Evaluation of the corrosion inhibition effect of the combined admixture of rosemary and cinnamon cassia oil on mild steel in weak acid electrolyte

Abstract

The corrosion resistance of mild steel (MS) in 0.5 M H2SO4 and HCl solution with specific concentrations of the intermixture of rosemary and cinanamon cassia essential oil extracts (RCC) was studied by potentiodynamic polarization method, open circuit potential analysis (OCP) and optical macroscopy. Information obtained showed RCC effectively inhibited MS corrosion from the lowest to the highest concentrations in both acids with lowest inhibition result of 95.30% and 94.19%, and highest inhibition efficiency of 99.21% and 97.69%. RCC exhibited dominant cathodic inhibition effect in H2SO4 due to suppression of the reduction reactions while in HCl RCC displayed mixed inhibition properties due to surface coverage effect in the presence of Cl− anions. OCP showed RCC increased the thermodynamic tendency of MS to corrosion in H2SO4 solution despite effective inhibition performance with significant electronegative shift in corrosion potential. In HCl significant electropositive potential displacement was observed relative to the potential of the control MS due to adsorbed protonated RCC molecules unto the steel. Adsorption of RCC molecules on MS aligned with Langmuir, Frumkin and Freundlich isotherm models through chemisorption mechanism in both acids with average correlation coefficient value above 0.9. Optical images of MS in both acids without RCC showed severe surface degradation with the degree of degradation being higher from H2SO4 solution. Optical images from RCC inhibited steel depict effective surface protection.