Mild steel corrosion inhibition by nicotinamide as a green inhibitor: An electrochemical, thermodynamic and theoretical insight

The nature of inhibition, mechanism of adsorption and effect of concentration of nicotinamide (NCA) on corrosion of mild steel (MS) in 0.5 M H2SO4 were evaluated by potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) methods. Tafel plot reveals that NCA inhibits corrosion of mild steel and it acts as a mixed-typed inhibitor in acidic medium. The inhibition efficiency of NCA depends upon its concentration as well as temperature and it increases on increasing both concentration and temperature. The inhibition efficiency attained was 92.7% at 10-1 M at 328 K while it was 77.6% at 10-1 M at 298 K. The adsorption of NCA onto MS surface facilitates corrosion inhibition and the mechanism follows El-Awady adsorption isotherm model. The values of 0 ?Gads, ?Hads0and ?Sads0 indicate the involvement of chemisorption in the adsorption of inhibitor. The increase of charge transfer resistance from 2.404 ohm center dot cm2 in H2SO4 to 26.47 ohm center dot cm2 and decrease in electrical double layer capacitance from 55.62 center dot 10-4 F center dot cm-2 in H2SO4 to 7.45 center dot 10-4 F center dot cm-2 in the presence of 10-1 M NCA in EIS study signifies the mitigation of corrosion of MS. The scanning electron microscopy (SEM) confirmed the adsorption of NCA on MS and the development of the protective layer/film that leads to the corrosion inhibition. The mechanism of inhibition through the adsorption of NCA was also ascertained by quantum chemical calculation & density functional theory (DFT) studies. All the experimental and theoretical findings reveal that Nicotinamide is an efficient green inhibitor.