Analysis of the Ce(III) chloride, Ce(III) nitrate, and Ce(III) propionate as corrosion inhibitor of the aluminum alloys in NaCl solution

Green corrosion inhibitors, Ce(III) chloride, Ce(III) nitrate, and Ce(III) propionate, were tested in NaCl solution with the aim to evaluate their inhibitory effect on 7049 aluminum alloy and to propose a mechanism of their inhibitive action. Corrosion properties of the formed inhibitor layer were analyzed using electrochemical impedance spectroscopy, while the pit formation resistance was analyzed using potentiodynamic polarization tests. Morphology of the formed pits was evaluated by scanning electron microscope/energy-dispersive spectroscopy analysis. It was shown that Ce(III) propionate in NaCl solution has a noticeably higher protective ability than Ce(III) chloride and Ce(III) nitrate. The presence of cerium, propionate anions, and Al-O bonds in the inhibitive layer on the 7049 aluminum alloy surface was confirmed by X-ray photoelectron spectroscopy analysis. This indicates the formation of Ce propionate complexes and bonds via oxygen atoms from carboxylate anions with the metal surface. Density-functional theory methods were used for the geometry optimization of possible Ce propionate complexes as corrosion inhibitors.