Exercises
69
where D is the gas flow in compartment T, V m is the molar volume, ΔP is the
increase in oxygen partial pressure of compartment T (in bar), P t is the total
pressure in compartment T (in bar), ℓ is the thickness of the pellet, and S is the
surface area of the pellet.
1. Using cm as units of length, give units for the flux J S,O 2 .
2. Calculate the specific flux of oxygen for the following conditions:
Data
T = 550 °C  D = 4.25 # 10
−3
L s
−1
  ΔP = 1.932 Pa  ℓ = 0.2 cm
V m = 22.4 L mol
−1
  P t = 1 bar  S = 1.13 cm
2
3. In the steady state, the oxygen partial pressure at the entrance of compartment T is 5 # 10
−2
Pa and that of compartment CE is 0.21 bar (air). Calculate
the potential difference ΔE between the two compartments when the pressure
increase ΔP for compartment T is 1.932 Pa at 550 °C.
4. The total electric resistance R t of the solid solution was measured in air at
550 °C. The geometric factor k of the sample is 0.755 cm
−1
. The measured
resistance increases to 6.29 Ω. Calculate the total conductivity of the solid
solution.
5. Deduce the electronic transport number in air. What can we conclude about
the validity of the answer to question 3?
Exercise 2.9 – Determination of conduction mode in α-AgI
by Tubandt method
To determine the mode of conduction in silver iodide α-AgI, we use Tubandt
method with the electrochemical setup shown schematically in figure 26.
FRXORPHWHU
3W
$J
$
&
%
,
Figure 26 – Setup to measure transport number of α-AgI.