Fluoride vaporization and crystallization of CaF2–CaO–Al2O3–(La2O3) slag for vacuum electroslag remelting.

The vaporization and crystallization of CaF 2 –CaO–Al 2 O 3 slags with different La 2 O 3 contents for electroslag remelting were investigated by various analytical methods. The results show that the main volatiles from investigated slag within 7.4 wt% La 2 O 3 content at 1723 K are CaF 2 and AlF 3. The weight loss of CaF 2 –CaO–Al 2 O 3 -(La 2 O 3) slags decrease with increase of La 2 O 3 content in both thermo gravimetric experiment and vacuum condition. The addition of La 2 O 3 within 7.4 wt% reduces the viscosity and breaking temperature of investigated slag, and the change of viscosity is not the main reason to inhibit the fluoride vaporization. The vapor pressure of CaF 2 and AlF 3 at 1723 K decreases with increase of La 2 O 3 content because of the changes in component activity. Thus, fluoride vaporization becomes weakened. The crystalline phases of CaF 2 –CaO–Al 2 O 3 slag are 11CaO·7Al 2 O 3 ·CaF 2 and CaF 2 , while the crystalline phases of slag within 7.4 wt% La 2 O 3 content are (CaLa)Al 3 O 7 , La(AlO 3) and CaF 2. The La 2 O 3 addition can decrease the crystallization temperature of CaF 2 and prevent the precipitation of 11CaO·7Al 2 O 3 ·CaF 2. • The vaporization and crystallization of CaF 2 –CaO–Al 2 O 3 -(La 2 O 3) were analyzed by TG-DSC. • The viscosity of CaF 2 –CaO–Al 2 O 3 -(La 2 O 3) slag was measured. • The crystalline phases ((CaLa)Al 3 O 7 , La(AlO 3)) were found in CaF 2 –CaO–Al 2 O 3 -7.4wt% La 2 O 3 slag. [ABSTRACT FROM AUTHOR]