The impact of oxidation on the optical properties of Si–SiC materials

Abstract

Silicon carbide is an interesting candidate for high-temperature solar receiver due to its high solar absorptivity and its resistance to oxidation in air. Its oxidation stays passive with the formation of a protective silica layer up to 1900 K. Nevertheless, silica presents a lower spectral emissivity than silicon carbide in the solar range. Therefore the growth of a silica layer may affect the values of the spectral emissivity and therefore the surface receiver thermal efficiency. We have investigated here how high-temperature ageing in air affects the spectral emissivity and the thermal efficiency of commercial Si–SiC materials. We were able to correlate the variations of the spectral emissivities to the advancement of the oxidation using scanning electron microscopy, ellipsometry and 3D profilometry. Especially we observed a significant improvement of the surface receiver thermal efficiency due to the increase of the surface roughness that increases the solar absorptivity.