Inhibition mechanism of sodium laurate to underdeposit corrosion of carbon steels in NaCl solutions

Abstract

In a self-designed occluded corrosion cavity (OCC) simulated cell, the inhibition mechanism of sodium laurate (C₁₂H₂₃O₂Na) to the underdeposit corrosion of the N80 steel in a neutral 0·2 mol L^–1 NaCl solution was studied by electrochemical methods, including measurements of polarisation curves, coupling currents, polarisation resistances, electrochemical impedance spectra (EIS) and ion selectivity of the scale film. The results show that C₁₂H₂₃O₂^– could form a monomolecular adsorption film on the N80 steel surface in the studied solution, whose adsorption behaviour would follow Flory–Huggins isotherm model, and inhibit both anodic and cathodic processes. C₁₂H₂₃O₂^– displays good inhibition performance to the underdeposit corrosion of the N80 steel in the studied system, which could be mainly attributed to the inhibition to the electrode processes of the bulk cathode and occluded anode, the increase in the resistance of the corrosion deposit layer and the prevention to the autocatalysing acidification effect in OCC. The last two factors might be related to the conversion of the deposit layer from anion selectivity to cation selectivity and the formation of a hydrophobic layer on the wall of the micropores in the deposit layer by adsorption of C₁₂H₂₃O₂^–.