Investigation of corrosion protection performance of poly(N-methylpyrrole)-dodecylsulfate/multi-walled carbon nanotubes composite coatings on the stainless steel

In this study, composite coatings which consist of multi-walled carbon nanotubes (MWCNTs) and poly(N-methylpyrrole)-dodecylsulfate (PNMPy-DS) were fabricated on a stainless steel. Firstly, electrodeposition of the PNMPy-DS film was performed by potentiodynamic method on a steel substrate in an aqueous solution containing N-methylpyrrole, oxalic acid and sodium dodecylsulfate. Then, a second layer on the polymer-coated stainless steel was formed by two different ways: (a) the dropping of Nafion® solution containing MWCNTs and (b) the electrodeposition of MWCNTs at a constant potential. The cyclic voltammetry, FT-IR spectroscopy and SEM techniques were used for the characterization of the PNMPy-DS and MWCNTs modified PNMPy-DS (PNMPy-DS/MWCNTs) coatings. Corrosion protection tests of these coatings were examined in 0.5 mol L−1 H2SO4 solution by potentiodynamic polarization and EIS techniques. These tests exhibit that the PNMPy-DS/MWCNTs composite coatings ensure powerful protection for the stainless steel against corrosion. This result is caused by the negatively charged MWCNTs and Nafion® on the surface of polymer layer and dodecylsulfate dopant in the polymer structure electrostatically repulse the corrosive sulfate ions and retard their reach to metal surface.