Influence of phytic acid on the corrosion behavior of iron under acidic and neutral conditions

Highlights: • PA can effectively inhibit the corrosion of iron as a mixed type inhibitor in acidic solutions. • Phytate behaves like an environmentally-friendly film former and can form stable metal chelate complexes on the iron surface under neutral conditions. • Adsorption of PA on the iron surface obeys the Langmuir adsorption isotherm under acidic conditions. • The binding mode between PA and the iron substrate is strongly dependent on the pH value of the solutions. - Abstract: The influence of phytic acid (PA) on the corrosion of iron under acidic and neutral conditions was investigated by means of Electrochemical Impedance Spectroscopy (EIS) and polarization curve methods. The electrochemical results indicate that, PA can effectively inhibit the corrosion of iron as a mixed type inhibitor in H₂SO₄ solution; however, PA tends to react with the dissolved Fe (II) ions, forming stable metal chelate complexes with strong anodic inhibition action on the iron surface, in Na₂SO₄ solution. Fourier Transform Infrared Spectroscopic (FTIR) analysis confirms the existence of PA or its salts on the iron substrates. X-ray Photoelectron Spectroscopic (XPS) characterization demonstrates that PA adsorbs on the iron surface mainly in the form of undissociated molecules under acidic condition, while phytate ions may bind to the iron substrate through connection of C-O-P bond with oxidized iron surface under neutral condition. The great difference in binding mode between PA and the iron substrate makes PA act as either a corrosion inhibitor or a film former under different conditions