Taurine as a Green Corrosion Inhibitor for AISI 4130 Steel Alloy in Hydrochloric Acid Solution

The inhibition ability of 2-aminoethanesulfonic acid (taurine) against the corrosion of AISI steel 4130 in 1M HCl solution was evaluated by polarization, impedance (EIS), and chronoamperometry. Polarization studies indicated that taurine retards both cathodic and anodic reactions through chemical adsorption and blocking the active corrosion sites. The adsorption of this compound obeyed the modified Langmuir adsorption isotherm. EIS data shows that as the inhibitor concentration increased, the charge transfer resistance of steel increased, while double layer capacitance decreased. Kinetic and thermodynamic parameters such as activation energy, enthalpy, entropy, and free energy of activation and adsorption were calculated. Gibbs free energy indicated that the adsorption process is spontaneous. Atomic force microscopy (AFM) and optical microscopy were used to study the steel surface. Surface studies show that the surface of a sample in solution with inhibitor molecules looks more uniform, with less roughness, than that in the uninhibited solution. Results obtained from quantum chemical studies show excellent correlations between quantum chemical parameters and experimental inhibition efficiencies using density functional theory (DFT).