Measurements of hydrogen permeation through fused silica and borosilicate glass by electrochemical pumping using oxide protonic conductor

The hydrogen diffusion parameters of fused silica and bolosilicate glass in the temperature range from 673 to 1073 K and 673 to 773 K, respectively, were studied by a measuring apparatus developed based on the coulometric titration of an electrochemical cell made of an oxide protonic conductor. The measured values were in good agreement with those reported in the literature. From the hydrogen activity dependencies of both permeability and diffusibility, it was concluded that in fused silica and borosilicate glass, most of the hydrogen permeation takes place in the form of hydrogen molecules passing through the large holes induced in the structure with random arrangements of SiO4 tetrahedra. The solubility in the form of hydrogen molecules estimated by the permeability and diffusion coefficient values was two orders of magnitude smaller than that of hydrogen dissolved in the form of hydroxyl radicals. The migration rate of the hydrogen in the form of hydroxyl radicals is far smaller than the movement of hydrogen molecules. This fact is also suggested by the small H/D substitution rate observed by infrared absorption spectra.