Microporous ceramic coated SnO 2 sensors for hydrogen and carbon monoxide sensing in harsh reducing conditions

Abstract

The stability and sensing characteristics of SnO 2 sensors coated with amorphous microporous Si–B–C–N layers have been studied in oxygen free atmospheres. The synthesis of amorphous Si–B–C–N-ceramics has been realized through pyrolysis of poly(organoborosilazanes) in argon. The Si–B–C–N layers with the thickness of about 1 μm after single deposition/pyrolysis step are amorphous, crack-free and microporous with mean pore diameters of about ∼7 Å which is larger than the kinetic diameter of H 2 and CO molecules, allowing in this way their diffusion towards the bottom SnO 2 sensing layer. Transient response characteristics and sensor signals of uncoated SnO 2, 3 times and 5 times Si–B–C–N-coated SnO 2 sensors exposed to CO (10, 20 and 120 ppm) and H 2 (40, 400 and 900 ppm) in nitrogen at 350 and 530 °C are obtained. Uncoated SnO 2 sensor at 530 °C is irreversibly reduced to tin in H 2 while Si–B–C–N-coated SnO 2 sensors show reversible resistance changes while exposed to CO and H 2.