Influence of Al2O3 content on molten structure and viscosity of CaO-SiO2-MgO-Al2O3-FeO slags with CaO/SiO2=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.