Structural characteristics and viscous behaviors of Al2O3–CaO–SiO2–Fe2O3 slags

• Increasing Al2O3 content from 4.16wt% to 17.07wt% raises slag viscosity and apparent activation energy from 132.13 to 174.83 kJ/mol, indicating enhanced structural polymerization. • Liquidus temperature initially decreases with Al2O3 addition (from 1365°C to 1287°C) but then increases to 1356°C at higher Al2O3 content, reflecting amphoteric behavior. • Higher temperatures depolymerize the slag structure by reducing complex AlO4 units and promoting simpler silicate monomers, while Al2O3 addition promotes polymerization via AlO4 tetrahedra and complex Si–O units. • The study provides critical insights for optimizing steelmaking operations and waste slag utilization by linking slag composition, structure, and viscosity.