Composite Epoxy Coating Reinforced by Silane-modified Micro-Al2O3 Particles for Long-time Anti-corrosion Protection in Solution of Seawater Salinity

Abstract

Marine pipelines in subsea oil and gas production systems are exposed to very corrosive high salinity condition and demand high anti-corrosion coatings. Superhydrophobic particles have long been used to make the rough structure of the superhydrophobic surface for anti-corrosion protection. Epoxy coatings are considered to be one of the best protective method for metals because the epoxy resins have very good chemical resistance, strong adhesion to the substrate, good mechanical and insulating properties. However, the application of epoxy coatings has been limited in many cases due to their characteristics such as brittleness and sensitivity to micro-cracks owing to their three-dimensional network structure, low impact toughness, and poor fatigue property. In recent years, second phase particles for toughening the epoxy matrix have attracted a lot of attention. A noticeable increase in both the shear strength and adhesive peel strength appeared mainly due to high levels of dispersion of the high modulus nanoparticles and effective interfacial interactions with the epoxy matrix. Many studies have reached similar conclusions.So far, numerous studies have been performed to determine the effect of adding reinforcement inorganic particles on the wear and erosion resistance of the epoxy coatings, and the electrochemical characterization of those particle-reinforced epoxy coatings was normally studied for short exposure time. However, no studies have been carried out on the corrosion resistance properties of superhydrophobic particle-reinforced epoxy coatings with long exposure time in corrosive solution.This work aims the development of superhydrophobic micro-Al2O3 as reinforced particles for epoxy coating under long-time exposure to solution of seawater salinity, and comparison of the effects of using hydrophilic and superhydrophobic micro-Al2O3 as reinforced particles on the protection property of epoxy coating. Epoxy composites filled with both silane functionalized Al2O3 (SF-Al2O3) and unfunctionalized Al2O3 (UF-Al2O3) were fabricated at a filler loading of 26 vol.% micro-particles. The SF-Al2O3 particles exhibited a water contact angle of 156.5°. Electrochemical testing including open circuit potential, impedance and phase angle measurements showed that SF-Al2O3 epoxy have better corrosion resistance as compared to pure epoxy after 144 d immersion in solution of seawater salinity (3.5 wt% NaCl), while the coatings with UF-Al2O3 showed failure after 36 d immersion. Scanning electron microscope analysis revealed a very good condition of the SF-Al2O3 epoxy coating after 144 d immersion. It is clearly observed that silane-modified particles were very effective on the anti-corrosion protection property of composites in high salinity solution. The results may have important implications for the design of particles reinforced polymeric composite coatings.