Phase formation in gels of the apatite-anorthite system

Phase formation in heat-treated composites containing anorthite gel and flu orapatite has been investigated. For the sol-gel synthesis TEOS, Al(NO3)(3) 9H(2)O, Ca(NO3)(2) . 4H(2)O, (NH4)(3)PO4 . 3H(2)O, NH4F and CaF2 were used as precursors. The gel mixtures were treated from 200 to 1250 degrees C. I t was found that the gels remain in an amorphous state up to 900 degrees C. From X-ray diffraction structural analysis of anorthite gel-glasses heat t reated at 600 degrees C and 800 degrees C it was found that a shift of the first maximum occurred from 1.85 to 1.77 Angstrom, which could be interpret ed as a transformation of the gel-glass structure with increasing temperatu re. During the heat treatment of the mixed gels from the apatite-anorthite system it was found that fluorapatite is present as a major crystal phase a t 950 degrees C. At 1250 degrees C anorthite and gehlenite are the major cr ystalline phases.