Synergistic Corrosion Inhibition of Cold Rolled Steel by Methyl Violet and Chloride Ions in Sulphuric Acid Solution

Abstract

The corrosion inhibition of cold rolled steel in sulphuric acid solution by methyl violet in the absence and presence of chloride ion has been studied. The adsorption of methyl violet on the steel surface is found to obey the Langmuir adsorption isotherm with and without chloride ion. The studies reveal that the single methyl violet is not an effective inhibitor for cold rolled steel in sulphuric acid solution, but the complex of methyl violet and chloride ion shows a quite well inhibition. A synergistic effect was observed and discussed. The thermodynamic parameters such as adsorption free energy, adsorption heat and adsorption entropy, kinetic data such as apparent activation energy and pre-exponential factor were calculated and discussed. Potentiodynamic polarization researches show that single methyl violet mainly acts as a cathodic-type inhibitor, however the mixture of methyl violet and sodium chloride acts as a mixed-type inhibitor and shows dominant effect on the cathodic reaction.