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.
Highlights
Acid solutions are widely used in industry
(8) and presence of the inhibitors, Electrochemical frequency modulation is a non destructive technique as electrochemical impedance spectroscopy that can directly and rapidly give values of the corrosion current without a prior knowledge of Tafel constants .The great of the electrochemical frequency modulation (EFM) is the causality factors, which serves as an internal check on the validity of the EFM measurement .With the causality factors the experimental EFM data can be verified (Bosch et al, 2001, Abdel- Rehim et al, 2006)
The surface coverage, of the metal surface by the adsorbed inhibitor was evaluated from weight loss measurements using equation 3
Summary
Acid solutions are widely used in industry. Zinc is a metal with numerous industrial applications and is mainly used for the corrosion protection of steel (Manov, 1999). Looking at its increasing use, the study of corrosion inhibition is of paramount importance. The dissolution behavior of zinc in acidic and nearly neutral media is known to be inhibited by nitrogen and sulfur-containing organic compounds. Such compounds contain electron-donating groups that decrease the corrosion rate by increasing the hydrogen overvoltage on the corroding metal (Gad Allah et al, 1989). Nitrogen-containing compounds are commonly applied as corrosion inhibitors with HCl. Efficiency of aldehyde and amino acids as inhibitors of corrosion for different metals in different corrosive environments had been studied by several workers www.ccsenet.org/mas. The major objective of the present work was to study the effect of tetrahydrocarbazole derivatives as corrosion inhibitors for Zn in 0.4 M HCl solution
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