Ultrafine hydroxyapatite powders (Ca10(PO4)6(OH)2) with 40-90 m2/g specific surface area were synthesized by the reaction between Ca(OH)2 suspensions and H3PO4 solutions at room temperature. The influence of the size of the starting Ca(OH)2 powder, mixing rate and concentration of starting raw materials on the characteristics of the hydroxyapatite powder produced were studied by X-ray powder diffraction, infrared spectroscopy, specific surface area measurements and transmission electron microscopy. The reproducibility of experimental results was also investigated. When a H3PO4 solution was added once to a Ca(OH)2 suspension, the reproducibility of the result became lower. An increase in the concentrations of the starting raw materials promoted the formation of ultrafine needle-shape hydroxyapatite particles with smaller crystallite size and higher specific surface area. The characteristics of the hydroxyapatite produced did not depend on the size of starting Ca(OH)2 powder.

Keywords: Hydroxyapatite, Specific surface area, Nanometer-sized particles, Crystallite