Mechanisms of High-Temperature Corrosion Resistance in Al–Si–Cr and Ni–Cr Coatings for Low-NOx Combustion Boilers

To address the issue of high-temperature corrosion of coal-fired boiler water-cooled walls, an Al–Si–Cr coating with rare earth element is developed using heat-curing ceramic coating technology in this study. The corrosion resistance of both Al–Si–Cr and Ni–Cr coatings is investigated under laboratory and actual boiler conditions using X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. Results indicate significant coatings’ mass increase over time under laboratory conditions, with corrosion mass gain following a power function of time. The dense structure of the Al–Si–Cr coating and the rare earth elements effectively prevent the diffusion of corrosive gases, providing superior gaseous corrosion resistance. However, the dissolution of Al₂O₃ in high-temperature molten salt causes cracks, reducing its resistance in such environments. Ni–Cr coating oxides react with corrosive gases, diminishing its resistance to gaseous corrosion. Nevertheless, Cr inhibits the sulfidation of Ni in molten sulfate and stabilizes NiO, enhancing its corrosion resistance in molten salt. The Al–Si–Cr coating demonstrates outstanding anti-coking and corrosion resistance in the boiler. This study provides a promising new solution for enhancing the corrosion protection of water-cooled walls in coal-fired boilers.