Glass Formation & Properties of Oxyfluoronitride Glasses

In this research the effect of fluorine addition on glass formation, properties and crystallisation in the Ca-Si-Al-O-N system is studied. Two glass forming regions at 20 eq.% N, 1 eq.% F and 20 eq.% N, 5 eq.% F at 1650°C were determined by firing of 50 and 75 compositions, respectively. With fluorine incorporation into this system, the glass forming region becomes larger and expands mainly towards Ca rich compositions where fluorine lowers their liquidus temperatures by up to 800°C. Porous glasses were found at the Si rich corner of both glass forming regions investigated as a result of loss of volatile SiF 4 . In this case there is no sufficient modifier cation (Ca 2+ ) to form one non- bridging oxygen per Si and prevent the formation of Si-F bonds. Also it is found that the addition of minor amounts of fluorine (1 eq.%) to these glasses enables the nitrogen content to be increased to 40 eq.% which is significantly higher than the nitrogen solubility limit in Ca-SiAlON system (26 eq.%).