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This part of EN 623 specifies a manual method of making measurements for the determination of volume fraction of major phases in advanced technical ceramics using micrographs of polished and etched sections, overlaying a square grid of lines, and counting the number of intersections lying over each phase. NOTE 1 This method assumes that the true phase volume fractions are equivalent to area fractions on a randomly cut cross-section according to stereological principles. NOTE 2 Guidelines for polishing and etching of advanced technical ceramics can be found in Annexes A and B. The method applies to ceramics with one or more distinct secondary phases, such as found in Al2O3/ZrO2, Si/SiC,or Al2O3/SiCw. If the test material contains discrete pores, these can be treated as a secondary phase for the purpose of this method provided that there is no evidence of grain pluck-out during polishing being confused with genuine pores. NOTE 3 If the material contains more than about 20 % porosity there is a strong risk that the microstructure will be damaged during the polishing process, and measurement of volume fraction of pores may become misleading. Secondary phase volume fractions or porosity present at levels of less than 0,05 are subject to considerable error and potential scatter in results. A larger number of micrographs than the minimum of three is normally needed to improve the consistency and accuracy of the results. NOTE 4 Many ceramics contain small amounts of secondary glassy phases. In order to make a reasonable estimate of glassy phase content, the glass material between crystalline grains should be readily observable, and thus should be at least 0,5 µm in width. The method in this European Standard is not considered appropriate for narrow glassy films around grains. This method assumes that the selected regions of a prepared cross-section are statistically representative of the whole sampled section.