Molecular Dynamics Insights into Microstructure, Viscosity and Surface Tension of Steelmaking Slag

The microstructure, ionic transport, diffusivity-based viscosity estimates, and surface tension of CaO–SiO2–FeO–MgO(–Al2O3) steelmaking slags were investigated in the homogeneous liquid state by molecular dynamics simulation. The effects of basicity and Al2O3 were examined separately; basicity was varied from 1.4 to 2.6 in the Al2O3-free series, whereas Al2O3 content was varied from 0 to 10 wt.% at a fixed basicity of R=2.2. Increasing basicity depolymerizes the silicate network, as indicated by the decrease in bridging oxygen and degree of structural complexity and the shift of Qn species toward lower-order units. At R=2.2, increasing Al2O3 promotes the formation of a more interconnected Si–O–Al network, accompanied by an increase in bridging oxygen. These structural variations are associated with corresponding changes in ionic diffusion and diffusivity-based viscosity estimates. Increasing basicity enhances ionic mobility and lowers the viscosity estimate, whereas increasing Al2O3 at R=2.2 reduces ionic mobility and increases the estimate. The calculated surface tension shows an overall increasing trend with both basicity and Al2O3 content, qualitatively consistent with the comparison models. The results provide a unified atomic-scale assessment of composition-dependent structure, transport behavior, and surface-tension trends in FeO-bearing steelmaking slags.