Solutions to exercises
277
6. Figure 114 shows the general form of the response of an amperometric sensor
in contact with a gaseous mixture containing oxygen and water vapor. The
first step is associated with the oxygen limiting current and the second with
that of the water vapor. The current at which these steps occur is directly
related to the molar fraction of these species in the mixture.
Figure 114 – Form of response
of amperometric sensor in contact
with a gaseous mixture containing
oxygen and water vapor.
7. Drilling a small-diameter orifice in a controlled and reproducible manner
proves to be a difficult operation. To avoid this, the system may be improved
by depositing a porous layer on the cathode to act as a diffusion barrier
against the gas that is being analyzed (fig. 115).
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Figure 115 – Schematic of an amperometric sensor
in which the oxygen supply is limited by a porous layer.
Solution 5.12 – Coulometric oxygen sensor
1. We begin by extracting by electrochemical reduction all the oxygen from the
interior compartment. Under these conditions, we can write P
0
int
O 2 . . Next
we reverse the polarization and we measure the charge required to raise the
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