A DFT study of chlorine based copper corrosion and its inhibition

Corrosion is the destructive attack of a metal by a chemical or electrochemical reaction with its environment. Due to its good mechanical properties and electrical and thermal conductivity, copper is one of the most useful metals. Likewise, the chemistry of chlorine on metal surfaces is involved in many technological processes, such as corrosion. Corrosion and its inhibition gain interest both on the experimental and theoretical sides. This work investigates the Cl adsorption on the metallic Cu (100), Cu (110), and Cu (111) surface and inhibitor effect of organic and inorganic inhibitor candidates on Cu (100) surface. Cl adsorption was studied at varying coverage from 1 ML to 1/16 ML and at different adsorption positions (4-fold, 3-fold (fcc, hcp), 2-fold (brg, l-brg, s-brg) and 1-fold (on top)). Inhibition effect of azole derivatives such as pyrazole and imidazole, relatively small atomic and molecular species such as O, H, OH, CO and HCO3, and ammonia and chromic acid were studied on clean Cu (100) surface. Moreover, Cl adsorption energies in the presence of inhibitor atoms/molecules were also calculated. The results show that adsorption energies on different clean copper surfaces are coverage dependent. On average, Cl adsorption energy changes between +19 kJ/mol to -204 kJ/mol, -19 kJ/mol to -193 kJ/mol and +66 kJ/mol to -196 kJ/mol for Cu (100), Cu (110) and Cu (111), respectively. The preferable adsorption sites are 4-fold, 2-fold s-brg and 3-fold fcc, respectively. Among the tested inhibitor molecules azole derivatives, surface ions, chromic acid and ammonia were found to be stable on the surface. However, inhibition effect of these molecules could not be observed due to the high electron affinity of chlorine. Along with the copper surface, any co-adsorbed molecule becomes an electron donor for the chlorine, only making its adsorption stronger.