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

Abstract

To enhance the thermal stability of cermet-based photothermal 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 Cr₂N 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.