A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. Johannesburg, 2015. / The synthesis and applications of carbon nanomaterials (CNMs) such as carbon nanofibres (CNFs), carbon nanotubes (CNTs) and carbon nanospheres (CNSs) have attracted a lot of attention due to their unique chemical and physical properties. For the synthesis of CNMs with desired morphology to occur, one needs to consider three components, namely, the catalyst, carbon source and source of power. However, the cost of the catalysts involved in making CNMs is one of the challenging factors. Due to properties such as high aspect ratio, CNM use as fillers in polymer nanocomposites has been on the forefront to improve the mechanical strength of polymer materials such as polyesters. Due to their hydrophobic nature, the interaction between the filler and matrix tends to be problematic.
In this study, we investigated the use of a waste material, coal fly ash as a catalyst for the synthesis of CNMs using the chemical vapour deposition method. The use of CO2 and C2H2 as carbon sources, either independently or together, was also employed. A comparison of two different ashes was also investigated. Lastly, the use of these synthesized and acid treated CNMs as fillers was examined. The catalysts and synthesized CNMs were characterised using SEM, TEM, EDS, laser Raman spectroscopy, XRD, BET, TGA and Mössbauer spectroscopy. The mechanical properties were investigated by testing the tensile, flexural and impact properties.
The synthesis of CNMs using fly ash as a catalyst without pre-treatment or impregnating with other metals was achieved. Optimum yields and uniform morphology was obtained at 650 oC, at a flow rate of 100 ml/min using H2 as a carrier gas and C2H2 as a carbon source. Mössbauer spectroscopy revealed that cementite (Fe3C) was the compound responsible for CNF formation.
Further, CNMs were formed over fly ash as a catalyst, using CO2 as a sole carbon source, an additive and a carbon source before reacting with C2H2. Duvha was
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found to be a better fly ash catalyst compared to Grootvlei and an optimum loading was achieved at 0.25%. Treating the CNFs with HCl/HNO3 resulted in the highest tensile, flexural and impact strengths.
This study / GR 2016
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/21271 |
| Date | January 2016 |
| Creators | Hintsho, Nomso Charmaine |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | Online resource (173 leaves), application/pdf |
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