Influence of Microstructure and Atomic-Scale Chemistry on Iron Ore Reduction with Hydrogen at 700°C

Steel is the most important material class in terms of volume and environmental impact. While it is a sustainability enabler, for instance through lightweight design and magnetic devices, its primary production is not. Iron is reduced from ores by carbon, causing 30% of the global CO2 emissions in manufacturing, qualifying it as the largest single industrial greenhouse gas emission source. Hydrogen is an attractive alternative reductant. Although this reaction has been studied for decades, its kinetics is not well understood, particularly the wustite reduction step, which is much slower than hematite reduction. Some rate limiting factors of this reaction depend on the microstructure and local chemistry. Here, we report on a multi-scale structure and composition analysis of iron reduced from hematite with pure H2, reaching down to near-atomic scale. The microstructure after reduction consists of nearly pure iron crystals, containing inherited and acquired pores and cracks. We observe several types of lattice defects that accelerate mass transport inbound (hydrogen) and outbound (oxygen) as well as chemical impurities in the form of oxide islands that were not reduced. With this study, we aim to open the perspective in the field of carbon-neutral iron production from macroscopic processing towards the underlying microscopic reduction mechanisms and kinetics.