The synergistic corrosion inhibition study of different chain lengths ionic liquids as green inhibitors for X70 steel in acidic medium

For this study, three corrosion inhibitors with different anionic carbon chain lengths, 1-vinyl-3-methylimidazolium iodide ([VMIM]I), 1-vinyl-3-proplylimidazolium iodide ([VPIM]I) and 1-vinyl-3-butylimidazolium iodide ([VBIM]I) were studied on the corrosion of X70 steel in 0.5 M H2SO4 solution at 298 K by electrochemical measurements, weight loss methods, scanning electron microscope (SEM), FTIR spectra, atomic force microscopy (AFM) and theoretical calculation. Three inhibitors with synergistic effect of iodide ions are mixed-type inhibitors with excellent inhibition efficiency. The order of corrosion inhibition efficiency is: [VMIM]I < [VPIM]I < [VBIM]I according to theoretical and experimental study, indicating the inhibition performance was improved with the increase of alkyl chain length attached to imidazolium ring, owing to its electron-donating effect of alkyl groups. The adsorption of three inhibitors including physisorption and chemisorption obeyed Langmuir adsorption isotherm.