Diazenyl derivatives as efficient corrosion inhibitors for mild steel in HCl medium: Gravimetric, electrochemical and computational approach

In present investigation diazenyl derivatives, namely, (E)-4, 4(E)-4, 4 '-(((4-(2-amino-6-phenyl-2H-1, 3-thiazin-4-yl) phenyl) diazenyl) methylene) bis (6-phenyl-6H-1, 3-thiazin 2amine) (ATPA) and (E) 1(4((bis (5-amino1, 3,4- thiadiazol-2-yl) methyl) diazenyl) phenyl) ethanone (ATPE) were synthesized and used as corrosion inhibitor for mild steel (MS) in 15 % HCl solution. Corrosion inhibition studies were performed by weight loss, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization methods. Potentiodynamic polarization result demonstrates that ATPA and ATPE offered inhibition efficiency of 97.11 and 96.02 %, respectively at 200 ppm concentration and 303 K temperature. Calculated standard free energy of adsorption values were found in the range of -38.47 to -40.84 kJmol(-1) for ATPA and -36.91 to -39.19 kJmol(-1) for ATPE, suggesting the mixed type adsorption of ATPA and ATPE on MS surface. The adsorption of ATPA and ATPE on MS surface obeyed Langmuir adsorption isotherm. Morphological analysis performed on uninhibited and inhibited samples by field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) techniques suggested the formation of protective layer of inhibitor molecules on MS surface. According to polarization results, both compounds behave as anodic inhibitors. Theoretical data of ATPA and ATPE obtained from Density functional theory (DFT), Monte Carlo simulation (MCS) and Molecular dynamic simulation (MDS) supports the experimental observations.