Corrosion Inhibition Behaviour and Adsorption Characteristics of Dapsone Derivatives on Mild Steel in Acid Medium

Two newly synthesized Dapsone derivatives viz., 3-[(4-{4-[(1H-Indol-3-ylmethylene)-amino]-benzenesulfonyl}-phenylimino)-methyl]-1H-indole (IABPI) and 5-[(4-{4-[(Thiophen-2-ylmethylene)-amino]-benzenesulfonyl}-phenylimino)-methyl]-thiophene (TABPT) were investigated as corrosion inhibitors for mild steel in 0.5 M H2SO4 media by using chemical and electrochemical techniques. Potentiodynamic polarization studies indicated that these two inhibitors behaved as mixed type. These inhibitors were found to obey Langmuir isotherm model. Using this isotherm, thermodynamic adsorption parameters were evaluated. EIS studies showed that the polarization resistance (RP) and double layer capacitance (Cdl) of the inhibitors are concentration dependent. FTIR technique was used to identify the interaction of inhibitor with mild steel surface, whereas persistency of thin protective film of inhibitors on the mild steel surface was carried out by using EDX and SEM.