Heterogeneous crystallization of calcium hydrogen phosphate anhydrous (monetite)

The crystal growth of monetite (CaHPO4, DCPA), the least stable calcium phosphate has been investigated by the seeded growth method from solutions supersaturated exclusively with respect to this phase alone. The kinetics of crystal growth was measured at constant supersaturation at 37 degrees C, pH 6.0. The measurements of the rates of crystal growth of DCPA showed a second order dependence on the relative supersaturation of the solutions with respect to DCPA, suggesting that the rate determining step is surface diffusion of the growth units to the active growth sites of the crystals. The heterogeneous crystallization of brushite (CaHPO4 center dot 2H(2)O, DCPD) on DCPA seed crystals in solutions supersaturated with respect to both DCPD and DCPA showed that DCPD nucleation and growth took place selectively by heterogeneous nucleation on the DCPA seed crystals. The same parabolic dependence of the rates on the relative supersaturation of the solutions with respect to DCPD was found, showing that the mechanism was the same as in the case of growth of DCPA on DCPA seed crystals. Seeding of solutions supersaturated with respect to both DCPA and DCPD at pH 6.0, 37 C with collagen type II in powdered form, resulted to the formation of an apatitic solid. The morphology of the crystals formed on the collagenous matrix suggested that the identified mineral was probably the result of rapid hydrolysis of metastable calcium phosphatephases. The formation of the mineral phase on collagen took place past long induction time periods inversely proportional to the relative supersaturation with respect to DCPD and showed that the collagen substrate did not stabilize calcium phosphate at the same conditions at which DCPA did. (C) 2016 Published by Elsevier B.V.