Influence of Al 2 O 3 content on molten structure and viscosity of CaO-SiO 2 - MgO-Al 2 O 3 -FeO slags with CaO/SiO 2 =1.6

This study investigates the effect of Al₂O₃ content on the structure and flow properties of high-basicity (R₂= 1.6) and low-FeO slag formed at the lower boundary of the cohesive zone in gas-injection blast furnaces. The role of Al₂O₃ in influencing the fluidity and molten structure of slag before dripping in gas-injection blast furnaces was analyzed by using viscosity-temperature tests, FITR, Raman, NMR and XPS spectroscopy, and molecular dynamics (MD) simulations. The results show that as the Al₂O₃ content increases, the free running temperature of the slag shows an upward trend, reaching its minimum at an Al₂O₃ content of 14.18 wt.%. Al₂O₃ promotes the transition of silicate structures from chain-like to more complex ring or layered structures, thereby increasing the polymerization degree of the melt. Spectroscopic and MD simulation analyses indicate that the addition of Al₂O₃ disrupts the original Si-O-Si bonds, forming more Si-O-Al and Al-O-Al bonds. Moreover, the structural stability is enhanced by the decreasing of bond lengths of these bonds. The findings demonstrate that under high-basicity conditions, Al₂O₃ primarily participates in the silicate structure in the form of [AlO₄] tetrahedra to complicate the structure of the melt.