posted on 2022-01-19, 13:38authored byBinghui Sun, Lei Wang, Ying Sun, Jie Ren, Yingxin Yang, Huan Liu, Dongdong Liang, Aoyu Li, Cong Wang
The
development of high-temperature-tolerance solar selective absorbing
coatings (SSACs) is beneficial to improve the conversion efficiency
of concentrated solar power. In the present work, a TiN/Mo/WNx-Si3N4 bilayer/SiO2 cermet-based SSAC was developed, which was deposited on different
substrates by magnetron sputtering. The designed WNx-Si3N4 SSAC exhibits a high solar absorptivity
of 0.952, accompanied by a relatively low emissivity of 0.059 at 25
°C and 0.134 deduced at 600 °C. Moreover, the WNx-Si3N4 SSAC deposited on a
stainless-steel (SS) substrate shows great thermal stability at 650
°C in vacuum. The solar absorptivity shows a slight decrease
from 0.952 to 0.939 and the emissivity at 25 °C decreases from
0.059 to 0.045 after being annealed at 650 °C in vacuum. Furthermore,
when being annealed at 700 °C in vacuum, the WNx-Si3N4 SSAC deposited on the quartz glass
substrate still keeps stable, but the coating on the SS substrate
is dramatically destroyed. A comprehensive failure analysis was conducted
utilizing FT-IR, SEM, Raman, and XPS characterizations. The degradation
of the WNx-Si3N4 SSAC deposited on the SS substrate at 700 °C is caused by the
severe elemental diffusion between the absorbing layers and the antireflection
layer. Moreover, the cracks induced by the thermal stress provide
rapid channels for elemental diffusion.