Synthesis of the lead-calcium HAP solid solutions

Abstract

A series of lead-calcium hydroxylapatite solid solution was synthesized by the precipitation method. Characterization by various means confirmed the forming of the continuous solid solution over a whole Pb/(Pb+Ca) mole fraction range. An obvious deviation of both a and c lattice parameters from Vegard’s rule was observed. The solids of XPb = 0–0.51 were typically prism crystals with hexagonal pyramid as a termination (particle size 50–100 nm); those of XPb = 0.61–0.69 were the typical hexagonal columnar crystals with pinacoid or hexagonal pyramid as termination, which elongated along c axis (particle size 200–600 nm); those of XPb = 0.80–1.00 were the typical prism crystals with hexagonal pyramid as termination (particle size 2–20 μm). The phosphate peak area for the symmetric P-O stretching decreased with increasing Pb/(Pb + Ca) ratio and disappeared as the Pb/(Pb + Ca) ratio > 0.61, and two phosphate peaks of the P-O stretching were diminished with the increase in XPb. These variations could be caused by a slight tendency of larger Pb2+ to prefer the M(II) sites and smaller Ca2+ to occupy the M(I) sites in the apatite structure.