HUMIDITY SENSORS USING MANGANESE OXIDES

Unique humidity sensing properties of electrolytic manganese dioxide ( EMD) and its calcination products (Mn2O3 and Mn3O4) were investigated. These oxides gave resistive type elements which reduced d.c. resistan ce on exposure to humidity at room temperature. The humidity sensing b ehavior was strongly dependent on the oxides, reflecting the differenc es in microstructure. The use of a mixture of these oxides (hybrid sys tem) was found to be effective for optimizing humidity sensing perform ances not only in d.c. mode but also in a.c. mode. The elements attach ed with a pair of Pt and Cu electrodes, on the other hand: showed resp onse to humidity in EMF mode in the high relative humidity (RH) range above 60%. This suggests that proton conduction in the oxides increase s with increasing RH, becoming comparable to or larger than electronic conduction at high RH. The EMF response was discussed on an electroch emical cell model constructed on a mixed conducting diaphragm. (C) 199 8 Elsevier Science S.A. All rights reserved.