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Authors: Janjua, Sohail Ahmad
Keywords: Natural Sciences
Issue Date: 2007
Publisher: Pakistan Institute of Engineering and Applied Sciences Nilore, Islamabad, Pakistan
Abstract: This thesis describes the experimental study of the sooting discharges in which a variety of carbon clusters is produced. The regenerative sooting discharges have been studied and their carbon cluster forming characteristics are compared with the non-regenerative sooting discharges. A large number of experimental arrangements have been used in which sublimation and sputtering processes were investigated in detail to understand the basic mechanisms for the formation of carbon clusters. The effects of experimental parameters on the clusters formed in the two types of carbonaceous discharges i.e. the non-regenerative and the regenerative sooting discharges are reported. Continuous as well as pulsed operations of the discharges have been studied. The carbon clusters are produced in carbonaceous environments where either the high temperature arc discharges sublime the graphite electrodes or the glow/arc discharges in the graphite hollow cathodes take place with sputtering being the dominant mechanism. Regenerative soot is shown to have different characteristics and constituents compared with those in the non-regenerative soot. We have shown that small clusters dominate in the regenerative sooting discharges. The basic constituents of the two types of soot are also different; in the case of the regenerative soot C 3 is the basic constituents while for the non- regenerative soot C 2 seems to be an essential basic unit. Emission spectroscopy of the non- regenerative discharges indicates the predominance of diatomic carbon C 2 in the continuous as well as the pulsed modes. C 2 is the main sublimed species. Under these conditions cage closure leading to fullerenes and nanotubes is more likely. Mass spectrometry with an ExB Wien velocity filter has been used to complement the results of emission spectroscopy in the case of the regenerative soot. The mass spectra from graphite hollow cathode duoplasmatron ion source clearly show that C 3 is the major surviving specie along with other clusters C 4 & C 5 with lesser yields. The environment of the twin plasmas in the duoplasmatron ion source is such that higher clusters cannot survive and are fragmented into smaller clusters with C 3 as the dominant end product.
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