Nigella sativa extract phytochemicals: Effective green/bio-active anti-corrosion agent for steel protection in saline media

Abstract

This research aims to develop a low-VOC silane (sol-gel) coating functionally protected by novel non-toxic metal-organic networks (MONs) based on extracted Nigella sativa bio-molecules/Zinc nitrate. The effectiveness of the silane coating containing the MONs pigment was investigated via electrochemical (i.e., EIS) and accelerated (i.e., salt spray) corrosion experiments. Based on the electrochemical tests' results in the solution phase, an efficiency of 67.8% and a mixed-type corrosion mitigation mechanism were obtained for the hybrid pigment to protect the mild steel against the NaCl media. Moreover, adding the synthesized MONs into the silane coating matrix dramatically increased its protection performance. Fourier-transform infrared spectroscopy (FT-IR) results revealed that the coating’s curing index is affected after the MONs pigment’s inclusion in the silane matrix. The change in the coating curing index increases the silane film crosslinking density, improving coating adhesion to the metallic substrate and then enhancing its anti-corrosion protection performance. The electrochemical tests were employed in the presence of artificial defects to study the active protection performance of the silane layer. Results indicated that the active anti-corrosion protection performance of the silane coating was significantly improved after employing the synthesized MONs in its structure. Adsorbing the inhibitive species in the scratched region of the silane coating and fabricating the inhibitive film at this region is the main protection mechanism, which was illustrated via SEM/EDS analysis.