bluuebunny/crossref_metadata_2025 huggingface dataset:
Gas‐Filled Bubbles in Ionic Solids
Authors: OHRING MILTON , TAI KING LIEN
Published: June 2006

A device to selectively introduce gases into a melt of KCl from which single crystals or oriented bicrystals are being pulled is described. The insoluble gases (e.g. Ar, Cl2, N2, and CO2) were incorporated into the growing crystals in the form of bulk and grain boundary bubbles having a decided crystallographic appearance. The as‐grown bubbles of Ar and Cl2 were extended along the growth axis, whereas those of N2 and CO2 were compressed in this direction. The bubble shapes are expected to depend on surface energy considerations and on the way in which the gas interacts with the solid; the bubble geometries were qualitatively consistent with available data on the theoretical adsorption behavior of these gases on (100) crystal faces of KCl. On annealing under load, the bubbles became highly faceted. Only the very stable (100) plane developed; this indicates the extreme anisotropy of the surface energy even at temperatures approaching the melting point. The failure of bubbles to evolve completely into cubes is probably due to the difficulty of establishing growth habits normal to the (100) plane.
Optical Spectra of 3d Transition Metal Ions in MgO 3·52O3 Spinel
Authors: REED J. S. , KAY H. F.
Published: June 2006

Large gem‐quality boules of MgO·3.5A12, O3 spinel, both pure and incorporating controlled amounts of Ti3, V3+, Cr3+, Mn2, Fe2+, Co2+, or Ni2+ were synthesized by a modified verneuil technique. Each crystal was characterized by measuring the lattice parameter, chemical composition, and density. Using thin polished slices as specimens, the absorption spectrum of each crystal was measured from 400 to 50, 000 cm−1, and band centers and order‐of‐magnitude oscillator strengths were calculated from the spectrum for each specimen. For these well characterized crystals, the absorption spectra were interpreted satisfactorily in terms of crystal field theory when the complete individual spectrum as well as the spectrum of the host matrix was considered. On this basis, the oxidation state and coordination of the 3d ion could be determined. Covalent bonding effects were of definite significance in these spinels and caused an inexact correspondence between observed band centers and those predicted by the Orgel diagrams. The ratio Dq (tetrahedral)/Dg (octahedral) was 0.67 in the 1:3.5 spinel and verified the theoretical relation expressing this ratio in terms of a constant, 4/9, times the fifth power of the ratio of the site radii. Coordination preferences of the incorporated transition metal ions are also discussed.
Sublimation Pressure and Sublimation Coefficient of Single‐Crystal Lead Selenide
Authors: HANSEN EDWARD E. , MUNIR ZUHAIR A. , MITCHELL MARTHA J.
Published: June 2006

The torsion‐Langmuir and torsion‐effusion methods, respectively, were used to study the sublimation characteristics of oriented single‐crystal and powdered lead selenide. Analysis of the data showed that the sublimation coefficient is unity over the experimental range. From combined free‐surface and equilibrium data the expression for the sublimation pressure of PbSe from 887° to 1052°K was found to be log P(atm) =‐ (1.226±0.015) 104/T+(8.163±0.154), where T is the absolute temperature and the errors are standard deviations. Third‐law calculations of the heat of sublimation at 298°K gave 55.66±0.20 kcal/mol PbSe.
Mechanical Properties and Fracture Behavior of Chemically Bonded Composites
Authors: STETT MARK A. , FULRATH R. M.
Published: June 2006

The effect of chemical bonding between phases of a glass matrix‐metal composite on strength and fracture behavior was investigated. When no chemical bonding occurs, strengthening can be achieved through the mechanical formation of an interface between the dispersant and matrix. Even greater strengthening can be obtained by the formation of a chemical bond. Strengthening occurs by the limitation of the Griffith flaw size and is controlled by micromechanical stress concentrations developed on loading. Internal stresses developed on cooling from the fabrication temperature control the path of fracture. A chemical bond counteracts the micromechanical stress concentration and therefore increases the strength.
Fatigue Behavior of a High‐Density Graphite and General Design Correlation
Authors: LEICHTER H. L. , ROBINSON E.
Published: June 2006

The fatigue behavior of a high‐density graphite was investigated in reverse bending up to 5×108 cycles at room temperature. Fatigue life was analyzed statistically, using a Weibull distribution and a homologous stress. The homologous stress is the ratio of applied stress in fatigue to the expected first‐cycle strength. The first‐cycle strength was calculated from bending tests of similar materials or “mate” specimens, using the Weibull statistical strength theory to correct for the significant size effect. Homologous stress gives an essentially invariant fatigue correlation for many graphite grades and may be used to estimate fatigue life under a wide variety of operating conditions. The practical endurance limit for graphite corresponded to a homologous stress of about 47%.
Strength‐Anisotropy‐Grain Size Relations in Ceramic Oxides
Authors: KIRCHNER H. P. , GRUVER R. M.
Published: June 2006

On the basis of high strengths observed at small grain size and crack formation observed at moderate grain size, a large grain‐size dependence of the strength of rutile ceramics was predicted. This dependence was investigated by experiment, and a grain‐size exponent greater than ‐1/3 was found. Tabulating literature data on the grain‐size dependence of strength and the degree of anisotropy of several oxide ceramics demonstrated a correlation between the degree of anisotropy and the grain‐size exponents; the grain‐size exponent increases with increasing anisotropy. The mechanism of fracture of single‐phase ceramics composed of anisotropic crystals is discussed.
Differential Thermal Calorimetric Determination of the Thermodynamic Properties of Kaolinite
Authors: NICHOLSON PATRICK S. , FULRATH RICHARD M.
Published: June 2006

Four samples of kaolinite were investigated to determine the exothermic reaction enthalpy by differential thermal calorimetry. The measured 9 kcal/mol for the 980°C exothermic reaction enthalpy corresponds to the calculated heat of crystallization of silica at this temperature. Literature evidence discounts the crystallization of the other participating phases, mullite and silicon spinel. An NaOH extraction technique was used to remove the amorphous silica from a kaolinite fired at 850°C; this extraction removed the 980°C exotherm. It is tentatively suggested, therefore, that most of the heat release at 980°C on firing kaolinite accompanies the reaction SiO2(amorphous) → SiO2(β‐quartz).
Creep of Polycrystalline MgO and MgO‐Fe2O3 Solid Solutions at High Temperatures
Authors: TERWILLIGER G. R. , BOWEN H. K. , GORDON R. S.
Published: June 2006

Polycrystalline MgO and MgO‐Fe2O3 solid solutions (0.10 to 8.08 wt% Fe2O3) were fabricated to almost theoretical density by vacuum hot‐pressing. Specimens were creep‐tested in air under four‐point dead‐load conditions between 1000° and 1400°C at stresses between 50 and 550 kg/cm2. Steady‐state creep was never achieved in the experiments, which sometimes lasted more than 50 h. The strain rate vs time (t) data were described by an equation of the form =c1/(t+C2)p, which is consistent with the assumptions that creep occurs at least in part by a “viscous” mechanism and that grain growth occurs simultaneously. Doping MgO with Fe2O3 enhanced the viscous contributions to creep and inhibited the nonviscous ones. Creep rates in these specimens increased with increasing Fe2O3 additions. The occurrence of simultaneous grain growth during the high‐temperature creep of magnesiowustite (i.e. MgO‐Fe2O3 solid solutions) was used in establishing the strain rate vs grain size dependence. The results of this study are consistent with a transition between grain boundary and lattice diffusion mechanisms as the grain size increases (4 to 44 μan). The creep of polycrystalline MgO is a mixed process in that viscous and nonviscous (dislocation) contributions are present.
Change of Molar Volume and Interdiffusion Coefficients in the System MgO‐Cr2O3
Authors: GRESKOVICH C. , STUBICAN V. S.
Published: June 2006

The interdiffusion coefficients in the system MgO‐Cr2O3 were measured in the MgO phase. They are concentration‐dependent and increase linearly, below 1600°C, with increasing mole fractions of cation vacancies. Interdiffusion coefficients calculated by the Boltzmann‐Matano and Wagner treatments for the system MgO‐Cr2O3 are compared; some of those obtained by the Boltzmann‐Matano treatment are about 70% greater than those obtained by Wagner's analysis. Wagner's treatment gives correct values for the interdiffusion coefficients. The results of the Boltzmann‐Matano treatment show the effect of neglecting the molar volume change in the system.
Bismuth Phosphate Glasses
Authors: TIWARI A. N. , SUBBARAO E. C.
Published: June 2006

Homogeneous glasses are formed in the Bi2O3‐P2O5 system up to 35 mol% (63.8 wt%) Bi2O3. In property vs composition plots, the thermal expansion coefficient and tan δ exhibit minima, and hardness and activation energy for conduction show maxima at about 20 mol% Bi2O3. The deformation temperature of the glasses also increases abruptly at this composition. This anomalous behavior is interpreted in terms of a change in the function of Bi3+ ions from network formers to network modifiers.
Infrared Spectroscopy of Reacted Mixtures of Otay Bentonite and Lime
Authors: GLENN GEORGE R.
Published: June 2006

Mixtures of three types of lime, bentonite, and water were analyzed by infrared spectroscopy after three years of reaction at 23°C under conditions approaching 100% rh and after hydro‐thermal reaction at 40°, 80°, and 170°C. The procedure was effective for analysis of complex mixture components. New compounds identified in the 23°C mixtures were calcium carbonate as well as hydrates of calcium silicate and calcium aluminate. Tobertnorite was identified in all 170°C mixtures, with indications of serpentine and possibly chlorite in mixtures containing dolomitic lime, particularly the monohydrated form. Remnants of initial components not used in the reaction were also noted. Implications for analysis of compound structures are discussed, with particular reference to lattice substitution of aluminum and magnesium.
Hot Hardness, Thermal Diffusivity, and Electrical Resistivity of Uranium Oxycarbides
Authors: HENRY JACK L. , BLICKENSDERFER ROBERT , PAULSON DANTON , BATES J. LAMBERT
Published: June 2006

Several predominantly single‐phase uranium oxycarbide compositions were examined to determine the effect of oxygen content on the hot hardness, thermal diffusivity, thermal conductivity, and electrical resistivity. Little difference was noted in hot hardness over the low‐temperature range; however, increased oxygen content appears to reduce the hardness above 700°C. Thermal diffusivity and thermal conductivity are reduced by increased oxygen content. This decrease is most pronounced at lower temperatures, and the temperature dependence varies significantly with oxygen content. The thermal diffusivity of oxycarbides having small percentages of oxygen decreases with increasing temperature, whereas that of oxycarbides with greater oxygen content increases, very slightly. The thermal conductivity data are in fair agreement with those reported for the monocarbide. Electrical resistivity is increased by increased oxygen content and shows a positive temperature dependence. The data indicate that electronic conductivity at 1500°C accounts for approximately 85% of the total thermal conduction at the 2‐at.%‐oxygen level and approximately 95% of the total at the 16‐at.%‐oxygen level.
Diffusion in Portland Cement Clinker
Authors: CHRISTENSEN N. H. , SIMONSEN K. A.
Published: June 2006

Experimental data on the interfacial reaction between portland cement clinker and molten coal ash at 1400° to 1500°C are consistent with a mechanism involving diffusion in the melt as the rate‐controlling step. The formation and growth of well‐defined zones between the reactants are characteristic of the reaction. Equations were solved for diffusion with two moving interfaces. On the basis of these equations and data from the lime‐alumina‐silica phase equilibrium diagram, the diffusion coefficient for CaO in the interstitial melt in the clinker is about 5±10‐6 cm2/s at 1500°. The results imply that the clinkering reaction in the burning of portland cement clinker is also controlled by diffusion in the melt.
Creep in Yttria‐ and Scandia‐Stabilized Zirconia
Authors: EVANS P. E.
Published: June 2006

Compression creep measurements at constant load on ZrO2‐6 mol% Sc2O3 (grain size ∼1 μm), ZrO2‐6 mol% Y2O3 (grain size ∼17 μm), and heat‐treated ZrO2‐6 mol% Sc2O3 (grain size ∼2 μm) yield activation energies of 89, 86, and 74 kcal/mol, respectively. The creep rates are linearly proportional to the inverse square of the grain size of the material. A stress exponent, n, of 1.5 was found for the scandia‐doped zirconia and two regimes, with n=1 and 6, were found for the yttria‐doped zirconia. These data, supported by metallographic evidence, are interpreted as showing that n=1 is associated with cation diffusion control of creep, n=6 with local propagation of inter‐crystalline cracks, and n=1.5 with a transition region.
Wetting of Ceramics by Liquid Aluminum
Authors: RHEE S. K.
Published: June 2006

The wettability of AlN, TiB2, TiN, and TiC by liquid aluminum was investigated by the sessile drop technique at 2×10‐7 torr or less. The contact angle decreased linearly with increasing temperature in all cases. Variation of the contact angle with temperature is correlated with the surface tension of the drop, and the Zisman‐type relation is established. The critical surface tensions (Rγc) of AlN, TiB2, TiN, and TiC are 664, 700, 713, and 725 dynes/cm, respectively. These values are correlated with the melting point of the ceramics. The Zisman relation is discussed and applied to calculation of the work of adhesion. The surface tension of liquid aluminum varies linearly with temperature: γLv (dynes/cm) = 948–0.202T (°K).
Fracture Induced in Al2O3 Bicrystals by Anisotropic Thermal Expansion
Authors: MAR HENRY Y. B. , SCOTT WILLIAM D.
Published: June 2006

Bicrystals of Al2O3 were fabricated to study the effects of thermal expansion anisotropy on fracture in a model system containing one grain boundary. Fractures occurred perpendicular to the directions of maximum tensile stress in bicrystals with thermal expansion coefficient differences as low as 0.31×10−60C−1 and originated at the boundary, probably in areas of high residual stress associated with pores. Numerical stress analysis of two‐dimensional model bicrystal configurations showed that stresses induced by thermal expansion anisotropy are maximal in a region localized along the bicrystal boundary.
Electrochemical Studies in Glass: I, The System NiO‐Na2Si2O5
Authors: LACY ALTON M. , PASK JOSEPH A.
Published: June 2006

A solid electrolyte electrochemical cell of the type Pt|Ni:NiOa=1∥ZrO2+7.5% CaO∥Ni:NiOa<1+glass|Pt was used to measure the activities of NiO in sodium disilicate glass from 750° to 1100°C. The data indicate a solubility varying from 11 mol% (5.0 wt%) at 800° to 20 mol% (9.3 wt%) at 1100°C. From the variation in NiO activity, the activity of sodium disilicate in glass solution was estimated; from these combined data partial molar free energies and entropies of solution of NiO and Na2Si2O5 and free energies and entropies of mixing were calculated. A partial phase diagram for the system NiO‐Na2Si2O5 proposed from solubility data indicates a eutectic at ∼12 mol% (5.3 wt%) NiO at 830°C.
Preparation and Characterization of High‐Purity HfTiO4
Authors: MAZDIYASNI K. S. , BROWN L. M.
Published: June 2006

The double decomposition of hafnium and titanium tetrakis tertiary amyloxides was used to produce high‐purity stoichiometric submicron HfTiO4 powders. The particle size range was 50 to 400 Å. X‐ray diffraction of a 1:1 mixture, as‐prepared and heated to ∼750°C, indicated that the material is 95% orthorhombic HfTiO4. The TGA, BET, DTA, and high‐temperature X‐ray analysis of the as‐prepared powders are also reported; the ir absorption and reflection frequencies of HfTiO4 were determined. The homogeneity and stoichiometry of the powder were demonstrated by electron microscopy and wet chemical analysis. Mixed oxides prepared in this manner were sintered in an ambient atmosphere at 1650° to 1700°C for 4 h or Ionger into a body of nearly theoretical density and uniform microstructure.
Characterization of Alkoxy‐Derived Yttria‐Stabilized Hafnia
Authors: BROWN L. M. , MAZDIYASNI K. S.
Published: June 2006

High‐purity submicron HfO2−Y2O3 powders were prepared by the simultaneous hydrolytic decomposition of hafnium and yttrium alkoxides. Compositions of 1 to 7 mol% Y2O3 in HfO2 were studied by high‐temperature X‐ray diffraction, electron microscopy, BET surface area measurements, emission spectrographic analysis, TGA, and DTA. X‐ray diffraction and atomic absorption were used to determine the Y2O3 concentration. Hot‐pressing or cold‐pressing and sintering of the powders resulted in nearly theoretically dense bodies with uniform microstructure containing grains 1 to 5 μm in size. Surface reflection ir spectra were obtained for monoclinic, tetragonal, and cubic specimens. Fully cubic HfO2 with 7 mol% Y2O3 additions was obtained at a relatively low temperature. The hot‐pressed specimens, initially slightly oxygen‐deficient or gray HfO2‐x, were reoxidized at 1000°C with no deleterious effects; thin sections were translucent to incident light.
Separation of Phases by Spinodal Decomposition in the Systems Al2O3−Cr2O3 and Al2O3−Cr2O3−Fe2O3
Authors: SCHULTZ A. H. , STUBICAN V. S.
Published: June 2006

Separation of phases was investigated in the hexagonal (rhombohedral) systems Al2O3−Cr2O3 and Al2O3−Cr2O3−Fe2O3. The binary system shows a miscibility gap with a Tc of 950°C; the miscibility gap for the ternary system was determined for a constant Cr2O3 content of 16.6 mol%. Dark field transmission electron microscopy of solid solutions annealed within the miscibility gap showed dark and light lamellas ∼50 to 200 Å thick. X‐ray diffraction results for the solid solutions in the ternary system indicated that, in the early stages of annealing, broadening occurred only on (hkl) reflections where l≠0. There was no major change in the X‐ray diffraction patterns of the annealed solid solutions in the binary system. Electron diffraction results indicated, however, that phase separation in both systems proceeded in the [001] direction. Solid solutions in the binary system separated very slowly; the separation could be enhanced hydrothermally. The mechanism of the separation of phases in both systems is spinodal and proceeds as follows: solid solution→intermediate modulated phase→equilibrium phases.
Chain‐Folding Mechanism for Growth of BaO 2B2O3 Crystal in Its Melt
Authors: LAIRD J. A. , BERGERON C. G.
Published: June 2006

The linear growth rate of a BaO.2B2O3 crystal in its melt was measured as a function of temperature; a growth mechanism was proposed which involves the folding of chains of boroxol rings back and forth on the crystal surface. At small undercoolings, the growth rate appeared to be limited by the number of suitable nucleation sites for a chain to attach to the crystal; at large undercoolings, it appeared to be limited by the rate of orientation of the chains at the crystal‐melt interface.
Determination of Axial Stress in Clad Glass Fibers
Authors: KROHN DAVID A.
Published: June 2006

The axial stress in clad glass fibers was measured by photoelastic techniques and compared with calculated values. In general, there was good agreement when the hydrostatic stress development was included in the calculation. The systems studied were primarily those which would produce a surface compression. Fibers of a soda‐lime‐silica glass clad with a high‐silica glass gave the largest surface compression, 46,000 psi.
Nickel‐Zinc Ferrites: I, Effect of Composition on the Magnetic Properties of a Nickel‐Zinc‐(Cobalt) Ferrite
Authors: BROCKMAN F. G. , MATTESON K. E.
Published: June 2006

By varying the mole percent of Fe2O3 in a nickel‐zinc‐(cobalt) ferrite in very small increments, it was found that an optimum composition exists. Deviations from this composition as small as 0.1% can cause a decrease in resistivity by e.g. a factor of 1000. The ferrite is stoichiometric at the optimum composition, and its resistivity has a narrow, sharp maximum; the μoQ product is also maximal. Such a coincidence has not been previously observed. The usual eddy‐current relation between resistivity and ac losses fails to explain this phenomenon because of the very high resistivities involved.
Thermogravimetric Study of the High‐Temperature Oxidation of Cu and Fe With and Without Vitreous Coatings
Authors: KING R. M.
Published: June 2006

The study of the oxidation of Cu and Fe by continuous recording of weight gain is described. Equations are given for the rates of oxidation at several temperatures of the metals, both uncoated and enamel‐coated. Uncoated Cu was less strongly oxidized than uncoated Fe, but coated Cu was more strongly oxidized than coated Fe. The presence of CoO in the coating caused no significant difference in the action of the enamels on the metals.
Knoop Hardness Anisotropy and Plastic Deformation in Mn‐Zn Ferrite Single Crystals
Authors: ITO TAKEO
Published: June 2006

The Knoop hardness anisotropy and plastic deformation markings around the DPH indentation were investigated for an Mn‐Zn ferrite single crystal. Knoop hardness values, which depended primarily on the crystallographic direction, were represented on a standard stereographic triangle. The hardness was maximum in the <001> direction and minimum in the <111> and <011> directions. The patterns of the plastic deformation markings show that the ferrite deforms plastically at room temperature by {110} <110> and {111} <110> slip.
Oxidation‐Reduction Kinetics in MnO
Authors: BRANSKY I. , TALLAN N. M. , WIMMER J. M. , GVISHI M.
Published: June 2006

The oxidation‐reduction kinetics of MnO in CO/CO2 atmospheres at 1230°C were measured by gravimetric and electrical conductivity techniques. The dependence of the kinetics on time, inert gas dilution, total pressure, and specimen thickness indicates that the kinetics are controlled by a slow surface reaction step. Attempts to analyze the data quantitatively using equations for linear heat flow in a solid with a radiation boundary condition were unsuccessful.
Infrared and Raman Spectra of Zirconia Polymorphs
Authors: PHILLIPPI C. M. , MAZDIYASNI K. S.
Published: June 2006

The infrared and Raman frequencies of monoclinic zirconia and of stabilized and metastable tetragonal and cubic zirconias were established. Infrared spectra were examined by the powder transmission (CsI pellet) and surface reflection techniques. The effects of heating, grinding, and adding stabilizing oxides on the ir spectra were determined. The spectra develop additional bands as the crystal symmetry is lowered, and certain of these bands are highly sensitive to strain‐induced distortions of the crystal lattice. Practical applications of ir and Raman spectroscopy to zirconia technology are discussed.
Static Fatigue of Graphite
Authors: WILKINS B. J. S.
Published: June 2006

The static fatigue behavior of an extruded graphite was determined. The relation between time‐to‐rupture and the homologous fatigue stress (i.e. the ratio of the applied stress to the instantaneous fracture stress) is shown at two levels of applied stress. The significance of this relation is discussed, and its use in predicting cumulative fatigue damage is indicated.
High‐Temperature Creep Behavior of Polycrystalline SrZrO3
Authors: NEMETH J. , YOUDELIS W. V. , PARR J. GORDON
Published: June 2006

The high‐temperature creep behavior of sintered polycrystalline SrZrO3 containing 1.35 wt% Fe2O3 was investigated as a function of temperature, stress, grain size, and strain level over the ranges 1160° to 1275°C, 780 to 3110 psi, 0.45 to 2.04 μm, and 0.0014 to 0.014, respectively. A constant‐load 4‐point (pure bending) method was used to load the specimens. The creep rate is time‐dependent, decreasing exponentially with strain, i.e. , where the decay constant (β=118, measured at the 1560 psi stress level over the strain range 0.0014 to 0.014) is independent of temperature and grain size. No significant grain growth occurred during creep. The activation energy of 169±10 kcal/mol obtained for creep is relatively independent of temperature, stress, grain size, and strain level over the ranges investigated. The creep rate is directly proportional to the cube of the stress and the reciprocal of the grain size; this result is consistent with nonviscous creep theories based on dislocation generation and climb as the rate‐controlling deformation mechanism.
Wetting of TaC by Liquid Cu and Liquid Ag
Authors: RHEE S. K.
Published: June 2006

Wetting of TaC0.97±0.01 by liquid Cu and liquid Ag was studied by the sessile drop method. The cosine of the contact angle increased linearly with increasing temperature in both systems. The critical surface energy for spreading was 1098 ergs/cm2 at 1605°C for Cu and 688 ergs/cm2 at 2160°C for Ag. The work of adhesion, which was 1759 ergs/cm2 at the melting point for Cu and 321 ergs/cm2 at the melting point for Ag, increased parabolically with increasing temperature in both systems. The surface energy of TaC0.97±0.01 was estimated to be 1804±706 ergs/cm2.
Magnetic Behavior and Microstructure of Vanadium Phosphate Glasses
Authors: FRIEBELE E. J. , WILSON L. K. , KINSER D. L.
Published: June 2006

The magnetic properties and microstructures of the vanadium phosphate glass system over the composition range 60 to 90 mol% V2O5 were investigated to study magnetic ordering in the glass and the effect of microstructure on its magnetic properties. Direct antiferromagnetic coupling between V4+ ions in the glassy matrix exists, and a transition temperature near ‐ 70°C was observed. As‐cast glasses with high V2O5 concentrations separated into two glassy phases; this separation increased the ESR line width as a result of inhomogeneity broadening. The separation, which concentrated the vanadium ions in a vanadium‐rich phase, caused a hysteresis in the plot of ESR line intensity vs temperature at the transition temperature. Reduction of the vanadium ions by dextrose added to the melt enhanced phase separation and resulted in weak antiferromagnetic transitions at +70° and ‐120°C, the Neel temperatures of VO2 and V2O3, respectively.
Influence of the Shape of Dispersed Particles on the Elastic Behavior of Composite Materials
Authors: ROSSI R. C. , COST J. R. , JANOWSKI K. R.
Published: June 2006

Young's modulus was measured on a series of composites of magnesium oxide which contained low concentrations of graphite as flakes, fibers, and nearly spherical particles. The measured modulus was in excellent agreement with predictions of elastic behavior based on particle shape. Not only do the results indicate that accurate predictions of elastic moduli are possible, but also that the shape of dispersed particles has a dominating influence on the elastic properties of composite materials at low concentrations of an included phase.
Internal Friction of Proton‐Exchanged Li2O·Al2O3·2SiO2 Glass
Authors: ISMAIL A. , ABDEL‐LATIF A. , DAY DELBERT E.
Published: June 2006

Protons were introduced into the surface of an Li2O·Al2O3·2SiO2 glass fiber (0.5 mm in diameter) by ion exchange in NH4HSO4 at 366°C for 21 h. Infrared absorption measurements established that the protons were associated with bridging oxygen ions. After ion exchange, the magnitude of the alkali internal friction peak decreased and a new peak appeared at ∼220°C. This new peak is attributed to the interaction of alkali and hydrogen ions, independent of the presence of nonbridging oxygen ions.
Short‐Time Creep Transition for Hardened Cement Paste
Authors: SELLEVOLD ERIK J. , RICHARDS CEDRIC W.
Published: June 2006

Short‐time creep recovery tests in two‐point bending were performed on hardened cement paste beams water‐cured at #100° and 25°C. The experimental variables were pore structure, equilibrium moisture content, and temperature. The recovery curves were analyzed using linear viscoelastic concepts, which revealed a transition in the time range 0.2 to 10s which is both linear with stress and reproducible. A lognormal distribution of retardation times characterizes the transition. It is tentatively proposed that internal redistribution of capillary water is responsible for the transition. Experimental observations which support this view are: (1) The size of the transition increases with increasing amounts of capillary water for saturated pastes; (2) the transition strength decreases greatly when the capillary water is removed; (3) the apparent activation energy of the transition (3.8 kcal/mol) agrees well with that for viscous flow of water.
Critical Surface Energies of Al2O3 and Graphite
Authors: RHEE S. K.
Published: June 2006

Based on the wetting properties of a‐Al2O3, and pyrolytic graphite by liquid metals, the critical surface energy for spreading was determined and compared with the surface energy of the ceramics. The surface energy γ‐8 (ergs/cm2) of the (0001) surface of a‐Al2O3 is estimated to be 892–0.12T (°C), that of the c plane of pyrolytic graphite 1139–0.13T (°C), and that of the a plane of pyrolytic graphite 1300–0.17T (°C). Also, the liquid‐solid interfacial energies were calculated and found compatible with the values reported in the literature. The surface energy of liquid Ag or liquid Cu is not significantly affected by carbon.
Structure and Reactivity of Chromium‐Doped Tricalcium Silicate
Authors: FIERENS PAUL , VERHAEGEN JEAN‐PIERRE
Published: June 2006

The correlation between the structure and reactivity of Cr‐doped tricalcium silicate was studied by ir spectrophotometry and X‐ray diffractometry. A very sensitive method of detection of defects (thermostimulated exoelectron emission) allowed differentiation of three types of electron traps; the activation energy for the third trap was 0.8 eV. These crystal defects seem to be associated with sites of high Cr concentration (disordered structure) which may also be responsible for the increased reactivity of the doped phases. The reactivity of the system tricalcium silicate‐H2O (w/c=0.6) was studied by an electrical conductometric method. Curves of conductivity vs time for tricalcium silicate with varied Cr concentrations indicated significant differences in hydration kinetics.
Crystal Growth and Observation of the Ferroelectric Phase of PbZrO3
Authors: SCOTT B. A. , BURNS GERALD
Published: June 2006

High‐purity single crystals of PbZrO3 suitable for electrical measurements were grown from solutions in the PbO‐ZrO2‐PbF2‐B2O3 system. Dielectric, hysteresis‐loop, and optical measurements confirmed the existence of an intermediate ferroelectric (FE) form, previously observed only in ceramics, just below the transition temperature (Tc#232°C). The temperature stability range of the FE phase, which cooling curve measurements show to vary from 12° to 26°C, appears to be related to crystal stoichiometry. The maximum value of spontaneous polarization is P8(max)#24 μC/cm2, assuming that the FE phase possesses rhombohedral symmetry.
Surface Domain Reorientation Produced by Abrasion and Annealing of Polycrystalline BaTiO3
Authors: CUTTER I. A. , McPHERSON R.
Published: June 2006

The abraded surface of polycrystalline BaTiO3 was examined by X‐ray diffraction methods. The distorted layer produced by abrasion on 320‐grade SiC consists of (1) a region extending to the bottom of the deepest scratches in which the domains tend to be oriented with their c axes perpendicular to the surface and (2) a transition layer below this in which the orientation varies with depth. The orientation changes little on annealing until recrystallization begins at #900°C; however, annealing at 1100° to 1400°C produces an α‐domain reorientation. Possible explanations for these effects are discussed in terms of dislocations introduced by deformation during abrasion and grain size in the recrystallized surface layer.
Controlled Spherulitic Crystallization in 3BaO‐5SiO2 Glass
Authors: FREIMAN S. W. , ONODA G. Y. , PINCUS A. G.
Published: June 2006

Morphological stages in the internal crystallization of a 3BaO‐ 5SiO2 glass were investigated. Spherulitic crystallization occurred between 800° and 950°C. After long times at the crystallization temperatures, the spherulites changed, apparently by secondary crystallization. Above 950°C, lath‐like crystals are formed by recrystallization of the spherulites. The effects of nucleation‐and‐growth heat treatments on the rate and morphology of crystallization were studied. The peak nucleation temperature was between 700° and 725°C, and all the crystalline forms were 3BaO.5SiO2.
Glass Formation in the Pseudobinary Metallic Selenide Systems MmSen‐Ge1.5As0.5Se3
Authors: AGGARWAL I. D. , MOYNIHAN C. T. , MACEDO P. B. , MECHOLSKY J. J. , SRINIVASAN G. R.
Published: June 2006

The glass‐forming regions were investigated for pseudobinary systems of the composition XMmSen‐(1–X)Ge1.5As0.5Se3 (MmSen=PbSe, CdSe, BaSe, ZnSe, or La2Se3). Systems containing PbSe, CdSe, and BaSe contain substantial regions of glass formation, and differential scanning calorimetry, electron microscopy, and water corrosion tests were used to characterize these glasses. The glasses were generally phase‐separated, and the available data suggest that for PbSe melts the region of liquid‐liquid immiscibility spans almost the entire pseudobinary composition range. A few studies of glass formation were conducted for CdSe‐MmSen‐Ge1.5As0.5Se3 pseudoternary and MmSen‐GeSe2 binary melts.
Dependence of Melt Oxygen Activity and Water Retention on Composition of Amber Glass
Authors: HARDING FOSTER L.
Published: June 2006

Proportionalities were developed which are felt to express melt oxygen activity and free‐oxygen‐ion activity in amber glass melts. These expressions indicate that increased modifier levels generally increase melt oxygen activity. The field strength of the modifier cations is also involved in determining the melt oxygen activity. Glasses with higher field strengths resulted in lower melt oxygen activities. Compositional changes also affected the level of dissolved water retained by the glasses. Direct and indirect polarization influences on bridging‐oxygen sites were felt to play a dominant role in determining water concentration. Alkalis with higher field strengths and high SiO2 levels favored higher water‐retention levels.
Correlation of Structure and Electrical Properties of 55FeO‐45P2O5 Glass
Authors: DOZIER A. W. , WILSON L. K. , FRIEBELE E. J. , KINSER D. L.
Published: June 2006

The ac and dc characteristics of 55 mol% FeO‐45 mol% P2O5 glass were measured as functions of time of heat treatment at 600° and of the ratio Fe3+/Fetotal. The dc resistivity behavior at constant temperature (for bulk specimens) was correlated with the appearance and growth of crystals in a glassy matrix, as indicated by data obtained with a Guinier‐De Wolff X‐ray camera. Dispersions appeared in plots of tan δne vs frequency; a hypothesis explaining the appearance of these peaks is presented.
Effect of Temperature and Water‐Solid Ratio on Growth of Ca(OH)2 Crystals Formed During Hydration of Ca3SiO5
Authors: BERGER R. L. , McGREGOR J. D.
Published: June 2006

The growth behavior, time of nucleation, and morphology of Ca(OH)2 crystals formed during the hydration of Ca3SiO5, at 15°, 25°, and 35°C at water‐solid ratios (w/s) from 0.3 to 5.0 were studied by optical microscopy. In samples with w/s >0.5 growth of Ca(OH)2 in the c‐axis direction is initially dominant. Growth in this direction ends after a few hours, but growth perpendicular to the c axis continues for several days and produces a dendritic morphology. Growth behavior is not so well defined for w/s <0.5, in part because of the large number of unhydrated particles engulfed. Increasing temperature resulted in an increase in the number of Ca(OH)2 nuclei and a decrease in nucleation time and crystal size. Increasing the w/s ratio improved the euhedral character of the Ca(OH)2 crystals, decreased the number of engulfed Ca3SiO5 particles, and increased the nucleation time. Dendritic morphology was most pronounced in the samples for which w/s= 1. Growth rates and the ultimate size of the Ca(OH)2 crystals varied within a given sample. The effects of temperature and the w/s ratio on the heat evolved during the hydration were studied by isothermal calorimetry. The times of nucleation of crystalline Ca(OH)2 estimated from calorimetry were similar to those derived from growth curves determined by optical microscopy.
Stress Relaxation Modulus of a Commercial Glass
Authors: MILLS J. J. , SIEVERT J. L.
Published: June 2006

The stress relaxation modulus in compression of a container glass was investigated over a wide range of strain, time, modulus, and temperature. The glass is a linear viscoelastic liquid up to 2% strain, and the modulus is a smooth function of time, with no pseudorubbery plateau apparent down to a modulus of 10° dynes/cm2. The data cover 4 decades in time and a range of almost 100°C above the glass transition, T0=536°C. Within experimental error, changes in temperature simply shift the modulus‐vs‐time curve along the time axis without altering its shape. This behavior implies that the same mechanism controls both the bulk and shear spectra. The shift factors fit the WLF equation well with values for the parameters c1 and c2 of 16.7±0.2 and 345±5°C, respectively. Data from the literature for silicate glasses agree with these parameters.
Na‐K Exchange in Silicate Glasses
Authors: URNES SIGMUND
Published: June 2006

Electrolytic Na‐K displacement in commercial sheet glass was studied. Concentration profiles and compressive surface stresses were determined.
Optical Spectra of Cu2+ and Ni2+ in Intermediate Aluminate Spinels
Authors: REED JAMES S.
Published: June 2006

Optical absorption spectra were determined for well characterized intermediate spinels, NiAl2O4 and CuAl2O4, equilibrated over a range of temperatures. The absorption spectra were interpreted satisfactorily in terms of crystal field theory and were consistent with results of detailed X‐ray analyses. Covalent bonding caused some band shifts and changes in the ratio Dq(tetr. coord.)/Dq(oct. coord.) and the net stabilization energies of the transition metal cation.
Machining, Surface Work Hardening, and Strength of MgO
Authors: RICE ROY W.
Published: June 2006

Machining of MgO by sawing, grinding, sanding, and polishing introduces a surface layer of dense slip whose depth depends on material (e.g. yield stress and grain size) and machining parameters. Cracks, which were always more shallow than the depth of slip, extended from sawn and, to a lesser extent, from ground surfaces into single crystals and some large grains. Annealing removed the slip and decreased surface grain growth in fine‐grained bodies but in general did not result in recrystallization. Surface work hardening increases hardness; it also increases bend strengths of some single crystal orientations and of larger‐grained bodies, especially those with limited intragranular porosity. Fine‐grained bodies were weakened by machining.
Characterization and Sintering Behavior of Ba and Sr Ferrites
Authors: S.REED JAMES , FULRATH RICHARD M.
Published: June 2006

Barium oxide is essentially insoluble in BaO·6Fe2O3, and the nominal compositions BaO·5.5Fe2O3, and SrO·5.5Fe2O3 used commercially may consist of the 1:6 phase and, respectively, one and two minor phases. Compacts formed by mechanical pressure filtration in a magnetic field are characterized by oriented aggregates of platy particles with planar faces and planar and curved edges. The preferred growth of faces and especially larger faces with curved edges leads to fewer edge‐face‐edge contacts and to a greater degree of collective orientation.
Electron‐Microprobe Study of Field‐Assisted Bonding of Glasses to Metals
Authors: BOROM MARCUS P.
Published: June 2006

Quantitative electron‐microprobe evidence is presented for the specific reactions which occur at electrodes during field‐assisted bonding of glasses to metals. Adherence mechanisms are discussed in relation to conventional glass‐metal sealing techniques. It is concluded that the electric field drives electrochemical reactions which contribute to bond formation by first bringing the surfaces into large‐area contact, as a result of both dielectric forces and electrochemical removal of the high points on the metal, and then maintaining the interfacial bonding structure, established by dissolution of the substrate oxide.
Control of Laser Damage in LiNbO3
Authors: PETERSON G. E. , GLASS M. , CARNEVALE A. , BRIDENBAUGH P. M.
Published: June 2006

Low‐frequency (510 MHz) paramagnetic resonance studies of all available undoped LiNbO3 crystals revealed Fe contamination of the order of 10 to 100 ppm. By using care during crystal growth, the amount of this impurity can be substantially reduced, and crystals with reduced susceptibility to laser damage are produced.
Electrical Properties of ZnO‐Bi2O3 Ceramics
Authors: MORRIS WILLIAM G.
Published: June 2006

The nonlinear volt‐ampere characteristics and small‐signal ac capacitance and resistance of sintered ZnO containing 0.5 mol% Bi2O3 were measured. Many of the electrical properties are related directly to the microstructure, which consists of conductive ZnO grains separated by a continuous amorphous Bl2O3, phase. The origin of the nonlinear conduction in the intergranular phase was confirmed by experiments with evaporated thin films. The proposed conduction mechanism in varistors containing ZnO and Bi2O3 is a combination of hopping and tunneling in the amorphous phase.
Interdiffusion in CoO‐NiO Solid Solutions
Authors: STIGLICH J. J. , COHEN J. B. , WHITMORE D. H.
Published: June 2006

Interdiffusion coefficients were measured in CoO‐NiO solid solutions over the range 1000° to 1600°C in air and at po2=5×10−8 atm. Isothermal values of the interdiffusion coefficients in this system increased exponentially with the CoO concentration. Comparison of the present results with cation‐tracer diffusion coefficients for this system measured under similar conditions by Chen and Peterson shows that a Darken‐type equation relating the interdiffusion coefficient to the cation‐tracer diffusivities is valid for these data.
Oxidation Properties of (U, Pu)O2 Solid Solutions
Authors: TENNERY V. J. , GODFREY T. G.
Published: June 2006

Air oxidation of (U, Pu)O2 solid solutions having Pu/(U+Pu) ratios of 0.2 and 0.25 was studied using a recording thermal balance. For Pu/(U+Pu)=0.2, the original fluorite MO2 phase oxidized first to tetragonal M3O7; further oxidation at 450°C<T<600°C gave a two‐phase mixture of M'3O8 and a cubic phase having a0≃5.43 Å. Kinetic analysis of these oxidation stages indicated that the Erofeev nucleation model explains the data reasonably well, with ΔH≃40 kcal/mol for the formation of M3O7 and ΔH≃40 kcal/mol for the oxidation of M3O7 to M'3O8+ the cubic phase. Oxidation above M3O7 (O/M=2.35) resulted in mechanical disintegration of the samples because of the presence of the M'3O8 phase. For Pu/(U+Pu) = 0.25, both isothermal and programed air oxidation of homogeneous samples up to 800°C led to a compound with a maximum O/M≃2.35, i.e. M4O9.4, an fcc phase having a0=5.428 Å; these samples were not converted to powder by the oxidation.
Mass Transport in the Diffusional Creep of Ionic Solids
Authors: GORDON RONALD S.
Published: June 2006

A mass transport equation which takes into account parallel diffusion paths for both anions and cations was derived and applied to the diffusional creep of polycrystalline ionic solids. From the results of the analysis, several limiting conditions were found for grain‐boundary‐ and lattice‐diffusion‐controlled kinetics. These conditions depend on temperature, grain size, and type and concentration of cation impurities. Examples of these limiting situations are given for the creep of polycrystalline Fe‐doped MgO and transition‐metal‐doped Al2O3.

A mass transport equation which takes into account parallel diffusion paths for anions and cations was derived and applied to the diffusional creep of polycrystalline ionic solids. The effect of grain size and cation impurities of variable valence in solid solution on the relative contributions of lattice and grain‐boundary diffusion of different ionic species in polycrystalline MgO and Al2O3 was examined. Depending on the temperature, grain size, impurity level, and O2 partial pressure, several limiting conditions were found:

Limit I: At very small grain sizes and reasonably small cation lattice diffusivities the creep rate will be controlled by the slower‐moving ion in the grain‐boundary regions (i.e. Coble creep).

Limit II: For intermediate grain sizes and cation lattice diffusivities the creep rate will be controlled by cation lattice diffusion when anion transport is significantly faster near grain boundaries than in the lattice (i.e. Nabarro‐Herring creep).

Limit III: For an appropriate combination of large grain size and high cation lattice diffusivity the creep rate will be controlled by anion boundary diffusion (i.e. Coble creep).

Well‐defined examples of limits I and II have been observed in the creep of Fe‐doped polycrystalline MgO, and tentative evidence exists for limit III. Most results of studies of creep in polycrystalline Al2O3 (doped and undoped) fall within limit II, with some overlap with limit III.

The model developed in the present work explains much of the data in the literature in which creep rates correspond to cation lattice mobilities. It is concluded that in the creep of polycrystalline ionic solids anion transport near grain boundaries is rapid and can, in some circumstances, be rate‐controlling. It should also be possible to apply this model to sintering and thermal‐grooving data for such systems, particularly for Al2O3, in which cation lattice diffusion is frequently observed to be rate‐controlling.32
Third‐Power Stress Dependence in Creep of Polycrystalline Nonmetals
Authors: CANNON W. ROGER , SHERBY OLEG D.
Published: June 2006

Published results on the high‐temperature creep of polycrystalline nonmetals indicate that under high stresses many of them obey the equation εασn, where ε is the steady‐state creep rate, σ the applied stress, and n a constant which is usually either 3 or 5. A fifth‐power stress dependence is observed in most pure metals; the creep rate is thought to be controlled by a slip creep process involving dislocation climb. Third‐power dependence is not merely a combination of fifth‐power‐dependent slip creep and first‐power‐dependent Nabarro‐Herring creep but appears to be controlled by a separate mechanism. This mechanism may be associated with Nabarro's dislocation climb model or with Weertman's microcreep model involving charged dislocations. It appears that the ratio of the anion radius to the cation radius is usually >2 in nonmetals for which n=3 and >2 in those for which n=5.
Enhancement of Fracture Properties of Wustite by Precipitation
Authors: MENDELSON MEL I. , FINE MORRIS E.
Published: June 2006

Both the fracture‐initiation energy, γi, and the fracture strength, σf, of 99.5% dense wustite (grain size 23 μm) were substantially increased by (1) precipitating coherent‐coplanar Fe3O4, and (2) decomposing the wustite eutectoidally to α‐Fe+Fe3O4, forming a continuous α‐Fe network at the former wustite grain boundaries. The increase in γi, and σf resulting from the presence of 13 vol% Fe3O4 in wustite was attributed to the difference in cleavage habits between the precipitates and matrix and to crack‐front pinning. The continuous α‐Fe network increased the fracture stability in that fracture was not catastrophic but progressed in steps. The improvement in γi and σf was attributed mainly to the plastic work in fracturing the α‐Fe.