Theoretical study of corrosion inhibition on copper in transformer oil

摘要

Addition of metal inhibitor to corrosive transformer oil was employed to prevent the formation of semi-conductive Cu2S on copper surface. The formation of impermeable layer is the key process, however, little attention were paid on this process. Here, we performed aging experiment with benzotriazole and benzimidazole type inhibitors on copper strips in corrosive transformer oil. The experiment shows that the N1 position required free coordinating site for the protective layer formation. And molecules with substituent in C2 position are sensitive to the effectiveness of inhibition. Also, DFT calculation was employed to investigate the molecular structure, electronic properties. It is found that none of EHOMO, ELUMO, energy gap and dipole moment is correlated to the structure-reactivity. However, the steric analysis shows strong impact on the impermeable layer formation, suggesting end-on orientation stacking model in the chemisorption process. Furthermore, we afforded inhibiting results by introducing free coordinating size like amino and thiol group at C2 position. These experiments and analysis results offered us deeper understanding to the process of suppression with inhibitor and theoretical guide for inhibitor design in transformer oil.