bluuebunny/crossref_metadata_2025 huggingface dataset:
Dehydration Series in the System CaSiO3— SiO2— H2O
Authors: IAN HARKER R.
Published: June 2006

Hydrothermal studies show a dehydration series involving CSH(I), tobermorite, xonotlite gyrolite, truscottite (reyerite), silica, and wollastonite. The synthetic equivalents of gyrolite and Qruscottite (reyerite) have ideal compositions very close to 2CaO.3SiO2.2H2O and 3CaO.5SiO2.1SH2O respectively. With rising temperature the following reactions take place: (1) CSH(1) or tobermorite + silica = gyrolite (+H2O); (2) gyrolite + silica = truscottite + H2O; (3) gyrolite = tobermorite + truscottite + H2O (high pressure); (4) gyrolite = xonotlite + truscottite + H20 (low pressure); (5) tobermorite = xonotlite + H20; (6) truscottite = xonotlite + quartz + H2O; (7) xonotlite = wollastonite + H2O. Data on reactions (l), (5), and (7) confirm results of previous workers. The water pressure‐temperature curves or bands, except the one involving the breakdown of tobermorite, are steep. This curve crosses the curve representing the breakdown of gyrolite at a quintuple point. None of the reactions was reversed, and the temperatures indicated are approximate and are based on runs of about 4‐weeks duration. For much shorter times somewhat higher temperatures are needed to cause the reactions, and conversely in much longer runs slightly lower temperatures might suffice. The silica was usually amorphous, cristobalite, or quartz with a mineralizer and therefore of higher activity than quartz alone. Up to 2 % alkali fluorides facilitated the formation of gyrolite; this is probably related to the fact that apophyllite in many cases accompanies gyrolite in amygdules. Truscottite (reyerite) forms very easily, and the rarity of reported occurrences, compared with those of xonotlite, gyrolite, and opaline silica, suggests that some workers may have overlooked it.
Effect of Secondary Crystalline Phases on Dielectric Losses in High‐Alumina Bodies
Authors: FLOYD JAMES R.
Published: June 2006

An effort was made to determine the cause of high dielectric losses at 106 cps and 25°C in dense, essentially alkali‐free, high‐alumina bodies. Emphasis was placed on secondary crystalline phases in the fired bodies. The flux systems BaO‐SiO2, CaO‐MgO‐SiO2, and SrO‐SiO2 were investigated. All high‐alumina bodies having high dielectric losses contained one of the synthetically formed feldspars, BaO.Al2O3.2SiO2, CaO.Al2O3.2SiO2, or SrO.Al2O3.2SiO2. The mechanism by which the feldspars caused the high dielectric losses was tentatively attributed to thermal expansion mismatch. The expansion curves of the feldspars were similar, but they were lower than the expansion curve of alumina.
Magnetic Properties of Ilmenite‐Hematite Solid Solutions
Authors: JEFFERSON CLINTON F. , WEST RUSSELL O.
Published: June 2006

The magnetic and dielectric properties of some ilmenite‐hematite solid solutions are reported. These properties resemble those of the ferrites. Compositions possessing high electrical resistivities and low dielectric losses were prepared. The introduction of manganese into the system (1 ‐ x)Ni1‐vMnvTiO3+ xFe2O3 increases the room temperature magnetic moments and decreases the resistivities.
Influence of Surface Condition on the Strength of Polycrystalline MgO
Authors: HARRISON W. B.
Published: June 2006

The mechanical behavior of high‐purity (greater than 99.9%) polycrystalline MgO, with relative density exceeding 9875, is described. By fracto‐graphic techniques, it was determined that inter‐granular cracks initiate fracture. These cracks originate from the extension of surface flaws into the MgO and are particularly severe in areas of high, localized, intergranular porosity. Ceramic machining techniques, such as diamond sawing and lapping with coarse abrasives, induce these surface flaws and limit the strength of MgO. The effectiveness of lapping, thermal conditioning, and chemical polishing techniques in removing these flaws and producing a substantial increase in mechanical strength is shown to be dependent on grain size and porosity.
Annealing and Yield Stress of NaCl Single Crystals
Authors: ROTHWELL W. S. , GREENLER R. G.
Published: June 2006

Annealing experiments on NaCl single crystals are reported, showing that the expected decrease in yield strength is significantly modified by stress history, impurities, and furnace atmosphere. Annealing in air can result in a higher yield stress than that obtained without annealing. The lower limit obtained for the critical resolved shear stress of NaCl single crystals is 35 g per mm2.
Electron Microscopic Technique for Determining the Percent Crystallinity of Glass‐Ceramic Materials
Authors: CARRIER GERALD B.
Published: June 2006

With the discovery of techniques for controlling the nucleation and crystallization of many glass compositions came the need for improved methods for determining the percent crystallinity of a variety of glass‐ceramic materials where the crystal size was generally too small for analysis with the polarizing microscope. The development of areal analysis, lineal analysis, and point‐counting methods is reviewed. The application of the point‐counting method employing electron microscopy and diffraction to glass‐ceramic materials is discussed and demonstrated.
Transmission Electron Microscopy of Glass‐Ceramics
Authors: DOHERTY P. E. , LEOMBRUNO R. R.
Published: June 2006

A new technique has been developed by which thin sections of glass‐ceramics can be prepared for direct observation by transmission electron microscopy. Techniques for identifying crystalline phases are discussed, and the degree of crystallinity in several glass‐ceramics is presented.
Dielectric Measurements on Glass at Very High Pressure
Authors: CHAKRAVORTY D. , CROSS L. E.
Published: June 2006

A method of making dielectric measurements in situ under pressures up to 60 kbars is described. This technique has been used to investigate the effect of very high pressure on the activation energy for conduction in an aluminosilicate glass system. The activation energy increased rapidly at first with pressure and then exhibited saturation at pressures above 30 kbars. This investigation also showed a remanent increase in the activation energy in a glass compacted at a pressure of 42.2 kbars. The results obtained are discussed in the light of current models for the charge migration in soda glass.
Phosphate‐Halide Systems: III, Constitution of Glasses in the System NaPO3,‐LiF
Authors: WESTMAN A. E. R. , KRISHNA MURTHY M.
Published: June 2006

The constitution of glasses in the system NaPO3‐LiF with the M/P ratio varying from 1.66 to 1.22 and melted in laboratory air and in dry air has been determined. It has been found that when the glasses are melted in laboratory air and quenched immediately after the components have melted into a liquid, most of the fluorine is retained by the glasses; if, however, the melts are heated further, fluorine is gradually replaced by oxygen. Weight‐loss determinations on the glasses in the solid state and on the melts agree with the foregoing conclusions. In dry air very little fluorine is lost from the melts even after 1 hour. Chromatographic and infrared analyses show that glasses retaining fluorine contain considerable amounts of monofluoro‐orthophosphate groups; only about half the fluorine is present, however, in this form. The distribution of the remaining fluorine is not known.
Square‐Loop Ferrites for Logic Application
Authors: FRESH DONALD L. , WEST RUSSELL G.
Published: June 2006

The effects of composition, post sintering, and operating temperature in a square‐loop ferrite system of interest for performing logic functions in digital telemetry applications are described. Ceramic processing methods used in preparing the multiaperture ferrite cores for this study are also described. Magnetic hysteresis loop characteristics of squareness ratio (Ra), magnetic induction switched (δBm), critical switching field (Hc, and maximum permeability (μm,) are reported as a function of zinc concentration in the system Mg0.5‐tMn0.8ZnxFe1.7O4abc. These characteristics are also investigated as a function of the post‐sintering treatments of air quenching and nitrogen annealing for the composition Mgo.35Zn0.15 Isel Essentially identical results are obtained for both the air‐quenching and the nitrogen‐annealing treatments. Significant hysteresis loop characteristics are shown at various operating temperatures in the range −78° to + 100°C.
Microstructure of Periclase
Authors: TREFFNER WALTER S.
Published: June 2006

The microstructure of magnesia grains obtained from coarse crystalline and cryptocrystalline magnesites and from seawater and brines is illustrated and the influence of the amount and type of impurities on the development of periclase is discussed. The factors which affect direct peri‐clase‐periclase bonding in basic brick are reviewed; the microstructural effects of additions of sesquioxides are shown. The complex reactions between periclase and chromite spinel are considered with reference to direct periclase‐chromite bonding. The formation of secondary periclase is briefly described.
Microcrystalline BaTiO3 by Crystallization from Glass
Authors: HERCZOG ANDREW
Published: June 2006

The properties and composition of glasses suitable for crystallization of BaTiO3 are described. The crystallization of certain glasses results in a nearly complete recovery of BaTiO3, besides the feldspar BaAl2SiO3 as a minor phase. The mechanism of crystallization was investigated by thermal analysis, viscosity, and grainsize measurements as a function of the temperature whereas density data were used for evaluation of the BaTiO3 content. Within the range 30 to 60% by volume of BaTiO3 at about 1μ grain size, the measured dielectric constant increased from 100 to 1200. The calculated partial dielectric constant of the Titanate phase at this grain size was about 3500. As the grain size approached 0.1μ, the dielectric constant decreased and became nearly independent of the temperature because of the predominance of surface states. Other effects were attributed to special structural characteristics, such as absence of porosity and clamping of the titanate particles within the microcrystalline matrix. Data are also presented on dielectric constant and loss tangent at different frequencies, dc breakdown strength, dc resistivity, and ferroelectric properties as a function of the grain size of the crystallized material.
Direct Bonding of Basic Brick
Authors: DAVIES BEN , WALTHER FRANK H.
Published: June 2006

Direct bonding in burned magnesite‐chrome refractories is described as a mineralogical phenomenon and as a factor governing brick properties. Hot‐load tests are recommended as a supplement to hot modulus tests to obtain a meaningful picture of high‐temperature strength. The importance of purity of ingredients is thus made more apparent. Direct‐bonded brick from open‐hearth service are shown to have a lower level of slag absorption. The result was reproduced in a unique laboratory diffusion furnace and a relation between silicate buildup and original brick purity is established.
Phase Equilibria in the System Boron Carbide‐Silicon Carbide
Authors: SECRIST D. R.
Published: June 2006

The system boron carbide‐silicon carbide is quasi binary and contains a eutectic of composition 70 ± 2 wt% B4C and 30 ± 2 wt% Sic at a temperature of 2300°± 20° C. The solid solubility of both B4C in Sic and Sic in B4C is less than 2 wt% at this temperature, based on metallographic and X‐ray analyses. The Sic corresponds to the hexagonal (a) allotrope when the compositions contain more than 50 wt% Sic. The cubic (p) form of Sic is stabilized in compositions which contain less than 50 wt% Sic.
High‐Temperature Behavior of MoSi2 and Mo5Si3
Authors: CHERNIACK GEORGE B. , ELLIOT A. GRANT
Published: June 2006

The high‐temperature stability and behavior of MoSi2 was studied by heating dense sintered specimens under a vacuum of 10−5 mm Hg in the temperature range 1700° to 2000°C. The resulting material was examined using physical measurements, X‐ray analysis, and metallographic techniques. The decomposition of MoSi2 into Mo5Si3 is described. The Mo5Si3‐MoSi2 eutectic temperature was determined as 1900° C, and the melting points of MoSi5 and Mo5Si3 were determined as 1980° and 2085° C, respectively.
Use of Interdiffusion to Determine Crystalline Solubility in Alkali Halide Systems
Authors: SHORT JAMES M. , ROY RUSTUM
Published: June 2006

Measurement of the discontinuities in the concentration‐distance graphs describing interdiffusion of the components in the binary systems NaF‐LiF and NaCl‐RbCl gave the crystalline solubility limits just below the eutectic temperatures. These are 8 mole % LiF in NaF and 1.5 mole % NaF in LiF at 625° C and 6 mole % NaCl in RbCl and 0.8 mole % RbCl in NaCl at 515°C. Experiments in the complex systems NaCl‐Kl and NaF‐LiF‐MgF2 showed that the method was inapplicable to nonbinary systems where the phase compositions at intermediate stages in the interdiffusion do not correspond to those of the final equilibrium assemblage.
Vapor Pressure of Magnesium Fluoride
Authors: HAMMER REUBEN R. , PASK JOSEPH A.
Published: June 2006

The vapor pressure of MgF2 was measured over the temperature range 1413° to 1614°K by the Knudsen effusion and torsion‐effusion methods. Experimental data could be expressed by the equations log PKnudaen= 9.147 ‐ 20,183/T and log PToraion= 8.311 ‐ 18,960/T in the temperature range of solid magnesium fluoride (1413° to 1536°K) and by the equations log PKnudaen= 6.065 ‐ 15,44O/T and log PToraion= 6.737 ‐16,480/T in the temperature range of liquid magnesium fluoride (1536° to 1614°K). The MgF2 vapor was shown to be essentially monomeric. The heat of vaporization (or sublimation) at 298°K was calculated to be 88.0 ± 1.0 kcal per mole. A continuous weighing procedure was devised for use with the Knudsen effusion method. An electromagnetic torque method of measurement was developed for use with the torsion‐effusion method.
Analysis of Fracture Probabilities in Nonuniformly Stressed Brittle Materials
Authors: WEIL N. A. , DANIEL I. M.
Published: June 2006

The results of theoretical studies on the effect of nonuniform stress fields encountered in prismatic beams under bending on the fracture of brittle materials are described. Derivations were carried out to determine the risk of rupture of bending specimens subjected to a symmetrical four‐point load of arbitrary spacing, the symmetric three‐point loading and pure bending forming limiting cases of this more general loading. The analysis was based on materials obeying the Weibull distribution function with assumptions for either volumetric or surface flaw dispersion conditions. The predicted strengths of bending and tensile specimens are compared. An analytical method for the determination of the three Weibull parameters from a pure bending test is proposed. This method, based on the best fit of a theoretical curve to the experimental data, was applied successfully to experimental results on Columbia Resin, a brittle amorphous polymer.
Flux Growth of Chrysoberyl and Alexandrite
Authors: FARRELL E. F. , FANG J. H.
Published: June 2006

Chrysoberyl (A12BeO4) and alexandrite (Al2BeO4:Cr) crystals have been grown successfully by the flux‐melt method in lengths from 0.1 to 10.0 mm. A satisfactory composition for chrysoberyl is PbO 66.6, A12O3 16.7, and BeO 16.7 mole yo; for alexandrite, LizMoOQ 40.4, MooB 50.6, A12O3:Cr 4.5, and BeO 4.5 mole yo. Morphological characteristics of the crystals produced are described.
Fabrication and Plastic Behavior of Single‐Crysta MgO‐NiO and MgO‐MnO Solid‐Solution Alloys
Authors: LIU T. S. , STOKES R. J. , LI C. H.
Published: June 2006

A method of producing solid‐solution MgO‐NiO and MgO‐MnO single crystals is presented. The compressive yield strength of MgO increased nearly fourfold when small amounts of either NiO or MnO were in solid solution in MgO. The cleavage and slip behavior of these alloy crystals was identical to that of MgO.
Electrical Conductivity in the System ZrO2—CaZrO3
Authors: TIEN T. Y.
Published: June 2006

The electrical conductivity of compositions in the system ZrO2‐CaZrO3 was examined. The composition of maximum conductivity in this system is within the cubic solid‐solution region close to the low‐calcia cubic solid‐solution phase boundary. The conductivity decreases from the single‐phase cubic solid solution to both of the adjacent two‐phase regions; the decrease is more rapid on the ZrO2‐rich two‐phase side. This effect is discussed on the basis of differing microstructures.
Studies in Germanium Oxide Systems: II, Phase Equilibria in the System Na2O—GeO2
Authors: MURTHY M. KRISHNA , AGUAYO J.
Published: June 2006

Phase equilibrium relations in the system Na2O‐GeO2 have been determined using standard quenching techniques supplemented by differential thermal analysis. Two congruently melting compounds, Na2O·GeO2 and 2Na2O·9GeO2, exist; the melting points are 1103°± 15°C and 1073°± 3°C, respectively. The eutectic temperature between GeO2 and 2Na2O·9GeO2 is 950°±f 10°C at 94.5 wt GeO2. The eutectic temperature between 2Na2O · 9GeO2 and Na2O·GeO2 is 790° f 10°C at about 75 wt% GeO2. Both the refractive index and the density of glasses in the system Na2O‐GeO2 exhibit maximum values at about 16 to 18 mole % Na2O. The Ge‐O‐Ge absorption band at 890 cm−1 shifts toward lower wave numbers with the addition of Na2O.
X‐Ray Microbeam Studies of Fracture Surfaces in Alumina
Authors: GUARD R. W. , ROMO P. C.
Published: June 2006

Studies using a double‐crystal X‐ray spectrometer to measure crystal distortion at various depths below the fracture surfaces of polycrystalline alumina have shown two zones of distortion. Zone I, of high distortion, extends about 10μ; zone II, having much lower distortion, extends over 50μ (in excess of one grain diameter). Both zones are observed in specimens fractured at 20° and at 1700°C. The primary difference observed between specimens broken at the two temperatures is that zone I has a much higher misorientation in the 1700°C fractures than in 20°C fractures; zone I1 is quite similar for the two temperatures. Since zone I appears in all reflections and is about one half grain diameter in depth, it is proposed that this distortion arises from basal and nonbasal slip in those grains through which the fracture crack passes. Since zone II is observed only in the (0330) and (2240) reflections, it is proposed that this distortion is the result of basal slip only. From these data the plastic work of fracture is estimated as about 1500 ergs per cm2. This estimate is probably high by 10 to 25%. The value for the work of fracture is relatively independent of temperature. The method described in this work permits study of the deformation in the thin layers near the fracture surface in any material.
Formation of Ettringite Immediately After Gaging of a Portland Cement
Authors: SCHWIETE HANS ERNST , NIËL EGID M. G.
Published: June 2006

The formation of ettringite during the initial stages of hydration in commercial portland cement was determined by electron microscopy (diffraction and replica techniques) and by infrared spectrography. The initially formed ettringite is stabilized by a high Sod2‐ concentration in the liquid phase of the cement paste. Hemihydrate and potassium carbonate acted as stabilizers while providing a high sulfate concentration in the liquid phase.
Etched Structures Dependent on Sidewise Motion of 180° Domains in BaTiO3
Authors: DeVRIES R. C.
Published: June 2006

Sidewise motion of 180° domains in BaTiO3 single crystals during electrical poling with a wet electrode technique results in etch pit patterns strikingly similar to dislocation patterns in other crystals. The etching behavior of the pits is also consistent with that of small 180° domains in this material. Very small inclusions are also revealed in a poled and etched crystal as small round 180° domains representing regions which could not be reversed by the electric field. It is suggested that dislocations in tetragonal BaTiO3, may also be revealed in this manner. The origin of the small circular 180° domains is revealed by a photomicrograph of the “hanging up” of a moving 180° domain wall as it encounters defects during sidewise motion through the crystal. Based on this photomicrograph a wall energy calculation was made for the 180’domain in a BaTiO3 single crystal in which the sidewise motion of the wall is treated as a surface tension phenomenon. Good agreement with the accepted value of 1.4 ergs per cm2 was obtained if a correction was made for the potential drop through the material of lower dielectric constant used in the poling process.
Kinetics of the Reduction of Lead Compounds and Glasses
Authors: HAERTLING G. H. , COOK R. L
Published: June 2006

The kinetics of the gas–solid reduction reactions of high purity dry hydrogen with selected lead compounds and glasses was investigated. Materials studied were PbO, Pb2SiO4, PbSiO3, PbZrO3, PbTiO3, lead zirconate titanate (54/46, Zr/Ti ratio), lead orthosilicate glass, and lead metasilicate glass. A constant pressure (1 atm) hydrogen flow (2 liters per minute) system was used in reacting the powdered materials at specified constant temperatures. The extent of reduction was quantitatively determined by (1) weight loss of the reacted specimen, and (2) dew point of the reaction atmosphere. Expressions are presented for relating both the weight loss and the dew point to the fraction of reduction, a. The activation energies for the reduction reactions were calculated from plots of log h (reaction rate constant) versus 1/T°K. Activation energies obtained were 18.4, 19.9, 21.0, 34.6, 46.5, and 47.0 kcal per mole, respectively, for the first six compounds. The lead glasses, which reacted below their melting ranges, were reduced appreciably less than the lead compounds.
Miscibility Gap in the System Sodium Oxid Silica—Sodium Sulfate at 1200°C
Authors: PEARCE M. L. , BEISLER J. F.
Published: June 2006

The two‐liquid region in the system soda–silica–sodium sulfate is investigated and the results compared with the limited data available in the literature. An extensive two liquid + tridymite field, not previously reported, is also defined. The variation of the activity coefficient of sodium sulfate with soda/silica ratio is derived from the miscibility data.
Release of Fission Gas During Fissioning of UO2
Authors: CARROLL R. M. , PEREZ R. B. , SISMAN O.
Published: June 2006

Equilibrium fission‐gas release rates from single crystal U02 specimens were studied at temperatures from 400° to 13OO°C and with neutron fluxes from 1 × 1013 to 4 × 1013 neutrons per cm2.second. The behavior of the fission‐gas release for different neutron flux levels and temperatures indicates that two processes are occurring. One release method appears to be caused by a disturbance of the specimen surface by fission recoils. A temperature‐dependent process dominates the gas release above about 7OOOC. This high‐temperature release, once thought to be by diffusion, is now postulated to be controlled by a trapping process. A first‐approach mathematical model is given in which a concentration of traps is assumed to be controlled by fission density, temperature, burnup, and initial structure of the specimen. It is also assumed that the trapped gas has an escape probability which increases with temperature.
Thermal‐Mechanical History and the Strength of Magnesium Oxide Single Crystals: I, Mechanical Tests
Authors: STOKES R. J.
Published: June 2006

Various dislocation impurity interactions in magnesium oxide and their effect on mechanical properties between room temperature and 1000°C are discussed. (1) Impurity precipitate particles in single crystals can be redistributed by heat treatment. Their size and density affect the lattice resistance to the motion of fresh dislocations and thus affect the yield strength at room temperature. Above 1200°C impurities go into solid solution and the strength decreases to 0.7 times the as‐received fully‐precipitated value. (2) Fresh dislocations can be locked by heating above 600°C to produce yield phenomena at room temperature. The upper yield strength increases with time and temperature particularly when the aging temperature exceeds 1000°C. Locking is attributed to the diffusion of impurities and point defects to dislocations. (3) The basic temperature dependence of yield strength contains two regions: (a) Up to approximately 500°C the strength decreases rapidly, suggesting a dislocation cutting mechanism during flow. Material preheated above 1200°C shows a stronger dependence than as‐received material. (b) Above 500° C strength decreases linearly at a rate equal to the decline in elastic modulus. Superimposed on this basic temperature dependence curve there is, for material preannealed above 1200° C, a hump due to reprecipitation between 500° and 1000°c.
Substitution of Aluminum and Gallium in Single‐Crystal Yttrium Iron Garnets
Authors: LINARES ROBERT C.
Published: June 2006

Single crystals of yttrium iron garnet with substitutions of aluminum and gallium were grown from lead oxide‐fluoride, lead borate, and barium borate fluxes. Crystals were grown both by slow cooling and by the gradient technique. The aluminum and gallium contents of these crystals were measured; the amount of substitution and its distribution in one crystal and in the mass of crystals in a run were determined. Crystals grown by slow cooling were badly segregated with respect to aluminum and gallium content whereas gradient‐grown crystals were very uniform.
Phase Relations in the System Boron Oxide–Silica
Authors: ROCKETT T. J. , FOSTER W. R.
Published: June 2006

The suggested phase diagrams for the system B2O3‐SiO2 as drawn from the findings of previous investigators are presented. These diagrams show the wide controversy regarding this system. The principal difficulties in obtaining reliable equilibrium data are the volatilization of B2O3, the hydration of B2O3‐rich glasses, and the great viscosity of B2OrSiOz melts. In this investigation firings were made in sealed platinum capsules. Where necessary, they were opened and studied under xylene to eliminate hydration. Phases were identified by optical and X‐ray methods. The liquidus was obtained by determination of the temperatures at which the stable phases of SiO2 completely dissolved in the borosilicate melts. The criteria used for equilibrium are discussed.
Dissolution in Ceramic Systems: III, Boundary Layer Concentration Gradients
Authors: OISHI Y. , COOPER A. R. , KINGERY W. D.
Published: June 2006

By use of electron microbeam probe analysis on quenched samples, the concentration distribution of CaO, A12O3, and SiO2 was determined across the boundary layer between molten calcium aluminum silicates and dissolving or growing sapphire and fused silica. A definite shift in the concentration ratios of the solvent components was found near the interface. Analysis of diffusion flux equations for a ternary system successfully related the shift in concentration ratio to the intrinsic diffusion coefficient for each component. For alumina dissolution in a melt rich in CaO, evidence of incongruent dissolution was observed with the formation of new phases, CaO· 6Al2O3 and CaO· 2A12O3.
Room‐Temperature Isothermal Elastic Constants of Single‐Crystal Magnesia
Authors: SWICA JOSEPH J. , CRANDALL WILLIAM B.
Published: June 2006

Isothermal technical elastic moduli for three crystallographic orientations of magnesium oxide single crystals were determined. Excellent correlation between these isothermal moduli and reported adiabatic moduli was realized. Non‐Hookean behavior at low stresses was not observed.
Optical Spectra of the Various Valence States of Vanadium in Na2 O.2SiO2 Glass
Authors: JOHNSTON W. D.
Published: June 2006

Optical absorption data are presented for Na2O2SiO2 glass containing vanadium equilibrated in various states of oxidation. Spectra of 5+, 4+, and 3+ vanadium were derived. The variation in amounts of the three species is in accord with mass action considerations. The spectra are related to crystal field assignments.
Calculation of Oxygen Ion Activities in Sodium Silicate and Sodium Borate Melts
Authors: PEARCE M. L.
Published: June 2006

Activity data were calculated using the previously reported results for the variation of oxygen ion activity with composition and the best available thermodynamic data for the heats of formation of sodium monoxide, carbon dioxide, and sodium carbonate. The results are discussed in the light of the data for other systems and recent concepts of the structure of melts.
Viscosity and Density of Boron Trioxide
Authors: NAPOLITANO ALBERT , MACEDO PEDRO B. , HAWKINS EARL G.
Published: June 2006

Extensive and accurate viscosity values for molten B2O3 are reported over the continuous range from 20 poises (at 1400°C) to 1010 poises (at 318°C). The measurements were made with a wide‐range rotating‐cylinder viscometer. The melts were pretreated by bubbling superdry nitrogen through them to ensure a minimum water content. Above 800°C the temperature dependence of the viscosity curve obeyed the Arrhenius equation; below 800°C the curvature was smooth showing no breaks. At the low temperatures, although its curvature decreased, the viscosity curve did not obey the Arrhenius equation. Densities were determined between 411° and 1400°C. Over this range the volume expansion coefficient changed by 1 order of magnitude from 3.35 × 10−4/°C to 3.34 × 10−5/°C. The liquid volume expansion coefficient above 1200°C was smaller than that of the glass below the glass transition temperature, indicating some type of structural rearrangement in B2O3.
Thermodynamic Study of Nonstoichiometric Niobium Pentoxide
Authors: BLUMENTHAL R. N. , MOSER J. B. , WHITMORE D. H.
Published: June 2006

The partial pressure of oxygen in equilibrium with a niobium dioxide‐niobium pentoxide mixture was determined from electrochemical cell measurements over the range 800° to 1070°C and from thermogravimetric gas‐equilibrium measurements at 1000° and 1200°C. These measurements compare favorably with those of previous investigators. An isopiestic technique was used to determine the composition at 100°C intervals for nonstoichiometric Nb2O5 in equilibrium with NbO2 between 900° and 1100°C. The departure from stoichiometry for Nb2O5 decreased from Nb2O4.81 at 1090°C to Nb204.887 at 889°C. The partial pressure of oxygen in equilibrium with different compositions of nonstoichiometric Nb2O5 was determined from electrochemical cell measurements over the range 800° to 1070°C and from thermogravimetric measurements by equilibrating the nonstoichiometric Nb2O5 specimen with an H2/H2O gaseous mixture at 900° to 1200°C. Th_e relative partial molar enthalpy of oxygen, ΔII O2 for the Nb2O5 ‐χ phase (calculated from the cell measurements) was independent, within experimental error, of both temperature and composition, the average value being ‐164 kcal/ mole. These equilibrium measurements were compared with the therrnogravimetric study of nonstoichiometric Nb2O5 by Kofstad and Anderson and a departure from their relation χ (Nb2O5‐χ) ∝pO2‐1/6 was observed at the low oxygen end of the homogeneous phase field.
Sintering in Active Nickel Oxide
Authors: BROWN R. A.
Published: June 2006

Decomposition of nickel oxalate at 450°C in a stream of oxygen for 0.5 hr produced very reactive nickel oxide. Sintering rates in this material were faster (by factors up to 40) than in unreactive nickel oxide, produced by calcining nickel oxalate at 900°C for 5 hr in air. The Arrhenius activation energies for densification were significantly different in the two systems. Preliminary studies confirmed that normal grain growth, which follows a law of the form G3=kt, occurs in nickel oxide.
Thermal Analysis of Some Barium and Strontium Titanyl Oxalates
Authors: GALLAGHER P. K. , THOMSON J.
Published: June 2006

The thermal decompositions of BaTiO(c2O4)2.‐ 4H2O, BaTiO(OH)2C2O4.2H2O, SrTiO(C2O4)2.‐ 4H2O, and SrTiO(OH)2C2O4.H2O were investigated using TGA, DTA, and effluent gas analysis. The stoichiometry of the decompositions is discussed and it is proposed that a reduced state of titanium is formed as an intermediate.
Elasticity and Internal Friction of Polycrystalline Yttrium Oxide
Authors: MARLOWE M. O. , WILDER D. R.
Published: June 2006

Young's modulus and internal friction of polycrystalline yttrium oxide were determined from room temperature to 1658°C by sonic techniques. A linear relation was found between volume fraction porosity and Young's modulus at room temperature. The effect of porosity on room temperature internal friction is also discussed. Young's modulus decreased linearly with increasing temperature to 1000° to 1100°C, where a slight anomaly was observed accompanied by an internal friction peak. The modulus was again linear from 100° to 13500°C. Above this temperature a rapid decrease in elastic modulus occurred with a rapid increase in internal friction.
Observations of Neutron Damage in BeO Single Crystals
Authors: RAU ROBERT C. , BARTRAM S. F. , LACEFIELD K.
Published: June 2006

Observations of neutron damage were made on BeO single crystals irradiated at pile ambient temperature. The crystals darkened during irradiation and often exhibited cracking parallel to the basal plane. Irradiation produced many small defect clusters in the crystals and caused a significant increase in their hardness. X‐ray diffraction photographs of irradiated crystals showed duplex reflections and continuous streaking between certain spots.
High‐Temperature Thermophysical Properties of Zirconium Carbide
Authors: GROSSMAN LEONARD N.
Published: June 2006

An apparatus based on the method of Jain and Krishnan was developed for property measurements in the temperature range from measurable radiant emission to the thermal stability limit of metallic materials. Apparatus and experimental techniques for cylindrical specimens with length‐to‐diameter ratios >4 are described. The theory of the method is reviewed, practical formulations are developed, and error sources are analyzed. The following properties were determined for zirconium carbide in the range 1000° to 2500°K: thermal conductivity, spectral thermal emittance at 0.65μ spectral thermal emittance at 0.65μ as a function of time in vacuum, electrical resistivity, and total thermal emittance. A compilation of experimental values for other physical properties of ZrC is given.
Phase Equilibria in the System Tungsten—Carbon
Authors: SARA R. V.
Published: June 2006

Quenching from high temperatures, supplemented by differential thermal analysis, has shown that the tungsten‐carbon binary is characterized by eutectic temperatures of 2710° and 2760°C between W and W2C, and between W2C and a new high‐temperature phase (β‐WC), respectively. Carbon solubility in excess of stoichiometric W2C is evident only at 2525°C, the eutectoid temperature between W2C and WC. W2.35C melts congruently at 2795°C. A new fee phase (β‐WC), stable only above 2525°, has been discovered between W2C and α‐WC. The cubic phase is formed by a periteci reaction at approximately 2785°C and has a broad homogeneity range ear the solidus. The phase, α‐WC, decomposes into β‐WC and C at 2755°C, approximately 25°C below the melting temperature.
Vapor‐Deposited Borides of Group IVA Metals
Authors: GEBHARDT J. J. , CREE R. F.
Published: June 2006

The formation of vapor‐deposited TiB2, ZrB2, and HfB2 at 1400°C was studied with respect to the influence of process variables on structure and stoichiometry. Stoichiometric, nonporous deposits of TiB2 were obtained; ZrB2 and HfB2 deposits contained β‐rhombohedral boron. Precision lattice parameters were determined for the three diborides. The effect of codeposited boron on these parameters appeared to be slight. A small degree of preferred orientation existed in materials made under these conditions, indicating that crystallites tend to be deposited with c axes parallel to the substrate. Grain size, orientation, porosity, and stoichiometry are influenced and therefore should be controllable by process variation.
Detection and Measurement of Inhomogeneities in Glass by Small‐Angle Scattering of X Rays
Authors: RUSSELL C. K. , BERGERON C. G.
Published: June 2006

Slope analyses of small‐angle scattering curves were used to determine the particle size of submicroscopic, immiscible regions in a lead silicate glass heat‐treated for various times at constant temperature. Particle‐size estimates made from electron micrographs indicated relatively good agreement between the two methods.
Solid Solutions in the System Urania—Rare‐Earth Oxides: I, UO2‐GdO1.5,
Authors: BEALS R. J. , HANDWERK J. H.
Published: June 2006

The extent and nature of solid solution formation in the system urania‐gadolinia were investigated. Compositions sintered in hydrogen, in argon, and in air were analyzed by chemical and X‐ray methods. Extensive solid solution exists between uranium dioxide and gadolinium sesquioxide. Some anomalies in the lattice parameters of the solid solutions are interpreted.
Comparative Method and Choice of Standards for Thermal Conductivity Determinations
Authors: MIRKOVICH V. V.
Published: June 2006

An improved version of the comparative method thermal conductivity apparatus was designed. Its accuracy was determined by measuring the conductivity of alumina with standards made of the same alumina and by cross‐checking the conductivities of alumina, forsterite, Pyroceram Code 9606, and zirconia. The thermal stabilities of Pyroceram Code 9606 and zirconia were examined to establish their values as thermal conductivity reference materials. It was concluded that: (1) With this apparatus accurate thermal conductivity data can be obtained and (2) Pyroceram Code 9606 can be recommended for use as a primary standard for the low thermal conductivity range.
Effect of pH on the Chemical Preparation of Barium‐Strontium Titanate
Authors: SCHREY FRANK
Published: June 2006

Lanthanum‐doped Ba0.6Sr0.44TiO (OH)2C2O4.4H2O was prepared by precipitation from a pH‐controlled oxalic acid solution for conversion to the titanate. TGA and DTA support the proposed formula of a hydrated, mixed hydroxyoxalate. Density and resistivity measurements of the titanates are correlated as a function of lanthanum content.
Behavior of Interlayers of Glass‐to‐Tungsten Seals
Authors: TAKAMORI TAKESHI , TOMOZAWA MINORU
Published: June 2006

The relation of the stability of glass‐to‐tungsten seals to glass composition was studied. Colors of interlayers in the seals depended on alkali content of the glasses. The interlayers were identified, by X‐ray diffraction, as WO2, W18O49, and alkaline tungsten bronzes. Differences in the thermal expansion of these substances were considered with respect to the seal strength. Sodium‐ and potassium‐free glasses did not form tungsten bronzes at the interface, and seals between such a glass and tungsten were more durable than seals between an ordinary alkali‐containing glass and tungsten. An accelerated procedure for detecting potential leaks in seals was tested. Effects of heat treatment on colors of sealed specimens were also observed.
Dielectric and Structural Investigations of the System BaTiO3‐BaHfO3
Authors: PAYNE WILLIAM H. , TENNERY VICTOR J.
Published: June 2006

Dielectric measurements and X‐ray diffraction studies were made in the system BaTiO3‐BaHfO3 for polycrystalline specimens containing from 0 to 30 mole % BaHfO3. The maximum in the dielectric constant for each composition in creased as the BaHfO3 concentration was in creased to 16 mole % and then decreased with further BaHfO3 additions. Room‐temperature lattice constants and hysteresis loops were meas ured for all compositions. A partial solid‐state phase diagram is suggested for the solid solution area of the system. The phase diagram and the dielectric behavior of the system up to 16 mole % BaHfO3 are explained on the basis of Devonshire's thermodynamic theory. The ferroelectric‐paraelectric transition in the composition containing 16 mole % BaHfO3 was essentially of second order and occurred between a ferroelectric rhombohedral phase and a paraelectric cubic phase.
Effects of Radiation‐Induced Damage Centers in Lead Zirconate Titanate Ceramics
Authors: GLOWER DONALD D. , HESTER D. L. , WARNKE D. F.
Published: June 2006

A study of the nuclear reactor irradiationinduced changes in the electrical and lattice properties of ferroelectric Pb(Zr0.65Ti0.35)O3+ 1 wt% Nb2O5 revealed that these changes in properties are caused by different damage centers. The changes observed in electrical properties were: (1) Pr decreased but P3 remained constant, (2) double (antiferroelectric‐type) hysteresis loops were formed, (3) an increase by a factor of 5 in grain size did not affect the radiation damage rate in the ceramics, (4) an increase in irradiation temperature of 100°C above room temperature doubled the damage rate, (5) EC for unpoled ceramics was insensitive to irradiation until integrated fast neutron fluxes of lo18 nvt (and the associated γ‐dose) were exceeded and thereafterECincreased exponentially, (6) aging of the radiation‐induced damage did not occur at room tem perature, (7) the damage centers which affected the electric properties were temperature annealed, the annealing temperature depending on the particular material, (8) the introduction of lattice strain, as observed by changes in the longitudinal wave velocity (phonon mean free path length), did not appear to be related to changes in electrical properties. These changes in electrical and thermal properties are consistent with the published data for irradiated triglycine sulfate, Rochelle salt, barium titanate, and guanidinium aluminum sulfate and it is suggested that a common damage model may be constructed for all these ferroelectric materials.
Evaporation of Silicon from Molybdenum Silicides at High Temperature and in Hard Vacuum
Authors: BLAIR G. R. , LEVIN HERMAN , O'BRIEN R. E.
Published: June 2006

The nature of the degradation of molybdenum disilicide coatings on molybdenum at 3110° to 4000°F in hard vacuum (10−7 torr) was investigated. Degradation occurred as a selective silicon loss by the successive transformations: MoSi2→Mo5Sia →Mo3Si →Mo. Comparison of estimated emittance values with surface composition of the coating indicated an abrupt decrease in emittance from 0.5 to 0.3 corresponding to the transformation Mo5Si3→Mo3Si.
Hypothesis on a High‐Temperature, Solid‐state Galvanic Cell Composed of Refractory Metal Electrodes and a Calcia‐Stabilized Zirconia Electrolyte
Authors: Buyers A. G.
Published: June 2006

Application of heat to a tantalum‐calcia stabilized zirconia‐tungsten cell, in which the tantalum‐zirconia interface has been bonded previously, produced emf's in the range 673° to 2273°K. The origin of these potentials was proposed tentatively to be solid‐state chemical reactions involving the oxidation of tantalum metal and the reduction of ferric ion present as an impurity oxide in the stabilized zirconia. Thermal gradients in the zirconia produced opposing Seebeck potentials at temperatures higher than 1073°K. Resistivity measurements performed with solid zirconia electrolytes resulted in the hypothesis that electric conduction in these materials was electronic in stabilized zirconia impregnated with tantalum species and ionic in stabilized zirconia which had undergone no tantalum reaction.
Light Scattering and Spinodal Decomposition in Glasses
Authors: Goldstein Martin
Published: June 2006

It is shown that the well‐known anomalous Rayleigh scattering of phase‐separated glasses, which can be accounted for by the assumption of nucleation of a new phase followed by diffusion‐controlled growth, can also be qualitatively accounted for by the assumption that the phase separation is occurring within the spinodal region of the phase diagram; here there is no nucleation barrier to phase separation, only a diffusional barrier. A distinction between the two mechanisms in any actual system can be made only by the use of other experimental tools, such as electron microscopy. A quantitative theory of this process proposed by Cahn is examined; it is concluded that light scattering probably reveals only the later stages of the process, rather than the initial stages dealt with by Cahn's theory.
Microstructures of Alkali Halide Eutectics LiF‐NaF and NaF‐NaCl
Authors: Penfold D. , Hellawell A.
Published: June 2006

The microstructures of the directionally frozen eutectics are described and it is shown that the interphase separations vary in a manner similar to metallic eutectics. Addition of impurity to the binary mixtures produces cellular growth and the reactions of the lamellar LiF‐NaF and ribbonlike NaF‐NaCl to these freezing conditions are described.
Plastic Deformation of MgO Single Crystals up to 1600°C
Authors: Copley Stephen M. , PASK JOSEPH A.
Published: June 2006

Stress‐strain curves are presented for MgO single crystals, compressed with (100) and (111) stress axes, for temperatures from 1000° to 1600°C. The yield stress of (100) specimens decreases slightly in this temperature range. The strain‐hardening rate passes through a maximum at about 1100°C and decreases by a factor of about 8 at 1600°C. Above about 1100°C, the strain rate of (100) specimens is considerably less sensitive to changes in stress and the shape of the stress‐strain curves changes. The yield stress of (111) specimens decreases rapidly with increasing temperature without a change of slope up to 1600°C. The ratio of the yield stresses for (111) and (100) specimens decreases continually from 1200° to 1600°C. Various stress rates were used to obtain a measure of strain hardening at 1300°C. Static recovery experiments were carried out at 1000° and 1400°C. At 1000°C static pinning occurred during the unloaded period; at 1400°C orthorecovery occurred. Stress‐strain curves were analyzed by a dynamic approach based on the length of moving dislocation line in the crystal and the average dislocation velocity.
Effect of Impurities on the Strength of Polycrystalline Magnesia and Alumina
Authors: Rasmussen Jewell J. , Stringfellow Gerald B. , Cutler Ivan B. , Brown Sherman D.
Published: June 2006

The bending strength of pure and alloyed magnesium oxide and aluminum oxide was studied. The magnesium oxide was doped with nickel oxide and cobalt oxide, both of which form a complete series of solid solutions with magnesia. The aluminum oxide was doped with ferric oxide which has limited solid solubility in aluminum oxide, with titanium dioxide which also has limited solid solubility in alumina, and with chromic oxide which forms a complete series of solid solutions with alumina. The modulus of rupture was corrected to a standard grain size and porosity to determine the intrinsic effects of the impurities on the modulus of rupture. The results indicate that the formation of NiO‐MgO and Coo‐MgO solid solutions increases the strength of MgO. The formation of Cr2O3‐Al2O3, Fe2O3‐Al2O3, and TiO2‐Al2O3 solid solutions, however, has no intrinsic effect on the strength of sintered alumina.
Calculation of Ionic Crystal Surface Energies from Thermodynamic Data
Authors: Walton A. O.
Published: June 2006

An attempt was made to correlate theoretical surface energy calculations with empirically derived relations between surface energy, lattice energy, and molar volume. An equation linking these parameters is discussed in terms of real surface effects and is found to be consistent with the few available experimental values of surface energy obtained by cleavage techniques.
Metallographic Observation of the Monoclinic‐Tetragonal Phase Transformation in ZrO2
Authors: Fehrenbacher L. L. , Jacobson L. A.
Published: June 2006

The monoclinic‐tetragonal phase transformation of ZrO2 was examined with a vacuum hot‐stage microscope. Polished sections of vacuum‐sintered 99.7% pure ZrO2 were observed from room temperature to 1300°C. The rapid formation of platelet substructure within ZrO2 grains in the temperature range 1050° to 1150°C was associated with the heating transformation. Photomicrographs and motion pictures were taken of the specimen as the transformation progressed. The surface deformation was irreversible, preventing observation of the phase inversion on cooling. From these hot‐stage studies, supplementary DTA, X‐ray, and thermal expansion data, and other existing information, it is concluded that the transformation is of the diffusionless, athermal type, characteristic of Fe‐Ni martensitic transformations.