Iron element behavior and microstructure evolution of mullite–corundum ceramics in high‐temperature CO atmosphere

Abstract This study focuses on the corrosion behavior of Al 2 O 3 –SiO 2 refractory materials under high‐temperature CO atmospheres in hydrogen metallurgy, systematically revealing the occurrence form of Fe element in mullite–corundum ceramics with different Fe 2 O 3 contents. By simulating hydrogen metallurgy conditions and integrating thermodynamic analysis, phase evolution, and microstructural characterization, a dual intragranular and grain boundary corrosion mechanism was identified: (1) Fe 3+ in the [Al/FeO 6 ] octahedron of the mullite crystals were reduced to Fe 2+ and leached out of the lattice, resulting in charge imbalance and lattice distortion within the structure, thus reducing the stability of the mullite crystal. (2) Migrated Fe and impurities element at grain boundaries promote glass phase precipitation, while leached Fe 2+ reduces glass viscosity by disrupting Si–O networks, forming low‐viscosity liquids that accelerate mullite dissolution. Results demonstrate a critical Fe 2 O 3 doping threshold (10 wt%), beyond which mullite undergoes reductive dissociation accompanied by hercynite and low‐melting phase formation (ferrocordierite, fayalite). Hercynite and glass phase contents exhibit near‐linear increases with Fe content. This work clarifies the valence of the Fe element and its gradient‐driven microstructural failure mechanisms under hydrogen metallurgy conditions, providing theoretical foundations for optimizing reduction‐resistant mullite‐based linings.