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 CO32− 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.