Electrochemical and surface analytical characterization study of the inhibition effect of boiled red onion extract on tin corrosion in 0.2 M Maleic acid medium

The effect of two different forms of red onion extracts (boiled red onion skin extracts (BROE) and filtered red onion juice (FROJ) on the corrosion and the passivation of the tin corrosion in 0.2 M Malic acid were compared which showed that BROE method is more effective. The inhibition efficiency of BROE against tin corrosion in 0.2 M Maleic acid was studied using electrochemical and surface analytical methods. The electrochemical polarization curves displayed the active/passive transition of the anodic behavior of the tin electrode. The electrochemical impedance measurements demonstrated the effect of increasing BORE concentration on the inhibition efficiency (eta %) (to a eta(max) = 94% at 300 mg/L of BORE). In general, the inhibition efficiency (i.e. surface coverage) increased with BORE concentration and the adsorption mechanism fitted the Langmuir adsorption isotherm model. The effect of temperature on the corrosion of tin in 0.2 M Maleic acid without and with certain concentration of BROE was studied in the temperature range of 293-333 K. Studying the effect of temperature on the inhibition efficiency showed a decline in eta values as the temperature was increased. The results of EDS and SEM presented that BROE possess a capability to protect tin surface in 0.2 M Maleic acid. We found satisfactory agreement between electrochemical and surface analytical measurements. Good correlation between the major effective constituents of the extract and the inhibition mechanism was obtained.