| Stainless steels were widely used in metallurgical industry as well as in auto, architectural, shipbuilding, aviation, energy and other fields. The research and development on nuclear power steels are receiving more and more attention with the development of nuclear power industry in recent years. The trace amount of elements in stainless steels and nuclear power steels such as arsenic, antimony and tin can cause great influence on the steels, as a result, the amount of these elements should be strictly controlled, especially in nuclear power steels. The determination of arsenic, antimony and tin by hydride generation-atomic fluorescence spectrometry (HG-AFS) has many advantages such as lower detection limit, little interference from the matrix and good precision that are incomparable by chemical analytical methods.At present, the national standard methods for determination of arsenic and antimony in steels and alloy by HG-AFS had been established, but not for the determination of tin. In this paper, we used the type of AFS-820 twin-channel atomic fluorescence spectrometer, established the methods for determination of arsenic, antimony and tin in stainless steels and nuclear power steels by HG-AFS through the optimization of instrumental parameters, proper selection of masking agents and reducing agents. The methods were validated by the determination of standard samples of stainless steels and nuclear power steels as well as the intercomparison of other methods. Meanwhile, we provided technical and experimental support for the establishment of the national standard method for determination of tin in steels and alloy.In chapter one, the background, content and meaning of this research was introduced. The background knowledge of related research fields was reviewed and the theoretical basis, analytical performance, interference and application of HG-AFS were introduced in detail.In chapter two, the instruments, agents and preparation of standard solution were introduced, and the schematic diagram of the type of AFS-820 twin-channel atomic fluorescence spectrometer was presented.In chapter three, the establishment and research of the methods for the determination of arsenic and antimony in stainless steels and nuclear power steels by HG-AFS were introduced. The influence of instrumental parameters on the test results such as lamp current, negative pressure of photomultiplier tubes, carrier gas flow rate, shielding gas flow rate, the height of atomizer, reading time, delaying time and other parameters were studied. The influence of varied reducing agents and acidity on the fluorescence intensity of arsenic and antimony, and the interference in the simultaneous determination of arsenic and antimony were studied. L-cysteine was selected as the pre-reducing agent, which can reduce arsenic and antimony in low acidity. The reducing mechanism of L-cysteine was studied, considering the reduction of L-cysteine as that L-cysteine reacted with KBH4 to form a series of intermediates, whose structure and chemical characteristics changed dramatically with the change of acidity, thus influencing the hydride generation of arsenic and antimony. The measuring range of these methods were determined by the lower limit of quantitation of these methods and the upper content limit of common samples. The detection limit of arsenic and antimony in these methods were 0.012μg·L-1 and 0.015μg·L-1 respectively. Compared with the existing national standard methods, the methods that we established had advantages of simple, less consuming of agents and lower detection limits.In chapter four, the establishment and research of the methods for determination of tin in stainless steels and nuclear power steels by HG-AFS were introduced. The influence of varied acids and acidity on the hydride generation (HG) of tin was studied, and we found that the hydride of tin can occur only in a very narrow range of acidity. The buffer solution of citric acid- sodium citrate was used as reaction medium for the HG of tin to improve the accuracy of the test. The influence of co-exciting ions on the determination of tin, and the masking mechanism of citric acid on nickel were studied. The masking effect of citric acid on nickel was considered as that citric acid reacted with nickel to form complex compound, and the masking effect of citric acid was better in lower acidity. The different opinions on the mechanism of HG of tin were reviewed, and the acidic influence on the hydride generation of tin was discussed from the point of electronegativity. As the electronegativity of tin is lower than that of H+, H+ will preferentially act with BH4- to form complex compound, thereby restraining the hydride generation of tin. |
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