Crystallization kinetics of Al2O3-Yb2O3 glasses

Crystallization kinetics of Al2O3-Yb2O3 glass microspheres with two different compositions was studied by DTA. Heating rates ranging from 3 to 15 A degrees C min(-1) were used for DTA measurement. The DTA curves obtained were transformed into the dependence of conversion, alpha, on temperature. The model f(alpha) = alpha (n) (1 - alpha) (m) , i.e., the model of Sestak and Berggren, was found suitable for the description of crystallization kinetics. The best fit of experimental data was obtained if the full set of measured conversion degrees was used for calculation of kinetic parameters. In this manner, the following results were obtained: A = 6.10 x 10(20) min(-1), E = 4.68 x 10(5) J mol(-1), n = 0.634, m = 1.037 for 30 wt% Al2O3-70 wt% Yb2O3 glass, and A = 6.98 x 10(25) min(-1), E = 5.97 x 10(5) J mol(-1), n = 0.562, m = 0.975 for 45 wt% Al2O3-55 wt% Yb2O3 glass.