Structural Behavior of Al3+ in Mould Flux Glasses of CaO-SiO2-Al2O3-Na2O-CaF2 System

Quenched glass samples of CaO-SiO2-Al2O3-Na2O-CaF2 system were prepared within the composition of continuous casting mould flux, and the chemical composition and Raman spectra were detected subsequently. The degree of polymerization and structural behavior of Al3+ were investigated on the base of the quantitative calculation of structure species. The experimental data showed that the dominant structure species are Q(i) (i =0, 1, 2) of the Si-O tetrahedrons in the liquid mould flux, and the degree of polymerization decreases with the increasement of basicity and the decreasement of Al2O3 content. Al-O tetrahedrons and Al3+ cations coexist in the liquid mould flux, and the mole fraction of Al-O tetrahedrons increases with the increasement of basicity and Al2O3 content. Under the condition of the mole ratio Al/(Al + Si)< 0.19, the structural behavior of Al3+ is stable in the liquid mould flux. Considering the variation of mould flux composition during Al-killed steel continuous casting process, the initial content of Al2O3 and SiO2 in the mould flux should be controlled appropriately according to the transition point Al/(Al + Si).