A differential scanning calorimeter study of the monoclinic (P21/b)↔hexagonal (P63/m) reversible phase transition in hydroxyapatite

The apparent transition temperature (Tc) and enthalpy (ΔH) of monoclinic (P21/b)↔hexagonal (P63/m) reversible phase transition in stoichiometric (Ca/P=5/3) hydroxyapatite were investigated as a function of heating/cooling rate by means of a differential scanning calorimeter (DSC), in the heating/cooling rate range of 0.5–3.0 K/min. The apparent Tc value slightly increased and decreased with increasing heating and cooling rates, respectively, while the apparent ΔH value was almost same within the experimental error.