bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrical Properties of Single Crystals, Bicrystals, and Polycrystals of MgO
Authors: OSBURN C. M. , VEST R. W.
Published: June 2006

The high oxygen pressure conductivity of high‐purity single‐crystal magnesium oxide at high temperatures varied as the 1/4 power of the oxygen partial pressure with a 3 eV activation energy; the low pressure conductivity varied as the ‐1/6 power of the pressure with an activation energy of 4 eV. The predominant defects proposed are (1) holes and singly ionized Mg vacancies at high pressure and (2) electrons and doubly ionized oxygen vacancies at low pressures. The effect of impurities was noted. Changes in the grain boundary conductance relative to the crystal conductance of MgO were observed as a function of temperature and pressure, but not as a function of grain boundary orientation, transport direction, or total impurity content. Increased high pressure ionic conductivity in polycrystalline material offered possible evidence for increased grain boundary diffusion.
Ionic Transport Numbers of Group IIa Oxides Under Low Oxygen Potentials
Authors: ALCOCK C. B. , STAVROPOULOS G. P.
Published: June 2006

The ionic transport numbers of BeO, MgO, CaO, and SrO in single‐crystal and polycrystalline samples were examined under low oxygen potentials between 900° and 1180°C. The oxygen potentials were fixed by using metal/metal‐oxide electrodes in electrochemical cells with the samples of the alkaline earth oxides as solid electrolytes. The electromotive forces of these cells were compared with the emf values obtained from similar cells of high stability using high‐purity thoria‐based electrolytes. From the results it could be concluded that under comparable conditions of low oxygen pressure the electron transport number increases with increasing ionic radius of the group II element. Only BeO and MgO approach electrolytic behavior, and this occurs at relatively high oxygen pressures (>10‐10atm).
Electrochemical Cells and Electrical Conduction of Pure and Doped Al2O3
Authors: BROOK R. J. , YEE J. , KRÖGER F. A.
Published: June 2006

Data concerning the types of charge carrier responsible for electrical conduction in single‐crystal aluminum oxide are reviewed, and explanations are offered for discrepancies in terms of the experimental conditions. Measurements on undoped and Co2+ and Mg2+ doped crystals, made using a volume guard to avoid surface and gas conduction, are used to describe Al2O3 as an ionic conductor with Al interstitial ions as the principal charge carriers at high oxygen activity. A defect model is proposed and the mobility of Ali3+, the concentration of Ali3+ in undoped crystals, and the equilibrium constant for defect formation at high temperatures are estimated.
Influence of Grain Growth on Dielectric Properties of Nb‐Doped BaTiO3
Authors: KAHN MANFRED
Published: June 2006

Effects of grain size and grain growth in Nb‐doped BaTiO3 on temperature and frequency dependencies of the dielectric constant were investigated. When 0.65 μm powder is sintered to an average grain size of 1 μm, two dielectric constant peaks indicate the presence of Nb‐free BaTiO3 and of Nb‐containing material. Single peaks are observed above room temperature after additional grain growth or when 0.07 μm powder is sintered to an average grain size of 1 μm. The Curie point of pure BaTiO3 with 1 μm grains is 4 to 6°C lower than that of material with grains >10 μm. Thermodynamically, this behavior is accounted for by a phase inversion stress ∼ the room‐temperature stress.
Effects of Grain Growth on the Distribution of Nb in BaTiO3 Ceramics
Authors: BUESSEM W. R. , KAHN MANFRED
Published: June 2006

Measurements of Nb diffusion into large‐ and small‐grained BaTiO3 disks show a high ratio of grain boundary to bulk diffusivity. Well defined X‐ray diffraction lines are found in Nb‐doped BaTiO3 only when significant grain growth occurs during sintering. When grain growth of a 0.65 μm grain size powder is limited at ∼1 μm, excess line broadening results. This is attributed to the simultaneous presence of Nb‐free and Nb‐rich regions. Because of its low bulk diffusivity little Nb penetrates into the original BaTiO3 grain cores, and a solid solution forms only in the regions of recrystallization. When grain growth is limited, the “sintering reaction” results in a non‐homogeneous system; when appreciable grain growth occurs, most of the original grain cores are eliminated and an essentially uniform system is obtained.
Helium Migration in Natural and Synthetic Vitreous Silica
Authors: SHELBY J. E.
Published: June 2006

Permeation, diffusion, and solubility of helium in several types of vitreous silica were measured. The activation energy for diffusion increases slightly with increasing hydroxyl concentration; no other significant trends were noted. These results are interpreted in terms of a random‐network structural model.
Method of Comparing Solid‐State Kinetic Data and Its Application to the Decomposition of Kaolinite, Brucite, and BaCO3
Authors: HANCOCK J. D. , SHARP J. H.
Published: June 2006

A method of comparing the kinetics of isothermal solid‐state reactions based on the classical equation for analysis of nucleation‐and‐growth processes is described. In this method, plots of In In (1‐α) vs In (time), where α is the fraction reacted, are used to distinguish reaction mechanisms. Even nonintegral slopes obtained for values of the fraction reacted from 0.15 to 0.50 may indicate whether the reaction rate is diffusion‐ or phase‐boundary‐controlled. The problems of ascertaining zero time and self‐cooling (or heating) of the reacting sample can be observed in the analysis but do not cause severe difficulties in interpretation, as they can for analyses based on reduced‐time plots. The analysis is applied to the dehydroxylation of kaolinite and of brucite and the decomposition of BaCO3.
A Chemical Interpretation of Static Fatigue
Authors: WIEDERHORN S. M.
Published: June 2006

The effect of water on the growth of cracks in glass is discussed. Crack motion is believed to result from a stress‐enhanced chemical reaction between water and glass and is influenced strongly by the crack‐tip OH− ion concentration. This hypothesis is supported by the observation that crack‐velocity data can be correlated with measurements of pH in slurries of ground glass and water. Variation of the measured pH from 5 to 12, depending on glass composition, suggests a wide pH variation at crack tips. The types of chemical reactions that establish the slurry pH are discussed, and it is noted that the slurries behave as weak acids, buffered solutions, or salts of weak acids, depending on glass composition.
Computation of Residual Stresses in Quenched Al2O3
Authors: BUESSEM W. R. , GRUVER R. M.
Published: June 2006

A method of computing the residual stress profile in quenched A12O3 rods was developed. For these calculations, certain material parameters must be determined. Thus, strain rate was measured as a function of stress for 96% A12O3 at 1300° to 1500°C, and the heat‐transfer rates of cylindrical samples quenched in several media were determined. Using calculated temperature distributions and measured strain rates, plastic strains were computed for the entire quenching period, and these strains were converted to a profile of residual room‐temperature stresses. The substantial increases in flexural strength observed in Al2O3 after it is quenched (thermally conditioned) are considered to originate in the residual compressive surface layers.
Thermal Expansion, Compressibility, and Polymorphism in Hafnium and Zirconium Titanates
Authors: LYNCH R. W. , MOROSIN B.
Published: June 2006

Using X‐ray diffraction techniques, thermal expansion and compressibility were measured on the orthorhombic compounds HfTiO4, Hf1.26Ti0.74O4, and ZrTiO4 (both quenched and cooled slowly from 1300°C). The thermal expansion of HfTiO4 is highly anisotropic; the thermal expansion coefficients along the crystallographic axes are αa=+(8.7±0.5)×10−6°C−1, αb=−(5.2±0.5)×10−6°C−1, and αc=+ (5.3±0.5)×10−6°C−1. The thermal expansion of Hf1.26Ti0.74O4 was similar to that of HfTiO4 but that of ZrTiO4 was markedly less anisotropic. The compressibilities of HfTiO4 and ZrTiO4 also differed markedly. All compounds investigated, however, behaved similarly in exhibiting a polymorphic transition to a high‐pressure phase having the monoclinic baddeleyite (ZrO2) structure. The polymorphism can be explained qualitatively on the basis of crystal structure.
Kinetics of Carbothermal Reduction of Quartz Under Vacuum
Authors: KHALAFALLA S. E. , HAAS L. A.
Published: June 2006

The kinetics of reduction of 0.2 mol of –70?mesh quartz particles by 0.2 mol of graphite were determined in a batch reactor between 0.25 and 10−0torr. The effects of temperature, CO partial pressure, SiO2phase transformation, and alkali and alkaline‐earth oxide additives on the rate of reaction were studied. Increasing CO overpressure retarded carbothermal reduction. At 1400−C, addition of 5 wt% alkali oxide inhibited the reaction, whereas the same amount of alkaline‐earth oxide decreased the induction time; CaO was the best promoter. The initial reaction rate obeyed the cubic power law of nucleation growth at weight losses <15%, with an apparent activation energy of 77 kcal/mol. At higher weight losses, the Austin‐Rickett equation with an exponent near 2 was more applicable. The results are consistent with a model based on a transitory phase intermediate.
Final Sintering of Cr2O3
Authors: OWNBY P. D. , JUNGQUIST G. E.
Published: June 2006

The effect of oxygen activity on the sintering of high‐purity Cr2O3 is shown. Theoretical density was approached at the equilibrium O2 partial pressure needed to maintain the Cr2O3 phase (Po2=2×10−12 atm). The presence of N2 in the atmosphere during sintering did not prevent final sintering. The addition of 0.1 wt% MgO at this equilibrium pressure effectively controlled the grain growth and further increased the sintered density to very near the theoretical value. The solute segregation of MgO at the grain boundaries, followed by nucleation of spherulites of magnesium chromite spinel on the boundaries, accounted for the grain‐growth control. It is speculated that these isolated spherulites locked the grain boundaries together, changing the fracture mode of the sintered oxide from inter‐to intragranular and also that larger MgO additions produced a more continuous spinel formation at the boundaries, resulting in decreased sintered density. Weight loss, which was also monitored as a function of O2 activity, correlated with the changing predominant volatile species in the Cr‐O system.
Fracture and Healing Effects in Mica Crystals
Authors: LEONESIO ROBERT B.
Published: June 2006

Crack propagation and healing in mica were studied by a fracture‐mechanics approach. The energy/unit area for initial fracture, healing, and subsequent fracture was measured in He, air, H2O, H2, and vacuum under both humid and dry conditions. The recleaving energies observed were lower or higher than the original fracture energies, depending on the test conditions.
Effect of Oxide Defect Structure on the Electrical Properties of ZrO2
Authors: KUMAR ARUN , RAJDEV DILIP , DOUGLASS D. L.
Published: June 2006

The defect structure of monoclinic ZrO2 was studied by measuring the transfer numbers and electrical conductivity as functions of O2 pressure and temperature. The data suggest a defect structure of doubly ionized oxygen vacancies at low pressures, i.e. <10−19 atm, and singly ionized oxygen interstitials at pressures >10−9 atm. Zirconia is primarily an ionic conductor below #700°C and an electronic conductor at 700° to 1000°C for 10−22≤Po2≤1 atm.
Measurement of Fracture Surface Energy of SiC
Authors: COPPOLA J. A. , BRADT R. C.
Published: June 2006

The fracture surface energies of 5 polycrystalline silicon carbides were measured at room temperature using the double‐cantilever‐beam, notched‐beam, and work‐of‐fracture methods. All methods yielded comparable fracture surface energies,
Influence of Anisotropy and Water Vapor on the Solid‐State Reaction of CaO and Beta Quartz
Authors: BURTE Arvind S. , NICHOLSON PATRICK S.
Published: June 2006

The kinetics of the solid‐state reaction of CaO and β‐quartz were studied between 1000° and 1200°C in wet and dry N2. Parabolic kinetics were observed in all cases; Ca2SiO4 was the only reaction product. The reaction was faster on the basal plane of the β‐quartz than on the prism plane, and although moisture enhanced the reaction rates on both planes, the enhancement of the basal‐plane reaction was significantly higher. Activation energies and results of marker experiments indicated that Ca2+ diffusion in the product was rate‐controlling and that α‐Ca2SiO4 possibly formed on the basal plane of the β‐quartz and α'‐Ca2SiO4 on the prism plane. A model for the observed kinetic enhancement in the presence of moisture is proposed on the basis of creation of interstitial Ca2+ sites in the products.
Phase Behavior in the Sm‐B System
Authors: SOLOVYEV G. I. , SPEAR K. E.
Published: June 2006

Phase equilibria in the samarium‐boron system were investigated by X‐ray and metallographic techniques. Melting behavior and temperatures, or limits for these temperatures, were determined and used in constructing a temperature‐composition phase diagram. Four intermediate binary phases were found: SmBx (x=2.0±0.6), SmB4, SmB6, and SmB66. The tetra‐ and hexaborides were well known, and phases isomorphous with SmB66 have been reported, but the SmBx phase gives an X‐ray diffraction pattern different from that of any known boride. Lattice constants were calculated for the 3 phases with known structures; the composition dependence of the values for the tetra‐ and hexaborides indicates that both phases have measurable composition ranges. Measured Vickers’microhardness values increase markedly for phases with increasing boron content. The SmBx phase is very soft compared to most boride phases.
Mechanical and Ionic Relaxation in Na2O·3SiO2 Glass
Authors: HIGGINS T. J. , MACEDO P. B. , VOLTERRA V.
Published: June 2006

Mechanical relaxation in Na2O·3SiO2 glass was measured. The data are compared with dielectric relaxation results for the same glass. The mechanical and electrical relaxation processes have not only the same activation energy but also (within experimental error) the same average relaxation time and distribution of relaxation times. From this result, it may be concluded that the mechanical loss in single‐alkali silicate glass arises from the same ionic process that is associated with long‐range ionic diffusion.
Phase Equilibria in the System SrO‐CdO‐V2O5
Authors: BROWN JESSE J.
Published: June 2006

Phase equilibria in the system SrO‐CdO‐V2O5 in air were established from data obtained by DTA, quenching, and high‐temperature solid‐state reaction experiments. The SrO‐V2O5 boundary system contains 4 compounds at SrO to V2O5 molar ratios of 4:1, 3:1, 2:1, and 1:1. A fifth compound with a molar composition of ∼10:3 with the apatite crystal structure was also found; it may, however, be a hydroxyapatite phase. The CdO‐V2O5 system contains the compounds 3CdO·V2O5, 2CdO·V2O5, and CdO·V2O5. The latter compound exhibits a rapid reversible polymorphic transition at 180°C. Complete solid solubility exists in the SrO‐CdO system. The most probable compatibility relations were determined from the data available for the SrO‐CdO‐V2O5 ternary system. Limited solid solubility exists between SrO·V2O5 and CdO·V2O5, and the high‐temperature CdO·V2O5 polymorph is stabilized to room temperature by solid solution of SrO·V2O5. Evidence for the existence of 2 ternary compounds with limited local solid solubility is also presented.
Spheroidization of Tubular Voids in Al2 O3 Crystals at High Temperatures
Authors: YEN C. F. , COBLE R. L.
Published: June 2006

Cracks introduced into single‐crystal sapphire broke up after annealing, first into channels of cylindrical voids and ultimately into rows of spherical pores, with the thicker gap spacings in the original crack remaining open. Breakup of the cylindrical voids on subsequent annealing conformed to the models for surface‐diffusion‐controlled material transport. At the temperatures of measurement, the magnitudes of the calculated surface diffusivities agree well with values reported previously.
Phase Equilibria in the System CaO‐BaO‐WO3
Authors: KREIDLER ERIC R.
Published: June 2006

The 1200°C isothermal section of the system CaO‐BaO‐WO3 was studied in detail. The system contains one ternary compound, Ba2CaWO6, which can exist in binary equilibrium with BaO, CaO, Ba3WO6, Ba2WO5, BaWO4, and Ca3WO6. The composition range of solid solutions based on the ternary compound extends from Ba2CaWO6 to Ba1.86Ca1.14WO6 at 1200°C. Solid solubility along the binary join BaWO4‐CaWO4 was studied in the interval 1000° to 1340°C. Maximum solid solubilities occur at the eutectic temperature (1340°±10°C) and are 18 mol% CaWO4 in BaWO4 and 3.5 mol% BaWO4 in CaWO4. A phase diagram is given for the BaWO4‐CaWO4 system. Evidence is presented which shows that Ba2WO5 is a stable phase, and the BaO‐WO2 phase diagram is revised accordingly. There are 3 polymorphs of Ba2WO5 related by rapid reversible inversions at 1385°±5° and 1490°±10°C. The low‐temperature form of Ba3WO6. is tetragonal (α=8.65(2) Å and c=16.43(4) Å), not cubic as previously reported. The compounds Ca6WO9, BaW2O7, BaCa2WO6, Ba5CaW2O12, and Ba1.5Ca1.5WO6 reported in earlier studies were not confirmed.
Optical Absorption Spectroscopy of ThO2
Authors: CHILDS B. G. , HARVEY P. J. , HALLETT J. B.
Published: June 2006

The optical absorption spectra from 200 to 2700 nm were determined for arc‐fused ThO2 crystals of much higher purity than any available hitherto. The fundamental absorption edge for these crystals lies at a much higher energy (∼5.9 eV) than the apparent edge reported previously for less pure specimens. This apparent edge is shown to result from one or more prominent high‐energy absorption bands superimposed on the true edge for such specimens. By comparing the spectra for different specimens subjected to thermal and γ‐irradiation treatments, 31 distinct absorption bands were revealed in the ThO2 spectrum. A full analysis of certain crystals by spark‐source mass spectrometry gave no strong correlation between specific band areas and individual impurity‐element concentrations. Most of the bands, however, are believed to be associated with the impurity content.
Phototropic Glasses Activated by TlCl
Authors: SAKKA SUMIO , MACKENZIE J. D.
Published: June 2006

Phototropic glasses in which TlCl crystallites play an active role were developed. When glasses containing Tl and Cl were reheated at 420° to 480°C for 3 to 20 h, phototropic glasses were obtained which were transparent, translucent, or opaque, depending on the temperature and time of heat treatment. X‐ray powder diffraction patterns of these glasses indicated the presence of TlCl crystallites. The optical absorption in the visible region which developed in the glass after uv exposure was similar to that developed in TlCl crystals prepared by melting TlCl powder. These facts suggest that the phototropy is caused by TlCl crystallites precipitated in the glass by heat treatment. Optical absorption was measured during both darkening and bleaching of the glass.
High‐Temperature Deformation of Polycrystalline Fe2O3
Authors: CROUCH A. G.
Published: June 2006

The effects of stress, temperature, grain size, porosity, and O2 partial pressure on the creep of polycrystalline Fe2O3 were studied in the range 770° to 1105°C by tests in 4‐point bending and compression. Deformation rates are controlled by the stress‐directed diffusion of either oxygen or iron. Diffusion coefficients computed from the Nabarro‐Herring formula modified by including an empirical porosity‐correction term are also consistent with the values reported for oxygen and iron.
Effect of Microstructure on Measurements of Fracture Energy of Al2O3
Authors: SIMPSON L. A.
Published: June 2006

Alumina specimens were fabricated under a wide range of conditions using cold‐pressing and sintering techniques. Fracture energies were measured by an analytical technique (notched beam) and by the Tattersall‐Tappin method. Problems in using the latter method are discussed. The effects of porosity, pore distribution, and grain size on fracture energy are evaluated. Connected porosity has a deleterious effect on fracture energy. A grain‐size effect dominates in dense material; the fracture energy decreases with increasing grain size.
Strength of Pyrolytic SiC Coatings of Fuel Particles for High‐Temperature Gas‐Cooled Reactors
Authors: EVANS A. G. , PADGETT C. , DAVIDGE R. W.
Published: June 2006

Methods for measuring the strength of a hemispherical shell were developed and applied to SiC coatings obtained from reactor fuel particles. These methods allow independent evaluation of the strengths of the inner and outer layers of the coatings. The applied loads are related to the maximum tensile stress using strain‐analysis techniques. Coatings from standard SiC fuel particles have a median outer‐surface strength of 620 MN m−2 and a median inner‐surface strength of 720 MN m−2. These strengths relate only to a small region of the tested hemisphere, and statistical analysis is used to obtain strengths for complete spherical shells under internal pressure, the condition relevant to reactor performance. This procedure reduces the median working strength to 105 MN m−2, with failure occurring preferentially from the outer surface. A second statistical analysis shows that the critical failure stress for 1 particle in 104 (the reactor design requirement) is 22 MN m−2. A fracture‐mechanics analysis of strength indicates that failure occurs by the extension of inherent flaws at the surface. These flaws are associated with surface roughness. Strength was substantially improved by reducing this roughness by controlling the conditions of deposition of the coating and the topography of the underlying pyrocarbon layer. Greatly superior coatings were thus prepared; their median failure stress under internal pressure was 560 MN m−2 and the 1‐in‐104 failure stress 195 MN m−2.
Study of Ordering in High‐Quartz Solid Solutions by Substitutions Affecting Superlattice Reflections
Authors: RAY SATYABRATA
Published: June 2006

Ordering of the interstitial and network atoms in stuffed high‐quartz solid‐solution (ss) phases was studied by correlating suitable substitutions in the structure with the resultant changes in the superlattice reflections arising from these phases. In an MgO·Al2O3·3SiO2 high‐quartz ss, the special ordering of the interstitial Mg atoms, which produces satellite reflections around superlattice positions, was disturbed by replacement of ∼20 mol% of the MgO by Li2O or ZnO. The interstitial atoms were further disordered by larger substitutions. The streaked superlattice reflections arising from an Li2O·Al2O3·2SiO2 high‐quartz ss disappeared on replacement of ∼40 mol% of the Li2O by MgO. This result implies that the interstitial Li atoms are ordered and were disordered by the substitution. The superlattice reflections were much intensified when ∼25 mol% of the SiO2 was replaced by GeO2. However, these reflections were intensified to a lesser degree when presumably both SiO2 and Al2O3 were partially replaced by GeO2 and Ga2O3, respectively. These observations strongly suggest an ordering of the network Si and Al atoms, which, together with the ordering of the interstitial Li atoms, contributed to the original streaked superlattice reflections.
Electrical Conduction of Rare‐Earth‐Doped BaTiO3 Single Crystals
Authors: MURAKAMI TOSHIAKI , NAKAHARA MOTOHIRO , MIYASHITA TADASHI , UEDA SHOHEI
Published: June 2006

The effect of 0.2 to 0.8 at.% rare‐earth ions on the conductivity of melt‐grown BaTiO3 crystals was studied by optical absorption, luminescence, Hall coefficient, and electrical conductivity measurements. The conductivity is proportional to the dopant concentration in these crystals; such is not the case in BaTiO3 ceramics. A rare‐earth ion substitutes on the Ba2+ site and yields a donor.
Model for Reaction Between CaO Particles and Portland Cement Clinker
Authors: JOHANSEN VAGN
Published: June 2006

The reaction of CaO particles in a cement clinker is described by a simple model for diffusion‐controlled dissolution of spheres. The experimental results agree well with those predicted from data obtained in independent diffusion experiments. Under certain conditions it is possible to determine the maximum size of CaO particles which can react with C2S to give C2S within a given reaction time; further, for a given size distribution of CaO particles, the content of free CaO in the clinker after a given burning time can be estimated.
Effects of Particle‐Size Distribution in Initial‐Stage Sintering
Authors: COBLE R. L.
Published: June 2006

Diffusion models for the initial‐stage sintering of spherical particles were developed for distributions of particle sizes. A linear array of particles with different sizes was treated quantitatively; number, rather than weight, distributions are considered directly to permit summation of particle‐pair interactions. Evaluation of a single particle size which will characterize the equivalent shrinkage of the distributed array of random particles yields a size much smaller than that which would designate the division at 50 wt% finer conventionally used. Also, the effective size is smaller for the lattice‐diffusion model than for the grain‐boundary‐diffusion‐controlled model. The results show that the rates for binary mixtures are intermediate between the behaviors of the end‐member sizes, in accordance with previous experimental findings. A square array of equal spheres with contacting interstitial spheres was also analyzed. Coherent shrinkage requires a retardation of shrinkage along the diagonal contacts (due to tensile loads). Procedures for evaluating the stress transfer were generated for this and similar particle packings. The calculated shrinkage rate is again intermediate between that predicted from previous models and the end‐member sizes.
Application of Deformation Maps to the Study of In‐Reactor Behavior of Oxide Fuels
Authors: ROBERTS J. T. A. , VOGLEWEDE J. C.
Published: June 2006

Deformation maps that describe the mechanical behavior of oxide nuclear fuels in and out of reactor were constructed from experimental data using the approach of Ashby. By incorporating the effects of changes in composition and microstructure into the rate equations a map was constructed to describe the in‐reactor mechanical behavior of a fully restructured mixed (U,Pu) oxide fuel. The implications of this map are discussed in relation to the modeling of fuel behavior.
Electrical Charge Transport in Single‐Crystal CaWO4
Authors: RIGDON M. A. , GRACE R. E.
Published: June 2006

A combination of ac and dc electrical conductivity measurements was used to characterize the charge transport in single crystals of CaW04 which were equilibrated with H2‐H2O‐Ar gas mixtures. Measurements were made from 900° to 1300°C and at PH2O/PH2 ratios from 0.02 to 3.0. The ac conductivity at 1000°C varied from 51.4×10−6 to 5.89×10−6 mho/cm for PH2O/PH2=0.02 and 2.0, respectively; the dc conductivity changed from 51.0±10−6 to 5.42×10−6 mho/cm under the same experimental conditions. The partial logarithmic derivative of dc conductivity with respect to PH2O/PH2 was −1/2 between 1000° and 1300°C. The results may be described by a paired‐defect model of oxygen vacancies and oxygen interstitials (majority defects and minority electrons).
Isothermal Grain Growth of Pressure‐Sintered PLZT Ceramics
Authors: LANGMAN RICHARD A. , RUNK ROBERT B. , BUTLER SIDNEY R.
Published: June 2006

PLZT specimens 99.99% of theoretical density containing 7 at.% La with a 65/35 Zr/Ti atom ratio were fabricated with average grain diameters of ∼1 μm by pressure sintering. The dense, single‐phase specimens were isothermally heat‐treated in a low PbO activity atmosphere. For grain diameters from 1 to 5 μm, grain growth obeyed the D3‐D03=k't relation, with an apparent activation energy of 86 kcal/mol. The mechanism controlling the grain‐growth rate is consistent with a solid‐solution impurity drag caused by an La ion concentration gradient near the grain boundaries.
Interaction of Hardened Cement Paste and Water
Authors: WITTMANN F. H.
Published: June 2006

Adsorption of water vapor on a clean surface changes the surface free energy. It is shown that, using the Griffith criterion, the change of strength as function of moisture content can be explained by assuming a change of surface energy. In colloidal particles surface energy creates considerable hydrostatic pressure. A change in elastic modulus and shrinkage as well as swelling can be related to a change in hydrostatic pressure in individual gel particles. Creep is affected primarily at the higher relative humidities. The main parameters of a proposed model for hydrated portland cement are surface free energy and disjoining pressure. On this basis the mechanical behavior of hardened cement paste is discussed. A phase transition of adsorbed water near ‐90°C is discussed. The influence of this effect on the mechanical behavior of hardened cement paste can be understood when a change in interfacial energy is taken into consideration.
A Simple Microscopic Method for the Quantitative Definition of the Topological Properties of Structures, Particularly Sintered Materials
Authors: FUNDAL ERLING
Published: June 2006

Quantitative description of the structure of nodules of cement clinker, which depends on conditions in the rotary kiln, is important to the cement chemist. An equation which permits rapid quantitative definition of the topological properties of clinker, or other materials, by the otherwise time‐consuming tangent count is evaluated. The possibility of applying this method in an automatic analyzer is also discussed.
Electrical Conductivity of Coal Slag
Authors: FREDERIKSE H. P. R. , HOSLER W. R.
Published: June 2006

The electrical conductivity of natural and synthetic slags (containing 14 to 36 wt% Fe) was measured from 1200 to 1700 K at O2 pressures from 1 to 2×10−6 atm. The conductivity is relatively high (∼10−2Ω−1 cm−1 at 1700 K) and stems from the transfer of electrons between Fe2+ and Fe3+ ions. Anomalies in the conductivity around 1600 K are the result of devitrification of the glass samples.
Influence of Grain Size on Effects of Thermal Expansion Anisotropy in MgTi2O5
Authors: KUSZYK J. A. , BRADT R. C.
Published: June 2006

Properties relating to the effects of thermal expansion anisotropy were measured as functions of grain size in hot‐pressed dense MgTi2O5. Samples with grains smaller than ∼3 μm exhibited none of the microcracking attributed to thermal expansion anisotropy, whereas those with larger grains had all the characteristics. An energy criterion is proposed to explain the grain‐size effect on microcracking in ceramics exhibiting high degrees of thermal expansion anisotropy.
Ferroelectric‐Paraelectric Phase Transition in Lead Titanate Containing Lattice Defects
Authors: SHIRASAKI SHIN‐ICHI , TAKAHASHI KOICHIRO , KAKEGAWA KAZUYUKI
Published: June 2006

A series of lead titanates containing lattice defects was prepared and characterized in terms of inhomogeneously distributed vacancies, □Pb and □O•. The tetragonal lattice strain and the Curie temperature varied as functions of the Pb or O deficiency in the crystals. The tetragonal strain for these crystals decreased slowly with increasing temperature as the Curie temperature was approached. The phase transition, which extends over a temperature interval, is interpreted according to a model in which microregions in the crystal differ in composition and therefore have different Curie temperatures.
Phase Equilibria in the TiO2‐Rich Region of the System BaO‐TiO2
Authors: O'BRYAN H. M. , THOMSON J.
Published: June 2006

Phase relations in the system BaO‐TiO2 from 67 to 100 mol% TiO2 were investigated at 1200° to 1450°C in O2. Data were obtained by microstructural, X‐ray, and thermal analyses. The existence of the stable compounds Ba6Ti17O40, Ba4Ti13O30, BaTi4O9, and Ba2Ti9O20 was confirmed. The compound BaTi2O5 is unstable and either forms as a reaction intermediate below the solidus or crystallizes from the melt. The compounds Ba6Ti17O40 and Ba4Ti13O30 decompose in peritectic reactions, and BaTiO3 and Ba6Ti17O40 react to form a eutectic. Special conditions are required for the formation of Ba2Ti9O20, which decomposes in a peritectoid reaction at 1420°C. The new phase diagram is presented.
Slow Crack Growth in Cement Paste
Authors: NADEAU J. S. , MINDESS S. , HAY J. M.
Published: June 2006

The dependence of crack velocity on stress intensity was measured in hardened cement paste. Fracture toughness, modulus of rupture, and dynamic elastic modulus were also measured to permit calculation of the time‐to‐failure (life expectancy) of stressed cement paste. The double torsion method was used for slow crack growth studies and fracture toughness measurements. Fracture toughness was also measured by a notched‐beam method; the agreement between the two methods was excellent. The crack‐velocity‐stress‐intensity curve for cement paste resembles that of glass in water. The slope of the log V‐log KI curve is ∼35.
Kinetics of Kaolinite Dehydroxylation
Authors: ANTHONY GAYLORD D. , GARN PAUL D.
Published: June 2006

When kaolinite is heated under pressures of self‐generated H2O vapor from 0.4 to 3.2 atm, the dehydroxylation is best described by a nucleation‐and‐growth equation withmvarying from 1.10 to 2.16 as the pressure is increased. The temperature coefficient of the rate constant, expressed as an apparent activation energy, varies from 62.4 to 260 kcal/mol. The H2O vapor evolved in a self‐generated‐atmosphere sample holder was automatically swept into a gas chromatograph at fixed intervals. The measurement is specific for H2O.
Mechanical Properties of 3BaO·5SiO2 Glass‐Ceramics
Authors: FREIMAN S. W. , ONODA G. Y. , PINCUSI A. G.
Published: June 2006

Flexural strengths, elastic moduli, and fracture energies of 3BaO·5SiO2 glass‐ceramics with a variety of microstructures were determined. Flexural strength depends on the size of spherulites in the microstructure and on the amount of glassy phase remaining in the material. Higher strengths were achieved in glass‐ceramics containing a tabular, rather than a spherulitic, microstructure. The addition of small quantities of Na2O to the original glass promoted production of the higher‐strength tabular morphology after only 10 min of crystallization at 775°C. The increase in the strength of the glass‐ceramics over that of the glass resulted from an increase in the fracture energy and elastic modulus of the material. The microstructure had little effect on the size of the flaws introduced by abrasion.
Interdiffusion Coefficients in SiO2‐K2O Melts
Authors: MAY HENRI B. , WOLLAST ROLAND
Published: June 2006

Chemical diffusion coefficients for Si were measured in potassium silicate compositions containing from 64 to 85 wt% SiO2; unidirectional diffusion couples were heated for 0.1 to 720 h at 600° to 1400°C. The diffusion coefficients, which were calculated by the Boltzmann‐Matano method, are described for a silicate containing 70 wt% SiO2 by:

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The diffusion coefficients decreased with increasing O2 pressure. Below 800°C, the coefficients decreased with increasing SiO2 concentration; above 800°C, their dependence on SiO2 concentration was too weak to detect by the methods used. On the basis of a simple structural model for the glass, it was possible, from a phenomenological analysis of the diffusion, to establish a relation between the oxygen self‐diffusion coefficient and the chemical diffusion coefficient for a given composition.
Fracture Toughness and Spalling Behavior of High‐Al2O3 Refractories
Authors: LARSON D. R. , COPPOLA J. A. , HASSELMAN D. P. H. , BRADT R. C.
Published: June 2006

The fracture energies and spalling resistance of high‐Al2O3 refractories were studied. The fracture energies, γWOF and γNBT, were measured by the work‐of‐fracture and the notched‐beam‐test methods, respectively. Spalling resistance, as measured by the relative strength retained in a water quench, correlated well with the thermal‐stress resistance parameter applicable to stable crack propagation under conditions of thermal shock, (γWOF/α2E0). Many of the refractories exhibited high ratios of γWOF to γNBT; such high ratios were shown analytically to maximize the parameter (R1111=E0γWOF/S12) which describes the resistance to catastrophic spalling. The increase of crack length with increasing quenching temperature difference (ΔT) was somewhat less than that predicted theoretically; the discrepancy was attributed to an increase of crack density with ΔT. In general, the results show that fracture energy is important in establishing the spalling resistance of high‐Al2O3 refractories.
Creep of Polycrystalline MgO‐FeO‐Fe2O3 Solid Solutions
Authors: TREMPER R. T. , GIDDINGS R. A. , HODGE J. D. , GORDON R. S.
Published: June 2006

Steady‐state creep experiments were performed on hot‐pressed polycrystalline MgO doped with Fe. Dead‐load 4‐point bend creep tests were conducted at stresses of 26 to 270 kg/cm2, at temperatures of 1250° to 1450°C, in O2 partial pressures of 1 to 10−9 atm, on specimens with grain sizes of 10 to 65 μm. Viscous steady‐state creep was always observed when the grain size was stable. Experiments at variable PO2's and temperatures were used to identify regimes of high (117 ± 10 kcal/mol) and low (81 ± 5 kcal/mol) activation energy. In the latter, creep rates were nearly independent of Fe dopant concentration and PO2, whereas in the former creep rates were enhanced by increasing PO2's and Fe dopant levels. The high‐ and low‐activation‐energy regimes were interpreted as diffusional creep controlled primarily by Mg lattice diffusion and O grain‐boundary diffusion, respectively.
Single‐Crystal Diffraction Patterns from Vitreous Carbon
Authors: WHITTAKER A. GREENVILLE , TOOPER B.
Published: June 2006

In contrast to the broad X‐ray diffraction maxima typical of vitreous materials, electron diffraction studies revealed many regions that give single‐crystal patterns. Although some of the patterns are those of graphite, as expected, many that were obtained corresponded to other carbon crystal forms, e.g. chaoite and carbon VI. In addition, ring patterns of lonsdaleite and diamond were found, and patterns that do not correspond to any known carbon allotrope were obtained.
A New BaO‐TiO2 Compound with Temperature‐Stable High Permittivity and Low Microwave Loss
Authors: O'BRYAN H. M. , THOMSON J. , PLOURDE J. K.
Published: June 2006

The dielectric properties of ceramics in the TiO2‐rich region of the BaO‐TiO2 system were investigated. In the composition range between BaTi4O9 and TiO2, another compound, Ba2Ti9O20, can be obtained when calcining and sintering conditions are controlled carefully. When dense and single‐phase, this ceramic has excellent dielectric and physical properties. At 4 GHz, the dielectric K= 39.8, Q= 8000, and τK (temperature coefficient of dielectric constant) =−24 ± 2 ppm/°C.
Anodic Proton Injection in Glasses
Authors: CARLSON D. E.
Published: June 2006

Protons were injected into glasses at high temperatures using anodes such as molten NH4HSO4, Pt in forming gas, and graphite in an atmosphere containing H2O vapor. Large electric fields develop near the anode surface of the glass and create an ion‐depleted region beneath the anode. The electrical conduction characteristics are attributed mainly to the motion of protons in the high‐field region. The ir absorption data indicate that injected protons exist in at least 3 bonding configurations in a proton‐exchanged region beneath the depleted region. The proton concentration in the exchanged region is estimated to be ∼80 to 95% of the Na concentration in the normal glass.
Dc Conductivity of Ge‐S‐Ag and As‐S‐Ag Glasses
Authors: KAWAMOTO YOJI , NAGURA NAGAO , TSUCHIHASHI SHOJI
Published: June 2006

The dc conductivity in GeS2‐GeS‐Ag2S and As2S3‐Ag2S glasses was measured over the range – 20° to 80°C using an electrode of 1 at.% Ag amalgam to avoid polarization. The room‐temperature conductivity varies with increasing Ag2S content from 10−15 to 10−4Ω−1 cm−1 for GeS2‐GeS‐Ag2S glasses and from 10−16 to 10−5Ω−1 for As2S3‐Ag2S glasses. Also, the transport numbers of Ag ions in the glasses were measured by the Hittorf and emf methods. The results show that all glasses in both systems, except for compositions with low Ag2S contents, are purely ionic conductors because of the presence of Ag ions, so that they may be regarded as solid electrolytes.
Alkali Tungstates: Stability Relations in the Systems A2O WO3‐WO3
Authors: CHANG LUKE L. Y. , SACHDEV SURESH
Published: June 2006

Phase relations in the systems alkali monotungstate‐tungsten trioxide were investigated in the range 600° to 1100°C.In the Li system, compounds with an A2O/WO3 ratio of 1:2 and 1:4 are stable and melt incongruently at 745° and 805°C, respectively. In the Na system, the 1:2 compound melts congruently at 746°C, whereas the other 2 sodium tungstates (1:4 and 1:6) melt incongruently at 835° and 913°C, respectively. The K system includes compounds of 1:2, 1:3, 1:4, and 1:6 which melt incongruently at 684°, 842°, 912°, and 964°C, respectively. Eutectic points between the 1:l and 1:2 compounds in these respective systems are at 692°C and 56 mol%WO3, 622°C and 56.3 mol% WO3, and 633°C and 63 mol%WO3. In the Rb and Cs systems, the 1:2 and 1:3 compounds form complete solid‐solution series, and their melting temperatures increase with increasing WO3 content, respectively, from 690° to 868°C and from 732° to 902°C. The 1:6 compounds are also stable in these systems and melt incongruently at 1040° and 1046°C, respectively.
The Yttria‐Hafnia System
Authors: STACY D. W. , WILDER D. R.
Published: June 2006

Phase equilibria in the yttria‐hafnia system were investigated by high‐temperature and room‐temperature X‐ray diffraction. The HfO2 transformation, solid solution limits, and liquidus temperatures are given. A tentative phase diagram is proposed.
Phase Diagram of a Portion of the System Na3AlF6‐AlF3‐Al2O3.
Authors: FOSTER PERRY A.
Published: June 2006

The system Na3AlF6‐AlF3‐Al2O3 was investigated by a combination of quenching, optical microscopy, and X‐ray powder diffraction techniques in order to define liquidus temperatures, univariant lines, and invariant points. Phase fields for the primary crystallization of cryolite, chiolite, aluminum fluoride, α‐alumina, and η‐alumina were located. A ternary peritectic point contained 28.3% AlF3‐4.4% Al2O3‐67.3% Na3AlF6 at 723°C. A eutectic point of composition 37.3% AlF3‐3.2% Al2O3‐59.5% Na3AlF6 occurs at 684°C.
Microstructure Analysis and Stress‐Strain Behavior of a Model Refractory System MgO‐CaMgSiO4
Authors: SNOWDEN WILLIAM E. , PASK JOSEPH A.
Published: June 2006

The effects of a silicate boundary phase on the high‐temperature stress‐strain behavior of MgO materials have been studied using a model system MgO‐CaMgSiO4 (monticellite, CMS). Specimens were fabricated by hot‐pressing, or by hot‐pressing and annealing, and contained up to 15% silicate phase. The boundary phase consisted primarily of CMS. The stress‐strain behavior of these specimens in the range 1200° to 1400°C was strongly dependent on the degree of continuity of the grain boundary phase and on the temperature.
Dependence of Electrical Conductivity of ZnO on Degree of Sintering
Authors: TAKATA MASASUKE , TSUBONE DAISUKE , YANAGIDA HIROAKI
Published: June 2006

The electrical resistivity of ZnO doped with Al2O3 was measured in air and under reduced pressure (∼0.5 mm Hg) in the range from 30° to 680°C as a function of the degree of sintering. The data obtained were explained in terms of the effects of the microstructure of the sintered body and the chemisorbed oxygen. There are two mechanisms of electrical conduction involved, only one of which is affected by the microstructure.
Dependence of the Fictive Temperature of Glass on Cooling Rate
Authors: MOYNIHAN CORNELIUS T. , EASTEAL ALLAN J. , De BOLT MARY ANN , TUCKER JOSEPH
Published: June 2006

An equation derived by Ritland relating the cooling rate and fictive temperature for glasses without memory is extended to those with memory, i.e. those which exhibit a spectrum of relaxation times. Provided that the spectrum of relaxation times is temperature‐independent, the limiting fictive temperature, T′f, obtained when a glass is cooled through the transition region, is shown to be related to the cooling rate, q, by d In |q|/d(1/T'f)=‐Δh★/R

where R is the ideal gas constant and Δh★ the activation enthalpy for the relaxation times controlling the structural relaxation. Values of T′f vs q obtained from enthalpy measurements by differential scanning calorimetry are presented for B2O3, 0.4Ca(NO3)2—0.6KNO3, and borosilicate crown glasses; Δh★ is equal, within experimental error, to the activation enthalpy for shear viscosity. Values of T′f from volume and enthalpy measurements obtained at the same cooling rate for the borosilicate crown glass are equal.
Controlled Surface Flaws in Hot‐Pressed SiC
Authors: PETROVIC J. J. , JACOBSON L. A.
Published: June 2006

Controlled semi‐elliptical surface flaws were produced in hot‐pressed SiC by Knoop microhardness indentation. Flawed specimens were placed in 4‐point bending in order to determine their critical stress intensity factor, KIC, at both room and high temperatures. Room‐temperature fracture and KIC values after annealing were sensitive to the annealing environment; this behavior correlated with the active/passive nature of the oxidation process. Flaw healing was observed for annealing exposures in air. Room‐temperature KIC values increased with increasing annealing temperature. High‐temperature KICvalues decreased with increasing temperature as a result of a decrease in the fracture surface energy.
Aqueous Corrosion of Soda‐Silica and Soda‐Lime‐Silica Glass
Authors: CLARK D. E. , DILMORE M. F. , ETHRIDGE E. C. , HENCH L. L.
Published: June 2006

Corrosion of a 20Na2O‐10CaO‐70SiO2 (mol%) glass by water was investigated using ir reflection spectroscopy, solution analysis, electron microprobe, and Auger electron spectroscopy. Corrosion proceeds at a much slower rate in the ternary glass than in a 20Na2O‐80SiO2 glass. Within the Na‐depleted layer of the ternary glass, a Ca‐enriched zone develops—1500 A from the surface. The role of CaO in both the early and later stages of corrosion is discussed.
Photochromic Effect in Fe‐Doped PLZT Ceramics
Authors: TANAKA KATSUHIKO , HAMAKAWA YOSHIHIRO , WAKING KIKUO , MURATA MICHIHIRO
Published: June 2006

The photochromic effect in Fe‐doped transparent PLZT ceramics was investigated. The ceramics are darkened by irradiation with blue light having a wavelength of <4800 Å. The induced dark state is stable at room temperature and can easily be bleached back to its original transparent state by heat treatment at ∼200°C. The photo induced optical density change depends strongly on the transparency of the ceramic. Response times for the darkening and bleaching have been investigated as a function of the excitation light intensity and the temperature of the ceramic. A tentative model explaining the observed effect is proposed, and the photochromic mechanism is discussed on the basis of a charge‐transfer process between the photo activated Fe3+ and Fe4+ impurities in the ceramic.
Strength‐Size Relations in Ceramic Materials: Investigation of an Alumina Ceramic
Authors: BANSAL GIRRAJ K. , DUCKWORTH WINSTON H. , NIESZ DALE E.
Published: June 2006

Bend strengths of two sizes of specimens of an alumina ceramic were determined under conditions that either enhanced or restricted sub critical crack growth. The specimen sizes differed in each linear dimension by a factor of five and the effective size of small specimens was varied by the use of both 3‐ and 4‐point bending. Strength was dependent on specimen size under both crack‐growth conditions, and the dependence was associated with variations in flaws at fracture origins. The experimental data were analyzed for applicability of Weibull's statistical relations and in terms of fractographic examinations of strength‐controlling flaws.