Electron microscopy characterisation of polycrystalline silicon carbide
- Authors: Ndzane, Nolufefe Muriel
- Date: 2014
- Subjects: Electron microscopy , Silicon carbide
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10553 , http://hdl.handle.net/10948/d1020634
- Description: This dissertation focuses on an electron microscopy investigation of the microstructure of SiC layers in TRISO coated particles deposited by chemical vapour deposition under different experimental conditions, which include temperature, concentration of gases and deposition time. The polycrystalline β-SiC was deposited from the decomposition of methyl trichlorosilane MTS in the presence of hydrogen (H2) as carrier gas. Scanning electron microscopy (SEM), using the backscattered electron (BSE) mode, was used to image the microstructure of and defects in the SiC layers of TRISO particles. Electron backscatter diffraction (EBSD) in the SEM was used to determine the SiC grain sizes and distribution thereof in TRISO particles deposited under different conditions. For samples with a poor EBSD indexing rate, transmission Kikuchi diffraction and transmission electron microscopy (TEM) investigations were also carried out. From the results, the effects of growth temperature on the SiC microstructure, specifically on the grain size and shape and the porosity were determined. The effects of cooling or non-cooling of the gas inlet nozzle on the SiC microstructure were also investigated. TEM and scanning TEM (STEM) analyses of the SiC layers in TRISO particles were performed to image the defects and reveal the crystallinity of SiC layers. The microstructure and composition of SiC tubes fabricated by reaction bonding (RB) was also investigated by using electron microscopy and Raman spectroscopy. SEM-BSE imaging of RBSiC samples allowed the identification of impurities and free silicon in the RBSiC. Finally, the penetration of the metallic fission product, palladium, in reaction bonded SiC at a temperature of a 1000ºC is determined. A brief comment on the suitability of RBSiC as candidate for fuel cladding in a PWR is made. A short discussion of the suitability of the characterisation techniques used is included at the end.
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- Date Issued: 2014
Factors that contribute to teachers' job satisfaction/dissatisfaction as perceived by teachers in Libode District: A case study of two schools
- Authors: Mvo, Nelisa Enid
- Date: 2013
- Subjects: Teachers -- Job satisfaction
- Language: English
- Type: Thesis , Masters , M Ed
- Identifier: vital:18442 , http://hdl.handle.net/11260/d1007266
- Description: The study investigates factors that contribute to job satisfaction/dissatisfaction in a case study of two Public Senior Secondary Schools as perceived by teachers of Libode District in the Eastern Cape. The point of departure of the study is the fact that the researcher has observed high rate of resignations and transfers of teachers. The study was conducted through a case study design. A total of thirty-five sample subjects from both schools were selected using purposive methods. The instruments used to collect the data were the questionnaires and interviews. The targeted population was teachers teaching in both schools at the area of the research site. Pilot study was done. Ethical issues were taken into consideration. The data collected was, analyzed and interpreted within a specified time frame. The findings were based on the data collected; thereafter the conclusions and recommendations were drawn based on the findings of both the quantitative and qualitative methods. The main findings of the study indicated clearly that poor working conditions, low salaries and ill discipline of learners contribute to job dissatisfaction. Findings were discussed in the context of the main and sub research questions and recommendations were made. The study will help the Department of Education to identify teachers' concern regarding job satisfaction/dissatisfaction.
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- Date Issued: 2013