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Deposition of silicon carbide coatings on alumina particles in a microwave plasma-assisted spouted bed reactor
Thesis (PhD)--University of Pretoria, 2018.
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| Language: | English |
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University of Pretoria
2019
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| _version_ | 1867613654155788288 |
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| access_status_str | Open Access |
| author2 | Crouse, Philippus L. |
| author_browse | Crouse, Philippus L. |
| author_facet | Crouse, Philippus L. |
| collection | Thesis |
| dc_rights_str_mv | © 2019 University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. |
| description | Thesis (PhD)--University of Pretoria, 2018. |
| format | Thesis |
| id | oai:repository.up.ac.za:2263/68695 |
| institution | University of Pretoria (South Africa) |
| language | English |
| last_indexed | 2026-06-10T12:39:34.803Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UPSpace — University of Pretoria Institutional Repository |
| publishDate | 2019 |
| publishDateRange | 2019 |
| publishDateSort | 2019 |
| publisher | University of Pretoria |
| publisherStr | University of Pretoria |
| record_format | dspace |
| source_str | UPSpace — University of Pretoria Institutional Repository |
| spelling | oai:repository.up.ac.za:2263/68695 Deposition of silicon carbide coatings on alumina particles in a microwave plasma-assisted spouted bed reactor Crouse, Philippus L. u27071279@tuks.co.za Barry, John van der Walt, Jaco Bissett, Hertzog Van Laar, Jean H. UCTD Chemical Engineering Plasma Physics Nuclear Materials Engineering, built environment and information technology theses SDG-09 Engineering, built environment and information technology theses SDG-12 Thesis (PhD)--University of Pretoria, 2018. Alumina particles were successfully coated with silicon carbide (SiC) layers in a microwave plasma-assisted spouted bed reactor. Methyltrichlorosilane (MTS) was used as precursor for the SiC deposition reaction, and argon served as both carrier and plasma gas. The microwaves were guided from a generator along a rectangular waveguide. A quartz tube was mounted between two support flanges and positioned perpendicular to the metallic waveguide. A graphite nozzle was inserted into the bottom of the quartz tube to bring about the spouting action of the bed. A metallic grid was installed at the top of the tube to prevent particles exiting the reaction zone. Process parameters under investigation were enthalpy, pressure and the hydrogen-to-MTS ratio. The design of experiments (DoE) followed that of a Box-Wilson 3-dimensional central composite design (CCD), covering a wide range of experimental parameters, within the capability of the system. The measured growth rates ranged from 50 μm/h to 140 μm/h, with mass deposition rates from 19.1 g/(h·m2) to 331 g/(h·m2). Response surface methodology (RSM) and analysis of variance (ANOVA) yielded 3D surface contour plots for navigating the design space, and the models indicated the most significant term to be pressure. Characterisation techniques for the SiC layers included scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) spectroscopy, X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray (EDX) spectroscopy and Fourier-transform infrared (FTIR) spectroscopy. These techniques assisted in developing a colour chart as well as a similar morphological chart used to indicate the change in morphology of the layers throughout a 2D design space. High enthalpy and pressure values tended to produce dark-coloured layers, often accompanied by carbon-rich deposits. XPS characterisation also indicated the presence of organosilicons, likely the remnants of unreacted or partially-reacted MTS compounds embedded in the layers. It is evident that within the design space, the optimal region for SiC deposition requires high enthalpy (~ 5 MJ/kg) and pressure (> -60 kPag), with reasonable hydrogen-to-MTS ratios (~ 5:1). The quality (i.e. crystallinity, particle size, Si:C ratios) of the layers appears to improve at these conditions, at the expense of decreased deposition rates. Brunauer–Emmett–Teller (BET) analysis indicated a pore size distribution showing the majority of pore sizes to be below 20 nm, classified as mesoporous. Heat treatment of the particles (in air at 1 000 °C) yielded an increased oxygen content within the layers, likely a result of oxidation of the Si and SiC. By contrast, the chlorine content decreased, indicative of the organosilicon reactions forming volatile hydrogen chloride (HCl). SEM images demonstrated that the layer boundaries became sharper and more defined after heat treatment. A 2D finite-element model was developed to assist in investigating the effect of the plasma parameters on the SiC deposition mechanism. Limited access to computing power required careful consideration and simplification of the model, while still successfully coupling relevant physical processes, such as laminar flow, heat transfer, plasma chemistry and chemical vapour deposition (CVD) processes. Some experimental observations were successfully predicted by the model, such as the total volume of the quartz tube occupied by the plasma zone, gas temperatures during operation (~ 1 000 °C), gas velocities (~ 2 m/s to 12 m/s), and the effect of a SiC layer growing on the reactor walls. Other results comparable with literature values include the electron densities (~ 5.93 × 1019 m-3) and energies (~ 1.22 eV). The deposition rates on the particles were not in agreement with experimental results, likely due to a simplified MTS decomposition mechanism, as well as the use of a temperature dependent sticking coefficient. National Research Foundation (NRF) South African Nuclear Energy Corporation (NECSA) mi2026 Chemical Engineering PhD Unrestricted SDG-09: Industry, innovation and infrastructure SDG-12: Responsible consumption and production 2019-03-25T07:45:44Z 2019-03-25T07:45:44Z 2019-04-11 2018 Thesis Van Laar, JH 2018, Deposition of silicon carbide coatings on alumina particles in a microwave plasma-assisted spouted bed reactor, PhD Thesis, University of Pretoria, Pretoria, viewed yymmdd <http://hdl.handle.net/2263/68695> A2019 http://hdl.handle.net/2263/68695 en © 2019 University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. application/pdf University of Pretoria |
| spellingShingle | UCTD Chemical Engineering Plasma Physics Nuclear Materials Engineering, built environment and information technology theses SDG-09 Engineering, built environment and information technology theses SDG-12 Deposition of silicon carbide coatings on alumina particles in a microwave plasma-assisted spouted bed reactor |
| title | Deposition of silicon carbide coatings on alumina particles in a microwave plasma-assisted spouted bed reactor |
| title_full | Deposition of silicon carbide coatings on alumina particles in a microwave plasma-assisted spouted bed reactor |
| title_fullStr | Deposition of silicon carbide coatings on alumina particles in a microwave plasma-assisted spouted bed reactor |
| title_full_unstemmed | Deposition of silicon carbide coatings on alumina particles in a microwave plasma-assisted spouted bed reactor |
| title_short | Deposition of silicon carbide coatings on alumina particles in a microwave plasma-assisted spouted bed reactor |
| title_sort | deposition of silicon carbide coatings on alumina particles in a microwave plasma assisted spouted bed reactor |
| topic | UCTD Chemical Engineering Plasma Physics Nuclear Materials Engineering, built environment and information technology theses SDG-09 Engineering, built environment and information technology theses SDG-12 |
| url | http://hdl.handle.net/2263/68695 |