Nanosized hydroxyapatite powders from microemulsions and emulsions stabilized by a biodegradable surfactant

Abstract

Ultrafine hydroxyapatite powders have been successfully synthesized in inverse microemulsions and emulsions consisting of petroleum ether as the oil phase, 1.0 M CaCl2 solution as the aqueous phase and biodegradable KB6ZA as the surfactant. The titration of 0.6 M (NH4)2HPO4 aqueous solution into the inverse microemulsion and emulsions containing 25.0 and 35.0 wt% aqueous phase, resulted in hydroxyapatite precursors that were nanometer sized and more or less spherical in morphology. However, they underwent a considerable degree of particle coarsening when calcined at 650 °C for 6 h. A nanocrystalline hydroxyapatite powder, which exhibited a dendritic agglomerate morphology, was synthesized in an oil-in-water emulsion containing 90.0 wt% aqueous phase. It shows an average particle size of 25 nm upon calcination at 650 °C for 6 h, as little particle coarsening and growth in crystallite size were observed at the calcination temperature. The inverse microemulsion- and emulsion-derived hydroxyapatites exhibit a degree of type B carbonate substitution, which cannot be eliminated by calcination in air at 650 °C.