Zirconia-based coatings for the protection of ferritic-martensitic steels in a molten salt environment for CSP technology

Abstract

The ferritic-martensitic 9Cr-1Mo steel was coated with a sol-gel ZrO2-3%molY2O3 solution by dip-coating. The protective properties of the coating were evaluated in contact with Solar Salt for CSP applications. The coated and uncoated steels were tested at 500 °C in contact with the Solar Salt for 2000 h. Gravimetric, microstructural and compositional studies were performed to compare their behaviour, against corrosion. Results revealed the beneficial influence of the coating on the corrosion resistance of P91 in contact with molten nitrate salt. Weight gain of the coated samples remained practically unaltered throughout the test, while the uncoated samples showed a weight increase with the formation of multi-layered, non-adherent corrosion layers that were spalled during the test. The microstructural and compositional study performed on the samples shows the maintenance of the coating layer and the presence of a 5.18 μm-thick diffusion layer primarily composed of Fe-Zr species, which reduce the ionic diffusion and improve the protective properties. Results reveal the possible suitability of the proposed system as a potential solution to the severe corrosion problems industrial tanks and pipes in contact with Solar Salt.