Effect of light-burned MgO on the microstructure and electrochemical corrosion behavior of carbonatable protective coatings

A novel γ-C 2 S-MgO-based coatings were developed for steel protection by providing a carbonated layer on the surface of the steel. The effects of light-burned MgO on the coating's microstructure and electrochemical corrosion behavior were analyzed through XRD, FTIR, SEM, and electrochemical tests. The results showed that the incorporation of MgO inhibited the nucleation and growth of calcite, improved the cementation ability of carbonization products, and optimized the pore structure of the coating. Compared to the γ-C 2 S group, the addition of MgO provides a two-stage densifying effect: it reacts with water and carbonate dioxide to generate magnesium carbonates at the first stage; then the partial crystalline transformation of magnesium carbonate occurs during the immersion process, provoking coating secondary compaction in the late period. The corrosion current density of the coating without film-forming components soaked in 3.5 wt% NaCl solution for 21 days maintained below 0.001 μA∙cm −2 . The impedance value of the EIS test reaches 10 6 Ω·cm 2 . • Crystalline transformation of CM coating carbonates densified the pore structures. • Magnesium carbonates formed by water immersion differed from conventional findings. • Excessive swelling of MgO after immersion decreases long-term coating protection. • The coating showed good anti-corrosion property with an impedance over 10 6 Ω·cm 2 .