bluuebunny/crossref_metadata_2025 huggingface dataset:
Uniaxial Tensile and Flexural Stress Rupture Strength of Hot‐Pressed Si3N4
Authors: GOVILA R. K.
Published: June 2006

Uniaxial tensile stress rupture testing of hot‐pressed silicon nitride NC‐132 was carried out at 1000°, 1200°, and 1300°C in air at various applied stress levels and the corresponding times‐to‐failure were measured. Fracture occurred from both surface and internally initiated flaws. Fractographic evidence for failure‐initiation sites and the associated presence of subcritical (slow) crack growth are presented. Limited flexural stress rupture tests at 1200°C in air were also carried out and the data are compared. The uniaxial tensile and flexural stress rupture tests are much more sensitive in revealing the time‐dependent crack‐growth behavior than flexural stress rate tests.
Structural Analysis of Metadickite
Authors: OKADA KIYOSHI , OSSAKA JOYO
Published: June 2006

The structure of metadickite, which was a dehydration phase of a dickite from Shokozan mine, Hiroshima, Japan calcined at 600°C for 24 h, was investigated by X‐ray radial distribution function (RDF) analysis and the correlation method. The RDF curve showed the coordination numbers of both Si and Al atoms to be four and the structural regularity was observed up to ∼0.8 nm. Several structural models for metadickite were examined by the correlation method and the most likely model is considered to be the arrangement built up of SiO4 tet‐rahedral sheets, similar to the original dickite, and an adjacent edge‐shared AlO4 tetrahedral chain, with a 6‐4‐4 type oxygen atom distribution.
Microhardness of NaCl Bicrystals
Authors: HARRIS L. B. , HOWES V. R. , CUTMORE N. G.
Published: June 2006

Microhardness measured on cleaved surfaces of nominally pure and lightly calcium‐doped NaCl bicrystals showed a modest increase at the grain boundary that could be attributed to segregation of calcium and a larger increase in both bulk and boundary produced by rapid cooling. Variations observed due to the influence of moisture, to nonuniform quenching rate, and to precipitation at the boundary suggest that the quench hardening is due to residual impurity other than calcium.
Migration of Large Gas‐Filled Pores in Potassium Chloride Due to a Temperature Gradient
Authors: LEMAIRE P. J. , BOWEN H. K.
Published: June 2006

The migration of gas‐filled pores in KCl subjected to a temperature gradient occurs by a vaporization‐condensation mechanism. In many cases the vaporization step, rather than gas‐phase diffusion, can limit the rate of migration. Movement of large (>100 μm), argon‐filled pores in pure and Ba‐doped KCl was observed using hot‐stage microscopy. Velocities of large pores in pure KCl were limited by the diffusion rates of KCl monomers and dimers in argon. This observation is consistent with a model in which the vaporization rate is moderately reduced due to widely spaced surface ledges, but is still rapid with respect to gas‐phase diffusion. The velocities of large pores in 10 and 40 ppm Ba‐doped samples were significantly lower than those in pure samples. A model was developed which explains these decreased migration rates in terms of impurity poisoning of surface kink sites. The model couples detailed expressions for vaporization kinetics with those for gas‐phase diffusion rates.
Residual Stresses in Hot‐Pressed Si3N4 Grooved by Single‐Point Grinding
Authors: KIRCHNER H. P. , ISAACSON E. D.
Published: June 2006

Hot‐pressed silicon nitride plates were grooved by single diamond points with varying degrees of flatness mounted on a wheel rotating at varying speeds. The plates were divided into bars and the remaining strengths were measured. The depths of damage were measured and used to calculate the theoretical strengths. For sharp diamonds and in some cases for diamonds with flat tips, the measured strengths were less than the theoretical strengths. The differences between the measured strengths and the theoretical strengths are attributed to the presence of residual loads acting to wedge open the cracks.
Interdiffusion and Phase‐Boundary Reaction Between Silicate Glass Surface and Aqueous CsCl Solution
Authors: Franek H. J. , Wegener W. , Frischat G. H.
Published: June 2006

Technical silicate glass samples with fresh fracture surfaces or HF‐etched surfaces were treated in aqueous CsCl at 90°C for 10 to 85 min. Reaction profiles were determined quantitatively using a SIMS technique. The Cs2O concentration at the glass surface increased with increasing time, followed by penetration of Cs+ ions into the glass. The profiles can be described assuming a model which contains both a surface phase‐boundary process and an interdiffusion process in the glass for which D=5.10−17 cm2 s−1.
Comparative Study of Vibrational Characteristics of Fluorozirconate and Fluorohafnate Glasses
Authors: Bendow B. , Banerjee P. K. , Drexhage M. G. , Goltman J. , Mitra S. S. , Moynihan C. T.
Published: June 2006

The vibrutional characteristics of fluorozirconate and fluorohafnate glasses have been determined from ir reflectivity and Raman scattering. Fluorohafnate‐based glasses possess lower ir oscillator strengths than fluorozirconate glasses, and their fundamental absorption peaks are shifted to a lower frequency. The dominant Raman peaks, however, are nearly identical for both glasses.
Interfacial Energies in the Si/SiC System and the Si+C Reaction
Authors: Minnear W. P.
Published: June 2006

The high ratio of the SiC grain‐boundary energy to the Si(l)/SiC interfacial energy is used to explain two microstructural observations: (1) the penetration of dense SiC by Si(l), and (2) the morphology of the SiC formed when glassy carbon is reacted with Si(l). Comments are made concerning the mechanism of the Si+C reaction and the effect of sintering aids on the SiC grain‐boundary energy.
Relative Energies of 〈011〉 Tilt Boundaries inNiO
Authors: Dhalenne G. , Déchamps M. , Revcolevschi A.
Published: June 2006

The variation of the relative energy of symmetrical 〈011〉 tilt boundaries in nickel oxide was studied as a function of misorientation by measuring the angle of the groove formed following thermal etching of bicrystals. Cusps on the energy curve were observed for high‐coincidence angles.
Effect of Glass‐Frit Size Distribution on the Microstructure of RuO2‐Based Thick‐Film Resistors
Authors: Biggers J. V. , McKelvy J.R. , Schulze W. A.
Published: June 2006

Ru02‐based resistor inks were formulated with four glass‐frit particle size distributions. Microstructural features, namely the RuO2 ring size distribution, were shown to be related to the frit size distribution in the fired resistors.
Grain‐Size Dependence of Fracture Energy in Ceramics
Authors: Claussen Nils , Mussler Bernhard , Swain Michael V.
Published: June 2006

A simple model incorporating thermal elastic anisotropy stresses is used to calculate the microcrack zone size around cracks in Al2O3. It is found that the ratio of microcrack zone size to grain size is almost constant for notched beam tests, but increases with grain size for double cantilever beam data. It is suggested that notched‐beam ratios of fracture toughness are related to crack initiation, whereas double cantilever beam values are related to propagation and reflect R‐curve behavior of the material.
Thermodynamic Activities in the Cubic Phase Ti‐O‐N by High‐Temperature Mass Spectrometry
Authors: GRANIER B. , CHATILLON C. , ALLIBERT M.
Published: June 2006

The ternary phase diagram of Ti‐O‐N exhibits a wide region of cubic solid solutions between TiO and TiN. The thermodynamic activities of titanium and titanium monoxide were measured in such solutions with a multiple Knudsen cell mass spectrometer at high temperature (1800 K). This technique allows experimental conditions to be specified, e.g. fragmentation processes and equilibrium conditions for the vaporization. The solid solutions of TiO‐TiN exhibit a slight positive deviation from ideality.
Glass‐Forming Systems Involving GeO2 with Bi2O3, Ti2O, and PbO
Authors: NASSAU K. , CHADWICK D. L.
Published: June 2006

The previously studied system GeO2‐Bi2O3‐TI2O was extended with the addition of PbO using air‐ and water‐quenched melted samples. Large areas of glass formation were found in the systems GeO2–Bi2O3–PbO and GeO2–PbO–Tl2O at all but the lowest GeO2 contents. Glasses were examined by powder X‐ray diffraction, differential thermal analysis, thermomechanical analysis, and Archimedes’technique to obtain glass transition and crystallization exotherm temperatures, thermal expansion coefficients, and densities, which are presented in diagrams for the GeO2‐PbO binary and for the two ternary systems. Based on calculated values of λ0, the wavelength for zero material dispersion, compositions in this system may be useful for construction of ultralow‐loss optical waveguides in the μm region.
Dilatational Relaxation in Cylindrical Seals
Authors: SCHERER GEORGE W.
Published: June 2006

This paper presents a viscoelastic thermal stress analysis which illustrates the importance of dilatational stress relaxation in cylindrical seals. When the core is elastic and the cladding is glass, dilatational stress relaxation has no significant influence on the stresses in the seal. However, when the core is glass and the cladding is elastic, this relaxation has a profound effect. For the latter seal, the setting temperature is weakly dependent on seal dimensions. In fact, stress development during cooling can be accurately predicted from the “fluid core” analysis by Scherer and Cooper, using the fictive temperature of the glass as the setting temperature.
Comparisons of Static and Impact Loading Damage in Zinc Sulfide
Authors: KIRCHNER H. P. , LARCHUK T. J.
Published: June 2006

Contact damage was induced in CVD zinc sulfide by static and impact loading using glass spheres. Calculations based on the relation between the residual depth of the indentation and the ratio of the hardness to Young's modulus were used to estimate the dynamic hardness and impact load. Comparisons of applied loads, threshold loads for crack formation, and crack lengths for static and impact indentations at equal indentation radii show that predictions of impact damage using data from static loading are inadequate.
Self‐Diffusion of Er and Hf in Polycrystalline Er2O3‐Stabilized HfO2
Authors: TESCH R. J. , WIRKUS C.D. , BERARD M.F.
Published: June 2006

Tracer self‐diffusion coefficients for Er and Hf were measured in polycrystalline Er2O3‐stabilized HfO2 (fluorite phase) at compositions between 10 and 40 mol% Er2O3 and temperatures between 1700° and 2033°C. In some instances, grain‐boundary coefficients were also determined. The Hf volume coefficients were generally slightly smaller than Er coefficients, but neither showed a strong composition dependence, a finding most likely attributable to extensive clustering of charged defects which apparently rendered a large proportion of the “notional” defects essentially immobile. The activation energies for volume coefficients were very large, ranging from 630 to 760 kJ‐mol−1, and generally decreased with increasing Er2O3 content.
Formation of Cubic Boron Nitride from Rhombohedral Boron Nitride by Explosive Shock Compression
Authors: Sato Tadao , Ishii Toshihiko , Setaka Nobuo
Published: June 2006

When rhombohedral BN, which has a layer structure with a three‐layered stacking sequence, was shock‐compressed at 40, 60, and 100 GPa, it was converted to cubic BN. Hexagonal BN was converted to wurtzite‐type BN under the same conditions. These results indicate that the transformation proceeds by a diffusionless mechanism in which the stacking sequence of the BN layers in the starting materials is retained during the process.
Effects of Specimen Size on Strength of Sintered Silicon Nitride
Authors: And Yusuke Katayama , Hattori Yoshinori
Published: June 2006

The strength of sintered silicon nitride was measured by three‐point bending, four‐point bending, and expanded‐ring tests at room temperature. The data obtained were analyzed using Weibull statistics. The results indicate that effective volume is the major factor determining strength.
Phase Equilibria in the Pseudoternary System ZrO2−Y2O3−Cr2O3 at 1600°C in Air
Authors: Yoshimura Masahiro , Jayaratna Manikpurage , Sōmiya Shigeyuki
Published: June 2006

The pseudoternary system ZrO2‐Y2O3‐Cr2O3 was studied at 1600°C in air by the quenching method. Only one intermediate compound, YCrO3, was observed on the Y2O3−Cr2O3 join. ZrO2 and Y2O3 formed solid solutions with solubility limits of 47 and 38 mol%, respectively. The apex of the compatibility triangle for the cubic ZrO2, Cr2O3, and YCrO3 three‐phase region was located at =17 mol% Y2O3 (83 mol% ZrO2). Below 17 mol% Y2O3, ZrO2 solid solution coexisted with Cr2O3. Cr2O3 appears to be slightly soluble in ZrO2(ss).
Preparation and Properties of Heavy‐Metal Fluoride Glasses Containing Ytterbium or Lutetium
Authors: Drexhage M. G. , El‐Bayoumi O. H. , Moynihan C.T. , Bruce A. J. , Chung K.‐H. , Gavin D. L. , Loretz T. J.
Published: June 2006

Beginning with a 19BaF2−27ZnF2−27YbF3−27ThF4 (mol%) base glass, compositional modifications were made to improve optical properties and glass‐forming ability. Replacement of YbF3 by LuF3 removed a strong near‐ir electronic absorption band, and small additions of LiF and NaF improved glass quality. The multicomponent BaF2/ThF4 glasses had higher refractive indices and lower expansion coefficients than fluorozirconate and fluorohafnate glasses. In the 6 to 10 μm region, these materials exhibit absorption coefficients an order of magnitude lower than those reported for other heavy‐metal fluoride glasses.
A omparative Study of the Fatigue Properties of Synro and Borosilicate Glass
Authors: Cook R.F. , Lawn B.R. , Dabbs T. P. , Reeve K. D. , Ramm E. J. , Woolfrey J. L.
Published: June 2006

Comparative measurements have been made of the dynamic fatigue response of synroc and borosilicate glass specimens in water, using an indentation flaw technique. The results are presented in terms of a universal plotting scheme which allows for simple appraisal of the “lifetime” capabilities of the materials. Synroc is intrinsically stronger than borosilicate glass, but the fatigue susceptibilities are similar.
Fracture Features at Internal Fracture Origins in a Commercial Crystallized Glass
Authors: Lewis David , Spann Joseph R.
Published: June 2006

Failures in samples of a commercial crystallized glass subjected to intense pulsed electron‐beam irradiation resulted information of numerous full (circular) fracture mirrors. These features, resulting from simultaneous fracture initiation at internal sites, are of sizes corresponding to the range of fracture stresses found in extensive flexure tests, suggesting that the strength of this ceramic may be controlled by intrinsic (volume) defects.
Thermal Conductivity of Lead Borate Glasses
Authors: Ammar M. M. , Halawa M. M. , Ghoneim N. A. , Abbas A. F. , El Batal H. A.
Published: June 2006

Thermal conductivity of glasses in the system PbO‐B2O3 at 30°C were determined by steady‐state methods. The values decrease progressively with increasing PbO content. The experimental thermal conductivities and those calculated from factors representing the contributions of individual oxides (on a weight percent basis) agree fairly well.
Reaction Rates of BaTiO3 and SrTiO3
Authors: UUSIMÄKI A. , VÄHÄKANGAS J. , LEPPÄVUORI S.
Published: June 2006

The temperature dependence of the reaction rates in a 50(BaTiO3)‐50(SrTiO3) ceramic mixture (wt%) was studied by high‐temperature X‐ray diffraction. The data were fitted to two theoretical models and times for complete reactions and activation energy were calculated. Use of the results in electronic material applications is discussed.
Oxygen‐Pressure Dependence of Cation Interdiffusivity in Magnesiowustite Solid Solutions
Authors: SATA N. , GOTO K. S.
Published: June 2006

Cation interdiffusivity in magnesiowustite solid solutions was measured as a function of temperature and oxygen pressure. During diffusion, the local composition of Fe2+ and Fe3+ was always equal to the equilibrium composition with the oxygen pressure in the. gas phase. The interdiffusivity is empirically expressed as D=DP0P021/n expβXFe. The interdiffusivity increases exponentially with iron mole fraction between 30 and 80 mol% Fe at a given oxygen pressure and temperature. The value of β was between 8 and 10 with the 1/n value 1/2 to 1/5 at 1250° to 1350°C. This oxygen‐pressure dependence of the interdiffusivity is equal to that of the product of defect concentration (Roth‐type cluster) and correlation factor. From the result, iso‐interdiffusivity lines are drawn in the broad range of the magnesiowustite solid solution in the MgO‐FeO‐Fe2/3O quasi‐ternary system.
Nonstoichiometry in Acceptor‐Doped BaTiO3
Authors: CHAN N. ‐H. , SHARMA R. K. , SMYTH D. M.
Published: June 2006

The effect of added Al, as an acceptor impurity, on the equilibrium electrical conductivity of large‐grained, polycrystalline BaTiO3, is consistent with a previously proposed defect model which involves only doubly ionized oxygen vacancies, electrons, holes, and acceptor impurities. The behavior is an extension of that of undoped BaTiO3, in which an accidental net acceptor excess already plays an important role. Comparison of the derived active acceptor content with the amount of added Al indicates that Al is <50% effective in creating acceptor levels. The magnitude of a small Po2‐independent conductivity component, necessary to fit the observed conductivity minima, increases with added Al content. This is consistent with a contribution from extrinsic oxygen vacancy conduction.
Success Probability in Fabrication of Long, High‐Strength Optical Fibers
Authors: Oh S.M. , Ferris K.D.
Published: June 2006

To predict success probability in fabrication of multikilometer‐length fibers as a function of on‐line proof‐stress level, strength data for 100‐m gage lengths were used in the modified Weibull analysis. The results are discussed with regard to actual fabrication yields of 1.38‐GPa (200 kpsi) on‐line proof‐tested chemically‐vapor‐deposited fibers.
Scanning Transmission Electron Microscope Analysis of Solute Partitioning in a Partially Stabilized Zirconia
Authors: Rao B. V. Narasimha , Schreiber T. P.
Published: June 2006

Solute partitioning and grain‐boundary chemistry in a commercial Y2O3‐bearing partially stabilized zirconia were studied by scanning transmission electron microscopy. The ceramic contained a mixture of twinned monoclinic (minor) phase and cubic (major) phase. Fine‐scale precipitation was noted within the cubic phase. The average measured YiO3 concentrations in the two phases were near those that would be expected from the binary phase diagram, indicating that solute partitioning approaches completion.
Potassium Beta''‐Alumina Membranes
Authors: CROSBIE G.M. , TENNENHOUSE G.J.
Published: June 2006

Although single‐crystal beta‐ and beta''‐aluminas can be ion‐exchanged by immersion in molten nitrates, polycrystalline membranes of Na‐β'‐Al2O3 fracture on contact with molten KNO3. A KCl vapor ion‐exchange process allows synthesis of leaktight potassium‐ion‐conducting β''‐Al2O3 membranes. Material properties, including results of electrical tests with molten potassium electrodes, are reported for a 12.65% K2O, 0.7% Li2O, 86.65% Al2O3 composition.
Influence of Annealing on the Electrical Conductivity of Polycrystalline ZrO2+8 Wt% Y2O3
Authors: MOGHADAM F. K. , STEVENSON D. A.
Published: June 2006

The electrical conductivity of partially stabilized zirconia was investigated as a function of frequency (2 Hz to 100 kHz) and temperature (400° to 1000°C) by measuring ac admittance on a 2‐probe cell using Lissajous figures. The dependence of the conductivity on annealing time was investigated with in situ conductivity measurements for prolonged annealing at 800°, 900°, and 1000°C. The aging behavior of two commercial zirconias was studied. At higher temperatures (7<750°C) the decrease in total conductivity arises mainly from changes within the grains, whereas at lower temperatures the decrease arises principally from the grain boundaries. Differences in initial conductivity and aging rates between samples from the two sources were related to grain size and impurity effects.
Fabrication of Grain‐Oriented Bi2WO6 Ceramics
Authors: KIMURA T. , HOLMES M. H. , NEWNHAM R. E.
Published: June 2006

Grain‐oriented Bi2WO6 ceramics were fabricated by normal sintering techniques. Platelike crystallites were initially synthesized by a fused salt process using an NaCl‐KCI melt. When calcined at <800°C, the Bi2WO6 crystallites are 3∼5 μm in size and, at >850°C, =100 μm. After dissolving away the salt matrix, the Bi2WO6 particles were mixed with an organic binder and tapecast to align the platelike crystallites. Large particles were easily oriented by tapecasting but the sinterability of the tape was poor. Preferred orientation of small particles was increased by tapecasting and grain growth during sintering further improves the degree of orientation. Sintering above the 950°C phase transition, however, results in discontinuous grain growth and low densities. Optimum conditions for obtaining highly oriented ceramics with high density occur at sintering temperatures of 900°C using fine‐grained powders which yield orientation factors of =0.88 and densities of 94% theoretical.
Temperature Dependence of KIC for High‐Pressure Hot‐Pressed Si3N4 Without Additives
Authors: Shimada M. , Koizumi M. , Tanaka A. , Yamada T.
Published: June 2006

Temperature dependence of KIC values for Si3N4 bodies sintered at high pressures without additives was studied from room temperature to 1400°C. Little change in KK was found in this range.
Fracture of Directionally Solidified Multicrystalline Silicon
Authors: Chen C. P. , Leipold M. H. , Helmreich D.
Published: June 2006

Fracture toughness data is given for multicrystalline silicon which has been prepared by directional solidification. Results indicated a KIC of 0.8 to 0.87 MN /m3/2, which is consistent with data for single‐crystal silicon.
Mixed‐Alkali Effect in Low‐Alkali Germanate Glasses
Authors: Cordaro J. F. , Tomozawa M.
Published: June 2006

Direct‐current conductivities of mixed‐alkali Na2O‐K2O‐GeO2 glasses with ∼0.02 mol% total alkali were investigated. No minima in conductivity isotherms were indicated as K2O is substituted for Na2O. However, a conductivity‐suppressing effect with the‐addition of K2O to Na20‐GeO2 glass was demonstrated, from the comparison with the conductivity ofNa2O‐GeO2 glasses of varied sodium content (0.0079∼0.30 mol% Na2O.
Strengthening of a Sintered Silicon Nitride by a Post‐Fabrication Heat Treatment
Authors: Clarke D. R. , Lange F. F. , Schnittgrund G. D.
Published: June 2006

The strength improvement of an injection‐molded and sintered silicon nitride ceramic (15.5 wt% Y2O3+10.1 wt% SiO2) produced by an oxidation heat treatment at 1500°C is reported. The ceramic retains its strength after prolonged intermediate temperature exposure in air, whereas the untreated material suffers various degrees of cracking.
Carbide Coatings on Graphite Fibers by Liquid Metal Transfer Agent Method
Authors: NIEH T. G. , VIDOZ A. E.
Published: June 2006

Titanium and zirconium carbide layers were produced on the surface of graphite fibers. The process allows a controlled reaction of the fibers with the carbide‐forming elements dissolved hi a molten tin bath, which acts as the transferring medium. The coatings were analyzed by optical and scanning electron microscopy, energy dispersive X‐ray analysis, and X‐ray diffraction. It was found that they consist of two distinct layers, one with the binary carbide composition in contact with the fiber core and an exterior one having a ternary carbide composition. The coatings are brittle, continuous, and uniform along and across the fibers and show good adherence to the carbon core. The carbide growth process is diffusion‐controlled with an activation energy of 184 kJ/mol. The coated fibers are readily wetted by molten aluminum.
Accident Condition Performance of Fuels for High‐Temperature Gas‐Cooled Reactors
Authors: GOODIN D.T.
Published: June 2006

The performance of TRISO‐coated high‐enriched uranium/ low‐enriched uranium fissile and ThO2 fertile fuel particles was studied under simulated accident conditions at temperatures up to 2700°C. A total of 1663 fuel particles from eight irradiation capsules with burnups covering the range of design conditions was tested. The test data show very low failure fractions compared with predictions of previous models and provide the empirical basis for a single model for TRISO coating performance.
Mechanics of Transformation‐Toughening in Brittle Materials
Authors: McMEEKING R. M. , EVANS A.G.
Published: June 2006

Particles which undergo a stress‐induced martensitic transformation are known to toughen certain brittle materials. The enhanced toughness can be considered to originate from the residual strain fields which develop following transformation and tend to limit the crack opening. The increased toughness can estimated from the crack‐tip stress‐intensity change induced by the transformation of a volume of material near the crack tip. It is found that the initial zone, prior to crackgrowth, provides no change in stress intensity. As the crack grows, the zone (associated with a positive transformation strain) induces a stress‐intensity reduction that rises to a maximum level after some crack propagation. The influence of particle‐size distribution on the stress‐intensity reduction is also discussed.
Composition and Properties of Hot‐Pressed SiC‐AIN Solid Solutions
Authors: RUH ROBERT , ZANGVIL AVIGDOR
Published: June 2006

High‐density SiC‐AIN compositions were fabricated from powder mixtures by hot‐pressing in the 1700° to 2300°C temperature range. At 2100°C, a 2H solid solution was found from =35 to 100 wt% AlN. The single‐phase solid solution samples had steep composition gradients of >10%/μm within the grains. Lattice parameters closely followed Vegard's law. For compositions with <35% AIN, multiphase assemblages were found. Increasing grain size was observed for increasing firing temperature for SiC and AIN. Grain size of the solid solutions was significantly smaller than for SiC or AIN fired to the same temperature. Microhardness values decreased linearly in the solid solution region with increasing AIN content. Flexural strengths of SiC and AIN decreased with increasing firing temperature and increasing grain size. The strengths of SiC, AIN, and the solid solutions were low for materials hot‐pressed at 2100°C.
Lead‐Ion Stability in Vitreous Systems
Authors: KRAJEWSKI A. , RAVAGLIOLI A.
Published: June 2006

A new glaze composition was characterized and compared with one studied previously in order to evaluate structural model relating lead‐ion stability and coloring‐ion content to the vitreous system in which they are found. This model is based on the geometrical arrangement of the ionic network, depending in turn on the preferred coordination of the cations involved. The stability of the ionic structure, as indicated by release of Pb2+ on acid attack, is correlated with the coordination of sites occupied by network modifiers, i.e. cations producing cubic coordination were associated with increased Pb2+ release, whereas the opposite ccurred with those producing anti prismatic coordination.
Dissolution Kinetics of β‐Si3N4 in an Mg‐Si‐O‐N Glass
Authors: TSAI R. L. , RAJ R.
Published: June 2006

The rate of dissolution of β‐Si3N4 into an Mg‐Si‐O‐N glass was measured by working with a composition in the ternary system Si3N4‐SiO2‐MgO such that Si2N2O rather than β‐Si3N4 was the equilibrium phase. Dissolution was driven by the chemical reaction Si3N4(c)+SiO2(l)→Si2N2O(c). Analysis of the kinetic data, in view of the morphology of the dissolving phase (Si3N4) and the precipitating phase (Si2N2O), led to the conclusion that the dissolution rate was controlled by reaction at the crystal/glass interface of the Si3N4, crystals. The process appears to have a fairly constant activation energy, equal to 621 ±40 kJ‐mol−1, at T=1573 to 1723 K. This large activation energy is believed to reflect the sum of two quantities: the heat of solution of β‐Si3N4 hi the glass and the activation enthalpy for jumps of the slower‐moving species across the crystal/glass interface. The data reported should be useful for interpreting creep and densification experiments with MgO‐fluxed Si3N4.
Defect Structure of TiTa2O7 at Elevated Temperatures
Authors: Eror N.G. , Balachandran U.
Published: June 2006

The electrical conductivity of polycrystalline TiTa2O7 was measured at 1000° and 1050°C as a function of oxygen partial pressure from 10−1 to 10−21 MPa. In the apparent n‐type region, the value of m in σn∝PO2−1/m was found to be ∼6 in the region >10−17 MPa and ∼4from 10−16 to 10−9 MPa. The conductivity appeared to be p‐type for P02<10−5 MPa. The measured data are explained on the basis of the presence of small amounts of acceptor impurities in the undoped sample.
Effect of Packing Pressures and Particle Size Variations on the Reaction Kinetics for PbTiO3 and PbZrO3 Formation
Authors: Hankey Dana L. , Biggers James V.
Published: June 2006

The rate constant for solid‐state reactions for PbTiO3 formation was increased by a factor of three by increasing the packing pressures. Similarly, rate constants for PbZrO3 formation were shown to increase with decreasing ZrO2 particle and crystallite sizes. Quantitative X‐ray diffraction analyses were utilized to determine the extent of the reactions.
Thermal/Strain History Effects on Creep of Refractory Concrete
Authors: BRAY D. J. , SMYTH J.R. , McGEE T.D.
Published: June 2006

A temperature and stress cycling technique was developed to examine the effects of thermal/strain history on creep of refractory concrete. Creep of a 90+% Al2O3 refractory concrete and a high‐purity calcium aluminate cement was investigated under stresses of 3.4 to 20.7 MPa at 500° to 1200°C. It was found that on initial heat‐up of a cured specimen of either the concrete or cement, the ΔHc∼130 to 170 kJ/mol. After subsequent cycling of the temperature, ΔHC∼620 to 720 kJ/mol. The stress exponent for the initial application of stress was <1. For subsequent cycling of the stress n>2.5. It was determined from these and other results that multiple “deformation” processes are acting simultaneously on initial heat‐up of the form:

image

These processes include crystallization, phase changes, sintering, stress‐aided sintering, and steady‐state creep. Mechanisms of creep and failure are discussed.
Yttrium, an Isoelectric Donor in α ‐ Al2O3
Authors: EL‐AIAT M. M. , KRöGER F. A.
Published: June 2006

Measurements of dc electrical conductivity and emf of single crystal and polycrystalline α‐Al2O3 doped, respectively, with 100 and 300 ppm yttrium show that yttrium, although isoelectronic with aluminum, is a donor. The electronic energy level of the donor is attributed to O2‐ next to Y3+, its level being forced up as a result of the large size of the yttrium ion. The donor activity of Y supports the view that the favorable effect of Y on the oxidation of super alloys is due to reduced diffusion of Al in the bulk through a reduced concentration of Ali… without a marked increase in the concentration of V…Al.
Influence of Particle Size on the Sintering Kinetics of Ultrapure Sodium Chloride
Authors: THOMPSON R. J. , MUNIR Z. A.
Published: June 2006

Sodium chloride particles with size fractions covering the range <38 to 180 μm were sintered in air at T=973 to 1048 K. At any given time and temperature, the degree of densification was found to be a decreasing function of particle size. Calculated activation energies from these densification results showed a corresponding dependence on particle size, i.e. higher energies were associated with the sintering of larger size fractions. Surface‐area reduction measurements showed a similar trend with respect to particle size. These results are discussed in terms of simultaneous contributions from densifying (bulk diffusion) and nondensifying (evaporation‐condensation) processes in the sintering of sodium chloride.
Effect of Fining Agents on the Solarization of a Borosilicate Glass
Authors: Vitko J. , Shelby J. E.
Published: June 2006

The effects of both fining agents and TiO2 concentration on the solarizability of a borosilicate glass proposed for solar energy applications have been determined. Optical and ESR measurements indicate that chlorine‐fined glasses are much less susceptible to solarization than are arsenic‐fined glasses. Titanium dioxide acts as a solarization suppressant with either fining agent. The observed increase in optical absorption in the visible region is in marked contrast with the recent report of a solar‐induced decrease in optical absorption in the infrared range for soda‐lime silicate glasses.
Spectral Response of Photochromic Glass at High Excitation Intensity
Authors: Kivlighn H. D. , Reichman J. , Casagrande L.
Published: June 2006

A conventional photochromic glass, heat‐treated at 570°C for 20 h, was evaluated for its darkening kinetics for selected absorption wavelength intervals between 600 and 1000 nm. Excitation levels of 25, 45, and 90 mW/cm2 were used. Equilibrium absorption coefficients were measured as a function of depth of penetration of the excitation radiation and were fitted to an exponential function used to calculate related surface absorption coefficients. Optical bleaching radiation present in the excitation source, as well as the transverse monitoring beam, probably contribute to lower than intrinsic absorption characteristics.
Electronic Conductivity, Seebeck Coefficient, and Defect Structure of LaFeO3
Authors: MIZUSAKI JUNICHIRO , SASAMOTO TADASHI , CANNON W. R. , BOWEN H. KENT
Published: June 2006

Electronic conductivity and Seebeck coefficients of LaFeO3 were measured as a function of temperature (1000° to 1400°C) and P(O2) (105 to 10−13 Pa). Electronic conduction was found to be n‐type in the lower P(O2) range, and p‐type in a higher P(O2) range. The calculated carrier mobilities suggest a hopping‐type conduction mechanism. The carrier concentrations were calculated as a function of P(O2) and the defect structure was described. It was found that the electrical properties of LaFeO3 are determined not only by the concentration of oxygen vacancies, but also by the La/Fe ratio.
Temperature Dependence of the Iron Acceptor Level in Aluminum Oxide
Authors: BLUM J. B. , TULLER H. L. , COBLE R. L.
Published: June 2006

Optical absorption measurements were performed on undoped and iron‐doped Al2O3 single‐crystal samples cut from the same wafer. Measurements were made in the ultraviolet spectral range at 7=25° to 500°C. A shoulder observed at 4.8 eV in the absorption spectrum of the iron‐doped sample at 25°C was attributed to a valence band‐to‐iron acceptor level transition. This structure shifted to lower energies as the temperature increased at a rate of 5.6°lO−4 eV/°C.
Effect of Variations in Polymerized Oxides on Sintering and Crystalline Transformations
Authors: YOLDAS B. E.
Published: June 2006

This work shows that molecular structural variations can be introduced in oxide systems, including AI2O3, ZrO2, TiO2, and SiO2, by controlled hydrolysis and polymerization reactions during the formation of oxides from metal alkoxides. The chemical and stoichiometric makeup of hydroxides and oxides is not fixed and changes rapidly as a function of molecular size in the region where the size is extremely small. It was also observed that internal structural variations significantly alter the sintering behavior of oxide powders and affect their subsequent crystalline transformations.
Coating of Crystalline Nuclear Waste Forms to Improve Inertness
Authors: STCMTON D. P. , ANGEIINI P. , CAPUTO A. J. , LACKEY W. J.
Published: June 2006

Microspheres of a crystalline waste form prepared by sol‐gel processing were successfully coated with layers of pyrolytic carbon and silicon carbide to isolate the radioactive wastes from the biosphere. A separate process for cesium immobilization was developed, which loads 5 wt% Cs onto zeolite particles for subsequent coating. Pyrolytic carbon‐coated particles showed leach rates =2 to 4 orders of magnitude less than the candidate reference borosilicate glass waste form. Aqueous leach‐test results of coated waste forms were below detection limits of such sensitive analytical techniques as atomic absorption and inductively coupled plasma atomic emission.
Viscoelastic‐Elastic Composites: II, Sandwich Seal
Authors: SCHERER GEORGE W. , REKHSON SIMON M.
Published: June 2006

The viscoelastic analysis of the sandwich seal is compared with experimental results. Agreement is good for cooling, heating, and isothermal holds. The importance of accounting for the effect of structural relaxation on glass properties is demonstrated. Based on the observation that the average relaxation time of the seal at the setting temperature is constant, two simple and accurate procedures are presented for estimating the setting temperature of a seal using minimal experimental data.
Inertia as a Factor in the Dynamic Strength of Brittle Materials
Authors: Lankford James
Published: June 2006

Previous strength determinations of ceramics subject to impulsive loads were interpreted in terms of a theory based on material inertia. Recent experiments are described, which show (1) that the dynamic strengthening mechanism is athermal, as required by the inertial theory, and (2) that microcrack growth, rather than initiation, is suppressed by the inertial effect.
Crystallization of Ultrafine Amorphous Si3N4 During Sintering
Authors: Sawhill Howard T. , Haggerty John S.
Published: June 2006

Ultrafine amorphous Si3N4 powders were synthesized from laser‐heated gases and cold‐pressed into pellets for sintering experiments. At temperatures >1300°C, the powders crystallized with a concurrent, linearly proportional decrease in surface area. These powders densified on a local scale without additives or pressure.
The Intergranular Phase in Hot‐Pressed Silicon Nitride: III, A Refinement of the Elemental Composition
Authors: Clarke D. R. , Zaluzec N. J.
Published: June 2006

An improved sensitivity analysis of the oxygen and nitrogen content of the phase‐separated intergranular glass phase in hot‐pressed silicon nitride is reported. The compositional ranges derived from the analyses are illustrated in the Si3N4‐SiO2‐MgO‐Mg3N2 behavior diagram.
Thermal Expansivities and Temperature Coefficients of Refractive Indices for Molten Salts
Authors: Govinda Rao B. , Rao K. J.
Published: June 2006

An empirical relation for temperature–independent molar polarization is suggested. When this relation was used, the thermal expansivity was estimated correctly from refractive index data.
Zirconia‐Stabilized Cubic Europia
Authors: MOORE D. A. , FERGUSON I. F.
Published: June 2006

The system Eu2O3‐ZrO2 was studied, concentrating attention on the region 0 to 33 mol% ZrO2, which is of interest for fast‐reactor neutron absorber applications. The addition of ∼20% ZrO2 to Eu2O3 resulted in stable cubic phases. Results are compared for coprecipitated powders and pellets prepared from mechanically mixed powders fired at 1300°C and 1S50°C. The thermal stability of cubic structures at 600°C and 800°C for 8000 h was also demonstrated.
Viscoelastic‐Elastic Composites: III, Bead Seal
Authors: REKHSON SIMON M. , SCHERER GEORGE W.
Published: June 2006

The viscoelastic analysis of bead seals is compared with experimental results. Good agreement is demonstrated for cooling, heating, and isothermal holds. Different setting temperatures, Tsz and Tso, are shown to pertain to the axial and radial stresses, respectively. Simple formulas are presented with which the change of setting temperature with stiffness ratio, n, can be predicted. The Hull‐Burger equations with Ts=Ts(n) incorporated are shown to describe adequately the variation of stresses with the glass‐to‐metal diameter ratio in a bead seal.
High‐Temperature Defect Structure of Acceptor‐Doped Strontium Titanate
Authors: EROR N. G. , BALACHANDRAN U.
Published: June 2006

The defect structure of acceptor‐doped (Fe, Al, Cr) polycrystalline strontium titanate was investigated by measuring the equilibrium electrical conductivity as a function of oxygen activity (10−21≤ao2≤1) and temperature (85°C≤T≤ 1050°C). The electrical conductivity was n type with ∼−1/4 dependence on a02 for a02<10−10. For a02>10−8, the observed data for Fe‐ or Al‐doped samples were proportional to ∼1/4.5 power of a02. In this region for Cr‐doped samples, the value of m in.σp αa02+1/m varies from ∼4.80 to ∼9.00 as the concentration of Cr is increased from 460 to 10 000 ppm. The onset of p ‐type conductivity depends on the amount. of acceptor impurity added to the sample. The absolute values of the conductivity in the acceptor‐doped samples were lower in the n‐type region than those for undoped SrTiO3. The conductivity minima shift toward lower oxygen activity with increasing acceptor concentration. For the entire oxygen activity rangae used in this study, the defect structure of SrTiO3 is dominated by the added acceptor impurities.
Inhibition of Nuclear Waste Glass Leaching by Chemisorption
Authors: BUCKWALTER C. Q. , PEDERSON L. R.
Published: June 2006

The durability of a simulated nuclear waste containment glass was investigated by static leaching tests in six types of leaching containers. Glass corrosion in lead containers was reduced by more than two orders of magnitude from that measured in Teflon, whereas aluminum containers resulted in nearly a one order of magnitude reduction. Relatively minor effects on glass leaching were measured in copper, tin, and titanium containers. The results have strong implications concerning the choice of materials in possible waste package designs.
Chemistry of Uranium in Aluminophosphate Glasses
Authors: SCHREIBER HENRY D. , BALAZS G. BRYAN , WILLIAMS BARBARA J.
Published: June 2006

The U(VI)‐U(V)‐U(IV) redox equilibria were monitored in two sodium aluminophosphate base compositions at a variety of melt temperatures, imposed oxygen fugacities, and uranium contents. The higher redox states of uranium were quite soluble in the phosphate glasses, whereas U(IV) would readily precipitate from the melts as UO2. Comparisons of the uranium redox equilibria established in phosphate melts vs those in silicate melts indicated that the coordination sites of the individual uranium species are generally the same in both solvent systems although they differ in detail.
Reaction of Fused Silica With Hydrogen Gas
Authors: TSO STEPHEN T. , PASK JOSEPH A.
Published: June 2006

Fused silica and flowing hydrogen gas react in the experimental temperature range of 1200° to 1400°C to form SiO and H2O vapors. Above a critical flow rate of hydrogen gas, the reaction rate is independent of gas flow rate and is not transport‐controlled. The apparent activation energy for the overall process was 343±33 kj /mol (82±8 kcal/mol). The rate‐limiting step is deduced to be desorption of the product from the glass surface.
Fabrication of Nonadditive Mica Ceramics by Hot Isostatic Processing
Authors: Hattori Takeo , Shigemori Atsushi , Mohri Jun‐Ichi , Yoshimura Masahiro , Somiya Shigeyuki
Published: June 2006

Powder compacts of synthetic mica (fluorphlogopite) encapsulated in a boro–silicate glass tube were isostatically hot–pressed in a Roy–Tuttle–type pressure vessel. Synthetic mica was sintered to a density of 2.60 g/cm3 (91.2% of theoretical density) without additives under 98 MPa of water at 800°C for 45 min.
Comparison of Lead Release Test Methods
Authors: Weinstein Jerry G. , McCauley Ronald A.
Published: June 2006

Three methods for measuring trace lead release levels were compared. Atomic absorption spectroscopy proved to be the most accurate and was used as the reference method. The dithizone colorimetric dye method yielded less reliable results. The lead–ion–specific electrode method, which gave results comparable to atomic absorption spectroscopy, was less expensive, faster, and easier to use.
Temperature Dependence of Strength and Fracture Toughness of ZrO2 Single Crystals
Authors: Ingel R. P. , Lewis D. , Bender B. A. , Rice R. W.
Published: June 2006

Results of strength and fracture–toughness tests on single crystals of partially stabilized ZrO2 at temperatures above and below the tetragonal–monoclinic transformation temperature are reported. The temperature dependence of toughening mechanisms is discussed with respect to theories for phase–transformation toughening and other toughening mechanisms.
Effect of Water Content on Mechanical Properties of Na2O‐SiO2 Glasses
Authors: Takata M. , Tomozawa M. , Watson E. B.
Published: June 2006

Na2O‐SiO2 glasses with high water contents (up to =72 wt%) were prepared under high‐pressure hydrothermal conditions. Hardness, crack initiation, and glass‐transition temperature were investigated. The hardness and the glass‐transition temperature decreased and the crack initiation threshold increased with increasing water content, which suggests that dissolved water promotes deformation by plastic flow.
Investigation of Glasses Using Surface Profiling by Spectrochemical Analysis of Sputter‐Induced Radiation: I, Surface Profiling Technique with High In‐Depth Resolution
Authors: BACH HANS , BAUCKE FRIEDRICH G. K.
Published: June 2006

Experimental equipment was developed to investigate concentration gradients in solid surface layers; the radiative de‐excitation of elements and molecules which are ejected from the ion beam‐bombarded solid and the luminescence excitation within the surface layer are recorded spectrographically. Examples show how elemental composition profiles can be calibrated with respect to depth. An in‐depth resolution of a few nanometers can be obtained. The original profiles are distorted by energy and charge transfer and by other peculiarities connected with ion‐beam etching; the extent to which these distortions must be taken into consideration in interpreting the results is discussed. Interdiffusion‐controlled solid‐state reactions of thin oxide films with a glass substrate were investigated. Advantages and disadvantages of the method for analysis and concentration profiling of glass surfaces and oxide layers on glasses in glass research and industry are discussed.
Diffuse Ferroelectric Phase Transitions in Ba(Ti1‐yZry)O3 Ceramics
Authors: HENNINGS D. , SCHNELL A. , SIMON G.
Published: June 2006

Very high and broad Curie maxima are observed in ceramic Ba(Ti1‐yZry)O3 mixed crystals, which are often used for the preparation of ceramic dielectrics. The ferroelectric‐to‐paraelectric phase transition of ceramic Ba(Ti1‐yZry)O3 was studied using dielectric measurements, quantitative DTA, X‐ray diffraction, and determination of the remanent polarization. At higher Zr concentrations, it was found that ferroelectric and paraelectric phases coexist in a wide temperature region. Up toy =0.16, the phase transition remains first order. The diffuse character is promoted by the small energy difference between the ferroelectric and paraelectric phases appearing at higher Zr content. It can be best described by a normal distribution of Curie temperatures using the phenome‐nological theory of Devonshire and the Newton‐Raphson mathematical approximation.
Stannous‐Stannic Equilibrium in Molten Binary Alkali Silicate and Ternary Silicate Glasses
Authors: PYARE RAM , NATH P.
Published: June 2006

The stannous‐stannic equilibrium in binary alkali silicate and ternary silicate glasses was studied by equilibrating glassmelts with air at 1400°C. The Sn2+‐Sn4+ equilibrium shifts more toward the oxidized state with increasing ionic radii of the alkali ions or with increasing concentration of the alkali ions in the same series of glasses. The slope of the straight lines obtained on plotting log (Sn4+)/(Sn2+)(pO2)n/2 vs mol% R2O increased in the order Li→Na→K. In ternary silicate glasses having the base glass composition 20Na2O·10RO·70SiO2, the Sn2+‐Sn4+ equilibrium shifts more toward the reduced state, with increasing bond strength between the divalent cations and the nonbridging oxygens. With increasing temperature, the equilibrium shifts more toward the reduced state.