The Study On Zircona No₂ Sensor

Gasoline engine electronic control fuel injection system (EFI) is being used to upgrade gradually from the traditional three-way catalytic control technology to lean-burn combustion control technology with less HC and CO emissions of harmful gases and more efficient. However, more NOx (NO+ NO₂) of harmful gases will be brought along, for which gave birth to NOx sensor needs. Due to simple structure, without reference gas, wide gas test range and the output potential testability, zirconia-based mixed-potential-type NOx sensors have become the vehicle of the research focus. In this paper, the characteristics of planer zirconia-based mixed-potential-type NO₂ sensors using spinel-type ZnFe₂O₄ and NiO sensing electrodes were studied. And method of doping YSZ in sensing electrodes was used to improve the sensor performance.In chapter one, the development of zirconia-based NOx sensor was introduced. The characteristic of solid electrolyte and sensitive electrode materials were also introduced in this section. At last, AC impedance testing technology was presented in the study of solid electrolyte gas sensor.In the chapter two, the content,technology path,innovations and a number of experimental reagents,instrumentation equipments and testing methods of this dissertation are presented .In the chapter three, preparation of ZnFe₂O₄ and its gas sensitivity were studied. The spinel-type ZnFe₂O₄ powders were prepared by solid state reaction,sol-gel method respectively, and studied by XRD and SEM. On this basis, planar mixed-potential-type NO₂ sensor using yttria-stabilized zirconia (YSZ) and ZnFe₂O₄ sensing electrode was fabricated by means of screen-printing method. Its characteristics of EMF and response time were studied in the different NO₂ concentration and temperature. The results show that higher EMF can be obtained with the increasing of NO₂ concentration, and the present sensor is found to give a linear correlation between EMF and the logarithm of NO₂ concentration from 61.8ppm to 494ppm. However, the response time of the sensor were long at the temperature of 600℃, and the EMF of sensor was decreased with the work temperature increasing.In the chapter four, the research of mixed-potential-type NO₂ sensor using YSZ-loaded ZnFe₂O₄ sensing electrode were introduced. YSZ was attempted to dope in ZnFe₂O₄ which was prepared by sol-gel method. 1# and 2# mixed-potential-type NO₂ sensors using YSZ electrolyte with ZnFe₂O₄ and ZnFe₂O₄ (+YSZ) were fabricated respectively. Their characteristics of EMF, response time and AC complex impedance were studied. It was found that the EMF of both sensors has a good linear correlation with the logarithm of NO₂ concentration, but their EMF and sensitivity decrease with the work temperature increasing. 2# sensor has showed higher EMF and sensitivity than 1# in the same temperature and NO₂ concentration. Their response time also shows good repeatability, and their up response time is longer than down response time. But 2# sensor gives a quicker response time than 1#. In addition, AC complex impedance also showed 2# sensor has a lower boundary reaction activation resistance. Based on the microstructure of electrode and sensing principle, It was speculated that the increasing of three-phase boundary (TPB) of YSZ loading in the ZnFe₂O₄ was the major contributing factor for the enhance characteristics of 2# sensor.In the chapter five, mixed-potential-type NO₂ sensors using NiO, NiO (+YSZ) sensing electrodes were studied. NiO powders were prepared by solid state reaction, and were studied by XRD and SEM. Planer mixed-potential-type NO₂ sensors using yttria stabilized zirconia electrolyte with NiO and NiO (+YSZ) were fabricated respectively and their NO₂ sensitivity was tested. The result showed that both sensors have good sensitivity and good linear correlation with the logarithm of NO₂ concentration between 60-600ppm. Also, their sensitivity and EMF were decreased with the work temperature of sensor increasing. But both of their response time were quick and also show good repeatability. The sensor with NiO (+YSZ) sensing electrode has higher sensitivity,EMF and shorter response time than the sensor with NiO sensing electrode. Finally, all the results of the present work are outlined, and it is suggested that something should be done in the next stage.