Molecular dynamics study on interfacial diffusion characterization of nanoparticle TiO2 and metal Fe in high-temperature molten salt thermal energy storage system

Abstract

Previous experimental studies have found that nanoparticle TiO2 doping into molten salts can mitigate the corrosive effect of molten salts on metals; however, the microscopic mechanism behind this phenomenon has not been fully understood. In this paper, the diffusion characteristics and microstructural features of the interface between nanoparticle TiO2 and metal Fe at high temperatures were simulated by molecular dynamics (MD) method, and an attempt was made to explain the corrosion inhibition mechanism from the microscopic point of view. The results show that when the temperature ranges from 698 to 1298 K, TiO2 and Fe behave in a mutual diffusion way at the interface, where a stable diffusion layer has been formed gradually. As the temperature rises, the diffusion intensifies and the diffusion layer becomes thicker. Moreover, an energy gradient is built up at the interface, indicating that the atoms that are closer to the interface have larger energies. The binding energy at the TiO2/Fe interface increases with the increasing of temperature, and its makes the atoms at the interface undergo the diffusion-remodeling behavior and form new coordination compounds: Ti2Fe, TiFe2, TiFe4, Ti(FeO2)3, Ti8Fe35O64, FeO, etc. This is in general agreement with the observations in experiments.