La ions in precipitated hydroxyapatites

摘要

Hydroxyapatites were synthesized by precipitation from an aqueous solution with La~(3+) (0-0.75%) and with carbonate (0-6.1%) at controlled pH 7.0. Uptake of La~(3+) was 90-95% complete. Relatively low Ca/P (1.54-1.63) ratios were attributed to nonstoichiometry. Carbonate in samples was identified by IR spectroscopy as B-type carbonate. Lattice parameters of the hexagonal apatite structure were not affected by the La~(3+) content. Noncarbonated samples heated to 800 deg C transform partially to #beta#-Ca_3(PO_4)_2. Thermogravimetric analysis showed release of 0.4 mol adsorbed and 1 mol crystalline water up to 400 deg C and decomposition of carbonate up to 900 deg C in the samples. Luminescence data obtained for Gd-containing hydroxyapatites prove that Gd~(3+) ions are not incorporated in the precipitated hydroxyapatite. These findings suggest that, in the La-containing samples, La~(3+) is surface adsorbed and not incorporated in hydroxyapatite.