Multiphase analysis with EDX elemental maps:: software implementation and application to (Bi,Pb)2Sr2Ca2Cu3O10+δ high-Tc superconducting tapes

For the microstructural characterization of a large number of materials EDX elemental maps have proven to be indispensable, In this paper EDX elemental maps are used for determining quantitatively the phase fractions and grain sizes of secondary phases. Because of the anisotropic cross-section of (Bi,Pb)(2)Sr2Ca2Cu3O10+delta tapes, several elemental maps of adjacent specimen areas are mounted to a new single image reflecting the anisotropy and showing a larger area of the cross-section. For this application, elemental maps are combined as RGB images by a calibration procedure, which assures a single colour for the matrix material, i.e. (Bi,Pb)(2)Sr2CaCu2Odelta+delta/(Bi,Pb)(2)Sr2Ca2Cu3O10+delta, in all RGB images. These images are then processed by a numerical filter which (i) expands the grey scale from 5-6 bits as acquired to 8 bits and (ii) improves the statistical precision of the images by pixel condensation, Finally, the images are evaluated using the concentration histogram image (CHI) approach. In the CHIs apertures are drawn around the regions of highest intensity, each corresponding to a certain phase. The number of pixels within the aperture are counted for each phase. From these data the volume fractions of the phases are calculated and written to a file. The correct position and size of the apertures determines the quality of the obtained phase fractions. The implemented software yields intensity contour plots in the CHI which simplifies greatly the correct positioning and scaling of the apertures. The shape of the apertures can be either rectangular, elliptic or irregular, i.e. user defined, In the applications shown in this paper only user defined apertures were used. The software for image processing was implemented in the COREL 7.0 script language on a WINDOWS operating system. The implemented scripts offer a large number of indispensable features not covered by other software. In addition the data can be acquired, processed and displayed on a single platform, i.e. MS Windows(TM). This configuration yields quick data transfer via the dynamic data exchange interface both of the images acquired by a LINK ISIS EDX system and the calculated output data. This method has been applied to high-T-c superconducting (Bi,Pb)(2)Sr2Ca2Cu3O10+delta tapes and clearly demonstrates that a new quality has been established for the characterization of this material. The tapes are strongly textured and have secondary phase fractions of < 5 vol%. The limitations, errors and minimum detectable phase fractions are specified for the investigated material. The minimum detectable phase fraction by EDX elemental mapping was found to be 0.1 vol% and is tower by an order of magnitude compared to X-ray diffraction. The method could still be improved by a more sophisticated handling of pixels containing contributions of two phases. (C) 1999 Elsevier Science Ltd. All rights reserved.