201 SYNTHESIS AND CHARACTERIZATION OF SODIUM AND CARBONATE-CO-SUBSTITUTED FLUORAPATITES Ezzeddine BEN SALEM a , Samia NASR a , Pierre GRAVEREAU b and Khaled BOUZOUITA a* 1 Laboratoire de Chimie Industrielle, Ecole Nationale d’Ingénieurs de Sfax, B.P. 1173, 3038 Sfax, Tunisie 2 Institut de Chimie de la Matière Condensée, Université de Bordeaux I,CNRS[UPR9048] 87 Avenue du Dr Schweitzer 33608 Pessac Cedex (Reçu le 10 Mai 2012, accepté le 08 Avril 2013) ABSTRACT: Sodium and carbonate co-substituted fluorapatites (Ca 10-x Na x (PO 4 ) 6-x (CO 3 ) x F 2 , 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 - 2 3 CO ions were incorporated into the apatite structure only until x=2. Above this value, the excess of CaCO 3 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 - 2 3 CO group substituting the - 3 4 PO 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 CO 2 and formation of CaO. Key words: Fluorapatite; Carbonate; Sodium; Substitution; Hydrothermal synthesis RESUME: Des fluoroapatites co-substituées au sodium et au carbonate (Ca 10-x Na x (PO 4 ) 6-x (CO 3 ) x F 2 , 0≤x≤3) ont été synthétisées par la méthode hydrothermale. Les poudres obtenues ont étés analysées par diffraction des rayons X, spectroscopie infrarouge, thermogravimétrie et mesure de la surface spécifique. Les résultats obtenus montrent que l’incorporation simultanée des ions carbonate et sodium dans la structure apatitique n’est possible que jusqu’à x=2. Au- delà de cette valeur, l’excès de CaCO 3 ne prend pas part à la réaction. L’affinement structural par la méthode Rietveld de l’échantillon monosubstitué montre que les ions Na + sont localisés dans les deux sites cationiques et l’absence des ions carbonate dans les tunnels anioniques. Il s’agit donc d’une substitution de type B. Les ions - 2 3 CO substituent les ions - 3 4 PO dans des postions correspondant à deux faces du tétraèdre du groupement phosphate. Le traitement thermique des poudres réalisé sous air à 1000°C révèle une décomposition partielle de la phase apatitique carbonatée avec départ de CO 2 et formation de CaO. Mots-clés: Fluoroapatite; Carbonate ; Sodium; Substitution; méthode hydrothermale 1. INTRODUCTION Over the last three decades, hydroxyapatite (Ca 10 (PO 4 ) 6 (OH) 2 , HA) has gained much interest as a biomaterial thanks to its chemical composition and crystallographic structure similar to those of the mineral phase of the hard tissues, contributing largely to its biocompatibility and bioactivity [1- 4]. However, in comparison to synthetic HA, biological apatite is nonstoechiometric, and it contains several species such as Na + , K + , Mg 2+ , Zn 2+ , F - , - 2 3 CO , etc. Among these ions, which have a strong influence on physical-chemical, biological and mechanical properties of the apatite, - 2 3 CO is the most abundant one in the bone [5]. Carbonated apatite is more reactive and soluble than pure HA [6-8]. In the HA structure, - 2 3 CO ions can replace, either, the two OH - and - 3 4 PO ions, leading to A- or B-type carbonated HA, respectively. They can also substitute both ions simultaneously, leading * Correspondant author, e-mail : khaled.bouzouita@ipeim.rnu.tn Journal de la Société Chimique de Tunisie, 2013, 15, 201-210