90
2 – Methods and techniques
Numerical evaluation gives
6.29
0.755
t
σ =
0.12 S cm
t
1
σ =
−
5. The expression relating the electronic conductivity to the specific oxygen
flux measured by semipermeability is
RT
4 F
J
h
2
S,O 2
σ =
#
RT
4 F
J
8.314 823
4 96 480
6.49 10
h
2
S,O
2
10
2
σ =
=
−
#
#
#
#
3.53 10 S cm
h
3
1
σ =
−
−
The electronic transport number t h is
t h
t
h
σ
σ
=
#
.
.
t
0 12
3 53 10
h
3
=
−
#
.
t
29 10
h
2
=
−
The relatively high electronic transport number should decrease the potential
difference calculated in question 3.
Solution 2.9 – Determination of conduction mode in α-AgI
by Tubandt method
1. 2 The first two observations allow us to conclude that the electronic transport number in α-AgI is negligible (t el ≈ 0),
2 the constant mass of pellet C indicates that the anionic transport number
in α-AgI is negligible (t an ≈ 0),
2 the mass variations in the anode and the cathode indicate that α-AgI is
a purely cationic conductor (t c ≈ 1).
2. The variation in mass is given by
m
F
Q M
F
It
M
Ag
Ag
Δ =
=
m
96 480
0.1 3600
107.9
Δ =
#
#
m 402.6 mg
Δ =