Abstract
Fluoride evaporation of CaF2–CaO–Al2O3–MgO–TiO2-(Li2O) slag with different Li2O contents for vacuum electroslag remelting was investigated by thermogravimetry (TG), differential scanning calorimetry (DSC), and mass spectrometer (MS) measurements in conjunction with thermodynamic analysis, and the effects of Li2O on the melting temperature and viscosity of slag were studied. Furthermore, the variation of slag structure was analyzed by Fourier transformation infrared (FTIR) spectroscopy. The results show that, with the increase in Li2O content from 0 to 5.15 wt%, the evaporation of fluoride from the molten slag increased significantly, melting temperature and viscosity of slag decreased. Moreover, the evaporating species from Li2O-bearing slag were mainly LiF and CaF2 under a vacuum of 10 Pa. LiF evaporation was generated rapidly from molten slag due to the high vapor pressure of LiF when the temperature exceeded 800 °C, and the evaporation of CaF2 occurred above 1000 °C. Higher vacuum could increase the evaporation of fluoride. The vapor pressures were in the following sequence: LiF > CaF2 > MgF2 >AlF3 > AlOF. Additionally, FTIR analyses revealed that the O2− provided by Li2O would depolymerize [AlO4]-tetrahedral structures from Q4 units to Q3 and Q2 units, leading to decreasing the viscosity consequently.
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