Annaik Genson

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 calciumalumino- 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-Al-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.

Ca-SiAlON Glasses: Effects of Fluorine on Glass Formation and Properties

Oxynitride glasses are effectively alumino-silicate glasses in which nitrogen substitutes for oxygen in the glass network, resulting in increases in glass transition and softening temperatures, viscosities (by two to three orders of magnitude), elastic moduli and microhardness. Calcium alumino-silicate glasses containing fluorine are known to have useful characteristics as potential bioactive materials. Therefore, the combination of both nitrogen and fluorine additions to these glasses may give useful bioglasses with enhanced mechanical stability. This paper gives a review of oxynitride glasses and reports glass formation and evaluation of glass properties in the Ca-Si-Al-O-N-F system. Within the previously defined glass forming region in the Ca-Si-Al-O-N system, homogeneous, dense glasses are formed. However, addition of fluorine affects glass formation and reactivity of the glass melts and can lead to fluorine loss as SiF4, but also nitrogen loss, and cause bubble formation. At high fluorine and high Ca contents under conditions when Ca- F bonding is favoured, CaF2 crystals precipitate in the glass. It was found that fluorine expands the glass forming region of Ca-Sialon system and facilitates the solution of nitrogen into the melt.

Effect of fluorine and nitrogen anions on properties of Ca-Si-Al-O glasses

The preparation of bulk glasses in Ca-Si-Al-O-N-F system with the composition in equivalent % of 28e/oCa:56e/oSi:16e/oAl:100-X-Ye/oO:Xe/oF:Ye/oN are reported. The glass formation behaviour and properties of this new range of glasses are examined in detail. Fluorine decreases the glass transition temperature, the density and the mechanical properties of the glasses while nitrogen increases them. Therefore, it appears that fluorine acts as a network modifier while, on the contrary, nitrogen acts as a network former even in presence of fluorine.