Effect of the C1(-) content on the formation and dissolution of precipitates in a soda-lime-silica glass

The glass with composition 13Na(2)O-11CaO-76SiO(2) (mol%) undergoes subliqu idus phase separation via a binodal mechanism. Below the binodal temperatur e, Tb, the glass separates into two amorphous phases, silica-enriched dropl ets and a silica-poor matrix. Small-angle X-ray scattering (SAXS) is used t o study the formation process of the droplet phase at 600 degreesC, as well as, the inverse process where the precipitates dissolve after in increase in temperature, A small amount of 0.47 mol% Cl- in the glass causes a drast ic change of the kinetics and thermodynamics of the phase separation proces s in comparison with the pure glass: the phase separation is accelerated an d the maximum volume fraction of the silica droplet phase is increased. The results of dissolution experiments demonstrate that due to the Cl content Tb increases by about 60 K. So, the main effect of Cl in the glass is inter preted asa shift of the miscibility gap to higher temperatures resulting fr om a higher thermodynamic driving force. (C) 2001 Elsevier Science B.V. All rights reserved.