Positron lifetimes in pores of some low-silica zeolites: influence of water content, crystal size and structural type

Positron annihilation lifetime spectroscopy has been used for observation of the free voids in low silica zeolites, of LTA and FAU structure and different crystal size, before and after their heating at different temperatures below 200 °C. Sizes of crystals of the zeolite samples, as well as their structures and water contents, were characterized by X-ray diffraction, scanning electron microscopy, thermogravimetry, and particle size distribution measurements. The number of positron lifetime components as well as their values and intensities, after water removal from the zeolite structure, vary. However, changes are not uniform in all investigated zeolites. The differences are compared and discussed in the dependence of different structure types and crystal sizes of investigated zeolites.