| With the development of technology and science and the improvement of economic and social level, more and more cars come into millions of households and indeed bring great convenience to people’s life; at the same time also bring some environmental pollution problems. NO2 and NO (referred as NOX) emissions from automobile exhaust have bad effects on the human and the environment. Therefore, researchers worked for years in the automobile exhaust NOX sensor, which mixed-potential-type NOX sensor based on zirconia has the advantages of simple structure, low cost, high sensitivity, fast response and becomes the attention spot. In this thesis, the author prepared 3 kinds of type NO2 gas sensor based on 8YSZ mixed potential type, and the performance of each sensor has been studied. Try to improve the performance of the sensor by exploring the new composition or new structure of the sensitive electrode materials and optimizing the microstructure of the composite oxide electrode materials. This thesis mainly includes the contents as follows:1. Ultrafine-structure La0.65Sr0.35MnO3 (referred to as LSM) powders synthesized by self-propagating combustion method have been used to fabricate sensing electrodes (SEs) for NO2 mixed-potential sensors based on yttria-stabilized zirconia (YSZ). This type of sensor was found to provide better NO2 sensitivity than sensors with LSM powders synthesized by traditional solid-state methods. It was found that changing the sintering temperature from 1000℃ to 1300℃ had a significant effect on the morphology of LSM-SEs which could change the sensor response. At the sintering temperature of 1300℃, the response values of the sensor have good linear relationship (sensitivity 36.6 mV/decade). The AC impedance was applied to test the sensor in different concentrations NO2 gas. In addition, the device has good repeatability and stability. And, in the presence of NO, CO2, CO, and NO2, the sensor exhibited good NO2 selectivity.2. With the ball milling process, layered-structure Bi2W2O9 powders synthesized by solid-state reaction have been used to create an electrode for a mixed-potential-type NO2 sensor. It was found that this NO2 gas sensor provide good sensitivity to NO2 at 500℃, owe to the grain refinement treated by ball milling for about 16 h. The electromotive force generated showed a good linear ship to the logarithm of NO2 concentration (30-500 ppm); and with analysis of the impedance spectroscopy, the conductance of the electrode was linear to the logarithm of NO2 concentration. In addition, the device has good repeatability for 200ppm NO2 and good stability even after 2 months. The influence of CO2 was also examined and found to have little impact on the sensitivity of the device to NO2.3. Successfully, perovskite oxide Bi2WO6 with layered-structure has been synthesized by hydrothermal method. A planar NO2 sensor based on YSZ and Bi2WO6 sensing electrode has been fabricated. The device equipped with Bi2WO6 ball-milling shows the fast response and large sensitivity (58.27mV/decade) at 500℃. The performance of this device is similar with sensor using Bi2W2O9 as sensitive electrode materials, and also the output voltage and the sensitivity of this device is somewhat higher. Finally, the sensing characteristics of the sensor in the ppb NO2 atmosphere was studied and the sensor showed good response signal to the NO2 gas over the range of 50-2500ppb at 500℃. The electromotive force generated was linear to the logarithm of NO2 concentration. The test results revealed that the sensor have good repeatability and stability. This shows that the sensor has a certain practicality at lower concentration. |
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