Abstract:
Corrosion remains a major problem in the manufacturing industries and the whole world at large, hence the need to con
trol it. Organic molecules have been used in the past and recent times because they have certain advantages over inorganic
molecules. Information on the use of indole derivatives as anti-corrosive agents is scanty. In this work therefore, two indole
derivatives, 6-benzyl-2H-indol-2-one and 3-methylindole were investigated for their ability to provide protective coverage
on the surface of low carbon steel (LCS) and serve as anti-corrosive agents. Their corrosion rates and inhibition efficiencies
were determined by weight loss, gasometric, electrochemical and theoretical methods. Images of LCS in the absence of inhibi
tor and acid, in the presence of acid only and in the presence of acid and inhibitors were recorded with the aid of Scanning
Electron Microscopy (SEM). Quantum mechanical calculations on the energies of the frontier molecular orbitals (FMOs)
were performed using the density functional theory. The FMOs energies were used to calculated the reactivity descriptors
which inform about the inhibition capacity of the molecules. Monte Carlo simulation was used to perform the adsorption
of the molecules on the surface of Fe(110). These molecules inhibit the corrosion of LCS with inhibition efficiencies of the
inhibitors increasing at lower temperature, with all the inhibitors having their highest inhibition efficiencies at 303 K and at
the concentration of 10 × 10–5 M. Potentiodynamic polarisation curves revealed that both inhibitors are mixed-type inhibitors.
The SEM images revealed that the surface of the low carbon steel was protected by these organic inhibitors. The activation
energies (12.21–55.40 kJ/mol) and the Gibb’s free energy values (− 4.51 to − 8.58 kJ/mol) obtained from the weight loss
method supported a physical adsorption mechanism. The adsorption was found to obey Langmuir adsorption isotherm. All
theoretical results are consistent with experimental results. These molecules could be adopted for use as anti-corrosive agents
in the oil, gas and manufacturing industries.
