分层化金属陶瓷光热转换涂层的微结构构筑与热稳定性

Microstructure building and thermal stability of cermet-based photothermal conversion coatings with layered structures

针对金属陶瓷基光热转换涂层高温热稳定性不足的核心问题,提出构筑吸光纳米颗粒分层化结构来替代传统金属陶瓷涂层中纳米颗粒随机分布的结构,这不仅可以抑制高温下涂层中纳米颗粒的团聚和长大,而且能够增强涂层与太阳光的交互作用,达到热稳定性和选择吸收性能的同步提升.基于此思想,本文设计并制备了Cr/AlCrN/AlCrON/AlCrO多层金属陶瓷光热转换涂层,对其微结构、光学性能和热稳定性进行了详细的研究.研究结果表明,沉积态涂层的吸收率达到了0.903,发射率为0.18.3,而且在500℃、大气环境下退火1000 h后,涂层的吸收率竟提高至0.913,发射率也仅有0.199,表现出良好的光谱选择吸收性和优异的高温热稳定性.微观组织分析发现,在AlCrON吸收层内形成了AlN,Cr_(2)N纳米颗粒嵌于非晶陶瓷电介质基体的稳定双相复合结构,并且AlN,Cr_(2)N纳米颗粒呈分层化规则排列.时域有限差分(FDTD)模拟表明,纳米粒子的分层化分布可以将光子囚禁在AlCrON层内,从而增强太阳光和涂层的作用时间和强度,有助于提升涂层对太阳光的吸收,而且退火过程中纳米颗粒的长大会减小颗粒之间的间距,使得涂层消光光谱红移,能够更好地匹配太阳辐射谱,同时这种特殊的结构能够有效地避免纳米颗粒之间的团聚,从而实现对涂层选择吸收性能和热稳定性的双重调控.

To enhance the thermal stability of cermet-based photo thermal conversion coatings,the present paper proposes a novel strategy to replace the randomly distributed nanoparticles with layered structure.This kind of structure can not only suppress the agglomeration and rapid growth of nanoparticles,but also enhance the interaction between the absorber and sunlight.Thus,the thermal stability and selectivity can be simultaneously improved by this unique kind of structure.Then,a Cr/AlCrN/AlCrON/AlCrO multilayer cermet-based photothermal conversion coating is designed and fabricated by multi-arc ion plating.The microstructure,optical properties and thermal stability of the multilayer coating are studied in detail.The optical properties tests show that the absorptance and emittance of the as-deposited coating achieve 0.903 and 0.183,respectively.More importantly,after being annealed at 500℃in air for 1000 h,the absorptance reaches 0.913 and the emittance arrives at 0.199,implying the enhanced selectivity and thermal stability,which are ascribed to the formation of nanolaminates,in which a series of alternating sublayers is observed in the AlCrON absorber.The nanolaminate is a two-phase composite structure composed of layered AlN and Cr_(2)N nanoparticles distributed in amorphous dielectric matrix.According to the finite difference time domain(FDTD)simulations,this unique kind of microstructure can trap photons in the coating,which is beneficial to enhancing the interaction intensity and time between the sunlight and absorbing sublayer,and thus improving the absorption of sunlight.In addition,the reduction of particle spacing during annealing will lead to the red shift of extinction spectrum,which will better match the solar radiation spectrum.At the same time,this kind of structure can avoid the agglomeration of nanoparticles,which can simultaneously tune the optical properties and thermal stability.