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High performance and ultralight carbon nanotube wires for power transmission

Final Report Summary - HPCNTW (High performance and ultralight carbon nanotube wires for power transmission)

The ethos of this research programme is to operate at the interface between science and technology, relying on the exciting structure and properties of carbon based nanomaterials, here in particular carbon nanotubes. The project has started with the aim to achieve the highest level of control in the synthesis area of carbon nanotubes following by formation of macroscopic ultra-light and strong fibres and wires targeting electrical applications. The program is exploring deep scientific understanding of material synthesis, evaluation of its properties by extensive testing and developing a broad range of applications in the areas of electricity generation, power transportation and highly efficient electrical machines.
A high level of synthesis control has been achieved in the early stages of this project by diameter control of individual carbon nanotubes, through an extensive optimisation of the synthesis reaction parameters in the direct spinning reactor. Considering the very wide range of catalyst particle sizes, which are possible in substrate or floating catalyst CVD synthesis methods, the tuneable range of nanotube diameters, which can now be produced, is surprisingly very narrow, and it is in great agreement with the objectives of this project. The objective to make nanotubes all of very similar diameter, in one batch, was particularly targeting electrical properties of these materials. As example, a batch of pure armchair carbon nanotubes was produced, which is a key requirement to carry out any further electrically oriented testing and applications. The project was able to satisfy this goal following a special molecular caging method involving sulphur or special carbon based compound. The size range of carbon nanotubes obtained was very narrow, but more importantly we were able to produce carbon nanotubes with the armchair configuration, which are known for their highly conducting metallic behaviour. Further on during the project we learned how to arrest the catalyst particles during the synthesis process of the nanotubes directly with carbon to achieve another diameter set control and generate material with the opposite end of electrical properties, towards a fully semiconducting behaviour.
Following from the successful synthetic approaches to produce the correct nanotubes it was then necessary to achieve a suitable large scale output of the material and in this case manufacturing of fibres and wires, for subsequent evaluation of their macroscopic properties. The assembly of wires is relatively easy, as this process relies on manual assembly of as spun fibres. We were able to adjust the diameter of carbon nanotube wires from few microns to few millimetres, depending on the number of individual fibres used in the assembly process. The more challenging step was based on the successful application of the electrical insulation to the surface of the fibres, which enabled proper evaluation of the CNT wire performance. In this part of the project different polymeric coatings were investigated and developed as insulation for the CNT wires and also different thicknesses to suit desirable applications.
The DC and AC characteristics of the as produced fibres and insulated wires were intensively studied. Dedicated four-point probe contact system with atmosphere and temperature controls was used for DC studies whereas the AC characteristics were carried out using more advanced network analyser system. The initial evaluation of the CNT fibres showed a significant performance in the current carrying capacity. Moreover as these fibres are significantly lighter than metals (about 10x the density of copper) the assessment with respect to the specific properties, were outstanding.
It is worth mentioning that the mechanical properties of these fibres are also significantly better as compared to the metal conductors. The carbon nanotube fibres have about an order of magnitude higher tensile and fatigue performance as compared with copper wires.
Finally, the exploration of the applications for our carbon nanotube wires was very successful. Various working electrical devices were constructed in order to carry out full assessment of performance and outline of clear benefits. The prototypes constructed so far are: an electrical transformer, a mini electricity generator an Ethernet cable and heater. All these devices are currently extensively tested and a suitable feedback is prepared to identify their level of readiness or areas needed for further improvements.