Course notes
57
In the oxygen partial pressure domain where the concentration of no electronic
charge carrier dominates, we obtain
J
4F L
RT
O
2
e
(1)
h
(2)
2
σ
σ
=
+
`
j
Experimentally (fig. 19), we measure the specific oxygen flux J O 2 given by
J
V
D
P
P S
L
O
m
e
2
Δ
=
#
#
where D is the gas flow, V m is the molar volume of the gas, ΔP is the variation
in pressure due to the enrichment of the most-oxygen-deficient gas, P e is the
total pressure of the gas at the entrance, L is the sample thickness, and S is the
surface area of the sample.
YDULDEOH3 2
3 H IL[HG
VDPSOH
¨3
IORZPHWHU
XSVWUHDP
JDXJH3 LQ
GRZQVWUHDP
JDXJH3 RXW
2 SXPS
Figure 19 – Schematic diagram of experimental cell
for measuring flux specific to electrochemical semipermeability.
Determining the electronic transport numbers t e and t h requires measuring the
total conductivity and calculating the electronic conductivities from the flux
due to electrochemical semipermeability.
2.2.6 – Blocking electrode method
The principle is based on measuring, in a mixed ionic-electronic conductor
(MIEC),
2 the ionic conduction alone by using an electron-blocking electrode made
of a purely ionic conductor, or
2 the electronic conduction alone by using an ion-blocking electrode made
of a purely electronic conductor.