| Magnesium alloy, the lightest metallic structural material and a kind of functional material for special purposes, is widely used in the fields of automotive, electronics, telecommunications and other industries. Currently, the main standard analytical methods for magnesium and magnesium alloy are spectrophotometry, AAS, gravimetry and titration. With the rapid development of automotive and advanced manufacturing industries, demands for new analytical methods have been proposed. Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES) with its advantages of lower detection limits, higher precision, less interference, wider linear range and simultaneous multi-elements analysis, unparalleled to chemical analysis method, has been become one of the most important analytical tools in laboratory.Determination of magnesium alloy by ICP-AES method has been reported in some literatures, but there is seldom systematic and standardization research work available for simultaneous determination of multi-elements. In this paper, simultaneous determination of 17 elements in magnesium and magnesium alloy by ICP-AES method has been studied. By optimizing the operating conditions, selecting analytical lines, deduction spectral background, elimination the spectral interferences and etc., the ICP-AES method for analysis of magnesium and magnesium alloy has been built which covers the determination range from major contents to trace contents. Further more, the method was verified by the analysis of multi-elements in the synthesized samples and certified reference materials, and the uncertainty of analytical results has also been evaluated. This work provides technical and experimental basis for the establishment of a new standard method for ICP-AES analysis of Mg-alloys.In chapter 1, the background, contents and the purpose of this research work are briefly introduced. Some conceptual background and basic knowledge of ICP-AES methods related to this research are summarized. Theoretical basis and analytical capability are also introduced. Moreover, by focusing on domestic and foreign research progresses of elimination interferences, correction methods and applications of ICP-AES, the main problems of ICP-AEC method existed in recent time are outlined.In chapter 2, experimental condition including instruments parameters, reagents and preparation for standard solution are introduced, the detection limits of the analytical lines for all the 17 elements in spectral tables are collected and reviewed.In chapter 3, the effects of instrument parameters including incident power, nebulizer gas flow rate and observation height on analytical signals, spectral background, excitation temperature, and matrix effect have been systemically studied. The mechanism of the effects was also discussed in this chapter. The experimental results showed that the incident power not only affected analytical line intensity, but also affected spectral background. The line intensity is increased with the increase the incident power, it can be attributed to the increase of the ICP temperature, at the same time the background is also significantly increased, which results in the decrease of the ratio of signal to background (SBR). On the other hand, lower power would result in notable matrix effects, increase of power will restrain this interference, but it damages detection limits, and also increases the risk of melting the torch. The flow rate of carrier gas affected the temperature, electron density and their distribution in the plasma, and also affected analysis residence time in center channel and atomization efficiency. The experimental results showed that most elements had peak intensity at instrument compromised height 15 mm. Integrated the effects of incident power, nebulizer gas flow rate and observation height, the parameters can be set only in a very narrow range for optimization. Deviation from the optimum working conditions, higher power damages detection limits; larger carrier gas and higher observation height mean more severe interference, while lower observing height results bad detection limits and high level interference; small carrier gas will restrict the generation of aerosols. In order to obtain optimal SBR and the lowest level of interference, the best working conditions for all the analyte elements and for simultaneous determination of multi-elements have been given in this chapter.In chapter 4, selection of analysis lines, spectral interferences and correction of interferences have been studied. Various magnesium alloys, especially some alloys containing component elements with complicate spectrum such as zirconium, manganese and rare-earths and etc., the spectral interferences have not been reported yet up to now. Based on the review of the data of spectral interferences taken from the Winge's ICP-AES Altas and Boumans' Line Coincidence Tables for ICP-AES and others, a selected analytical lines table for the ICP-AES analysis of various kinds of Mg-alloys is firstly presented in this paper. Validation of the presented data is verified by the analysis of standard Mg-alloys including those alloys containing complicate components. The experimental results showed that the non-spectral interference lines meet the needs for the analysis of high and low content components in the simulated samples, the relative error was less than 5%; while the error resulted from some lines with serious spectral interferences would be more than 10%, even some analysis lines cannot be available in the analysis of low-level components. In case the spectral interferences have been corrected, more satisfactory results can be obtained for those components with high concentration. So in sample analysis, especially in the determination of low-level components, non-spectral interference line is the best choice. When choosing spectral line with interference, appropriate correction method must be adopted.In Chapter 5, by integrating the data of operating parameters and line selection, the ICP-AES method of simultaneous determination of multi-elements in magnesium and magnesium alloy has been built. Sample preparation has been discussed based on the line sensitivity and total salinity in sample solution. A suitable acidity of nitric acid (1+3) was experimentally ascertained for sample dissolution. The ultimate acidity of sample solution was controlled in range of 2%~7%. In case silicon or zirconium is existed in sample and need to be determined, an appropriate amount of hydrofluoric acid must be added. Based on the GB/T 13748 specification of magnesium alloys, there sets of calibration curves were given for the analysis of different content ranges of components.In chapter 6, satisfactory results were obtained by analyzing certified reference materials, simulation samples, different brands of magnesium alloys and pure magnesium. It is proved that the established method is simple, rapid; the analysis result is accurate and reliable. Compared with FAAS and chemical analytical methods, there was no deviation on accuracy and precision, and standard deviation was less than the method precision. To evaluate the recovery of the method, results showed that the major component was 95%～105%, and trace components was 80%～120%. The uncertainty of analytical results of some elements was also evaluated. The source of uncertainty was discussed and evaluated in detail by determination of copper in magnesium alloy. |
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