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 volume and 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.
Kan-Sen Chou received his bachelor degree from National Taiwan
University in 1972 and doctoral degree
from Iowa State University Hsinchu , Taiwan
Tzy-Kuang Lee obtained his master degree from Chemical Engineering Department of NTHU in 1997. He carried out most of the experimental work reported in this article.
Feng-Jiin Liu is now both a doctoral candidate at Chemical Engineering Department of NTHU and also an instructor of Chemical Engineering Department at National Lien Ho College of Technology and Commerce,
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