Mixed phosphate-sulfate fluor apatites as possible materials in dental fillers

Abstract

A series of sulfate-phosphate apatite samples of formal composition Na x Ca 10-x (SO 4 ) x (PO 4 ) 6-x F 2 (x = 1,2,…,6) were prepared by solid state reactions and hydrothermal techniques. Rietveld analyses based on X-ray diffraction data clearly indicate that the samples synthesized by solid state reaction of the reactants Na 2 SO 4 , CaSO 4 , CaF 2 , and Ca 3 (PO 4 ) 2 consist of a mixture of two apatite end-members Na 6 Ca 4 (SO 4 ) 6 F 2 and Ca 10 (PO 4 ) 6 F 2 which contradicts previous work assuming a solid solution series between the end-members. The X-ray diffraction powder patterns of the samples synthesized by hydrothermal methods show a splitting of reflections which can be interpreted as a monoclinic reduction of the hexagonal symmetry, thus representing an apatite-like phase of the solid solution series with sulfate and phosphate groups. The hydrothermally synthesized compounds exhibit physical properties that are required for dental applications where apatite-like phases are used as fillers in composite materials.