Corrosion behavior and EIS study of steel in an alkaline medium containing chlorides with Catechol inhibitor

The study of the inhibitory effect of Catechol (ortho-dihydroxybenzene) for corrosion protection of steel in an alkaline environment was continued.Previously, we performed electrochemical studies of Catechol additives in a model electrolyte simulating the composition of the pore liquid of concrete.The principal possibility of the action of catechol as an inhibitor of steel corrosion in a certain range of concentrations has been shown.These studies were carried out by the linear polarization resistance (LPR) method, which allows monitoring the corrosion activity of the metal during its exposure in the electrolyte.However, this method is indirect (the corrosion rate is conditionally estimated in proportion to the polarization resistance of the system).Therefore, this publication presents the results of direct corrosion experiments on the mass loss of samples during monthly exposure in solutions with different concentrations of Catechol.It is established that effective protection of steel from corrosion is observed in the concentration range from 0.5 to 5 g/L of Catechol, which is in good agreement with the results of LPR monitoring.The results of EIS studies of changes in the state of the system over time at low (0.1 g/L) and optimal (1 g/L) Catechol concentrations are presented.Based on the results of previous and current studies, a conclusion is made about the possible mechanism of the protective action of Catechol, explaining the decrease in its effectiveness, both at low concentrations (< 0.1 g/L) and with an increase in its content above 5 g/L.Being a strong antioxidant, Catechol is rapidly consumed, oxidized by oxygen at low concentrations.At a higher content, it permanently limits the concentration of oxygen in the electrolyte, preventing corrosion with oxygen depolarization.Also, being absorbed on the surface of the steel, it performs a certain blocking.An increase in the concentration of more than 5 g/L enhances the reducing effect of Catechol on surface iron oxides, leading to the predominance of Fe(II) compounds with less protective effect compared to Fe(III).