Investigating Centaurea napifolia Extracts for Zinc Electroplating Efficiency and Corrosion Prevention: Experimental and Surface Analysis

Abstract The ability of Centaurea napifolia extracts, hydro-methanolic (HME), methylene dichloride (MDE), ethyl acetate (EAE), and n-butanol (BE), to inhibit carbon steel (CS) corrosion in acidic environments and to function as additives in mild steel (MS) electroplating baths with pure zinc is assessed in this study. Potentiodynamic polarization, gravimetric method, scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS), profilometer, and electrochemical impedance spectroscopy (EIS) were used in this investigation to evaluate the corrosion behavior. Brightness, thickness, and adhesion strength served as indicators of the zinc's quality when deposited on the various substrates. The findings demonstrated that the addition of plant extracts enhanced the coating's quality, resulting in less porous plates with improved adhesion, increased brightness, and more corrosion resistance. The optimal corrosion rate is 0.038 mm/y obtained in the presence of 3.2 g/l of BE in the electroplating bath, compared to 1.137 mm/y without the additive and 3.783 mm/y for unplated MS. Moreover, the current density decreased from 0.3235 mA/cm² for unplated MS to 0.0972 mA/cm² and 0.0033 mA/cm² for plated without additive and when adding 3.2 g/l of the BE, respectively. The extracts were also evaluated as CS corrosion inhibitors in a 1M HCl solution. The results show that the inhibitor's ability to stop the corrosion reaction increased as the concentration went up but decreased as the temperature went up, with a maximum efficiency of 700 ppm (81%), 800 ppm (73%), 700 ppm (82%), and 700 ppm (78%), for HME, MDE, EAE, and BE, respectively. The adsorption process of all the extracts on the metallic surface obeys the Langmuir isotherm. The thermodynamic parameters of adsorption were calculated and discussed, and the results indicated that the adsorption was physical, spontaneous, and exothermic.