ReaxFF-based Molecular Dynamics Study On The Surface Oxidation Of Aluminum Melt And Amorphous FeCr Alloy

The properties of metals are closely related to the morphology of the surface oxides of metals.On the one hand,metals naturally oxidize in an oxidizing atmosphere,forming an oxide film on the surface.The presence of an oxide film can greatly destroy the mechanical properties of the metal and even cause the material to fail.The oxidation of metals has brought huge economic losses to the whole world.On the other hand,the structure and morphology of oxides can be controlled by controlling factors such as temperature,pressure,time,and crystal orientation during oxidation.Metal oxide-based functional materials prepared under controlled conditions have been widely used in catalysis,energy,electronic components,and other fields.The adjustment of oxide structure requires a deep understanding of the oxidation mechanism of metal materials.At the beginning of the oxidation reaction,the atoms on the metal surface are rearranged,which is the decisive link in the oxide structure.Due to the limitations of experimental methods,it is difficult to capture the evolution of the interface structure and the behavior of atoms in the process of oxidation by in situ observation.Therefore,the initial study of metal oxidation relies on computational simulations.In this paper,the molecular dynamics of the reaction were used to explore the mechanism of the initial oxidation of aluminum melt and the interfacial evolution during the oxidation of iron-chromium amorphous.The main contents of this article are as follows:(1)In this work,we performed reactive molecular dynamics simulation to investigate the oxidation mechanism of aluminum melt on an atomic scale.Our results focus on the island-like nucleation on the melt surface and the following growth of the oxide film.The oxide grows via ion diffusion and the diffusion of O anions plays a greater effect.The evolution of the diffusion coefficient indicates an island-by-layer growth on the aluminum melt.Kinetically,the oxide growth obeys a linear law during the nucleation stage and switches to a logarithmic law after a closed oxide film forms.Besides,we emphasize the effect of oxygen content and ambient temperature on the formation of oxides.(2)Amorphous FeCr alloy is an excellent coating material with strong oxidation resistance depending on the Cr-rich oxide on the surface.In this work,the oxidation mechanism of amorphous FeCr alloys was investigated.The oxidation process of amorphous and crystalline ferrochrome alloys was compared.It was found that in the early stage of oxidation,oxygen was selectively adsorbed around the chromium element,and then formed chain-shaped chromium oxide nuclei.The amorphous structure has stronger reactivity.Therefore,amorphous FeCr alloys have a faster oxidation rate at the initial oxidation stage.Compared with crystal FeCr alloys,amorphous Fe-Cr alloys have thicker inner oxide film and thinner outer oxide film.The increase of chromium content in amorphous ferrochrome alloys can promote the oxidation rate in the initial oxidation stage and retard the growth of the outer oxide layer.In addition,the increase in temperature can promote the oxidation especially the high-coordinated oxide.In this paper,the effect of atomic arrangement on the growth and morphology evolution of metal surface oxides is systematically described.The selectivity of surface oxidation reaction and the dependence of reaction conditions on atomic scale were revealed.It provides theoretical guidance for the anti-corrosion work of metal materials and the preparation of oxide-based functional materials.