bluuebunny/crossref_metadata_2025 huggingface dataset:
Uncertainty in Minimum Lifetime Predictions
Authors: JACOBS DAWN F. , RITTER J. E.
Published: June 2006

The uncertainty in minimum lifetime predictions based on crack velocity, static fatigue, and dynamic fatigue data is estimated by both a Monte Carlo simulation technique and the law of propagation of errors. The statistical analysis of typical data for glass shows that the 2 techniques give similar estimates for the uncertainty in minimum lifetime predictions as long as the coefficient of variation of the experimental parameters does not exceed ∼10%. The estimated uncertainty in the minimum lifetime is used to place confidence limits on failure predictions.
Pressure and Temperature Dependence of the Elastic Moduli of Polycrystalline MgF2
Authors: RAI C. S. , MANGHNANI M. H.
Published: June 2006

The pressure and temperature derivatives of the bulk (Ks) and shear (μ) moduli of two polycrystalline MgF2 specimens measured to 5 kbars and 200°C, using the ultrasonic pulse‐echo‐overlap method are, for specimens A and B, respectively: dKs/dP 5.06 and 5.10;dμ/dP 0.72 and 0.73;dKs/dT ‐0.160 and‐0.155 kbar/deg.; dμ/dT ‐0.092 and ‐0.088 kbar/deg. The ambient elastic modulus results are in agreement with the iso‐tropic values calculated from the previous single‐crystal experimental data and theoretically derived values based on the rigid‐ion model. The measured dKs/dP and dμ/dP are significantly higher than the corresponding theoretical values based on the rigid‐ion model calculations (the rigid‐ion model predicts negative dμ/dP). However, the measmed dKs/dT and dμ/dT are in fairly good agreement with the calculated values based on the previous single‐crystal and recent polycrystalline data of other investigators. The present results for MgF2 are discussed in light of velocity‐density systematics for the rutile‐structured difluorides and oxides.
Material and Mode Dispersion in GeO2·B2O3·SiC2 Glasses
Authors: FLEMING J. W.
Published: June 2006

Material and mode dispersion in fibers made from glasses in the system GeO2‐B2O,3‐SiO2 have been calculated using refractive index dispersion results for these glasses. Refractive indices were measured on bulk glass specimens using the minimum deviation method at wavelengths from 0.4358 to 1.0830 μm. The resultant data were then fitted to a 3‐term Sellmeier dispersion relation for each glass composition. The fitted equations and a recent theory on the relation of the optimum index profile in a graded index optical waveguide to pulse dispersion were used to calculate the exponent α, which characterizes the shape of the profile, for several practical fiber models. The most effective profile shape for reducing pulse dispersion is a function of wavelength, composition, and fictive temperature. The present data were used elsewhere to predict accurately the optimum profile for minimization of pulse dispersion in several fiber systems consisting of germanium borosilicate glasses.
High Temperature Tensile Creep of Magnesium Oxide Single Crystals
Authors: CLAUER A. H. , WILCOX B. A.
Published: June 2006

The creep behavior and the dislocation substructure developed during creep were investigated for 〈011〉 oriented MgO single crystals creep tested in tension. Creep deformation was studied over stress and temperature ranges of 29.0 to 86.2 MN/m2 and 1200 to 1500°C, and the minimum creep rate, ε, was found to obey the relation:

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where σ= applied tensile stress, k= the Boltzmann constant, T= absolute temperature, n= 3.8 to 4.5, and A = ll × 10−2 (MN/m2)‐4 s‐1. Dislocation substructures developed during creep were studied by transmission electron microscopy and etch pitting techniques. At 1400°C, the dislocation density, ρ, at 0.10 tensile creep strain depended on applied stress as ρασ2.1. Numerous dislocation loops and long straight dislocations were present, but subboundaries were seldom observed. The results are discussed in terms of two possible operative creep mechanisms: (1) a recovery process based on annealing out of dislocation dipoles and loops, and (2) dislocation glide limited by atmospheres of charged defects surrounding dislocations.
Evidence for Suppression of Radiation Damage in Li‐Doped MgO
Authors: CHEN Y. , ABRAHAM M. M.
Published: June 2006

The net production of stable intrinsic defects in MgO, such as anion vacancies and divacancies, produced by electron and neutron irradiations is shown to be suppressed by doping with Li impurities.
Pore Growth in Sintered Thoria
Authors: MORGAN C. S. , McCORKLE K. H. , POWELL G. L.
Published: June 2006

Sintered ThO2 will sometimes undergo a decrease in density, i.e. become more porous, if held at high temperature for a sufficient time. The bulk density of sol‐gel ThO2 sintered to 99% of theoretical density at 1200°C will decrease steadily at 1800°C in air to <90% of theoretical after ∼ 15 h. Gas‐release measurements from such porous ThO2 specimens annealed in air or in vacuum indicate that some gases move through the material freely at 1800°C. The only gases that could contribute to the decrease in density are the oxides of sulfur and carbon, which, if they exist, could be produced or eliminated rapidly by controlling the annealing environment. However, the density decrease appears to depend on factors that affect grain growth, rather than on the generation or elimination of postulated gases.
Compatibility of Ceramics with Liquid Na and Li
Authors: SINGH R. N.
Published: June 2006

A thermodynamic criterion was developed for predicting the compatibility of insulating ceramics with liquid Na and Li. Nonmetallic impurities in liquid metals were shown to have a profound effect on the compatibility behavior of ceramics. Attempts were made to identify the structural parameters which affect the corrosion behavior of ceramics in liquid Na and Li.
Phase Equilibria in the System Na2SiO3‐Li2SiO3
Authors: WEST ANTHONY R.
Published: June 2006

Phase equilibria were studied for the system Na2SiO:rLi2SiO3. The 2 end‐member metasilicates show limited mutual solid solubility with the (Na2‐χLiχ)SiO3 solid solutions being particularly extensive at solidus temperatures (0 x 1.06). Ordering of the latter solid solution occurs at the NaLiSiO;) composition with asupercellx= 6asubcellDuring cooling of the solid solutions, metastable phase transformations occur; a twinned monoclinic metastable phase, low (Na, Li)2SiO3, has been characterized.
Phase Equilibria in the System Na2SiO3‐Li2SiO3‐SiO2
Authors: WEST ANTHONY R.
Published: June 2006

Ternary phase relations have been studied and several modifications made to Kracek's phase equilibrium diagram. These include location of the primary phase fields of Na6Si8O19 and Li2Si2O5. Metastable phases and polymorphs were often encountered, notably a primary phase, δ‐Na2Si2O5, and a new polymorph of Li2Si2O5.
Electrode Polarization of Glasses
Authors: KIM CHULHO , TOMOZAWA MINORU
Published: June 2006

The low‐frequency dielectric characteristics of soda‐lime and sodium‐silicate glasses were determined as a function of temperature, electrode materials, surface condition, and specimen thickness. The resulting large dielectric constant (often called electrode polarization) was dependent on surface condition of the glass specimen when evaporated metal electrodes were used and insensitive to surface condition when paste electrodes were used. The space charge mechanism was suggested as an explanation for these phenomena. The dependence of the dielectric constant on frequency and specimen thickness agrees with predictions of theory
Phase Separation of Glasses in the System SrO‐B2O3‐SiO2
Authors: BAYLOR RICHARD , BROWN JESSE J.
Published: June 2006

The region of stable liquid‐phase separation in the system SrO‐B2O3SiO2 was found to extend from the SrO‐SiO2 binary join, across the ternary region, to the SrO‐B2O3 join. The boundary of the region rich in network‐forming oxides lies between the SiO2‐B2O3 boundary and the 2.5‐mol% SrO isopleth, whereas the maximum SrO content is between 30.3 and 35.2 mol% (42 to 48 wt%) SrO at an SiO2: B2O3 ratio of 4:1. The microstructures of glasses quenched from the immiscibility region were characterized by scanning electron microscopy. Evidence is presented of both stable and metastable phase separation and of microseparation and coring in disperse‐phase spheres rich in network‐forming oxides.
Abrasive Surface Deformation of Sapphire
Authors: BECKER PAUL F.
Published: June 2006

The depth of slip and the size of deformation twins introduced into sapphire by abrasive grinding depend on surface orientation. Enhanced depths of slip minimize surface chipping and striations, and grinding can result in basal slip depths of 30 μm and twins 75 μm in size. Basal twins in nonbasal surfaces are largest for single‐point diamond abrasion directions parallel to a 〈1100〉 basal twin shear direction, whereas optically detectable rhombohedral twins are produced only in 30° and 60° surfaces.
TiO2 Produced by Vapor‐Phase Oxygenolysis of TiCI4
Authors: SUYAMA YOKO , KATO AKIO
Published: June 2006

The formation of TiO2 powders by oxygenolysis of TiCI4 was studied with emphasis on the effects of reaction conditions on the particle size of the products. The particle size of TiO2(anatase) decreased with increasing reaction temperature or O2concentration and with decreasing TiCI4 concentration. The results are compared with those for the oxygenolysis of AlBr3and SiCI4. It was found that the reactivity of metal halides with O2 is closely related to the ease of dissociation of the first halogen atom.
Surface Analysis of a Treated Soda‐Lime Glass
Authors: BINKOWSKI N. J. , HEITZENRATER R. F. , STEPHENSON D. A.
Published: June 2006

The physicochemical properties of the surface of a soda‐lime glass were characterized with X‐ray photoelectron spectroscopy and transmission electron microscopy. A variety of chemical and physical treatments (e.g. grinding, fire polishing, and acid and base rinses) resulted in large changes in surface chemistry.
Mechanical Properties of the Directionally Solidified MgO‐MgAl2O4 Eutectic
Authors: KENNARD F. L. , BRADT R. C. , STUBICAN V. S.
Published: June 2006

Mechanical properties from room temperature to 1600°C are reported for the directionally solidified MgO‐MgAl2O4 eutectic. Strength, although modest, showed little decrease to 1600°C, exhibited totally elastic behavior, and appeared to be related to colony size rather than fiber spacing. Work‐of‐fracture was low, increased only moderately at 1600°C, and failed to reveal any potential for the classical toughening of fiber composites. Microhardness, which exhibited classical Petch behavior related to the fiber spacing, exceeded the values for the constituent phases. It was concluded that these microstructures inhibit plastic flow and may prove most useful at high temperatures.
Composition Limits and Magnetic Properties of Sintered Y2.66Gd0.34FexAl0.677Mn0.09O12 Garnets
Authors: GRESKOVICH C. , PALMER G. G.
Published: June 2006

Single‐phase garnet solid solutions can be synthesized between the composition limits of x=4.18 and x=4.22 in Y2.66Gd0.34FexAl0.677Mn0.09O12 at temperatures between 1340° and 1500°C in O2. Solid solutions occur only on the Y2O3‐excess side of the stoichiometric garnet composition. Electromagnetic properties and microstructural features of sintered garnets depend critically on small changes in Fe content in the vicinity of the garnet solid‐solution region. An intergranular spinel‐type second phase exists for compositions when x>4.22 and has a deleterious effect on remanent induction and magnetic loss at 3 GHz. The relative density of powder compacts sintered for 16 h at 1500°C in O2 increases with increasing Fe content (i.e. as x increases) in the garnet solid solution.
Particle Size Distribution of Coprecipitated Mn‐Zn Ferrite Powders
Authors: MENDELSON M. I.
Published: June 2006

The particle size distribution of 0.07‐ to 0.35‐μm powders was measured by quantitative electron microscopy using an areal analysis. Measurements of at least 15 particles were required to characterize each size distribution. The specific surface area calculated from the size distributions satisfactorily agreed with that measured by the BET method. For the powders with surface area of 4.4 to 9.7 m2/g, the particle size distributions were generally narrow. In many cases the distributions were near log normal.
Phase Equilibria in the System SrO‐PbO‐SiO2
Authors: SAMANTA S. C. , HUMMEL F. A.
Published: June 2006

Phase relations in the ternary system were determined by solid‐state reaction, quenching, and electron microscopy of the immiscible liquid region. The limits of the stable 2‐liquid region and the approximate limits of the metastable 2‐liquid region were determined. Relations in the region of homogeneous glass formation in the system, which included the joins SrSiO3‐PbSiO3, SrSiO3‐Pb2SiO4, and SrSiO3‐Pb4SiO6, were determined by quenching. The solid‐solution limits of SrSiO3 in Pb2SiO4 and Pb4SiO6 and of PbSiO3 in SrSiO3 were established. Two new compounds were discovered, 3SrO.2PbO.SiO2 and 2SrO.3PbO.SiO2, and extensive solid‐state trials permitted the compatibility triangles to be established. The accumulated data were assembled in the form of an equilibrium diagram for the system, including joins, boundary lines, and isotherms.
Three Anisotropies in Vitreous Silica
Authors: NASSAU K. , SHIEVER J. W.
Published: June 2006

Plasma‐torch fused‐silica boules of low OH content showed an optical anisotropy in the as‐grown state which disappeared after annealing in O2; this behavior was related to an EPR anisotropy which also depended on annealing, probably involving Fe2+ and Fe3+, respectively. High‐temperature (1200° to 1500°C) deformation experiments performed in a modified DTA machine on slabs cut parallel and perpendicular to the preparation symmetry axis also showed an anisotropy, corresponding approximately to a factor of 2 in the viscosity. This anisotropy was also observed in commercial worked fused silica of high and low OH (water) content, made from purified Si compounds or natural quartz, and was not removed by annealing for 5 days at 1200°C in O2. The deformation rate of fused silica decreases as water content is reduced from high to medium, but there is little further change when water content is decreased to a very low level.
Drying and Resaturation Effects on Internal Friction in Hardened Cement Pastes
Authors: SELLEVOLD ERIK J. , RADJY FARIBORZ
Published: June 2006

A set of mature hardened cement paste beams which had been cured at room temperature were dried to different extents and resaturated. The low‐temperature internal friction response of the beams was measured. The size of the internal friction peaks near −90°C indicates that the internal surface area of the dried resaturated beams is significantly smaller than that of virgin beams.
Compositions of Solutions in Contact with Hydrating Tricalcium Silicate Pastes
Authors: YOUNG J. F. , TONG H. S. , BERGER R. L.
Published: June 2006

The concentration of ionic species in the solution in contact with hydrating tricalcium silicate (C3S) has been studied as a function of time and in the presence of admixtures. The ionic product for calcium hydroxide (CH) was calculated as a function of time and correlated with calorimetric measurements and crystal growth data. The results support the hypothesis that nucleation of CH crystals controls the induction period and that their subsequent growth controls the second heat peak. The influence of admixtures can be predicted from their influence on CH crystal growth. However, solution data indicate that the system cannot properly be compared with the growth of pure CH; the combined role of C‐S‐H and CH must be considered. Some implications for C3S hydration are discussed.
Sodium Diffusion in Glass: I, Single‐Alkali Silicate
Authors: LIM CHUNG , DAY DELBERT E.
Published: June 2006

The isotope effect for 22Na/24Na diffusion was measured for three 25‐mol% alkali‐silicate glasses. A multiple diffusion mechanism wherein the Na ions diffuse both singly (vacancy mechanism) and in pairs (interstitialcy mechanism) provided the best agreement with the experimental data. According to this tentative model, diffusion by Na ion pairs predominates at low temperatures, and the fraction of Na ions diffusing singly increases with increasing temperature. In the glasses investigated, nearly all of the Na ions diffuse singly in the vicinity of the transformation range.
Deformation‐Mechanism Maps for LiF and NaCl
Authors: VERRALL R. A. , FIELDS R. J. , ASHBY M. F.
Published: June 2006

Data on the plasticity and creep of poly crystalline LiF and NaCl are presented; much of the data is drawn from the published literature, but new measurements of hardness as a function of temperature for both materials are also included. The data are fitted to rate equations which describe the mechanisms by which the salts deform. The results are then assembled to give deformation‐mechanism maps which show the regime of stress and temperature over which each mechanism is dominant.
Spalling and Cracking in Alumina by Compression
Authors: ADAMS MARC , SINES GEORGE
Published: June 2006

Crack damage produced by compressive loads in a dense alumina ceramic was studied with a replication technique that recorded damage done to the specimen's surface. The characteristics of the spalling produced in an externally pressurized, tubular specimen were evaluated at twelve stress levels up to failure. The study revealed that crack extension begins at a compressive stress approximately one quarter of that required to cause failure and that the amount of crack damage increases greatly as the failure stress is approached. The nature of the spalled particles and the mechanisms of spalling are discussed. Mechanisms of compressive failure are suggested.
Thermal Expansion and Chemical Durability of Phosphate Glasses
Authors: MINAMF TSUTOMU , MACKENZIE JOHN D.
Published: June 2006

The thermal expansion coefficient and aqueous dissolution rate were measured for alkali phosphate glasses containing a third and fourth component. For a given series, both properties increased monotonically as the radii of the alkali ions increased. The observed expansion coefficients were in the range 99 to 286 × 10−7°C−1. A small mixed‐alkali effect was observed for both properties.
Sintering of Low‐Density Glasses: I, Theory
Authors: SCHERER GEORGE W.
Published: June 2006

An analysis is presented which describes the rate at which a cubic array of cylinders densifies by viscous flow driven by surface energy reduction. The cubic array is proposed as a model for the microstructure of low‐density, open‐pore materials such as gels and flame‐hydrolysis preforms. The parameters of the model structure (cylinder length and radius) can be deduced from Hg penetration porosimetry.
Sintering of Low‐Density Glasses: II, Experimental Study
Authors: SCHERER GEORGE W. , BACHMAN DAVID L.
Published: June 2006

Densification rates are reported for 3 classes of porous glass materials: soot preforms made by flame hydrolysis, silica gel, and phase‐separated and leached borosilicate glass. Viscosity values obtained by fitting the densification data to the theory of Part I of the present study are in reasonable agreement with viscosity measured by beam bending using fully sintered glass of the same type.
Sintering of Low‐Density Glasses: III, Effect of a Distribution of Pore Sizes
Authors: SCHERER GEORGE W.
Published: June 2006

The sintering model presented in Part I is extended by considering a Gaussian distribution of pore sizes in the body. The effect of the breadth of the distribution on the densification kinetics is demonstrated; this effect is small except for very broad distributions. The greatest change occurs in the last few percents of shrinkage since the largest pores close relatively slowly. The range of pore sizes typically found in flame hydrolysis preforms or silica gel is narrow enough that the sintering kinetics are adequately described in terms of a single pore size. The specific surface area is shown to be independent of the breadth of the distribution.
Phase Relations and Stability Studies in the Si3N4‐SiO2‐Y2O3 Pseudoternary System
Authors: LANGE F. F. , SINGHAL S. C. , KUZNICKI R. C.
Published: June 2006

Composite powders were hot‐pressed to determine the phase relations in the Si3N4‐SiO2‐Y2O3 pseudoternary system. Four quaternary compounds, Si3Y2O3N4, YSiO2N, Y10Si7O23N4, and Y4Si2O7N2, were identified. Studies of polyphase and single‐phase materials in this system showed that these 4 compounds are unstable under oxidizing conditions. Materials within the Si3N4‐Si2N2O‐Y2Si2O7 compatibility triangle precluded the unstable compounds, and are extremely resistant to oxidation.
Structural Characterization of HTGR Pyrocarbon Fuel Particle Coatings
Authors: TENNERY V. J. , YUST C. S. , KRAUTWASSER P. , BEATTY R. L.
Published: June 2006

Four characterization techniques were used conjointly to assess the irradiation stability of propylene‐derived pyrocarbon coatings on fuel particles for the high‐temperature gas‐cooled reactor (HTGR). The resultant data further clarify the structural properties of the coatings. The characterization methods include oxygen‐plasma etching, small‐angle X‐ray scattering, optical anisotropy evaluation, and transmission electron microscopy. The results of the analysis of pyrocarbon coatings subsequently irradiated in the high‐flux isotope reactor are compared. The optimal microstructure in these pyrocarbons exhibits spheroidal growth features ranging in size from < 0.1 to ∼1 μm and a relatively homogeneous distribution of fine fibrous carbon around the larger growth features.
Preparation, Characterization, and Properties of Dy‐Doped Small‐Grained BaTiO3 Ceramics
Authors: YAMAJI A. , ENOMOTO Y. , KINOSHITA K. , MURAKAMI T.
Published: June 2006

The effects of Dy doping and sintering parameters on the properties of BaTiO3 ceramics were studied. The average grain size decreases with increasing Dy content and is controlled at ∼1.5 μ m by 0.8 at.% Dy. The Curie temperature change, associated with ≤1.2 at.% Dy, is <3°C. The dielectric constant is ∼2600 for specimens doped with 0.8 at.% Dy, calcined at 1200°C, and sintered at 1450°C. The dielectric constant variation with ambient temperature is much less than that of conventional BaTiO3 ceramics. Lattice constant c decreases with increasing Dy concentration whereas a increases slightly. The effects of grain size on dielectric constant, lattice parameters, and linear thermal expansion coefficient are more pronounced than the chemical effects of Dy doping in the ferroelectric state, whereas in the paraelectric state, these characteristics are almost independent of grain size as well as Dy concentration. The decrease in the frequency of occurrence of 90° twins with decreasing grain size implies that internal stress, which develops when BaTiO3 ceramics are cooled below Tc, strongly influences the effects of grain size.
Radiation‐Induced Mobility of Substitutional Hydrogen in MgO
Authors: CHEN Y. , ABRAHAM M. M. , TEMPLETON L. C.
Published: June 2006

The distribution of hydrogen between substitutional sites and Mg(OH)2 precipitates in MgO single crystals depends on the thermal treatment of the crystal. Isochronal annealing studies of quenched and slow‐cooled crystals indicate that the substitutional H, as monitored by the O–H stretching frequency at 3296 cm‐1, is not mobile at <800 K. However, under the influence of electron irradiation, H is mobile below room temperature. The net result of the irradiations is the appearance of the paramagnetic vacancy left behind by the H and an enhancement of the amplitude of the Mg(OH)2 absorption band. The mobility of the substitutional H, which was found to be a strong function of the irradiation temperature, was greater at 290 K than at 85 K. A mechanism for the displacement of the substitutional H is proposed.
Effect of Grinding on Flaw Geometry and Fracture of Glass
Authors: MECHOLSKY JOHN J. , FREIMAN S. W. , RICE ROY W.
Published: June 2006

Fracture mechanics is combined with fracture surface analysis to analyze brittle failure of glass bars which were tested relative to the direction of grinding. Grinding essentially produces two sets of flaws from which failure occurs. In the most severe set, formed basically parallel to the grinding direction, the ratio of the average depth (a) to the half‐width (b) is 0.5. In the less severe set, formed perpendicular to the grinding direction, the average a/b ratio is 1.6. In both sets the most severe flaws are generally associated with a particularly deep grinding groove or gouge. The strength reduction resulting from testing perpendicular to the grinding direction results from the larger flaw size and slightly higher stress‐intensity factor resulting from the greater ellipticity of the flaws formed parallel to the grinding grooves and perpendicular to the tensile axis. Detailed analysis of these 2 sets of flaws causing failure of appropriately oriented specimens shows that (1) the fracture mirror radius, r, occurs at a constant stress‐intensity level independent of flaw geometry; (2) unsymmetric fracture mirrors result from unsymmetric, irregular flaws leading to unsymmetric stress‐intensity distributions; (3) is constant for semielliptical flaws; and (4) fracture energy calculated from an expression including mirror constants, the flaw‐to‐mirror size ratio, and the flaw geometry agrees with measured values over a wide range of a/b values.
Thermally Induced Wavy Hertzian Fracture
Authors: BAHAT DOV
Published: June 2006

Reproducible “complexed” Hertzian cones were formed in glass as a result of thermally induced tensile stresses. These cones differ from normal cones by having wavy profile patterns, indicating two modes of fracture operating alternately. One mode is shallow and the other steep, together averaging a crack angle of 18.9 ± 1°. The thermal technique offers new test conditions for studying Hertzian fracture.
Defect Structure of α‐Al2O3 Doph with Magnesium
Authors: MOHAPATRA S. K. , KRÖGER F. A.
Published: June 2006

The conductivity of single crystals of Al2O3+ Mg and the ionic and electronic transference numbers were measured at high temperatures as a function of orientation, oxygen pressure, and temperature. Optical absorption in the visible range was measured on cooled annealed crystals. The results are interpreted on the basis of a model with either Ali3‐ or VO as the dominant native defects and lead to expressions for the ionic mobility as a function of T and orientation, and for the position of the MgAl’level in the forbidden gap.
Interaction Between UO2 Pellets and Cladding in Water Reactor Fuel Pins
Authors: WADDINGTON J. S. , ROBERTS GEOFFREY , DICKSON I. K.
Published: June 2006

The contribution of mechanical interaction between fuel and cladding to the change in length of a fuel pin has been identified from an analysis of data from the Steam‐Generating Heavy‐Water Reactor. A model which accounts for this effect uses the creep properties of fuel and cladding.
The System Zirconia‐Scandia
Authors: RUH ROBERT , GARRETT H. J. , DOMAGALA R. F. , PATEL V. A.
Published: June 2006

The system zirconia‐scandia was investigated using X‐ray diffraction analysis, differential thermal analysis, metallographic analysis, and melting point studies. Results reveal the monoclinic α1 phase (0 to 2 mol% Sc2O3), the tetragonal α2’phase (5 to 8% Sc2O3), the rhombohedral β phase (9 to 13% Sc2O3), the rhombohedral γ phase (15 to 23% Sc2O3), the rhombohedral δ phase (24 to 40% Sc2O3), and the cubic % phase (77.5 to 100% Sc2O3). The monoclinic α1 phase and the tetragonal α2’phase were found to transform to the tetragonal α2 phase over a wide temperature range depending on composition. The β, γ, and α phases transformed to a cubic phase at temperatures of %600%, 1100%, and 1300%C, respectively. A maximum melting point of %2870%C was found at %10% Sc2O3 and a eutectic at %2400%C at 55% Sc2O3.
Measurement and Interpretation of CO and Kr + Xe in Irradiated ThO2‐Containing HTGR Fuel Particles
Authors: LINDEMER T. B.
Published: June 2006

The irradiation of microspheres of ThO2 and Th0.81U0.19O2in the form of high‐temperature gas‐cooled reactor (HTGR) particles resulted in the buildup of CO as well as Kr + Xe within the particle. The particles were later equilibrated at 1325T2270 K, crushed, and the CO and Kr + Xe contents were measured. Oxygen released as CO can be represented by the expression O/f=74.6F exp (–7400/T), where O/f is the moles of oxygen released per mole of fissioned actinide, F is fission per initial heavy‐metal atom, and T is the equilibration temperature. This oxygen release is reasonably consistent with that predicted from thermodynamic data for the oxides of the fuel and fission products. The burnup dependence of the release of Kr and Xe to the void space within the particle was consistent with published data and approached the theoretical value for the 233u‐235U system, (Kr+Xe)/f0.32.
Chemical Instability of Metal‐Deficient Hexagonal Ferrites with W Structure
Authors: LOTGERING F. K. , VROMANS P. H. G. M.
Published: June 2006

The hexagonal ferrite W=BaFe2+2Fe3+16O27, which is in equilibrium with oxygen under 0.015 atm at 1350°C, is oxidized in the range 250° to 1100°C in the same atmosphere to BaFe3+16+2x Fe22‐3x>xO27 with 2–3x<0.03. The metal‐deficient W structure is chemically unstable and decomposes after longer annealing at the same temperature. This difference in oxidation and decomposition rate is attributed to a difference in the diffusion rate of barium and iron ions.
Directionally Solidified Ceramic Eutectics
Authors: ASHBROOK R. L.
Published: June 2006

The aligned structures which result from the directional solidification (DS) of ceramic eutectics are of interest because of their potential for use in electronic devices and as structural materials. Techniques for growing DS ceramic eutectics are briefly discussed. The principles and controlling parameters of DS eutectic growth are described. The criteria for plane‐front growth and the effect of growth rate on interlamellar or interfiber spacing are discussed. Examples of the effect of growth parameters on the alignment of the microstructure are given. Examples of the mechanical properties of directionally solidified oxide‐oxide ceramics are also cited.
Redox Equilibria of Multivalent Ions in Silicate Glasses
Authors: LAUER HOWARD V. , MORRIS RICHARD V.
Published: June 2006

Experimental studies were made on the compositional dependence of the redox equilibrium of Eu in synthetic silicate liquids, together with an empirical model describing the observed compositional dependence. Electron paramagnetic resonance (EPR) was used to measure the concentration ratio of Eu2+ to Eu3+ in various glasses formed by rapidly quenching silicate liquids. The compositional field studied comprised mixtures of SiO2, TiO2, Al2O3, CaO, MgO, and Na2O. The proposed model describes the Eu2+/Eu3+ ratio over the entire compositional field in terms of parameters easily related to each glass composition. The general applicability and utility of the model is further demonstrated by its application to the Fe2+‐Fe3+, Ce3+‐Ce4+, and Cr3+‐Cr6+ redox reactions in binary alkali oxide silicate glasses of Li, Na, and K.
High‐Temperature Reaction Between Cemented Tungsten Carbide and Copper
Authors: YAMAGUCHI TAKASHI , OKADA MOTOHIDE
Published: June 2006

Interdiffusion in the system cemented tungsten carbide‐molten copper has been studied in the range ≤1120°C with special emphasis on the effects of WC grain size and Co content. Techniques used for analyzing the diffusion layers obtained are EPMA, optical microscopy, and microhardness measurement. A Cu‐bonded WC layer develops with simultaneous diffusion of Co from the cemented carbide into the bulk copper. The Cu‐bonded WC layer grows until a Co‐rich layer forms at the Cu/WC‐Co interface; further heating pushes the Cu‐bonded WC layer deep into the bulk cemented carbide without any significant change in layer thickness. When the WC grain size is reduced and the cobalt content increased, the penetration of copper into cemented carbides increases. A tentative mechanism of interdiffusion has been proposed based on the experimental results.
Multiphase Ternary Diffusion Couples
Authors: CHRISTENSEN N. H.
Published: June 2006

The study of diffusion couples whose reactants or products have multiphase structure gives useful insight into ceramic reactions. When a coarse‐scaled resolution is applied, multiphase regions may be treated similarly to 1‐phase regions with respect to diffusional behavior. In the phase diagram of ternary diffusion couples, a moving boundary occurs where the diffusion path crosses a 3‐phase field in any direction or a 2‐phase field along a tie line. The problems of simple dissolution, incongruent dissolution, 1‐phase layer growth, and 2‐phase layer growth are discussed for structures of solid solution‐free solids dispersed in continuous melts.
Characterization of Additive‐Modified Beta Alumina Ceramics by Nuclear Magnetic Resonance
Authors: ROTH W. L. , CHUNG INTAIK , STORY H. S.
Published: June 2006

Sintered compacts of beta alumina have been made with additives of Li2O, MgO, NiO, CaO, and Y2O3. The motional narrowing and quadrupole interactions of sodium were investigated as a function of temperature and additive concentration by wide‐line NMR. The Li2O, MgO, and NiO additives are incorporated in the beta alumina structure and enhance Na motion; CaO dissolves and inhibits Na motion; and Y2O3 forms a second phase and has no effect on the Na. The effects of the additives are explained by the size and charge of the additive cation, and intragranular and intergranular conductivity in doped beta alumina ceramics are predicted.
Activation Energies in the Diffusional Creep of Polycrystalline Ceramics
Authors: HODGE J. D. , LESSING P. A. , GORDON R. S.
Published: June 2006

A mixed diffusional creep mechanism in a polycrystalline ceramic can cause the apparent activation energy to vary with temperature and grain size. For mechanisms involving parallel transport paths for the same ion (e.g. cation lattice and grain‐boundary diffusion), the process with the lowest activation energy will be dominant (i.e. rate‐limiting) at low temperatures and the process with the highest activation energy will dominate at high temperatures. However, for mechanisms involving coupled and parallel diffusional steps (e.g. cation lattice and anion grain‐boundary diffusion), the process with the lowest activation energy will be dominant at high temperatures whereas the high‐activation‐energy process will dominate at low temperatures. Examples of these effects are presented for the diffusional creep of polycrystalline MgO and A12O3 doped with Fe. Variations in creep activation energy with grain size and temperature are only significant when the difference in activation energies for the competing processes is significant and the temperature range investigated is large.
Composition of Solutions in Contact with Hydrating β‐Dicalcium Silicate
Authors: TONG H. S. , YOUNG J. F.
Published: June 2006

The concentration of ionic species in the solution in contact with hydrating dicalcium silicate (C2S) has been studied as a function of time and in the presence of admixtures. The ionic product for calcium hydroxide increases quite slowly and saturation levels are not greatly exceeded at any time. Small quantities of C3S control the ionic concentrations and cause considerable super‐saturation with respect to calcium hydroxide. The implications of the present data with respect to C2S hydration are discussed.
A One‐Dimensional Model of Stretching Float Glass
Authors: NARAYANASWAMY O. S.
Published: June 2006

One of the important steps in the manufacture of glass by the float process is the control of glass thickness by stretching the ribbon. The first step in a program to model the stretching of float glass is discussed. A simple, 1‐dimensional analysis is presented for the mechanics of stretching a free ribbon, i.e. one without edge constraints in the stretching region. For the case of a stiff (“cold”) ribbon, the present analysis yields closed‐form solutions which are generally valid but do not encompass all phenomena of interest. The stretching of a “hot” ribbon is, therefore, treated quantitatively by computer simulation. This approach is used to illustrate the differential attenuation of the width and thickness of hot ribbons. In another numerical example, the caculated width attenuation is compared with the results of in‐plant measurements.
Dielectric and Electromechanical Properties of (Li, Na)NbO3 Ceramics
Authors: HENSON R. M. , ZEYFANG R. R. , KIEHL K. V.
Published: June 2006

Permittivity, dielectric loss tangent, radial coupling coefficient, and radial frequency constant have been measured as a function of composition for pressure‐sintered Li.rNa1‐xNbO3 in the range 0.015≤x≤0.15. An anomaly in each of these properties when plotted as a function of composition is associated with a structural transition between 2 ferroelectric phases; this transition lies near room temperature for compositions where x∼0.12. Compositions near this phase boundary exhibit room‐temperature properties which are of interest for high‐frequency filter applications.
Structural Integrity in Severe Thermal Environments
Authors: EVANS A. G. , CHARLES E. A.
Published: June 2006

The theory of structural stability of ceramics in severe thermal environments was explored via the use of precracking. It was shown that structural stability should be possible when an array of precracks is used, but that the precracks required for this purpose are relatively large. The approach is thus limited to systems which are not required to sustain a significant mechanical stress. Preliminary quenching experiments on short cylinders confirmed that stabilization can be achieved by precracking.
Structural Analysis of the Transition Phases in the Kaolinite‐Mullite Thermal Sequence
Authors: LEONARD A. J.
Published: June 2006

Dehydroxylation phases of a kaolinite from Zettlitz, Czechoslovakia, were investigated by radial electron density distribution (RED) and X‐ray spectroscopy. Special emphasis was placed on the 2 amorphous or poorly crystallized transition phases, i.e. metakaolinite (600° to 800°C) and the spinel structure (900°C). The RED diffraction method, which is particularly suited to the study of such materials, indicated (1) a particularly expanded tetrahedral configuration for the Al atoms in metakaolinite and (2) a pure Al2O3 spinel structure. The first result confirms earlier observations; the second eliminates, for the experimental conditions and kaolinite studied, the possibility of the formation of an Al‐Si spinel structure with the AI and Si occupying the octahedral and tetrahedral interstices, respectively. Complementary measurements on the AlKα line shifts for the same samples support the present interpretation. Determination of the apparent Si coordination number by the same spectroscopy procedure revealed a regular 4 coordination for all phases except the end‐member mullite.
Creep Behavior and Grain‐Boundary Sliding in Polycrystalline A12O3
Authors: CANNON W. ROGER , SHERBY OLEG D.
Published: June 2006

The creep properties of polycrystalline A12O3 (grain size 14 to 65 μm) were examined under compressive stresses of between 4,000 and 18,000 psi (27.6 and 124 MPa) in the range 1600° to 1700°C. Two distinct types of behavior were observed. The creep rate of medium‐grained specimens (14 to 30 μm) could be described by ασ1.2/d2 where σ is the applied stress and d is the grain size. These results are consistent with the Nabarro‐Herring creep mechanism. For the coarse‐grained (65 μm) specimens, the creep rate was related to the stress by ασ2.6. This behavior was not related to cracking; instead, a dislocation mechanism was thought to be rate‐controlling. Considerable evidence for grain‐boundary sliding was seen, and measurements showed that grain‐boundary sliding contributed between 46 and 77% of the total strain in the 3 medium‐grained specimens examined and between 38 and 50% in the 3 coarsegrained specimens examined.
Self‐Diffusion of 60Co in Co1‐xO Single Crystals of Controlled Stoichiometry
Authors: RAHMAN S. F. , BERARD M. F.
Published: June 2006

Cobalt tracer self‐diffusion coefficients were determined in single crystals of Co1‐x O at 1037° to 1350°C and for x=0.002 to 0.00s. In crystals with x fixed at 0.005, the results were

The activation energy in this constant‐stoichiometry case was identified as the enthalpy of motion for Co ions moving via a vacancy jump mechanism. Based on known stoichiometry rela‐ tions, a published activation energy for Co self‐diffusion mea‐ surements in air was corrected to yield an enthalpy of motion in excellent agreement with the number given above. At a constant temperature of 115O0°±2°C, the Po2 dependence of Co self‐ diffusion was

The Po2 expynent suggests that the predominant mobile ion defects are singly ionized Co vacancies. Simple defect reactions with no modifications for defect clustering were adequate to explain all results obtained.
Crystallization of As2Se3‐As2Te3 Glasses
Authors: LOEHMAN RONALD E. , ARMSTRONG ALAN J.
Published: June 2006

Differential scanning calorimetry studies of As40SexTe60‐x glasses with 0≤x≤60 show a 2‐stage crystallization when 5≤x≤35, followed by a double‐peaked melting endotherm. The enthalpy of crystallization for the low‐temperature species is independent of composition and equals 11.6±0.9 cal/g for x≤25, whereas that for the high‐temperature species decreases from 2.2±0.2 cal/g for x = 5 to 1.1±0.3 cal/g for x =15. The total enthalpy of melting also is independent of composition and equals 18.8±1.2 cal/g for x≤25. No crystallization was observed for xe40. The high‐temperature phase has the mono‐clinic As2Te3 structure; that of the low‐temperature phase was not identified. Annealing experiments for compositions with x = 15 or 20 gave time‐temperature transformation maps. A kinetic analysis of the data was inconclusive.
Inhomogeneity‐Packing Density Relations in Binary hwders
Authors: MESSING GARY L. , ONODA GEORGE Y.
Published: June 2006

A theoretical procedure for determining the specific volume of an inhomogeneous binary mixture having a large radius ratio is presented. The procedure is based on the hypothesis that the Furnas model holds on a local level. The methodology developed is demonstrated using two hypothetical compositional distribution functions. In one case the compositional distribution describes changes that occur from a completely unmixed to a completely mixed state. The second utilizes the normal distribution for describing smaller compositional variations.
Strength Degradation of Thermally Tempered Glass Plates
Authors: MARSHALL D. B. , LAWN B. R.
Published: June 2006

An earlier theory of contact‐induced strength degradation of brittle materials is extended to include plates in residual surface compression. The scale of the strength‐controlling flaw is predicted by indentation fracture mechanics, with the modifying effect of the residual field incorporated into both indentation and strength equations. Experimental verification of the predictions is obtained from diamond‐pyramid indentation tests on thermally tempered glass plates. As with untempered plates, the theory accounts for the load dependence of the strength loss; it also explains the insensitivity of the degradation characteristics to initial flaw distribution and identifies toughness as the controlling material parameter. Most significant, however, is the demonstration that surface strengthening can produce dramatic improvements in degradation resistance. The possibility of obtaining all parameters necessary for a complete degradation analysis of a given tempered inaterial entirely by routine indentation/strength testing is discussed.
Effect of Composition on the Mechanical Properties of Aluminosilicate and Borosilicate Glasses
Authors: EAGAN ROBERT J. , SWEAREKGEN J. C.
Published: June 2006

Elastic moduli and fracture toughness were determined for several glasses in the systems soda‐alumina‐silica, calcia‐alumina‐silica, and soda‐boric oxide‐silica. Results for the aluminosilicates are analyzed in terms of Al3+:Na+ ratios. The mechanical properties do not show maxima or minima at the Al3+:Na+ ratio of 1, in contrast to conductivity, helium permeability, and refractive index. The moduli and toughness increase with Al3+:Na+ ratio, which is consistent with increased coherency of the glass network. Glasses which contain B2O3 instead of Al2O3 have slightly higher moduli but are considerably tougher. The moduli of calcium aluminosilicate glasses are ∼25% greater than sodium aluminosilicates, whereas the fracture toughnesses are similar.
Permeation Eccentricities of He, Ne, and D‐T from Soda‐Lime Glass Microbubbles
Authors: SOUERS P. C. , MOEN I. , LINDAHL R. O. , TSUGAWA R. T.
Published: June 2006

Permeation of 3He, Ne, and D‐T (deuterium‐tritium) was studied through batches of several million glass microbubbles. Although the calculated permeabilities agree roughly with literature data, the bubbles show several vagaries. Isothermal outgassing is not exponential but shows “tails” that become more pronounced at lower temperatures. An isotopic disproportionation effect occurs in the bubble loading at 698 K. Gas that has permeated the glass walls is more deuterium‐rich and the effect is increased by large amounts of 3He in the feed gas. Finally, a slow and unexplained leakage occurs when loaded bubbles are stored for many months at 243 K. Data are also presented on bubble size distributions and mean wall thicknesses.
Aging of Dielectric Dispersion in PLZT Relaxor Ceramics
Authors: SCHULZE W. A. , BIGGERS J. V. , CROSS L. E.
Published: June 2006

The effect of aging on the temperature dependence of permittivity (K) and tan δ as a function of frequency was examined for both ferroelectric and antiferroelectric PLZT compositions. All compositions aged near their transition temperatures exhibited a marked decrease in dispersion between the aging temperature and the temperature of the high frequency (100 kHz) permittivity peak. These results are discussed in terms of the Smolenskii model for dielectric relaxation.
Enhanced Thermal Stress Resistance of Structural Ceramics with Thermal Conductivity Gradient
Authors: HASSELMAN D. P. H. , YOUNGBLOOD G. E.
Published: June 2006

The hypothesis is presented that the maximum tensile thermal stresses in brittle ceramics can be reduced significantly by a redistribution of the temperature profile using a spatially varying thermal conductivity. On the basis of a hollow circular cylinder subjected to radially inward or outward steady‐state heat flow, it is shown that such a spatially varying thermal conductivity can lead to significant decreases in magnitude of the maximum tensile thermal stress. Possible techniques of creating such thermal conductivity variations are discussed briefly.
Compounds and Properties of the System Si‐Al‐O‐N
Authors: LAND P. L. , WIMMER J. M. , BURNS R. W. , CHOUDHURY N. S.
Published: June 2006

A product or quasi‐equilibrium diagram for compounds formed in the system Si‐Al‐O‐N at 1800°C in 1 atm N2 is presented, X‐ray diffraction data for phases are given, and the reaction and sintering processes are discussed. Data for the lattice expansion of the β‐Si3N4 structure accompanying the incorporation of Al‐O is presented and used to calculate theoretical densities.
Mullite Crystallization from SiO2‐Al2O3 Melts
Authors: RISBUD SUBHASH H. , PASK JOSEPH A.
Published: June 2006

SiO2‐Al2O3 melts containing 42 and 60 wt% A12O3 were homogenized at 2090°C (∼10°) and crystallized by various heat treatment schedules in sealed molybdenum crucibles. Mullite containing ∼78 wt% A12O3 precipitated from the 60 wt% A12O3 melts at ∼1325°± 20°C, which is the boundary of a previously calculated liquid miscibility gap. When the homogenized melts were heat‐treated within this gap, the A12O3 in the mullite decreased with a corresponding increase in the Al2O3 content of the glass. A similar decrease of Al2O3 in mullite was observed when crystallized melts were reheated at 1725°± 10°C; the lowest A12O3 content (∼73.5 wt%) was in melts that were reheated for 110 h. All melts indicated that the composition of the precipitating mullite was sensitive to the heat treatment of the melts.