bluuebunny/crossref_metadata_2025 huggingface dataset:
Ion Exchange in Sodium Borosilicate Glasses
Authors: VARSHNEYA A. K. , MILBERG M. E.
Published: June 2006

The kinetics of K+‐Na+ exchange in sodium borosilicate glasses containing 20 mol% Na2O were studied as a function of glass composition and exchange time and temperature. The distribution of K in the glass after exchange in molten KNO3 was determined using an electron microprobe. In those specimens which were not chemically attacked by the molten salt, the K profiles were consistent with Fickean behavior. The calculated interdiffusion coefficients varied with local composition in each specimen. This composition dependence and its variation with temperature could be fitted approximately to a mixed‐alkali model using the Nernst‐Planck relation for diffusive fluxes. However, some deviation from this behavior, presumably as a result of the generation of microscopic stresses around an exchange site, was observed. The dependence of the apparent activation energy, Ẽ, on the B/Si ratio was analogous to that of the activation energy for ionic conduction in these glasses: Ẽ decreased with increasing fraction of nonbridging oxygen. This result disagrees with the presumed behavior in sodium aluminosilicate glasses.
Optical Absorption of the Transition Elements in Vitreous Silica
Authors: SCHULTZ PETER C.
Published: June 2006

The optical absorption of 3d transition elements in fused silica was studied. A series of high‐quality silica glasses doped with 0.01 to 0.1 wt% of each transition element (V through Cu) was prepared by a vapor hydrolysis technique. Their optical spectra were measured, and their practical absorptivities were calculated between 200 and 2000 nm. In the proposed waveguide use range (∼ 850 nm), V and Cr appear to absorb most (apract= 2.6 and 1.2 dB/km ppbw−1 (metal), respectively) and Cu the least (apract≃0). Comparisons are made with data for conventional glasses.
Nature of Intergranular Phase in Nonohmic ZnO Ceramics Containing 0.5 Mol% Bi2O3
Authors: WONG J.
Published: June 2006

The intergranular phase obtained by sintering a binary mixture of ZnO + 0.5 mol% Bi2O3 was isolated by using a dilute solution of HCIO4, which etches ZnO preferentially. The combined results of selected‐area electron diffraction and microscopy, microprobe analysis, and X‐ray diffraction strongly indicate that the intergranular material is a polycrystalline phase of tetragonal β‐Bi2O3 (P421c), rather than the amorphous ZnO‐Bi2O3 phase reported earlier. It appears that the nonohmic behavior in this prototype metal‐oxide varistor must be an interfacial property associated with the semiconducting ZnO grains separated by thin layers of high‐resistivity Bi2O3.
Raman Study of Isothermal Devitrificatn Kinetics of NaPO3 Glass
Authors: EXARHOS G. J. , RISEN W. M.
Published: June 2006

A laser Raman spectroscopic method was developed by which the increase in crystallinity of a devitrifying glass can be monitored continuously and isothermally at the devitrification temperature, without sample quenching, in a molecularly specific manner that yields high‐quality kinetic data for the glass‐crystal transformation. Applied to the study of vitreous (NaPO3)n(gl), the method yielded continuous data which were fitted, by a nonlinear least‐squares method, to an equation of the form α(t) = 1‐ exp (‐kNtN) with sufficient precision to permit optimization with respect to both N and kN. The values of N and kN vary with glass thermal history, i.e. with variations in time of heating at Tg for otherwise identical samples, although the material does not phase separate. The activation energy from any plot of In (kN)1/N vs (1/T) does not vary, but the offset of the curves indicates different preexponential terms in the Arrhenius expression. The results are analyzed in terms of current theories.
The System CaO‐ThO2‐ZrO2
Authors: ROEDER E. W. F. , WILSON H. J. C.
Published: June 2006

The present investigation did not confirm the conclusion of Ruff et al. that certain compositions within the system CaO‐ThO2‐ZrO2 might solidify in the vitreous state. Although many ZrO2‐rich samples were translucent after they were melted in an induction plasma torch, X‐ray diffraction indicated a crystalline structure of the fluorite type. When samples were annealed at 1400°C, the metastable phase decomposed, and translucency was lost. A section of the system at 1600°C is presented, together with a preliminary description of a pyrochlore‐type compound with the approximate composition 2CaO·2ThO2·5ZrO2.
Substituted Hydrated Calcium Silicates Obtained in Autoclave Hydration
Authors: CHIOCCHIO GERARDO , COLLEPARDI MARIO , TURRIZIANI RENATO
Published: June 2006

Hydrated calcium silicates containing Al3+] or Fe3+] were prepared by autoclaving C3S and β‐C2S in the presence of C3A or C2F at 190°C. Al3+] and Fe3+] diffuse into the crystal lattice of α‐C2SH and C3SH1.5. Solid solutions containing Al3+] and Fe3+] were placed in contact at 25°C with sources of sulfates, either in aqueous stirred suspensions or as pastes. Al3+] and Fe3+] remain stable in the solid solution, inhibiting the formation of ettringite. This absence of ettringite can explain the resistance of autoclaved cement pastes and concretes to sulfate attack.
Strength Degradation of Soda‐Lime‐Silica Glass During Dynamic Loading
Authors: YAMADA HISAO
Published: June 2006

The strength degradation of soda‐lime‐silica glass during dynamic loading was studied by using a fracture‐mechanics approach. The theoretical and experimental results indicate that subcritical flaw growth during loading causes the strength degradation.
Vaporization Kinetics of Na2SO4 from 900° to 1200°C
Authors: UHLIG G. F. , DAVIS H. H. , GRAHAM H. C.
Published: June 2006

Continuous weight‐change measurements were used to determine the vaporization kinetics of Na2SO4 from 900° to 1200°C in 150 torr O2. Simple evaporation of the sulfate was indicated. An activation energy for vaporization of 71 kcal/mol was calculated. Vaporization results obtained for Na2SO4 on oxide substrates indicated an Na2SO4‐Cr2O3 reaction; however, no Na2SO4‐ZrO2 reaction was observed.
ESR Study of Devitrification Processes
Authors: ARAFA S. , ASSABGHY F. , FAHMY H. , ALLAM M. , SABEK D.
Published: June 2006

The radiation‐induced ESR centers in glasses with different Ti concentrations were studied to elucidate crystallization processes in the glass. The parameters of the induced ESR absorption associated with the T2 center were investigated systematically as a function of heat treatment. The induced T2 centers in the glasses containing small concentrations of Ti characteristically decreased in intensity as nucleation began and disappeared completely in devitrified samples. A mechanism is proposed for the destruction of the T2 center as nucleation proceeds to crystallization. Supporting X‐ray diffraction evidence is given. The systematic decrease in the ESR intensity of this radiation‐induced center provides a means of monitoring devitrification processes in glasses.
Reaction Products in Magnesium Oxychloride Cement Pastes. System MgO‐MgCl2‐H2O
Authors: MATKOVlĆ BORIS , POPOVIĆ STANKO , ROGIĆ VINKO , ŽUNIĆ TONČI , YOUNG J. FRANCIS
Published: June 2006

The calcining temperature of the basic magnesium carbonate influences both the reactivity of the resultant MgO and the reaction products in the system MgO‐MgCl2‐H2O. The reaction products identified by X‐ray diffraction are: Mg3(OH)3Cl·4H2O (phase 5), Mg2(OH)3Cl·4H2O (phase 3) and Mg(OH)2. The present paper discusses the relationship between the properties of MgO and the observed reaction products.
Fracture Behavior of ZrO2‐Zr Composites
Authors: VIRKAR ANIL V. , JOHNSON D. LYNN
Published: June 2006

Zirconium oxide‐zirconium 2‐phase alloys with composition 40 at.% Zr‐60 at.% O (23 vol% metal phase) were prepared by hot‐pressing mixtures of the oxide and the metal powders. The microstructure consisted of oxide grains completely surrounded by the metal phase. The effective fracture surface energy, γeff, was determined using the double cantilever beam (DCB) technique and crack lengths were determined by compliance calibration. Rapidly cooled specimens, in which the tetragonal to monoclinic phase transition would cause residual stresses, exhibited γeff values as much as 70% greater than stress‐relieved specimens (65 J/m2 and 38 J/m2, respectively). A shift in the tetragonal ⇋ monoclinic transition temperature in the as‐hot‐pressed and the rapidly cooled specimens, compared to the stress‐relieved specimens, confirmed the existence of residual stresses. The fracture strength, σeff, measured in 3‐point bending, was found to be independent of the thermal treatments. Scanning electron microscopy and optical microscopy revealed that the fracture is transgranular.
Raman Scattering of Carbonate Ions Dissolved in Potassium Silicate Glasses
Authors: VERWEIJ H. , VAN DEN BOOM H. , BREEMER R. E.
Published: June 2006

Raman spectra of glasses, prepared from a mixture of K2CO3 and SiO2, give evidence for the presence of almost isolated planar CO32‐ ions, dissolved in the glass. It appears that measurement of the Raman spectra is a useful nondestructive method for the determination of the CO32‐ concentration in glasses.
Elastic Moduli and Refractive Indices of Aluminosilicate Glasses Containing Y2O3, La2O3, and TiO2
Authors: MAKEHIMA AKIO , TAMURA YOSHIAKI , SAKAINO TERUO
Published: June 2006

Glasses in the system Al2O3‐Y2O3‐SiO2, containing TiO2 and La2O3, were investigated. Glasses of high refractive index and elastic modulus were developed. The observed Young's and shear moduli of these glasses show good agreement with theoretical values. Agreement was also found between the observed and calculated values of refractive index when the Appen's empirical coefficients were used.
Heat Transfer in VO‐MO (M = Ni, Co, Mn) Solid Solutions
Authors: MURANEVICH A. KH.
Published: June 2006

The thermal conductivity of VO‐MO (M = Ni, Co, Mn) solid solutions was studied at 100° to 1100°K. In semiconductor compounds V0.96Ni0.05O, V0.95Co0.05O, and V0.95Mn0.05O, at >500°K, the electron thermal conductivity (increasing with temperature) was established using the Wiedemann‐Franz relation. The magnitude of the phonon mean free path, as evaluated for some compounds, is close to the lattice constant, indicating that phonons are strongly scattered by structural defects.
Corrosion of Lead Glasses in Acid Media: I, Leaching Kinetics
Authors: WOOD SUSAN , BLACHERE J. R.
Published: June 2006

The leaching kinetics of lead glasses (25 to 35 mol% PbO‐75 to 65 mol% SiO2; some with K2O and A12O3, additions) were determined in 10% acetic acid. Except for a ternary glass (SiO2‐PbO‐K2O) which had a linear dependence on time, all compositions exhibited a linear dependence on the square root of time for the amount of Pb and K removed. Increasing the SiO2: PbO ratio or the Al2O3 content improved the durability whereas adding K2O to a binary PbO‐Si02 glass greatly increased the corrosion rate. Activation energies for the rates of Pb and K removal were determined for three compositions and it was deduced that the diffusion of H+ controlled the leaching for binary and 4‐component glasses whereas dissolution of the silica network was rate‐controlling for the ternary.
Corrosion of Lead Glasses in Acid Media: II, Concentration Profile Measurements
Authors: WOOD SUSAN , BLACHEFE J. R.
Published: June 2006

Lead concentration profiles were measured in a binary lead silicate glass corroded by acid using ahd a‐backscattering technique. These profiles were characteristic of those predicted for an interdiffusion process and revealed a surface layer deficient in lead. Diffusion coefficients for Pb2+ were calculated, together with values of the total amount of lead removed at the various experimental temperatures and times. Good agreement was found between these data and those previously obtained experimentally. All diffusion coefficient values were high and, correspondingly, activation energy values were low compared with those predicted by the literature for similar glass compositions. This difference was justified from consideration of the leaching process.
Defect Structure and Electrical Properties of KTaO3
Authors: DEPUTY GERALDINE O. , VEST R. W.
Published: June 2006

The electrical conductivity and thermoelectric power of KTaO3 were measured from 900° to 1300°C over a range of oxygen partial pressures. The isothermal electrical conductivity showed a minimum at an oxygen partial pressure corresponding to the transition between p‐type and n‐type behavior. A point defect model was developed which involved fully ionized potassium and tantalum vacancies, singly and doubly ionized oxygen vacancies, holes, and electrons. The values of all pertinent equilibrium constants were calculated from the experimental data and the nonsimplified neutrality condition was solved to give each of the defect concentrations as a function of temperature and oxygen partial pressure. The calculated conductivity agreed extremely well with the experimental data over the full temperature and oxygen partial pressure range, and the band gap derived from these calculations (3.43 eV) was in excellent agreement with the reported value (3.5 eV).
Vacuum Vaporization in the System MgO‐Cr2O3
Authors: SATA TOSHIYUKI , LEE HONG LIM
Published: June 2006

The vaporization of the system MgO‐Cr2O3 was studied in a vacuum of 10−5 torr (10−3N/m2) at 1500° to 1700°C using the Langmuir and Knudsen methods. It was found that the phases in the system vaporize nearly congruently and the logarithm of the vaporization coefficient, α, of MgCr2O4 increases linearly with increasing reciprocal temperature. Alpha tends to unity at a temperature near the melting point (2525±23°C). The additivity rule can be applied to the Langmuir vaporization rates on the basis of the surface area ratios of the phases in the 2‐phase system MgO‐Cr2O3. The enthalpies of vaporization of MgCr2O4 were 695.0 and 549.2 kcaVmol for activated and equilibrium processes, respectively.
The Nature of the Alumina‐Rich Phase in the System La2O3‐Al2O3
Authors: ROPP R. C. , LIBOWITZ G. G.
Published: June 2006

Of the two formulas previously reported for the compound on the alumina‐rich side of the system La2O3‐Al2O3, present experimental results indicate that LaAl11 O18 is correct. This compound melts congruently at ∼2000°C and has a hexagonal structure with lattice parameters of a0= 5.561± 0.007 Å and c0=22.041± 0.004 Å. Compositions fired at 1650° showed invariant powder diffraction patterns whereas those fired at 1450°C exhibited X‐ray patterns which varied both in numbers and relative intensities of lines. When the samples which had been initially fired at 1450° were refired at 1650°, the X‐ray patterns changed to the invariant 1650°C pattern. This behavior appears to be related to an ordering mechanism in which the La3+ cations are distributed between two types of cation sites in the hexagonal lattice.
Ionic Conduction of Li2O‐2SiO2 Glass Under DC Potential
Authors: TAKIZAWA KAZUTAKA
Published: June 2006

A charging current flows under a dc potential applied to electrodes on Li2O 2SiO2 glass, producing effects that cannot be ignored. These effects aid in understanding the behavior of the charging current when charges are transported across the boundaries between the electrodes and the glass and are more important, even at room temperature, for glasses with relatively good conductivities, e.g. Li2O‐2SiO2 glass. The current for lithium ion penetration into the cathode was estimated from the amount of the lithium in the cathode material. The phenomenological comparison of the current determined by subtracting the penetration current from the charging current indicates that this resultant current is not only attributed to accumulation of the lithium ions transported from the bulk of Li2O 2SiO2 glass into the surface layer adjacent the cathode, but also to displacement (toward the anode) of the oxygen ions in the lithium‐depleted region developed near the anode. This conclusion is qualitatively confirmed by the observed depth concentration profiles of oxygen distributed in the surface layers adjacent the electrodes.
Stress Intensity Factor Estimates for a Peripherally Cracked Spherical Void and a Hemispherical Surface Pit
Authors: BARATTA FRANCIS I.
Published: June 2006

Stress intensity factors are estimated for three‐dimensional defects which occur in ceramic bodies. The two idealized cases considered are a spherical void with a circumferential crack at its equator stressed by uniaxial tension at infinity and a hemispherical pit at a free surface of a semi‐infinite body also stressed by uniaxial tension with a circumferential crack at the semiequator of the pit. These stress intensity factors, which are given as a function of the crack length L to radius R of the spherical void or hemispherical pit, are considered as estimates because of the approximate nature of the analysis.
Single‐Crystal Boundary Migration in Hot‐Pressed Aluminum Oxide
Authors: MONAHAN R. D. , HALLORAN J. W.
Published: June 2006

The growth of sapphire filaments embedded in hot‐pressed alumina was studied at 1672°C. In undoped alumina, a constant growth rate of 1.17×10‐6 cm/s was observed. The initial growth rate into MgO‐doped alumina was 4.6×10‐8 cm/s, decreasing with increasing matrix grain size. Observed rates of boundary migration were larger than those of previously reported data.
Phase Equilibria in the System Al4C3‐Be2C‐SiC
Authors: SCHNEIDER G. , GAUCKLER L. J. , PETZOW G. , ZANGVIL A.
Published: June 2006

The 1860°C isothermal section of the system Al4C3‐Be2C‐SiC was investigated on hot‐pressed samples. The equilibrium relations involve previously known phases SiC, Be2C, A14C3, Al,SiC4, and seven newly found compounds. On the binary Al4C3‐Be2C, three phases with molar ratios 3:1, 1:1, and 1:3 occur with large homogeneity ranges and deviations of stoichiometry. In the ternary, four phases with molar ratios Al4C3:Be2C:SiC of 4:1:1, 4:2:1, 4:2:2, and 8:1:4 occur. All newly found compounds show hexagonal symmetry with a∼0.33 nm and c ranging from 1.65 to 5.45 nm, except Al4C3=3Be2C, which is cubic with a= 0.4611 nm.
The Nature of CaO Produced by Calcite Powder Decomposition in Vacuum and in CO2
Authors: EWING JAY , BERUTO DARIO , SEARCY ALAN W.
Published: June 2006

Specially reactive (sr‐) CaO can be produced by decomposing 1‐ to 10‐μm particles of CaCO3 in vacuum at ∼650°C. Particles of sr‐CaO appear unchanged in dimension from the original CaCO3, but have internal pores with surface areas of 92 m2/g, more than twice the surface areas reported in a previous study for CaO made from calcite in vacuum at about the same temperature. Weak and broad X‐ray diffraction peaks in normal CaO first become discernible only after about half the CO2 content of a calcite sample has been lost, but the molar surface areas of samples decomposed in vacuum or in 0.1 torr CO2 are linear functions of the extent of reaction. The sr‐CaO, therefore, must be a phase with ion positions and spacings like those of normal CaO. Background pressures of CO2 (up to ∼1 torr) influence the surface area of the CaO by increasing the pore dimensions at the CaCO3‐CaO reaction interface. Sintering of the CaO is negligible at 650°C in CO2 pressures of≤0.1 torr, but sintering is pronounced in CO2, at 9 torr pressure.
SiC‐Fission Product Reactions in HTGR TRISO UC2 and UCxQy Fissile Fuel: II, Reactions Under Isothermal Conditions
Authors: SMITH C. L.
Published: June 2006

The performance of irradiated TRISO UC2 and TRISO UC4.301.3 HTGR fissile fuel particles was studied by postirradiation isothermal heating at 1600° to 2000°C to evaluate HTGR fuel performance models. Test conditions were similar to reactor conditions predicted for hypothetical core heatup events evaluated during safety and licensing studies. Less than 2% of the particles experienced failure of all coating layers with rapid gaseous and metallic fission product release (pressure vessel failure). Lanthanide fission product, Cs‐137, and Kr‐85 release occurred in the remaining particles by diffusion through intact outer pyrocarbon layers after SiC‐lanthanide fission product reactions had penetrated the SiC layers. The rates of SiC‐fission product reactions depended on the fission density of the test samples and were less than or equal to those observed in a thermal gradient. Test results showed the HTGR fuel performance models to be very conservative.
Formation of Chemically Coprecipitated Barium Ferrite
Authors: ROOS W.
Published: June 2006

The formation of chemically coprecipitated barium ferrite was studied using differential thermal analysis, static magnetic measurements, X‐ray analysis, and ferromagnetic resonance measurements. The investigation showed that the formation process of coprecipitated BaFe12O19 differs significantly from that of conventionally prepared BaFe12O19. The DTA diagram showed a large exothermal peak at 760°, indicating hexaferrite formation. Intermediate phases, such as α‐Fe2O3and BaFe2O4 were not observed during the reaction process.
The Elastic Modulus and Fracture of Boron Carbide
Authors: HOLLENBERG G. W. , WALTHER G.
Published: June 2006

Young's modulus at room temperature and the fracture surface energy, up to 1200°C, were determined for boron carbide specimens with 0 to 15% porosity. Sonic modulus measurements indicated that the Young's modulus decreased as porosity increased in a manner characteristic of the cylindrical pore model. The fracture surface energy appeared to be independent of porosity but was inversely related to temperature. Fractography supported the low values of fracture surface energy that were obtained.
Chemical Diffusion in Polycrystalline Al2O3
Authors: WANG H. A. , KRÖGER F. A.
Published: June 2006

Chemical diffusion in poly crystalline α‐Al2O3 doped with Ti or Fe was studied through the movement of a color front on oxidation of reduced samples. The diffusion is faster in polycrystal‐line than in single‐crystal material. The oxygen pressure dependence of the rate of diffusion indicates that neutral interstitial oxygen is the major mobile species at the grain boundaries. A theory is presented which accounts for the data and explains the difference in the rates of oxidation and reduction and their dependence on oxygen pressure. Grain boundaries with precipitates of FeAl2O4 or TiAl2O5 appear to transport oxygen faster than clean boundaries.
High‐Temperature Phase Relations in the System Y2O3‐Y2O3·WO3
Authors: KURIBAYASHI KIYOSHI , YOSHIMURA MASAHIRO , OHTA TATSUO , SATA TOSHIYUKI
Published: June 2006

Phase relations in the system Y2O3‐Y2O3·WO3 were studied at >1400°C. Yttrium oxide with the rare‐earth C‐type structure transformed into a hexagonal structure at 2360° and melted at 2400°C. The eutectic between Y2O3 and 3Y2O3·WO3 was 2334°C at ∼90 mol% Y2O. 3Y2O3·WO3 with a rhombohedral structure changed into a cubic phase at 1765° and melted at 2360°; 5Y2O3·2WO3 with a tetragonal structure changed into the cubic phase at 1740°C. This cubic phase was stable at >1740° and had a solid‐solution range of 69 to 75 mol% Y2O3 at 1800°C. 7Y2O3·4WO3 melted incongruently at 2107°C. Y2O3·WO3 with a monoclinic structure (α’phase) transformed into an orthorhombic structure (e phase) at 1470°, then into a tetragonal structure (β phase) at 1600° to 1700°C. This compound melted incongruently at 1706°C. A phase diagram is given.
Structure and Properties of Portland Cement Clinker Doped with CaF2
Authors: ODLER IVAN , ABDUL‐MAULA S.
Published: June 2006

The structure and properties of laboratory‐made portland cement clinkers doped with different amounts of CaF2 and fired at different temperatures were studied. The phase C3A was gradually replaced by C11A7°CaF2 and the β‐to‐γ polymorphic transition was enhanced due to CaF2 doping. In cements made from CaF2‐doped clinkers, the hydration of C3S and β‐C2S was retarded. The intrinsic properties of the hydration products were altered, resulting in decreased compressive strength at equal degrees of hydration. Both effects depended on the firing temperature of the clinker.
Phase Equilibria in the System Fe‐Al‐O
Authors: MEYERS C. E. , MASON T. O. , PETUSKEY W. T. , HALLORAN J. W. , BOWEN H. K.
Published: June 2006

The composition limits for the spinel solid solution Fe(Fe1‐x Alx)2O4 were determined experimentally as a function of oxygen pressure at 1280°, 1380°, and 1500°C, using precise lattice parameter measurements. The results were combined with information from the literature to develop self‐consistent stability diagrams of P02 vs cation fraction at constant temperatures for the iron‐aluminum oxide system.
Influence of Temperature Increases During the Induction Period of C3S Hydration on the Microstructure and Strength of C3S Mortars
Authors: BOYER J. P. , BERGER R. L.
Published: June 2006

Rapid increases in temperature during the “dormant period” of Ca3SiO5 paste hydration cause a high degree of solution supersaturation in respect to Ca(OH)2. This thermally induced instability creates an increased number of stable Ca(OH)2 nuclei, resulting in a significant increase in the number of Ca(OH)2 crystals and a decrease in the average Ca(OH)2 size in the hydrated paste. The treatment also results in an increased rate of hydration. Unlike low‐porosity ceramic systems where changes in precipitate size and distribution influence strength, the change in size and distribution of Ca(OH)2 crystals in C3S pastes had no apparent influence on strength when all strength was considered as a function of gel‐space ratio.
Mechanical Properties of Fine‐Grained Magnesium Oxide at Large Compressive Strains
Authors: CRAMPON J. , ESCAIG B.
Published: June 2006

Fine‐grained polycrystalline MgO specimens were deformed in compression at constant strain rates of ∼6.7×10−6 s−1 to 6.7×10−5 s−1 at 1173 to 1423 K. Both mechanical data and microstructural observations are distinctive of a diffusion‐accommodated flow, where the grain‐size parameter is of prime importance in enhancing plasticity. Under suitable experimental conditions, superplastic strain was achieved in specimens; no change was detected in the equiaxed‐grain shape configuration. Finally, the effect of grain growth during deformation was considered; specimens of initial grain size ∼0.1 μm showed an apparent hardening which was quasi‐linear with time.
A Mechanism for Strengthening Fluorine‐Containing Lithium Aluminum Silicate Glass‐Ceramics
Authors: HOLLAND H. J. , GULATI S. T.
Published: June 2006

A 0.4% difference in the unit cell volume of β‐spodumene was found between the exterior surface and the interior of a fluorine‐containing glass‐ceramic. The smaller cell volume of the interior places the exterior in compression and is believed to be largely responsible for the increase in strength of this material over that of lithium aluminum silicates which do not contain fluorine. The stress calculated from these data is consistent with the measured strength values. The compressive layer was ∼140 μm thick and is depleted in fluorine. Experimental and calculated deflection data from thin surface slices taken from one side confirm the differential lattice volume‐strengthening mechanism in fluorine‐containing lithium aluminum silicate glass‐ceramics.
Effect of Number of Impacts on Erosion of Polycrystalline MgF2 in the Elastic‐Plastic Response Regime
Authors: GULDEN M. E.
Published: June 2006

Targets of MgF2 were subjected to impact conditions from single‐particle to 1010 impacts, simulating a natural dust environment (quartz particles) in the subsonic velocity regime. The functional relation of erosion to particle size and velocity predicted by the elastic‐plastic impact model is followed for this system. Impact damage is characterized by a heavily deformed contact area between particle and target, with radial cracks propagating outward from the contact zone and with subsurface lateral cracks propagating outward on planes nearly parallel to the surface. The laterally cracked regions are responsible for most of the erosion loss. This type of damage is also consistent with the elastic‐plastic model. For a given particle size‐velocity test condition, the volume of material removed for a single impact can vary over three orders of magnitude. This large variation is due primarily to differences in particle orientation during impact which results from the irregular shape of the angular natural quartz particles. For these conditions there is no significant difference between the amount of material removed by the first impact and by subsequent impacts on the damage area of the initial impact. The results imply that there is no incubation period or damage‐enhancement effect for erosion in the elastic‐plastic impact response regime.
Absorption Effects in STEM Microanalysis of Ceramic Oxides
Authors: BENDER B. A. , WILLIAMS D. B. , NOTIS M. R.
Published: June 2006

A scanning transmission electron microscope (STEM) equipped with an X‐ray energy dispersive spectrometer (EDS) was used for quantitative X‐ray tnicroanalysis of an MgO‐10 mol% NiO ceramic. Using the Cliff‐Lorimer standardless ratio technique for quantitative X‐ray microanalysis, absorption of the Mg characteristic X rays, particularly by oxygen in the specimen, was found to be a critical problem and corrections were required. This problem is characteristic of low atomic number oxide ceramics. However, preferential absorption of characteristic X rays by carbon contamination buildup during X‐ray analysis was negligible. A grain‐boundary composition profile, corrected for absorption, showed no segregation of the Ni to the grain boundary, in agreement with current segregation theory.
Behavior of Bubbles in Glassmelts: I, Dissolution of a Stationary Bubble Containing a Single Gas
Authors: WEINBERG MICHAEL C. , ONORATO PAULETTE I. K. , UHLMANN DONALD R.
Published: June 2006

The quasi‐stationary approximation was used to calculate the rates of dissolution of O2 and CO2 gas bubbles from a soda‐lime glassmelt. An analytic expression for the bubble radius as a function of time, R(t), was obtained when surface tension was neglected and numerical results for R(t) were found when surface‐tension effects were included. These results were compared with those found by previous investigators. Also, an asymptotic expression for R (t) was derived and used to calculate bubble dissolution times.
High‐Temperature Deformation of Stoichiometric 239PuO2
Authors: PETROVIC J. J. , LAND C. C.
Published: June 2006

The deformation behavior of Stoichiometric 239PuO2 was examined at 800° to 1500°C, using direct and diametral compression. Maximum ductility was observed at 1000°C, but above this temperature both strength and ductility decreased and the fracture mode changed from transgranular to inter‐granular. The deformation activation energy measured at 1000°C was 598 kJ/mol. Comparison to the deformation behavior of hypostoichiometric 239PuO2‐x suggests that high‐temperature dislocation motion becomes more difficult with increasing O/Pu ratio due to effects of stoichiometry on diffusion rates. Deformation mechanisms in 239PuO2 appear to be a combination of dislocation motion and grain‐boundary sliding.
Electrical‐Mechanical Analog Applied to Crack Growth in Glass‐ Glass‐Ceramic Composites
Authors: VIRKAR ANIL V.
Published: June 2006

It has been shown that the electrical‐mechanical analog is exact under certain conditions. This exactness was confirmed by determining voltage as a function of crack size on a center‐cracked and an edge‐cracked aluminum foil. The technique was also used to determine the crack velocity‐stress intensity factor diagram from the growth of a microcrack in a glass‐glass‐ceramic composite system. The crack length‐time relation was determined by measuring voltage‐time across a vapor‐deposited gold film on the specimen surfaces.
The System MgO‐MgCl2‐H2O at 23°C
Authors: URWONGSE LADAWAN , SORRELL CHARLES A.
Published: June 2006

Solubilities of MgO in aqueous HC1 solutions at 23°±3°C were measured and combined with analyses of neat magnesium oxychloride cements, cured in sealed containers, to construct an equilibrium phase diagram for the system MgO‐MgCl2‐H2O. Specific gravities and acidities of solutions saturated with MgO and relative humidities of vapor phases over sealed samples were measured and combined with XRD data to define the compositions in equilibrium with two crystalline phases. Studies of relative reaction rates indicated that the 5–1–8 phase crystallizes more rapidly than the 3·1·8 phase and that cements near the 3·1·8 composition react rapidly with atmospheric CO2 to form the chlorocarbonate phase.
Phase Relations in the System MgO‐V2O3‐VO2 at 1200°C
Authors: OSHIMA HIROTOSHI
Published: June 2006

Phase relations in the quasi‐ternary system MgO‐V2O3‐VO2 at 1200°C were studied using the quenching technique under controlled O2 atmospheres. A new phase of a type zVOy Mg2−xV1+xO4 (0<x<1, y≥1.5, z>0) was found with a compositional region along the MgV2O4‐Mg2VO4 join. Equilibrium PO2 observed for Mg2−xV1+xO4 is quite different from that for VnO2n‐1 with an equal ratio of V3+/V4+, corresponding to the V3+ stabilities in two types of compounds. Thus, the phase relations in the ternary system were constructed on a conventional triaxial diagram as a function of PO2.
The Role of Grain‐Boundary Sliding in Fracture of Hot‐Pressed Si3N4 at High Temperatures
Authors: TSAI R. L. , RAJ R.
Published: June 2006

A new type of internal friction experiment was used to investigate the kinetics of grain‐boundary sliding in hot‐pressed Si3N4. The measured sliding resistance in NC‐132 was greater than in HS‐110 and HS‐130 materials.
Effects of Internal Stresses Due to a Dispersed Phase on the Fracture Toughness of Glass
Authors: NADEAU J. S. , DICKSON J. I.
Published: June 2006

The effects of thermal contraction mismatch on the toughening of glass by a dispersed phase were measured in a model system. Three toughening mechanisms were observed: prestressing of the dispersed phase, deflection of the crack by the stress field of the particle, and crack bowing between particles; deflection provided the greatest toughening. Toughening was increased by increasing particle size, decreasing particle spacing along the crack front, and increased particle spacing along the crack path.
Dissolution of Multicomponent Bubbles
Authors: WEINBERG MICHAEL C. , SUBRAMANIAN R. SHANKAR
Published: June 2006

The behavior of an isolated, stationary, multicomponent gas bubble in a glassmelt containing several dissolved gases is considered. The relevant mass‐transport equations are formulated and calculations are performed for the case of two diffusing gases using a quasi‐stationary model and a numerical solution of the exact mass‐transfer equations. The results obtained from these two approaches are compared. The factors which govern the dissolution or growth of a bubble are thermodynamic and kinetic in origin. The tendency of a bubble to grow or shrink at long times is controlled by departure from overall equilibrium, whereas the short‐time bubble dynamics may be dominated by kinetic effects. As a result of the existence of these dual influences, maxima and/or minima occur in the functional dependence of the bubble radius on time.
Kinetics of Surface‐Layer Formation on Simulated Nuclear Waste Glass
Authors: PICKERING S.
Published: June 2006

Waste glass immersed in water at high temperatures and pressures rapidly develops a surface layer. The growth of this layer was followed semi quantitatively using an optical interference technique. Growth rates were measured as a function of temperature and pressure in distilled water and 1% NaCl solution. Pressures of 25 to 85 × 103 Pa had no measurable effect at 200°C on glass immersed in water. At a pressure of 25 × 105 Pa the growth rate increased with temperature in both water and salt solution. The rates were described in terms of activation energies (83.4 kj/mol for water and 53.0 for salt solution) with approximately equal rates in both solutions at 240°C. The rates of growth were linear in all cases. The surface layer began to exhibit cracks when its thickness exceeded =2.5 μm and it eventually spalled.
A Gas‐Probe Analysis of Structure in Silicate Glasses
Authors: SHACKELFORD JAMES F. , BROWN BRIAN D.
Published: June 2006

An analysis of helium and neon transport in vitreous silica is consistent with a statistically distributed structure of the random network. The jump distance, d, for diffusion in common borosilicate glass is greater than in vitreous silica due to the additional modifier ions, Na+. The addition of Na+ or K+ to a silicate structure produces an increase in d. The vibrational frequencies for a gas atom in a “doorway” (v*) and in a solubility site (v) indicate structural trends such as phase separation.
The Effect of Striae on the Strength of Glass
Authors: CAPPS WEBSTER , SCHAEFFER HELMUT A. , CRONIN DAVID J.
Published: June 2006

Severe striations caused by compositional inhomogeneity had no significant effect on the strength of either annealed glass disks or those strengthened by an ion‐exchange surface compression technique. Electron microprobe and interferometric measurements revealed that the striae were caused by variations in the SiO2/Al2O3 ratio rather than by variations in alkali concentration and therefore did not adversely influence the ion‐exchange process.
Oxidation of Silicon Nitride Hot‐Pressed with Ceria
Authors: BABINI G. N. , BELLOSI A. , VINCENZINI P.
Published: June 2006

Short‐term (<30 h) oxidation of CeO2‐doped hot‐pressed Si3N4, studied at 773 to 1623 K in flowing dry air, resulted in parabolic‐weight gain curves and in oxidation‐rate constants nearly independent of the amount of grain‐boundary second phase. Exolution of CeO2 crystals occurs from the oxide layer; their morphology depends on oxidation temperature. Either a direct redox reaction between CeO2 and Si3N4 or solution of Si3N4 in the glassy silica‐rich oxide layer, followed by its oxidation by dissolved oxygen, have been proposed as possible oxidation mechanisms, both appearing strongly dependent on the low solubility of cerium oxides hi silicate melts. The value of the activation energy for oxidation of 385 kj·mol−1 suggests additive and impurity migration from the bulk to the Si3N4/oxide reaction interface as the most probable rate‐limiting step.
Preparation of Sinterable Cubic Aluminum Oxynitride by the Carbothermal Nitridation of Aluminum Oxide
Authors: Rafaniello William , Cutler Ivan B.
Published: June 2006

Sinterable cubic aluminum oxy nitride (ALON) has been prepared by carbon reduction of aluminum oxide inflowing nitrogen. Three different sources of Al2O3 (A12O3 from clay, commercial A12O3, and A12O3 derived from AlCl3.6H2O) and two different sources of carbon (carbon black and starch) were used. Pressed pellets of ALON powder were sintered in N2 at 1950°C greater than 95% of theoretical density.
Swelling Properties of Synthetic Alkali Silica Gels
Authors: STRUBLE LESLIE J. , DIAMOND SIDNEY
Published: June 2006

A suite of 10 synthetic sodium silica and sodium calcium silica gels was prepared to explore the basic mechanism of expansion of concrete by alkali‐silica reaction. Methods were developed for measuring the free swelling capacity and the maximum swelling pressure generated by these gels when they are allowed access to free water. Free swelling ranged from as little as 0.5 to as much as 80%, maximum swelling pressures recorded varied from as little as 0.1 to almost 11 MPa, the latter well in excess of the tensile strength of most concretes. The relations observed between alkali:silica ratio of the gel and its free swelling and swelling‐pressure characteristics were suggestive but not straightforward. The presence of calcium in the synthetic gels did not noticeably reduce their activity with respect to either test.
Fracture of A12O3 in Combined Tension/Torsion: I, Experiments
Authors: Petrovic J. J. , Stout M. G.
Published: June 2006

Combined tension/torsion tests were performed on solid A12O3 rods at principal stress ratios σ2/σ1 of 0 (pure tension), ‐0.17, ‐0.38, ‐0.78, and ‐1.0 (pure torsion). The tensile principal stress at fracture σ1 increased with increasing compressive principal stress σ2, resulting in a higher strength in torsion than uniaxial tension. The ratio σ1 (torsion)σ1 (tension) was 1.31 for A12O3, in general agreement with limited torsional data for brittle materials in the literature. Brittle fracture data in the tension‐compression quadrant of principal stress space show an interesting dichotomy since strengthening is observed in torsional investigations, whereas weakening is observed for pressurized‐tube studies. This difference may be either a pressurized‐tube test artifact or a real effect due to the presence of stress gradients.
Fracture of Al2O3 in Combined Tension/Torsion: II, Weibull Theory
Authors: PETROVIC J. J. , STOUT M. G.
Published: June 2006

The Weibull statistical fracture theory for multiaxial stresses has been extended to conditions of combined tension/torsion loading. At fracture, a tensile principal stress ratio σ1 (tension/torsion) σ1 (uniaxial tension) greater than one is predicted which is dependent on stress state, Weibull modulus, and fracture location. Comparison to experimental tension/torsion data for Al2O3 shows that the Weibull theory, although predicting correct trends, generally underestimates strengthening effects of the compressive principal stress, thus providing a conservative failure prediction. This discrepancy may be related to influences of stress state on crack‐tip “process zone” behavior.
Crack Stability in the Work‐of‐Fracture Test: Refractory Applications
Authors: NAKAYAMA J. , ABE H. , BRADT R. C.
Published: June 2006

The conditions necessary to achieve valid work‐of‐fracture tests were examined for several aluminosilicate refractories. On the basis of an energy balance, construction of a test stability diagram permitted evaluation of the effects of refractory properties, specimen dimensions, and the testing machine characteristics to determine the optimum test conditions. The results illustrate the important experimental features necessary to achieve stable work‐of‐fracture measurements.
Behavior of Bubbles in Glassmelts: III, Dissolution and Growth of a Rising Bubble Containing a Single Gas
Authors: ONORATO PAULETTE I. K. , WEINBERG MICHAEL C. , UHLMANN DONALD R.
Published: June 2006

Finite difference solutions of the mass transport equations governing the dissolution (growth) of a rising gas bubble, containing a single gas, in a glassmelt were obtained. These solutions were compared with those obtained from an approximate procedure for a range of the controlling parameters. Applications were made to describe various aspects of O2 and CO2 gas‐bubble behavior in a soda‐lime‐silicate melt.
Microstructure of SrTiO3 Boundary‐Layer Capacitor Material
Authors: FRANKEN P.E.C. , VIEGERS M.P. A. , GEHRING A. P.
Published: June 2006

SiTiO3 capacitor material with indiffused Bi2O3 was studied using SEM, ESCA combined with Ar+ ion‐etching, and TEM equipped with EDX. The apparent thickness of a second‐phase layer observed with SEM was found to be influenced by in‐depth effects. ESCA and TEM results show that only a 10‐ to 100‐nm thick layer of second phase is present between the SrTiO3 grains. In addition, it was found with TEM that the outer part of each grain contained Bi (at most 2 at.%), representing a diffusion layer. These results have implications for the boundary‐layer model proposed to explain the dielectric properties.
The Glass System SiO2‐B2O3‐Bap‐Na2O for High‐Numerical‐Aperture Optical Fibers
Authors: MITACHI SEIKO , SHIBATA SHUICHI , TAKAHASHI SHIRO
Published: June 2006

The glass system SiO2‐B2O3‐BaO‐Na2O was investigated to obtain high‐refractive‐index glasses for high‐numerical‐aperture (N.A.) optical fibers. Compositions having a mole ratio [B2O3]/[BaO+Na2O]=2 have unique properties. They are both highly viscous and chemically durable despite the fact that they contain highly alkaline metals and alkaline‐earth metals. Glass properties at this mole ratio are favorable for optical fibers. It is proposed that the composition for core glass of high‐N. A. optical fibers be based on this mole ratio.
Small‐Angle X‐Ray Scattering Analysis of Nucleation in Glass: III, Gold Ruby Glasses
Authors: WILLIAMS JOHN A. , RINDONE GUY E. , McKINSTRY HERBERT A.
Published: June 2006

Small‐angle X‐ray scattering (SAXS) studies of the striking gold ruby glasses show that both tin oxide and gold are necessary for a satisfactory ruby. Increasing tin oxide decreases the striking speed, whereas increasing gold concentration increases it. Once the ruby color has been struck, further heat treatment causes little change. The presence of tin oxide aids the nucleation and solubility of gold in the glass. Particles in the glass which struck to purple are fairly large (22 nm (220 Å)). Particle sizes for the livery ruby are >100 nm (1000 A).
Effect of Water Content on the Electrical Conductivity of Na2O≅3SiO2 Glass
Authors: TAKATA M. , ACOCELLA J. , TOMOZAWA M. , WATSON E.B.
Published: June 2006

Na2O–3SiO2 glasses with up to ≅12 wt% water were prepared under high‐pressure, hydrothermal conditions and their electrical conductivities were measured. The conductivity (σ) was found to depend on H2O content in a manner similar to the “mixed‐alkali” effect. At constant temperature, σ decreased initially with increasing H2O content to a minimum at 3≅4 wt% H2O and increased with further increase in water content. Infrared spectroanalysis of these glasses was made to determine the type of water present in the glass and the results were interpreted in the context of the measured activation energy and preexponential factor of dc conductivity. The sodium ion diffusion coefficient for a glass containing 0.76 wt% H2O was less than that of water‐free glass and in agreement with the electrical conductivity results.
Concurrent use and order of use of cocaine and alcohol: behavioural differences between users of crack cocaine and cocaine powder
Authors: Gossop Michael , Manning Victoria , Ridge Gayle
Published: June 2006

Aims The study investigates patterns of cocaine use and alcohol use when these substances were taken on their own, the order of administration of alcohol and of cocaine when the two substances were taken together, and changes in the doses of alcohol and of cocaine when the two substances were taken together. The study further investigates differences in the combined use of the two substances by users of cocaine powder and crack cocaine.

Design Entry criteria for the study were current (previous 30 days) use of both alcohol and cocaine. Study participants (n = 102) were recruited from clinical and non‐clinical settings. Data were collected by face‐to‐face structured interviews.

Findings Different patterns of combined cocaine and alcohol use were reported by cocaine powder and crack cocaine users. Cocaine powder users tended to take increased doses of both cocaine and alcohol when these were used in combination. During high‐dose crack using episodes, crack users tended to drink lower amounts of alcohol than usual. Cocaine powder users tended to use cocaine and alcohol concurrently. Crack users tended to use alcohol at the end of crack‐using sessions.

Conclusions The observed differences are not understood clearly but may be influenced by differential effects of route of administration upon absorption, bioavailability and the balance of euphoric/dysphoric effects. Research studies of the combined use of cocaine and alcohol should distinguish explicitly between the use of cocaine by different routes of administration, and this should be specified in the description of subject samples.