Effect of MgO on the fluoride vaporization and crystallization of CaF2–CaO–Al2O3–(MgO) slag for vacuum electroslag remelting.

The vaporization and crystallization of CaF2–CaO–Al2O3 slags with different MgO contents for electroslag remelting were investigated by various analytical methods. The results show that the main volatiles from investigated slag with 8.8 mass% MgO content at 1723 K are CaF2 and AlF3 and contain trace MgF2. The mass loss of CaF2–CaO–Al2O3–(MgO) slag decreases with the increase of MgO content. The addition of MgO within 8.8 mass% has little effect on the viscosity of investigated slag, implying that the viscosity change is not the reason to inhibit the fluoride vaporization. At 1723 K, the vapor pressures of CaF2 and AlF3 decrease with the increase of MgO content; thus, fluoride vaporization becomes weak. The fluoride vaporization of slag with MgO addition under vacuum at 1823 K is also inhibited. The MgO addition can decrease the crystallization temperature of 11CaO·7Al2O3·CaF2, but excessive MgO addition can lead to the precipitation of MgO. [ABSTRACT FROM AUTHOR]