FORMATION OF CARBONACEOUS NANOPARTICLES FROM METHANE IN NON-EQUILIBRIUM PLASMA FLOW REACTOR

Date

2025-8

Author

Şen, İbrahim Burak

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Carbon is the fourth most abundant element in the universe. It can be found in various forms such as graphene, graphite, fullerene, diamond and more. Graphite and nanodiamonds are the two crystalline structured forms of carbon. Graphite is being used in battery production due to its high thermal and electrical conductivity and intercalation capacity. Bulk diamond is used in cutting tools while nanodiamond is used for bioimaging and quantum computing. Although the synthesis of these materials in a thermally equilibrated medium is well-established, their direct synthesis from gas phase to solid free-standing particles in non-equilibrium flow-through plasmas is not yet fully understood due to difficulties in particle nucleation and rapid film formation at the reactor walls. In this thesis, methane conversion into carbonaceous nanoparticles was tested through a variety of experiments and characterization methods to make a preliminary study for nanodiamond particle formation which was enabled by integration of a Stairmand-type cyclone separator used to eliminate contaminated particles through mobility differences. Size-separated, hence, purified particles were subjected to intensive characterization via XRD, Raman, TGA, and TEM. All operating parameters – pressure, gas composition and plasma power - effected crystalline sizes, however, residence time of particles had the strongest influence. Increased residence time led to formation of highly anisotropic particles whose grain sizes were calculated from XRD and Raman. In-plane crystalline size was 2.2 nm and crystalline size in stacking direction was 1.43 nm for highest graphitized particle. However, HRTEM images showed these particles contained bigger grains sized up 8 nm while depicting an evolutionary pathway for how morphology of particles changed with varying residence time. It was concluded that compared to synthesis of Si, metal oxides and other nanocrystals, crystalized carbonaceous nanoparticle formation in such plasmas is more energy intensive, favoring high pressures and is more dependent on residence time.

Subject Keywords

Graphite, Non-equilibrium plasma reactor, Synthesis, Methane conversion, Carbon characterization

URI

https://hdl.handle.net/11511/116194

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Graduate School of Natural and Applied Sciences, Thesis