Ultra-High Temperature Ceramics (UHTC)

Ultra-refractory ceramics are a subclass of refractory ceramics and are classically defined as having melting temperatures in excess of 3,000°C. However, their use at very high temperatures must be considered in relation to the surrounding atmosphere, and several definitions are possible. They are currently undergoing rapid development for use in the space sector, for example as heat shields for hypersonic-speed space vehicles, and in the energy sector for propulsion, nuclear power, solar energy, etc.

These ultra-refractory ceramics are formed from borides, carbides or nitrides of transition metals, essentially titanium, zirconium, hafnium, niobium, tantalum, and come in solid form – with or without the inclusion of reinforcing fibers –, thin layers or formed by infiltration into a fibrous preform so as to elaborate a composite material. The most widely studied at present are ZrB ₂ -SiC, HfB ₂ -SiC, the presence of silicon carbide SiC improving resistance to high-temperature oxidation.

In this article, these different ultra-refractory ceramics are presented and some of their properties are given. Their production methods, fields of application and high-temperature performance in various oxidizing atmospheres are presented, with concrete examples. The evolution of their composition to withstand extreme environments is mentioned. Numerous prospects are opened up for the wider use of these materials, which are currently being developed more on a laboratory scale.