Mechanism of B 2 O 3 modifying viscosity and structure in electric-smelt furnace slag: Insights from experiments and thermodynamic calculations

The physicochemical properties of electric smelting furnace (ESF) slag are the core factors governing the smelting efficiency of the direct reduced iron-ESF process. In this study, the regulation mechanism and microcosmic interaction mechanism of B 2 O 3 addition on the physicochemical properties of the CaO–SiO 2 –MgO–Al 2 O 3 –FeO slag system were systematically investigated using the rotating cylinder method, FactSage thermodynamic calculation, Fourier-transform infrared spectroscopy and Raman spectroscopy. The results indicate that as the B 2 O 3 content increases, the slag viscosity exhibits a monotonically decreasing trend, the resistance to viscous flow diminishes, and fluidity is significantly improved. Furthermore, the viscosity-reducing effect of B 2 O 3 is more pronounced at lower temperatures, and slags with high B 2 O 3 contents concurrently exhibit a greater degree of superheat. FactSage thermodynamic calculations reveal that at 1273 K with low B 2 O 3 additions, the primary phases of the slag system are melilite, wollastonite, clinopyroxene, and CaAl 2 Si 2 O 8 . When the B 2 O 3 content reaches 10%, the liquid phase fraction in the slag exceeds 60%, becoming the dominant phase. Spectral structural analysis demonstrates that B 2 O 3 addition significantly intensifies the asymmetric B–O stretching vibrations in [BO 3 ] groups and the vibrational peaks of [BO 2 O − ] structures. The BO/Si ratio in the slag continuously rises from 2.05 to 2.18, signifying a substantial increase in the number of bridging oxygens, which drives the polymerisation of the [SiO 4 ] and [AlO 4 ] structures toward greater complexity.