Impedance spectroscopy at dielectric gassensors

Intercligital capacitors (lDC) with gassensitive coatings are frequently used as gassensors. In this work organically modified silicates (heteropolysiloxane, HIPS) as gassensitive coatings were investigated with impedance spectroscopy. The investigated dielectric gassensors are thin film IDCs on a silica glass substrate. Coated with a HPS film, the sensors have a high sensitivity to S02 (ranges 1-200 vpm and 10-6000 vpm) and a low cross-sensitivity to other gases. An electrical relaxation model for the sensitive film of these IDCs was developed. The electrical relaxation of the bulk of the sensitive layer and the adsorbed gases is very similar to a Debye dipolar relaxation. A first attempt was made to describe the electrode processes with a Warburg impedance and a double layer capacitance. The electrode processes and gravimetric adsorption isotherms indicate that S02 is absorbed into the bulk of the sensitive layer. Another result is that electrode processes could be one reason for the irreversible adsorption Of S02.