Zirconia lambda

Coillard, V., Juste, L., Lucat, C. and Menil, F. (2000) Nitrogen-monoxide sensing with a commercial zirconia lambda gauge biased in amperometric mode. Meas. Sci. Technol., 11, 212—20. 

Figure 1,3 shows the trend in worldwide production levels of ionic conductor-grade yttria-stabilised zirconia over time. It is evident that in 1970 there was very small production at a rather high price. However, the introduction of the zirconia lambda sensor to control the emissions of automobiles in the 1970s had a large effect on the production rate, and price has dropped steadily since that time. The price in 2000 was about 50 per kg in 50 kg lots but this is expected to... 

The Lambda probe consists of a solid-state electrolyte (yttrium-stabilized zirconia) that is covered with porous platinum - electrodes on the inside (1) and outside (2) (see Fig.). 

T24.1 One of the most popular lambda sensors contains zirconia (ZrO ) as a solid electrolyte. This material has a high conductivity for 0 ions at elevated temperatures. The cell responds to the changes in O2 partial pressure in exhaust gas. The reduction potential for 02(g) + 4e" — 20 (s) is proportional to p(02, reference)/p(02, exhaust gas), with partial pressure of O2 in the air as the reference. (See Section 24.49(b) Solid anionic electrolytes and refer to Fig. 24.9). 

If two such electrodes are separated by a thin layer of only zirconia, the application of a potential will lead to the pumping of oxygen from the cathode to the anode. This device can be used as an amperometric sensor for oxygen if a diffusion barrier restricts the flux of oxygen to the cathode. Note that similar devices are also often used as potentiometric sensors according to the Nernst equation (i.e., the lambda-probe in cars with catalytic converters). In this case one side of the cell has to act as a reference, e.g., by using ambient air. 

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