A NOVEL STRUCTURE FOR DETECTING ORGANIC VAPORS AND HYDROCARBONS BASED ON A PD-MOS SENSOR

The maximum operating temperature of MOS gas sensors is limited to about 250 °C. Therefore only hydrogen and several hydrocarbons like acetylene or alcohols like ethanol can be detected with these sensors. At these low temperatures there is mainly a high sensitivity for hydrogen, which is also responsible for the sensitivity to the other substances, when it is catalytically dissociated from their molecules at the sensor's surface. In this paper a Pd-MOS sensor together with a Pt-coil catalyst is presented. This Pt coil is mounted together with the sensor on one holder. The temperature of the coil can be increased to more than 1100 °C, while the Pd-MOS sensor itself it kept at a constant temperature between 100 °C and 190 °C. With this arrangement it is possible to detect trichloroethylene, acetone, i-butane, n-hexane, chloroform and ether. For all these substances there is no sensitivity without the catalyst. Furthermore it is seen that the sensitivity for acetylene, ethanol and methanol can be increased (about 200-300%). The experiments show that there are different 'threshold temperatures' of the catalyst for different gases. This effect can be used to analyse a multicomponent gas mixture by varying the temperature of the catalyst. © 1990.