Novel thiophene symmetrical Schiff base compounds as corrosion inhibitor for mild steel in acidic media

► The aim of the present investigation is to examine the inhibitory action of two Schiff bases. ► Compounds are mixed type (cathodic/anodic) inhibitors. ► Inhibition efficiency (% IE) increases with increasing concentration of compounds. ► Adsorption of compounds on mild steel surface obeys Langmuir’s isotherm. The inhibiting effect of two Schiff bases on the corrosion of the mild steel (MS) in 1 M HCl has been studied by electrochemical impedance spectroscopy (EIS) and Tafel polarisation measurements. The Schiff bases, 4,4′-bis(3-carboxaldehyde thiophene) diphenyl diimino ether ( L 1) and 4,4′-bis(3-carboxaldehyde thiophene) diphenyl diimino ethane ( L 2), were synthesized using 3-carboxaldehydethiophene and its corresponding amine. Polarisation curves reveal that both compounds are mixed type (cathodic/anodic) inhibitors and inhibition efficiency (% IE) increases with increasing concentration of compounds. It is suggested that their effects depend on their concentrations and the molecular structures. Adsorption of compounds on mild steel surface is spontaneous and obeys Langmuir’s isotherm.