Effect of TiC incorporation on the optical properties and oxidation resistance of SiC ceramics

In concentrating solar power (CSP) technologies, the absorber material should be spectrally selective under severe operating conditions, i.e., similar to 1000 degrees C under air atmosphere. SiC-TiC nanocomposites could be good candidates for this application due to their spectral selectivity at room temperature; however, their behaviour under CSP operating conditions is unknown. Therefore, the spectral selectivity and oxidation resistance of TiC-SiC composites were studied up to 500 degrees C, in air, and at various compositions. During heating, the emittance increased with the temperature. After heating, the TiC grains at the surface were oxidized to TiO₂, while SiC grains showed good behaviour. However, despite little oxidation, the spectral selectivity of the nanocomposites remained interesting after heating. Specific oxidation tests of up to 9 days at 1000 degrees C in air showed an increase in the oxidation resistance with the amount of SiC. This result is the consequence of the formation of a protective layer of SiO₂ that prevents oxidation of the TiC grains. The composition of 30 at% TiC-70 at% SiC is a good compromise between low oxidation and good selectivity. (authors)