Abstract
Fossil-free iron production is essential to mitigate the substantial CO2 emissions of the steel industry, which accounts for approximately 8% of global emissions and remains a major contributor to climate change. Among emerging solutions, hydrogen-based direct reduction of iron ores has attracted significant attention as a promising pathway toward the decarbonization of ironmaking. In this talk, I will present our recent investigations into the direct reduction of iron ores under elevated hydrogen pressures of up to 100 bar at 700 °C. The reduction kinetics and associated microstructure evolution were systematically studied using in-situ synchrotron high-energy X-ray diffraction, enabling time-resolved tracking of phase transformations during reduction. By applying kinetic models, the rate-limiting steps of the individual reduction reactions were identified and further elucidated through complementary analyses using scanning electron microscopy and X-ray nano-tomography.
Our results demonstrate that increasing hydrogen pressure significantly accelerates reduction kinetics across all reaction steps and lowers the onset temperatures of phase transformations. Despite these enhancements, the reduction of wüstite to metallic iron remains the rate-limiting step, governed by a localized phase-boundary-controlled mechanism. The influence of hydrogen pressure on reduction behavior is discussed in terms of both thermodynamic driving forces and microstructural kinetics. Overall, this work provides new insights into the role of hydrogen pressure in controlling reduction kinetics and microstructure evolution during hydrogen-based direct reduction, offering fundamental guidance for process design, optimization, and the development of next-generation green ironmaking technologies.