Nanotubes have become an even greater asset for industry as researchers have used them to create a ceramic coating that is able to control heat radiation.

The breakthrough offers great promise in fields that require protection from temperature extremes. For example, the ceramic coatings currently used in the gas turbines that power aircraft engines offer structural stability at high temperatures, but do not control the heat. By using a ceramic coating engineered with nanotubes that behave as thermal antennas, the researchers have found a potential way to control the spectrum and direction of high-temperature heat radiation, dramatically improving engine performance.

The study has now been published with the title ‘High-Temperature Polaritons in Ceramic Nanotube Antennas’ in the journal Nano Letters. Here the researchers outline how, “… boron nitride nanotubes control radiation through oscillations of light and matter, called polaritons, inside the ceramic material. High temperatures excite the polaritons, which the nanotubes – as antennas – then couple efficiently to outgoing heat radiation.” Adding that the discovery, “… open new avenues for engineering radiative heat transfer.”

TEM images of boron nitride nanotubes. a) shows lower magnification image with a scale bar showing 50 nm, while b) shows higher magnification with a scale bar of 5 nm.

It also notes how this new class of ceramics is able to more efficiently use heat by not simply absorbing it, but by redirecting it for other uses. It also means that there is less heat stress not only on the structure but also on the coating itself.

“By controlling radiation at these high temperatures, we can increase the lifetime of the coating,” says Zubin Jacob, one of the study’s researchers and an associate professor of electrical and computer engineering at Purdue. “The performance of the engine would also increase because it could be kept hotter with more isolation for longer periods of time.”

The Purdue University press release explains, how, “The work is part of a larger search in the field for a wide range of materials that can withstand higher temperatures. In 2016, Jacob’s team developed a thermal ‘metamaterial’ – made of tungsten and hafnium oxide – that controls heat radiation with the intention of improving how waste heat is harvested from power plants and factories.”

The researchers were able to leverage the high-frequency optical phonons present in boron nitride nanotubes to create strong mid-IR thermal antenna emitters at high temperatures (938 K).

The team are now working on ways to develop the coating further, specifically finding ways that the nanotube antennas could be used to accelerate heat radiation, or possibly be used as part of an enhanced cooling system. The antennas could even be adopted for sending information in very precise directions or wavelengths.

Given the growing use of ceramic raw materials in space exploration and satellites, military hardware, modern construction, and even futuristic communication systems the results of this study could be far reaching.  

As Jacob concludes, “Polaritonic ceramics can be game changing and we want them to be used widely.”


Photo credit: Purdue& Nano Letters