<i>Marañon</i> Nutshell Extract as a Carbon Steel “Green” Inhibitor in Marine Environments

Natural <i>marañon</i> nutshell extract was obtained by mechanical compression. The extract was combined with ethanol and a nonionic surfactant, and it was labeled as EES. The EES inhibitor effect on S135 carbon steel, exposed to a simulated marine-coastal environment (SME), was deduced by mass loss measurement, adsorption isotherm, electrochemical measurements, and surface analysis. The Langmuir adsorption isotherm suggested that a monolayer of the <i>marañon</i> extract was attached by physical-chemical interaction with the steel surface. The increase in the protective efficiency of the adsorbed EES inhibitor was ascribed to the gain of the surface coverage as a function of the inhibitor concentration. It was considered an antioxidant activity of the inhibitor, attributed mostly to the Fe-ion capture by anacardic acid and the posterior ion chelation. This fact was collaborated by the negative zeta potential of the <i>marañon</i> nutshell extract, added to the SME. Electrochemical impedance spectroscopy (EIS) diagrams revealed that the steel polarization resistance (<i>R</i> _p) increased as a function of the inhibitor concentration, while the thickness (<i>d</i>) of the Fe-oxide layer was reduced to ≈0.50 nm.