Microstructure and properties of zirconium silicide surface layers on zirlo for improved nuclear fuel cladding
- Authors: Ngongo, Sinoyolo
- Date: 2017
- Subjects: Zirconium alloys Zirconium
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/20098 , vital:29107
- Description: Zirconium alloys have important applications as nuclear reactor fuel cladding material. In this study the microstructure and properties of zirconium silicide synthesized by heating ZIRLO (which is an alloy of zirconium and niobium) in contact with silicon powder has been investigated. The silicide acts as a coating layer to protect the ZIRLO from oxidation which is associated with hydrogen pick-up. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to investigate the morphology and crystal structure of the silicides respectively. Heating of ZIRLO with silicon powder was carried out in a Webb 89 Vacuum Furnace for various temperatures (1000–1400 °C) and times (4–8 hours) in an argon atmosphere or under vacuum, which resulted in the diffusion of silicon into the ZIRLO and the formation of zirconium silicide layers. The sample heat treated for 8 hours at 1000 °C did not show any evidence of inter-diffusion between the ZIRLO and silicon, this suggests that a temperature of 1000 °C is not sufficient to facilitate the formation of a silicide layer. The formation of the silicide layer was however observed after heat treatments at 1200 °C and 1400 °C using SEM and TEM. The silicide formed at 1200 °C as a layer on the ZIRLO sample and voids were observed in this layer, most likely due to the Kirkendall effect which occurs in solid state diffusion. The results suggest that Zr has a larger flux than Si as the voids formed in the ZIRLO. The temperature of 1400 °C appears to exceed the ideal required for silicide formation on the surface of ZIRLO, since the silicon infiltrated very far into the ZIRLO and in fact reacted with the entire ZIRLO sample. Both these samples were heat treated for 8 hours in an argon atmosphere. Silicide layers without voids were obtained in the case where ZIRLO and Si were heat treated for 8 and 4 hours at 1200 °C in an argon atmosphere and under vacuum respectively. The average penetration rate, calculated from the aforementioned heat treatments, of Si into Zr was calculated to be 4.5 μm/hour. The diffusion coefficient of Si in Zr was also estimated and it differs by about a factor of 104 from the reported value Zr into Si diffusion coefficient.
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- Date Issued: 2017
Investigating the prevailing knowledge about co-operatives in South Africa and the determinants of their success
- Authors: Frans, Nonyameko
- Date: 2013
- Subjects: Cooperative societies -- South Africa , Cooperative societies -- Management
- Language: English
- Type: Thesis , Masters , MBA
- Identifier: vital:8862 , http://hdl.handle.net/10948/d1020206
- Description: The development of co-operatives has been increasingly seen, both globally and in developing countries, as a key strategy for a high economic growth rate, job creation and poverty alleviation. In trying to address these challenges, the South African government has been promoting co-operatives as an instrument for economic growth and socio-economic integration. Despite the realisation of the important role that cooperatives could play, not enough research has been done on the successes and failures of these organisations in achieving economic growth and socio-economic development in countries. The present study is an attempt to address this research gap. The primary objective of this study was to increase the success of co-operatives in South Africa by investigating the prevailing nature of operations of co-operatives and the determinants of the success of these organisations. More specifically, the study gathered qualitative information about co-operatives, identified which factors influence co-operatives in general and investigated which of these factors are the most important determinants of the success of these organisations in South Africa. A census was conducted of the 110 co-operatives registered in the database of the Leadership Academy (LA) of the NMMU Business School. Only 50 executive members of 26 co-operatives participated in the study (response rate of 23.6 percent). The empirical results revealed that the two most critical success factors for co-op success were the handling of finances and leadership; that language groups viewed coop success differently; and that females provide stronger leadership than males in cooperatives. The results also showed that skills development is an important factor in achieving these critical success factors. These results presented important managerial implications for the success of co-operatives.
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- Date Issued: 2013