Oxygen depleted boundary layer

One of the principal objections centers on the nonlinear calibration curve for the determination of blood oxygen partial pressures. This resulted from the formation of an oxygen-depleted boundary layer near... 

D2, relative to the action of oxygen at the three boundary point. This depletion layer can be represented by a square parallelepiped of height x, of width 1 and of length L, with x y. 

Example 3 (Fig. 5.70c) illustrates a solid-gas contact, more precisely the contact between the n-type semiconductor Sn02 with O2 gas. At low temperatiures the adsorbed oxygen cannot penetrate the interior, but remains adsorbed on the surface. It traps electrons from the boundary layer and makes this positively charged, producing a depletion layer of increased resistance. This is the basic principle of the Taguchi sensor, which we will discuss later. Such effects must also be discussed at elevated temperatmes when phase equilibrium with oxygen is established. 

Besides, our model allows a depletion layer to appear, liitked to an electron transfer which, contrary to the electronic mechanism described by Yamazoe, is not located perpendicularly to the metal, but at the three boundary poiirts. As in Figure 10.36, the intensity of the induced depletion is greater than the depletion provoked by the adsorption of oxygen on the oxide alone. 

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