| 摘要 |
<p>An improved exhaust gas sensor for use in sensing the partial pressure of oxygen in the exhaust gases from an internal combustion engine has titania ceramic elements (46,48) in each of which two electrodes (40, 42, 44) are embedded. The electrodes in the past have been made from pure platinum, this precious metal being required to enable the sensor electrodes to survive at temperatures up to about 900°C in the hostile gaseous environment. Even with the use of this platinum electrode material, electrode failures have occurred. These now have been found to be caused by the formation of platinum carbide from the chemical reaction of the platinum electrode material with exhaust gas constituents. Also, Pt loss has occurred from oxidation thereof and vapourization of the oxide. It has been found that deterioriation of sensor electrodes from an alloy consisting essentially of platinum and another material having a lower vapour pressure and lower surface tension than platinum. Specifically, an alloy consisting essentially of platinum and another metal selected from the group consisting of gold and rhodium may be used. An alloy of platinum and gold is preferred. Annealing the titania element electrodes functions, as does the alloy formation, as a means for increasing the magnitude of the energy required for reaction of the Pt with carbon or oxygen.</p> |
