Immiscibility and Crystallization in A1 ₂ O ₃ ‐SiO ₂ Glasses

Abstract

Metastable glass‐in‐glass separation was observed on rapid quenching of A1 2 O 3 ‐SiO 2 melts containing from 10 to 50 mol% A1 2 O 3 . Nucleation and subsequent crystallization of mullite within the high‐alumina‐dispersed glass phase may occur either during cooling from the melt or on reheating. The metastable binary two‐liquid region is compositionally defined, and a structural interpretation of the phase separation and the effects of small oxide additions on it is offered. Evidence for both classical and possible spinodal nucleation mechanisms during liquid segregation in this system is presented.