Nitrogen oxides-sensing characteristics of WO3-based nanocrystalline thickfilm gas sensor

TiO2 added tungsten trioxides with grain size of about 3 nm, were synthesiz ed by sol-coprecipitation of WCl6 and TiCl4 solution with ammonium hydroxid e and surfactant. Tungsten trioxide and titanium oxides were also synthesiz ed by sol-precipitation from WCl6 and TiCl4, respectively. After calcining these materials, the thick film sensors were fabricated by the screen-print ing technology. These materials were investigated about the characteristics of their structural properties by means of X-ray diffraction (XRD) measure ments, the surface morphology by the SEM photography and specific surface a rea by the BET method. The grain size of precursor obtained by coprecipitat ion 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 f ilms showed higher sensitivity to NOx over wide temperature ranges, than th ose 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 import ant 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, an d good selectivity at 350 degrees C. (C) 1999 Elsevier Science S.A. All rig hts reserved.