Synthesis Of Branched Carbon Nanotubes And Composite Materials By Chemical Vapor Deposition

Carbon nanotubes (CNTs) have attracted great attention due to their excellent physical, chemical, electrical properties, and their fascinating potential application. In this paper, the synthesis of CNTs by cobalt catalyzed pyrolysis of dimethyl sulfide was studied; the influences of experimental parameters, such as reaction temperature and gas flow rate, on CNT growth were investigated; the growth process of branched CNTs was systematically analyzed, and a fundamental understanding of the nucleation and growth mechanism of the branched CNTs, and the controllable preparation were achieved. The influence of the concentration of dimethyl sulfide on the morphology and structure of Co₉S₈ nanowires-filled CNTs and the filling mechanism was investigated, to achieve a simpler and controllable preparation method. The main results in the thesis are summarized as follows:1. CNTs have been synthesized by catalytic pyrolysis of dimethyl sulfide, the growth process of CNTs is very sensitive to the experimental temperature, To find the appropriate temperature for the pyrolysis of C2H6S, three experiments were carried out at different temperatures: 800, 900 and 1000°C. Dimethyl sulfide concentration and flow rate have great influence on the morphology of the product. When the concentration of dimethyl sulfide is high, carbon atoms could cover the catalyst surface, leading to the loss of catalytic activity; so the obtained product is short CNTs or carbon nanofibers, and the graphitization is poor. The optimum dimethyl sulfide vapor concentration for CNTs growth is around 3.36-5.48%. A large number of branched CNTs can be formed when the concentration of dimethyl sulfide is high. These branched CNTs have long branches, possessing great potential applications in the field of nano-devices. There were few products when the the concentration of dimethyl sulfide is low. The growth mechanism of the branched CNTs was discussed and a simple growth model was proposed.2. Through chemical vapor deposition Y-junction and related carbon nanotubes were synthesized, the diameters of product vared from 30 to 70nm, the outer diameter of the Y-junctions carbon nanotube was about 60⁷0nm, while the inner diameter was about 30⁴0nm. The structure of products were characterized by SEM, TEM, Raman and XRD patterns, the results show that the prepared carbon nanotubes have ideal structures and high purity. A single Y-junctions carbon nanotube was selected to test the conductive properties of the three branches, the test results show that the tested carbon nanotubes have a typical metallic conductivity.3. Co₉S₈ nanowire-filled CNTs have been synthesized. The concentrations of dimethyl sulfide plays a key factor in the growth process of Co₉S₈ nanowire-filled CNTs. In the experiments dimethyl sulfide not only provides carbon source, but also provides sulfur source which is essential for the process of filling. The optimum dimethyl sulfide vapor concentration for Co₉S₈ nanowires-filled CNTs is around 1.26%-1.47%. When the dimethyl sulfide concentration is higher than 1.47%, the products are Y-junction carbon nanotubes; when the dimethyl sulfide concentrations is lower than 1.26%, the products are short hollow carbon nanotubes. The growth mechanism of Co₉S₈ nanowire-filled carbon nanotubes is "Filling carbon nanotubes with Co₉S₈ Nanowires through in situ catalyst transition."...