Electrical conductivity study on synthetic faujasites type X and Y

Abstract

The electrical conductivity of synthetic zeolites, types X and Y has been studied to give information about the distribution and possibility of migration of the exchangeable cations, located at various sites. The Na⁺ samples were exchanged with K⁺, Cs⁺, Ag⁺, Li⁺, and NH₄⁺. The various cationic forms were pressed into pellets and treated at 430°C under high vacuum for 24 hours. After cooling, the electrical conductivity and capacity was measured as a function of frequency (500–20,000 c/s) at various temperatures from −20°C up to 500°C. For each sample the reversibility was investigated. The experimental results allow the calculation of the specific conductivity, the real (ε′) and imaginary (ε″) part of the complex dielectric constant (ε*) and the loss factor tgδ.The results show an ionic conductivity: the specific conductivity depends on the nature of the exchangeable cations as follows: Cs⁺ > K⁺ > Ag⁺ > Na⁺ > Li⁺. There is a different conductivity mechanism in the high temperature region compared with the low temperature region. At high temperatures (T > 400°K) the activation energy is independent of frequency. At low temperatures, a dielectuc absorption phenomenon occurs. The activation energy, calculated for this process was somewhat higher, but of the same order of magnitude as that of the high temperature region. It is suggested that the migration of the exchangeable cations in the supercage to interstitial positions gives rise to this dipole absorption phenomenon.A comparison of the decationated Y zeolites with Na⁺Y and Na⁺X made it possible to attribute the conductivity to the cations in the supercage only. The exchangeable cations in the cubo-octahedra and in the hexagonal prisms lower the activation energy of the moving cations. Thus the energy of activation of X zeolites is lower than of Y zeolites.