Processing of nanocrystalline hydroxyapatite particles via reverse microemulsions

Nanocrystalline hydroxyapatite (HAP) particles were synthesized at room temperature using reverse microemulsions, in which cyclohexane was used as the organic phase, mixed surfactant with TX-100 and 1- pentanol, and CaCl₂ solution as aqueous phase. The reactor systems with aqueous/organic volumetric ratios 1:10, 1:5, 2:5, and 1:2 were carefully selected for the microemulsion processing by the pseudo-ternary phase diagram and the electric conductivity measurement of the emulsion. The as-obtained HAP nanoparticles with carbonate substitution and broadening X-ray diffraction (XRD) traces were similar to the fine powder of human bone, despite of the aqueous/organic volumetric ratio in the emulsion. No obvious other’s phase occurred after as-obtained particles calcined under different temperature till 700 °C. In the emulsion-derived precursors, the HAP particles based on spherical morphology were prepared into the size between 15 ∼ 30 nm as a low volumetric ratio of 1:10 or 1:5 was applied. As the volumetric ratio increased to 2:5, the HAP particles with rod-like shape of (140∼280) × (10∼80) nm were formed. Practical implication of the results is that the nanocrystalline bone-like hydroxyapatite can be obtained via the emulsion processing at room temperature without further calcinations.