Ultra high temperature ceramic

Ultra-high-temperature ceramics (UHTCs) are a class of refractory ceramics that offer excellent stability at temperatures exceeding 2000 °C being investigated as possible thermal protection system (TPS) materials, coatings for materials subjected to high temperatures, and bulk materials for heating elements. Broadly speaking, UHTCs are borides, carbides, nitrides, and oxides of early transition metals. Current efforts have focused on heavy, early transition metal borides such as hafnium diboride (HfB₂) and zirconium diboride (ZrB₂); additional UHTCs under investigation for TPS applications include hafnium nitride (HfN),zirconium nitride (ZrN),titanium carbide (TiC),titanium nitride (TiN), thorium dioxide (ThO₂),tantalum carbide (TaC) and their associated composites.

Beginning in the early 1960s, demand for high-temperature materials by the nascent aerospace industry prompted the Air Force Materials Laboratory to begin funding the development of a new class of materials that could withstand the environment of proposed hypersonic vehicles such as Dyna-soar and the Space Shuttle at Manlabs Incorporated. Through a systematic investigation of the refractory properties of binary ceramics, they discovered that the early transition metal borides, carbides, and nitrides had surprisingly high thermal conductivity, resistance to oxidation, and reasonable mechanical strength when small grain sizes were used. Of these, ZrB₂ and HfB₂ in composites containing approximately 20% volume SiC were found to be the best performing.

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