Investigation of Inhibitive Effects of 2-Mercaptobenzimidazole (2-MBI) and Polyethyleneimine (PEI) on Pitting Corrosion of Austenitic Stainless Steel

In the present study, pitting corrosion of 316 austenitic stainless steel has been investigated in 3.5% NaCl solution at temperatures of 25, 40 and 60 °C using electrochemical methods (Cyclic potentiodynamic polarization (CPP) and Electrochemical impedance spectroscopy (EIS)). Then, inhibitive effects of 2-Mercaptobenzimidazole and Polyethylenimine with different concentrations on pitting corrosion of this alloy were analyzed. Adsorption behavior of the inhibitors on the substrate surface was also investigated using Fourier-transform infrared spectroscopy (FT-IR) and atomic force microscopy (AFM). Finally, microstructural studies were used by optical microscopy (OM) and scanning electron microscopy (SEM). The results showed that pitting corrosion of this alloy was well prevented by both inhibitors. However, corrosion resistance of 2-MBI was better than corrosion resistance of PEI and the results of OM and SEM showed better adsorption of 2-MBI compared to PEI. The highest pitting potential (626 mV vs. saturated calomel electrode (SCE)) was obtained in the presence of 2-MBI, while for PEI was 410 mV vs SCE. Also, it is found that desorption of inhibitors occurred at 60 °C and the effect of good inhibition did not occur at temperatures above 60 °C (inhibition efficiency for optimum concentration of PEI at 25 and 60 °C is 90.23 and 49, respectively). EIS and cyclic polarization tests showed that thickness of the passive layer increases with increasing the inhibitor concentration, which increases alloy corrosion resistance. The result showed that 2-MBI and PEI inhibition mechanism is deposition of single protective layer and double-layer adsorption, respectively.