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 c(w) from 3 x 10(-4) to 27 wt%. In terms of a reduced glass transition temperature T-g* = T-g/T-g(GN), where T-g(GN) is T-g of the melt containing c(w) approximate to 0.02 wt% total water, a uniform dependence of T-g* on total water content (c(w)) is evident for silicate melts. T-g 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 T-g is less pronounced, but it does not vanish even at the largest water contents reported (approximate to27 wt%). T-g* vs. c(w) is fitted by a three-component model. This approach accounts for different transition temperatures of the dry glass, hydroxyl and molecular water predicting T-g 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. (C) 2003 Published by Elsevier B.V.