bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetics of Recrystallization and Grain Growth in Cu2O
Authors: ZIKOVSKY L. , VAGNARD G. , DANIEL J. S.
Published: June 2006

The kinetics of recrystallization and grain growth in Cu2O prepared by oxidation of Cu at 1030°C were studied. A critical strain of 8% at 700°C is necessary to cause recrystallization during subsequent annealing at 1020°C. Grain‐growth kinetics fit the expression D3–D03=kt with an activation energy of 83±2 kcal/mol.
Titanium Centers Induced in Borate Glasses by Irradiation
Authors: ARAFA SALAH
Published: June 2006

The electron paramagnetic resonance of alkali borate glasses containing Ti was observed at 9.1 GHz before and after room‐temperature X irradiation. The irradiation‐induced spectra can be separated into (1) the well‐known complex borate resonance with an average g value greater than that of the free electron (2.0028) and (2) a resonance with a lower g value. The latter resonance consists of two asymmetric ESR lines, one broad and the other narrow, whose characteristics are reported. These lines were not observed in the corresponding Ti‐free base glasses; they arise from induced Ti centers. The broad asymmetric line (T1) corresponds to a Ti3.1 ion in sixfold coordination, whereas the narrow asymmetric line (T2) corresponds to a Ti3+ ion in a different structural configuration. Lines T1 and T2 are stable at room temperature, not easily saturated with microwave power, and exhibit behavior independent of the complex borate resonance. The total relative intensity of these lines depends on the total Ti concentration in the glass, the Ti4+/Ti3+ ratio in the glass before irradiation, and the structure of the glass.
Relation of Composition of Hydrogarnet to Resistance to Sulfate Attack
Authors: MARCHESE B. , MASCOLO G. , SERSALE R.
Published: June 2006

Crystallographic changes resulting from the entry of Si into the cubic lattice of tricalcium aluminate hexahydrate were examined in an effort to understand the sulfate resistance of hydrogarnets. Low‐SiO2 hydrogarnets were prepared by hydrothermal treatment of specially prepared glasses. The lattice constants of the unit cell of C3AH6 decreased when Si4+ ions were introduced. In investigating the low‐Si members of the C3AH6‐grossularite series, only those with well‐defined Si contents of 1, 3, and 6 Si4+ ions/unit cell were found; the lattice constants were 12.52, 12.47, and 12.41 Å, respectively. Intermediate lattice constants represent mixtures of at least two members. A content of 0.125 SiO2/formula unit, corresponding to 1 Si4+ ion in the unit cell of C3AH6, is not sufficient to produce resistance to sulfate attack; the lowest SiO2 content which results in such resistance appears to be 0.375 SiO2/formula unit or 3 Si atoms/unit cell.
Inhomogeneous Dehydroxylation of Talc
Authors: DAW JEFFREY D. , NICHOLSON PATRICK S. , EMBURY J. DAVID
Published: June 2006

Dehydroxylation and enstatite development during the decomposition of talc were investigated by transmission electron microscopy using in situ heating. Bubbles and voids are produced during dehydroxylation, and enstatite then precipitates near the voids. Evidence of preferential bubble nucleation at dislocations was obtained. Enstatite crystallites of random orientation were observed initially but on further heating the product phase was formed topotactically.
Intrinsic Nonstoichiometry in Single‐Phase Pb(Zr0.5Ti0.5)O3
Authors: HOLMAN R. L. , FULRATH R. M.
Published: June 2006

Two‐phase crucibles made of Pb(Zr,Ti)O3 with small additions of either PbO or (ZrxTi1‐x)O2, which provide atmospheres of constant PbO activity, permit study of intrinsic nonstoichiometry by thermogravimetry. The width of the single‐phase region can be determined by alternate equilibration of a sample with crucible atmospheres of high and low PbO activity. The width of this region for Pb(Zr0.5Ti0.5)O3 is 2.48 mol% PbO at 1100°C.
Thermal‐Stress Fracture of a Thermomechanically Strengthened Aluminosilicate Ceramic
Authors: GEBAUER J. , KROHN D. A. , HASSELMAN D. P. H.
Published: June 2006

The thermal‐stress fracture behavior of an aluminosilicate ceramic thermomechanically strengthened by surface compression was investigated using quenching in silicone oil. Comparison with the behavior of the unstrengthened ceramic showed that the strengthening increased the critical quenching‐temperature difference required to initiate fracture and also increased the strength retained. The room‐temperature strength was not increased further when the strengthened material was quenched from temperatures above the softening point. On the basis of a simple mechanical model, the observations of the critical quenching‐temperature difference and strength retained in the temperature range of brittle behavior were verified theoretically. It is concluded that, to improve thermal‐stress resistance of ceramics and to avoid catastrophic failure, strengthening by surface compression is to be preferred to increasing the inherent strength of the material.
Determination of Stoichiometry Variations in LiNbO3 and LiTaO3 by Raman Powder Spectroscopy
Authors: SCOTT B. A. , BURNS G.
Published: June 2006

Raman spectroscopy of powders is shown to be a sensitive technique for detecting stoichiometry variations. The method makes use of the broadening of the Raman‐active modes which occurs when the translational symmetry of the lattice is reduced on deviation from simple, fixed cation ratios in the structure. Application of the technique to the LiNbO3(ss) system shows that the room‐temperature solid‐solution range does not exceed 50±0.5 mol% Nb2O5 and that congruent LiNbO3(ss) at 51.4 mol% Nb2O5 is thermodynamically unstable below ≅800°C. Similarly, application of the Raman method to the LiTaO3(ss) system indicates that congruent LiTaO3(ss) at 51.0 mol% Ta2O5 is unstable at temperatures <1000°C.
Kinetics of the Thermal Decomposition of BeSO4
Authors: JOHNSON D. W. , GALLAGHER P. K.
Published: June 2006

Freeze‐dried BeSO4 was prepared from BeSO4·4H2O. Thermal analyses of the tetrahydrate showed a stepwise water loss through the dihydrate and monohydrate to anhydrous BeSO4. The sulfate decomposition of both reagent‐grade and freeze‐dried BeSO4 proceeded by a single step. Isothermal sulfate decomposition of both materials followed the contracting area model and gave activation energies of 51 to 54 kcal/mol.
Method for Determining Resistance of Mortars to Sulfate Attack
Authors: EUSTACHE J. , MAGNAN R.
Published: June 2006

Recognizing that the sulfate resistance of mortars is affected by conditions of use, temperature, cement content, plasticity, and mortar defects, particularly those of aggregate‐cement bonding, a new test for sulfate resistance was developed. Samples 2 by 2 by 10 cm are half‐immersed in an MgSO4 solution. The appearance and compressive strengths of the immersed and exposed parts are recorded at intervals and compared with those of water‐stored samples. This method is quantitatively reliable, selective, rapid, and inexpensive. Results for cements tested in this way are presented, and the physical and chemical characteristics of durable mortars are elucidated. The test was used to demonstrate the sulfate resistance of a new calcium silicate cement.
Preparation of Cathodochromic Sodalites
Authors: SCHIPPER D. J. , VAN DOORN C. Z. , BOLWIJN P. T.
Published: June 2006

Sodalites were prepared by both solid‐state and low‐temperature (80°C) hydrothermal reactions. Induction of cathodo‐chromism was studied and optimized. Undoped halide sodalites can be activated by firing in an oxidizing atmosphere. The coloration and optical bleaching sensitivities depend strongly on both the method of preparation and the activation treatment. The factors which determine the cathodochromic properties, e.g. bromine content, Al/Si ratio, and oxygen content, are discussed.
Internal Friction of Ion‐Exchanged Li2O.Al2O3.2SiO2 Glass
Authors: ISMAIL A. , ABDEL‐LATIF A. , DAY DELBERT E.
Published: June 2006

Fibers of Li2O.Al2O3.2SiO2 glass were ion‐exchanged for 1 to 300 min in an NaNO3 bath at 366°C. The internal friction and the Li and Na concentration profiles were measured. As Na progressively replaced Li, the alkali internal friction peak became smaller while a new peak (mixed‐alkali peak) appeared and increased in magnitude. These changes in internal friction are similar to those that occur when a second alkali is added to glasses prepared by conventional melting. The magnitudes of both internal friction peaks in the ion‐exchanged glass depended on the overall composition of the glass; that of the alkali peak depended on the composition of the unexchanged glass core, whereas that of the mixed‐alkali peak depended on the composition of the exchanged layer on the glass surface. When the exchanged surface layer was dissolved, the original alkali peak was restored, and the mixed‐alkali peak disappeared. Changing the alkali distribution did not affect the mixed‐alkali peak much; however, it caused the alkali peak to shift to higher temperatures and become smaller. The height of the alkali peak can be used to determine the maximum depth of penetration of the second alkali.
Crystallization of BeO, Be2SiO4, and SiO2 from Li2MoO4‐MoO3
Authors: OSMER JUDITH A. , CHASE A. B.
Published: June 2006

Single crystals of phenacite (Be2SiO4), bromellite (BeO), and tridymite (SiO2) were grown from an Li2MoO4‐MoO3 flux. Phenacite, with rhombohedral symmetry, grew in three distinct shapes with aspect ratios (length/width) as follows: needles (>3), rods (>1.1 to 1.5), and rhombohedral‐faced crystals (=1). The latter grew as single crystals; the others were twinned on the . For most experiments the temperature was held constant at 1165°C and the Li2MoO4/MoO3 ratio at 1/16. The growth mechanism for crystallization was the evaporation of MoO3. The system produced one to three phases, depending on the BeO/SiO2 ratio. Bromellite grew until a BeO/SiO2 ratio of 0.8 was attained. It grew as a hemipyramidal crystal having a short prism with a curved top or as a hexagonal plate. The pyramid‐ and prism‐shaped crystals were twinned, although a few hexagonal plates were single. Tridymite grew in small hexagonal plates when the BeO/SiO2 ratio was less than 1.5. The effect of temperature, nucleation, and flux composition on crystal shape, twinning, and occurrence is discussed.
Anionic Conductivity in Halogen‐Containing Lead Silicate Glasses
Authors: SCHULTZ PETER C. , MIZZONI MARY SPLANN
Published: June 2006

The existence of anionic conductivity in halogen‐containing lead silicate glasses was proved by Tubandt tests and electron microprobe examinations. Direct‐current volume resistivities, loss tangents, and dielectric constants are reported for analogous glasses containing F−, Cl−, Br−, and I− and compared to those of the parent glass. The densities of the materials do not correlate with the dielectric‐constant data.
Fabrication of Transparent Electrooptic PLZT Ceramics by Atmosphere Sintering
Authors: SNOW GARY S.
Published: June 2006

PLZT electrooptic ceramics were fabricated by a unique atmosphere sintering technique. The ceramics produced were significantly more transparent than those obtained by ordinary O2 sintering methods; in fact, they were comparable in transparency to those obtained by hot‐pressing. To achieve good transparency, the powder must be batched with excess PbO, which at the sintering temperature is present as a liquid phase at the grain boundaries. Sintering was conducted at 1200°C for 60 h in an atmosphere containing O2 and a relatively high partial pressure of lead oxide.
Property‐Composition‐Substructure Relations in Na2O‐TiO2‐SiO2 Glasses
Authors: BABCOCK C. L.
Published: June 2006

Published data on optical properties and specific volumes of Na2O‐TiO2‐SiO2 glasses located in 7 primary phase fields are represented quantitatively in terms of linear mole fraction equations. These equations are used to calculate a primary phase diagram of this system. The fidelity of the representation of experimental data is compared with that obtained using the Huggins‐Sun method.
Fracture Toughness of a Partially Stabilized ZrO2 in the System CaO‐ZrO2
Authors: GREEN DAVID J. , NICHOLSON PATRICK S. , EMBURY J. DAVID
Published: June 2006

The room‐temperature fracture behavior of partially stabilized ZrO3 (PSZ) in the system CaO‐ZrO2 was investigated. Fracture energy was measured using standard single‐edge‐crack and work‐of‐fracture techniques. Attempts were made to relate the fracture toughness parameters to the microstructure of the material. Stable crack propagation was always observed; a model is proposed to explain these observations on the basis of the formation of a microcrack zone at the tip of a propagating crack. The occurrence of initial stable crack propagation is explained in terms of an increase in microcrack zone size. The possibility that crack stability results from testing geometry superimposed on the microcracking stability is also discussed.
Pb5(Ge,Si)3O11 Ferroelectrics
Authors: EYSEL W. , WOLFE R. W. , NEWNHAM R. E.
Published: June 2006

The compound Pb5Ge3O11 is an optically active ferroelectric with a transition temperature near 177°C. Solid solutions containing up to 62% Si replacing Ge were prepared from the melt. Increasing the Si content lowers the melting point, Curie point, and coercive field. Permittivity measurements on single crystals indicate a simple second‐order phase change.
Effect of Anions on Hot‐Pressing of MgO
Authors: LEIPOLD M. H. , KAPADIA C. M.
Published: June 2006

Anion impurities (S2−, Cl−, F− and OH−) are shown to be deleterious to the densification of MgO by hot‐pressing. The magnitude of the effect decreases in the order in which the anions are listed and is reduced as temperature increases. The effect is suggested to result from gas pressures within the compact and die cavity, and the magnitude of interference with densification is related to both the vapor pressure of the impurity and its rejection from the lattice (insolubility).
Interdiffusion in the System CaF2‐SrF2
Authors: SCHEIDECKER RALPH , BERARD M. F.
Published: June 2006

Interdiffusion coefficients were determined in single‐crystal (Ca,Sr)F2 solid solutions in the temperature range 1100° to 1320°C. The composition dependence of the coefficients passes through a maximum that shifts toward higher CaF2 concentrations at higher temperatures. Extrapolation of the interdiffusion coefficient to extremes of composition provides impurity diffusion coefficients that agree well with tracer results. The changes in activation energy with composition can be explained readily on the basis of cationic radii and lattice parameters.
Surface‐Diffusion Theory for Drying Creep Effect in Portland Cement Paste and Concrete
Authors: BAŽANT ZDENĚK P. , MOSCHOVIDIS ZISSIS
Published: June 2006

An attempt is made to introduce quantitative analysis into the complex problems of the mechanism of drying creep in cement paste. The main source of creep is assumed to be the change in thickness of hindered adsorbed water layers caused by diffusion of water, coupled with diffusion of solids dissolved from the confining adsorbent particles. The basic equations of equilibrium and irreversible thermodynamics governing the problem are formulated, reduced to an initial‐boundary value problem, and solved numerically. Computer studies have indicated that the drying creep effect is very likely caused by nonlinear coupling between the diffusion of water and that of solids in the hindered adsorbed layers.
Plastic Deformation of Al2O3During Abrasion
Authors: CUTTER I. A. , McPHERSON R.
Published: June 2006

X‐ray diffraction line broadening examination of the debris produced by abrasion of polycrystalline Al2O3on a 320‐grade diamond‐impregnated lap showed that heavy plastic deformation is associated with the abrasive process. Annealing of the debris resulted in an increase in crystallite size at temperatures >800°C but only minor changes in microstrain. This behavior contrasts with the large reduction in microstrain reported for ball‐milled Al2O3with similar initial crystallite size. The results are consistent with recovery during formation of the debris particles. A transient temperature of 900° to 1200°C was estimated from the plastic work done, assuming that material is removed by a mechanism similar to that observed in the abrasion of metals.
Effect of Minor Third Components on Metastable Immiscibility Boundaries of Binary Glasses
Authors: TOMOZAWA MINORU , OBARA RICHARD A.
Published: June 2006

An equation was derived which relates the change in the metastable immiscibility temperature, ΔTm, caused by a minor third component and the corresponding liquidus temperature change, ΔTl. This relation is expressed as

image

where Tm and Tl are the initial immiscibility temperature and liquidus temperature, respectively, S is the entropy of binary liquid, and ΔS is the change in the configurational entropy. For a qualitative estimate, the relation ΔTm∼ΔTl is satisfactory. To evaluate the above equation quantitatively, the entropy must be known. The entropy equation of Charles based on the number of nonbridging oxygen pairs and bridging oxygen atom was used and a reasonable estimate was made of the change of the immiscibility temperatures for selected systems.
Review of Thermodynamic Properties of the Cr‐N System
Authors: DE LUCA J. P. , LEITNAKER J. M.
Published: June 2006

Existing thermodynamic data for the Cr‐N system were analyzed. High‐temperature heat contents measured by Sato were reevaluated, and the heat capacity of Cr2N was determined to be 15.05+6.58×10−3T (°K) and that of CrN 11.10+ 1.58×103T. Using these heat capacities and an estimated ΔS°298, f of 20×1 cal/°K‐g atom N for the formation of the nitrides, second‐ and third‐law calculations for all available vapor‐pressure data were made. The two calculations agreed very well for the data of Mills. The heats of formation of Cr2N and CrN are ‐31.8×1.0 and ‐28.4×1.5 kcal/mol, respectively. A partial phase diagram of the Cr‐N system is presented.
Effect of Oxygen Partial Pressure on the Creep of Polycrystalline Al2O3 Doped with Cr, Fe, or Ti
Authors: HOLLENBERG GLENN W. , GORDON† RONALD S.
Published: June 2006

Steady‐state creep was studied in hot‐forged polycrystalline Al2O3 (3 to 42 μm) of nearly theoretical density doped with≤1 cation % of Fe, Ti, or Cr. Tests were conducted at stresses between 10 and 550 kg/cm2 at 1375° to 1525°C under O2 partial pressures of 0.88 to 10−10 atm. Except in the 10‐μm Fe‐doped material tested at very small stresses, slightly nonviscous creep behavior was generally observed. The effects of Po2 on the creep rate indicated that increased concentration of a divalent (Fe2+) or quadrivalent (Ti4+) impurity in solid solution enhances the creep rate of polycrystalline Al2O3. The activation energies for the creep of Fe‐ and Ti‐doped Al2O3 samples (148 and 145 kcal/mol, respectively) were significantly higher than that for Cr‐doped material (114 kcal/mol). Taking into account the effects of Po2, temperature, and grain size, it was concluded that the steady‐state creep of transition‐metal‐doped Al2O3 is controlled by cation lattice diffusion.
Slip Systems in Al2O3
Authors: SNOW J. D. , HEUER A. H.
Published: June 2006

Crystallographic notation for Al2O3 is reviewed, with particular reference to the correct basis to be used in describing slip systems. A Groves‐and‐Kelly calculation showed that the combination of pyramidal slip on {11¯02}<11¯01> and basal slip on (0001){112¯0} will allow homogeneous deformation of Al2O3 polycrystals. Furthermore, operation of either the {101¯1}<1¯011> or the {011¯2}<2¯021> slip system will also satisfy the Von Mises criterion, since each system is capable of 5 independent deformation modes. Electron microscopy of an Al2O3 polycrystal deformed ≅5% at 1150°C under a hydrostatic confining pressure confirmed that pyramidal slip had occurred.
Model for the Deformation of Hyperstoichiometric UO2
Authors: YUST C. S. , McHARGUE C. J.
Published: June 2006

The results of deformation studies of stoichiometric and hyperstoichiometric uranium dioxide single crystals are briefly reviewed. The observed differences in slip system and dislocation substructure are rationalized in terms of a proposed model for the deformation of hyperstoichiometric single crystals.
Use of the Notched‐Beam Test for Evaluation of Fracture Energies of Ceramics
Authors: SIMPSON L. A.
Published: June 2006

The mathematical analysis of the notched‐beam specimen for fracture‐energy determination considers a beam containing a zero‐volume crack, i.e. a crack with zero width. Such a configuration is difficult to reproduce in practice with ceramics, and artificially cut notches with widths large relative to the scale of the ceramic microstructure are usually used. Evidence is presented which suggests that incorrect results can be obtained using such notches even when real cracks exist at the notch root. The effects of notch width and depth are examined for Al2O3, graphite, and SiC. A tentative specification of a root‐crack‐notch‐radius relation is proposed for the application of this technique to ceramics.
Application of Iterative Deconvolution Technique to Ion‐Exchange Study of Glass
Authors: VARSHNEYA A. K. , MENCIK Z.
Published: June 2006

Potassium profiles measured with an electron microprobe along a normal to the surface of chemically strengthened sodium borosilicate glass were deconvoluted to correct for the finite resolution (∼3 μm) of the microprobe. The deconvolution procedure was conducted using a modified iterative Fourier technique and an experimentally measured “beam function.” The latter measurement constituted the most important source of error, particularly since the beam function is influenced by density variations near the interface of the glass specimen and its mount. Marked improvements over results obtained using a constant beam function resulted when an empirical variable beam function was included in the deconvolution procedure.
Defect Structure of Ta2O5
Authors: STROUD J. E. , TRIPP W. C. , WIMMER J. M.
Published: June 2006

Electrical conductivity, thermoelectric power, and weight change were measured for polycrystalline Ta2O5 from 900° to 1400°C. The predominant ionic and electronic defects in this temperature range are oxygen vacancies and electrons. The oxygen‐vacancy and electron mobilities are 8.1 × 103exp (−1.8 eV/kT) and ∼0.05 cm2/V‐s, respectively. At O2 partial pressures near 1 atm, the ionic‐defect concentration is essentially fixed by the presence of lower‐valence cation impurities, and the total electrical conductivity is predominantly ionic, whereas at low Po2's the conductivity is electronic and proportional to PPo2−1/6.
Thermodynamics of the System Cu‐O and Ruby Formation in Borate Glass
Authors: BANERJEE SUBRATA , PAUL A.
Published: June 2006

The CuO‐Cu2O and Cu2O‐Cu equilibria in glass solution were studied in 30Na2O 70B2O, and 25Na2O · 10Al2O3· 65B2O3 glasses at varied partial pressures of O2 and temperatures. The CuO‐Cu2O equilibrium was studied in a Pt crucible atpO2= 1 to 0.05 atm with ∼0.5 wt% Cu; the Cu2O‐Cu equilibrium was studied in Cu crucibles at much lower pO2's (10−14 to 10−17 atm), where no detectable amount of CuO was present. Plots of log [CuO]/[Cu2O]1/2) and log ([Cu2O]1/2/[Cu]) (where the brackets designate concentrations in glass solution) vs log pO2 gave best‐fit lines having slopes of ∼ 1/4. From the variation of the equilibrium constant with temperature, the enthalpies of the reactions °Cu2O(glass soln) + 1/4 O2 (g)→ CuO(glass soln) and Cu(glass soln)1/4 O2(g)→ Cu2O(glass soln) in the glasses were estimated to be − 14.57 and − 54.34 kcal/mol, respectively; these values are near the data for isolated Cu‐O systems. The enthalpy for the solution of Cu in glass was estimated to be + 23.7 kcal/mol. On heat treatment, the best ruby was formed in glasses melted at pO2= 10−14 atm; at higher pO2's no ruby was formed, and at pO2≤10−15 the glass produced progressively poorer rubies. Using the thermodynamic data estimated for the system Cu‐O in glass, possibilities for the precipitation of pure solid Cu and Cu2O are discussed. It was shown that Cu2O is primarily responsible for the bright red ruby color in glass.
Ion Depletion of Glass at a Blocking Anode: I, Theory and Experimental Results for Alkali Silicate Glasses
Authors: CARLSON D. E.
Published: June 2006

A theory is presented for the ion depletion of glass beneath a blocking anode. The theoretical model is based on the assumption that the alkali ions in an alkali silicate glass have a much greater mobility than the nonbridging oxygen ions in the alkali‐depleted region. In this case, the dc conduction properties of the glass are determined by the motion of the uncombined oxygen ions in the depleted region. Expressions are derived for the spatial variation of the uncombined oxygen ions and for the current‐voltage relations in the high‐ and low‐field limits. In the high‐field limit, the theory predicts that the current will vary exponentially with the voltage; this behavior is shown in sodium silicate glasses.
Subcritical Crack Growth in Vitreous Carbon at Room Temperature
Authors: NADEAU J. S.
Published: June 2006

The velocity of crack propagation was measured as a function of stress intensity in vitreous carbon at room temperature. The double‐torsion technique was used. In one vitreous carbon, the relation between crack velocity and stress intensity wasimageIn another vitreous carbon, repeated crack arrest prevented determination of the V‐K1dependence. Vitreous carbon in air is virtually immune to static fatigue, compared with soda‐lime glass in air. The ratio of times to failure when the materials are loaded to equal fractions of the critical stress intensity is log (τvc/τsly)≃33. In addition to subcritical crack growth, other fracture mechanical properties, e.g. the modulus of rupture and critical stress intensity factor, were measured. These measurements confirmed the presence of a compressive surface layer on vitreous carbon.
Thermal Expansion of Beta Eucryptite
Authors: SCHULZ H.
Published: June 2006

The axial thermal expansion coefficients of 2 samples of β‐eucryptite were measured. At room temperature one sample showed an ordered distribution and the other a disordered distribution of the Al, Si, and Li atoms. The thermal expansion of the axes and the cell volume are explained in terms of a temperature‐dependent dynamic disorder process of the Li atoms.
Influence of Cr and Fe on Formation of α‐Al2O3 from γ‐Al2O3
Authors: BYE G. C. , SIMPKIN G. T.
Published: June 2006

The effect of Cr and Fe in solid solution in γ‐Al2O3 on its rate of conversion to α‐Al2O3 at 1100°C was studied by X‐ray diffraction. The δ form of Al2O3 was the principal intermediate phase produced from both pure γ‐Al2O3 and that containing Fe3+ in solid solution, although addition of Fe greatly reduced crystallinity. Reflectance spectra and magnetic susceptibilities showed that Cr exists as Cr6+ in γ‐Al2O3 and as Cr3+ in α‐Al2O3, with θ‐Al2O3 as the intermediate phase. The intermediates formed rapidly, and the rates of their conversion to α‐Al2O3 were increased by 2 and 5 wt% additions of Fe and decreased by 2 and 4 wt% additions of Cr. An approximately linear relation observed between α‐Al2O3 formation and decrease in specific surface area was only slightly affected by the added ions. This relation can be explained by a mechanism in which the sintering of δ‐ or θ‐Al2O3, within the aggregates of their crystallites, is closely coupled with conversion of cubic to hexagonal close packing of O2‐ ions by synchro‐shear.
Polymer Mixtures in Na2O.Sb2O3.GeO2 Glasses
Authors: RIEBLING E. F.
Published: June 2006

Ternary Na2O.Sb2O3.GeO2 glasses (with various [Na]/[Na + Sb] ratios) that contained ≥65 mol% GeO2 were prepared. Their densities (volumes), refractive indices, and infrared spectra were determined and their colors noted. The ternary glasses with ≥88 mol% GeO2 exhibit nearly additive volumes, refractivities, and frequencies for the main Ge‐O vibration. Ternary glasses with lesser amounts of GeO2 exhibit a variety of behaviors, depending on the [Na]/[Na + Sb] ratio. Small amounts of Sb2O3 cause significant volume and refraction deviations, as well as changes in νGe‐O, that can be associated with gradual elimination of GeO6 octahedra. All the information supports a model for the glasses with 65 to 88 mol% GeO2 that involves a degree of depolymerization that is greater when Na2O and Sb2O3 are present together than when either is present alone.
Dislocation Structures in Sapphire Deformed by Basal Slip
Authors: PLETKA B. J. , MITCHELL T. E. , HEUER A. H.
Published: June 2006

Dislocation structures in sapphire deformed by basal slip at 1200° to 1500°C were studied by transmission electron microscopy. Long dislocation dipoles of edge character are formed by interactions of dislocations on parallel basal planes (“edge‐trapping”); screw dislocations annihilate by cross‐slip. The accumulation of dislocation dipoles leads to work‐hardening, but the dipoles also break up into smaller loops by climb, causing recovery. Eventually a steady state of zero work‐hardening is reached, where the rate of accumulation of dipoles by edge‐trapping is equal to their rate of annihilation by climb. From these observations, it is suggested that dislocation climb plays an important role in the deformation process for basal slip in the range 1200° to 1500°C.
Thermodynamics of CuAlO2 and CuAl2O4 and Phase Equilibria in the System Cu2O‐CuO‐Al2O3
Authors: JACOB K. T. , ALCOCK C. B.
Published: June 2006

The standard Gibbs free energies of formation of CuAlO2 and CuAl2O4 were determined in the range 700° to 1100°C, using emf measurements on the galvanic cells (1) Pt,CuO +] Cu2O/CaO‐ZrO2/O2,Pt; (2) Pt,Cu +] CuAlO2+] Al2O3/CaO‐ZrO2/ Cu +] Cu2O,Pt; and (3) Pt,CuAl2O4+] CuAlO2+]Al2O3/CaO‐ZrO2/O2,Pt. The results are compared with published information on the stability of these compounds. The entropy of transformation of CuO from tenorite to the rock‐salt structure is evaluated from the present results and from earlier studies on the entropy of formation of spinels from oxides of the rock‐salt and corundum structures. The temperatures corresponding to 3‐phase equilibria in the system Cu2O‐CuO‐Al2O3 at specified O2 pressures calculated from the present results are discussed in reference to available phase diagrams.
Phase Equilibria in the System MgO‐B2O3
Authors: MUTLUER T. , TIMUCIN M.
Published: June 2006

Phase equilibria in the system MgO‐B2O3 were investigated using DTA and quenching techniques. The system contains 4 invariant points. The compounds MgO·2B2O3 and 2MgO·B2O3 melt incongruently at 995° and 1312°C, respectively, whereas 3MgO·B2O3 melts congruently at 1410°C. A eutectic occurs at 1333°C and 71% MgO.
Sodium Diffusion in Glass: II, Mixed Na‐K Silicate Glasses
Authors: LIM CHUNG , DAY DELBERT E.
Published: June 2006

The isotope effect for 22Na/24Na diffusion was used to investigate the sodium ion transport mechanism in mixed Na‐K silicate glasses. A combined vacancy‐interstitialcy mechanism provided the best agreement with the experimental 22Na/24Na isotope effect data. At low temperatures sodium diffusion occurs predominantly by 2‐atom interstitialcy jumps, but with increasing temperature an increasing fraction of the ions diffuse by a single‐atom vacancy mechanism.
Heat Transfer and Temperature Control in an Annealing Lehr for Float Glass
Authors: CHUI GRANGER K.
Published: June 2006

This paper presents an analytical model of a float glass annealing lehr, considering radiation between the moving ribbon and its enclosure and the convection of gas in a flue system. Results illustrate the use of mathematical modeling to improve design and operation. A linear algorithm, verified by “computer experiments,” is proposed for on‐line temperature control.
Coefficient of Thermal Expansion and Dynamic Response to Pulsed Energy Deposition in HfO2‐TiO2 Compositions
Authors: CARLSON G. A. , ANDERSON J. L. , BRIESMEISTER R. A. , SKAGGS S. R. , RUH ROBERT
Published: June 2006

The coefficient of thermal expansion and the dynamic response to pulsed energy deposition were investigated in the 25 to 60 mol% TiO2 region of the system HfO2‐TiO2. Thermal expansion results revealed very low coefficients (≅1 × 10−6/°C) for the 30 to 40% compositions and relatively high coefficients (≅3 × 10−6/°C) for the 45 to 60% TiO2 compositions. The 25% TiO2 composition fell between these two groups. Dynamic response measurements revealed considerably lower free surface velocities for the 30 to 40% TiO2 compositions than for the 45 to 50% TiO2 compositions. Calculation of Grueneisen parameters, using the thermal expansion and dynamic response data, revealed low values for the 30 to 40% TiO2 compositions and an increase by a factor of 2 to 3 for the 45 and 50% TiO2 compositions.
Phase Equilibria in the System Li2O‐BeO‐SiO2
Authors: QUINTANA PATRICIA , WEST A. R.
Published: June 2006

The equilibrium phase diagram for the system Li2O‐BeO‐SiO2 contains only one ternary compound, Li2BeSi04. Liquidus relations for compositions containing 33 mol% SiO2 were determined; 10 liquidus invariant points were located and 7 subsolidus compatibility triangles. The most refractory compositions lie on the join BeO‐Li2BeSiO4, with a solidus temperature of 1320°C. Metastable phases observed were a high‐quartz phase, Li2x(Si1‐xBex)O2, x 0.33; phase X which is probably a metastable orthosilicate between Li2BeSiO4 and Be2SiO4; and phase Y which lies on the join Li2BeSiO4‐SiO2. The crystal chemistry and glass network‐forming properties of BeO are discussed.
Microstructure and Kinetics of Crystallization of MgO‐Al2O3−Si02Glass‐Ceramics
Authors: ZDANIEWSKI WIESLAW A.
Published: June 2006

Quantitative X‐ray diffraction and microscopy were used to study the morphology development and overall crystallization rate between 900° and 990°C of MgO‐Al2O3−SiO2glasses with added ZrO, TiO2, CaF2, or CeO2. Three basic stages of micro‐structural development were distinguishable: I, an induction period, II, a spherulitic crystallization stage, and III, a final crystallization stage. The duration of the induction period, the crystallization rate of the high‐quartz solid solution, and the microstructures varied markedly with prior nucleation treatment and the type of modifier present in a glass of nearly equal silica content. The roles of major (high‐quartzss, high cordierite) and of minor crystalline and liquid phases in textural development are discussed, and it is postulated that nucleants (ZrO2, TiO2) act also as growth‐modifying “impurities” in crystal growth.
Dynamic Fatigue of Float Glass
Authors: CHANDAN H. C. , BRADT R. C. , RINDONE G. E.
Published: June 2006

The dynamic fatigue Of bulk float glass was measured Over a wide range of stressing rates. The results are compared with theoretical predictions based on integration of (K1, V) diagrams. It is thought that there are distinct differences in the growth of microcracks and macrocracks in glass, particularly with regard to the region of transport control.
Kinetics of Sicl4 Oxidation
Authors: POWERS D. R.
Published: June 2006

The oxidation rate of SiCl4was studied at 1100° to 1300°C. The reaction was first order in SiCl4and zero order in O2up to a 20‐fold excess of O2. At higher O2concentrations, the reaction becomes first order in oxygen. The activation energy for the reaction was 96 ± 5 kcal/mol which is approximately the CI3SiCI bond energy. The reaction SiCl4→ SiCl3+ Cl is proposed as the rate‐determining step.
Microstructure of Mature Alite Pastes
Authors: MARCHESE BERNARDO
Published: June 2006

Tricalcium silicate and Fe‐bearing alite pastes hydrated 4 years and portland cement paste hydrated 33 days were studied by SEM, TG, and XRD. SEM studies of the effect of water, NaCl, and MgSO4 solutions on the microstructure of alite are reported. The characteristics of the attack were clarified by examining both sides of the fracture plane. The Ca(OH)2 phase present in the fresh fracture surface is very unstable toward water, NaCl, and MgSO4 solutions. When exposed to MgSO4 solution the Ca(OH)2 reacts, producing Mg(OH)2 and CaSO4·2H2O. The C‐S‐H gel phase is more resistant to the various reactants. The presence of calcite, aragonite, and Ca(OH)2 and their proportion in the surface layer depend on the characteristics of the environment.
Weakest Link Theory Reformulated for Arbitrary Fracture Criterion
Authors: BATDORF S. B. , HEINISCH H. L.
Published: June 2006

A primary objective of statistical fracture theory is to predict the probability of failure for an arbitrary stress state when the failure statistics are known for a particular stress state, e.g. simple tension. It is proved that a rule for accomplishing this (given without proof by Weibull) is valid for shear‐insensitive cracks, i.e. on the assumption that only the component of stress normal to a crack plane contributes to its fracture. Four failure criteria for shear‐sensitive cracks are considered and the results are compared with test data.
Yttria Hydroxy‐Salt Binders
Authors: HOLCOMBE C. E.
Published: June 2006

Binder phase (primarily chloride or nitrate) formation was examined in YX3‐NaOH‐H2O, Y2O3‐acid‐H2O, and Y2O3‐salt‐H2‐O systems. The cementitious phase consisted mostly of plate‐ (or needle‐) shaped hydroxy salts of the general formula Y2(OH)6‐m XmnH2O, where m and n normally equal one. These binders were examined by X‐ray diffraction and thermal analysis techniques. Nitrate binders decompose to Y2O3 by 600°C, whereas chloride binders form oxychlorides that sublime or convert to Y2O3 after oxygen replacement of chlorine (in air) at >1000°C. Although nitric and hydrochloric acid solutions form porous (< 50% dense) plasterlike bodies in 2 to 10 min of reaction with Y2O3 powder, salt solutions (i.e. NH4NO3 Mg(NO3)2, NH4Cl, and YCl3‐ ∼6H2O) slow the reaction considerably (48 h to 4 weeks), allowing 70‐ to 80%‐dense cements to form. The effects of formation conditions on physical properties of binders were studied. Examination of scandium and lanthanide oxides showed that several behave in the same way as yttria.
Characterization of Organosilicon‐Infiltrated Porous Reaction‐Sintered Si3N4
Authors: MAZDIYASNI K.S. , WEST ROBERT , DAVID LARRY D.
Published: June 2006

Polymeric organosilicon compounds such as hexaphenylcyclo‐trisilazane and methylphenyl polysilane were used to infiltrate porous reaction‐sintered silicon nitride. The in situ thermal decomposition of the infiltrated body under controlled atmosphere and temperature resulted in pronounced changes in the microstructure, increased densities, and significantly improved room‐temperature strength. The silicon oxynitride phase present in some as‐received materials is eliminated and the ratio of α‐ to β‐phase silicon nitride increases during infiltration processing
Phase Equilibria in the System LiF‐AlF3‐Na3AlF6‐Al2O3
Authors: CASSIDY ROGER T. , BROWN JESSE J.
Published: June 2006

The phase equilibria relations in the binary system Li3AlF6‐A12O3, the ternary system Li3AlF6‐Na3AlF6‐Al2O3, and the quaternary system LiF‐AlF3‐Na3AlF6‐Al2O3 were investigated using a combination of X‐ray powder diffraction, DTA, quenching, and optical microscopy techniques. The compatibility relations at 500°C for these systems and for the ternary liquidus surface were determined. The binary system had a eutectic at 754°C and 1 mol% A12O3. The ternary liquidus surface contained a eutectic at 66 mol% Li3AlF6, 29 Na3AlF6, 5 A12O3, and 670°C, a peritectic at 51 mol% Li3AlF6, 42.5 Na3AlF6,65 A12O3, and 683°C, and a reaction point at 65 mol% Li3AlF6, 33 Na3AlF6, 2 A12O3, and 693°C. The 500°C ternary isothermal section contains one 2‐phase and three 3‐phase regions. The quaternary system contains seven compatibility tetrahedra at 500°C.
X‐Ray Characterization of Sr3SiAl10O20 and Ba3SiAl1()O20 and Luminescence Properties on Activation with Ce3+
Authors: KONIJNENDIJK W. L. , VERLIJSDONK J. G. , van de SPUKER W. H. M. M. , BOOGERD G. M.
Published: June 2006

THE existence of a compound with the formula Sr6Si2Al18O37 was reported by Dear.1 The unindexed powder diffraction pattern of this compound is listed as ASTM No. 10–25. In this note we present evidence that the composition of this phase is Sr3SiAl10O20 rather than Sr6Si2Al18O37. We report the indexed powder diffraction pattern and give some luminescence data for activation with Ce3+. Cell parameters of other new compounds with a structure related to that
Mechanisms of Dentification During Reaction Hot‐Pressing in the System Si‐Al‐O‐N
Authors: RAHAMAN M. N. , RILEY F. L. , BROOK R. J.
Published: June 2006

Three powder compositions near the β'‐sialon phase (Si6‐zAl2OzN8‐z) were hot‐pressed at 1963 K and pressures of ∼7 to 35 MPa. The compositions, having z values near 0.75, were prepared from mixtures of α‐Si3N4, Al2O3, and AIN. It is shown that two processes operate sequentially during hot‐pressing. For compositions with the most grain‐boundary phase, the densification rate at a given density, (dp/dt), increases linearly with the applied stress, cr. For the composition with the least grain‐boundary phase, the rate could be described by the equation (dp/dt)∞(σ‐σ0)2, where σ0 is a threshold stress which varies with density and the powder composition. For the composition with an intermediate amount of grain‐boundary phase, the rate varies as (σ‐σ0)2 below ∼20 MPa and increases linearly with σ above 20 MPa. The two processes are interpreted in terms of grain‐boundary sliding limited by a threshold stress and a liquid‐phase solution‐diffusion‐reprecipitation process.
Compressive Strength of Low‐Porosity Hydrated Portland Cement
Authors: RELIS M. , SOROKA I.
Published: June 2006

Theoretical considerations and test data indicate that, in the low‐porosity range, the strength of set cement can be better predicted from its Whp*×Gc*IPf ratio than from its porosity or gel concentration; in this range (Pf=0.16 to 0.28), therefore, the ratio in question constitutes a more basic and general strength‐determining factor. At advanced stages of hydration, however, the set cement is stronger than can be expected from its Whp*×Gc*/Pf ratio, apparently due to aging effects.
Analysis of Effect of Heat‐Transfer Variables on Thermal Stress Resistance of Brittle Ceramics Measured by Quenching Experiments
Authors: SINGH★ J. P. , THOMAS J. R. , HASSELMAN★ D. P. H.
Published: June 2006

Heat‐transfer theory was used to analyze the variables which control the thermal stress fracture of brittle ceramic specimens subjected to rapid cooling by quenching into fluid media. Expressions were derived for the maximum quenching temperature difference to which circular solid cylindrical specimens can be subjected in terms of the pertinent properties of the material and fluid media. Appropriate thermal stress resistance parameters were derived. The specimen density was introduced as an additional property which controls thermal stress resistance. Recommendations were made for procedures to be followed in conducting quenching experiments.
Fractographic Criteria for Subcritical Crack Growth Boundaries in 96% Al2O3
Authors: KIRCHNER H. P. , GRUVER R. M.
Published: June 2006

The percent intergranular fracture (PIF) was measured along radii extending from fracture origins in 96% A12O3 specimens, fractured at various loading rates and temperatures, and plotted vs estimates of stress intensity factors (K1) at the corresponding crack lengths. Two types of curves were observed. The first was similar to curves previously observed for hot‐pressed alumina. In this case the subcritical crack‐growth boundary was located approximately where the minimum in the PIF occurred near K1=4MPa·m½, as was also the case for hotpressed alumina. Therefore, the location of this minimum or the projecting grams formed by intergranular fracture as the crack velocity increased can be used as criteria for locating the subcritical crack‐growth boundary. The second type of curve lacks the minima in PIF characteristic of the first type and is characterized by a gradual trend toward higher PIF beginning at K1=3MPa·m½. This type of curve may be caused by acceleration of the crack to high crack velocities at values of K1 approximately equal to or slightly greater than those necessary to cause critical crack growth on the lower fracture‐energy planes in sapphire. Assuming that this is the case, the K1 at which the trend toward higher PIF begins can be used to calculate the radius to the critical flaw boundary for this type of fracture.
States of Sulfur in Alkali Borate Glasses
Authors: AHMED A. A. , El‐SHAMY T. M. , SHARAF N. A.
Published: June 2006

Simple binary alkali borate glasses of differing alkali content (alkali = Li, Na, or K) containing sulfur were prepared and their absorption spectra were measured in the range of 200 to 700 nm. The absorption bands obtained were used to determine the stable states of sulfur in these glasses by directly comparing them with published data. The following states of sulfur were identified and their ranges of stability were determined: the S2 molecule in glasses containing at least 15 mol% alkali oxide, the S3− and S2− in glasses containing 20 to 30 mol% Na2O or K2O, and the polysulfide ion (Sx2−) in glasses of 30 to 35 mol% Na2O or K2O.
Grain‐Boundary Diffusion of 60Co and 51Cr in NiO
Authors: CHEN W. K. , PETERSON N. L.
Published: June 2006

Grain‐boundary diffusion of 60Co and 51Cr in bicrystals and polycrystals of NiO was measured at temperatures <0.6 Tm at various equilibrium oxygen partial pressures, using a tracer‐sectioning technique. Values of D′δ were obtained using the Whipple and Suzuoka analyses. The results show that, for both 60Co and 51Cr, grain‐boundary‐enhanced diffusion is observed and the temperature dependence of D′δ is about the same as that of the respective bulk diffusivity,/). The effects of equilibrium oxygen partial pressure and the type of gram boundary on D′δ are not detectable within experimental error.
Acoustic Emission in the Fracture of Glass Plates
Authors: NADEAU JOHN S.
Published: June 2006

The ring‐down counting method was used to measure acoustic emission (AE) during the subcritical cracking of float‐glass plates. It was found that AE emanated primarily from surface flaws and that a flaw =4 μm deep was capable of producing one AE count. The dependence of AE count rate on experimental parameters such as system gain and specimen size was determined and the use of AE simulators for calibrating AE systems was examined. The results were used to show how data on different ceramic materials might be compared.
The Intergranular Phase in Hot‐Pressed Silicon Nitride: I, Elemental Composition
Authors: CLARKE D.R. , ZALUZEC N. J. , CARPENTER R. W.
Published: June 2006

The elemental composition of the noncrystalline intergranular phase in two MgO‐fluxed hot‐pressed silicon nitrides, determined by X‐ray microanalysis and electron energy loss spectroscopy in the transmission electron microscope, is reported. The composition is similar in both and lies near the SiO2‐MgSiO3 tie line with impurities of Ca, Al, and Cl. No nitrogen could be detected in the noncrystalline phase, implying that the nitrogen concentration was below the experimental detectability limit.
The Intergranular Phase in Hot‐Pressed Silicon Nitride: II, Evidence for Phase Separation and Crystallization
Authors: CLARKE D. R. , ZALUZEC N. J. , CARPENTER R. W.
Published: June 2006

Compositional and morphological evidence obtained using transmission electron microscopy is presented indicating that the noncrystalline phase in a hot‐pressed silicon nitride can undergo phase separation. The compositional range determined for the phase separation is close to the known miscibility gap in the pseudobinary system SiO2‐MgO. Crystallization of Si2N2O and MgSiO3 from the noncrystalline phase is also evident, suggesting that it can contain some dissolved nitrogen and that the intergranular phase may be crystallizable.
Thermoelectric Study of Cobaltous Oxide Defect Structure
Authors: Chen H.‐C. , Mason T. O.
Published: June 2006

The thermoelectric coefficient of cobaltous oxide was measured as a function of temperature and oxygen activity between 1000° and 1400°C. Results conform to ideal point defect theory at high temperature and high oxygen activity. Minority electrons are detected near the low‐oxygen activity phase boundary. At low temperature and high oxygen activity, deviations from ideality are detected in that oxygen exponents of the hole concentration exceed that predicted by Ideal point defect theory.