Processing of fine hydroxyapatite powders via an inverse microemulsion route

Abstract

A submicrometer-sized hydroxyapatite powder has been synthesized via an inverse microemulsion processing route, which uses cyclohexane as the oil phase, mixed poly(oxyethylene)5 nonyl phenol ether (NP-5) and poly(oxyethylene)9 nonyl phenol ether (NP-9) as the surfactant phase, and an aqueous CaCl2 solution as the water phase. In comparison with the hydroxyapatite powder prepared by directly reacting (NH4)2HPO4 with CaCl2 in an aqueous solution, the microemulsion processing route led to a significant refinement in the particle size, particle size distribution, and the degree of particle agglomeration. XRD phase analysis indicates that a high-purity crystalline hydroxyapatite powder was obtained when the microemulsion-derived precursor was calcined at 800°C. In contrast, there existed impurity phases such as β-Ca3(PO4)2 and CaO in the conventionally processed hydroxyapatite powder after calcination at various temperatures up to 1200°C. This shows that the microemulsion processing route results in the formation of a more homogeneous ultrafine powder precursor than that obtained from the conventional processing route.