Stress-Induced Failure Study on a High-Temperature Air-Stable Solar-Selective Absorber Based on W-SiO2 Ceramic Composite

A stress-induced failure study on a high-temperature air-stable ceramic composite solar selective absorber (SSA) based on a W-SiO2 system is reported. The as-prepared SSA exhibits excellent spectral and structural stability after annealing in air at 500 degrees C for 36 h, proving its thermal stability against air corrosion. However, once the temperature is elevated to 600 degrees C, optical performance degradation and coating cracking happens. The X-ray diffraction (XRD) patterns reveal that an O-induced phase transition process from alpha-W to beta-W occurs at the interface between the W IR reflector and W-SiO2 layer during deposition. The phase transition induces immense internal stress, which becomes the incentive of crack generation. Further increasing the annealing temperature, drastic structural changes of oxidized W become the driving force for crack propagation and hole expansion, leading to a failure analogous to a volcanic eruption. To improve the temperature limit of coating, a Ni-SiO2 stress buffer layer is introduced and successfully reduces the internal stress through Ni atom substitution for W atoms. Therefore, the optimized SSA keeps stable at 600 degrees C and the cracking temperature increases to 650 degrees C. These results suggest that the W-SiO2-based SSA is a good candidate for air-stable high-temperature solar thermal conversion.