bluuebunny/crossref_metadata_2025 huggingface dataset:
Interactions Between Cement Minerals and Hydroxycarboxylic‐Acid Retarders: II, Tricalcium Aluminate‐Salicylic Acid Reaction*
Authors: DIAMOND SIDNEY
Published: June 2006

Extensive apparent adsorption of salicylic acid from aqueous solution, previously reported to occur on C3A (and on hydrated calcium aluminates and calcium aluminate sulfates as well), is attributed in large part to precipitation of an amorphous hydrolysis product containing salicylic acid. The product is somewhat gelatinous, especially when generated in salicylic acid solutions of intermediate concentration, but measured BET surface areas were not particularly high. The initial product is not stable, but partly decomposes or rearranges on continued shaking, returning some salicylic acid to the solution. Nearly saturated solutions inhibit the hydrolysis of C3A somewhat, but what product is formed seems entirely amorphous. In contrast, solutions of intermediate concentration do not slow hydrolysis and rapidly generate some tetracalcium aluminate hydrate as well as the amorphous product.
Heat Capacities of Glasses and Liquids in the Pseudobinary System GexAs40‐xS60
Authors: SCHNAUS URBAN E. , MARSHALL ANN , MOYNIHAN CORNELIUS T.
Published: June 2006

Heat capacities were measured from 180° to 720°K for glasses and liquids in the vitreous system GexAs40‐xS60, (the subscripts signify atomic percent). Glass heat capacities are well described by the Debye function for the vibrational heat capacity of solids. A maximum in the glass transition temperature, Tg, and a minimum in the heat‐capacity change at Tg, δCp, occur near the composition for which x=30. These extrema are ascribed to a change near that composition in the effect of replacing As with Ge from network‐making to network‐disrupting.
Relative Activity of Oxygen Ions in Molten Sodium Phosphate as Determined from the Solubility of Sulfur Trioxide
Authors: KATO AKIO , NISHIBASHI REIKO , NAGANO MASAMITSU , MOCHIDA ISAO
Published: June 2006

The solubility of sulfur trioxide in sodium phosphate melts with Na2O/P2O5 ratios from 1.0 to 1.4 was investigated at 653° to 1021°C. The oxygen‐ion activity estimated from the solubility of SO3 increased exponentially as the Na2O/P2O5 ratio increased. This compositional dependence of the activity is discussed on the basis of a polymer model.
Relation of Alkali Mobility and Mechanical Relaxation in Mixed‐Alkali Silicate Glasses
Authors: FLEMING JAMES W. , DAY DELBERT E.
Published: June 2006

Internal friction and Na and K self‐diffusion coefficients for (I–X)Na2OXK2O‐3SiO2 glasses were measured. Alkali diffusion was measured between 300° and 500°C using radioactive isotopes and a thin‐sectioning technique; internal friction was determined at room temperature to 500°C at 0.1 to 2000 Hz. Comparison of the data for alkali diffusion and internal friction in Na‐K glasses with those for other mixed‐alkali glasses shows that the mixed‐alkali peak is related to alkali mobility. It is concluded that the mechanism of mixed‐alkali internal friction is cooperative rearrangement of dissimilar alkali ions, with the slower‐moving ion controlling the rate of reorientation.
Helium Migration in TiO2‐SiO2 Glasses
Authors: SHELBY J. E.
Published: June 2006

Helium permeability, diffusivity, and solubility were measured for a series of TiO2‐SiO2 glasses containing up to 10.3 mol% TiO2. The activation energies for helium permeation and diffusion decrease with increasing TiO2 concentration. The enthalpy of solution is independent of composition, as are the infinite‐temperature values for the permeability, diffusivity, and solubility. It is concluded that the observed changes in activation energies result from changes in the strain energy necessary to distort the R‐O‐R’bond. The average diffusional jump distance appears to be essentially independent of composition, as would be expected from the small changes observed in the molar volume as TiO2 replaces SiO2 in these glasses.
Static and Cyclic Fatigue Behavior of a Polycrystalline Alumina
Authors: KROHN D. A. , HASSELMAN D. P. H.
Published: June 2006

The fatigue behavior of a polycrystalline alumina was investigated. Stress conditions consisted of a static tensile stress and a static tensile stress with superposed sinusoidal cyclic stress. The alumina exhibited the expected static fatigue behavior; a cyclic fatigue effect characterized by a frequency and amplitude dependence was also observed. Possible mechanisms of cyclic fatigue in brittle materials are discussed.
Reexamination of Experimental Strength‐vs‐Grain‐Size Data for Ceramics
Authors: CARNIGLIA S. C.
Published: June 2006

The Orowan, Petch, and Knudsen equations were examined against 46 sets of strength‐vs‐grain‐size data. For the 30 sets which are most discriminating, represented by 229 averaged‐data points, the variances of the Orowan‐Petch and Knudsen treatments are ∼4.5 and ∼17.1 kpsi2, respectively. Statistical considerations give preference to the Orowan‐Petch treatment at a high confidence level in these 30 cases, showing that the Knudsen equation does not remove systematic variations of strength as a function of grain size. The Orowan‐Petch treatment also appears to provide a sounder basis for extrapolation. The identification of the Orowan and Petch equations with postulated physical models permits interpretation of data in terms of probable underlying causes. Several examples are discussed and in most cases agree at least qualitatively with present understanding. A satisfactory physical model for Petch behavior in “nonyielding” ceramics is needed.
Some Aspects of the Thermal History of Lunar Glass
Authors: COOPER A. R. , VARSHNEYA A. K. , SARKAR S. K. , SWIFT J. , KLEIN L. , YEN F.
Published: June 2006

Electron microprobe examination revealed that glassy lunar fragments had inclusions as well as boundaries between mineral glasses of different compositions. Glassy lunar spherules (40 to 60 μm in diameter) showed detectable heterogeneity less marked than that of the fragments. The room‐temperature refractive indices and densities of the spherules are changed by heat‐treating them at 500° to 7O0°C. The large increases (as much as 2% in density and 0.7% in index of refraction) are difficult to explain on the basis of classical glass‐transition phenomena alone unless extremely rapid cooling rates are assumed. Further, the spherules darkened significantly when they were heated in air or a medium vacuum (∼10−5 mm Hg) above 625°C.
Microstructure and Indentation Hardness of an MgO‐Li2O‐Al2O3‐SiO2‐TiO2 Glass‐Ceramic
Authors: DONALD I. W. , McCURRIE R. A.
Published: June 2006

The crystallization of an MgO‐Li2O‐Al2O3‐SiO2 glass containing TiO2 as a nucleating agent was investigated using replication electron microscopy. The hardness varied in a complex manner with the heat‐treatment time but correlated to some extent with the observed changes in microstructure.
The Freezing Point of Water in Porous Glass
Authors: BLACHERE J. R. , YOUNG J. E.
Published: June 2006

Lowering of the freezing point of water in porous glass was studied by a DTA technique. The samples contained a spectrum of average pore sizes. The freezing‐point lowerings measured from melting and freezing curves correlated, as predicted by simple capillary theory, with the average pore size of the sample. This result is discussed in terms of capillary‐condensation theory and theories of frost damage in porous materials.
Electrode “Polarization” in Alkali‐Containing Glasses
Authors: CARLSON D. E. , HANG K. W. , STOCKDALE G. F.
Published: June 2006

A model is proposed to explain the phenomenon of electrode “polarization” in glasses containing alkali oxides. The application of a dc potential to Pt electrodes on an alkali‐containing glass causes a large electric field to develop in the immediate vicinity of the anode. This high‐field region is formed by local dissociation of the alkali oxides and displacement of the dissociated ions from the region. A major hypothesis of the model is that the nonbridging oxygen ions in this region can move and can determine the electrical characteristics of the sample. Large electric fields can also develop at a partially blocking cathode as a result of the pileup of alkali ions beneath the cathode surface. Permanent compositional changes occur near both electrodes under such conditions. The model was confirmed by dc electrical measurements, electron‐microprobe data, and oxygen‐evolution data. Important physical parameters of the model were calculated from the data.
Strength of Titania and Aluminum Silicate Under Combined Stresses
Authors: ELY RICHARD E.
Published: June 2006

Room‐temperature strengths are reported for titania and aluminum silicate in various biaxial stress states. Results are compared with failure criteria based on either energy or internal‐friction concepts. In general, more complete and reliable data for ceramic materials are needed before specific failure criteria can be designated.
Computerized Prediction of Glass Compositions from Properties
Authors: HUFF N. T. , CALL A. D.
Published: June 2006

A computer technique is described which allows prediction of glass compositions which have arbitrary sets of properties. The technique involves equations which can be used to calculate the properties of a glass when only its composition is known. The application of the method to soda‐lime silicate glasses is discussed.
Relation of Microindentation Hardness to Glass Composition
Authors: GEOROFF A. N. , BABCOCK C. L.
Published: June 2006

Microindentation hardness measurements on Na2O‐CaO‐SiO2 and Na2O‐Al2O3‐SiO2 glasses showed that Knoop hardness numbers are linearly related to oxide compositions expressed in mole fraction. Evaluations of the data indicate that these linear relations are unique for each of the primary crystallization phase fields of the glasses studied.
Chemical Vapor Deposition of Epitaxial Films of Yttrium Iron Garnet and Gallium‐Substituted Yttrium Iron Garnet and a Thermodynamic Analysis
Authors: GENTILMAN RICHARD L.
Published: June 2006

Epitaxial single‐crystal films of yttrium iron garnet (YIG) and Ga: YIG (Y3Fe5‐xGaxO12) were grown by chemical vapor deposition. The garnet is deposited by the reaction of gaseous metal chlorides with O2 at 1150°C and 5 torr. The chlorides are generated in‐line by reacting Cl2 gas with a Y‐Fe(‐Ga) alloy. A computer‐aided thermodynamic calculation was developed to determine which of several possible solids in a multicomponent CVD system will be deposited for a given set of growth conditions. The calculation determines an intermediate equilibrium among all gaseous species and then identifies the solid phase most favored to be deposited from the supersaturated gas phase. The results of the calculations agreed well with experiment and have been useful in finding the conditions for optimum growth of garnet. This type of calculation can be applied to other multicomponent CVD systems.
Influence of Additives on the Microstructure of Sintered Al2O3
Authors: ROSSI GIULIO , BURKE JOSEPH E.
Published: June 2006

During an investigation to determine the effect of additives in inhibiting exaggerated grain growth, it was observed that several gave strikingly similar microstructures with pore clusters at grain centers surrounded by substantially pore‐free annular regions. A few very large pores were found at the grain boundaries and occasionally in the small‐pore‐free annular regions. The development of this structure is explained as a sequence of exaggerated grain growth followed by normal grain growth. A discontinuous grain‐boundary liquid phase facilitates the final grain‐growth step and takes part in the coalescence of fine pores into coarse pores.
Compressive Creep and Hot Hardness of U‐Pu Carbides
Authors: TOKAR MICHAEL
Published: June 2006

The compressive creep of carbides having the composition U0.79Pu0.21C1.02 and a sintered density of 11.8 g/cm3 was studied at 1300°, 1400°, and 1500°C and stresses of 2000, 4000, and 6000 psi. The equation which best fitted the data was

The dominant creep mechanism was probably grain‐boundary sliding. The hardness of monocarbides with various U/Pu ratios was measured from room temperature to 1200°C. Probable mechanisms of deformation are discussed.
Thin‐Film Studies of the Reduction of SiO2 by Al
Authors: PRABRIPUTALOONG K. , PIGGOTT M. R.
Published: June 2006

The reaction between Al and SiO2 at 700° to 850°C was examined under high vacuum using thin Al films on SiO2 plates. The reaction products were analyzed by electron diffraction. The only nongaseous reaction product was Si, which was observed only when the reaction was conducted at a pressure low enough to inhibit the oxidation of Si to a gaseous product, presumably SiO. The reaction was very rapid, and the dwell time observed in bulk by Standage and Gani was apparently absent. The activation energy of the reaction is 17±4 kcal/mol.
Hydration of Beta Dicalcium Silicate Alone and in the Presence of CaCl2 or C2H5OH
Authors: COLLEPARDI MARIO , MASSIDDA LUIGI
Published: June 2006

Beta C2S was hydrated at room temperature with and without added CaCl2 or C2H5OH by methods previously studied for the hydration of C3S, i.e. paste, bottle, and ball‐mill hydration. The amount of reacted β‐C2S, the Ca(OH)2 concentration in the liquid phase, the CaO/SiO2 molar ratio, and the specific surface area of the hydrate were investigated. A topochemical reaction occurs between water and β‐C2S, resulting in the appearance of solid Ca(OH)2 and a hydrated silicate with a CaO/SiO2 molar ratio of ≃1. As the liquid phase becomes richer in Ca(OH)2, the first hydrate transforms to one with a higher CaO/SiO2 ratio. Addition of CaCl2 increases the reaction rate and the surface area of the hydrate but to a much lesser extent than in the hydration of C3S, whereas C2H6OH strongly depresses the hydration rate of β‐C2S, as observed for C3S hydration.
Introduction to the Thermodynamics of Spinodal Decomposition
Authors: HASKELL R. W.
Published: June 2006

The thermodynamics of spinodal decomposition is presented in detail on the basis of Hillert's one‐dimensional model. The flux equation governing the initial kinetics of such processes is also developed. Similarities and comparisons to the Cahn‐Hilliard phenomenological theory are noted.
Effect of Melting History on the Mechanical Properties of Glass: I, Role of Melting Time and Atmosphere
Authors: SPROULL JAMES F. , RINDONE GUY E.
Published: June 2006

The pristine strength of 0.5Li2O·0.5K2O·2SiO2 glass measured in 3‐point bending under liquid nitrogen was studied as a function of melting time and atmosphere at a constant melting temperature. The atmosphere over the melt was one of the most important parameters affecting the pristine strength. The most significant time‐dependent melting effects and the highest strengths resulted from melting in a dry atmosphere of O2 or air. In contrast, vacuum‐melted and Ar‐melted glasses had the lowest strengths. Melting in N2 or CO2 led to intermediate strengths. The presence of water vapor in the atmosphere during melting was detrimental to strength in those cases where very high strengths had been obtained with dry gases. The introduction of water vapor into those gases which in the dry state had led to low‐strength glasses did not significantly affect the strength. The effects of the atmosphere in leading to oxygen‐deficient or excess‐oxygen glasses on the formation or dissolution of microheterogeneous regions were correlated with the pristine strengths of the glasses.
Processing Parameters and Properties of Lithium Ferrite Spinel
Authors: BANDYOPADHYAY G. , FULRATH R. M.
Published: June 2006

Polycrystalline compacts of lithium ferrite with varying stoichiometry were sintered using a packing‐powder technique and high‐O2 atmosphere to control the material loss from the system. These specimens were used to study the influence of sintering time and temperature and stoichiometry on the densification, microstructural characteristics, dc resistivity, and hysteresis‐loop parameters of lithium ferrite. The influence of the packing‐powder composition was also investigated.
Strength and Absorbed Energy in Instrumented Impact Tests of Al2O3
Authors: BERTOLTTI RAYMOND L.
Published: June 2006

By use of strain‐gage instrumentation to record impact loads as a function of time, the flexural strength at high strain rates and the energy absorbed in Charpy impact fracture of an alumina were measured. The energy absorption by Al2O3impact specimens is shown to result principally from elastic mechanical loading. Extraneous energy losses in the Charpy test can easily exceed the magnitude of this mechanical specimen‐loading energy and are shown to be inherent sources of error in impact testing of brittle materials.
Application of Fracture Mechanics to Space‐Shuttle Windows
Authors: WIEDERHORN S. M. , EVANS A. G. , FULLER E. R. , JOHNSON H.
Published: June 2006

The fracture properties of an ultralow‐expansion glass intended for use in windows for the Space Shuttle were characterized by strength and fracture‐mechanics techniques to provide reliable design data. Proof‐test diagrams for predicting minimum times‐to‐failure under specified service loads were developed from measurements of subcritical crack growth in water and air. Failure predictions were confirmed from strength measurements in water. In vacuum (<10−4torr), the fracture behavior was similar to that of other high‐SiO2glasses, as evidenced by the absence of subcritical crack growth and by insensitivity of the critical stress intensity factor to temperature.
Phase Relations in the System Bi2O3‐WO3
Authors: HODA SYED N. , CHANG LUKE L. Y.
Published: June 2006

Phase relations in the system Bi2O3‐WO3 were studied from 500° to 1100°C. Four intermediate phases, 7Bi2O3· WO3, 7Bi2O3· 2WO3, Bi2O3· WO3, and Bi2O3· 2WO3, were found. The 7B2O · WO3 phase is tetragonal with a0= 5.52 Å and c0= 17.39 Å and transforms to the fcc structure at 784°C; 7Bi2O3· 2WO3 has the fcc structure and forms an extensive range of solid solutions in the system. Both Bi2O3· WO3 and Bi2O3· 2WO3 are orthorhombic with (in Å)a0= 5.45,b0=5.46, c0= 16.42 and a0= 5.42, b0= 5.41, c0= 23.7, respectively. Two eutectic points and one peritectic exist in the system at, respectively, 905°± 3°C and 64 mol% WO3, 907°± 3°C and 70 mol% WO3, and 965°± 5°C and 10 mol% WO3.
Preparation of High‐Coercivity BaFe12O19
Authors: HANEDA KOICHI , MIYAKAWA CHOJI , KOJIMA HIROSHI
Published: June 2006

Particles of BaFe12O12 were prepared by chemical coprecipitation; their magnetic properties were studied. A coercive force of 6000 Oe, one of the highest reported for isotropic BaFe12O19, was obtained. X‐ray and Moessbauer studies were conducted to examine the mechanism of formation. Superparamagnetic α‐Fe2O3 was present during synthesis. Ferrites were sintered from these precipitated powders by both the usual method and a hot‐press‐forging method. The observed magnetic characteristics result from partial orientation of defect‐free single‐domain coprecipitated powders.
Interdiffusion and Association Phenomena in the System NiO‐Al2O3
Authors: MINFORD W. J. , STUBICAN V. S.
Published: June 2006

The rate of formation of NiAl2O4 by reaction between single crystals of NiO and Al2O3 can be described by k= 1.1 × 104 exp (−108,000 ± 5,000/RT) cm2/s. In NiO the behavior of D as a function of concentration supports the Lidiard theory of diffusion by impurity‐vacancy pairs. A good fit of the theory to the experimental results was obtained by assuming that Al3+ ions diffuse as [AlNi· VNi]’pairs. The diffusion coefficient of pairs, Dp, obeys the equation 6.6 × 10−2 exp (−54,000 ± 3,000/RT) cm2/s. The free energy of association for pairs was calculated to range from 6.5 kcal/mol at 1789°C to 9.0 kcal/mol at 1540°C. The interdiffusion coefficients in the spinel showed a constant small increase with increasing concentration of Al3+ dissolved in the spinel.
Light Scattering from a Metastable Immiscible Na2O‐CaO‐SiO2 Glass
Authors: SHETTERLY D. M.
Published: June 2006

Light scattering was measured for samples of a metastable immiscible Na2O‐CaO‐SiO2 glass which had been heat‐treated to develop a droplet microstructure. The angular scattering profiles obtained were fitted to scattering curves generated using the model of Shetterly and Stubler. The results indicate that, even at fairly short times, the mechanism of growth in this glass is ripening.
Residual Stress Measurement Using Acoustic Emission
Authors: EVANS A. G.
Published: June 2006

An analysis is presented which shows how acoustic emission caused by microcracking is expected to vary during an elastically reversible load cycle. The acoustic emission rate during unloading can be predicted directly from the acoustic emission rates observed during the loading and holding periods of a test cycle. Any discrepancy between the measured and predicted rates during unloading indicates irreversible behavior. A measure of the severity of the residual stress that results from irreversibility can be determined from the measured acoustic emission.
Elastic Properties of Monoclinic Hafnium Oxide at Room Temperature
Authors: DOLE S. L. , HUNTER O. , WOOGE C. J.
Published: June 2006

The Young's and shear moduli of polycrystalline monoclinic hafnium oxide were determined by the sonic resonance method at room temperature as a function of volume fraction porosity. The Spriggs equation empirically described the data and the zero porosity moduli as 283.6 GN/m2 and 109.2 GN/m2 for Young's and shear moduli, respectively. The Debye temperature calculated from the elastic constants was 484°K. Several specimens had anomalously low moduli values, attributed to microcracking. Grain size and internal friction measurements showed that the microcracking occurred in specimens with grain sizes > 2 to 3 μm and was characterized by high internal friction.
Subsolidus Equilibria and Stabilization of Tetragonal ZrO2 in the System ZrO2‐Al2O3‐SiO2
Authors: SORRELL CHARLES A. , SORRELL CHARLES C.
Published: June 2006

The irreversible reaction between zircon and alumina to form mullite and zirconia was observed to proceed very slowly at 1480°C, confirming the existence of a stable join between mullite and zirconia in addition to the join between mullite and zircon. Attempts to determine equilibrium assemblages in powder samples of several combinations of the constituents at 1300° and 1400°C were unsuccessful. Metastable tetragonal ZrO2 was observed in fired powder samples containing kaolinite, in fired zircon‐alumina samples, and in calcined gels prepared from zirconyl nitrate, aluminum nitrate, and colloidal silica in water. Tetragonal ZrO2 was the dominant crystalline phase in gels fired for 24 h at 800°, 950°, and 1100°C; the thermal stability of the phase was enhanced by Al2O3 and by SiO2, but most effectively by mixtures of the two. Line broadening measurements and electron microscope observation indicate that the tetragonal ZrO2, with apparent crystallite sizes between 0.009 and 0.1 μm, develops as an intergrowth with, and is stabilized by, the amorphous matrix of Al2O3 and SiO2.
The Effective Medium Theory of Diffusion in Composite Media
Authors: DAVIS H. TED
Published: June 2006

The effective medium theory is developed for diffusion in random composite media. It is demonstrated that the theoretical diffusivity depends crucially on whether concentration or chemical potential is taken to be the field variable for describing transport.
The System HfO2‐Eu2O3
Authors: SCHEIDECKER R. W. , WILDER D. R. , MOELLER H.
Published: June 2006

The system HfO2‐EuzO3 was investigated at ∼5 mol% intervals over a temperature range of 960° to 1900°C, by X‐ray analysisof quenched specimens. Liquidus temperature measurements made over the entire system showed the lowest liquidus temperature of 1930°± 15°C to be located at ∼96 mol% Eu2O3 A large fluorite solid solution region was also found to exist at higher Of HfO2 concentrations over the entire temperature range.
The System Erbia‐Zirconia
Authors: DURAN P.
Published: June 2006

The subsolidus phase relations of the ZrO2‐rich region of the system Er2O3‐ZrO2 were studied by high temperature X‐ray diffractometry and thermal expansion measurements. Compositions in the entire system were examined by X‐ray diffraction at room temperature. The range of existence of the solid solutions based on ZrO2 and Er2O3 was determined by the precision lattice parameter method. Two hexagonal compounds were found: the first is formed at 40 mol% Er2O3 and decomposes above 1500°C into a fluorite‐type cubic solid solution; the second is formed at 70 mol% Er2O3 and decomposes above 1700°C into a C‐type cubic solid solution.
Silicate‐Containing Sodium Beta‐Alumina Solid Electrolytes
Authors: HSIEH M. Y. , DE JONGHE L. C.
Published: June 2006

Sodium beta‐alumina solid electrolytes were prepared containing up to 7.5 wt% SiO2 and their density, soda content, micro‐structure, and ionic resistivity were studied. The resulting microstructures have glassy sodium ahminosilicate phases inhomogeneously distributed. The glassy phase collects preferentially at triple grain junctions, but occasionally penetrates along some grain boundaries as a thin layer (10 to 20 Å). Alpha‐alumina is also present, especially with high silica content and when the samples are not protected with β‐alumina powder during sintering. The total specific ionic resistivity follows a dependence on silicate content typical of 2‐phase mixtures.
Instability of Cylindrical Voids in Alumina
Authors: GUPTA T. K.
Published: June 2006

It is shown from experimental observation that cylindrical voids in polycrystalline alumina are unstable. When isothermally annealed, they undergo various configurational changes, in accordance with the theoretical prediction, prior to an ultimate breakup into rows of spherical voids. The breakup occurs by ovulation, if the aspect ratio is appropriate. If the required aspect ratio is not met, cylindrical voids are directly transformed into spherical voids by spheroidization. The predominant mechanism for void breakup on thermal anneal confirms a model for surface‐diffusion‐control material transport. The estimated surface‐diffusion coefficients at the experimental annealing temperatures agree, within an order of magnitude, with the values reported in the literature.
Wetting of Aluminum Nitride by Nickel Alloys
Authors: TRONTELJ MARIJA , KOLAR DRAGO
Published: June 2006

The effect of the addition of alloying elements to Nion Ni wetting of AIN was investigated. Pure Ni is nonwetting, but adding Hf, Zr, or Ti caused Ni to wet, whereas V, Nb, Ta, Cr, Mo, and W did not change the wetting angle. In wetting systems, the alloying elements form nitrides and the change in the wetting angle is related to the change in the Gibbs free energy of formation of the nitrides formed in the contact layer.
Hydrogen Diffusion and Solubility in Silicon Carbide
Authors: CAUSEY R. A. , FOWLER J. D. , RAVANBAKHT CAMRAN , ELLEMAN T. S. , VERGHESE KURUVILLA
Published: June 2006

Tritium diffusion coefficients and deuterium solubilities were measured for silicon carbide. At 500° to 1300° C, measured tritium diffusion coefficients were much lower than the recorded values for metals, whereas the activation energies for diffusion were much higher (30 to 75 kcal/mol). The solubility of deuterium in silicon carbide decreased as temperature increased and exhibited a pressure dependence of ∼P1l2.
Mg Distributions at Grain Boundaries in Sintered Alumina Containing MgA12O4 Precipitates
Authors: JOHNSON W. C.
Published: June 2006

It is demonstrated that spinel (MgAI2O4) grain‐boundary precipitates in A12O3 doped with 0.1 wt% MgO can be misinterpreted as solute segregation when analyzed with surface‐sensitive techniques which lack adequate spatial resolution. Further, it is shown that since Mg is preferentially removed during the inert‐ion sputter etching of MgAI2O4, Mg composition vs depth profiles obtained with sputtering from alumina surfaces containing spinel precipitates are not a valid measure of the Mg distribution.
Ternary Compounds in the System La‐Co‐O
Authors: JANECEK J. J. , WIRTZ G. P.
Published: June 2006

The compounds LaCoO3, La4Co3Ol0, and La2CoO4 were synthesized and characterized by powder X‐ray diffraction. Lanthanum cobaltate, LaCoO3, has the rhombohedra1 modification of the perovskite structure, whereas La4CO3O10 and La2CoO4 have perovskite‐related structures based on face‐centered orthorhombic lattices. The lattice parameters of these ternary phases are dependent on the conditions of preparation. Six invariant reactions in the system La‐Co‐O are summarized in a portion of the 1130°C isothermal section.
Effect of TiB2 and Boron Additions on the Stability of Wurtzite‐Type Boron Nitride at High Temperatures and Pressures
Authors: AKASHI TAMOTSU , SAWAOKA AKIRA , SAITO SHINROKU
Published: June 2006

Shock‐synthesized wurtzite‐type BN(w‐BN) and mixtures of w‐BN–TiB2 and w‐BN–ß were treated at high temperatures and pressures. The effect of TiB2 and boron additions on the transformation of w‐BN to zinc blende‐type BN(z‐BN) was studied at 1000° to 2200°C and 55 to 68 kbars. The formation region of z‐BN was shifted toward higher temperatures by TiB2 additions and toward lower temperatures by boron additions.
Hot‐Pressing of Si3N4 with Y2O3 and Li2O as Additives
Authors: BOWEN L. J. , CARRUTHERS T. G. , BROOK R. J.
Published: June 2006

The rates of densification and phase transformation undergone by α‐Si3N4 during hot‐pressing in the presence of Y2O3, Y2O3−2SiO2, and Li20−2Si02 as additives were studied. Although these systems behave less simply than MgO‐doped Si3N4, the data can be interpreted during the early stages of hot‐pressing as resulting from a solution‐diffusion‐reprecipitation mechanism, where the diffusion step is rate controlling and where the reprecipitation step invariably results in the formation of the β‐Si3N4 phase.
Powder Diffraction Patterns and Structures of the Bismuth Oxides
Authors: MEDERNACH JOHN W. , SNYDER ROBERT L.
Published: June 2006

The structures of the bismuth oxides are discussed and evaluated. Calculated powder diffraction patterns were made for all reported phases with known crystal structures. Comparing the calculated and experimental patterns indicates that the α and β polymorphs are well characterized. All previous observations concerning δ‐Bi2O3 are explained using a primitive cubic crystal structure model. The existence of an fee Bi2O3 is in doubt. Calculated patterns are given for all reported nonstoichiometric and suboxides of bismuth.
Finite Element Analysis of Stresses in Glass‐to‐Metal Foil Seals
Authors: VARSHNEYA A. K. , PETTI R. J.
Published: June 2006

Stresses in glass‐to‐metal foil seals were measured using photo‐elastic techniques and calculated using finite element analysis. Cases considered were one in which the metal remains elastic during cooling and one in which the metal yields under the action of developed stresses at some stage during cooling. Calculated and measured values agreed very well using a coarse spatial resolution limited by the measurements. Spatial resolution of the calculations was then made finer to obtain the stress distribution in the immediate vicinity of the foil tip more precisely. Observed fractures in such seals are discussed in terms of these stresses. The effect of the metal foil geometry on the magnitude of the critical stresses was studied using finite element analysis. The relative merits of using various foil geometries are discussed in relation to lowering the seal failure probability.
HCl Leaching Rate and Microstructure of Phase‐Separated Borosilicate Glasses
Authors: TAKAMORI TAKESHI , TOMOZAWA MINORU
Published: June 2006

The leaching rate in HCl solution and the glass transition temperature (Tg) of a borosilicate glass (SiO2 70, B2O3 23, and Na2O 7 wt%) were measured as a function of heat treatment for glass‐in‐glass phase separation. The leaching rate varied together with Ty, approaching an equilibrium value unique to the heat‐treatment temperature. As the heat‐treatment temperature decreased, the equilibrium leaching rate increased. These results plus electron microscopy of sample structure established that the leaching rate is primarily controlled by the composition of the chemically less durable phase, and the effect, if any, of microstructure size is small. In contrast to previous reports, extremely long heat‐treatment times were required to attain the equilibrium composition.
Low‐Temperature Heat Capacity and Structure of Alkali Silicate Glasses
Authors: HIRAO KAZUYUKI , SOGA NAOHIRO , KUNUGP MASANAGA
Published: June 2006

The heat capacities of several alkali silicate glasses were measured at 77 to 300 K. The experimental results of these glasses were analyzed using the three‐band theory. The characteristic temperatures (θ1, θ3, and θE) obtained were used to determine the nature of atomic interactions in glasses. The variation in the characteristic temperatures depended on the type and amount of cations, which agreed with the infrared spectra for single‐ or mixed‐alkali silicate glasses.
The Microstructure and Distribution of Impurities in Hot‐Pressed and Sintered Silicon Nitrides
Authors: KRIVANEK O. L. , SHAW T. M. , THOMAS G.
Published: June 2006

Two hot‐pressed (HS 130 and NC 132) and two sintered silicon nitrides (with MgO·Al2O3 and Y2O3 additives) were examined in detail by X‐ray diffraction, emission spectroscopy, medium‐and high‐resolution electron microscopy, and X‐ray microanalysis. The overall morphologies of the four materials are quite comparable. Very thin (10 to 20 Å) intergranular glassy films were detected in all the materials at almost all grain and interphase boundaries. The composition of these glasses was determined by X‐ray microanalysis using a 200‐Å electron probe and the softening temperature was estimated from available phase diagrams. The results are in good agreement with the known softening temperatures for the four silicon nitrides, thereby confirming the central role played by glassy phases in determining the high‐temperature mechanical properties of these materials.
Effect of Si3N4 Powder Reactivity on the Preparation of the Si2N2O‐Al2O3 Silicon Aluminum Oxynitride Solid Solution
Authors: SEKERCIOGLU I. , WILLS R. R.
Published: June 2006

Dense high‐purity Si2N2O‐Al2O3 silicon aluminum oxynitride (O'‐sialon) was prepared by reactive hot‐pressing of an Si3N4‐Al2O3‐SiO2 mixture. The formation of a single‐phase material was found to be critically dependent on the Si3N4 powder in the Si3N4‐Al2O3‐SiO2 starting mixture. It is suggested that evolution of a chlorine‐ and nitrogen‐containing species may enhance the reactivity of Si3N4 in this reaction. Densities of O'‐sialons are very similar to that of Si2N2O (2.82 g/cm3), the widely quoted value in the ceramics literature of 3.1 g/cm3 for the density of Si2N2O being incorrect.
Vaporization of Silica in Steam Atmosphere
Authors: CHENG MING‐CHU , CUTLER IVAN B.
Published: June 2006

The effect of temperature and steam pressure on the vaporization and corrosion of silica was studied by measuring weight loss as a function of time. The reaction rate increased exponentially with temperature up to 1200°, with a maximum rate of reaction at ∼1350°C. Above this temperature the rate abruptly decreased with increasing temperature. The pressure dependence of the reaction was approximately linear. The activation energy was ∼25 kcal/mol for the reaction at 0.84 and 14.5 atm steam.
Rate‐Controlling Factors in the Carbothermic Preparation of UO2‐UC2‐C Microspheres
Authors: STINTON D. P. , TIEGS S. M. , LACKEY W. J. , LINDEMER T. B.
Published: June 2006

Rate‐controlling factors in the conversion of UO2+ C microspheres to UC2+ C were investigated using a fluidized‐bed furnace (13 cm in diam.). Examination by X‐ray diffraction, ion microprobe, and microstructural observation revealed that the conversion of UO2 to UC2 began at the surface of the microsphere and progressed toward the central unreacted core. Kinetic models for solid state reactions in spheres were evaluated by using quantitative mass spectrometric data on the rate of evolution of CO during conversion. This analysis revealed that the rate of conversion was controlled by reaction at the outer surface of the microsphere. Also, decreased partial pressures of CO accelerated the rate of reaction.
Solubility Limits in Binary (Ca,Mn) Chalcogenides
Authors: LEUNG CHI‐HUNG , VAN VLACK LAWRENCE H.
Published: June 2006

Solid solubilities progressively decrease in the systems CaS‐MnS, CaSe‐MnSe, and CaTe‐MnTe. In CaS‐MnS, full solid miscibility extends from 1150° to 1500°C, the liquidus minimum. With CaSe‐MnSe, this range is 1070° to 1340°C. The solid miscibility gap between CaTe and cubic MnTe intercepts the liquidus as a eutectic at 1050°C. The solid solutions follow Vegard's law closely.
Eutectic Studies in the System Si3N4‐Si2N2O‐Mg2SiO4
Authors: LANGE F. F.
Published: June 2006

Melting experiments have established three important eutectics in this system: (1) the Si3N4‐Mg2SiO4 binary eutectic composition, 0.07Si3N4+0.93Mg2SiO4 at 1560°C, (2) the Si2N2O‐Mg2SiO4 binary eutectic composition, 0.17Si2N2O+ 0.83Mg2SiO4 at 1525°C, and (3) the Si3N4‐Si2N2O‐Mg2SiO4 ternary eutectic composition, 0.04Si3N4+0.14Si2N2O+0.82Mg2SiO4 at 1515°C. Systematic replacement of MgO with CaO in the ternary eutectic reduced its melting temperature to 1325°C for a CaO/MgO molar ratio of 0.67. The results of this study are discussed in relation to fabrication, microstructure, and high‐temperature strengths.
Dynamic Effects of Liquids on Crack Growth Leading to Catastrophic Failure in Glass
Authors: MICHALSKE TERRY A. , FRECHETTE V. D.
Published: June 2006

Crack growth in glass plates, up to supercritical velocities, was produced by controlled strain, velocity being measured continuously by superimposing a tuned‐frequency sonic signal during cracking. Cracks, which were accelerated to supercritical velocity in the presence of water, showed an order of magnitude jump in velocity and an associated cavitation scarp on the crack surface marking the onset of catastrophic failure. The crack velocity immediately preceding catastrophic failure is termed the critical velocity. Measurement to the cavitation scarp was suggested as a means to determine the size and shape of critical flaws in bend‐test specimens. The velocity jump was explained in terms of a drag effect which may result from crack topographical features as well as viscous drag forces. A model involving liquid cavitation was formulated to predict critical velocity as a function of environmental parameters. Experiments in some aqueous solutions suggested preferential transport of water to the crack tip.
Infrared Spectra of Superionic Conducting Glasses in the System AgI‐Ag2O‐GeO2
Authors: MINAMI TSUTOMU , IMAZAWA KAZUHIRO , TANAKA MASAMI
Published: June 2006

Infrared spectra of superionic conducting glasses in the system AgI‐Ag2O‐GeO2 were compared with crystalline (hexagonal and tetragonal forms) and glassy GeO2. It was found that glasses with the mole ratio Ag2O/GeO2= l are almost entirely composed of octahedral GeO6 groups. As the ratio deviates from unity, the content (which is probably low) of the tetrahedral GeO4 groups increases. The composition dependence of glass transition temperatures is explained on the basis of this structural evidence.
Characterization of Sintered MgO Compacts with Fluorine
Authors: IKEGAMI TAKAYASU , KOBAYASHI MICHIKO , MORIYOSHII YUSUKE , SHIRASAKI SHIN‐ICHHI , SUZUKI HIROSHIGE
Published: June 2006

Characterizing the properties of F−‐doped MgO indicated new roles for fluorine ions in accelerating densification: (1) increased strains in MgO before rapid densification and (2) the thermal generation of enormous oxygen ion vacancies. Immediately after rapid shrinkage, fluorine‐containing species vaporized from the compact in appreciable amounts.
Morphology of Creep Fracture of a Phase‐Separated Borosilicate Glass
Authors: TAKAMORI TAKESHI , TOMOZAWA MINORU
Published: June 2006

A phase‐separated borosilicate glass with interconnected microstructure was stretched in the viscoelastic temperature range. When elongated, significant necking and subsequent fracture occurred. SEM study of the fractured samples revealed an enormous amount of crazing on the surface and void formation in the bulk of the samples near the fractured edges.
Effects of Space Charge, Grain‐Boundary Segregation, and Mobility Differences Between Grain Boundary and Bulk on the Conductivity of Polycrystalline Al2O3
Authors: TIKU S. K. , KRÖGER F. A.
Published: June 2006

The potential difference between grain boundary and bulk and the concentrations of native and foreign point defects in the bulk, the grain boundary (gb), and the subgrain boundary space‐charge region (sg) of polycrystalline Al2O3 doped with acceptors are computed for the case that the dopants segregate at the grain boundaries, with either the ionized or the nonionized acceptor as the dominant species. Expressions are derived for the effective dc conductivity of a polycrystalline material on the basis of a model in which the grain has one or two shells with conductivities different from that of the bulk. Combination of the two results yields expressions for the effective ionic and electronic conductivity of doped A12O3 as a function of grain size with distribution coefficients gb/sg, mobility ratios in the various regions, and equilibrium constants as parameters. At impurity concentrations normally found in ceramics, the contribution by subgrain boundaries to conductivity may be neglected. The theoretical results are compared to published data for Al2O3:Mg, Fe, and Ti.
Infrared Spectra of a Water‐Containing Glass
Authors: BARTHOLOMEW R. F. , BUTLER B. L. , HOOVER H. L. , WU C. K.
Published: June 2006

Infrared absorption was measured on an NajO‐K2O‐ZnO‐Al2O3‐SiO2 glass with up to ∼11 wt% water. Fundamental and overtone‐combination bands were observed at 1.41, 1.91, 2.22, 2.87, and 6.1 μm. Molar absorptivities were determined for the hydrated glass for H2O and OH levels using the molar absorptivity calculated for the 2.22‐μm band in the as‐melted glass. By this procedure the concentration of molecular water and OH groups could be determined separately. These results show that the OH content of the hydrated glass, as determined from the 2.22‐μm band, is constant at >7 wt% H2O; additional H2O is attributed to molecular water only. Good agreement was found between these data and H2O/OH molecular ratios obtained from NMR.
Crack Growth from Small Flaws in Larger Grains in Alumina
Authors: KIRCHNER H. P. , RAGOSTA J. M.
Published: June 2006

Crack growth in alumina was simulated for the case of small flaws in larger surface crystals to determine the range of crystal sizes and loading rates in which single‐crystal fracture energies would be expected to control fracture. This control should be expected only for large crystals and very high loading rates.
Crystallization of Nuclear Waste Disposal Glass
Authors: BOULOS E. N. , DePAULA R. P. , El‐BAYOUMI O. H. , LAGAKOS N. , MACEDO P. B. , MOYNIHAN C. T. , REKHSON S. M.
Published: June 2006

The rate of bulk crystallization and shear viscosity η of a zinc borosilicate simulated nuclear waste disposal glass (SNWDG) were measured above the glass transition temperature Tg. Using recent theories and experimental data for the temperature dependence of η at <Tg, the crystallization rate below Tg was calculated; well below Tg the SNWDG (and, more generally, any high‐silica glass) will not crystallize appreciably over any important time period for radioactive decay of fission products.
Thermophoretic Deposition of Small Particles in the Modified Chemical Vapor Deposition (MCVD) Process
Authors: WALKER K. L. , GEYLING F. T. , NAGEL S. R.
Published: June 2006

Thermophoresis is conclusively established as the particulate deposition mechanism in the MCVD process by comparing experimental measurements and quantitative theoretical predictions. The deposition efficiency, E, is defined as the fraction of the silica in the gas stream (initially as SiCl4) that is deposited. For normal MCVD operating conditions, the deposition efficiency is only a function of the equilibrium temperature, Te, at which the gas and walls equilibrate downstream of the torch and the temperature, Tr, at which reaction occurs. The deposition efficiency is ∼0.8[1‐(Te/Tr)]. It is determined that Te is a strong function of the torch traverse velocity, the traverse length, the temperature of the ambient environment, and the tube wall thickness but only a weak function of the gas flow rate. At high gas flow rates, the efficiency is limited by incomplete reaction.
Gibbs Energy of Formation of Lead Zirconate
Authors: JACOB K. T. , SHIM W. W.
Published: June 2006

The Gibbs energy of formation of zirconia‐saturated lead zirconate was determined by emf measurements on the solid state cells

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at 800 to 1400 K. The results obtained differ significantly from those reported in the literature based on vapor‐pressure measurements, using Knudsen effusion and transportation techniques and assuming that the vapor phase consisted entirely of monomeric PbO molecules. A reanalysis of the data obtained in the earlier vapor‐pressure studies, using mass‐spectrometric measurements on polymeric PbO species in the gas phase, gives Gibbs energies of formation of lead zirconate which are in better agreement with those obtained in this study. Recent electrochemical measurements using CaO‐ZrO2 and PbF2 solid electrolytes are in good agreement with the present study. The results obtained in this study are also consistent with the phase diagram which shows decomposition of the zirconate to tetragonal zirconia and a liquid phase rich in PbO at 1843 K.
Thermal Segregation of Cations in Iron Aluminate Spinels
Authors: PETUSKEY W. T. , BOWEN H. K.
Published: June 2006

Thermal segregation experiments were performed on open and encapsulated wafers of Fe(Fe1.51Al0.49)O4 spinels using CO2 laser radiation as a heat source. The correlation of “apparent” marker movement and cation segregation led to the conclusion that the free exchange of gaseous oxygen at the external spinel surfaces is necessary to cause significant redistribution of aluminum and iron in a temperature gradient. This was explained by the different mobilities of different cations in a net vacancy (low. Effectively no segregation was observed for the zero vacancy flux condition.
Galvanic Cell Measurements with Stabilized Zirconia and Platinum Probes
Authors: DUDNEY N. J. , COBLE R. L. , TULLER H. L.
Published: June 2006

A galvanic cell technique was developed to measure the ionic and electronic transference numbers of metal oxides at high temperatures. The cell uses stabilized zirconia probes in addition to the conventional metal probes. With both types of probes, measurements of the transference numbers for electronic, ionic, or mixed conductors are possible and surface polarization effects are readily detected. Measurements of yttria‐doped ceria and urania demonstrate the advantages of the technique over the available methods.
Effect of Gamma Radiation on the Strength of Plate Glass of Varying Arsenic Content
Authors: Swift H. R.
Published: June 2006

Samples of plate glass containing a small amount of arsenic oxide as well as arsenic‐free samples were subjected to gamma radiation from a cobalt‐60 source after which modulus of rupture measurements were made. The arsenic‐containing glass showed a significant increase in strength upon irradiation while the arsenic‐free glass became weaker.
Electrical Conductivity of Pure and Yttria‐Doped Uranium Dioxide
Authors: DUDNEY N.J. , COBLE R.L. , TULLER H.L.
Published: June 2006

The conductivities of both pure urania and urania doped with <10 mol% yttrium were measured as a function of the oxygen partial pressure between 800° and 1400°C. Yttrium enhances the p ‐type electronic conductivity for near‐stoichiometric oxygen concentrations, allowing the hole mobility to be determined as μ=(5547/T) exp(‐0.032 aJ/kT) cm2/Vs, confirming a small polaron transport model. Using this mobility, the hole concentration in pure urania was calculated as a function of the degree of nonstoichiometry and temperature and then compared to models for the formation of defect clusters. Increasing numbers of mobile holes created per excess oxygen ion with increasing temperature indicate that the holes must dissociate from the oxygen defect clusters at high temperature and suggest that the oxygen defects may dissociate as well.