Dielectric studies of zeolite systems. Part 1.—Na+Fe3+-Y zeolite with polar and non-dipolar adsorbates

Abstract

Under selected conditions studies have been made over the range 6 Hz to 140 kHz and 100 to 560 K of dielectric absorptions in Na⁺₂₃Fe³⁺₁₁-Y zeolite, first evacuated at 10^–5 Torr and 720 K, then with controlled contents of H₂O, NH₃, SO₂, CH₃CN, CO₂ or C₂H₄. Adsorption isotherms were measured simultaneously with a vacuum microbalance. 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 the d.c. ionic conductance a separate dielectric absorption (I) was measured in the zeolite itself and further distinct processes, absorptions II, III, IV were characterized both in frequency and intensity (via Fuoss–Kirkwood parameters) and in activation enthalpy and entropy terms (via Eyring parameters) for H₂O, NH₃, SO₂ or CH₃CN adsorbed species. Processes II and III arise from ion-jumping within the lattice: IV comes from hindered adsorbate polar molecule motion. Of these, only III was fully characterized and virtually unchanged for the non-dipolar adsorbates. The processes are discussed in relation to the known details of the zeolite structure.