bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermodynamic Calculations for the Chemical Vapor Deposition of Silicon Carbide
Authors: KINGON ANGUS I. , LUTZ LEONARD J. , LIAW P. , DAVIS ROBERT F.
Published: June 2006

A computer code, SOLGASMIX‐PV, was used to calculate CVD phase diagrams useful for the preparation of silicon carbide from commonly used precursors. The results show that in order to prepare single‐phase β‐SiC it is necessary to closely control thermodynamic parameters such as pressure, temperature, and the concentrations of the precursor and carrier gases. The system Si‐C‐H is substantially different from that of Si‐C‐H‐Cl, the latter being more complex, with single‐phase β‐SiC occurring under conditions very different from those of the former. The calculated CVD phase diagrams are compared with calculated and experimental data from the literature. The fundamental importance of a thermodynamic equilibrium description of the CVD system is emphasized.
Measurement of Dynamic Hardness by Controlled Sharp‐Projectile Impact
Authors: MARSHALL DAVID B. , EVANS ANTHONY G. , NISENHOLZ Z.
Published: June 2006

Impact of ZnS by a pyramidal projectile was used to provide a measurement of the dynamic hardness and to obtain direct comparison of the contact damage produced by static loading and impact. The dynamic hardness was evaluated from measurements of residual contact dimensions as a function of impact velocity, over the velocity range 5 to 40 m.s‐1. The value obtained (Hd=5.0 GPa) was higher than the static hardness (HS= 1.9 GPa). The higher hardness in impact causes more extensive cracking, an increase in the elastic recovery of the depth of the residual contact impression, and a smaller plastic zone surrounding the contact site. The relative extents of cracking in impact and static loading are predicted by a quasistatic indentation fracture mechanics analysis along with the appropriate values of hardness.
Electrical Conduction in β‐Bi2O3 Doped with Sb2O3
Authors: MIYAYAMA MASARU , KATSUTA SHINICHI , SUENAGA YOSHIHIRO , YANAGIDA HIROAKI
Published: June 2006

Electrical conduction in tetragonal β‐Bi2O3 doped with Sb2O3 was investigated by measuring electrical conductivity, ionic transference number, and Seebeck coefficient. The β‐Bi2O3 doped with 1 to 10 mol% Sb2O3 was stable up to 600°C and showed an oxygen ionic and electronic mixed conduction, where the electron conduction was predominant at low oxygen pressures. The oxygen‐ion conductivity showed a maximum at 4 mol% Sb2O3, whereas the activation energy for the ionic conduction remained unchanged for 4 to 10 mol% Sb2O3‐doped specimens. These results were interpreted in terms of the oxygen vacancy concentration and the distortion of the tetragonal structure. The electron conductivity and its oxygen pressure dependence decreased with increasing Sb2O3 content. The fact that Sb5+ is partially reduced by excess electrons in heavily doped β specimens at low oxygen pressures is explained.
Preparation of Bi4Ti3O12 Powders in the Presence of Molten Salt Containing LiCl
Authors: KIMURA TOSHIO , KANAZAWA TAKANOBU , YAMAGUCHI TAKASHI
Published: June 2006

The reaction between Bi2O3 and TiO2 in molten LiCl‐KCl was examined with special emphasis on the reaction mechanism and the size of Bi4Ti3O12 particles. The oxides reacted with LiCl to form an intermediate compound, which changed into Bi4Ti3O12 on extended heating. Potassium chloride retarded the reaction between the oxides and LiCl and promoted the change from the intermediate compound to Bi4Ti3O12. Bi4Ti3O12 particles prepared in the flux were platelike, irrespective of the preparation conditions, but their size depended on reaction temperature and time, the ratio of LiCl to KCl, and the amount of flux.
Strength Retention in SiC Ceramics after Long‐Term Oxidation
Authors: Becher Paul F.
Published: June 2006

The room‐temperature flexural strengths of Sic ceramics change with increasing oxidation time at 1200°C. When certain impurities (e.g. alumina, WC, and possibly others) are present, the strength continuously decreases ∼50% after 4500 h because of subsurface pit formation. Materials containing B and C or Si exhibit strength increases (≥240% after 4500 h). Surface oxide growth rates substantially decrease at times ≥1850 h, which corresponds to an increase in cristobalite formution.
Properties of Glasses in the System AgI‐Ag2O‐B2O3
Authors: Frischat Günther H. , Speyer Sabine , Wegener Wolfgang
Published: June 2006

Glasses with AgI contents between 75 and 50 mol% were prepared in the pseudo‐binary system AgI‐Ag2O‐B2O3 by different methods and at varied cooling rates. Glass transition temperatures, densities, and thermal expansion coefficients were measured and compared with literature data. Thermal history markedly injuences the properties.
Fluorine Treatments of Soda‐Lime Silicate Glass Surfaces
Authors: Brow Richard K. , LaCourse William C.
Published: June 2006

A series of soda‐lime silicate glasses was treated for varied times at different temperatures with 1, 1‐difluoroethane. Sodium and calcium fluorides formed on the surface of the treated glasses. Formation of NaF is proportional to the square root of time, implying a diffusion‐controlled reaction. Structural relaxation decreases the rate of bloom formation at high temperatures.
Phase Transitions and Therrnoluminescence of a Plasma‐Sprayed Zinc Silicate Phosphor
Authors: Takamori Takeshi , Dove Derek B. , Huffine Coy L.
Published: June 2006

A plasma‐sprayed zinc silicate phosphor was heat‐treated at ∼800°C informing gas; the major phase present was the metastable β phase, as revealed by bright yellow fluorescence under uv excitation. On heat treatment at ∼1000°C in air, a green, fluorescence developed as a result of the formation of the stable a phase. However, its thermo luminescence characteristics were different from those of the original P1 phosphor used for spraying
Effect of Surface Condition on Oxygen Self‐Diffusion Coefficients for Single‐Crystal Al2O3
Authors: Oishi Yasumichi , Ando Ken , Suga Nobuhiko , Kingery W. David
Published: June 2006

Oxygen self‐diffusion coefficients were determined for two Al2O3 single crystals by the isotope‐exchange technique, using chemically polished and Ar ‐ion‐milled samples. Results represented by D=562 exp[–665(kJ/mol)/RT] cm2/s are lower than those for diamond‐paste‐finished samples and near Reed and Wuensch's results. The oxygen diffusion coefficient determined using crushed particles and the microscopically measured ratio of surface area to volume agreed with these values
Effect of Ratio of Surface Area to Volume on Oxygen Self‐Diffusion Coefficients Determined for Crushed MgO‐Al2O3 Spinels
Authors: Ando Ken , Oishi Yasumichi
Published: June 2006

Oxygen self‐diffusion coefficients for single‐crystal MgO‐Al2O3 spinels previously determined for crushed particles were recalculated using the microscopic suface area of the sample, as was done for alumina. The corrected results agree well with those of Reddy and Cooper.
Diffusional Reaction‐Bonding of Si3N4 Ceramics Under High Pressure
Authors: Kaba Takahlro , Shimada Masahiko , Koizumi Mitsue
Published: June 2006

Diffusional reaction‐bonding of Si3N4 ceramics was accomplished by maintaining surnples at 3.0 GPa and 1800°C for 1 h. Interfaces of bonded samples were examined by scanning electron microscopy, Vickers microhardness measurements, and electron probe microanalysis. These results indicate that strong bonding between sintered ceramic bodies is achieved by a diffusional reaction at high temperature and pressure.
Detection of Thin Intergranular Cobalt Layers in WC‐Co Composites by Lattice Imaging
Authors: Jayaram Vikram , Sinclalr Robert
Published: June 2006

Much discussion has taken place concerning the contiguity of the carbide phase in sintered WC‐Co composites. In the present study, the lattice fringe imaging technique was used to demonstrate that WC grains which appear macroscopically contiguous are sometimes truly so at the atomic level. In other instances, they are separated by films of cobalt ∼1 nm thick.
Influence of Boron on Chemical Interdiffusion in SiC During Conversion of Silicon Fibers to SiC
Authors: Friederich Kilian M. , Coble Kobert L.
Published: June 2006

The influence of boron additions on the diffusivities of Si and C in SiC was studied by modtfying an experiment described by Kato and Okabe. The diffusivities of both species are considerably enhanced by adding as little as 10 ppb boron. A method to investigate the transport mechanisms in SiC is provided by this modified experiment.
Effect of Crystallites on Surface Damage and Fracture Behavior of a Glass‐Ceramic
Authors: MORENA R. , NIIHARA K. , HASELMAN D.P.H.
Published: June 2006

A study was conducted of the effect of crystallization on the fracture toughness, strength, and resistance to surface damage of glass‐ceramic materials with a range of microstructures obtained by different heat treatments. The hardness indentation method was used as a quantitative tool to simulate mechanical surface damage. In the uncrystallized glass and in the glass‐ceramic heat‐treated to result in a uniform fine‐grained structure, crack size increased monotonically with indentation load. In contrast, in the glass‐ceramics heat‐treated to result in a microstructure consisting of larger crystallites (a few micrometers) contained within a fine‐grained matrix, a discontinuity in the crack size vs load curve presented evidence for crack‐pinning at crack sizes which were a small multiple of the intercrystallite spacing. At the position of crack‐pinning, the fracture toughness showed a discontinuous increase with increasing crack size that was attributed to crack deflection. The strength of the glass and fine‐grained glass‐ceramic measured in biaxial flexure decreased monotonically with indentation load. The strength at low values of indenter load of the glass‐ceramic heat‐treated to yield the coarser crystallites within the fine‐grained matrix was independent of indentation load, indicating stable crack propagation prior to fast fracture. At the higher values of indenter load, the coarse‐grained glass‐ceramics exhibited a monotonic decrease in strength with increasing indentation load. The results of this study indicate that the strengthening observed on crystallization of a glass can be attributed to a combination of a decrease in flaw size achieved at a given mechanical surface treatment, an increase in fracture toughness, and a modification in the mode of crack propagation.
Preparation of High‐Silica Glasses from Colloidal Gels: II, Sintering
Authors: JOHNSON D.W. , RABINOVICH E.M. , MacCHESNEY J.B. , VOGEL E.M.
Published: June 2006

The sintering of dried colloidal SiO2 gels, whose preparation and properties are reported in Part I, is described. The effects of various sintering parameters were studied and the conditions for achievement of the best optical quality include the use of: a pretreatment of the SiO2 at ∼925°C, moderate heating rate (∼400°C/h), He+CI2 atmosphere, 1500° to 1600°C sintering temperature, and 1 to 4 h sintering time. Dynamic sintering kinetic studies (heating rate=400°C/h) show that this SiO2 sinters to nearly theoretical density by about 1380°C. However, optical transparency is achieved by removal of minor residual porosity at above 1500°C. Isothermal sintering data fit to a model assuming interconnecting cylinders of SiO2 predict the proper activation energy for the viscosity if initial stages of sintering are considered. Residual porosity in sintered glasses is related to large interstices in the unsintered gel.
Preparation of High‐Silica Glasses from Colloidal Gels: III, Infrared Spectrophotometric Studies
Authors: WOOD D.L. , RABINOVICH E.M. , JOHNSON D.W. , MacCHESNEY J.B. , VOGEL E.M.
Published: June 2006

The gel process for making silica was studied by infrared spectrophotometry of solid samples in various stages of dehydration. Spectra were recorded in the high‐frequency overtone region (2500 to 8000 cm‐1) as well as in the region of fundamental absorption (200 to 4000 cm‐1), depending on the nature of the sample. Molecular water was distinguished from silanol groups and the effects of hydrogen bonding were observed. Drying and heat treatment of gels at low temperatures (<150°C) causes a loss of unbonded included water, but significant loss of hydrogen‐bonded water occurs only with relatively high‐temperature heat treatments (>800°C). Hydration of siloxane groups on pore surfaces and attachment of water molecules by hydrogen bonding to these surface silanol groups is reversible for heat treatments up to 1025°C. At higher temperatures (>1025°C), active sintering takes place, converting the porous structure into a homogeneous silica network. In this process, surface silanol groups become isolated within the silica network, giving rise to vibrational frequencies characteristic of internal ‐OH groups. Also, at the higher temperatures silanol groups react to form siloxane groups with loss of H2O. A model is presented for formation of a gel in which hydrogen bonding initiates association of colloidal particles, followed by strengthening through interparticle solid silica precipitation.
Mechanical Properties of Mullite
Authors: MAH TAI‐IL , MAZDIYASNI K. S.
Published: June 2006

The mechanical properties of alkoxy‐derived, high‐purity, translucent, theoretically dense mullite (3AI2O3.2SiO2) were investigated over the temperature range room temperature to 1500°C. Large agglomerates were found to contribute to the formation of porosity nests which act as strength‐controlling flaws at room temperature as well as at high temperatures. Despite the slow crack growth above 1300°C, a slight increase in fracture stress and a large increase in KIc were observed up to 1500°C. These increases are explained by the dominance of energy dissipation through plastic relaxation in the plastic zone over grain‐boundary sliding due to the presence of the glassy phase.
Electrical Conductivity of TiO2‐V2O5‐P205 Glasses
Authors: HIRASHIMA HIROSHI , NISHII KOTA , YOSHIDA TETSURO
Published: June 2006

The dc conductivities (σ) of V2O5‐P2O5 glasses containing up to 30 mol% TiO2 were measured at T=100° to ∼10°C below the glass‐transition temperature. Dielectric constants from 30 to 106 Hz, densities, and the fraction of reduced V ion were measured at room temperature. The conduction mechanism was considered to be small polaron hopping between V ions, as previously reported for V2O5‐P2O5 glass. The temperature dependence of σ was exponential with σ=σ0exp(‐W/kT) in the high‐temperature range. When part of the P2O5 was replaced by TiO2,σ increased and W decreased. The hopping energy depended on the reciprocal dielectric constant which, in this case, increased with increasing TiO2 content.
Durability and Properties in Alkali Aluminofluorophosphate Glasses
Authors: TICK PAUL A.
Published: June 2006

Glass‐forming and properties of glasses in the systems AI‐Li‐Na‐K‐P‐O‐F are presented. Useful durability, which is defined as a weight less in deionized water at 95°C of <1 mg/cm2.h, limits the range of properties available. These boundaries are represented by Tgs of 305°±25°C, density of 2.63±0.02 g/cm3, and refractive indices of 1.46±0.01.
Oxidation‐Reduction and the Major Type of Ionic Disorder in α=AI2O3
Authors: KRÖGER F. A.
Published: June 2006

The oxidation‐reduction constants of AI2O3:Ti and AI2O3 are derived from experimental data on the basis of models with aluminum vacancies or oxygen interstitials as dominant species. Reasonable agreement between the experimental values of the enthalpies involved and published theoretical values are found in both cases. Combination with the enthalpies of oxidation determined from acceptor‐doped AI2O3 leads to values of the enthalpy of disorder for the four possible mechanisms. All agree equally well with computed values. Published microstructure studies point to Frenkel disorder of oxygen as the dominant ionic disorder mechanism. Empirical potentials used in theoretical computations appear to be preferable to nonempirical ones, at least for computations related to oxygen defects.
Reaction of Anatase and Rutile with Barium Carbonate
Authors: AMIN AHMED , SPEARS MARLENE A. , KULWICKI BERNARD M.
Published: June 2006

PTC materials with the nominal composition (Ba0.997La0.003) (Ti1.012Mn0.0005)O3.025 were prepared from reagent‐grade barium carbonate and commercial grades of anatase and rutile. Both forms of TiO2 had approximately the same crystallite size. The solid state reaction was followed by thermal analysis and by X‐ray diffraction and gravimetric measurements during isothermal heat treatments. The reaction kinetics for both mixtures were virtually the same. However, some variations in microstructural development during sintering were observed, which may be related to subtle differences in crystallite character deriving from the different crystal structures of the TiO2.
Oxygen Potential of U0.85Zr0.15O2+x Solid Solutions at 15000°C
Authors: Une Katsumi , Oguma Masaomi
Published: June 2006

Oxygen potentials for U0.85Zr0.15O2+x solid solutions with the fluorite structure (prepared at 1500°C) were measured at 1500°C by a thermogravimetric technique. The oxygen potentials were 12 to 20 kJ/mol lower than those of pure UO2+x at a given oxygen‐to‐metal ratio; they cannot be represented as a function of mean uranium valence.
Velocity Exponent in Solid‐Particle Erosion of Silicon
Authors: Scattergood Ronald O. , Routbort Jules L.
Published: June 2006

The velocity dependence of the solid‐particle steady‐state erosion rate of (111) silicon single crystals was measured for a range of particle types (Al2O3, SiC, and SiO2) and two sizes (40 and 270 μm) from velocities of 30 to 150 m/s. Power‐law velocity dependence was found in all cases, but the velocity exponent n decreases with increasing size, contrary to current theories which predict a constant n. One possible interpretation of this effect is considered.
Effect of Trace Impurities on Devitrification of Vitreous Silica
Authors: Bihuniak Peter P.
Published: June 2006

Devitrification rates were measured for a series of vitreous silica glasses doped with trace levels of alkali metal oxide (1.6 to 57.8 molar ppm) and aluminum oxide (22 to 73.3 molar ppm). The devitrification rate varies inversely with the molar ratio of aluminum oxide to alkali metal oxide, a direct consequence of the effect of these trace impurities on viscosity.
Photochemical Reaction in a Reduced Soda‐Lime‐Silica Glass Containing Ce3+ and As3
Authors: Hosono Hideo , Abe Yoshihiro , Kawazoe Hiroshi , Imagawa Hiroshi
Published: June 2006

The photochemical reaction between Ce3+ and As3+ in a reduced 16Na2O. 11CaO.73SiO2 glass (mol%) was examined by exposing it to an Xe or Hg arc. In addition to Ce4+, a paramagnetic As(II)OS center having C2v symmetry and a trapped electron center were identified by ESR. The As(II)O defect is the origin of the unidentified ESR signal which correlates with the discoloration of a borosilicate glass developed for solar energy application.
Products of Reaction Between PbO and Nb2O5 in Molten KCl or NaCl
Authors: Kimura Toshio , Machida Masataka , Yamaguchi Takashi , Newnham Robert E.
Published: June 2006

Lead oxide and niobium oxide were heated in molten KCl or NaCl to examine the participation of chlorides in the reaction between the oxides. Alkali ions partially replace Pb ions in PbNb2O6, and Cl ions form PbCl2. The substitution of alkali ions for Pb stabilizes the tetragonal form ofPbNb2O6. The reactivity of NaCl with Nb2O5 was much greater than that of KCl; the extended substitution resulted in the formation of an NaNbO3 phase with incorporated Pb.
Magnesium Titanate Spinel: A Ceramic Phase for Immobilization of Technetium‐99 from Radioactive Wastes
Authors: Khalil M. Yasser , White William B.
Published: June 2006

Technetium‐99 can be dissolved in Mg2TiO4 spinels to form solid solutions with low dissolution rates. These materials are possible host phases for 99Tc in ceramic nuclear waste forms.
Property/Morphology Relations in Alkali Silicate Glasses
Authors: SHELBY J. E.
Published: June 2006

The effects of glass composition and thermal history on the glass‐transformation range behavior, as indicated by thermal expansion curves, and on chemical durability, as indicated by the acid etch rate, were measured for binary lithium, sodium, and potassium silicate glasses and for the lithinm/sodium and lithiumlpotassium mixed‐alkali silicate glasses. The results were used to determine the phase‐separation boundaries and the limits of interconnectivity of each phase for all five systems. The results demonstrate the utility of such studies for the characterization of the morphology of glass‐forming systems.
Reaction Sequence in the Formation of Lead Zirconate‐Lead Titanate Solid Solution: Role of Raw Materials
Authors: HIREMATH B. V. , KINGON ANGUS I. , BIGGERS JAMES V.
Published: June 2006

The reaction sequence in the formation of Pb(Zr0.6Ti0.4)O3 (PZT 60/40) was investigated as a function of PbO and ZrO2 raw material variations, using powder X‐ray diffraction. Particular emphasis was placed on the final stages of reaction in the formation of PZT solid solution. Based on the present work, a more detailed reaction sequence is being proposed for Pb(Zr0.6Ti0.4)O3 and similar compositions. This reaction sequence is believed to account for many of the apparent discrepancies which have appeared in the literature.
Barium Titanate Perovskite Sintered with Lithium Fluoride
Authors: HAUSSONNE J. M. , DESGARDIN G. , BAJOLET PH. , RAVEAU B.
Published: June 2006

The sintering of barium titanate with, respectively, 1 and 2 wt% LiF for two stoichiometries, Ti/Ba=1 and 0.975, was studied using two calcined powders. One was pure barium titanate; the other contained BaTi03 plus BaC03 and TiO2 that did not react when burning. The sintering chronology—intermediate phases, appearance, and disappearance of a liquid phase that has been pointed out for the first time—is directly dependent on the used calcined powder, on the LiF amount, and on the firing schedule. In the same way, the obtained perovskite symmetry varies during sintering from tetragonal to cubic and then to a second tetragonal form, whereas most of the Li and F disappear from the ceramic with two different kinetics.
Cation Self‐Diffusion in Cr2O3
Authors: Hoshino Kazutomo , Peterson N. L.
Published: June 2006

Self‐diffusion of 51Cr was measured both parallel to and perpendicular to the c axis in single crystals of Cr2O3 as a function of oxygen partial pressure at 1490° and 1570°C. The oxygen‐partial‐pressure dependence of the diffusivity indicates that cation self‐diffusion occurs by a vacancy mechanism. The values of the self diffusion coefficients determined in this experiment are about 104 times smaller than those previously reported in this temperature range.
Synthesis of Metal Phosphates Using SiP2O7
Authors: Bamberger Carlos E. , Begun George M. , Heatherly Dale E.
Published: June 2006

A new, alternative, route to the synthesis of metal phosphates, using SiP2O7 as a reagent, was studied. The reaction of SiP2O7 with metal oxides yields a solid mixture of silica and metal phosphates; its reaction with metal fluorides yields solid metal phosphates and gaseous mixtures of SiF4 and POF3.
Crystal Chemistry and Phase Relations in the System Li2O‐Fe2O3‐TiO2
Authors: YAU YU‐CHYI , HUGHES JOHN M.
Published: June 2006

Above 755°C, compounds along the spinel join LiFe5O8‐Li4Ti5O12 form a complete solid solution and below that temperature a two‐phase region separates the ordered LiFe5O8 and the disordered spinel phase. At 800° and 900°C, cubic LiFeO2 (ss) and monoclinic LizTi03 (ss) exist on the monoxide join LiFeO2‐Li2TiO3. The distributions of cations in both the spinel and monoxide structures were calculated as a function of equilibrium temperature and composition. Sub‐solidus equilibria in the system Li2O‐Fe2O3‐TiO2 at 800° and 900°C were determined for compositions containing ∼50 mol% Li2O.
Milling and Suspension Behavior of A12O3 in Methanol and Methyl Isobutyl Ketone
Authors: SACKS MICHAEL D. , KHADILKAR CHANDRASHEKHAR S.
Published: June 2006

Milling and suspension behavior of Al2O3 were studied in two suspending liquids, i.e. methanol (MeOH) and methyl isobutyl ketone (MIBK). Properties were investigated for various mixed solvent ratios. Ball‐milling studies were carried out on powders containing “hard” agglomerates. Agglomerate breakdown was monitored by rheology, sedimentation density, and particle size measurements and by direct microscope observations. Particle size reduction kinetics were observed to decrease at high MIBK/MeOH ratios due to increased flocculation in these suspensions. Suspension behavior of deagglomerated (by ball‐milling 20 h) Al2O3 was also investigated. Rheology, sedimentation density, and sedimentation “particle” size distribution measurements demonstrated that increased flocculation occurred at high MIBK/MeOH ratios. Electrophoresis measurements indicated that this behavior was due to decreased electrostatic repulsion between particles. Suspension stability (against flocculation) was analyzed using DLVO theory.
Thermochemistry of the Aluminas and Aluminum Trihalides
Authors: CARNIGLIA STEPHEN C.
Published: June 2006

Consistent standard free energies of formation of gibbsite, bayerite, boehmite, and diaspore; their respective transition aluminas, α‐Al2O3; and AlF3, AlCl3, H2O3 HF, and HCl are compiled from 298.16 to 2100 K from literature review, computations, and estimates. Significant adjustments and additions to earlier compilations are included. Revised analysis is made of the gibbsite‐to‐α‐A12O3 transition series and of reactions of appropriate aluminas with HF and HCl, comparing them with experimental data. These updated ΔG° tables should also yield accurate ΔG° data for many other alumina reactions, e.g. with SiO2, M2O, MO, etc.
Low‐Temperature Dielectric Properties of Ceramic Potassium Tantalate (KTaO3)
Authors: CHEN Z. X. , ZHANG X. L. , CROSS L. E.
Published: June 2006

Dielectric properties of KTaO3 ceramic fabricated by both conventional sintering and sintering followed by isostatic hot pressing (HIP) were measured at T=4.2 to 300 K over a frequency range from 400 Hz to 4 MHz. The weak field response shows a faint peak near 10 K which has a clear relaxation character, as in high‐purity single crystals. The general response is well reproduced by the Barrett function, but additional polarizability with relaxation character is also in evidence at higher temperatures. No dielectric hysteresis was observed at high fields for cycling frequencies down to 0.04 Hz anywhere in the temperature range.
Criteria for Physical Modeling of Electric Glassmelting Furnaces
Authors: HRMA PAVEL
Published: June 2006

The conditions for dynamical similarity between an electric glassmelting furnace and its physical model are discussed. It is suggested that the most critical features which have to be matched are the total energy balance for the furnace melting end, the ratio of the throughput to the circulation velocity of the glassmelt, and the temperature variation of the viscosity and electrical conductivity of the melt. Criteria based on these factors are proposed and details of the calculation of parameters needed to design a physical model are given.
Mechanical, Thermal, and Microstructural Properties of Neutron‐Irradiated SiC
Authors: CORELLI J.C. , HOOLE J. , LAZZARO J. , LEE C.W.
Published: June 2006

The thermal and electrical conductivities, fracture strength, swelling, and microstructure of sintered alpha‐phase Sic and siliconized reaction‐bonded Sic materials were studied before and after irradiation with reactor neutrons. The effects of helium gas on the properties were studied using boron enriched in 'OB to produce helium from 10B(n, α) 7Li. The decrease in thermal conductivity after irradiation is due to enhanced phonon scattering by radiation‐induced defects. Electrical, mechanical, and thermal properties exhibit partial recovery after heat treatment to 1000 to 1500 K. An overall consistency is observed in radiation‐produced property changes and annealing and a model is presented to explain the changes.
EPR Evidence for an Osmotic Mechanism of Cement Hydration
Authors: Lasiç Danilo D.
Published: June 2006

Electron paramagnetic resonance measurements made during cement hydration are consistent with the osmotic model of cement solidification. Uncharged water‐soluble spin probes probably reflect the growth and cross‐linking of fibrils, where as the formation of a gel coating in the initial stage can be followed with charged spin probes. Retardation and acceleration efects are explained on the basis of concentration differences across the semipermeable gel surface which separates the water solution and the gel coating of the cement grain.
Preparation of Mn‐Zn Ferrites Having a Low Temperature Coefficient of Permeability
Authors: Gallagher Patrick K. , Gyorgy E. Michael , Johnson David W. , Robbins Murray , Vogel Eva M.
Published: June 2006

Substitutions of Ge, and to a lesser extent Ga, for Zn in manganese‐zinc ferrite were found to increase the initial permeability (μ) from ∼200 to ∼1000. The relative temperature coefficient of permeability is very low (<0.02%) over the range ‐40° to +80°C. These desired properties are achieved without controlling the atmosphere during sintering und subsequent cooling provided rhat the utmo sphere contains≥1 vol% 02.
Beta Sic Powders Produced by Carbothermic Reduction of Silica in a High‐Temperature Rotary Furnace
Authors: Wei George Chia‐tsing
Published: June 2006

Sinterable β‐Sic powders were synthesized by carbothermic reduction of silica with carbon in a high‐temperature rotary furnace. The powders were character ized as to sinterability, surface area, particle size, and morphology.
A Radioactive Tracer Method for Measuring the Relative Surface Areas of Small Samples
Authors: Brown Sherman D. , Van Bao Tran , Wirtz Gerald P.
Published: June 2006

A new method for measuring the relative surface area of small samples is described. The method is based on liquid‐sorption theory and uses stearic acid tagged with 14C. Relative surface area data on alumina samples deposited under various conditions by the anodic spark process are reported. The method was validated successfully using BET data taken on alumina samples.
Factors Influencing Residual Surface Stresses due to a Stress‐Induced Phase Bansformation
Authors: GREEN DAVID J. , LANGE F. F. , JAMES MICHAEL R.
Published: June 2006

An X‐ray diffraction technique was used to measure the residual surface stresses on ground surfaces of Al2O3/ZrO2 (tetragonal) composites. To accomplish this, it was necessary to use a radiation for which the penetration depth was small (large wavelength), e.g. CrKα radiation. It was found that these materials could have compressive stresses as high as 1 GPa on their surface, which is a result of the molar volume associated with the tetragonal‐to‐monoclinic ZrO2 phase transformation. This transformation was induced by the grinding stresses and a reasonable correlation between the amount of ZrO2 transformed and the magnitude of the residual stresses was established. Evidence was found that the transformation depth is controlled by the amount of stabilizing oxide added to the ZrO2 and by the ZrO2 grain size. In the materials studied, transformation depths were found to be typically <20 μm.
The Influence of Piezoelectric Grain Resonance on the Dielectric Spectra of LiNbO3 Ceramics
Authors: XI YAO , McKINSTRY H. , CROSS L.E.
Published: June 2006

It has often been suggested that the higher frequency dispersion (f∼107∼108 Hz) evident in the dielectric response of high‐permittivity ferroelectric ceramics might be associated with piezoelectrically driven resonant mechanical motion of individual grains. The hypothesis certainly appears reasonable, but so far no direct verification appears to have been attempted. Our discovery that the individual crystallite resonances are well preserved in poled LiNbO3 bicrystals suggested that we explore the dispersion of LiNbO3 ceramics. In both conventionally sintered and uniaxially hot‐pressed ceramics, the dielectric dispersion around 108 Hz has obvious resonant character. Using a modified ECAP computer program demonstrated that both the real and imaginary components of the impedance can be quantitatively described using the equivalent circuit models for the coupled individual grain resonances.
Lithium Carbonate/Sodium Sulfate Eutectic—An Additive for Improving Glass Production
Authors: BROWN PATRICK M. , BORYTA DANIEL A.
Published: June 2006

A phase diagram for the system lithium carbonate/sodium sulfate was developed by DTA measurements in a CO2 atmosphere. The lithium carbonateisodium sulfate eutectic composition from that system improved glassmelting, speeded fining, and reduced the viscosity of a standard fiber glass when used as an additive. Improved melting rates were postulated to result from reaction of lithia with glass‐forming components at a relatively low temperature. Lithia is formed by decomposition of Li2CO3 or Li2CO3/Na2SO4 eutectic in air at or near their melting points.
Strength and Fatigue of Fluoride Glass Optical Fibers
Authors: Sakaguchi Shigeki , Mitachi Seiko
Published: June 2006

Strength and fatigue characteristics of fluoride glass optical fibers, used as a new infrared transmission medium, were examined. A correlation parameter between mirror size and tensile strength of 0.826 MPa.m12 was obtained, and a fatigue parameter of 16.2 was determined from a dynamic fatigue test at 20°C and 60% rh.
Growth of Beta Alumina on Aluminum Oxide
Authors: Hodge James D.
Published: June 2006

The rate of growth of a beta alumina reaction layer at an interface between alpha alumina and sodium aluminate was determined. The data for the growth of this reaction layer were found to obey a parabolic rate law. Further analysis of the data indicated that the reaction is controlled by oxygen diffusivity in beta alumina.
Inhomogeneous Density in Die Compaction: Experiments and Finite‐Element Calculations
Authors: Broese Van Groenou Arnold , Lissenburg Rokus C.D.
Published: June 2006

X‐ray density measurements and two‐color powder displacement observations were used to determine the reliability of the cylindrical test cell as a source of data for a plasticity model of granular materials. Calculations with such a model agree well with the experimental density distribution, for the cylindrical test cell itself and for a cylindrical die, compacted from one side by means of a profiled plunger.
Crystallography of the Directionally Solidified NiO‐CaO Eutectic
Authors: Fragneau Marc , Revcolevschi Alexandre
Published: June 2006

Crystallographic relations between the two solid solutions forming the eutectic of the system NiO‐CaO were studied by X‐ray diffraction and scanning electron microscopy. The ionic arrangement at the phase interface can be described by alternate (111) planes of metal and close‐packed oxygen ions.
Grain‐Boundary Resistivity of Stabilized Zirconia Films
Authors: Miyayama Masaru , Inoue Hiroyuki , Yanagida Hiroaki
Published: June 2006

The influence of grain‐boundary density on the resistivity of grains and grain boundaries in stabilized zirconia films, made by a modified doctor blade method using Al2O3 as a sintering agent, was investigated at 300° to 500°C. Only cubic zirconia was detected by X‐ray diffraction. However, electron probe microanalysis showed that the Al concentration was preferentially enriched near grain boundaries. The resistance per square centimeter of grain‐boundary surface decreased with increasing grain‐boundary density in the range 170 to 310 cm‐1.
Properties of Isostatically Hot‐Pressed Silicon Nitride
Authors: Richerson David W. , Wimmer JamesM.
Published: June 2006

Hot isostatic pressing was studied for densification of reaction‐bonded Si3N4 containing various levels of Y2O3. Near‐theoretical density was achieved for com positions containing 3 to 7 wt% Y2O3. An Si3N4‐5 wt% Y2O3 composition had a 4‐point flexural strength at 1375°C of 628 MPa and survived 117 h of stress rupture testing at 1400°C and 345 MPa.
Linear Thermal Expansion Coefficients of Mullite‐Matrix Aluminosilicate Refractory Bodies
Authors: PERETZ I. , BRADT R.C.
Published: June 2006

Twenty‐seven mullite‐matrix aluminosilicate refractory bodies in three different refractory systems were synthesized and their thermal expansions were measured and then correlated with their corundum and mullite contents by regression analyses. Thermal expansion coefficients were also calculated from the physical properties of the individual constituent phases. It is concluded that the best estimator of the thermal expansion of these materials is the regression analysis based on the volume percentage mullite content and that those bodies based on tabular alumina aggregates are the most predictable. For the best predictions, only a single raw material system, or very similar raw material systems can be considered.
Thermoelectric Determination of Cation Distributions in
Authors: TRESTMAN‐MATTS A. , DORRIS S. E. , KUMARAKRISHNAN S. , MASON T. O.
Published: June 2006

Thermoelectric coefficient measurements in the system Fe3O4‐Fe2TiO4 were used to determine the cation distributions from 600° to 1300°C. The cation distributions obeyed the relation

‐RT In K=‐9.61+2(‐0.0154T)b+0.0256T (kJ/mol)

where KFecd is the iron distribution constant and b is the tetrahedral Fe3+ concentration. Low‐temperature extrapolations agreed with experimental magnetometry and lattice parameter results. With the incorporation of a subregular size‐mismatch term, agreement with high‐temperature thermodynamic data was achieved. A solvus at intermediate temperatures was correctly predicted by the model.
Phase Equilibria in the Systems Rare‐Earth Sesquioxide‐Beryllium Oxide
Authors: YEN TUNG‐SHENG , KUO CHU‐KUN , HAN WEN‐LONG , QUI YING‐HUI , HUANG YU‐ZHEN
Published: June 2006

Phase equilibria in systems comprised of a rare‐earth or yttrium sesquioxide and beryllia were studied. Two types of beryllates, stable and metastable, with molecular ratios of 1:2 and 3:2, were found: their formation and stability are discussed in terms of crystal chemistry.
Infrared‐Transparent Mullite Ceramic
Authors: PROCHAZKA S. , KLUG F. J.
Published: June 2006

Mullite ceramic, transparent in the infrared, was prepared by hot‐pressing and hot‐isostatically pressing starting materials derived from alkyloxides. A composition with 72.3 wt% Al2O3 yielded transparent, submicrometer grain size bodies at 1630°C, whereas higher temperatures produced glass‐containing microstructures. A composition with 76 wt% A12O3 formed precipitates of α‐Al2O3 at the consolidation temperature, which could be removed by subsequent annealing between 1800° and 1850°C. Spectral transmittance and absorption coefficients of the bodies are reported. The formation of the second phases was linked to phase equilibria and grain growth that promoted compositional equilibration of the mullite phase. The results suggest adjustments to phase boundaries in the high‐temperature segment of the SiO2‐Al2O3 phase diagram.
Rearrangement of Porous CaO Aggregates During Calcite Decomposition in Vacuum
Authors: BERUTO DARIO , BARCO LUIGI , SEARCY ALAN W.
Published: June 2006

High‐resolution SEM photographs, N2 adsorption isotherms, Hg porosimetry, and micrometer measurements were used to characterize CaO particle shapes and pore‐size distributions that result when calcite crystals are decomposed in vacuum at 686°C. The surface area of the CaO produced from large calcite crystals is constant at 116.4 m2/g independent of the extent of reaction. The volume occupied by a CaO aggregate is 98±2% that of the original calcite crystal. The ∼54% total porosity is comprised of 42% pores of ∼5 nm cross section and 12% pores of ∼10 μm cross section. The duplex pore structure is formed by a diffusionless repacking of CaO particles that initially form with a more uniform distribution of particles and pores.
Communications of the American Ceramic Society Estimation of Thermochemical Data for Calcium Silicate Hydrate (C‐S‐H)
Authors: Fujii Kinjiro , Kondo Wakichi
Published: June 2006

Calcium silicate hydrate (C‐S‐H) can be viewed as a solid solution, 0.833Ca(OH)2.SiO2.0.917H2O‐xCa(OH)2, at equilibrium at 30°C. On this basis, the change in Gibbsfree energy (ΔGr) in the solid‐solution reaction was calculated from solubility duta for C‐S‐H in water. The change in ΔGrwith real ratio decreased notably for the higher calcium contents (CaO/Si021.7; ×0.867). Thermochemical values for C‐S‐H (CaO/SiO2=1.7) were estimated to be ΔH°=‐2890 kJ/mol, ΔG°=‐2630 kJ/mol, and S°=200 J1/mol.K at 298 K.
Sphere‐on‐Tape Method of Rapid Selected‐Area Thinning of Samples for Transmission Electron Microscopy
Authors: van Groenou Arnold Broese , van Oers Déanis J. C.
Published: June 2006

By using an instrumentation recorder with Al2O3 tape loaded on the reverse side with an Al2O3 sphere 4 mm in diameter, flat samples were thinned locally to a thickness of 10 μm. About 90 min is required for two‐sided thinning of a ferrite sample 200 μm thick, followed by 30 h of ion‐milling. Transmission electron micrographs showing details of glass gaps in magnetic recording heads were obtained. The method is also thought to be useful for making thin cross sections of complicated structures.
Melting Reactions of Soda‐Lime‐Silicate Glasses Containing Sodium Sulfate
Authors: Taylor Theodore D. , Rowan Kurt C.
Published: June 2006

Various Na2SO4‐Na2CO3‐CaCO3‐SiO2 combinations were studied by differential thermal analysis to elucidute the role of Na2SO4 in soda‐lime‐silica glassmelting reactions. It was found that Na2SO4 encourages the formation of wollastonite at 850° to 900°C. The solid‐state reaction of Na2Ca(CO3)2 occurs very readily at temperatures in the vicinity of 400°C. The Na2Ca(CO3)2 must therefore be considered a major constituent in glass batches containing both soda ash and limestone.
Attempted Glass Formation in Pure KHSO4
Authors: MacFarlane Douglas R.
Published: June 2006

Recent attempts to vitrify KHSO4 have been fruitless, bringing into question the glass‐forming ability of this, the only hitherto known glass‐forming sulfate. Since KHSO4 is easily converted to the pyrosulfate at temperatures above its melting point, it is likely that previously reported KHSO4 glass samples were actually mixtures of the bisulfate and the pyrosulfate, with the pyrosulfate aiding vitrification.
Microscopic Characterization of Pb0.9l La0.09(Zr0.65Ti0.35)0.98O3
Authors: Little J. A. , Yao P. c.
Published: June 2006

A microstructural study of a lead‐lanthanum zirconate‐titanate was conducted to examine the effects of the lead oxide used as a sintering aid. Although amorphous grain‐boundary phases are present in lead zirconate‐titanates sintered by a similar procedure, no such phase was found by careful microscopic examination.
Electronic Spectra and Coordination of Ni2+ in Potassium Borate Glass and Melt to 1000°C
Authors: Lin Ted‐Cheng , Angell C. Austen
Published: June 2006

A quantitative visible‐uv spectroscopic study of local structure‐sensitive electronic transitions resulting from Ni2+ doped into sodium borate in the glassy and liquid states up to 1000°C was conducted using a simple windowless Pt‐cell technique with a high‐temperature spectrophotometer. Analysis of the spectra shows that Ni2+ is distributed between distorted tetrahedral and octahedral sites in a temperature‐dependent equilibrium with ΔH =44.4 kJ. mol−1 in the liquid and a much smaller but nonvanishing value in the glass.
Phase Equilibria of Nuclear Waste Ceramics: The Effect of Oxygen Fugacity
Authors: RYERSON F. J.
Published: June 2006

Wasteform phase assemblages and radionuclide immobilization are described for a Synroc‐D bulk composition processed at 1200°C under oxygen fugacities (f O2) ranging from air to those approximating graphite‐CO‐CO2 buffer. All processing conditions produce assemblages of titanate and aluminate crystalline phases plus alkali aluminosilicate glass. In all cases the important radionuclides are immobilized in crystalline phases which have been shown to be highly leach‐resistant.
Mechanisms of Failure from Surface Flaws in Mixed‐Mode Loading
Authors: MARSHALL DAVID B.
Published: June 2006

Mechanisms of failure from surface cracks in combined tension and shear are identified by directly observing the cracks during failure testing. Under the combined influences of residual contact stresses and applied loading, indentation cracks propagate stably and realign normal to the principal applied tension prior to failure. Annealing of indentation flaws causes relaxation of the residual stresses and thereby leads to a change in the mechanics of fracture; unstable propagation occurs from the initial crack at a critical applied loading, with an abrupt change in fracture plane. Strengths of indentation flaws and machining damage in both the as‐formed and annealed states are measured as a function of flaw orientation relative to an applied uniaxial tension. Strength variations of indentations and machining flaws are similar. The results are assessed in terms of various proposed mixed‐mode fracture criteria, and the implications of the results for nondestructive testing using scattering of surface acoustic waves are discussed.
Behavior of Atoms at the Surface of a K2O · 3siO2 Glass—A Molecular Dynamics Simulation
Authors: GAROFALINI STEPHEN H.
Published: June 2006

Recent ion scattering spectroscopy (ISS) studies indicate that an excess of K ions occurs at the surface of a K2O · 3SiO2 glass. Molecular dynamics (MD) computer simulations were used to evaluate the short‐time dynamic behavior of atoms at the surface of such a glass in order to determine a mechanism for the K ion enrichment. In the simulations, a bulk glass of several hundred atoms was melted using three‐dimensional periodic boundary conditions, and subsequently quenched to lower temperatures. Periodic boundary conditions were removed in one dimension near room temperature so as to create free surfaces. The distribution of species perpendicular to the free surface was determined. The MD simulations show that K ions can build up at the outermost surface of the glass within several picoseconds after formation of the surface.
Morphological Analysis and Growth of Crystallites During Annealing of ZnO
Authors: LOUËR DANIEL , VARGAS RODOLFO , AUFFRÉDIC JEAN‐PAUL
Published: June 2006

A detailed analysis of the crystallite shape of zinc oxide produced by thermal decomposition of zinc hydroxynitrate was performed as a function of temperature from 280° to 700°C. The shape and size were analyzed by X‐ray line‐broadening measurements. Evolution from cylinder to right hexagonal prism shapes is observed during annealing of the loose powder. A homothetic growth of crystallites is observed through the initial stage of annealing. Relations between surface area and X‐ray crystallite size are presented and discussed in terms of the packing factor. Results suggest that two parallel growth processes take place during annealing.
Oxygen Activity Dependence of the Electrical Conductivity of Li‐Doped Cr2O3
Authors: HUANG R.F. , AGARWAL A.K. , ANDERSON H.U.
Published: June 2006

The electrical conductivity of Li‐doped Cr2O3 was investigated as a function of PO2, temperature, and dopant content. Results show that the electrical conductivity remains almost unchanged with decreasing P O2 in the high‐P O2 region but decreases rapidly at low P O2. A second phase was found in samples which contained more than 0.85 mol% Li. The results are explained by a model in which the concentration of charge carriers is dependent on the acceptor dopant and oxygen vacancy concentration.
Effect of Stress on Water Diffusion in Silica Glass
Authors: NOGAMI MASAYUKI , TOMOZAWA MINORU
Published: June 2006

The diffusion of water in silica glass was measured as a function of applied uniaxial stress and hydrostatic pressure at selected temperatures. It was found that the diffusion coefficient of water increased exponentially with increasing tensile stress and decreased with increasing compressive stress and increasing hydrostatic pressure. The activation volume for water diffusion in silica glass was found to be ∼170 cm3/mol at 192°C and ∼72 cm3/mol at 350°C. The solubility of water in glass showed a trend opposite to the diffusion coefficient, namely, it decreased exponentially with increasing tensile stress and increased with increasing compressive stress and hydrostatic pressure. These stress (or pressure) dependences were attributed to the shift of the glass‐water reaction equilibrium.