PREPARATION AND CHARACTERIZATION OF FLUORIDE-SUBSTITUTED APATITES

Apatites were prepared with three different fluoride concentrations: 0 .0 mM (pure hydroxyapatite) 2.5 mM and 5 mM. Reactions were performed in aqueous medium using a reaction between diammonium orthophosphate a nd calcium nitrate 4-hydrate and ammonium fluoride at temperatures of 3 degrees, 25 degrees, 60 degrees and 90 degrees C. The effects of rea ction temperature and fluoride concentration on the crystal morphology , phase purity and crystallinity of the precipitates were observed, us ing transmission electron microscopy (TEM), X-ray diffraction (XRD), F ourier transform infrared (FTIR) spectroscopy and ion chromatography. Transmission electron micrographs revealed that the crystallites preci pitated at 3 degrees C were spheroidal, but became increasingly acicul ar with increasing precipitation temperature. X-ray diffraction result s indicated that all the materials produced were phase pure and that t he crystallinity of apatites prepared at higher precipitation temperat ures was higher than those prepared at lower precipitation temperature s. A significant difference in the a-axis dimension of fluoride-substi tuted apatites was observed, as compared to hydroxyapatite. FTIR spect roscopy revealed a hydroxyl band at 3568 cm(-1), along with a broad pe ak of adsorbed water in the region of 3568 cm(-1) to 2670 cm(-1) in th e hydroxyapatite and fluoride-substituted apatite powders. Hence by ca reful selection of the precipitation conditions and fluoride contents, the composition and morphology of fluoride-substituted apatite may be controlled and this has interesting implications for the development of these materials for biomedical implantation.