Kinetic analysis of the crystallization of HAp from ACP upon annealing at four different heating rates in the DTA analysis: 5, 10, 20 and 50 °C/min. Activation energies calculated from the slopes of the linear fits in three different models: Kissinger, Augis-Bennett and Ozawa (a). Logarithmic rate constants determined from the exothermic DTA peak surface areas at different timepoints of the reaction as a function of temperature for different reaction orders, n: 0, 1/2, 2/3 and 1 (b). Linear fits in the Piloyan (c) and the Johnson-Mehl-Avrami (d) methods used to determine the values of the Avrami exponent, n.