MAGNESIUM-CONTAINING CARBONATE APATITES

Hydroxyapatites precipitated at pH 7.0 and 9.0 with and without carbon ate and with different amounts of magnesium were studied Mg uptake, Ca /P ratios, and lattice constant data indicate that Mg is incorporated into the apatite lattice. IR spectra demonstrate the formation of B-ty pe carbonate apatites with carbonate substituting for phosphate. Decom position of carbonate-containing apatites at elevated temperatures up to 1000 degrees C is more gradual for apatites prepared at pH 9.0 than for those prepared at pH 7.0 for which an abrupt loss of carbonate oc curs after 600 degrees C. Compounds synthesized without added carbonat e partially transform to beta Ca-3(PO4)(2) (TCP) at about 700 degrees C. Greater transformation to TCP occurs as the Mg incorporation is inc reased, indicating the insertion of Mg into TCP and consequent stabili zation of the TCP. SEM micrographs show increases in the size of cryst allites when apatites are precipitated with Mg (in the 0.2-1.5% range) , providing further evidence for Mg incorporation into the apatite str ucture. (C) 1997 Elsevier Science Inc.