Exercises
125
(YSZ) implies that the oxygen flux does not reach the electrode consisting
of the platinum layer on the YSZ micro-point. We thus consider that the
platinum electrode is in equilibrium with the environmental pressure P O 2 .
The platinum micro-electrode in contact with the oxide measures the oxygen
activity at the oxide surface. Qualitatively graph the potential across the
electrochemical chain.
4. The partial pressure of the gas in contact with the points is fixed at 0.5 # 10
−6
bar.
Determine the pressure P *
O 2 given that the potential difference measured between the two platinum wires is 40 mV at 1 452 °C.
5. Taking into account the oxygen activity at the surface of the membrane,
the semipermeability flux at the surface of membrane P* is linear (fig. 53).
Based on this figure, evaluate the oxygen flux at 1 425 °C if P 3 = 0.2 bar
and P 1 = 0.5 # 10
−6
bar.
6. Give the expression for semipermeability flux as a function of electronic
conductivity of the electrolyte on each side of the membrane if P 3 is much,
much greater than P 2 .
7. Evaluate the electronic conductivity for a 4-mm-thick tablet.