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.

本研究提出采用布拉格相干衍射成像（Bragg coherent diffraction imaging, BCDI），探究赤铁矿与磁铁矿小晶体在发生“蒸汽-铁”反应的氢气还原过程中形成的扩散势垒。本研究将在加热样品池中，对经过充分表征的300纳米级生长赤铁矿（Fe₂O₃）晶体，以及微米级聚焦离子束（Focused Ion Beam, FIB）切割的磁铁矿（Fe₃O₄）样品，在逆向流动的稀释氢气或水蒸气环境下开展测试。本研究将利用BCDI的应变敏感性，获取反应过程中原位的应变三维分布图像。该反应的两个反应方向均出现反应速率动力学阻滞现象，其成因被归因于性质不明的缺陷的形成。本研究旨在阐明晶体缺陷在该反应的反应速率与循环稳定性中所发挥的作用，以及氢与气态水相互作用下铁氧化物与金属铁之间的相互转化机制。本研究契合两项相互关联的地球保护目标：氢能存储与无碳炼钢，以降低全球二氧化碳排放。