SiF4 pressures above CaF2+ CaO + SiO2 melts

The dissolution and evolution measurements of SiF4(g) with CaF2+ CaO + SiO2 melts have been carried out by Sieverts' method at 1450 °C. The equilibrium pressure of SiF4, PSiF4, above the melts increases exponentially with the decrease in the basicity of the calcium silicate which constitutes the melts, while it is less than the vapour pressure of CaF2 above the melts when NCaO/NSiO2 1.5. The effects of CaF2 concentration on PSiF4 are practically constant in the CaF2-rich region. These results were analysed by applying a random-mixing model among O0, O–, O2–, F0 and F–. The results suggest that the behaviour of CaF2 added to silicate melts can be interpreted as a competitive reaction between F– and O2– on the silicate network and that the ability of F– to disrupt the silicate network is far less than that of O2–.A calcium fluorosilicate which is considered to have Si—F bonds in addition to Ca—F bonds was detected in the solid samples obtained by rapid cooling of the melts equilibrated with SiF4 gas at > 104 Pa.