Thermogravimetric and thermokinetic investigation of the dehydroxylation of a hydroxyapatite powder

The dehydroxylation of HA powder was investigated using thermogravimetric analysis over the range of room temperature to 1250 °C. The kinetic result of dehydroxylation of HA was calculated by means of the Ozawa–Flynn–Wall method. According to calculated activation energy-conversion degree plot, the kinetics of HA dehydroxylation was identified as a comprehensive one, which included four reaction-rate-controlling processes with different activation energies and four successive conversion stages kinetically controlled by different rate-controlling processes. These four reaction-rate-controlling processes were interpreted as OH−-anion diffusion through HA, OH−-anion debonding from HA lattice, the lattice constitution of OA, and 2OH−→H2O↑+O2− at the reaction interface.