Basic investigations of the conductivity behavior of aluminosilicate zeolites were conducted in a gas atmosphere, using impedance spectroscopy under in situ conditions where so-called zeolitic water molecules were still present in the channel and cage system (figure 13). Natural zeolites of stilbite and phillipsite structure types were used for single crystal investigations, while natural compacted ‘ceramic’ phillipsite was used to clarify influences of polycrystallinity on conductivity. At a given water partial pressure, the effect of polar organic molecules on conductivity was investigated under isothermal in situ conditions. It could be shown that the observed interaction processes were mainly adsorptive and that catalytic oxidation of polar gaseous organic compounds was taking place at much higher temperatures, where the zeolite structures were already irreversibly altered and zeolitic water was almost completely desorbed. Dependent on different parameters affecting the zeolite single crystal conductivity behavior, a schematic model was developed to describe the features observed.

Influence of Ions and Molecules on Single Crystal Zeolite Conductivity under in situ Conditions. O.Schäf, H.Ghobarkar, F.Adolf, P.Knauth: Solid State Ionics, 2001, 143[3–4], 433-44

Figure 13

Conductivity of Monocrystalline Stilbite

(a: in contact with water vapour, b: in contact with liquid water)