Measuring oxygen concentration in automobile exhaust gas

摘要

A device for measuring the concentration of O2 has a solid electrolyte (12) with an inner electrode (132) on its inside to which a reference gas is fed and an outer electrode (131) on its outside to which the gas to be measured is fed. The outer electrode (131) has a protective layer (11) which consists of coarse particles with fine particles packed in between them and bonded with a metal oxide derived from an inorganic binder. The ratio of the mean particle size of the coarse particles RB to the mean particle size of the fine particles RA is /- 30 : 1 and the content of fine particles with respect to the total content of particles is between 15 and 80 wt.%. Also claimed are: (i) a device in which the protective layer (11) is formed by applying a slurry to the outer electrode (131) which is obtained by dispersing thermally stable coarse and fine particles in a liquid medium. The applied slurry is dried and the layer obtained is fired. The value RB/RA is /- 10 if ( epsilon x d)L is within the range of 20 x 10<-5> to 30 x 10<-5> where epsilon , d and L correspond respectively to a porosity, a mean pore size in mu m and a protective layer thickness in mu m; and (ii) a device in which the slurry is applied by deposition.