29Si T1 relaxation in alkali silicate glasses: a method for detecting glass-in-glass phase separation

High resolution nuclear magnetic resonance (NMR) has been used to measure relaxation times, T1, in alkali silicate glasses. Two-component relaxation was observed in lithium silicate glasses. In glasses close to the sodium disilicate composition, the relaxation was one component but, with decreasing sodium content, this becomes two component. In heat-treated sodium silicate glasses two components appear to grow from the single component and the extent of growth depends upon the heat-treatment temperature and time. The results for all systems are explained in terms of phase separation and an insight into the Qn distribution is also presented.