Thermal stability of porous A-type carbonated hydroxyapatite spheres

Porous A-type carbonated hydroxyapatite (CHAp) spheres were synthesized in the high-pressure hydrothermal system by the template-directed method. The thermal stability of porous A-type CHAp spheres was first studied via calcining in the wide temperature range from 393 K up to 1173 K, analyzed by FT-IR, XRD and SEM. The results showed that the decomposition of porous A-type CHAp spheres went through two stages, owing to the release of the carbonate from the OH⁻ channel and the collapse of apatite-type structure above 973 K, consecutively. The nanoparticles in situ replaced the flakelets of porous CHAp spheres and packed closely into new regular porous Ca₃(PO₄)₂ spheres.