The oxidation of Fe/Ni alloy surface with supercritical water: A ReaxFF molecular dynamics simulation

LQ Ai and HS Huang and YS Zhou and M Chen and YJ Lu, APPLIED SURFACE SCIENCE, 553, 149519 (2021).

DOI: 10.1016/j.apsusc.2021.149519

A ReaxFF force field for Fe/Ni/H/O is developed to describe the interactions between Fe/Ni binary alloy surface and supercritical water (SCW). The energies and charge distributions of surface binding are compared with DFT calculations to validate the developed force field. ReaxFF molecular dynamics (MD) simulations are performed to investigate the oxidation mechanism of Fe/Ni alloy surface in SCW. Simulation results show that SCW selectively oxidizes Fe on the alloy surface. Fe atoms dissolve into SCW, leading to the dealloying of the alloy surface. Bond order analysis and energy calculation reveal that the selective oxidation is because Fe has stronger bonding with O and higher mobility in alloy than Ni. Disordered Fe/Ni alloy has a faster oxidation rate than ordered Fe/Ni alloy. This result is explained by the lower migration energy cost of the O atom in a local Fe-rich structure on the alloy surface. The anti-oxidant mechanism of Ni is due to its role in stabilizing the alloy lattice structure and increasing the migration energy barrier of oxygen through the alloy surface layer. Adjusting the content and distribution of nickel atoms in the alloy might improve the oxidation resistance of iron-nickel alloys.

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