Synthesis of Compositionally Regulated Hydroxyapatite from Ca(OH)2 and H3PO4

Ca(OH)2 and H3PO4 were used as starting materials for synthesizing hydroxyapatite (HAp). When the stoichiometric amount of 1mol/l solution of H3PO4 was added dropwise to a Ca(OH)2 slurry in a N2 at-mosphere, pH of the slurry was shifted from 11.7 to 3.7, and resultant HAp became Ca-deficient. The Ca/P molar ratio of HAp was strongly affected by pH of the reaction slurry. Stoichiometric HAp(Ca/P=1.67) was prepared by keeping the slurry at pH=7.0 with a tris (hydroxymethyl) aminomethane solution (Tris buffer) and by aging for 48h at 60°Cin a N2 atmosphere. The Ca/P molar ratio of HAp was regulated by using Tris buffer to 1.66 under pH=6.0 and to 1.68 under pH=8.0, respectively. The stoichiometric HAp was stable up to 1300°C, and the lattice constants of the HAp calcined at 1100°C were a0=0.94185(2)nm and c0=0.68807(2)nm.