Abstract
This research is focused on structural and electrical characterisation of tin oxide (SnO2) applied as a thick film and investigation of its properties as gas sensitive material. Micron sized SnO2 powder was milled in an agate mill for six hours to fabricate SnO2 nanopowder, which was afterwards sieved by 325 mesh sieve and characterized by XRD and SEM. This powder was used as functional part in the production of thick film tin oxide paste containing a resin vehicle with 4 wt. % nanosize glass frits acting as permanent binder. The glass frits where additionally milled for twelve hours in the agate mills to nanosized powder and sieved by a 325 mesh sieve as well. The achieved thick film paste was screen printed on alumina and fired at 850oC peak temperature for 10 minutes in air. After the sintering process, thick film samples where characterized by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The reflectivity was measured on the same samples by UV-VIS spectrophotometer: the band gap was determined from the slope of reflectance. After that a matrix of different interdigitated electrode structure of PdAg paste was printed and sintered using the mentioned sintering conditions. The tin oxide thick film was printed over the interdigitated electrodes as a top layer and sintered again under the same conditions. The total electrical resistance was measured as a function of the electrode spacing and temperature. A negative temperature coefficient (NTC) was identified and measured in the range from room temperature (27°C) to 180°C in a climate chamber. Finally the samples were placed into a gas reactor with NOx and CO gas and the resistance was measured in the same temperature range (27°C-200°C).
Highlights
Solid state gas sensors are one of the most used and the most present type of gas sensors for commercial applications in auto industry, airplane industry, heavy industry, environmental monitoring etc
scanning electron microscopy (SEM) micrographs of SnO2 powder and thick film are shown in Fig 2 and Fig. 3, respectively, confirming the small grain size of both
Micron sized SnO2 powder was milled in an agate mill to fabricate SnO2 nanopowder, which was afterwards characterized by X-ray powder diffraction (XRD) and SEM
Summary
Solid state gas sensors are one of the most used and the most present type of gas sensors for commercial applications in auto industry, airplane industry, heavy industry, environmental monitoring etc. SnO2-based gas sensors have been the subject of much research [2] due to the advantage of a relatively low operating temperature, long term stability and low cost. In this work we have used milling as a simple, low cost method to reduce the grain size of the starting SnO2 powder and glass frit used in thick film paste.
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