Thermodynamic study of mild steel corrosion in hydrochloric acid by new class synthesized quinoxaline derivatives: Part II

The inhibition action of (E)-7-chloro-3-(4-methoxystyryl)quinoxalin-2(1H)-one (Q1) and 7-chloro-2-(4-methoxyphenyl)thieno(3.2-b)quinoxaline (Q2) have been investigated for mild steel corrosion in 1 M HCl at different temperatures ranges (303–333 K) using potentiodynamic polarization curves. It was found that the studied compounds exhibit a very good performance as corrosion inhibitors for mild steel in 1 M HCl. Results show that the inhibition efficiency increases with decreasing temperature and increasing inhibitors concentration. Thermodynamic parameters such as adsorption heat ( ), adsorption entropy ( ) and adsorption free energy ( ) were obtained from experimental data at temperatures ranging from 303 to 333 K. Other thermodynamic parameters such as E a , , and pre-exponential factor have been calculated and discussed. Adsorption follows the Langmuir isotherm with negative values of free enthalpy suggesting a spontaneous adsorption process.