Ultrasonically accelerated synthesis of hydroxyapatite

Ultrasonic energy was used to accelerate the formation of hydroxyapatite (HAp). The experiments were carried out in aqueous systems on two different sets of reactants: (1) a mixture of Ca₄(PO₄)₂O(TetCP) and CaHPO₄ · 2H₂O (brushite) and (2) α–Ca₃(PO₄)₂ (α–TCP). The reaction systems were exposed to ultrasound of 20 kHz for various times ranging from 5 to 80 min. The products were characterized by XRD and SEM. Parallel experiments without ultrasound were carried out for calibration. The results show that the ultrasound substantially accelerates both reactions. With ultrasound, the time required for the TetCP-brushite system to complete the reaction forming HAp was reduced from 9 h to 25 min at 25 °C, and from 3 h to 15 min at 38 °C. At 87 °C, α–TCP does not hydrolyze within 1 h in de-ionized water unless the pH is adjusted. Hydrolysis of α–TCP was induced by sonication in less than 20 min, and longer treatment results in the formation of a homogeneous sol of HAp.