Effects of carbonate on hydroxyapatite formed from CaHPO_4 and Ca_4(PO_4)_2O

摘要

Carbonated hydroxyapatites were formed via reactions in NaHCO_3/NaH_2PO_4 solutions from a mixture of particulate tetracalcium phosphate (TetCP) and anhydrous dicalcium phosphate (DCPA). Reactions were followed by determinations of pH and ion concentrations. The solids formed were analyzed by XRD and FTIR. Rates of heat evolution were established by isothermal calorimetry. Reactions in the absence of NaH_2PO_4 did not reach completion within 24 h. Constitution of reactants to achieve a DCPA-to-NaHCO_3 ratio of 1, in conjunction with the presence of NaH_2PO_4 as a buffer, was found to be optimal for formation of apatite with no remaining reactant. The amount of carbonate incorporated in this apatite was 4-5 wt%. Calorimetry indicated the reaction mechanism to depend on the bicarbonate concentration in solution. The presence of NaH_2PO_4 was found to increase the reaction rate but decrease the extent of carbonate uptake.