Magnesium action on the stability of fluorapatite.

Fluorapatites with various magnesium contents (Mg-FAp) were synthesized at pH 7.4 and 80 degrees C. The contraction of their c-axis dimensions observed in X-ray diffraction analysis, together with the results of chemical analyses, suggested that Mg2+ ions may substitute into the apatite crystals to a limited extent. The apatites became less well crystallized with increase in magnesium content. At any given magnesium-calcium feed-in molar ratio (Mg/Ca)f, the magnesium uptake by Mg-FAp was higher than that by the corresponding F- -free Mg-HAp. Therefore, the former became amorphous at lower (Mg/Ca)f than the latter. However, in terms of crystallographic considerations, the Mg-FAp synthesized at high (Mg/Ca)f revealed its apatitic features after pyrolysis at 1,000 degrees C, while Mg-HAp displayed the tricalcium phosphate X-ray pattern.