Brent Foy (Committee Member), Gregory Kozlowski (Committee Member), Amit Sharma (Advisor)
Master of Science (MS)
The bottom-up analysis of Carbon Nanotube synthesis is not well understood. Specifically, the question as to how carbon adsorbs to a substrate inclusive of a sup- ported catalyst may lead to the energetically favorable structure of a hexagonal close- packed structure along the wall, or walls, of the tube. A first time simulation using COMSOL Multiphysics has been generated in order to capture the gas-phase mech- anism which leads to carbon production. It is thought that the carbon adsorbs and the walls are formed from the bottom up and the inside out for multi-wall CNTs. The studies involved accurately setting up a simulation to capture chemical kinetics, mass transport, heat transfer, and fluid flow. It is shown that a variation in inflow velocity yields a variation in efficiency of ethylene cracking in the reactor. When the residence time is increased the outlet concentration of ethylene is lowered, as expected. This means that variations in con- centrations can be accounted for through varying initial parameters. Chemical reactions involving ethylene decomposition from GRI-Mech 3.0  is imported and the validity of the Troe Form chemical kinetics was tested. Using equilibrium calculations with the use of an ICE (Initial, Concentration, Equilibrium) table, 0-D studies using the high pressure limit of the rate constant and the Troe Form of the rate constant were used in separate tests for comparison. It was subse- quently showed that the Troe Form kinetics do not accurately determine the expected concentrations. The chemical species concentration, gas pressure, temperature, and velocities were calculated for a final set of approximately 32 gas-phase reactions. A nearly completed set of gas-phase and surface reactions were compiled but only the most important chemical reactions were implemented in the present studies to form a basis for future analysis. The results of the present study shows production of amorphous carbon within the gas-phase, which is not high enough for CNT growth, implying the impor- tance of surface hydrocarbon reactions in the CNT production in a CVD reactor.
Department or Program
Department of Physics
Year Degree Awarded
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