British researchers have reported on a new low-cost, large-area method for production of a carbon-nanotube-carbon-fibre composites with superior electrical properties.
Lightweight carbon fibre reinforced polymers (CFRPs) have revolutionised a range of industries, finding application in everything from aerospace and structural engineering, to the automotive and sporting goods sectors. Thanks to their excellent mechanical properties and low mass, CFRPs are regularly used in aircraft chassis, such as the Airbus A380. However, their low electrical conductivity means that metals must be used alongside CFRPs to avoid the build-up of charges due to lightning strikes and air friction.
This had led to a growing research effort to develop composite materials that retain CFRP’s mechanical properties, while also being electrically conductive. A team of researchers, led by Ravi Silva from the University of Surrey, have reported on their work in the latest issue of Carbon [doi:10.1016/j.carbon.2014.03.038]. Silva and his colleagues have created a “fuzzy” fibre composite, using carbon nanotubes, which shows an increase in electrical conductivity of up to 510 % when compared to standard CFRP.
To produce the fuzzy CFRP, carbon nanotubes were grown directly onto the carbon fibre, a process generally carried out using Chemical Vapour Deposition (CVD). However, CVD requires a reactive atmosphere, along with temperatures above 700 °C, which can cause significant degradation of the fibre. Instead, the team developed a low temperature solution called photo-thermal-CVD (PTCVD), whereby the carbon fibre substrate is water-cooled, while optical radiation is used to heat the catalyst on the fibre to a much higher temperature, facilitating CNT-growth.
Because of this setup, their PTCVD system requires less energy to grow nanotubes on the fibre, and once the halogen lamps are switched off, the new fuzzy composite cools down quickly, increasing the sample throughput to up to 8 times that of conventional CVD. Due to its lower operating temperature, PTCVD-produced composites suffer from far less mechanical degradation – only 9.7% reduction in tensile performance – than those produced using CVD.
Conductivity tests on the fuzzy-CFRP confirms that the addition of CNTs changed the electron transport mechanism in the material from charge-hopping to Ohmic – this explains the huge improvement in electrical conductivity. When compared to the conventional CFRP, the fuzzy composite showed improvements of 510% in the out-of-plane conductivity and 330% in the in-plane conductivity. As the technique uses standard industrial processes throughout, the team are confident that it can be applied to existing bulk manufacturing techniques for CFRPs.
Carbon 74 (2014), pp. 319–328 [doi:10.1016/j.carbon.2014.03.038]
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