Molecular diffusion and solubility of hydrogen isotopes in vitreous silica

Deuterium permeation, diffusion, and solubility measurements have been made for several types of vitreous silica at temperatures ranging from 0 to 800 °C. The activation energies for permeation and diffusion were found to be somewhat temperature dependent. Isotope exchange between structural hydroxyl and the diffusing deuterium was found to occur at temperatures ?300 °C. Certain types of vitreous silica also react with the diffusing gas to form metastable deuteroxyl at ?600 °C. Isothermal hydrogen-isotope solubility was shown to be described by the Langmuir adsorption isotherm at pressures up to 1400 atm, whereas the temperature dependence of hydrogen-isotope solubility was adequately described by a statistical-mechanics model. Combination of these two models leads to a universal expression for hydrogen solubility from 0 to 800 °C and from 0 to 1400 atm.