SPIN-COATED THIN-FILMS OF SIO2-WO3 COMPOSITES FOR DETECTION OF SUB-PPM NO2

Thin films of SiO2-WO3 composites with various SiO2 contents (0-20 wt% ) were prepared by means of sol-gel method. The grain size of WO3 decr eased with increasing SiO2 content, resulting in an increase in NO2 se nsitivity. On the other hand, the response transient to NO2 was brough t to be the quickest at 5% SiO2. The thin film of SiO2 (5%)-WO3 was fa r more sensitive to NO2 than the thin film or sintered block of pure W O3. It could detect dilute NO2 (0.1-2 ppm) in air at 350 degrees C sen sitively and fairly selectively. The NO2 sensing characteristics were stable over the whole test period of 10 days. (C) 1997 Elsevier Scienc e S.A.