Abstract
Magnesium-substituted fluorapatites (Ca10-xMgx(PO4)(6)F-2 with 0 <= x <= 6) were prepared by hydrothermal method. The samples were characterized by chemical analysis, X-ray diffraction,, infrared spectroscopy and specific surface area measurements. For x <= 2.5, the X-ray diffractior, patterns of the as-prepared powders corresponded to a single phase of an apatite structure. Above this value, a second phase NH4MgPO4 center dot H2O was identified. The (Ca+Mg)/P molar ratios and lattice parameters data indicated that the substitution of Mg for Ca was limited to x=2.5. This limit is higher than that obtained by the precipitation synthesis. The specific surface area of the as-prepared powders increased from 45 to 92 +/- 2 m(2)/g, for x varying from 0 to 2.5, respectively. At 800 degrees C and higher, the calcination of the powders with 0<x <= 2.5 led to the crystallization of the Mg2F(PO4) phase. Its formation resulted from an amorphous phase, and no decomposition of the apatites was detected.