Professor Milo Shaffer’s research team at Imperial College London is making great progress in the search for
new techniques to enable the clean, scalable, production of Multi Walled Carbon Nanotubes (or MWCNTs to use the appropriate acronym).

Since the discovery of Buckminster Fullerine or ‘Buckyballs’ by the 1996 Nobel Prize laureates Robert F. Curl, Harold W. Kroto, and Richard E. Smalley, the capability of carbon atoms to form well-defined, covalently-linked structures such as balls, sheets and tubes at first fascinated and subsequently excited scientists with their range of prospective technological applications. Some of these opportunities are already being put into practical use. Bulk nanotubes are being used as composite fibres in polymers, improving the mechanical strength, as well as the thermal and electrical properties of finished aerospace and automotive composite structures. Used in inks, MWCNTs enable direct printing of electrical circuits and show great promise as the basis for new generations of biosensors and fuel cell components. The list of applications seems to grow on a daily basis.

The holy grail for many researchers is to discover the means to precisely control the submicron quality, morphology and dimensions of these structures and to optimise yields from catalysts and precursors, enabling the industrial scale precision manufacture of these materials.

Using a multiple zone Lenton PTF ‘Precision Tube Furnace’ and precisely controlling the precursor injection into the apparatus, Professor Shaffer and his team of researchers at Imperial College are able to control the length diameter and alignment of the nanotubes films as they initiate and grow onto quartz substrates. Many different growth conditions have been explored, but a typical synthesis involves injecting a solution ranging from 0.2% to 9.6% ferrocene by weight, dissolved in toluene, into the Lenton PTF ‘Precision Tube Furnace. The vapours are carried in a flow of argon-hydrogen carrier gas preheated to 200°C and reacted at temperatures ranging from 550°C to 940°C within the main furnace tube. The overall nanotube diameters can be varied appreciably in the range from 10nm to 100nm as the ferrocene concentration is adjusted and also as the furnace temperature is adjusted. Extending the injection time over which the precursors are injected up to 7 hours causes the tube lengths to increase, with scanning electron micrographs showing lengths up to several millimetres. This phenomenal length to diameter ratio, which can reach over a million to one, is particularly intriguing and can provide important benefits in many applications. The ability to precisely optimise production of MWCNT for specific reaction times and temperatures using the Lenton furnace, as well as optimising catalyst and precursor ratios are key first steps in attaining large scale industrial production.