Stress‐Induced Failure Study on a High‐Temperature Air‐Stable Solar‐Selective Absorber Based on W–SiO 2 Ceramic Composite

A stress‐induced failure study on a high‐temperature air‐stable ceramic composite solar selective absorber (SSA) based on a W–SiO 2 system is reported. The as‐prepared SSA exhibits excellent spectral and structural stability after annealing in air at 500 °C for 36 h, proving its thermal stability against air corrosion. However, once the temperature is elevated to 600 °C, optical performance degradation and coating cracking happens. The X‐ray diffraction (XRD) patterns reveal that an O‐induced phase transition process from α‐W to β‐W occurs at the interface between the W IR reflector and W–SiO 2 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–SiO 2 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 °C and the cracking temperature increases to 650 °C. These results suggest that the W–SiO 2 ‐based SSA is a good candidate for air‐stable high‐temperature solar thermal conversion.