The investigation of thermal stability of Al/NbMoN/NbMoON/SiO2 solar selective absorbing coating

Abstract

The thermal stability of the Al/NbMoN/NbMoON/SiO2 solar selective absorbing coatings is investigated to determine its potential applications in concentrated solar power (CSP). The coatings are deposited on stainless steel (SS) substrate by using magnetron reactive sputtering method, which exhibit high solar absorptance (αs = 0.948) and low thermal emittance (ε = 0.11, at 400°C). The coatings are aged (in vacuum and air) at different temperatures and time durations. The aging effect is characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and Vis.-IR spectroscopy. There is no significant change in surface morphology and spectral selectivity (performance criterion (PC) value is 0.021) of the coating after aging at 500°C for 240h in vacuum. The coatings also keep high spectral selectivity (PC = 0.034) after aging at 450°C for 200h in air. Unfortunately, the value of PC increases to 0.161 when the coating is aged at the temperature of 500°C for 200h in air, which is attributed to diffusion and oxidation in the absorbing layers and degradation of the dense surface morphology and structure, as evidenced by XRD and SEM analysis. These results indicate that the Al/NbMoN/NbMoON/SiO2 coatings is stable up to 500°C in vacuum and below 450°C in air, which means enough thermal stability for potential applications in parabolic trough CSP.