KINETICS AND MECHANISM OF CRYSTALLIZATION OF GEHLENITE GLASS PURE ANDDOPED WITH CO2+, EU3+, CR3+ AND TH4+

The crystallization of glasses of gehlenite composition, 2CaO . Al2O3 . SiO2, pure and doped with 0.02 mol cobalt, europium, chromium and th orium per one mole of gehlenite, was studied using differential therma l analysis. The kinetics of crystallization of all examined glasses ar e described by the Avrami equation: alpha=1-exp(-kt(n)). The activatio n energy of the crystallization process of the undoped glass is 740 kJ /mol and the parameter n is equal to 1.5. The activation energies of c rystallization of doped glasses are 645, 670, 680 and 800 kJ/mol and t he parameters n are 1.21, 1.38, 1.41 and 1.54 for europium, thorium, c obalt and chromium as dopants, respectively.