Fluoride ion-promoted reaction of β-tricalcium phosphate to fluoridated hydroxyapatite

Solvothermal reaction of β-tricalcium phosphate (β-TCP) [Ca3(PO4)2] with ammonium fluoride in water-1-octanol biphase proceeds to afford fluoridated hydroxyapatite (FHAp) [Ca10(PO4)6(OH)2(1−x)F2x] quantitatively. It was found that FHAps with various fluoride contents were more easily prepared under mild reaction conditions and that higher crystallinity of FHAp was obtained, compared with the reaction of α-TCP with fluoride ions. The solvolysis reaction of β-TCP did not proceed without fluoride ions, whereas the reaction of α-TCP proceeded with or without fluroide ions. This indicates that the former reaction is promoted by fluoride ions.