Theoretical X-ray diffraction patterns have been calculated for powders of very small faujasite (FAU) and ZSM-5 (MFI) crystallites. These calculated patterns give the first realistic picture of the expected appearance of X-ray powder diffraction patterns of ultrasmall crystals of these well known commercial zeolites. The X-ray patterns were calculated using SKIP – small-crystal interference program – a program originally written to assist in the interpretation of X-ray diffraction patterns of synthetic zeolites and layered materials. The results are somewhat surprising in that they suggest that the crystallite size of faujasite must fall to below 4–5 unit cells before the resulting pattern diverges significantly from the asymptotic pattern. In contrast, the calculated X-ray pattern of ten-unit-cell ZSM-5 crystallites is scarcely recognizable.
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Schlenker et al. (1996) studied this question.