KINETICS AND MECHANISMS OF OCTACALCIUM PHOSPHATE DISSOLUTION AT 37 DEGREES-C

Octacalcium phosphate (OCP) is regarded as an important biomineralization precursor during the formation of hydroxyapatite. In the present work, the kinetics of dissolution of OCP has been studied at 37-degrees-C over a range of undersaturations using the constant composition method. The kinetics data are analyzed in terms of recent crystal growth theories using a nonlinear least-squares procedure. A rate equation is derived for a spiral dissolution following a detachment-desorption-volume diffusion mechanism at very low kink densities. Volume diffusion appears to provide little resistance to OCP dissolution compared with processes occurring at the crystal surface. It is suggested that the ions detached from the crystal steps undergo surface diffusion before escaping into the bulk solution.