Gas-kinetic interactions of nitrous oxides with SnO2 surfaces

The kinetics of interaction of nitrous oxides (NOx) with SnO2 sensor surfaces were investigated. It is shown that NO, similar to CO, undergoes a simple reducing interaction with SnO2 sensor surfaces producing a conductivity increase. In comparison, NO2 was found to exhibit a highly complex behaviour. At surface temperatures lower than 200 degrees C, NO2 was found to reversibly oxidise SnO2 surfaces independently of the NO2 concentrations applied. In this latter case, reduced conductivities were observed. Approaching surface temperatures of the order of 400 degrees C, a reducing interaction took over which gave way to the normally observed oxidising behaviour as NO2 concentrations above 1 ppm were applied. In this latter high-temperature/high-concentration regime, poisoning effects were observed which caused the sensor resistance baseline to drift away. These latter results indicated that the poisoning effect of NO2 on SnO2 surfaces is associated with the formation of higher molecular species containing two nitrogen atoms at least. (C) 1998 Elsevier Science S.A. All rights reserved.