Electrochemical and theoretical investigation for some pyrazolone derivatives as inhibitors for the corrosion of C-steel in 0.5 M hydrochloric acid

Abstract

Relative stabilities of the tautomers of three 3-methyl -1H-pyrozol-5(4H)-one derivatives were computationally investigated in gas-phase and in aqueous phase applying the Bpw91 level of theory with the 6-311G(d, p) basis sets. Pyrazolones derivatives were utilized to inhibit the general and pitting corrosion of C-steel in 0.5 M HCl using galvanostatic, potentiodynamic anodic polarization and electrochemical impedance spectroscopy (EIS) techniques. The outcomes indicate that pyrazolones derivatives are effective mixed inhibitors. The inhibition efficiency is improved with the concentration of additives. The inhibitory action of pyrazolones derivatives was interpreted by its adsorption on the steel surface according to Freundlich isotherm. The pitting potential was shifted into a more noble potential indicating that the pyrazolone derivatives act as pitting corrosion inhibitors. Performed applying the density functional theory (DFT) with the Bpw91/6-311G(d, p) in addition to boundary conditions with plane wave basis set. The results of these theoretical calculations were used to obtain information about molecular descriptors, which were correlated with the order of inhibitory efficiency of these inhibitors. There are good agreements between the results obtained by quantum chemical calculations and those obtained using electrochemical measurements.