Interfacial and corrosion characterization of zinc rich-epoxy primers with carbon nanotubes exposed to marine bacteria
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2017 by NACE International. Nowadays, it is accepted that in aerobic conditions, marine electroactive biofilms induce faster oxygen reduction on active/passive alloys immersed in seawater. Besides, these alloys undergo a shift of open circuit potentials (OCP) towards noble direction after biofilm settlement, OCP can be shifted up to 350 mV vs. saturated calomel electrode (SCE). For steel structures, zinc rich epoxy coatings are an effective corrosion prevention and protection method in marine environment. Zinc rich coatings can protect the steel by two mechanisms: the first as a physical barrier or mass transfer effect and the second as cathodic protection effect by promoting electrochemical reactions within the coating. Recently, electrochemical studies reveals that the presence of CNT (Carbon Nanotubes) in zinc rich and multifunctional coatings can enhance the corrosion resistance properties by improving both protection mechanisms. In this work, a marine environment due to the presence of marine bacteria was exposed to three different zinc rich epoxy coated-steel samples with different CNT additions. The electrochemical activity was monitored by using OCP (open circuit potential) and EIS (electrochemical impedance spectroscopy). Surface analysis by scanning electronic microscopy (SEM) correlated the electrochemical behavior of zinc-rich epoxy coated samples at different exposure times. The results demonstrated the influence of CNT in biofilm formation and the barrier vs. the electrochemical effect mechanisms. Favorable conditions for long lasting settlement of biofilms were observed at Zn and Zn-1xCNT coating type. EIS showed the influence of CNT in the impedance response for different CNT content. The lowest impedance magnitude was obtained at the highest CNT content due to the promotion of more electrochemical activity within the coating.
