INHIBITION OF IRON CORROSION USING TWO NEWLY SYNTHESIZED SCHIFF BASE COMPLEXES IN ETHANOLIC HYDROCHLORIC ACID MEDIA

Two different Schiff base complexes were tested as corrosion inhibitors for iron in hydrochloric acid medium (prepared in ethanol) at different temperatures using potentiodynamic polarization measurements. The obtained results reveal that increasing HCl concentration at 35°C increased the anodic and cathodic current density values. Moreover, anodic current density peak was observed at concentrations >1M HCl. However, the magnitude of corrosion rate CR in presence of complexes is suppressed as its tendency to increase with acid concentration. On the other hand, the values of corrosion potentials (around −300 mV(SCE)) were not affected by the addition of any complex. The inhibition efficiency values increase with an increase in complex concentrations in which Hg- complex achieves higher protection efficiency than Zn-complex. The adsorption processes follow the Langmuir isotherm. Concerning the effect of temperature, results demonstrate that increasing the temperature leads to an increase in the corrosion rate of iron and a decrease in the inhibition efficiencies of the complexes. The rise in activation energy Ea values in presence of the complexes explains the corrosion inhibition obtained through physical adsorption. Also, higher ∆H° values indicate higher protection efficiency. ∆S° has negative value for the blank and the complexes solutions indicating that the system passes from a more to a less orderly arrangement.