A comparative study of two corrosion inhibitors: 1,4-diallyl-6-chloroquinoxaline 2,3-(1h,4h)-dione (1a) and 1,4-diallyl-6-nitroquinoxaline-2,3-(1h,4h)-dione (1b)

Abstract

Corrosion inhibition by 1,4-diallyl-6-chloroquinoxaline-2,3-(1H,4H)-dione (1a) and 1,4-diallyl-6-nitroquinoxaline-2,3-(1H,4H)-dione (1b) on mild steel was studied in 1.0 M HCl solution by using the electrochemical techniques and the weight loss measurements at temperature 308 K. The results obtained clearly revealed that inhibitors (1a) and (1b) behave as a mixed type inhibitors and adsorbed onto the mild steel surface by chemisorption. The weight loss results indicate that inhibitors (1a) and (1b) are good corrosion inhibitors and their optimum inhibition efficiency reaches up to 95% and 89% respectively, at a concentration of 10–3 M and a temperature of 308 K. In addition, the potentiodynamic polarization studies indicate that (1a) and (1b) are mixed-type corrosion inhibitors and EIS show that the transfer resistance increases with the increase in the inhibitor concentration. The adsorption of the molecules of the inhibitors (1a) and (1b) onto the mild steel surface was found to follow the Langmuir adsorption isotherm. The values of the change in Gibbs free energy of adsorption (ΔGads) strongly support the chemisorption of the molecules of the studied inhibitors on the mild steel surface. The results obtained from electrochemical and weight loss measurements were in reasonable agreement.