Reactive molecular dynamic simulation of water induced iron corrosion and its prevention mechanism

Abstract

Corrosion of iron and mild steel in water and in chloride media is a costly problem for industry, and it also raises safety concerns. Organic molecules containing heteroatoms are commonly used to control it. In most of the reported work, though, the electronic structure of the inhibitor molecule and the breakdown of the metal-water interface have been treated as two separate problems. It is therefore still not clear how a simple electronic descriptor is related to the film that actually builds up on a corroding iron surface. Keeping this in view, our study evaluates the iron corrosion inhibition performance of five aromatic compounds, anthracene, anthrone, xanthene, xanthone, and xanthione, using density functional theory (DFT) calculations and reactive molecular dynamics simulations. Simulations revealed the real-time evolution of iron corrosion in aqueous media, showing the formation of iron oxide and hydroxide at the metal surface. Among all inhibitors, xanthione showed the most stable adsorption on the iron surface, driven by van der Waals and electrostatic interactions sustained by electron donation from sulfur and oxygen heteroatoms. This xanthione-surface interaction appears to form a stable interfacial barrier, which should suppress corrosion. Among the five molecules, xanthione has the smallest gap of 3.18 eV between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), and it also gives the most compact adsorbed film. Electrochemical tests on mild steel in 3.5 wt% NaCl gave a corrosion current density of 16.4 × 10 −6 A/cm 2 and a corrosion rate of 7.522 mpy, and these values are used here as the reference for the simulated ranking. The comparison made in this work is a qualitative one, since adsorption energies have not been computed and the electrochemical data are for the uninhibited substrate. Even so, the study relates a single electronic descriptor to the packing of the inhibitor film, which can serve as a quick screening route while looking for new inhibitors for iron.