Investigation of fluoride evaporation from CaF2–CaO–Al2O3–MgO–TiO2–(Li2O) slag for electroslag remelting

Abstract

AbstractThe isothermal kinetics of fluoride evaporation from CaF2–CaO–Al2O3–MgO–TiO2–(Li2O) slag with varying Li2O content were investigated in the temperature range 1743–1803 K by thermogravimetric analysis. Thermodynamic calculations and viscosity measurements were applied for studying the evaporation mechanism of fluoride. The results showed that the evaporation ratio increases with increasing Li2O content and temperature. The volatile constituents from the molten slags, mainly LiF and CaF2, were detected and their concentrations calculated. The fluoride evaporation is primarily affected by the vapour pressure of LiF and CaF2, viscosity of the slags, and melt-component activities under given experimental conditions. On the other hand, mass transfer of the gas is not the rate-controlling step that affects fluoride evaporation from the slags. The activation energy for fluoride evaporation gradually decreased from 193 ± 11 to 113 ± 3 kJ mol−1 as the Li2O content in the slags increases from 0 to 5.48 wt%. These results hold great theoretical significance for developing low-fluoride slags for electroslag remelting.