Reactive Molecular Dynamics Study Of The Oxidation Behavior Of Iron-Based Alloy In Supercritical Water

A theoretical study of the oxidation behavior of iron-based alloy in the supercritical water (SCW) has been carried out based on ReaxFF force-field molecular dynamics simulation. An atomic model has been proposed to simulate the initial chemisorption reactions and atoms diffusion behavior across the oxide layer. Simulation results imply that Cr addition has an important effect on the oxidation behavior of iron-based alloy. In the initial stage of oxidation, H2O prefers to adsorb on the Cr atom, and some species in the form of Cr(OH)(4) are observed on the FeCr alloy surface. Once an initial oxide layer is formed, further oxidation is controlled by the migration of vacancy. The O vacancies are formed at the oxide/FeCr alloy interface and migrate toward the steam, whereas Fe vacancies are formed at the oxide/steam interface and migrate toward the FeCr alloy. Attributed to the stronger binding energy of O-Cr bond than O-Fe bond, the Cr diffusivity in the oxide is less than Fe atoms. Thus, double oxide layers, including the inner Fe-Cr-O layer and outer Fe-O layer, are formed on the FeCr alloy, which is in good agreement with previous experimental observation.