High temperature oxidation of Zr- and Hf-carbides: Influence of matrix and sintering additive

Ultra-high temperature ceramics having melting points above 3500 K and high thermal conductivities are envisaged as future receivers of concentrating solar power plants. The high pressure and solar temperature reactor (Réacteur Hautes Pression et Température Solaire, REHPTS) implemented at the focus of the Odeillo 5 kW solar furnace was used to investigate the oxidation of three refractory carbides containing different sintering additives (HfC/MoSi2, ZrC/MoSi2, ZrC/TaSi2) that could be considered as promising candidates. The concentration of the additive, TaSi2 or MoSi2, was 20 vol%. Each kind of sample was oxidized in air for 20 min at 1800, 2000 and 2200 K. Experiments were filmed using a video camera and the gaseous phases were analyzed in situ by mass spectrometry. Various post-test characterizations have shown that the nature of the carbide and additive strongly affects the composition of the oxide layer and therefore the high-temperature behaviour.