The impact of process variables on the chemical vapour deposition of silicon carbide

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dc.contributor.advisor De Villiers, Johan Pieter
dc.contributor.postgraduate Cromarty, Robert Douglas en
dc.date.accessioned 2013-09-10T07:01:46Z
dc.date.available 2013 en
dc.date.available 2013-09-10T07:01:46Z
dc.date.created 2013-05-30 en
dc.date.issued 2013 en
dc.date.submitted 2013-05-30 en
dc.description Thesis (PhD)--University of Pretoria, 2013. en
dc.description.abstract High temperature gas cooled nuclear reactors often make use of Tristructural Isotropic (TRISO) coated fuel particles. In these particles, a layer of silicon carbide plays the key role of providing mechanical strength and acting as a diffusion barrier so preventing the release of fission products. TRISO particles are produced by a chemical vapor deposition (CVD) process in a spouted bed coater. Operating conditions of chemical vapor deposition processes are known to influence the properties of the deposited material. In the case of silicon carbide deposited by pyrolysis of methyltrichlorosilane (MTS) in a hydrogen atmosphere, process parameters that may influence the properties of the silicon carbide deposited include deposition temperature, MTS concentration and hydrogen flow rates. In this study the coating process was investigated using a laboratory scale spouted bed CVD coater. In all the test work conducted, carbon coated zirconia particles were used as a starting material. Only silicon carbide was deposited during these trials. Process parameters investigated were temperature, MTS concentration and hydrogen flow rate. The range investigated was 1250 °C to 1550 °C for temperature, 0.5 % to 2.5 % for MTS concentration and 10.0 l.minute-1 to 15.0 l.minute-1 for hydrogen flow. This covered the range that is typically used for small-scale production coaters. Two different gas inlet configurations, a conventional water cooled inlet and an inlet without any cooling, were used in the investigation. Properties of the coating process, such as the deposition rate and coating efficiency, as well as material properties were measured. Material properties investigated included: density, crush strength, micro-hardness, fracture toughness, nano-hardness, Young’s modulus, elemental composition, phase composition and microstructure. It was found that, of the variables investigated, temperature had the strongest effect while hydrogen flow rate had the least effect on material properties. There was considerable variability in all measured parameters; this introduced considerable uncertainty into the predicted effects of process conditions on material properties. en
dc.description.availability unrestricted en
dc.description.department Materials Science and Metallurgical Engineering en
dc.identifier.citation Cromarty, R.D. 2012, The impact of process variables on the chemical vapour deposition of silicon carbide, PhD thesis, University of Pretoria, Pretoria, viewed yymmdd <http://hdl.handle.net/2263/31597> en
dc.identifier.other B13/9/1049 en
dc.identifier.other B13/9/1049
dc.identifier.uri http://hdl.handle.net/2263/31597
dc.language.iso Eng en
dc.publisher University of Pretoria en_ZA
dc.rights © 2012 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. en
dc.subject Methyltrichlorosilane en
dc.subject Triso en
dc.subject Spouted bed en
dc.subject Chemical vapor deposition en
dc.subject Free silicon mechanical properties en
dc.subject Deposition efficiency en
dc.subject Deposition rate en
dc.subject Morphology en
dc.subject Silicon carbide en
dc.subject UCTD en_US
dc.title The impact of process variables on the chemical vapour deposition of silicon carbide en
dc.type Thesis en


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