bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal Conductivity of Refractory Castables
Authors: RUH EDWIN , RENKEY ALBERT L.
Published: June 2006

Thermal conductivity measurements were made on various refractory castabales of both dense fireclay and high‐alumina types as well as on several insulating castables. These tests, covering mean specimen temperatures of 200° to 2000°F, indicated how the thermal conductivity of a castable material varies with thermal history. The measurements were made using a modified ASTM C 201–47 apparatus.
Effect Of Grain Boundaries on Diffusion‐Controlled Processes in Aluminum Oxide
Authors: PALADINO A. E. , COBLE R. L.
Published: June 2006

Oxygen ion diffusion coefficients in single‐crystal Al2O3 are several orders of magnitude less than alminum ion diffusion coefficients in polycrystalline Al2O3. In polycrystalline Al2O3, oxygen ion diffusion is enhanced by the presence of grain boundaries as in the chloride ion diffusion in the alkali halides. Creep and sintering of polycrystalline Al2O3 occur at a faster rate than is possible through control by lattice diffusion of oxygen; the rates are in fair quantitative agreement with cation diffusion. It is tentatively concluded that enhanced oxygen diffusion in regions adjacent to boundaries allows aluminum ion bulk diffusion to be rate controlling for these processes. The electrical conductivity in Al2O3 is too high to be related to either anion or cation diffusion and is predominantly electronic.
Epitaxial Growth of Spinel by Reaction in the Solid State
Authors: ROSSI RONALD C. , FULRATH RICHARD M.
Published: June 2006

The condensed‐state reaction between single crystals of Al2O3 and MgO was conducted in air at 1560°C. Spinel formed as two product layers which were shown to agree with the proposed mechanism. The crystallographic orientation of the parent crystals had no effect on the rate of spinel growth. The orientation of the spinel grown from sapphire was the same as that found by other investigators for isomorphic crystals. The orientation of spinel grown from periclase was largely dependent on the transport mechanism across the periclase‐spinel interface.
Preparation and Properties of Uranium and Thorium Monosulfides
Authors: SHALEK P. D.
Published: June 2006

Uranium and thorium monosulfide bodies were made by the reaction of H2S with the metal at low temperature followed by homogenization and sintering at high temperature. Some US‐ThS solid solutions also were made. The effect of homogenization and firing temperature, S/metal ratio, impurities, and atmosphere on the densification, structure, and properties of these bodies is discussed. The properties evaluated include melting point, electrical resistivity, thermal conductivity, thermal expansion, hardness, strength, oxidation behavior, and compatibility.
Magnetostrictive Ferrites with Small Change in Coupling Coefficient from 0° to 20°C
Authors: BROCKMAN F. G. , BECK P. W. , STENECK W. G.
Published: June 2006

Ferrite materials which possess electromechanical coupling coefficients of 30% or more over the temperature interval 0° to 20°C were developed by the control of the various anisotropies. A high order of temperature stability of the coupling coefficient was achieved by a new technique in which a number of ferrites are combined in a composite core structure. Composite transducers made by the technique emerge as single bodies adn not as a composite made up of discrete parts.
Phase Studies in the Binary System MgO–Ta2O5
Authors: BASKIN Y. , SCHELL D. C.
Published: June 2006

The objective of this investigation was to determine subsolidus phase relations in the system MgO–Ta2O5 and to obtain accurate crystallographic data on the compounds formed. MgO and Ta2O5 formed three compounds: Mg4Ta2O9, Mg3Ta2O8, and MgTa2O6. Mg4Ta2O9 and MgTa2O6 appeared to be stable up to their melting points, whereas Mg3Ta2O8 was stable only between 1475° and about 1675°C. X‐ray diffraction and density data are presented for the three compounds.
Compressive Creep of Polycrystalline Beryllium Oxide
Authors: VANDERVOORT RICHARD R. , BARMORE WILLIS L.
Published: June 2006

Compressive creep of polycrystalline beryllium oxide was studied in the temperature range 2500° to 2800°F. The apparent activation energy for creep was 96.0 kcal per mole and the creep rate was linearly dependent on the applied stress. Results were consistent with the Nabarro‐Herring creep mechanism. Experimental evidence showed that extrapolation of data to 3200°F was possible.
Study of Crystallization of Glass Coatings on Metal by Electron Microscopy
Authors: CARLSON W. A. , SANFORD E. A. , CRANDALL W. B.
Published: June 2006

Controlled growth of crystals and immiscible phases in glass coatings on steel increased their resistance to mechanical and thermal shock. The electron microscope was used to follow crystal and immiscible phase development during heat treatment and to study the effect of crystals on fracture propagation in several complex glass compositions applied to metals by standard enameling techniques. Initial firing temperature, heating rates, heat treatment, and other enamel processes were found to affect the nature of the phases developed in the coatings. Crystals and immiscible phases caused fracture paths to be disrupted, resulting in nonconchoidal types of failure. A correlation is made between resistance to thermal shock and fracture properties.
Phase Equilibria for the Ternary Fused‐Salt System NaF–BeF2–UF4
Authors: EICHELBERGER J. F. , HUDGENS C. R. , JONES L. V. , PISH G. , RHINEHAMMER T. B. , TUCKER P. A. , WITTENBERG L. J.
Published: June 2006

The phase equilibrium diagram for the ternary fused‐salt system NaF–BeF2–UF4 was based on evidence from differential thermal analysis, polarized light microscopy, and X‐ray examination of samples obtained from thermal‐gradient quenching studies and from high‐temperature filtration experiments. All the stable compounds in the binary systems NaF–BeF2 and NaF–UF4 displayed primary‐phase fields in the ternary system, including a new subsolidus compound which was observed and tentatively assigned the formula NaF · 4UF4. No ternary compounds or solid solutions were observed. The following three eutectics were found in the ternary system: (1) 72.5 NaF, 17.0 BeF2, and 0.5 mole % UF4 at 486°C, (2) 56.0 NaF, 43.5 BeF2, and 10.5 mole % UF4 at 339°C, and (3) 43.5 NaF, 56.0 BeF2, and 0.5 mole % UF4 at 345°C.
High‐Temperature Steady‐State Creep in Rutile
Authors: HIRTHE WALTER M. , BRlTTAIN JOHN O.
Published: June 2006

The primary objective of this research was to study the interaction of point defects and dislocations in rutile at elevated temperatures. The steady‐state creep rate was obtained for near‐stoichiometric and vacuum‐reduced compression specimens in the range 1050° to 1325°K and for stresses from 2(108) to 9(108) dynes per cm2. For a constant stress, strain, and temperature, the activation energy for creep varies continuously from 67 kcal per mole for the near‐stoichiometric condition to about 33 kcal per mole for the highest degree of reduction. The activation energy for creep in hydrogen‐reduced rutile is about 80 kcal per mole and this leads to the conclusion that the rate‐controlling mechanism and/or defect are not the same for hydrogen‐ and vacuum‐reduced rutile. A model based on the interaction of piled‐up dislocations on a single slip system and high‐density polygon walls formed during creep is proposed to explain steady‐state creep in rutile.
High‐Pressure Effects on Oxide Glasses: I, Densification in Rigid State
Authors: MACKENZIE J. D.
Published: June 2006

Densification of SiO2, GeO2, and B2O3 glasses in the rigid state was studied at pressures up to 80 kb and at temperatures up to 600°C in different pressure‐transmitting media. The infrared, ultraviolet, and nuclear magnetic resonance absorptions of the compressed glasses were examined. Densification increased with time, temperature, pressure, and more important, with applied shear. This process of volumetric shrinkage in the rigid state at low temperatures is fundamentally different from that at temperatures at or above the glass transition. A qualitative model involving mutual entanglement of parts of the random glassy network is postulated to explain the observed results.
Kinetic Studies of Crystallization of Synthetic Mica Glass
Authors: CHEN F. P. H.
Published: June 2006

The mechanism of crystallization of a synthetic mica glass was studied on the basis of microstructures and reaction kinetics. Uniform crystallization of this glass was found to occur by a two‐stage process. The glass first transformed to an intermediate pseudocrystalline phase from which mica crystals subsequently were formed. The kinetics of the reaction leading to this intermediate pseudocrystalline phase were studied quantitatively by microscopic methods. The nucleation of this intermediate phase was found to be heterogeneous. The growth of the rim of the plate‐shaped intermediate phase was an interface‐controlled process having an activation energy of 84 kcal per mole. The rate of growth of the intermediate phase was found to be consistent with previous relations that describe the kinetics of growth of crystals from a glass. The final mica phase initially formed at the interfaces of the intermediate phase and parent glass phase; later it progressively formed within the intermediate phase.
Pyrolytic Synthesis of Titanium Diboride
Authors: GANNON R. E. , FOLWEILER R. C. , VASILOS T.
Published: June 2006

Titanium diboride was synthesized by the vaporphase reaction of the chlorides of titanium and boron on a heated substrate. Under certain described conditions, the resulting deposit was found to have a preferred atomic arrangement which could be described as alternating layers of titanium and boron atoms perpendicular to the plane of deposition. Room‐temperature physical properties were determined and are reported.
Preparation of Ceramic Semiconductors from High‐Vanadium Glasses
Authors: HAMBLEN D. P. , WEIDEL R. A. , BLAIR G. E.
Published: June 2006

A number of phosphate glasses with unusually high vanadium content were studied with respect to some of their electrical properties. It was found that 75 to 85 wt% V2O5 could be reacted with various metaphosphates (Ba, Pb, Li, Na, Cd, V, and K) resulting in good‐quality reproducible glasses in 500‐g melts. The electrical resistance of these glasses appeared to be particularly dependent on their thermal history below the liquidus but above the transformation range. A large change in specific resistance resulted when vitreous specimens were heat‐treated to produce varying amounts of devitrification. For a specimen containing potassium metaphosphate, resistivity was reduced from about 103 to 10 ohm‐cm.
Diffusion Sintering: I, Initial Stage Sintering Models and Their Application to Shrinkage of Powder Compacts
Authors: JOHNSON D. LYNN , CUTLER IVAN B.
Published: June 2006

Consideration is given to several geometrical models that contribute to shrinkage. Various shapes of particles, vacancy sinks, and diffusion paths are described as they affect sintering shrinkage. These simplified models are extended to compacts of nonuniform particles so that much of the kinetics of sintering of a substance can be determined by measuring shrinkage rates of powder compacts. A nonideal compact may sinter as though it had once been an ideal compact after a specific amount of shrinkage has occurred. This shrinkage is characteristic of the particular compact and its origin and is independent of temperature.
Thermal Decomposition of Some Substituted Barium Titanyl Oxalates and Its Effect on the Semiconducting Properties of the Doped Materials
Authors: GALLAGHER PATRICK K. , SCHREY FRANK
Published: June 2006

Thermal analysis has been performed on BaTiO(C2O4)2.4H2O, Ba0.6Sr0.4TiO(C2O4)2.4H2O, Sr(TiO(C2O4)2.4H2O, Ba0.9Pb0.1TiO(C2O4)2.4H2O, and BaTi0.9Zr0.1O(C2O4)2.4H2O. It was observed that the strontium compound decomposes differently than the others. Previous investigators have proposed conflicting mechanisms for the pyrolysis of the barium salt and these results are discussed in comparison with this work. The electrical resistivity and temperature coefficient of fired lanthanum‐doped materials were found to vary with the calcination temperature. Maximum conductivity was observed in samples calcined at 900°C whereas maximum positive temperature coefficient was observed for materials calcined at 1050°C. Particle sizes of the calcined material were compared with grain sizes in the fired pieces and correlated with the electrical properties. A cursory examination was made on the effects of fabrication pressure, 1.25 to 15 tsi, on the electrical conductivity. Both the conductivity and positive temperature coefficient were found to increase with decreasing fabrication pressure.
Oriented Hexagonal Ferrite Compounds for Application at Millimeter Wave Frequencies
Authors: HODGES L. R. , HARRISON G. R.
Published: June 2006

Oriented hexagonal ferrite compounds of the formula BaO·[(2 ‐ × ‐ y)NiO·xCoO·yZnO] ·‐(7.8 —δ‐G)Fe2O3·δAl2O3 are discussed for x = 0 to 0.8; y = 0 to 2.0; and δ= 0 to 1.0. Preparation procedures are described briefly. X‐ray techniques are used to determine the degree of orientation of the samples. Cobalt and aluminum substitutions result in a change of 4000 to 19,000 oersteds in anisotropy field for the range of substitutions made. Magnetization and anisotropy field data are reported for all substitutions. The temperature characteristics of the magnetization and the anisotropy field are reported for many of the compounds. The application of these materials in millimeter resonance isolators operating in the frequency region of 18 to 60 Gc is discussed briefly.
Mechanical Properties of Pure, Dense Magnesium Oxide as a Function of Temperature and Grain Size
Authors: VASILOS T. , MITCHELL J. B. , SPRIGGS R. M.
Published: June 2006

The elastic modulus and transverse bend strength of pure, dense magnesia were determined as a function of grain size (1 to 190μ) and temperature (30° to 1500°C). The elastic modulus was essentially independent of grain size over the temperature range covered. The transverse bend strength for magnesia revealed a 1/6 power dependency versus grain size at low temperatures, i.e. STB= 50,000 G−1/6 At temperatures above approximately 600°C, the strength of specimens of all grain sizes tested decreased with temperature and the grain size dependence, of strength also decreased. Nonlinear load‐deflection behavior was observed at temperatures above approximately 700°C and etch pit observations of dislocations produced during deformation and fracture of large‐grain magnesia specimens revealed extensive slip in grains adjacent to the fracture area.
Calculated High‐Temperature Elastic Constants for Zero Porosity Monoclinic Zirconia
Authors: SMITH C. F. , CRANDALL W. B.
Published: June 2006

A method was developed for hot‐pressing 80 to 95% dense, polycrystalline specimens of commercially available, unstabilized, monoclinic zirconia. The elastic moduli of these specimens were measured by a sonic method in the range 25° to 1000°C. Application of mathematical expressions developed for the porosity dependence of elastic moduli of refractory oxides led to the calculation of Young's and shear moduli of this material at zero porosity in this temperature range.
Effect of Metal Additions on the Microstructure of Zirconia
Authors: RUH ROBERT , TALLAN NORMAN M. , LlPSITT HARRY A.
Published: June 2006

The diffusion of titanium into zirconia was studied to determine the mechanism by which increased sintering occurred in the metal‐modified zirconias. Results revealed that the increased sintering occurred only when compositions above the solubility limit were fired considerably above the melting point of the titanium. Examination of the system Ti‐Zr‐0 revealed that considerable liquid was present at these firing temperatures. This liquid phase promoted the sintering of the zirconia. The increased sintering did not occur for compositions above the solubility limit fired below the temperature of liquid phase formation, or for compositions below the solubility limit fired considerably above or below the melting point of titanium.
Electrical Properties and Defect Structure of Zirconia: I, Monoclinic Phase
Authors: VEST R. W. , TALLAN N. M. , TRlPP W. C.
Published: June 2006

The defect structure of monoclinic zirconia was investigated by measuring the oxygen partial pressure dependence of the electrical conductivity and sample weight. Techniques were developed to calculate the degree of nonstoichiometry and the mobility of the charge carriers from electrical and weight change data. ZRO2 was found to be an amphoteric semiconductor at 1000°C with the transition from n‐type to p‐type conductivity occurring at 10–16 atm. The predominant defect in the oxygen excess region was shown to be completely ionized zirconium vacancies. The positive holes arising from the zirconium vacancies were found to have an extremely small mobility.
Thermal Stability of Barium Ferrite (BaFe12O19)
Authors: VAN HOOK H. J.
Published: June 2006

Compositions in the system Fe2O3‐FeO‐BaO in the vicinity of the compound BaFe12O19 were studied at temperatures from 1300° to 1550°C and oxygen pressures from 10−2 to 102 atm. Equilibrium relations involving several barium ferrous ferrites are described. Barium ferrite can be crystallized congruently from the melt at 40 atm oxygen pressure and 15400°C.
Studies in Lithium Oxide Systems: XIII, Li,O.Al2O3.2SiO2‐Li2O.Al2O3.2GeO2
Authors: TlEN T. Y. , HUMMEL F. A.
Published: June 2006

Complete solid solubility was demonstrated to occur between LiAlGeO4 and the low temperature form of Li AlSiO2 (a‐eucryptite). Hydrother‐mal preparation was necessary for the silicate‐rich compositions. Under atmospheric pressure, about 65 mole % LiAlGeO4 entered the β‐eucryβ‐tite phase at 1150°C, but solid solutions containing more than 25 mole % LiAlGeO4 exsolved if held at lower temperatures. Directional thermal expansion data were obtained by X‐ray diffraction methods on both α‐ and β‐eucryptite and their solid solutions. Substitution of Ge4+ for Si4+ produced no significant difference in the thermal expansion coefficients in the α and β phases. An increase in the lattice parameters in the a and c directions took place as expected when Ge4+ (0.53 A) was substituted for Si4+ (0.39 A).
Effect of Silicone Quenching and Acid Polishing on the Strength of Glass
Authors: FLETCHER PETER C. , TILLMAN J. J.
Published: June 2006

Soda‐lime glass rods 5 mm in diameter were quenched in silicone oil and also in a saturated hydrocarbon oil of similar viscosity. The effect of etching, etching and quenching, and etching, quenching, and re‐etching was examined in relation to the strength of the rods. Rods quenched in the silicone oil were no stronger than those quenched in the hydrocarbon oil. Etched rods had a strength of 300,000 psi. Quenching these high‐strength rods reduced their strength to 110,000 psi. This decrease in strength may be explained in terms of the formation of crystalline and noncrystalline microflaws during the heating and cooling cycle. Re‐etching, after quenching, resulted in rods with a maximum strength of 384,000 psi.
Thermal Decomposition of Europium Hydroxide
Authors: RAU ROBERT C. , GLOVER W. J.
Published: June 2006

The thermal decomposition of europium hydroxide in an air atmosphere was investigated by means of weight‐loss measurements, infrared spectroscopy, X‐ray diffraction analysis, and electron microscopy. These studies showed that EU(OH)° decomposed at temperatures between 225° and 300°C into EuOOH, which was stable up to about 425°C. Between 435° and 465°C this compound decomposed into cubic Eu2O3, which was stable until its inversion to the high‐temperature monoclinic form. X‐ray diffraction data were collected for Eu(OH)3 and EuOOH and showed that the trihydroxide has a hexagonal crystal structure and the oxyhydroxide is possibly orthorhombic. The Eu(OH)2, EuOOH, and cubic EunOa powders contained particles up to several microns in size consisting of agglomerates of crystallites in the size range 200 to 400 A. The single monoclinic Eu2O3 sample studied contained crystallites whose average size was greater than 2000 A.
Solubility and Crystal Growth of ZnAl2,O4 and AI2O3 in Molten PbF2 Solutions
Authors: GIESS EDWARD A.
Published: June 2006

The solubility of ZnAl2O4 (gahnite spinel) and NZOI (corundum) in their respective molten PbF2 solutions was determined by a sealed‐tube quenching method between 900° and 1250°C. Differential thermal analysis was used below 900°C. The solubilities (crystal‐constituent/ PbF2 weight ratio) at 1200°C were 0.151 for A12O3 and 0.108 for ZnAl2O4, whereas at 900°C they were 0.093 and 0.048, respectively. These results are compared with those of single‐crystal growth experiments and the crystalline products are described.
Ionic Conductivity of Cubic Solid Solutions in the System CaO—Y2O3—ZrO2
Authors: STRICKLER D. W. , CARLSON W. G.
Published: June 2006

The ionic conductivity of cubic solid solutions in the system CaO ‐Y2O3‐ZrO2 was examined. Particular Y2O3‐ZrO2 binary compositions were more conductive at elevated temperatures (>600°C) than either CaO‐ZrO2 binary or CaO‐Y2O3‐ZrO2 ternary compositions. The higher ionic conductivity appears to be related to a lower activation energy rather than to the number of oxygen vacancies dictated by composition. Those compositions of highest conductivity lie close to the cubic‐monoclinic solid‐solution phase boundary. Conductivity‐temperature data are presented that indicate a reversible order‐disorder transition for Y2O3‐ZrO2 cubic solid solutions containing 20 and 25 mole % Y2O3. The transference number for the oxygen ion at 1000°C for Y2O2‐ZrO2 cubic solid solutions is greater than 0.99.
Effect of Powder Parameters on Grain Growth in Manganese‐Zinc Ferrite
Authors: YAMAGUCHI T.
Published: June 2006

The effect of calcination and ball milling on the grain growth in Mn‐Zn ferrite is presented. Rates of grain growth and the effect of ball milling on the growth behavior were observed for ferrite powders calcined above and below the recrystallization temperature. It is shown that in addition to particle size and distribution, calcination temperature was a critical factor responsible for the growth behavior of ferrite.
Growth of Single Crystals of BaTiO3 by Exaggerated Grain Growth
Authors: DeVRIES R. C.
Published: June 2006

Grain‐growth experiments with steep temperature gradients and with polycrystalline aggregates seeded with single crystals were carried out to explore the feasibility of growing large crystals of BaTiO3 in the solid state. It is shown that both methods resulted in a large increase in size of crystals normally obtained by sintering but that the rapid grain‐boundary motion resulted in high porosity. Definite orientation dependence of grain‐boundary velocity is demonstrated, and growth in a 〈110〉 direction was found to be at least as fast as 2 mm per hour.
Preparation and Crystallographic Properties of A2+B22+O4, Type Calcium and Strontium Scandates
Authors: CARTER J. R. , FEIGELSON R. S.
Published: June 2006

The compounds CaSc2O4 and SrSc2O4 were synthesized by solid‐state reaction of the component oxides at temperatures ranging from 950° to 1400°C. Both calcium and strontium monoscandates are orthorhombic and analogous to CaFe2O4. Lattice parameters for CaSc2O4a re ao= 9.461, bo= 11.122, co= 3.143 and for SrSc2O4, ao= 9.698, bo= 11.302, co= 3.185. Based on four molecules per unit cell, the X‐ray density for CaSc2O4 is 3.89 g per cm3 and that for SrSc2O4 is 4.59 g per cm3.
Effect of Starting Materials on Phase Relations in the System CaO—Al2O3—H2O
Authors: CROWLEY M. S.
Published: June 2006

Phase relations in the system CaO‐Al2O3‐H2O from 40° to 500°F have been determined by hydrothermal techniques. Very high purity starting materials (luminescent‐grade CaCO3) must be used if the correct phase relations for this system are to be determined. A phase diagram of the system made by using reagent‐grade CaCO3 is compared with the diagram obtained from the luminescent‐grade material. The general effect of introducing foreign ions into the system is to promote the formation of the dicalcium aluminate hydrate phase. Adding various clay structures to starting mixtures had relatively little influence on the resulting phases. The action of additives on calcium aluminate cements depends on such factors as the phase relations, the nature of the hydrated alumina, and the interrelations of these factors with variable pH, foreign ions, and pressure‐temperature variations.
Oxygen Ion Diffusion in Single‐Crystal and PoIycrystaIIine Yttrium Iron Garnet
Authors: PALADINO A. E. , MAGUIRE E. A. , RUBIN L. G.
Published: June 2006

The oxygen ion self‐diffusion coefficient was determined for single‐crystal and polycrystalline yttrium iron garnet (Y3Fe5O12). The rate of exchange between oxygen gas enriched with the stable isotope 18O and solid yttrium iron garnet was measured. Oxygen ion diffusion rates were found to be the same in single‐crystal and 8μ polycrystalline Y3Fe5O12 between 1100° and 1400°C. This is in contrast to previous measurements of anion diffusion in several alkali halides and in AI2O3 where a strong dependence of diffusion rates on the presence of grain boundaries was found. Enhancing oxidation rates in dense, reduced yttrium iron garnet at low temperature by minimizing the final fired grain size in the sintering process does not appear to be possible on the basis of the results obtained in this investigation. The temperature dependence of the diffusion coefficient of oxygen measured at 100 torr can be represented by D= 0.40 exp (‐65.4/RT) cm2 per second.
Creep, Strength, Expansion, and Elastic Moduli of Sintered BeO As a Function of Grain Size, Porosity, and Grain Orientation
Authors: FRYXELL R. E. , CHANDLER B. A.
Published: June 2006

Physical properties are presented for extruded and sintered BeO from 25° to 1400° C as a function of porosity (0 to 15%), grain size (5 to 100μ), and grain orientation (random to 80% preferred). The elastic constants and linear thermal expansion are sensitive to the degree of preferred grain orientation. Measurements on polycrystalline specimens permitted calculation of the anisotropy in single crystals of BeO for these properties. Modulus of rupture data are treated in terms of the Knudsen equation, and compressive creep data have been used to estimate the diffusion coefficient controlling strain rate at 1200°C.
Humidity Drying of Plastic Clay
Authors: LANCASTER BRIAN W. , McCARTNEY ERIC R.
Published: June 2006

The humidity drying cycle gives rise to surface and body cracks in plastic clay. The cracks appear in the initial stages when the clay is being heated in a saturated atmosphere. Various factors affecting cracking in this initial heating stage were studied using a purified kaolin in the plastic state, and appropriate experimental models were used to isolate certain aspects for study. It is shown that the condensation of moisture on the clay surface is the major factor influencing the cracking of the plastic clay. The effect of thermal diffusion is insignificant and the loss of mechanical strength is of secondary importance. The balance af evidence from the literature and from this study indicates that capillarity plays a major part in the movement of moisture and the production of stresses during drying. When air spaces are present in the body, thermal capillarity may become important. Stresses caused by thermal expansion oppose those caused by drying shrinkage, while the thermal expansion of capillaries will have a negligible effect.
Microstructure of Chromite‐Periclase at 1650° to 2310°C
Authors: SCHEERER P. E. , MIKAMI H. M. , TAUBER J. A.
Published: June 2006

Progressive solid solution of chromite in periclase occurs with increasing temperature. Solid solution is virtually complete except for a few coarse remnants at 1980° C and these are gone at 2090° C. Specimens cooled slowly exhibit exsolution structures, whereas specimens quenched from the higher temperatures consist essentially of a single solid‐solution phase. Two periclase structure phases are indicated by X‐ray patterns in some quenched specimens. Silicate alters the relations between chromite and periclase in specimens cooled slowly and facilitates segregation of spinel from the solid solution in quenched specimens. Textural features observed in electrically fused specimens are similar to those resulting from predominantly solid‐state reactions in specimens fired to 2200°C.
Mechanical Properties of Hot‐Pressed Zirconium Carbide Tested to 2600°C
Authors: LEIPOLD MARTIN H. , NIELSEN THOMAS H.
Published: June 2006

Tensile, creep, and modulus of elasticity data were determined for hot‐pressed zirconium carbide. The material was relatively impure, containing 1 to 2% nitrogen and 1 to 2% free carbon. Tension and creep properties, which were measured to 2600° C, indicated that above 2100°C the strength was 2000 psi or lower and the elongation was 40% or more, thus signifying little structural usefulness. It is proposed that the results were influenced by impurities at the grain boundaries. Room‐temperature modulus of elasticity values averaging 51.6 × 106 psi were obtained by dynamic methods.
Mechanical Behavior of Single‐Crystal and Polycrystalline Cesium Bromide
Authors: JOHNSON LAWRENCE D. , PASK JOSEPH A.
Published: June 2006

Plastic‐deformation studies were made of cesium bromide which exhibits no cleavage planes. Single crystals were found to be “soft” and ductile if they were favorably oriented relative to the loading axis to activate the {110}∝001〈 slip systems. Kink bands were formed by applying a compressive load normal to a {100} plane. Cross slip was found to occur during deformation at all test temperatures. Tensile loads applied normal to {100} and {110} planes caused fracture along {110} planes, whereas compressive loads normal to {100} planes forced fracture along {112} planes. The ductility of polycrystalline cesium bromide was found to be limited because of the lack of five independent slip systems. The specimens with smaller grains showed less strain at fracture and greater strain hardening than the larger‐grained specimens. The mechanism fracture was intergranular up to 300° C.
Relation of Single‐Crystal Elastic Constants to Polycrystalline Isotropic Elastic Moduli of MgO: II, Temperature Dependence
Authors: CHUNG DAE‐HYUN , LAWRENCE WILLIS G.
Published: June 2006

The technical adiabatic elastic moduli E[hkl] and Ghkl of single crystals of magnesium oxide were measured over the temperature range 298° to about 1600°K by a Förster‐type resonance method. These data were compared with the low‐temperature values (80° to 560°K) of the principal elastic constants cij and coefficients Sy reported by Durand. Combining Durand's data and the present data, the elastic moduli for single‐crystal magnesium oxide were evaluated for the temperature range 80° to 1600°K. Young's modulus and the shear modulus of densely formed isotropic polycrystalline magnesium oxide were measured over the temperature range 298° to 1600°K. The data on the elastic constants of the single crystals were compared with the measured elastic moduli of the isotropic polycrystalline magnesium oxide on the basis of the Voigt‐Reuss‐Hill approximation. The temperature dependence of the elastic moduli was fitted into the expression M = Mc— BT exp (—Tc/T) suggested by Wachtman et al.; mean deviations were less than 0.4% for the temperature range considered. The significance of the present data is discussed with particular emphasis on the following points: (1) the temperature variation of the elastic modulus is a function of thermal expansion, (2) the temperature dependence of the elastic modulus can be well described by the foregoing expression for a wide range of temperature, (3) the expression gives a value of the elastic modulus at 0°K, and (4) it may be possible to make use of measurements on the elastic properties of a densely sintered polycrystalline material to obtain information heretofore obtainable only from the corresponding single‐crystal data.
Phases in the Binary Systems PbO—La2O3, Gd2O3, and Sm2O3
Authors: WARZEE MADELEINE H. , MAURICE MARCEL , HALLA FRANZ , RUSTON WALTER R.
Published: June 2006

In the binary system PbO–LazO3 only one compound, 4PbO.La2O3, exists; it is flanked by two eutectics. The structure of the compound, although of lower symmetry, is intimately related to the C modification of the rare earths. Below 800° to 1000°C, metastable solid solutions are formed from oxide mixtures coprecipitated from mixed solutions of the nitrates, the cubic parameter a= 5.66 A, if extrapolated to pure La2O3, corresponding to half the a parameter of the C form of La2O3. The solid solutions existing between the compositions La2O3–2Pb0 and pure La2O3 have a cubic face–centered lattice and obey Vegard's rule. The systems of PbO with Sm2O3 and Gd2O8 are quite similar to that with La2O3. The compound Sm2O3.4Pb0 decomposes at 1000°C with evaporation of PbO; Sm2O3 remains in the B modification.
Influence of CaCO3 on the Hydration of 3CaO·Al2O3
Authors: FELDMAN R. F. , RAMACHANDRAN V. S. , SEREDA P. J.
Published: June 2006

The influence of CaCO3 on the hydration of 3CaO Al2O3 containing about 90% C3A is studied with compacts of their mixtures proportioned to 0, 2.5, 10, 20, and 50 wt% CaCO3. The compacts are exposed to H2O in liquid and in vapor phase, the attendant expansion being measured as a function of time. Differential thermal analysis, infrared absorption, and X–ray diffraction are used in conjunction with this technique. It is shown that the hydration reaction of 3 CaO · Al2O3 is suppressed by CaCO3 additions and that this is due primarily to the formation of the low form of calcium carboaluminate on the surface of the C3A grains. Expansion measurements of the compacts during the reactions show that this technique indicates the progress of hydration and detects the formation of the carboaluminate at an early stage of the reaction. Using the same technique, a study at 50% relative humidity provides the basis for the conclusion that C3A reacts with CaCO3 under these conditions by a direct mechanism.
Strength of Glass—The Griffith Method Revised
Authors: SHAND ERROL B.
Published: June 2006

Techniques are described which widen the application of the Griffith method for studying brittle fracture and which improve its accuracy. Methods are given for the evaluation of the intensities of semielliptical surface flaws which can be used for fracture flaws of the size and type found in commercial glassware. Techniques are described for scoring flaws of this character. This revised method is used experimentally to study the effects of various glass treatments on breaking stress. Data on stress fatigue are used to compare the specific fracture energy at fatigue limits with conventional values of surface energy. Other data on fracture velocity obtained from the stress–fatigue curves are used for the critical review of a recently proposed theory of stress fatigue.
Anion Diffusion in α‐Cr2O3
Authors: HAGEL WILLIAM C.
Published: June 2006

Oxygen‐18 exchange between gaseous oxygen, held at a pressure of 125 mm Hg in a Pt10Rh chamber, and spheres of α‐Cr2O3 containing three or less grains was determined from 1100° to 1450°C. Isotope equilibrium on crystal surfaces appears to be quickly established, and the rate‐determining factor is self‐diffusion conforming to the relation D = 15.9 exp(‐101,000/ RT) cm2sec−1. Changing sphere diameters caused no detectable variation in diffusion coefficients. Anions are the much slower diffusing species in this oxide.
Factors and Mechanisms Affecting the Positive Temperature Coefficient of Resistivity of Barium Titanate
Authors: MacCHESNEY J. B. , POTTER J. F.
Published: June 2006

The chemistry of semiconducting lanthanum‐doped barium titanate was examined to determine the factors critical to the positive temperature coefficient of resistivity exhibited by this material. This phenomenon was sensitive to oxidation under certain nonequilibrium conditions. Inhomogeneity is thought to result from such conditions and to produce regions of different resistivity throughout the ceramic body. The existence of high resistivity layers was demonstrated by analysis of dispersions in ac resistance at audio frequencies. Association of these layers with crystallite surfaces, i.e. grain boundaries, was demonstrated by resistivity measurements of semiconducting single crystals before and after oxygen treatments.
Interdiffusion Studies of the System FexO‐MgO
Authors: RIGBY E. BERTRAND , CUTLER IVAN B.
Published: June 2006

The solid‐state reaction between Fe,O and MgO is best described as counterdiffusion of the magnesium and iron ions through a relatively rigid oxygen ion lattice of the rock salt structure. A relation between a mutual diffusion coefficient and a controlled cation vacancy concentration was determined by an analysis of the concentration‐penetration curve of the Fe,O‐MgO solid solution. The diffusion coefficient increased approximately exponentially with a linear increase of the cation vacancy concentration. This may be represented by a linear increase of the entropy of activation with vacancy concentration. The enthalpy of activation for the diffusion reaction, 47.5 kcal per mole, remained independent of vacancy concentration.
Preparation and Fabrication of Molybdate Single Crystals for Optical Maser Studies
Authors: RUBIN J. J. , THOMAS R. A.
Published: June 2006

Molybdates containing trivalent rare‐earth ions are of interest for optical maser studies. Large single crystals of CaMoO4 were pulled by the Czochralski technique. The addition of Nb5+ ions to the melt led to consistently high optical quality CaMoO4:Nd3+ crystals. This improvement resulted in optical maser resonators with thresholds approaching the range required for continuous wave operation at room temperature.
Electrical Conductivity of Single and Polycrystalline Near‐Stoichiometric Rutile in the Range 600° to 1400°C
Authors: GREENER E. H. , BARONE F. J. , HIRTHE W. M.
Published: June 2006

The electrical conductivity of both single‐crystal and sintered near‐stoichiometric rutile was investigated over the range 600° to 1400°C and the oxygen pressure range 0.005 to 1.0 atm. Above 1200°C, the conductivity of single‐crystal and sintered rutile obeys the relation σ∼Po2−1/4. This can be explained on the basis of the excitation of the first electron from an oxygen ion vacancy‐two trapped electron defect associated with a departure from stoichiometry. The attendant activation energy for this mechanism is 1.8 ± 0.1 ev as calculated from the In σ vs. 1/T curves. The conductivity below about 900°C is independent of oxygen pressure and has been associated with impurity controlled defects. Activation energies of 1.0 ± 0.05 ev for the c direction and 1.5 ± 0.05 ev for the a direction and for sintered specimens were obtained for this mechanism. The electrical conductivity in the range 900° to 1200°C can be interpreted on the basis that the preceding two mechanisms act in parallel.
Deformation of Polycrystalline MgO at Elevated Temperatures
Authors: COPLEY STEPHEN M. , PASK JOSEPH A.
Published: June 2006

Stress‐strain curves for five types of polycrystalline MgO are presented as a function of temperature. All types were nominally dense and pure but differed in grain size, composition, and porosity. Above 1200°C deformation occurred by grain boundary shearing accompanied in some cases by slip; below 800°C, specimens fractured primarily by grain boundary parting with little permanent strain. Between 800° and 1200°C, one type deformed plastically by slip; the other four types were brittle. The observed behavior is analyzed in terms of the presence of mobile dislocations, the resistance to dislocation motion, and the strength of grain boundaries.
Formation and Properties of Barium Metaplumbate
Authors: NITTA TSUNEHARU , NAGASE KANEOMI , HAYAKAWA SHIGERU , IIDA YOSHIO
Published: June 2006

The preparation and the physical and electrical properties of BaPbO3 ceramics are described. The compound was formed by firing an equimolar mixture of BaCO3 and Pb3O4 in oxygen at 880°C. To produce the stoichiometric compound on firing in air at 980°C it was necessary to use an excess of PbO (molar ratio, Pb/Ba = 1.278). A well sintered ceramic was obtained only with a stoichiometric composition with a sintered density of 7.78. Free BaCO3 was found in the fired bodies including the PbO‐rich compositions. The electrical resistively of BaPbO3 was 8.3 × 10−4 ohm‐cm at 25°C with a temperature coefficient of +0.15%/°C.
Color and Structural Character of CdS‐CdSe Pigments
Authors: EROLES A. J. , FRIEDBERG A. L.
Published: June 2006

A study was conducted to characterize the solid phases of cadmium‐sulfur‐selenium red pigments. Continuous solid solution of CdS and CdSe and obedience to Vegard's law were confirmed by X‐ray diffraction analysis. An increased rate of color formation was realized by using smaller reactant particles. Thermal decomposition of the CdS‐CdSe solid solution involved the reappearance of the CdS‐CdSe mixtures with subsequent transformation of these resulting compounds.
The System Zirconium—Carbon
Authors: SARA R. V.
Published: June 2006

Phase relations in the system zirconium‐carbon were established by DTA, X‐ray, and metallo‐graphic methods. Only one phase, a monocar‐bide with the NaCl structure, was found. The low‐carbon phase boundary for the monocarbide contains 38.5 at.7, carbon between 1900’and 3300OC. The carbon‐rich boundary between 2850” and 330O°C is at 48.9 at.% carbon. ZrC melts congruently at 342O°C and 46 at.% carbon. The lattice parameter versus composition curve shows a maximum at 46 at.% carbon. The Zr‐ZrC eutectic is at 186O°C and 1 at.% carbon; the Zr‐ZrC eutectic is at 285O°C and 65 at.% carbon. Liquidus curves are inferred from the invariant points.
Fe‐Ta Oxides: Phase Relations at 1200°C
Authors: TURNOCK A. C.
Published: June 2006

Subsolidus phase relations of the oxides in the system Fe‐Ta‐O were experimentally determined at 1200°C, 1 atm total pressure, and variable partial pressures of oxygen. Tantalum pentoxide reacts readily with either ferrous or ferric oxide at subsolidus temperatures and the following ternary compounds have been synthesized: Fe4Ta209, Fe3Ta2O8‐1, FeTaO4, FeTa2O6, solid solutions between the latter two compounds, and tantalian magnetites. The compositions of solid solutions between FeTaO4 and FeTa2O6 were very sensitive to variation of oxygen pressure. This sensitivity explains the oxidation behavior of tapiolite. The incorporation into magnetite of up to 7 at.% Ta was demonstrated, with a resulting increase in the size of the unit cell and decrease in magnetic permeability.
Phase Relations and Glass Formation in the System PbO‐GeO,
Authors: PHILLIPS BERT , SCROGER MARGARET G.
Published: June 2006

Phase relations in the system PbO‐GeO2 were determined using the quenching technique. The five compounds detected were: 4PbO‐GeO2, 3PbO‐2GeO2, PbO‐GeO2, and PbO‐4GeO2. The 3:2 and 1:1 compounds melt congruently at 744° and 799°, respectively. The 4:1 compound melts incongruently at 726°C to PbO plus liquid, whereas the 1:4 compound melts incongruently to GeO2 plus liquid at 790°C. The 1:2 compound has a temperature range of stability between 707° and 730°. The data indicate that no liquid immiscibility gap exists in the system. Indices of refraction for glasses in the system were compared with lead silicate glasses. An addition of ∼65%PbO to GeO2 is required to prepare a glass with an index near 2.0 whereas with SiO2, ∼85% PbO is required. It appears that the lead germanate glasses have higher indices than all other two‐component oxide glasses. The addition of PbO to GeO2 decreases the rutile‐to‐quartz transformation temperature from 1000°C for pure GeO2 to 990°C. Infrared spectra of lead germanate glasses (∼60w% PbO) show that transmission is good up to 5.5μ but decreases drastically between 5.5 and 6.5μ.
Crystallization and Solubility of Zircon and Phenacite in Certain Molten Salts
Authors: Ballman A. A. , Laudise R. A.
Published: June 2006

Single crystals of zircon as large as 0.7 cm and phenacite as large as 1.5 cm were grown from molten alkali metal vanadates and molybdates. The best crystals were obtained by slow cooling melts of Na2O·3MoO3 or Li2O·3MoO3 saturated with zircon or phenacite from 1400° to 900°C at a rate of 2° per hour. Crystals grown on a seed by a thermal gradient process contained inclusions although rates up to 1 mm per day were obtained. Zircon crystals could be doped with Nd3+, Eu3+, Pr2+, Fe3+, Cr3+, and Mn2+. The rare earths fluoresced at their characteristic frequencies but no fluorescence was observed from the transition metal ions. Zircon crystals had the characteristic habit, being bounded by m (110) and p (111) faces. Phenacite had a rhombohe‐dral habit when grown above 1000° and crystallized as hexagonal needles below that temperature. The solubility of zircon in Na2O·3MoO3 obeys the Van't Hoff equation with a heat of solution of 5.5 kcal per mole. The heat of solution of zircon and phenacite increased when V2O5 was substituted for MoO3 in the solvent, increased when NazO was substituted for Li2O, and increased further when K2O was substituted. The solubility was higher in solvents containing V2O5 than in those containing Moo3. Solvent‐solute interactions were strongest when the solvents were strong Lewis acids since zircon and phenacite behave as bases.
Structural Changes Accompanying Deformation in Pyrolytic Graphite
Authors: Kotlensky W. V. , Martens H. E.
Published: June 2006

Electron microscopy and X‐ray diffraction techniques were used to follow the structural changes in pyrolytic graphite which accompany deformation produced by applying a stress parallel to the substrate. Basal slip and an increase in preferred orientation account for deformations up to 14%. The mechanism by which deformation above 14% occurs is not well understood. Some evidence indicates that deformations above 14% may be associated with fracture across the basal planes with subsequent basal slip, an increase in porosity, and a very slight increase in preferred orientation. Rows of etch pits which may delineate an array of dislocations were observed in a specimen heated at 3000° C without load.
Electrical Properties of Crystallized Glasses in the System MgO‐Al2O3‐SiO2‐TiO2
Authors: KUMAR S. , NAG B. B.
Published: June 2006

The glass composition MgO 15.5, Al2O3 19.5, SiO2 58.5, and TiO2 6.5 (wt%) was crystallized under controlled conditions in the range 900° to 1140°C and the electrical properties were studied. The activation energy for dc and ac conduction in the uncrystallized specimen was 32.0 and 27.4 kcal/mole, respectively; the corresponding values for the crystallized specimens were about 18.5 and 11.6 kcal/mole. X‐ray studies and color of the crystallized specimens suggested the presence of magnesium aluminum titanate crystals in which part of the titanium was reduced to the Ti3+ state. These semiconducting phases were suggested as being responsible for the sharp change in the electrical properties and for the appearance of an apparent dielectric relaxation peak. Changes in the electrical properties with increasing crystallization temperature may be related to the nature, size, and shape of the crystals.
Dislocation Damping in Rutile Single Crystals
Authors: CARNAHAN R. D. , BRITTAIN J. O.
Published: June 2006

Rutile (TiO2) crystals exhibited amplitude dependent internal friction behavior characteristic of that associated with dislocation damping. The generation of excess nonstoichiometric defects decreased damping, particularly for the (1|01) [1|01|] extended dislocation system. An increase in test temperature decreased damping, suggesting that ionized defects may interact more strongly with dislocations than the defects characteristic of lower temperatures.