Inhibition effects of N-phosphono-methyl-glycine/Zn2+ mixtures on corrosion of steel in neutral chloride solutions

Electrochemical and surface analytical techniques were combined in order to investigate the corrosion inhibition of a carbon steel rotating disc electrode (rde) by N-phosphono-methyl-glycine (NPMG)/Zn2+ mixtures with a concentration ratio of 1:1 between NPMG and zinc cations, in chloride solutions. From polarization curves it was shown that the NPMG/Zn2+ mixture retarded both the anodic and cathodic partial reactions of the corrosion process. Inhibition efficiency, estimated from electrochemical impedance measurements, increased from approximately 85 to 95% when inhibitor concentration increased from 10 to 100 mg/l. Analysis of the composition with XPS suggested that the films consisted mainly of hydrous ferric oxides (Fe(OH)3 and FeOOH), with small amounts of Fe-NPMG complex, ZnO and corrosion products. AES depth profiling showed that the most protective surface film (that formed in the solution containing 100 mg/l of inhibitor) was thicker compared to that formed in the solution with low inhibitor concentration. [Material: 1018].