Abstract
D.Phil.
The work that is presented in this thesis describes the numerous detailed investigations that were conducted with a custom-made horizontally aligned, water-cooled, gas-filled DC arc-discharge reactor.
A focus of the investigations was the establishment of the effects of high purity graphite electrodes in ultra-high purity (UHP) He, H2 or mixtures thereof, in the absence of a metal catalyst on the reaction. These studies showed that higher yields of MWCNTs were formed in reactions between graphite electrodes in H2 than in He. Additionally, a range of gaseous hydrocarbons were formed in H2 that were not formed in He.
After the initial parameters were established, investigations examined the effects on the products that were formed by the addition of high purity Cu to graphite. The data from these studies revealed that H2 played a pivotal role in the reactions and that metallic copper nanoparticles were the active catalysts. In particular, they showed that when the Cu/C mole ratio and particle size ranges were fixed (i.e. 0.20 and < 150 μm respectively), then branched CNTs were exclusively found in a collar deposited around the cathode, with bamboo-shaped CNTs formed in the reaction chamber. Characterisation of these products revealed that the Cu nanoparticles were probably molten during the reactions and thus a growth model was proposed in which it was suggested that dehydrogenation reactions of gaseous hydrocarbon species on the surfaces of unsupported molten copper nanoparticles led to the formation of either bamboo-shaped or branched CNTs.