What is rock analysis?
Rock analysis provides important information regarding a rock’s composition and is utilized in both academic geology as well as in petrochemical, steel, ceramic, and automotive applications. Modern techniques seek to determine not just a sample’s bulk composition, but also its homogeneity and micro-scale structure. Energy-dispersive X-ray spectroscopy (EDS) is a critical tool for this analysis, as it can provide large-scale quantitative mapping of rocks, revealing microscopic phases across the entire sample.
Why use energy-dispersive X-ray spectroscopy?
Modern EDS X-ray analysis is capable of automatically acquiring EDS hyperspectral datasets over entire samples without needing to be monitored by an analyst. From this data, various maps can be extracted including qualitative and quantitative elemental distribution maps and phase maps. Here, large area, standards-based quantitative EDS mapping was applied to a monzogabbro rock sample in order to determine the possibilities and challenges of such large-scale analysis.
Large-scale quantitative EDS mapping
A monzogabbro rock sample was mounted in epoxy, ground, and polished. A field-emission scanning electron microscope (FE-SEM) with a Thermo Scientific UltraDry EDS Detector was then used to analyze the sample surface, and the resulting EDS data and images were processed using Thermo Scientific Pathfinder Software.
As is evident in the figure below, there were quite a few regions that did not contain sample, representing the mounting epoxy or the fracture space. Dynamic templates for EDS data acquisition were used to avoid collecting data at these pixel positions to expedite data collection.
The resulting peak shapes in the EDS spectra were evaluated using standard spectra for all elements except Al and Fe. Standards were used for quantification except in the case of F, P, S, Cl, Cr, Cu, Y, and Zr where standardless quantification was used because appropriate EDS standards were not available; oxygen was calculated by stoichiometry.
Driving novel advances with quantitative surface characterization
SEM-EDS instrumentation, combined with cutting-edge analytical software such as Pathfinder X-ray Microanalysis Software, enables quantitative elemental mapping at the micro-scale across entire samples, even with the rigor of standards-based analysis. Notably, while it was applied to rock analysis in this case, many other industries could benefit from accurate, large-scale EDS mapping, including materials science, ceramics, metals, and even semiconductor manufacturing. Any application in which compositional information is needed at the micro-scale across relatively large samples.
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Stephen M. Seddio is a product specialist at Thermo Fisher Scientific.