Nanostructure affects electrochemical behaviour of protective coatings

PI coatings provided the galvanised steel substrate with corrosion protection during the test period, but showed differences in electrochemical behaviour of the coatings. Quelle: Carlos CaetanoFotolia.com

Russian and Finnish researchers synthesised two types of polyimide coatings (PI) on galvanised steel panels: a new amino-quinone coating (AQ) and a conventional pyromellitic (PM) coating. They studied and compared the coatings in terms of chemical structure, microstructure and corrosion performance in 0.5 M NaCl solution. The results showed that, although both PI coatings provided the galvanised steel substrate with corrosion protection during the test period, there were differences in electrochemical behaviour of the coatings. That could be primarily explained by the different nanostructures. The AQ PI coating was structurally heterogeneous and discontinuous and acted like a defect-containing coating. This coating showed a significant decrease in protectivity during the test. Conventional PI coating was homogeneous in structure and behaved like a defect-free coating. It provided the galvanised steel substrate with effective corrosion protection all through the 960 h test. The paper is available in Progress in Organic Coatings, November 2011, vol. 72, issue 3, pp. 269-278.