Crystallization and colloidal stability of calcium phosphate phases

The interfacial energy of calcium phosphate powders has been determined through contact angle measurements using thin-layer wicking techniques. The much smaller interfacial energy of octacalcium phosphate (OCP) in contact with water compared with that of hydroxyapatite (HAP) supports the observation that the crystallization of the latter may be preceded by an OCP phase which can serve as a template for apatite growth. The colloidal stabilities of calcium phosphates of colloidal dimensions were also investigated. The relative stabilities of OCP, dicalcium phosphate dihydrate (DCPD), and HAP dispersions could be explained by invoking the concepts of Lewis acid-base interactions in addition to the two other more traditional types of interactions that are involved in the Derjaguin-Landau-Venvey-Overbeek (DLVO) theory, namely, electrical double-layer repulsion and van der Waals attraction.