Characterization and thermal decomposition of synthetic carbonate apatite powders prepared using different alkali metal salts.

Two types of synthetic carbonate apatite [potassium-containing carbonate apatite (CAK) and sodium-containing carbonate apatite (CANa)] were prepared and characterized by thermogravimetric analysis, X-ray diffraction analysis (XRD) and Fourier transform infrared spectroscopy. The chemical formulas of carbonate apatite were determined to be Ca9.36K0.12(PO4)5.12(CO3)0.88(OH)1.73 and Ca8.72Na1.33(PO4)4.96(CO3)1.04(OH)1.80, respectively. Thermogravimetric analysis showed that the final weight loss at 1,200°C reached about 11.2% for CAK and 13.9% for CANa. Carbonate loss gradually occurred above 150°C and continued to 1,200°C. The crystallinity of the apatite phase was found to be much improved between 800 and 850°C for CAK and 750 and 800°C for CANa, where rapid carbonate loss occurred. A small amount of CaO formed above 900°C. For CANa, NaCaPO4 also formed above 700°C in both apatites. Although the lattice parameters of the carbonate apatites varied with temperature, the final a and c lattice parameters attained constant values of 0.9421 and 0.6881 nm.