Effect of Heat-Treatment for Nucleation on the Crystallization of MgO-Al₂O₃-SiO₂ Glass Containing TiO₂

Abstract

The effect of heat-treatment for nucleation on the crystallization of MgO-Al₂O₃-SiO₂ glass containing TiO₂ was investigated. The glass having a composition 16.7MgO⋅22.3Al₂O₃⋅61SiO₂ (wt%) and containing 10wt% of TiO₂ as nucleating agent shows phase separation, whereas the glass of a similar basic composition without nucleating agent does not show phase separation. The rate of nucleation of Mg-Al-titanates [x(MgO⋅2TiO₂)y(Al₂O₃⋅TiO₂)] crystals was the largest when heat-treated at 760°C. Spherical particles with a mean diameter of 100-150Å are confirmed to precipitate before the crystallization of main crystals β-quartz and petalite (MgO⋅Al₂O₃⋅SiO₂) takes place. The nucleation from the quenched glass takes place even at a temperature (730°C) lower than the glass transition temperature (T_g=750°C). The temperatures at which the precipitation of β-quartz and petalite take place become higher, and the size of Mg-Al-titanate crystal becomes smaller as the number of the small particles formed in the first heat-treatment increases.