The Role of the Mesh Size of Modified Mica in CO2–Cl– Environment Resistant Epoxy Coatings

The corrosion resistance of pure epoxy resin coatings in oil and gas fields must be enhanced by the addition of filler to meet the demands of the severe service environment, particularly under an environment with high Cl^– and CO₂ contents. In this work, mica materials with different mesh sizes (400^#, 800^#, and 1250^#) were first modified to enhance compatibility with epoxy resin, and then 35 wt % modified mica was doped into epoxy resin to prepare composite coatings, and the effect of the modified mica mesh on the corrosion resistance of the composite coatings in a high Cl^– environment containing CO₂ was studied. For these materials, the thermal stabilities of the epoxy resin coatings with modified mica were analyzed using a thermogravimetric analyzer, the service environment was simulated by an autoclave, the electrochemical characteristics were studied using an electrochemical workstation, and the surface characteristics were observed by scanning electron microcopy. The results showed that mica was improved by modification with a silane coupling agent, and that with an increase in the mesh size, the uniform distribution of the mica, open circuit potential, capacitance arc radius, and adhesion of the composited coating first increased and then decreased, while the self-corrosion current density, water absorption, and diffusion coefficient showed the opposite trend. When the mesh size of the modified mica was 800^#, the highest charge transfer resistance (7.404 × 10⁸ Ω cm²), and adhesion (7.26 MPa), and the smallest double electric layer capacitance (6.814 × 10^–9 F cm^–2), composite coating capacitance (3.866 × 10^–10 F cm^–2), self-corrosion current density (3.441 × 10^–10 A cm^–2), final saturated water uptake (2.03%), and diffusion coefficient (5.306 × 10⁷ cm² s^–1) were observed, indicating that the composite coating with the 800^# modified mica soaked for 240 h still had the best corrosion resistance. Finally, a corrosion resistance evolution mechanism was proposed for composite coatings containing epoxy resin with different mesh sizes of modified mica.