Investigation on the inhibition effect of aspartic acid and Zn²⁺ions on carbon steel surface in aqueous solution

A protective film has been formed on the surface of carbon steel in aqueous environment using a synergistic mixture of an environment-friendly inhibitor, aspartic acid, and Zn2+. The synergistic effect of aspartic acid (AS) in controlling corrosion of carbon steel has been investigated by gravimetric studies in the presence of Zn2+. The formulation consisting of AS and Zn2+ has an excellent inhibition efficiency. The results of potentiodynamic polarization revealed that the formulations are of mixed-type inhibitor. Impedance studies of the metal/solution interface indicated that the surface film is highly protective against the corrosion of carbon steel in the aqueous environment. X-ray photoelectron spectroscopic analysis of the protective film showed the presence of the elements iron, nitrogen, oxygen, carbon, and zinc. The spectra of these elements in the surface film showed the presence of oxides/hydroxides of iron(III), Zn(OH)2, and [Fe(III)/Fe(II)–Zn(II)-AS] complex. Further, surface characterization techniques such as Fourier transform infrared spectroscopy, scanning electron microscopy, and atomic force microscopy are used to ascertain the nature of the protective film formed on the carbon steel surface.