Corrosion inhibition and adsorption properties of some manganese metal complexes on mild steel in sulfuric acid solutions

• H.T. Rahal¹, A.M. Abdel-Gaber², R. Al-Oweini³ and R.N. El-Tabesh⁴

¹ Department of Chemistry, Faculty of Science, Lebanese International University, Al Khyara, West Bekaa, Lebanon
² Department of Chemistry, Faculty of Science Alexandria University, Ibrahimia, P.O. Box 426, Alexandria 21321, Egypt
³ College of Arts and Sciences, University of La Verne, La Verne, CA 91750, USA
⁴ Department of Chemistry, Faculty of Science, Beirut Arab University, P.O.Box 11-50-20, Riad El Solh 11072809 Beirut, Lebanon

Abstract: Metal complexes are frequently employed in industry as key compounds in medicinal chemistry. The interaction between metal complexes and metal surfaces is crucial in corrosion chemistry. Open circuit potential-time measurements, electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization techniques are used to investigate the effects of two manganese metal complexes, Mn₂(PAB)₄(Phen)₂ and Mn₂(PAB)₃(Phen)₂(OH) abbreviated as MnP₄ and MnP₃OH, on the corrosion of mild steel in sulfuric acid solutions. The chemical and structural characteristics of the complexes are confirmed using powder X-ray diffraction, thermal gravimetric analysis and FTIR. Both complexes act as potential corrosion inhibitors, with inhibition efficiencies of 90% at 10^–3 mol·L^–1. Potentiodynamic polarization curves suggest that MnP₄ and MnP₃OH are anodic type inhibitors. The impedance responses indicate that the corrosion process of mild steel is activation controlled. The obtained results revealed that the inhibition efficiency decreases with increasing temperature, which is suggestive of physical adsorption mechanism. The corrosion inhibition mechanism was further corroborated by the values of kinetic and thermodynamic parameters obtained from the experimental data.

Keywords: acid corrosion, corrosion inhibitors, Mn-metal complexes, mild steel, physical adsorption

Int. J. Corros. Scale Inhib., 2024, 13, no. 2, 708-726
doi: 10.17675/2305-6894-2024-13-2-4

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