The Investigation On The WTI-Al₂O₃ Composite Cermet-based Solar Selective Absorbing Coating With High-temperature Tolerance

Solar selective absorbing coating is the key component in the solar energy absorber,and its sound integrated optical properties and long-term thermal stability directly determine the solar-thermal conversion efficiency.Therefore,it is of great significance to research and develop the solar selective absorbing coating with well-established performance.W-Al₂O₃ cermet-based solar selective absorbing coating has been widely used in commercial absorber manufacturing,but its high temperature（>550oC）application is restricted due to unresolved thermal stability problem.To this end,in this thesis,we proposed the alloying of W nanoparticles（NPs）with Ti to improve the thermal stability of W-Al₂O₃-based cermet film,in terms of that alloying is an effective way to improve the thermal stability of metal NPs.Based on the well-performed W-Al₂O₃cermet-based solar selective absorbing coating and the guidance of optical simulation,we developed a new WTi-Al₂O₃ cermet-based solar selective absorbing coating with a structure of SS substrate/W infrared reflective layer/ultra-thin Al₂O₃ barrier layer/WTi-Al₂O₃ high metal volume fraction（HMVF）layer/W-Al₂O₃ low metal volume fraction（LMVF）layer/Al₂O₃ anti-reflection layer,demonstrating a high solar absorptance⁹3%and a low thermal emissivity¹0.3%@500°C after annealing at600°C for 840 h in vacuum.The obtained optical properties are competive among the previous reports in the literatures.It is revealed that the segregation of solute Ti atoms and their partial oxidation to form local protective layer onto the NPs could suppress the outward diffusion of W and wild agglomeration of NPs,thereby ensuring the microstructure and interface structure stability at elevated temperatures,in favor of enhancing the thermal tolerance of the coatings.This concept of thermal enhancement is quite different from the conventional method by using refractory alloy or compound NPs dispersed into ceramic matrixes.It is expected that the WTi-Al₂O₃ cermet-based solar selective absorbing coatings have great potential for high-temperature solar thermal applications.