bluuebunny/crossref_metadata_2025 huggingface dataset:
Growth and Dissolution of Gas Bubbles in Molten Boric Oxide
Authors: BROWN R. B. , DOREMUS R. H.
Published: June 2006

The dissolution of air, N2, and O2 bubbles in molten B2O3 was measured by injecting the gases directly into the melt at 550°C and recording changes in bubble size with time. The shrinkage of air and N2 bubbles followed a relatively simple equation for bubble dissolution, from which the diffusion coefficient of N2 in molten B2O3 was calculated. Oxygen had a lower diffusion coefficient but a higher solubility than N2; the rapid diffusion of O2 from O2 bubbles was accompanied by absorption of N2 from the melt, which subsequently diffused from the bubble. Evidence for a strong decrease of O2 solubility in B2O3 with increase of temperature was found, which, together with the high solubility, indicated strong chemical interaction of O2 with molten B203.
Structural Units in K2O‐PbO‐SiO2 Glasses by Raman Spectroscopy
Authors: VERWEIJ H. , KONIJNENDIJK W. L.
Published: June 2006

Raman spectra of glasses in the system K2O‐PbO‐SiO2 and of crystalline K2O·4SiO2, K2O·2SiO2, K2O·SiO2, PbO, PbO· SiO2, K2O· PbO ·4SiO2, K2O· 4PbO ·8SiO2, and K2O ·2PbO· 2SiO2 are reported and used to identify some of the structural units of the glasses. It is indicated that, in the glasses, silicate networks are present which are similar to those in crystalline K2O ·2SiO2, K2O ·SiO2, PbO ·SiO2, and K2O· PbO· 4SiO2, and to those in vitreous SiO2 and 0.30PbO0.70SiO2 glass.
Early Hydration of a Superhigh‐Early‐Strength Portland Cement Containing Chromium
Authors: TERAMOTO HIDEO , KOIE SHICHlRO
Published: June 2006

Readily water‐soluble, chromium‐containing phases exist among the principal clinker minerals of a superhigh‐early‐strength portland cement manufactured by adding small amounts of chromium, manganese, and fluorine to the cement raw mix. The effects of these phases on the early hydration of the cement were investigated. The phases dissolve in the mixing water and release K+, Na+, CrO42‐, and SO42‐ into the liquid phase. Because of the presence of CrO42‐, the Ca(OH)2 and ettringite crystals formed during hydration grew thicker than those in cement pastes lacking the ion. This growth behavior enhances the early mechanical strength of the cement.
Reactive Vaporization of Soda‐Lime‐Silica Glass Melts
Authors: SANDERS DAVID M. , SCHAEFER HELMUT A.
Published: June 2006

Water‐vapor‐assisted transport of glass constituents from a soda‐lime‐silica melt was studied, using atomic spectroscopy for analysis of vapor condensates and microprobe analysis to determine diffusion profiles. The data presented indicate that the vaporization process is controlled by a surface membrane which has a composition different from the bulk composition. The influence of this effect on glass homogeneity is discussed.
Glass Memory Behavior: Linear Volume Response in the Annealing Region
Authors: CORSARO ROBERT D.
Published: June 2006

Glass memory behavior has been investigated at temperatures within the glass transformation region. A previous paper presented a phenomenological description of the volume response of B2O3 glass to single small pressure changes applied after thorough sample equilibration. The present paper applies the Boltzmann superposition principle to this description to predict the volume response of B2O3 glass to successive small pressure changes of the type which reveal appreciable memory behavior. These predictions were tested by performing such multiple pressure‐jump experiments. The experimental data agreed with the theoretical predictions without the adjustment or reevaluation of any of the parameters used.
Uses of Raman Spectroscopy in Cement Chemistry
Authors: BENSTED JOHN
Published: June 2006

Laser‐Raman spectroscopy is largely complementary to ir spectroscopy, but spectral interpretation is simpler. Lack of homogeneity in clinker minerals, direct study of white portland cement hydration, characterization of clinker minerals, identification of the various calcium sulfate forms, and effects of carbonation are discussed.
Effects of Temperature and Microstructure on the Elastic Properties of Selected Eu2O3‐HfO2 Compositions
Authors: SUCHOMEL R. R. , HUNTER O.
Published: June 2006

Europium sesquioxide is of interest as a control material for reactors because it has several large‐cross‐section isotopes which are formed successively on neutron capture. Elastic properties of Eu2O3 and selected Eu2O3‐rich Eu2O3‐HfO2 compositions were investigated by the sonic technique from room temperature to 1500°C. Sintered monoclinic Eu2O3 was found to have anomalously low room temperature moduli and to exhibit hysteresis on thermal cycling. Fine‐grained hot‐pressed Eu2O3, as well as sintered specimens that contained at least 6 mol% HfO2 did not exhibit these anomalous characteristics.
Mixed‐Mode Fracture from Controlled Surface Flaws in Hot‐Pressed Si3N4
Authors: PETROVIC J. J. , MENDIRATTA M. G.
Published: June 2006

The room‐temperature mixed‐mode fracture of commercial hot‐pressed Si3N4 was examined using controlled surface flaws in 4‐point bending, oriented at various angles 6 with respect to the outer fiber tensile stress direction. Catastrophic fracture paths were non‐coplanar with the initial flaw plane, and the stress intensity factor ratio KI/KIC was < 1 for fracture in modes II and III. A non‐coplanar maximum strain‐energy release rate fracture criterion best described mixed‐mode fracture.
Solid Fission Product Diffusion in Irradiated Coated Particles
Authors: RÖHRIG H. D. , STÖVER D. , NEEF N. , HECKER R.
Published: June 2006

Solid‐fission‐product diffusion was studied in pyrolytic carbon (PyC) coated particles. A method for determining diffusion coefficients is described. Changes in fission‐product concentration profiles in the PyC are measured as a function of post‐irradiation annealing time and temperature. The influence of irradiation history and type of PyC on the diffusion behavior of Cs isotopes is demonstrated.
Reduction of Errors in Ceramic Bend Tests
Authors: HOAGLAND R. G. , MARSCHALL C. W. , DUCKWORTH W. H.
Published: June 2006

Mechanical tests of most ceramics are subject to more stringent requirements than tests of materials which can undergo plastic deformation. The present paper identifies and discusses sources of stress concentrations and spurious displacements which may be imposed during 4‐point bend tests of ceramic materials. Particular areas of concern involve unequal moments at the inner loading points, twisting resulting from skewed contact lines, wedging stresses at point contacts, and counter moments produced by friction at the loading‐point‐specimen interface. A bend fixture incorporating design features which significantly reduce these effects is described, and results of measurements of the surface stresses in calibration specimens under load in the fixture are presented.
Strength Degradation of Brittle Surfaces: Sharp Indenters
Authors: LAWN B. R. , FULLER E. R. , WIEDERHORN S. M.
Published: June 2006

A theory of strength loss for brittle surfaces in contact situations, developed in a previous paper for “blunt” indenters, is extended to the case of “sharp” indenters. A prior fracture mechanics analysis of crack growth beneath ideal cone indenters serves as the basis for predetermining the prospective surface degradation of ceramic components in service. Compared to blunt indenters, sharp indenters can cause severe degradation at lower contact loads. However, at high loads, the extent of degradation becomes remarkably insensitive to details in the indenter geometry. Essential theoretical predictions are verified by bend tests on glass slabs. Effects of indenter “sharpness” and initial specimen surface flaw state are investigated systematically, along with some secondary rate effects in the contact process. The possibility of minimizing degradation via adjustment of material parameters (including hardness) or surface condition (e.g. residual stresses, frictional properties) is briefly discussed.
Some Kinetic Considerations Regarding the Double‐Torsion Specimen
Authors: VIRKAR ANIL V. , JOHNSON D. LYNN
Published: June 2006

In the double‐torsion specimen, crack velocity is a function of the shear wave velocity. At a constant load above the critical load required for crack propagation, crack velocity asymptotically approaches a constant value which is proportional to the shear wave velocity and is dependent on specimen geometry and load. The maximum possible crack velocity under a constant load is proportional to the shear wave velocity multiplied by the ratio of the specimen thickness to its width. For the case of constant deflection with an initial load greater than the critical load, crack velocity goes through a maximum and arrests, for a sufficiently long specimen. Testing‐machine compliance increases the length that such a crack will attain before arrest. The load required for rapid crack propagation is only slightly greater than the critical load; stable crack growth in the absence of stress corrosion guarantees an accurate determination of the fracture energy.
Electrical and Magnetic Properties of Iron‐Nickel Sulfide Ceramics
Authors: KASAHARA YUKIO , NITTA TSUNEHARU , HAYAKAWA SHIGERU
Published: June 2006

Solid solutions of (Fe,Ni)S were prepared by the metal oxide‐carbon disulfide reaction sintering method. These ceramics have the hexagonal NiAs structure, and their lattice parameters depend on the Fe‐Ni ratio. The magnetization of these ceramics reduces with decreasing Fe content between 100/0 (Fe/Ni) and 50/50, increases between 50/50 and 40/60, and decreases again between 40/60 and 0/100. The electrical resistivity reduces uniformly with decreasing Fe content of the ceramics.
Effect of Gypsum on the Hydration and Strength of C3S Pastes
Authors: BENTUR A.
Published: June 2006

The paste hydration of C3S containing different amounts of gypsum was studied. Reaction rates and the composition of hydrated products were evaluated. The gypsum influenced the quantity and quality of the hydrated products by accelerating the hydration process and, at the same time, lowering the intrinsic strength of the gel. Variations in intrinsic strength correlated linearly with the C/S ratio of the CSH gel. The effect of gypsum on strength was interpreted in terms of its influence on the extent of hydration and on the chemical composition of the gel.
Effect of Processing on Microstructure and Mechanical Behavior of Magnesium Oxide
Authors: SWEETING TRUETT B. , PASK JOSEPH A.
Published: June 2006

Polycrystalline MgO specimens were fabricated from two powders by hot‐pressing in graphite or alumina dies and annealing in air, in vacuum, or within the graphite die in vacuum. Parameters affected were density, grain size, and visual appearance, which was considered to be dependent on grain boundary structure. The formation of a boundary liquid phase with one type of powder tended to eliminate the effect of the processing variables. The character (microstructure) of the specimens was correlated with their mechanical behavior in compression at a constant strain rate at 1200°C.
Theoretical Strength of Dried Green Bodies with Organic Binders
Authors: ONODA GEORGE Y.
Published: June 2006

A theoretical analysis is performed to determine the intrinsic variables which affect the green strength of ideal dry bodies held together by organic binders. The parameters which influence strength (i.e. types of bonds formed, the amount of binder, the density of the ceramic, the packing density, and the cohesive or adhesive strength of the binder) are determined.
Effect of Microcracking on the Thermal Diffusivity of Fe2TiO5
Authors: SIEBENECK H. J. , HASSELMAN D. P. H. , CLEVELAND J. J. , BRADT R. C.
Published: June 2006

The effect of microcracking on the thermal diffusivity of polycrystalline Fe2TiO5 subjected to a range of annealing treatments was investigated. At fine grain size (∼1 μm), the thermal diffusivity exhibited the decrease with increasing temperature common for dielectrics. Extensive microcracking in the larger‐grain‐sized materials significantly decreased their thermal diffusivity. On heating, the microcracked materials exhibited increased thermal diffusivity at elevated temperatures which can be attributed primarily to microcrack closure and healing; on cooling, they exhibited a pronounced hysteresis, attributable to irreversible crack opening and closing. Thermal cycling closed the hysteresis curves, which suggests permanent changes in microcrack morphology. It appears that microcracking is a promising technique for tailoring ceramic materials to a combination of high thermal shock resistance and good insulating capability.
Crack Healing and Strengthening of Thermally Shocked Alumina
Authors: GUPTA T. K.
Published: June 2006

Crack healing and strengthening of thermally shocked alumina are related to pore evolution in the microstructure during annealing. Grain growth is not necessary for either an increase or a decrease in strength following heat treatment.
Thermal Expansion of Calcium Monoaluminate
Authors: FISCHER G. R. , BOOTH J. R. , GEIGER J. E.
Published: June 2006

The linear and the crystal‐lattice thermal expansions of monoclinic CaO·Al2O3 were determined. The average coefficient α of linear thermal expansion between 22° and 1200°C is 7.7 × 10−6/°C. The crystal lattice expands anisotropically with expansion coefficients along the principal axes of the strain ellipsoid of 9.8, 7.3, and 5.9 × 10−6/°C for the same temperature interval.
Plane Stress Analysis of Phase Transformations in Brittle Materials
Authors: ALVAREZ I. S. , COOPER A. R.
Published: June 2006

A numerical analysis of the Crank‐Nicolson type is used to determine the temperature distribution and phase‐boundary position for a slab‐shaped sample that is cooled or heated through a phase transition under the assumption that heat transfer controls the kinetics of the transition, thus the phase boundary remains planar. First‐order and second‐order transitions (Ehrenfest) are considered, as is a mixed transformation with partially first‐order and partially second‐order behavior. Stress and temperature distributions are calculated for each type. Particular interest is attached to the surface stress. Results are presented using the thermal and elastic properties of quartz. The results are interpreted in reference to brittle fracture during cooling. When slow crack growth is possible, it is shown that, for a purely first‐order transformation, the likelihood of fracture decreases as the cooling rate increases; for a second‐order transition, fracture becomes less probable as the cooling rate decreases. For a mixed transition, an optimum cooling rate can minimize the probability of fracture.
Suggested Chemistry of Zinc Oxychloride Cements
Authors: SORRELL CHARLES A.
Published: June 2006

Solutions of ZnCl2 were prepared from ZnCl2·nH2O and by reaction of zinc metal with HCl. Specific gravities and pH values were determined as a function of composition. A ternary phase, 4ZnO·ZnCl2·5H2O, was precipitated when the ZnCl2 solutions were diluted to a pH of 5.48 ± 0.05. Mixtures of ZnO with ZnCl, and HCI solutions were equilibrated in sealed containers and analyzed by X‐ray diffraction. The resulting phase diagram shows 2 ternary phases, 4ZnO·ZnCl2·5H2O (4·1·5) and ZnO·ZnCl2·2H2O (1.1.2), both of which are soluble to the extent of < 1 wt% in ZnCl2 solutions. Thermogravimetric data indicate that the 1.1.2 phase loses half the constituent H2O at ∼230°C and the remainder, with ZnCl2, at higher temperatures. The 4.1.5 phase dissociates to ZnO and 1.1.2 at ∼160°C. The system ZnCl2‐H2O is not binary, but is a section through the ternary system ZnO‐HCl‐H2O, with the solubility curve of the 4.1.5 phase intersecting the ZnCl2‐H2O section in dilute solutions.
Migration Losses in Single‐Crystal Ionic Conductors: Sodium Beta Alumina and
Authors: GRANT R. J. , HODGE I. M. , INGRAM M. D. , WEST ANTHONY R.
Published: June 2006

Dispersions have been observed in the ac conductivity of 2 single‐crystal ionic conductors, Na β‐alumina and LiGaO2. The results have been analyzed in the complex modulus formalism, M°, where M°= (ε°)−1. It is suggested that these dispersions represent conductivity losses and are similar to those observed in glasses. The losses are related to the mechanism of ion migration and may be a characteristic feature of many ionically conducting crystalline materials.
Synthesis and Evaluation of Doped Y2O3‐Stabilized ZrO2 for the Production of Hydrogen
Authors: BROWALL K. W. , DOREMUS R. H.
Published: June 2006

The preparation and characterization of single‐phase sintered ceramic materials based on Y2O3‐stabilized ZrO2 with oxides of Ti, Zn, Ce, Cr, Mn, and U/Fe as third‐component additives are described. These materials were prepared for a process to produce high‐purity hydrogen and were evaluated for this process via measurements of electrical conductivity, stability, and transport number. Compositions with oxides of Ce and Cr in Y2O3‐stabilized ZrO2 are shown to be the most promising candidates.
Concurrent Measurement of Volume, Grain‐Boundary, and Surface Diffusion Coefficients in the System NiO‐Al2O3
Authors: HIROTA KAZUO , KOMATSU WAZO
Published: June 2006

Surface, grain‐boundary, and volume inter diffusion coefficients for the NiO‐Al2O3 system were measured concurrently by using a diffusion couple consisting of an A12O3 bicrystal and an NiO single crystal. The A12O3 bicrystals having various tilt angles were fabricated by firing 2 single crystals to be joined in an H2 atmosphere at 1800°C for 30 h. Diffusion profiles over the surface, along the grain boundary, and in the bulk of the bicrystal were determined with an electron probe microanalyzer. Mathematical analysis of the diffusion profiles gives Ds= 7.41×10‐2 exp (‐35,200/RT), Dgb= 2.14×10‐1 exp (‐63,100/RT) (tilt angle =30°), and Dv= 1.26×104 exp (‐104,000/RT). The grain‐boundary diffusion coefficient increases with the mismatch at the boundary.
Strength of Selenium Glass in the Transformation Range
Authors: III DAVID LEWIS , LaCOURSE W. C. , HARDY DONALD B.
Published: June 2006

Flexural strength was measured on high‐purity selenium glass over a wide range of temperatures and strain rates. This glass exhibited wide variations in strength and other properties as temperature and strain rate varied. The strength of glassy Se increased significantly with temperature over 2 temperature ranges, and the highest strength occurred at temperatures just below the glass transition region. The flexural strength also increased with strain rate at all temperatures investigated. Substantial evidence of crack blunting was found in tests at 25°C.
Pore Structure of Calcium Silicate Hydrate in Hydrated Tricalcium Silicate
Authors: DAIMON MASAKI , ABO‐EL‐ENEIN SALAH A. , ROSARA GIRO , GOTO SEISHI , KONDO RENICHI
Published: June 2006

Adsorption of N2 and water vapor was studied in completely hydrated tricalcium silicate and in fully hydrated tricalcium silicate from which Ca(OH)2 had been extracted. Compared with results obtained using N2, water vapor adsorption led to increased values for small‐pore volume, peak shifts to smaller sizes, and decreased values for large‐pore volume. Marked hysteresis was observed in the case of water vapor adsorption; the resorption branch apparently represents the true pore structure. Extraction of Ca(OH)2 from the paste increased the calculated volume of small pores strikingly, suggesting that adsorption is hindered by Ca(OH)2; this tendency is more obvious in water vapor adsorption. The adsorption measurements indicate the existence of two kinds of pores, i.e. a wider intergel‐particle pore and a smaller pore existing within the gel particle. The latter pore was further classified into intercrystallite and intracrystallite pores.
Low‐Field Magnetic Properties of Amorphous Alloys
Authors: EGAMI TAKESHI
Published: June 2006

The transition‐metal‐based ferromagnetic amorphous alloys made by the continuous splat‐quenching method are excellent soft magnetic materials with low coercivity. Furthermore, their low‐field magnetic properties are sensitive to heat treatments and can be greatly improved by such treatments. A review of low‐field properties of these alloys such as anisotropy, remanence, and coercivity (as‐received and after heat treatments) is presented together with data on the Fe80B20 amorphous alloy and the effect of fast‐neutron irradiation.
Heat Capacity and Structural Relaxation of Enthalpy in As2Se3 Glass
Authors: EASTEAL A. J. , WILDER J. A. , MOHR R. K. , MOYNIHAN C. T.
Published: June 2006

The evolution of enthalpy of As2Se3 glass during structural relaxation in the glass transition region was measured via differential scanning calorimetry for two types of time‐temperature programs: rate‐heating at 10 K/min following a cool at a constant rate (‐20 to ‐0.31 K/min) and isothermal annealing following a temperature step from an equilibrium state. The rate‐heating data yield kinetic parameters for the structural relaxation which predict accurately the evolution of the enthalpy during isothermal annealing. The glass heat capacities were independent of cooling rate within experimental precision (≤0.2%). In this respect, As2Se3 is unlike previously studied glasses whose heat capacities are more dependent on thermal history.
High‐Temperature Mechanical Properties of Mullite Under Compression
Authors: DOKKO P. C. , PASK JOSEPH A. , MAZDIYASNI K. S.
Published: June 2006

The high strength potential of single‐phase mullite was investigated under compressive stress‐strain and creep testing conditions at 1400° and 1500°C. In single‐crystal experiments, no plastic deformation and, hence, no dislocation glide was observed. Polycrystalline mullite was deformed via the Nabarro‐Herring mechanism accompanied by grain‐boundary sliding and some cavitation. In stress‐strain tests, deformation was enhanced by intergranular separation.
Tritium Diffusion in A12O3 and BeO
Authors: FOWLER J. D. , CHANDRA DIPANKAR , ELLEMAN T. S. , PAYNE A. W. , VERGHESE KURUVILLA
Published: June 2006

Tritium diffusion in aluminum and beryllium oxides was studied by recoiling tritium into specimens and measuring the time rate of tritium release during postirradiation heating. Results were consistent with classical diffusion solutions and gave single values for the diffusion activation energy over the temperature range of measurement for single‐crystal, sintered, and powdered specimens. Varying amounts of tritium were released as tritiated water even after attempts to remove most of the water absorbed by the specimens. Condensable amounts of tritium ranged from <20% for single‐crystal specimens to as high as 90% for some powders. Alumina containing 0.2% MgO gave tritium diffusion coefficients 4 to 5 orders of magnitude higher than those for undoped A12O3, implying a significant impurity effect on tritium diffusion. Measured diffusion coefficients were many orders of magnitude lower than hydrogen diffusion coefficients in metals. When a simple equilibrium permeation model was used which neglected tritium partition effects at interfaces and enhanced diffusion along grain boundaries, it was shown that thin coatings of beryllium or aluminum oxides on metal substrates could markedly reduce tritium permeation rates through metals. The present results may be applied in the future to fusion reactors where tritium inventories will be high and tritium diffusion within the blanket region undesirable.
Defect Structure of α‐Al2O3 Doped with Titanium
Authors: MOHAPATRA S. K. , KRÖGER F. A.
Published: June 2006

Titanium‐doped α‐Al2O3 exhibits a high‐temperature conductivity which is ionic at high oxygen pressures and electronic at low oxygen pressures. Both are isotropic. The temperature dependence of conductivity under conditions where equilibrium with the atmosphere is not maintained indicates both the position of the energy level of titanium (TiAlx) in the forbidden gap and the temperature dependence of the mobility of the native ionic defects (Al vacancies, VAlm). Optical absorption responsible for the pink color of the reduced crystals is measured as a function of po2 and is used to determine concentrations of Ti3+ and Ti4+. Parameters for the equilibrium constants of the reactions involving electrons by which the composition of Al2O3:Ti and undoped Al2O3 is varied are determined. The chemical diffusion data by Jones et al. are described quantitatively.
Influence of Citric Acid on Reactions in the System 3CaO·Al2O3‐CaSO4·2H2O‐CaO‐H2O
Authors: TINNEA J. , YOUNG J. F.
Published: June 2006

The influence of citric acid on paste hydration of 3CaO· Al2O3 in the presence of CaSO4·2H2O and Ca(OH)2 was studied using X‐ray diffraction, scanning electron microscopy, and conduction calorimetry. The time at which the citric acid is added (either prior to or with the mixing water) determines how it affects the reactivity of the aluminate. Immediately after the paste is gaged citric acid promotes a more rapid reaction, but later reactions are retarded. Hexagonal calcium aluminate hydrates, ettringite, and monosulfate were all detected as early hydration products. The influence of citric acid on the hydration of 3CaO·Al2O3 slabs immersed in saturated CaSO4·2H2O solutions was also studied and a reaction scheme proposed.
Strength and Toughness of a Ceramic Reinforced with Metal Wires
Authors: ZWISSLER J. G. , FINE M. E. , GROVES G. W.
Published: June 2006

Composites consisting of fine stainless steel fibers 6, 12, or 25 μm in diameter in a matrix of wustite were prepared by hot‐pressing. The fracture stress (σF) of unnotched beams and the critical stress‐intensity factor (K1C) for crack initiation in notched beams were measured; both increased linearly with the volume fraction of fiber. These improvements were attributed partially to the action of yielding fibers which bridged the crack surfaces; plastic deformation of fibers at the crack tip was thought to play a role. Large increases (largest for the 25‐μm fibers) in the total work of fracture (γF) were attributed to the work done in fracturing crack‐bridging fibers. For long cracks bridged by fibers, over a substantial fraction of the crack, the critical applied stress intensity factor for further crack propagation increased strongly with increasing bridged crack length. The form of this increase could be accounted for by considering the negative stress intensity factor resulting from the closure forces exerted on the crack by the bridging fibers.

Based on a thesis submitted by J. G. Zwissler for the Ph.D. degree at Northwestern University, Evanston, III., June 1976.

Supported by the U. S. Office of Scientific Research, Office of Aerospace Research, Grant No. AF–AFOSR–73–2431 and by a fellowship from the International Nickel Co.
Phase Equilibria in the System CaF2‐AlF3
Authors: CRAIG DOUGLAS F. , BROWN JESSE J.
Published: June 2006

The phase diagram of the system CaF2‐AlF3 was established from microscopic, powder X‐ray diffraction, quench, and DTA data obtained from samples encapsulated in sealed Pt tubes and either reacted in the solid state or melted. Two compounds, CaAlF5 and Ca2AlF7, melted incongruently at 873°° 3° and 845°°3°C, respectively. Previously unreported Ca2AlF7 was successfully indexed as orthorhombic with α0= 18.22 Å, b0=9.06 Å, and c0= 7.11 Å. The only eutectic in the system exists at 836°° 3°C and 37.5 mol% AlF3.
Observation of Potassium βm‐Alumina in Sintered Alumina
Authors: BLANC MICHEL , MOCELLIN ALAIN , STRUDEL J. L.
Published: June 2006

Potassium‐containing plate‐like precipitates having the βm‐alumina structure were identified within intergranular spinel inclusions in MgO‐doped sintered aluminum oxide ceramics. Transmission electron microscopy revealed the corresponding epitaxial relation: (0001) βm{111} spinel and 1120 βm110 spinel. Chemical analyses and quantitative metallography suggested that in α‐Al2O3 the 1800°C solubility limits of magnesium and potassium do not exceed 300 to 400 ppm and 5 to 10 ppm by weight, respectively.
Calculated Thermodynamic Data and Metastable Immiscibility in the System SiO2‐Al2O3
Authors: RISBUD SUBHASH H. , PASK JOSEPH A.
Published: June 2006

Thermodynamic data on activities, activity coefficients, and free energies of mixing in SiO2‐Al2O3 solutions were calculated from the phase diagram. Positive deviations from ideal mixing in the thermodynamic data suggest a tendency for liquid immiscibility in both SiO2‐ and Al2O3‐rich compositions. The calculated data were used to estimate regions of liquid‐liquid immiscibility. A calculated metastable liquid miscibility gap with a consolute temperature of ∼1540°C at a critical composition of ∼36 mol% Al2O3 was considered to be thermodynamically most probable; the gap extended from ∼11 to °49 mol% Al2O3 at 1100°C. SiO2‐rich glass compositions showed evidence of glass‐in‐glass phase separation when examined by direct transmission electron microscopy.
Fracture Stress as Related to Flaw and Fracture Mirror Sizes
Authors: BANSAL GIRRAJ K. , DUCKWORTH WINSTON H.
Published: June 2006

Fractographically observed critical‐flaw boundaries in strength‐tested specimens of 2 polycrystalline ceramics were used in calculating critical stress‐intensity factors (KIC)‐ Each ceramic exhibited a KIC which had little or no dependence on critical‐flaw characteristics and which agreed with the value obtained from independent determinations on artificially precracked specimens. Analyses both of fracture‐mirror sizes and of water‐enhanced subcritical crack growth data supported the evidence that K1C is a material constant. The fracture‐mirror analysis further indicated that the parameter A/KIC, where A is the fracture‐mirror constant, is a dimensionless, material‐independent constant.
Crystalline Compounds and Glasses in the System B2O3‐NaF‐NaBF4
Authors: MAYA LEON
Published: June 2006

The system B2O3‐NaF‐NaBF, has been studied by subjecting selected compositions to thermal treatment in the range 400° to 600°C. Weight losses, chemical analyses, ir, Raman, and X‐ray diffraction techniques were used to define the composition of the crystalline phases and the structural units being formed in the system. The stoichiometry of the BF3 evolved from NaBF4‐B2O3 mixtures indicated that a composition corresponding to Na2B3F5O3 was formed in mixtures containing up to 33.3 mol% B2O3. At higher boron oxide concentrations, Na2B3F5O3 was consumed, yielding 2NaF.3B2O3. The crystalline compounds Na3B3F6O3, 2NaF.3B2O3, and phase B (apparently NaF.B2O3) were formed in the system. The compound Na3B3F6O3 appeared as the stable oxygen‐containing species in NaBF4‐NaF mixtures of low oxide content. The main fluorine‐containing structural units of the system are BF4, (–O)3BF, (–O)2BF2, (–O)2BF, whereas the main structure for binary NaF‐B2O3 mixtures is (–O)3BF.
Compressive Creep of CoO Single Crystals
Authors: NEHRING V. W. , SMYTH J. R. , McGEE THOMAS D.
Published: June 2006

Uniaxial compressive creep of single‐crystal CoO was investigated at 1000° to 1290°C and stresses of 1200 to 2100 psi. The activation energy for creep at inflection and steady state was ≅50 kcal/mol. The stress exponent was ≅5 at both inflection and steady state. The results are explained in terms of diffusion‐controlled dislocation motion.
Process Variables in the Preparation of UN Microspheres
Authors: SHOUP ROBERT D.
Published: June 2006

Precursor uranium dioxide plus carbon microspheres were formed by injecting a mixed urania and carbon sol into an immiscible solvent. After being reduced in hydrogen, the microspheres were heated to between 1400° and 1525°C in Ar to form a dense intermediate mixture of UO2 and UC. When exposed further to N2 at temperature, a dense UN particle was formed. In an alternate method, the carbothermal conversion was performed entirely in N2, resulting in particles of lower density. Flexibility in conversion methods and conditions permits one to obtain relatively high‐purity UN microspheres with densities between 65 and 90% of theoretical.
Effects of Grain Size and Microcracking on the Thermal Diffusivity of MgTi2O5
Authors: SIEBENECK H. J. , HASSELMAN D. P. H. , CLEVELAND J. J. , BRADT R. C.
Published: June 2006

The laser flash technique was used to study the effect of grain size on the thermal diffusivity of polycrystalline MgTi2O5 from 25° to 800°C. Microcracking decreased the thermal diffusivity by as much as a factor of two with the decrease increasing with increasing grain size. When specimens were heated then cooled, the thermal diffusivity exhibited a horizontal flat figure‐eight hysteresis. This hysteresis, which appeared to be a function of the thermal history, was attributed to a balance between crack healing, or closure, at high temperatures and the growth of existing cracks or the formation of new cracks during cooling.
Rational Molecular Engineering of Ceramic Materials
Authors: ROY RUSTUM
Published: June 2006

Most of the advances in modern ceramics have been based on the development of a new material. A rational approach to the design and execution of such innovative syntheses can be made more scientific and less serendipitous. The understanding of molecular architecture and the principles of structure building can only be based on the science of crystal chemistry and solid‐state thermodynamics. This review presents a summary of the principles and state‐of‐the‐art empirical data in relevant crystal chemistry and the correlates found in phase‐equilibrium diagrams. It deals explicitly with the role of metastable equilibrium in the formation and use of technological materials. It also summarizes the major classes of experimental facilities needed for sophisticated molecular engineering. Several examples are presented as successful paradigms of rational molecular engineering, covering different size ranges of creative architecture from 10 A to 10 μm. Likely future developments in this area are proposed as being based principally on 2‐ (or multi‐) phase materials, and/or on noncrystalline phases based on the entire composition range of ceramics, and on combinations of ceramics with metals and, possibly, polymers.
Determination of Mass Transport Mechanism of Rutile by Sinusoidal Profile Decay Method
Authors: KITAZAWA KOICHI , KURIYAMA TAISUKE , FUEKI KAZUO , MUKAIBO TAKASHI
Published: June 2006

Amplitude decay of sinusoidal surface profiles on the c surface of TiO2 single crystals was measured in air over the range 1500 to 1700 K. The rate of decay was proportional to –2.75 powers of the sinusoidal wave length (4.3 to 17.6 μrn), indicating that volume diffusion is the dominant mass‐transport mechanism. The effective volume diffusion coefficient, Deff, given agreed with tracer diffusion data for the Ti ion. Hence Deff was assumed to be equal to the self‐diffusion coefficient of the Ti ion as oxygen ion transport along the surface was enhanced. No anisotropy was observed for transport on this surface.
Temperature Dependence of the Raman Spectra of ZrO2
Authors: ISHIGAME M. , SAKURAI T.
Published: June 2006

Raman spectra of ZrO2 were measured in the range 300° to 1600°K. Irreducible components of the Raman spectra were obtained from polarization measurements at room temperature, and the symmetries of the Raman‐active modes in the monoclinic phase were determined. The temperature dependence of the spectra shows a hysteresis. In the temperature range of phase change, two kinds of Raman lines coexist. Six Raman‐active mode frequencies were found in the tetragonal phase at high temperatures. Analysis of the spectra showed that the Raman‐active modes in the tetragonal phase are affected by strain introduced into the crystals during the phase transformation.
Kernel Migration for HTGR Fuels from the System Th‐U‐Pu‐C‐O‐N
Authors: LINDEMER T. B. , PEARSON R. L.
Published: June 2006

Nuclear fuels for the high‐temperature gas‐cooled reactor (HTGR) consist of spherical kernels of actinide compounds contained in gaslight pyrolytic carbon and SiC. The fuel kernels migrate up the temperature gradient and into the coating layers. A theoretical analysis of in‐reactor migration data indicates that a solid‐state diffusion process controls the migration rate in fissioned Th0.84U0.16C2, UO2, ThO2, PuO2‐x, and Th0.8U0.2O2 particles. The theoretically based kernel migration coefficient (KMC) measured in units (cm/s) °K2 (oK/cm)‐1, is thus used to correlate the laboratory and in‐reactor data. The KMC values for Pu‐containing particles may be dependent on the initial and in‐reactor O/Pu values. The other in‐reactor KMC values were apparently not dependent on the extent of fission, the fission of either 233U or 235U, or the presence of an SiC coating layer. Laboratory KMC values were obtained for unirradiated ThO2, UO1.65 N0.25,UC2 ThC2, and Th0.84U0.16C2 particles and generally appeared to be consistent with in‐reactor data.
Dispersion‐Strengthened Glass Matrices–Glass‐Ceramics, A Case in Point
Authors: BOROM MARCUS P.
Published: June 2006

Previous explanations of strengthening of glass‐ceramics after heat treatment to produce crystallization are discussed. Explanations relating strength enhancement in brittle material systems either to flaw size limitation by interparticle spacing or to the increase in the system modulus as a result of the presence of a higher modulus dispersed phase were found to be inadequate. The measured loss of strength in glass‐ceramics with increasing temperature indicated strength enhancement as a result of thermomechanically induced stresses in the system.
Oxygen Stoichiometry in LaMn1‐xCuxO3+y by Thermogravimetry
Authors: VOGEL E. M. , JOHNSON D. W. , GALLAGHER P. K.
Published: June 2006

Thermogravimetry in reducing atmospheres was used to study the oxygen Stoichiometry of several Cu‐substituted lanthanum manganates. The oxygen content of the samples at various levels of reduction (to La2O3, MnO, and Cu) was calculated from the gravimetric data. Freeze‐dried samples prepared by firing at 1100°C in O2 and cooling in O2 had the following composition: LaMnO3.13, LaMn0.7Cuo.3O2.96, LaMn0.5Cu0.5O2.93, and LaMn0.3Cu0.762.71. Single‐phase perovskite structure was obtained in all but the last. The lanthanum manganate LaMnO3.13 was reduced to LaMnO3.00, which shows considerable stability. A 50% substitution of Cu for Mn gave LaMn0.5 Cu0.5O2.93, indicating that the ions involved were mostly Mn4+ and Cu2+. This compound could be reduced to LaMng0.5Cu0.5 O2.26 (largely Mn2+ and Cu1+) without destroying the perovskite structure. This reduced phase could be reoxidized to the original oxygen level but subsequent reduction required considerably higher temperatures and was accompanied by the precipitation of Cu‐rich phases. Samples with a Cu:Mn ratio 30:70 and 70:30 were O‐deficient. The compound LaMn0.7 Cuo.3O2.96 reduced to LaMn0.7Cu0.3O2.54, a relatively stable composition. The highly Cu‐rich sample LaMn0.3Cu0.7O2.71 was easily reduced.
Isothermal Crack Healing and Strength Recovery in UO2 Subjected to Varying Degrees of Thermal Shock
Authors: BANDYOPADHYAY G. , KENNEDY C. R.
Published: June 2006

Isothermal crack healing and strength recovery were investigated in UO2 pellets subjected to varying degrees of thermal shock by water quenching. It is shown, as was speculated in an earlier paper, that crack density and/or crack width in the specimen strongly influence the subsequent healing behavior. Experimental data were used to demonstrate that, under the present thermal shock conditions, the time required for complete healing increased exponentially with the number of cracks/unit length of the specimen.
Fabrication of Reaction‐Sintered Sialon
Authors: WILLS R. R. , STEWART R. W. , WIMMER J. M.
Published: June 2006

A factorial design experiment was conducted to determine the major parameters affecting the densification of mixtures having the composition (in mol%) 50 Si3N4, 25 A12O3, and 25 A1N. Improved densities of the resulting sialon were achieved using a longer milling time and SN‐502 Si3N4 powder. However, sialon samples prepared from the SN‐502 powder contained some of the X‐phase, whereas those fabricated from AME Si3N4 powder did not. This difference is considered to be due to the higher SiO2 content of the SN‐502 powder and its greater susceptibility to partial hydrolysis during the milling process. Reaction‐sintered sialon (97.2% theoretical density) fabricated using AME powder had a room‐temperature bend strength of 352

MN/m2 (51,000 psi) and exhibited slow crack growth at 1300° and 1400°C. It is suggested that this is not an inherent property of sialon but is due to the presence of a calcium‐containing grain‐boundary phase, as in hot‐pressed Si3N4.
Subsolidus Phase Equilibria in the System Na2O‐Bi2O3‐TiO2 at 1000°C
Authors: UCHIDA KENJI , KIKUCHI TAKESHI
Published: June 2006

Subsolidus phase relations in the system Na2O‐Bi2O3‐TiO2 at 1000°C were investigated by solid‐state reaction techniques and X‐ray diffraction methods. Five ternary compounds were observed in the system: Na0.5Bi4.5Ti4O15; Na0.5Bi0.5TiO3; a cubic pyrochlore solid solution composed of xNa2O.25Bi2O3.(75−;x) TiO2 where x is 2.5 to 3.75; a new compound Na0.5Bi8.5Ti7O27 indexed with the orthorhombic cell of a= 5.45, b= 5.42, and c= 36.8 Å; and an unidentified phase with the probable composition NaBiTi6O14.
NMR Relaxation Study of Adsorbed Water in Cement and C3S Pastes
Authors: BLINC R. , BURGAR M. , LAHAJNAR G. , ROŽMARIN M. , RUTAR V. , KOCUVAN I. , URŠIČ J.
Published: June 2006

The deuteron and proton spin‐lattice and spin‐spin relaxation times T1 and T2 of adsorbed water in commercial portland cement and tricalcium silicate pastes were studied as functions of the hardening time at room temperature. The time dependence of the water self‐diffusion coefficient of tricalcium silicate pastes was also followed. The proton and the deuteron T1 and T2 decrease markedly as hydration increases and the pastes harden due to the increase in the active surface and the number of adsorptive sites, thus providing convenient tools for studying the nature of the hydration process.
Kinetics of Crystal Growth of Calcium Tungstate from Solutions in Sodium Tungstate Melts by Continuous Cooling
Authors: ROY B. N. , APPALASAMI S.
Published: June 2006

Crystallization kinetics of calcium tungstate from unstirred supersaturated solutions in sodium tungstate melts was studied by continuous cooling from initial crystallization temperature TO=1000° to 800°C to room temperature at cooling rates RT=0.67° to 3.3°C min−1. Crystals were examined by optical microscopy and analyzed by various methods. The main crystal growth was diffusion‐rate‐controlled. The final crystal growth was rate‐controlled by the development rate of excess solute concentration. Diffusion rate constant (kD) values were estimated. These values increased with cooling rate and initial crystallization temperatures but they are very much smaller than the rate constants for diffusion‐controlled growth of calcium tungstate from lithium chloride melts.
Effect of the Phase Transformation on the Fracture Behavior of BaTiO3
Authors: POHANKA R. C. , FREIMAN S. W. , BENDER B. A.
Published: June 2006

The fracture energy of BaTiO3 increased with increasing grain size at 25°C in the ferroelectric 4 mm symmetry state and remained constant at 150°C in the paraelectric m 3m state. In general, observed flaw sizes agreed with those predicted from fracture mechanics equations. The fracture energy measurements combined with previously reported strength measurements were analyzed in terms of fracture mechanics principles to determine the effect of internal stresses on fracture. The analysis showed that the effect of internal stress on fracture for a given flaw size can be determined from a combination of fracture energy and strength measurements at two temperatures. The increase in fracture energy with grain size in the ferroelectric state is attributed to ferroelastic twin formation and wall motion.
A Test of the Second‐Phase and Impurity‐Segregation Models for MgO‐Enhanced Densification of Sintered Alumina
Authors: JOHNSON W. C. , COBLE R. L.
Published: June 2006

To determine if MgO added within the solubility limit in Al2O3 is sufficient to suppress discontinuous grain growth, an undoped alumina pellet was sintered next to a preequilibrated, two‐phase mixture of spinel (MgAl2O1) and alumina. The MgO‐doped outer surface of the undoped pellet did sinter to full density; metallography confirmed that the sample was free of second phase. Grain boundaries were analyzed with a scanning Auger microprobe, which showed that the grain boundaries of the inner porous region had approximately the same Ca segregation as those in the dense outer shell region. Therefore, it was concluded that the beneficial effect of magnesium is due neither to second‐phase pinning nor to Ca impurity segregation.
Microstructure of Y2O3 Fluxed Hot‐Pressed Silicon Nitride
Authors: CLARKE D. R. , THOMAS G.
Published: June 2006

Detailed microstructural analysis of a 10 mol% Y2O3 fluxed hot‐pressed silicon nitride reveals that, in addition to the yttrium‐silicon oxynitride phase located at the multiple Si3N4 grain junctions, there is a thin boundary phase 10 to 80 Å wide separating the silicon nitride and the oxynitride grains. Also, X‐ray microanalysis from regions as small as 200 Å across demonstrates that the yttrium‐silicon oxynitride, Y2Si(Si2O3N4), phase can accommodate appreciable quantities of Ti, W, Fe, Ni, Co, Ca, Mg, Al, and Zn in solid solution. This finding, together with observations of highly prismatic Si3N4 grains enveloped by Y2Si(Si2O3N4), suggests that densification occurred by a liquid‐phase “solution‐reprecipitation” process.
Raman Spectroscopic Study of the Reactions in a Potassium Carbonate‐Silica Glass‐Forming Batch
Authors: VERWEIJ H. , VAN DEN BOOM H. , BREEMER R. E.
Published: June 2006

Raman investigation results are presented for the reaction products formed in a glass‐forming batch. With Raman spectroscopy it is possible to identify the various glassy and crystalline phases which occur during the reactions. This is demonstrated on a batch containing 30 mol% K2CO3 and 70 mol% SiO2. It is also shown that CO2 gas is released via an intermediate glassy product. A qualitative description of the reaction process is given.
Fracture of Soda‐Lime Glass Tubes by Field‐Assisted Ion Exchange
Authors: ABOU‐EL‐LEIL MAHMOUD , COOPER A. R.
Published: June 2006

The field‐assisted ion exchange of K+ and Na+ in soda‐lime glass tubes fdled with and immersed in molten KNO3 was Investigated. Stress distribution deduced from photoelastic measurements agrees well with that calculated from analogy to thermal stresses. Fracture was observed when a critical exchange depth was reached. The effects of tube dimension, surface condition, temperature, electric current density, current interruption, and current reversal on the critical exchange depth were studied. Calculated stresses for fracture originating on the tensile side of tubes exchanged on one side only agree with the independently measured fracture stresses of similar tubes. Fracture originating on the compressive side is believed to be related to “spalling” under biaxial compressive stresses which were frequently observed on the compressive surface.
Optical and Magnetic Properties of Some Transition Metal Ions in Barium Phosphate Glass
Authors: BERRETZ MANFRED , HOLT SMITH L.
Published: June 2006

In barium phosphate glass containing first‐row transition metal ions, the ions appear to possess normal oxidation states: Cr3+, Mn3+, Fe2+,3+, Co2+, Ni2+, and Cu2+. Room temperature and 77°K spectra for Cr3+‐, Mn3+‐, Fe2+,3+‐, Ni2+‐, and Cu2+‐containing glasses can be interpreted, on the, basis of octahedrally coordinated metal ions, whereas the spectrum of the Co2+ glass correlates with a tetrahedrally coordinated metal ion. Magnetic moments for the glasses are similar to those for the spin‐only values of the various metal ions.
Phase Equilibria in the System Li2O‐CaO‐SiO2
Authors: WEST A. R.
Published: June 2006

Phase relations in the system Li2O‐CaO‐SiO2 were studied by the quenching method. Four stable ternary compounds were found (Li2Ca3Si6Ol6, Li2Ca4Si4O13, Li2Ca2Si2O7, and Li2CaSiO4) as well as phase Y, which is probably a metastable orthosilicate fairly close to Ca2SiO4 in composition. X‐ray powder data are given for the new phases. Eleven subsolidus compatibility triangles and thirteen liquidus invariant points were located. Melting relations were determined for that part of the system bounded by Li2SiO3, Li2CaSiO4, Ca2SiO4, and SiO2. The join Li2SiO3‐CaSiO3 is binary.