Abstract
Porous ceramics made from ceramic fiber, kaolin and sodium salt of carboxylmethyl cellulose (CMC) was investigated as a humidity sensor. Ac impedance at a frequency of 100 Hz was utilized to measure resistance of samples under various humid atmospheres. The conductivity changed by about 4-5 orders of magnitude when the relative humidity (RH) varied from 10 to 90%. Other properties such as reproducibility and response time were also recorded and found satisfactory. The sensing mechanism was discussed based on their microstructures, such as surface area, mesopore volume and sodium content. In general, at low humidity, surface area and water adsorption plays the dominant role, while at high humidity, mesopore volumeand capillary condensation become important. Positive correlation exists between resistance and quantities of water taken up by the sample. Our results also indicated the key contribution from the extractable sodium at surface in promoting conductivity through water adsorption.