Comparative assessing on corrosion protection effects of zinc rich ethyl silicate primers modified with undoped and HCl doped PAni–clay nanocomposite

Abstract

This paper presents the works carried out to synthesise undoped and doped polyaniline–clay nanocomposite (PAniCN) by chemical oxidative polymerisation of aniline monomers in the presence of Cloisite 30B nanoclay powders. Fourier transform infrared analysis was used to characterise the synthesised nanocomposites. Electrical conductivity test was used to compare the conductivity of different PAniCN powders. The synthesised nanocomposites were added to a zinc rich ethyl silicate primer to modify the barrier properties of the primer. Unmodified and modified primers were applied on the carbon steel panels separately. The corrosion protection performances of different primers were evaluated via determining open circuit potential (OCP) and electrochemical impedance spectroscopy during immersing in 3·5% sodium chloride solution for a period of 120 days. Electrochemical impedance spectroscopy analysis showed that the coating resistances Rc of modified primers were higher than the original primer. Coating resistance of the undoped and doped PAniCN modified primers and original primer were reached to 6·056×103, 5·565×103 and 2·773×103 Ω cm2 after 120 days of immersing respectively. Open circuit potential measurements were carried out in order to evaluate the cathodic protection ability and duration. These measurements revealed that although the undoped PAniCN modified primer showed the highest resistance, the OCP of the panels coated with this modified primer pass through safety region [−0·86 V(SCE)] after 120 days of immersion. Besides salt spray test (according to ASTM B117-03) was used as a widespread accelerated test to evaluate the protection performances of primers. In salt spray test spots of rust appear on the surface of the panels coated with undoped PAniCN modified primer after 1500 h of exposure. The results of OCP measurement test were confirmed by the results of salt spray test.