SYNTHESIS OF COMPOSITIONALLY REGULATED HYDROXYAPATITE FROM CA(OH)2 AND H3PO4

Ca(OH)2 and H3PO4 were used as starting materials for synthesizing hyd roxyapatite (HAp). When the stoichiometric amount of 1 mol/l solution of H3PO4 was added dropwise to a Ca(OH)2 slurry in a N2 atmosphere, 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) aminomet hane solution (Tris buffer) and by aging for 48 h at 60-degrees-C in a N2 atmosphere. The Ca/P molar ratio of HAp was regulated by using Tri s buffer to 1.66 under pH = 6.0 and to 1.68 under pH = 8.0, respective ly. The stoichiometric HAp was stable up to 1300-degrees-C, and the la ttice constants of the HAp calcined at 1100-degrees-C were a0 = 0.9418 5 (2) nm and c0 = 0.68807 (2) nm.