Dielectric properties of faujasites: comparison between types X and Y during dehydration

The dielectric properties of two faujasites, X and Y, were studied in a wid e range of frequencies (10-10(6) Hz) at several temperatures and for variou s outgassing temperatures TT (100-400 degrees C). Conductivity measurements were undertaken with the aim of describing the possible mechanisms of cond uction in these materials. The polarization conductivity is ascribed to the cations in the large cages (supercages). The d.c. conductivity is related to the migration of the exchangeable cations over relatively large distance s. The corresponding activation energies vary from 0.58 to 0.9 eV for NaX a nd from 0.61 to 0.85 eV for NaY. These energies vary with TT in a different way for each zeolite. Two relaxation domains, attributed to the cations on sites II and III', are a function of the dehydration temperature. The acti vation energies are 0.41-0.58 eV. These two processes are shown by the tech nique of the thermally stimulated currents-relaxation map analysis. (C) 200 0 Elsevier Science B.V. All rights reserved.