Surface structure and properties of fluoridated calcium hydroxyapatite

The surface structure and properties of synthetic calcium hydroxyapatite (CaHap) treated with different concentrations of F− ions at neutral pH were investigated by a variety of techniques. The adsorption isotherm of F− ions on CaHap below 0.03 mol dm−3 exhibited the Langmuir type and the saturated amount was estimated to be 1.7 ions nm−2. This value is lower than 2.88 ions nm−2 of surface OH− number calculated from the crystal structure of CaHap, proving that all the surface OH− ions are not replaced with F− ions. The deuteration of column OH− ions of CaHap was interfered with F− ions replaced for OH− ions in the entrance of OH− columns along c-axis, that is, on a b face. When the samples were treated above 0.04 mol dm−3, the surface phase of CaHap was dissolved to produce calcium fluorapatite, so that, the deuteration of column OH− ions of CaHap was more promoted than the materials treated below 0.03 mol dm−3. The surface H2PO4− and HPO42− ions of CaHap were not replaced with F− ions.