Nucleation and crystal growth of dicalcium phosphate dihydrate on titanium powder

Abstract

The nucleation and crystal growth of dicalcium phosphate dihydrate (CaHPO4 · 2H2O DCPD or brushite) on titanium powder surface has been studied in metastable supersaturated solutions at 37°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 μm, 20–45 μm, 63–90 μm and 90–125 μm). The induction period τ, before the initial crystal growth of DCPD, varied markedly with the relative supersaturation σ. The initial growth rate R C of brushite is strongly size-dependent, whereas τ is relatively constant for the different particle sizes. Plots of Ln R C versus Ln σ, for each particle size, gave an apparent order of 3.4±0.2 for the crystallization of brushite on titanium surface. The interfacial energy γ estimate of 22.9±1.2 mJ m-2, from the kinetic results, was in the same order of magnitude than that for sparingly soluble salts. Observations by scanning electron microscopy showeed many platelets of DCPD covering the titanium powder surface.