铌硅基中高温选择性吸收涂层的稳定性研究

Mid- and high-temperature selective absorber is one of the key apparatus of solar thermal power generation. The solar selective absorbers should exhibit high- temperature thermal stability in air rather than in vacuum, as well as high solar absorptance and low thermal emittance. The traditional coating in which Molybdenum and Tungsten nanoparticles were used exhibited poor atmospheric thermal stability. Intermetallic with not only metal bonds but also ionic and covalent bonds shows high thermal stability in air..In this research, The absorbing layer contains two thermally stable components, Niobium silicon intermetallic (Nb5Si3) was used as absorbing particles, Niobium silicon nitride (NbSiN) and Tin-doped Indium oxide (ITO) were used as dielectric material, respectively, and the Nb5Si3 nano particles would scatter in the dielectric NbSiN or ITO. Firstly，the difference of emittance between low temperature and high temperature was studied, and the influence of fill factor and structure on emittance of high temperature. Lower emittance of high temperature and high thermal stable coatings would be achieved by spectrum tailoring and theoretical design. Secondly, the degradation mechanism of high temperature in air was researched by structure, composition and interface states. The influence of adding Nitrogen and ITO to the coating on compactness would be researched, and the effect of compactness and thermal stability would be deeply discussed. The research would become the theoretical foundation for non-vacuum mid- and high- temperature solar selective absorbers.

太阳能中高温选择性吸收涂层是太阳能中高温利用的关键材料，除了需要具有较高的吸收率和较低的发射率，高温稳定性是制约其实用化的一大障碍。传统中高温选择性吸收涂层采用金属钼和钨等单质金属纳米粒子为吸收粒子，大气稳定性差；金属间化合物原子间的键合不仅有金属键，也包括离子键和共价键，具有较强的高温稳定性。.本项目拟采用高温稳定的铌硅金属间化合物为吸收粒子，分别采用铌硅的氮化物和氧化铟锡作为介质材料，形成介质材料包覆纳米粒子的吸收层。首先分析低温发射率和高温发射率的区别，研究填充因子、膜系结构对高温发射率的影响，对膜系进行光学设计和光谱裁剪，降低涂层高温发射率；其次对涂层热处理前后的结构、成分、界面状态等分析，得到高温条件下膜层性能退化机理，重点研究氮元素和易结晶氧化铟锡掺入对膜层致密性的影响，以及致密性和高温稳定性的关系。本课题的研究将为降低发射率和提高涂层稳定性开辟新的路径，具有重大的科学意义。

中高温选择性吸收涂层是槽式太阳能热发电技术的核心，要求太阳光谱可见光到近红外范围内具有高的吸，同时在红外波段具有较低的发射率，能有效地将太阳能转化为热能；传统的单一金属陶瓷的高温稳定性制约了该技术在大气下使用的规模化推广，本项目采用高温稳定的铌硅金属间化合物取代传统的Mo、W等单一金属，利用金属间化合物的高温稳定性实现涂层的稳定性，结果表明：.氮掺杂和ITO掺杂能有效构建出不同消光系数和折射率的单层膜，软件模拟和实际制备均得到了高吸收低发射的涂层，最佳性能：吸收率为95.27%，发射率为4.2%；研究了Nb-Si-N和Nb5Si3-ITO薄膜致密性和高温稳定性的关系，得到致密性是高温稳定性的基础，氮掺杂和ITO掺杂均能有效的提高涂层的稳定性。通过研究退火前后Nb5Si3-ITO膜层厚度的变化，得到大气条件下高温稳定性变差是吸收层被氧化造成的；.以Nb5Si3-ITO为基础研究了不锈钢衬底上制备选择性吸收涂层的光学性能和热稳定性，并对膜层进行了优化，降低500℃的发射率。制备在Mo-Ag为红外高反射层上的涂层初始光学性能最优 (α=95.27%，εRT=4.2%)，但含银的涂层大气热稳定性较差。Mo为红外高反射层的涂层具有最佳的热稳定性， 500℃/120 h退火后吸收率仅下降0.41%，发射率仅上升0.1%；通过改进膜系结构，500℃发射率由19.4%下降到11.3%；改良涂层依然具有较好的高温稳定性，大气下500℃退火120 h后，光学性能几乎保持不变 (α=93.18%，εRT=8.5%，ε500℃=12.5%)。

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