Inhibition effect of nicotinamide and its Mannich base derivatives on mild steel corrosion in HCl

Mannich base derivatives of nicotinamide (NA), namely N-(morpholino(phenyl)methyl)nicotinamide (NMB) and N-(phenyl(piperidin-1-yl)methyl) nicotinamide (NPB), were synthesized, characterized and studied as corrosion inhibitors for mild steel (MS) in 1.0 M hydrochloric acid using gravimetric, electrochemical experiments and theoretical calculations. Nicotinamide was also subjected for all these studies. The adsorption of NA, NMB and NPB molecules on the mild steel surface in the presence of 1.0 M HCl was found to be spontaneous and obey the Langmuir adsorption isotherm as well as Dubinin-Radushkevich isotherm. Tafel polarization measurements evidenced that all the studied inhibitors are of mixed type. EIS measurements showed that the addition of NA, NMB and NPB decreases the double-layer capacitance (C (dl)) and consequently increases the charge transfer resistance (R (CT)) of the corrosion process. FT-IR analysis, SEM micrographs and AFM analysis confirmed the presence of inhibitor film and its role on the MS surface. Quantum chemical calculations at the DFT level were achieved to correlate electronic structure parameters of NA, NMB and NPB molecules with the experimental results.