bluuebunny/crossref_metadata_2025 huggingface dataset:
Nucleation and Crystallization of NaNbO3 from Glasses in the Na2O‐Nb2O5‐SiO2 System
Authors: LAYTON M. M. , HERCZOG ANDREW
Published: June 2006

Transparent glass‐ceramics, in which the major phase was NaNbO3, were obtained by heat treatment of glasses in the Na2O‐Nb2O5‐SiO2 system. The structure of the glass and the changes occurring during crystallization as a function of temperature and heating rate were examined by X‐ray diffraction, transmission and replication electron microscopy, density, and other measurements. On heating, a rather abrupt formation of uniformly dispersed particles was observed. In the early stages of crystallization, these particles contained NaNbO3 as loose, radially grown dendrites of identical crystal orientation which became dense during later stages of crystallization. The particle sizes ranged from 200 to 10,000 A, depending on the SiO2 content of the glass. Transparency of the crystallized material was dependent on the particle size rather than on the amount of NaNbO3 formed. The temperature at which crystallization occurred increased with the heating rate whereas the viscosity at crystallization decreased. For a given value of the rate of crystal formation per °C of temperature increase, the product (viscosity)n× (heating rate) was constant. The nucleation and growth phenomena which occurred in these glasses was attributed to microheterogeneities of higher Nb2O5 content which formed part of the glass structure.
Plastic Softening of Magnesium Oxide at High Temperatures by Nickel Oxide Addition
Authors: DAY R. B. , STOKES R. J.
Published: June 2006

Magnesium oxide single crystals containing 0.3% nickel oxide were tested in tension at high temperatures. The stress‐strain relationship and deformation modes were similar to those identified for pure magnesium oxide. Alloy specimens had lower yield and ultimate strengths than pure magnesia at all temperatures above 1200° C and showed a greater tendency for kinking, polygonization, and recrystallization. It is proposed that the reducing atmosphere in the furnace causes the alloy crystals to decompose by the removal of oxygen and internal precipitation of nickel. The excess vacancies so produced enhance the nonconservative mobility of dislocations.
Vapor Pressure, Enthalpy, Evaporation Coefficient, and Enthalpy of Activation of the Beryllium Nitride (Be3N2) Decomposition Reaction
Authors: HOENIG CLARENCE L. , SEARCY ALAN W.
Published: June 2006

Beryllium nitride (Be3N2) vaporizes congruently in the range 1640° to 1960°K by the reaction Be, N2(c) = 3Be(g) + N2(g). The equilibrium nitrogen partial pressure, in atmospheres, at the composition for congruent sublimation is given by the expression log PN2= [(–1.952 ± 0.038) × 104]T−1+ (6.509 ± 0.207). The measured enthalpy of decomposition (370 ± 5 kcal at 298° K) yields an enthalpy of formation for Be3N2(c) of –136 ± 6 kcal/mole. The upper limit to the evaporation coefficient at 1600° to 2000°K can be set as 10–4 by comparison of equilibrium data to Langmuir data obtained with a sample of 18% porosity. The apparent enthalpy of activation for the reaction is 409 ± 7 kcal/mole at 1800°K for the porous Langmuir specimen. An expression is developed to predict the temperature dependence of the reduced apparent pressures in Knudsen studies of substances with low evaporation coefficients in terms of the enthalpy of activation. The variation in temperature dependence of the Langmuir measurements and Knudsen measurements with three different‐sized orifices is consistent with predictions from this expression.
Effect of Stoichiometry on the Thermal Expansion of TaCx
Authors: FRIES R. J. , WAHMAN L. A.
Published: June 2006

The X‐ray thermal expansion of TaCx was measured over the composition range from TaC0.789 to TaC0.997 at temperatures to 1000°C. The average thermal expansion coefficient, α, increased with increasing formula weight; α from 25° to 1000°C is 6.04, 6.37, and 6.96 × 10−6/°C for TaC0.789, TaC0.912, and TaC0.997, respectively.
Oxide Glasses in Light of the “Ideal Glass” Concept: I, Ideal and Nonideal Transitions, and Departures from Ideality*
Authors: ANGELL C. A.
Published: June 2006

This two‐part paper develops a basis for discussing glass properties which has features in common with standard “actual vs. ideal” treatments of physicochemical behavior, by defining thermodynamically an ideal state for the glass and discussing the states of the actual glasses in terms of their “departures from ideality.” The glass transition, which freezes the state of the actual glass, is seen as the consequence of the progress of the liquid toward the ideal state, which, for kinetic reasons, is unattainable. The single complexion limit of the Gibbs‐DiMarzio treatment for chain polymers and a minimum volume zero excess entropy condition related to random close packing for simple liquids are seen as complimentary descriptions of the ideal state, which also sets the thermo‐dynamic low‐temperature limit to the liquid state. Glasses formed from simpler molten salt and concentrated aqueous solution systems appear to approach the ideal state and thus provide a behavior pattern against which departures from ideality in the more complex silicate and borate glasses of practical interest may be assessed. In part I general aspects of the problem posed by the glass transition phenomenon are discussed, a dynamic interpretation for simple glasses in terms of the state of phonon excitation of the glassy solid is conjectured, and the concepts of ideal and nonideal (practical) glasses and glass transitions are elucidated from consideration of thermodynamic and kinetic factors involved in the volume relaxation of liquids toward the glassy state. Attention is given to units for describing departures from ideality to permit comparisons among different systems. The limited data for inorganic glasses are examined. Departures from ideality, as usually found in the physicochemical comparison of “actual” with “ideal” behavior, are attributable to specific interactions among the particles of the system, but magnitudes also depend on heat capacity changes. The former factor reaches a maximum in vitreous SiO2 which thus may be one of the least ideal of glasses.
Oxide Glasses in Light of the “Ideal Glass” Concept: II, Interpretations by Reference to Simeple Ionic Glass Behavior*
Authors: ANGELL C. A.
Published: June 2006

The conclusions from Part I of this paper, that glasses formed from certain fused salt mixtures and aqueous electrolyte solutions closely approach a thermodynamically ideal state, is the basis for a discussion of various properties of molten oxide mixtures and the glasses that may be formed from them. The relevant properties of the simple ionic liquids are summarized, and the electrical conductance behavior of a halide analog of the silica‐alkali oxide systems is analyzed to provide a bridge for relating the nonideal behavior of the complex glasses to the near‐ideal behavior of the simple ion systems. Specific cases of silicate and borate glass behavior discussed are the compactibility of high‐silica glasses, the transport behavior in the region of the “boron anomaly,” the relation between viscosity and electrical conductance, and certain structural problems concerning the coordination of multivalent cations in melts and glasses. Finally, some points from the development pertaining to glass‐crystal relations and the nucleation problem are considered.
Subliquidus Immiscibility in Binary Alkali Borates
Authors: SHAW R. R. , UHLMANN D. R.
Published: June 2006

The phase boundaries of subliquidus immiscibility in the lithium, sodium, potassium, rubidium, and cesium borate systems were determined. Two‐phase structures were developed in thermal gradients and examined by direct‐transmission electron microscopy. No opalescence was observed. Microstructures were of the order of a few hundred angstroms. The extent of immiscibility in each system was determined by the approximate intersection of the immiscible phase boundary with the glass transition region.
Precipitation and Coarsening of Magnesioferrite in Dilute Solutions of Iron in MgO
Authors: WIRTZ G. P. , FINE M. E.
Published: June 2006

The precipitation and coarsening of magnesioferrite in MgO containing 1% Fe, prepared at 1440°C and aged at 700° and 800° C in air, were investigated by quantitative electron microscopy and magnetic analysis. The particles are superparamagnetic. The results of the two methods agree. The volume fraction of precipitate quickly reaches essentially its final value; then the particles grow according to the law of diffusion‐controlled coarsening. The precipitate becomes anisotropic at long aging times.
Calculation of Residual Stresses in Glass
Authors: NARAYANASWAMY O. S. , GARDON ROBERT
Published: June 2006

Lee, Rogers, and Woo presented a theory for calculating the stresses produced in glass by tempering. Unlike earlier treatments, theirs takes account of the viscoelastic properties of glass. The purpose of this paper is to evaluate this theory by comparison with experimental data. Discrepancies were found to exist between calculated and observed stress distributions. For cases in which glass is quenched from initial temperatures well above the strain point, these discrepancies result from the numerical formulation of the theory, not from any shortcomings of the theory itself. A modification of this formulation brought calculated and observed stresses into good agreement. For quenching from lower initial temperatures, the present theory could not be brought into agreement with experimental data. The reasons for this are briefly considered in the context of the structural heterogeneity of tempered glass and its possible effects on residual stresses.
Wetting of Binary Aluminum Alloys in Contact with Be, B4C, and Graphite
Authors: MANNING CHARLES R. , GURGANUS T. B.
Published: June 2006

Sessile drop contact angles between liquid aluminum alloys and solid beryllium, boron carbide, and graphite were measured to 840°C under vacuum and in helium. Little wetting occurred between most of the combinations, but at 20% magnesium the contact angle on beryllium decreased to 68°. Low contact angles were noted for the binary aluminum alloys on graphite coated with titanium.
Methanol Vapor Adsorption on Silica and Soda‐Lime‐Silica Glass
Authors: SEWELL P. A. , MORGAN A. M.
Published: June 2006

Methanol vapor adsorption isotherms on vitreous silica and soda‐lime‐silica glasses were measured by gas chromatography in the low‐pressure region of the physical adsorption isotherms after the adsorbents had been degassed in a dry atmosphere at successively higher temperatures. The isosteric heats of adsorption indicate that after strong degassing treatments each methanol molecule is adsorbed by the formation of a single hydrogen bond with the surface, but after low‐temperature degassing more than one hydrogen bond is formed for each adsorbed molecule.
Synthetic Photochromic Sodalite
Authors: WILLIAMS E. F. , HODGSON W. G. , BRINEN J. S.
Published: June 2006

Synthetic photochromic sodalite was prepared (1) by solid‐state reaction, (2) from zeolite X‐SO2 or zeolite X‐H2S, and (3) hydrothermally; the preparations are compared and discussed. X‐ray diffraction, ultraviolet and visible light absorption (transmission and reflection), and ESR data served to follow the reactions and characterize the products. The content of sulfur and chlorine and the S: C1 ratio affect the depth of color and the bleaching rate. The partial substitution of other halogens for C1 may speed up or slow down the coloring rate as a function of electronegativity. Fluorine may shift the visible absorption maximum from 5300 to 5100 Å. Stoichiometry and ESR data indicate that the photochromism is effected by the transfer of an electron between sulfur as S2= and a C1 vacancy between four sodium atoms.
Substructure Classification of Silicate Glasses
Authors: BABCOCK C. L.
Published: June 2006

It is proposed that silicate glasses be classified in terms of substructures uniquely identified with primary crystallization phases. All glasses having compositions within the ranges or areas covered by a given primary crystallization phase field should constitute a separate glass type or class. This classification is definitive for properties determined principally by the silica frameworks or substructures. Such composition‐property relations can be reproduced by independent investigators if the properties are measured under temperature equilibrium conditions.
Solid State Reactions in Lithium Ferrite
Authors: POINTON A. J. , SAULL R. C.
Published: June 2006

The conventional sintering of lithium ferrite from the normal constituents lithium carbonate and hematite is facilitated by the decomposition of the lithium carbonate in the intimate mixture about 400°C below the decomposition point in the pure state. However, at temperatures in excess of 1000°C, there is an irreversible loss of lithium and oxygen from the ferrite with a marked change in the density and the magnetic moment due to solid solution or second phase formation. Attempts to reduce the loss of oxygen and, possibly, lithium, by the application of a substantial oxygen pressure during sintering are accompanied by a retardation of the formation and densification processes.
Microstructure and Magnetic Properties of Lead Ferrite
Authors: TOKAR MICHAEL
Published: June 2006

Unoriented lead ferrite specimens were prepared by calcining and sintering techniques. Specimens having an initial composition of Pb0.5Fe2O3 had the best permanent magnet properties (for nondoped material). The effects of small amounts of added oxides on the microstructure and magnetic properties were also determined. Silica and boria were most effective in raising the (BaHa)max to over 1.4 × 106 G.Oe as compared to 0.9 to 1.1 × 105 G.Oe for commercial un oriented barium ferrite magnets. Optical and electron microscopy revealed that silica and boria form low melting phases as the specimens are sintered, which, acting as fluxes (probably by a solution‐precipitation mechanism), enhance the densification of the magnets, thereby raising the Br, and (BaHa)max, values. On cooling, these nonmagnetic low‐melting phases are retained at the ferrite grain boundaries where they inhibit domain wall motion which would otherwise lead to a reduction in coercive force. Although these magnets are termed “un oriented” to distinguish them from “oriented” ferrites which are purposely aligned before sintering, a slight orientation is imparted to the polycrystalline compact during the pressing operation before sintering. The silica and boria additions increase the degree of orientation by accelerating the rate of densification. The increase in orientation accounts for part of the increase in Br, and (Ba, Ha)max.
Kinetics of Precipitation and Measurements of Strain in the System MgO‐Al2O3‐Cr2O3
Authors: STUBICAN V. S. , GRESKOVICH C. , McKINSTRY H. A.
Published: June 2006

A quantitative X‐ray technique for measuring precipitation strains has not been previously applied in metallic or oxide systems. The Warren‐Averbach analysis of strain was used to determine the buildup of elastic strain energy in the spinel crystalline solution matrix (gross composition = 60 mol% MgAl2O2+ 40 mol% Cr2O3) during the isothermal (1135°C) precipitation of a metastable (coherent) monoclinic phase. The elastic strain energy of the spinel crystalline solution matrix increased to a maximum of about 3.1 × 107 ergs/cm3 for a reaction time of 8 h. There was a marked decrease in the elastic strain energy during the initial precipitation of the equilibrium corundum crystalline solution with the composition (Al3+0.72 Cr3+0.25)O3. An overall diffusion activation energy for precipitation of the mono‐clinic phase was approximately 86 kcal/mol.
High‐Temperature Hemispherical Spectral Emittance of Uranium Oxides at 0.65 and 0.70 μm
Authors: HELD PETER C. , WILDER D. R.
Published: June 2006

Hemispherical spectral emittances were measured for uranium oxides. The compositions ranged from UO1.05 to UO2,20 the bulk densities from about 8 to more than 10.6 g/cm3, the apparent porosities from less than 0.5 to 19.0%, and the temperatures from about 450° to about 2400°K. The data were taken at wavelengths of 0.656 and 0.70 μm. The emittance is high in all cases (from about 0.70 to above 0.90) and increases with increasing wavelength. The emittance is not strongly sensitive to temperature, porosity, density, surface finish, or stoichiometry. The high emittance values are linked to the absorption edge observed for uranium oxides in the visible portion of the spectrum.
Kaolinite Dehydroxylation Kinetics
Authors: JOHNSON HOWARD B. , KESSLER FRANK
Published: June 2006

The rates of dehydroxylation of three kaolinites which varied in particle thickness were studied from 417° to 480°C under very low water vapor partial pressures. The dehydroxylation rate was directly proportional to the surface area and had an activation enthalpy of 41.0 kcal/mol. The data did not fit either a diffusion‐controlled or a phase‐boundary‐controlled reaction in the radial direction, even when the particle diameter distribution was taken into account. The reaction appears to proceed through the kaolin particles by a pseudo‐phase‐boundary‐controlled mechanism, principally in the [001] direction.
Pressure Sintering of Gallium Arsenide
Authors: STOLLAR W. P. , MOSS H. I.
Published: June 2006

Pressure sintering of gallium arsenide was studied in vacuum at 900° to 1000 °C and 9000 to 43,200 psi. The optical transmission of nearly theoretically dense gallium arsenide was about one‐fourth less than that of equally thick single crystals. Density‐time curves indicated that at least two densification mechanisms occur and apparently overlap. Microscopic observations indicated that plastic flow was one of the mechanisms. Plastic flow was further evidenced by the crystallographic texture of the grains, as determined by X‐ray diffractometry. The rapid initial plastic flow densification stage is not adequately described by the McClelland densification rate equation. Diffusional secondary densification mechanisms may be operative at higher densities.
Role of Catalysts in the Transformation of Germanium Dioxide
Authors: KOTERA YOSHIHIDE , YONEMURA MICHIKO
Published: June 2006

The role of some alkali compounds as catalysts in the polymorphic transformation of germanium dioxide was investigated by DTA and high‐temperature X‐ray diffraction. When a lithium or potassium salt is used, a solid state reaction first occurs between, the salt and germanium dioxide to form alkali germanate compounds which, in a crystalline or glassy state, catalyze the transformation. The effects of various catalysts on the transformation are discussed by comparing the activation energies.
Electrical Resistivity of Titanium‐Containing Glasses
Authors: TAKAMORI TAKESHI , SEO HIROKICHI , TASHIRO MINORU
Published: June 2006

Titanium‐containing glasses were prepared by fusion of a base glass (BaO·B2O3SiO2) and TiO2 and/or Ti2O3 in Ar. Their resistivities did not vary with melting time and temperature. Interaction of Ti4+ and Ti3+ in the glasses was deduced by spectroscopy, but the valence states in the batch compositions were preserved in the glasses, according to the chemical analysis. Glasses containing either Ti4+ or Ti3+ had very high resistivities, whereas the glass prepared by melting a mixture of a Ti4+‐containing and a Ti3+‐containing glass had much lower resistivity. All results confirmed the possibility of controlling the resistivity by batch composition for these glasses.
Role of Iron in Calcium Phosphate Glasses
Authors: BISHAY A. M. , MAKAR L.
Published: June 2006

Some physical properties okf phosphate glasses con‐taining up to about 26 mol% Fe2O2 were studied. Pronounced changes in properties were observed at compositions containingabout 6, 10, and 13 mol% Fe2O3. The X‐ray diffraction spectra of devitrified (heat‐treated) samples showed new compounds near these compositions. Electron spin resonance and optical studies confirmed the presence of Fe3+ and Fe2+ in both 4‐ and 6‐coordination. An increase in total iron in these samples was associated with a decrease in the ratios Fe2+ 4‐coordinated/Fe3+ 6‐coordinated 6‐coordinated and Fe3+ 4‐coordinated/Fe3+ 6‐coordinated up to about 2.0 mol% Fe2O3, as shown by the intensity of the optical absorption bands at about 2.0 and 1.0 μm and by the intensity of the ESR lines at g⋍4.2 and 2.0, respectively. Samples containing up to 4.3 mol% Fe2O3 showed an increase in Fe3+ concentration and a decrease in Fe2+ concentration after gamma irradiation. The electrical conductivity and activation energy decreased sharply with increasing Fe2O3 content.
Plastic Deformation and the Fracture Surface Energy of Sodium Chloride
Authors: WIEDERHORN S. M. , MOSES R. L. , BEAN B. L.
Published: June 2006

A correlation between plastic deformation at crack tips in sodium chloride and the measured value of the fracture surface energy is presented. Plastic deformation can either aid or hinder crack growth, depending on the mode of deformation at the crack tip. If plane‐stress deformation occurs, crack motion is hindered by step formation, dislocation generation, and plastic blunting of the crack tip. If plane‐strain deformation occurs, crack motion is aided by stress fields that arise from the deformation. The specific surface free energy of sodium chloride, {100} plane, is estimated to be less than 0.37 J/m2.
Final Stage Sintering of ThO2
Authors: JORGENSEN P. J. , SCHMIDT W. G.
Published: June 2006

The addition of CaO to ThO2inhibits discontinuous grain growth and allows sintering to proceed to theoretical density by maintaining a high diffusion flux of vacancies from the pores to the grain boundaries. The optimum amount of CaO added is 2.0 mol%, which exceeds the solid solubility limit. A model of second‐phase inclusions impeding grain boundary motion was used to explain the results.
Crystal Chemistry and Phase Equilibria in the System CdO‐PbO‐O
Authors: KEESTER KENNETH L. , WHITE WILLIAM B.
Published: June 2006

The subsolidus portion of the system CdO‐PbO‐O was investigated at high temperatures and oxygen pressures in cold‐seal pressure vessels. Specially prepared cadmium hydroxide precipitate was used to achieve reaction equilibria. Two ternary oxide phases exist in the system: Cd2PbO4 is stable under all conditions investigated; CdPb2O5 dissociates (2CdPb2O5⇋ Cd2PbO4+Pb3O4+O2). The P‐T univariant curve was mapped. Compatibility triangles illustrate the phase equilibria of the system. Cell constants for Cd2PbO4 are: a0=5.671, b0=9.902, C0= 3.139, all ±0.001 Å. The space group was determined as Pbam (Pba2); Cd2PbO4 is isostructural with the Sr2PbO4 structure type. Derived average metal‐oxygen distances are: Cd–O 2.35 and Pb–O 2.08 Å. The structure of CdPb2O5 is not known.
Preparation and Characterization of Submicron Hafnium Oxide
Authors: MAZDIYASNI K. S. , BROWN L. M.
Published: June 2006

Submicron hafnium oxide powder prepared by hydrolytic decomposition of alkoxides was studied. The particle size range of this powder was 10 to 50 Å. Emission spectrographic analysis of the powder after it was calcined at 250°C for 0.5 h indicated a purity of >99.995%. Up to 320°C, the powder showed no crystallinity by X‐ray analysis. The amorphous HfO2 was isothermally aged at 5° to 10°C intervals between 200° and 500°C. X‐ray diffraction patterns indicate a sharp transition from an amorphous state to the monoclinic phase at 325°C. High‐temperature X‐ray studies and DTA suggest nucleation and growth of small crystallites at 420°C leading to conversion to monoclinic HfO2 at 480°C. BET surface area measurements and TGA of the powders were also conducted. A powder which transformed at 325°C to the monoclinic phase was isothermally aged below 325°C for 150 h without change.
Paramagnetic Resonance and Optical Absorption in Gamma‐Ray Irradiated Alpha Quartz: The “Al” Center
Authors: WEEKS R. A.
Published: June 2006

The optical absorption spectra between 1.0 and 8.5 eV and the electron paramagnetic resonance spectra at 10 GHz of a synthetic crystal of α‐quartz grown on a z plate were measured as a function of 60Co γ‐ray irradiation and thermal treatment. After initial irradiation, an estimate of a lower limit for the concentration of centers contributing to the resolved optical bands gave N≳1016 cm‐3 for each band. An estimate of the concentration of spins of each of the distinct paramagnetic species gave N<3×1015 cm‐3 with the exception of the “Al” center for which N∼3×1015 cm‐3. Thermal bleaching and re‐irradiation of the crystal showed that the defects with bands in the 1.0 to 6.5 eV region were independent of the defects with bands in the 5.5 to 8.5 eV region and that undetected precursor defect configurations were altered by heating to form those defects whose optical bands (5.5 to 8.5 eV) increased after the second irradiation. The only correlation observed between paramagnetic defects and defects producing optical absorption bands was between the “Al” center and a band at 8.45 eV; the correlation was quite weak.
Phase Equilibrium in the System MgO‐H2O at High Temperatures and Very High Pressures
Authors: YAMAOKA SHINOBU , FUKUNAGA OSAMU , SAITO SHINROKU
Published: June 2006

Phase equilibrium in the system MgO‐H2O was investigated from 500° to 1450° C at 5 to 40 kbars by a quenching technique using a piston‐cylinder apparatus. Brucite decomposed to periclase plus vapor at 810° and 10 kbars, 945° and 20 kbars, 1000° and 32 kbars, and 975°C and 40 kbars. The slope of the decomposition P‐T curve became steeper with increasing pressure, infinite at 32‐ kbars and 1000C, and then negative above 32 kbars. The extrapolation of this curve to lower pressures agrees well with data of other workers who used hydrothermal techniques.
Elastic and Anelastic Response of Polycrystalline UO2‐PuO2
Authors: NUTT A. W. , ALLEN A. W. , HANDWERK J. H.
Published: June 2006

A sonic resonance technique was used to investigate the room‐temperature elastic and anelastic properties of physically mixed U0.8PU0.2O2 as a function of density, stoichiometry, and cation homogeneity. The effect of porosity on the elastic moduli was linear and is described by E=2102.7 (1–2.03P)± 13.5 Kbars for the Young's modulus, G=823.5(1–2.05P)± 9.1 kbars for the shear modulus, and B= 1584.8(1–1.89P)± 59.1 kbars for the bulk modulus, where P is the volume fraction porosity. Poisson's ratio was 0.28 and was not a function of porosity. The Debye temperature of U0.8Pu0.2O2 computed from the Young's and shear moduli for theoretically dense specimens was 379°K. Variation of the O/M ratio from 1.968 to 2.006 produced no significant change in either the damping capacity or the elastic moduli of single‐phase 80%UO2‐20% PuO2 solid solutions. An approximate 24% decrease of the room‐temperature Young's and shear moduli and an approximate increase by a factor of 14 in the internal friction were observed with gross modifications of plutonium cation homogeneity. Preliminary results suggest that internal friction measurements might be used to assay the homogeneity of UO2‐PuO2 solid solutions.
Electrical Conductivity of Glasses in the Systems P4O10‐V2O5 and P4O10‐WO3
Authors: CALEY R. H. , MURTHY M. KRISHNA
Published: June 2006

The electrical conductivities of P4O10‐V2O5 and P4O10‐WO3 glasses were compared. The P4O10 content of a glass from each system was replaced by increasing amounts of several oxides. The conductivity of the vanadium phosphate glass was insensitive to oxide replacement, in contrast to the conductivity of the tungsten phosphate glass, which decreased by almost five decades when a small amount of V2O5 was introduced. The change was attributed to the effect of oxidation‐reduction on the tungsten ions.
Structural Role of Zinc Oxide in Glasses in the System Na2O‐ZnO‐SiO2
Authors: HURT J. C. , PHILLIPS C. J.
Published: June 2006

Glasses containing 50 to 75 mol% SiO2 and up to 35 mol% ZnO were studied using thermal expansion, density, molar volume, refractive index, molar refractivity, internal friction, and infrared absorption data. Increasing the zinc oxide content in the glasses decreased the thermal expansion and increased the density, refractive index, and the activation energy for the alkali‐ion diffusion internal friction peak. Infrared absorption from 1500 to 70 cm‐1 indicated the presence of both six and four oxygen coordination for the zinc cation.
Low‐Silica Glasses Based on Calcium Aluminates
Authors: ONODA G. Y. , BROWN S. D.
Published: June 2006

An exploratory study of the effects of compositional variation on glass formation in low‐silica aluminate compositions revealed that CaO is essential for glass formation at ordinary quenching rates. Other oxides, such as Li2O, MgO, BaO, ZnO, Na2O, K2O, BeO, B2O3, and PbO, can be present in the glass in limited amounts (in some cases up to 30 mol%). A necessary, but insufficient, condition for easy glass formation is that the ratio of oxygen ions to network‐forming cations (assumed to be Si4+and Al3+) be ∼2.5. The glass‐forming compositions were also characterized by liquidus temperatures below ∼1500°C (2732°F). Young's modulus ranged from 13.0 to 17.8×106psi. Glasses containing network‐modifying cations with high field strengths generally had the higher moduli. Strength (420,000 to 650,000 psi in 0.3‐mil fibers), static fatigue, viscosity, annealing, and surface tension were studied to a limited extent for the composition (in mol%) 30Al2O3‐4SiO2‐60CaO‐6MgO.
Transition Metal Ions as Spectroscopic Probes for Detection of Network Structure in Novel Inorganic Glasses
Authors: INGRAM M. D. , DUFFY J. A.
Published: June 2006

Spectra of divalent transition metal ions in ZnCl2, KOAc‐Ca(OAc)2, KNO3‐Ca(NO3)2, and K2SO4‐ZnSO4 glasses are presented. Ions with low octahedral site preference energies (e.g. CO2+) can be used as “probes” for divalent cations in glass and can indicate the presence or absence of network structures. Thus ZnCl2 glass has a tetrahedral network structure, analogous to vitreous BeF2, but KOAc‐Ca(OAc)2 and KNO3‐Ca(NO3)2 glasses contain potassium ions and discrete acetatocalcate(II) and nitratocalcate(II) “complex ions.” The structure of acetate and nitrate glasses is discussed in terms of the ideal glass concept.
Studies of Chemical Bonding in Glasses by X‐Ray Emission Spectroscopy
Authors: DODD CHARLES G. , GLEN G. L.
Published: June 2006

Silicon and aluminum Kβ band X‐ray emission spectra of a series of lithia‐aluminosilica (LAS) glasses were determined using the X‐ray spectrometric systems of commercially available electron microprobes. Comparison with spectra of reference materials, including glassy and crystalline forms of silica, high‐quartz‐phase crystals of the L:A:S‐1:1:2 (mol ratio) composition (high‐eucryptite), and 6‐ and 4‐coordinated aluminum oxides, led to tentative assignment of spectral peaks to specific electronic transitions. Molecular orbital theory and crystallographic structural data were used to assign bands in crystalline materials. The LAS glass spectra indicated progressive bond weakening with decreasing silica content; the Kβ peak shifts permitted approximate calculation of the decreases in Si–O and Al–O bond energies, which were as great as 30 kcal/mol relative to SiO2 (for the L:A:S‐1:1:2 glass).
Dielectric and Piezoelectric Properties of Pb(Co1/3Nb2/3)O3‐PbTiO3‐PbZrO3 Solid Solution Ceramics
Authors: KUDO TOSHIYUKI , YAZAKI TAKEHITO , NAITO FUMIO , SUGAYA SHOJI
Published: June 2006

Ceramic and piezoelectric properties of the Pb(Co1/3Nb2/3)O3‐PbTiO3‐PbZrO3 system were investigated. The system contains rhombohedral, tetragonal, and pseudocubic phases at room temperature. The triple point is at 0.07Pb(Co1/3Nb2/3)O3‐0.43PbTiO3‐0.50PbZrO3. High dielectric constants (750 to 1500) and radial coupling coefficients (40 to 45%) and low average temperature coefficients of resonant frequency (of the order of 10‐6°C) were obtained for compositions near the morphotropic phase boundary.
Thermal‐Stress Crack‐Initiation Method for Ranking Ceramic Materials
Authors: CARDEN A. E. , ANDRAE R. W.
Published: June 2006

A test is described which permits ranking of brittle materials according to their resistance to thermal fracture under steady‐state conditions. A water‐cooled probe and a small, thin, annular disk specimen heated by a radiator are used. Tests on AUC graphite and on a series of composites of transition‐metal pseudobinary solid‐solution carbides with graphite were very reproducible and reliable. A thermal‐stress analysis for the graphite agreed well with the test results.
Habit Changes of Sapphire Grown from PbO‐PbF2, and MoO3‐PbF2 Fluxes
Authors: CHASE A. B. , OSMER JUDITH A.
Published: June 2006

Single crystals of Al2O3 (sapphire) were grown from PbO‐PbF2 and MoO3‐PbF2 fluxes; they varied from flat plates (PbF2‐rich melts) to equidimensional crystals (PbO‐ or MoO3‐rich melts). The primary growth planes are basal {0001}, first‐order rhombohedral {1011}, and second‐order rhombohedral {0112}. The habit change is interpreted on the basis of F‐ contamination and Pb2+ surface adsorption. Possible ion species in the melts and their relative importance on crystal growth from these systems are discussed.
High‐Pressure Experiments on Yttrium Iron Garnet
Authors: GELLER S. , ESPINOSA G. P. , CRANDALL P. B.
Published: June 2006

High‐pressure‐high‐temperature experiments carried out on YIG and on 3Y2O3+5Fe2O3 mixtures gave expected results and do not corroborate the recent report by Shimada, Kume, and Koizumi indicating the existence of a “dense ferrimagnetic perovskite allotropic form of yttrium iron garnet.” The results of experiments by Marezio, Remeika, and Jayaraman on the high‐pressure decomposition of synthetic garnets are discussed. The garnet {Y3}[Sc0.6Fe1.4](Fe3)O12 is more stable than YIG under the same conditions of pressure and temperature; this alone disproves the Marezio et al. hypothesis relating stability vs pressure to ionic site preference. The stability of YIG is more sensitive to oxygen fugacity at high temperatures and atmospheric pressure than are those of YAG and YGaG. Thus relative compressibility and equilibrium oxygen vapor pressure are the important parameters.
Thermal Expansion of Composites as Affected by the Matrix
Authors: TUMMALA R. R. , FRIEDBERG A. L.
Published: June 2006

Summary and Conclusions

Thermal expansion measurements of composite systems containing hard dispersions embedded in brittle and semibrittle matrices indicate the importance of (1) the magnitude of the stress developed in the matrix and (2) the crack propagation behavior of the matrix. The thermal expansion of these composites can be predicted if the residual stress developed as a result of the difference in the expansions of the components does not exceed a critical value defined by the modified Griffith equation. This critical stress varied considerably with the nature (brittle, semibrittle, or ductile) of the matrix.
Emanation and Surface Gas Labeling Methods of Studying the Solid‐State Reaction of ZnO and Fe2O3
Authors: BALEK VLADIMÍR
Published: June 2006

The solid‐state reaction of ZnO and Fe2O3 was studied by emanation and surface gas labeling methods based on measurement of radioactive inert gas release. These methods, especially in combination, supplement information on the formation of zinc ferrite. The methods are especially sensitive to initial changes in the material during thermal reaction. Measurement of the release of radon and xenon from the sample, DTA, and dilatometry can be accomplished simultaneously with the apparatus.
Direct‐Current Polarization During Field‐Assisted Glass‐Metal Sealing
Authors: WALLIS G.
Published: June 2006

Thin plates of borosilicate glass were polarized near the annealing point with a dc voltage of typically 600 V. From the measurements of capacitance and current, the width of the polarized region and the electric field within the region were deduced. The results indicate that the glass layer adjacent the anode becomes depleted of positive sodium ions and of compensating negative charge. As a result, the electric field in the layer acquires a maximum value of the order of 106 V/cm. Some implications of the process with regard to field‐assisted glass‐metal sealing are discussed.
Vapor Growth of Al2O3 Bicrystals
Authors: PARKER H. S. , HARDING C. A.
Published: June 2006

Bicrystals containing symmetrical tilt boundaries with either the

or the

direction as the rotation axis were vapor‐grown at 1740°C using the reaction 2AlCl3(g)+3CO2(g) + 3H2(g)→.Al2O3(s) + 6HCl(g) + 3CO(g). Specimens as large as 3 by 5 by 20 mm were produced in 24 h. Chemical purity of the specimens is high, with <0.1 ppm total cation impurities, as determined by activation analysis.
Phase Equilibria in the System Na3AlF6−AlF3
Authors: FOSTER PERRY A.
Published: June 2006

The phase diagram for the system Na3AlF6−AlF3 was determined by quenching and microscopy supplemented with DTA and X‐ray powder diffraction. Primary crystallization fields for cryolite, chiolite, and aluminum fluoride are defined. Liquid containing 30 wt% AlF3 is in peritectic equilibrium with solid cryolite and chiolite at 741°C; solid chiolite and aluminum fluoride are in equilibrium with liquid at the eutectic composition 39 wt% AlF3 and 694°C.
Chemical Vapor Deposition of Polycrystalline Al2O3
Authors: WONG PHILIP , ROBINSON McDONALD
Published: June 2006

Polycrystalline Al2O3 was chemically vapor‐deposited onto sintered Al2O3 substrates by reaction of AlCl3 with (1) H2O, (2) CO:H2, and (3) O2 at 1000° and 1500°C and 0.5 and 5.0 torr. Although the thermodynamics of all these reactions predict the formation of solid Al2O3, the deposition rate of the first reaction was considerably greater than that of the second. The third reaction was so slow that no measurable deposit was formed in 6 h at 1500°C. Formation of dense deposits of α‐Al2O3 was favored by increasing temperature and decreasing pressure. Microstructural examination of the dense deposits showed long columnar grains, the largest of which extended through the deposit from the substrate to the surface.
Relations Between Crystalline Phases, Crystal Size, Water Loss, and Thermolumineseence in the System ZrO2−H2O
Authors: BETTINALI C. , FERRARESSO G.
Published: June 2006

The effects of thermal treatment, crystalline phases, and crystal size on thermolumineseence in the system ZrO2−H2O were studied. The results suggest that thermolumineseence is not affected by the water content and that it is strongly dependent on the degree of crystallinity and on crystal size. An interpretation of the changes in the glow curves is suggested on the basis of the data.
Effect of Surface Finish on Structural Ceramic Failure
Authors: KINNEY KARL R. Me , HERBERT CHARLES M.
Published: June 2006

The relation between fracture strength and surface finish of brittle nonmetallic materials was examined and related to surface‐crack theory. Specimens used in an experimental illustration were made of a commercially available 96%‐pure alumina with an average grain size of 3.8 μm and a porosity of about 6%. Several groups of specimens, each having a different surface finish, were used in a biaxial ball‐and‐ring
Oxygen Concentration Cell Measurements of Ionic Transport Numbers in PZT Ferroelectrics
Authors: EZIS A. , BURT J. G. , KRAKOWSKI R. A.
Published: June 2006

Several ceramic oxides of the perovskite structure exhibit ferroelectric properties and therefore are characterized by pyroelectric and piezoelectric behavior. One such ceramic is the solid solution lead zirconate‐lead titanate (PZT). To determine the range of ionic charge conduction in PZT, experiments were performed using an electrochemical oxidation cell. Results indicate that the ionic transport number of Pb(Zr1−x, Tix)O3 decreases monotonically with increasing values of x over the range 0.05<x<0.35. Electronic conduction becomes dominant above x=0.40. These results are relatively independent of temperature from 425° to 650°C.
Microstructure and Reflectance of a PbO‐B2O3‐SiO2 Glass with Crystalline Opacifier Additions
Authors: DENNIS M. D. , BRADT R. C.
Published: June 2006

Crystalline opacifiers were added to a lead borosilicate glass which was already opaque from phase separation of droplets in a region of liquid‐liquid immiscibility. A reflectance enhancement maximum was observed with these additions. Microstructural variations correlated with reflectance measurements, indicating that the maintenance of two‐phase immiscibility is essential to opacity in these systems.
Electrochemical Studies in Glass: III, The System CoO‐Na2Si2O5*
Authors: LACY ALTON M. , PASK JOSEPH A.
Published: June 2006

A solid electrolyte electrochemical cell of the type Pt|Ni: NiOa=1‖ZrO2+7.5% CaO‖Co:CoOa<1+Na2Si2O5 glass|Pt was used to measure the activities of cobaltous oxide in Na2Si2O5, glass from 700° to 1100°C. From the variation in CoO activity, the activity of NS2 glass in solution was calculated. Partial molar free energies and entropies of solution and free energies and entropies of mixing of these components were calculated from activity data. A partial phase diagram for the CoO‐Na2Si2o5 system is proposed from the solubility data of this study. The solubility of CoO in Na2Si2O5 glass varies from 44 to 52 mol% (∼24 to 31 wt%) over this temperature range. Comparison of partial molar entropies of Fe0.95O, CoO, and NiO in glass solution suggests that the structure is basically the same for a given O/Si ratio. Solubility limits are determined by the relative strengths of the –cation–O–cation– and –Si–O–cation‐bond assemblages.
Polymorphism of LiGa5O8 and of LiGa5O8‐MgGa2O4Solid Solutions
Authors: DATTA R. K.
Published: June 2006

High‐temperature X‐ray diffraction and differential thermal analyses showed that LiGa5O8 exists in two polymorphs related by the first‐order transition at 1138°±3°C of the low‐temperature simple‐cubic form, space group (probably) O7, to the high‐temperature spinel (fcc) form, space group Oh7. The transition is rapid, and the high‐temperature form in pure LiGa5O8 could not be quenched to room temperature under the conditions used. However, the high‐temperature polymorph can be quenched under equilibrium conditions when 40 mol% or more MgGa2O4 is present. The subsolidus equilibrium relations in the system MgGa2O4‐LiGa5O8 are discussed.
Hot‐Pressing and Mechanical Properties of Al2O3 with an Mo‐Dispersed Phase
Authors: RANKIN D. T. , STIGLICH J. J. , PETRAK D. R. , RUH ROBERT
Published: June 2006

Compositions of alumina with a molybdenum dispersed phase were investigated in the 0 to 5 vol% Mo range. These compositions were also prepared with a 0.5 wt% MgO addition. All specimens were fabricated by hot‐pressing, and near theoretical densities were achieved. Specimens were characterized by metallographic and X‐ray diffraction analyses, and microhardness, elastic moduli, tensile strength, and fracture energy were determined. Results revealed that Mo additions did not affect grain growth; in contrast, MgO additions significantly inhibited grain growth. However, Mo additions did reduce the elastic moduli and microhardness but did not measurably affect the tensile strength. Tensile strength was dependent on grain size and fitted the G−1/3 relation. The fracture energy of Al2O3+5% Mo was 50% greater than that of Al2O3. Specimens were successfully hot‐pressed with a micro‐structure graded from that of Al2O3 to that of the 5% Mo composition.
Compressive Creep of Al2O3 Single Crystals
Authors: BERTOLOTTI RAYMOND L. , SCOTT WILLIAM D.
Published: June 2006

Aluminum oxide single crystals deformed by dislocation glide and deformation twinning during compressive creep at 1400° to 1700°C. The activation energy for basal slip was a function of the applied stress and agreed with activation energies previously measured by observation of yielding phenomena. The overcoming of a large Peierls‐Nabarro stress is the most probable rate‐controlling mechanism. Rhombohedral twinning, a significant deformation mode in creep, depends on surface damage for nucleation. The activation energy for rhombohedral twin growth, a function of the applied stress, is substantially lower than that for basal slip. When basal slip and rhombohedral twinning occur concurrently, creep by basal slip results, but the presence of twins can substantially reduce the creep rate.
Elastic Properties of 0.98Li2O‐1.0Al2O3‐nSiO2 Glasses and Keatite‐Phase Glass‐Ceramics
Authors: FIELD M. B. , TUCKER R. W.
Published: June 2006

Bulk physical properties such as elastic moduli, thermal expansions, and moduli of rupture were measured for a series of 0.98Li2O‐1.0ALO3‐nSiO2 glasses and the corresponding keatite solid‐solution‐phase glass‐ceramics. The SiO2 content ranged from n=4 to 12. The magnitude of the elastic properties of the glasses changed monotonically with increasing SiO2 content. The properties of keatite‐phase glass‐ceramics depended almost linearly on SiO2 content, but their behavior differed qualitatively from that of the glasses.
Deformation of Hyperstoichiometric UO2 Single Crystals
Authors: YUST C. S. , McHARGUE C. J.
Published: June 2006

Hyperstoichiometric UO2 single crystals having O/M ratios from 2.06 to 2.10 were deformed in compression. The active slip plane for deformation, as evaluated from slip traces, has an orientation between (112) and (111). The critical resolved shear stresses for hyperstoichiometric specimens are approximately the same as those for stoichiometric specimens; the dislocation structures, as revealed by transmission electron microscopy, however, are very different and suggest more rapid motion and/or climb of dislocations in the hyperstoichiometric samples. The response to strain rate changes during deformation also reflects the difference in deformation behavior of hyperstoichiometric and stoichiometric crystals.
Alkaline‐Earth‐Fluoride—LaF3 Systems with Implications for Electroslag Melting
Authors: NAFZIGER R. H. , RIAZANCE N.
Published: June 2006

Liquidus and solidus curves in the systems CaF2‐LaF3, SrF2‐LaF3, BaF2‐LaF3, and MgF2‐LaF3 under ½ atm helium pressure were determined by thermal analysis as an aid in the selection of suitable fluxes for electroslag melting of reactive metals. The systems CaF2‐LaF3, SrF2‐LaF3, and BaF2‐LaF3 each contain (1) one eutectic, (2) no intermediate phases, and (3) two solid solutions whose lattice parameters vary linearly with composition. The liquidus curves in the systems SrF2‐LaF3 and BaF2‐LaF3 exhibit maxima. The system MgF2‐LaF3 is of the simple eutectic type with no detectable terminal solid solutions. The smallest temperature interval observed between a fluoride‐flux liquidus and the melting point of Ti occurs at the dystectic composition in the system SrF2‐LaF3. Differences in density between metal and flux are more favorable in the system BaF2‐LaF3 than in pure LaF3. These observations suggest potential advantages of using fluxes from the systems studied for electroslag melting of reactive metals.
Grain Growth in Very Porous Al2O3 Compacts
Authors: GRESKOVICH C. , LAY K. W.
Published: June 2006

Extensive grain growth was observed by scanning electron microscopy in very porous Al2O3 compacts, even at densities <40% of theoretical. After ∼7% shrinkage at 1700°C, the grain size increased from ∼0.3 to 0.51 μm in a compact having a relative green density of 0.31. During grain growth in highly porous compacts, the grains appear initially to be chainlike, then to be oblong, and finally to be equiaxed. The proposed mechanism of initial grain growth involves the filling of necks between adjacent grains followed by the movement of the grain boundary through the smaller grain. Although grain growth in very porous compacts is quite different from coalescence and ordinary grain growth, the kinetics are similar.