Crystallisation in SiO2-Al2O3-ZnO-TiO2 glass: process mechanism

Devitrification of a frit based on the oxide system SiO2-Al2O3-ZnO, using bulk glass as well as powdered glass samples with different particle sizes was studied. The following major crystalline phases were identified: gahnite (ZnAl2O4), (alfa)-quartz, cristobalite, and a solid solution exhibiting the (beta)-quartz structure, which contained SiO2, Al2O3, and ZnO and whose composition varied with temperature. Depending on the size of the glass (frit) samples, gahnite was found to devitrify directly from the initial glassy phase or from the solid solution with a (beta)-quartz structure, which appeared to act as a precursor. BCT/327