DTA and X‐Ray Analysis Study of Nucleation and Crystallization of MgO‐Al ₂ O ₃ ‐SiO ₂ Glasses Containing ZrO ₂ , TiO ₂ , and CeO ₂

Crystallization sequences of glasses with compositions in the tridymite primary phase field of the MgO‐Al 2 O 3 ‐SiO 2 system were studied by DTA, X‐ray diffraction, and other techniques. Crystallization was catalyzed by the addition of 7 wt% of either ZrO 2 or TiO 2 . Up to 10 wt% CeO 2 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. Ce 2 Ti 2 O 4 (Si 2 O 7 ). 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 ZrO 2 , but no crystalline TiO 2 was detected. In the presence of CeO 2 , TiO 2 was a more effective catalyst than ZrO 2 . Although CeO 2 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.