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. (C) 2002 Elsevier Science B.V. All rights reserved.