Cyclohexylamine an effective corrosion inhibitor for mild steel in 0.1 N H2SO4: Experimental and theoretical (molecular dynamics simulation and FMO) study

Abstract

Cyclohexylamine (CHA) was tested as an anti-pitting and anti-cracking agent for Mild Steel (MS) in 0.1 N H2SO4 using experimental and theoretical techniques. Experimental techniques used are, weight loss, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS). The surface study was carried out by Metallurgical Research Microscopy (MRM) and SEM techniques. Molecular Dynamics Simulation (MDS) and Frontier Molecular Orbital (FMO) studies were performed by Density Functional Theory (DFT). The kinetic and thermochemical parameters like hardness, electrophilicity, nucleophilicity, electron-donating and accepting tendency, work function, back donation energy, Proton Affinity (PA), MS/CHA interaction energy, binding energies, etc., were investigated and discussed at length. Frequency calculation on geometry optimized structure of CHA was carried out to obtain theoretical IR spectra. The mechanism of inhibition was investigated both by theoretical and experimental techniques. The maximum corrosion inhibition efficiency (CIE) shown by CHA at 1000 ppm was 81.06%. The electrochemical impedance spectroscopy (EIS) showed an increase in charge transfer resistance with an increase in the concentration of inhibitor justifying the physisorption process. MRM shows an increase in coating thickness with CHA concentration. SEM image shows a decrease in the roughness of MS surface with CHA concentration. The BOD and COD of wastewater were found within the permissible limit.