Processing of hydroxyapatite via microemulsion and emulsion routes.

Hydroxyapatite powders have been prepared by reacting CaCl2 and (NH4)2HPO4 in bicontinuous microemulsion, inverse microemulsion and emulsion, which have the same components as cyclohexane, non-ionic surfactant (NP5 + NP9) and aqueous solution. The characteristics of the resulting hydroxyapatite powders, such as the particle size, particle size distribution, chemical homogeneity and the degree of particle agglomeration, are strongly affected by the structure of the reaction medium. Both bicontinuous and inverse microemulsions led to the formation of much finer hydroxyapatite powders than that prepared from the emulsion composition. The two fine hydroxyapatite powders are sintered to a relative density of >95% theoretical density at 1000 degrees C, compared with a relative density of <73% theoretical density for the emulsion-derived one. The two microemulsion-derived hydroxyapatites also exhibit a higher sintered density and are more refined in grain size than that of the emulsion-derived one when sintered at 1200 degrees C for 2h.