Adsorption, electrochemical and theoretical studies on the protective effect of N-(5-bromo-2-hydroxybenzylidene) isonicotinohydrazide on carbon steel corrosion in aggressive acid environment

A new Schiff base, N-(5-bromo-2-hydroxybenzylidene) isonicotinohydrazide (NBHI), has been synthesized and studied as an inhibitor of X70 carbon steel (CS) corrosion in aggressive 1 M HCl environment using gravimetric, electrochemical impedance spectroscopy (EIS) tests, potentiodynamic polarization (PDP) and scanning electron microscopy (SEM). The inhibition efficiency was found to increase with increase in NBHI concentration but decreased with rise in temperature. Inhibition efficiencies up to 96.7%, 97.0% and 94.2% were obtained respectively for weight loss, EIS and polarization measurements at 1.00 mM and 303 K. Polarization studies indicate that NBHI essentially behaved as a mixed-type inhibitor controlling both anodic and cathodic reactions. EIS results indicated that charge transfer resistance (R ct ) increased while double layer capacitance (C dl ) decreased with increasing NBHI concentration. The adsorption of NBHI onto the X70 CS surface obeyed Langmuir adsorption isotherm. SEM analysis supported the protective film formation of NBHI on the steel surface. Quantum chemical calculations were used to study NBHI reactivity and the results complimented well with the experimental data.