Water and the glass transition temperature of silicate melts

Literature data on the effect of water on the glass transition in silicate melts are gathered for a broad range of total water content cw from 3 × 10−4 to 27 wt%. In terms of a reduced glass transition temperature Tg∗=Tg/TgGN, where TgGN is Tg of the melt containing cw≈0.02 wt% total water, a uniform dependence of Tg∗ on total water content (cw) is evident for silicate melts. Tg∗ decreases steadily with increasing water content, most strongly at the lowest water content where H2O is dominantly dissolved as OH. For water-rich melts, the variation of Tg∗ is less pronounced, but it does not vanish even at the largest water contents reported (≈27 wt%). Tg∗ vs. cw is fitted by a three-component model. This approach accounts for different transition temperatures of the dry glass, hydroxyl and molecular water predicting Tg∗ as a weighted linear combination of these temperatures. The required but mostly unknown water speciation in the glasses was estimated using IR-spectroscopy data for hydrous sodium trisilicate and rhyolite.