Density of vitreous silica

The density of vitreous silica was varied by changes in thermal history, water concentration, and concentration of dissolved gases. Previous assumptions that the fictive temperature of vitreous silica is identical to the heat treatment temperature are incorrect at higher treatment temperatures. Contrary to earlier reports, maxima in density do not occur for fictive temperatures below 1650 °C for vitreous silica. An increase in water concentration of 1 wtppm results in a decrease in density of 0.96 ppm for vitreous silicas with the same fictive temperatures. Changes in density due to water concentration changes in irradiated, hydrogen-loaded vitreous silica are larger than those for water created during manufacturing. At high concentrations, dissolved H2 and D2 expand the glass, offsetting much of the increase in mass of the sample due to the presence of the dissolved gas. The magnitude of this effect can be partially explained by treating the glass as an elastic solid and assuming that the dissolved gas exerts an internal pressure on the glass equal to the original gas pressure.