Dielectric studies of zeolite systems. Part 2.—Ag-X zeolite with dipolar and non-dipolar absorbates

Abstract

Studies have been made over the range 6 Hz to 130 kHz and 170 to 450 K of dielectric absorptions in Ag-X zeolite evacuated at 10^–5 Torr and 520 K and also with controlled contents of H₂O, NH₃, CH₃CN or C₆H₆: adsorption isotherms were measured simultaneously. Introduction of a Teflon film with the compacted dielectric disc gave blocking-electrode conditions when the d.c. conductance was disturbingly large. In addition to this d.c. ionic conductance a separate dielectric absorption (I) was measured in the zeolite itself and further distinct processes, absorption II and III were characterized both in frequency and intensity (via Fuoss–Kirkwood parameters) and in activation enthalpy and entropy terms (via Eyring parameters). Processes I and II arise from ion-jumping within the lattice and are discussed in relation to their most probable mechanisms. Absorption III in Ag-X/H₂O is due to H₂O reorientation: it appears (sharply) at H₂O contents above 160 molecules per unit cell and has an effective strength (µ_eff≈ 1.8 D) equivalent to that of the free H₂O molecule.