J.E. Shelby

Thermal expansion of amorphous metals

Abstract The thermal expansion of three commercial amorphous metals has been measured from room temperature to above the crystallization temperature. The results clearly demonstrated the glassy nature of these materials and show the reduction in volume which results from crystallization. The glass transformation temperature is more evident here than on the usual differential scanning calorimeter curves. The activation energies associated with the glass transformation and crystallization are derived from data taken as a function of heating rate. The measured temperatures for the glass transformation and crystallization from the thermal expansion measurements are the same as those obtained from DSC measurements at the same heating rate.

Influence of water on the viscosity and thermal expansion of sodium trisilicate glasses

Abstract The transformation range viscosity, activation energy for viscous flow and the dilatometric critical temperature of sodium trisilicate glasses are all decreased by addition of water, whereas the thermal expansion coefficient in the elastic region is not altered to a significant extent. Although these effects are similar to those observed in vitreous silica, they are considerably reduced in magnitude. Since sodium trisilicate glasses are already highly depolymerized by the presence of Na 2 O, the additional depolymerization due to small additions of water does not seem adequate to explain these results. It is suggested that water behaves similarly to the alkali oxides and that the results of this study may be due to an extreme case of the mixed-alkali effect.

Characterization of glass microstructure by physical property measurements

Abstract The effect of glass composition and thermal history on the thermal expansion, viscosity, chemical durability, glass transformation temperature, and helium permeability of lead borate glasses was measured. A detailed characterization of the morphology of these glasses was obtained from the results of these studies. The results indicate that the phase separation region extends from just above 0.0 mol% PbO to approximately 20 mol% PbO. Essentially all of the glasses consist of isolated droplets dispersed in a continuous matrix (confirmed by SEM and optical microscopy). The physical property measurements indicate that the matrix phase is nearly pure B2O3 for glasses containing between 0 and 10 mol% PbO and approximately 20 PbO·80 B2O3 for glasses containing between 10 and 20 mol% PbO. The “borate anomaly” was also evident in the thermal expansion coefficient and glass transformation temperatures of these glasses.

The reduction of iron in soda-lime-silicate glasses by reaction with hydrogen

Abstract The reduction of ferric iron in commercial soda-lime-silicate glasses by reaction with hydrogen was studied as a function of time, temperature, and hydrogen pressure by means of optical spectroscopy and electron spin resonance. The results indicate that the reduction process is controlled by the permeation of hydrogen molecules in the glass and can therefore be described by the tarnishing model for permeation-controlled reactions.

Colloidal silver formation at the surface of float glass

Abstract The formation of colloidal silver during the heating in air of silver films on float glass has been observed. The presence of colloidal silver gives to a yellow color and an absorption band centered at 400–420 nm. The results of this study indicate that the formation of colloidal silver is strongly dependent upon the concentration of stannous tin in the glass. The optical density of the absorption band induced in the glass is much greater for samples silvered on the tin-rich face of the glass and varies with the thermal history of the sample. Removal of the outer few micrometers of the glass surface results in a radical change in the amount of colloidal silver formed. Silver colloids are formed only if the sample is heated in an atmosphere containing oxygen, suggesting that the silver must be ionized before it will diffuse into the glass. The colloid formation process has an activation energy of approximately 30 kcal/mol, which is very near that reported for silver-sodium interdiffusion in similar glasses.

Effect of structural relaxation on helium diffusion and solubility in vitreous B2O3

Abstract Helium permeation, diffusion, and solubility in vitreous B 2 O 3 were measured as a function of thermal history and as a function of time at constant temperature. Volume relaxation measurements were also made on similar specimens. The correspondence between the effective relaxation times for gas mobility and molar volume suggests that the changes observed in both properties results from the same changes in the glass structure. This relaxation mechanism is described by the expression τ ′ = 10 −4 exp(-18 000/ RT ), where τ′ is in seconds and the activation energy is in cal/mole. It is concluded that helium mobility is a function of the molar volume of the glass.

Helium migration in alkali galliosilicate glasses

Abstract Helium migration has been measured for lithium, sodium, and potassium galliosilicate glasses. The results are compared with those from earlier studies of helium mobility in sodium and lithium aluminosilicate glasses. The concentration dependence of the helium permeability of glasses in all five glass-forming systems exhibits an abrupt change in behavior when the concentration of the intermediate oxide exceeds that of the alkali oxide. This effect appears to be related to changes in the effect of the intermediate oxide on the atomistic structure of the glass. Morphology effects have also been found to influence strongly, helium migration in the glasses containing lithium when the concentration of the intermediate oxide is relatively small.

Surface characterization of weathered low-iron float glass

Abstract The weathering of low-iron float glass under accelerated testing has been studied by a variety of surface characterization techniques including optical spectroscopy, optical and scanning electron microscopy, dye penetration testing, surface profile measurements, and resonant nuclear reaction profiling. The results indicate that the weathering process results from the formation of a low density film on the glass surface by the interdiffusion of mobile ions from the glass and protons from the water. The rate of formation of this film was found to be a strong function of the near-surface composition of the glass.

Hydrogen transport in a machinable glass-ceramic☆

Abstract A commercial, machinable glass-ceramic (CGW-9658) has been found to change color from white to dark grey upon exposure to hydrogen isotopes at temperatures of 500°C and above. This process has been studied by optical microscopy and electron spin resonance as a function of temperature, gas pressure, and hydrogen isotope used. The results demonstrate a one-to-one correspondence between the diffusion-controlled reduction of ferric iron by hydrogen and the visually observed width of the reacted zone.

Properties of a solar aluminaborosilicate sheet glass

Abstract Solar energy applications place unique requirements on sheet glass including very low solar absorption, outstanding stability of absorption in the outdoor environment, low cost, and elastic formability for making concentrating mirrors. The Solar Energy Research Institute and Corning Glass Works have developed a new solar sheet glass. In evaluations reported in this paper, the new glass has shown outstanding chemical durability and optical and mechanical properties.