Nitrogen oxides-sensing characteristics of WO3-based nanocrystalline thick film gas sensor

TiO2 added tungsten trioxides with grain size of about 3 nm, were synthesized by sol-coprecipitation of WCl6 and TiCl4 solution with ammonium hydroxide and surfactant. Tungsten trioxide and titanium oxides were also synthesized by sol-precipitation from WCl6 and TiCl4, respectively. After calcining these materials, the thick film sensors were fabricated by the screen-printing technology. These materials were investigated about the characteristics of their structural properties by means of X-ray diffraction (XRD) measurements, the surface morphology by the SEM photography and specific surface area by the BET method. The grain size of precursor obtained by coprecipitation of TiCl4 (4 wt.%) and WCl6 was about 3 nm and that of WO3 precursor by simple precipitation was about 8 nm. TiO2 added WO3 nanocrystalline thick films showed higher sensitivity to NOx over wide temperature ranges, than those of pure WO3 or the simple mixture of WO3 and TiO2 powder. It was shown that the particle size and surface area of sensing materials make an important role of the sensing characteristics of WO3-based thick film sensor. The TiO2 added WO3 nanocrystalline sensor showed excellent sensitivity to low level NOx concentrations (0.5-30 ppm), fast response, recovery reaction, and good selectivity at 350 degrees C. (C) 1999 Elsevier Science S.A. All rights reserved.