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

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.