Microporous ceramic coated SnO2 sensors for hydrogen and carbon monoxide sensing in harsh reducing conditions

The stability and sensing characteristics of SnO2 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 mu m after single deposition/pyrolysis step are amorphous, crack-free and microporous with mean pore diameters of about similar to 7 angstrom which is larger than the kinetic diameter of H-2 and CO molecules, allowing in this way their diffusion towards the bottom SnO2 sensing layer. Transient response characteristics and sensor signals of uncoated SnO2, 3 times and 5 times Si-B-C-N-coated SnO2 sensors exposed to CO (10, 20 and 120 ppm) and H-2 (40,400 and 900 ppm) in nitrogen at 350 and 530 degrees C are obtained. Uncoated SnO2 sensor at 530 degrees C is irreversibly reduced to tin in H2 while Si-B-C-N-coated SnO2 sensors show reversible resistance changes while exposed to CO and H-2. (C) 2010 Elsevier B.V. All rights reserved.