An introduction to the glass formation and properties of Ca-Si-Al-O-N-F glasses

Ca-Sialon glasses have been known for some time [1] and they are effectively calcium-alumino-silicate glasses containing nitrogen which improves their mechanical properties. Calciumalumino-silicate glasses containing fluorine are known to have useful characteristics as potential bioactive materials [2]. Therefore, the combination of both nitrogen and fluorine additions to these glasses may give useful bioglasses with enhanced mechanical stability.Addition of fluorine to oxynitride glasses was not reported previously and this paper gives the first report of the glass forming regions (and evaluation of some properties) in the Ca-Si-Al-O-N-F system. Within the previously defined [1] glass forming region in the Ca-Si-AI-O-N system, homogeneous, dense glasses are formed. Addition of fluorine extends the glass forming region but also increases the reactivity of the glass melts. One major problem is fluorine loss as SiF₄, but also loss of nitrogen, which affects the final composition and results in porous samples. To suppress the fluorine loss and CaF₂ precipitation, consideration of the ratio of cations to fluorine and the coordination number of Al atoms is important. Discussion of the role of cations in these oxyfluoronitride glasses is presented.