Seeded growth of calcium phosphates: effect of different calcium phosphate seed material

Seed crystals of OCP, TCP, and HAP are effective nucleators of DCPD in stable supersaturated solutions under conditions in which DCPD is the predominant phase. The crystals will grow with the second-order kinetics (TCa = 5.0 X 10(-3)M, Tp = 1.0 X 10(-2)M [pH, 5.60]) characteristic of DCPD. TCP is the least efficient, DCPD growth taking place only after an initial induction period. In all instances, the rate of DCPD crystallization is proportional to the square of the supersaturation with respect to DCPD, and the reaction is surface controlled. Scanning electron micrographs show an amorphous or microcrystalline precursor to the development of the characteristic platelets of DCPD. In stable supersaturated calcium phosphate solutions at a physiologic pH (TCa = 1.4 X 10(-3)M, Tp = 8.0 X 10(-4)M [pH, 7.40]), only OCP and HAP seed crystals are effective nucleators. The efficiency of OCP as a nucleator adds further evidence for its participation as a precursor in the precipitation of HAP under these conditions.