Electrochemical, Morphological and Anti-corrosive Characteristics of Pyrazine Derivatives for Mild Steel Corrosion in Aggressive Medium: A Comparative Study

The anti-corrosive characteristics of 2,5-dimethylpyrazine (2,5-DMP) and 2,6-dimethylpyrazine (2,6-DMP) on the corrosion of mild steel in 0.5M sulfuric acid have been studied by gravimetric method and electrochemical techniques (potentiodynamic polarization, linear polarization resistance and electrochemical impedance measurement) to observe the adsorption of these pyrazine derivatives at the metal/solution interface. The results obtained have revealed that 2,5-DMP performs more efficiently in comparison with 2,6-DMP showing an efficiency of 97.12% at a concentration of 10(-2)M. The polarization curves clearly indicate that both chemicals act as a mixed-type inhibitors showing a predominance toward the cathodic reaction. Langmuir's isotherm model was found to adequately describe the adsorption of both these inhibitors onto the mild steel surface. The calculated value of the free energy for the adsorption process, eveals a strong chemisorbed bond as well as a spontaneous adsorption process between the tested inhibitors and the mild steel surface. Surface morphological analysis of the MS specimens treated with these inhibitors has been conducted using energy-sispersive atomic X-ray spectroscopy. The results obtained have shown a good agreement with the results obtained from electrochemical techniques. Quantum chemical calculations have also been performed using hyperchem 8.0.6 package to supplement the findings from the preceding techniques.