Effect of Al2O3-MWCNTs on anti-corrosion behavior of inorganic phosphate coating in high-temperature marine environment

Abstract

Chemically bonded aluminum phosphate coating modified with Al2O3-MWCNTs was prepared for anti-corrosion in high-temperature marine environment. α- Al2O3 was successfully and conveniently coupled to the multi-walled carbon nanotubes by surface modification. Then the hybrid materials mixed with coating materials were applied on heat-resistant steel using high-pressure airless spraying. The success of the hybridization was verified by characterizing the composition structure and morphology of Al2O3-MWCNTs. Simultaneously, adhesion, electrochemical, and scanning electron microscopy (SEM) experiments were conducted to characterize the protective performance of the coating under different ablation times. One noteworthy phenomenon showed by the thermogravimetric analysis results is that the initial decomposition temperature of Al2O3-MWCNTs was increased by 100 °C compared with pure MWCNTs, which provided a basis for the application of the ceramic coatings in oxidation-resistant environment at 600 °C. The results of adhesion experiments showed that the dry bonding force of the ceramic coating with Al2O3-MWCNTs added on the substrate /coating interface was 3 times higher than that of the pure coating. The coating had the best surface quality following ablation at 600 °C thanks to Al2O3-MWCNTs, which gave it a denser mosaic structure on the outside and a three-dimensional mesh structure on the interior. This structure provided outstanding shielding properties and additional electron channels. Additionally, the Rct value was 34.7 kΩ.cm2 after 100 h of high temperature ablation, which was 345 times of that without added coating. In general, the results showed that the corrosion resistance of the coating with Al2O3-MWCNTs as the reinforcing phase was still maintained at a high level.