Phase Analysis Using EDS Data

Energy dispersive spectroscopy using spectral imaging acquisitions (SI-EDS) provides an improved analytical method for the characterization of SEM/EDS materials.

The Thermo Scientific NORAN System 7 X-ray microanalysis system with the option of direct-to-phase (DTP) combines a series of automated analytical operations which enables an SEM/EDS operator to capture an improved picture of the sample in a shorter time span than the traditional elemental mapping based techniques. The processing steps leading to the automatic complete description of the distribution and chemical description of every phase is described.

Background

All the important chemical features in a sample must be understood in materials analyses. To better understand the distribution and quantification of EDS data, the internal engine with the NORAN System 7 has been built around the acquisition and processing of SI-EDS data.

Selection of elements comes prior to the analysis in elemental mapping. The knowledge of the spatial distribution of the elements will be lost after the analysis. The SI-EDS provides a clearer understanding of the spatial distributions of features within a material than any other EDS technique. The elemental maps can be extracted from the data and displayed at any time even if an element is overlooked in the initial analysis as the SI-EDS acquisitions save a complete spectrum at each pixel location in the scanned area making the return to the data set to map a new element simple.

The Thermo Scientific Xphase software option is used for phase analysis of simple mixtures whereas for complex samples, the phase analysis method in Thermo Scientific COMPASS software option can be used. In the SI-EDS acquisition, we can run a multivariate statistical analysis (MSA) on the data. The hazards of initiating the analysis based on assumptions about its elemental composition are eliminated as input is required from the analyst.

The combined software gives phase distribution and spectral results for any sample that can be interpreted easily. But their generic nature requires some interpretation of the spectra to fully characterize and understand the localized phases that the software identifies. The SI-EDS spectra is used as the input to search against a user-defined database of named spectra. All of these steps can be performed in a semi-automatic or fully automatic sequence. The analysis does not require input on the part of the operator as the results will be identical no matter who runs the analysis.

The direct-to-phase (DTP) technique provides automatic chemical phase analysis during spectral imaging acquisition.

The elemental distribution mapping, spectral matching and the multivariate statistical analysis are combined and the most coherent picture of a material’s composition is displayed in the DTP analysis. This process can even be done during acquisition providing definitive and quick answers. An acquisition can be terminated when the composition of the phases reaches a designated threshold value. Little further interpretation is needed when the acquisition is complete and the data can be output to a report.

Results

The utility of the DTP routine and the improvement of the characterization of materials using the phase-based analysis are presented. The vertical full-scale (VFS) of the maximal spectrum of the whole acquisition and the maximum intensity of the simple X-ray map of the matrix material are shown in the measured values.

Known Phases of Metallic Wires

The utility of the DTP technique is shown using this sample as control experiment. Figure 1 shows analyses of the known phases of metallic wires of six elements.

Analyzing known phases of metallic wires

Analyzing known phases of metallic wires

Analyzing known phases of metallic wires

Figure 1. Analyzing known phases of metallic wires

It requires considerable time and expert analysis to determine the overlaps in the six elements. This essential information is identified by the DTP.

Phases with Heavy Peak Overlaps

The DTP routine has the capability to separate phases in situations where highly overlapped peaks in the cumulative spectrum of all phases exists (shown in Figure 2). Four distinct phases in the sample are isolated by DTP. A clear answer with highly overlapped peaks found in the spectrum cannot be obtained by simple phase techniques with elemental maps.

Analyzing phases with heavy elemental peak overlaps

Figure 2. Analyzing phases with heavy elemental peak overlaps

Phases with Similar Elements

Figure 3 shows a simple turbine blade material that has decomposed into three phases. The challenge is in separating the phases as all the four primary elements are in all of the phases. In simple elemental maps, the difficulty is in the selection of the proper elements to provide the phase information. As the selection of all elements does not usually provide good results, expert selection is required. The DTP routine identified and localized all the phases in the material even for low volumes.

Analyzing phases with the same elements

Figure 3. Analyzing phases with the same elements

Phases with Subtle Elemental Differences

The geological sample shown in Figure 4 is similar to the sample shown in Figure 3, but they are found in different proportions. The data was collected for a greater volume of X-rays due to the subtle composition differences between the phases in this sample. The acquisition time depends on the composition level of the unique elements of the important phases.

Analyzing phases with subtle elemental differences

Figure 4. Analyzing phases with subtle elemental differences

Summary

The determination of all of the unique phases within a sample is the primary importance in EDS analysis described from elemental maps. Relying on elemental maps will not present the full picture of the sample’s composition. Different chemical features can be investigated as the analysis and display of mapping data in various formats are possible with the SI-EDS acquisitions. The efficiency of the lab is increased as the calculations are performed during the idle time of computer in this phase analysis.

Conclusion

The stage for a richer understanding of the spatial distributions of material features is set by the SI-EDS acquisitions on the Thermo Scientific NORAN System 7 X-ray microanalysis system. The best EDS data is provided as all the tools necessary to perform phase analysis on both stored and real-time spectra imaging acquisitions with XPhase, COMPASS and Spectral Match are available with the DTP routine.

This information has been sourced, reviewed and adapted from materials provided by Thermo Fisher Scientific – Materials & Structural Analysis.

For more information on this source, please visit Thermo Fisher Scientific – Materials & Structural Analysis.

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