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

Cermet-based solar selective absorbing coatings are widely used, however, the long-term thermal instability and pretty high infrared emissivity at high temperatures (> 550 degrees 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 similar to 93% and a very low thermal emissivity of 10.3% @500 degrees C even after annealing at 600 degrees C for 840 h 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.