On the thermal stability and performance evaluation of Si doped transition metal nitride/oxide nanolayered multilayer-based spectrally selective absorber for high-temperature photothermal applications

Developing an absorber coating with high absorptance (alpha) in the solar spectrum region and low thermal emittance (epsilon) in the infrared region for concentrated solar power (CSP) applications, operating at temperatures > 400 ?C, is still a great challenge. Herein, we describe a multilayer solar selective coating on stainless steel 304 (SS 304) substrates with alpha of 0.954 and epsilon of 0.07. The multilayer solar selective coating consists of: (1) tungsten (W) infrared reflector layer, (2) titanium aluminum nitride (TiAlN) absorber layer, (3) titanium aluminum silicon nitride (TiAlSiN) absorber layer, (4) titanium aluminum silicon oxy-nitride (TiAlSiON) semi-absorber layer and (5) titanium aluminum silicon oxide (TiAlSiO) anti-reflection layer. The compositions of the individual layers have been selected in such a way that they easily form protective layers of Al2O3, TiO2 and SiO2 on the coating surface when exposed to high temperature in air. Further, addition of Si in different layers not only improves the thermal stability but also helps in densifying the microstructure of the layers. Moreover, the presence of multilayer structure hinders the formation of pinholes and pores along with columnar microstructure, a typical characteristic of the sputter deposited transition metal nitrides and oxides. This unique coating design, thus, leads to high spectral selectivity (alpha/epsilon) of 13.6 on SS 304 substrate along with thermal stability up to 600 ?C for 1000 h in vacuum under cyclic heating conditions. These properties of the developed solar absorber coating demonstrate its suitability for evacuated receiver tubes in CSP plants.