Fabrication of TiO2 coated metallic wires by the sol-gel technique as a humidity sensor

An humidity sensor based on a TiO2 coated metallic wire has been prepared by the sol-gel technique. TiO2 is deposited on a commercial Fe-based wire by dip-coating from alcoholic solutions of titanium tetraisopropylalkoxide. Several experimental conditions are studied as: the acid activation of the wire surface, the interaction of the wire with the titanium solution and the drying and calcination steps. The coating process is repeated four times to fabricate the final sensor. A capacitive humidity sensor was developed by sputtering deposition of a semicylindrical gold electrode on the TiO2 coated wire resulting from the coating processes. The sensing principle is based in the changes of the complex impedance of the capacitive device as a result of the humidity dependence of the electric permittivity of the TiO2 ceramic coating. The functionally of the sensor device can be expanded by the simultaneous characterization of the temperature dependence of the electric resistance of the inner metallic wire. (C) 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.