Adsorption and corrosion inhibitive properties of 2-amino-5-mercapto-1,3,4-thiadiazole on mild steel in hydrochloric acid media

Abstract

In this study, adsorption of 2-amino-5-mercapto-1,3,4-thiadiazole (2A5MT) on mild steel (MS) surface in 0.5 M HCl solution and its corrosion inhibition effect was studied in both short and long immersion times (over 120 h). For this purpose, a series of techniques, such as potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), linear polarization resistance (LPR), thermogravimetric analysis (TGA), surface photographs, hydrogen evolution ( V H 2 – t ) and change of open circuit potential with immersion time ( E ocp– t) were utilized. The values of activation energy for MS corrosion and the thermodynamic parameters, such as adsorption equilibrium constant ( K ads), free energy of adsorption (Δ G ads), adsorption heat (Δ H ads) and adsorption entropy (Δ S ads) values were calculated and discussed. The potential of zero charge ( E pzc) of MS in inhibited solution was studied both after short and long immersion times by EIS method, and a mechanism of adsorption process was proposed. Results showed that 2A5MT performed excellent inhibiting effect for the corrosion of MS in 0.5 HCl solution and inhibition efficiency is higher than 99% after 120 h at 1.0 × 10 −2 M. The high inhibition efficiency was discussed in terms of strongly adsorption of inhibitor molecules on the metal surface and forming a protective film. Surface photographs showed a good surface coverage on the metal surface. TGA results indicated that the surface inhibitor film has relatively good thermal stability.