Electrolyte thoria , doped

By measuring the equitibrium EMF of this cell, Engell (1962) reported high positive deviation from ideality in this system. Seetharaman Abraham (1968) used a similar technique but used Thoria doped with Yttria as the solid electrolyte. They used the following cell... 

Doped zirconia, yttria and thoria Other oxides (magnesia, alumina, etc.) Electrolytic conductor Nonconductors... 

Figure 13.4 Electrolytic domains for calcia-stabilized zirconia (CSZ), yttria-doped thoria (YDT), and magnesia partially stabilized zirconia (MgPSZ) [47, 48],...

Thus, Wagner s theory can be used to predict how much oxygen will permeate the tube in any given time. If the tube material is predominantly an electronic conductor, this permeability becomes a measure of the chemical dlffuslvity for oxygen in the compound. However, if it is a solid electrolyte material, e.g., doped zirconia or thoria, the permeability is limited by electronic conduction. Thus, some of the best estimates of positive hole conductivity in the oxide solid electrolytes have come from "gas permeability" studies made on tubes of these materials. 

On the same diagram the electrolytic domains for calcia stabilised zirconia and yttria doped thoria is shown. There is a certain uncertainty on the exact limit of these domains. One can see for instance that for measurement in molten copper at say 1200 C, no problem with electronic conductivity of zirconia should be met down to an O2 partial pressure of 10 " atmosphere. On the other hand measurement in steel at I600 C appears to be limited to between 10 8 and 10 " atm. 

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