The physical properties of materials at ultra high temperatures have drawn significant attention in recent years. The need for a material with high mechanical stability and heat dissipation at the operating temperatures of rocket and hypersonic vehicles (e.g., nozzles, leading edges and engine components) has stimulated research efforts in the field of ceramic matrix composites. The development of new chemically reacted, ultra high temperature materials has been a focus of attention since they can be used in extreme environments with rapid heating and oxidising conditions at temperatures above 1600degC.
The term ultra high temperature materials (UHTCs) is often used to refer to the carbides, nitrides and borides of Group IV-V transition metals. These non-oxides with melting points and operation times in excess of 3000 degC provide a unique combination of metal-like and ceramic-like characteristics. This makes them attractive for structural applications with a requirement to withstand extremely high temperatures, extreme heat fluxes and chemically reactive plasma environments.
Compared with oxide ceramics, the carbides and nitrides of UHTCs offer a number of advantages: They do not have a large lattice mismatch with oxygen and do not suffer from crystallisation, thus having better mechanical properties. They also exhibit superior oxidation resistance and a lower coefficient of thermal expansion.
In order to achieve a better understanding of the physical properties of these materials, experimental and computational studies are conducted. These include time domain optical reflectance measurements of thin films to evaluate diffusivity, oxidation resistance and phase transformations at elevated temperatures, Joule heating experiments to determine the temperature dependence of their electrical conductivity, and chemical reactivity to investigate the effect of varying proportions of boron and carbon on their oxidation behaviour.