Influence of cooling modes on purity of solid-state synthesized tetracalcium phosphate

Pure tetracalcium phosphate powder (TTCP) was prepared by a solid-state phase reaction at 1500 °C. Effects of cooling modes on the synthesizing process of TTCP powder and its thermal behavior at different heating temperatures were investigated by XRD and FTIR. The results show that cooling in dry air tends to promote formation of single phase TTCP, while in situ cooling in furnace results in a mixture of hydroxyapatite (HAP) and CaO. The examination of the thermal behavior of TTCP indicates that there exists a decomposing zone in the range of 500 °C–1200 °C, in which the high-temperature synthesized TTCP phase is transformed during the subsequent cooling process. This was confirmed by three additional cooling treatment routes that provide significant experimental evidence to the cooling modes effect on the purity of TTCP. The phase transformation course of starting materials heated to elevated temperatures was further studied by TGA–DSC analysis with the aid of XRD and FTIR, in order to fully understand the complicated synthesizing process of TTCP.