Stress-Enhanced Diffusion in Glass. I. Glass under Tension and Compression

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Abstract
This paper describes a new technique for the determination of diffusion constants of gases in gas-solid systems. The method demands a careful analysis of the transient quantity of gas flowing after the gas pressure at the boundary is discontinuously changed. The exact quantity of gas flowing is recorded by a mass spectrometer. The method was used to study the effect of high tensile stress upon the diffusion constant of helium and other gases in glass. The diffusion constant of helium was found to be a true constant with dilation of the glass until the stress became about one-half the breaking stress of the glass. Beyond this point the diffusion constant increased, and under very high stress was a factor of ten larger than its original value. No apparent change was produced in the glass, and reduced stress gave the same diffusion constant as previously, indicating reversibility of the effect with stress. It was further determined that equal and even larger compressional stresses on the same glass specimen had little or no effect upon the diffusion constant. The effect of shear stress upon the diffusion constant is dealt with in the following paper. The magnitude of the observed increase in diffusion constant is larger by a considerable factor than can be explained by a straight-forward extension of prevalent theories of diffusion in glass. If it is assumed that the glass sample dilates on an atomic scale, i.e., each atom being isotropically displaced by the stress, then calculations show that the diffusion constant should not be strongly increased under stress. Observation of the large increase then points toward the opening of flaws or voids within the glass. Diffusion of hydrogen, heavy water, oxygen, and nitrogen is discussed and upper limits for diffusion of the latter three under high stress are set.

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