The Equilibria Between SiF4(g) and CaF2 + CaO + SiO2 Melts at 1450°C

Abstract 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 P SiF4 above the melts increases exponentially with decrease of basicity in calcium silicate constituting the melts, while it is less than the vapour pressure of CaF2 above the melts when N CaO/N SiO2 ≥ 1.5. The effects of CaF2 concentration on P SiF4 are practically constant in the CaF2-rich region. These results were analysed by applying a random model among Oo, O−, O2−, Foand F−. The results suggested that the behaviour of CaF2 added into 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 made by rapid cooling of the melts equilibrated with SiF4 gas at more than 104Pa.