bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Stress and Strain on Producing Hackle in a Glass Plate
Authors: BARSOM JOHN M.
Published: June 2006

The effect of thermally induced stress and strain on producing hackle was studied for both symmetric and asymmetric temperature distributions through the thickness of a glass plate. A relation was obtained between stress and strain and hackle for glass from 1/8 to 1/2 in. thick at 100° to –110°F. The bath temperatures used were those of ice at 32°F, a mixture of dry ice and acetone, and water at 100°F.
Initial Sintering of α‐Cr2O3
Authors: HAGEL WILLIAM C. , JORGENSEN P. J. , TOMALIN D. S.
Published: June 2006

Since the difference between oxygen‐ion and cation diffusion coefficients is greater for α‐Cr2O3 than for α‐Fe2O3 or α‐Al2O3, a study of initial‐sintering kinetics was undertaken to show unequivocally which species is rate controlling. Fine powders of α‐Cr2O3, obtained by thermal decomposition of reagent‐grade (NH4)2Cr2O7, were lightly compacted and their isothermal rates of shrinkage were determined between 1050° and 1300°C. Resultant data follow volume‐diffusion sintering models, and calculated diffusion coefficients agree with, those measured for oxygen ions in α‐Cr2O3. There is little evidence that oxygen diffusion along grain boundaries becomes so enhanced that chromium ions are left in control of the process.
Sublimation of Aluminum Oxide in Hydrogen
Authors: READEY D. W. , KUCZYNSKI G. C.
Published: June 2006

The sublimation of single‐crystal Al2O3spheres and plates in pure, dry H2was studied. The kinetics of this process are controlled by diffusion of the volatile gaseous products through the stagnant gas boundary layer adjacent to the surface. The evaporating species are probably the lower oxides of aluminum obtained by reduction of Al2O3with hydrogen. The etching of the surface by heating in dry H2was also studied. The basal planes developed most easily. The facets formed were fine steps consisting of basal and prismatic planes. Condensation of the vapors in the form of small crystallites of thin plates and whiskers of Al2O3was observed in the colder regions of the furnace.
Phenomenological Theory of High Permittivity in Fine‐Grained Barium Titanate
Authors: BUESSEM W. R. , CROSS L. E. , GOSWAMI A. K.
Published: June 2006

The anomalously high permittivity in fine‐grained ceramic barium titanate is explained by the absence of 90° twinning within the grains, giving rise to internal stresses as the ceramic cools below the Curie temperature. Using the Devonshire phenomenological thermodynamic method and a simplified model, the stresses involved are calculated. At these stress levels, the reduced strain calculated on this model agrees well with X‐ray data for the fine‐grained material. The limitations and possible developments of the proposed model are discussed.
Creep of Dense, Polycrystalline Magnesium Oxide
Authors: PASSMORE E. M. , DUFF R. H. , VASILOS T.
Published: June 2006

Creep of polycrystalline MgO was studied using four‐point transverse bending at 1380° to 1800°K and stresses from 1000 to 5000 psi. The effects of temperature, stress, and grain size on the creep rate were determined for grain sizes from 2 to 20μ. Activation energies for creep decreased sharply with increasing grain size from 96,000 cal/mole at 2μ to 54,100 cal/mole at 5.5μ and then remained constant over the grain‐size range 5.5 to 20μ. Creep was attributed in part to a stress‐directed diffusional mechanism controlled by extrinsic oxygen ion diffusion in the 5.5 to 20μ grain sizes, although the calculated ionic self‐diffusion rates were higher than those predicted by the Nabarro‐Herring theory. It is suggested that the discrepancy may be due to a vacancy formation mechanism, which is consistent with the observed formation of dislocation substructure and preferentially distributed porosity during creep, as well as with the observed decrease in creep rate with increasing creep strain.
Grain‐Boundary Reactions in Magnesia‐Chrome Refractories: Application of the Electron Probe, II
Authors: de MENEZES I. , STUBICAN V. S.
Published: June 2006

When a magnesia‐chrome refractory is heated in air a reaction layer develops around the chromite grains. This layer is magnesioferrite at 800°C; above 800° it comprises a solid solution of spinel of the type Mg(Al,Cr,Fe3+)2O4 and a magnesiowustite solid solution. As the temperature increases, the composition of the spinel in the reaction layer changes toward enrichment in chromium and aluminum and impoverishment in iron. A direct‐bond chromite‐periclase, well defined at about 1750°C, is formed essentially by diffusion. In slowly cooled specimens the average composition of the spinel in the reaction layer in the direct bond approximates to Mg(Al0.05Cr0.40‐Fe0.10)2O4. The order of diffusion of the individual ions from chromite to periclase is: Fe ≫ Cr > Al. This order can be explained by considering the charge and size of ions involved and the energy required to create cation vacancies. In specimens quenched from high temperatures the concentration of the magnesium‐rich phases in the silicate pockets increases in the direction of the periclase grains whereas the calcium‐rich phases are concentrated at the center of the pockets.
Equilibria in KAlF4‐Containing Systems
Authors: PHILLIPS BERT , WARSHAW C. M. , MOCKRIN I.
Published: June 2006

Stability relations in the systems KF‐AlF3, KAlF4‐RbAlF4, and KAlF4‐RbAlF4‐KBF4 were established using DTA, direct observational analysis, and quenching techniques. Two KF‐AlF3 compounds, K3AlF6 and KAlF4, are stable and, on cooling, cubic KAlF4 inverts (between ‐23° and +50°C) to an orthorhombic modification. On heating, the cubic form is stable to the congruent melting temperature of 574°± 1°C. Melting points of K3AlF6, and AlF3 are 985° and 990°C, respectively. The compounds KAlF4 and RbAlF4 form a complete solid solution with a relatively narrow solidus‐liquidus interval. As little as 5 mole % RbAlF4 in the KAlF4 lattice greatly affects the low‐temperature inversion, causing it to occur below the temperature of liquid nitrogen (−196°C).
Solid Solution of Titanium Dioxide in Aluminum Oxide
Authors: WINKLER E. R. , SARVER J. F. , CUTLER IVAN B.
Published: June 2006

The solid solution limit of titanium dioxide in Al2O3 was investigated using diffuse reflectance and cathodoluminescence measurements on polycrystalline Al2O3 doped with 1.0 mole % or less TiO2. The samples had been fired in air at 1300°C. The diffuse reflectance spectra indicated that the solid solubility limit is between 0.25 and 0.30 mole %. Cathodoluminescence spectra indicated that both Ti3+ and Ti4+ are present in air‐fired samples whereas only Ti3+ is present in hydrogen‐fired samples.
Surface Composition of Porous Glass
Authors: HAIR MICHAEL L. , CHAPMAN IAN D.
Published: June 2006

Both boron and silicon were detected on the surface of porous glass. Infrared and adsorption data show five or six times more boron in the surface than can be expected from chemical analysis of the porous glass. It is suggested that the excess of boron in the surface occurs during the leaching of the base glass.
Sintering Characteristics and Properties of PuS and PuP
Authors: KRUGER O. L. , MOSER J. B.
Published: June 2006

The compounds PuS and PuP were prepared by high‐temperature homogenization of the product from the reaction of H2S or PH3 gas with partly decomposed plutonium hydride. Studies of sintering characteristics of pellets fired in vacuum and in an argon atmosphere showed that these materials can be sintered to densities slightly greater than 90% of theoretical. The sintering process appears to be complex due to changes of mechanism with increasing temperature. Weight loss data indicate that PuP has a higher effective vapor pressure than PuS but under conditions of fuel irradiation (1 atm pressure of inert gas) PuP has a much lower rate of vaporization. Microstructural examinations and lattice constant measurements verify that monosulfide and monophosphide can exist as substoichiometric compounds. Curvature of the sulfur‐rich phase boundary toward greater sulfur solubility at high temperatures is indicated from the X‐ray data. Density, melting point, thermal expansion, microhardness, Seebeck coefficient, electrical resistivity, thermal diffusivity, heat capacity, and thermal conductivity are reported.
Tellurite Glasses
Authors: YAKHKIND A. K.
Published: June 2006

The boundaries of regions of glass‐forming compositions were determined in binary tellurite systems with alkali, alkaline‐earth, and heavy‐metal oxides, and in the ternary systems TeO2‐WO3‐Ta2O5, TeO2‐WO3‐BaO, TeO2‐WO3‐Bi2O3, and TeO2‐WO3‐Tl2O. On the basis of a structural interpretation of liquid immiscibility in binary oxide systems and of X‐ray diffraction investigation of the structure of tellurite glasses, a crystallochemical interpretation of glass formation is proposed, as well as a method for calculating the modifier‐poor boundaries of the regions of glass‐forming compositions in binary systems. An investigation of the crystallizability, density, optical constants, spectral transmission characteristics, and chemical durability of the tellurite glasses as functions of their chemical compositions has led to the development of a new flint‐type optical glass, with nd= 2.1608 and v= 17.4, possessing a high chemical durability and resistance to devitrification.
Ferroelectrics of Ultrafine Particle Size: I, Synthesis of Titanate Powders of Ultrafine Particle Size
Authors: KISS KLARA , MAGDER JULES , VUKASOVICH MARK S. , LOCKHART ROBERT J.
Published: June 2006

Two methods used to synthesize high‐purity ferroelectric titanate powders in controlled, narrow size distributions, with average particle diameters <1000 A, were: (1) isothermal pyrolysis of barium titanyl oxalate or mixed calcium‐barium titanyl oxalates as low as 550° and 825°C, respectively, average particle sizes depending strongly on the pyrolysis temperature; and (2) hydrolysis of titanate esters in barium hydroxide. Using solvent media of controlled polarity, high‐purity stoichiometric BaTiO3 was obtained with average sizes as small as 100 A. Factors affecting stoichiometry and particle size are discussed in terms of assumed reaction mechanisms.
Ferroelectrics of Ultrafine Particle Size: III, Thin Barium Titanate Layers for Capacitors
Authors: LOCKHART ROBERT J. , MAGDER JULES
Published: June 2006

The large change in the dielectric constant of barium titanate near 120°C was smoothed out by the use of very small particle sizes and additions of tantalum oxide. Unsupported thin sheets of the material showed the same electrical properties as thick pellets. Stacked capacitors made from these sheets, using platinum electrodes, showed a maximum capacitance change over the range 25° to 180°C of 19 to 27%, based on the room‐temperature value.
Constitution of Mixed‐Alkali Phosphate Glasses: IV, Constitution of Lithium‐Cesium Phosphate Glasses
Authors: MURTHY M. K. , WESTMAN A. E. R.
Published: June 2006

The constitution of lithium‐cesium phosphate glasses was determined by paper chromatographic techiques. Because of the rather high hygroscopicity, glasses with M/P ratio >1.33 could not be prepared. With increase in cesium/lithium ratio, the tripoly and tetrapoly fractions increased, indicating a definite cationic effect. The significance of the results is discussed.
Activity‐Composition Relations in Co2SiO4‐Fe2SiO4 Solid Solutions at 1180°C
Authors: MASSE D. P. , ROSÉN ERIK , MUAN ARNULF
Published: June 2006

Activity‐composition relations of cobalt orthosilicate in cobalt‐iron‐orthosilicate solid solutions were determined at 1180°C by studying the equilibrium between these solid solutions, silica, metallic cobalt, and a gas phase of known oxygen pressures. The solution shows a slight positive deviation from ideality.
Electron Microscopy of Etched Plagiodase Feldspar
Authors: SEIFERT K. E.
Published: June 2006

Single crystals of plagiodase feldspar were selectively etched by immersion in aqueous solutions of Na2CO3 and K2CO3 for 48 hr and in 48% HF for 1 to 3 sec. The etched surfaces are replicated using a two‐stage Formvar‐carbon replica shadowed with palladium. These replicas reveal that etching varies in different twin lamellas and that etch pits align along twin boundaries.
Chemical Reaction in a Hot‐Pressed Al2O3‐Glass Composite
Authors: STETT MARK A. , FULRATH R. M.
Published: June 2006

The effects of hot‐pressing variables on a chemical reaction within a two‐phase system were studied. The reaction between alumina and sodium disilicate glass to form nephelite (Na2O·‐Al2O3·2SiO2) was investigated using X‐ray diffraction, electron microprobe, and petrographic techniques. The nephelite nucleated at the surface of the alumina and grew into the glass matrix.
High‐Temperature Microscopic Investigation of Tricalcium Silicate and Dicalcium Silicate Phases in Portland Cement Clinker
Authors: CHROMY STANISLAV
Published: June 2006

Birefringence was measured as a function of temperature up to 1400°C for (1) alite and various types of belite in portland cement clinker, and (2) alite in fused cement. The characteristic optical changes in alite and belite grains which accompany polymorphic transformations and facilitate, in certain cases, determination of the modification without necessitating the separation of the pure phase are given. The β and α’modifications were differentiated for belite from clinker and also for alite in fused cement. A method is described for measuring birefringence of minerals at high temperatures, as well as the apparatus and the preparation of samples.
Metastable Immiscibility in the B2O3–SiO2 System
Authors: CHARLES R. J. , WAGSTAFF F. E.
Published: June 2006

Using the phase diagram and a simple solution model, a subliquidus miscibility gap was estimated for the B2O3‐SiO2 system. The predicted coexistence boundary, showing a consolute temperature of 520°C, was flat and symmetrical and extended across the complete binary. Gradient furnace heat treatments of selected compositions in this system resulted in phase separation which corresponded closely to the coexistence boundary initially predicted. Calculations and preliminary experimental results indicate that temperatures and compositions exist wherein metastable three‐liquid immiscibility occurs in R20–B203‐SiO2systems.
The Svstern Zirconia‐Hafnia
Authors: RUH ROBERT , GARRETT H. J. , DOMAGALA R. F. , TALLAN N. M.
Published: June 2006

The ZrO2‐HfO2 system was investigated by metallo‐graphic, X‐ray diffraction, and microprobe analysis using are‐melted samples which had been annealed and quenched. The monoclinic‐tetragonal inversion was investigated by DTA and high‐temperature X‐ray diffraction analysis. Results reveal that zirconia and hafnia are completely miscible in all proportions in the binary system. Within experimental error, the melting points of the compositions lie roughly on a straight line connecting the melting points of oxides. There is a continuous increase in the monoclinic‐tetragonal inversion temperature as the composition moves from ZrO2 to HfO2. The lattice parameters of the monoclinic phase follow smooth curves which have a negative deviation from Vegard's law.
Eletrical Properties of Glasses in the System PbO‐Al2O3‐B2O3‐SiO2
Authors: BUCHANAN R. C. , ZUEGEL M. A.
Published: June 2006

Glasses in the system Pb0–Al2O3‐B2O3‐SiO2 are chemically stable over a wide composition range and have very desirable electrical characteristics such as high electrical resistivities and activation energies for conduction. Variations in these electrical properties were studied as a function of composition changes within the system, the object being to identify the role of the constituent oxides in achieving the highest activation energy and resistivity values consistent with moderate preparation temperatures. Measurements were made in the temperature range 25° to 400°C on carefully prepared glass disks in which the individual oxide components or different oxide ratios such as PbO/SiO2, Al2O3/SiO2, and BsO3/SiO1 were systematically varied. The activation energy and resistivity values obtained ranged from 1.2 to 1.6 ev and 10° to 1014 ohm‐cm, with dielectric constants ranging from 9 to 19 and densities from 4.30 to 4.50 g/cmY. Indications were that, for the composition range studied, the behavior manifested was basically that of the binary PbO‐SO2 glass with additions of Al2O3 or B2O3, even in small concentrations, sharply increasing the activation energy for conduction while lowering the density.
Plasma Heat Transfer in Verneuil Crystal Growth
Authors: WILLIAMS D. T. , SMITH W. A.
Published: June 2006

The heat transfer processes in the growth of single crystals in a verneuil plasma torch were investigated. Heat transfer from the plasma to the crystalline boule was enhanced to a substantial degree by recombination of dissociated diatomic gases in the region of the boule tip. Boule tip temperatures were affected by the location of the boule in the plasma, distance of the boule from the powder probe, the feed rate and grain size of the powder being fed, the rf plate power of the generator, and the powder gas flow rate. Boule temperatures depended critically on heat loss by radiation from its side. It is predicted that refractory crystals require higher plasma input power as the boule becomes longer, if crystal growth rate is to be maintained.
Stress Relief Mechanisms in Magnesia‐ and Yttria‐Stabilized Zirconia
Authors: KING ALAN G. , YAVORSKY PAUL J.
Published: June 2006

Stabilized zirconias exhibit pronounced photoelastic effects when viewed with transmitted polarized light. Thin sections reveal stress concentrations around pores and inclusions and at grain boundaries. The yield point of these materials, at some high temperature, is exceeded and plastic deformation tends to relieve these stress concentrations. The microhardness measurements of magnesia‐stabilized zirconia indicate both solution hardening and solute segregation and help to explain the physical behavior of this system as the amount of MgO is varied.
Coherent Precipitation in the System MgO‐Al2O3‐Cr2O3
Authors: GRESKOVICH C. , STUBICAN V. S.
Published: June 2006

An isothermal section of the ternary system MgO–Al2O3‐Cr2O3 was determined at 1700°± 15°C to delineate the stability field for spinel crystalline solutions (cs). Crystalline solutions were found between the pseudobinary joins MgAl2O4–Cr2O3 and MgCr2O4‐Al2O3, and the binary join MgAl2O4‐MgO. The first two crystalline solutions exhibit cation vacancy models while the latter can probably be designated as a cation interstitial model. Precipitation from spinel cs may proceed directly to an equilibrium phase, (Al1‐xCrx)2O3, with the corundum structure or through a metastable phase of the probable composition Mg(Al1‐xCr)26O40. The composition and temperature limits were defined where the precipitation occurs via metastable monoclinic phases. The coherency of the metastable monoclinic phase with the spinel cs matrix can be understood by considering volume changes with equivalent numbers of oxygens and known crystallographic orientation relations. Electron probe and metallographic microscope investigations showed no preferential grain boundary precipitation.
Liquidus Relations in the Quaternary Subsystem CaAl2O3‐CaAl4O7‐Ca2Al2SiO7‐MgAl2O4
Authors: RAO M. RAMAKRISHNA
Published: June 2006

Equilibrium diagrams for the joins CaAl4O7‐MgAl2O4, CaAl4O4‐Ca2Al2SiO7‐MgAl2O4, and Ca2Al2O4–Ca2Al2SiO7‐MgAl2O4 were determined by the classical quenching method and hot stage microscopy. Liquidus relations in the quaternary subsystem are discussed. Two univariant curves are located within the composition tetrahedron. The quaternary invariant point is a peri‐tectic. Technological application of results is indicated.
High‐pressure Synthesis of PbCrO3
Authors: DeVRIES R. C. , ROTH W. L.
Published: June 2006

A new compound with the composition PbCrO3, with Cr in the valence state of 4, was synthesized at high pressures above a pressure‐temperature line extending from about 50 kbars at 750°C to 60 kbars at 1450°C. PbCrO3 can be quenched and retained at 1 atm but decomposes on heating above 275° C at the same pressure. PbCrO3 is considered to be an equilibrium phase at high pressures because it was synthesized from mixtures of PbO: CrO2 as well as from several other mixtures of compounds in the Pb‐Cr‐0 system. The new phase has the cubic perovskite structure and is the only known compound with Cr4+ in an octahedral site. PbCrO3 crystallizes primarily as black cubes which are often twinned on (111).
High‐Temperature Reactions of Clay Mineral Mixtures and Their Ceramic Properties: IV, Dimensional and Weight Changes on Refiring and the Pore‐Size Distribution of Fired Kaolinite‐Muscovite‐Quartz Mixtures with 25 Wt% Quartz
Authors: COLE W. F. , CROOK D. N.
Published: June 2006

Dimensional and weight changes on refiring of clay mineral mixtures were used as a measure of moisture expansion and moisture uptake, respectively. Pore‐size distributions were measured by the mercury penetration method. With specimens containing more than 15% muscovite, the moisture expansion had a peak value when fired between 1000° and 1050°C. At 1050° the magnitude of moisture expansion and moisture uptake was approximately linear with the muscovite content. For specimens with less than 15% muscovite, the variation of moisture expansion with mica content was complex and this was ascribed to the fact that muscovite particles coated with kaolinite behaved differently from bulk mica in the original firing treatment and on subsequent exposure to moisture. The volume percentage of pores greater than 0.2μ in diameter increase as the muscovite content and firing temperature increased and reached a maximum when moisture expansion was at a maximum. The volume percentage of pores less than 0.2μ in diameter decreased under the same conditions but increased slightly in specimens of low muscovite content because the kaolinite reacted on firing with the mica which it coated.
Formation of Silicon and Titanium Carbides by Chemical Vapor Deposition
Authors: PEARCE M. L. , MAREK R. W.
Published: June 2006

A major difference is demonstrated in the mechanisms whereby silicon and titanium carbides are deposited at high temperatures from gas mixtures containing the appropriate tetrachloride, hydrogen, and methane. For silicon carbide, reduction of the halide by hydrogen to elemental silicon is involved, whereas for titanium carbide the process does not involve elemental titanium. It is proposed that initial formation of pyrocarbon is required for the deposition of titanium carbide near 1200°C or that gas phase reactions involving subhalides are important.
Plastic Deformation of Cuprous Oxide
Authors: VAGNARD GERARD , WASHBURN J.
Published: June 2006

Slip line and transmission electron microscopy observations on the plastic deformation of cuprous oxide were made on large‐grained polycrystalline specimens. The specimens were prepared by the complete oxidation of OFHC copper strips in air followed by a high‐temperature anneal. Plastic deformation occurred by motion of α(100) dislocations on (100) glide planes. Some dislocation segments of a(110) Burgers vector were present but were probably formed by recombination reactions between α(100) dislocations. The unusual structure of Cu20, which can be described as two interpenetrating and identical frameworks of copper and oxygen which are not cross‐connected by any primary copper–oxygen bonds, did not result in any unusual behavior of dislocations. The effect of temperature on plasticity was explained in the same way as for other materials of less complex structure, such as MgO.
Fabrication and Characterization of Isostatically Hot‐Pressed MgO
Authors: LEIPOLD M. H. , NIELSEN T. H.
Published: June 2006

Isostatic hot‐pressing was used to fabricate solid MgO bodies of high purity (with respect to metallic impurities) to 90 to 95y0 density with high translucency and a grain size of approximately 0.2μ. The densified material contained significant amounts of brucite as a result of water in the starting material which was not removed during vacuum baking. The fabricated pieces showed many cracks which were apparently introduced into the compacts before densification. When the hot‐pressed pieces were reheated, the brucite decomposed, the density increased, and the porosity coalesced while grain growth occurred. The general technique appears to be usable for fabricating finely divided powders if powder degassing and predensification procedures are improved.
Elasticity and Anelasticity of Uranium Oxides at Room Temperature: II, Hyperstoichiometric Oxides
Authors: FORLANO ROBERTO J. , ALLEN A. W. , BEALS R. J.
Published: June 2006

The Young's modulus and internal friction of hyperstoichiometric uranium oxide at room temperature were determined by a sonic technique. Young's modulus decreased, whereas internal friction increased, with increasing O/U ratios. These effects are attributed to the precipitation of U4O9. A complete microstructural characterization is needed.
Phase Equilibria and Liquid Immiscibility in the System PbO‐B2O3‐SiO2
Authors: JOHNSON DAVID W. , HUMMEL F. A.
Published: June 2006

A detailed study of the system Pb0–B203–Si02 was undertaken because of the interest in lead borosilicate fluxes and the possibility of producing opaque low‐melting enamels by controlled liquid‐phase separations. Studies in the portion of the system containing greater than 60% PbO produced little change from previous work. The shape of the liquidus surface beneath the two‐liquid region and the shape of the immiscibility dome were determined. Much of the observed immiscibility is metastable, particularly for compositions containing greater than 40% SiO2. Using the electron microscope provided information on the way the rate of formation, stability, and texture of the immiscible liquids are affected by composition, time, and temperature. Finally, a high‐temperature centrifuge was constructed to separate the immiscible liquids and thus define tie lines within the immiscibility dome.
Energies and Grooving Kinetics of [001] Tilt Boundaries in Nickel Oxide
Authors: READEY D. W. , JECH R. E.
Published: June 2006

Relative energies of symmetrical [001] tilt boundaries in nickel oxide bicrystals were determined from the dihedral angle at the groove root with a surface profilometer. At 1535°C in air, the relative grain boundary energy increases with tilt angle up to about 20 degrees and then remains relatively constant with increasing angle. A strong temperature dependence of boundary energy is explained by segregation of point defects to the boundary. Grooving kinetics are controlled by volume diffusion of nickel, and a theoretical discussion of mass transport in nonstoichio‐metric solids is given, predicting this behavior under certain conditions.
Chemical Diffusion and Phase Equilibria in the Vanadium‐Carbon System Above 1900°C
Authors: ADELSBERG L. M. , CADOFF L. H.
Published: June 2006

Direct reaction of liquid vanadium and graphite resulted in the carbon‐diffusion‐controlled formation of V2C (below approximately 2160°C) and VC scales below 2670° C. Parabolic growth behavior for both phases was observed; the growth constant for VC was expressible as K, V”= 2.13 exp ‐ (67,000/RT) cm2/sec. The growth rate of V2C was lower at 2000” than at 1900°C. The chemical diffusivity of carbon in VC above 2160°C was estimated to be Dcv”= 0.26 exp ‐ (58,300/RT) cm2/sec. Several contributions to the vanadium‐carbon binary diagram are presented. The VC + C = liquid eutectic point was determined to be at C/V = 1.15 ± 0.05 at 2670°± 50°C.
High‐Temperature Mechanical Properties of Ceramic Materials: V, (Zn0.65, Mg0.35)2SiO4
Authors: BENECKI W. T. , HUMMEL F. A.
Published: June 2006

The composition (0.65Zn,0.35Mg)2 SiO1 was investigated. Its thermal expansion was 32 × 10‐7/°C from room temperature to 1000°C. Modulus of rupture was approximately 7000 psi between room temperature and 800°C, whereas Young's modulus held at approximately 11 × 10° psi over the same range. The substitution of 0.35 m oles Mg++ for Zn++ in Zn2Si04 causes little change in many of the physical properties, but the solid solution sinters much more readily than pure Zn2Sio4. The willemite solid solution studied has very good thermal shock resistance between room temperature and 1000°C.
High‐Temperature Cermets: 11, Wetting and Fabrication
Authors: MANNING CHARLES R. , STOOPS ROBERT F.
Published: June 2006

Wetting tests were performed with refractory metal‐ceramic combinations selected on the basis of previous compatibility studies. Sessile drop contact angles between liquid Cr, V, Pt, Rh, Mo, and Mo‐Re alloy and solid ThO2, HfO2, ZrO2, HfC, TaC, and ZrC were measured at temperatures up to 2800° C in helium. Little wetting occurred between these metals and the refractory oxides, but Mo and the Mo‐Re alloy did wet the refractory carbides. Microscopic examination of the metal‐ceramic interfaces showed that HfC‐Mo‐40 wt% Re and ZrC‐Mo‐40 wt% Re had highly desirable wetting and solubility characteristics for making cermets. Specimens were fabricated from these two systems with 25 and 50 vol% metal by cold‐pressing and sintering and by hot‐pressing. The microstructures of these cermets consisted of small, uniformly dispersed carbide particles in Mo‐Re matrixes. The hardnesses and transverse rupture strengths of these cermets indicate that they have considerable promise for high‐temperature applications.
Effect of Cationic Field Strengths on the Liquidus of Oxide Systems
Authors: STOCH L.
Published: June 2006

The relation between the liquidus and cationic field strengths in binary and ternary oxide systems was studied. In binary systems, lowering of the melting point of an oxide due to the presence of a second oxide as indicated by the appropriate liquidus curve is a function of the ionic potential of the cation of the second oxide. The liquidus curve shows that solubility of an oxide in a binary melt is approximately proportional to the difference in the reciprocals of the ionic potentials of the cations of the two components.
Initial Sintering of MnXO‐Al2O3
Authors: KESKI J. R. , CUTLER I. B.
Published: June 2006

Effects of manganese oxide on the initial sintering kinetics of compacts of 5‐μ diameter alumina were studied by isothermal shrinkage measurements from 1450° to 1650°C. The observed rates were characterized by assuming a volume‐diffusion mechanism. Variations in sintering rate with both oxygen partial pressure in the furnace and impurity concentration, as well as the observed activation energy, indicated oxygen‐ion diffusion was the rate‐limiting step during densification.
Effect of a Metastable Precipitate on the Electrical Properties of an Li2,O‐SiO2 Glass
Authors: KINSER D. L. , HENCH L. L.
Published: June 2006

Glass structural differences in a 17.5 wt% (30 mole %) Li2O‐SiO2 glass resulting from thermal treatments in the annealing‐transformation range were studied using electron microscopy, X‐ray analysis, and dc and ac electrical properties. Metastable, crystalline lithium metasilicate precipitates and subsequently redissolves prior to the appearance of the equilibrium lithium disilicate crystals. The lithium metasilicate gives rise to dielectric loss peaks in the 100 hz to 1 Mhz range which can be rationalized on the basis of the Maxwell‐Wagner‐Sillars heterogeneous dielectric model.
Crystallization Kinetics of Internally Nucleated Vitreous Silica
Authors: WAGSTAFF F. E.
Published: June 2006

It has recently been observed that cristobalite can hetero‐geneously nucleate and grow internally in vitreous silica. When the glass‐crystal composite is cooled to room temperature, β‐cristobalite is metastably retained as a result of the large tensile stresses developed during cooling. Although these crystals are not obvious, they can be readily observed with a polarizing microscope or polariscope. As long as the cristobalite does not transform when cooled to room temperature, repeated increments of crystal growth can be measured on the same growing crystal. Crystal growth was measured on electrically melted quartz glass at 1350° to 1620°C. The observed growth rates were linear with time and were the lowest that have been measured in vitreous silica. The kinetic data agreed with the general form of the crystal growth equation μ= (AΔT)/ν. Since the growth is internal and free from surface contamination, the measured rates are considered to be very near the intrinsic rates for the material.
Compressive Creep of Uranium Carbide
Authors: STELLRECHT D. E. , FARKAS M. S. , MOAK D. P.
Published: June 2006

The compressive creep rates of slightly hyperstoichi‐ometric uranium carbide were determined in vacuum at 1200° to 1600°C and 3000 to 10,000 psi. The equation best describing the minimum creep rates of uranium carbide over this range is:

é= 1.8 × 10−3σ3 exp (‐90,000/RT)
Quaternary System U‐C‐O‐N at 1700°C: Phase Relations in the Low‐Nitrogen Region
Authors: HENRY JACK L. , BLICKENSDERFER ROBERT , THOMPSON GERALD G.
Published: June 2006

Phase relations in the system U‐C‐O‐N at 1700°C were established at nitrogen levels up to an atomic ratio N: C 1:3 by microstructural and X‐ray analyses of sintered powder compacts. The extent of the solid‐solution field of uranium oxycarbonitride was established on the ternary plane U‐C0.75No.0.25‐O. The maximum solubility of oxygen in the solid solution is 14 at.%, corresponding to a composition U0.50C0.27O 0.14N0.09 compared to 17 at.% on the U‐C‐O plane. Nine other phase fields were established on the U‐C‐O C0.75N0.25‐O plane, all of which contain a uranium oxycarbonitride solid‐solution phase and a gaseous phase of CO and N.2. Equilibrium pressure varies from about 0.01 torr in phase fields containing free uranium to about 200 torr in the field containing solid solution +“UC2” (oxy‐gen‐containing dicarbide) + C + UO2. Lattice parameters of the solid‐solution phase were determined. A field containing solid solution and UzC3 exists to about 3.5 at.% O and 2 at.% N at the hyperstoichiometric boundary of the solid‐solution field. An isothermal phase diagram for the low‐nitrogen region of the U‐C‐O‐N system is proposed.
Properties of Sodium‐Lithium Niobate Solid Solution Ceramics with Small Lithium Concentrations
Authors: NITTA TSUNEHARU
Published: June 2006

The structural, dielectric, and piezoelectric properties of the solid solution (Na1‐x,Lix,)NbO2 were studied. Solid solution ceramics with x values up to 0.14 occur as a single phase. The phase diagram from 0° to 600°C is given. The low‐temperature phase has a perovskite pseudo‐monoclinic structure and inverts to a pseudotetragonal structure at a temperature that decreases with increasing x. The high‐temperature phase is pseudocubic, and the minimum transition temperature from the pseudotetragonal to the pseudocubic structure is 350° C near x= 0.04. Anomalies in the dielectric constant vs. temperature curve agree well with the transition temperatures, although no anomaly was observed at the temperature of transition from the pseudotetragonal to the pseudocubic phase when x was less than 0.06. Lithium ions in the system facilitate the transformation from the antiferro‐electric to the ferroelectric state produced by applying an electric field. A new ferroelectric phase becomes stable when x is greater than 0.07. Poled ferroelectric specimens had a planar coupling coefficient of 0.232, a dielectric constant of 220, and a frequency constant of 3352 kc‐mm. The piezoelectric properties disappear not at the transition temperature but at the temperature at which strain exhibits an anomaly when x is greater than 0.07. A perovskite phase with a pseudorhombohedral subcell exists as an intermediate phase for x greater than 0.10, the exact value depending on the preparation method. The phase can be easily converted to pseudomonoclinic when the ceramic is fired at 1180° to 1220°C.
Interface Reactions Between Metals and Ceramics: IV, Wetting of Sapphire by Liquid Copper‐Oxygen Alloys
Authors: CHAKLADER A. C. D. , ARMSTRONG A. M. , MISRA S. K.
Published: June 2006

The wettability of sapphire single crystals by liquid copper which contained oxygen added as cupric oxide was investigated using the sessile drop technique in vacuum at 1230°C. Additions of cupric oxide to copper, varying from 1 to 72% of copper weight, resulted in rapid chemical reaction at the solid‐liquid interface with a significant reduction of the contact angle, the final value being dependent on the oxygen in the system. In all cases the interfacial product was CuAlO2. A linear relation between the fourth power of the basal radius of the molten drop and the amount of oxygen present was observed. The initial stage of the reaction could be explained by the formation of a Cu2O layer at the interface, followed by reaction between Cu2O and Al2O3 to form CuAlO2.
Development of Two‐Phase Structure in Glasses, with Special Reference to the System BaO‐SiO2
Authors: III T. P. SEWARD , UHLMANN D. R. , TURNBULL DAVID
Published: June 2006

Vapor deposition was used to obtain homogeneous glass films of several BaO‐SiO2 compositions in the region of the metastable miscibility gap. The films were electron‐beam heated in the electron microscope, and the phase separation process was observed. At low BaO contents, separation was characterized by the appearance of discrete, amorphous, second‐phase particles. For compositions near the center of the miscibility gap, separation resulted in two continuously interconnected phases similar to those in the corresponding bulk glasses. In the thinnest of these films, the process proceeded by the coalescence of isolated particles into the interconnected second‐phase submicrostructure. At high BaO contents, rapid crystallization of the films prevented study of the separation process. Two processes which could lead to coalescence of discrete second‐phase particles into an interconnected submicrostructure are discussed. It is suggested that coalescence may occur when either of these processes results in the particles approaching within some small distance of each other. It is indicated that under appropriate conditions, this requirement may be satisfied by either process. These conclusions, together with the present observations of BaO‐SO2 thin films and those previously reported for bulk samples, indicate that observations of final phase‐separated morphologies are inadequate for specifying the processes by which those morphologies arose.
Influence of Orientation on Properties of Grain Boundaries in NaCl
Authors: GIMPL M. L. , McMASTER A. D. , FUSCHILLO N.
Published: June 2006

Simple (100) tilt, twist, and double‐tilt bicrystals of NaCl, grown by the Kyropoulos technique from melts of high‐purity NaCl, alone and with controlled impurity additions, were examined for mechanical strength and structure of the grain boundaries. Grain boundary fracture strengths, measured in three‐point bending, showed that high‐purity bicrystals with simple tilt orientations were stronger than those with simple twist at high mismatch angles (37° to 45°). The results did not show a functional dependence of strength on angle of mismatch in either tilt or twist bicrystals. Pips observed on parted grain boundaries of high‐purity NaCl (100] twist and double‐tilt bicrystals were believed to represent regions of continuity across the boundary. This feature was rare in similar‐purity NaCl (100) tilt bicrystals. Separate additions of 100 ppm SiO2, CaCl2, FeCls, and KCl to the melt had no apparent effect on the character of the grain boundary. However, an addition of 1000 ppm CaCl2 nearly doubled the strength of a (1001) 30° twist bicrystal, whereas the same addition weakened a (100) 45° tilt bicrystal. Sodium chloride (100) tilt grain boundaries, examined in situ under dark‐field illumination, showed randomly distributed spots, believed to be impurity segregations, with their maximum density at the boundary. The spot densities increased with increasing tilt angle for angles of 15° and greater. The spots were not observed in the low‐angle tilt boundaries (<15°) and were seen only in intermittent clusters in the few twist bicrystals examined.
Synthesis of Rhenium Ditelluride
Authors: SORRELL CHARLES A.
Published: June 2006

A single phase, ReTe2, formed between 450° and 935°C in sealed, evacuated fused silica tubes. The compound may be indexed on a triclinic unit cell, but an unequivocal unit cell cannot be chosen without single‐crystal X‐ray data. The compound dissociates at 935°± 5°C in sealed tubes to solid rhenium and liquid tellurium with a high vapor pressure. No ternary compounds are found in the system Re‐Pb‐Te.
Ferroelectric and Structural Properties of the Pb(Sc1/2Nb1/2)1‐x,Tix,O3 System
Authors: TENNERY VICTOR J. , HANG KENNETH W. , NOVAK RICHARD E.
Published: June 2006

Extensive solid solution was observed in the system Pb(Sc1/2/,Nb1/2,)1‐x,Tix,O3. In the range 0 ≤ x ≤ 0.425 a rhombohedral ferroelectric phase was stable at 25° C. In the range 0.45 ≤ x ≤ 1.00 a tetragonal ferroelectric phase was stable at this temperature. The phase diagram of the system below 500° C strongly resembles that of PbZrO3−PbTiO3. The compound Pb(Sc1/2Nb1/2)O3 exhibited rhombohedral perovskite cell symmetry below the ferroelectric ↔ paraelectric transition temperature, and the angle a was acute. The radial coupling coefficient was 0.46 for the composition Sc1/2Nb1/2)0.575Ti0.4250O3. At 25°C this composition consisted primarily of the rhombohedral phase with a small amount of the tetragonal phase present. The ferroelectric ↔ paraelectric transition occurred over a temperature range in the rhombohedral phase field. The spontaneous polarization was finite at temperatures considerably above the temperature of the permittivity maximum for a given rhombohedral solid solution.
High‐Quartz Solid Solution Phases from Thermally Crystallized Glasses of Compositions Li2O2,MgO).Al2O3,nSiO2
Authors: RAY SATYABRATA , MUCHOW G. M.
Published: June 2006

Thermally crystallized glasses of compositions (Li2,O2, MgO).Al2O3.nSiO2 were studied by X‐ray powder diffraction methods. High‐quartz solid solution phases developed at relatively low temperatures and, for n 3.5, transformed at higher temperatures to keatite solid solution phases. Associated phases, if present, were Mg spinel and/or cordierite, or a few other trace phases. The a crystallographic axis (a0) of high‐quartz solid solutions decreased with increase of MgO and/or SiO2. The c crystallographic axis (c0) decreased with increasing MgO; it also decreased with increasing SiO2, but only when MgO content was low. X‐ray diffraction photographs of single crystals of high‐quartz solid solutions of compositions LiaO.Al2O3.nSiO3 demonstrated that the maintenance of a basic high‐quartz structure is the basis of the solid solution relation. Three modifications of the high‐quartz structure were recognized in the Li2O‐Al2O3−SiO3 system. These modifications were based on the occurrence and positions of superlattice reflections. The high‐quartz solid solution from Li2O Al2O3−2SiO2, showing streaky reflections in its precession photographs, suggested a defective structure. The term “high‐quartz solid solution,” with or without additional prefixes specifying the compositional series and modification, was considered the preferred nomenclature for these solid solution phases.
Possible Existence of Dense Ferrimagnetic Perovskite Allotropic Form of Yttrium Iron Garnet
Authors: SHIMADA M. , KUME S. , KOIZUMI M.
Published: June 2006

Mixed oxides with the same chemical composition as yttrium iron garnet (YIG) were maintained at 900°C and 20 kbars for 30 min. X‐ray diffraction showed that the product was single‐phase. Since the diffraction pattern could be indexed as a structure similar to yttrium ortho‐ferrite, YFeO3, the product was considered to be a deformed type of perovskite. Subsequently, the lattice constants were calculated to be a= 5.27, b= 5.57, and c= 7.59 A. Both measured and calculated densities were about 6% greater than those of YIG. This material, therefore, can be called a dense allotropic form of YIG. Ferrimagnetism was observed in this phase; the Curie temperature and the magnetic moment at room temperature were estimated to be 625° C and 63 emu/g, respectively. This dense form converted to YIG on heating at 900° C for 4 hr in air. The transformation of YIG to a dense form at high pressures is inconsistent with the results reported by Marezio et al. Some possible reasons for this discrepancy are discussed.
The System PbO‐Chromium Oxide in Air
Authors: NEGAS TAKI
Published: June 2006

Phase relations in the system PbO‐chromium oxide were determined in air at high temperatures and are considered in terms of the PbO‐Cr2O3−O2 ternary because of reactions with atmospheric oxygen. Although not necessarily binary at all temperatures, four established subsystems characterize the air equilibria and indicate oxidation‐reduction of chromium. The PbO‐PbCrO4 join contains the compounds Pb5CrO3 and Pb5CrO8 and consists of two portions, PbO‐Pb2CrO6 and Pb2CrO5−PbCrO4 The former is binary at all temperatures studied, while the latter exists only below 753° C because of the decomposition of PbCrO4 at 753°C to Pb2CrO5 and Cr2O3 with oxygen evolution. Similarly, the join PbCrO4−Cr2O3 exists only below 753°C yielding to Pb2CrO3−Cr2O3 equilibria above this temperature.
Crystal Field Studies of Co2+ in α‐Zn3(VO4)2
Authors: NATH D. K. , HUMMEL F. A.
Published: June 2006

Complete solid solubility was found in the system Cog‐(VO4)2−α‐Zn3(VO4)2. Optical spectra of Co2+‐containing α‐Zn3(VO4)2 samples are discussed in the light of crystal field theory. The calculated and theoretical frequencies were in good agreement for octahedral symmetry in the zinc sites. The crystal field parameter Dq was consistent with the ionic approximation rule. The nephelauxetic ratio did not show any relation to cation‐anion distance. Most probably the expanding d‐d electron clouds of Co2+ interacted.
High‐Temperature Creep of Polycrystalline Magnesia: I, Effect of Simultaneous Grain Growth *
Authors: TAGAI HIDEO , ZISNER TUVIA
Published: June 2006

The creep of pure magnesia (99.9 +% MgO) was tested in transverse bending at temperatures from 1200° to 1500°C, strain rates near 10−2%/hr, and grain sizes of 4 to 50μ. In most cases, grain growth during the test affected the apparent creep behavior more than all the other variables combined. An analytical graphical method was used to separate the grain growth effect from other effects and to obtain more meaningful creep data. Creep occurred primarily by a viscous mechanism (Nabarro‐Herring type, cation‐lattice‐diffusion controlling) with a minor amount of plastic creep (dislocation climb). The agreement with previous creep data was good.
High‐Temperature Creep of Polycrystalline Magnesia: II, Effects of Additives *
Authors: ZISNER TUVIA , TAGAI HIDEO
Published: June 2006

The creep of magnesia doped with 0.035 to 2.26 cation % of nine other oxides and three binary mixtures thereof and of three seawater products (about 96, 98, and 99.5y0 MgO) was evaluated in transverse bending at 1200° to 1500°C, with strain rates of about 10−2%/hr, and average grain sizes of 5 to 50p. The results obtained were compared with those for pure magnesia. Most additives accentuated the plastic (diffusion‐controlled) nature of the creep process presumably by pinning dislocations and/or slowing grain growth. In most cases the rate‐determining diffusing species seemed to be the cation, Mg, but in two cases it was suspected that oxygen boundary diffusion was controlling. Porosities above ˜10% appear to increase the temperature dependence of creep, probably by introducing boundary sliding. The agreement of the creep data with those of other diffusion‐controlled processes (electrical conductivity, sintering, and grain growth) is demonstrated.
Elastic Constants of Single Crystal Calcium Molybdate (CaMoI4)
Authors: WACHTMAN J. B. , BROWER W. S. , FARABAUGH E. N.
Published: June 2006

The seven elastic compliances and seven elastic constants of single crystal calcium molybdate were determined by a resonance method. The compliance s16, which is zero for higher symmetry tetragonal crystals, need not be zero for crystals of lower tetragonal symmetry and contributes significantly to the orientation dependence of the elastic moduli of calcium molybdate. The values of the compliances and their standard errors (based on 41 measurements) in units of 10−11m2/N are s11= 0.974 + 0.005, s33= 0.958 ± 0.004, s44= 2.720 ± 0.009, s66= 2.471 ± 0.022, s12=−0.380 ± 0.010, s13=−0.230 ± 0.009, and s16= 0.433 ± 0.010.