M.Tech. / Owing to the difficulties in the procurement of internationally certified reference materials for iron and steel, local firms are using their own standards manufactured by casting techniques. It is necessary to assess the integrity of these materials using international standards as control to these in-house reference materials. Macro and micro-examination were carried out to reveal the nature of reference materials and hence evaluate their quality. The consistency of chemical composition of standard materials and the accuracy of the analyses based on the in-house standards were evaluated. The results showed that local standards were characterised by gross casting defects. In comparison the imported standards had micro-structural uniformity and free from casting defects. This shows the essential difference in production method. Casting has severe limitations when it comes to the production of components of low segregation and internal soundness. First, the partitioning of solutes between solid and liquid phases invariably leads to segregation and loss of homogeneity. Second, the volumetric change accompanying solidification results in shrinkage cavities. If stringent production controls are not observed, the proprietary standards are bound to have a widely varying chemical composition. In this regard, the calibration and standardisation would essentially be flawed. Hence the subsequent chemical analyses of standards cannot be reliable. It is necessary to establish an analytical methodology that yields reliable results. Standards used for calibration should have a high degree of chemical purity and homogeneity. The study covers other possible production options for standards that can be used for accurate calibration and standardisation of spectrometers for chemical analysis of iron and steel. The use of vacuum melting followed by rapid casting in special chill mould is recommended.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uj/uj:2155 |
| Date | 12 March 2012 |
| Creators | Kilongozi, Si-umba Isidore |
| Source Sets | South African National ETD Portal |
| Detected Language | English |
| Type | Thesis |
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