Comparative Studies on the Corrosion Inhibition of Three Different Organic Heterocyclic Compounds as Corrosion Inhibitors for Mild Steel in Hydrochloric Acid

Three organic inhibitors, based 5-Chloroisatin’s bases, namely, 1-allyl-5-chloro-indoline-2,3-dione (TZACI). 5-chloro-1-(2-(dimethylamino) ethyl) indoline-2,3-dione (TZCDI),5-chloro-1-octylindoline-2,3-dione (TZCOI) were influence on corrosion inhibition of mild steel in 1.0M hydrochloric acid solution. The inhibition efficiency increased with the increase of a compound concentration in the case of these three inhibitors, which have the mixed type behavior proposed by the polarization studies. Impedance measurements showed that after the addition of inhibitors, charge-transfer resistance increased and double-layer capacitance decreased, involving increased inhibition efficiency. The adsorption of three inhibitors on a steel surface obeyed Langmuir model. Free energy of adsorption showed that the type of adsorption was physical for TZACI and chemical for the TZCDI, TZCOI. Scanning electron microscopic analyses confirm the formation of the protective film on the surface.