THEORETICAL AND EXPERIMENTAL STUDIES FOR THE CORROSION INHIBITION POTENTIALS OF (4-(2-METHOXYPHENYL)-3- THIOSEMICARBAZIDE) FOR MILD STEEL IN 1.0 M HCL

The adsorption behavior and inhibition mechanism of (4-(2-Methoxyphenyl)-3- thiosemicarbazide) (2Metho-TSC) on corrosion of mild steel in HCl were studied by potentiodynamic polarization AC resistance and current voltages in 1.0 M HCl at 293 K. While Ecorr value was -0.518 mV in uninhibited solution, it shifted slightly in the positive direction in inhibited solutions with the increase of inhibitor concentration. The currents density of anodic and cathodic regions has lower compared to that of 1.0 M HCl solution. icorr value was 158.78 μA·cm−2 in uninhibited solution and 15.64 μA.cm−2 at the 1×10-2 M concentration of 2Metho-TSC. When the inhibitor concentration increases, the corrosion current density value decreases, and the suppression efficiency value increases. The percentage inhibition efficiency values ranged of 2Metho-TSC from 68 to 90 %. The values of Rpblank and Rpinh are 110 and 1019 Ω.cm-2 , CPEblank and CPEinh are 348 and 15 μF.cm-2 respectively. As the Rp value increases, the CPE value decrease as the inhibitor concentration increases, most likely due to decreased local dielectric constant and/or increased thickness of the metal/solution interface. The adsorption of corrosion inhibitor on the surface of mild steel conforms to the Langmuir model [1]. Adsorption equilibrium constant and adsorption free energy were determined. The value of ΔG°ads is -37.8 kJ.mol-1 of 2Metho-TSC, it is suggested that the adsorption of these inhibitors involve two types of interactions chemisorption and physisorption. The density functional theory (DFT) at the B3LYP functionals with the 6-311G (d,p) basis set were performed for 2Metho-TSC