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Abstract: Different ion-selective coatings were prepared. Electrochemical impedance spectroscopy was used to investigate the failure behaviour of the coatings immersed in 5wt.% KCl solution at 60°C. The corrosion product was analysed by scanning electron microscopy, Fourier transform infrared spectroscopy and energy dispersive spectroscopy. Results show that the products were mainly ferrous oxide for bipolar and anionic coatings. Some KCl and K elements were observed in varnish and cationic coating, in addition to ferrous oxide. The results indicate that bipolar and anionic coatings can inhibit ion permeation because of ionic selectivity and increasing of the cross-link density of the coatings facilitated by silane coupling agent KH550. [Copyright &y& Elsevier]

Abstract: A bipolar coating, which is composed of inner layer epoxy with nano SiO2 modified by cetyltrimethylammonium bromide (CTAB) (containing positive fixed charge) and outer layer epoxy with nano SiO2 modified by sodium dodecylbenzenesulfonate (SDBS) (containing negative charge), was prepared in this paper. Its deterioration process after exposure to 5% KCl solution was also studied by EIS measurement and SEM observation. The results indicate that the impedance module of the bipolar coating is about 1E+9ohm after a longer time immersion period. The bipolar coating has a better anti-corrosion capacity than that of epoxy coating. The cation-selective outer layer in bipolar coating inhibits the aggressive anion, such as Cl− ion, passing through the outer coating. Similarly, the anion-selective inner layer inhibits the metal cation passing through the inner coating. Thus the bipolar coating can protect the metal substrate from corrosion effectively. The p–n junction of bipolar coating, which has great charge storage ability, is the key factor in the anti-corrosion capacity of bipolar coating. [Copyright &y& Elsevier]