Determination of the Activation Energies of Phase Transition for Calcium Orthophosphates Based on Powder X‐Ray Diffraction Data

Kinetic studies of the transformation calcium orthophosphates metastable precipitates are performed under different synthesis conditions. The phase composition and degree crystallinity investigated by X-ray powder diffraction analysis. In acidic solution, CaHPO 4 . 2H 2 O (DCPD) (DCPA) formed at early stage precipitation, with range 17–35%. Specifically, DCPD 30 °C anhydrous DCPA 50 °C. alkaline solution (pH 8–10), only amorphous forms orthophosphate precipitated, which is explained high supersaturation. effect pH on illustrated solubility isotherms pure orthophosphates. It determined activation energy from patterns. Based this relationship developed, energies for recrystallization 10.2 13.1 kJ mol−1, respectively, transition to – 36.7 mol−1. Further most thermodynamically stable hydroxyapatite occurs 5.2 These findings critical phosphate minerals.