Synergistic effect of imidazole dicarboxylic acid and Zn2+ simultaneously doped in halloysite nanotubes to improve protection of epoxy ester coating

Abstract

Halloysite nanotubes as inhibitor container were introduced in an epoxy ester coating. To obtain synergistic impact of both inorganic and organic inhibitors, 4,5-imidazole dicarboxylic acid and Zn2+ were simultaneously doped in the halloysite nanotubes modified with 3-aminopropyltriethoxysilane (MHNTs). The electrochemical and surface analysis tests in NaCl solution showed that a mixture of inhibitors is able to provide higher corrosion inhibition for steel compared with the single inhibitors. With the mixture of the organic and inorganic moieties, an inhibition efficiency of 90% was achieved at the end of the 24 h test. Introducing of doped MHNTs in epoxy ester enhanced the barrier effects and active corrosion protection. EIS and EDS studies on the scratched coatings confirmed the effective active protection resulted from incorporation of double-doped MHNTs into the polymeric coating. As a result of salt spray test, lower disbonded area was found for the scratched epoxy ester film bearing the double-doped MHNTs. The precipitation of zinc hydroxide and a complex of Zn2+/Fe2+-IDC might be the main reason for the superior function.