Investigation on the structure, fluoride vaporization and crystallization behavior of CaF2-CaO-Al2O3-(SiO2) slag for electroslag remelting

The structure, vaporization behavior and crystallization of CaF2-CaO-Al2O3 slags with different SiO2 contents for electroslag remelting were investigated by employing the TG and DSC measurements in conjunction with the Raman spectroscopy measurement for linking the macroscopic physicochemical property and microstructure information. The results show that SiO2 addition makes the depolymerized aluminate units polymerized into fully polymerized QAl4 unit and Al-O-Al complex structural groups. With the SiO2 content increasing to 6.1 mass%, the vaporization rate of fluoride increases because the SiF4 possessing higher vapor pressure is formed and the SiO2 addition can promote the formation of AlF3. As SiO2 content is further increased to 8.6 mass%, the vaporization rate of fluoride decreases because the mass transfer becomes slower. The more complex slag structure resulted from SiO2 addition dramatically decreases the crystallization temperature of the primary crystalline phase and the size of crystalline particles in the solidified slag.