SYNTHESIS AND CHARACTERIZATION OF SINGLE WALLED CARBON NANOTUBES

Abstract

The revolutionary discovery of carbon nanotubes (CNTs) in 1991 by Sumio Iijima further led to powerful research in the field of science. The attractive properties of this unique materials has opened a great number of potential applications e.g. one dimensional conductors, super capacitors, reinforcing fibers, hydrogen storage, electron field emitters & also in the field of medical sciences. Even with rapid technical progresses there is still much great effort required in the development of a synthesis method suitable for commercial applications. A foremost runner is the chemical vapour deposition (CVD) technique. Nucleation and growth of CNTs are induced by the decomposition of carboncontaining gases such as - CO, CO2, CH4, C2H4 etc, over a metallic catalyst at temperatures between 600 0C and 1400 0C. CVD is the most widely used technique to produce CNTs in large quantities and much development has been done in its synthesis from the point of view of cost reduction, mass production & purification techniques. But the greatest challenge of CVD process remains with the growth mechanism. In CNT Synthesis by CVD method is the most important reaction step seems to be diffusion of carbon through the metal catalyst and the most active metals like iron, cobalt and nickel. But their catalytic action depends upon the type of precursor, the type of substrate and the reactive gases used. Till date few investigations of the chemical and morphological evolution of the catalyst during CVD process have been performed. This thesis mainly focuses on the synthesis and characterization of single walled carbon nanotube using Iron/Cobalt - Molybdenum - Magnesium oxide (Fe/Co: Mo: MgO) based catalysts under the gases like Argon and Methane atmosphere between 27 0C and 875 0C. The main reaction took place at 875 0C for 20 minutes which results in the growth of CNT. VI According to the nature of the catalyst during synthesis we optimize atmosphere of gases, their flow rate and temperature at which reaction has to be carried out. After the reaction, samples were cooled down by microprocessor based controller from 875 0C to 27 0C in the argon atmosphere. The microscopic images showed that iron, molybdenum and magnesium can be used for typical nanotube synthesis as catalyst for CNT nucleation and growth. Grain size reduction during reactions in the catalyst precursor and the transformation of precursors into metallic phase are the main requirements for nanotube growth. The reaction during the reduction of the precursor is further related with the nucleation and growth of nanotubes. In case of iron based catalyst system, where the breakdown of metastable carbides act as a boost of nanotube formation, the emergence of carbides in the molybdenum system after 20 minutes stops further carbon nanotube growth.