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.

M.Sc. / Emulsions are not widely used in industry for wear-metal-in-oil determinations and this study was undertaken in order to evaluate such a possibility. The use of emulsified standards was compared to aqueous standards for the calibration of an emulsified used lubricating oil sample. The traditionally used methods of ashing in a muffle furnace and dilution with the organic solvent, xylene were also evaluated in comparison with the emulsion methodology. Inductively coupled plasma optical emission spectrometry (ICP-OES) was used for the wear-metal-in-oil analysis. The performance characteristics of each method were compared for the following metals: AI, Cr, Cu, Fe, Ni, and Pb. The used oil sample and emulsified standards were acid treated and emulsified in water {1% wlw) using tetralin as solvent and triton X-100 as surfactant. This evaluation included the calibration characteristics, precision and accuracy obtained, as well as the results of recovery studies. The emulsification method was found to be comparable to the ashing and dilution methods in terms of calibration and only Cr, Cu, Fe and Pb concentrations were found. The precision of the emulsification method was found, in general, to be close to or less than 2% RSD. The used oil matrix also contained leaked petroleum from a problem car engine. An accurate determination of lead was consequently impossible since the high lead content led to sedimentation. The use of the internal standard, indium, was evaluated for its effectiveness in correcting possible matrix effects that were evident from the results obtained in the recovery studies. The recovery studies showed the Cr and Pb determinations to be adversely affected by internal standardization. An alternative approach for matrix effect correction, the common analyte internal standardization (CAIS) method was also investigated. This method held promise for allowing the use of aqueous standards, instead of oil or emulsion standards, for the calibration of the emulsified oil samples. Three different applications of the CAIS technique were investigated and all proved unsuccessful.

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