bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurement of Oxygen Diffusion in Dy2O3 and Gd2O3 by Studying High‐Temperature Oxidation of the Metals
Authors: BASLER D. B. , BERARD M. F.
Published: June 2006

Studies of the oxidation of Gd and Dy at PO2's from 10−0.3 to 10−14.5 atm and temperatures from 727° to 1327°C indicate both semiconducting and ionic‐conducting domains in the sesquioxides formed. At higher temperatures, where dense coarsegrained oxide layers developed, the rate of oxidation in the high‐P02 semiconducting domain yielded oxygen diffusion coefficients in Dy2O3 in excellent agreement with literature values derived from oxidation of partially reduced oxide single crystals. Under the same conditions, the oxidation of Gd yielded oxygen diffusion coefficients in cubic Gd2O3 which are considerably below literature values for monoclinic single‐crystal Gd2O3. At lower temperatures, porous scales were formed, and apparent diffusion coefficients derived from oxidation rates show a smaller temperature dependence than the high‐temperature data. At low PO2, the oxides behave as ionic conductors, and metal oxidation rates result in estimates of the electronic contribution to the electrical conductivity of the order of 10−6 to 10−7Ω−1 cm−1.
Mixed‐Alkali Effect and Interdiffusion of Na and K Ions in Glass
Authors: DOREMUS R. H.
Published: June 2006

When 2 alkali ions are present in a glass, its electrical conductivity is reduced compared to that of glasses containing only one of these ions. Measurements of electrical mobility and tracer diffusion show that the mobilities of individual ions are reduced by the presence of a second ion. Thus, theories have been proposed to explain the mixed‐alkali effect in terms of ionic interactions. However, experiments on interdiffusion of Na and Ag or K ions in soda‐lime glass indicate that at sufficiently low temperatures the mobilities of the interdiffusing ions are not influenced by the presence of the second ion. Therefore, it is postulated that structural rearrangement of the glass is required for the mixed‐alkali effect.
Thermogravimetry of Lithium Spinel Ferrites
Authors: BANDYOPADHYAY G. , FULRATH R. M.
Published: June 2006

The material‐loss behavior of spinel ferrites on heat treatment was characterized by thermogravimetry. Most of the work was done on the system LiFeO2‐Fe2O3, where both Li and O2 loss were considered. The weight‐loss behavior of Ni and Zn ferrites was studied for comparison.
Analysis of Bond Formation in Vitrified Abrasive Wheels
Authors: BRECKER JAMES N.
Published: June 2006

The formation of bonds in vitrified abrasive wheels is treated as a transient viscous flow process to determine if particles in a wheel are in direct contact. Two initially separated solid spheres are found to be drawn together by surface tension, so that particles are indeed in contact during a typical firing cycle. Because of this interparticle contact, wheels will be stiffer when loaded in compression, when the high‐elastic‐modulus particle carries the load, than when in tension, when the low‐modulus bond carries the load. The occurrence of interparticle contact explains several observations on wheel performance.
Kinetics of the Hydration of Tricalcium Silicate
Authors: FUJII KINJIRO , KONDO WAKICHI
Published: June 2006

The hydration of tricalcium silicate was followed at a water/C3S ratio of 0.7 between 5° and 50°C by determining free lime and combined water. Free lime was estimated by the o‐cresol method, whereas combined water was calculated from the amount of free water remaining in the paste as determined by extraction with methyl ethyl ketone. The ratio of free lime to combined water was constant throughout the hydration; this ratio indicated that CSH(II) may be represented as 1.68CaO · SiO2· 2.58H2O. When maximum supersaturation of the solution with Ca2+] is attained, the induction period terminates and the reaction proceeds rapidly, probably as the result of propagative surface nucleation‐growth of CSH(II). Kinetic equations were derived for these reactions. When the surface of C3S is entirely covered by CSH(II), the reaction becomes slow and is controlled by diffusion of water. Constants involved in the kinetic equations are evaluated and discussed.
Chemistry of Vaporization of Refractory Materials
Authors: GILLES PAUL W.
Published: June 2006

Most recently the practical importance of high temperature vaporization reactions has appeared in the synthesis of pure materials through vapor transport reactions and in the study of the movement of materials in nuclear power reactor experiments. The most recent basic development is the establishment, at temperature, of the range of nonstoichiometry in oxides. Long‐standing applications of vaporization studies are in the measurement of thermodynamic properties and the discovery of new species. A discussion is given of the principles of physical chemistry important in vaporization studies, notably the concepts of equilibrium, phase behavior, thermodynamics, solid solution, and kinetics. The important factors influencing equilibrium vaporization phenomena are discussed and illustrated. A proper course of a vaporization study consisting of 9 stages is proposed. The important experimental techniques of Knudsen effusion, Langmuir vaporization and mass spectrometry are discussed. The principles, the factors, the course of a study and the experimental techniques and procedures are illustrated by recent work on the Ti‐O system.
Devitrification of Glasses in the Akermanite‐Gehlenite System
Authors: ORSINI P. GIORDANO , BURI A. , MAROTTA A.
Published: June 2006

The devitrification behavior of specimens with compositions 2CaO · (1‐x)MgO ·xAl2O3· (2‐x)SiO2, 0≤x≤1, was studied. The crystallizing phases were identified by X‐ray diffraction, and the transformation temperatures were determined by differential thermal and/or thermodilatometric analysis. The microhomogeneity of the glasses was investigated by electron microscopy and small‐angle X‐ray scattering. Glasses with x≤0.6 devitrify through an intermediate phase, merwinite. Conclusions are drawn about the mechanism of devitrification, taking into account phase separation and the possible distribution of the different anions in the glasses studied. The activation energy for the first stage of devitrification was calculated on the basis of a Johnson‐Mehl growth‐rate equation for x= 0.4.
Ion‐Exchange Parameters of Glass/Molten Salt Systems
Authors: STEYN W. M. , de WET W. J.
Published: June 2006

In a systematic study of the parameters characterizing the ion‐exchange process in borosilicate glass/binary molten nitrate systems, values of the thermodynamic equilibrium constant (K) and the nonideality constant (n) were determined over an extensive temperature range. The value of n decreases with an increase in temperature; in some systems, the glass is characterized by a value of n <1. The parameter n is expected to be more important than K, and its value should have a direct bearing on transport and conductance properties of the glass.
Phase Separation in the System (Fe,Mn)O
Authors: GOODWIN CHARLES A. , BOWEN H. KENT , KINGERY W. D.
Published: June 2006

Transmission electron microscopy was used to observe variations in composition in single crystals of FeyMn1–yO1+]xon a scale of 100 to 500 Å. Compositional fluctuations were resolved as lamellar‐like striations oriented primarily in the [100] direction. Specimens had been equilibrated at 900°C in oxygen partial pressures within the monoxide phase region and then quenched to room temperature. A region of solid‐solid immiscibility in the monoxide phase field is proposed. A different submicrostructure resulted from low‐temperature decomposition (150°C) due to localized heating when samples were prepared by ion‐bombardment thinning.
High‐Pressure Synthesis of Perovskites Pb(Li1/4Nb3/4)O3 and Pb(Li1/4Ta3/4)O3
Authors: MATSUOKA TOMIZO , KAWASHIMA SYUNICHIRO , MATSUO YOSHIHIRO , HAYAKAWA SHIGERU , IKEDA TSUTOMU , NAKAUE AKIMITSU , INOUE KATSUHIKO , YAGI YOSHIRO
Published: June 2006

Complex perovskite‐type compounds with the general formula Pb(B+1/4B5+3/4)O3, where B+= Li+ and B5+= Nb5+ or Ta5+, were synthesized using a high‐pressure technique and studied by X‐ray powder diffraction. The X‐ray patterns were indexed on the basis of a cubic cell with a0= 4.071 Å for Pb(Li1/4 Nb3/4)O3 and a0= 4.052 Å for Pb(Li1/4Ta3/4)O3. Electrical properties of the new perovskites were also studied.
Effect of Crystallizing the Grain‐Boundary Glass Phase on the High‐Temperature Strength of Hot‐Pressed Si3N4 Containing Y2O3
Authors: TSUGE AKIHIKO , NISHIDA K. , KOMATSU M.
Published: June 2006

The effects of fabrication variables on the high‐temperature strength of hot‐pressed Si3N4 containing 5 wt% Y2O3 were studied. Materials containing a crystalline grain‐boundary phase, formed as a consequence of a high‐temperature presintering heat treatment and identified as Si3N4·Y2O3, had high‐temperature strengths significantly superior to those observed for materials containing a glass phase.
Calculation of Cooling Rate and Induced Stresses in Drawing of Optical Fibers
Authors: PAEK U. C. , KURKJIAN C. R.
Published: June 2006

The rate of cooling of fused‐silica fibers and the generation of stress in clad fibers of fused silica and 96%‐silica glass (∼125 μm OD) pulled at 1750°C were studied. Experimental cooling rates reported by previous workers were fitted using low‐ and high‐temperature heat‐transfer coefficients derived from their data. The birefringence which developed in clad fibers consisting of silica and 96%‐silica glass was measured and found to change in sign as a function of the magnitude of the pulling stress. A model involving differences in viscosity (mechanical stress) as well as differences in expansion coefficient (thermal stress) is proposed to account for this behavior.
Optical and EPR Studies of Redox Interactions of Polyvalent Ions (Cr, Cu) in Glass
Authors: KOBAYASHI KEIJI
Published: June 2006

Chromium centers in isolated Cr ions and Cr(III)‐Cu(II) redox interactions were investigated by optical and EPR spectra. Line shapes and intensities of high‐field Cr(III)‐Cu(II) superimposed EPR absorption lines were sensitive to alkali content of host glasses. High‐field chromium g values (1.94 to 1.99) and intensities (190 to 3600) were calculated. The increase in g values from 1.96 to 1.98 is related to an increase in Cr(V) and to a conversion from Cu(I) to Cu(II) with increased alkali content. Two components of Cr powder spectra near g= 2.0 and g= 5.0 correspond to isolated octahedral Cr centers described by Landry et al. Cr‐Cr pair structure was not observed for low Cr2O3 concentrations. Three components of optical absorption bands near 340 nm, 430 to 460 nm, and 600 nm were measured in Cr(III)‐Cu(II) redox systems. Electronic interactions of Cr(III)‐Cu(II) redox systems and the structure of Cr centers are discussed.
Subsolidus Phase Equilibria in the System SrO‐B2O3‐SiO2
Authors: BAYLOR RICHARD , BROWN JESSE J.
Published: June 2006

The subsolidus compatibility relations in the system SrO‐B2O3‐ SiO2 were determined by solid‐state reaction techniques and X‐ray powder diffraction methods. The system was found to contain 11 subsolidus compatibility relations, one stable ternary compound (Sr3B2SiO8), and one metastable ternary compound with a probable composition SrB2Si2O8.
Auger Spectroscopic Analysis of Bioglass Corrosion Films
Authors: CLARK A. E. , PANTANO C. G. , HENCH L. L.
Published: June 2006

Auger spectroscopy and ion beam milling were used to determine surface compositional profiles on a series of bioglass implant materials after exposure to simulated body conditions. Four glasses were examined, a soda‐lime‐silica glass and 3 compositions produced by adding 3, 6, and 12 wt% P2O5 to the ternary glass. An SiO2‐rich layer is formed on the surface of all glasses investigated. As P2O5 is added to the bulk composition, a second film rich in Ca and P forms at the SiO2‐rich film‐water interface. The rate of formation of the Ca‐P film increases as the P2O5 content of the bulk glass increases. When glasses are corroded under identical conditions, the thickness of the Ca‐P layer increases as the P2O5 content of the bulk composition is increased.
Compound‐Glass Waveguides Fabricated by a Metal Evaporation Technique
Authors: NAGEL S. R. , PEARSON A. D. , TYNES A. R.
Published: June 2006

Glass fiber optical waveguides consisting of a potassium silicate glass core and SiO2 cladding were produced by a potassium metal evaporation technique. An evacuated fused‐silica tube containing an evaporated deposit of K was heated to temperatures sufficient to form a uniform potassium silicide layer on its inner surface. This layer was oxidized and reacted with the SiO2tubing at high temperatures to form a potassium silicate glass. The tube was then collapsed to give a solid rod preform with a potassium silicate core. Fibers drawn from such preforms exhibit moderately low optical loss. The fabrication technique is described, and a representative loss spectrum is presented.
Reactions and Equi ibria in Magnesium Oxych oride Cements
Authors: SORRE CHARLES A. , ARMSTRONG CHARLES R.
Published: June 2006

Phase equi ibria in the system MgO‐MgC 2‐H2O at 2°±3°C were determined and the reactions by which the equi ibrium phases, 5Mg(OH)2 MgC 2 8H2O and 3Mg(OH)2 MgC 28H2O, deve op were studied by X‐ray diffractometry. As reactive MgO is disso ved by magnesium ch oride so utions, a thixotropic suspension is converted to a ge, which then crysta izes to form the ternary oxych oride phases. Insufficient y active MgO disso ves more s ow y so that, in an open system, bu k composition can shift by evaporation of water, resu ting in crysta ization of a nonequi ibrium phase assemb age, with residua magnesium ch oride so ution and unreacted MgO. Imp ications of these nonequi ibrium reactions for the performance of magnesium oxych oride cements are discussed.
Fracture‐Strength Anisotropy of Sapphire
Authors: BECKER PAUL F.
Published: June 2006

At 22°C, the bend strength of as‐ground sapphire bars with different orientations of tensile surface and tensile axis varies from 4×104 to 12×104 psi as a result of the anisotropies of machining damage and fracture energy. Generally, the strength‐controlling surface flaws caused by grinding are of constant size; failure from such flaws is affected by grinding‐induced slip and twinning. Surface striations, which occur when there is negligible subsurface slip, can lead to stress concentrations, whereas twins can lead to increases in flaw size; each of these effects reduces strength. In addition, the large anisotropy in fracture strength, which is not predicted by the elastic anisotropy, is controlled by the anisotropic fracture energy. Approximation of the attractive forces across the fracture plane based on elastic moduli and interplanar distance can be used to understand the fracture energy anisotropy.
Capillarity and Mass Transport at the Ni‐AhOs Interface
Authors: HENRICHSEN R. A. , LI CHE‐YU
Published: June 2006

The morphology of periodic gratings at the Ni‐Al2O3 interface was investigated. The faceted gratings observed are related to the equilibrium shape of Al2O3 particles embedded in an Ni matrix. The interfacial diffusional process at the Ni‐Al2O3 interface was studied by observing the decay of sinusoidal gratings as a function of orientation. The orientation dependence of the interfacial diffusion observed for Ni‐Al2O3 is similar to that of the surface diffusion observed for Ni‐Al2O3.
Infrared Reflectance Spectra of Lead Glasses Corroded in Acid
Authors: WOOD SUSAN , BLACHÈRE J. R.
Published: June 2006

Infrared reflectance spectra of lead glasses are reported. Changes in the spectra on addition of K2O and Al2O3 to a binary PbO‐SiO2 composition were observed, and comparisons were made between standard specimens and specimens corroded at several temperatures in 10% acetic acid. The leached glasses developed spectra very similar to that of fused quartz, indicating the formation of a surface silica layer as the corrosion proceeds. Assignments are made to the various spectral features and rationales put forward to explain their changes during leaching.
Strength and Failure Predictions for Glass and Ceramics
Authors: RITTER J. E. , MEISEL J. A.
Published: June 2006

Fracture mechanics has provided the means for making failure predictions regarding the lifetime of a glass or ceramic component in service. The background necessary for making these failure calculations from crack velocity and fatigue strength data is presented. The analysis of these types of data gives conservative failure predictions for soda‐lime glass in water. Also, how these fracture mechanics concepts (with the appropriate experimental data) can be used as an index to the fatigue resistance of a material is described.
Phase Relations and Thermal Expansion in the System HfO2‐TiO2
Authors: RUH ROBERT , HOLLENBERG G. W. , CHARLES E. G. , PATEL V. A.
Published: June 2006

The system HfO2‐TiO2 was investigated in the 0 to 60 mol% TiO2 region using X‐ray diffraction analysis, differential thermal analysis, melting‐point studies, and dilatometry. For samples quenched from 1500° and 1250°C, single‐phase HfTiO4 is present ∼36 to 53% TiO2, with HfO2 coexisting as a second phase below 36% TiO2 and TiO2 coexisting as a second phase above 53% TiO2. Room‐temperature lattice parameters of the hafnium titanate phase decreased linearly with composition for samples quenched from 1500°C and furnace‐cooled from 1600°C. High‐temperature lattice parameter studies confirmed the expansion anisotropy of the hafnium titanate phase in the single‐phase region. Linear thermal‐expansion measurements revealed very low coefficients (< 1 × 10−6/°C) for compositions in the 30 to 40% TiOs range and relatively high coefficients (∼4× 10−6/°C) for the 25, 45, 50, and 60 mol% TiO2 compositions. The low expansion was attributed to microcracking.
Experimental Errors in Estimating Times to Failure
Authors: THORBY P. N.
Published: June 2006

The errors associated with subcritical crack propagation experiments are discussed with respect to both the usual equation for estimating time to failure and another time‐to‐failure equation which uses an exponential relation for region I data. Data obtained on soda‐lime silicate glass were used to illustrate the large differences in estimated times to failure and the large coefficients of variation in the estimates of time to failure when the relations are extrapolated past the experimentally obtained data points
Static Fatigue Limit with Particular Reference to Glass
Authors: WILKINS B. J. S. , DUTTON R.
Published: June 2006

After a review of the literature on the static fatigue limit, it was concluded that the normal method for its determination, using time‐to‐rupture data, is inadequate. There are very few experimental demonstrations of the existence of a true fatigue limit, and it is difficult to measure its value with any statistical confidence. An alternative experimental approach is suggested which is based on measuring the change in strength distribution of a representative sample after a high‐temperature anneal under a fixed tensile stress. This stress weakens weak specimens in the as‐received distribution, whereas strong specimens gain in strength. Those specimens whose strength remains constant demonstrate the existence of a fatigue limit and can be used to calculate a numerical value. The results are analyzed on the basis of the Charles‐Hillig stress corrosion theory, which has been slightly modified to facilitate the examination of the parameters associated with the fatigue limit. This analysis relates the static fatigue limit to the effective surface energy appropriate to the fatigue mechanism, i.e. corrosion caused by water vapor. Some implications of the modified model are discussed.
Relaxation of Thermal Stress in Phase‐Separated Borosilicate Glasses
Authors: TAKAMORI TAKESHI
Published: June 2006

Although the “apparent” viscosity of borosilicate glasses is known to increase with the progress of phase separation, temperatures at which the thermal strain is relieved are seen to decrease by the increase of phase separation. This behavior is explained by the difference in the “real” viscosity of each phase in the phase‐separated glass and by the very low thermal expansion of the higher viscosity SiO2‐rich phase. The “annealing point” based on ASTM designations loses its meaning for phase‐separated glasses of this type.
Heat Capacity and Structural Relaxation of Mixed‐Alkali Glasses
Authors: MOYNIHAN C. T. , EASTEAL A. J. , TRAN D. C. , WILDER J. A. , DONOVAN E. P.
Published: June 2006

Heat capacities of a series of mixed‐alkali glasses of composition (in mol%) 24.4(Na2O + K2O)‐75.6SiO2 were measured in the transition region by differential scanning calorimetry. The glass heat capacities at 700 K and the equilibrium liquid heat capacities are the same for all glasses on a per‐g atom basis and equal, respectively, to 5.6 ± 0.1 and 6.8 ± 0.1 cal/g atom K. The glass transition temperatures exhibited negative deviations from additivity, but the heat capacity curves in the transition region of all the glasses for identical heating rates and thermal histories could be superimposed on the same reduced plot. This behavior indicates that the shapes of the structural relaxation functions are the same for all the glasses. These results support Shelby's conclusion that there is no unique “mixed‐alkali effect” on thermodynamic or structural relaxation properties and that the term should be reserved for properties relating to ionic transport.
Phase Equilibria in the System CaO‐PbO‐SiO2
Authors: SAMANTA S. C. , HUMMEL F. A.
Published: June 2006

Phase relations in the ternary system were determined by solid‐ state reaction, quenching, and electron microscopy of the immiscible liquid region. The limits of the stable 2‐liquid region and the approximate limits of the metastable 2‐liquid region were determined. Relations in the region of homogeneous glass formation in the system, which included the joins CaSiO3‐PbSiO3 and CaSiO3‐Pb2SiO4, were determined by quenching. Two new compounds were discovered, 3CaO‐PbO.SiO2 and 2CaO.3PbO.SiO2, and extensive solid‐state trials permitted the compatibility triangles to be established. The accumulated data were assembled in the form of an equilibrium diagram for the system including joins, boundary lines, and isotherms.
Increase of Annealing Point of 96% SiO2 Glass on Incorporation of Carbon
Authors: ELMER THOMAS H. , MEISSNER HELMUTH E.
Published: June 2006

The annealing point of reconstructed 96% SiO2 glasses is markedly increased by incorporating carbon in porous glass and firing in a dry, nonoxidizing atmosphere. Numerous pyrolyzable organic compounds can be used as a source of carbon. Furfuryl alcohol, which is miscible in water, is preferred since it can be readily polymerized in the porous glass into a nonvolatile resin by heating. Relatively low concentrations of furfuryl alcohol are sufficient to markedly increase the viscosity of the final fired glasses. Infrared spectra show that carbon is an excellent dehydroxylating agent, removing silanol and boranol groups which, if left in the structure, soften the final glasses.
Binary Titania‐Silica Glasses Containing 10 to 20 Wt% TiO2
Authors: SCHULTZ PETER C.
Published: June 2006

A series of glasses in the TiO2‐SiO2 system was prepared by the flame hydrolysis boule process. Clear glasses containing as much as 16.5 wt% TiO2 were obtained. More TiO2 caused opacity due to phase separation and anatase/rutile crystallization during glass boule formation. Glasses in the 12 to ∼17 wt% TiO2 range were metastable and showed structural rearrangements on heat treatment at temperatures as low as 750CEC (∼200° below the annealing point). These changes were accompanied by large changes in thermal expansion. Thermal treatment can be designed to produce almost any desired expansion between α‐200+700=−5 × 10‐7/°C and +10 × 10‐7/°C. Zero expansion between 0 and 550°C was obtained. Evidence that these changes are due to phase separation and anatase formation is presented. Viscosity data in the glass transition range, refractive index, and density are also presented.
Discussion of Thermally Activated Approaches to Glass Fracture
Authors: GERBERICH W. W. , STOUT M.
Published: June 2006

A review of the Charles and Hillig approach to thermally activated crack growth mechanisms indicates that this theory may be applicable to cracking in vacuum at high temperatures but not to stress‐corrosion cracking in aqueous solutions. For stress‐corrosion mechanisms, the ramifications are 2‐fold: (1) Thermal activation analysis shows that the true activation energy in soda‐lime glasses is closer to 0.55 × 105J/mol (13.2 kcal/mol) than to the 1.2×105J/mol (29 kcal/mol) obtained using the Charles and Hillig approach; and (2) other models for slow crack growth controlled by bulk diffusion of H2, OH‐, or Na+‐H+are suggested and shown to be consistent with much of the observed phenomena.
Characterizing Opacity of Translucent Ceramic Materials
Authors: THOMAS M. B. , DOREMUS R. H.
Published: June 2006

A method for characterizing the opacity of translucent ceramic materials was developed based on the Kubelka‐Munk theory of scattering. From a single reflectivity measurement, the scattering coefficient S, which determines the optical quality of the material, was determined for materials with low absorption. From the scattering coefficient, the reflectivity or transmittance for a particular thickness was calculated. When there was appreciable absorption in the sample, it was necessary to make three reflectivity measurements and to use the general Kubelka‐Munk equations in order to obtain accurate values of S, reflectivity, and transmittance.
The System K2O‐BaO‐SiO2
Authors: GUNAWARDANE R. P. , GLASSER F. P.
Published: June 2006

Phase equilibrium studies of compound formation and liquidus and solidus surfaces of the system K2O‐BaO‐SiO2 are presented. The system contains 3 ternary compounds: K4BaSi3O9, K8BaSi10O25, and K2Ba3Si8O20. Both high and low polymorphs of the third have fields on the ternary liquidus surface. Solid solution with SiO2 depresses the high‐low inversion from 1030°C at K2Ba3Si8O20 to 835°C at 70.2 mol% SiO2. Data for 20 liquidus invariant points were found; 8 are thermal maxima and 12 are eutectics or peritectics. The isofracts of quenched glasses were determined.
Surface Segregation of Aluminum (Spinel Precipitation) in MgO Crystals
Authors: KINGERY W. D. , ROBBINS W. L. , HENRIKSEN A. F. , JOHNSON C. E.
Published: June 2006

MgO single crystals containing 0.006 and 0.187 wt% Al in solid solution at 1850°C were quenched and slow cooled. Analysis of the Al distribution near the surface with ion microprobe mass analysis indicated an increased Al concentration and near‐surface precipitation within a region × to 4 μ thick in the slow‐cooled samples and a much smaller enhanced concentration in the region 0.1 to 0.2 μ from the surface in the quenched samples.
Deformation of Polycrystalline MgO at High Hydrostatic Pressure
Authors: AUTEN T. A. , RADCLIFFE S. V.
Published: June 2006

Vacuum‐hot‐pressed MgO polycrystals were deformed in compression at hydrostatic pressures up to 1000 MPa in an effort to obtain gross plastic deformation at room temperature. Although transmission electron microscopy observations indicated an increase in dislocation density at pressures > 400 MPa, direct optical observations during deformation indicated that microfracturing persists as a mode of deformation throughout the stress‐strain curves at even the highest test pressures. As in previous investigations, pressures > 400 MPa led to a transition from completely brittle to ductile behavior, as indicated by stress‐strain plots, but direct optical observations suggested that the apparent transition is an effect of pressure on the mode of crack propagation.
Surface Finish Effects and the Strength‐Grain Size Relation in SiC
Authors: CRANMER D. C. , TRESSLER R. E. , BRADT R. C.
Published: June 2006

The effect of surface finish on the strength‐grain size relation was investigated for dense hot‐pressed SiC. Failure initiated predominantly via the propagation of extrinsic machining‐induced flaws for the range of grain sizes and machining grit sizes studied. These results are consistent with the region of large‐grain‐size flaw control as delineated by Prochazka and Charles. The severity of machining‐induced flaws, relative to the machining grit size, decreased with increasing machining grit size and decreasing SiC grain size.
Electrical Conduction in Single‐Crystal Thallic Oxide: II, Effects of Annealing at 923°K in Oxygen Pressures from 0.01 to 1 Atmosphere
Authors: SHUKLA V. N. , WIRTZ G. P.
Published: June 2006

The low‐temperature conductivity of thallic oxide (Tl2O3) is relatively insensitive to the equilibrium partial pressure of oxygen during annealing at 923°K, i.e. the maximum variation is ∼15% over the range of 0.01 to 1 atm O2, with a relative maximum occurring at ∼0.2 atm. The insensitivity in conductivity results from the compensating effects of increasing mobility and decreasing carrier concentration with increasing oxygen pressure during annealing. At low oxygen pressures, defect interactions complicate the interpretation of the measurements, but a calculated Fermi energy on the order of 0.8 eV is sufficiently close to other reported values to confirm the model of a highly degenerate semiconductor with a simple S‐like conduction band described by a parabolic density‐of‐states function.
Space‐Charge Contribution to Grain‐Boundary Diffusion
Authors: VAN M. F. , CANNON R. M. , BOWEN H. K. , COBLE R. L.
Published: June 2006

The contributions of the space‐charge cloud to impurity and self‐diffusion in the grain‐boundary region of ionic materials are shown by calculations for doped KC1. The magnitude of these effects is modest (< 103Dl) and limited in dimension (10 to 200 Å). Both enhancement and reduction in the charge cloud contribution to boundary diffusivities are predicted. In the charge cloud, appreciable diffusivity enhancement is indicated only for the ion on the sublattice opposite that of the principal impurity. The large boundary‐diffusion enhancements and boundary widths often reported in “pure” and doped samples cannot be explained by the space‐charge contribution.
Effect of Water Vapor on Sodium Vaporization from Two Silica‐Based Glasses
Authors: SANDERS DAVID M. , HALLER WOLFGANG K.
Published: June 2006

The influence of water vapor pressure on the equilibrium sodium vapor densities over well‐stirred silica‐based glass melts was investigated. Sodium was assumed to be present in the vapor as Na and NaOH molecules, and the activity of Na.O in the melt was calculated as a function of water vapor pressure above the melt.
Subsolidus Phase Equilibria in the System Bi2O3‐TiO2‐Nb2O5
Authors: KIKUCHT TAKESHI
Published: June 2006

The subsolidus phase equilibria in the system Bi2O3‐TiO2‐Nb2O5 at 1100°C were determined by solid‐state reaction techniques and X‐ray powder diffraction methods. The system was found to contain 4 ternary compounds, i.e. Bi3TiNbO9, Bi7Ti4NbO21, a cubic pyrochlore solid solution having a compositional range of 3Bi2O3·x TiO2 (7–x)Nb2O5 where x ranges from 2.3 to 6.75, and an unidentified phase, 4Bi2O3·11TiO2·5Nb2O5.
Crystallization of a Cerium Phosphate Glass
Authors: EL‐BAYOUMI OSAMA H. , SUBRAMANIAN K. N.
Published: June 2006

Cerium phosphate glass containing 21 mol% cerium oxide and 79 mol% phosphorus oxide was prepared by melting a mixture of cerous oxalate and ammonium dihydrogen phosphate under normal atmospheric conditions. A heat‐treatment schedule was obtained from DTA of this glass. Specimens of heat‐treated samples for TEM observations were prepared by chemical and mechanical polishing techniques to observe the progress of nucleation, phase separation, and crystallization of this glass. Phase separation in the glass foil was also followed by electron‐beam heating in the microscope. The crystalline compounds separated were identified by using electron and X‐ray diffraction techniques.
Ambipolar Diffusion Contribution to High‐Temperature Thermal Conductivity of Titanium Carbide
Authors: BETHIN JAMES , WILLIAMS WENDELL S.
Published: June 2006

The odd thermal conductivity behavior of transition metal carbides–Kincreasing with increasingT–has been interpreted as resulting from the strong scattering of electrons by carbon vacancies and polar optical phonons and from the strong scattering of phonons by vacancies and conduction electrons. These scattering processes have been used in a Callaway analysis to fit the thermal conductivity of TiC from the liquid He temperature to 1000 K; however, at the highest temperatures a residual contribution toKwas noted which increased with increasingT.An analysis of the Lorenz function has indicated that this contribution is electronic. The present work indicates, using a theory modified for semimetals, that the additional conductivity may be ambipolar diffusion (electron‐hole migration and recombination).
Refining in the Glassmelting Process
Authors: NĚMEC LUBOMlAR
Published: June 2006

Refining mechanisms for a soda‐lime glassmelt containing bubbles are proposed, based on photographic observations and data in literature. The equation expressing the removal of bubbles from the glassmelt by ascension has been derived from a linear relation between bubble size and time. Experimental and theoretical studies have shown that heterogeneous bubble nucleation occurs during refining. An additive relation between SiO2 (sand) dissolving tune and the theoretical refining time resulting from heterogeneous bubble nucleation has been verified for As2O3+ NaNO3, Na2SO4, and NaCl additions to a soda‐lime glass batch.
Optical Absorption of Na2O‐WO3 Glass Containing Transition‐Metal Ions
Authors: DUFFY J. A.
Published: June 2006

Several transition‐metal ions are soluble in Na2O‐WO3 glass (1:1.63 mole ratio); from their d‐d spectra it is concluded that the sites these ions occupy in the glass are not necessarily the same as those occupied when the transition‐metal ion is coordinated in heteropolytungstate anions. The tungstate glass appears to have coordinating properties similar to those of “discrete‐anion” glasses (e.g. nitrate and acetate glasses) rather than to those of network‐type glasses. In the glass, the tungstato‐metal complexes apparently do not decompose readily; their stability is similar to that of phosphato‐metal complexes in phosphate glasses.
Strength Degradation of Glass Resulting from Impact with Spheres
Authors: WIEDERHORN S. M. , LAWN B. R.
Published: June 2006

The nature and extent of degradation incurred by glass surfaces impacted with spheres of steel and tungsten carbide were studied. The residual strength after impact depends on the velocity, radius, and density of the projectile; on the toughness and (indirectly) the hardness of the target; and, to a lesser degree, on the preexisting mechanical condition of the surface. The damage morphology involves modification of the basic Hertzian cone crack pattern by median (radial) cracks and crushed glass at the impact site. The essential features of the degradation may be predicted by a theoretical analysis of residual strength as a function of impact velocity as derived from indentation fracture mechanics. This study accounts, in particular, for a threshold velocity for significant strength loss, above which further strength decrease is relatively slight. Small, but significant, discrepancies between observed and predicted degradation characteristics are attributed to the departure from ideal Hertzian fracture geometry and to the dynamic nature of the contact. However, it is suggested that quasi‐statically based theory may be used for estimating the strength of structural ceramics in small‐particle impact situations.
Nonuniformity of Potassium Ions in β‐Alumina Ceramics
Authors: YASUT ITARU , DOREMUS R. H.
Published: June 2006

A nonuniform distribution of K was found in β‐alumina that had been in contact with sodium polysulfide or sodium nitrate melts containing small amounts of K. Large β‐alumina grains in contact with the melt had approximately the equilibrium concentration of K expected from studies on single crystals of β‐alumina, but surrounding grains contained little or no K. Thus the mobility of K ions in grain boundaries in β‐alumina appears to be very low. Stresses from K concentration at the ceramic surface could enhance other incipient sources of failure such as seal stresses, cracks, and other defects.
Effect of Phase Separation on HF Etch Rate of Borosilicate Glasses
Authors: TOMOZAWA MINORU , TAKAMORI TAKESHI
Published: June 2006

Etch rates of borosilicate glasses in HF were studied as a function of heat‐treatment time and temperature for liquid‐in‐liquid phase separation. It is shown that, when the phase‐separated glass has an interconnected microstructure, the composition of the chemically less durable phase is the dominant factor in HF durability. When the phase‐separated glass has a dispersed alkali‐borate‐rich (chemically less durable) phase embedded in a silica‐rich matrix, the HF etch rate is constant, independent of the extent of phase separation.
Thermodynamically Predicted Miscibility Gap in the System BeF2LiF
Authors: VALLET C. E. , BRAUNSTEIN J.
Published: June 2006

A thermodynamically predicted miscibility gap has been computed from activity‐coefficient data in molten BeF2‐LiF, with the consolute temperature at 534°C and composition 0.781 mole fraction BeF2. The Cook‐Hilliard relation was verified for compositions on the binodal and spinodal curves in this system, which is structurally analogous to silicate systems.
Stress Analysis of the Double‐Torsion Specimen
Authors: TRANTINA G. G.
Published: June 2006

The double‐torsion specimen was analyzed with a 3‐dimensional elastic finite‐element stress analysis. A crack‐front configuration where the stress intensity is constant over ≅ 1/2 of the specimen thickness was determined. That value of the stress intensity is nearly equal to the “strength‐of‐materials” value. The stress intensity is nearly constant for crack lengths > 0.55 × specimen width (W) and ligament lengths > 0.65W.
High‐Temperature Phase Diagram for the System Zr.
Authors: ACKERMANN O R. J. , GARG S. P. , RAUH E. G.
Published: June 2006

The melting, eutectic, peritectic, solidus, and liquidus temperatures in the system Zr‐O have been measured directly by a simple optical pyrometric technique requiring only a few hundred milligrams of sample. The saturation solubility of oxygen in α‐Zr(s) between 1270° and 1980°C and the lower phase boundary of the ZrO2–α phase between 1900° and 2400°C have been measured by an isopiestic equilibration method. The oxygen solubility limit in α‐Zr(s) agrees well with previous low‐temperature studies and reaches a maximum solubility of 35°1 at.% O at the eutectic temperature, 2065°°5°C. The maximum melting temperature of α‐Zr(ss) is 2130°°10°C and corresponds to a composition of 25°1 at.% O. Both of these temperatures are approximately 150° higher than previously reported. Liquidus compositions above the eutectic temperature were obtained via mass spectrometry from the kinetic behavior of the liquid solution‐ZrO2–x(s) mixture as it approached equilibrium at 2125°°5°C. The lower phase boundary or solidus of the ZrO2–x phase departs appreciably from ideal stoichiometry above 1900°C and smoothly reaches its most reduced composition, 61 at.% (ZrO1.56), near 2300°C. The solidus is retrograde at higher temperatures. The melting temperature of the stoichiometric dioxide is 2710°°15°C.
Elastic Moduli of Refractory Spinels
Authors: PORTER D. F. , REED J. S. , III DAVID LEWIS
Published: June 2006

Elastic moduli of spinel phases in the system Mg(Al, Cr, Fe)2O1 were determined from sonic analyses of porous, polycrystalline specimens prepared by hot‐pressing. A special iterative least‐squares technique (ILS) and standard curve‐fitting techniques were used to obtain moduli at zero porosity by extrapolation. A minimal standard error of estimate was achieved in all cases by using an exponential form for the porosity dependence and the ILS technique. Moduli were checked for self‐consistency. Extrapolated moduli for MgAl2O1 agreed well with respective moduli calculated from single‐crystal elastic constants and Birch's law. Longitudinal and shear sound velocities decreased with increasing phase density in the solid‐solution systems and systematics indicate that elastic moduli of arbitrary solid solutions can be estimated to lt; ± 10% from the phase density.
Preparation, Structure, and Selected Catalytic Properties of the System LaMn1‐xCuxO3‐y
Authors: GALLAGHER P. K. , JOHNSON D. W. , VOGEL E. M.
Published: June 2006

Samples of LaMn1‐xCuxO3‐y in the range 0≤x≤0.8 were prepared from freeze‐dried solutions of the nitrates. Samples with x≤0.6 were single‐phase perovskites. At higher values of x, the samples contained La2CuO4 and CuO as well as the perovskite phase. Samples of LaMn1−x,Cux,O3−y supported on ceramic monoliths or when mixed with powdered A12O3 exhibit catalytic activity for the oxidation of CO. Greatest activity is shown for 0.4≤x≤0.7. Although the catalysts are severely poisoned by SO2, 2% H2O in the gas stream causes only slight deactivation. Activities of other oxide catalysts were also measured and compared. Rate constants per unit surface area at 200° to 400°C follow the order Co3O4>Pt>LaMn1−xCuxO3−y (0.4≤x≤0.7)>copper chromite>La1−xSrx,MnO3≤ other substituted LaMnO3 materials, CuO, or La2CuO4. The perovskite catalyst is more stable than Co3O4 or copper chromite when heated in 10% H2+ 90% N2.
Effects of Porosity and Grain Size on the Magnetic Properties of NiZn Ferrite
Authors: IGARASHI HIDEJI , OKAZAKI KIYOSHI
Published: June 2006

The effects of porosity and grain size on the magnetic properties of NiZn ferrites were examined on groups of specimens with controlled porosity and grain size; both the permeability and theB‐H loop were measured. The demagnetizing factor, which is proportional to porosity, was estimated on the basis of the permeability‐porosity relation determined. The discussion of the permeability‐grain size relation takes into consideration the dependence of domain wall spacing on grain size. The experimental results for the B‐H loops indicate that the remanent magnetic flux density is independent of grain size and the coercive field is independent of porosity. Both the remanent magnetic flux density‐porosity and the coercive field‐grain size relations are explained via the formulas proposed.
Ternary Diffusion with Two Moving Boundaries
Authors: CHRISTENSEN N. H.
Published: June 2006

The problem of unidirectional diffusion with 2 moving boundaries is pertinent to the study of reactions between condensed phases. The solution for binary diffusion is presented, and an eigenvector approach is outlined for the solution of the problem in a ternary diffusion system. The complete solution is given for some specific situations. Typically, the diffusion path deviates from the series of simple mixtures and tends to follow the direction of the minor eigenvector. This behavior is also true for cases where linear approximations are applicable.
Fracture Properties of Polycrystalline Lithia‐Stabilized β“‐ Alumina
Authors: VIRKAR ANIL V. , GORDON RONALD S.
Published: June 2006

The critical stress‐intensity factor, K1C, and the fracture strength, σf, have been investigated on both hot‐pressed and sintered lithia‐stabilized β”‐alumina. The hot‐pressed material possessed a strong preferred orientation with many of the basal planes aligned perpendicular to the direction of hot‐pressing. Both K1C and σf were found to be orientation‐dependent. Two regimes of fracture were identified. In fine‐grained material (<120 μm), the strength was slightly dependent on grain size.

For larger grain sizes, the strength decreased rapidly with increasing grain size and the fracture mode was almost entirely transgranular. The K1C values for sintered β”‐alumina were in the same range as those obtained on the hot‐pressed material.
Diffusion of 51Cr in MgO Crystals
Authors: WEBER G. W. , BITLER W. R. , STUBICAN V. S.
Published: June 2006

An arc fusion technique was used to grow single crystals of MgO with an aliovalent impurity level of ∼ 250 ppm. Diffusion coefficients for Cr3+ in single‐crystal MgO were measured from 1353° to 1553°C using a high‐specific‐activity isotope,51 Cr. The diffusion coefficient of 51Cr for both arc‐grown and vapor‐deposited MgO crystals can be characterized by an activation energy of 70.0±2.1 kcal/mol. These results are comparable with the interdiffusion coefficients in Cr2O3‐MgO when the interdif‐fusion D is extrapolated to low Cr concentrations.
Low‐Angle Grain‐Boundary Macrostructure in Large‐Diameter Czochralski White Sapphire
Authors: YIP V. F. S. , BRANDLE C. D.
Published: June 2006

Large‐diameter Czochralski sapphire crystals grown in several orientations were occasionally found to contain complex networks of low‐angle grain boundaries. The subboundaries lie in major low‐index crystallographic planes which are uniquely determined by the gowth orientation. The major subboundary planes were the (11¯00) and (011¯0) for crystals gro_wn_in the direction normal to the (r)‐(1¯012) plane and the (1¯21¯0) and (21¯1¯0) planes for crystals grown in the 90°‐[1120] direction. The formation of the subboundary macrostructure was attributed to an excessive temperature gradient during seeding and is not related to growth rate, impurity content, or annealing.
New Lines in the Raman Spectra of Carbons and Graphite
Authors: VIDANO R. , FISCHBACH D. B.
Published: June 2006

An extensive survey of the Raman spectral activity of a wide variety of carbon materials has produced experimental evidence for at least five structure‐sensitive lines or bands. In addition to the well‐known, always present 1580 cm−1 graphite line and the 1360 cm−1 disordered carbon line, there is a disorder line at ∼1620 cm−1 that is responsible for the apparent blue‐shift of the graphite line in very disordered carbons; and there are lines at ∼2700 and ∼2735 cm−1 that are strong in graphite and annealed carbons but absent in very disordered carbons. These additional lines increase the capability of Raman spectroscopy to characterize carbon materials.
Phase Equilibria and Ordering in the System ZrO2‐Y2O3
Authors: STUBICAN V. S. , HINK R. C. , RAY S. P.
Published: June 2006

The phase diagram for the system ZrO2‐Y2O3 was redetermined. The extent of the fluorite‐type ZrO2‐YzO3 solid solution field was determined with a high‐temperature X‐ray furnace, precise lattice parameter measurements, and a hydrothermal technique. Long range ordering occurred at 40 mol% Y2O3 and the corresponding ordered phase was Zr3Y4OL12. The compound has rhombohedra1 symmetry (space group R 3), is isostructural with UY6Ol2 and decomposes above 1250±50°C. The results indicate that the eutectoid may occur at a temperature <400°C at a composition between 20 and 30 mol% Y2O3 Determination of the liquidus line indicated a eutectic at 83± 1 mol% Y2O3 and a peritectic at 76 ± 1 mol% Y2O3.
Mechanism and Kinetics for the Formation of Uranium Mononitride by the Reaction of Uranium Dioxide with Carbon and Nitrogen
Authors: MUROMURA TADASUMI , TAGAWA HIROAKI
Published: June 2006

The mechanism and kinetics of UN formation by reaction of a pellet of mixed UO2 and C with N2 were studied for temperatures of 1420° to 1750°C. The reaction followed the first‐order rate equation; the activation energy was 83 kcal/mol. Only UN1−xCx was produced. The lattice parameter variation of UN1−xCx had a minimum and a maximum during reaction; at the maximum, UN1−xCx+ C + N2 were in equilibrium. The overall reaction was divided into four stages: (1) formation of UN1−xCx from UO2, (2) decarburization of UN1−xCx, (3) formation of UN1−xCx with the equilibrium composition, and (4) pure UN formation. The lowest reaction rate was in stage (4).
Aluminum Oxyhydroxides Formed by the Reaction of Methyl Esters with Sodium Aluminate Solution
Authors: BEAUFILS JEAN , SETTON RALPH , MAZIERES CHARLES
Published: June 2006

Properties of the aluminum oxyhydroxide formed by the reaction of methyl acetate on solutions of sodium aluminate are examined. The solid has a high specific surface and gives an X‐ray diffraction pattern different from those of other known oxyhydroxides. A quite different product (coarse bayerite) is obtained when esters which cannot have an enolic form are used. A possible formation mechanism of the oxyhydroxide is discussed.