Defect Engineering in Wüstite: Unlocking Control Over Iron Morphologies in Gas-Solid Reduction.

Area of Science:

• Materials Science
• Chemical Engineering
• Metallurgy

Background:

• Hydrogen-based direct reduction (HyDR) is key for sustainable steelmaking.
• Iron microstructure evolution significantly impacts HyDR efficiency and stability.
• Interplay between defects, pore dynamics, and reduction chemistry in iron oxides needs further clarification.

Purpose of the Study:

• To explore iron morphological evolution during reduction with H₂ and CO across a full concentration range at 900 °C.
• To establish a direct link between wüstite (FeₓO) lattice distortions and resultant iron microstructure.
• To understand how defect engineering in FeₓO modulates iron morphologies.

Main Methods:

• Investigated iron reduction using H₂ and CO at 900 °C across varying gas concentrations.
• Analyzed the relationship between lattice distortions in wüstite (FeₓO) and iron microstructure.
• Examined defect concentration in FeₓO and its influence on reduction pathways.

Main Results:

• Low CO concentrations (< 80%) led to limited defects, single-point nucleation, and filament-shaped iron whiskers.
• H₂ and high CO concentrations (> 80%) induced high defect density, multi-point nucleation, and tumor-shaped iron structures.
• Defect concentration in FeₓO directly governs lattice distortions and subsequent iron morphology.

Conclusions:

• Defect engineering in FeₓO is a critical factor in controlling iron microstructure during reduction.
• Understanding these defect-microstructure relationships offers insights for optimizing HyDR processes.
• This work provides a multiscale perspective for enhancing efficiency and sustainability in materials processing.