Corrosion Inhibitors for the Preservation of Carbon Steel in Hydrochloric Acid Medium

In industrial procedures, acid solutions are widely used to remove rust. Pickling steel and ferrous metals with hydrochloric acid is common. Corrosion not only wastes material resources and energy, but it can also result in major accidents and contribute to environmental damage in some cases, especially those that use acids in the pickling process. Corrosion is believed to be responsible for the loss of 5 tons of mild steel per second around the world. As a result, several synthetic inhibitors are utilized to minimize the corrosive media’s aggressiveness. This chapter focuses on the corrosion inhibition by new 1H-pyrrole-2,5dione derivatives, namely 1-phenyl-1 H -pyrrole-2,5-dione (PPD) and 2 1-(4-methylphenyl)-1 H -pyrrole-2,5-dione (MPPD) were synthesised and their inhibitive action against the corrosion of carbon steel in 1 M HCl solution were investigated at 308 K by weight loss, potentiodynamic polarization curves, and electrochemical impedance spectroscopy (EIS) methods. The results showed that the investigated 1 H -pyrrole-2,5-dione derivatives are good corrosion inhibitors for carbon steel in 1 M HCl medium, their inhibition efficiency increased with inhibitor concentration, and MPPD is slightly more effective than PPD. Potentiostatic polarization study showed that PPD and MPPD are mixed-type inhibitors in 1 M HCl. Impedance experimental data revealed a frequency distribution of the capacitance, simulated as constant phase element. The results obtained from electrochemical and weight loss studies were in reasonable agreement. The adsorption of MPPD and PPD on steel surface obeyed Langmuir’s adsorption isotherm. Thermodynamic data and XPS analysis clearly indicated that the adsorption mechanism of 1 H -pyrrole-2,5-dione derivatives on carbon steel surface in 1 M HCl solution is mainly controlled by a chemisorption process. Quantum chemical calculations using the Density Functional Theory (DFT) were performed on 1 H -pyrrole-2,5dione derivatives to determine the relationship between molecular structures and their inhibition efficiencies.