Influence of fluorine content in apatite-mullite glass-ceramics

The nucleation and crystallization of a series of glasses based on 4.5SiO(2).3Al(2)O(3).1.5P(2)O(5).(5 - z)CaO.zCaF(2) with a Ca:P ratio corresponding to apatite were studied. In these glasses, the objective was to investigate the influence of fluorine content and z was varied from 3 to 0. All the glasses studied crystallized to fluorapatite (FAP) and mullite with the exception of the glass containing no fluorine, which crystallized to P-tricalcium phosphate (Ca-3(PO4)(2)) and anorthite (CaAl2Si2O8). Glasses that contained sufficient fluorine to form FAP bulk nucleated to give FAP without a nucleation hold. Thermal gravimetric analysis demonstrated a significant weight loss corresponding to the crystallization of mullite, which increased with the fluorine content of the glass and also with decreased particle size. The loss was attributed to volatile SiF4. The glass transition temperature decreased with increased fluorine content of the glass.