A DFT study on corrosion mechanism of steel bar under water-oxygen interaction

Abstract

Corrosion of steel bar is a major problem influencing the long-term performance of reinforced concrete structures. It is known that both oxygen and water involve in the initiation of corrosion of steel bars and determine the formation of the final corrosion products. In this paper, the interaction of oxygen and water on the Fe (1 0 0) surface have been simulated by using density functional theory (DFT), to study the mechanism of steel bar corrosion and the formation process of the corrosion product (FeOOH). The results show that the preadsorbed water on the iron surface has little effect on the O2 adsorption, but the adsorption of O2 weakens the interaction between H2O and iron surface. On the other hand, the preadsorbed oxygen strengthens the adsorption of H2O via the formation of hydrogen bond between the O atom of O2 and the H atom of H2O. Strong interaction of oxygen and water promotes the dissociation of O2 and H2O molecules on the Fe (1 0 0) surface, and forms a Fe-O and two Fe-OH groups on the iron surface. Moreover, it is found that the Fe-OH group is unstable, and reacts easily with the newly introduced O atom to form the FeOOH, which confirms that FeOOH is the main corrosion product of steel bar instead of Fe-OH. This work could provide a microscopic insight into the mechanism of reinforcement steel corrosion.