Reversion of precipitates in phase separated soda lime silica glass

Abstract

The glass with composition 13Na2O‐11CaO‐76SiO2 (mol%) undergoes subliquidus phase separation via a binodal mechanism. At temperatures below the binodal temperature, Tb = 978 K, the glass separates into two amorphous phases, silica‐enriched droplets and a silica‐poor matrix. Small‐angle X‐ray scattering was used to study the formation of the droplet phase at 923 K as well as the process of reversion where the precipitates dissolve after an increase in temperature. After a heat treatment of 48 h at 923 K the system is in the stage of coarsening. However, the equilibrium volume fraction of the droplet phase, we = 0.073, has not yet precipitated. The reversion of the droplets was studied at T = 983 K and T = 963 K. For T > Tb, the precipitates dissolve completely by an interdiffusion process resulting in a decrease of the silica concentration of the droplets, while the phase boundary is preserved over long times. For T < Tb, the reversion process shows two distinct stages. In the first stage, the silica concentration inside the droplets decreases and all precipitates shrink until the concentration in the matrix reaches its new equilibrium value. Afterwards, the largest droplets grow again by slow coarsening.