Mechanism of Corrosion and Corrosion Inhibition of Tin in Aqueous Solutions Containing Tartaric Acid

The electrochemical behavior of tin metal in tartaric acid solutions of different concentrations was investigated. Some amino acids, namely, alanine, glycine, glutamic acid and histidine were used as environmentally safe inhibitors for the tin dissolution process. Different electrochemical techniques including, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) were used. The metal surface was examined via scanning electron microscopy (SEM). The E/I curves showed that the anodic behavior of tin exhibits active/passive transition. The active dissolution of tin was increased by increasing tartaric acid concentration. Glycine was found to give the highest corrosion inhibition efficiency at a concentration of 0.02 mol dm-3. The corrosion inhibition process is based on the adsorption of the amino acid molecules on the metal surface. The adsorption process was found to obey the Freundlich isotherm, and the adsorption of glycine on Sn has an adsorption free energy of-10.2 kJ/mol which reveals physical adsorption of the amino acid molecules on the metal surface. The experimental impedance data are in good agreement with the polarization experiments. An equivalent circuit model was proposed for fitting of the experimental impedance data, and to simulate the electrode/electrolyte interface