Effect of Inorganic and Organic Constituents Ligands on Corrosion Inhibition of Mild Steel in Aqueous Solutions

Abstract

This study is divided into two parts, the first part deals with the use of some para-Hydroazopyrazolone (antipyrine) derivatives as corrosion inhibitors for mild steel in HCl solutions. This confirmed using different techniques, such as: weight loss, potentiodynamic polarization, electrochemical impedance spectroscopy and electrochemical frequency modulation. In addition to study the stability of these derivatives in acidic media and spectrophotometric determination of dissolved iron in the corrosive media. The results revealed that these derivatives act as mixed type inhibitors and they adsorbed on mild steel surface following Langmuir adsorption isotherm. The inhibition efficiency was found to depend on the type of the substituent group present in the molecules such as: OCH3, CH3 & Cl present in para-Hydroazopyrazolone nucleus. On the other hand, compare the corrosion inhibition data obtained from weight loss with that obtained from Tafel extrapolation, EIS and EFM techniques. Moreover, ability of these derivatives to mitigate the pitting corrosion of mild steel in synthetic sea water has been discussed. The morphology of mild steel surface by scanning electron microscopy and energy dispersive x-ray (SEM & EDX) reported before and after exposing to the aggressive medium were done. Beside the electronic spectra of the formed film and the residual inhibitor solution are discussed. This revealed that these derivatives are adsorbed onto the surface to form a defensive film to isolate the mild steel surface from the aggressive medium. Some quantum chemical indices (EHOMO, ELUMO, dipole moment and energy gap) and mechanism of corrosion inhibition have been demonstrated. The results indicated that these derivatives influence the inhibition efficiency in the following order: -OCH3 > -CH3 > -Cl. These results reveal a good correlation between the theoretical data and the experimental results hoping to get some general ideas to guide the composing of inhibitor in reality. In the second part, rare earth metals (Sm3+ & La3+) have been investigated as anti-corrosion substances for mild steel in produced water environment as a practical application. Produced water is the by-product accomplished with petroleum activities. When, the salinity of produced water is about 27800 ppm, so the localized pitting is the proper form of corrosion that attacks mild steel surface. The techniques utilized in this approach are as before at 25 ºC. Iron content (dissolved iron) is measured by spectroscopy and pH values of solutions are recorded. Data declared that %IE rose with addition of rare earth metals and decreased with raising temperature. Langmuir’s adsorption isotherm was the best fit with the revealing data. The thermodynamic activation parameters are demonstrated. Surface examination using SEM & EDX techniques were employed for surface analyzing of uninhibited and inhibited mild steel surface. The % inhibition demonstrated from different methodologies was in a good agreement. Rare earth compounds especially chloride can be used as effective, ecofriendly and alternative to other toxic inorganic. This claim supported by the former results of the chemical and electrochemical methodology utilized.

Keywords: mild steel, para-Hydroazopyrazolone, HCl, EFM, EIS, SEM, EDX, Rare earth metals, produced water.