Aqueous Black Seed (Nigellasativa L.) Extract-Mediated Corrosion Inhibition in Mild Steel Exposed to 3.5% NaCl: Effect of Temperature, pH, Time, and In Situ Analysis Using Atomic Force Microscopy

Atomic force microscopy (AFM)-based analysis on the corrosion inhibition properties of aqueous black seed extract for mild steel exposed to 3.5% NaCl solution is reported here. At ~ 600 ppm inhibitor concentration, corrosion rate and inhibition efficiency are found to be ~ 0.18 ± 0.1 mpy and ~ 94%, respectively. The superior corrosion inhibition is due to the adsorption of the phytochemicals onto the metallic surface, as confirmed from spectroscopic analysis. Findings show the suitability of the black seed extract for practical applications at neutral pH and room temperature. AFM and magnetic force microscopy indicate lower surface roughness and nearly pristine topography for the inhibitor-protected specimens. In situ AFM analyses indicate delayed formation of surface irregularities for the inhibitor-protected specimens. The obtained results clearly show the superior corrosion inhibition efficiency of the aqueous black seed extract against mild steel under simulated sea water condition.