Ammonia is a promising alternative hydrogen carrier that can be utilized for the solid-state reduction of iron oxides for sustainable ironmaking due to its easy transportation and high energy density. The main challenge for its utilization on an industrial scale is to understand the reaction kinetics under different process conditions and the associated nitrogen incorporation in the reduced material that originates from ammonia decomposition. In this work, the effect of temperature on the reduction efficiency and nitride formation is investigated through phase, local chemistry, and gas evolution analysis. The effects of inherent reactions and diffusion on phase formation and chemistry evolution are discussed in relation to the reduction temperature. The work also discusses nitrogen incorporation into the material through both spontaneous and in-process nitriding, which fundamentally affects the structure and chemistry of the reduced material. Finally, the effect of nitrogen incorporation on the reoxidation tendency of the ammonia-based reduced material is investigated and compared with that of the hydrogen-based reduced counterpart. The results provide a fundamental understanding of the reduction and nitriding for iron oxides exposed to ammonia at temperatures from 500 to 800 °C, serving as a basis for exploitation and upscaling of ammonia-based direct reduction for future green steel production.

Excellent properties (durability, wear and corrosion resistance) and long service life under extreme conditions are essential for the successful application of metallic materials in the energy sector. In particular, for future fusion applications, high Cr ferrous alloys (in our case Eurofer) are of great interest. Importantly, modified microstructure with higher dimensional stability improves corrosion and wear resistance properties. In this study, we successfully manipulate the desired type of microstructure, which could provide a solution to current challenges in such a high temperature, highly corrosive and highly irradiated environment, using a novel technique of cryogenic processing (CP). The research identifies the CP-driven changes not only to the microstructure, but also to the local chemistry and bonding state of the key alloying elements. The correlations and individual phenomena associated with CP have been evaluated using state-of-the-art techniques such as atom probe tomography and synchrotron-based in-situ scanning photoemission spectroscopy. This novel process and its novel microstructural manipulation opens up new possibilities for materials processing for future energy applications.