Inhibition effect of the corrosion of mild steel in acidic solutions by Vanillin-4-methylthio semicarbazone and Vanillin-4-ethylthiosemi-carbazone

Inhibition effect of Vanillin-4-methylthiosemi carbazone(VMTSC) and Vanillin-4-ethylthiosemi carbazone (VETSC) for the corrosion on mild steel in aqueous solution containing 1N H₂SO₄ was investigated by weight loss, potentiodynamic polarization technique, electrochemical impedance spectroscopy and scanning electron microscopy. The results of weight loss study showed that the inhibition efficiency increases with increase in concentration of the inhibitors. Potentiodynamic polarization data showed that Vanillin-4-ethylthiosemicarbazone (VMTSC) and Vanillin-4-ethylthiosemicarbazone (VETSC) behave as mixed type inhibitor in 1N H₂SO₄. Electrochemical impedence spectroscopy was used to investigate the mechanism of the corrosion inhibition. The surface morphology of the mild steel samples both in absence and presence of inhibitor at optimum concentration was examined via Scanning Electron Microscopy (SEM). The adsorption of this compound was found to obey Langmuir adsorption isotherm. The value of ΔG°_ads was less than 40kj mol^-1 indicating electrostatic interaction between the charged inhibitor molecules and the charged metal surface, i.e., physical adsorption. Various thermodynamic parameters were calculated to investigate the mechanism of corrosion inhibition.