The effect of phosphate source on the sintering of carbonate substituted hydroxyapatite

Carbonate hydroxyapatite (CHAp) was synthesized by a wet precipitation method. In the synthesis, calcium oxide, H₃PO₄ and (NH₄)₂HPO₄ were applied as reactants. NH₄HCO₃ in the amount of 0.05–0.20 mol per 0.3 mol of H₃PO₄ or (NH₄)₂HPO₄ was used as the source of CO₃^2? groups. Sintering was carried out using powders and uniaxially pressed samples of carbonate and non-carbonate hydroxyapatites. The influence of synthesis conditions as well as sintering atmosphere on sinterability and phase composition of the final ceramic materials was evaluated. It was found that using properly synthesized CHAp powders and CO₂ atmosphere during heat-treatment it was possible to obtain dense CHAp ceramics with 1% of CaCO₃ as the secondary phase at the temperature 300–350 °C lower than that required for non-carbonate hydroxyapatite. Chemical stability and bioactive potential of CHAp–CaCO₃ ceramics were confirmed by in vitro tests.