Abstract: Fluoridating holds considerable promising for improving thermos stability of calcium-deficient hydroxyapatite with reserving pristine good biocompatibility and bio-activity. In this paper, synthetic products and their thermo stability are studied with different fluorine additions under the same chemical precipitation condition by X-ray diffraction (XRD). Dicalcium phosphate dihydrate (DCPD) is the main product with few hydroxyapatite (HA) when no fluorine is added; mixture of calcium-deficient fluoridated hydroxyapatite (D-FHA) and DCPD appears in products when fluorine is added, and only D-FHA remains in products of Sample 04F. Influence of fluorine on the synthetic process is proved to accelerate the transformation from DCPD to D-FHA. Synthetic products are further sintered to investigate the thermo stability. Dehydration occurs only in Sample 00F and Sample 02F when heated at 200℃, which does not appear in Samples 04F—10F. D-FHA of Sample 04F begins to decompose into β-Ca3(PO4)2 and β-Ca2P2O7 at 600℃. The temperature of D-FHA decomposition rises and the stability improves with the increasing fluorine addition.

Key words: hydroxyapatite; fluoridation; X-ray diffraction (XRD); calcination; phase transformation