5-methyl-2,4-dihydropyrazol-3-one and 5-methyl-2-phenyl-2,4-didhydropyrazol-3-one as copper corrosion inhibitors in acidic media

The present study analyses the copper corrosion behaviour of 5-methyl-2,4-dihydropyrazol-3-one (MHPO) and 5-methyl-2-phenyl-2,4-dihydropyrazol-3-one (MPPO) in 0.1 M sulphuric acid, using loss of mass, polarization curves (PC) and electrochemical impedance spectroscopy (EIS). The electrochemical results show that these organic compounds are mixed inhibitors that act preferentially on cathodic sites, inhibiting corrosion by blocking active sites on the metal surface. Changes in electrochemical parameters are related to the adsorption of the organic inhibitors on the metal surface, leading to the formation of a protective film which grows with the increase in exposure time in the medium. The adsorption of both compounds obeys Langmuir's adsorption isotherm and is physical in nature. Their inhibition efficiencies are favoured by high EHOMO energy, and by a decrease in the E_L-H energy gap.