Synthesis in Pure Ethanol and Characterization of Nanosized Calcium Phosphate Fluoroapatite

A fluoridated calcium phosphate CPF powder was synthesized in anhydrous ethanol starting from Ca(OEt)2, H3PO4, and NH4F reagents. Two other materials, CP and CF, were also obtained without, respectively, the fluoride and the phosphate source to understand the mechanism of formation of the CPF solid. The vacuum-dried precipitate CF was fully crystallized and identified as calcium fluoride CaF2. In contrast, the vacuum-dried precipitates CPF and CP, which have Ca/P ratios close to 1.67, were amorphous to XRD. The amorphous sample CPF had the same chemical composition as that of a fluoroapatite Ca10(PO4)6F2 compound. The XPS spectroscopy showed that this amorphous solid CPF was homogeneous and was not a mixture of Ca9(PO4)6 and CaF2 phases. The thermal behavior was studied by TGA, DTA, XRD, SEM, and IR spectroscopy. The analyses confirmed the homogeneity of the amorphous CPF precipitate, which crystallized, at 460 °C into a pure fluoroapatite phase. The starting nanosized CPF powder has shown its high reactivity with a very active sintering at 500 °C.