Electrochemical study and experimental simulation of the synergistic effect of a formulation based on Ficus pumila Linn. Leaves extract and zinc sulfate on the XC38 steel corrosion inhibition in NaCl solution

Abstract

The inhibitive activity of a mixture of Ficus pumila Linn. leaves hydroalcoholic extracts (HEFP) and zinc ions against corrosion of XC38 steel in NaCl solution was investigated. Electrochemical measurements (potentiodynamic polarization and electrochemical impedance spectroscopy at and around the corrosion potential) and surface analysis (SEM/EDX) have shown that the presence of zinc ions considerably increases the inhibitive capacity of HEFP. However, appropriate concentrations of zinc ions (50 and 100 ppm) and of HEFP (200 ppm) are necessary to have an optimal inhibitive effect. The formation of organometallic complexes between zinc ions and some organic compounds of HEFP (polyphenols and carbohydrates) are the determining step of the synergistic inhibition. Since the main inhibitive agents in plant extracts are polyphenols, a simulation of this inhibitive character was electrochemically done with a mixture of flavonoid (quercetin), phenolic acid (gallic acid) and zinc ions in order to elucidate the inhibition mechanism. The obtained results showed that the electrochemical behavior of XC38 steel in the presence of this mixture is quite similar to that obtained in the presence of HEFP + Zn2+ formulation. The proposed inhibition mechanism, which explains the good inhibitive efficiency observed in presence of the HEFP + Zn2+ formulation, is based on concerted reactions between the steel oxidation products (Fe2+ and Fe3+), the zinc ions and the Iron(II) and Iron(III) complexing agents present in the extract.