Unmanned aircraft flying in the upper atmosphere.
Reusable spacecraft would make space exploration both more cost-effective and accessible, which is why space agencies have been actively pursuing their development. However, spaceplanes are subjected to extreme temperatures on exiting and re-entering the atmosphere. So, materials which can withstand the scorching temperatures are needed in their construction.
Scientists from the National University of Science and Technology (NUST) in Moscow have now fabricated a ceramic material which is more heat resistant than any other.
The previous material to hold the title of “most heat resistant” was tested in 2016 by a team from the Imperial College London. Using a laser heating technique which allowed them to test the material at extreme temperatures, they calculated that a chemical compound of the elements hafnium, a transition metal, and carbon had the highest melting point ever recorded at the time. Their findings showed hafnium carbide melted at just under 4000 degrees Celsius.
Prior to the discovery of hafnium carbide’s high melting point, researchers from Brown University used computer modeling to predict a material made from hafnium, carbon and nitrogen would be the most heat resistant material. Their simulations showed such a material would melt at over 4100 degrees Celsius, roughly two-thirds the temperature of the surface of the sun.
Knowing the predictions made by the researchers at Brown, the NUST scientists set out to fabricate hafnium carbonitride and test it in comparison to hafnium carbide.
To create the material, they subjected powdered hafnium and carbon to high-energy collisions from balls within a cylindrical grinder called a ball mill. Ball mills are often used in ceramics to grind material into fine particles. Following the high-energy ball milling, the researchers combusted the resulting composite hafnium and carbon particles in a nitrogen atmosphere.
The hafnium carbide and hafnium carbonitride samples were then placed on graphite plates to be tested in a vacuum environment. When heated with a battery using molybdenum electrodes, the melting point of hafnium carbonitride was revealed to be higher than that of hafnium carbide.
Because the melting point of hafnium carbonitride is so high — above 4000 degrees Celsius — it could not be measured precisely in a laboratory. Future experiments will use a laser technique to determine exact measurements, like the one used by the Imperial College London to determine the melting point of hafnium carbide.
The material’s ability to withstand high heats as well as it’s mechanical toughness makes it a promising candidate for use in the areas of aircraft which are exposed to the highest temperatures including the nose fairings, jet engines, and wings. Additionally, the researchers intend to test hafnium carbonitride in hypersonic conditions.