Scientists from the National University of Science &Technology MISiS, Russia’s leading technological university of steelmaking and metallurgy, developed a ceramic material with the highest melting point among existing known compounds.
The material has an exceptional combination of thermal, physical, and mechanical properties. These properties provide great potential for use in the most heated components of aircraft, including jet engines, nose fairings, and front edges of wings operating at more than 2000°C.
The material will be particularly useful for space agencies such as NASA and ESA, which are actively building reusable spaceplanes. Some of the benefits of reusable spacecraft include the cost of delivering people and cargo to the orbit, dropping considerably, and time intervals between flight reducing as well.
Dmitry Moskovskikh, head of the Center for Constructional Ceramic Materials at NUST MISIS, said:
Currently, significant results have been achieved in the development of such devices. For example, reducing the rounding radius of the sharp front edges of the wings to a few centimeters leads to a significant increase in lift and maneuverability, as well as reducing aerodynamic drag. However, when exiting the atmosphere and re-entering it, on the surface of the wings of the spaceplane, temperatures of about 2000 degrees C can be observed, reaching 4000 degrees C at the very edge. Therefore, when it comes to such aircraft, there is a question associated with the creation and development of new materials that can work at such high temperatures.
The scientists aimed to develop a material that had high mechanical properties and the highest melting point ever. They decided to work with a triple hafnium-carbon-nitrogen system, hafnium carbonitride (Hf-C-N). Researchers from Brown University previously suggested that Hf-C-N would have resistance to oxidation, high thermal conductivity, and the highest melting point (around 4200°C) among all known compounds.
The NUST MISIS scientists used a method of self-propagating high-temperature synthesis to obtain HfC0.5N0.35 (hafnium carbonitride) with a high hardness of 21.3 GPa, which is higher than in other materials including HfB2/SiC/TaSi2 (18.1 GPa) and ZrB2/SiC (20.9 GPa).
Veronika Buinevich, a post-graduate student at NUST MISIS, explained:
It’s hard to measure a material’s melting point when it exceeds 4000 degrees C. Therefore, we decided to compare the melting temperatures of the synthesized compound and the original champion, hafnium carbide. To do this, we placed compressed HFC and HfCN samples on a graphite plate shaped like a dumbbell, and covered the top with a similar plate to avoid heat loss.
All experiments were performed in a deep vacuum. The team connected the plates to a battery via molybdenum electrodes, and since the cross-section of graphite plates differs, the maximum temperature was grasped in the narrowest part. Then, they simultaneous heated the new material, hafnium carbide, and carbonitride. The results, published in Ceramics International, showed that the carbonitride has a higher melting point than hafnium carbide.
The melting point of the new ceramic material is approximately 4000°C or more, though it could not be determined precisely in the laboratory.
