bluuebunny/crossref_metadata_2025 huggingface dataset:
Grain‐Boundary Diffusion in MgO
Authors: WUENSCH B. J. , VASILOS T.
Published: June 2006

Grain‐boundary diffusion of Ni2+ was investigated in polycrystalline MgO and also in isolated grain boundaries in natural and prepared bi‐crystals of MgO. Concentration distributions were determined with the aid of both electron microbeam probe spectroscopy and X‐ray absorption analysis. Results from diffusion couples in which a surface was maintained at constant concentration during the diffusion annealing indicate that grain‐boundary diffusion is the predominant transport mechanism in polycrystalline MgO at temperatures below 1700°C. Lattice diffusion becomes increasingly important at higher temperatures and eventually becomes the dominant mechanism. Concentration distributions for diffusion couples in which a fixed amount of NiO was supplied to the surface of the couple as a thin initial plating resemble those for lattice diffusion but yield anomalously high values for apparent lattice diffusion coefficients. Grain‐boundary diffusion in MgO is not confined to a layer of atomic dimensions but extends over a zone of the order of microns. The activation energy for grain‐boundary diffusion is less than that for lattice diffusion and is between 1 and 2 ev. Grain‐boundary diffusion was observed even in tilt boundaries with a mismatch as low as 6°.
Thermal Conductivity of Titanium Carbide, Zirconium Carbide, and Titanium Nitride at High Temperatures
Authors: TAYLOR R. E. , MORREALE J.
Published: June 2006

The thermal conductivity of titanium carbide, zirconium carbide, and titanium nitride was measured by a variety of techniques in the temperature range 200° to 2000° C. The titanium nitride results are a factor of four higher than the previously published values at 1000°C and show a positive temperature coefficient for the thermal conductivity rather than the negative coefficient previously reported in other work. Recent thermal conductivity data on Tic confirm earlier data obtained by the writers which differed from previous literature values. Contemporary theory fails to explain the temperature dependency of the phonon and/or electron contribution to the heat conduction in the refractory interstitial compounds.
Metastable Ferroelectric Sodium Niobate
Authors: DUNGAN R. H. , GOLDING R. D.
Published: June 2006

Properties of a metastable ferroelectric NaNbOa phase are described. This ferroelectric phase was induced by the application of a field greater than 50 kv per cm at a temperature in excess of 100°C. The ferroelectric state was evidenced by a spontaneous polarization of the order of 30 microcoulombs per cm2 and by fairly strong piezoelectric coupling. The ferroelectric phase, once induced, was stable with time and up to 270° C.
Nonmagnetic Inclusions in Ferrites for High‐speed Switching
Authors: BABA PAUL D.
Published: June 2006

A technique is described for obtaining fast switching in square‐loop ferrites. Domain wall motion is inhibited by addition of nonmagnetic inclusions such as thorium oxide and palladium. The magnetization is then reversed by the faster nonuniform rotational mode of switching. Coincident current switching times as low as 0.10‐μsec were measured for samples containing inclusions. A control sample of the same composition, but without inclusions, had a switching time of 0.85μsec. This technique improved the stability of ferrite properties with respect to firing time and temperature and the presence of reactive impurities. For example, the coercive force varied by no more than ±2% within a 4‐hour range of firing times and only ±6% variation was noted for a 50°C range of firing temperatures. A similar stabilizing effect occurred when inclusions were added to a ferrite containing 0.03 at.% calcium, a reactive impurity.
Magnetic Properties of Gadolinium‐Yttrium‐Iron‐Indium Garnets
Authors: MAGUIRE E. A. , GREEN J. J.
Published: June 2006

Polycrystalline garnets with the general composition Gd3‐xYxFe5‐yInuO12 were investigated. Ferrimagnetic resonance line widths at S‐ and X‐bands and saturation induction are reported. The temperature dependence of the magnetization was determined on materials in which x= 0 to 3 and y = 0 to 1. Special emphasis is given to compositions having relatively stable magnetizations over the range 20° to 100°C.
Infrared Properties of Magnesium Oxide
Authors: HANNA RINOUD
Published: June 2006

The absorption spectrum of polycrystalline and single‐crystal magnesium oxide was determined in the 4000 to 166 cm−1 spectral region. In the range 4000 to about 1100 cm−1, the absorption coefficient of the polycrystalline MgO was higher than that of the single‐crystal MgO owing to scattering by the grain boundaries. This scattering decreased with increase of the grain diameter. No difference in reflectivity could be detected between the polycrystalline and single‐crystal material in the 4000 to 300 cm−lwave number region. The optical constants, n and k, were determined by the classical dispersion theory, assuming a single oscillator. From the maximum reflectivity, the resonance frequency was at 428 cm−1; the value obtained from the acoustical vibration was at 475 cm−1. The corresponding s factors were 0.64 and 0.72, respectively.
High‐Temperature Oxidation of Molybdenum Disilicide
Authors: WIRKUS C. D. , WILDER D. R.
Published: June 2006

The oxidation of MoSi2in air at atmospheric pressure was studied by electron diffraction, X‐ray diffraction, and thermogravimetric analyses. The oxidation process occurs in two parts: (1) formation of MoO3and SiO2at temperatures below the boiling point of MoO3, and (2) formation of Mo5Si3and SiO2at higher temperatures. Evidence is presented which indicates that oxygen permeation through a silica layer, which may be of a mixed crystalline‐glassy nature, controls reaction rate at high temperatures and that Mo5Si3is present directly beneath the protective oxide. The activation energy for oxidation of MoSi2above 1200°C was calculated as 81.3 kcal mole−1.
General Fracture Method for Preparation of Foils for Transmission Electron Microscopy
Authors: HULSE C. O. , TICE W. K.
Published: June 2006

A mechanism for crack propagation is presented to explain the production of thin foils when a brittle material fractures. A general technique for continuing this process and collecting the foils for electron microscopy is described. This method has been successful with every material examined, although there was considerable variation in the number and sizes of foils produced. The materials studied include single‐crystal MgO, LiF, twinned KAlSi3O8 (microcline), CaCO3, Ge, Si, Zn, MgAl2O4, Al2O3, and glasses, and the polycrystalline materials SiC, talc, MgO, and Al2O3 all in order of relative success. A brief review of other electron transmission sample preparation methods is included with special reference to those most similar to the method described herein.
Electronic Conductivity of Calcia‐Stabilized Zirconia
Authors: KRÖGER F. A.
Published: June 2006

The promotion of n‐type electronic conduction by relatively small concentrations of donors in the presence of a large concentration of calcium, which is an acceptor, is explained by assuming that most of the calcium is present as neutral calcium ion‐oxygen vacancy pairs or clusters. Evaluation of experimental data on the basis of this model leads to an enthalpy of pairing of calcium ions with oxygen ion vacancies of –2.7 ev.
Thermal Decomposition of Brucite: II, Kinetics of Decomposition in Vacuum
Authors: GORDON RONALD S. , KINGERY W. D.
Published: June 2006

Polycrystalline samples, thin single crystals, and—325 mesh powders of brucite decomposed according to a first‐order rate equation consistent with a random nucleation process in beds of micron‐sized particles formed by disruption during the very early stages of the process and consistent with electron and optical microscope observations. Kinetic data for the decomposition of thick single crystals were more complex but could be fitted to an interface‐model equation which predicts that decomposition will be controlled by the movement of an interface reaction along the basal plane. Physical disruption of these crystals was confined initially to the outer edges of the crystals and proceeded along the basal plane in the form of a contracting disk. Since the decomposition occurs in cracked material and not at a strict interface, the fit of the data to the interface model may be fortuitous.
Sintering Kinetics Study Using Reduced Variables
Authors: MARLOWE M. O. , WILDER D. R.
Published: June 2006

Assuming that a temperature‐dependent endpoint density occurs in the sintering process, a scheme for describing the progress of sintering is developed using reduced variables. A sine function is given to describe the path. Experimental results from the literature are compared to this function for calcium fluoride, glass, thorium oxide, aluminum oxide, and copper, and for magnesium oxide with a eutectic addition. New results are presented and compared for yttrium oxide, erbium oxide, dysprosium oxide, and aluminum oxide. The correlation between the data and the sine function is very high. Apparent activation energies are given.
Equilibrium Oxygen Pressures Over Solid Solutions of Urania‐Yttria and Urania‐Lanthana at 1100° to 14OO°C
Authors: HAGEMARK K. , BROLI M.
Published: June 2006

Using a thermobalance, the oxygen content of urania containing small amounts of yttria or lanthana was determined as a function of the oxygen partial pressure at 1100° to 1400°C. Values for the partial free enthalpy, the partial enthalpy, and partial entropy of oxygen were calculated. Equilibrium oxygen pressures over the solid solutions (U, Y, or La)O2+x were higher than for pure UO2+X. Both the partial enthalpy and partial entropy of oxygen decreased with the addition of yttrium and lanthanum, the change being larger in the latter case. The effects observed experimentally are discussed on the basis of differences in charge and size of the foreign cation relative to the uranium ion.
Effect of Stress on Durability of Ion‐Exchanged Surfaces
Authors: ROTHERMEL DAPHNE L.
Published: June 2006

The leachability of ion‐exchanged alkali alumino‐silicate glasses in water and in acid was shown to be a function of the stress at the surface. Alkali aluminosilicate glasses formed by ion exchange under conditions resulting in surface compression were more durable than similar unstressed alkali aluminosilicate glasses melted from batch. Conditions which produced incomplete exchange at the surface, resulting in lower compressive surface stresses, led to a less durable glass surface. Where potassium from a salt bath was being exchanged for sodium in the glass, leachability was inversely proportional to the percent surface exchange.
Hertzian Stress Cracks in Beryllia and Glass
Authors: TURNER D. N. , SMITH P. D. , ROTSEY W. B.
Published: June 2006

The effect of Hertzian stresses resulting from loads acting at the points of contact of beryllia spheres was determined. As‐drawn glass and glass ground with various grades of silicon carbide were indented with beryllia spheres, 1 in. in diameter. Also, pairs of these beryllia spheres were pressed together. Circular cracks due to Hertzian stresses were produced; an optical technique was developed for detecting them in a beryllia surface. The outer crack radius was proportional to the cube root of the maximum applied load. Average values obtained for the respective inner crack radii were used to determine average values of the minimum load to fracture these materials. The average minimum load to fracture 1 in. diameter beryllia spheres in air at room temperature under dynamic loading was 235 1b. The crack radius in glass and beryllia was about 20% greater than the radius of the contact surface. This was not significantly affected (in glass) by flaw density. It is considered that the Hertz analysis does not give the correct location and value of the maximum tensile stress when finite displacements of material occur.
Sintering Study in the Partially Vitreous As‐S‐Se System
Authors: CARRELL M. A. , WILDER D. R.
Published: June 2006

A study of sintering of vitreous As‐S‐Se spheres has indicated relations concerning the viscous flow mechanism. Sphere‐sphere geometric models are proposed to relate surface area to the sintering rate; one such model accurately describes the relation observed. In sphere‐sphere sintering, the slope of the logarithm of the ratio of neck radius to the initial radius plotted against the logarithm of time is compositionally dependent Three types of internal structure are suggested in order of increasing arsenic content: (a) a system of chains and rings with arsenic “pinning points,” (b) trigonal As(S,Se)3 elements bound together by Se‐Se, Se‐S, and/or S‐S linkages, and (c) a dense network of entirely As‐S and/or As‐Se linkages. When the ratio of surface area to final equilibrium surface area was plotted against time of sintering, the relation was linear. This indicates a constant dissipation of internal energy by a flow process. Deviation from this linear relation exists for structures involving ring and long chain configurations at viscosities above approximately 107.5 poises, suggesting the presence of non‐viscous properties. A linear shrinkage equation was obtained for compositions where slopes of logarithm of the ratio of neck radius to the initial radius plotted against the logarithm of time of sintering were greater than 0.5.
Crystallite Size Measurements on Thoria Gel
Authors: BANNISTER M. J.
Published: June 2006

As part of a detailed study of the sintering behavior of thoria gel, the crystallite size distribution in the gel was measured by electron microscopy. The distribution is in quantitative agreement with BET surface area and X‐ray crystallite size measurement, and X‐ray diffraction line profiles calculated using the measured size distribution agree with experiment. The relative accuracies of the integral and half‐maximum intensity breadth techniques, and the relation between the size distribution and the crystallite size measured by each technique are discussed. Some implications of this work to the sintering study are mentioned.
Strengthening of Sapphire by Precipitates Containing Titanium
Authors: HSU S. E. , KOBES W. , FINE M. E.
Published: June 2006

Sapphire single crystals alloyed with 0.5 cation % Ti and aged at 1500° C to form a precipitate showed considerable increase in hardness and fracture strength over unalloyed sapphire. It is suggested that propagation of a crack requires local plastic deformation and that precipitate particles interfere with local plastic deformation.
Chemically Strengthened, Leached Alumina and Spinel
Authors: KIRCHNER HENRY P. , GRUVER ROBERT M. , WALKER RALPH E.
Published: June 2006

Low‐expansion solid solution surface layers formed by chemical reactions at high temperatures were used to chemically strengthen alumina and spinel bodies. Solid solutions in the system Al2O3‐Cr2O3 strengthened alumina, and solid solutions in the system MgO·Al2O3‐MgO·Cr2O3 strengthened spinel. Prior treatments with aqueous hydrofluoric acid were used to remove intergranular material and increase the thickness of the solid solution layers. The relative compressive stresses, distribution of the flexural strengths, and thermal shock resistance of the strengthened materials were investigated.
Effect of Temperature and Oxygen Partial Pressure on the Oxidation of Titanium Carbide
Authors: STEWART READ W. , CUTLER IVAN B.
Published: June 2006

The oxidation of powdered titanium carbide was followed by weight gain measurement, using a thermogravimetric apparatus, between 600° and 850°C. The oxygen partial pressure effect was investigated between 6.5 and 645 mm Hg. The oxidation was parabolic with an activation energy of 46 ± 2 kcal/mole which was essentially independent of the overpressure. The rate of oxidation was dependent onpo2¼ below approximately 800°C. Above this temperature the rate was proportional topo2¼. The oxidation of single‐crystal TiC above 850° C produced porous rutile films. The rates of oxidation were between linear and parabolic time dependence.
Electrical Properties and Defect Structure of a (0.13YO1.5·0.87ThO2) Electrolyte
Authors: WIMMER J. M. , BIDWELL L. R. , TALLAN N. M.
Published: June 2006

High‐density sintered disks of the composition 0.13YO1.5·0.87ThO2 are shown to be mixed conductors at high oxygen pressures (>10−6 atm) by electrical conductivity and electrochemical cell measurements. The ac and dc conductivity measurements were made between 900° and 1600°C over a wide range of oxygen partial pressures. A blocking‐electrode polarization technique for determining transference numbers was not applicable at high oxygen pressures but appeared to work at the lower pressures, indicating a transition to n‐type behavior. The electrochemical cell measurements show essentially completely ionic behavior at low oxygen pressure but indicate at least 0.1% electronic contribution at 10−13 atm at 1000°C. The lower oxygen pressure limit for completely ionic behavior has not been determined but extends below the equilibrium pressures of an Mn‐MnO2, Cr‐Cr2O3 electrochemical cell at 1000°C.
Oxidation Kinetics of Participate Silicon Monoxide
Authors: PULTZ W. W. , HERTL W.
Published: June 2006

The air oxidation of particulate silicon monoxide to cristobalite was studied in the range 820° to 1040°C. This SiO neither disproportionates nor volatilizes in this range. An activation energy of 23.8 ± 2.0 kcal/mole for the diffusion of oxygen was obtained from a measure of the differential rate of reaction at various temperatures for various fixed percents of conversion up to 24%. The reciprocal time needed to reach a fixed percent of conversion up to 30%, at various temperatures, gave an activation energy of 24.2 ± 1.5 kcal/mole. It is concluded that the diffusional activation energy is 24.0 ± 2.0 kcal/mole.
Activity‐Composition Relations in Orthosilicate and Metasilicate Solid Solutions in the System MnO‐CoO‐SiO2
Authors: BIGGERS J. V. , MUAN ARNULF
Published: June 2006

Activity‐composition relations in Mn‐Co orthosilicate and metasilicate solid solutions were determined at 1200° to 1250°C by equilibrating selected phase assemblages with metallic cobalt and a gas phase of known oxygen potentials at a total pressure of 1 atm. The orthosilicate solid solution shows a slight negative departure from ideality, whereas the metasilicate solid solution is ideal. The stability data derived for the Mn2SiO4 and MnSiO3 end‐members are in good agreement with those previously determined from the system MnO‐“FeO”‐SiO2. The free‐energy change for the reaction 2CoSiO3= Co2‐SiO4+ SiO2 was determined to be ‐3.8 kcal at 1250°C.
Decomposition Kinetics of CaYb2O4
Authors: BARRY THOMAS L. , STUBICAN V. S. , ROY RUSTUM
Published: June 2006

The kinetics of decomposition of CaYb2O4 were studied using quantitative analysis by X‐ray diffraction methods and a modified method of “standard binary mixtures.” This type of method was required as total composition remained constant with only the phase assemblage changing. The experimental factors considered in obtaining meaningful results from such a procedure are covered. The linearity of the fraction decomposed or concentration unreacted versus time curves at various temperatures revealed that the decomposition proceeded according to “zero‐order” kinetics. The activation energy for this process was 100 kcal/mole.
Effect of Adsorbed Water on the Spreading of Organic Liquids on Soda‐Lime Glass
Authors: SHAFRIN ELAINE G. , ZISMAN W. A.
Published: June 2006

The spreading behavior and equilibrium contact angle, θ, of organic liquids on soda‐lime glass surfaces were observed at relative humidities (rh) varying from 1 to 95%. Increasing rh increased θ for many nonhydrophilic liquids on glass; no comparable effects occurred with nonadsorptive solid surfaces. The decrease in wettability of the glass with increasing rh resulted from the physical adsorption of a surface layer of water molecules sufficient to convert the normally high‐energy glass surface into one that behaves as a low‐energy surface, i.e. a surface with a low critical surface tension for spreading, γc, toward nonhydrophilic liquids. As the thickness of the adsorbed water layer increased, glass behaved like a surface with progressively decreasing γc, approaching that of bulk water. These results are discussed in relation to the effect of moisture on the spreading or adhesion of resins to glass and other hydrophilic solids.
Ionic Equilibria in Liquid Silicates
Authors: MASSON C. R.
Published: June 2006

Liquid silicates, in common with phosphates and probably other oxygen‐containing inorganic polymers which are stable at high temperatures, contain in general a multitude of anionic species ranging in size and complexity from simple “monomeric” groupings such as SiO44− and P043− to continuous, cross‐linked networks of infinite molecular weight. The average size and distribution of these species in binary systems may be inferred, at least approximately, from thermodynamic data in combination with polymer theory on the assumption that the activity coefficients of the constituents are arrayed in geometric series. This is equivalent to assuming ideal mixing of polymeric segments. As anticipated, deviations from the theory become significant at the gel point, which varies with the nature of the cation. The significance of these concepts in relation to the constitution of glasses is discussed. In particular, it is indicated that a glass may consist of sol and gel portions, the complexity and relative proportions of which vary with the nature of the cation and the silica content. In theory, the ion SiO44− is the most abundant single species of discrete silicate ion at all silica contents.
Viscous Relaxation and Non‐Arrhenius Behavior in B2O3
Authors: TAUKE J. , LITOVITZ T. A. , MACEDO P. B.
Published: June 2006

Ultrasonic shear and longitudinal measurements were made in Bz03 from 650° to 1000° C. From these data both the shear and volume relaxation time spectra were determined. The spectra had the same temperature dependence, although the volume spectrum was always broader than the shear spectrum. The shear relaxation process can be represented by a single relaxation time above 800° C in the region where the shear viscosity is Arrhenius. Both processes exhibit an increasingly broad distribution of relaxation times in the non‐Arrhenius region. The temperature dependence of the shear spectrum was analyzed in terms of a distribution of activation energies. A surprising conclusion of this study is that activation energies at low temperatures are smaller than the activation energy in the Arrhenius region.
Piezoelectric Properties and Phase Relations of Pb(Mg1/3Nb2/3)O3‐PbTiO3−PbZrO3 Ceramics with Barium or Strontium Substitutions
Authors: OUCHI HIROMU
Published: June 2006

When a small amount of Ba or Sr is substituted for Pb in Pb(Mg1/3 Nb2/3)O3‐PbTiO3‐Pb2rO3, the morphotropic boundary and the compositions which show the highest planar coupling coefficient and dielectric constant shift slightly toward the decreasing PbTiO3 content. The tetragonality of Pb(Mg1/3Nb2/3)O3‐PbTiO3 and Pb(Mg1/2 Nb2/3)‐O3‐PbTiO3‐PbZrO3 ceramics decreased with increasing Ba or Sr content. The lattice parameter (α axis) in the rhombohedral or pseudocubic phase increased with the increase of Ba but decreased with the increase of Sr substitution. Although the Curie temperature was lowered with the increase of Ba or Sr, the dielectric constants of the ceramics were increased. The dielectric and piezoelectric properties of the ternary compositions near the morphotropic boundary were improved through selection of sub‐stituent and base composition. A planar coupling coefficient of 0.66 and a low Young's modulus were obtained with substitution of 5 mole % Ba. A dielectric constant greater than 3500 and a planar coupling of 0.63 can be obtained by substituting 5 mole % Sr.
Phase Equilibrium in the System CrO2‐Cr2O3
Authors: FUKUNAGA OSAMU , SAITO SHINROKU
Published: June 2006

The CrO2‐Cr, O3 equilibrium curve has been determined up to 35 kbars and 1400° C with a piston‐cylinder apparatus. The phases were determined by magnetic, X‐ray, and microscopic examination. The phase boundary can be represented by a straight line log P versus 1/T plot, where log P= 5.3 ‐ 1400/T. These results can be extrapolated to agree reasonably well with the results of previous investigations using gas pressure techniques.
Graphitic Materials Hot‐Worked with a Dispersed Liquid Carbide: Thermal and Electrical Conductivity
Authors: WHITE J. L. , KOYAMA K.
Published: June 2006

Graphitic materials produced by hot‐working with a dispersed liquid‐carbide phase (termed HWLC graphites) have high thermal and electrical conductivities compared with hot‐worked or conventional graphites prepared without additives. Thermal diffusivity and electrical conductivity were measured at room temperature on two HWLC materials containing either molybdenum carbide or zirconium carbide. This process of liquid‐phase sintering with compressive deformation imposes a strong preferred orientation on the predominantly graphitic material, and the resulting thermal conductivity in the preferred direction of the layer planes is greater than the thermal conductivity of copper or silver. Thus, liquid‐phase stress sintering induces in graphitic materials an essentially new microstructure that provides a means of realizing the inherent high thermal conductivity of the graphite layer plane in a massive body.
Preparation of High‐Purity Submicron Barium Titanate Powders
Authors: MAZDIYASNI K. S. , DOLLOFF R. T. , SMITH J. S.
Published: June 2006

Simultaneous hydrolytic decomposition of barium bis isopropoxide and titanium tetrakis tertiary amyloxide was used to produce stoichiometric BaTiO3. The particle size range was 50 to 150 Å. The purity was 99.98+%, the major contaminant being silicon from the glass apparatus. The homogeneity and stoichiometry of the powder were demonstrated by electron microscopy and wet chemical analysis. X‐ray and infrared analyses indicate that the material, as‐prepared and helium‐dried at 5O°C, has the titanate crystal structure. The powder sinters at 1300°C to a high density, translucent body with a uniform microstructure. The experiments suggest that the alkoxy‐based preparation of oxides may provide a broad base for improving the quality and reproducibility of electrical and structural ceramics.
Phase Relations in Refractory Metal‐Oxygen Systems
Authors: CHANG LUKE L. Y. , PHILLIPS BERT
Published: June 2006

Phases and phase relations in the tungsten‐oxygen, molybdenum‐oxygen, tantalum‐oxygen, and niobium‐oxygen systems are reviewed.
Optimization of Properties of Photoconductive Oxide Glasses
Authors: ČÁSLAVSKÁ V. , STRICKLER D. W. , ROY RUSTUM
Published: June 2006

Using as a base the Cd0‐B2O3‐Si02 photoconducting glass previously found, various systematic substitutions and additions were made to determine their influence on the photoresponse of these glasses. Complete substitution of GeO2 for SiO2 led to the highest photocurrents observed in these glasses and to a shift of the spectral response into the visible region.
Annealing of Irradiation‐Induced Thermal Conductivity Changes in ThO2‐1.3 wt% UO2
Authors: MACEWAN J. R. , STOUTE R. L.
Published: June 2006

The thermal conductivities of sintered pellets of ThO2‐1.3 wt% U02 were measured at 60°C before and after irradiation. The irradiation temperature was below 156°C, and the exposures varied from 3.1 × 1014 to 4.7 × loL7 fissions/cm3. Each fission fragment damaged a region of 2.2 × 10‐16 cm3 with the reduction in conductivity saturating by about 1017 fissions/cm3. Samples having exposures from 1015 to 1016 fissions/cm3 were annealed isothermally at 651 °C or isochronally from 300° to 1200° C to study the annealing of damage. Most of the annealing occurred between 500° and 900°C. The width of this interval plus the slow isothermal annealing suggest that the damage is annealed by a number of single order processes with a spectrum of activation energies from 1.8 to 3.9 eV or, less probably, by a high order process with an activation energy of 3.55 ± 0.4 eV.
Mechanical Relaxations in Mixed‐Alkali Silicate Glasses: I, Results
Authors: Shelby James E. , Day Delbert E.
Published: June 2006

The internal friction of silicate glasses containing mixtures of Li‐Na, Li‐K, Li‐Rb, Li‐Cs, Na‐K, Na‐Rb, Na‐Cs, and K‐Rb was measured from ‐180° to 500°C at a frequency of 0.4 Hz. Values for the density, index of refraction, and dynamic shear modulus are also reported. With small additions of a second alkali, a new internal friction peak was observed in addition to the two peaks originally present in the glasses containing only one alkali. The magnitude of this new peak was especially sensitive to small amounts (less than 1 mol%) of a second alkali. Activation energies are given for the alkali peak in Li‐Cs glasses and for the new internal friction peak in Li‐Na glasses.
Time and Length Corrections in the Analysis of the Initial Stages of Diffusion‐Controlled Sintering
Authors: LAY K. W. , CARTER R. E.
Published: June 2006

All models of the initial stages of sintering assume instantaneous heating of the shrinkage specimens to the sintering temperature. However, the time to reach the sintering temperature and the accompanying shrinkage can seriously affect the apparent shrinkage‐time dependence that is used to identify the shrinkage mechanism. The thermal expansion of unsintered compacts is shown to be identical with that calculated from published thermal expansion coefficients. The correct initial hot length of a shrinkage compact is therefore the cold length corrected for thermal expansion. The time to heat a shrinkage specimen was measured and is identical with both the calculated heating time and that determined by extrapolating a length vs. time plot to the initial hot length. The length and time corrections obtained from this extrapolation are compared with those obtained by the methods of Johnson and Cutler and of Anderson.
Development of Noncrystalline Material in Subsolidus Reactions Between Silica and Alumina
Authors: STALEY W. G. , BRINDLEY G. W.
Published: June 2006

Reactions between corundum and cristobalite in mixed powders and at interfaces between sintered pellets at 1500°C and in various forms of reaction couples at 1550°C were studied by quantitative X‐ray diffraction, electron microprobe analysis, and optical microscopy. The results indicate that a noncrystalline product is an important transitional phase in reactions under subsolidus conditions. When corundum is used as a coarse powder (particle size 20 to 30 μm), the amount of noncrystalline material produced can be as much as 30 to 40% of the total reactants, and the amount of mullite is correspondingly small. When corundum is used as a single crystal, the development of a noncrystalline phase is notably increased. Microprobe analyses of coarse powders reacted at 1500°C show a noncrystalline phase of the approximate composition Al2O3·12SiO2. Calculations based on the X‐ray analyses indicate a higher proportion of alumina in the noncrystalline material, and it is suggested that alumina‐rich zones may form adjacent the corundum surfaces where they are not resolved in the microprobe analysis.
Kinetics of Zircon Synthesis
Authors: RAMANI S. V. , SUBBARAO E. C. , GOWHALE K. V. G. M.
Published: June 2006

The synthesis of zircon from ZrO2and SiO2at fixed temperatures from 1200° to 1400°C was studied as a function of time up to 16 h. Quantitative X‐ray diffraction was used to estimate the phases in the product. Quartz transforms to cristobalite through an amorphous transitional phase. Assuming a homogeneous reaction model, analog computer simulation of reactions was used to determine the rate constants at different temperatures. In the temperature range studied, the transitional phase is the most reactive form of silica in zircon synthesis, followed by cristobalite.
Thermal Conductivity of Transition Metal Carbides
Authors: RADOSEVICH L. G. , WILLIAMS WENDELL S.
Published: June 2006

Previous measurements of the thermal conductivity of TiC, ZrC, and NbC by the present authors showed that at low temperatures the phonon‐electron scattering in these materials is strong and gives rise to an unusual temperature dependence of the lattice thermal conductivity. The Callaway analysis of those data is now extended to include the high‐temperature data of Taylor for TiC. The analysis of the thermal conductivity of TiC from 2° to 2000°K indicates that: (1) For samples with higher carbon contents, it is necessary to modify the phonon‐electron relaxation rate at low temperatures and (2) a strong point‐defect scattering term is required to explain the high‐temperature data. This scattering is due primarily to force‐constant changes rather than mass changes which are introduced by the presence of vacancies.
Phase Separation in Borosilicate Glasses as Seen by Electron Microscopy and Scanning Electron Microscopy
Authors: ELMER T. H. , NORDBERG M. E. , CARRIER G. B. , KORDA E. J.
Published: June 2006

Microstructures of two sodium borosilicate glasses were examined. Electron micrographs of replicas of water‐etched fracture surfaces show that the microphases increase in size with the temperature and time of heat treatment. The relative amounts of soluble and insoluble microphases remain essentially unchanged. Scanning electron micrographs of completely leached glasses show that the insoluble phase is randomly interconnected. Scanning electron micrographs of colloidal deposits in the pores of the leached glass, which result from acid leaching of the heat‐treated base glass, are shown. Electron micrographs showing re‐solution of the phases are also included.
Deformation and Fracture of MnTe and MnSe‐MnTe Solid Solutions
Authors: RIEWALD PAUL G. , VAN VLACK LAWRENCE H.
Published: June 2006

Single crystals of MnTe and solid solutions in the system MnSe‐MnTe were prepared; selected surfaces were indented with either a Vickers or a Knoop microindenter. Information on mechanical behavior was obtained by observation of slip traces and by study of Knoop hardness anisotropy. Hexagonal NiAs‐type MnTe and MnTe‐rich Mn(Te,Se) solid solutions show plastic deformation attributable to {1012} twinning, basal slip, and pencil glide in 〈1120〉. Fracture occurs as primary {0001} and secondary {1010} cleavage. Vickers and Knoop hardnesses were greater on the basal plane than on prism planes. Cubic MnSe‐rich Mn(Te,Se) solid solutions show both {111}〈110〉 and {110}〈110〉 slip with {100} and {110} fracture in crushed fragments and around surface indentations. Knoop hardness anisotropy is like that in MnSe. The rate of solid solution hardening is greater than for comparable substitutions of sulfide ions in the MnSe matrix.
Sublimation Coefficient of Tin Selenide
Authors: BLAIR R. C. , MUNIR Z. A.
Published: June 2006

Free‐surface and equilibrium sublimation pressure measurements indicate that the sublimation coefficient of tin selenide is essentially 1 from 726° to 975°K. Torsion‐Langmuir measurements from 726° to 879°K gave the following expression for the free‐surface pressure: log P (atm) = (7.021°0.161)‐(1.036°0.013)104/T. The third‐law heat of sublimation calculated from these results was 51.5±0.3 kcal/mol SnSe. Similar treatment of the equilibrium pressures obtained by the torsion‐effusion method from 789° to 975°K gave the following least‐squares expression: log P (atm) = (7.473±0.133)‐(1.069±0.012) 104/T. The third‐law ΔH208 was 52.8±0.5 kcal/mol.
Effects of Lithium and Oxygen Losses on Magnetic and Crystallographic Properties of Spinel Lithium Ferrite
Authors: RIDGLEY D. H. , LESSOFF H. , CHILDRESS J. D.
Published: June 2006

The effects of sintering temperature and cooling rate on the magnetic and crystallographic properties of lithium ferrite were studied. The magnetic moments and lattice parameters increased with increasing sintering temperature; these increases result from correlated oxygen and lithium oxide losses. Either annealing at lower temperatures or slow cooling under O2 causes reoxidation of the Fe2+ formed at higher temperatures with attendant decreases in moment and lattice parameter and gradual precipitation of α‐Fe2O3 as a second phase. The products formed on rapid cooling are equivalent to solid solutions of spinel lithium ferrite with Fe3O4, and those formed on slow cooling, to solid solutions of lithium ferrite and γ‐Fe2O3 with precipitation of α‐Fe2O3. Lithium losses and α‐Fe2O3 precipitate amounts are calculated. The magnetic moment of stoichiometric lithium ferrite at 25°C is 3736±20 G; the lattice parameter at 28°C is 8.3296±0.0005 Å.
Analysis of Complex ESR Spectra Induced in Potassium Borate Glasses
Authors: ARAFA S. , BISHAY A.
Published: June 2006

Electron spin resonance studies showed that gamma‐irradiated potassium borate glasses display complex spectra. These were resolved into five overlapping resonances by a thermal bleaching technique. The resonances differ in nature and stability, suggesting that they belong to different paramagnetic centers (I, II, III, IV, and V) induced by irradiation. The relative concentrations of these centers change with K2O concentration; the stability increases in the order V<I<II<III<IV. The measured g values for these centers were: (I) g1⋍2.002, g2⋍2.010, g3⋍2.034; (II) gavg⋍2.0087; (III) g⋍2.008; (IV) g⋍2.002; and (V) g⋍2.000. These values suggest that centers I, II, and III may be caused by trapped‐hole centers, whereas centers IV and V are attributed to trapped electron centers. Centers I and II have hyperfine structures with an 11B nucleus producing a five‐line‐plus‐a‐shoulder spectrum and a four‐line spectrum, respectively. The resonance attributed to center V was very weak and was observed only in glasses which contained more than 20 mol% K2O.
Dielectric Aging in Tetragonal Solid Solutions of Calcium Titanate in Barium Titanate
Authors: COHEN A. , BRADT R. C. , ANSELL G. S.
Published: June 2006

The dielectric aging phenomenon was observed in tetragonal polycrystalline solid solutions of calcium titanate in barium titanate between 30° and 90°C, and the 90° ferroelectric domain microstructures were analyzed using replica electron microscopy and statistical procedures. The results show a correlation between aging rate and 90° domains that may be satisfactorily interpreted in terms of the internal residual stress relaxation theory of aging.
Effect of Small Amounts of Porosity on Grain Growth in Hot‐Pressed Magnesium Oxide and Magnesiowustite
Authors: GORDON R. S. , MARCHANT D. D. , HOLLENBERG G. W.
Published: June 2006

Grain growth was studied at 1300°, 1400°, and 1500°C in nearly theoretically dense (0.1 to 0.8% porosity) hot‐pressed magnesium oxide (99.99+%) and magnesiowustite (0.10 and 0.48 wt% Fe2O3). Small amounts of porosity had large effects on the kinetics of grain growth. Grain growth is probably porosity‐controlled in MgO at all temperatures and in magnesiowustite at 1400° and 1500°C if pores remain on grain boundaries or at grain intersections. The tendency for the entrapment of porosity is enhanced as the temperature is increased and as the dopant (Fe2O8) concentration is decreased. Small amounts of porosity (<1%) can cause limiting growth situations at grain sizes well below 100 μm. The Fe2O3 dopant stabilizes squared grain growth kinetics at 1300°C and decreases the rate of grain growth at all three temperatures.
Boron Coordination in PbO.2B2O3 and BaO·2B2O3 Melts
Authors: LAIRD J. A. , BERGERON C. G.
Published: June 2006

A partial molar volume technique was used to estimate the coordination number of oxygen ions around a boron ion in PbO·2B2O3 and BaO·2B2O3 melts. The boron coordination number appeared to be lower in the melt than in the crystal of PbO·2B2O3, whereas it was nearly the same in the melt and crystal of BaO·2B2O3.
Studies in the System BaO‐Al2O3−SiO2: VI, The System Celsian‐Silica‐Alumina *
Authors: SEMLER C. E. , FOSTER W. R.
Published: June 2006

Phase equilibrium relations in the celsian‐silica‐alumina portion of the system BaO‐Al2O3−SiO2 were revised on the basis of data obtained from isothermal firing and from the quenching method. These data verify the existence of a celsian‐silica compatibility join by reducing the extent of the mullite field shown in previous diagrams and extending the boundaries of the celsian primary field. The system celsian‐silica‐alumina is divided into two ternary subsystems, one having a eutectic point and the other an invariant reaction point. The eutectic for the subsystem celsian‐silica‐mullite is located at BaO 19, Al2O3 15, and SiO2 66 wt% and 1296°± 3°C. The pertinent invariant point for the subsystem celsian‐mullite‐alumina, located at BaO 26, Al2O3 27, and SiO2 47 wt% and 1554°± 4°C, is a reaction point.
Intermediate‐Stage Densification in Vacuum Hot‐Pressing of Alumina
Authors: ROSSI R. C. , BUCH J. D. , FULRATH R. M.
Published: June 2006

The densification kinetics preceding the final‐stage densification of Al2O3 hot‐pressed in vacuum between 1150° and 1350°C and between 2000 and 6000 psi were analyzed. The analysis suggests a diffusion‐controlled creep mechanism but is not necessarily consistent with a Nabarro‐Herring vacancy model. The measured activation energy, 116 kcal/mol, agrees with the activation energy for the final stage of densification and for the self‐diffusion of Al ions in Al2O3. It is proposed that the pore structure (i.e. open or closed) defines the stage of densification and, further, that pore structure has a profound effect on the apparent diffusion coefficients.
Reaction of UC with Nitrogen from 1475° to 1700°C
Authors: LEITNAKER J. M. , LINDEMER T. B. , FITZPATRICK C. M.
Published: June 2006

The reaction of nitrogen with arc‐melted UC was studied from 1475° to 1700°C at an N2 pressure of about 400 torr. The reaction appeared to proceed toward equilibrium in distinct stages: (1) UC and N2 reacted to form UC2 and UC0.8N0.2; (2) UC2 reacted with N2 to produce more UC0.3N0.2 and free C; and (3) this U(C,N) reacted with N2 to produce more free C and the equilibrium product, a high‐N U(C,N). These results are consistent with known thermodynamic and phase behavior in the U‐C‐N system.
Crack Healing in Glass
Authors: WIEDERHORN S. M. , TOWNSEND P. R.
Published: June 2006

Cracks in soda‐lime‐silica glass specimens closed spontaneously; the recovery in strength was determined by fracture mechanics techniques. Approximately 80% strength was recovered in cracks formed by mechanical shock, whereas approximately 20% was recovered in cracks that closed after being held open to the atmosphere for several minutes. The high strength recovery in the mechanically shocked specimens is attributed to the very active surface formed during fracture. If the surface is allowed to adsorb O2or H2O vapor, the activity is reduced, and healing is less complete. Crack healing can introduce surface flaws into glass that cannot be detected by current methods of nondestructive testing.
Analysis of Brittle Fracture Stress Statistics
Authors: HEAVENS J. W. , MURGATROYD P. N.
Published: June 2006

Methods for determining the parameters of the Weibull distribution function from the results of brittle fracture tests are considered. Linearization, direct (least‐squares) curve fitting, and maximum likelihood techniques are applied to a set of data for the fracture of glass specimens in cross‐bending and the results compared. It is suggested that the maximum likelihood method is to be preferred since it is completely objective and involves no arbitrary assumptions. However, none of the methods yields reliable results for functions involving three parameters for small sets of data.
NaF‐KF‐K2NbF7 Fused Salt Temperature‐Solubility Diagram
Authors: McCAWLEY FRANK X. , BARCLAY JAMES A.
Published: June 2006

Freezing and eutectic temperatures were determined for the NaF‐KF‐K2NbF7 ternary system and the NaF‐K2NbF7, KFK2NbF7, and NaF‐KF binary systems. The compound KF‐K2NbF7 freezes congruently at 770°C; eutectics occur at 708° and 724°C for high‐ and low‐K2NbF7 mixtures, respectively. The NaF‐K2NbF7 eutectic freezes at 658°C. The ternary system has two eutectics, a high‐KF mixture and a high‐K2NbF7 mixture, which occur at 663° and 652°C, respectively.
Effect of Microstructure on Deformation of Polycrystalline MgO
Authors: LANGDON TERENCE G. , PASK JOSEPH A.
Published: June 2006

Six types of polycrystalline MgO, one nominally fully dense and the others having porosities of ∼1 to 2%, were tested in compression up to 1400°C. At 1200°C and above, all materials deformed plastically; two of the materials, both porous, also exhibited plastic flow at temperatures down to 800°C, and a third at 1000°C. A qualitative analysis of the microstructures of these materials indicated that the differences in behavior arose primarily because of variations in the size and distribution of pores and in the concentration of impurities at the grain boundaries. It is suggested that the following factors aid plasticity below ∼1200°C: (1) Strong grain boundaries, in the absence of excessive impurities, permit buildup of stress concentrations with consequent nucleation of slip on the {100} system and the extension of slip across the boundaries and (2) clusters of very fine pores within the grains allow some mass accommodation.
Spinodal Decomposition in the System CoFe2O4‐Co3O4
Authors: TAKAHASHI M. , GUIMARÃES J. R. C. , FINE M. E.
Published: June 2006

A miscibility gap exists in the spinel‐structured region of the pseudobinary CoFe2O4‐CO3O4 system in air. Phase decomposition inside the miscibility gap was investigated by transmission electron microscopy and by X‐ray diffraction. In samples containing 35 and 50 cation % Fe, the first observable changes on aging at 500°C were appearance of side bands on X‐ray diffraction photographs of powder samples and of a periodic structure under the electron microscope. When specimens which contained 50 cation % Fe were aged at 700°C, the first observed change was another set of diffraction lines; homogeneously distributed fine particles were also observed. The former behavior was attributed to spinodal decomposition and the latter to classical nucleation and growth.
The System ThO2‐P2O5
Authors: LAUD K. R. , HUMMEL F. A.
Published: June 2006

The existence of compounds with 1:1, 3:2, and 3:1 ThO2:P2O5 ratios in the system ThO2‐P2O5 was confirmed. A 1:2 compound found by previous workers was not investigated, and their 2:1 compound was not detected; however, extensive solid solution on either side of the 3:2 compound was established. The linear thermal expansion behavior of the compounds and solid solutions was determined.
Ti‐Rich Nonstoichiometric BaTiO3: III, High‐Temperature Thermodynamic and X‐Ray Diffraction Measurements *
Authors: PANLENER R. J. , BLUMENTHAL R. N.
Published: June 2006

A thermodynamic and high‐temperature X‐ray diffraction study was performed on polycrystalline nonstoichiometric BaTiO3. The oxygen composition was measured from 940° to 1215°C at O2 partial pressures between 10−10 and 10−21 atm by a thermogravimetric technique. The isothermal weight change data exhibit a two‐slope behavior. The data at the lower pressures indicate that the maximum observable weight change is influenced by impurities, whereas the data at the higher pressures appear to exhibit native nonstoichiometric behavior. Values of ΔH̄o2 and ΔS̄o2 were calculated for the higher O2 partial pressure region; ΔH̄o2 is consistent with the O vacancy formation energies obtained by Long and Blumenthal from electrical conductivity measurements. High‐temperature X‐ray measurements indicate that the cubic structure is stable in the range investigated. Lattice parameters and coefficients of expansion were obtained from 200° to 1100°C in pure O2; lattice parameters of reduced BaTiO3 at 1100°C are also presented.
Micromechanics Analysis of Porous and Filled Ceramic Composites
Authors: AGARWAL B. D. , PANIZZA G. A. , BROUTMAN L. J.
Published: June 2006

A finite element analysis was used to calculate the internal stresses and deformations everywhere within spherically filled or porous ceramic materials. This analysis accounts for interactions between inclusions and demonstrates the importance of these interactions on stress fields around the inclusions. Modulus of elasticity and Poisson's ratio were calculated for porous and filled ceramics. The predicted modulus is compared with experimental data for two glass composites; the agreement is excellent.