High-temperature tolerance in WTi-Al2O3 cermet-based solar selective absorbing coatings with low thermal emissivity

Abstract

Cermet-based solar selective absorbing coatings are widely used, however, the long-term thermal instability and pretty high infrared emissivity at high temperatures (>550°C) are still challenging issues to be addressed, which essentially lies in suppressing the growing up and agglomeration behaviors of metal nanoparticles (NPs) and maintaining the interface integrity in the multi-layer stacked structure. Herein, we develop and explore WTi-Al2O3 cermet-based absorbing coatings, demonstrating a solar absorptance of ~93% and a very low thermal emissivity of 10.3% @500°C even after annealing at 600°C for 840h in vacuum. It is revealed that the surface segregation of solute Ti atoms from the parent alloyed NPs and their partial oxidation to form protective layer restrain outward diffusion of W element, agglomeration of NPs, and interface structure degradation, in favor of enhancing the thermal tolerance of the coatings. These results suggest that the WTi-Al2O3 based absorbing coating is a good candidate for high-temperature solar thermal conversion.