Optical properties and thermal stability of Ag/TiAlONM/TiAlOND/AlON spectral selective coating

A new spectral selective coating using Ag as metal reflector has been optimized based on the optical properties of TiAlON and AlON single layer. The absorptance is 95.32% and the emittance is 9.65% at 550 °C calculated by integrating spectral reflectance in the spectral region of 2.5–25 μm wavelength. The microstructure and thermal stability of Ag/TiAlONM/TiAlOND/AlON spectral selective coating was characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), Auger electron spectroscopy (AES) and high-resolution transmission electron microscopy (HRTEM), respectively. It shows that the thickness of TiAlONM, TiAlOND, and AlON layer is 68 nm, 27 nm and 35 nm, respectively. The solar absorptance has reduced by 2.9% and the thermal emittance has increased by 3.2% after annealed at 600 °C for 168 h. TiAlON which is stable up to 700 °C in vacuum, could act as a barrier layer for inhabiting diffusion of Ag element into absorb layer. Unlike the single layer, spectral selective coating gets crystallized after annealed, which is attributed to the internal stress of the coating. Thus, Ag/TiAlONM/TiAlOND/AlON spectral selective coating can be excellent candidate for high temperature applications.