GAS-SENSING PROPERTIES OF DIFFERENT ALPHA-SNWO4-BASED THICK-FILMS

Screen-printing technique has been used to fabricate alpha-SnWO4 thick films on alumina substrates. alpha-SnWO4 powder was prepared by heati ng an equimolar mixture of SnO and WO3 powders both in vacuum-sealed s ilica tubes and in argon atmosphere at 600 degrees C for about 15 hour s. Screen-printed thick films were sintered in air for an hour at diff erent temperatures between 550 degrees C and 850 degrees C in order to get different mixed-oxide structures from the partial decomposition o f alpha-SnWO4. X-ray diffraction and EDS (Energy Dipersive Spectroscop y of X rays) have been used for the characterization of the phase stru cture and composition of the films. The electrical conductivity togeth er with gas-response properties of the films was measured at different temperatures between room temperature and 500 degrees C. H2S, H-2, CO , CH4 and SO2 at different concentrations in synthetic air were used a s test gases in the measurements. The powder fused in vacuum had bette r gas-response properties than that fused in argon atmosphere. The sin tering temperature of screen-printed thick films was found to affect t heir gas-response properties, with an optimum sintering temperature at 550 degrees C. The alpha-SnWO4 phase alone in the films showed both h igh sensitivity and selectivity to low concentrations of H2S at temper atures between 150 degrees C and 300 degrees C.