Inert gas solubility in binary germania–silica glasses

Helium and neon solubility have been measured in vitreous silica, vitreous germania, and in a series of binary GeO ₂–SiO ₂ glasses. Measurements were made over a broad temperature range using a saturation-outgassing method. The enthalpy of solution of these gases is smaller for vitreous germania than for vitreous silica. Inert gas solubility decreases rapidly as silica is initially replaced by germania in the network, with a more gradual decrease in solubility with continued reduction in silica content. Solubility measurements at varying pressures establish that inert gas solubility in vitreous germania obeys Henry’s Law up to 1 atm of gas pressure, as has already been established for vitreous silica. Additional helium solubility and diffusivity measurements were made using the permeation method at temperatures below 300 °C. Helium diffusivity also decreases as silica is replaced by germania, with an approximately linear dependence on composition. The activation energy for diffusion increases as the germania concentration increases. Results of this study are attributed to changes in interstice size and/or distribution as a function of glass composition and experimental temperature.