WATER-ASSISTED AND THERMALLY-ENHANCED PROTONIC CONDUCTION IN HZSM-5, EFFECT OF GAMMA-IRRADIATION ON THE ELECTRIC PROPERTIES

Analysis of the a.c. conductivity of HZSM-5, in the 0.1-100 kHz frequency region and the 300-700 K temperature range, reveals semiconducting features based predominantly on an ionic mechanism. This is reflected in a low-frequency Cole dependence of the Z"(Z') impedance and in a linear dependence of the epsilon"(epsilon') dielectric constant throughout the temperature range. Thee zeolite Bronsted sites are the active centers responsible for the ionic conduction. As the conductivity drops to 373 K, sorbed water seems to participate in the conduction as a vehicle assisting the proton mobility. Above 373 K, the conductivity continues to rise as an indication of critical transition into a thermally enhanced ionic conduction. Both low-temperature sorbed water and high-temperature thermal motion are necessary to ensure a firm contact at the aggregate surfaces, where conduction takes place. Gamma-irradiation also participates in the conduction by creating new sites sensitive to the same parameters governing the conduction mechanism.