Large-Area Quantitative Phase Mapping
Figure 6 : Element-based phase map from the region analyzed in Figure 3 indicating the presence of fi ve mineral phases. Image width=115 µm.
by matching against a spectral library. In this example, careful manual thresholding of each of the element maps results in the identifi cation of the fi ve mineral phases implied from earlier visual observation of the X-ray element maps. T is falls short of the seven phases that were identifi ed by COMPASS ( Figure 4 ). For example, in this case, the pyrite (FeS 2 ) and chalcopyrite CuFeS 2 were not diff erentiated. However, the sphalerite (ZnFe)S was identifi ed as distinct from the pyrite (FeS 2 ). T e threshold for Zn was suffi cient to achieve diff erentation between chalcopyrite and sphalerite whereas the threshold for Cu was insuffi cient to diff erentiate between pyrite and chalco- pyrite. With enough eff ort, it may be possible to extract all 7 phases. However, the human interaction (and bias), the manual
eff ort, and the uncertainty involved create limitations for this technique.
Large-area phase mapping. Precision stage movements allow separate SEM image frames to be stitched together forming large-area images and maps. T is is how a large-area COMPASS phase map can be constructed ( Figure 7 ). Unlike the qualitative element maps shown in Figure 3 , the COMPASS large-area phase map can be fully quantifi ed. Each of the phases in Figure 7 may be put through the same sizing analysis typically performed on metallographic images. Information such as average area of each phase, % phase area, and average phase perimeter are easily extracted. Table 2 shows these results for the phase map in Figure 7 . Note that over the entire fi eld additional
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www.microscopy-today.com • 2017 March
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