Investigation of fluoride vaporization from CaF2CaOAl2O3 slag for vacuum electroslag remelting

In this study, five types of CaF2CaOAl2O3 slags with varying CaO/Al2O3 mass ratio and CaF2 content were selected for investigating the vaporization behavior of slag bearing high CaF2 content by thermo gravimetry and ion and molecule coexistence theory. The results show that the volatile product of slag is the AlF3. The vaporization rate is affected by the vapor pressure of AlF3, mole number of complex molecules and the viscosity of slag. For all slags, the vaporization rate of slag bearing approximately 70 wt% CaF2 and 30 wt% Al2O3 is the fastest due to the ultra-high vapor pressure of AlF3. In the test of slags containing 70 wt% CaF2, vaporization rate firstly decreases, then increases with CaO/Al2O3 mass ratio increasing from 0.05 to 1.10 and 2.00. In the case of slags containing same CaO/Al2O3 mass ratio, vaporization rate firstly increases, then decreases with CaF2 content decreasing from 68.9 wt% to 48.1 wt% and 28.7 wt%. Slag T5 bearing approximately 30 wt% CaF2, 33.9 wt% CaO and 36.1 wt % Al2O3 has lower electrical conductivity, slower vaporization rate and larger sulfide capacity, which will be economical, environmentally friendly and suitable for vacuum electroslag remelting.