Segmenting the image set utilizes standard image processing arithmetical and logical operations to code criteria for constituent identification based upon the BE and XR image intensities. For example, in the backscattered electron image, the ferrite phase is brightest, and is discriminated via image processing using the operation: 245 if (BE_IMAGE> 240) ELSE O. This creates a binary image with intensity 245 if a pixel in the BE image is greater than 240 while zeroing pixels not meeting that criteria. If free lime is present, it may overlap the BE intensities of ferrite. In this case, high signal levels in the calcium image and bright BE image regions may be combined to effect the separation.
Alite is second brightest component and can usually be discriminated using the BE image. The belite gray level range generally overlaps that of tricalcium aluminate. This initially appeared to provide a problem but, as tricalcium aluminate and belite are chemically distinct, the aluminum XR image is used to threshold both tricalcium aluminate and ferrite; subsequently the ferrite portion is subtracted using the ferrite image created as described above. The resulting tricalcium aluminate binary may then be subtracted from the belite/ tricalcium aluminate composite image to provide an image of belite distribution.
Alkali sulfates are regions of K and S, or Na and S, or K and Na and S, depending upon the phases present. Calcium sulfates (gypsum, bassanite, anhydrite) are the S-bearing regions not associated with the alkalies. Re-examination of these regions in the BE image may allow further discrimination into the calcium sulfate forms based upon their BE intensities. Periclase is identified by a high Mg content and dark backscattered image signal. Supplementary materials are taken on a case-by-case basis utilizing data collected on their chemistry. Slag has a high Mg and moderate Ca, calcined kaolin has aluminum and silicon, while multi-component fly ashes are generally more complex.
Fig. 7 (upper) provides images of the segmented phases for alite, belite, tricalcium aluminate, ferrite, gypsum, periclase, and alkali sulfate. In the center is the backscattered electron image, for comparison, and be low this is a composite image showing locations and boundaries of all the phases. The lower portion of Fig. 7 shows the composite image at a larger scale reconstructed so that each of the phases is displayed in its own false color. The black areas are epoxy-filled spaces.
Fig. 7. Segmented phases (upper image set) and merged into a composite image ready for area analysis (lower). Field width, 150 µm.