Polymer Group Research

Nanotube Synthesis

Arc grown tubes

Carbon Nanotubes were first recognised in 1991, forming in the electric arc discharge between two graphite electrodes. ( 12 ) Material evaporates from one electrode and deposits on the other in the form of nanoparticles (~60%) and nanotubes (~40%). Purification is achieved by competetive oxidation in either the gas or liquid phase. Unfortunately, despite optimisation, yields are still low and the cost can be around $500 a gram after purification. This original route is still preferred by many researchers, as the nanotubes are staight and of high crystallinity, and the process is relatively straightforward on the small scale.

Catalytically grown tubes

It has long been known that carbon filaments grow on metal surfaces exposed to hydrocarbon gas at temperatures between 500-1100 C, although the product is typically much larger than the typical nanotube and amorphous apart from a central crystalline core. Recent work has adjusted the process, using carefully prepared dispersions of metal catalyst, and produced filaments equivalent to arc-grown nanotubes. A whole range of other structures are also possible, with the graphitic layers at different angles to the tube axis or with the whole tube growing as a coil. ( 13 ) This technique can produce large amounts of material at low costs, and without need for further purification, although the concentration of defects is usually high. Single-wall nanotubes can be grown  by using either a supported catalyst or a high temperature and pressure CO disproportionation method (HiPCO).

Laser evaporation technique

Carbon nanotubes form in the plume of carbon vapour evaporated by a laser from a graphite target held at 1200 C. Adding metal dispersions to the target results in the formation of single wall tubes, and, under some conditions crystalline ropes of very similar single-wall tubes. ( 14 )

Other techniques

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