Sulfa Guanidine Azo Derivatives as Environmentally - Friendly Corrosion Inhibitors for Nickel in HCl Solution: Theoretical and Experimental Study

The protection influence of three sulfa guanidine azo derivatives against nickel corrosion was studied in 0.5 M HCl solutions at 25oC. Measurements were conducted under various experimental conditions using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and electrochemical frequency modulation (EFM) techniques. These studies have shown that sulfa guanidine azo derivatives are very good ‘‘green”, mixed-type inhibitors. Electrochemical frequency modulation (EFM) and electrochemical impedance spectroscopy (EIS) method of analysis are also presented here for monitoring corrosion. Corrosion rates obtained from both EFM and EIS methods are comparable with those recorded using Tafel extrapolation method, confirming validation of corrosion rates measured by the latter. The inhibitive action of these sulfa guanidine azo derivatives was discussed in terms of blocking the electrode surface by adsorption of the molecules through the active centers contained in their structures following Langmuir adsorption isotherm. Quantum chemical method was also employed to explore the relationship between the inhibitor molecular properties and its protection efficiency. The density function theory (DFT) is used to study the structural properties of sulfa guanidine azo derivatives in aqueous phase in an attempt to understand their inhibition mechanism. The protection efficiencies of these compounds showed a certain relationship to highest occupied molecular orbital (HOMO) energy, Mulliken atomic charges and Fukui indices.