A machinable carbon aerogel composite with a low thermal conductivity and enhanced mechanical properties

Carbon aerogels are prepared via the sol–gel polymerisation of resorcinol with formaldehyde, followed by supercritical drying and carbonisation. The fabricated carbon aerogels have low densities in the range 0.028–0.196 g cm−3, ultra-low thermal conductivities in the range 0.0259–0.0707 W (m K)−1 and high specific surface areas (>520 m2 g−1). The carbon aerogel composites are reinforced with short carbon fibres by adding the carbon fibres to the resorcinol–formaldehyde solution to reduce their brittle nature and improve their machinability. The compressive strength of the composites containing 2 wt-% carbon fibres is 1.75 MPa, which is 56% higher than that of pure carbon aerogel. Both fracture toughness and compressive strength of these composites are improved. These composites also have good machinability, with the ability to maintain their shape after being machined with traditional steel tools. Furthermore, the composites with nanoporous structure exhibit ultra-low thermal conductivity up to 1400°C.