Detection of DEMP vapors using SnO2-based gas sensors:: understanding of the chemical reactional mechanism

Tin dioxide-based gas sensors make it possible to detect diethyl methyl phosphonate vapors (DEMP). However, the responses present drifts that can be observed vs. time. Such a problem raises the question of the reliability of these devices. The results presented in this article are two-fold: first, they are concerned with the study of the thermal degradation of DEMP by thermal degradation in an oxidizing atmosphere, and second, they are involved in the characterization of the chemical degradation on the tin dioxide-based gas sensors. Gas chromatography and infrared spectroscopy shows that, from 300 degreesC on, the thermal degradation of DEMP leads to the formation of ethylene (gas phase) and ethyl methyl phosphonic acid (condensed phase). Given that thermal degradation may occur at the sensor's surface, which can reach temperatures as high as 500 degreesC, these results showed that responses obtained using the DEMP vapors are principally due to ethylene and the drift in the responses vs. time is probably due to the adsorption of phosphorous compounds to the sensor's surface. The aim of this article is to describe the reactional mechanism of the DEMP interaction at the surfaces of tin dioxide-based sensors for temperatures ranging from 200 to 500 degreesC. (C) 2003 Elsevier Science B.V. All rights reserved.