Effects of FeO and <i>w</i>(CaO)/<i>w</i>(SiO₂) on the viscosity and structure of CaO-7 mass pct MgO-15 mass pct Al₂O₃–SiO₂–FeO slag melt

In blast furnace smelting with high-alumina ore, the permeability of high-alumina slag affects operational stability. The viscosity of the melt is a critical determinant of slag permeability. However, the viscosity behaviour and structural characteristics of high-alumina slag melts containing FeO remain insufficiently understood. In this study, the rotating cylinder method and Raman spectroscopy were employed to investigate the effects of the FeO content (5–20 mass pct) and w(CaO)/ w(SiO 2 ) (C/S, 1.2–1.6) on the viscosity and structural properties of a CaO-7 mass pct MgO-15 mass pct Al 2 O 3 –SiO 2 –FeO high-alumina slag melt. The experimental results show that the melt viscosity decreased with increasing FeO content and C/S ratio (from 1.2 to 1.4). However, when C/S was increased to 1.6, the viscosity initially increased and then decreased. The flow activation energy decreased with increasing FeO content and C/S. The thermal stability of the melt improved with higher FeO content, whereas it initially decreased and then increased with an increase in C/S. Raman spectroscopy results suggest that the viscosity reduction was primarily caused by the depolymerisation of silicate structures, involving the transformation of Q 2 into Q 1 and Q 0 , which led to an increase in the NBO/Si ratio. Increasing C/S from 1.4 to 1.5 caused an abnormal increase in viscosity, which can be attributed to the effect of ion arrangement densification outweighing that of silicate network depolymerisation. This study enhances the understanding of viscosity behaviour in high-alumina slag melts, providing a theoretical basis for the smelting of high-alumina ores.