ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1972.tb11208.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

Permeation, diffusion, and solubility of helium in several types of vitreous silica were measured. The activation energy for diffusion increases slightly with increasing hydroxyl concentration; no other significant trends were noted. These results are interpreted in terms of a random‐network structural mode

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1972.tb11209.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

The electrical resistance of liquid sulfur was measured from just below the polymerization temperature to the vaporization point. Turning points in the resistance vs temperature curve, resulting presumably from polymerization and depolymerization, and a sharp decrease in resistance at 212°C agree well with previous results. Between ∼230° and 420°C, the resistance decreased without discontinuity. The resistance of selenium increased sharply by 3 orders of magnitude on melting and then decreased steadily by 5 orders of magnitude until the experiment was ended at 700°C. In both liquids, the electrical resistance as a function of temperature decreased more rapidly than that of an ideal intrinsic semiconductor whose molecular structure is stable over the temperature interval investigated. This rapid decrease is believed to result from chain dissociation and ring sci

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1972.tb11210.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

Simplified structural models for mullite were investigated, and ir frequencies were calculated for the simplest model which gave the theoretical number of ir‐active frequencies compatible with the observed spectrum. This model, which consists of independently vibrating structural units, gives plausible frequency assignments which agree well with other published data for silicates and aluminates. These assignments explain the spectral changes observed during formation of mullite from heated clay minerals. The model does not take into account the changes in stoichiometry and distortion caused by compositional variation

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1972.tb11211.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

An optical method of temperature measurement, developed for semitransparent media, was tested using molten glass. The beam from a helium‐neon laser was passed through glass, and the attenuation of the beam was measured. Since the monochromatic absorptivity of the glass was a monotonic function of temperature, the attenuation of the beam indicated the temperature of the glass. The optical method was used to measure the one‐dimensional temperature profile in a slab of molten glass with an accuracy of ±5°F. The temperature gradient within the slab was of the order of 200°F/in. The method is useful when the medium is isothermal along the length of the laser beam, the medium does not significantly scatter radiation, and the monochromatic transmissivity of the medium based on the laser path length

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1972.tb11212.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

A method of comparing the kinetics of isothermal solid‐state reactions based on the classical equation for analysis of nucleation‐and‐growth processes is described. In this method, plots of In In (1‐α) vs In (time), where α is the fraction reacted, are used to distinguish reaction mechanisms. Even nonintegral slopes obtained for values of the fraction reacted from 0.15 to 0.50 may indicate whether the reaction rate is diffusion‐ or phase‐boundary‐controlled. The problems of ascertaining zero time and self‐cooling (or heating) of the reacting sample can be observed in the analysis but do not cause severe difficulties in interpretation, as they can for analyses based on reduced‐time plots. The analysis is applied to the dehydroxylation of kaolinite and of brucite and the dec

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1972.tb11213.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

The kinetics of the growth of Al2O3whiskers by the reaction of Al with a trace amount of H2O in an H2atmosphere were studied. The activation energy in the region of constant growth rate was ∼77 kcal mol−1. This activation energy value, in the light of thermodynamic calculations and other theoretical considerations, suggests that the rate‐determining step in the growth of these whiskers is the dissociation of H2O molecules on the surface of

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1972.tb11214.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

The effect of water on the growth of cracks in glass is discussed. Crack motion is believed to result from a stress‐enhanced chemical reaction between water and glass and is influenced strongly by the crack‐tip OH−ion concentration. This hypothesis is supported by the observation that crack‐velocity data can be correlated with measurements of pH in slurries of ground glass and water. Variation of the measured pH from 5 to 12, depending on glass composition, suggests a wide pH variation at crack tips. The types of chemical reactions that establish the slurry pH are discussed, and it is noted that the slurries behave as weak acids, buffered solutions, or salts of weak acids, depending on glass comp

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1972.tb11215.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

Variations in the thermal expansion coefficients, elastic moduli, and fracture strengths of Li2O‐SiO2glass‐ceramics were determined as a function of nucleation treatment and volume fraction of crystals present. Strength enhancement was attributed to a decrease in the mean free path between crystals as crystallization proceeds. It is postulated that the eventual reduction in strength in some glass‐ceramics is caused by the development of localized cracks at the crystal‐glass interface as a result of the volumetric changes which occur during crystall

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1972.tb11216.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

Sapphire and ruby were very difficult to press‐forge because they deformed without cracking only in a limited temperature range before they melted. Spinel crystals were somewhat easier and MgO, CaO, and TiC crystals much easier to forge. The degree of recrystallization that occurred during forging (which was related to the ease and type of slip intersections) varied from essentially zero in Al2O3to complete (i.e. random polycrystalline bodies were produced) in CaO. Forging of bi‐and polycrystalline bodies produced incoherent bodies as a result of grain‐boundary sliding. Strengths of the forged crystals were comparable to those of dense polycrystalline bodies of similar grain size. However, forged and recrystallized CaO crystals were ductile at lower temperatures than dense hot‐pressed CaO. This behavior is attributed to reduced grain‐boundary impurities and porosity. Fracture origins could be located, indicating that fracture in the CaO occurs internally as a result of surface work hardening caused by

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1972.tb11217.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY