Formation of hollow spheres of hydroxyapatite in plasma spraying

Hydroxyapatite (HA) particles are subjected to melting at high temperature when used to plasma spray a coating onto a metallic substrate. Accordingly, changes in the melting temperature and morphology of the HA particles are of importance in defining the coating characteristics. The HA particles were plasma sprayed into water and their melting temperature and structure change were analysed using SEM. The results showed that, under the same conditions of spraying, the melting level changed with particle size and more hollow spheres were formed by the molten HA particles, which may have resulted from gaseous P2O5 and H2O arising from decomposed Ca-10(PO4)(6)(OH)(2) at a high temperature and also from the volume contraction of HA powder particles as a result of fast cooling. In this study, only the morphology of the HA hollow spheres was examined. These hollow spheres will have important applications in the tissue engineering field and in the optimisation of plasma spraying parameters for HA coatings.