Effect of 2-mercaptobenzimidazole and its polymeric film on the corrosion inhibition of brass (60/40) in ammonia solution

Copper and its alloys (brass) represent an important type of material that meets the requirements of many industrial applications in chemical and power industries and nuclear stations. Like most metallic materials, brass alloys suffer from corrosion, especially from selective corrosion. Taking into account the conditions in which these alloys are used, the corrosion of these alloys, and risks of rupture of their structures, it appeared necessary to find solutions against the corrosion of these alloys. For these reasons, an organic inhibitor has been used to minimize this type of corrosion, and electrochemical measurements coupled with acoustical emission have been used to characterize their efficiency. The inhibiting action of 2-mercaptobenzimidazole (2-MBI) on the corrosion of brass (60140) in an ammonia solution has been investigated by electrochemical measurements (polarization curves and electrochemical impedance spectroscopy) coupled with the acoustic emission technique. The studies revealed that, while 2-MBI provides excellent corrosion inhibition, its polymeric film, poly(2-MBI), previously deposited by electrochemical means, was not very protective. It was found that the presence of 2-MBI increases the inhibition efficiency at every studied concentration and temperature, and inhibits both cathodic and anodic reactions, indicating a mixed type of inhibition. The decrease in corrosion current was associated with the positive shift in the corrosion potential. The marked dependence of this inhibitor effectiveness with respect to the pH of the ammonia solution on the one hand, and the disagreement observed with the Langmuir and Temkin isotherms on the other hand, suggested that 2-MBI acts like an interphase inhibitor.