Sintering behaviour of carbonated hydroxyapatite prepared at different carbonate and phosphate ratios

In the present work, the effect of varying the carbonate to phosphate (CO32−/PO43−) molar ratios from 0.5 to 4 on the sintering behaviour of carbonated hydroxyapatite (CHA) synthesized by a wet chemical method were investigated. The sintering was performed under carbon dioxide atmosphere at 900 °C to maintain the B-type CHA structure. The derived powders as well as the sintered samples were characterized to determine the phase present, crystallographic parameters, the functional group resulting from the substitution of CO32− for PO43−, microstructural evolution under different molar ratios, bulk density, Vickers hardness and fracture toughness. It was found that as the CO32−/PO43− ratio increase, this was accompanied by an increased in the c/a lattice ratio. The sintering studies indicated that the all the CHA was thermally stable and retained the apatite structure after sintering. The relative density of the sintered CHA was found to decrease along with the Vickers hardness and fracture toughness as the CO32−/PO43− ratio increased from 0.5 to 4. The improvement in the mechanical properties was associated with improvement in the relative density and the larger grain size of the sintered samples.