Comparative Study of Pyridine and Pyrimidine Derivatives as Corrosion Inhibitors of C38 Steel in Molar HCl

Corrosion inhibition of C38 steel in 1 M HCl was investigated in the absence and presence of different concentrations of two imidazo derivatives namely, 2-phenylimidazo[1,2-a]pyridine (P1) and 2-(m-methoxyphenyl) imidazo[1,2- a] pyrimidine (P5). Weight loss, potentiodynamic polarization and electrochemical impedance spectroscopy techniques were employed. Impedance measurements showed that the double-layer capacitance decreased and charge-transfer resistance increased with increase in the inhibitors concentration and hence increasing in inhibition efficiency. Potentiodynamic polarization study showed that all the inhibitors act as mixed-type inhibitors. The inhibitors were adsorbed on the steel surface according to the Langmuir adsorption isotherm model. From the adsorption isotherm, some thermodynamic data for the adsorption process were calculated and discussed. Kinetic parameters activation such as activation energy, pre-exponential factor, enthalpy of activation and entropy of activation were evaluated from the effect of temperature on corrosion and inhibition processes. E (%) values obtained from various methods used are in good agreement.