Isothermal DTA study on crystallization of mica composition-based glass

Isothermal differential thermal analysis (DTA) was used to study the crystallization of a glass with a composition close to that of mica (NaMg3AlSi3O10F2), with TiO2 added as a nucleating agent. Two distinct crystallization exotherms in DTA were attributed to the formation of MgTi2O5 followed by NaMg3AlSi3O10F2. By using the Johnson-Mehl-Avrami equation, the activation energy for precipitation of each crystalline phase was evaluated and the crystallization mechanism was analyzed. Results indicate that NaMg3AlSi3O10F2 growth is a two-dimensional process, controlled by the crystal-glass interface reaction. The average value of activation energy is 256 +/- 11 kJ/mol and 275 +/- 7 kJ/mol corresponding to MgTi2O5 and mica, respectively. (C) 1997 Elsevier Science B.V.