Humidity sensor based on zeolite for application under environmental conditions

Abstract

This work evaluates two different zeolite-based humidity sensors. In the first case, interdigital capacitive sensors (IDC-S) were fabricated on the surface of Al2O3 ceramic substrates, using electrode gaps of 20 μm, and were coated with films of LTA-type (Lind Type A) zeolite with Si/Al ratio of 1.28. Complex impedance spectroscopy (IS) was used to measure the sensor response, which was related to the change in capacitance of the interdigital electrodes and, in turn, to the electrical properties of the zeolites. The zeolite-based sensors were characterized in terms of the effects of changes in humidity and temperature on the sensor response.The results showed that this sensor provided detectable capacitance changes at very low water contents (up to 300 ppmv of H2O in N2), at temperatures ranging from 25 to 100 °C, and was therefore suitable for moisture trace measurements.In the second part of the work, evaluation was made of a humidity sensor based on ZSM-5 (Zeolite Socony Mobil - 5) zeolite. Interdigital capacitive sensors were fabricated on the surface of Al2O3 ceramic substrates, with electrode gaps of 20 μm, and were coated with films of ZSM-5. The results showed that the sensor was capable of good performance (detection limit of ∼7.32% RH) and was suitable for use under a broader range of environmental conditions (∼39% RH - 96% RH), compared to sensors based on other materials such as polyimide (detection limit of 20% RH) and TiO2 (detection limits from 10% to 30% RH).