Oxidation in Air at 1400 K and Optical Properties of Inconel 625, FeCrAlloy and Kanthal Super ER

The materials used for the design of solar receivers are one of the critical parts of the concentrated solar power (CSP) plants. An increase in the working temperature of a solar receiver could induce an increase in the efficiency of the CSP plants. Historically, stainless steels were used for solar receivers. However, one limit of these materials is their poor creep resistance at high temperature. Nowadays, Ni-based alloys are used, but they are limited at 1400 K by their oxidation resistance. Thus, to reach higher temperatures, other materials have to be used. Alumina-scale formers, such as FeCrAlloy, possess a very good oxidation resistance at high temperature. The Kanthal Super ER also shows an excellent oxidation resistance. Consequently, FeCrAlloy and Kanthal Super ER were oxidized at 1373 K in air up to 48 h and compared to the currently used nickel-based alloy Inconel 625. Inconel 625 shows an important mass gain followed by the spallation of its oxide scale. On the contrary, FeCrAlloy and Kanthal Super ER have a low mass gain (less than 0.40 mg cm−2) with an adherent oxide layer up to 48 h. Besides the oxidation resistance, the materials have to possess a high solar absorptivity and a total emissivity as low as possible. Oxidized Inconel 625 shows both high solar absorptivity and total emissivity. The other mentioned materials are more suitable due to their high solar absorptivity (> 0.70 for oxidized FeCrAlloy, > 0.80 for oxidized Kanthal Super ER) and their relatively low total emissivity (< 0.35 for oxidized FeCrAlloy, < 0.45 for oxidized Kanthal Super ER). Due to its high oxidation resistance and high solar absorptivity, the Kanthal Super ER seems to be the best candidate for the solar receiver application.