Synthesis, characterization and thermal behavior of apatitic tricalcium phosphate

Apatitic tricalcium phosphate Ca9(HPO4)(PO4)5(OH) is a calcium orthophosphate that transforms into β-tricalcium phosphate Ca3(PO4)2 by heating above 750 °C. This work deals with powder synthesis using a wet precipitation method. An experimental design is applied to precise the influence of the synthesis parameters on the chemical composition (e.g. the Ca/P molar ratio). The Ca/P ratio of the precipitates varies greatly according to the pH value and the temperature of synthesis. A more or less important increase of the Ca/P ratio can occur with the ripening time in dependence on the value of the previous parameters. A reproducible synthesis of pure apatitic tricalcium phosphate (TCP) powders is attained by refinement of the parameters. The study is completed by physicochemical characterizations and the thermal behavior of the powders. X-ray diffractometry and differential thermal analysis are necessary to insure the purity of TCP powders. The decomposition of the apatitic TCP into β-TCP during heating influences the sintering behavior.