Inhibitors for chemical cleaning of iron with tannic acid

The effect of tannic acid on the corrosion of iron was studied using electrochemical impedance spectroscopy (EIS). This study was conducted at different conditions including pH, immersion time, additives and temperature. The impedance of iron in neutral solutions was found to be due to a charge transfer and to a diffusion process through the formed layer on the iron surface. The magnitude of the two processes is time dependent. The effect of 2-mercaptobenzimidazole (2-CBI), 2-mercaptobenzoxazole (2-CBO) and 2-mercaptobenzothiazole (2-CBT)- was also studied. These additives were found to inhibit the corrosion of iron in tannic acid solution at the tested conditions. Moreover, 2-CBI was found to reduce the value of charge transfer resistance (R-ct) of an iron electrode that was previously covered with corrosion products. The shape of the impedance plots at 45 degrees C was similar to those recorded at 25 degrees C. However, R-ct was always higher in the presence of 2-CBI, especially at shorter immersion times.