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

Highlights: •Oxidation of HfC sintered with addition of 10%vol. TaSi₂ or ZrSi₂ was investigated. •Tantalum addition favours the production of mixed oxide that reduces damaging. •The influence of oxidation on the optical properties of the surfaces is discussed. •Both chemical surface changes and roughness evolution may impact optical properties. -- Abstract: 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.