Corrosion protection of epoxy-clay nanocomposite coatings on metallic substrates in saline environments containing alkaline copper quaternary ammonium wood preservatives

Abstract

In this study, the epoxy-clay nanocomposites (ECNs) containing 0.5, 1.0, and 2.0 wt-% of organophilic modified clay (OMC) with CTAB as intercalating agent were prepared and applied in anticorrosion for metallic substrates in the forms of cold-rolled steel (CRS) electrode/steel panel/screw in saline condition containing 2 wt-% of alkaline copper quaternary (ACQ) ammonium.

The corrosion resistance of CRS coated with ECN was evaluated under saline conditions, both in the presence and absence of ACQ, through a series of electrochemical corrosion tests. E_corr of CRS-decorated with neat epoxy coating shifted from −611 to −624 mV in saline solution by introducing 2 wt-% of ACQ, implying that Cu²⁺ existing in saline solution with ACQ may speed up oxidation rate of iron. Moreover, E_corr of CRS electrode coated with ECN-0.5 containing 0.5 wt-% of OMC platelets shifted from −624 mV to −595 mV, indicating that clay platelets existing in ECN coating may effectively increase the diffusion pathway of Cu²⁺/oxygen gas as supported by the concentration of Cu²⁺ in ACQ determined by ICP-MS after electrochemical measurements and barrier property of oxygen gas was evaluated using a gas permeability analysis (GPA) technique, therefore slow down the oxidation rate of iron. Moreover, increasing the clay loading in ECN, the ECN-1 and ECN-2 exhibited the E_corr = −571 and − 552 mV, respectively, indicating that the higher loading of dispersing OMC in epoxy matrix may provide a much longer pathway length of Cu²⁺ and O₂ gas. Accelerated salt-spray corrosion of steel panel and screw in aggressive medium were also evaluated according to ASTM B-117. The results obtained from the salt-spray tests aligned well with those from the electrochemical evaluations. Adhesion and wear resistance of ECN coatings were also investigated by ASTM 3359 and ASTM D 4060, respectively.