bluuebunny/crossref_metadata_2025 huggingface dataset:
Oxidation of Thin Sheet Reaction‐Sintered Silicon Nitride
Authors: WARBURTON J. B. , ANTILL J. E. , HAWES R. W. M.
Published: June 2006

Oxidation of reaction‐sintered silicon nitride was studied in damp air. The formation of “passive” silica films was investigated at 1 atm and 700 to 1100°C and some limited work on weight loss behavior was performed in vacuo of 10−8 to 10−5 atm at 1050 to 1200°C. Passive behavior was dominated by reaction in the pore network. Oxidation was extensive at 900 to 1000° but slight at 700 to 800°C. At 1100°C a protective skin limited reaction. Weight loss in vacuo was slight at 1050°C. The vacuum pressure required to suppress the weight loss increased from 4 to 5 × 10−7 atm at 1050° to 1.5 to 2.5 × 10−5 atm at 1200°C.
Lattice Misorientation and Displaced Volume for Microhardness Indentations in MgO Crystals
Authors: ARMSTRONG R. W. , WU C. Cm.
Published: June 2006

Diamond pyramid indentations on (001) surfaces were studied by X‐ray diffraction microscopy and scanning electron microscopy. These methods reveal the patterns of internal strains and external surface relief, respectively, which accompany various deformation (and cracking) processes at the indentation sites. These processes are controlled by the formation of sessile 〈110〉 dislocations which prevent additional straining of the crystals along [001]. The results provide evidence that the local crystal work‐hardening behavior is important in determining the microhardness values.
The Dominant Type of Atomic Disorder in α‐Al2O3
Authors: MOHAPATRA S. K. , KRÖGER F. A.
Published: June 2006

Comparison of the energy of formation per defect, as deduced from experimental results on α‐Al2O3 doped with donors and acceptors on the basis of various models, with theoretical values calculated by Dienes et al. for various disorder models shows closest correspondence of the exFrimentd values with the smallest theoretical values (obtained for Schottky disorder). This indicates that the theoretical results are reliable and that Schottky disorder is the major type of atomic disorder in α‐Al2O3. Creep data on Al2O3:Fe by Hollenberg and Gordon make it possible to determine the enthalpy of Frenkel disorder of Al.
Chemomechanical Effect in Doped and Intrinsic Silicon
Authors: YOST GERALD H. , WILLIAMS WENDELL S.
Published: June 2006

The electrochemical environment of a solid affects its near‐surface hardness. Westwood showed that a zero zeta potential for a nonmetal in an electrolyte can correspond with a maximum surface hardness; the present study shows that for doped and intrinsic silicon the concentration of electrolyte which gives the most negative zeta potential corresponds with a minimum surface hardness.
Variation of Densities and Refractive Indices in Tempered Glass
Authors: GARDON ROBERT
Published: June 2006

A knowledge of density distributions in tempered glass is helpful in better understanding the tempering process. Since the densities and refractive indices of a glass are uniquely related, density distributions were determined by a schlieren technique which gives a direct measure of index gradients. The advantages of this nondestructive approach are that it yields the location of each density fraction within the glass and that it is equally applicable to fragments and whole pieces of tempered glass. Thus, it also allows observation of changes in local densities which accompany fracture and the release of internal stresses.
Kinetic Study of Cu+−Cu2+ Equilibrium in Sodium Na2O−Al2O3−B2O3 Glass
Authors: SINGH SARYOO PRASAD , PRASAD GUR , NATH P.
Published: June 2006

The Cu+−Cu2+ equilibrium in sodium aluminoborate glass with an air atmosphere was studied at 950°, 1050°, and 1150°C. Equations suggested to represent the equilibrium reaction between oxidized and reduced species and oxygen were critically examined. An equation to represent the Cu+−Cu2+ equilibrium reaction was suggested. The reaction was observed to follow first‐order kinetics. Enthalpy of the reaction was—12.5 kcal/mol.
Creep of Hardened Portland Cement Paste Under Cyclic Temperature
Authors: RAINFORD E. C. , TIMUSK J.
Published: June 2006

Sealed cement paste specimens (water/cement ratio 0.5), loaded at 28 days to a constant stress/strength ratio of 0.2, were subjected to cyclic temperatures of 90° to 23°F (32.2° to —5°C) and their creep behavior was studied in relation to the amplitude, frequency, and mean value of the cyclic temperature. Temperature cycling increased creep above that which occurred at the mean temperature and this creep may be greater than that which would occur at the highest temperature. Assuming that creep is a rate‐process phenomenon, it is possible to predict the creep under one temperature regime, given the creep under another and the temperature histories of both. Also, the ratio (creep under cyclic temperature/creep at the mean constant temperature) bears a hyperbolic cosine relation to the temperature amplitude; thus, if all else is equal, a greater amplitude gives a greater creep. Within the limits of the experiment, the greater the period of the cyclic temperature the greater the creep. The increase in creep above that at mean temperature appears to be greater when the mean temperature is in the range where evaporable water freezes. Irrecoverable creep appears to increase with the amplitude of temperature as well as with temperature per se. The influence of variable temperature on creep is explained in terms of the superimposition of hygrothermal diffusion on stress‐induced moisture diffusion in the creeping specimen, as well as the influence of temperature on the diffusion coefficient of the diffusing mass.
Spectral Variation of SKβ Emission with Sulfur Content in As‐S Glasses
Authors: OOBA SHIGEKI , UENO SEIICHI , GOHSHI YOHICHI
Published: June 2006

The bonding and chemical state of sulfur in binary As‐S glasses were investigated by determining the SKβ spectra with a vacuum 2‐crystal X‐ray spectrometer equipped with Ge(ll1) crystal analyzers. For glasses with sulfur contents <60 at.%, the spectra were similar to those of realgar (crystalline As4S4) and orpiment (crystalline As2S3); the profile of the SKβ spectrum did not change when half the sulfur was replaced by selenium. For sulfur contents > 60 at.%, the spectra became progressively similar to that of elemental sulfur with increasing sulfur content. It was found that S‐S bonding occurs in the high‐sulfur glasses.
Criteria for the Selection of Liquids for Physical Models of Glass Tanks
Authors: GUARGA RAFAEL A.
Published: June 2006

The similarity between models and prototypes of glass tank furnaces is analyzed, considering both the hydrodynamic and thermodynamic aspects of the problem. By applying inspectional analysis to the Navier‐Stokes equations and to the first principle of thermodynamics, suftkiently similar conditions are obtained between model and prototype. Such conditions are used to choose the best liquid to simulate the melted glass. It is concluded that the selection of a liquid for the model requires that the hydrodynamic and thermodynamic aspects of the problem be considered, that a set of conditions may be established to ensure the similarity between model and prototype, and that such conditions may generally be fulfilled by real liquids.
Crack‐Front Curvature and Glass Slow Fracture
Authors: QUACKENBUSH C. L. , FRECHETTE V. D.
Published: June 2006

Fracture‐surface markings on glass samples broken under liquid decane indicate that region II constitutes a transition between environmentally assisted and environmentally free fracture modes. Region II itself is subdivided into two stages, both characterized by negative crack‐front curvature. This reversed curvature develops initially to allow more time for diffusion of the environmental agent to the middle portion of the fracture front and leads to increased local stress which activates the environmentally independent fracture mode at the center of the fracture front. Most of region II occurs in the latter mixed‐mode fracture condition.
β→α Transformation in Polycrystalline Sic: II, Interfacial Energetics
Authors: MITCHELL T. E. , OGBUJI L. U. , HEUER A. H.
Published: June 2006

The β→α transformation in polycrystalline Sic occurs by the rapid growth of composite grains consisting of α‐SiC plates “sandwiched” between grains of recrystallizedp‐SiC. Growth of these composite grains into the fine‐grained β matrix occurs much more rapidly than thickening of the α plates into their β“envelopes.” A phenomenological analysis of the energetics of these several growth processes is presented and it is shown that the observations can be explained by the extreme anisotropy of the interfacial energy between β− and α−SiC; {lll}β(0001)α interfaces have much lower energies than random, β/α interfaces. In reaction‐sintered Sic, this anisotropy is manifested by rapid growth of a seeds along their basal planes into the epitaxial β reaction product; slow growth occurs perpendicular to the basal planes.
Plastic Deformation Behavior and Dislocation Structure of CdTe Single Crystals
Authors: HALL E. L. , SANDE J. B. VANDER
Published: June 2006

Single‐crystal CdTe specimens were deformed in compression at 25°, 200°, 300°, and 500°C to various levels of plastic strain and to failure. Deformation characteristics at each temperature are given as curves of shear stress vs shear strain and the effect of test temperature on deformation behavior is examined. The dislocation structure of the CdTe samples deformed at high temperatures is examined using transmission electron microscopy. The relation between the deformation properties and the corresponding microstructure in CdTe is explored using previously developed models to describe metallic and nonmetallic crystalline materials.
Microstructure of SiC Prepared by Chemical Vapor Deposition
Authors: SHINOZAKI SAMUEL S. , SATO HIROSHI
Published: June 2006

Silicon carbide prepared by chemical vapor deposition at a substrate temperature of ∼1400425‐429°C was investigated. Optical microscopy showed that the growth characteristic is dendritic; the deposits consist of columnar blocks within each of which the orientation of crystals is approximately the same. Small pores occur along the boundaries of these blocks. Transmission electron microscopy revealed finer details of the growth characteristics. The crystals were mostly 3C in structure, but crystals with 2H and one‐dimensionally‐disordered structures were also found. The 3C crystals are mostly dendritic, but some columnar growth with alternating twin bands occurs. Both 2H and one‐dimensionallydisordered crystals exhibit a columnar habit, reflecting the difference in crystal symmetry from 3C. In all these crystals, the c axis (or one of the <111> axes in 3C crystals) lies perpendicular to the substrate.
Effect of Gadolinium on Magnetite Exsolution in a Garnet Matrix
Authors: LAVAL J. Y.
Published: June 2006

Magnetite exsolves from a garnet matrix via a pretransformed nucleus when gadolinium is substituted for yttrium in yttrium iron garnet. The effect of gadolinium on the exsolution mechanism was studied by X‐ray microanalysis using a transmission electron microscope; a strong decrease in gadolinium concentration was found within the pretransformed nuclei. The ionic structure of the garnet lattice indicates that Gd3+ ions allow a shear process which leads to the pretransformed nuclei, whereas with Y3+ ion diffusion is the only process for magnetite exsolution.
Suppression of Cavity Formation in Ceramics: Prospects for Superplasticity
Authors: EVANS A. G. , RICE J. R. , HIRTH J. P.
Published: June 2006

Ceramics exhibit macroscopic stress/strain rate relations that should lead to superplastic extension. However, premature fracture is normally encountered, due to the formation and growth of grain‐boundary cavities. Thus, cavity nucleation and growth were analyzed in an attempt to identify microstructures and/or strain‐rate regimes that would suppress cavity evolution and hence allow superplasticity. Analysis of cavity nucleation indicates that fine‐grained materials devoid of grain‐boundary amorphous phases and inclusions should sustain substantial deformation rates without nucleating cavities, especially if solid‐solution additions that encourage rapid grain‐boundary diffusion (while not excessively decreasing surface energy) are identified. The analysis of void growth indicates that high relative surface diffusivities are also desirable, indicating that alloy additions that do not depress (and probably enhance) the relative surface diffusivities must be selected.
Effect of Irradiation Temperature on the Growth of Helium Bubbles in Boron Carbide
Authors: HOLLENBERG G. W. , MASTEL B. , BASMAJIAN J. A.
Published: June 2006

Boron carbide, in nuclear reactor neutron absorber applications, generates large quantities of helium, some of which is trapped in small bubbles within the grains. Transmission electron microscopy was used to examine the size distribution, shape, and density of these bubbles in boron carbide irradiated, at 540° to 1850°C, to burnups of 62 × 1020 captures/cm3. Bubble density was reduced but bubble diameter was increased at high temperatures. Bubbles were flat disks at low temperatures and more equiaxed at higher temperatures.
The Effect of Atmosphere on the Sintering of Fe3O4 and Fe2O3 Powders at Low Temperatures
Authors: HAYES P. C.
Published: June 2006

The sintering kinetics of submicrometer Fe3O4 and Fe2O3 powders were investigated at 300° to 500°C. Using measurements of the rate of reduction of surface area, the coefficients of surface diffusion on the oxides are estimated for a range of oxygen partial pressures. The surface‐diffusion coefficients appear to be independent of PO2 for magnetite and only slightly dependent on PO2 for hematite.
The Interaction of Molten Silicon with Silicon Aluminum Oxynitrides
Authors: WILLS R. R. , SEKERCIOGLU I. , NIESZ D. E.
Published: June 2006

Silicon aluminum oxynitride solid solutions (sialons) based on β‐Si3N4 and Si2N2O behave differently in contact with molten sih'con. The Si2N2O‐based sialons convert to almost pure Si3N4, apparently through a two‐step decomposition and solution‐precipitation reaction, whereas the β‐Si3N4 sialons are preferentially attacked at the grain boundaries. The composition of the grain‐boundary phase appears to control the rate of reaction.
Solid‐State Kinetics of LaAl11O18
Authors: ROPP R. C. , CARROLL B.
Published: June 2006

Synthesis of LaAl11O18 by the solid‐state reaction of La2O3 and Al2O3 occurs in two stages, i.e. LaAlO3 forms immediately at 1450°C in air but LaAl11O18 formation is very slow and requires up to 141 days. First‐order kinetics were observed and an activation energy of 118±4 kcal was calculated. Formation of LaAl11O18 depends on external O2‐gas partial pressure. In an N2‐gas atmosphere, the very slow formation of LaAl11O18, observed in air, is slowed even further. Possible mechanisms are also discussed.
Oxidation of CVD Si3N4 at 1550° to 1650°C
Authors: HIRAI TOSHIO , NIIHARA KOICHI , GOTO TAKASHI
Published: June 2006

A thermo gravimetric study of the oxidation behavior of chemically vapor‐deposited amorphous and crystalline Si3N4 (CVD Si3N4) was made in dry oxygen (0.1 MPa) at 1550° to 1650°C. The specimens were prepared under various deposition conditions using a mixture of SiCl4, NH3, and H2 gases. The crystalline CVD Si3N4 indicated a parabolic oxidation kinetics over the whole temperature range, whereas the amorphous CVD Si3N4 changed from a parabolic to a linear law with increased temperature. The oxidation mechanism is discussed in terms of the activation energy for the oxidation and the microstructure of the formed oxide films.
Swelling and Gas Release in ZnO
Authors: SOLOMON A. A. , HSU F.
Published: June 2006

Swelling and gas release in a model ceramic system, ZnO, were studied under known internal and external pressures, oxygen partial pressures, and temperatures. When gas was not released, the instantaneous swelling strain rate was: εα(DF exp‐Q/RT) where DF is the instantaneous pressure driving force for swelling, Q= 141 ± 13 kcal/mol, and RT has its usual meaning. For a fixed initial driving force for swelling, the strain rate decreased as t−1/3 where t is time. Volumetric swelling strains of ≥ 11% were measured prior to gas release, indicating that swelling is not simply reversed sintering. Gas release was usually observed and occurred by the interconnection of inter‐granular porosity. A resintering process immediately followed gas release, but at a slower rate than the initial sintering rate at the same density. Analysis of the swelling experiments yielded a surface energy of ∼0.3 J/m2 at 920°C for ZnO.
Studies on the Acid Resistance of E Glass
Authors: RAMACHANDRAN B. E. , PAI B. C. , BALASUBRAMANIAN N.
Published: June 2006

The acid resistance of E glass was studied by treating the material in HC1. During the acid treatment, nonsiliceous ions were leached out from the glass structure, due to ion exchange. The parameters which govern the removal are the concentration of the acid, time of contact, and acid temperature. At lower acid concentrations (<2N), calcium oxide and aluminum oxide could not be removed completely. By increasing the concentration of the acid to 4N, most of the nonsiliceous ions were leached out. The number of ions removed increases with the increase in treatment time and temperature. When the glass was treated with 4N HCI for a long time, there was a fluctuation in the total number of ions removed. The teachability of E glass is explained using the Muggins formula and the R2O/SiO2 ratio.
Solid Solutions in the System Taeniolite‐Sodium Taeniolite and Their Properties
Authors: KONDO RENICHI , DAIMON MASAKI , ASAGA KIYOSHI , NISHIKAWA TADAHIRO , KITAJIMA KUNIO , DAIMON NOBUTOSHI
Published: June 2006

Solid solutions in the system taeniolite (KMg2LiSi4O10F2)‐sodium taeniolite (NaMg2LiSi4O10F2) were synthesized to study the solid solubility and swelling characteristics. Based on their melting behavior, crystals were grown for X‐ray structural analysis. A complete solid solution series does not form in this system; there are two types of micas, K‐rich taeniolite (0≤x<0.5, x= Na/Na + K) and Na‐rich taeniolite (0.8<x≤l). The Na‐rich taeniolite exhibits swelling properties, which become less pronounced with increasing potassium content. Melting and crystallization behavior were investigated by DTA. Solid solutions with higher sodium content melted at lower temperatures and crystallization occurred over a wide range of temperatures. To obtain larger crystals, the samples containing small crystallites were remelted at slightly above their melting points, then cooled slowly.
Phase Relations and Crystal Structures of Zn and Cd Tungstates
Authors: MORELL DOUGLAS J. , CANTRELL JOSEPH S. , CHANG LUKE L. Y.
Published: June 2006

The systems ZnO‐WO3 and CdO‐WO3 show similar phase relations, each having a 1:1 phase. Invariant points established are 1182°C and 56 mol% ZnO, 1090° and 34 mol% ZnO, and 1105° and 31.5 mol% CdO. The crystal structure of CdWO4, determined by the single‐crystal method, was isostructural with ZnWO4, a wolframite type. Cell dimensions are a=0.5013, b= 0.5090, and c= 0.5866 nm and γ= 91.46° with a space group P2/b and Z = 2. The measured and calculated densities are 7.83 and 7.79 g/cm3, respectively. ZnWO4 and CdWO4 formed a complete series of solid solutions at 900° to 1160°C, above which melting occurred.
Ferroelectric Energy Conversion with PZT Ceramics Under Shock Loading
Authors: BAUER F. , VOLLRATH K. , EYRAUD L. , FETIVEAU Y.
Published: June 2006

The behavior of various PZT compositions under shock loading shows that obtaining high energy densities requires ceramics having a high remanent polarization and a low permittivity, which release their energy by a ferroelectric → antiferroelectric phase transition. Few “hard” PZT ceramics have these properties. The results are presented and discussed.
Humidity‐Sensitive Electrical Conduction of MgCr2O4‐TiO2 Porous Ceramics
Authors: NITTA TSUNEHARU , TERADA ZIRO , HAYAKAWA SHIGERU
Published: June 2006

The crystalline phase, microstructure, semiconduction, and humidity‐sensitive electrical conduction of MgCr2O4‐TiO2 ceramics were studied. A solid solution with TiO2 up to 30 mol% occurs as a single phase with a pure MgCr2O4‐type spinel structure. The humidity‐sensitive electrical conduction of the MgCr2O4‐TiO2 porous ceramics is the most promising for humidity‐sensing devices.
Refinement of Stress Intensity Factor Estimates for a Peripherally Cracked Spherical Void and a Hemispherical Surface Pit
Authors: Baratta Francis I.
Published: June 2006

An improvement on the first attempt to define stress intensity factors for these cases is presented. The improvement is realized by refining the parameters k and m in the interpolative stress intensity equation. The refinement is obtained by utilizing finite element results for specific crack length‐to‐defect radius ratios. Comparison to other data in the literature is considered good.
Darkening Kinetics of Photochromic Glass at High Excitation Levels
Authors: Kivlighn Herbert D. , DeIasi Richard
Published: June 2006

A conventional copper sensitized photochromic glass was subjected to three excitation intensities, 21 mW/cm2, 45 mW/cm2, and 108 mW/cm2, between 0.3 μm and 0.4 μm. The effect of glass heat treatment as well as excitation intensity on the equilibrium absorption and the darkening rates is described. Results indicated that both the equilibrium absorption and the rate of darkening increase with excitation intensity.
Thermal Etching and Grain‐Boundary Grooving Silicon Ceramics
Authors: ROBERTSON WAYNE M.
Published: June 2006

Polished polycrystalline specimens of Si, Sic, and Si3N4 were heated to high temperatures and the rate of thermal etching was measured. Grain‐boundary grooving occurred on silicon by surface diffusion, with a surface‐diffusion coefficient given by
image

Silicon carbide surfaces became extremely rough and very little grain‐boundary grooving occurred. Silicon nitride decomposed in an N2‐H2, atmosphere with an activation energy of 757 kJ/mol, which was very near the activation energy calculated from thermochemical data. The surfaces became fairly rough but grain‐boundary grooves formed by an evaporation processsimilar to that for decomposition.
Agglomerate and Particle Size Effects on Sintering Yttria‐Stabilized Zirconia
Authors: RHODES W. H.
Published: June 2006

The initial‐, intermediate‐, and final‐stage sintering of fine crystallite yttria‐stabilized zirconia was studied. Experiments were conducted on powder lots of differing agglomerate size and one specially prepared agglomerate‐free powder. Initial‐stage sintering kinetics were compared with a sintering study on larger crystallite size calcia‐stabilized zirconia to access the Herring scaling law. It was found that agglomerates limit attainable green density, interfere with the development of microstructure, impede initial‐stage sintering kinetics, and limit the potential benefit of fine crystallites on final‐stage sintering. An gglomerate free powder centrifuge‐cast to 74% green density was sintered to 99.5% of theoretical density in a 1 h 1100°C cycle, which is ∼300°C lower than necessary for an agglomerated but equal crystallite size powder.
Ceramic Surfaces: Theoretical Studies
Authors: STONEHAM A. M.
Published: June 2006

This paper surveys recent developments in the calculation of surface energies, surface tensions, defect structure, and related surface phenomena. The way in which theory can complement experiment in understanding the surface behavior of stoichiometric and nonstoichiometric ceramics is discussed.
Room‐Temperature KIc Values for Single‐Crystal and Polycrystalline MgAl2O4
Authors: Stewart R. L. , Iwasa M. , Bradt R. C.
Published: June 2006

The Klc values for (100), (110), and (111) single‐crystal MgAl2O4 as well as those for polycrystalline MgAl2O4 with transgranular and intergranular fractures are presented and discussed on the basis of their elastic moduli. It is observed that the single‐crystal toughnesses are directly related to the elastic modulus. Polycrystalline and single‐crystal toughnesses are comparable; however, the intergranular fracture has the lowest toughness.
Producing a Semielliptical Flaw in a Glass Surface
Authors: Hudson R. L. , Frechette V. D.
Published: June 2006

A semielliptical flaw was produced by differential expansion of a brass bar cemented to a glashd surface. Crack growth was monitored by continuous observation in polarized light.
Vapor Pressures of Simple Silicate Glass Melts
Authors: Kassis N. , Frischat G. H.
Published: June 2006

Partial and total vapor pressures over Na2O.3SiO2 anhd Rb2O.3SiOz melts were determined at 1150° to 1300°C with the Knudsen‐effusion method. A Pt Knudsen cell was placed on a microbalance so that the weight loss due to effusion from the Knudsen hole could be recorded continuously. The specific vaporization rates are between ∼3.10−6 and 3.10−4 gcm−2 s−1; the corresponding vapor pressures are between ∼3.10−2 and 3 Pa.
Self‐Diffusion Coefficient of Oxygen in Single‐Crystal Forsterite
Authors: Ando Ken , Kurokawa H. , Oishi Y. , Takei H.
Published: June 2006

Self‐diffusion coefficients of the oxygen ion in single‐crystal forsterite were determined by the gas‐solid isotope exchange technique. The results in the 1472° to 1734°C range were described by D =2.85 (10−2 exp (−416 kJ/mol/RT)cm2/s. In preparing the diffusion sample, argon‐ion milling gave a less defective surface condition than did chemical polishing.
Microstructural Observations on Hot‐Pressed Si3N4
Authors: Greskovich C.
Published: June 2006

The development of microstructure in hot‐pressed SiaN4 was studiehd for a typical Si3N4 powder with and without BeSiN2 as a densification aid. The effect of hot‐pressing temperature on density, α‐ to β‐Si3N4 conversion and specific surface area showed that BeSiN2 appears to increase the mobility of the system by enhancing densification, α‐ to β‐Si3N4 transformation, and grain growth at temperatures between 1450° and 1800°. These processes appear to occur in the presence of a liquid phase.
Mechanisms Responsible for Strain‐Rate‐Dependent Compressive Strength in Ceramic Materials
Authors: Lankford J.
Published: June 2006

Compressive strength of SiC and Al2O3 is determined over a wide range in loading rate. The results are interpreted in terms of the tensile growth of axial microcracks, controlled by two distinct mechanisms. The first is a material‐dependent, thermally activated process operative at strain rates 102s; the other is a relatively material‐independent, strain‐rate‐sensitive inertial process which controls failure at higher loading rates.
Preparation and Identification of Ca2Zn4Ti15O36—A New Structure Type
Authors: BARTRAM STANLEY F. , FOSS WARREN M
Published: June 2006

A ternary oxide containing Ca, Zn, and Ti was characterized by chemical and X‐ray analysis as Ca2Zn4Ti15O36. It crystallizes with rhombohedral symmetry in space group R3, or possibly R3. The hexagonal cell dimensions are α= 1.0371±0.0005 and c=2.0938±0.0010 nm; density is 4.18 g/cm3. Ca2Zn4Ti15O36 is the first member of this new type of structure to be synthesized; several other examples were also prepared. The mineral davidite is probably isostructural with these pure synthetic compounds and the mineral senaite appears to have a closely related structure.
Optimum Schedule for Annealing Flat Glass
Authors: NARAYANASWAMY O. S.
Published: June 2006

This paper formulates and solves the problem of optimum annealing of glass in which one seeks to minimize either residual stress or annealing time. An approximate analysis shows that residual stress is a weighted integral of cooling rates and that an optimum schedule is obtained when the cooling rate is inversely proportional to the square root of the weighting function. Several multibreak annealing schedules are investigated. It is found that a practical and nearly optimum schedule in this class is a two‐break schedule that cools glass most slowly in a 65°CC interval and most rapidly outside this interval. It yields an optimum stress significantly lower than that of a constant‐rate annealing schedule. Furthermore, the optimum is not very sensitive to minor changes in the schedule.
Nonlinear Annealing of Glass
Authors: GARDON ROBERT
Published: June 2006

Transient as well as residual stresses were measured in laboratory experiments on annealing by nonlinear cooling schedules. The data on transient stresses, in particular, were incompatible with a classical view of annealing but they could be explained by a more recent model of annealing, in which account is taken of structural as well as stress relaxation. The potential utility of nonlinear annealing schedules is also discussed briefly.
When is a Beam a Plate?
Authors: Baratta Francis I.
Published: June 2006

Formulas associated with simple beam or plate theories are used extensively in structural design, to determine You's modulus, and to determine fracture strength of brittle nonmetallic materials. The question may arise as to whether the proper ratio of beam‐width‐to‐beam‐depth is such that the bent structural element can be considered as a beam and, if not, what is the correction factor that should be used with the simple beam formula. These questions are answered for a range of structural metallic and brittle nonmetallic materials.
Defect Structure of PLZT Doped with Mn, Fe, and Al
Authors: Härdtl K. H.
Published: June 2006

Practically pore‐free Mn‐, Fe‐, and Al‐doped PLZT ceramics were prepared using isostatic hot‐pressing. The incorporation of the dopants in the perovskite lattice of PLZT (Pb0.9La0.1 |Zr0.5Tio.5O3+δ) ceramics was analyzed from measurements of the density, lattice constants, and weight loss during sintering. It was deduced that Mn, Fe, and Al are incorporated as trivalent ions at (Zr, Ti)4+ sites and that charge compensation is effected by elimination of cation vacancies present in the undoped PLZT.
Prediction of Immiscibility Boundaries of the Systems K2O‐SiO2, K2O‐Li20‐SiO2, K20‐Na2O‐Si02, and K2O‐BaO‐SiO2
Authors: KAWAMOTO Y. , TOMOZAWA M.
Published: June 2006

In earlier work, a prediction method of the immiscibility boundary of a ternary silicate glass system was developed involving two known binary immiscibility boundaries and a measured immiscibility temperature of one ternary glass composition. In the present work, the method is extended to the case where one of the two binary immiscibility boundaries is not known and is applied as an example to ternary silicate systems containing K2O. First, the immiscibility boundary of the system K2O‐SiO2 is estimated by measuring the immiscibility temperatures of three glasses in the system K2O‐Li2O (or Na2O)‐SiO2. Using this result the immiscibility boundaries of the systems K2O‐Li2O‐SiO2, K2O‐Na2O‐SiO2, and K2O‐BaO‐SiO2 are estimated. The results agree reasonably well with the experimentally determined immiscibility temperatures at selected compositions.
Gaseous‐Transport‐Controlled Chlorination of CoO in Flowing Oxygen Chlorine‐Argon Mixtures at 1000 K
Authors: McNALLAN M.J. , LIANG W. W.
Published: June 2006

Thde chlorination rate of CoO was measured in 1 % CI2‐Ahd mixtures at 1000 K as a function of oxygen partial pressure and total volume flow rate. At oxygen partial pressures >4053 Pa (0.04 atm), the rate of chlorination was found to be controlled by the transport of CoCI2(g) across the gas boundary layer. The good agreement obtained between the calculated and measured rates suggests that the partial pressure of CoCI2(g) at the gas‐solid interface is determined by the equilibrium between Co3O4(s) and the partial pressure of Cl2(g) and O2(g) in the gas mixtures. At lower partial pressures of oxygen, the rate is controlled by mixed gas diffusion of Cl2(g) and CoCI2(g) species through the gas boundary layer.
Electron Microscopy Study of the Effect of Iron in Reaction‐Sintered Silicoa Nitride
Authors: SHINOZAKP S. , MILBERG M. E.
Published: June 2006

The microstructure, crystal structure, and chemical composition of reaction‐sintered Si3N4 containing iron were studied using conventional and scanning transmission electron microscopy. It was found that the grains of β‐Si3N4 were large and blocklike with well‐developed facets, a series of voids along some grain boundaries, a subgrain of iron silicide near the periphery, and penetration of iron silicide into the three‐grain junctions and grain boundaries. At some distance from each β‐Si3N4 grain was a region of small α‐Si3N4 grains, with no evidence of iron silicide. Between this region and the β‐Si3N4 grain was a zone containing both α‐ and β‐Si3N4 and iron silicide. These observations suggest that the large β‐Si3N4 grains grow in liquid iron silicide, that the smaller α‐Si3N4 grains grow from the vapor, and that the latter are converted to the β form by solution in, and reprecipitation from, liquid iron silicide.
Fracture of Isotropic and Textured Ba Hexaferrite
Authors: IWASA M. , LIANG E. C. , BRADT R. C. , NAKAMURA Y.
Published: June 2006

The effects of texture and temperature on the fracture toughness of an oriented Ba hexaferrite were studied. An isotropic ferrite was also measured. Anisotropy of Kle at room temperature in the oriented ferrite was a factor of 3, with the transgranular fracture having a Klc of 2.83 MN‐m−3/2. Toughness decreased with increasing temperature, exhibiting two regions of behavior: a low‐temperature brittle elastic fracture region of —(dKlc/dT) of 10‐−4 MN · m−3/2. °C−1 and a distinct high‐temperature region of 10‐−2 MN · m−3/2. °C−1 which exhibited 100% grain‐boundary fracture.
Electrical Breakdown Strength of Alumina at High Temperatures
Authors: YOSHIMURA M. , BOWEN H. K.
Published: June 2006

The dc electrical strength of sapphire and poly crystalline alumina was studied up to 1400°C. The electrical strength was essentially identical for both materials. It was > 106 V/cm at room temperature and decreased gradually with temperature up to 900°C (2.6×105 V/ cm), then dropped rapidly to 2×104 V/cm at 1400°C for a sample thickness of ∼ 100 μm. The electrical strength decreased with the sample thickness. It was inversely proportional to the thickness for samples thicker than ∼ 600 μm at 1200°C. The breakdown behavior was explained on the basis of a thermal breakdown model.
Reaction Mechanisms in the Formation of PZT Solid Solutions
Authors: CHANDRATREYA S. S. , FULRATH R. M. , PASK J. A.
Published: June 2006

The solid‐state reactions occurring in the system PbO‐TiO2‐ZrO2 were investigated using constant heating rates up to 1000°C. DTA, dilatometric length changes, and XRD analysis were used for characterization. PbO and TiO2 reacted exothermally to form the product PbTiO3 with a large volume expansion between 450° and 600°C. Formation of PbZrO3 from PbO and ZrO2 occurred endothermally with a large volume expansion between 700° and 800°C. The expansion was due to reaction topology, differential molar volumes of products and reactants, and the pellet microstructure. In the formation of PZT from ternary powder mixtures, PT formed between 450° and 600°C, followed by PZT formation at >700°C with no measurable amounts of PbZrO3 formed as determined by XRD analysis. The analysis of the mechanisms indicates that the overall kinetics of homogeneous PZT solid‐solution formation are determined by either the ionic transport within the perovskite lattice or the phase‐boundary reactions leading to perovskite formation and not by the diffusion of Ti across PbO, which is relatively rapid.
Fracture Toughness of Fused SiO2 and Float Glass at Elevated Temperatures
Authors: SHINKAI N. , BRADT R. C. , RINDONE G. E.
Published: June 2006

The fracture toughnesses of fused SiO2 and float glass were measured at high temperatures. In both glasses, low‐temperature regions of elastic fracture were identified and correlated with the elastic moduli and their temperature dependence. A viscous flow contribution to the fracture toughness was identified in the fused SiO2 at T>800°C. Similar indications of viscous flow were also noted in the float glass, although at much lower temperatures.
Rapid Quenching Technique Using Thermal‐Image Furnace for Glass Preparation
Authors: Tatsumisago Masahiro , Minami Tsutomu , Tanaka Masami
Published: June 2006

A new technique combining a thermal‐image furnace and a twin roller is described for quenching the melt to form glass. The technique was applied to the simple system Li2O‐SiO2, since its fundamental parameters in the estimation of critical cooling rate are available. Glass flakes were obtained in the composition Li4SiO4, for which a very large critical cooling rate (∼109 K·s−1) was needed for glass formation.
Changes in Zeta Potential During Hydration of C3S With and Without CaCl2 Additions
Authors: Singh N. B. , Ojha P. N.
Published: June 2006

C3S and C3S+2% CaCl2 were hydrated for varied times; the degree of hydration and zeta potential were determined. In the absence of CaCl2, the duration of the induction period was 5 h, whereas when CaCl2 was added, an induction period of 1 h was observed. The zeta potential was positive, maximum, and constant during induction.
High‐Temperature Thermoelectric Power Measurements in Wustite
Authors: HODGE J. D. , BOWEN H. K.
Published: June 2006

High‐temperature thermoelectric power was measured on single‐crystal samples of wustite in equilibrium with a carbon dioxide‐carbon monoxide atmosphere. These measurements were made using a “heat pulse” technique which allowed the thermoelectric power of a sample to be determined in seconds. The short time required for this measurement precluded any possibility of an ionic contribution to the measured thermoelectric power. The results of this study are similar to those of earlier workers in that the measured thermoelectric power changed sign from positive to negative with increasing defect concentration. A defect model for wustite is proposed to explain these results. This model assumes a defect structure dominated by clusters of four vacancies coordinated around a trivalent iron cation in a tetrahedral position. Due to the high negative charge of such a cluster, electron holes are trapped in octahedral sites adjacent the cluster vacancies. Conduction occurs through the thermally activated hopping of these trapped holes between cluster near‐neighbor sites. The high defect concentrations in wustite result in these near‐neighbor sites being shared between different clusters. It is therefore possible for a given electron hole to hop through the crystal on a continuous path of near‐neighbor sites. A modified Heikes‐type equation is used to show that such a model is consistent with the measured values of the thermoelectric power. The proposed model is qualitatively consistent with other studies using X‐ray and neutron diffraction, electrical conductivity, and diffusion.
Decomposition of Two Aluminum Sulfates and Characterization of the Resultant Aluminas
Authors: KATO ETSURO , DAEMON KEIJI , NANBU MASAO
Published: June 2006

Two special types of anhydrous aluminum sulfate with extreme grain shapes were prepared; one, obtained by precipitation from concentrated sulfuric acid solution, is rhombohedral near cubic single‐crystal grains and the other, from acetic acid solution, consists of very thin flaky particles. The morphology of sulfate and calcined alumina, the sulfate decomposition, the η‐α alumina transformation, and the crystallite growth of α alumina were studied and compared with those processes for reagent‐grade sulfate. The morphology of anhydrous sulfate was shown to greatly affect the heat‐treatment characteristics of alumina and the sulfate decomposition behavior.
Raman Spectroscopy of Heat‐Treated B2O3‐SiO2 Glasses
Authors: FURUKAWA TOSHIHARU , WHITE WILLIAM B.
Published: June 2006

Raman spectra were measured on B2O3‐SiO2 glasses heat‐treated at different temperatures and for different periods of time. It was found that the intensity ratio of the 810‐ and 475‐cm−1 bands depended on the thermal history and composition of glass. The intensity vs heat‐treatment temperature curve exhibited a maximum in the glass‐transition temperature range. High‐temperature Raman spectra were measured on 0.5B2O3‐0.5SiO2 glass, both with increasing and decreasing temperature, between room temperature and 600°C. Above 300°C with increasing temperature, the intensity of the 810‐cm−1 band decreased, whereas the intensity of the 475‐cm−1 band increased. The changes reversed with decreasing temperature. The reversible change of the intensity of the two bands was interpreted as a reversible formation and decomposition of boroxy rings with temperature. The reaction becomes very sluggish below the glass transition so that the intensity ratio stayed constant below 300°C.
Precipitation in LiF‐MgF2 Solid Solutions
Authors: KRSTIC VLADIMIR D. , NICHOLSON PATRICK S. , PURDY GARY R.
Published: June 2006

Precipitation was studied for LiF single crystals containing up to 4 wt% MgF2. Replica electron microscopy observations, combined with hardness and lattice parameter measurements, showed that, irrespective of the level of MgF2, precipitation consistently occurs during quenching. Rapidly cooled crystals with lower MgF2 concentrations (<1 wt%) develop large cruciform particles of a metastable phase with approximate composition MgF2‐6LiF. Lower cooling rates or higher MgF2 contents caused transformation of these metastable particles to rod‐shaped stable MgF2 phase. This occurs via nucleation on the metastable crosses. The large misfit between the LiF matrix and the MgF2 phase causes development of an incoherent interface and an associated disturbance of a propagating crack was observed near each MgF2 particle.
Sintering of MgF2‐LiF Solid Solutions
Authors: CIARLO JULIE , NICHOLSON PATRICK S.
Published: June 2006

The influence of additions of 0, 2, 3.5, and 5% LiF on the sintering kinetics of MgF2 were studied using microcylindrical samples on a hot‐stage microscope. The sintering rate of MgF2 was markedly enhanced, doubling at 650°C when the LiF was increased from 3.5 to 5 mol%. An approximate model is suggested explaining the observed sintering enhancement based on the increased concentration of fluorine ion vacancies.
Sintering of Inhomogeneous Binary Powder Mixtures
Authors: MESSING GARY L. , ONODA GEORGE Y.
Published: June 2006

A geometric model for the sintering of inhomogeneous, binary powder mixtures having a large size ratio is presented. The model is demonstrated for a hypothetical mixture in which the heterogeneity is described by a normal distribution function. The model is demonstrated for the case of the fine fraction sintering only and for the case of both components sintering. Relative to the prediction for the homogeneous mixture, shrinkage is observed to be either “enhanced,”“retarded,” or the same, depending on the compositional limits of heterogeneity and the level of sintering.
Transient and Synergistic Effects in Solid‐Particle Erosion of Silicon
Authors: SCATTERGOOD R. O. , ROUTBORT J. L.
Published: June 2006

Studies of Al2O3 particles impacting (111) silicon single crystal surfaces at normal incidence show that the initial shape or transient in the weight loss vs dose curve depends on the condition of the surface prior to erosion. If the surface is pre‐eroded by particles larger than the incident particles, a decelerating transient is observed, while an accelerating transient is observed when the surface is pre‐eroded by particles smaller than the incident particles. The transient effects can be used to describe the results of mixing experiments when two sizes of particles are used simultaneously.
Degradation of Plasma‐Sprayed Alumina on Metal Substrates in Physiological Media
Authors: Drummond J. L. , Simon M. R. , Brown S. D. , Blattner R. J.
Published: June 2006

Plasma‐sprayed alumina coated on 316L stainless steel and Ti‐6A1–4V ELI substrates was aged in deionized‐distilled water, saline solution, Ringer's solution, and medium‐199. Reduction in adherence was observed after aging in all media with statistical analysis indicating at least two different processes occurring in the tensile pull‐off (adherence) tests.
Effect of Gamma Radiation on Glass Leaching
Authors: McVAY G. L. , PEDERSON L. R.
Published: June 2006

Significant increases in the leaching rate of PNL 76–68, a complex simulated nuclear waste glass, were observed to occur in the presence of gamma radiation. Some of the enhanced leaching is due to the generation of nitric acid from air radiolysis in the leach vessel. Nitric acid appears to preferentially attack zinc and lanthanides, both of which normally build up on the surface of the glass when leached in nonacidic solutions. Increased rates were also found for samples irradiated while leaching but with air excluded to eliminate nitric acid formation, indicating that water radiolysis products may also be important. Samples irradiated prior to leaching showed dissolution rates indistinguishable from those of unirradiated specimens.
Analysis of Thermal Stress Resistance of Partially Absorbing Ceramic Plate Subjected to Asymmetric Radiation, I: Convective Cooling at Rear Surface
Authors: THOMAS J. R. , SINGH J. P. , HASSELMAN D. P. H.
Published: June 2006

An analysis is presented of the thermal stresses in a partially absorbing brittle ceramic flat plate asymmetrically heated by radiation on the front surface and cooled by convection on the rear surface with a heat transfer coefficient, h, being finite or zero. For finite A, the transient thermal stresses are a function of h, whereas the steady‐state thermal stresses are independent of h. The maximum value of tensile thermal stresses occurs at an optical thickness μa= 2 and equals zero for μa= 0 or ∞. For an optical thickness μa<10.7, the steady‐state thermal stresses exceed the transient stresses, with the converse being true for μ10.7. The maximum tensile thermal stresses occur in the front surface where the temperatures are highest. For h=0, the tensile thermal stresses increase with increasing value of optical thickness. The role of the material properties which control the thermal stress resistance under conditions of combined radiation heating and convection cooling are discussed. Appropriate thermal stress resistance parameters are proposed.
High‐Temperature Conductivity and Creep of Polycrystalline AI2O3Doped with Fe and/or Ti
Authors: EI‐AIAT M. M. , HOU L. D. , TIKU S. K. , WANG H. A. , KRÖGER F. A.
Published: June 2006

Partial ionic and electronic dc conductivities and compressional creep rate were measured for hot‐pressed poly crystalline AI2O3made from AI‐isopropoxide (AI2O3(II)). The undoped material was found to contain 1.5×1018cm−3fixed valency acceptors (Mg). Properties of undoped material and material doped with Fe or Ti were investigated as a function of grain size, dopant concentration, oxygen pressure, and temperature. No fast ionic conduction along grain boundaries is found in either acceptor‐ or donor‐dominated material. Absolute values of self‐diffusion coefficients calculated from conductivity and creep indicate that both effects are limited by migration of AI, involvingVAI“in donor‐, AI,” in acceptor‐dominated material. In creep, oxygen is transported along grain boundaries in a neutral form (Oip). ThepO2dependence of σtand σhare as expected on the basis of a defect model. That of creep is weaker for reasons that are not entirely clear. An ionic conductivity with low activation energy, observed at low temperature, is attributed to the presence of AI‐silicate second phase.
Luminescence of Fe3plus; in Metaphosphate Glasses: Evidence for Four‐ and Six‐Coordinated Sites
Authors: Fox K. E. , Furukawa T. , White W. B.
Published: June 2006

Ferric iron‐substituted sodium metaphosphate and calcium metaphosphate glasses exhibit a very weak luminescence that can be observed under laser excitation. Broad emission bands at 16 000 cm−1 and at 12 000 cm−1 are assigned to the 4T1→6A, transitions of Fe3plus; in four‐ and six‐coordinated sites respectively. The interpretation is supported by crystal field theory calculations based on known absorption spectra of Fe3plus;.
Strength of Beta‐Alumina Tubes
Authors: Trantina G. G.
Published: June 2006

Environmental strength tests of diametrally loaded rings and internally pressurized tubes were conducted with beta alumina. The strength exhibits a large amount of scatter and a size effect which can be characterized with a Weibull statistical treatment.