Diffusion of Helium Through Several Glasses*

A bstract The rates of diffusion, R , of helium through four glasses of varied composition have been measured as a function of temperature up to and including the “transformation points” of the glasses. Two borosilicates, a lead glass, and a soda glass were studied, and the effect of heat treatment was investigated. A plot of log R vs. 1 /T , in general, proved to be made up partly of a straight line and partly of a curving line at temperatures where the glass became soft enough to relieve strain. The borosilicates showed either no break or only a slight break at the “transformation point,” whereas the lead and soda glasses showed more pronounced changes in slope near the “transformation point.” The borosilicates showed a shift to higher rates with heat treatment; and the lead glass, a shift to lower rates. It is believed that completely annealed glass would show a linear log R vs. 1 /T relation over the entire temperature range. The permeability of the glass to the diffusion of helium at any temperature decreases as the percentage of basic oxides or of cations increases. This may be interpreted in terms of the atomic arrangement in these glasses.