Immersion behavior of plasma-sprayed modified hydroxyapatite coatings after heat treatment

The effect of heat treatment was studied on plasma-sprayed hydroxyapatite (HA) coatings modified by addition of SiO2, CaO, P2O5 and Na2O. Morphological and chemical changes of these heat-treated coatings underwent in simulated body fluid (SBF) were also investigated. The results showed that during plasma spraying, P2O5 and SiO2 enhanced the thermal decomposition of the HA structure, while CaO and Na2O did not. Annealing of the coatings in air at 650 °C led to recrystallization of amorphous calcium phosphate and effectively increased the conversion of non-apatite phase (TCP) into apatite. The heat treatment also resulted in a reduction of ‘flake-type’ structures associated with plasma-sprayed coatings. When immersed in SBF, the SiO2- and CaO-containing HA coatings did not show apatite precipitation in contrast to three other types of samples. That because of their TCP content showed the formation of apatite spherulites after 30-day immersion in SBF.