Abstract
The corrosion inhibitory effect of two 3,5-bis(disubstituted)-4-amino-1,2,4-triazole derivatives, namely 3,5-bis(4-tolyl)-4-amino-1,2,4-triazole (K1) and 3,5-bis(3,4-dimethoxyphenyl)-4-amino-1,2,4-triazole (K2), for mild steel in 2 M H3PO4 has been studied using electrochemical impedance spectroscopy (EIS), Tafel polarization curves and weight loss measurements. It was found that the inhibition efficiency of the two investigated inhibitors increases with increase in concentration of inhibitors and decreases with increase in temperature. K1 and K2 show corrosion inhibition efficiency of 80.00 and 86.35%, respectively at 10(-3) M and 308 K. Impedance experimental data revealed a frequency distribution of the capacitance, simulated as constant phase element. Potentiostatic polarization study showed that K1 and K2 are mixed-type inhibitors in 2 M H3PO4. The results obtained from electrochemical and weight loss studies were in reasonable agreement. The adsorption of K1 and K2 on steel surface obeys Langmuir's adsorption isotherm. The correlation between inhibition efficiency and molecular structure of the inhibitors is investigated by determination of chemical indexes, which were performed using density functional theory (DFT) at (B3LYP/6-31G) (d,p) level. Monte Carlo simulations were further performed to simulate the adsorption of K1 and K2 on Fe (110) surface in the presence of water and the results show that K2 is more effective as corrosion inhibitor for mild steel in 2 M H3PO4 medium than K1. (C) 2016 Elsevier B.V. All rights reserved.