SYNTHESIS, CHARACTERIZATION AND HIGH-TEMPERATURE ANALYSIS OF AL-CONTAINING HYDROXYAPATITES

Hydroxyapatites were synthesized by precipitation from an aqueous solu tion with Al3+ (0-0.75%) and with carbonate (0-6.1%) at controlled pH (7.0 and 9.0). The uptake of Al3+ was almost complete at pH 7.0 and cl ose to 60% at pH 9.0. Relatively low Ca/P ratios were obtained. Carbon ate in the samples was identified as B-type carbonate. The lattice par ameters of the hexagonal apatite structure were not affected by the Al 3+ content. Broadening of the X-ray diffraction peaks indicated a lowe ring of the crystallinity with increasing Al3+ content of the samples. Noncarbonated samples prepared at pH 7.0 and heated to 700 degrees C transform partially to beta-Ca-3(PO4)(2). Thermogravimetric analysis s howed the release of adsorbed water in the 80-120 degrees C range, cry stalline water at 120-600 degrees C, simultaneous water and carbonate release at 400 degrees-600 degrees C and total carbonate loss at 900 d egrees C. It is suggested that in the samples of the present work Al3 ions are surface adsorbed. The relationship found between Al3+ and wa ter content and the crystallinity of the samples is discussed.