Interpretation of the “intermediate frequency” dielectric spectra of synthetic zeolites X

Abstract

The dielectric spectra of synthetic zeolites X (13X and 10X) were studied in the frequency range 1 Hz-4 GHz at T=+ 25°C on samples hydrated at various rates. They all showed a distributed “intermediate frequency” relaxation domain. It is shown that the distribution can be explained by the superposition of a finite number of non distributed elementary domains; 3 in the case of zeolite 13X, 4 in the case of zeolite 10X. Each elementary domain is attributed to a population of cations existing in the zeolite. The relaxation mechanisms giving elementary domains are interpreted by jumps of cations from one location to another in a given site (S_I′↔ S_I′, S_II↔ S_II′, S_III′↔ S_III′). Analysis of the parameters characterizing the elementary domains (critical frequency, amplitude) allows the determination of the number, nature and location of the cations of each population of the crystalline lattice. These results are in agreement with those obtained by X-ray diffraction spectroscopy. The study as a function of the hydration rate allows the determination of the interactions between the water molecules adsorbed and the zeolite structure. The interactions with the surface are very strong for the first water molecules adsorbed. For hydrations higher than 15 molecules/cavity solvation of the cations can be observed.