bluuebunny/crossref_metadata_2025 huggingface dataset:
Nature and Thermal Evolution of Amorphous Hvdrated Zirconium Oxide
Authors: LI VAGE J. , DOI K. , MAZIERES C.
Published: June 2006

The thermal behavior of amorphous hydrated zirconium oxide and its coprecipitates with other oxides was studied. Solid solution with a limit of solubility seems to exist in the amorphous coprecipitates. A relation with the high‐temperature solid solution was established. The structure of the amorphous zirconia was studied by X‐ray and neutron diffraction; a thin plate model related to the structure of tetragonal zirconia is proposed. Heating the precipitates in an oxygen‐free atmosphere produced a black nonstoichiometric oxide and stabilization of the tetragonal form.
Kinetics of the Graphite‐Uranium Dioxide Reaction from 1400° to 1756°C
Authors: LINDEMER T. B. , ALLEN M. D. , LEITNAKER J. M.
Published: June 2006

The reaction of microspheres of UOz with graphite was studied from 1400° to 1756°C. When a spherically symmetrical layer of carbide was produced around the UO2 core, only UC2 was formed, and the diffusion of oxygen through this layer was rate‐controlling. The Arrhenius relation for this system is kD= 21.0 exp(−90, 000/RT) cm2/s

The reaction of a geometrically nonsymmetrical configuration of UO2 and UC2 was also studied. Comparison of the reactions in the symmetrical and nonsymmetrical systems demonstrated that the kinetic behavior of the two systems is quite different and that the conversion in the nonsymmetrical system was 2 to 5 times faster. The importance of these observations to kinetic results reported in the literature for analogous systems is discussed.
Glasses Resistant to Sodium Vapor at Temperatures to 700°C
Authors: BURGGRAAF A. J. , VAN VELZEN H. C.
Published: June 2006

Glasses resistant to attack by sodium vapor at temperatures up to 700°C were developed from the CaO‐Al2O3‐MgO‐BaO‐B2O3 system. The resistance of these glasses decreases sharply above the transformation temperature. The glasses have a high water content, have good wetting properties, and adhere well to materials such as aluminum oxide and niobium; thus they can be used as solder glasses and metalizing components. The surface layer formed on the glass during attack by sodium vapor has a specific electrical resistance which is lower by 2 to 3 orders of magnitude than that of glass not exposed to sodium vapor.
Elastic Constants of Polycrystalline BeO as a Function of Pressure and Temperature
Authors: SOGA NAOHIRO
Published: June 2006

The sound velocities of polycrystalline BeO and their pressure and temperature derivatives were determined by a pulse superposition method. The derivatives found from the measurements at pressures up to 2 kbars and near 25° are: (∂ul/∂P)T= 6.48×10−3 km/s kbars, ∂S/∂P)T= 0.33×10−3 km/s kbars, ∂L/∂T)P=−2.8×10−4 km/s deg, and ∂S/∂P)T=−2.0×10−4 km/s deg. The very low value of ∂S/∂P)T is anomalous for crystalline solids but may be expected from the crystal structure in view of similar anomalous behavior found in other solids with the wurtzite structure. The Grüneisen parameter calculated from the pressure derivatives of sound velocities was small compared with the Grüneisen parameter obtained from thermal properties. This result seems to indicate that the thermal expansivity of BeO does not change with temperature in proportion to the specific heat at low temperatures.
Monticellite and Forsterite Crystalline Solutions
Authors: BIGGAR G. M. , O'HARA M. J.
Published: June 2006

New data for monticellite crystalline solutions confirm that monticellite (CaMgSiO4 is unstable at atmospheric pressure. On the join forsterite‐monticellite, the estimated range of stable monticellite crystalline solutions is 89 to 93 mol% monticellite at 1200°C and 75 to 92 mol% at 1490°C. The range of forsterite crystalline solution is 93 to 100 mol% forsterite at 1200°C and 81 t0 100 mol% at 1490°C. These results can be applied to the proportions of phases present in impure periclase refractories at service temperatures.
Lead Zirconate‐Lead Titanate Piezoelectric Ceramics with Iron Oxide Additions
Authors: WESTON T. B. , WEBSTER A. H. , McNAMARA V. M.
Published: June 2006

An investigation of the effects of small additions of Fe2O3 to lead zirconate‐lead titanate ceramics with compositions between 45 and 60 mol% lead zirconate has shown that, with 2 moles of PbO to balance each mole of Fe2O3, the solubility of Fe2O3 was about 0.8 wt% in compositions near the tetragonal‐rhombohedra1 boundary. The dielectric constant and dissipation factor for both rhombohedra1 and tetragonal materials were decreased by addition of iron oxide, whereas the mechanical quality factor and frequency constant were increased. The dependence of the electromechanical properties on grain size was qualitatively similar for both undoped and iron oxide‐doped materials; the presence of iron oxide inhibited grain growth and lowered the limiting grain size below which the electromechanical properties change rapidly with grain size.
X‐Ray Stress Analysis of WC‐Co Cermets: II, Temperature Stresses*
Authors: FRENCH DAVID N.
Published: June 2006

The effect of cobalt content on the temperature stress in WC‐Co cermets was measured using both the “one‐exposure” and “two‐exposure” X‐ray diffraction techniques. In the one‐exposure technique, strain is measured by comparing lattice spacings in the stressed, d8, and unstressed, d0, conditions. Nonresolution of the a1‐a2 doublet caused by adding Co to annealed WC shifts the apparent peak position to higher diffraction angles (smaller d8). Thus, the proper choice of d0 must be made so that in measuring both d0 and d8 similar diffraction peak profiles are used. These conditions have not always been considered, causing some previously reported results to be open to question. With the two‐exposure technique, no such difficulties exist, because similar peaks are compared at the two angular positions used for measuring d on the same sample. Because of shallow X‐ray penetration in WC, only biaxial temperature stresses at the surface are measured. These stresses are compressive, varying from ‐53, 000 psi for WC + 10 vol% Co to ‐24, 300 psi for 37 vol% Co. This trend is in disagreement with previous theories, which predict greater compressive stress as Co content increases.
X‐Ray Microtopographs of Alpha Alumina Whiskers
Authors: MINAGAWA SHIGEKAZU , GEJYO TETSUO
Published: June 2006

Alpha alumina whiskers grown by the vapor reaction 2A1 + 3H2O° Al2O3+ 3H2 were examined by X‐ray microtopography. Topographs of whiskers PO to 60 μm in diameter were taken by (1120) and (00012) diffraction; most a and c whiskers (growth direction 〈1120〉 and 〈0001〉, respectively) were free from dislocations. Chemical etching of a whisker cross section with orthophosphoric acid or potassium bisulfate did not produce etch pits. Growth of alumina whiskers through axial dislocation appears improbable.
Phase Equilibria in the 1375°C Isotherm of the System Sr‐Ti‐O
Authors: McCARTHY GREGORY J. , WHITE WILLIAM B. , ROY RUSTUM
Published: June 2006

The phase relations in a portion of the 1375° isotherm of the system Sr‐Ti‐O were determined. The following ternary phases were identified: Sr2TiO4, Sr3Ti2O7, Sr4Ti3O10, SrTiO3(ss), and what is believed to be SrTi12O19. The experimental techniques used in the determination of tha phase diagram are somewhat uncommon and are discussed in depth. Diffuse reflectance spectra were obtained for several compositions of SrTiO3(ss). The broad absorption maximum shown in these spectra is attributed to Ti3+.
Hot‐Working of Aluminum Oxide: I, Primary Recrystallization and Texture
Authors: HEUER A. H. , SELLERS D. J. , RHODES W. H.
Published: June 2006

Polycrystalline aluminum oxide was hot‐worked at 1750° to 1950°C and at stresses <21, 000 psi using a press‐forging technique. No ductility problems were encountered, and maximum true strains and strain rates of ‐1.25 and 0.2/min, respectively, were observed. Deformed samples often showed grain elongation in addition to a marked basal crystallographic texture, which suggested that basal slip was the predominant deformation mode. However, nonbasal slip, grain boundary sliding, and diffusional deformation were all thought to contribute to the ductility. Primary recrystallization occurred during or after the deformation and resulted in equiaxed microstructures, although the basal texture was retained. Because of a severe shear strain gradient during deformation, nonuniform microstructures were usually obtained, and this provided a means for growing single crystals by strain anneal. Although no conclusions can be drawn concerning the origin of the recrystallization texture, it is suggested that pores are preferential sites for recrystallization nuclei. MgO in solid solution (1/4%) retarded primary recrystallization.
Optical Reflectance Spectra of Cr3+ in MgO Solid Solutions
Authors: MONTGOMERY THOMAS S.
Published: June 2006

The effect of Cr3+ concentration in an MgO crystal lattice on the crystal field splitting energy, 10 Dq, and on other electronic transitions was studied. Optical reflectance spectra showed a linear increase in 10 Dq with increasing Cr3+ concentration up to the limit of solid solubility. The Racah parameter, B, decreased and the energy of the 4T1g→4A2g transition increased with increasing Cr3+ concentration. The increase in 10 Dq was related to the decrease in lattice parameter.
Fracture of Sapphire
Authors: WIEDERHORN S. M.
Published: June 2006

The fracture of sapphire was studied using the double‐canti‐lever‐cleavage technique. Fracture surface energies were 7.3 and 6.0 J/m2 for the (100) and (012) type planes, respectively. Attempts to measure the fracture surface energy on the (0001) plane were unsuccessful. The failure of sapphire to fracture along the basal plane was attributed to the fact that these planes lack electrostatic charge neutrality. The possibility of fracture‐induced dislocation motion in sapphire at room temperature was investigated using etch‐pit techniques, but no evidence for dislocation motion could be found. Fracture behavior on (012) planes was erratic, varying from boule to boule. The topology of surfaces formed by crack propagation along this plane is described, but no explanation for the erratic behavior or the observed fracture features is given.
Elastic Properties of Polycrystalline Yttrium Oxide, Holmium Oxide, and Erbium Oxide: High‐Temperature Measurements
Authors: MANNING W. R. , HUNTER O.
Published: June 2006

The Young's and shear moduli of polycrystalline yttrium oxide, holmium oxide, and erbium oxide were determined from room temperature to 1000°C using the sonic resonance technique. The bulk modulus and Poisson's ratio were computed as functions of temperature for each oxide. The Young's, shear, and bulk moduli decreased linearly with increasing temperature, whereas Poisson's ratio remained constant. The first and second Grüneisen constants, γ and δ, were calculated from the bulk modulus data and shown to be virtually independent of temperature. The Soga‐Anderson equation adequately described the bulk modulus data for each oxide.
Oxidation Kinetics of Single Crystal Titanium Nitride by Optical Measurements
Authors: PEARCE M. L. , BASCH C.
Published: June 2006

Oxidation of single crystals of titanium nitride was studied from 540° to 780°C using the optical interference produced by the thin oxide film formed on the surface. The kinetics are strictly diffusion‐controlled rather than reaction‐controlled, as observed by other workers for the initial oxidation of the polycrystalline material. This conflict is rationalized on the basis of the material differences and particularly the crystalline nature and perfection of the oxide film. The activation energy derived is in excellent agreement with that reported in the literature for the diffusion‐controlled oxidation of polycrystalline titanium nitride and titanium metal.
Early Hydration of Tricalcium Silicate: A Solid Reaction with Induction and Acceleration Periods
Authors: KONDO RENICHI , DAIMON MASAKI
Published: June 2006

The hydration of tricalcium silicate was studied using a sample with a limited particle size distribution. The hydration reaction was analyzed as an example of general solid reactions having induction and acceleration periods. The first product, which may have a structure similar to the reactant, forms on the surfaces of reactant grains. The nuclei of the stable product are produced in the first product layer and act as reaction centers; the main reaction to form a stable product occurs rapidly in the acceleration period. In the hydration of calcium silicates, hydrates produced in this stage are poorly crystalline and metastable and change gradually into a more stable form.
Thermal Behavior of Pyrite and Its Relation to Carbon and Sulfur Oxidation in Clays
Authors: SCHORR J. R. , EVERHART J. O.
Published: June 2006

The thermal behavior of pyrite in air was studied. A one‐step mechanism for the oxidation of pyrite to hematite exists and accounts for previously reported weight‐loss, DTA, and gas train data which implied a two‐step mechanism. Proper control of the oxidation temperature is very important in completing the pyrite oxidation.
Irradiation Testing (Pulse Conditions) of the Ternary Fuel System for the Power Burst Facility
Authors: BEALS R. J. , KERN R. S.
Published: June 2006

The Power Burst Facility (PBF) is a flexible, pulse‐type nuclear reactor constructed to provide high thermal neutron fluxes during short period power excursions. The PBF reactor core is composed of a fuel in the system UO2‐ZrO2CaO. The performance requirements imposed on this fuel necessitated a testing program to establish out‐of‐pile and in‐pile characteristics of the fuel. This paper presents some of the in‐pile test results obtained under pulse conditions, and out‐of‐pile results on selected fuel compositions to verify phase and volume stability of the ternary fuel. Compositions of 16 and 35 mol% urania were investigated from 2000° to 2700°C in‐pile.
Determination of Donor Gradients Within Surface Barriers Formed on Dense Cd‐Doped Barium Titanates
Authors: VOJNOVICH T. , MCGEE T. D.
Published: June 2006

Surface barriers were formed on dense Gd‐doped barium titanates by a reduction‐reoxidation process. The distribution of donors within the partially reoxidized barriers was determined from capacitance measurements using blocking contacts and from resistance measurements using ohmic contacts. The incremental barrier capacitance behaved as a depletion‐layer capacitance when measured as a function of bias voltage. A donor gradient αc was determined from the capacitance‐voltage behavior of the depletion layers by using a linear‐graded model to describe the donor distribution through the depletion layers. A donor gradient ar was indirectly determined from resistance profiles of the surface barriers formed on the reduced titanates by a second reoxidation. The donor gradients ac and ar were in good agreement, with both gradients decreasing for the higher reoxidation temperatures and/or the longer times used in forming the barriers. This behavior is explained by assuming that the reoxidation process is diffusion‐controlled and by qualitatively relating the gradients to assumed oxygen profiles within the barriers.
Physical Properties and Structure of Silicate Glasses: I, Additive Relations in Alkali Binary Glasses
Authors: ROBINSON HOWARD A.
Published: June 2006

Correlations between certain physical properties, P, and all eighteen compositional ratios between the five ionic parameters of the system were studied with a computer for the five alkali silicates. Linear relations were found between P and the alkali/silica, alkali/oxygen, and silica/alkali ratios for certain regions of the glass field when the P's are expressed in proper molar terms. Specific volume and heat of formation data indicate three linear regions with two sharp break points between. The log electrical resistivity and the volatilization loss show two such regions and only the second break point. The break points, while structural in origin, must therefore occur for different reasons. The break points are the same for all P's and coincide with the eutectics. The constants of the linear relations are the partial molar quantities associated with P. Break points are not found in the molar refractivity data, so that no change in ligancy for these systems is indicated.
Phase Composition of Reduced and Reoxidized Barium Titanate
Authors: AREND H. , KIHLBORG L.
Published: June 2006

Reducing high‐purity BaTiO3 in hydrogen for 1 h at 1275°C leads to an oxygen deficiency x= 0.0036 in BaTiO3–x with maintenance of the tetragonal/cubic perovskite‐type structure. Reduction at 1325° C leads to x= 0.0073 and brings about transformation to the hexagonal modification. Up to 1500°C (x= 0.0233) no further phase change occurs. Annealing the oxygen‐deficient hexagonal phase in oxygen at 850° C for 2 h produces stoichiometric samples which are still hexagonal, whereas the tetragonal/cubic structure is restored by heating for 1 h at 1350°C. The unit cell found for the hexagonal phase is somewhat smaller than previously reported.
Volume Change on Freezing of ALO,
Authors: TYROLEROVA P , LU W.‐K.
Published: June 2006

The volume change on freezing of AI2O3 was determined by rapidly cooling a molten droplet and measuring the inner porosity of the solidified bead. With the experimental arrangement used, the inner porosity of the droplet corresponds directly to the shrinkage on freezing. The values of 19.9 and 20.1%, obtained for two initial materials, agree well with previously published data determined by more complicated experimental techniques.
Origin of Water‐Induced Toughening in MgO Crystals
Authors: SHOCKEY D. A. , GROVES G. W.
Published: June 2006

The toughening effect of water on MgO, as measured by the increase in apparent surface energy of a double cantilever beam specimen, is shown to derive directly from the increased roughness of the fracture surfaces when a crack propagates in water. Dimethyl formamide, a medium reported to produce a larger Rebinder effect (surface softening) in MgO than water, has no effect on the fracture surface or fracture toughness of MgO.
Crystallization and Phase Transformation in TiO2‐Opacified Porcelain Enamels: I, Theory
Authors: EPPLER R. A.
Published: June 2006

The theory of nucleation and growth was used to develop equations describing the crystallization and phase transformation processes occurring during the firing of a TiO2‐opacified porcelain enamel. The concentrations of ana‐tase and of rutile depend on four parameters: the rate of inversion of anatase to rutile, the percentage of crystallization which is to anatase, the solubility, and a crystallization rate constant.
Crystallization and Phase Transformation in TiO2‐Opacified Porcelain Enamels: 11, Cornparison of Theory with Experiment
Authors: EPPLER R. A.
Published: June 2006

Equations were developed to predict the concentrations of anatase and rutile in a TiO2opacified porcelain enamel as a function of the time and temperature of firing. These equations were applicable over the entire useful firing range: from 660° to 940°C and from 1 to 64 min. The constants in these equations yield solubility data as well as the appropriate rates. The solubility versus temperature curve is bimodal. The activation energies are 87.4 kcal/mol for inversion of anatase to rutile, 32.0 kcal/mol for crystallization of anatase, and 28.3 kcal/mol for crystallization of rutile.
Strength of Flame ‐ Fusion ‐ Grown Magnesium ‐ Aluminum Spinel
Authors: GRABMAIER J. G. , FALCKENBERG H. R.
Published: June 2006

Alumina‐rich single crystals of Mg‐Al spinel with molar ratios of 1.7 to 3.5 were grown by flame fusion. The fracture load of these crystals was measured. It was found (1) that in unannealed crystals the strength increased with increasing alumina content and (2) that strength was influenced by the temperature of heat treatment. The strength increased with increasing annealing temperature above 650°C up to a maximum value; the temperature at which this value was reached depended on the molar ratio of the spinel and the duration of annealing. This behavior can be explained as a precipitation strengthening, as is typical of alloys. Pre‐precipitation is thought to be the cause of the observed strengthening.
Ultraviolet Absorption of Pentavalent Vanadium in Binary Alkali Borate Classes
Authors: PAUL A. , RUSIN J. M.
Published: June 2006

The ultraviolet absorption of vanadium(V) in R2O‐B2O3 glasses (R represents Li, Na, or K) and in aqueous buffer solutions was investigated. In glasses of variable R2O:B2O3 ratio, a change in the absorption spectra similar to the [VO4]3‐ → [VO3(OH)]2‐ change in aqueous solution was observed. It is suggested that vanadium(V) in these glasses may be present as either [VO4]3‐ or [VO3O1/2]2‐ (O1/2 indicates a bridging oxygen ion), depending on the basicity of the melt. The critical R2O concentration, above which this change in vanadium(V) environment occurs with increasing alkalinity, is 24, 26, and ≅30 mol%, for K2O, Na2O, and Li2O, respectively.
Diffusion of Iron and Nickel in Magnesium Oxide Single Crystals
Authors: BLANK STUART L. , PASK JOSEPH A.
Published: June 2006

Diffusion kinetics and mechanisms were studied in the FexO‐MgO (vacuum), NiO‐MgO (vacuum and air), and Fe203‐MgO (air) systems. In the FexO‐MgO system, Fe entered MgO by a redox reaction; the diffusivity and activation energy depended on concentration. In the NiO‐MgO system in air the diffusivity depended on concentration and the activation energy did not; in vacuum both the diffusivity and activation energy were concentration‐independent. In the Fe2O3‐MgO system in the MgO phase the activation energy and diffusivity did not depend on concentration. Because of impurities, the diffusion results were for the extrinsic region. Formation of trivalent ions and consequent chemically created vacancies in the FexO‐MgO and NiO‐MgO (air) systems resulted in the concentration dependence of diffusivity. Concentration dependence of activation energy in the FexO‐MgO system is associated with structural changes due to a change with concentration of the Fe3+ octahedraI/Fe3+ tetrahedral ratio. In the Fe2O3‐MgO system structural changes do not occur during diffusion because this ratio remains constant.
Characterization of Mixed Uranium Antimony Oxides USbO5 and USb3O10
Authors: AYKAN KAMRAN , SLEIGHT ARTHUR W.
Published: June 2006

The system U‐Sb‐O was examined in air up to 1000°C for ternary compounds. The products were characterized by chemical analysis, density determinations, TGA, X‐ray diffraction techniques, and magnetic measurements. The ternary compounds found were USbO5 and USb3O10. All cations are pentavalent in these new compounds, which are crystallographically related to α‐UO3 and U3O8.
Glasses Formed from Molten Acetates
Authors: BARTHOLOMEW ROGER F. , LEWEK STANLEY S.
Published: June 2006

Glass formation in metal acetate systems was investigated; the tendency for these systems to form glasses is so great that even lithium and lead acetates are readily quenched to glass. Glass formation is favored near eutectic compositions in binary systems. Physical and optical properties of representative glasses are given.
Absorption Spectra of First‐Row Transition Metal Ions in Glasses
Authors: WILLIAMS D. J.
Published: June 2006

Certain optical transitions were calculated for the first‐row transition metal ions Ti3+, V3+, Cr3+, Fe2+ Co2+, and Ni2+ in a silicate matrix. The calculations were performed at 7 inter‐ionic distances for each ion because the metal‐ion‐to‐oxygen interionic distances are unknown; the silicate oxygen charge was varied from 1.00 to 2.00 in each case because the true charge on silicate oxygens is also unknown. Integrals used in the calculations were calculated using Slater and self‐consistent field wave functions, and computer programs were used to evaluate all integrals. Equations were derived for calculating all optical transitions for these ions in octahedral fields; the extension to fields of other symmetry is trivial. Several optical transitions were computed to obtain the calculated orders of magnitude for the optical transition. The results for self‐consistent field wave functions are lower than expected; they indicate that the transition metal ion in glasses is situated in fields near the size of aquo complexes.
Kinetics of the Reaction of UC2 and Nitrogen from 1500° to 1700°C
Authors: LINDEMER T. B. , LEITNAKER J. M. , ALLEN M. D.
Published: June 2006

The kinetics of the reaction of UC2 spheres with nitrogen was studied from 1500° to 1700°C. A metallographic method was used to determine the time‐dependent conversion of UC2 to U(C,N) and free C. The conversion appeared to be controlled by the diffusion of solid carbon in solution to sites where it could precipitate as free carbon. These sites were the surface of the sphere and particles of free carbon that existed within the original UC2. An increased distribution of these internal sites decreased the distance for carbon diffusion and resulted in an increased rate of reaction. The UC2 appeared to undergo a very rapid initial reaction that resulted in the uptake of 1 to 5 at.% nitrogen in the UC2 at these temperatures.
Self‐Radiation Damage in Curium‐244 Oxide and Aluminate
Authors: MOSLEY W. C.
Published: June 2006

Self‐radiation from α‐decay of 244Cm causes lattice swelling, phase transformations, and loss of structure in several Cm compounds. In Cm oxides, the percentage swelling at saturation decreases with decreasing symmetry: Swelling in fluorite (fee) CmO2 (∼0.3%) is approximately twice that in bee C‐type Cm2O3; monoclinic Cm2O3 does not swell. CmO2 swells with time according to Δa/α=3.0×10−3(1–e−1.7×104λt), essentially the same relation as for PuO2 and AmO2. The rate of structure loss of Cm oxides decreases with increasing temperature of prior heatings. In CmAlO3 the metamict state is produced before swelling reaches saturation. Radiation‐induced transformation at room temperature produces metastable phases that normally exist at higher temperatures, e.g. bcc C‐type Cm2O3 transforms to hexagonal A‐type Cm2O3, and rhombohedral CmAlO3 becomes cubic.
Influence of Dynamic Calcination on Crystallite Growth of Submicron Rare‐Earth Oxides
Authors: MAZDIYASNI K. S. , BROWN L. M.
Published: June 2006

The crystallite growth of rare‐earth oxide powders with particle sizes of 10 to 30 Å obtained by the hydrolytic decomposition of alkoxides was investigated. These powders were compared with commercially available powders with average particle sizes from 1000 Å to 10 μm. Static and dynamic atmosphere tests were made, the latter by continuous tumbling during calcination. Dynamic calcination controlled crystallite growth effectively while maintaining uniform particle size. Typical arithmetic mean particle sizes were 250 Å for powders calcined at 800°C for 24 h with tumbling and ∼400 Å for powders calcined under identical conditions without tumbling. TGA, X‐ray diffraction, and emission spectrographic analyses were used to characterize the powders. Electron microscopy and BET surface area measurements demonstrated the importance of the dynamic calcination method in the growth of primary crystallites into larger particles during the presintering stage of the processing of these powders.
Effect of Microstructure on Pulse Electrical Strength of MgO
Authors: BEAUCHAMP E. K.
Published: June 2006

Pulse electrical strengths of hot‐pressed MgO containing 0.3 wt% LiF were measured. Strengths as high as 5.9×108 V/in. were obtained on samples 99.8% of theoretical density with 1‐to 3‐μm grain size. An increase of either porosity or grain size resulted in a monotonic decrease in strength. Single‐crystal strengths of 4.0×106 V/in. were obtained by polishing samples chemically. A simple recessed‐electrode configuration eliminated corona effects.
Thermal Expansion of Pb3O4
Authors: SORRELL CHARLES A.
Published: June 2006

Thermal expansion of Pb3O4 was investigated by high‐temperature X‐ray diffraction. The coefficient in the a0 direction is 14.6×10−6/°C. Expansion in the c0 direction is 32% greater, with a coefficient of 19.3×10−6/°C. Coefficients of expansion are linear from 25° to 490°C and are comparable with those of tetragonal and orthorhombic PbO.
Phase Equilibria in the System MnO‐“FeO”‐ZrO2‐SiO2
Authors: SHULTZ R. L. , MUAN ARNULF
Published: June 2006

Phase equilibrium relations in the liquidus temperature region of the system MnO‐“FeO”‐ZrO2‐SiO2 and of its bounding systems MnO‐ZrO2, MnO‐ZrO2‐SiO2, and MnO‐“FeO”‐ZrO2 were determined by the quenching technique. The equilibrations were carried out at sufficiently low O2 pressures to keep most of the Mn and Fe in divalent states. The results obtained were combined with literature data for the other bounding binary and ternary systems to present phase diagrams showing liquidus surfaces and interrelations between coexisting liquid and solid‐solution phases. Applications of the data to refractory problems are discussed.
Spontaneous Deformation Phenomena in Partially Crystallized Glasses
Authors: SPROULL JAMES F. , RINDONE GUY E.
Published: June 2006

Unusual deformation phenomena accompanying partial crystallization were observed during heat treatment in the softening temperature range of Li‐Na‐Si glasses. Glassy lumps or protuberances formed at the surfaces of fibers 0.5 mm in diameter; rods and plates showed even greater distortions, their original shapes often becoming unrecognizable. Liquid‐liquid immiscibility accompanying the crystallization of a 0.7Li2O.0.3Na2O.2SiO2 glass was believed to follow, rather than precede, crystallization. Explanations of these phenomena are proposed.
Ti‐Rich Nonstoichiometric BaTiO3: I, High‐Temperature Electrical Conductivity Measurements
Authors: LONG S. A. , BLUMENTHAL R. N.
Published: June 2006

Equilibrium electrical conductivity of nonstoichiometric poly‐crystalline BaTiO3 with varying Ba:Ti ratios was investigated at temperatures between 800° and 1200°C and P o2 from 10−22 to I atm. A transition from p‐type to n‐type conductivity was observed. Although the electrical conductivity of different specimens varied slightly, these differences did not appear to be a function of the Ba:Ti ratio in the region investigated. An intrinsic band‐gap energy of ∼3.1 eV was calculated from the temperature dependence of the minimum conductivity. The O2 partial pressure dependence of the isothermal n‐type conductivity cannot be described by simple defect models incorporating only singly or doubly ionized O vacancies. Likewise, simple defect models incorporating cation vacancies are not consistent with the observed pressure dependence of the p‐type conductivity. More complex defect models which correspond to the observed behavior over the entire range of temperature and Po2 will be discussed in a subsequent paper.
Discrepancies in Elastic Constant Data for MgO Polycrystals and Single Crystals
Authors: SPETZLER H. A. , ANDERSON D. L.
Published: June 2006

Elastic properties and their pressure and temperature derivatives are commonly measured on polyerystalline sintered aggregates and assumed to adequately describe the behavior of an ideal aggregate of single crystals without regard to strain of the individual grains. Similarly, it is commonly assumed that by suitably averaging data for single crystals, the properties of an aggregate can be calculated. Ultrasonic results for polyerystalline MgO measured to 8 kbars and 800°K are presented to point out the limitations of these assumptions and to illustrate the anomalous behavior of polyerystalline material. Previous measurements on single‐crystal and polyerystalline MgO are tabulated, and sources of error are discussed.
Interactions Between Cement Minerals and Hydroxycarboxylic‐Acid Retarders: I, Apparent Adsorption of Salicylic Acid on Cement and Hydrated Cement Compounds
Authors: DIAMOND SIDNEY
Published: June 2006

A radioisotope assay method was developed to measure the apparent adsorption of salicylic acid on cement and hydrated cement compounds at concentrations of salicylic acid in aqueous solution up to 0.2 wt%, thus including the range of concentrations used for hydroxycarboxylic‐acid retarders in concrete. Previously published data were available only for concentrations below 0.01%. The results confirm that there is only limited apparent adsorption on dicalcium and tricalcium silicates, whereas apparent adsorption on paste‐ and bottle‐hydrated products of these compounds is significant. Apparent adsorption on tricalcium aluminate is strong and is greater at intermediate concentrations than near saturation. A similar pattern was observed for apparent adsorption on “C4AF,” but the amounts removed from solution were much less. Experiments with C4AH13, C3AH0, and ettringite revealed that hydrated calcium aluminate and aluminate sulfate compounds also remove major amounts of salicylic acid from solution.
Viscosity‐Drift Technique for Determination of Critical Liquid‐Liquid Immiscibility Temperature of Glasses
Authors: HALLER WOLFGANG , SIMMONS JOSEPH H. , NAPOLITANO ALBERT
Published: June 2006

The time dependence of the low‐temperature viscosity was used to determine the occurrence of phase separation in glass systems and to measure the critical immiscibility temperature. The technique is fast and easily performed and can be applied to materials with very low immiscibility gaps. Immiscibility temperatures for several technically important glass compositions are given.
Preparation of Small‐Grained and Large‐Grained Ceramics from Nb‐Doped BaTiO3
Authors: KAHN MANFRED
Published: June 2006

Barium titanate powders with average grain sizes of 0.07 and 0.65 μm were coated with an organic Nb ester, using a liquid‐solid mixing process. Small‐grained (1 to 3 μm) ceramic dielectrics from both powders and large‐grained (>50 μm) dielectrics from the 0.65 μm powder were fired using 0 to 2 at.% Nb. Microstructures, densities, and electrical resistivities were investigated.
Kinetics of the Decomposition of Freeze‐Dried Aluminum Sulfate and Ammonium Aluminum Sulfate
Authors: JOHNSON D. W. , GALLAGHER P. K.
Published: June 2006

Conventional thermoanalytical techniques confirmed earlier studies on the stoichiometry of the decomposition of aluminum sulfate and ammonium aluminum sulfate (alum). The kinetics of the sulfate decomposition of freeze‐dried aluminum sulfate, of sieve fractions of reagent grade aluminum sulfate, and of freeze‐dried alum were studied isothermally at several temperatures between 635 and 770°C. The activation energy, a preexponential term, and a degree‐of‐fit parameter are presented. The calculations are based on several kinetic models for each data set. The freeze‐dried aluminum sulfate fits a contracting area model with an activation energy of 69 kcal/mol, and the reagent grade aluminum sulfate fits the contracting volume model with an activation energy of 74 kcal/mol. Both were calculated using a fraction reacted (alpha) of 0.15 to 0.90. The freeze‐dried alum was fitted with less precision to a first order model with an activation energy of 83 kcal/mol over the range of alpha 0.3 to 0.9.
Electrical Resistance of Liquid Sulfur to 420°C and of Liquid Selenium to 700°C
Authors: VEZZOLI GARY C.
Published: June 2006

The electrical resistance of liquid sulfur was measured from just below the polymerization temperature to the vaporization point. Turning points in the resistance vs temperature curve, resulting presumably from polymerization and depolymerization, and a sharp decrease in resistance at 212°C agree well with previous results. Between ∼230° and 420°C, the resistance decreased without discontinuity. The resistance of selenium increased sharply by 3 orders of magnitude on melting and then decreased steadily by 5 orders of magnitude until the experiment was ended at 700°C. In both liquids, the electrical resistance as a function of temperature decreased more rapidly than that of an ideal intrinsic semiconductor whose molecular structure is stable over the temperature interval investigated. This rapid decrease is believed to result from chain dissociation and ring scission.
Infrared Frequency Calculations for Ideal Mullite (3Al2O3·2SiO2)
Authors: MACKENZIE K. J. D.
Published: June 2006

Simplified structural models for mullite were investigated, and ir frequencies were calculated for the simplest model which gave the theoretical number of ir‐active frequencies compatible with the observed spectrum. This model, which consists of independently vibrating structural units, gives plausible frequency assignments which agree well with other published data for silicates and aluminates. These assignments explain the spectral changes observed during formation of mullite from heated clay minerals. The model does not take into account the changes in stoichiometry and distortion caused by compositional variations.
Optical Method of Measuring Temperature in Hot Glass
Authors: JERYAN R. A. , ERYOU N. D. , GLICKSMAN L. R.
Published: June 2006

An optical method of temperature measurement, developed for semitransparent media, was tested using molten glass. The beam from a helium‐neon laser was passed through glass, and the attenuation of the beam was measured. Since the monochromatic absorptivity of the glass was a monotonic function of temperature, the attenuation of the beam indicated the temperature of the glass. The optical method was used to measure the one‐dimensional temperature profile in a slab of molten glass with an accuracy of ±5°F. The temperature gradient within the slab was of the order of 200°F/in. The method is useful when the medium is isothermal along the length of the laser beam, the medium does not significantly scatter radiation, and the monochromatic transmissivity of the medium based on the laser path length is 0.1.
Kinetics of Growth of Al2O3 Whiskers
Authors: MINAGAWA SHIGEKAZU
Published: June 2006

The kinetics of the growth of Al2O3 whiskers by the reaction of Al with a trace amount of H2O in an H2 atmosphere were studied. The activation energy in the region of constant growth rate was ∼77 kcal mol−1. This activation energy value, in the light of thermodynamic calculations and other theoretical considerations, suggests that the rate‐determining step in the growth of these whiskers is the dissociation of H2O molecules on the surface of Al2O3.
Decomposition of Mullite
Authors: DAVIS ROBERT F. , AKSAY ILHAN A. , PASK JOSEPH A.
Published: June 2006

Free surfaces of 2:1 mullite (2Al2O3·SiO2) specimens decomposed with the evolution of SiO and O2 when they were heated at high temperatures under low partial pressures of O2; this reaction was analyzed thermodynamically. In addition, bubbles were observed at internal interfaces between mullite and fused‐SiO2 diffusion couples. These bubbles, when formed at 1 atm ambient pressure between 1650° and 1800°C, resulted from reaction of Si particles and residual SiO2‐rich glass in the fused cast mullite.
Effect of Green Density on the Initial‐Stage Sintering Kinetics of UO2s
Authors: WOOLFREY J. L.
Published: June 2006

The kinetics of the initial‐stage sintering of a UO2powder in H, were investigated over the range 600° to 1200°C by dilatometry. Decreasing green density below #40% of theoretical leads to progressively reduced rates of sintering. Initiation of the effect is related to a critical value of the ratio of pore size to particle size at which pores become stabilized and inhibit local shrinkage. Green density did not affect the sintering law or the apparent activation energy for sintering. A constant apparent activation energy for sintering of 86±8 kcal/mol was found, indicating that diffusion of the same species is rate‐controlling over this temperature range. Above 900°C, the rate‐controlling mechanism is consistent with grain‐boundary diffusion of the uranium ions.
Equilibrium Cation Distribution in NiAl2O4, CuAl2O4, and ZnAl2O4 Spinels
Authors: COOLEY RICHARD F. , REED JAMES S.
Published: June 2006

Stoichiometric NiAl2O4, CuAl2O4, and ZnAl2O4 spinels were prepared and equilibrated at temperatures from 600° to 1400°C. The parameters u and x, denoting the oxygen position and fraction of divalent cations on tetrahedral sites, respectively, were determined from a detailed X‐ray diffraction analysis. In NiAl2O4, x increased from 0.07 at 595° to 0.26 at 1391°C; in CuAl2O4, x decreased from 0.68 at 613° to 0.64 at 1195°C; and in ZnAl2O4, x decreased from 0.96 at 905° to 0.94 at 1197°C. The form of the temperature dependence of x could not be described using theoretically based equations advanced in the literature. A more general equation which allows for a non‐distributional contribution to the configurational entropy was derived and observed to properly describe the temperature dependence; the results indicate that short‐range order is of definite significance in these intermediate aluminate spinels.
Interactions Between Cement Minerals and Hydroxycarboxylic‐Acid Retarders: III, Infrared Spectral Identification of the Aluminosalicylate Complex
Authors: DIAMOND SIDNEY
Published: June 2006

The amorphous salicylate‐bearing product precipitated when C3A and related compounds are placed in contact with salicylic acid in aqueous solution and the residual contents of the solutions were examined by ir spectroscopy. Comparison with spectra of several aluminosalicylate complexes and crystalline aluminosalicylic acid indicated that the amorphous product is a hydroxylated chelate complex designated as Al(sal)OH, precipitated over a period of time from the cationic aluminosalicylate complex Al(sal)+, which is formed rapidly in solution.
Transient Creep in Fe‐Doped Polycrystalline MgO
Authors: GORDON R. S. , TERWILLIGER G. R.
Published: June 2006

The transient creep rate in polycrystalline Fe‐doped MgO (grain size 4 to 19 μm) follows the exponential time relation The initial strain rate, , depends linearly on stress, and the relaxation time, τ, is thermally activated. Two mechanisms for the transient were considered, i.e. (1) viscous grain‐boundary sliding with elastic accommodation and (2) transient diffusional creep. Although the results are not conclusive, transient diffusional creep appears to be the most promising mechanism.
Settling of Particles in Fresh Cement Pastes
Authors: WHEELER J. , CHATTERJI S.
Published: June 2006

Critical comparison of the results of previous experimental studies of the settling of cement pastes at different water‐cement ratios exposed inconsistencies in published theories. Development of a γ‐ray densitometer made it possible to measure the change in density of columns of freshly prepared cement paste with time of settling in containers of clear poly(methylmethacrylate) plastic. Paste density increased at all levels in the columns; the changes were greater at the greater depths, suggesting that the settlement was developing in compression. After the rates of hydration contraction occurring within the pastes were corrected for, the initial velocities of settlement of the solids at the tops of the columns satisfied the Kozeny‐Carman equation.
Prediction of Thermal‐Shock Resistance During Heating at Very High Rates
Authors: NEWMAN RICHARD L.
Published: June 2006

A method of treating spalling failure during initial heat‐up is presented. The assumptions include very high rates of convective heating, failure at hot surfaces from shear stresses, statistical failure, and failure defined by multiple crack intersection. On the basis of this and other work, it is concluded that scale‐model tests are, in general, inappropriate.
Formation of Defects in Glass Under Electron Bombardment
Authors: YAMAMOTO TOKUJI , SAKKA SUMIO , TASHIRO MEGUMI
Published: June 2006

Needlelike crystals grew from a fragment of glass bombarded with intense electron beams in an electron microscope. This phenomenon was limited to glasses containing mobile atoms such as Na and Pb, to fresh surfaces, and to the part of the sample not coated with carbon film. When there was a relatively thick carbon film on the surface, prolonged electron bombardment caused the formation of bubbles within the fragments.
Calcination and Cementing Properties of CaCO3‐SiO2 Mixtures
Authors: KLEMM W. A. , BERGER R. L.
Published: June 2006

Calcium carbonate‐silica mixtures produced by carbonation of wollastonite and pseudowollastonite and by intergrinding precipitated CaCO3 with SiO2 flour were calcined. At calcination temperatures of <850°C, mixtures of β‐Ca2SiO4 and CaO were formed. The quantities of these products were determined by X‐ray diffraction, and their dependence on calcination time, temperature, and the degree of homogeneity of the starting material was determined. Kinetic data were also obtained. Calcined materials mixed with water and compacted under pressure hardened slowly at room temperature and more rapidly under atmospheric steam or autoclave conditions. The relation between compressive strength, porosity, curing time, and temperature was determined.
Electrical Relaxation in Na2O·3SiO2 Glass
Authors: PROVENZANO V. , BOESCH L. P. , VOLTERRA V. , MOYNIHAN C. T. , MACEDO P. B.
Published: June 2006

The electrical relaxation associated with alkali diffusion in Na2O·3SiO2 glass was studied from 0.2 Hz to 700 kHz at –1° to 163°C. A formalism for analysis of electrical relaxation in conducting dielectrics which associates the nonexponential decay of the electric field to zero and the dispersions in the dielectric constant and the conductivity with a distribution of relaxation times for the electric field was developed and is shown to be in qualitative accord with current molecular theories of electrical relaxation in alkali silicate glasses. A relation between the dc conductivity, the limiting high‐frequency dielectric constant, and the average electric field or conductivity relaxation time was derived and is verified experimentally for the Na2O·3SiO2 glass. The distribution of electric‐field relaxation times for the glass is broad, asymmetric on a logarithmic scale, and weighted in favor of the shorter relaxation times; the distribution narrows with increasing temperature. A reduced electrical relaxation curve which can be used to compare electrical and mechanical relaxations in Na2O·3SiO2 glass was generated.
Lanthanum Dependence of Elastic and Piezoelectric Properties of PLZT Ceramics with a Zr/Ti Ratio of 65/35
Authors: MEITZLER A. H. , O'BRYAN H. M.
Published: June 2006

The elastic and piezoelectric properties of PLZT ceramics with a 65/35 Zr/Ti ratio undergo pronounced changes as La is added to the structure. At the rhombohedral‐tetragonal phase boundary, material constants plotted as functions of La concentration show strong discontinuities in slope; these discontinuities provide a precise means of locating the boundary. The radial‐mode coupling factor, kp, compliance coefficient, S11E, and piezoelectric coefficient, d31, attain peak values at the boundary, whereas Poisson's ratio, σE, and the resonance‐frequency constant exhibit pronounced minima. This behavior is evidence of the increasing ferroelastic sensitivity of the material as the distortion angle of the rhombohedral phase approaches a minimum.
Preferred Orientation in Al2O3 Substrates
Authors: DiMARCELLO F. V. , KEY P. L. , WILLIAMS J. C.
Published: June 2006

The degree of preferred orientation (texture) of doctor‐bladed polycrystalline 99.5% Al2O3 substrates from 3 sources was evaluated by qualitative optical and quantitative X‐ray analyses. The substrates exhibit a fiber texture in which the basal planes lie preferentially in the plane of the substrate. The same texture is weakly evident in the unfired materials. The strength of the texture in fired substrates varies from lot to lot and among suppliers, but its character remains essentially the same. Measurements of dielectric constant, flexural strength, and thermal expansivity are consistent with the observed texture. The possible origins of the texture and its importance in substrate applications are discussed.