Hanan T. Rahal

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Zinc oxide (ZnO) nanoparticles (NPs) were synthesized using the coprecipitation method. The resulting NPs were characterized by X‐ray diffraction, transmission electron microscopy, and Fourier transform infrared spectroscopy. The surface morphology of the coatings has been characterized by scanning electron microscopy (SEM). SEM images show a uniform and homogeneous distribution of ZnO‐NPs in polyurethane (PU) coatings while aggregates appear in epoxy coatings. Using tensile stress–strain test, the effect of the addition of ZnO‐NPs on the mechanical properties of PU and epoxy coatings was examined. The addition of ZnO‐NPs has enhanced the Young's modulus and the tensile strength of PU and epoxy coatings. Through the open‐circuit potential and electrochemical impedance spectroscopy measurements, the anticorrosive properties of PU‐ or epoxy‐coated mild steel panels containing ZnO‐NPs have been investigated in 0.5 M NaCl solution. Nyquist impedance plots for PU and epoxy coatings in PU‐ or epoxy‐coated mild steel panels containing ZnO‐NPs were tested in the absence and presence of ZnO‐NPs have different responses. It has been shown that the dispersion of ZnO‐NPs significantly improves the anticorrosive performance of PU coatings. A PU coating containing 700 mg/kg ZnO‐NPs is recommended to achieve better mechanical properties and corrosion resistance.

The thermodynamic, inhibitive and synergistic properties of Fragaria ananassa (strawberry) and Cucurbita pepo L (zucchini) leaf extracts on the corrosion of mild steel in Hydrochloric acid solutions were examined by potentiodynamic polarization curves measurements and electrochemical impedance spectroscopy (EIS) technique as well as optical photographic study. Fourier transform infrared spectroscopy (FTIR) and UV-Spectroscopy were applied to predict the possible functional groups and constituents of both leaf extracts. Potentiodynamic polarization curves proved that Fragaria ananassa and Cucurbita pepo L leaf extracts act as mixed type inhibitors for mild steel in 0.5 M HCl solutions. Impedance plots indicated that the corrosion process occurred under activation control. Thermodynamic parameters proved that the formation of the activated complex is an endothermic association instead of a dissociation step. The inhibitive efficiency of these leaf extracts relies on their physical adsorption on the metal surface rather than the complexation with Fe²⁺ ions. Cucurbita pepo L leaf extract is more efficient than Fragaria ananassa as a corrosion inhibitor for mild steel in 0.5 M HCl. The synergistic effect between both extracts may be due to co-adsorption between their molecules, which could be either competitive or co-operative adsorptions. The synergistic parameter value S was higher than unity indicating a cooperative synergistic effect.

The inhibitory nature, thermodynamics and adsorptive properties of Phaseolus vulgaris L. extract, known as Fasolia seed extract were evaluated for carbon steel and zinc alloy corrosion in 0.5 M HCl using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. Theoretical fittings for kinetic-thermodynamic and Flory–Huggins models have been studied in order to elucidate the mode of adsorption of P. vulgaris L. seed (PS) extract on zinc alloy and carbon steel. The findings have shown that the mechanism of adsorption occurs through electrostatic interactions between the extract molecules and the metal surface.

Polyaniline (PAni) has been electropolymerized on stainless steel surface (SS321) by cyclic voltammetry technique from aqueous solutions of 0.1 M aniline in 0.1 M acetic acid, oxalic acid, hydrochloric acid and sulfuric acid solutions. The anticorrosion performance of PAni coating electropolymerized in sulfuric acid solution was investigated in 0.1 M NaOH solutions using potentiodynamic polarization curves technique. The influence of scan rate, cycle number, formation temperature, as well as supporting electrolytes on the anticorrosion performance of PAni film were investigated. The polymer film formation in presence of acetic or hydrochloric acid is attributed to the oxidative mechanism in contrary to the reductive mechanism proposed in presence of oxalic or sulfuric acid. The best protection efficiency of PAni coatings was obtained when prepared in acetic acid solution. The morphology of PAni coatings before and after polarizing SS 321 in 0.1 M NaOH solutions was examined using scanning electron microscope (SEM) and Energy dispersive x-ray (EDX). It was noted that PAni coating morphology was highly influenced by the nature of acid anion present.