The role of soybean meal extracts proteins in the inhibition of mild steel acid corrosion

In this research, the mild steel corrosion inhibition effect of three extracts from soybean meal and a soybean protein commercial sample was examined using mass loss tests, electrochemical im-pedance spectroscopy (EIS) and potentiodynamic polarization (PDP). The anti-corrosive proper -ties of soybean meal extracts were investigated normalizing the peptide/protein amount. The in-hibitors were chemically characterized by spectroscopic studies and HPLC. The morphological characterization of the mild steel surface was performed by SEM. Our results demonstrated that all inhibitors showed the same inhibition efficiency if the normalization in peptide/protein amount was performed, indicating proteins/peptides as the class of molecules responsible for in-hibiting corrosion. For example, for 100 mg L-1 in protein content, the inhibition efficiency was 84 and 82%, respectively, from electrochemical impedance and polarization curves results, and 89 and 93-94% after 2 and 24 h immersion time, respectively, from mass loss measurements. Po-larization curves indicated that all inhibitors behave as a mixed-type inhibitor, more explicit for the cathodic branch. The SEM results suggest that all extracts promoted a protective action against corrosion of the mild steel in H2SO4 solution.