The improved solar weighted absorptance and thermal stability of desert sand coated with transition metal oxides for direct particle receiver

Direct particle receiver of the concentrated solar power (CSP) with a supercritical CO 2 (sCO 2 ) Brayton cycle is based on the solid particles to achieve high efficiency at high temperature. Among all kinds of solid particles, desert sand is abundant and cheap, however its solar weighted absorptance and thermal stability remain to be improved. In this work, the dark desert sands were obtained by in-situ coating transition metal oxides via sol-gel combustion process . The thermal stability of the resultant samples was analyzed according to the changes in composition , morphology and optical properties before and after thermal treatment at 800 °C for 200 h. Based on the characterization of UV–Vis–NIR diffuse reflectance spectroscopy , the solar weighted absorptance of each sample was calculated. Compared with the original particles, all of dark desert sands have the improved solar weighted absorptance, and the highest value of 0.8635 belongs to desert sand coated with spinel CuMn 2 O 4 . Moreover, compared to the original desert sand, each dark desert sand has superior thermal stability. In addition, the specific heat of particles was measured at different temperatures, and it is found that the coating has lesser effects on the specific heat of desert sand. The solar weighted absorptance of dark desert sand nearly unchanged after attrition and the coating remained well maintained on the surface of the sample. This work provides a practical and feasible way to enhance the solar weighted absorptance and thermal stability of desert sand, making it possible to apply in sCO 2 CSP.