Effect of Mixed-Ligands Copper Complex on the Corrosion Inhibition of Carbon Steel in Sulfuric Acid Solution

Abstract

The effect of Bis-phenanthroline chloro copper(II) chloride di-para-aminobenzoic acid tetrahydrate complex [Cu(Phen)2Cl]Cl (pABz)2·4H2O, CuPAB, on the corrosion behavior of carbon steel in 0.5 M sulfuric acid solutions were studied by electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization techniques. The shift of corrosion potential and the variation in the anodic Tafel line slope values, obtained from polarization measurements, indicated that CuPAB acts as a mixed-type inhibitor. Impedance suggests that inhibition of the complex is assisted by their adsorption at the metal/solution interface. Theoretical fitting of different adsorption isotherms such as Langmuir, Flory–Huggins, and the kinetic–thermodynamic models has been tested. The adsorption isotherm parameters indicate that the adsorption behavior of complex on the metal surface is not ideal. The high binding constant of CuPAB showed a stronger interaction between the metal surface and the complex. The obtained data revealed that CuPAB complex has remarkable inhibiting effects on the corrosion of steel in 0.5 M H2SO4. Spectrophotometry measurements were employed to investigate the stability of the complex in acidic media. The thermodynamic activation parameters were calculated. The data explained that the inhibition takes place through the adsorption that is neither physical nor chemical but a combination of both (physicochemical).