Evaluation of effects of sulfur containing organic substances on the corrosion of mild steel in acidic environment

The inhibition effects of Rodanin-N-Acetic Acid (R-NA), 2-Thiohydantoin (2-THD), 3-Thiophene Acetic Acid (3-THA), 2-Thiophene Acetic Acid (2-THA) on the corrosion behavior of mild steel (MS) in 0.1M HCl solution was studied in relation to the concentrations and temperatures using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and linear polarization resistance (LPR) techniques. From long-term tests in different concentrations of organic substances, hydrogen gas evolution (VH2 ? t) and polarization resistances with immersion time of MS were also measured. The surface morphology of MS after their exposure to 0.1M HCl solution with and without 1.0×10?2 M of organic substances with the different immersion times was examined by scanning electron microscopy (SEM). For each of the organic substances, the values of activation energy (Ea) for the MS corrosion and the thermodynamic parameters (Kads, ?Gads,) were calculated and discussed. The potential of zero charge (PZC) of the MS in 0.1M HCl solutions containing 1.0×10?2 M of organic substances was studied by the EIS method, and a mechanism for the adsorption process of organic substances was proposed. The results showed that investigated organic substances performed excellent inhibiting effect for the corrosion of the MS, except for 2-THA. The highest inhibition efficiency has been found R-NA