Computed X-ray powder diffraction patterns for ultrasmall zeolite crystals

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. (orig.)