Protection of storage bins against corrosion using polymer-based epoxy coatings applied onto carbon steel and 13% chromium stainless steel

Abstract

The conductive polymers, polyaniline (PANI) and poly(orthoethoxyaniline) (POEA) doped with organic sulpho-5-salicylic acid (SSA) and titanium dioxide (TiO2), were carefully incorporated into a conventional epoxy resin using a commercially available solvent (Xylene). The aim was to create new anti-corrosion epoxy coatings effective in protecting carbon steel (AISI 1010) and stainless steel (420 SS) metal surfaces, particularly in corrosive environments such as marine and acidic conditions. The epoxy coatings developed and applied onto two steels, such as zinc phosphates (ZP), PANI-SSA/TiO2 and POEA-SSA/TiO2, were subjected to meticulous analysis involving zero charge point (qpzc), contact angle (CA), Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM) and immersion testing in marine solutions. The evaluation of corrosion resistance in the zinc phosphate coatings (ZP), polyaniline (PANI-SSA/TiO2), and poly(orthoethoxyaniline) (POEA-SSA/TiO2) epoxy coatings was executed meticulously through a range of methodologies: open circuit potential (OCP), linear polarization resistance (LPR), potentiodynamic polarization curves (Tafel plots), electrical impedance spectroscopy (EIS), and solution iron analysis. These comprehensive assessments were carried out in extensive long-term immersion tests within a 3.5% NaCl solution at pH 4.5. Notably, the application of PANI-SSA/TiO2 and POEA-SSA/TiO2 coatings has significantly enhanced corrosion resistance, achieving improvements of two to four times compared to commercial zinc phosphate (ZP) coatings on 1010 carbon steel. This superior performance is attributed to the enhanced protection provided by the passivation barrier,indicating that these coatings could potentially replace conventional zinc phosphate-based anticorrosion coatings. Notably, the corrosion resistance of stainless steel substrates protected by PANI-SSA/TiO2 and POEA-SSA/TiO2 coatings improved substantially by four to eight times—compared to that of carbon steel substrates.