The effect of adsorbed water on electrochemical properties of Al alloys
Al alloys are widely used in many applications due to their light weight and good mechanical properties. However, sometimes localised corrosion of Al alloys may occur and cause failure of the material with serious consequences. Being a reactive metal, a so-called passive film spontaneously forms on Al surface, which is thin oxide layer and able to protect Al alloys from corrosion in mild environments. In corrosive environments, e.g., aqueous solutions containing Cl ions, corrosion may occur due to breakdown of the passive film formed on the Al surface. During many decades, extensive research efforts, mostly experimental, have been made worldwide to study the corrosion mechanism of corrosion of Al alloys. It is well known that Cl ions can attack the passive film and cause breakdown of the oxide film, leading to imitation of corrosion. However, a fundamental understanding of the passive film formation and the mechanism of passivity breakdown of Al alloys are still missing at atomistic scale. In recent years, theoretical approach has opened up new possibility to gain deep insights into corrosion mechanisms. By using DFT calculations, the interactions between adsorbents, such as oxygen species (O atoms/O2, OH- and H2O et al.) and aggressive ions (chloride ions, i.e. Cl-), with the oxide-covered Al surface could be determined, which play a key role in the passive film breakdown process. By now, researchers have paid considerable attention on the Al-H2O system, whereas the role of Cl- and the interplay of Cl- together with other oxygen species have not been studied in detail. In our first published paper (Applied Surface Science, 357, Part B, 2028–2038), it was shown that the interaction between adsorbed O and Cl- and bare Al surface could contribute to the passivity or repassivation processes. However, in reality, most commonly Al surface is covered by a thin Al oxide layer, which is quite different from adsorbed O. It is necessary to take a step further to reveal the effects of O and Cl- on the more realistic oxide-covered Al surface. In the planned research work, we will continue to do further DFT calculation to study this complex system to gain a fundamental understanding of the corrosion initiation of Al alloys caused by Cl ions in aqueous solutions. In this step, we will focus on one crucial issue, i.e., the effect of adsorbed water on the electrochemical properties of Al alloys. Such study is expected to contribute significantly new knowledge to corrosion science. The C3SE medium allocations perfectly meet the need for the DFT calculations and storage of our systems under study, considering that our calculating systems include about several hundreds atoms.