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Schlagwörter:
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Zusammenfassung:
Two simple analytical functions containing a single structural parameter are derived by consideration of boundary conditions for the so-called “column length distribution” of crystallites. Assuming spherically shaped crystallites the distribution functions of the diameters are derived. The type I distribution includes “atomic” dispersion while type II corresponds to a minimum crystallite size. The use of such functions, rather than the application of the Warren-Averbach analysis to X-ray line profiles, is shown to be favoured in the case of highly dispersed and unstrained supported metal catalysts. These functions fit the line profiles of a series of Pt/SiO2 catalysts extremely well. For these catalysts the type I distribution gives the best fit at low dispersion levels dH of 6 and 21%, whereas for dH = 40% crystallite dispersion of type II seems normal. Additionally the related X-ray dispersions dX have good correlation with the hydrogen chemisorption values dH.
