P. Dutronc et al., A POTENTIALLY SELECTIVE METHANE SENSOR-BASED ON THE DIFFERENTIAL CONDUCTIVITY RESPONSES OF PD-DOPED AND PT-DOPED TIN OXIDE THICK LAYERS, Sensors and actuators. B, Chemical, 16(1-3), 1993, pp. 384-389
Derived from a concept suggested by E. M. Logothetis et al., Proc. 2nd
Int. Meet. Chemical Sensors, Bordeaux, France, 1986, p. 175, two diff
erential sensing devices, based on the different catalytic properties
of palladium and platinum, are proposed. The first one consists in cov
ering two screen-printed layers of pure tin dioxide by Pd and Pt-doped
filters. No major difference is observed between these sensors, proba
bly because of the lack of thickness of the screen-printed filters. In
the second device, tin dioxide is directly doped with palladium for o
ne sensor and with platinum for the other. The difference in the respo
nse to methane is now sufficient to consider the feasibility of a diff
erential device. However, such sensors have no long-term stability whi
ch can only be achieved by covering the layers with inert filters. The
se filtered SnO2:Pd and SnO2:Pt sensors, now satisfactory as far as di
fferential sensitivity and long-term stability are concerned, also exh
ibit an important differential response to ethanol, but fortunately re
verse to that to methane. The latter result enables a sensing device t
o be constructed which is selective to methane with respect to ethanol
, and insensitive to changes in relative humidity and/or gas flow.