Diffusion of Hydrogen and Deuterium in Fused Quartz

Abstract

A mass spectrometer was used to record the transfer of hydrogen and deuterium through hollow, thinwalled cylinders of fused quartz over the temperature range of 300–1000°C. Steady‐state gas permeation measurements resulted in permeability values which agree well with the literature; however, results of transient experiments which provide a direct means of measuring diffusion coefficients did not agree with so‐called ``normal'' diffusion. The deviation from normal diffusion increases with increasing temperature. Measurements were made of the temperature variation in the rate of release of deuterium from fused quartz resulting from replacement by dissolved hydrogen. A chemical exchange between the diffusing molecules (H₂ or D₂) and one or more species of trapped gas within the fused quartz is thought to be the principal cause of the nondiffusion‐like character of the high‐temperature gas transport. Activation energies were calculated for the permeability (H₂:8.88 kcal/mole. D₂:9.05 kcal/mole), diffusion (H₂:10.37 kcal/mole D₂:10.52 kcal/mole), and chemical exchange (15.5 kcal/mole) mechanisms. Experimental solubilities were compared with the so‐called normal solubilities (S_n=permeability/diffusion coefficient) and were found to exceed the normal to a greater extent with increasing temperature.