Spectral properties and thermal stability of solar selective absorbing AlNi–Al2O3 cermet coating

Abstract

A new solar selective absorbing coating of AlNi–Al2O3 cermet multilayer is designed and prepared on Cu or stainless steel (SS) substrate by magnetron sputtering. The coating consists of an IR-reflective metallic layer, an absorption bilayer and an anti-reflection layer from substrate to top. The IR-reflective metallic layer is Cu or Mo. The absorption bilayer consists of a high metal volume fraction (HMVF) AlNi–Al2O3 cermet sublayer and a low metal volume fraction (LMVF) AlNi–Al2O3 cermet sublayer. The anti-reflection layer is Al2O3. The optical performance (α/ε) of the coating is 0.94/0.07 on Cu substrate and 0.95/0.078 on SS substrate by optimizing the metal volume fraction and thickness of each layer. The samples deposited on SS substrate were heated at 500°C for 138h and 284h in vacuum to evaluate the optical stability. Experimental results showed that the high temperature stable AlNi intermetallic compound, instead of Mo in the traditional Mo–Al2O3 coatings, displayed a good thermal stability at 500°C. There is no significant change appearing in the optical properties of the coating after the heat treatment. It means that the new coating is a good potential candidate as a high temperature solar selective absorbing coating for parabolic trough concentrated solar power (CSP).