Atomistic Insights into Early-Stage Oxidation of -Fe₅C₂ and the Dependence on the Surface Structure

Iron carbides play a crucial role in many industrialfields, suchas the steel industry, catalysis, carbon material production, andso on. One of the main challenges is that iron carbides are highlysusceptible to being oxidized under service conditions, which cansignificantly reduce the performance and retard their industrial applications.However, the complex chemical structure of iron carbide materialsand the dynamic nature of the Fe-C-O system under reactiveconditions, such as the Fischer-Tropsch synthesis condition,hindered the understanding of the oxidation process. In this paper,structure evolution of the early-stage oxidation of chi-Fe5C2 was investigated through reactive force fieldmolecular dynamics simulations. The impacts of surface structure,oxygen coverage, temperature, and particle size were systemicallyexplored. It was found that the oxidation rate was not only relatedto the surface carbon content but also to the homogeneity of the subsurface.Meanwhile, the dynamic structure transformation during oxidation wasanalyzed by various correlation functions. The mechanism of counter-directionmigration of surface atoms during the oxidation process was illustrated,where carbon atoms migrate to the bulk region and iron atoms migrateto the surface. Our study reveals the atomistic dynamic mechanismof chi-Fe5C2 oxidation, which offers crucialinsights for catalyst oxidation and iron carbide materials.