Synthesis and characterization of functional gradient materials using Indian corals

The partial conversion of coralline hydroxyapatite (HA) into tricalcium phosphate (TCP) catalyzed by the thermal decomposition of silver oxide was investigated. The thermal analysis of HA powder mixed with 5 mol % Ag2O indicated the decomposition of silver oxide to be around 550 degrees C in the presence of HA. Subsequently a functional gradient structure was formed by spreading silver oxide on one surface of the HA compact of diameter 10 mm and then firing at 700 degrees C in air. The X-ray powder diffraction analysis confirmed the formation of alpha-TCP induced by the Ag2O decomposition. The content of alpha-TCP of the sintered pellet was found to decrease with the increasing depth from the surface of the pellet. In vitro solubility study in phosphate buffer of pH 7.2 showed the stability of the biphasic material as in between HA and TCP.