Mechanochemical synthesis of nanocrystalline hydroxyapatite from CaO and CaHPO4.

Ceramic hydroxyapatite phase was triggered to occur by high-energy mechanical activation of a dry powder mixture of calcium oxide (CaO) and anhydrous calcium hydrogen phosphate (CaHPO4). A singe-phase hydroxyapatite of high crystallinity was realised by >20 h of mechanical activation without further thermal treatment at high temperatures. The resulting hydroxyapatite powder exhibits an average particle size of approximately 25 nm and a specific surface area of 76.06 m2/g, as measured by multi-point BET technique. It was sintered to a density of 98.20% theoretical density at 1200 degrees C for 2 h.