Experimental and theoretical investigation of indole as a corrosion inhibitor for mild steel in sulfuric acid solution

The inhibiting effect of indole on the corrosion of mild steel Q235 in 0.1 M H 2 SO 4 was investigated through different approaches including weight loss, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), scanning electron microscope experiments, and theoretical calculations. Polarization curves reveal that the indole acts as a mixed-type inhibitor and the reaction mechanism in respect of either hydrogen evolution or mild steel dissolution has not been modified. EIS results imply that the water molecules adsorbed on the steel surface are substituted by the indole molecules and the inhibiting behavior of indole is probably due to the formation of an adsorptive film on the steel surface. Thus the thermodynamic and kinetic parameters are determined and discussed to give better understanding of the adsorption process. Theoretical calculations are also discussed in light of the optimized molecular structure of indole to gain further insight of the inhibition mechanism.