Large-Area Quantitative Phase Mapping
phases were found (14 in all). If desired, additional information such as parent-child phase composition of a particular grain and locked and liberated percentages may be extracted. Analysis of a ceramic composite T ere are applications where image analysis plus EDS phase typing is not even practical. In this next example, large-area COMPASS phase mapping was applied to the analysis of a complex ceramic composite. Figure 8 shows the area analyzed was just under 1 mm 2 , at 4,096 pixels on each side with a square pixel size of 0.24 µm. Data were collected until an average of 120 X-ray counts per pixel was attained. T e collection rate was 200,000 stored X-ray counts per second. Total collection time was approximately 3 hours. Figure 8a shows the BSE image for this ceramic composite. As in the previous example, however, the X-ray element maps ( Figure 8b ) provide only qualitative information about the large area analyzed. The COMPASS phase map in Figure 9 , with the phases identified and classified by their majority components in Table 3 , provides a better quantitative phase analysis of this engineered ceramic composite. The relative areal coverage of each identified phase is included in Table 3 . Carbon accounts for approximately 40% of the analyzed area of the composite. The quantitative results indicate that the 11 non-carbon phases of the composite are metals, metal-oxides, sulfides, or sulfates. The elemental EDS maps ( Figure 8b ) qualita- tively support this observation. While the phase map has been instructive and aesthetically pleasing, the results in Table 3 provide the detailed quantitative results upon which engineering decisions can be made. In this way, tabular results may be more valuable than the overlaid color phase maps themselves.
Discussion T e phase analyses here by COMPASS soſt ware demonstrate the capability of identifying and quantifying phases of interest within a material with no user bias and no apriori knowledge of the material. Other techniques are either prone to incomplete results, such as EDS element-based phase typing of regions selected after image contrast thresholding, or require X-ray acquisition times that are not practical, such as element-based or spectrum-based phase mapping techniques. While electron imaging plus spot-mode analysis may not be as accurate as COMPASS phase mapping, a logical question is whether the former technique holds a speed advantage.
In the crushed rock sample
analyzed in Figures 1 through 7 , the EDS data was collected in single frames of 512x384 pixels for a frame time of 30 seconds. At 500,000 X-ray counts stored per second, this resulted in an average of 76 X-rays per pixel. T is was suffi cient to create the COMPASS phase map displayed in Figure 7 with a 2 µm pixel size. The
Figure 7 : Large-area COMPASS phase map created by stitching together a 3×3 array of image fi elds like that in Figure 1 . Here each color is a distinct phase as shown in Table 2 . The time to collect and analyze the phases here was 270 seconds. Image width = 3.1 mm.
complete large area phase map was analyzed in 30 seconds × 9 frames = 270 seconds. T e productivity of COMPASS phase mapping can now be contrasted with the productivity of using the electron- image contrast to identify the grains of interest followed by EDS spot-mode analysis within each grain for phase typing as shown in Figure 2 . For the latter technique, the image acquisition of a single frame of suffi cient imaging resolution would take between 2 to 5 seconds. T is collection time depends on the effi ciency of the BSE detector and the acquisition parameters of the electron microscope. T e subsequent spot-mode analysis—assuming the need for 5,000 X-rays per spectrum for basic elemental typing of the grain and the defi ned collection rate of 500,000 X-rays per second—is roughly 10 milliseconds per grain times the number of phases in that grain (this method detected only 4 mineral phases in Figure 2 ). For the 2,233 grains identifi ed in Figure 7 at 10 milliseconds per grain, it will take at least 22 seconds to type each phase. Some additional overhead to
Figure 8 : Large-area X-ray maps of an engineered ceramic composite (a) BSE image. Image width = 0.98 mm. (b) X-ray element maps from the area imaged in (a).
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