The inhibition of mild steel corrosion in hydrochloric acid media by two Schiff base compounds

Schiff bases of 2-({-1-methyl-3-[(2-sulfanylphenyl)imino]butylidene}-amino)-1-benzenethiol and 2-({-1,2-diphenyl-2-[(2-sulfanylphenyl)imino]ethylidene}amino)-1-benzenthiol are investigated as corrosion inhibitors in acid solution. Polarization, electrochemical impedance spectroscopy, and weight loss measurements were performed on mild steel in 15% HCl with and without the inhibitors. A significant decrease in the corrosion rate of mild steel was observed in the presence of investigated inhibitors. Polarization curves indicate that both compounds are mixed inhibitors, affecting both cathodic and anodic corrosion currents. The adsorption of inhibitors on mild steel surface in 15% HCl was found to follow Langmuir adsorption isotherm. Thermodynamic adsorption parameters (Kads, ∆Gads) of studied Schiff bases were calculated using the Langmuir adsorption isotherm. Activation parameters of the corrosion process such as activation energies, Ea, activation enthalpies, ∆H*, and activation entropies, ∆S*, were calculated by the obtained corrosion currents at different temperatures.