bluuebunny/crossref_metadata_2025 huggingface dataset:
Initial Sintering Kinetics of Hyperstoichiometric Uranium Dioxide
Authors: LAY K. W.
Published: June 2006

The initial sintering kinetics of uranium dioxide powder compacts were determined as a function of temperature and stoichiometry (800°<T<1050°C, 2.03<O/U<2.16). The O/U values of the starting compacts were held constant throughout the shrinkage measurements to avoid difficulties caused by simultaneous shrinkage and oxidation or reduction. The shrinkage kinetics were interpreted as being controlled by uranium volume diffusion. The calculated diffusion coefficient was D= 1.3×10−6 exp (−55,000/RT) cm2/s when O/U=2.08. The diffusion coefficient was approximately proportional to the square of the excess O present, with some deviation at higher O/U values. This behavior can be explained by assuming that the U vacancy concentration is a function of the O activity.
Thermal Decomposition of Oxalates of Ammonium and Potassium
Authors: PAPAZIAN H. A. , PIZZOLATO P. J. , PATRICK J. A.
Published: June 2006

The thermal decomposition of oxalates of ammonium and potassium was studied by simultaneous TGA, DTA, and EGA (effluent gas analysis). Of the simple oxalates, the potassium compound is more stable than the lithium compound, as has been observed for the corresponding carbonates and sulfates. Ammonium oxalate is much less stable than either of the alkali metal oxalates. Potassium titanyl oxalate is less stable than potassium oxalate, and ammonium titanyl oxalate is more stable than ammonium oxalate.
Some Properties of Polymer‐Impregnated Cements and Concretes
Authors: AUSKERN ALLAN , HORN WILLIAM
Published: June 2006

Polymer‐impregnated cement and polymer‐impregnated concrete were prepared by vacuum‐filling cured and dried cement and concrete with a low‐viscosity monomer and polymerizing the monomer by a thermal‐catalytic or gamma‐radiation method. The strength and durability of the products are significantly better than those of the unimpregnated materials. Some observations involving monomer loading, polymerization, and polymer distribution are discussed. A simple model is presented which describes the variation in strength of cement and concrete with polymer content; the model is compared with experimental results.
Fracture Energy and Strength Behavior of a Sodium Borosilicate Glass‐Al2O3 Composite System
Authors: LANGE F. F.
Published: June 2006

Fracture energy and strength were determined for three series within a sodium borosilicate glass‐Al2O3 dispersed composite system. The average particle sizes of the Al2O3 dispersions were

, and

μm. Within each series, composites containing 0.10, 0.25, and 0.40 vol fractions of the Al2O3 dispersed phase were vacuum hot‐pressed. The fracture energy was determined at 77°K with the double cantilever specimen configuration. Strength was measured by a 4‐point flexural test. A significant increase in fracture energy was observed (up to 5 times the fracture energy of the glass without second‐phase dispersion). The fracture energy depended on the interparticle spacing and average particle size of the Al2O3 dispersion. These results could best be explained by a previously proposed model for the interaction of a crack front with a second‐phase dispersion. Surface roughness also contributed to the increased fracture energy. Some composites were strengthened significantly relative to the glass without a dispersion. Calculation of the crack size showed that the Al2O3 dispersion increased the crack size of the glass by ∼1 to 3 times the average particle size of the Al2O3 dispersion. Thus, the dispersion increased both the fracture energy and the crack size. These opposing parameters ultimately determined the strength behavior of these composites.
Stress Distributions in Al2O3 Bicrystal Tensile Specimens
Authors: GAGORIK J. E. , QUEENEY R. A. , McKINSTRY H. A.
Published: June 2006

Stress distributions in Al2O3 bicrystals were analyzed for certain misorientations across the grain boundary in straight‐sided tensile specimens with the grain boundary normal to the tensile axis. Stresses were found using the numerical analysis technique of direct stiffness calculations or by finite element analysis. When the anisotropy in elastic constants of the bicrystals was considered, misorientation of principal axes yielded stress concentrations at the boundary as high as 1.50. The assumption of uniform stress states in bicrystal mechanical response studies, therefore, is not generally accurate.
Structure and Thermomechanical Properties of Partially Stabilized Zirconia in the CaO‐ZrO2 System
Authors: GARVIE RONALD C. , NICHOLSON PATRICK S.
Published: June 2006

Partially stabilized zirconia (PSZ) ceramics in the system CaO‐ZrO2 were characterized. The microstructure, as revealed by optical microscopy, consisted of grains of pure ZrO2 distributed in a matrix of fully stabilized material. Electron microscopy showed that the matrix grains have a complex substructure of 1000‐Å domains of cubic and monoclinic ZrO2. The grains appeared to fit Ubbelohde's concept of a hybrid single crystal. Evidence obtained indicated that the substructure provides an effective stress‐relieving mechanism during thermal shock. It is proposed that initiation of phase inversion in pure ZrO2 domains, even at subtransition temperatures (by thermal stresses), creates an extremely large microcrack density. On the basis of Hasselman's thermal‐shock criterion, only quasi‐static crack propagation occurs during thermal shock of PSZ; evidence is presented to support this concept.
Ligand‐Field Spectra and Structure of Nickel in Silicate Glasses
Authors: TURNER WARREN H. , TURNER JUDY A.
Published: June 2006

The spectra of nickel dissolved in silicate and aluminosilicate glasses with alkali and alkaline‐earth modifiers were studied systematically as functions of composition, annealing and temperature, concentration of Ni2+, and redox conditions during melting. Although reducing conditions produced a gray scattering phase, only Ni2+ was observed as a dissolved species. Several glasses contained one of two Ni2+ species which corresponded to previously proposed 4‐ and 6‐coordinated species. Therefore, both octahedral and tetrahedral calculations could be made from directly observed bands free of overlapping. The results of these calculations suggest that the postulated tetrahedral species may instead be cubic (8‐coordinated). In addition, mixing of the Ni2+3T1g(P) level with Ni2+ 4p and/or ligand electron transfer bands was observed. Examination of the conditions that could produce the 8‐fold site on the basis of stereochemical and crystal‐chemical principles indicated that the packing requirements of the alkali‐oxygen, alkaline‐earth‐oxygen, and silicate polyhedra may preclude sites other than a large 6‐fold site or an even larger cubic (8) site. Thus, silicate glasses can be considered to consist of highly structured but disordered atomic arrangements.
Porosity Effects in Polycrystalline Graphite
Authors: WAGNER P. , O'ROURKE J. A. , ARMSTRONG P. E.
Published: June 2006

Thermal and physical properties of a series of porous, polycrystalline graphites have been measured. The solid matrix material was characterized by X‐ray diffraction measurements of crystallite size, interplanar spacing, and anisotropy. The pore structure was examined using electron micrography, porosimetry, permeability, and helium density measurements. Thermal and electrical conductivities and elastic modulus measurement results were correlated with the fractional porosities of the graphites.
Diffusion in the System K2O‐SrO‐SiO2: II, Cation Self‐Diffusion Coefficients*
Authors: VARSHNEYA A. K. , COOPER A. R.
Published: June 2006

Cation self‐diffusion coefficients were measured in the system 0.2K2O‐0.2SrO‐0.6SiO2 (wt fraction) by introducing a slab of glass previously irradiated in a reactor between two slabs of unirradiated glass. By heating the specimens for various times at temperatures above Tg, etching them sequentially, and counting the β‐ and γ‐activity, self‐diffusion coefficients for K and Sr were measured, and an upper limit for that of Si was estimated. At 530°C<T<830°C, DK≅36.5 exp (‐40,800/RT) and DSr≅0.17 exp (‐42,700/RT), although the fit to Arrhenius behavior was poor. At 750°C, the self‐diffusion coefficient for the Na impurity was almost the same as that for K, whereas that of Si was less than that of Sr.
Effect of Swelling on Thermal Conductivity and Postirradiation Densification of U3Si
Authors: HASTINGS J. , MacEWAN J. R. , BOURQUE L. R.
Published: June 2006

The effect of swelling porosity on the thermal conductivity of irradiated U3Si fuel was deduced from electrical conductivity measurements on samples with pore volume fractions of 0.01 to 0.27. The Maxwell‐Eucken expression adequately represents the data, with β= 1.9±0.1. Postirradiation annealing of samples at 400° to 750°C produces densification. Calculations confirm that the pores in as‐irradiated fuel are voids possibly containing a small amount of fission gas. Those retained after annealing are fission gas bubbles with internal pressure nearly in equilibrium with the surface tension of the surrounding solid.
Synthesis and Thermal Expansion of Polycrystalline Cesium Minerals
Authors: RICHERSON DAVID W. , HUMMEL F. A.
Published: June 2006

CsAlSi2O6, CsAlGe2O6, CsFeSi2O6, CsFeGe2O6, and CsBSi2O6 were prepared by reaction of Cs2CO3 and oxides and by a base‐exchange method. The compounds were characterized by optical examination and X‐ray diffraction. Dilatometric measurements of the linear thermal expansions of the cubic silicate pollucites gave relatively low coefficients, but the expansion of the germanate analogs is considerably higher. Attempts at synthesis of CsCrSi2O6 and CsCrGe2O6 and the special nature of CsBSi2O6 are briefly described.
Kinetics and Burst Phenomenon in ZrO2 Transformation
Authors: MAITI H. S. , GOKHALE K. V. G. K. , SUBBARAO E. C.
Published: June 2006

The monoclinic‐tetragonal transformation in ZrO2 was studied by DTA. The reverse transformation occurs at 850° to 1000°C, depending on the crystallite size, which is a function of the experimental variables. Isothermal kinetics are exhibited by material containing small crystallites; athermal behavior begins to appear as the crystallite size increases. On cooling, strain‐free samples undergo a very rapid transformation which is evident as a burst.
Thermal Grooving of MgO and Al2O3
Authors: MCALLISTER PATRICK V. , CUTLER IVAN B.
Published: June 2006

High‐purity polycrystalline MgO and Al2O3 were thermally grooved at 1500° and 1600°C. Accurate techniques were developed for following the growth of a single groove. For high‐purity samples growth kinetics were essentially similar to those reported in the literature but were determined to be controlled by volume diffusion. Specimens for thermal grooving were prepared from Al2O3 to which transition metal oxides (Fe2O39, MnO, and TiO2), which are known to accelerate shrinkage and sintering of Al2O3 powder compacts, had been added; the rate of groove growth was increased remarkably by minor amounts of these additives. Control of partial pressure indicated that Fe2+ and Ti4+ are the species active in promoting groove growth. Substantial evidence was found for volume diffusion as the mechanism controlling groove formation.
Kinetics of the Massicot‐Litharge Transformation During Comminution
Authors: LIN I. J. , NIEDZWIEDZ S.
Published: June 2006

The kinetics of the polymorphic transformation of massicot to litharge during prolonged dry‐grinding in a laboratory pebble mill were studied by quantitative X‐ray diffraction using the direct‐comparison method. The kinetics describe stages of (1) normal comminution and (2) particle agglomeration; the latter was confirmed by measuring relative specific surface areas. Both stages obey a modified logistic growth function which takes into account a strain‐induced martensitic (shear) transformation which occurs during reduction of particle size.
Lasing in a Phase‐Separated Glass
Authors: WEAVER E. A. , STEWART D. R. , NEILSON G. F.
Published: June 2006

Lasing parameters, optical absorption, fluorescent properties, and laser‐damage threshold were studied in samples of an Nd‐doped Ca‐Mg silicate glass which were phase‐separated to various degrees. The phase‐separation process was followed by low‐angle X‐ray scattering and electron microscopy. Lasing efficiencies increased when small amounts of phase separation were present, but in general efficiencies decreased and laser thresholds increased with increased phase separation. Optical absorption was essentially unchanged except for scattering at the shorter visible wavelengths. Fluorescent lifetimes and integrated intensities were virtually unchanged by various heat treatments. Laser‐radiation‐damage thresholds appeared to increase slightly with increased phase separation. Low‐angle X‐ray scattering showed that the particle size increased continuously with increasing heat‐treatment time, although the number density of particles decreased initially.
Effects of Grain Size and Porosity on Electrical and Optical Properties of PLZT Ceramics
Authors: OKAZAKI KIYOSHI , NAGATA KUNIHIRO
Published: June 2006

A group of transparent ferroelectric hot‐pressed (Pb0.92La0.08)‐(Zr0.65Ti0.35)0.98O3 specimens with controlled grain size and constant porosity and a group of similar specimens with controlled porosity and constant grain size were prepared. The electrical and optical constants and polarization‐reversal properties of these ceramics were determined as functions of grain size and porosity. When poled PLZT ceramics were aged, the polarization‐reversal characteristic was quite asymmetric, apparently because a space‐charge field, E8p, was generated during aging. From a detailed study of the behavior of the E8p, including its (1) generation with increasing aging time, (2) relaxation with repeated polarization reversals, (3) relaxation by heat depolarization, and (4) grain‐size and porosity dependence, it is concluded that the space‐charge layer is present inside every domain. This layer also explains the grain‐size dependencies of the remanent polarization, piezoelectric constants, and Curie point.
Deformation Texture and Magnetic Properties of BaO·6Fe2O3
Authors: HODGE M. H. , BITLER W. R. , BRADT R. C.
Published: June 2006

Compressive deformation of isotropic and magnetically wetoriented stoichiometric BaO‐6Fe2O3 was studied in creep and press forging modes in the temperature range 1000° to 1200°C at stresses to 6000 psi. Texture development was followed by electron microscopy and measured quantitatively by X‐ray diffraction. Magnetic properties of the deformation‐textured materials were correlated with changes in texture and grain morphology.
Thermal Decomposition of Sodalites
Authors: SCHIPPER D. J. , LATHOUWERS T. W. , van DOORN C. Z.
Published: June 2006

The decomposition of bromate and hydroxide sodalites was studied by DTA and TG. Bromate sodalite is converted exothermally at 600°C into bromide sodalite. Hydroxide sodalite loses water and is then converted endothermally into a carnegieite phase at 740°C. The conversion of hydroxide sodalite mixed with sodium halide into halide sodalite at temperatures >740°C proceeds via the decomposition of the hydroxide sodalite. After hydroxide sodalite is heated to temperatures between 600°C and the conversion temperature, it exhibits the photoluminescence of O2−.
Synthesis, Characterization, and Consolidation of Si3N4 Obtained from Ammonolysis of SiCl4
Authors: MAZDIYASNI K. S. , COOKE CHARLES M.
Published: June 2006

Thermal decomposition of silicon diimide, Si(NH)2, in vacuum resulted in very‐high‐purity, fine‐particle‐size, amorphous Si3N4 powders. The amorphous powder was isothermally aged at 50° to 100° intervals from 1000° to 1500°C for phase identification. Examination of ir spectra and X‐ray diffraction patterns indicated a slow and gradual transition from an amorphous material to a crystalline α‐phase occurring at 1200°C for >4 h and/or 1300° to 1400°C for 2 h. As the temperature was increased to ≥1450°C for 2 h, the crystalline β‐phase was observed. Phase nucleation and crystallite morphology in this system were studied by electron microscopy and electron diffraction combined with TG as functions of temperature for the inorganic polymer starting materials. Powders prepared in this manner with 4 wt% Mg3N2 added as a sintering aid were hot‐pressed to high‐density fine‐grained bodies with uniform microstructures. The optimum hot‐pressing condition was 1650°C for 1 h. Silicon concentration steadily increased as the hot‐pressing temperature or time was increased. A method for chemical etching for high‐density fine‐grained Si3N4 is described. Electrical measurements between room temperature and ∼500°C indicated dielectric constant and tan δ values of 8.3±0.03 and 0.65±0.05×10−2, respectively.
Rapid Crystallization of SiO2‐Al2O3 Glasses
Authors: TAKAMORI TAKESHI , ROY RUSTUM
Published: June 2006

The crystallization of Al2O3‐rich glasses in the system SiO2‐Al2O3 which were prepared by flame‐spraying and/or splat‐cooling was studied by DTA, electron microscopy, and X‐ray diffraction. Over a wide range of compositions, the crystallization temperature (Tx) remained near 1000°C, changing smoothly with composition. In all cases crystallization of mullite was detected by X‐ray diffraction. In the low‐Al2O3 region, coarsening of the microstructure during crystallization was observed by electron microscopy. In the high‐Al2O3 region mullite and γ‐Al2O3 cocrystallized; this behavior may be interpreted as evidence of a cooperative process of crystallization at the respective Tx's. The crystallite size of the mullite immediately after rapid crystallization increased continuously with increasing Al2O3 content. In light of the Tx data, the adequacy of the evidence for the proposed metastable miscibility gap in the SiO2‐Al2O3 system is questioned.
Influence of Precipitating Atmosphere on Sintering of ZrO2+12 Mol% Y2O3
Authors: THOMPSON M. A. , YOUNG D. R. , McCARTNEY E. R.
Published: June 2006

Solid solutions of ZrO2 and Y2O3 prepared by decomposing coprecipitated hydroxides exhibited differences in sinterability which did not correlate with variations in particle size, surface area, or purity. These differences were traced to the fact that some of the materials had been exposed to CO2 during preparation, whereas others had not. The presence of CO2 during precipitation stabilized the amorphous phase such that energy release and the onset of nucleation and crystal growth occurred at a higher temperature than in Ar‐prepared material. It is suggested that during preparation in CO2 a carbonate complex is formed, which decomposes on calcination, liberating CO2, some of which is trapped in voids formed by microsintering. The pressure of CO2 in the voids limits their removal.
Measurements of Electromotive Force in Al2O3‐Pitfalls and Results
Authors: YEE J. , KRÖGER F. A.
Published: June 2006

When guards are used to eliminate surface and gas conduction in emf measurements, thermocouple effects of the electrodes and guards must be taken into account, and unwanted gradients in gas composition must be eliminated. Results for single‐crystal and polycrystalline Al2O3 are given. Single crystals have an ionic transference number, t̄l of ≅1, with a possible small decrease as a result of electronic (hole) conduction at T>1450°C. Polycrystalline samples exhibit ti values of <I, with tel(=1‐tl) increasing with decreasing temperature and increasing O2 pressure. The electronic conduction results from movement of holes along grain boundaries.
CrO2‐Cr2O3 Phase Boundary Under High O2 Pressures
Authors: SHIBASAKI YASUO , KANAMARU FUMIKAZU , KOIZUMI MITSUE , KUME SHOICHI
Published: June 2006

The phase boundary between CrO2 and Cr2O3 was reinvestigated under high O2 pressures by using a new type of gas compressor. The boundary curve can be represented as log Po2= 7.16‐(3579/T). Using the observed data, ΔG°, ΔH°, and ΔS° for the reaction 2CrO2⇋Cr2O3+½O2 were calculated to be: ΔG°= ‐(1.55/100)T+7.60 kcal/mol, ΔH°= ‐8.19 kcal/mol, and ΔS°= (‐15.8/T)+0.0155 kcal/mol.
Strengthening of Alkali Halides by Divalent‐Ion Additions
Authors: CHIN G. Y. , VAN UITERT L. G. , GREEN M. L. , ZYDZIK G. J. , KOMETANI T. Y.
Published: June 2006

Single crystals of NaCl, NaBr, KCl, and KBr containing divalent additions of Ca2+, Sr2+, and Ba2+ were tested mechanically. In the solution‐treated condition, the yield strength, σv, as determined from compression testing in a 〈100〉 direction is essentially dependent on the concentration of the dopant only and is independent of the species of either the dopant or of the host material. All crystals soften on aging, with the exception of the NaCl:Ca2+, NaBr:Ca2+, and NaBr:Sr2+ systems. In addition, correlation was good between σv, and the Knoop hardness number, H, obtained by indentation with the long axis of the indenter aligned in 〈100〉. The equation is of the form σv=C(H–H0), where C≅ 0.21 for all four halide families and H0 is near the hardness value of the pure halides. Furthermore, H0≅5×10−3E111, the Young's modulus in the 〈111〉 direction. Hence σv≅0.21H–10−3E111.
Mechanisms of Glass Corrosion
Authors: SANDERS D. M. , HENCH L. L.
Published: June 2006

An approach is developed for understanding formation of gel films on glass surfaces during water exposure. Compositional and microstructural data from ir reflection spectroscopy, scanning electron microscopy, and electron microprobe analysis are used with parameters defined from solution‐analysis data to produce an SiO2 composition profile of the corroded surface. This model profile is compared with a measured profile and used to interpret differences in corrosion resistance of binary Li2O‐ and Na2O‐SiO2 glasses. Effects of corrosion temperature on surface gel structure are also discussed.
Review of Oxygen Activities and Phase Boundaries in Wustite as Determined by Electromotive‐Force and Gravimetric Methods
Authors: GIDDINGS ROBERT A. , GORDON RONALD S.
Published: June 2006

All data available in the literature regarding oxygen activities and composition limits for the wustite phase were analyzed critically. The most reliable activity data were collected into a composite in which (1) the partial molal free energy of oxygen varied linearly with composition and reciprocal temperature and (2) the partial molal enthalpy and entropy of oxygen varied linearly with composition and were independent of temperature. These linear variations of the thermodynamic properties are inconsistent with the presence of additional phases which have been reported within the wustite phase field. The composition limits of the wustite phase, which were computed from the composite, were in excellent agreement with Darken and Gurry's original phase diagram.
Optical Absorbance and Fluorescence in Pure and Doped ThO2
Authors: HARVEY P. J. , CHILDS B. G. , MOERMAN J.
Published: June 2006

Fluorescence spectra resulting from uv excitation of pure, Ca2+‐doped, and Y3+‐doped ThO2 were resolved into discrete bands at 395.4, 434.6, and 464.0 nm. These bands are related to absorption bands in the pure material at 238.9, 227.3, and 252.8 nm, respectively. The Ca2+ ‐ and Y3+‐doped ThO2 specimens showed an apparent absorption edge at 240 nm (213 nm is the true edge in pure ThO2). However, the fluorescence studies showed that this edge is, in fact, spurious, resulting from enhancement of the high‐energy absorbance bands by doping.
Ion Depletion of Glass at a Blocking Anode: II, Properties of Ion‐Depleted Glasses
Authors: CARLSON D. E. , HANG K. W. , STOCKDALE G. F.
Published: June 2006

The application of an electric field to an ion‐conducting glass at high temperatures will cause depletion of mobile ions beneath a blocking anode. The present study extends the investigation of ion depletion to several types of ion‐conducting glass and presents new data for the physical and chemical properties of depleted surfaces. Ion‐scattering spectrometry and electron microprobe analysis show that all positive monovalent and divalent ions are removed from the vicinity of the anode. The less mobile ion species are observed to pile up beneath the depleted region. Experimental data indicate that the removal of ions from the vicinity of the anode creates a microporous region that densifies at a rate determined by glass composition, temperature, and voltage. Ion‐depleted surfaces display a lower refractive index and an increased electrical resistivity compared to untreated glass. Ion depletion also imparts an enhanced chemical durability to glass surfaces and increases the breaking strength of some glasses.
Reversible Optical Density Changes in Composite Layers
Authors: GLIEMEROTH GEORG
Published: June 2006

Selected phototropic Ag‐halide‐containing glasses were heat‐treated and then centrifuged at high temperatures to eliminate the phase‐separated carriers of phototropy. Analyses of the sediment showed, in addition to Ag and halide ions, at least one additional component. On the basis of the results of the analyses, such ternary systems and similar related compositions were vapor‐deposited onto substrates. The resulting layers, 150 to 570 nm thick, were studied for phototropism. The best phototropic properties were achieved in the eutectic area of the ternary system Ag‐Br‐Cu.
Fracture of Glass in Vacuum
Authors: WIEDERHORN S. M. , JOHNSON H. , DINESS A. M. , HEUER A. H.
Published: June 2006

The fracture of 6 glasses was studied in vacuum, <10−4 torr (10−2 N/m2), as a function of temperature from 25° to 775°C. Subcritical crack growth was observed in 4 of the glasses. Activation energies for crack motion ranged from 60 to 176 kcal/mol. The glasses which did not exhibit slow crack growth were “anomalous” glasses with abnormal thermal and elastic properties. Critical stress intensity factors for these 2 glasses increased ∼10% as the temperature increased to ∼600°C. It is felt that subcritical crack growth is not the result of alkali‐ion diffusion or viscous flow but rather of a thermally activated growth process which depends on the crack‐tip structure in the glass. A narrow cohesive region at the crack tip favors subcritical crack growth, whereas a wide region favors abrupt fracture.
Effect of Alcohols on Crack Propagation in Glass
Authors: FREIMAN S. W.
Published: June 2006

The effect of straight‐chain alcohols having chain lengths of 6 to 12 carbon atoms on crack propagation in glasses was studied. The test was a modification of the double‐cantilever‐beam technique. Plots of crack velocity vs stress intensity factor, K, were trimodal, similar to those for glass tested in N2 gas of varying relative humidity. Crack velocities in the two regions of lowest K could be explained using a model derived by Wiederhorn for the effect of water on crack propagation and were independent of alcohol chain length. The chain length of the alcohol affected the results only in the water‐independent high‐K region, where crack velocity increased monotonically with decreasing chain length at a given K. There was no systematic effect of glass composition within the Na2O‐CaO‐SiO2 system, but crack velocities at a given K in a 3BaO‐5SiO2 glass were higher under all conditions than those in Na2O‐CaO‐SiO2 glasses.
Formation of Nepheline Glass‐Ceramics Using Nb2O5 as a Nucleation Catalyst
Authors: KIVLIGHN H. D. , RUSSAK M. A.
Published: June 2006

The crystallization of several Nb2O5‐catalyzed glasses in the Na2O.Al2O.SiO2 system was studied using DTA, X‐ray diffraction, and electron microscopy. The Nb2O5 was an effective nucleation catalyst; fine‐grained body‐nucleated glass‐ceramic materials containing hexagonal nepheline and NaNbO3 were obtained. The crystallization sequence and final crystalline phases in these compositions were quite different from those found in the equivalent TiO2 analogs. The addition of small amounts of carbides and nitrides at the expense of oxides in the initial glass batch markedly affected the final crystalline phases.
Accelerated Curing of Compacted Calcium Silicate Mortars on Exposure to CO2
Authors: YOUNG J. F. , BERGER R. L. , BREESE J.
Published: June 2006

The parameters affecting strength development in compacted cylinders of 3CaO‐ SiO2 and β‐2CaO‐ SiO2 mortars exposed to CO2 were investigated. Strength increased with time up to 81 min, the duration of the longest detailed study. The β‐2CaO‐ SiO2 develops strength more slowly initially, but both silicates achieved compressive strengths of 7,000 to 10,000 psi. The rate of increase in strength depends on both the amount of water used in molding the compact and the amount of water present in the CO2. Increasing CO2 pressures from 1 to 2 atm increased the rate of reaction, but a further increase to 4 atm had little additional effect. Carbonation occurs mainly in the outer portions of the cylindrical compacts. The initial reaction on exposure to CO2 appears to be accelerated hydration of the silicates to a CaO‐SiO2‐H2O‐like gel and calcite. The gel has a stoichiometry similar to that found in conventional hydration. Further reaction results in progressive carbonation of the gel, which decreases its lime content. The reaction products appear to be intimately dispersed in the microstructure.
Knudsen Effusion Study of the Vaporization of CdO(s)
Authors: TOM COYLE R. , LEWIS GORDON
Published: June 2006

Knudsen effusion studies were conducted on CdO(s) in fused‐SiO2 Knudsen cells from 889 to 1110 K. The orifice size was varied; the largest cell orifice yielded a calculated pressure significantly lower than could be accounted for by experimental error. Average‐slope‐ and average‐free‐energy‐function‐based values of ΔHc298 were 86.9 ± 1.1 and 88.8 ± 0.5 kcal/mol, respectively. The data from the present work were combined with those of previous investigators using a method discussed by McCreary and Thorn; a ΔHc298 of 88.2 ± 0.2 kcal/mol was obtained. Using this combined value for ΔHc298 and ΔSc298= 51.40 ± 0.1 eu (obtained from the literature), the equilibrium constant for the reaction CdO(s)= Cd(g)+ 1/2 O2(g) at 900 to 1380 K was calculated to be log K = 10.6‐18,800(I/T).
DTA and X‐Ray Analysis Study of Nucleation and Crystallization of MgO‐Al2O3‐SiO2 Glasses Containing ZrO2, TiO2, and CeO2
Authors: ZDANIEWSKI W.
Published: June 2006

Crystallization sequences of glasses with compositions in the tridymite primary phase field of the MgO‐Al2O3‐SiO2 system were studied by DTA, X‐ray diffraction, and other techniques. Crystallization was catalyzed by the addition of 7 wt% of either ZrO2 or TiO2. Up to 10 wt% CeO2 was also added to some glasses. Metastable solid solutions with the high‐quartz structure exhibiting varying lattice parameters commonly occurred at low temperatures, transforming into a high cordierite at higher temperatures. Depending on the composition and heat treatment, other phases also appeared, e.g. Ce2Ti2O4 (Si2O7). The rate of crystallization was markedly dependent on the catalyst. Colloidal precipitation of the catalyst accompanied by bulk crystallization of the glass was observed with ZrO2, but no crystalline TiO2 was detected. In the presence of CeO2, TiO2 was a more effective catalyst than ZrO2. Although CeO2 lowered the melting temperatures of the glass‐ceramics, it increased the stability of the glasses and inhibited volume nucleation, causing coarse structures to form on crystallization.
Local Atomic Arrangements in a Magnesiowustite Solid Solution
Authors: KRAWITZ A. , COHEN J. B.
Published: June 2006

Quantitative studies of diffuse X‐ray scattering and measurements of magnetization are reported for (Fe,Mg)O with 15.7 cation % Fe held in a reducing atmosphere at 1400°C and quenched. The diffuse scattering is greater for fast cooling than for slow cooling; in both cases, spinel precipitation occurs, but the amount is much larger in the latter case. From this scattering, short‐range order parameters were determined for the clustering between cations, and displacements were obtained between cations and anions. From the magnetic measurements the size of magnetic Fe ion clusters was obtained. Computer simulations of the cation arrangement with the measured short‐range order parameters indicate that the magnetic clusters cannot be accounted for by nearest‐neighbor Fe2+] clusters. However, clusters of Fe ions related by first‐ and/or second‐neighbor vectors are of the size found from the magnetic data.
Differential Thermal Analysis Investigation of the High‐Low Cristobalite Inversion Under Hydrostatic Pressure to 7 Kbar
Authors: COHEN LEWIS H. , KLEMENT WILLIAM
Published: June 2006

The high‐low inversion in polycrystalline cristobalite, synthesized from quartz at 1500°C, was investigated by differential thermal analysis to 7 kbar in hydrostatic apparatus. A region of anomalous curvature (d2T/dp2>0) exists to ∼1 kbar; at higher pressure, the low→high and high→low transition temperatures vary linearly with pressure, with slopes of ∼51.1 and 53. 6 deg kbar−1, respectively. Extrapolated 1‐bar intercepts are ∼232° and ∼209°C, respectively. It is concluded that high cristobalite is less compressible than low cristobalite near the inversion. The hysteresis between the high→low and low→high transition temperatures decreases with increasing pressure.
Compaction of Alumina Powder with a Fugitive Liquid
Authors: GUHA S. K. , CHAKLADER A. C. D.
Published: June 2006

Cold compaction behavior of several alumina powders of grain sizes between 5 and 0.05 μm average diameter was studied, both with and without a mixture of binder and lubricant (10 vol% epoxy resin). The compaction data, obtained up to 30,000 psi, were analyzed by Cooper and Eaton's equation [V*=a1 exp (‐k1/P)+]a2 exp (‐k2/P)], which indicated that the fractional volume compaction (V*) at pressure (P) depends on the particle size, shape, and most likely on the particle size distribution in the powder compacts, confirming the findings of Leiser and Whittemore. Addition of a binder‐lubricant to alumina affected primarily the values of the a coefficients and the possible final compact densities, whereas the values of the pressure coefficients k remained approximately constant, indicating that the pressure coefficients for the pore‐filling process were not affected by the presence of a lubricant.
Hydration of 3CaO·Al2O3 and 3CaO·Al2O3+] Gypsum With and Without CaCl2
Authors: TRAETTEBERG AUD , GRATTAN‐BELLEW P. E.
Published: June 2006

Paste samples of tricalcium aluminate alone, with CaCl2, with gypsum, and with gypsum and CaCl2 were hydrated for up to 6 months and the hydration products characterized by SEM, XRD, and DTA. Tricalcium aluminate hydrated initially to a hexagonal hydroaluminate phase which then changed to the cubic form; the transformation rate depended on the size and shape of the sample and on temperature. The addition of CaCl2 to tricalcium aluminate resulted in the formation of 3CaO · Al2O3· CaCl2·10H2O and 4CaO · Al2O3· 13H2O, or a solid solution of the two. The chloride retarded the formation of the cubic phase 3CaO · Al2O3· 6H2O; the addition of gypsum resulted in the formation of monosulfoaluminate with a minor amount of ettringite. When chloride was added to tricalcium aluminate and gypsum, more ettringite was formed, although 3CaO · Al2O3· CaSO4· 12H2O and 3CaO · Al2O3· CaCl2· 10H2O were the main hydration products.
Precipitation in Partially Stabilized Zirconia
Authors: BANSAL G. K. , HEUER A. H.
Published: June 2006

Transmission electron microscopy was used to study the sub‐structure of partially stabilized ZrO2 (PSZ) samples, i.e. 2‐phase “alloys” containing both cubic and monoclinic modifications of zirconia, after various heat treatments. Monoclinic ZrO2 exists as (1) isolated grains within the polycrystalline aggregate (a grain‐boundary phase) and (2) small plate‐like particles within cubic grains. These intragranular precipitates are believed to contribute to the useful properties of PSZ via a form of precipitation hardening. These precipitates initially form as tetragonal ZrO2, with a habit plane parallel to the {100} matrix planes. The orientation relations between the tetragonal precipitates and the cubic matrix are

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A Fracture‐Mechanics Study of ZnSe for Laser Window Applications
Authors: EVANS A. G. , JOHNSON H.
Published: June 2006

Fracture‐mechanics studies of chemically vapor‐deposited ZnSe show that this material has a low fracture toughness and is susceptible to water‐(moisture‐) dependent slow crack growth. Investigations of biaxial flexural strength indicate that fracture (in this configuration) is controlled primarily by surface flaws and that macrofracture mechanics adequately describe the propagation of typical preexisting flaws in this ZnSe. Crack growth can be detected consistently by the acoustic emission technique; fracture in air is preceded by precursor events which occur up to 2 s prior to catastrophic propagation. Failure diagrams generated from the slow‐crack‐growth parameters show that the lifetime requirements of the laser window can be achieved by overload proof‐testing to a proof ratio of 1.35 when the proper proof‐test precautions are implemented.
Predictability Gap Between Science and Technology of Cements: II, Physical and Mechanical Behavior of Hydrated Cements*
Authors: SEREDA P. J. , RAMACHANDRAN V. S.
Published: June 2006

Problems arising from the need to predict the in‐service properties of cementitious materials (characterized in Part I) are discussed. The significance of volume changes in cements owing to moisture, frost and sulfate attack, carbonation, and temperature is discussed in terms of existing knowledge. Factors which contribute to strength and the relevance of theories such as bonding action, porosity, surface area, microstructure and degree of hydration, and the phenomenon of creep are reported.
Effect of Fast Neutron Irradiation on the Structure of Boron Carbide
Authors: HOLLENBERG G. W. , CUMMINGS W. V.
Published: June 2006

The leading LMFBR control rod material, B4C, was examined by SEM, TEM, and X‐ray diffraction after irradiation up to 80 × 1020 captures/cm3 between 500° and 920°C. Bulk swelling was found to be the result of elastic and plastic strains, rather than dilation of the unit cell. Microcracking was observed and explained in terms of anisotropic swelling.
LPE Growth and Composition of Magnetic EuTm‐CaGe Iron Garnet Films
Authors: GIESS E. A. , GUERCI C. F. , CARDONE F.
Published: June 2006

The effects of growth temperature on the composition of CaGe‐substituted EuTm2Fe5O12 magnetic garnet films grown by isothermal liquid phase epitaxy are described for PbO‐B2O3‐Fe2O3 fluxed melts with a low CaO: GeO2 ratio of 0.233 and a relatively low PbO:B2O3 ratio of 11. Using increasingly larger quantities of CaO and GeO2 in these melts results in more sensitivity of the film relative magnetization and domain size to the growth temperature.
Phase Equilibria and Ordering in the System ZrO2‐CaO
Authors: STUBICAN V. S. , RAY S. P.
Published: June 2006

The phase diagram of the system ZrO2‐CaO for the region ZrO2‐CaZrO3 was redetermined. The extent of the cubic solid solution field was ascertained by using a high‐temperature X‐ray furnace, precise lattice parameter measurements, and a hydrothermal technique. At 850 ± 150°C, the cubic solid solutions decompose by a eutectoid reaction. A reasonable agreement for the position of the eutectoid in this system was obtained by comparing the extrapolated data from high temperatures with the data obtained by the hydrothermal technique. Only one ordered compound, CaZr4O9, with monoclinic symmetry, was found; this compound is unstable above 1310 ± 40°C.
Creep Behavior of a Model Refractory System MgO‐CaMgSiO4
Authors: SNOWDEN WILLIAM E. , PASK JOSEPH A.
Published: June 2006

The effects of the presence of a silicate boundary phase on the high‐temperature creep behavior of a model refractory system MgO‐CaMgSiO4 (monticellite, CMS) were studied at 1200° to 1450°C. A change in the dominant mechanism of deformation was determined with increasing temperature and decreasing applied stress. It was concluded that, at 1200°C, deformation is controlled by a dislocation mechanism in the MgO framework, whereas at higher temperatures creep is the result of simultaneous mechanisms but dominated by viscous deformation of the silicate boundary region.
Reactive Hot‐Pressing of Aluminas
Authors: CHAKLADER A. C. D.
Published: June 2006

Reactive hot‐pressing characteristics of boehmite and bayerite were studied with special reference to the microstructural development during sequential transformations to α‐alumina. Dense γ‐alumina loses its translucency when transformed to α‐alumina, due to the formation of pores in the system. Isothermal compaction data during reactive hot‐pressing were interpreted using a viscoelastic model.
Calculation of Metastable Two‐Liquid Tie Lines in Ternary Glass‐Forming Systems
Authors: STRNAD Z. , STRNAD P.
Published: June 2006

A general solution for calculating tie lines in ternary systems with two‐liquid phases is described. The calculation is based on the thermodynamic relations obtained by equating the chemical potentials of the components in the equilibrium liquid phases. Attention is focused on oxide glass‐forming systems. The basis for a numerical calculation procedure is outlined and the theoretical approach is illustrated with experimental data on the system Na2O‐BaO‐SiO2
A General Approach for the Statistical Analysis of Multiaxial Fracture
Authors: EVANS A. G.
Published: June 2006

A general approach for the statistical analysis of fracture under multiaxial states of stress was developed. The approach invokes a critical coplanar strain‐energy release‐rate fracture criterion and considers distributions of penny cracks in random and preferred orientations. The analysis predicts strength ratios that depend on the strength dispersion and the proximity to the lower bound. For example, the uniaxial and equibiaxial strength ratios well above the lower bound are 1.25 to 1.09 for a typical range of dispersions. Uniaxial and equibiaxial fracture data for alumina were analyzed and compared with the theory. A good correlation was obtained.
Electrical Properties of PrFeO3 and Pr2NiO4
Authors: LAUD K. R. , LOGOTHETIS E. M. , OTTO K.
Published: June 2006

The electrical conductivity of PrFeO3 and Pr2NiO4 was investigated at 300° thd 1000°C and at oxygen partial pressures of 1 to 10−20 atm and the phase relations and nonstoichiometry of these materials were studied. The results suggest that PrFeO3 is a semiconductor exhibiting intrinsic behavior at T>300°C and Po2>10−5 atm. The conductivity of Pr2NiO4 depends on Po2 and is thus related to deviations from stoichiometry. These results for Pr2NiO3 raise questions about the validity of the suggested semiconductor‐to‐metal transition model for explaining the electrical properties of La2NiO3 and Nd2Ni04.
Sodium Diffusion in High‐Silica Glass
Authors: LIM CHUNG , DAY DELBERT E.
Published: June 2006

Isotope effect and electrical conductivity measurements were used to investigate the mechanism of Na+ diffusion in high‐SiO2 glass. A Haven ratio near unity and comparatively high isotope effect values suggest a quasi‐interstitial mechanism for Na+ diffusion. At low Na+ concentration the Na+−Na+ separation distance is so large that the Na+ jumps become uncorrelated.
Low‐Temperature Sintering of Iron Oxides
Authors: KRAMER C. M. , GERMAN R. M.
Published: June 2006

To study agglomeration in iron oxides during low‐temperature sintering, submicron magnetite (Fe3O4) powders were processed in air and in vacuum at 773, 793, and 843 K. Specific surface area measurements were used to monitor sintering progress. Oxidation of the magnetite altered the sintering kinetics, which were dominated by surface diffusion in this temperature range.
Anomalous Stress Profiles in Ion‐Exchanged Glass
Authors: SANE A. Y. , COOPER A. R.
Published: June 2006

Photoelastic measurements on specimens sliced from ion‐exchanged slabs and cylinders have revealed a tension maximum in the distribution of the axial stress. This maximum is not predicted by the conventional stress analysis, which assumes a plane stress condition and ignores the existence of an additional characteristic distance, the thickness of the exchanged layer. A 2‐dimensional finite element analysis under a generalized plane strain condition showed that a tension maximum in the axial stress occurs if the thickness of the slice from the plate is neither smaller than the layer thickness nor much greater than the plate thickness.
Inhomogeneity‐Packing Density Relations in Binary Powders—Experimental Studies
Authors: MESSING GARY L. , ONODA GEORGE Y.
Published: June 2006

The purpose of this investigation was to determine if the bulk specific volume of inhomogeneous binary powder mixtures, with a large size ratio, corresponds to the theoretical values calculated from known compositional inhomogeneity data. The theoretical calculations are based on the assumption that the body packs according to the Furnas model on a local scale. To minimize the effects of particle geometry, experiments were performed with glass microbeads.
Grain Size/Microcracking Relations for Pseudobrookite Oxides
Authors: CLEVELAND J. J. , BRADT R. C.
Published: June 2006

Grain size‐microcracking trends are examined in the three pseudobrookite oxides MgTi2O5, Fe2TiO5, and Al2TiO5. These trends are toward smaller critical grain sizes, lower elastic moduli, and lower strengths with increased thermal expansion anisotropy. Extension of an energy criterion relates the micro‐cracking transition to the inverse square of the maximum difference in single‐crystal thermal expansion coefficients, Δαmax‐2.
Microcracking of Monoclinic HfO2
Authors: DOLE S. L. , HUNTER O. , CALDERWOOD F. W. , BRAY D. J.
Published: June 2006

Elasticity, internal friction, and thermal expansion were measured at temperatures up to 1500°C to characterize the micro‐cracking behavior of HfO2. Crack‐free HfO2 showed consistent, typical changes in these properties with temperature. Micro‐cracked HfO2 showed hysteresis in the elastic moduli and thermal expansion on thermal cycling. Internal friction increased with microcrack healing. Repeated thermal cycling and high‐temperature anneals markedly changed the microcrack system and a time‐ and atmosphere‐dependent aging effect in microcrack formation was noted.
Kinetics of Oxidation of Hot‐Pressed Silicon Nitride Containing Magnesia
Authors: CUBICCIOTTI D. , LAU K. H.
Published: June 2006

The oxidation of NC 132 hot‐pressed silicon nitride in dry oxygen was studied at 1521 to 1731K. The rate of O2 uptake and N2 release, as a function of time, was measured volumetrically. The ratio of N2 released to O2 consumed was smaller than expected from the stoichiometry of the oxidation reaction for Si3N4. The low value was attributed to impurities in the material. The oxidation rate followed the parabolic law with an activation energy of 440 kJ/mol. The corrosion scales (examined by microsurface techniques) were porous due to bubbles of released N2. The scales consisted of a mixture of unoxidized silicon nitride grains, crystalline oxides (SiO2 and MgSiO3containing other elements), and a glass phase. Reoxidation showed that the oxide scale was not protective. The magnesium profile in the subsurface layers indicated that the diffusion of magnesium in the unoxidized material was the rate‐limiting step in the oxidation.
Surface Charge of Vitreous Silica and Silicate Glasses in Aqueous Electrolyte Solutions
Authors: HORN J. M. , ONODA G. Y.
Published: June 2006

Surface charge variations as a function of solution ion concentration were investigated for vitreous silica‐aqueous electrolyte systems. Zero point of charge determinations for soda‐aluminosilicate and soda‐lime‐silicate glasses revealed little difference from the values for vitreous silica. Unlike sodium and barium ions, aluminum ions reverse the sign of the zeta potential for vitreous silica, indicating chemical interaction with the surface. The degree of their interaction depends on the hydration state of the surface. The positive surface charge created by aluminum ion adsorption can be reversed by adsorption of citrate ions from solution to surface aluminosilicate sites.