Nano-modified functional composite coatings for metallic structures: Part I-Electrochemical and barrier behavior

Abstract

Despite great efforts in polymeric coatings, premature failures of these coatings often cause structural corrosion. High-performance composite coatings by incorporation of nanomaterials are recently emerging multifunctional materials. Along this vein, this study aimed to evaluate the protective properties of nano-modified composite coatings. This work provided new insights into developing new high-performance nanocomposite coatings for strengthening the corrosion resistance of metallic structures. Three nanoparticles: carbon nanotubes (CNT), graphene nanoplatelets (GNP) and nano-silica (NS), were used as nanofillers for synthesizing epoxy-based nanocomposites. The new nano-modified composite coatings were systematically quantified to understand the link of tribological, mechanical, and electrical properties of the nanocomposites. The first part of this work focused on the electrochemical and barrier behavior of nanocomposites via electrochemical impedance spectroscopy (EIS) techniques and damage index. Results suggested that the 0.5–1.5 wt% NS and GNP based composites exhibited superior performance in corrosion inhibition, without damage recorded at the fresh stage. The corrosion resistance of 0.5 wt% NS composites still maintained intact after 100-hour accelerated exposure and remained as high as 92% capacity after 500-hour exposure. GNP composites also stayed with high corrosion resistance by 76% corrosion resistance after 500-hour exposure. As compared, CNT based composites exhibited a relatively lower corrosion resistance, with 85% at onset and 60% remaining capacity after long-term exposure. Water absorption results also confirmed a similar observation. The results from scanning electron microscopy revealed the coatings demonstrated good distribution of nanoparticles in the matrix. Integration of high-speed disk and ultrasonication has overcome nanoparticle agglomeration. However, large agglomeration was observed at higher concentrations. The results suggest the 0.5–1.5 wt% of nanofiller led to the most significant improvement in both mechanical and electrochemical properties.