Analysis of inhibitory properties of Ce-citrate as a green corrosion inhibitor of low alloy steel in neutral chloride solution

Abstract

The new environmentally friendly corrosion inhibitor Ce-citrate was analyzed in 0.05 M NaCl solution on the AISI 4130 steel. For comparison, corrosion inhibitor Ce-chloride is tested in the same concentration as Ce-citrate (0.3 mM). Inhibitor efficiencies were determined by applying electrochemical impedance spectroscopy and potentiodynamic polarization measurements. The results of electrochemical measurements, the contact angle measurements, as well as the surface appearance of the specimens after the immersion in the inhibitive NaCl solution for 96 h confirmed that the new environmentally friendly inhibitor (Ce-citrate) has a significantly higher protective ability than the Ce-chloride. The protective ability of Ce-citrate increases over time, according to the proposed mechanism of its action. In the inhibitive layer formed in NaCl solution containing Ce-citrate, XPS analysis revealed the presence of cerium in oxidation states CeIII and CeIV, citrate anions (carboxyl O–C═O group as well as C–OH and C–C and C–H bonds), oxide, hydroxide, and oxyhydroxide of iron (mainly FeOOH and Fe2O3). The mechanism of inhibitory action of Ce-citrate was proposed and analyzed in detail.