Crystallization of glasses – When to use the Johnson-Mehl-Avrami kinetics?

Applicability of the Johnson-Mehl-Avrami (JMA) model was tested based on the universal criterion of the kinetic peak asymmetry. Theoretical simulations were used to prepare variety of kinetic peaks with different asymmetries, which were described by the JMA model and the masterplot function z(α). Based on the correlation between the simulated crystallization peaks and the JMA description, the following intervals of the degrees of conversion corresponding to the z(α) function maxima can be attributed to the respective values of the correlation coefficients: αmax,z = 0.620 – 0.665 corresponds to the better correlation with the JMA model than r2 = 0.999; αmax,z = 0.585 – 0.705 indicates the correlation better than r2 = 0.995. These intervals are significantly more lenient than those proposed in the original derivation of the masterplot approach. Even at r2 = 0.995 the fit by the JMA model provides very accurate kinetic predictions utilizable for preparation of glass-ceramics.