Review article

Inhibition, kinetic and thermodynamic effects of new Azo derivatives on iron corrosion in acidic and alkaline solutions

*¹Loutfy H. Madkour and ²Zinhome UA

¹Chemistry Department, Faculty of Science and Arts, Baljarashi, Al-Baha University, P.O. Box. (1988), Al-Baha, Kingdom of Saudi Arabia

²Chemistry Department, Faculty of Science, Tanta University, 31527, Tanta, Egypt

*Corresponding author E-mail: loutfy_madkour@yahoo.com; Tel. +966 541945518; Fax: +966 77247272

Accepted 14 December 2014

Abstract

This investigation is designed to apply an advanced kinetic-thermodynamic model on the experimental data obtained from acidic and alkaline corrosion of iron using mono- and bis-azo dyes as corrosion inhibitors. The inhibition properties of the tested azo dyes on corrosion of iron in HNO₃ and NaOH media were analyzed by gravimetric, thermometric and polarization measurements. The three studied methods gave consistent results. Polarization study showed that all the inhibitors are mixed type in acidic, act mainly as cathodic in alkaline solution. The synthesized azo dye derivatives exhibit good inhibition properties, obeys the Frumkin adsorption isotherm. The large values of the change in the standard free energy of adsorption (∆G^o_ads), equilibrium constant (K_ads) and binding constant (K_b) revealed that the reactions proceed spontaneously and result in highly efficient physisorption mechanism and stronger electrical interaction between the double layer existing at the phase boundary and the adsorbing molecules. The inhibition efficiency depends on the number of adsorption oxygen sites (OH and OMe groups), their charge density and π-electron clouds. The inhibition efficiency evaluated via theoretical methods was well accorded with reported experimental ones, following the same order as: a-naphthyl- ligand >b -naphthyl>p-anisdine>p-toluidine >o-toluidine >m-toluidine derivative. This research might provide a theoretical inhibition performance evaluation approach for homologous inhibitors.

Keywords: Corrosion, inhibitor, mono- and bis-azo dyes, iron, HNO₃, NaOH