耐高温CrAlON基太阳能光谱选择性吸收涂层的制备与热稳定性

光谱选择性吸收涂层是太阳能光-热利用技术的核心部件,直接决定着整个系统的转换效率,为了提高涂层的选择吸收性和热稳定性,本文提出以金属氮化物替代金属纳米颗粒,构建纳米晶-非晶异质结构的思路,并采用多弧离子镀制备了Cr/CrAlN/CrAlON/CrAlN/CrAlON/CrAlO多吸收层光谱选择性吸收涂层,其吸收率达0.90,发射率为0.15,而且在500℃、大气条件下时效220 h后,涂层的吸收率升至0.94,发射率则降至0.10,并且能够保持稳定1000 h以上.微观组织分析表明,高温时效处理后,吸收层发生部分晶化形成了大量氮化物纳米颗粒,增加了对太阳光的散射和吸收,而CrAlO减反射层中的部分晶化形成了Al2O3和Cr2O3纳米颗粒,这不仅可以保护内部涂层不被氧化,而且Al2O3的形成可以增加太阳光的透过率,减少涂层表面反射,是多吸收层CrAlON基光谱选择性吸收涂层选择吸收性能提高的主要原因.同时,氮化物纳米颗粒被非晶基体均匀地分隔开来,形成了纳米晶-非晶异质结构,非晶在高温时效处理过程中只发生结构弛豫,从而有效地抑制了高温条件下的原子扩散,保证涂层中的纳米颗粒在高温下不发生明显团聚,这是多吸收层CrAlON基涂层具有良好热稳定性的最主要原因.这些研究结果对提高金属陶瓷光谱选择性吸收涂层的综合性能,实现更高效率的太阳能光-热利用具有重大意义.

Preparation and thermal stability of CrAlON based spectrally selective absorbing coatings

Spectrally selective absorbing coating is the core component of the utilization of solar energy.The spectral properties of selectively absorbing coating directly determine the conversion efficiency of constructing solar power plants.To enhance the selective absorbability and thermal stability,we propose an idea that these metal particles are replaced with transition-metal nitrides,and then coated with periodic nanocrystalline-amorphous heterogeneous structures.Double-absorbing layer Cr/CrAlN/CrAlON/CrAlN/CrAlON/CrAlO solar selective absorbing coatings with a high solar absorptance of 0.90 and a relatively low emittance of 0.15 are obtained by the cathodic arc ion plating technique.After the coating is aged at 500°C in air for 220 h,its absorptance increases to 0.94 and the emittance decreases to 0.10.More importantly,the coating exhibits an outstanding thermal stability with a selectivity of 0.94/0.11 even after being aged at 500°C for 1000 h in air.The microstructure analysis indicates that the multilayer coating consists of aperiodic CrAlN and CrAlON layers in addition to the Cr and CrAlO layers.Through the long-term aging,a small number of AlN,CrN and Cr2N nanocrystallites are observed to be homogeneously embedded in the CrAlN and CrAlON amorphous matrices.The nanoparticles in the CrAlN and CrAlON layers can effectively scatter the incident light into a broadband wavelength range,increasing the optical path length in the absorbing layers,and thus resulting in a pronounced enhancement in the absorptivity.A handful of Cr2O3 and Al2O3 nanograins are observed to be embedded in the amorphous CrAlO antireflection layer,which can effectively reflect the solar infrared radiation and the thermal emittance from the substrate,and thus resulting in pretty low infrared emissivity.The good thermal stability is attributed to the excellent thermal stability of the dielectric amorphous matrices and the sluggish atomic diffusion in the nanoparticles,which could effectively slow down the inward diffusion of oxygen and avoid agglomerating the nanoparticles.These results are of great importance for enhancing the overall performance of cermet spectrally selective absorption coating and also for improving the conversion efficiency of solar energy photo-thermal utilization.