lacharme Jean‐Pierre , Lehuede Patrice
Published: June 2006

A commercial floa olass was analyzed by secondary‐ion muss spectrometry. The depth profiles show important variations in the 40Ca+, 24Mg+, und 28Si+ ion intensities at the beginning of analyses, even on fresh fracture surfaces. Field‐induced migration of the ions or preferential sputtering cannot account for the observed variations in the secondary‐ion currents.
Ruby Glass Produced in a Pt‐Au Crucible
Authors: Liang Zhi Hong , Cooper Alfred R.
Published: June 2006

The observation that a ruby color is produced in soda‐lime glass doped with SnO2, melted in a PtSAu crucible, and reheated is described and briefly discussed.
Flux Growth of Calcium Molybdate Single Crystals
Authors: Arora Satish K. , Batra Naresh M. , Rao G. S. Trivikrama
Published: June 2006

Single‐crystal CaMoO4 was grown from unstirred, supersaturated solutions of molten LiCl by slowly cooling the fluxed melt from 750°C to the eutectic temperature at 5°C.h−1. Translucent bipyramidal crystals with lateral dimensions of 5.5 mm by 4.0 mm were recovered and characterized by EDAX, XRD, and optical microscopy.
Effect of Densification Conditions on the Stabilization of the Tetragonal Phase in ZrO2 Polycrystals
Authors: Pujari Vimal K. , Jawed Inam
Published: June 2006

The stability of the tetragonal phase in tetragonal zirconia polycrystals consolidated at 830 MPa for 2 to 5 s at 1400°C was studied. Consolidation under such conditions stabilizes the tetragonal phase because of the resulting grain size. Subsequent heat treatment of the samples for relatively long periods, however, tends to promote the tetragonal→monoclinic transformation.
Liquid‐Liquid Phase Separation in Heavy‐Metal Fluoride Glass
Authors: Suscavage Michael J. , El‐Bayoumi Osama H.
Published: June 2006

The microstructure of heavy‐metal fluoride glass of composition 28.SCdF2·5.0LiF·28.5AlF3·38PbF2 was investigated using scanning electron microscopy and energy‐dispersive X‐ray techniques. Liquid‐liquid phase separation was observed in crucible‐cooled glass samples. The volume fraction of the dispersed glass phase increased substantially as a result of heating the sample at 309°C for 1 h.
Damage Analysis of Creep in Bending
Authors: ROSENFIELD A. R. , DUCKWORTH W. H. , SHETTY D. K.
Published: June 2006

A model of creep behavior is described in which the ratio of creep rate in tension to that in compression depends on stress. It is suggested that the difference in rates is due to preferential microstructural damage formation in tension. Among the consequences of the model are creep‐rate/tress exponents in both tension and bending that increase with increasing stress, in accord with evidence reported in the literature.
Influence of Cyclic Tangential Loads on Indentation Fracture
Authors: LU MEI‐CHIEN , EVANS A. G.
Published: June 2006

An indentation method was used to analyze the damage induced by the cyclic tangential loading of contacting elastic bodies. The degree of damage was ascertained from direct observations and from failure strength measurements. Cyclic crack propagation was demonstrated to occur and is attributed to the development of irreversible deformation at the contact.
Oxidation Behavior of Oxynitride Glasses
Authors: Wusirika R. R.
Published: June 2006

Oxynitride glasses begin to oxidize in air when they are heated above 800°C. The oxidation starts with bubble formation on the surface. Continued oxidation leads to a white oxide layer on the surface. Magnesia‐ and lithia‐containing glasses formed crystalline layers, whereas soda‐ and baria‐containing glasses formed bubbly glass layers. The lithia‐, beryllia‐, and magnesia‐containing glasses have good oxidation resistance