Tungsten oxide is an idea material for NO2 sensing. It has been reported that tungsten oxide based gas sensors exhibit excellent NO2 sensing properties to cover environmental standard of NO2. The experts have done researches to investigate several properties of nano crystallites of tungsten oxide including NO2 sensing characteristics.
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In this study, an aqueous sol dispersing nano crystallites of WO3·2H2O was subjected to a centrifugal treatment for 1 or 10 h, to obtain two kinds of WO3·2H2O gels with very different morphology of crystals. The WO3 thick film devices fabricated with these gels were investigated to find that the devices prepared under proper conditions exhibited excellent NO2 sensing properties to cover environmental standard of NO2. The sensitivity to NO2 as well as the rate of response depended markedly on calcination temperature of the devices. The morphology of WO3 crystals, i.e. lamellae or disks, was almost the same as that of WO3·2H2O gel unless calcination temperature exceeded 500 °C. Based on the surface analysis using N2 adsorption technique, the above changes were estimated to result from a change in microstructure of the WO3 crystals.
