Characterization of hydroxyapatite particles plasma-sprayed into water

Optimization of plasma spraying parameters for producing hydroxyapatite (HA) is usually based on the relationship between the spraying parameters and the coating characteristic. However, the microstructural evolution during the flight of melted HA particles is usually neglected. In this paper, HA powder was plasma-sprayed into water to preserve the morphology of the flying melted HA particles, and the microstructure and phase composition of the sprayed particles were examined and elaborated. A central hollow structure and some novel morphologies of the melted HA particles were found. The central hollow structure was suggested to result from gaseous P2O5 and H2O decomposed from Ca10(PO4)6(OH)2 under high temperature, as well as the volume contraction of molten HA particle during cooling. The HA particles sprayed into water had a higher crystallinity and less impurity phase as compared with that of the HA coating. Furthermore, analysis on surface morphology and phase composition of the sprayed HA particles immersed in Simulated Body Fluid (SBF) seemed to demonstrate that the sprayed particles had a high bioactivity.