Sol–gel derived fluoridated hydroxyapatite films

Abstract Fluoridated hydroxyapatite [Ca 5 (PO 4 ) 3 (OH) x F 1− 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 CF 3 COOH, HPF 6 and NH 4 PF 6 were selected to add into mixed Ca(NO 3 ) 2 –P 2 O 5 ethanol solutions to form dipping sols. The dipping sol with CF 3 COOH led to an apatite film in which fluorine could not be detected in EDS. While the dipping sol, with HPF 6 or NH 4 PF 6 , could result in fluoridated hydroxyapatite films. The incorporation of fluorine could be attributed to the reactions of both HPF 6 or NH 4 PF 6 with the mixed Ca(NO 3 ) 2 –P 2 O 5 ethanol solution to form nano-sized CaF 2 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, HPF 6 was the best because its dipping sol was more stable and the resulting films had better morphology.