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doi: 10.1111/j.1151-2916.1966.tb13299.xpmid: N/A
Experimental data on the physical solubility of gases in fused silica are presented. A “free” volume for fused silica was calculated from these solubilities and was compared to the free volume calculated by other methods. The relation of this free volume to the molecular structure of fused silica is also discussed.
doi: 10.1111/j.1151-2916.1966.tb13300.xpmid: N/A
Values for the physical solubility of nitrogen as well as for the content of chemically dissolved nitrogen in glass melts are given. The form in which the nitrogen is present in the glass melts is discussed and an attempt is made to explain chemical interaction between nitrogen and the glass melt. The dependence of the amount of physically or chemically absorbed nitrogen on the nature of the furnace atmosphere is shown. The results offer an explanation for the presence of nitrogen often observed in bubbles of commercial glasses.
doi: 10.1111/j.1151-2916.1966.tb13301.xpmid: N/A
The solubility of sulfur trioxide in sodium silicate melts was determined from 1150° to 1250°C by equilibrating melts in gas mixtures of known contents of sulfur dioxide and oxygen. Sulfate forms according to the reactions: O2‐+ SO2+ 1/2O2= O2‐+ SO3= SO42‐. The data obtained at 1200°C were interpreted by the linear equation: log(SO42‐) = log(Pso2½Po21/2) + log Y in which Y is a function of the soda/silica ratio. A series of parallel lines was obtained. Relative free oxygen ion activities calculated for 1200°C were in good agreement with theoretical values calculated from the thermodynamic model of Toop and Samis.
doi: 10.1111/j.1151-2916.1966.tb13302.xpmid: N/A
The solubility of water vapor at 750° to 1050°C was determined for alkali borate melts containing 0 to 40 mole % Li2O, Na2O, or K2O. In all cases the solubility in these melts is linearly proportional to the square root of the H2O partial pressure. At pH2O = 1 atm and T= 900°C, o.5 to 2.2 mole % H2O are dissolved in the melts in equilibrium. In the potassium borate melts a minimum of solubility was observed at about 25 mole % K2O; in the sodium borate melts the minimum was at 35 to 40 mole % Na2O. In the lithium borate melts a minimum of solubility was not reached in the range of compositions investigated. These results are discussed in terms of a concept for the acid‐base properties of melts and glasses in which the position of the solubility minimum corresponds to the “neutral point” of an acidity‐basicity scale. Some corroborating qualitative observations concerning the evaporation of components from the glass melts and the chemical resistivity of the corresponding solid glasses are discussed.
CHAKLADER, A. C. D.; McKENZIE, L. G.
doi: 10.1111/j.1151-2916.1966.tb13303.xpmid: N/A
The temperature, pressure, and time dependence of bulk density and the compressive strength of clay and boehmite compacts subjected to reactive hot‐pressing were determined. The strength and the bulk density are linearly related to the extent of the dehydroxylation reaction which occurs during reactive hot‐pressing. In decomposition reactions the reactivity (for interparticle bond formation) and mobility (for densification) may result from the broken bonds and resultant unsatisfied valence links produced by the reaction. On the basis of this postulation, the following empirical relation, correlating the functional relation between strength or density and temperature and pressure was obtained: Application of this equation to the data obtained experimentally produced energy values, for both densification and interparticle bonding, which are much less than that of the activation energy or the enthalpy of the reaction involved. The different energy values for interparticle bonding and densification are believed to indicate different controlling modes for these processes.
doi: 10.1111/j.1151-2916.1966.tb13304.xpmid: N/A
A high‐temperature X‐ray diffraction study of a high‐purity PbZrO3 specimen at 25° to 236°C is reported. The symmetry of the perovskite sub‐cell of PbZrO3 was determined unambiguously by observing the splitting of the line groups N= 12 and N= 16 when the diffraction pattern was indexed on the basis of the perovskite cell being a unit cell for the structure. Diffractometer studies were conducted of the N= 12 line group using Fe Kα radiation and of the N= 16 line group using Cu Kα radiation. The ferroelectric phase of PbZrO3 possessed a rhombohedral sub‐cell with the angle α being acute. Stable two‐phase mixtures and considerable thermal hysteresis were observed at the antiferroelectric α ferroelectric transition temperature. A very weak “extra” diffraction line was observed in the diffraction patterns of the ferroelectric and paraelectric phases, indicating that the unit cells of these structures may be multiples of the perovskite subcell.
McHUGH, C. O.; WHALEN, T. J.; HUMENIK, M.
doi: 10.1111/j.1151-2916.1966.tb13305.xpmid: N/A
Finely divided molybdenum particles were dispersed in aluminum oxide to serve as inclusions for the inhibition of grain growth and secondary recrystallization during sintering. Conventional powder metallurgy techniques were used to fabricate compacts of aluminum oxide containing up to 16 vol% molybdenum. Three methods for developing a uniform dispersion of molybdenum particles in aluminum oxide are compared on the basis of the resulting microstructures. Specimens sintered in vacuum had densities approaching 98% of theoretical density with an average grain size of 2μ or less with no evidence of secondary recrystallization. The grain refinement is reflected in transverse rupture strength data with average strengths exceeding 80 kpsi and maximum strengths exceeding 100 kpsi.
SHONEBARGER, F. J.; BLAU, HENRY H.
doi: 10.1111/j.1151-2916.1966.tb13306.xpmid: N/A
A reproducible method for developing electrostatic charges by rubbing glass surfaces with a platinum electrode was developed as a quantitative approach to the study of glass surfaces. The charge‐producing characteristics of glass surfaces were correlated with glass compositions as well as with the conditions of formation of the glass surfaces and their subsequent histories. The sign and magnitude of charges generated on glass surfaces arose primarily from the ions removed from the surface films. The charge development characteristics of glass interfaces seem to yield some indications of the atomic arrangements at glass interfaces.
doi: 10.1111/j.1151-2916.1966.tb13307.xpmid: N/A
Microprobe studies were conducted on hot‐pressed polycrystalline MgO compacts, nominally 99.5 and 99.95% pure. Results indicated that in MgO some common impurities, such as Al, Ca, and Si, when present in amounts as small as 30 atomic ppm, were segregated to grain boundaries. Mutually incompatible segregated phases existed at grain boundaries. Other impurities such as Fe appeared to be uniformly distributed. Although some impurity agglomeration was noted, it was not required for impurity segregation. The presence of such agglomerates would complicate the problems of chemical analysis.
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