Synergistic inhibition effect of thionine and zinc ions on carbon steel corrosion in acidic media

In this research, the inhibition effect of thionine (Thn) and its synergistic effect with Zn2+ on the corrosion of a carbon steel A106 sample in 0.5 M sulfuric acid has been investigated using electrochemical potentiodynamic polarization technique and weight loss tests. Using Tafel polarization plots and corrosion rate calculations, it was revealed that Thn act as an effective inhibitor. It was found that the results of weight loss test and polarization method are in good agreement. The synergistic effect of zinc ions on the corrosion inhibition of steel in the presence of various concentrations of Thn was investigated, too. The addition of zinc ions enhances the inhibition efficiency considerably. Maximum inhibition efficiency was achieved about 97% for a system containing 20 ppm Thn and 16.7 mM Zn2+. The presence of zinc ions increases the degree of surface coverage. The synergism parameters "S", calculated from surface coverage, are found to be larger than unity for some of Thn concentrations. Thn behaved as a mixed type inhibitor in H2SO4 solution. It was investigated too, that the adsorption of Thn on the metal surface was obeyed Langmuir adsorption isotherm and adsorption was performed spontaneously. Investigating the adsorption mechanism proved that it is possible to form a complex between the initial Zn2+ layer on the steel surface with the protonated form of thionine.