Imaging Diffusion Barriers in Iron Oxides exposed to H2

Here we propose to use Bragg coherent diffraction imaging (BCDI) to investigate diffusion barriers forming during the hydrogen gas reduction of small crystals of hematite and magnetite undergoing the “Steam-Iron” reaction. We will examine well characterised 300 nm grown crystals of hematite (Fe2O3) and micron-sized FIB-cut samples of magnetite (Fe3O4) in a heater cell under flows of dilute H2 gas or H2O in reverse. We will use the strain sensitivity of BCDI to obtain 3D images of strain in situ during the reaction. Both directions of the reaction show kinetic blockages in the reaction rate, attributed to the formation of defects of unknown nature. We aim to understand the role of crystal defects in the reaction rate and cycling stability of the reaction, the interconversion of iron oxides and iron metal by the interaction of hydrogen and gaseous water. This addresses two overlapping planet-care goals, hydrogen storage and carbon-free steelmaking to reduce global CO2 emissions.