Poisoning porous element

Figure 12.3 Effect of (a) 105 ppm chlorine, (b) high molecular weight poisons and (c) 107 ppm sulphur dioxide on the response to 1% methane in air temperature 550° C. Rhodium porous element A, platinum porous element and palladium pellistor. ...

The rapid growth in demand for catalytic flammable gas sensors to operate in hostile atmospheres (leaded petrol atmospheres, gas compressor stations, etc.) and areas where routine calibration and maintenance are difficult and costly (North Sea gas and oil platforms) has stimulated the search for sensing elements which are resistant to poisons. These devices generally take the form of a platinum wire coil embedded in a porous bead comprising active catalyst either dispersed throughout a porous substrate (5-7) or as discrete layers within the substrate (8). 

For the same reason of impurities as stated above, the 3-electrode system can sometimes pose a problem, as leakage through the porous glass frit or ceramic fiber junction during deposition process can poison the electrolyte and thus deteriorate the electrical properties of the deposited semiconductor. It can be recalled that different ions (elements) can act as impurities in different semiconductors. For example, Cu ", Ag , K", Na", etc. can act as detrimental impurities in electroplated CdTe solar cells [29]. Some of these ions such as are contained in both Ag/AgQ and... 

Use of DBLs is effective to prevent metal element diffusion between Ni-based anode and steel. Nevertheless, as the DBLs are porous, they will unlikely contribute to prevent Cr evaporation and poisoning of electrodes in the long run. Besides, it was also shown that high depletion of Cr content in the bulk of... 

---