Anticorrosion mechanism of Al-modified phosphate ceramic coating in the high-temperature marine atmosphere

Phosphate ceramic coating modified with chromate passivated aluminium particles was prepared for corrosion protection in the high-temperature marine atmosphere. The corrosion performance of phosphate ceramic coating was improved by the synergetic effect of aluminium particles and chromate treatment. Phosphate ceramic coatings filled with passivated aluminium particles can withstand more than 10 salt spray-high temperature cycles and maintain good protective properties. The aluminium-modified phosphate ceramic coating exhibited an initial low-frequency impedance value of 1.26 × 10⁴ Ω·cm² in 3.5 wt% NaCl solution without significant decrease during 14 days of immersion. Furthermore, after 10 salt spray-high temperature corrosion cycles, the initial low-frequency impedance value of the prepared coating increased to 2.53 × 10⁴ Ω·cm², indicating good high-temperature corrosion resistance. A compact coating was obtained with the addition of passivated aluminium particles, as a barrier to corrosion media. Meanwhile, compared with natural oxidation film on aluminium particles, the Cr₂O₃ passive film formed by chromate treatment had lower adsorb energy and higher migration energy barrier for Cl ions, which was proved by DFT calculations. This work could provide a novel, economical and convenient method for corrosion protection in the harsh corrosive high-temperature marine atmospheres.