Abstract
Constant composition methods have been used to investigate the mechanisms of crystal growth and dissolution of calcium phosphate minerals. Interfacial tensions between water and each of these surfaces were calculated from measured contact angles using surface tension component theory. The interfacial tension values, -4.2, 4.3, 10.4 and 18.5 mJm-2 for dicalcium phosphate dihydrate (DCPD), octacalcium phosphate (OCP), hydroxyapatite (HAP) and fluorapatite (FAP), respectively, compare well with those calculated from dissolution kinetics experiments and provide information concerning the growth and dissolution mechanisms. The much smaller interfacial tensions of OCP and DCPD in contact with water compared with those of HAP and FAP support the observation that the crystallization of the latter phases was often preceded by the formation OCP and DCPD and that both OCP and DCPD could serve as precursors to apatite growth. In addition, the ability of a surface to nucleate mineral phases is closely related to the magnitude of the interfacial energies which are also important in understanding stability of calcium phosphate colloidal dispersions.
