Interfacial bonding and corrosion inhibition of 2-mercaptobenzimidazole organic films formed on copper surfaces under electrochemical control in acidic chloride solution

The interfacial bonding and the layered structure of 2-mercaptobenzimidazole (2-MBI) organic films adsorbed on electrochemically controlled copper surfaces and their corrosion inhibition effects in acidic chloride aqueous solution were investigated using an integrated approach of electrochemical methods and advanced surface analyses by X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry. It is shown that organic films formed on the copper surfaces are bi-layered with a chemisorbed inner layer and a physisorbed outer layer. In the chemisorbed inner layer, 2-MBI is bonded primarily by its nitrogen atoms with metallic and oxidized copper surfaces. Sulphur atoms are also involved in the bonding mechanism when metallic copper is directly accessible to the 2-MBI molecules. The initial presence of native copper oxides at the interface promotes the formation of Cu(I)-2-MBI metal-organic complexes in the chemisorbed inner layer using cathodic reduction to dissociate the oxide. Metal-organic complexes also form upon anodic polarisation due to Cu(I) ions generated by oxidation of the copper metal. 2-MBI effectively inhibits copper anodic dissolution in varying degrees, between 84% and 93%, depending on the pre-treatment used for the formation of the organic bi-layers. An enhanced protection of the substrate is obtained by adsorbing the 2-MBI inhibitor on an initially oxide-free surface, which is achieved by cathodic pre-treatment in absence of the inhibitor followed by 1 hour exposure to the inhibitor.