bluuebunny/crossref_metadata_2025 huggingface dataset:
Properties of Lithium‐Doped Hydrothermally Grown Single Crystals of Zinc Oxide
Authors: KOLB E. D. , LAUDISE R. A.
Published: June 2006

The piezoelectric, dielectric, and optical proper ties of hydrothermally grown ZnO were exam ined. Although the material was strained it was not electrically twinned and the values of the electromechanical coupling factors, k33 (= 0.47) measured by static loading and k31 (= 0.188) measured by the resonance‐antiresonance tech nique, compared favorably with those measured in vapor‐grown crystals. The concentration of Li + substituted on a Zn site which was necessary to compensate the crystals was about 5 × 1018atoms/cm3. This concentration could be ob tained easily by growth from hydrothermal solu tions containing 2.0 molal LiOH. It was neces sary to heat‐treat hydrothermally grown crystals at 800° for about 50 hours, to diffuse out inter stitial zinc, to obtain high‐resistivity material. Typical dc resistivities of 1010 ohm‐cm were ob tained by such treatment. There was a pro nounced anisotropy in the dielectric constant with K33 varying between 9.9 and 11.7 and K11 varying between 8.1 and 9.0 at 100 kc. The size and properties of Li +‐doped hydrothermal ZnO make it of interest for transducers.
Metastable Liquid Immiscibility in Alkali Metal Oxide–Silica Systems
Authors: CHARLES R. J.
Published: June 2006

A search was made for evidence of metastable phase separation in binary alkali metal oxide‐silica glasses which had been subjected to the usual glassmaking procedures of melting, relatively fast cooling, and annealing. Electron microscopy and electrical properties measurements were the principal tools of investigation. Evidence for phase separation in Li2O and Na2O silica systems is given together with critical temperature estimates. Although K2O‐SiO2 glasses showed some slight evidences of structural segregation it is concluded that binary K2O, Rb2O, and Cs2O silica glasses generally show simple solution behavior and allow reasonable correlations of properties with cation size, type, and separation.
Equations for Calculating Chain Length Distributions in Polyphosphoric Acids and Polyphosphate Glasses
Authors: WESTMAN A. E. R. , BEATTY R.
Published: June 2006

The Flory distribution of molecular weights of linear polymers resulting from the condensation of bifunctional monomers was used by Van Wazer to calculate the constitutions of thepoly phosphoric acids. Jost and Wodtcke proposed a modification to the Van Wazer approach for sodium phosphate glasses. By modifying and extending these ideas, it is shown that, by using a few empirical parameters, it is possible to calculate chain length distributions for polyphosphoric acids and polyphosphate glasses, which give a satisfactory fit to available data. These distributions are useful for smoothing and extrapolating data and for emphasizing deviations from the Flory distributions taken as “ideal”.
Proposed Fracture Theory of a Dispersion‐Strengthened Glass Matrix
Authors: HASSELMAN D. P. H. , FULRATH R. M.
Published: June 2006

A fracture theory is proposed for a composite system based on a continuous glass matrix. It is hypothesized that hard crystalline dispersions within the glass matrix will limit the size of Griffith flaws and strengthen the composite. Quantitative relations are derived for the effect of a dispersed phase on composite strength. At low volume fractions of the dispersed phase, the average flaw size is statistically reduced independent of the size of the dispersed particles. At high volume fractions of the dispersed phase, the average flaw size is governed by the average distance between particles dispersed in the matrix. The strength of a composite should, therefore, be a function of the volume fraction of the dispersed phase at low volume fractions and dependent on both the volume fraction and particle size of the dispersed phase at high volume fractions. For verification of the theory, cross‐bending strengths were measured on a sodium borosilicate glass containing varying volume fractions of spheroidized alumina over a range of particle sizes. The average distance between dispersed particles ranged from approximately 15 to 500μ. Good agreement with theory was found. Values of glass surface energy calculated from the experimental data agree well with literature data.
Fe‐Nb Oxides: Phase Relations at 1180°C
Authors: TURNOCK A. C.
Published: June 2006

Subsolidus phase relations of the oxides in the system Fe–Nb–O were experimentally determined at 1180°C, 1 atm total pressure, and variable partial pressures of oxygen. Niobium pentoxide reacts readily with either ferrous or ferric oxide at subsolidus temperatures and the following ternary compounds were synthesized: Fe4Nb2O9, FeNbO4, and FeNb2O6. It is shown that the rutile structure of NbO2 will take Fe‐Nb2O6 into solid solution and that the spinel structure of Fe3O4 will incorporate up to 7 at.% Nb.
Transmission Electron Microscopy of Thin Glass Samples
Authors: SEWARD T. P. , UHLMANN D. R. , TURNBULL DAVID , PIERCE G. R.
Published: June 2006

Mechanical thinning and fracturing techniques for preparing thin glass samples for direct‐transmission electron microscopy are discussed. A modification of the Doherty and Leombruno procedure for mechanically thinning ceramic materials is described. These techniques make possible more reliable electron microscope studies of fine‐scale submicrostructure in glass systems. Electron microscope observations on fused silica, an alkali borosilicate glass, and some binary silicate glasses are reported and discussed in terms of present understanding of glass structure.
Structural Interpretation of Immiscibility in Oxide Systems: IV, Occurrence, Extent, and Temperature of the Monotectic
Authors: LEVIN ERNEST M.
Published: June 2006

Liquid immiscibility data in known binary oxide systems are analyzed in relation to three fundamental aspects. Immiscibility in glassforming systems is related to differences in ionic field strengths or electrostatic bond strengths between the network cation with oxygen and the modifier cation with oxygen. If this difference is too small or too large, immiscibility is not present. Analysis also indicates that immiscibility is not to be expected in binary phosphate and vanadia systems. Factors governing the extent of immiscibility are essentially unrelated to its occurrence; in borate and silicate systems, immiscibility is inversely correlated with the number of oxygens per modifier cation in the modifier‐rich liquid. Temperature of the monotectic almost always lies between the melting point of the glass former and the first compound beyond the immiscibility gap. Properties of the monotectic, such as the primary phase under the two liquids and location of the eutectic, are fixed according to whether the monotectic temperature is above or below the melting point of the glass former. Principles of immiscibility are summarized.
Polarography in Molten Sodium Disilicate
Authors: BAAK TRYGGVE , FREDERICK R. LaMAR
Published: June 2006

Polarographic techniques using a rotating micro‐electrode are given. Experimental results cover concentrations and valence states of metal oxides in a sodium disilicate solution.
Volume Relations in Na2O·B2O3 and Na2O·SiO2 B2O3, Melts at 1300·C
Authors: RIEBLING E. F.
Published: June 2006

Density (and some viscosity) data are presented for binary sodium borate melts containing as much as 60 mole % Na2O and for ternary sodium silicoborate melts with B/Si <2.0 between 1000°C and 1300°C. The high‐temperature partial molar volume analysis of the binary sodium borate melts reveals about 50% BO4 tetrahedra at the 40 mole % Na2O composition, in agreement with recent NMR estimates for the binary glasses. No “boron anomaly” was found near 18 mole % Na2O at high temperature. The synthetic partial molar volume model that agrees best with experiment for all ternary melts studied involves the presence of some BO4 tetrahedra, the percentage of which varies with composition. This ternary model involves a high degree of internal consistency. No tendency toward extensive micro‐immiscibility was observed for ternary melts near the SiO2·B2O3 binary.
New Glassy and Polymorphic Oxide Phases Using Rapid Quenching Techniques
Authors: SARJEANT P. T. , ROY RUSTUM
Published: June 2006

Splat and other rapid quenching techniques were applied to a systematic study of simple oxides, and four new pure oxide glasses were obtained (V2O5, TeO2, MoO3, and WO2). The high‐temperature tetragonal form of WO3 coexists with a metastable short‐range‐order‐only phase. The structure of a new metastable high‐temperature phase, δ‐Ta2O6, resembles δ‐Nb2O6. Predominant phases found in quenched Al2O3 belong to the γ‐(spinel type) series.
Stability of Mullite as Derived from Equilibria in the System CoO‐Al2O3‐SiO2
Authors: DAYAL R. R. , JOHNSON R. E. , MUAN ARNULF
Published: June 2006

The free energy of reaction for the formation of mullite from its oxide components was derived from equilibrium studies in the system CoO‐Al2O3‐SiO2. Within this system there appears, at solidus temperature in a certain composition area, the phase assemblage mullite + silica + spinel (= cobalt aluminate) + liquid. Determination of the oxygen pressure of a gas phase at which metallic cobalt precipitates from this phase assemblage and from the phase assemblage spinel (= cobalt aluminate) + corundum in the system CoO‐Al2O3 permits calculation of ΔG° for the reaction 3Al2O3+ 2SiO2= Al6Si2O13. The value obtained at 1422°C is ‐5.8 kcal.
Equilibrium Order‐Disorder in Spinels
Authors: DATTA R. K. , ROY RUSTUM
Published: June 2006

The distribution of cations in different coordinations in the spinel structure as a function of equilibrium temperature was quantitatively determined for several phases. The spinels were synthesized and/or reacted at various temperatures and pressures. The relative X‐ray intensities of various reflections of the quenched phases were measured and compared with intensities calculated for various models of cation distribution. In NiAl2O4 the cation arrangements at 600° and 1550°C are (Al1.0)IV(Ni1.0 Al1.0)VIO4 and (Ni0.25Al0.75)IV(Ni0.75Al1.25)VIO4, respectively. In Ni2GeO4, between 610° and 1400°C, the concentration of Ni2+ ions in tetrahedral sites increases from 0 to 23% and in octahedral sites it decreases from 100 to 77% of total nickel present. All these transitions were reversible under equilibrium conditions and can be classified as second‐order “reconstructive transition of disorder.” Many spinels cannot be classified as normal or inverse but have a cation distribution which is an equilibrium function of the temperature.
Solubility of Iron in TiO2 (Rutile)
Authors: WITTKE JAMES P.
Published: June 2006

An upper limit to the solubility of iron in rutile was determined in the range 800° to 1350°C by X‐ray examination of mixtures of TiO2 and α‐Fe2O3 powders reacted in 1 atm oxygen pressure and quenched to room temperature. The results indicate somewhat lower solubilities than would be inferred from previous measurements; the solubility ranges from 3 cation % iron at 1350°C to 1% at 800°C. There is no detectable change in rutile lattice parameters with iron content up to the limit of solubility.
Phase Relations in the System FeO‐Fe2O3‐ZrO2‐SiO2
Authors: JONES T. S. , KIMURA SHIGEYUKI , MUAN ARNULF
Published: June 2006

Phase equilibrium relations in the liquidus‐temperature region of the system iron oxide‐ZrO2‐SiO2 in air were delineated by the quenching technique. Additional equilibration runs were made at other controlled oxygen pressures as well as in sealed containers. The results of all runs have been combined with literature data for the system in contact with metallic iron to locate approximately the quaternary liquidus invariant points within the system FeO‐Fe2O3‐ZrO2‐SiO2.
Particle Size Dependence of the Electrical Conductivity of NaCl
Authors: GRAHAM H. C. , TALLAN N. M. , RUSSELL RALSTON
Published: June 2006

The ac and dc conductivities of single‐crystal and polycrystalline NaCl were measured as a function of both temperature and particle size. The ac conductivity results for single‐crystal NaCl agreed well with the literature: intrinsic activation energy = 1.86 ev; extrinsic, impurity‐controlled range = 0.74 ev; extrinsic, association range = 1.16 ev; and the intrinsic‐extrinsic knee in the curve was at 103/T∼ 1.4°K−1 and σ0∼ 6 × 10−8 ohm−1 cm−1. In the intrinsic range, however, the total conductivity (σ0) was the sum of two ionic contributions: a steady state, nonblocked contribution (σθ and a blocked contribution (σ0—σθ). The activation energy for the dc steady state conductivity was 1.6 ev. When the extrinsic, impurity‐controlled contribution to the total conductivity was made insignificant by anion doping, the same 1.6 ev was the activation energy for the intrinsic ac conductivity at low temperatures. The data for the polycrystalline samples showed that ac conductivity increased inversely with particle size and dc steady state conductivity increased only slightly, if any, with decreasing particle size. It is postulated that the steady state conductivity is the result of the nonblocked ionic transport of sodium ions and that the ac portion of the total conductivity is due to the movement of chlorine ions which are blocked, giving rise to the polarization phenomenon. The increase in the ac conductivity with decreasing particle size is correlated with the enhanced movement of Cl− in the subgrain boundary region, as has been previously shown by diffusion measurements.
Mutual Indentation Hardness of Single‐Crystal Magnesium Oxide at High Temperatures
Authors: ATKINS A. G. , TABOR D.
Published: June 2006

The mechanical properties of single crystals of MgO were measured from 600° to 1700° C using the mutual indentation hardness technique. This method, which involves pressing together two similar crossed specimens, overcomes the problem of finding materials sufficiently rigid and chemically stable for use as indenters in conventional quasi‐static methods of indentation hardness testing. By this means the hardness of the hardest materials can be measured at very high homologous temperatures. Yield strengths at known strains are obtained from the hardness measurements and are presented. The form of the hardness impression very well depicts changes in the mode of deformation of MgO over different temperature ranges. Creep processes affect the measurements; a creep analysis can be applied, and from this activation energies for the creep mechanism are obtained.
Expansion Characteristics of Calcium Sulfoaluminate Hydrates
Authors: MEHTA P. K.
Published: June 2006

In contrast to the general belief that formation of calcium trisulfoaluminate hydrate is accompanied by expansion even under conditions of restraint, Chatterji and Jeffery speculated that formation of calcium monosulfoaluminate hydrate is mainly responsible for the expansion phenomenon. Because of the importance of calcium sulfoaluminate hydrates in sulfate disruption of portland cement concretes and in expansive cements used for making crack‐resistant concretes, the author, using data reported by Chatterji and Jeffery, attempted to reproduce their results. Some additional experiments were made to test the validity of their hypothesis. The results of the experiments showed that in every case, under conditions of restraint, it was formation of calcium trisulfoaluminate hydrate and not calcium monosulfate hydrate that caused significant expansions, which is contrary to the hypothesis of Chatterji and Jeffery.
Magnetic Properties of Yttrium‐Gadolinium‐Iron‐Aluminum‐Indium Garnets
Authors: MAGUIRE E. A. , GREEN J. J.
Published: June 2006

The saturation inductions of polycrystalline garnet materials with the general composition Y3–x GdxFe5–y–z AlyInZO12 were determined. The compositions investigated included yttrium substitutions of 0 to 50%, aluminum substitutions of 0 to 10%, and indium substitutions of 0 to 10%. Temperature dependences of the saturation inductions are reported with special emphasis on materials having small temperature coefficients in the 20° to 100°C region.
Thermal Expansion of Some Cubic Refractory Compounds of Thorium
Authors: ARONSON S. , CISNEY E. , GINGERICH K. A.
Published: June 2006

The thermal expansion of a number of cubic refractory compounds of thorium was measured by high‐temperature X‐ray diffraction. The coefficients of thermal expansion range from 7.5 to 8.2 × 10−6/°C for ThN, ThC0.84, ThP0.71, ThP0.61, and Th3P4 between 900° and 1300°, 1450°, 1750°, 1750°, and 1150°, respectively; the coefficients for ThS, ThB6, and ThO2 are in the range of 11.2 to 12.0 × 10−6/°C between 900° and 1400°, 1700°, and 2100°, respectively. The results are discussed in relation to other properties of these compounds.
Deformation of Poly crystalline Transition Metal Carbides
Authors: KELLY A. , ROWCLIFFE D. J.
Published: June 2006

Plastic deformation was studied in hot‐pressed poly crystalline specimens of titanium carbide, vanadium carbide, niobium carbide, tantalum carbide, and tungsten carbide tested in four‐point bending and under compression to 2100°C. Transition from brittle to ductile behavior occurred at approximately half the absolute melting temperature for each material. Above this temperature the yield strengths decreased exponentially with increasing temperature. Between the ductile‐brittle transition temperature and about 1900°C the apparent activation energy for flow in the carbides with the rock‐salt structure was near O.S ev/atom. Above 1900°C the value was approximately 2 ev/atom; the value for tungsten carbide was apparently 0.3 ev/atom to 2070°C. Vanadium carbide and titanium carbide recovered extensively on annealing for short times near 2000°C. No such recovery occurred in tungsten carbide under these conditions. The results for polycrystalline carbides were compared with available data for single crystals of titanium carbide.
Electrical Properties and Defect Structure of HfO2
Authors: TALLAN N. M. , TRIPP W. C. , VEST R. W.
Published: June 2006

The defect structure of high‐purity, polycrystalline HfO2 was investigated by measuring the oxygen partial pressure dependence of the electrical conductivity and the sample weight. From 1000° to 1500°C and above oxygen partial pressures of 10 −6, the conductivity is electronic and proportional to po21/5. The predominant defect is completely ionized hafnium vacancies. At lower oxygen partial pressures a broad shallow minimum in the lower temperature conductivity isotherms indicates the presence of an oxygen pressure independent source of electronic charge carriers. By combining the weight change and conductivity data, mobility values were found to vary from 1.6 × 10−3 to 3 × 10−4 cm2/V‐sec. The activation energies for the hole mobilities were calculated to be 0.2 ev above 1300° C and 0.7 ev below this temperature.
Tantalum Oxide Films Prepared by Oxygen Plasma Anodization and Reactive Sputtering
Authors: VRATNY F.
Published: June 2006

Anodic tantalum oxide thin‐film capacitors have proved quite satisfactory for circuit applications, although some minor limitations exist in the maximum usable dielectric thickness, current asymmetry, and allowable counterelectrode materials. For this reason, two processes of glow discharge anodization and dc diode reactive sputtering were investigated for the formation of tantalum oxide films. Dielectrics up to a maximum thickness of 3000 A could be prepared by these methods with equal or larger than anticipated capacitance per unit area and dielectric strengths of about one third of anodically formed tantalum oxide. The dc diode reactive sputtering process produces thickness variations over 50 cm2 of 4 to 20% compared with 4 and 1%, respectively, for glow discharge anodization and aqueous anodization. At the present time, the all‐vacuum methods are limited in applicability because of lower dielectric strength and lower formation rates.
Radiation‐Induced Defects and Structure of Barium Silicate Glasses
Authors: BISHAY A. M. , GOMAA IBRAHIM
Published: June 2006

The effect of increasing BaO on the intensity and position of absorption bands induced in barium silicate glasses was studied. Many of these glasses showed a two‐step process in the growth and thermal bleaching curves. This process was attributed to two types of defects in the glass, induced and intrinsic. Infrared absorption, molar volume, and X‐ray diffraction studies predicted structural changes at compositions containing about 22.5 and 27.5 mole % BaO. The results of gamma‐induced absorption were in Une with these predictions, supporting the view that color center studies can be used to detect changes in structure, especially when high radiation doses are applied.
Preparation of Thorium Carbides
Authors: IMAI HISASHI , HOSAKA SHINOBU , NAITO KEIJI
Published: June 2006

Some factors influencing the formation of thorium carbide from a mixture of thorium dioxide and graphite powder were studied. The effects of the molecular ratio of the reactants, reaction temperature, extrinsic properties (such as surface area, defects, and crystallinity of the materials), and the ambient pressure were examined. The molecular ratio of the reactants gave the most important effect on the composition of the final products. Thorium dicarbide was formed from a mixture having a molecular ratio (C/ThO2) of more than three and the reaction rate then obeyed the parabolic rate equation. To form thorium monocarbide, it is necessary to use a mixture having a ratio less than four. A tentative explanation of the reaction mechanism of ThC formation is given.
X‐Ray Studies of Lime‐Bentonite Reaction Products
Authors: GLENN GEORGE REMBERT
Published: June 2006

Calcium aluminate and calcium silicate hydrates were formed in mixtures of bentonite with water and various types of lime which had been sealed and cured for up to three years at 23°± 2°C and 100% relative humidity. Methods of analysis were X‐ray diffraction and electron microscopy. Hydrothermal treatment of the cured mixtures at 170°C for 12 hr produced well‐crystallized tobermorite with apparent lattice substitution of aluminum. The same result was obtained by hydrothermal treatment of identical uncured mixtures.
Magnetic Properties of Dense Lithium Ferrites
Authors: WEST RUSSELL G. , BLANKENSHIP A. C.
Published: June 2006

Dense lithium ferrite ceramic bodies prepared by hot‐pressing exhibited rectangular hysteresis loops. A number of physical properties of technical interest were evaluated and results given. These include initial permeability, dc resistivity, resonance Une width, geff factor, and saturation magnetization. The effect of 3–1 octahedral site ordering is discussed. Investigation was extended to the preparation of solid solutions of lithium ferrite and zinc ferrite (Lio.0.5Feo.0.5)1‐xZnx‐Fe2O4, where 0 ≤x≤ 0.7. Methods of separate control of remanent induction, Br, and coercive force, Hc, are described.
Refractory‐Melt Reactions in Vacuum Induction Melting of Nickel‐Base Alloys
Authors: SNAPE E. , BEELEY P. R.
Published: June 2006

The reactivity in vacuum of some molten nickel‐base alloys with various refractories was investigated. Contact angles between alloy drops and refractory disks were measured from photographs. Sections taken through the contact region were examined microscopically. Supplemental information was obtained by other methods. The important influence of carbon on metal‐refractory reactions was demonstrated; reduction of the refractory by carbon was the predominant factor by which oxygen was introduced into the melt. Recommendations are made concerning the choice of refractory and melting conditions for the alloys.
Effect of LiF on Hot‐Pressing of MgO
Authors: BENECKE MARK W. , OLSON NORMAN E. , PASK JOSEPH A.
Published: June 2006

Transparent polycrystalline specimens can be fabricated from fine MgO powder with a small LiF addition by a two‐step process: hot‐pressing and heat‐treating. The LiF addition allows MgO to be hot‐pressed to near theoretical density at reduced temperatures and stresses. The stress‐temperature‐time conditions must be designed to attain a hot‐pressed density of at least 99.5% of the theoretical density of MgO to obtain a transparent specimen during the subsequent heat treatment used in this study. Possible densification mechanisms are discussed.
Vaporization of Lead Zirconate‐Lead Titanate Materials: II, Hot‐Pressed Compositions at Near Theoretical Density*
Authors: NORTHROP DAVID A.
Published: June 2006

The vaporization of lead monoxide from lead zirconate‐lead titanate materials was studied by thermogravimetric techniques in vacuum with hot‐pressed pellets of near theoretical density. The initial step of the complex, two‐step vaporization observed in cold‐pressed pellets in an earlier investigation is absent. The rate‐determining step for both the porous, cold‐pressed, and pore‐free, hot‐pressed materials is the bulk diffusion of lead across a thickening lead‐depleted layer at the surface of the pellet and results in a parabolic time dependence. Although parabolic rate constants are slightly lower overall for the dense materials, the activation energies for the weight loss process remain approximately 38.5 and 35 kcal/mole for the pure and Bi‐doped Pb(Zr0.65Ti0.35)O3 compositions, respectively. Vaporization mechanisms and rates were unchanged under nitrogen or oxygen pressures up to 50 torr at 1000°C. Alumina Knudsen cells were used to study the equilibrium vapor above a powdered, hot‐pressed Pb(Zr0.65.Ti0.35)O3 composition. Mass spectrometric analysis of the vapor at 950°C showed that the vapor species and their relative abundances were the same as the equilibrium vapor species above pure lead monoxide. Continuous weight loss data from these cells gave an apparent vapor pressure that was 2% of the vapor pressure of pure lead monoxide at a given temperature, but gave the same second law enthalpy of vaporization. The overall vaporization process can be represented by the reversible equilibria: the diffusion of Pb2+ and O2‐ to the surface through a lead‐depleted region whose phases and compositions are determined by the subsolidus phase relations in the PbO‐ZrO2‐TiO2 ternary system, the reaction at or near the surface to form PbO, and the subsequent vaporization of PbO.
Single Crystals of (PbxSr1‐x) TiO3 Grown by Traveling Heater Method
Authors: DIBENEDETTO B. , CRONAN C. J.
Published: June 2006

A procedure is presented for growing single crystals of (PbxSr1‐x)TiO3 by passing solvent zones through poly‐crystalline rods of the same composition (THM). The solvent zone composition for homogeneous solid solution growth was chosen from the pseudoquaternary system 2PbO: 1B2O3‐2SrO:1B2O3‐PbTiO3‐SrTiO3. Crystals with compositions throughout the complete range of PbTiO3‐SrTiOs solid solutions were grown. Emphasis was placed on crystal compositions near (Pb0.25Sr0.78) TiO3 which have Curie temperatures just below room temperature. The dielectric constants, Curie temperatures, and optical properties of these single crystals are presented. Nonlinear dielectric and electrooptic behaviors are also demonstrated.
Grain Growth in UO2‐Al,O3 in the Presence of a Liquid Phase
Authors: LAY K. W.
Published: June 2006

The theory of grain growth in the presence of a liquid phase is examined using modifications of equations derived for coalescence of solid particles widely dispersed in a liquid. Although the grain diameter‐time relation can still be represented by d3=kt, the absolute growth rates are increased as the amount of liquid is decreased. The grain growth kinetics in UO2 compacts containing 0.5 wtyo A12O3 were studied for temperatures between 1960° and 2200°C. The interrelation of grain size, temperature, and time is in agreement with that predicted by the theory.
Magnetic Properties of A2+Cr2S4 Compounds with the NiAs Structure
Authors: TRESSLER R. E. , STUBICAN V. S.
Published: June 2006

The cation‐defective NiAs‐type polymorphs of MnCr2S4, FeCr2S4, and CoCr2S4 were prepared by high pressure‐high temperature heat treatments. The magnetizations of these specimens and NiCr2S4 were studied from 1.5'K to room temperature. All phases with the NiAs‐type structure were antiferromagneticalIy ordered below NBel temperatures of 70°, 200°, 300°, and 200°K, respectively. These data show a transition from ferrimagnetic to anti‐ferromagnetic ordering in the transformation spinel‐type ↔ NiAs‐type structure in the A2+Cr2S4 compounds.
X‐Ray Line Broadening Study of Explosively Shocked MgO and α‐Al2O3 Powders
Authors: HECKEL R. W. , YOUNGBLOOD† J. L.
Published: June 2006

The present study considers the structural effects of explosive‐shock treatments on MgO and α‐Al2O3 powders. An X‐ray line broadening analysis based on the Warren‐Averbach method shows a reduction in the X‐ray particle size and an increase in the microstrain as a result of the explosive treatments. The magnitude of the effect is similar to that observed in cold‐worked metals with regard to dislocation density and elastic strain energy. The total stored energy resulting from the explosive‐shock treatments is estimated to be about the same as the total surface energy of the powders.
Adiabatic Elastic Moduli of Vitreous Calcium Alurninates to 3.5 Kilobars
Authors: SOKOLOWSKI T. J. , MANGHNANI M. H.
Published: June 2006

“Pulse superposition” ultrasonic interferometry was used to measure elastic wave velocities and related elastic parameters of four vitreous calcium aluminate specimens at pressures up to 3.5 kbars at 25°C. The values obtained for the bulk (K2) and shear (μ) moduli and for Poisson's ratio (σ) were much higher than those reported for silicate glasses. The bulk moduli for the calcium aluminates, however, fit quite well with the relation between bulk modulus and specific volume per ion pair suggested by Soga and Anderson for 29 glasses. The (dvp/dP) value was highest (8.9×10−3 km/(s.kbars)) for the SiO2‐doped vacuum‐melted calcium aluminate and lowest (6.8×10−3 km/(s.kbars)) for the BaO‐doped air‐melted specimen. The BaO doping seemed to cause anomalous behavior in the shear wave velocity vs pressure relation; the (dv3/dP) value for the BaO‐doped air‐melted specimen was −4.1 ×10−3 km/(s.kbars). The differences in the compressibility at 1 bar and the rate of change of compressibility with pressure appear to be related to composition and melt conditions. The (dK3/dP) values ranged from 4.0 to 4.7 and the (dσ/dP) values from 6.8 to 7.5 ×10−4/kbars.
The Metastable Liquidus and Its Effect on the Crystallization of Glass
Authors: CAHN JOHN W.
Published: June 2006

There is a range of compositions and temperatures below the monotectic where the equilibrium solid cannot form directly from an undercooled single‐phase liquid. Thermodynamics requires either a prior liquid‐liquid Phase separation or a simultaneous formation of the second liquid if the solid is to form. The implications for controlled crystallization of glass are discussed.
Oxidation Kinetics of Powdered Silicon Nitride
Authors: HORTON RALPH M.
Published: June 2006

The oxidation kinetics of powdered silicon nitride were studied in dry oxygen and dry air at 1 atm pressure between 1065° and 1340°C. An automatic recording electrobalance was used to measure the weight gain as a function of time. Parabolic oxidation kinetics were observed with an activation energy of 61 kcal/mol in dry oxygen and 68 kcal/mol in dry air. The oxidation rate in dry oxygen was approximately twice that in air. The solid oxidation product was tridymite above 1125°C and amorphous silica at 1067°C.
Reaction of HF with Porous Glass
Authors: LOW M. J. D. , RAMASUBRAMANIAN N. , RAMAMURTHY P.
Published: June 2006

Infrared spectra were used to follow the reaction of HF with porous glass which had been dehydroxylated to various degrees. The fluoridation proceeded smoothly, and the surface hydroxyls were eliminated completely with samples which were not degassed or were degassed mildly (at temperatures up to approximately 500°C) so that appreciable amounts of water and hydroxyls were on the surface before the HF treatment. Samples which had been severely dehydroxylated before exposure to HF behaved differently, and several HF treatments were required to effect complete fluoridation. Experiments suggest that the replacement of hydroxyls by fluoride is negligible at room temperature, the dominant reaction being the formation of B‐OH and B‐F groups. The latter are unstable at higher temperatures and release HF, so that dehydroxylation can continue after physically adsorbed HF has been desorbed and pumped away.
Knudsen Cell Studies of the Vaporization of Samarium Dicarbide
Authors: STOUT NORMAN D. , HOENIG CLARENCE L. , NORDINE PAUL C.
Published: June 2006

The vapor pressure of SmC2 in equilibrium with graphite was measured by the Mnudsen effusion technique. Rates of weight loss from the cells were measured with an automatic recording balance. The apparent pressures varied with orifice size, and equilibrium pressures were calculated by extrapolation to zero orifice area. This work was combined with other studies to obtain log10 P(atm) = ‐ 13.869 × 103/T + 3.752 (1300°‐2050°K) for the Sm vapor pressure above SmC2‐C. Estimates of S°298 and cp were made for SmC2, and δH°298 was calculated to be 72.0 ± 2 kcal/mol for the reaction SmC2(s) = Sm(g) + 2C(s). This value combined with δH°v, 298= 48.6 kcal/mol for Sm gives a δ°f298 for SmC2 of 23.4 ± 2 kcal/mol.
Evaluation of A Statistical Thermodynamic Method for Calculating the Composition Dependence of Chemical Potentials in Nonstoichiometric Zirconium Carbide
Authors: DEPOORTER GERALD L.
Published: June 2006

Mathematical expressions for carbon and zirconium activities in zirconium carbide are derived from a statistical thermodynamic model, on the assumption that nonstoichiometry is due to vacancies in the carbon sublattice while the zirconium sublattice remains filled. The energy term in the partition function is obtained by using a first‐ and second‐neighbor quasi‐chemical model. Values for the parameters used in the model are determined from available data as a function of composition. For C/Zr atom ratios between 0.59 and 0.85 the energy parameters are approximately composition‐independent, whereas in the composition range 0.85 to 0.99 they are strongly composition‐dependent. The vibrational partition functions of C and Zr in zirconium carbide are estimated and are shown to influence the value obtained for the model parameters.
Crystallization of PbO·2B2O3 from Its Supercooled Melt
Authors: J. P. DE LUCA  , EAGAN R. J. , BERGERON C. G.
Published: June 2006

The growth of lead diborate and the viscosity of its melt were determined as a function of temperature. These data were used to examine several theories of the growth of crystals from the melt. The data were in good agreement with the theory of Tornbull and Cohen. At large under coolings the growth rate appeared to be controlled by the rate of diffusion across the crystal‐melt interface, whereas at smaller undercoolings the growth rate appeared to be controlled by reaction at the crystal‐melt interface.
Thickness Error in Quantitative Transmission Microscopy of Ceramics
Authors: GOKULARATHNAM C. V. , FREIMAN S. W. , DEHOFF R. T. , HENCH L. L.
Published: June 2006

The error in quantitative microscopic analysis of ceramic transmission specimens was experimentally evaluated for cases (1) when sample thickness is completely neglected and (2) when theoretical corrections for thickness are included. Errors in Pp; NL, and NA of as much as 373, 79, and 71%, respectively, are reduced to 15, 1, and 6% when the corrections are applied.
Aging in Tetragonal Ferroelectric Barium Titanate
Authors: BRADT R. C. , ANSELL G. S.
Published: June 2006

The aging phenomenon in tetragonal ferroelectric bairum titanate was investigated by optical microscopy and by electrical measurements. Transmission electron microscopy was used to observe in detail domain reactions which occurred during aging. Aging may be characterized as an exhaustion‐type process because of the increase in the apparent activation energy with time. It is concluded that aging is the relief of the residual stresses of the ferroelectric transition by the thermally activated nucleation of 90° domains.
Solubility of KUO3 in BaUO3
Authors: FUJINO TAKEO , NAITO KEIJI
Published: June 2006

The formation of a solid solution between cubic perovskne‐type KUO3 and pseudocubic BaUO3 was investigated. The reaction begins at 550°C, and the solubility of KUO3 reaches more than 30 mol% KUO3 in BaUO3 at 750°C. The region in which a single‐phase solid solution exists was determined. The variation of the lattice parameter of the reacted samples was caused by solid solution formation and by oxygen absorption. The electrical conductivities of the samples varied with composition and showed a distinct maximum. The activation energy for electric conduction was very low compared to that for UOz+x, or U3O8.
Tungsten Bronze Field and Melt Growth of Crystals in the Na2O‐BaO‐Nb2O5 System
Authors: GIESS E. A. , SCOTT B. A. , OLSON B. L. , BURNS G. , O'KANE D. F.
Published: June 2006

The extents of the liquidus and solidus fields were determined for tungsten bronze‐type solid solutions in the Na2O‐BaO‐Nb2O5 system by DTA and melt crystal growth experiments. Bronze‐type solid solutions exist to 7.1Na2O‐34.9BaO‐58Nb2O5 in the Nb2O5‐rich region and from 12Na2O‐38BaO‐50Nb2O5 to 4.6Na2O‐45.4BaO‐50Nb2O5 along the NaNbO2‐BaNb2O6 join, which includes NaBa2Nb5O15=10Na2O‐40BaO‐50Nb2O6. There is little, if any, solid solubility of compositions with a deficiency of Nb2O5. Curie temperatures decline rapidly and dielectric constant peaks broaden with Nb2O5 substitution because the Nb:O ratio becomes greater than the octahedral 1:3 ratio. Useful ferroelectrics exist along the NaNbO3‐BaNb2O6 join where the Nb:O ratio is 1:3. Large striae‐free crystals, with less optical scattering than Czochralski‐grown crystals, were grown from unseeded Na2O‐rich melts (e.g. 15Na2O‐37.5BaO‐47.5Nb2O5) cooled from 1520° to 1300°C at 2°C/h. Annealing effects on these crystals whose compositions lie on the NaNbO3‐BaNb2O6 join are discussed.
Metastable Immiscibility Surface in the System Na2O‐B2O3‐SiO2*
Authors: HALLER W. , BLACKBURN D. H. , WAGSTAFF F. E. , CHARLES R. J.
Published: June 2006

Opalescence and clearing techniques were used to determine the metastable immiscibility surface for sodium borosilicate solutions. These results indicate that a three‐liquid region, which may or may not be metastable to two‐liquid regions, underlies the immiscibility surface.
Limitation of Griffith Flaws in Glass‐Matrix Composites
Authors: NIVAS Y. , FULRATH R. M.
Published: June 2006

The effect of the limitation of Griffith flaws, introduced in an abraded surface of glass, on the strength of glass‐tungsten composites was investigated for small sizes of Griffith flaws. Hasselman and Fulrath's proposed fracture theory for this type of system extended to small flaw sizes. The use of tungsten spheres with two particle sizes or a wide distribution about one average size as the dispersed phase in a glass matrix decreased the average mean free path in the matrix more than could be achieved with a single particle size dispersion. Average mean free paths determined experimentally by statistical techniques were in good agreement with those calculated by Fullman's equation. This technique was successfully used when the dispersed phase had two particle sizes or a wide particle size distribution. The strong effect of internal stresses caused by a mismatch of thermal expansion of the phases in reducing the strength of a composite was demonstrated.
Crystal Growth in the System PbO‐B2O3
Authors: EAGAN ROBERT J. , De LUCA JOHN P. , BERGERON C. G.
Published: June 2006

The temperature dependence of the rate of growth of PbO/2B2O3 from lead borate melts with PbO/B2O3 mole ratios of 1/3,1/2, 2/3, and 1 was determined. The maximum growth rates occurred from those melts which contained a slight excess of PbO. The results are explained on the basis of a modification in the structure of the melt in the interfacial zone as the PbO content is changed. Such changes markedly affect the fluidity of the melt, alter the concentration of crystallizable species, and may reduce the driving force for crystallization.
Isothermal Phase Transitions in Ceramic Lead Zirconate
Authors: WEIRAUCH DONALD F. , TENNERY† VICTOR J.
Published: June 2006

Constant temperature permittivity measurements of ceramic lead zirconate near 230°C revealed that the paraelectric to ferroelectric, ferroelectric to antiferroelectric, and antiferroelectric to paraelectric phase transitions were isothermal transformations. On heating, the antiferroelectric phase transformed into a paraelectric phase. Cooling produced a transformation from the paraelectric into an intermediate ferroelectric phase which existed over a temperature range of about 5°C. On further cooling, the ferroelectric transformed into the antiferroelectric phase. Thermal expansion, relative permittivity, and dissipation factor data are reported.
High‐Temperature Creep of NaCl‐KCl Solid‐Solution Alloys
Authors: CANNON W. ROGER , SHERBY OLEG D.
Published: June 2006

The high‐temperature creep of polycrystalline NaCl‐KCl solid solutions and pure KCI was studied under constant compression stress at 600°C. The creep rate of the ionic solid‐solution alloys appeared to obey approximately Weertman's microcreep equation, = KDS, where D, is taken to be the diffusion coefficient of the cation and G the shear modulus of the material. Transient creep in the ionic alloys was similar to that in metallic solid‐solution alloys which depends on the third power of stress. These results support the view that creep in many polycrystalline metallic and nonmetallic alloys is controlled by the same mechanisms. The creep rate of pure KCI depended on stress to the 5.0 power, a dependence similar to that of most pure metals and to that reported for pure NaCl.
Analysis of Capillary Forces in Liquid‐Phase Sintering of Jagged Particles
Authors: CAHN JOHN W. , HEADY R. B.
Published: June 2006

It is predicted that contact geometries will markedly affect the kinds of interparticle forces and their dependence on liquid volume. The normal force between two spheres is maximum at infinitesimal liquid volumes, whereas for the corner‐on‐plane geometry it is zero and increases rapidly with volume. Sphere contacts have only normal forces, whereas contacts among jagged particles produce shears and torques which probably are important in particle rearrangement leading to densification.
Melting of Forsterite, Monticellite, Merwinite, Spinel, and Periclase Assemblages
Authors: BIGGAR G. M. , O'HARA M. J.
Published: June 2006

Experimental data which define melting temperatures and crystalline solution compositions show that the assemblage forsterite+monticellite+spinel+periclase melts near 1425°C and that the assemblage monticellite+merwinite+spinel+ periclase melts between 1406° and 1420°C. The melting of the former assemblage is a double reaction point. The forsterite crystalline solution contains 13 mol% monticellite and the monticellite crystalline solution contains 22 mol% forsterite. A projection system shows that the new data agree with much previous data but highlight inconsistencies in previous data for assemblages containing more CaO, such as merwinite+dicalcium silicate+spinel+periclase. These assemblages are encountered in magnesite refractories with CaO:SiO2<2.0 during firing and in service.
Thermal Expansion of Orthorhombic PbO
Authors: SORRELL CHARLES A.
Published: June 2006

Thermal expansion of orthorhombic PbO was investigated by high‐temperature X‐ray diffraction. The coefficients in the a0, and c0 directions are equal and <½ the coefficient in the b0 direction. The structure is described in terms of Pb–O chains extended in the a0 direction and bonded into layers in the b0 direction; appreciable Pb–Pb bonding is indicated. Coordination and bond distances observed in PbSiO3 and lead silicate glasses, which are similar to those of massicot, and PbnOn polymeric units reported in PbO vapor are interpreted as additional evidence of the importance of PbO chains as structural entities.
Elastic Properties of Oxide Solid Solutions: The System Al2O3−Cr2O3
Authors: ROSSI LOUIS R. , LAWRENCE WILLIS G.
Published: June 2006

Sound velocities, densities, and lattice parameters of hot‐pressed bodies of the solid‐solution series Al2O3−Cr2O3 were investigated. Measured lattice parameters deviated slightly from Vegard's law. The compositional dependence of the longitudinal sound velocity agreed well with the predictions of Birch; the observed dependence of the bulk modulus on ionic volume did not agree with the relation of Anderson and Nafe.
Relation Between the Compressive Strength and Porosity of Autoclaved Calcium Silicate Hydrates
Authors: MINDESS SIDNEY
Published: June 2006

Calcium silicate hydrates were produced by high‐pressure steam curing of compacted mixtures of hydrated lime, ground quartz, and water using various lime/silica ratios, molding pressures, and times and temperatures of curing. Compressive strengths ranged from 825 to 32,000 psi and porosities from 0.25 to 0.45. The strengths depended chiefly on total porosity and pore size distribution; phase composition was of secondary importance with certain exceptions. In general, strength decreased as the proportion of larger pores increased. Compressive strengths were best fitted by the Bal'shin relation, S=S0(1‐ɛ)m, or by the Ryshkewitch relation, S=S0e−be, where S=strength of porous material, S0=theoretical strength of similar nonporous material, ɛ=porosity, and b and m=empirical constants.
Strength Behavior of Polycrystalline Alumina Subjected to Thermal Shock
Authors: HASSELMAN D. P. H.
Published: June 2006

Theoretical predictions of crack propagation behavior in brittle solids under conditions of thermal shock were verified by water quenching of cylindrical polycrystalline alumina rods followed by strength testing. The calculated quenching temperature difference (ΔTO) required to initiate thermal‐stress fracture agreed fairly well with experiment. When fracture was initiated, strength decreased catastrophically, in agreement with theory. An expression for the strength remaining after thermal stress fracture was derived in terms of the pertinent physical parameters. Values of surface fracture energy similar to those reported in the literature agreed with experiment. Strength after thermal shock was predicted to be inversely proportional to the 1/4 power of the rod diameter; this prediction was supported by experimental data for two rod sizes. Over a range of quenching temperature differences ΔTΔT0 strength remained constant, in agreement with the theoretical expectation that the newly formed cracks were subcritical. Only at the highest quenching temperature differences could further decreases in strength be observed; the quantitative changes, however, were masked by nonlinear deformation (evidenced by permanent crack opening). It was concluded that, although thermal shock behavior of brittle ceramics can be approximated fairly well, reliable quantitative estimates require considerably more information about strength and surface fracture energies as a function of environment, stress distribution, strain rate, and temperature and specimen size effects.
Phase Equilibria and Physical Properties of Oxygen‐Deficient Zirconia and Thoria
Authors: CARNIGLIA S. C. , BROWN S. D. , SCHROEDER T. F.
Published: June 2006

The compositions of anion‐deficient zirconia and thoria in equilibrium with O2 were measured from 1 to 10−6 atm and 1400° to 1900°C; for ZrO2‐x (po2 in atm, and T in °K), log x∼−0.890‐[(0.400×104)/T]‐[(log p)/6]; for ThO2‐x, log x∼−1.870‐[(0.340×104)/T]‐[(log p)/6]. The ZrO2‐x‐Zr boundary was located at x=0.014 at 1800°C; thoria was single‐phase over the entire range. Consistent results were obtained when O2/inert gas mixtures were used, but use of H2/H2O and CO/CO2 at 1000° to 1200°C gave abnormal and, in the latter case, erratic data; side reactions in these atmospheres are inferred. The monoclinic‐tetragonal phase change of ZrO2 and the lattice thermal expansion, room‐temperature Young's modulus, and strength properties of ZrO2 and ThO2 bodies were not appreciably altered by oxygen deficiency. The lattice dimensions decreased slightly with departure from stoichiometry.