Inhibition of iron corrosion in acid solutions by Cefatrexyl: Behaviour near and at the corrosion potential

The corrosion inhibition of iron in HCl, HClO4, H2SO4 and H3PO4 solutions (1M for each) by cefatrexyl has been studied by polarization resistance (Rp) and electrochemical impedance spectroscopy (EIS) at the corrosion potential. The results obtained at 30 °C revealed that cefatrexyl acts as a weak inhibitor in HCl solution while it shows excellent inhibition performance in the remaining acids. Adsorption of cefatrexyl in HCl solution obeys Langmuir’s isotherm with a very low value of the free energy of adsorption ΔGads∘ (physisorption) while its adsorption in the other acids follows Temkin’s isotherm with very high negative values of ΔGads∘ (chemisorption). Data obtained from EIS measurements were analyzed to model the corrosion inhibition process through appropriate equivalent circuit models. The calculated values of the apparent activation energy (Ea) and the pre-exponential factor (λ) indicate that cefatrexyl blocks nearly the whole active centers of iron surface in H3PO4 solution even at elevated temperatures. The inhibition mechanism of cefatrexyl was discussed.