MICROSTRUCTURE AND ELECTRICAL-PROPERTIES OF AN ALPHA-HEMATITE CERAMIC HUMIDITY SENSOR

Alpha-Hematite porous ceramic material has been investigated as a humidity sensitive material, responding in the 0-95% relative humidity (r.h.) range. Alpha-Hematite powders, with controlled microporosity, were obtained through the topotactic decomposition reaction of alpha-goethite and sintered at 50-degrees-C steps in the 850-1100-degrees-C range. SEM, TEM and Hg intrusion porosimetry techniques were employed in the microstructural characterization of the sintered compacts. The electrical response was investigated by means of the volt-amperometric technique, at 300 frequency Hz and 1 V(pp) signal generator, in the 0-95% r.h. range. The use of different types of electrode configurations showed that the electrical response was largely affected by their geometry. The humidity sensitivity and the response time were also found to be influenced by the microstructure, i.e. by the sintering temperature. All the results are highly reproducible.