Formation of Nanocrystalline Hydroxyapatite in Nonionic Surfactant Emulsions

Nanosized hydroxyapatite (HA) powders were synthesized via a unique oil-in-water emulsion processing route using petroleum ether as the oil phase, KB6ZA as the nonionic surfactant phase, and aqueous CaCl2 solution as the water phase. An (NH4)2HPO4 solution was added to the oil-in-water emulsions to form hydroxyapatite. The resulting HA powders as examined by transmission electron microscopy are nanosized and crystalline. Very little growth in particle size of HA is observed upon calcination at 650 °C for 6 h. In contrast, the HA powders prepared by directly reacting (NH4)2HPO4 with CaCl2 in an aqueous solution and in a micellar system containing 3.2 wt % KB6ZA nonionic surfactant are much less crystalline than those formed in the oil-in-water emulsions. Moreover, the HA powders underwent extensive growth in crystallite and particle sizes when calcined at 650 °C for 6 h. A mechanism for the formation of nanocrystalline HA is proposed for the oil-in-water emulsions containing 2−11 wt % petroleum ether. The ...