Capacitive type No_x sensor operable at high temperature

Capacitive type NO sensor which is operable at high temperature was investigated in this study for monitoring NO in flue gases from gasoline engine vehicle. Although the high sensitivity is obtained at temperature lower than 400°C, it is negligibly small at temperature higher than 500°C on large part of the mixed oxide examined. On the other hand, BaSnO₃ or SrSnO₃ mixed with WO₃ exhibits the high sensitivity at temperature higher than 500°C. In particular, mixed oxide capacitor of SrSnO₃-WO₃ exhibited the high sensitivity to NO at 550°C. Since the capacitance of this oxide increased with increasing NO concentration, in the range from 10 to few 1000 ppm. NO concentration can be evaluated with the capacitance of the element. Furthermore, the capacitance of SrSnO₃ WO₃ is less sensitive to CO₂ H₂O and CO comparing that to NO. Consequently, mixed oxide of SrSnO₃-WO₃ is promising for the capacitive NO sensor operable at high temperature.