Response Characteristics of Thick Film Sensors Using Nano ZnO:Ni for Hydrocarbon Gas

Abstract

The effects of a Ni coating on the sensing properties of nano ZnO:Ni based gas sensors were studied for <TEX>$CH_4$</TEX> and <TEX>$CH_3CH_2CH_3$</TEX> gases. Nano ZnO sensing materials were prepared by the hydrothermal reaction method. The Ni coatings on the nano ZnO surface were deposited by the hydrolysis of zinc chloride with <TEX>$NH_4OH$</TEX>. The weight % of Ni coating on the ZnO surface ranged from 0 to 10 %. The nano ZnO:Ni gas sensors were fabricated by a screen printing method on alumina substrates. The structural and morphological properties of the nano ZnO : Ni sensing materials were investigated by XRD, EDS, and SEM. The XRD patterns showed that nano ZnO : Ni powders with a wurtzite structure were grown with (1 0 0), (0 0 2), and (1 0 1) dominant peaks. The particle size of nano ZnO powders was about 250 nm. The sensitivity of nano ZnO:Ni based sensors for 5 ppm <TEX>$CH_4$</TEX> gas and <TEX>$CH_3CH_2CH_3$</TEX> gas was measured at room temperature by comparing the resistance in air with that in target gases. The highest sensitivity of the ZnO:Ni sensor to <TEX>$CH_4$</TEX> gas and <TEX>$CH_3CH_2CH_3$</TEX> gas was observed at Ni 4 wt%. The response and recovery times of 4 wt% Ni coated ZnO:Ni gas sensors were 14 s and 15 s, respectively.