Tetrahydrocarbazole Derivatives as Corrosion Inhibitors for Zinc in HCl Solution

Abstract

The inhibition of the corrosion of zinc in 0.4 M HCl by (Z)-2-(2-(4-methoxyphenyl)hydrazono)-3-(5,6,7,8-tetrahydrocarbazol-9-yl)-3-oxopropanenitrile(1),(Z)-2-(2-(4-c hlorophenyl)hydrazono)-3-(5,6,7,8-tetrahydrocarbazol-9-yl)-3-oxopropanenitrile(2),(Z)-2-(2-phenylhydrazono)-3-(5,6,7,8-tetrahydrocarbazol-9-yl)-3-oxopropanenitrile(3)and (Z)-2-(2-(4-nitrophenyl)hydrazono)-3-(5,6,7,8-tetra hydrocarbazol-9-yl)-3-oxopropanenitrile (4) has been investigated at 30 °C using weight loss, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and electrochemical frequency modulation (EFM) measurements. Results obtained show that these investigated compounds are good inhibitors and their inhibition efficiencies (IE %) increase with the increase of inhibitor concentration and with rise of temperature. Moreover, polarization studies clearly reveal that the presence of inhibitors changes the mechanism of hydrogen evolution and that they act as mixed inhibitors. EIS study shows that charge transfer resistance increases with the inhibitor concentration. The adsorption of investigated compounds obeys Langmuir's adsorption isotherm. Effect of temperature is studied between 30 and 50 °C and determination of activation parameters is also discussed. The mechanism of adsorption had been explained on the basis of chemical structure of the investigated inhibitors. It was found that there is a good agreement between the different tested techniques.