THE EFFECT OF HUMIDITY ON TIN-OXIDE THICK-FILM GAS SENSORS IN THE PRESENCE OF REDUCING AND COMBUSTIBLE GASES

The effect of humidity on tin-oxide thick-film gas sensors has been st udied in the case of carbon monoxide, methane, methanol, butane and pr opane. The results are qualitatively explained under the assumption th at water molecules dissociate on the tin-oxide surface and produce hyd roxyl species capable of acting as electron donors. Moreover, palladiu m and vanadium, when used as additives, affect the overall behaviour o f sensors in the presence of water vapour. To reduce the effect of hum idity, thin organometallic films have been deposited on top of thick t in-oxide-based sensors in order to act as filters. The results show th at both the sensitivity of these sensors and the effect of humidity ar e decreased.