bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of a Fundamental Approach for the Statistical Analysis of Fracture
Authors: EVANS A. G. , JONES R. L.
Published: June 2006

Generalized relations between the strength distribution function and derivatives of the fracture probability are developed for five widely used testing methods for measuring the strengths of ceramic materials. The derived relations for three of these methods are used to analyze room‐temperature fracture strength data for hot‐pressed silicon nitride. Fracture of this material is shown to be controlled by internal flaws at strength levels up to and including the range where the tensile and flexural distributions overlap, but it is primarily surface‐flaw‐controlled toward the upper end of the flexural distribution.
Analysis of Localized Impact Damage in Biaxially Stressed Glass Plates
Authors: KIRCHNER H. P.
Published: June 2006

A fracture mechanics method was used to estimate the impact loads necessary to cause penetration of damage to various depths in glass plates stressed biaxially to several levels. Velocities of glass spheres necessary to obtain these impact loads were calculated using Hertzian theory. Penetrations estimated for given impact velocities were compared with experimental values; those resulting from impacts on compressively stressed surfaces were much smaller than those caused by impacts on tensile surfaces.
Characterization of the Thermally Contracting Tungstates Ta22W4O67, Ta2WO8, and Ta16W18O94
Authors: HOLCOMBE C. E. , SMITH D. D.
Published: June 2006

An investigation of the properties of high‐purity (>99 wt%) tantalum tungstates (Ta22W4O67, Ta, WO8, and Ta16W18O94) included determination of density (bulk and theoretical), refined lattice constants, maximum use temperatures, micro‐hardness, heat capacity, thermal expansion (contraction) and diffusivity, calculated thermal conductivity, and electrical resistivity. Usable to ∼ 1700 K in air or inert atmospheres, these tantalum tungstates have theoretical densities of 7.3 to 8.5 g/cm3, are relatively soft (120 to 655 kg/mm2 hardnesses), and are electrical insulators (6× 103 to 2× 108Ω.cm resistivities). The distinguishing properties of the materials are their thermal expansion (average CTE values from + 0.6×10−8/K to −5.1× 10−6/K at 293 to 1273 K), thermal expansion hysteresis with minimal observable microcracking, and thermal diffusivity
Reexamination of the Kaolinite‐to‐Mullite Reaction Series
Authors: CHAKRABORTY A. K. , GHOSH D. K.
Published: June 2006

The kaolinite‐to‐mullite reaction series was reexamined with special attention to the nature of the metaphase, the eontroversial spinel phase, and the cause of the exothermic peak at 980°C. Amorphous SiO2 forms during the exothermic reaction; it can be leached by alkali extraction. When the residual cubic phase is heated further, it forms mullite only. This result indicates that the cubic phase is an Al‐Si spinel and that metakaolinite is an AI2O3‐SiO2 compound. It was established that the exotherm exhibited by kaolinite at 980°C represents the sudden transformation of metakaolinite to Al‐Si spinel, the crystallization of mullite, and the liberation of amorphous SiO2. The AI‐Si spinel has the same composition as mullite, containing both AI(IV) and AI(VI). This spinel transforms into mullite at the second exothermic peak; no amorphous SiO2 is liberated.
Impurity Phases in Hot‐Pressed Si3N4
Authors: LOU L. K. V. , MITCHELL T. E. , HEUER A. H.
Published: June 2006

Impurity phases in commercial hot‐pressed Si3N4 were investigated using transmission electron microscopy. In addition to the dominant, β‐Si3N4 phase, small amounts of Si2N2O, SiC, and WC were found. Significantly, a continuous grain‐boundary phase was observed in the ∼ 25 high‐angle boundaries examined. This film is ∼ 10 Å thick between, β‐Si3N4 grains and ∼ 30 Å thick between Si2N2O and β‐Si3N4 grains.
Insolubility of Mg in β‐Si3N4 in the System Al‐Mg‐Si‐O‐N
Authors: GAUCKLER L. J. , WEISS J. , TIEN T. Y. , PETZOW G.
Published: June 2006

Solid‐solution formation of magnesium in β‐Si3N4 containing AlN:Al2O3 was investigated. Samples were hot‐pressed at 1700°C. Under the condition studied, very little or no magnesium entered the β‐Si3N4 lattice.
Volume and Grain Boundary Diffusion of Hf in Polycrystalline Er2 O3
Authors: SCHEIDECKER R. W. , BERARD M. F.
Published: June 2006

Hafnium diffusion was measured in polycrystalline Er2O3 with two impurity levels. A tracer sectioning technique was used and the diffusion coefficients were measured at 1601° to 1970°C. Volume diffusion of Hf showed both extrinsic and intrinsic behavior, with the transition temperature increasing with the impurity level present in Er2O3. The grain boundary diffusion was apparently extrinsic over the entire temperature interval.
β→α Transformation in Polycrystalline SiC: I, Microstructural Aspects
Authors: HEUER A. H. , FRYBURG G. A. , OGBUJI L. U. , MITCHELL T. E. , SHINOZAKI S.
Published: June 2006

The effects of annealing conventionally sintered, hot‐pressed, and reaction‐sintered Sic have been investigated by optical and transmission electron microscopy. In conventionally sintered and hot‐pressed bodies, “composite” grains consisting of α‐SiC plates sandwiched between recrystallized β‐SiC envelopes grow rapidly into the fie‐grained β matrix; thickening of these α plates within the p envelopes is relatively sluggish. The existence of the composite plates can be explained by the extreme anisot‐ropy of the interfacial energy between β‐ and α‐Sic: {111)β(000l)αinterfaces have energies several orders of magnitude lower than random β/α interfaces. In reaction‐sintered Sic, this anisotropy is manifested by rapid growth of α seeds along their basal planes into the epitaxial β reaction product; slow growth occurs perpendicular to the basal planes.
Contact‐Induced Static Fatigue of Annealed and Tempered Glass
Authors: CHANTIKUL P. , MARSHALL D. B. , LAWN B. R.
Published: June 2006

The role of environmentally assisted crack growth in the contact‐induced strength degradation of brittle surfaces was studied. Indentation fracture mechanics, incorporating a standard crack‐velocity function, are used to predict remaining strength as a function of contact load and duration. Strength tests on annealed and tempered glass disks, indented with a diamond pyramid or tungsten carbide sphere in a water environment, are in accord with the predicted degradation characteristics. The results indicate that fatigue effects are likely to be of only secondary importance in designing for maximum resistance to in‐service contact damage.
Structural Anisotropy and Birefringence in Microporous Glasses
Authors: TAKAMORI TAKESHI
Published: June 2006

Microstructural birefringence was observed by immersing microporous glass specimens in liquids with various refractive indices. The sign of the birefringence may be positive or negative depending on the base glass compositions, with the optic axis parallel to the direction of materials transport during leaching. The magnitude of the birefringence varies systematically as a function of the refractive index of the immersing liquid and depends on heat‐treatment conditions of the base glass (possibly on soluble minor‐phase compositions) as well as on leaching conditions (e.g. leaching temperatures and acid concentrations). This birefringence can be erased by soaking the specimens in a dilute alkali solution. Scanning electron micrographs before and after soaking indicate that the birefringence is created by the structural anisotropy of SiO2 gels produced as decomposed deposits from the soluble minor phase within the cavity of the silica skeleton.
Chemical Durability of Na2O‐K2O‐CaO‐SiO2 Glasses
Authors: DILMORE M. F. , CLARK D. E. , HENCH L. L.
Published: June 2006

The mixed‐alkali effect on chemical durability was evaluated for bulk and powdered Na2O‐K2O‐CaO‐SiO2 glasses. Two contributions to this effect are discussed, i.e. those of glass structure and corrosion solution. The magnitude of the mixed‐alkali effect depends on the pH of the corroding solution. For pH<9, alkali‐ion leaching is the major mode of glass corrosion, and the mixed‐alkali effect is large. However, for pH≥9 congruent glass dissolution is the rate‐controlling corrosion mechanism, and the effect is diminished. When ion exchange is the rate‐controlling corrosion mechanism the magnitude of the mixed‐alkali effect depends on the extent of reaction. Since the kinetics of corrosion are influenced by the ratio of glass surface area to solution volume (SA/V), results obtained when this ratio is large may be misleading if extrapolated to smaller ratios. Physical evidence of the mixed‐alkali effect in bulk glasses was obtained using scanning electron microscopy and ir reflection spectroscopy.
Compositional Changes as Evidence for Spinodal Decomposition in Glass
Authors: TOMOZAWA MINORU
Published: June 2006

The phase separation of some borosilicate glasses shows the gradual approach of 2‐phase compositions to those of equilibrium. The change in the etch (or leaching) rate is caused by the gradual change in the alkali borate‐rich phase composition and the gradual change in viscosity is caused by the gradual change of silica‐rich phase composition. The gradual change of the 2‐phase compositions rejects the classical nucleation and growth mechanism and supports the transformation mechanism developed by Hillert and Cahn. Although the latter mechanism covers both spinodal decomposition and nucleation and growth, the observed gradual change of two compositions for glasses with initial compositions falling near the center of the immiscibility dome is direct evidence of spinodal decomposition
Solid Electrolytes with a Glass‐Like Structure
Authors: LAZZARI M. , SCROSATI B. , VINCENT C. A.
Published: June 2006

Solid electrolytes formed by a formal partial substitution of iodide in AgI by a variety of oxoanions may be prepared in the vitreous state by fast‐quenching from the melt. Such materials, with few exceptions, are metastable and undergo thermal transitions into poorly conducting phases below the melting point. The conductance of a glassy electrolyte of this class was studied as a function of temperature and frequency. Features such as curved Arrhenius plots and high‐frequency dispersion are compared with similar observations in molten salt systems and the basis of such behavior is discussed.
Diversion Resistance of a Chloride Volatility Reprocessing System for UO2/ThO2 Fuel
Authors: BULLARD J. E. , PETCHUL J. J.
Published: June 2006

A chloride volatility process is considered for reprocessing 233U‐Th fuel. Isotopes of high gamma activity or neutron capture cross section are designated. The behavior of these isotopes in the process is related to their chemical states in the spent fuel, the free energies of reaction with C12 and/or CC14, and the volatilities of the chlorides.
Effect of Spatially Varying Thermal Conductivity on the Magnitude of Thermal Stress in Brittle Ceramics Subjected to Convective Heating
Authors: SATYAMURTHY K. , SINGH J. P. , HASSELMAN D. P. H. , KAMAT M. P.
Published: June 2006

The effect of a spatial variation of the thermal conductivity on the magnitude of the maximum tensile thermal stress in a solid circular cylinder subjected to sudden convective heating was calculated by finite element methods. The general results show that by lowering the thermal conductivity in the surface region of the cylinder, the magnitude of the maximum tensile thermal stress at the center of the cylinder is reduced significantly. The negative temperature dependence of the thermal conductivity in dielectric materials, which indirectly creates a spatial variation in thermal conductivity, also causes a significant decrease in the magnitude of the tensile thermal stresses, as demonstrated by a numerical example for aluminum oxide. It is also shown that a spatial variation in thermal conductivity can significantly affect the time to maximum tensile stress as well.
The Pore Structure of Hydrated Cementitious Compounds of Different Chemical Composition
Authors: BENTUR ARNON
Published: June 2006

The pore structure ofβ‐C2S, C3S, and portland cement pastes was investigated using mercury porosimetry and H2O and N2 adsorption. The β‐C2S had more total macro‐ and mesoporosities than C3S and portland cement pastes of a similar degree of hydration. C3S and portland cement pastes had similar total porosities but differed in the porosity size distribution. In the mesopore range, the various test methods gave different results. These differences are discussed on the basis of the various models proposed for cement paste. It is shown that shrinkage could be correlated with the volume of pores <0.03 μm, but not with total porosity.
A Treatment of Inelastic Deformation Around a Crack Tip due to Microcracking
Authors: HOAGLAND R. G. , EMBURY J. D.
Published: June 2006

A numerical procedure is described for modeling the number and distribution of microcracks around a crack tip as a function of the applied stress intensity. The procedure accounts, approximately, for microcrack‐microcrack and microcrack‐crack interactions. Starting with an array of sites where microcracks can form, the model computes the generation rate of microcracks with increasing stress intensity. The interaction between several neighboring sites leading to extension of the main crack is also apparent and, as a result, an R curve emerges from the calculation. The effects of changing the nature of the microstructural variables inserted into the model can be examined; the results of several calculations with differing microstructural properties are compared. These variables include texture and the statistical distribution of strength over the microcrack sites. The results indicate that texture can strongly influence the slope of the R curve, and the calculations demonstrate that a positively sloped R curve can be produced by the operation of microcracking mechanisms.
Transient Stress Intensity Factors for Edge and Corner Cracks in Quench‐Test Specimens
Authors: EMERY A. F. , KOBAYASHI A. S.
Published: June 2006

The transient temperature and stress fields in a quenched rectangular bar were computed and used to determine the stress intensity factors for midside and corner‐edge cracks. The stress intensity factors, K1, are presented as a function of time, flaw size, and aspect ratio. The variations of AT, along the crack edge are given and the self‐limiting growth of the crack depth is discussed in relation to the nonlimited surface growth.
Deformation Behavior of Sapphire Via the Prismatic Slip System
Authors: KOTCHICK D. M. , TRESSLER R. E.
Published: June 2006

The deformation behavior of α‐axis sapphire in tension from 1550° to 1850°C was studied in constant strain‐rate, differential strain‐rate, and differential‐temperature tests. The crystals deformed via the prismatic system, , resulting in stress‐strain curves with a significant yield drop, a region of work‐hardening which decreased in magnitude with increasing temperature, and a region of constant flow stress. The deformation was inhomogeneous with irregularly spaced slip bands containing a high density of glide dislocations and also basal dislocation debris. The flow behavior did not conform to simple diffusional or Peierls‐process models but could be rationalized on the basis of the creation of a super saturation of vacancies generated by the motion of jogs on gliding screw dislocations.
Behavior of Bubbles in Glassmelts: II, Dissolution of a Stationary Bubble Containing a Diffusing and a Nondiffusing Gas
Authors: WEINBERG MICHAEL C. , ONORATO PAULETTE I. K. , UHLMANN DONALD R.
Published: June 2006

The effect of a foreign nondiffusing gas on the rate of shrinkage of an oxygen bubble in a soda‐lime‐silica melt was studied. The rate of change of bubble radius with time was computed using the quasi‐stationary approximation. The effects of melt under saturation and initial fraction of foreign gas in the bubble are considered and compared with those calculated using previously derived expressions.
Nature of Incorporated Water in Hydrated Silicate Glasses
Authors: WU CHE‐KUANG
Published: June 2006

Silicate glasses show a wide range of responses to exposure to water or steam at high temperatures and pressure. The response patterns and the factors determining these patterns are discussed. The manner in which water is incorporated in the silicate glasses is elucidated by a study of the near infrared spectra and differential thermogravimetric analysis of hydrated glasses. Factors affecting relative amounts of tightly bonded and loosely bonded water are discussed.
Mixed‐Alkali Effect in the Dilute Foreign‐Alkali Region. Failure of the Strong Electrolyte/Cationic Interaction Model
Authors: MOYNIHAN C. T. , SAAD N. S. , TRAN D. C. , LESIKAR A. V.
Published: June 2006

Electrical conductivity and relaxation data were measured for glasses of composition 0.242[XK2O+(1‐X)Na2O]‐0.758SiO2 from 25° to 205°C and in the dilute Na+ ion composition range X= 0.9 to 1. The decrease in electrical conductivity σ when the majority alkali K+ is replaced with the foreign alkali Na+ is most rapid in the very dilute range X= 0.98 to 1 and becomes less rapid at larger Na+ contents. The electric field relaxation times agree well with the single‐alkali mechanical relaxation times. The electric field relaxation function becomes more exponential with increasing foreign alkali content, indicating a corresponding decrease in the concentration of mobile ions. Attempts to account for the decrease in σ with increasing foreign alkali content by assuming that the single‐alkali glass is a strong electrolyte and that the foreign alkali complexes with and immobilizes the majority alkali were unsuccessful. Calculated values of the number of majority alkali ions complexed by a foreign‐alkali ion were unreasonably large.
The Stability of Bredigite and Other Ca‐Mg Silicates
Authors: ESSENE ERIC
Published: June 2006

The phase Ca7Mg(SiO4)4, bredigite, is chemically and structurally distinct from α‐Ca2SiO4. Experiments on its lower stability limit represent a synthesis limit which is not likely to be an equilibrium boundary. Equilibrium experiments place its upper stability limit at 1372°C and 98 kPa by the reaction

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The experimental data also require a second reaction

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at the same pressure and temperature and imply that two other reactions relating these phases are located near 1372°C and 98 kPa. Location of these four reactions around an invariant point in P‐T space shows that bredigite is on the low‐pressure side of the reactions.
High‐Temperature Fatigue Behavior of Polycrystalline Alumina
Authors: JAKUS K. , SERVICE T. , RITTER J. E.
Published: June 2006

The strength and fatigue behavior of a 99.5% polycrystalline alumina were measured as a function of temperature. Both the strength and fatigue behavior remained essentially constant up to 500°C; from 800° to 1100°C the strength and fatigue resistance decreased markedly and at >1100°C macroscopic creep was observed. It is believed that the decrease in strength and fatigue resistance is caused by a grain‐boundary glassy phase enhancing subcritical crack growth. Proof‐testing at room temperature was effective in improving the strength distributions at both room temperature and 1000°C; however, at 1000°C it was not effective, due to crack growth during the proof test. The good agreement between proof‐test results and fracture‐mechanics theory indicates that the same flaws control the strength at room temperature and at high temperatures.
Subsolidus Equilibria in the System Li2O‐Al2O3‐Cr2O3
Authors: IZQUIERDO G. , WEST A. R.
Published: June 2006

On the join LiCrO2‐LiAlO2, solid solutions of formulas LiCri‐xAlxO2 (0<x<0.6) form. On the spinel join LiAl5O8‐“LiCr5O8,” solid solutions of formulas LiAl5‐xAlxO8 (0<x<3) form and the order‐disorder transition, observed in LiAl5O8 at 1295°C, occurs at increasingly lower temperatures with increasing Cr content. No evidence was found for the metastable polymorphs of LiAl5O8 reported by Datta and Roy. Ternary subsolidus equilibria at 1200° to 1300°C were determined for compositions containing <50% Li2O.
Kinetics Parameters and Thermodynamic Properties of Calcium Tungstate Crystal Growth from Lithium Chloride and Sodium Tungstate Melts
Authors: ROY B. N.
Published: June 2006

Using an ordinary Arrhenius equation kDl=k0e−EIRT, energy (E), enthalpy (ΔHa), entropy (ΔSa), and free energy (δGa) of activation and the preexponential factor (K0) were estimated for diffusion‐controlled crystal growth of calcium tungstate from solutions in lithium chloride and sodium tungstate melts. Although E was small and increased slightly with increased cooling rates (RT), there was no direct correlation. The ΔHa, ΔSa, and ΔGa were unaffected by the changes in RT and crystallization temperature (T0). The distance (d12) between a diffusing particle and its host crystal, necessary for a successful diffusion, was estimated. Such distances increased with T0 and RT for the system CaWO4‐Na2WO4 but, for the system CaWO4‐LiCl, they decreased with RT and increased with T0.
Structure and Properties of Portland Cement Clinker Doped with Zinc Oxide
Authors: ODLER IVAN , SCHMIDT OTTO
Published: June 2006

ZnO added to the raw meal accelerates the rate of portland clinker formation. Due to ZnO doping, the amount of alite and C2(AF) formed increases at the expense of belite and C3A. The ZnO is preferentially taken up by the interstitial phase. The initial rate of tricalcium silicate hydration is retarded and the formation of ettringite is moderately accelerated in cements made from ZnO‐doped clinkers. The set time of these cements is gradually prolonged and their strength development retarded with increasing degrees of ZnO doping.
Stress Relaxation in PZT
Authors: ESAKLUL K. A. , GERBERICH W. W. , KOEPKE B. G.
Published: June 2006

Time‐dependent deformation in the sonar transducer ceramic, PZT, was studied by stress‐relaxation techniques. Logarithmic stress relaxation was not observed but the data could be treated in terms of an analysis of thermally activated deformation by Reed‐Hill and Dahlberg. The room‐temperature activation energy and activation volume of the rate‐controlling deformation mechanism were measured as 25 kcal/mol and 7000 Å3, respectively. A dislocation model of the domain processes responsible for deformation, consistent with the experimental data, is presented.
The System Si3N4‐SiO2‐Y2O3
Authors: GAUCKLER L. J. , HOHNKE H. , TIEN T. Y.
Published: June 2006

Subsolidus phase relations were established in the system Si3N4‐SiO2‐Y2O3. Four ternary compounds were confirmed, with compositions of Y4Si2O7N2, Y2Si3O3N4, YSiO2N, and Y10(SiO4)6N2. The eutectic in the triangle Si3N4‐Y2Si2O7‐Y10(SiO4)6N2 melts at 1500°C and that in the triangle Si2N2O‐SiO2‐Y2Si2O7 at 1550°C. The eutectic temperature of the Si3N4‐Y2Si2O7 join was ∼ 1520°C.
Compressive Surface Stresses Developed in Ceramics by an Oxidation‐Induced Phase Change
Authors: LANGE F. F.
Published: June 2006

Silicon nitride/zirconium oxide hot‐pressed materials contain ZrO2‐2xN4x/3 (0.25≤x≤0.43), which readily oxidizes at ≥ 500°C to monoclinic ZrO2. The molar volume increase (∼4 to 5%) of this reaction was used to develop compressive surface stresses. The development of these useful surface stresses was demonstrated with an indentation technique used to measure the apparent critical stress intensity factor (Ka) on the surfaces of materials fabricated with 5 to 30 vol% ZrO2 and subsequently oxidized at 600° to 800°C. The increase in Ka was directly related to the oxidation kinetics and the initial volume content of the unstable phase.
Plastic Deformation of Fine‐Grained Alumina (Al2O3): I, Interface‐Controlled Diffusional Creep
Authors: CANNON R. M. , RHODES W. H. , HEUER A. H.
Published: June 2006

Plastic deformation in fine‐grained alumina polycrystals (grain size 1 to 15 μm) was studied. At least three distinct deformation mechanisms are important: diffusional creep, basal slip, and unaccommodated grain‐boundary sliding. The first and most important of these processes is addressed in this paper. Analysis of the deformation dynamics suggests that both lattice and grain‐boundary diffusion are important in the diffusional creep. Aluminum, rather than oxygen, lattice and grain‐boundary diffusion are rate‐controlling because oxygen diffusion is very slow in the lattice but very rapid in grain boundaries. Significantly, the diffusional creep can become interfacecontrolled at low stresses, causing the often‐reported non‐Newtonian creep behavior of fine‐grained alumina.
Iron Diffusion in Iron‐Aluminate Spinels
Authors: HALLORAN J. W. , BOWEN H. K.
Published: June 2006

The diffusion coefficient of 59Fe in iron‐aluminate spinels (Fe3O4‐FeAl2O4) was measured by serial sectioning. The results were analyzed with a defect model, assuming that the predominant defects were cation vacancies and interstitials. At 1380°C, diffusion occurs in Fe3O4 and Fe(Fe1.51Al0.49))O4 by an interstitial mechanism at low PO2 and a vacancy mechanism at high PO2* Diffusion of iron is by the vacancy mechanism for higher hercynite concentrations, except that the results for the end‐member, FeAl2O4, suggest an interstitial mechanism. At 10−6 atm O2, an Arrhenius plot of DFe exhibits a minimum for Fe3O4 and Fe(Fe1.51 A10.49)O4. This effect is explained in terms of a mechanism change. TheDFe is essentially independent of temperature in Fe(Fe1.03Al0.97)O4 and Fe(Fe0.54Al1.46)O4.
Strengthening of Glasses by Partial Leaching
Authors: DREXHAGE MARTIN G. , GUPTA PRABHAT K.
Published: June 2006

A technique for strengthening certain alkali borosilicate glasses is described. Porous surface layers of a desired thickness are created on an article, taking advantage of the phase separation and leaching phenomena in such glasses. The semiporous composite is then heated to sinter the high‐silica clad about the borosilicate core. On cooling, residual compressive stresses develop within the cladding. The mechanical properties of cylindrical specimens prestressed by this method were characterized by photoelastic measurements and moduius‐of‐rupture tests. Residual stresses as high as —410 MPa were observed and found to be in reasonable agreement with the form of a previously developed thermal‐stress model. The roles played by thermal tempering and stress‐relaxation effects are also discussed.
Internal Friction and Sodium Transport in Beta Alumina
Authors: SIMMONS J. H. , FRANKLIN A. D. , YOUNG K. F. , LINZER M.
Published: June 2006

Internal friction peaks near 100 K were observed for melt‐grown single‐crystal sodium β‐alumina with a <110> stress at 12 and 16 kHz. These data, combined with those of Barmatz and Farrow, produced limiting values for the activation energy and preexponential factor for the relaxation time, viz. 20 kJ/mol and 5.6×10−16 s and 23 kJ/mol and 7.4×10−18 s. Split‐interstitial Na+ions on mid‐oxygen sites could produce these peaks, but not simple interstitials on anti‐Beevers‐Ross sites. A relaxation mode calculation is given for the relaxation frequency in the internal friction experiment and for the electrical conductivity in the conducting plane for the split interstitial model.
Degradation of BaTiO3 Ceramic Under High ac Electric Field
Authors: SCHULZE W. A. , CROSS L. E. , BUESSEM W. R.
Published: June 2006

The degradation of ac and dc conductivity, field dependence of conductivity, and activation energy were studied for paraelectric BaTiO3 ceramic subjected to high alternating electric fields at 150°C. The time to failure for disks of three thicknesses was determined as the 3.5 power of field strength and a model was developed relating degradation to electrostrictive forces.
Ion‐Probe Measurement of Oxygen Self‐Diffusion in Single‐Crystal Al2O3
Authors: REED DAVID J. , WUENSCH B. J.
Published: June 2006

Anion self‐diffusion coefficients normal to (1102) were obtained for single‐crystal Al2O3 in a 1.3 × 10 3 N/m2 (10−5 torr) vacuum at 1585° to 1840°C. Tracer was supplied from an initial 650 to 1300 A Al218O3 layer produced by the oxidation of vapor‐deposited Al metal films in an 18O2 atmosphere at 520°C. Concentration gradients extended over depths of 3000 to 5000 A and were measured by mass spectrometry of material sputtered from the samples with a beam of Ar+ ions. Crystals which had not been preannealed to remove surface damage displayed enhanced diffusion. Diffusion coefficients from preannealed crystals may be described by D0=6.4×105cm2/s, with an activation energy of 188 ± 7 kcal/mol. The diffusion is interpreted as an extrinsic vacancy mechanism.
Consolidation of Participate Layers in the Fabrication of Optical Fiber Preforms
Authors: WALKER K. L. , HARVEY J. W. , GEYLING F. T. , NAGEL S. R.
Published: June 2006

Viscous sintering is experimentally identified through electron microscopy as the mechanism of consolidation of thin particulate layers in the fabrication of optical fibers. The rate of consolidation is primarily a function of the capillary number, C=[νl0(1 ‐ε0)1/3/(σts)], where ν is the glass viscosity, l0 the size of the initial void regions, ε0 the initial void fraction, σ the surface tension, and ts the sintering time. Numerical results indicate a sensitivity of the sintering rate to temperature, chemical composition of the particles, and gas thermal properties, primarily through the strong dependence of glass viscosity on these variables. These results are fully supported by the available experimental evidence. Under the conditions of the experiments, gas bubbles were occasionally produced; the causes are discussed.
Conduction and Dielectric Loss Mechanisms in β‐Alumina and Glass: A Discussion Based on the Paired Interstitialcy Model
Authors: INGRAM MALCOLM D.
Published: June 2006

A paired interstitialcy model is used as a basis for qualitative comparisons of conductivity and dielectric phenomena in β‐alumina crystals and in glass. Thus, the increase in the conductivity of sodium silicate glasses with increasing Na2O activity can be explained if the concentration of (Na2*)2+ interstitial pairs increases with increased polarizability of O2‐ ions, expressed in terms of the optical basicity parameter, Δ. Similarly, the occurrence of the pronounced minima in conductivity isotherms (the mixed‐alkali effect in glass) is attributed to disappearance of mobile interstitial pairs, e.g. (Li2*)2+ or (K2*)2+, and the stabilization (by polarization interactions) of apparently immobile mixed‐alkali pairs, (LiK*)2+. The phenomenon of coionic conduction in certain β‐alumina crystals is an interesting departure from this general pattern. The orientation dependence of the electrical modulus spectrum of monocrys‐talline β‐alumina highlights the presence of a bimodal distribution of relaxation times, in which the low‐frequency component (v0=1011 Hz) may arise from the rearrangement of interstitial pairs and the high‐frequency component (v0=2×1012 Hz) may arise from less hindered ionic motions. It is suggested that the motions of interstitial pairs and surrounding cations are mutually catalytic and that some form of combined motion is responsible for both the electrical and mechanical relaxations in β‐alumina and glass.
Phase Equilibria in the System CaF2‐AlF3‐Na3AlF6 and Part of the System CaF2‐AlF3‐Na3AlF6‐Al2O3
Authors: CRAIG DOUGLAS F. , BROWN JESSE J.
Published: June 2006

The complete phase‐equilibrium diagram of the system CaF2‐AlF3‐Na3AlF6 and the subsolidus portion of the system CaF2‐AlF3‐Na3AlF6‐Al2O3 were established from microscopic, powder X‐ray diffraction, quench, and DTA data obtained from samples encapsulated in sealed tubes and either reacted in the solid state or melted and recrystallized. The system Na3AlF6‐CaF2 contains a simple eutectic with no compound formation or solid solution. The system CaF2‐AlF3‐Na3AlF6 contains two ternary compounds, NaCaAlF6 and NaCaAl2F9, which melt incongruently at 735° and 712°C, respectively; NaCaAlF6 exists in three polymorphic forms with transitions at 610° and 722°C and NaCaAl2F9 is body‐centered cubic with a0= 10.765 Å. The three binary and two ternary compounds divide the system into eight compatibility triangles. Along the NaCaAlF6‐Na3AlF6 join, 7 mol% NaCaAlF6 is soluble in α‐cryolite at 525° and 42% in β‐cryolite at 731°C. The quaternary system Na3AlF6‐AlF3‐CaF2‐Al2O3 contains eight compatibility tetrahedra.
Transmission Electron Microscopy at Grain Boundaries of PTC‐Type BaTiO3 Ceramics
Authors: HAANSTRA H. B. , IHRIG H.
Published: June 2006

Transmission electron microscopy of the grain boundaries of Ti‐rich semiconducting PTC‐type BaTiO3 ceramics is described. At a width of 2 to 10 nm, there were no indications of intergranular second‐phase layers covering the grains. Second phase was segregated only at the contacts of three or more grains; electron diffraction confirmed the amorphous structure of this phase. Observed ferroelectric domains at the grain boundaries do not indicate a PTC‐specific orientation of ferroelectric domains due to the negative grain surface charge.
Transformational Superplasticity of Bi2WO6 and Bi2MoO6
Authors: WINGER L. A. , BRADT R. C. , HOKE J. H.
Published: June 2006

Transformational Superplasticity was studied in the compounds Bi2WO6 and Bi2MoO6. The magnitudes of transitional strain are related to the (Tt/TmP), s of the phase transitions and are proportional to the externally applied stresses. Strain‐rate sensitivities were similar, 0.85 and 0.86; however, the Bi2WO6 exhibited a strain‐axis intercept and the Bi2MoO6 a stress‐axis intercept. The grain‐size effect present in the Bi2WO6 supports an accommodated grain‐boundary sliding mechanism for the superplastic deformation process.
Fracture Toughness Determination of A12O3 Using Four‐Point‐Bend Specimens with Straight‐Through and Chevron Notches
Authors: MUNZ D. , BUBSEY R. T. , SHANNON J. L.
Published: June 2006

Fracture toughness of a sintered A12O3 was determined with four‐point‐bend specimens having either straight‐through or chevron notches. For the straight‐through notched specimens, measured KIc decreased with decreasing notch width. For the smallest notch width (66 μm) KIc= 3.42±0.13 MN m−¾. For specimens with chevron notches, a crack initiates and extends from the tip of the notch under increasing load. KIc is calculated from the maximum load without measuring crack length, under the assumption that the derivative of the compliance is the same as that for a specimen with a straight‐through crack. A refined calculation accounts for the truncated chevron crack shape at maximum load using Bluhm's slice model. For the chevronnotch configuration, a value of KIc= 3.49±0.11 MN m−¾ was measured, which appears to be independent of the initial notch length a0 (distance from the crack mouth to the tip of the triangular notch). An effect of a1 (length of the chevron notch at the surface) on KIc was observed, independent of whether the calculation of KIc was based on the straight‐through crack assumption or on the slice model.
Indentation‐Precracking and Double‐Torsion Methods for Measuring Fracture Mechanics Parameters in Hot‐Pressed Si3N4
Authors: GOVILA R. K.
Published: June 2006

The two widely used test methods, the indentation‐induced flaw (IIF) and the double‐torsion (DT), for measuring fracture mechanics parameters were directly compared using a commercial hot‐pressed Si3N4. The IIF method is simple for estimating the inherent flaw size of the as‐received material and in revealing the qualitative nature of slow crack growth as a function of temperature and strain rate. The critical stress intensity factor, Kic, for catastrophic failure at 20°C was 3.5 and 4.1 MN/m3/2 using IIF and DT methods, respectively. Crack velocities can be measured with greater accuracy using the DT method.
J‐Integral Measurements of the Fracture of 50% Alumina Refractories
Authors: HOMENY J. , DARROUDI T. , BRADT R. C.
Published: June 2006

The J‐integral experimental technique was used to study fracture initiation in burned refractory bricks and refractory casta‐bles of the 50% alumina variety. In a comparison of JIc and GIc, and 2ywof it is consistently observed that GIc<JIc<2ryWof. The quantities (JIc‐GIc) or (JIC/GIC), as well as (2ywof/GIc), can be applied to estimate the inelastic energy contribution to the crack‐tip process zone of these refractories. The latter two parameters distinctly classify the burned bricks and the casta‐bles into different fracture characteristics. As such, these parameters are potentially very useful in the microstruetural design of refractories.
Pseudobinary Phase Relations of Li2Ti3O7
Authors: MIKKELSEN J. C.
Published: June 2006

The Li2O‐TiO2 pseudobinary phase diagram was determined from 50 to 100 mol% TiO2 by DTA, microscopy, and X‐ray analysis; Li2Ti3O7 effectively melts congruently at 1300° and decomposes eutectoidally at 940°C. A solid solution based on Li2TlO3 from 50 to ∼65 mol% TiO3 was observed to exist at >930°C. A new metastable phase was discovered with a composition of ∼75 mol% TiO2 and with a hexagonal unit cell (8.78 by 69.86 × 10−1nm). Discrepancies in the literature regarding some of these phase equilibria are reconciled.
Analytical Electron Microscopy of Cement Pastes: I, Tricalcium Silicate Pastes
Authors: CARD J. A. , MOHAN K. , TAYLOR H. F. W. , CLIFF G.
Published: June 2006

One hundred sixty‐one particles of C‐S‐H from C3S pastes aged 1 to 180 days were analyzed. For pastes made from two C3S samples, the mean Ca:Si ratios were 1.52 and 1.61, respectively. The overall range of Ca:Si ratios was 1.21 to 1.96; most of the variation is considered to represent real differences in composition between individual particles. No significant correlations with curing time, degree of reaction, or morphological type of C‐S‐H were found.
Electrochemical Corrosion of Iron Magnesium Aluminate Spinel and Lanthanum Chromite in Molten Potassium Sulfate
Authors: Kaiser Gregory A. , Halloran John W.
Published: June 2006

Iron magnesium aluminate spinel and lanthanum chromite specimens are unaffected by immersion in molten K2SO4 in the absence of an electrical current, but are aggressively attacked in the presence of a direct current. Anodes are deteriorated by surface reactions, while cathodes are disintegrated due to enhanced salt penetration without gross chemical reactions.
The Systems ZnO‐Fe2O3‐SnO2 and MgO‐Fe2O3‐SnO2 at 1060°C
Authors: Tyson R. Michael , Chang Luke L. Y.
Published: June 2006

Zn2SnO4, an inverse spinel, and ZnFe2O4, a normal spinel, form a complete series of solid solutions in the system ZnO‐Fe2O33nO2. The variation of cell dimensions with composition varies from 0.8439 nm (ZnS2nO4) to 0.8660 nm (ZnS2nO4) and exhibits a positive deviation from a linear relationship. Mg2SnO4 and MgFe2O4, both predominantly inverse in nature, have only an incomplete series.
Residual Stresses in Dynamic Fatigue of Abraded Glass
Authors: Marshall D. B. , Lawn B. R.
Published: June 2006

The effect of residual contact stresses on the dynamic fatigue response of glass surfaces containing abrasion flaws is described. Indentation fracture theory is used as a theoretical basis for analyzing the experimental data. The results highlight a general need to incorporate a residual‐stress term in the fatigue equations for failure from natural flaws.
Continuous Poling Technique for PZT Fibers
Authors: Gururaja T. R. , Cross L. E. , Newnham R. E.
Published: June 2006

A new technique has been developed for poling long PZT fibers by advancing the fibers along two electrical contacts maintained at the required potential difference. Two ways of maintaining the electrical contact with the ceramic are described, leading to piezoelectric d33 coefficients of 400 to 450×10−12 C/N in poled fibers of PZT‐501A. Pre‐poled fibers can be used in fabricating ceramic‐polymer composites such as triple‐pillar configurations with piezoelectric fibers oriented in three perpendicular directions.
Model for Evaporation of a Grain‐Boundary Phase
Authors: Wuttig Manfred , Anderson Harlan U.
Published: June 2006

The surface profile which develops in the vicinity of a grain boundary precipitate in the course of evaporation is calculated. It is shown that the presence of the grain boundary precipitate affects the profile significantly if the product of the width of the grain boundary precipitate and the ratio of the evaporation rates of the unperturbed surface and the grain boundary precipitate is larger than one.
Joining of Self‐Bonded Silicon Carbide by Germanium Metal
Authors: Iseki T. , Yamashita K. , Suzuki H.
Published: June 2006

Two self‐bonded SiC bodies containing free Si were joined with liquid Ge at 1180°C in vacuum. Bond strength was measured by four‐point bending test in vacuum at high temperature. The join had a significant strength even above the melting point of Ge metal. Electron probe microanalysis of joint showed a liquid formation temperature of thinner interlayer was ∼1200°C.
Sintering of Si3N4‐Y2O3 Under Nitrogen Pressure
Authors: Galasso F. S. , Veltri R. D.
Published: June 2006

This study shows that the amount ofAl2O3 needed to form high density Si3N4‐15Y2‐O3 samples can be reduced by using high surface area Si3N4 powder and high N2 overpressure (high sintering temperatures) during the sintering process. The reduction in AI2O3 content results in improved oxidation resistance of the sintered samples.
Effect of Water Bath Temperature on the Thermal Shock of Al2O3
Authors: Becher Paul F.
Published: June 2006

The thermal stress resistance of aluminas is strongly influenced by the surface heat transfer coefficient (h). In liquid quenches, h, which is a function of boiling phenomena, varies with bath and sample temperature. Thus, while a 22°C water quench yields ΔTc values essentially independent of the alumina properties or correspondingly, sample thickness, t, raising the bath to 100°C leads to a strong size dependence of ΔTc (i.e. ΔTc >> ∼250°C for t<1.8 mm).
Effect of Loading Rate on Fracture Toughness of SiC at High Temperatures
Authors: Popp G. , Pabst R. F.
Published: June 2006

Loading rate sensitivity effects at high temperatures are brought about by a viscous metallic Si phase within an SiC mircostructure. The cross‐head speeds were 0.024 and 1260 mm/min. At 0.024 mm/min and 1200°C, KIC increases up to ∼12 MN/m3/2, whereas at 1260 mm/min, KIC remains nearly unaffected, comparable with the room temperature value of ∼4 MN/m3/2. The effect contradicts the normal behavior where KIC increases with increasing cross‐head speed. Fracture toughness data should therefore be determined as a Junction of loading rate, to account for viscous reactions at certain temperatures.
Effect of Fluorine on the Phase Separation of Na2O‐SiO2 Glasses
Authors: Markis Joanne H. , Clemens Kevin , Tomozawa Minoru
Published: June 2006

Immiscibility temperature of 13 mol% Na2O‐87 mol% SiO2 glass was found to increase with F addition. Electron micrographs indicated that the microstructure size did not change appreciably with F addition.
Biaxial Fracture Studies of a Glass‐Ceramic
Authors: SHETTY D. K. , ROSENFIELD R. , BANSAL G. K. , DUCKWORTH W. H.
Published: June 2006

Uniaxial and equibiaxial tensile strengths are reported for glass‐ceramic specimens exhibiting strength isotropy. Uniaxial strengths were determined in both 3‐ and 4‐point bend tests. Stressing rate was a controlled variable and the tests were conducted in both dry N2 and water environments, to provide data for different conditions of slow crack growth. There was little or no difference between strengths in the 3‐ and 4‐point bend tests, indicating the absence of a size effect. In comparable tests, the strength under equibiaxial tension was greater than under uniaxial tension. The biaxial strengthening became less pronounced with increased slow crack growth during testing. A maximum observed biaxial‐to‐uniaxial strength ratio of 1.21 resulted from ball‐on‐ring and uniaxial bend tests in dry N2. These results are attributed to differences in flaw severity between biaxial and uniaxial stressing. The decreasing strength ratios can be explained by a change in configuration of critical flaws due to slow crack growth. Numerical calculations, using a simplified two‐dimensional model of the strength‐controlling flaw, supported this hypothesis. The calculations also indicate that the slow crack growth exponent is smaller for the biaxial tension mode of stressing than for the uniaxial mode.
Controlled Transient Solid Second‐Phase Sintering of Yttria
Authors: RHODES W. H.
Published: June 2006

Compositions of La2O3‐Y2O3 were sintered to full density by a process which uses a controlled transient solid phase to retard grain growth sufficiently that pores remain on grain boundaries and are eliminated by solid‐state diffusion. The temperature is then decreased into a single‐phase region and the structural transition yields a pore‐free, single‐phase body. Optimum compositions are 8.1 to 12.1 mol% La2O3 for a sintering temperature of 2170°C and annealing temperatures of 1920° to 2020°C, resulting in materials with near‐theoretical total transmittances and specular transmittance within 6% of theoretical.
Energy Variations in Diffusive Cavity Growth
Authors: RICE JAMES R. , CHUANG TZE‐JER
Published: June 2006

The assignment of boundary values for the chemical potential and the calculation of energy‐release rates for the growth of creep cavities along grain boundaries by self‐diffusion are discussed. For simplicity, it is assumed that the boundaries are flat and that surface and grain‐boundary diffusion are the dominant transport mechanisms. As matter diffuses from the void surface into and along the grain boundary, misfit residual stresses are induced to alleviate the high stress concentration ahead of the cavity apex. As a result, the contribution of strain‐energy terms to the chemical potential can be neglected in typical cases. Also, contrary to the Griffith crack‐extension model, the energy dissipation incurred by diffusive removal of material from the cavity surface and deposition in the grain boundary is a major term in the energy transfers associated with cavity growth. The primary energy “sink” in diffusive cavity growth is shown to arise from the work done by the grain‐boundary normal stress when matter is inserted in the near‐tip region by diffusion, not from the loss of strain energy of matter that is removed from the cavity at its tip or from the work of bond separation. Thermodynamic restrictions on the angle formed by the void surfaces at their apex, where they join the grain boundary, are considered. Boundary values for the chemical potential are derived in a manner appropriate for arbitrarily large but elastic distortions of material near the cavity tip and, in contrast to most previous work in the area, the effects of surface tension (i.e. of “surface stress,” as distinct from surface energy) are included.
Time Relaxation of the Thermoelectric Power of Wustite
Authors: Hodge J. D. , Bowen H. K.
Published: June 2006

The change in the measured high temperature thermoelectric power of wustite with time was determined. At all compositions, it was found this quantity decayed from its initial value to a lower steady‐state value. It is felt that this decay is due to ionic contributions to the thermoelectric power which become significant when sufficient time is allowed for the motion of ionic defects in the thermal gradient.
Grain‐Size Determinations
Authors: Case E. D. , Smyth J. R. , Monthei V.
Published: June 2006

This study compares the grain sizes of dense, equiaxed gadolinia (Gd2O3) specimens as determined by light microscope/polished surface and by scanning electron microscope/fracture surface techniques. The average intercept lengths (AIL) as determined by the two techniques were found to differ only slightly. For Gd2O3 in the grain‐size range studied, a factor of ∼1.10 converts the fracture‐surface AIL to the polished‐surface AIL.
Thermal Decomposition of the Oxynitride of Germanium and the Heat Capacity of the Oxynitrides of Silicon and Germanium
Authors: Ehlert Thomas C.
Published: June 2006

Using the mass spectrometry‐effusion cell technique, Ge2N2O has been found to decompose under equilibrium conditions according to
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Between 850 and 1000 K, the free energy change for this reaction is given by
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The heat capacities of GezN2O and its silicon homolog between 296 and 738 K have been determined using differential scanning calorimetry. From these results it has been found that
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