Solid-state sensors for in-line monitoring of NO2 in automobile exhaust emission

摘要

Three types of planar solid-state sensors for measuring NO2 in a gas mixture has been designed and tested in the laboratory under controlled atmosphere between 573-723 K. The concentration of NO2 in the gas mixture was in the range of 0-500 ppm with the balance gas consisting of air. The three types of NO2 gas sensors that have been tested in this investigation can be schematically represented as follows: Pt, NO2 + air, NaNO3 + Ba(NO3)(2) NASICON disk Porous YSZ disk NO2 + air, Pt (I) Pt, NO2 + air, NaNO3 + Ba(NO3)(2) NASICON disk YSZ thin film NO2 + air, Pt (II) Pt, NO2 + air, Pt YSZ disk Au-Pd, NO2 + air, Pt (III) In sensor (I) the two solid electrolyte disks were attached by diffusion bonding at elevated temperature whereas in sensor (II) the (8 mol% Y2O3-ZrO2) YSZ thin film was deposited on (Na3Zr2Si2PO12) NASICON disk by radio frequency (RF) magnetron sputtering technique. The measured open circuit electromotive force (Emf) of each sensor was found to attain stable value at all the concentrations of NO2 in the gas mixture and also varied linearly as a function of the logarithm of the partial pressure of NO2 in the gas mixture. The time required to reach 90% of the stable emf at a fixed concentration of NO2 and at a constant temperature was found to be 30-40 min for sensor (I) and approximately 2-3 min for sensor (II) and (III). (C) 2003 Kluwer Academic Publishers. [References: 22]