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 investigat e the influence of fluorine content and z was varied from 3 to 0. All the g lasses studied crystallized to fluorapatite (FAP) and mullite with the exce ption of the glass containing no fluorine, which crystallized to P-tricalci um phosphate (Ca-3(PO4)(2)) and anorthite (CaAl2Si2O8). Glasses that contai ned sufficient fluorine to form FAP bulk nucleated to give FAP without a nu cleation hold. Thermal gravimetric analysis demonstrated a significant weig ht loss corresponding to the crystallization of mullite, which increased wi th 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.