Thermodynamic properties and comparative studies of quinoxaline derivatives as a corrosion inhibitor for mild steel in 1M H2SO4

The corrosion rates of mild steel in 1 M H2SO4 in the presence of 3-methylquinoxalin-2(1H)-one (Q1) and 3-methylquinoxalin-2(1H)-thione (Q2) were evaluated using weight loss, potentiodynamic polarization, and electrochemical impedance spectroscopy measurements. It is seen that the inhibition efficiencies increase with concentration of both inhibitors and the Q2 performed excellently as a corrosion inhibitor with its efficiency attaining more than 99 % at 10−3 M. In addition, it is noted that the inhibition efficiency of Q1 decreases while that of Q2 increases with immersion time. On the other hand, there was only a slight effect of temperature on the performance of Q2. The apparent activation energies, enthalpies, and entropies of the dissolution process and the free energies for the adsorption process in the presence of Q2 are determined and are discussed. Adsorption of Q2 on mild steel surface was investigated to consider basic information on the interaction between the inhibitor and the metal surface. It was found to obey the Langmuir adsorption isotherm.