Fibre Class: material’s thermal resistance is outstanding due to silicon carbide fuzz

A robust material has been created suitable for use in next generation engines, including rocket motors.

Fuzzy nano-fibres
Ajayan Research Group/Rice UniversitySilicon carbide nanotubes attached to separate silicon carbide fibers, used by NASA, entangle each other in this electron microscope image. The material created at Rice University is intended for a ceramic composite that would make rocket engines stronger, lighter and better able to withstand extreme heat.

‘Fuzzy’ fibres are being used to help composites withstand the heat and pressure of rocket engines.

A ceramic composite could make rocket engines stronger, lighter and better able to take extreme heat.

Silicon carbide fibres have been developed that act like Velcro and can strengthen composites used in advanced rocket engines subject to extreme temperatures of up to 1,600°C (2,912°F).

Usually, silicon carbide fibres used to strengthen ceramic composites are prone to cracking when exposed to oxygen, but a team from Rice University embedded silicon carbide nanotubes and nanowires into the surface of fibres being used by NASA.

The exposed parts of the fibres are curly and act like Velcro’s hooks and loops. The consequent strong interlocking connections protect the composite from cracking and forms a seal preventing oxygen from altering the fibre’s chemical composition. The work is has been described recently in the American Chemical Society journal *Applied Materials and Interfaces*.

Fuzzy nano-fibres
Ajayan Research Group/Rice University“Fuzzy” silicon carbide fibers used by NASA were enhanced at Rice University with silicon carbide nanotubes that act like hook-and-loop Velcro on the nanoscale. The material is intended to become part of a composite for stronger, lighter and more heat-resistant rocket engines and other aerospace materials.

Amelia Hart, a Rice graduate student, who had been studying the growth of carbon nanotubes on ceramic wool, collaborated with NASA research engineer Janet Hurst.

Hart said: “[Hurst] was partially converting silicon carbide from carbon nanotubes. We used her formulation and my ability to grow nanotubes and figured out how to make the new composite.”

The hooks and loops were grown by bathing silicon carbide fibre in an iron catalyst and a process used to produce high performance solids called ‘ water-assisted chemical vapour deposition’ was then used to embed a carpet of carbon nanotubes into the surface. The fibres were then heated in silicon nanopowder to a high temperature to change the carbon nanotubes into silicon carbide “fuzz”.

Hart said the method could allow turbo engines to become significantly lighter.

She said: “Before they used silicon carbide composites, many engine parts were made of nickel superalloys that had to incorporate a cooling system, which added weight to the whole thing.

“By switching to ceramic matrix composites, they could take out the cooling system and go to higher temperatures. Our material will allow the creation of larger, longer-lasting turbo jet engines that go to higher temperatures than ever before.”