bluuebunny/crossref_metadata_2025 huggingface dataset:
Ionic Conduction and Structure in Cesium and Thallium Silicate Glasses
Authors: OTTO K. , MILBERG M. E.
Published: June 2006

Density, NMR absorption, and ionic conductivity were measured for cesium and thallium silicate glasses. Results indicate that the cesium ions change their environment between 20 and 35 mole % Cs2O, possibly by means of a phase separation. These observations are consistent with the composition independence of the activation energy for conduction above 25 mole % Cs2O but do not reflect the rapid change in activation energy below 25 mole %. The extreme breadth of the 205Tl NMR Une varied with Tl2O content in the same manner as the activation energy for conduction. This result indicates that the distribution of ionic environments may provide a similar distribution of energy barriers to ionic motion. The relation between ionic conduction and structure appears to be different in cesium and thallium silicate glasses.
Compound Formation in the Systems Lithium‐Carbon and Lithium‐Boron
Authors: SECRIST D. R.
Published: June 2006

The phases present in the 2 to 50 at.% lithium region for the system lithium‐carbon below 700° C are carbon and stoichiometric Li2C2. The unit cell of Li2C2 was identified as primitive monoclinic. A lithium boride phase of composition LiBio10.85 ± 0.35 was synthesized in the lithium‐boron system for samples containing up to 50 at.% lithium. The Debye‐Scherrer X‐ray powder pattern for this phase can be indexed on the basis of a tetragonal unit cell. Lithium reacts with boron carbide to form lithium carbide and lithium boride.
Spontaneous Bubble Formation in Silicate Melts at High Temperatures: II, Effect of Wet Atmospheres and Behavior of Mixed Alkali Glasses
Authors: CABLE MICHAEL , RASUL C. G.
Published: June 2006

Earlier work with alkali silicates was extended. Time and temperature for originally melting the glass had little influence on bubble or foam formation. Water vapor in the furnace atmosphere lowered foaming temperature considerably. Mixed alkali glasses showed complex and unexpected behavior. Nucleation and growth of foam bubbles as well as foam stability are discussed.
Grain‐Boundary Segregation and Final‐Stage Sintering of Y2O3
Authors: JORGENSEN P. J. , ANDERSON R. C.
Published: June 2006

The addition of ThO2 to Y2O3 inhibits grain growth during sintering and allows the sintering process to proceed to theoretical density by maintaining a high diffusion flux of vacancies from the pores to the grain boundaries. The inhibition of grain growth is accomplished by the segregation of ThO2 solute at the grain boundaries, causing a decrease in the grain‐boundary mobility. The segregation of ThO2 at the grain boundaries can be inferred from the results of the microhardness and grain‐growth studies presented. Further evidence for segregation is provided by quenching experiments and surface activity experiments.
Polymorphism of Tricalcium Silicate and Its Solid Solutions
Authors: BIGARÉ M. , GUINIER A. , MAZIÈRES C. , REGOURD M. , YANNAQUIS N. , EYSBL W. , HAHN TH. , WOERMANN E.
Published: June 2006

In tricalcium silicate and its solid solutions six modifications were established: one rhombohedral (R), two monoclinic (MI, MII), and three triclinic (TI, TII, TIII). All these forms are rhombohedral or pseudorhombohedral and extremely similar; the variations in the X‐ray diagrams and the transformation enthalpies are minute. Only three of the five transitions were observed by both X rays and DTA: TI‐TII (600°), TIII–MI (980°), and MI–MII (990°); one was established by DTA (TII–TIII, 920°) and one by X rays only (MII–R, 1050°C). This scheme of polymorphism is compared critically with results of other authors, and the nature of the various displacive transformations is discussed. X‐ray and DTA investigations of solid solutions of Ca3SiO5 with Al2O3 and ZnO established the phase relations as functions of temperature and composition. With Al2O3, two modifications (TI and TII) were stabilized; and with ZnO, five polymorphs (TITII, MI, MII, and R). With both pure C3S and the solid solutions, the results are consistent and have a close bearing on the constitution of alites in portland cement clinker.
Structural and Chemical Alterations of Delta Fe2O3 and Their Effect on Magnetic Properties
Authors: CONLEY ROBERT F.
Published: June 2006

The defect structure, δ‐Fe2O3, was grown epitaxially with ultrafine, activated Al2Si2O5(OH)4. More uniform particle size and consistent structure result with this process than with auto‐nucleation. The low ferrimagnetic character is influenced by precipitation parameters. Magnetic properties and crystal order can be promoted by a novel thermal conversion process using a high‐boiling aliphatic hydrocarbon. The process induces the formation of a more complex iron oxide. A structure is believed to form of an order higher than δ‐Fe2O3 but lower than γ‐Fe2O3. Analyses (C, H, CO2, and H2O) are correlated with magnetic properties. Specimens having a mean particle size of 20 mμ were produced with coercivities up to 290 oe and remanent inductions up to 1800 gauss/cm3. Stability tests over a five‐year period showed no degradation.
Crystallization and Chemical Strengthening of Stuffed β‐Quartz Glass‐Ceramics
Authors: BEALL G. H. , KARSTETTER B. R. , RITTLER H. L.
Published: June 2006

Metastable solid solutions with the β‐quartz structure can be crystallized from most glasses in the system SiO2‐Mg(AlO2)2‐LiAlO2 as well as from many containing the additional components Zn(AlO2)2 Al(AlO2)3, Li2ZnO2, and Li2BeO2. Internal nucleation is afforded by additions of ZrO2 or TiO2. Either transparent or opaque crystalline materials can be formed from glasses containing about 70% SiO2. The transparency is due to a combination of low birefringence in the major stuffed β‐quartz phase and minute crystal size. Thermal expansions vary from ‐20 to +50 × 10−7/°C. Thermal stability is highly variable. Breakdown products include spinel, cordierite, β‐spodumene, willemite, mullite, and cristobalite. Magnesian compositions can be strengthened by a 2Li+⇌ Mg2+ ionexchange reaction. Abraded flexural strengths range from 30,000 to 160,000 psi.
Nonstoichiometry of ZrO2 and Its Relation to Tetragonal‐Cubic Inversion in ZrO2
Authors: RUH ROBERT , GARRETT HAROLD J.
Published: June 2006

The system Zr‐O was studied in the composition range 50 to 66.7 at.% O by metallographic analysis, high‐temperature X‐ray analysis, and lattice parameter determinations at room temperature. The solubility of zirconium in zirconia was determined from 1200° to 2000°C, and the cubic‐tetragonal inversion temperature of ZrO2 was shown to be lowered to approximately 1490°C for samples containing α‐Zr and oxide phase. Alpha zirconium has greater solubility in the cubic phase than in the tetragonal phase, and the inversion is revealed, in samples quenched from the cubic field, by the exsolution of α‐Zr, which is metallographically characterized as striations. At room temperature, the striations are oriented with the 111 and 11° planes of monoclinic zirconia.
Effect of Nitriding on Electrolysis and Devitrification of High‐Silica Glasses
Authors: ELMER T. H. , NORDBERG M. E.
Published: June 2006

Devitrification occurs near the cathode when reconstructed high‐silica glasses and fused quartz undergo electrolysis at 900°C. The crystalline phase is cristobalite and results from a concentration of alkali ions. Subsequent and more superficial crystallization around the alkali‐rich spot is caused by interaction of the glass with alkali vapors coming from the central spot. The degree of devitrification increases with the alkali content of the glass. Devitrification at constant alkali level can be reduced in reconstructed glasses by nitriding the porous glass with ammonia at a high temperature before consolidation. Devitrification decreases and viscosity and electrical resistivity increase as the nitriding temperature increases 500° to 1000°C. Nitrided glasses are more resistant to electrolytically induced devitrification than is fused quartz.
Phase Relations in the ZrO2‐MgO System
Authors: GRAIN CLARK F.
Published: June 2006

Phase relations were studied in the system ZrO2‐MgO with emphasis on the range 1350° to 1600°C. A phase relation was determined from samples, using precision lattice parameters, X‐ray diffraction line intensities, and petrographic observations, and from dynamic observations of the phases present using high‐temperature X‐ray diffraction techniques. Limits were established for the solubility of MgO in tetragonal ZrO2 and for the range of the cubic solid solution. The phase relations below 1240°C were complicated by hysteresis in the monoclinic to tetragonal inversion of ZrO2.
Electrical Resistivity of Refractories
Authors: WALLACE RICHARD W. , RUH EDWIN
Published: June 2006

Electrical resistivity was measured on commercially available materials, including high‐alumina, magnesia, magnesia‐chrome, zircon, and stabilized‐zirconia refractories, at temperatures to 2650°F. The tests were made using two‐, three‐, and four‐terminal measurements and the results are discussed. The four‐terminal measurements were made by a new method.
Substructures in Silicate Glasses
Authors: BABCOCK C. L.
Published: June 2006

Glass compositions are correlated with published data for refractive index, specific volume, and fluidity, which indicate the presence of different structural types in silicate glasses. These structural types are shown to be uniquely related to the composition areas of primary crystallization phase fields. It is suggested that these different structural types are to be understood as silicate framework structures or “substructures” in which other appropriate cations may be accommodated. The described data relations definitely establish the presence of different recognizable substructures in silicate glasses but do not permit judgments on their detailed characteristics.
Structure‐ProPertv Relation in Flexible Sandstone
Authors: DEVRIES R. C. , JUGLET D. B.
Published: June 2006

A quantitative microstructural study of the deformation of flexible sandstone confirms the “loose‐grain” model of the deformation behavior of this composite material. The study demonstrated the contribution of the micα‐quartz intergrowth to the bonding and confirmed that the role of mica in the flexibility of the composite is negligible. The microstructural evidence indicates that the quartz‐mica bond must have resulted from in situ growth of mica simultaneously with growth of quartz grains.
Deformation of Cube‐Oriented MgO Crystals Under Pressure
Authors: WEAVER C. W. , PATERSON M. S.
Published: June 2006

Plastic deformation in MgO crystals compressed parallel to a cube axis was studied under confining pressures up to 10 kbars at room temperature. The specimens were jacketed either in thick commercial rubber or in very thin latex. There were marked differences from behavior at atmospheric pressure, especially when thick rubber jackets were used at the higher pressures, at which they were in the glassy state; the stress‐strain curves of the MgO then tended to be abnormally high, and there was more marked activity of obliquely oriented slip planes. These effects can be attributed to additional stresses arising from the constraint of the rubber jackets, which can also give rise to kink bands at the longitudinal edges of the specimens. Such effects demonstrate the more effective hardening that arises from the interaction and intersection of the dislocations on oblique {110} slip planes and have important implications for the deformation of grains in the constrained conditions within polycrystalline specimens.
Defect Diffusion in Single Crystal Aluminum Oxide
Authors: JONES T. P. , COBLE R. L. , MOGAB C. J.
Published: June 2006

A defect diffusion coefficient was determined in single crystal aluminum oxide from 1400° to 1850°C by measuring the movement of the color boundary in a Ti3+− doped single crystal heated in air. In this temperature range the experimental data can be represented by

The interpretation developed is that this equation represents the diffusivity for a defect which contributes to aluminum self‐diffusion.
Reactions in the System ZrO2‐SrO
Authors: NOGUCHI TETSUO , ŌKUBO TSUTOMU , YONEMOCHI OSAMU
Published: June 2006

The liquidus curve of the system ZrO2‐SrO was investigated with a heliostat‐type solar furnace. The cooling curve of a specimen was obtained with a brightness pyrometer at 0.65 pm to determine the freezing point and other transition phenomena. The primary phases and the compounds formed in the system were also examined. The existence of SrgZra‐1O3x‐2 (n=4, 3, and 2) and of SrZrO2 was confirm. A tentative phase diagram of the system ZrQ2‐SrO at high temperatures is presented.
Nucleation and Growth of Magnesioferrite in MgO Containing 0.9% Fe3+
Authors: WOODS K. N. , FINE M. E.
Published: June 2006

The initial stage of precipitation of magnesioferrite from a supersaturated solid solution of 0.9 cation % Fe3+ in MgO at 500 °C was studied by fitting the magnetization curves to 7000 Oe at low temperatures with the Brillouin function. The averase umber of Fe3+ ions in a precipitate particle, increased monotonically with aging time from 9 in the as‐quenched condition to 88 after 16 h. The average spin quantum number per Fe3+ ion decreased to near its final value at an aging time corresponding to = 50. Thus the volume fraction of precipitate is near the final value when the average particle size is only about three unit cells of magnesioferrite.
Behavior of Urania–Rare‐Earth Oxides at High Temperatures
Authors: BEALS R. J. , HANDWERK J. H. , WRONA B. J.
Published: June 2006

Uranium dioxide becomes hypostoichiometric when hated above 1600°C or in a reducing atmosphere. Upon cooling, free metallic uranium is rejected. The role and the effect of rare‐earth oxide additives on the stabilization of urania at high temperatures in a hydrogen environment are evaluated. A tentative phase diagram for the system uraniagadolinia is proposed.
Mechanical Properties of Polycrystalline β‐Sic
Authors: GULDEN T. D.
Published: June 2006

The mechanical properties of chemically vapor‐deposited β‐Sic were measured in bending between room temperature and 1400°C. Material with grain diameters from less than 1 to 15 μm was tested. No grain‐size dependence of the bend strength of dense (<99% of theoretical) Sic was observed at any test temperature. The fracture strength of dense Sic remained approximately constant between room temperature and about 900°C and then increased sharply up to the maximum test temperature of 1215° to 1400°C. This increase in fracture stress coincided with the onset of plastic yielding detectable in the stress‐strain curves. The fracture mode of this material was transgranular cleavage at all test temperatures. The fracture stress of Sic of lower density, which was characterized by the presence of grain boundary flaws, decreased slightly at high temperature. The fracture mode of the low‐density (3.17 g/cm3) β‐Sic underwent a transition from predominantly transgranular at room temperature to predominantly intergranular at high temperature.
Mechanical Behavior of Lithium Fluoride at High Temperatures
Authors: DAY R. B. , JOHNSTON W. A.
Published: June 2006

Single crystals of lithium fluoride were pulled in tension at high temperatures; the results of these tests are compared with data for magnesium oxide. Interpenetration of {110}〈110〉 slip systems does not occur in LiF as readily as in MgO. Because of this lack of interpenetrability, plastic instability and completely ductile fracture do not occur in LiF below 700°C (0.87 Tmp); the high‐temperature tensile strength of LiF decreased very little from 300° to 700°C. This lack of interpenetrability of slip systems in LiF at high temperatures also had a profound effect on the deformation processes, the development of substructure, and the strain‐hardening and fracture characteristics of the material. This work emphasizes the importance of interpenetration of slip not only in the high‐temperature ductility and strain‐hardening processes but also in the maximum tensile strength which ionic crystals develop before fracture.
Phase Diagrams for the Systems MgCl2‐MgF2, CaCl2‐MgF2, and NaCl‐MgF2
Authors: SHARMA RAM A. , JOHNSON IRVING
Published: June 2006

Equilibrium phase diagrams for the systems MgCl2‐MgF2, CaCl2‐MgF2 and NaCl‐MgF2 were determined by differential thermal analysis, thermal analysis, and temperature‐composition equilibrium techniques. Simple eutectics were observed at 78.0±0.5 mol% MgCl2 and 628°±2°C in the MgCl2‐MgF2 system, at 87.5±0.5 mol% CaCl2 and 694°±2°C in the CaCl2‐MgF2 system, and at 95.5±0.5 mol% NaCl and 786°±3°C in the NaCl‐MgF2 system. The phase diagrams determined for these systems were compared with phase diagrams that were computed using Temkin's model. The phase diagrams of the CaCl2‐MgF2 and NaCl‐MgF2 systems were also compared with diagrams that were computed using the expression suggested by Flood et al. for reciprocal systems. The experimentally determined and computed phase diagrams agreed for the MgCl2‐MgF2 system but not for the CaCl2‐MgF2 and NaCl‐MgF2 systems.
Mechanical Relaxations in Mixed Alkali Silicate Glasses: II, Discussion*
Authors: SHELBY JAMES E. , DAY DELBERT E.
Published: June 2006

The internal friction of mixed Li‐Na, Li‐K, Li‐Rb, Li‐Cs, Na‐K, Na‐Rb, Na‐Cs, and K‐Rb silicate glasses is interpreted on the basis of the various explanations proposed for the mixed alkali effect. A direct correlation was found between the mechanical loss peak due to the stress‐induced movement of the alkali ions, i.e. the alkali peak, and the electrical loss properties. The large mechanical loss peak appearing when the alkalis are mixed was attributed to an interaction between dissimilar alkali ions such that an elastic dipole is formed. The absence of a comparable electrical loss peak was interpreted as indicating that the elastic dipole is electrically inactive. In glasses containing equimolar quantities of two alkalis, the activation energy and height of the new loss peak, i.e. the mixed peak, were more closely related to the size difference than to the mass difference of the alkali ions.
Magnetic Properties of Barium Ferrite Formed by Crystallization of a Glass
Authors: SHIRK B. T. , BUESSEM W. R.
Published: June 2006

A glass with composition 0.265 B2O3‐0.405 BaO‐0.33 Fe2O3 (mole ratio) was prepared by a fast‐quenching technique. When it is heat‐treated, this glass exsolves up to ∼45 wt% BaFe12O19 as the only magnetic phase. Magnetic measurements of glasses heated at various temperatures show that superparamagnetic, single‐domain, or multidomain magnetic behavior is present, depending on the thermal history. The volume of a typical superparamagnetic particle (calculated from the magnetic data) is equivalent to that of a sphere 47 Å in diameter. The intrinsic coercive forces of two heat‐treated glasses were independent of temperature at high levels of Hci (2600 and 2900 Oe) from 77° to 300°K. Another heat‐treated glass has an Hci of 5350 Oe at 300°K. Apparently, the coherent rotation model of Stoner and Wohlfarth describes the magnetic behavior of BaFe12O19 very well. The single‐domain critical size for BaFe12O19 was ∼0.5 μm. An attractive feature of this system is that the BaFe12O19 powder can be recovered from the barium‐borate‐rich matrix by leaching with a weak acid.
Reduction of Ions in Glass by Hydrogen
Authors: JOHNSTON W. D. , CHELKO A. J.
Published: June 2006

The reduction by hydrogen of Fe3+, Ce4+, and Sn4+ in soda‐lime‐silica glass was found to be diffusion‐limited in the glass transition temperature range (500°C). The reduction was studied in fibers by chemical analysis and in bulk samples by optical absorption. Reduction to Fe2+, Ce3+, and Sn2+ proceeds by a reaction of the type H2+2(ɛSi‐O)‐+2Fe3+→2Fe2++2(ɛSi–OH). Since the rate of reduction by hydrogen is quite similar for these systems and since reduction cannot be accomplished with CO, it is concluded that hydrogen is the diffusing species. A mechanism is developed in which hydrogen diffuses through the glass until it is trapped by a reducible ion.
Absorption Spectra and Concentration‐Dependent Luminescence of Mn2+ in Silicate Glasses
Authors: TURNER WARREN H. , TURNER† JUDY EASTMAN
Published: June 2006

Glasses activated with Mn2+ exhibit green to red luminescence. A widely accepted model proposes that these colors denote 4‐ and 6‐coordination, respectively, for Mn2+. The luminescence and absorption of Mn2+‐activated silicate glasses were studied; the luminescence changed from green to red with increasing Mn2+ concentration. The difference in the intensities of emission bands with peaks near 520 and 620 nm accounts for the luminescent color. No experimental evidence for a change in coordination from 4 to 6 was found. Exchange‐coupled groupings are proposed to explain red emission in these glasses and possibly in borate and phosphate glasses studied by other workers. Improved resolution of bands and theoretical calculations demonstrate that a covalent‐octahedral Mn2+ species can account for the spectral data for the silicate glasses.
Liquidus Behavior in the Silica‐Rich Region of the System PbO‐SiO2
Authors: CALVERT PAUL D. , SHAW ROBERT R.
Published: June 2006

The liquidus for the system PbO‐SiO2 was determined from 0 to 38 mol% (0 to 70 wt%) PbO. The shape of the liquidus indicates a possible metastable immiscibility region, and the degree of flattening is comparable to that in the system BaO‐SiO2. Immiscibility was confirmed by electron microscopy. The densities and refractive indices of these glasses are reported.
Oxygen Chemical Diffusion Coefficient of Uranium Dioxide
Authors: LAY K. W.
Published: June 2006

The diffusion of oxygen in UO2+α was measured between 600° and 1100°C. Samples with initial O/U values 2.08 and 2.04 were reduced in hydrogen; reduction was monitored continuously by electrical conductivity measurements. The relation between total conductivity and average O/U ratio was derived, and the diffusion coefficients were obtained. The validity of the electrical conductivity vs O/U relation was checked by measuring weight loss during reduction. Diffusion‐controlled kinetics were confirmed by oxygen gradient measurements. The oxygen chemical diffusion coefficient is given by D= 0.5 exp ‐ This equation agrees with previously determined values of the oxygen chemical diffusion coefficient of UO2+α.
Stress and Volume Relaxation in Annealing Flat Glass
Authors: GARDON ROBERT , NARAYANASWAMY O. S.
Published: June 2006

Laboratory simulation of the industrial process of annealing sheet glass has yielded data on the genesis of stresses in initially stress‐free glass. The experimental results differed from expectations based on classical annealing theory in that stresses began to develop in the annealing range even when the glass was being cooled at a constant rate, i.e. even in the absence of any changes of temperature gradients within the glass. Typically, these stresses account for 40% of the total residual stress in glass annealed according to a linear schedule. The remaining 60% are the well‐known thermoelastic stresses that arise later in the annealing process from the decay of temperature gradients in the glass. The stresses observed to arise in glass as it is being cooled at a constant rate are attributed to volume relaxation effects which, in parts of the annealing range, generate stresses rapidly enough that they are not dissipated by stress relaxation. A mathematical model of annealing is proposed that takes account of both stress and structural relaxation. The model fits the experimentally observed evolution of stresses during linear cooling. It also suggests that (with the activation energies of stress and structural relaxation about the same) the actual rate, at any given temperature, of structural relaxation is about 4 times lower than that of stress relaxation.
Gravimetric Determination of Defect Concentrations in NiO
Authors: TRIPP W. C. , TALLAN N. M.
Published: June 2006

Thermogravimetric measurements were made on NiO from 800° to 1100°C over the oxygen pressure range 10−1 to 10−4 atm. On the basis of complementary conductivity measurements showing a P(O2)1/5 oxygen pressure dependence, it is proposed that the predominant defects are described by an electroneutrality condition involving doubly ionized metal vacancies, impurities, and electron holes, 2[V”M]=[FM]+p. It is shown that for this defect model, the weight change relative to a low oxygen pressure reference weight is a measure of the effective vacancy concentration, defined as [V”M]eff≡[V”M]‐≡[FM], and therefore has the same oxygen pressure dependence as the electron hole concentration followed in the conductivity measurements. The expression [V”M]eff=0.168 P(O2)1/5 exp (−0.86±0.15/kT) is derived to express the effective vacancy concentration in NiO. The probable effective impurity content of the specimens used is calculated.
Kinetics of NiCr2O4 Formation and Diffusion of Cr3+ Ions in NiO
Authors: GRESKOVICH C.
Published: June 2006

The reaction kinetics for NiCr2O4 formation and the diffusion of Cr3+ ions into single‐crystal NiO were studied between 1300° and 1600°C in air. The experimental activation energy for NiCr2O4 formation was about 83 kcal/mol. After incubation, NiCr2O4 formed by a diffusion‐controlled process. The origin of pores at the NiO/NiCr2O4 interface is discussed. The concentration profiles of Cr3+ in NiO were linear because the interdiffusion coefficient was directly proportional to the mol fraction Cr3+. Theoretical considerations indicate that the interdiffusion coefficient equals 3/2 the self‐diffusion coefficient of Cr3+, which is rate‐determining. The interdiffusion coefficient at 1 mol% Cr2O3 can be expressed as D̄=4×10−3 exp (−55,000/RT) cm2 s−1.
Diffusion and Internal Friction in Na‐Rb Silicate Glasses
Authors: McVAY GARY L. , DAY DELBERT E.
Published: June 2006

The internal friction and self‐diffusion coefficients of sodium and rubidium ions for (l‐X)Na2O‐XRb2O‐3SiO2 glasses were measured. Diffusion was measured by radioactive isotopes and a thin‐sectioning technique at 350° to 500°C. Internal friction was measured at −140° to 500°C and 0.05 to 6000 Hz. The maximum height for the mixed‐alkali internal friction peak occurs at the composition at which the Na and Rb diffusion coefficients are equal. It is concluded that the mechanism responsible for the mixed‐alkali peak is a coupled, cooperative rearrangement of sodium and rubidium ions, with the slower moving ion controlling the rate of rearrangement. This mechanism should also apply to other mixed‐alkali silicate glasses since the internal friction for these systems is similar.
Thermal Conductivity of Nearly Stoichiometric Single‐Crystal and Polycrystalline UO2
Authors: MOORE J. P. , MCELROY D. L.
Published: June 2006

The thermal conductivities, λ, of single‐crystal and polycrystalline UO2 were measured from 80° to 420°K. The results indicate no observable difference in λ between single‐crystal and polycrystalline UO2, and both materials have broad peaks in λ at ∼220°K. The results were used with literature values to determine the effect of closed porosity on λ. The thermal conductivity of theoretically dense UO2 is described phenomenologically from 80° to 1400°K, where conduction is dominated by the phonon component. The phonon conduction is analyzed by comparison with ThO2. This analysis indicates that the high‐temperature λ is limited by 3‐phonon Umklapp scattering processes. Scattering by the disordered spins associated with the paramagnetic U ions contributes a large temperature‐independent phonon scattering term. This mechanism has a mean free path of about 51 Å, which implies that grain boundaries and impurities have a relatively insignificant effect on the phonon conduction far above the antiferromagnetic‐para‐magnetic transition at ∼ 30°K. This implication agrees with the experimental results.
Microstructure of Titania‐Opacified Porcelain Enamels
Authors: EPPLER R. A.
Published: June 2006

The microstructure of TiO2−opacified porcelain enamels was examined by optical microscopy and by transmission electron microscopy. The mosaic pattern found appears to correspond to the positions of the frit particles from which the enamel was made. Significant differences were observed in the crystallization behavior of adjoining frit particles. There is evidence that rutile grows from frit particle surfaces, whereas anatase is body‐nucleated. The anatase‐to‐rutile inversion is a ripening process rather than a phase transformation. Processes occurring during the firing of a TiO2 enamel include crystallization from single‐phase glass, crystallization from multiphase glass, and a ripening process.
Dynamic and Static Fatigue of Silicate Glasses
Authors: RITTER J. E. , SHERBURNE C. L.
Published: June 2006

Fatigue of silicate glasses was studied using both static and dynamic tests. Static fatigue data for acid‐etched soda‐lime silicate glass determined at 74°F in 50 and 100% rh can be represented by a single universal fatigue curve (UFC). The UFC for acid‐etched glass does not lie on the UFC of Mould and Southwick, which was determined for abraded soda‐lime silicate glass; the acid‐etched glass was less susceptible to static fatigue. The susceptibility of acid‐etched soda‐lime silicate glass to static fatigue differed little from that of pristine E‐glass and fused SiO2 fibers. Dynamic fatigue data for soda‐lime, E, borosilicate, and fused quartz glasses agreed well qualitatively and quantitatively with fundamental crack velocity data for these glasses; the dynamic fatigue theory of Charles was used in the comparison. The theoretical implications of these results are discussed.
Measurement of the Lattice Parameter of Wustite at High Temperatures
Authors: HAYAKAWA M. , COHEN J. B. , REED T. B.
Published: June 2006

The lattice parameter of wustite (Fe2O) single crystals was measured at high temperatures. Plots of both lattice parameter vs composition and lattice parameter vs temperature were linear, and no appreciable changes in slope were detected at the boundaries of the subphases suggested by Vallet and Raccah.
Direct‐Current Conductivity and Iron Tracer Diffusion in Hematite at High Temperatures
Authors: CHANG R. H. , WAGNER J. B.
Published: June 2006

The dc conductivity of natural single‐crystal α‐Fe2O3 was measured as a function of O partial pressure from 10−4 to 1 atm at 950° to 1422°C. The conductivity was independent of O2 partial pressure, indicating that hematite is an intrinsic semiconductor with lattice defect concentrations much lower than the concentration of intrinsic electrons (holes). The activation energy of the dc conductivity was 1.18 eV. The iron tracer (55Fe) diffusion coefficients, measured as a function of O2 partial pressure at 1200° and 1300°C, increased as the O2 partial pressure decreased, with a pressure dependence of ‐0.75; the iron therefore migrates interstitially.
Distribution of A‐Site and B‐Site Vacancies in (Pb,La)(Ti,Zr)O3 Ceramics
Authors: HÄRDTL K. H. , HENNINGS D.
Published: June 2006

It was shown experimentally that A‐site vacancies predominate in La‐substituted lead titanate‐zirconate (PLZT) solid solutions. The formation of B‐site vacancies is favored under increased PbO vapor pressure, but preparation of PLZT‐perovskite phases with B‐site vacancies only is impossible since the increase in the partial pressure of PbO is naturally limited by the condensation of liquid PbO at the grain boundaries of the ceramic.
Strength Degradation and Crack Propagation in Thermally Shocked Al2O3
Authors: GUPTA T. K.
Published: June 2006

Strength degradation and crack propagation in Al2O3 are shown to depend on the initial strength and grain size of the material. The strengths of single‐crystal sapphire and polycrystalline Al2O3 specimens with grain sizes of 10, 34, and 40 μm decreased discontinuously at the critical quenching temperature. In contrast, the strength of polycrystalline Al2O3 with a grain size of 85 μm decreased gradually as the quenching temperature increased. The strength retained after thermal shock and the extent of crack propagation decrease with increasing initial strength and grain size, respectively, in Al2O3.
Mechanics of Pressure Slip Casting
Authors: FENNELLY TERRENCE J. , REED JAMES S.
Published: June 2006

The quantitative mechanics of pressure slip casting an aqueous Al2O3 slip deflocculated with an organic polyelectrolyte were investigated at 50 to 500 psi. The specific resistance, casting rate, and microstructural characteristics of the resultant cakes were especially sensitive to the electrophoretic mobility of the slip. The mechanochemical action of the polyelectrolyte in effecting deflocculation was somewhat different from that of simple ionic electrolytes.
Phase Analysis in Zirconia Systems
Authors: GARVIE RONALD C. , NICHOLSON PATRICK S.
Published: June 2006

Linear calibration curves were developed for determining the content of free ZrO2 in partially stabilized zirconia ceramics by X‐ray diffraction techniques. Two methods were studied. The matrix method, in which free ZrO2 was considered to be distributed in a matrix (the cubic phase), gave approximately equal mass absorption coefficients for the monoclinic and cubic phases. The polymorph technique, in which the cubic phase was considered to be a polymorph of ZrO2 and in which integrated intensities were used, gave the better results.
Thermal Expansion of Nb2O5
Authors: MANNING W. R. , HUNTER O. , CALDERWOOD F. W. , STACY D. W.
Published: June 2006

The high‐temperature thermal expansion of monoclinic Nb2O5 was studied with X‐ray and dilatometric techniques. The X‐ray axial thermal expansion was anisotropic; the mean coefficients in the a, b, and c directions, respectively, were 5.3, 0, and 5.9×10−6°C‐1 from room temperature to 1000°C. It is proposed that this anisotropy causes microcrack formation in sintered polycrystalline samples. The bulk linear thermal expansion of both sintered and hot‐pressed samples was determined with a dilatometer from room temperature to 1200°C. A hysteresis effect between heating and cooling data observed for sintered samples was attributed to the occurrence and recombination of internal microcracks.
Pressure and Temperature Dependence of the Elastic Moduli of Na2O‐TiO2‐SiO2 Glasses
Authors: MANGHNANI MURLI H.
Published: June 2006

Ultrasonic interferometry was used to measure elastic‐wave velocities and moduli in six Na2O‐TiO2‐SiO2 glasses; three glasses contained 20 mol% TiO2 and three 25 mol% TiO2. The elastic moduli and their pressure derivatives varied systematically with the SiO2/Na2O molar ratio of the glasses. In the group of glasses which contained 20 mol% TiO2, dK/dP (K=bulk modulus) decreased linearly from 4.85 to 2.59 as the SiO2/Na2O ratio increased; in the other group, dK/dP decreased from 4.00 to 3.05. Similarly, dμ/dP (μ=shear modulus) decreased with the SiO2/Na2O ratio, but somewhat non‐linearly. The extrinsic and intrinsic contributions to the temperature dependencies of the elastic moduli are evaluated in light of the measured pressure dependencies of these moduli.
Interfacial Reactions and Wetting Behavior of Glass‐Iron Systems
Authors: HOGE CARL E. , BRENNAN JOHN J. , PASK JOSEPH A.
Published: June 2006

Interfacial reactions and enhanced wetting or spreading of Na2FexSi2O5+x and Na2–2xFexSi2O5 glasses on substrates of high‐purity (Marz) and commercial (Armco) iron were observed at 1000°C at low partial pressures of O2 and Na. Reactivity increased with increasing O/Si ratio in the glass, with the purity of the iron, and with decreasing gas pressure.
Effect of Composition on Glass‐Metal Interface Reactions and Adherence
Authors: BRENNAN JOHN J. , PASK JOSEPH A.
Published: June 2006

Reduction‐oxidation reactions and enhanced wetting or spreading of Na2FexSi2O5+x, and Na2NixSi2O5+x glasses on substrates of Fe, Co, Ni, Ni‐Fe, and Ni‐Co were observed at 1000°C at low partial pressures of O2 and Na as the O/Si ratio of the glass increased. When the substrate had a higher oxidation potential than the metal of one of the cations in the glass, e.g. CoO‐containing glass on Fe, metallic precipitates formed by redox reactions under all conditions. A redox reaction based on reduction of the valence of a cation in the glass, e.g. Fe3+ to Fe2+, also occurred. Adherence developed between substrates and glasses containing amounts of substrate oxide, either in the starting composition or formed by redox reactions, approaching saturation.
Calculation and Interpretation of Surface Free Energy of Wetting of E‐Glass by Vapors
Authors: HUANG R. J. , DEMIREL T. , McGEE T. D.
Published: June 2006

The surface free energy of wetting of E‐glass by water and benzene vapors was calculated from Bangham and Razouk's free‐energy equation. The method of Fu and Bartell for determining specific surface area was used to analyze the microstructure. The surface free energies, which were computed from adsorption isotherms obtained at temperatures from 18° to 20°C, had values from ‐235 to ‐254 ergs/cm2 and ‐71.1 to ‐72.4 ergs/cm2 for water and benzene adsorption, respectively, depending on temperature, surface geometry, and sample treatment. The lower affinity of E‐glass for benzene, which resulted in a smaller work of adhesion, suggests that active adhesion of hydrocarbons is impossible in the presence of bulk water. Microstructural analysis indicated that the water‐modified E‐glass surface contains micropores 23 Å in diameter.
Dielectric Properties of Explosively Compacted BaTiO3
Authors: GOSWAMI A. K.
Published: June 2006

Polycrystalline BaTiO3 was explosively compacted to nearly theoretical density, and its dielectric and piezoelectric properties were investigated. The compacted bodies did not exhibit dielectric hysteresis, a Curie point, or piezoelectric properties; their dielectric constant and dissipation factor increased linearly with temperature. The dielectric constant was much lower than those of similar dense bodies obtained by conventional sintering. These results may be interpreted in terms of weak intergranular bonding and increased numbers of defects generated in the shocked material. When explosively compacted bodies were sintered, normal ferroelectric and piezoelectric properties and improved microstructures were obtained.
Relation Between Strength, Fracture Energy, and Microstructure of Hot‐Pressed Si3N4
Authors: LANGE F. F.
Published: June 2006

A fracture mechanics approach was used to investigate the high strength of hot‐pressed Si3N4. Room‐temperature flexural strengths, fracture energies, and elastic moduli were determined for material fabricated from α‐ and β‐phase Si3N4 powders. When the proper powder preparation technique was used, α‐phase powder resulted in a high fracture energy (69,000 ergs/cm2), a high flexural strength (95,000 psi), and an elongated (fiberlike) grain morphology, whereas β‐phase powder produced a low fracture energy (16,000 ergs/cm2), a relatively low strength (55,000 psi), and an equiaxed grain morphology. It was hypothesized that the high strength of Si3N4 hot‐pressed from α‐phase powder results from its high fracture energy, which is attributed to the elongated grains. High‐strength Si3N4 has directional properties caused, in part, by the elongated grain structure, which is oriented preferentially with respect to the hot‐pressing direction.
Cyclic Fatigue of Hot‐Pressed Si3N4
Authors: KOSSOWSKY RAM
Published: June 2006

The cyclic fatigue behavior of two grades of hot‐pressed silicon nitride was investigated. Flat, cantilever‐type specimens were tested at temperatures up to 1300°C, in air, where the load was applied by an eccentric driver rotating at 1800 rpm, with a zero mean stress. The lifetime of the lower purity material at temperatures up to 1200°C was controlled by a stress corrosion mechanism. Above 1200°, and for both grades of material, plastic deformation, probably by grain boundary sliding, was rate controlling.
Effective Thermal Conductivity for Heat Transfer Through Semitransparent Solids
Authors: ANDERSON EDWARD E. , VISKANTA RAYMOND
Published: June 2006

The steady‐state effective thermal conductivity of fused quartz was examined analytically and experimentally for two classes of boundary conditions. These results are compared with several effective conductivity models which have been suggested for semitransparent solids. Mean effective conductivity results illustrate the effect of sample thickness, temperature, and boundary conditions as well as serving to evaluate the
Residual Stresses in Machined MgO Crystals
Authors: G. E. BERNAL , KOEPKE B. G.
Published: June 2006

The residual stresses introduced in MgO crystals by grinding on {100} surfaces in 〈100〉 directions were measured using photoelastic techniques. Grinding was conducted with two wheels; a 100‐grit diamond wheel removed material by brittle fracture, and a 46‐grit alumina wheel caused plastic flow and burnishing. Both wheels introduced a discrete, highly deformed layer adjacent the machined surface. In all cases the machined surfaces were under a residual tensile stress which became compressive within the deformed region. Beneath the deformed layer the residual stress patterns were distinctly different. In crystals ground with the alumina wheel the stresses became tensile again within 0.5 mm of the ground surface, whereas the subsurface stresses in crystals ground with the diamond wheel remained compressive to distances ≥1 mm. These residual stress distributions are discussed in terms of a simple model based on the superposition of mechanically and thermally induced stresses.
Subgrain Boundaries in MgO
Authors: NARAYAN J.
Published: June 2006

The structure of subgrain boundaries in as‐grown MgO was characterized by transmission electron microscopy. The types of subboundaries which occur quite frequently are (1) a pure tilt boundary consisting only of ½ [101]‐type dislocations (A set); (2) a tilt boundary consisting mainly of ½ [101] (A set) and ½ [011] (B set) dislocations; and (3) a mixed boundary with ½ [101] (A set), ½ [011] (B set), and ½ [01] (C set) dislocations. At the nodes the following dislocation reactions occur: ½ [011]+½ [10] =½ [110] and ½ [10]+½ [101] = [100]. The precipitation of impurities at the subboundaries and their role in pinning the subboundaries are discussed.
Reduction of SiO2 by Molten Al
Authors: PRABRIPUTALOONG K. , PIGGOTT M. R.
Published: June 2006

The bulk reaction of Al and SiO2 was reexamined in light of results of thin‐film work. When the bulk reaction was conducted under vacuum in such a way that the oxide film on the Al was almost completely absent, the reaction started immediately and proceeded at a rate more rapid than that observed by previous workers, who conducted the experiment in air at atmospheric pressure. Results obtained at 700° to 820°C indicate that the activation energy for the reaction is 42±5 kcal/mol when oxide films are absent from the surface of the molten Al.
Defect Structure of NiO‐CoO Solid Solutions
Authors: STIGLICH J. J. , WHITMORE D. H. , COHEN J. B.
Published: June 2006

Measurements at high temperature of integrated intensities of Bragg peaks were used to examine the defect structure in two NiO‐CoO solid solutions. The results indicate that the concentrations of vacant cation sites at 1100° to 1500°C are 4 to 10% and the tetrahedral occupations 2 to 5%. The concentration of these defects increases with temperature and partial pressure of O2. The mean‐square displacements of oxygen ions and cations increase with temperature and CoO concentration.
Thermal‐Shock Damage in SiC
Authors: COPPOLA J. A. , BRADT R. C.
Published: June 2006

Two silicon carbides with different fracture surface energies were subjected to increasingly severe thermal shock; the damage was monitored by changes in the specific damping capacity, elastic modulus, and fracture strength. The fracture strength followed predicted trends, but the strength losses did not correlate with the changes observed in damping and modulus. The differences in thermal‐shock resistance of the materials were related to the fracture surface energy; the body with the higher fracture energy had superior resistance to thermal‐shock damage.
Reaction of Cyanogen with SiO2 Surfaces
Authors: RUTTENBERG F. E. , LOW M. J. D.
Published: June 2006

Infrared spectra (4000 to 1300 cm−1) of SiO2 specimens with high surface areas which had been exposed to (CN)2 at 25° to 600°C were recorded. Sorption was slight at 25°, but extensive reaction occurred at higher temperatures. The main effects of the sorption were the decrease of the 3747 cm−1 band of surface Si‐OH groups and the buildup of a prominent band at 2310 cm−1 thought to be caused by surface Si‐NCO species rather than Si‐OCN species. The data suggest that, in addition to the isocyanate formed in the dehydroxylation reaction, HCN produced in that reaction led to the formation of Si‐CN and Si‐OH
Environment‐Sensitive Hardness and Machinability of Al2O3
Authors: WESTWOOD A. R. C. , MACMILLAN N. H. , KALYONCU R. S.
Published: June 2006

The influences of water, toluene, and n‐alcohols on the pendulum hardness of Al2O3 monocrystals and on the ease of drilling of mono‐ and polycrystalline Al2O3 were studied. Adsorption‐induced increases in pendulum hardness were produced by certain alcohol environments; these increases resulted in rates of drilling with diamond‐studded core bits of up to 10 times those measured under water. A correlation between pendulum hardness, machinability, and surface charge (as indicated by ζ‐potential measurements) was established and revealed that Al2O3 is hardest and most effectively drilled with a diamond core bit at its zero point of charge. The possible use of this correlation in developing more cost‐effective and ecologically viable cutting fluids for the machining of Al2O3 is discussed.
Effect of Small Additions of Al2O3 and Ga2O3 on the Immiscibility Temperature of Na2O‐SiO2 Glasses
Authors: TOPPING J. A. , MURTHY M. K.
Published: June 2006

Alumina and gallia were substituted separately for Na2O in amounts of 0.2, 0.5, 1.0, 1.5, 2.0, and 3.0 wt% in three Na2O‐SiO2 glass compositions (82, 84, and 86 wt% SiO2) within the immiscibility region. The immiscibility regions for each system extend to ∼1.5 mol% of the added oxide. In general, the addition reduced the immiscibility temperature (Tm), but at the edge of the immiscibility region (82% SiO2) the Na2O loss effect initially increased Tm. A structural model of the miscibility of Al2O3 added to silicate glasses is presented.
Conditions for Formation of ErB6
Authors: MAR RAYMOND W.
Published: June 2006

Erbium hexaboride was synthesized; it is a high‐temperature phase, stable over a limited temperature range and unstable with respect to dissociation to ErB4 and ErB12 at T<1975°C, although the lower temperature limit has not been determined precisely. Relatively slow cooling through its stable temperature range is required for the formation of ErB6.
Kinetics and Mechanism of the Thermal Decomposition of Si3N4
Authors: BATHA H. DEAN , WHITNEY E. DOW
Published: June 2006

The kinetics of the thermal decomposition of silicon nitride, Si3N4(s)→3Si(l)+2N2(g), were studied from 1490° to 1750°C using a static system. The reaction was followed by measuring the rate of increase of N2 pressure in the system as a function of time. In the initial stages, the decomposition followed first‐order kinetics, with the rate constant expressed as:

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In the later stages, the experimental data followed the Jander solid‐state kinetic law, with the Jander rate constant given by:

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The effects of excess Si and of Ar and N2 atmospheres on the reaction kinetics are also reported.
Dislocation Etchant for Beryllium Oxide
Authors: EHMAN MICHAEL F. , AUSTERMAN S. B.
Published: June 2006

A hydrochloric acid chemical etchant for BeO was refined and evaluated. The etchant, when used for 20 min at 120°C on chemically polished surfaces, produces distinctive pits at dislocations intersecting the (0001) and (101) surfaces. Correspondence of etch pits and dislocations was inferred by comparing the enlargement of pits with etching time and the constancy of pit density with continued etching. On {1010} surfaces, the etchant is not sensitive to sites of defect emergence and hence leaves a relatively flat, featureless surface. The etch rates and activation energies are given for {0001}, {1010}, and {101} surfaces. The reaction mechanism is discussed.