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 CaCl 2 solution as the water phase. In comparison with the hydroxyapatite powder prepared by directly reacting (NH 4) 2HPO 4 with CaCl 2 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-Ca 3(PO 4) 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.