The changes in the composition of the CaO-SiO2-CaF2 and CaO-Al2O3-CaF2 slags were measured after an equilibration at 1773 K to deduce the vaporisation loss of fluoride species. Furthermore, the volatilisation phenomena were discussed based on the thermodynamic fundamentals. In the CaO-SiO2-CaF2 system, the SiO2 and CaF2 contents simultaneously decreased at basicity B(≡(%CaO)/(%SiO2)) ≤ 1.0, while the content of CaF2 only decreased at basicity of the slags greater than about unity. On the other hand, the content of CaF2 only decreased in the entire composition range in the CaO-Al2O3-CaF2 system. The volatilisation behaviour of fluoride species from the slags could be explained from the thermodynamic assessment by taking the activity and the activity coefficient of CaF2 into account. From the measured results and the thermodynamic calculations, it could be concluded that the major volatilisation species in the relatively acidic (B ≤ 0.8-1.0) silicate melts would be SiF4 (g), while the CaF2 (g) would be a dominant vaporisation species in the relatively basic (B ≥ 1.0) silicate and in the aluminate melts.
All Science Journal Classification (ASJC) codes
- Condensed Matter Physics
- Physical and Theoretical Chemistry
- Metals and Alloys
- Materials Chemistry