Sol–gel derived fluoridated hydroxyapatite films

Fluoridated hydroxyapatite [Ca5(PO4)3(OH)xF1−x] films have reasonably good bioactivity and stability in the body, they could behave better than hydroxyapatite films in medical applications. In this work, a sol–gel method was adopted to prepare fluoridated hydroxyapatite films on titanium alloy. Three kinds of fluorine-containing reagents CF3COOH, HPF6 and NH4PF6 were selected to add into mixed Ca(NO3)2–P2O5 ethanol solutions to form dipping sols. The dipping sol with CF3COOH led to an apatite film in which fluorine could not be detected in EDS. While the dipping sol, with HPF6 or NH4PF6, could result in fluoridated hydroxyapatite films. The incorporation of fluorine could be attributed to the reactions of both HPF6 or NH4PF6 with the mixed Ca(NO3)2–P2O5 ethanol solution to form nano-sized CaF2 particles, which in turn, react with other species to form fluoridated hydroxyapatite during the film formation at 600 °C. Among the three fluorine-containing reagents, HPF6 was the best because its dipping sol was more stable and the resulting films had better morphology.