DETERMINATION OF LIGHT ELEMENTS IN STEEL AND MINERALS USING WDS ON SEM

摘要

Microanalysis by using scanning electron microscopes (SEM) is widespread in materials related sciences and industries. Due to its versatility, robustness and speed energy-dispersive X-ray spectrometry (EDS) is thereby widely-used and appropriate for the majority of analytical applications. For more demanding tasks however, requiring higher spectral resolution and trace element detection capabilities beyond the limits of EDS, wavelength-dispersive X-ray spectrometry (WDS) is the ideal technique for gaining even more precise data during microanalysis. A parallel beam WD spectrometer with grazing incidence collimating optics furthermore delivers outstanding sensitivity in the low-energy range of X-ray lines, facilitating the determination of light elements. Here, we present measurements of light elements including Be, B, C, N carried out on various steel, glass and mineral samples. The present WDS analyses for light elements were performed on a FE-SEM using Bruker's parallel beam WD spectrometer XSense? equipped with various multilayer dispersing elements. Amongst others, the present study shows results on boron quantification in glasses and on heterogeneous carbon distribution in steel. Three different industrial glasses with boron contents between ca. 2 wt% and 10 wt% were measured under (a) high-vacuum, and (b) low-vacuum (30 Pa) conditions. In order to avoid beam damage, the analysed areas were 30x20 μm in size. Boron was determined by WDS using an 80 A multilayer, all other elements by standardless EDS. A certified DURAN glass with 13 wt% B_2O_3 was used as reference material. The results of both analyses series (at high- and low-vacuum) are in good agreement with data gathered by XRF analysis of the samples. Mapping of carbon distribution in a steel sample (DP600; sample courtesy of Prof. M.G.D. Geers, Eindhoven University of Technology) has shown that a parallel-beam WDS on SEM is a powerful tool for distinguishing phases with only low but distinct carbon contents. In the investigated steel, martensite with carbon contents of 0.3 wt% can easily be distinguished by means of mapping from ferrite with carbon contents of 0.01 wt% (Fig. 1). We experienced that instantaneous carbon contamination is a severe problem during measurement. Advisable prerequisites for high quality carbon determinations are therefore: (1) strictly oil free vacuum, (2) a plasma cleaner, (3) an air jet, and (4) a cool finger (LN2).