Showing papers in "Journal of the American Ceramic Society in 1968"
TL;DR: In this paper, the thermal behavior of amorphous hydrated zirconium oxide and its coprecipitates with other oxides was studied and a relation with the high-temperature solid solution was established.
Abstract: The thermal behavior of amorphous hydrated zirconium oxide and its coprecipitates with other oxides was studied. Solid solution with a limit of solubility seems to exist in the amorphous coprecipitates. A relation with the high-temperature solid solution was established. The structure of the amorphous zirconia was studied by X-ray and neutron diffraction; a thin plate model related to the structure of tetragonal zirconia is proposed. Heating the precipitates in an oxygen-free atmosphere produced a black nonstoichiometric oxide and stabilization of the tetragonal form.
316 citations
TL;DR: In this paper, the authors measured the contact angles of aluminum drops on sapphire measured under vacuum conditions from 660° to 1250°C and found that van der Waals bonding then existed at a compound interface.
Abstract: Contact angles of aluminum drops on sapphire measured under vacuum conditions from 660° to 1250°C generally fell into three ranges. Large obtuse contact angles indicating interfacial energies greater than either of the two surface energies were obtained up to about 900°C; van der Waals bonding then existed at a compound interface. In the intermediate range, contact angles were 90° or slightly greater indicating a common interface with an energy, sγl, greater than sγg but less than lγg. Acute contact angles indicating a sγl less than sγg and greater than lγg occurred above about 950°C because of the formation of a high temperature complex surface structure with sγg > lγg. A hydroxylated sapphire surface has a lower sγg which increases with gradual dehydroxylation and conversion to the high temperature surface structure with a corresponding change in contact angle through the three ranges. Chemical bonding existed in the latter two ranges. Reactions occurred between Al and the sapphire surface to form volatile species at contact angles less than 90°. Molten Al normally has an oxide coating the effect of which appears to be removed at about 870° C.
187 citations
TL;DR: In this article, the densification and grain growth rate of pure MgO powder compacts are measured between 1450 and 1650°C in air and applied to the lattice diffusion model to calculate diffusion coefficients in fair agreement with the directly measured diffusion coefficients for magnesium.
Abstract: The densification rate and grain growth rate of pure MgO powder compacts are measured between 1450 and 1650° C in air. Densification rate in a semilog plot appears to be linear up to about 94% of the theoretical, followed by marked nonlinearity. The time dependence of grain growth is 1/2 at the beginning and then decreases considerably with further sintering. Application of lattice diffusion model to the densification and grain growth data gives calculated diffusion coefficients in fair agreement with the directly measured diffusion coefficients for magnesium; they are also in fair agreement with the literature value of the diffusion coefficients calculated from various other kinetic processes in MgO.
183 citations
TL;DR: In this article, the solubility of MgTiO3 in Al2O3 was measured as 1.10 × loW4, 3.00 × 10”4, 6.80 × 10−4, and 1.40 × 10-3 at 1530, 1630°, 1730° and 183O°C, respectively.
Abstract: On heat treatment in air the solubility of MgO or TiO2, in Al23 is too small to detect by lattice parameter shifts. The solubility of MgTiO3 in Al2O3 in air increased to the measured values, expressed as atomic fractions Mg:A1or Ti:A1of0.82 × lo-2, 1.43 × 10-2, and 1.75 × 10-2 at 1250°, 1650°, and 1850°C, respectively. In 1 atm hydrogen the TiO2 solubility expressed as the atomic fraction Ti:A1 is 0.55 × lo-2, 0.75 × 10W2, 1.15 × 10-2, and 1.50 × 10p2 at 1400°, 1500°, 1600°, and 1700°C, respectively. The increased solubility in H2 was attributed to reduction of the titanium ion. The solubility of MgO in A12O3 in vacuum (0.3μ)expressed as the atomic fraction Mg:A1 was measured as 1.10 × loW4, 3.00 × 10”4, 6.80 × 10–4, and 1.40 × 10-3 at 1530°, 1630°, 1730°, and 183O°C, respectively. These contents did not cause an observable change in lattice parameter, but a slight change was observed when MgO was dissolved in A12O3 in a hydrogen atmosphere.
155 citations
TL;DR: In this paper, it was shown that the microplastic effects produced by pressure of hard, sharp points on glasses do not occur by plastic flow, but by densification, and that the technology of glass cutting is dependent on residual stresses associated with densification.
Abstract: It is proposed as a working hypothesis that the many so-called microplastic effects produced by pressure of hard, sharp points on glasses do not occur by plastic flow, but by densification. An interferometric technique is illustrated, by means of which the existence of densification can readily be demonstrated and its magnitude estimated. It is concluded that the “hardness” number of glasses is best interpreted as a measure of the critical stress for yield by densification; that the hardness number has no necessary relation to tensile strength; and that the technology of glass cutting is dependent on residual stresses associated with densification.
145 citations
122 citations
TL;DR: The monoclinic-tetragonal inversion was investigated by DTA and high-temperature X-ray diffraction analysis using are-melted samples which had been annealed and quenched.
Abstract: The ZrO2-HfO2 system was investigated by metallo-graphic, X-ray diffraction, and microprobe analysis using are-melted samples which had been annealed and quenched. The monoclinic-tetragonal inversion was investigated by DTA and high-temperature X-ray diffraction analysis. Results reveal that zirconia and hafnia are completely miscible in all proportions in the binary system. Within experimental error, the melting points of the compositions lie roughly on a straight line connecting the melting points of oxides. There is a continuous increase in the monoclinic-tetragonal inversion temperature as the composition moves from ZrO2 to HfO2. The lattice parameters of the monoclinic phase follow smooth curves which have a negative deviation from Vegard's law.
118 citations
TL;DR: In this paper, a simple rapid quenching device was used to investigate the extent of liquid-liquid immiscibility in the system BaO-SiO2, and a metastable miscibility gap was found with an upper consolute point at about 10 mole percent BaO and 1460C.
Abstract: : A simple rapid quenching device was used to investigate the extent of liquid-liquid immiscibility in the system BaO-SiO2. A metastable miscibility gap was found with an upper consolute point at about 10 mole percent BaO and 1460C. Bulk glass samples of different compositions and heat treatments were examined by direct transmission electron microscopy to determine the phase separation morphology. At low BaO contents the separation was characterized by spherical barium-rich particles in a silica-rich matrix. For compositions near the center of the gap, the structure consisted of two phases, continuously interconnected throughout the bulk of the glass. At higher BaO contents spherical silica-rich particles were found in a barium-rich matrix. The dependence of the morphology on quench rate and heat treatment was investigated. Predictions of other authors concerning the occurrence of BaO-SiO2 immiscibility are compared with the present results. (Author)
117 citations
TL;DR: In this paper, a general application of the theoretical expressions to composite materials in which the included phase is contained at low concentrations has been proposed, where the shape of the included phases is considered as well as the moduli of the individual phases.
Abstract: The description of the elastic behavior of composite materials by mathematical expressions presently in the literature is restricted by the microstructural models on which they were based. An extension has been made to one of these expressions in which the shape of the included phase is considered as well as the moduli of the individual phases. The results allow a more general application of the theoretical expressions to composite materials in which the included phase is contained at low concentrations.
110 citations
TL;DR: The phase boundaries of subliquidus immiscibility in the lithium, sodium, potassium, rubidium, and cesium borate systems were determined by direct-transmission electron microscopy.
Abstract: The phase boundaries of subliquidus immiscibility in the lithium, sodium, potassium, rubidium, and cesium borate systems were determined. Two-phase structures were developed in thermal gradients and examined by direct-transmission electron microscopy. No opalescence was observed. Microstructures were of the order of a few hundred angstroms. The extent of immiscibility in each system was determined by the approximate intersection of the immiscible phase boundary with the glass transition region.
104 citations
TL;DR: In this paper, the authors developed a basis for discussing glass properties which has features in common with standard “actual vs. ideal” treatments of physicochemical behavior, by defining thermodynamically an ideal state for the glass and discussing the states of the actual glasses in terms of their departure from ideality.
Abstract: This two-part paper develops a basis for discussing glass properties which has features in common with standard “actual vs. ideal” treatments of physicochemical behavior, by defining thermodynamically an ideal state for the glass and discussing the states of the actual glasses in terms of their “departures from ideality.” The glass transition, which freezes the state of the actual glass, is seen as the consequence of the progress of the liquid toward the ideal state, which, for kinetic reasons, is unattainable. The single complexion limit of the Gibbs-DiMarzio treatment for chain polymers and a minimum volume zero excess entropy condition related to random close packing for simple liquids are seen as complimentary descriptions of the ideal state, which also sets the thermo-dynamic low-temperature limit to the liquid state. Glasses formed from simpler molten salt and concentrated aqueous solution systems appear to approach the ideal state and thus provide a behavior pattern against which departures from ideality in the more complex silicate and borate glasses of practical interest may be assessed. In part I general aspects of the problem posed by the glass transition phenomenon are discussed, a dynamic interpretation for simple glasses in terms of the state of phonon excitation of the glassy solid is conjectured, and the concepts of ideal and nonideal (practical) glasses and glass transitions are elucidated from consideration of thermodynamic and kinetic factors involved in the volume relaxation of liquids toward the glassy state. Attention is given to units for describing departures from ideality to permit comparisons among different systems. The limited data for inorganic glasses are examined. Departures from ideality, as usually found in the physicochemical comparison of “actual” with “ideal” behavior, are attributable to specific interactions among the particles of the system, but magnitudes also depend on heat capacity changes. The former factor reaches a maximum in vitreous SiO2 which thus may be one of the least ideal of glasses.
TL;DR: In this article, a subliquidus miscibility gap was estimated for the B2O3-SiO2 system using the phase diagram and a simple solution model, showing a consolute temperature of 520°C.
Abstract: Using the phase diagram and a simple solution model, a subliquidus miscibility gap was estimated for the B2O3-SiO2 system. The predicted coexistence boundary, showing a consolute temperature of 520°C, was flat and symmetrical and extended across the complete binary. Gradient furnace heat treatments of selected compositions in this system resulted in phase separation which corresponded closely to the coexistence boundary initially predicted. Calculations and preliminary experimental results indicate that temperatures and compositions exist wherein metastable three-liquid immiscibility occurs in R20–B203-SiO2systems.
TL;DR: In this paper, the authors discussed the fracture of thermally tempered glass in terms of both the stored elastic strain energy in the glass due to tempering and the elastic energy release rate Of crack extension, 9.
Abstract: The fracture of thermally tempered glass is discussed in terms Of both the stored elastic strain energy in the glass due to tempering and the elastic energy release rate Of crack extension, 9. The latter is used to obtain an analytical correlation between the maximum tensile stress and the average particle size at time of fracture. The theoretical predictions are supported by experimental data obtained for various glass thicknesses and temper levels.
TL;DR: In this paper, the thermal expansion behavior of synthetic β-spodumenes and several β-Spodumene-silica solid solutions was studied using high-temperature X-ray diffraction techniques.
Abstract: Synthetic β-Spodumene and several β-Spodumene-silica solid solutions were prepared, and their thermal expansion behavior was studied using high-temperature X-ray diffraction techniques. Data indicate that all β-Spodumenes are characterized by a pronounced anisotropy of thermal expansion much the same as that of the silica polymorph keatite. Anisotropy increases slightly and the volume expansion decreases as the compositions become richer in SiO2. Specimens with more than 80.8 wt% SiO2 at 130O°C and 1 atm contain P-cristobalite along with β-Spodumene. The lattice parameters of β-Spodumene compositions throughout the solid solution range were determined. The structural aspects of the anisotropy of thermal expansion are discussed.
TL;DR: In this article, the theory of grain growth in the presence of a liquid phase was examined using modifications of equations derived for coalescence of solid particles widely dispersed in a liquid, and the interrelation of grain size, temperature, and time was in agreement with that predicted by the theory.
Abstract: The theory of grain growth in the presence of a liquid phase is examined using modifications of equations derived for coalescence of solid particles widely dispersed in a liquid. Although the grain diameter-time relation can still be represented by d3=kt, the absolute growth rates are increased as the amount of liquid is decreased. The grain growth kinetics in UO2 compacts containing 0.5 wtyo A12O3 were studied for temperatures between 1960° and 2200°C. The interrelation of grain size, temperature, and time is in agreement with that predicted by the theory.
TL;DR: In this article, the interrelation of hardness, modulus of elasticity, and porosity was investigated in four gypsum systems, and it was shown that intergrowth and interlocking of crystals significantly affect mechanical behavior.
Abstract: The interrelation of hardness, modulus of elasticity, and porosity was investigated in four gypsum systems. Results suggest that intergrowth and interlocking of crystals significantly affect mechanical behavior, at least hardness and modulus of elasticity, E. In addition, both properties are related to porosity, p. This relation can be described empirically by the exponential expression E = Eo exp (— p).
TL;DR: In this paper, the wettability of sapphire single crystals by liquid copper which contained oxygen added as cupric oxide was investigated using the sessile drop technique in vacuum at 1230°C.
Abstract: The wettability of sapphire single crystals by liquid copper which contained oxygen added as cupric oxide was investigated using the sessile drop technique in vacuum at 1230°C. Additions of cupric oxide to copper, varying from 1 to 72% of copper weight, resulted in rapid chemical reaction at the solid-liquid interface with a significant reduction of the contact angle, the final value being dependent on the oxygen in the system. In all cases the interfacial product was CuAlO2. A linear relation between the fourth power of the basal radius of the molten drop and the amount of oxygen present was observed. The initial stage of the reaction could be explained by the formation of a Cu2O layer at the interface, followed by reaction between Cu2O and Al2O3 to form CuAlO2.
TL;DR: In this article, the authors analyzed the temperature dependence of the shear spectrum in terms of a distribution of activation energies and found that activation energies at low temperatures are smaller than the activation energy in the Arrhenius region.
Abstract: Ultrasonic shear and longitudinal measurements were made in Bz03 from 650° to 1000° C. From these data both the shear and volume relaxation time spectra were determined. The spectra had the same temperature dependence, although the volume spectrum was always broader than the shear spectrum. The shear relaxation process can be represented by a single relaxation time above 800° C in the region where the shear viscosity is Arrhenius. Both processes exhibit an increasingly broad distribution of relaxation times in the non-Arrhenius region. The temperature dependence of the shear spectrum was analyzed in terms of a distribution of activation energies. A surprising conclusion of this study is that activation energies at low temperatures are smaller than the activation energy in the Arrhenius region.
TL;DR: In this paper, the cubic field was widened when CaCO2 was substituted for CaO as a reagent, probably because of the formation of an intermediate active oxide, which may shed light on some of the discrepancies in the literature.
Abstract: The range of existence of the cubic phase in the system CaO-ZrO2 was determined at temperatures from 1300° to 1700°C, using the lattice parameter method. This technique could not be used at higher temperatures because of anomalous changes in the lattice parameter. The possibility of the existence of a compound, CaZr4O9, occurring at 20 mole % CaO, was inferred from X-ray data. The (hypothesized) compound appeared to undergo a phase transformation at about 1650°C. The cubic field was widened when CaCO2 was substituted for CaO as a reagent, probably because of the formation of an intermediate active oxide. This widening of the field may shed light on some of the discrepancies in the literature.
TL;DR: In this article, the authors used the technique of vapor deposition to obtain homogeneous glass films of several BaO-SiO2 compositions in the region of the metastable miscibility gap.
Abstract: : The technique of vapor deposition was used to obtain homogeneous glass films of several BaO-SiO2 compositions in the region of the metastable miscibility gap. The films were electron beam heated in the electron microscope and the process of phase separation was observed. At low BaO contents, the separation was characterized by the appearance of discrete, amorphous, second-phase particles. For compositions near the center of the miscibility gap, the separation process resulted in two continuously interconnected phases similar to those found in the corresponding bulk glasses. In the thinnest of these films the process was observed to proceed by the coalescence of isolated particles into the interconnected second-phase submicrostructure. At high BaO contents, rapid crystallization of the films prevented study of the separation process. Two processes which could lead to the coalescence of discrete second-phase particles into an interconnected submicrostructure are discussed. It is suggested that coalescence may take place when either of these processes results in the particles approaching within some small distance of each other. The results indicate that observations of final phase-separated morphologies are inadequate for specifying the processes by which those morphologies arose. (Author)
TL;DR: In this article, it is shown that a glass may consist of sol and gel portions, the complexity and relative proportions of which vary with the nature of the cation and the silica content.
Abstract: Liquid silicates, in common with phosphates and probably other oxygen-containing inorganic polymers which are stable at high temperatures, contain in general a multitude of anionic species ranging in size and complexity from simple “monomeric” groupings such as SiO44− and P043− to continuous, cross-linked networks of infinite molecular weight. The average size and distribution of these species in binary systems may be inferred, at least approximately, from thermodynamic data in combination with polymer theory on the assumption that the activity coefficients of the constituents are arrayed in geometric series. This is equivalent to assuming ideal mixing of polymeric segments. As anticipated, deviations from the theory become significant at the gel point, which varies with the nature of the cation. The significance of these concepts in relation to the constitution of glasses is discussed. In particular, it is indicated that a glass may consist of sol and gel portions, the complexity and relative proportions of which vary with the nature of the cation and the silica content. In theory, the ion SiO44− is the most abundant single species of discrete silicate ion at all silica contents.
TL;DR: In this paper, an extensive solid solution was observed in the system Pb(Sc1/2/,Nb 1/2,1-x,Tix,O3) consisting of the rhombohedral phase with a small amount of the tetragonal phase present.
Abstract: Extensive solid solution was observed in the system Pb(Sc1/2/,Nb1/2,)1-x,Tix,O3. In the range 0 ≤ x ≤ 0.425 a rhombohedral ferroelectric phase was stable at 25° C. In the range 0.45 ≤ x ≤ 1.00 a tetragonal ferroelectric phase was stable at this temperature. The phase diagram of the system below 500° C strongly resembles that of PbZrO3−PbTiO3. The compound Pb(Sc1/2Nb1/2)O3 exhibited rhombohedral perovskite cell symmetry below the ferroelectric ↔ paraelectric transition temperature, and the angle a was acute. The radial coupling coefficient was 0.46 for the composition Sc1/2Nb1/2)0.575Ti0.4250O3. At 25°C this composition consisted primarily of the rhombohedral phase with a small amount of the tetragonal phase present. The ferroelectric ↔ paraelectric transition occurred over a temperature range in the rhombohedral phase field. The spontaneous polarization was finite at temperatures considerably above the temperature of the permittivity maximum for a given rhombohedral solid solution.
TL;DR: In this paper, the authors measured the diffusion of oxygen in monocrystalline ScaO3, YzO3 and Dy,O2, HosO3 with a thermobalance technique and found that large diffusion coefficients and fairly low activation energies were found for this process.
Abstract: The diffusion of oxygen in monocrystalline ScaO3, YzO3, Dy,O2, HosO3, Er2O3, Tm2O2, and Lu2O3 was measured by a thermobalance technique. The reoxidation of partially reduced crystals of these materials was treated as a diffusion-controlled process with a moving boundary. Large diffusion coefficients and fairly low activation energies were found for this process, in agreement with a proposed migration mechanism which involves the inherently defective anion sublattice of these materials.
TL;DR: In this article, the kinetics of crystallization of Li2Si2O5 from glasses in the Li2O-SiO2 system were studied using quantitative X-ray diffraction.
Abstract: The kinetics of crystallization of Li2Si2O5 from glasses in the Li2O-SiO2 system were studied using quantitative X-ray diffraction. Analysis of the data using the Johnson-Mehl-Avrami equation showed that crystallization occurred through the nucleation and growth of rods. The spherulitic nature of the crystals was substantiated by petrographic examinations of the partially crystalline glass. Analysis of the temperature dependence of the crystallization rate using a modification of the Johnson-Mehl-Avrami equation showed that the activation energy for nucleation was a function of composition and thermal treatment.
TL;DR: In this paper, a small amount of Ba or Sr is substituted for Pb in Pb(Mg1/3 Nb2/3)O3-PbTiO3 -Pb2rO3, and the morphotropic boundary and the compositions which show the highest planar coupling coefficient and dielectric constant shift slightly toward the decreasing Pb TiO3 content.
Abstract: When a small amount of Ba or Sr is substituted for Pb in Pb(Mg1/3 Nb2/3)O3-PbTiO3-Pb2rO3, the morphotropic boundary and the compositions which show the highest planar coupling coefficient and dielectric constant shift slightly toward the decreasing PbTiO3 content. The tetragonality of Pb(Mg1/3Nb2/3)O3-PbTiO3 and Pb(Mg1/2 Nb2/3)-O3-PbTiO3-PbZrO3 ceramics decreased with increasing Ba or Sr content. The lattice parameter (α axis) in the rhombohedral or pseudocubic phase increased with the increase of Ba but decreased with the increase of Sr substitution. Although the Curie temperature was lowered with the increase of Ba or Sr, the dielectric constants of the ceramics were increased. The dielectric and piezoelectric properties of the ternary compositions near the morphotropic boundary were improved through selection of sub-stituent and base composition. A planar coupling coefficient of 0.66 and a low Young's modulus were obtained with substitution of 5 mole % Ba. A dielectric constant greater than 3500 and a planar coupling of 0.63 can be obtained by substituting 5 mole % Sr.
TL;DR: In this article, the Dorn method was used to measure the activation energy of creep in the initial stage of sintering uranium dioxide in hydrogen from 700° to 850°C. The activation energy was approximately 100 kcal/mole.
Abstract: The Dorn method, most commonly used to measure the activation energy of creep, was used to study the initial stage of sintering uranium dioxide in hydrogen from 700° to 850°C. The activation energy was approximately 100 kcal/mole. This result agrees with the value determined from analysis of isothermal shrinkage curves in the same temperature interval.
TL;DR: The structural, dielectric, and piezoelectric properties of the solid solution (Na1-x,Lix,NbO2) were studied in this article.
Abstract: The structural, dielectric, and piezoelectric properties of the solid solution (Na1-x,Lix,)NbO2 were studied. Solid solution ceramics with x values up to 0.14 occur as a single phase. The phase diagram from 0° to 600°C is given. The low-temperature phase has a perovskite pseudo-monoclinic structure and inverts to a pseudotetragonal structure at a temperature that decreases with increasing x. The high-temperature phase is pseudocubic, and the minimum transition temperature from the pseudotetragonal to the pseudocubic structure is 350° C near x= 0.04. Anomalies in the dielectric constant vs. temperature curve agree well with the transition temperatures, although no anomaly was observed at the temperature of transition from the pseudotetragonal to the pseudocubic phase when x was less than 0.06. Lithium ions in the system facilitate the transformation from the antiferro-electric to the ferroelectric state produced by applying an electric field. A new ferroelectric phase becomes stable when x is greater than 0.07. Poled ferroelectric specimens had a planar coupling coefficient of 0.232, a dielectric constant of 220, and a frequency constant of 3352 kc-mm. The piezoelectric properties disappear not at the transition temperature but at the temperature at which strain exhibits an anomaly when x is greater than 0.07. A perovskite phase with a pseudorhombohedral subcell exists as an intermediate phase for x greater than 0.10, the exact value depending on the preparation method. The phase can be easily converted to pseudomonoclinic when the ceramic is fired at 1180° to 1220°C.
TL;DR: In this paper, the microstructure of Sic from methyltrichlorosilane in a fluidized bed was studied over a range of deposition temperatures, carrier gas flow rates, and reactant fluxes.
Abstract: Vapor deposition of Sic from methyltrichlorosilane in a fluidized bed and the microstructure of the deposit were studied over a range of deposition temperatures, carrier gas flow rates, and reactant fluxes. The rate-determining factor for the deposition of Sic was the rate of supply of reactant. The microstructure of vapor-deposited Sic was primarily dependent on the deposition temperature; however, carrier gas flow rate and reactant flux had a secondary influence on microstructure. At low temperatures and high carrier gas flow rates, laminar deposits containing excess silicon were produced. At higher temperatures and lower carrier gas flow rates deposits were characterized by faulted columnar grains. The grain diameter increased from about LP at 1400°C to about 15 μ at 1800°C. The grain size also increased, but less markedly, with increasing reactant flux. The deposits characterized by columnar grains were predominantly β-Sic with traces of a-SiC and excess carbon.