Effect of CaF2 and CaO/Al2O3 ratio on evaporation and melting characteristics of low-fluoride CaF2–CaO–Al2O3–MgO–TiO2 slag for electroslag remelting

Abstract

ABSTRACT The present study focuses on the evaporation of fluoride from low-fluoride CaF2–CaO–Al2O3–MgO–TiO2 slag with varying CaF2 content and CaO/Al2O3 mass ratio and the melting characteristics of the slag. Moreover, thermodynamic and kinetic calculations are made to reveal the fluoride evaporation mechanism. The results show that the gaseous substance evaporated from the slag is mainly CaF2. The calculated vapour pressure in a sequence is CaF2 > MgF2 > AlF3 > AlOF. Furthermore, with the increase in CaF2 content from 15 to 30 wt-%, the evaporation of fluoride increases from 0.934 to 1.047%, and the melting temperature drops from 1480 to 1443°C. With the increase in the CaO/Al2O3 mass ratio from 0.8 to 1.4, the weight loss increases from 0.92 to 1.95% and then decreases to 1.70%, and the melting point drops from 1460 to 1324°C. The slag evaporation is controlled by the Valensi reaction mechanism, and its mechanism function is G(α) = α+(1−α)ln(1−α), which belongs to two-dimensional diffusion.