Evaluation of inhibitive and adsorption behavior of thiazole-4-carboxylates on mild steel corrosion in HCl

The present work describes the corrosion inhibiting properties of three synthesized thiazole-4-carboxylates namely, methyl (E)-5-(4-chlorophenyl)-2-(((E)-4-methylbenzylidene)hydrazono)-2,3-dihydrothiazole-4-carboxylate (T1), methyl (E)-5-(4-chlorophenyl)-2-(((E)-4-nitrobenzylidene)hydrazono)-2,3-dihydrothiazole-4-carboxylate (T2) and methyl (E)-2-(((E)-4-chlorobenzylidene)hydrazono)-5-(4-chlorophenyl)-2,3-dihydrothiazole-4-carboxylate (T3) towards corrosion of mild steel (MS) in 1.0 mol/L HCl. Various techniques like electrochemical measurements, SEM-EDX analysis, Density Functional Theory (DFT) and molecular dynamics (MD) simulations were employed to probe the effects of substituent groups on inhibition performances of investigated compounds. EIS studies indicated the adsorbed protective film's construction on the steel/electrolyte interface by tested molecules; its existence was affirmed by SEM-EDX analysis. Polarization studies revealed a mixed-type of corrosion inhibition activity. Their mode of adsorption was studied by using isotherm models, and the best match was found just in case of Langmuir adsorption isotherm. Electrochemical results showed that the polarization resistance was greatly increased, from an initial value for the MS (in 1.0 mol/L HCl) of 20.24 up to 256.7 Omega cm(2) for the inhibited solution (1.0 mol/L HCl with 5 x 10(-4) mol/L of T3). Tested compounds behaved as effective inhibitors for MS corrosion in HCl at all concentrations with better efficacy at an optimal concentration of 5 x 10(-4) mol/L. Among all the tested inhibitors, T3 exhibited the most effective performance with an inhibition of 92 %, and the order of the inhibition potency is found within the order of T3 > T2 > T1 by all utilized techniques. The morphological examinations of the surface of MS specimens were explored by using SEM/EDX analysis. DFT calculations were not in agreement with experimental results while MD simulations confirmed the dependence of inhibition performances on the molecular structure of tested compounds.