大气条件下AlCrON基光谱选择性吸收涂层的热稳定性

设计并制备了Cr/AlCrN/AlCrON/AlCrO光谱选择性吸收涂层,利用GIXRD、SEM、AFM和TEM研究了退火过程中涂层微结构的演变规律。结果表明,该涂层在大气条件下、500℃退火1000 h后,其吸收率由退火前的0.910提高至0.922,发射率由退火前的0.151降低至0.114,表现出优异的热稳定性。微观组织分析表明,AlCrN和AlCrON吸收层在退火过程中发生了部分晶化,形成了氮化物纳米颗粒,这可以增加对光的反射和散射,有助于提高涂层的吸收率;退火后AlCrO减反射层中则形成了少量的Cr₂O₃和Al₂O₃纳米颗粒,可以减少涂层表面对太阳光的反射,有助于降低涂层的发射率。同时,退火过程中Al原子向纳米颗粒表面偏聚,并在大气环境下发生氧化形成Al₂O₃层覆盖在纳米颗粒表面,能够起到阻止纳米颗粒长大的作用,这对于维持AlCrON基光谱选择性吸收涂层微结构和光学性能的稳定性具有重要的作用。此外,涂层中的非晶基体在退火处理中仅发生结构弛豫,并且由于非晶中的原子扩散非常缓慢,有助于抑制高温条件下涂层中纳米颗粒的扩散,保证纳米颗粒不发生团聚。

Thermal Stability of AlCrON-Based Solar Selective Absorbing Coating in Air

Metal-dielectric coatings consist of extremely fine metal particles embedded in dielectric matrices are considered promising as materials for high-temperature spectral selective absorption coating applications owing to their excellent thermal stability and integrated optical properties. However, during long periods of annealing under high temperatures, metal particles are prone to agglomerating, coarsening, oxidizing, and diffusing across different layers, resulting in changes in composition and microstructures. Correspondingly the metal-dielectric coatings would experience irreversible degradations in optical properties. Hence, a Cr/Al Cr N/Al Cr ON/Al Cr O multilayer solar selective absorbing coating has been designed and deposited on stainless steel by cathode arc ion plating to solve the above mentioned issue.This coating exhibited excellent thermal stability as the absorptance increased to 0.922, whereas, the emittance decreased to 0.114 after annealing at 500 oC for 1000 h in air. Microstructural characterization indicates that the increase in absorptance is attributed the formation of small amounts of Al N, Cr N, and Cr2 N nanocrystallites in the amorphous matrices of Al Cr N and Al Cr ON, which can effectively scatter the incident light into a broadband wavelength spectrum by increasing the optical path length in the absorbing layers, resulting in a pronounced enhancement in the absorptivity. A handful of Cr₂O₃ and Al₂O₃ nanograins are embedded in the amorphous Al Cr O antireflection layer, which can effectively reflect solar infrared radiation and thermal emittance from the substrate, resulting in relatively low infrared emissivity.Besides, good thermal stability is attributed to the excellent thermal stability of the dielectric amorphous matrices and slow atomic diffusion of nanoparticles, which could effectively slow down the inward diffusion of oxygen and avoid the agglomeration of nanoparticles. However, during high-temperature annealing, aluminum atoms in the nanoparticles appear to agglomerate on the surface. These aluminum atoms would oxidize in air and form a layer of Al₂O₃ covering these nanoparticles, preventing agglomeration and coarsening of nanoparticles.