Nucleation and crystal growth of dicalcium phosphate dihydrate on titanium powder

The nucleation and crystal growth of dicalcium phosphate dihydrate (CaHPO4 . 2H(2)O DCPD or brushite) on titanium powder surface has been studied in metastable supersaturated solutions at 37 degrees C and pH=5.50. These experiments were carried out using the constant composition method. In order to determine the effect of substrate size on the kinetics of brushite formation, we used four ranges of titanium particle size (< 20 mu m, 20-45 mu m, 63-90 mu m and 90-125 mu m) The induction period tau, before the initial crystal growth of DCPD, varied markedly with the relative supersaturation sigma. The initial growth rate R(c) of brushite is strong ly size-dependent, whereas tau is relatively constant for the different particle sizes. Plots of Ln R(c) versus Ln sigma, for each particle size, gave an apparent order of 3.4 +/- 0.2 for the crystallization of brushite on titanium surface. The interfacial energy gamma estimate of 22.9 +/- 1.2 mJm(-2), from the kinetic results, was in the same order of magnitude than that for sparingly soluble salts. Observations by scanning electron microscopy showed many platelets of DCPD covering the titanium powder surface.