Anticorrosive properties of the double-layer PANI-(graphene oxide)/epoxy coating in protecting carbon steel in saltwater

The work reports result in improving the anticorrosive properties of a commercial epoxy coating by forming a double-layer coating structure. First, a thin (ca. 5 mu m) electrically conductive polyaniline (PANI) coating was wormed directly on the carbon steel (CS) surface, on top of which a thicker (ca. 20 mu m) epoxy coating was applied. The inner PANI layer was also loaded with graphene oxide (GO). The resulting anticorrosive properties of the coatings were investigated in 3.5 wt.% NaCl employing electrochemical techniques, while the surface and cross-sectional morphology of the coatings was examined by scanning electron microscopy (SEM). The results showed that the commercial epoxy coating started gradually failing several days after its exposure to the electrolyte, while it took 37 days for larger pores to appear in the PANI/epoxy coating, which then gradually continued to fail. On the other hand, the PANI-GO/epoxy coating maintained its high corrosion resistance, without forming impedance-detectable pores, over the entire testing period (two months). The excellent corrosion protection properties of the PANI-GO/epoxy coating were prescribed solely to the presence of the underlying PANI-GO layer, which represents a better barrier for the transport of hydrated corrosive ions to the CS surface, through the combined action of charge (repulsion of hydrated corrosive anions and iron oxide film formation), surface energy (hydrophobicity), and blocking mechanisms.