Crystallization of whitlockite from a glass in the system CaO•P2O5•SiO2•MgO

The kinetics of crystallization of a glass with composition 30SiO(2). 24.14P(2)O(5). 28.61CaO . 17.25MgO (wt%) was studied with variable temperature, by differential thermal analysis. These results were interpreted according to revised theoretical models which describe the dependence of fraction crystallized on temperature and on the heating rate, and the dependence of the peak temperature on the rate of change in temperature. These models emphasize the differences in crystallization behavior between "as-prepared" glass samples, and the corresponding previously nucleated samples. These differences in behavior suggest that the kinetics of crystallization comprises a nucleation stage at temperatures of about 730 degrees C, and particle growth for temperatures higher than 800 degrees C. The temperature dependence of the fraction crystallized corresponds to a very high value of activation energy for growth (approximate to 763 kJ/mol), but this is still lower than the activation energy evaluated from the temperature dependence of viscosity.