Large-Area Quantitative Phase Mapping
Table 2 : Quantitative results from the COMPASS phase map of Figure 7 showing size characteristics for the 14 distinct mineral phases found.
Phase
CaO (AlSi)O2 CaO FeO2 CaO CuS
CuFeS2 (ZnFe)S
CaO FeO2 SiO2 CaO TiO2 SiO2
CaO (MgFe)O2 SiO2 (FeMg)O2 SiO2 FeS2
KAlSi3O8 MgO SiO2 SiO2
Grand Total
Count of particles 103
13 23 40
511 76
187 67
181 295 344 101 19
273 2233
Total area coverage (microns2)
79389 15616 58745 20509
918454 136600 127029 88136
170915 202356 1024380 84203 64600
309742 3300674
counts must be present in the spectrum to properly type the selected region as a particular phase. Again, this is difficult for regions of similar composition and for regions where the presence or absence of an individual minority element may define a distinct phase. In order to gauge the X-rays required for reasonable elemental typing of phases within a region, three spectra from the chalcopyrite CuFeS 2 region are displayed in Figure 5 . The only difference in these spectra is the number of X-rays present. Figure 5 shows that the spectra from a single pixel, a selected region within the phase, and the entire chalcopyrite phase contain 162, 5,000, and 2,000,000 X-rays, respectively. The 162 X-ray spectrum is insufficient even for basic elemental identification because the Fe K-series peaks contain only a few counts, which could be spurious noise events, and because the Fe-L peak was misidentified as oxygen. The 5,000 X-ray spectrum is sufficient for basic elemental identification but not sufficient for quantitative analysis. The 2,000,000 X-ray spectrum is
% area coverage 2.4%
0.5% 1.8% 0.6%
27.8% 4.1% 3.8% 2.7% 5.2% 6.1%
31.0% 2.6% 2.0% 9.4% 100%
Average particle perimeter
121 241 301 107 244 48
113 130 139 118 195 121 236 144 172
sufficient for both elemental identification and rigorous quantitative analysis to determine the phase type. X-ray counts required for phase typing. It is noteworthy that COMPASS phase mapping was able to determine phase identities with so few counts in each pixel (76 counts per pixel). T is is particularly true when comparing it with traditional EDS X-ray element-based phase mapping, which requires quantitative analysis of elements in a spectrum image data cube containing several thousand X-rays per pixel. T e sparse spectrum in Figure 5a is clearly insuffi cient for element-based phase mapping. T is limitation is demonstrated by generating element-based phase maps from this data set ( Figure 6 ). T ese element-based phase maps are generated by defi ning one or more X-ray intensity thresholds for each of the element maps. T is thresholding technique is similar to that used in Figure 2 to identify regions of interest within the BSE image. T e combined thresholds from each element map are then used to determine areas of distinct elemental composition, that is, phases. T e phases are then typed by either inspecting the major elements present or
Figure 5 : Spectra from the chalcopyrite CuFeS 2 region of Figure 4. (a) A single pixel with 162 X-ray pulses. (b) An area with about 5,000 X-rays. (c) The entire CuFeS 2 phase with 2 million X-rays.
2017 March •
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