JOURNAL of the Tunisian Chemical Society

Sodium and carbonate co-substituted fluorapatites (Ca_10-xNa_x(PO_4)6-x(CO₃)xF₂, 0≤ x≤3) were prepared via the hydrothermal method. The obtained powders were investigated by X-ray diffraction, infrared spectroscopy, thermogravimetric analysis and specific surface area measurements. Results indicate that both Na⁺ and CO₃^2- ions were incorporated into the apatite structure only until x=2. Above this value, the excess of CaCO₃ remained unreacted. For the monosubstituted sample, the structural refinement using the Rietveld method showed that Na⁺ is distributed between the two cationic sites. No carbonate ions were detected in the apatite anionic channel, indicating that the synthesised carbonated fluorapatite is of B-type. The CO₃^2- group substituting the PO₄^3- one is located in positions corresponding to two faces of the phosphate tetrahedron. The specific surface area of the substituted powders increased with the rise of the carbonate amount. When calcined at 1000°C in air atmosphere, the carbonated fluorapatite decomposed with a release of CO₂ and formation of CaO.

E. Ben Salem, S. Nasr, P. Gravereau, K. Bouzouita

Fluorapatite, Carbonate, Sodium, Substitution, Hydrothermal synthesis

Pages: 201-210