Effect of high temperature oxidation on the radiative properties of HfC-based ceramics

Hafnium carbide (HfC) is a promising material for high-temperature heat exchangers due to its high melting point (4170 K). Nevertheless, its fast oxidation into fragile hafnia prevents it from being used for open-air solar receivers. The incorporation of silicon-based compounds would reduce its oxidation kinetics and extend the lifetime of HfC-based elements. The oxidation behavior of HfC sintered with the addition of 10 vol% TaSi2 or ZrSi2 is here investigated. The optical properties on the as-received surfaces and on the oxidized ones were measured, especially the ratio of the 0.6-2.8 μm emissivity (close to the solar absorptivity α) to the total hemispherical emissivity ε. These optical properties are important parameters for applications using concentrated solar radiation.