DTA and X-Ray Analysis Study of Nucleation and Crystallization of MgO-Al2O3-SiO2 Glasses Containing ZrO2, TiO2, and CeO2

Crystallization sequences of glasses with compositions in the tridymite primary phase field of the MgO-Al₂O₃-SiO₂ system were studied by DTA, X-ray diffraction, and other techniques. Crystallization was catalyzed by the addition of 7 wt% of either ZrO₂ or TiO₂. Up to 10 wt% CeO₂ was also added to some glasses. Metastable solid solutions with the high-quartz structure exhibiting varying lattice parameters commonly occurred at low temperatures, transforming into a high cordierite at higher temperatures. Depending on the composition and heat treatment, other phases also appeared, e.g. Ce₂Ti₂O₄ (Si₂O₇). The rate of crystallization was markedly dependent on the catalyst. Colloidal precipitation of the catalyst accompanied by bulk crystallization of the glass was observed with ZrO₂, but no crystalline TiO₂ was detected. In the presence of CeO₂, TiO₂ was a more effective catalyst than ZrO₂. Although CeO₂ lowered the melting temperatures of the glass-ceramics, it increased the stability of the glasses and inhibited volume nucleation, causing coarse structures to form on crystallization.