ISOTHERMAL DTA STUDY ON CRYSTALLIZATION OF MICA COMPOSITION-BASED GLASS

Isothermal differential thermal analysis (DTA) was used to study the c rystallization of a glass with a composition close to that of mica (Na Mg3AlSi3O10F2), with TiO2 added as a nucleating agent. Two distinct cr ystallization exotherms in DTA were attributed to the formation of MgT i2O5 followed by NaMg3AlSi3O10F2. By using the Johnson-Mehl-Avrami equ ation, the activation energy for precipitation of each crystalline pha se was evaluated and the crystallization mechanism was analyzed. Resul ts 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 corresp onding to MgTi2O5 and mica, respectively. (C) 1997 Elsevier Science B. V.