Evaluating the efficacy of binary benzimidazole derivatives as corrosion inhibitors for carbon steel using multi-modal analysis and optimization techniques

The use of inhibitors is considered one of the most effective and efficient methods of combating. The development of mixtures of inhibitors with synergistic effect can improve effectiveness of corrosion control. In this work, the corrosion inhibition efficiency of 2-mercaptobenzimidazole (2-MBI) and 2-ethylbenzimidazole (2-EBI) and their mixture in one-molar HCl was evaluated. Moreover, by analysis of variance and response surface method, two correlations were developed for predicting inhibition effectiveness. The average difference between predicted and experimental values of corrosion rate and inhibition efficiency was 6.90 % and 2.86 %, respectively. The R-2 and R(2)adj values of the obtained models for predicting mixture efficiency were 0.9935 and 0.9913. Furthermore, the inhibition process was optimized, and the results showed that the best conditions for corrosion control occurs in mixing ratio of 75:25 (2-MBI:2-EBI), 130 ppm and 25 degrees C. In these conditions, the predicted rate and efficiency were 0.69 mm/y and 93.74 %. Results of hydrogen volume determination after 20 min showed a volume of 4, 1.8, 1.4 and 0.9 cm(3) for blank solution, 2-EBI, 2-MBI and mixture. The Nyquist plot confirmed that the optimum concentration is 130ppm. The inhibition efficiency values of the weight loss, electrochemical and polarization tests in optimal conditions had an error of <5 %. The highest inhibition efficiency of the developed mixture by electrochemical and polarization tests was 92.17 % and 93.87 %, respectively. Finally, the Gibbs free energy values ranged from -34.5126 to -39 .5446kJ.mol(-1). Also, the enthalpies obtained from the Van Hoff equation and the second law of thermodynamics were -4.6021 and -4 .4965kJ.mol(-1).