(135d) Microstructure and Mechanical Strength Evolution of Iron Oxide in Chemical Looping Combustion

The chemical looping combustion (CLC) is an advanced combustion technique that can separate carbon dioxide (CO₂) simultaneously. Iron oxides are widely used in chemical looping techniques because of their low cost and non-toxic, good reactivity and relatively high melting points. In CLC, redox reactions lead to the oxygen vacancy formation and ionic diffusion that affect the microstructure and mechanical strength of iron oxide and it’s subsequent chemical looping behavior. In this study, the microstructure and mechanical strength of pure Fe₂O₃ particles (300 μm) before and after redox testing were investigated to understand the relationship between the microstructure and mechanical behaviour.

Our results indicate that surface area of Fe₂O₃ particles drops sharply from 2.2029 m²/g to 0.4418 m²/g (surface area loss reaches 80%) when reduced for 30 min. Meanwhile, the bulk density and crushing strength of Fe₂O₃ particles were both decreased with different degrees. Besides, crushing strength of Fe₂O₃ particles was increased when the reduced particles subjected to oxidation with air. However, surface area of Fe₂O₃ particles continued decreased which was attributed to sintering effect in the oxidation process. Due to the ionic diffusion, porous structure in the interior of Fe₂O₃ particles was formed. So, the bulk density of Fe₂O₃ particles was firstly increased and then decreased in the oxidation process. Hg intrusion method was used to measure the pore size distribution of Fe₂O₃ particles before and after redox testing. During the reduction process, the losing of oxygen result in the creation of oxygen vacancies. The aggregation of oxygen vacancies causes the forming of macropores. In addition, microstructure (surface area, bulk density, pore size distribution) and the mechanical performance of Fe₂O₃ particles after different redox cycles were also taken into account.