Abstract
Physicochemical properties of a gas sensor with the Pd-SiO 2-Si-based sensitive element with an external catalyst element (CE) have been investigated. It is shown that as a result of the homolytical splitting of carbon-carbon bonds in alkane molecules, MOS sensors showed sensitivity to propane and butane both in inert and oxygen containing atmospheres. The dependencies of the sensor's signals on the temperature of the CE was obtained for different gas mixtures containing H 2, CH 4, C 3H 8 and C 4H 10. The temperature of the CE (platinum coil) located above the sensor could be varied within a wide range (up to 1100 K in the air and 700 K in helium), while the temperature of the sensitive element was kept constant (463 K). A semi-empiric model describing the temperature dependence of the sensor's signal was suggested. The magnitudes of the activation energy of the dissociation methane (3.5 eV) and propane (1.1 eV) on platinum was determined. When the initial rate of change of the flat-band voltage of the MOS capacitor ∂Δ U|∂t∣ t=0 t = 0 was taken as the sensor's signal, a linear dependence of the signal versus the propane and butane concentration in air from 100 to 2000 ppm was obtained. A possibility of using pulse heating of the CE for the formation of the sensor's signal was demonstrated.
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