Industrialization Of Oxygen Sensors And NO_x Sensors Based On Metal Oxide Semiconductors

A gas sensor is a device which can sense a certain kind of gas in the complex environment, detect the concentration, and then convert the relative information of the type and concentration into electrical signals to make it easy for people to detect, monitor, analysis and alert. Thus, it can be widely used in a series areas of critical need, such as food safety, environmental monitoring, public safety, process control, clinical diagnosis. The main purpose of this study is to find out new types of gas sensing materials and prepare gas sensors for the detection of different industrial pollutants.Because the traditional preparation of ZrO₂ oxygen sensor is very complex and its sensing performance is unstable as the temperature changes, which may greatly decrease the test accuracy, in this work, STF35 powder was prepared by solid state reaction and the oxygen sensors based on STF35 were fabricated by screen printing technology. The sensors show good sensitivity?0.23? and pretty fast response?100 ms?. With a MgO insulating layer, the sensors performed temperature insensitivity. Within the working temperature range, the STF35 oxygen sensors exhibited great selectivity due to their little response to CO and NO.In this work, we utilized lotus pollens as templates to prepare WO₃ microspheres; the intriguing structural features of the pollens, e.g. hollow sphere with highly porous double shells, were perfectly inherited by the WO₃ microspheres. And the hierarchically porous structure of the WO₃ microspheres was ideal for gas sensing. The WO₃ microsphere-based sensor exhibited a high sensitivity?S = 46.2? to 100 ppm NO gas with a pretty fast response and recovery speed?62 s/223 s? at 200 °C. Compared with NO sensors reported in literatures so far, the WO₃ microsphere-based sensor has among the highest sensitivity and fastest response/recovery.To further improve the WO₃ sensor's recovery speed to NOX, modified with Pd, the WO₃/SnO₂ multi-layer NOX sensors were prepared by screen printing technology. The sensors show great sensing properties of both high response and fast recovery towards NO in the range of 250 °C to 500 °C. With special structure of the Pd-modified WO₃ top layer, the sensors exhibited good response to NO gas, and the SnO₂ layer at the bottom provides electronic transmission channels contribute to vert fast recovery. And the screen printing technology was applied to fabricate this double-layer sensor which is very suitable for mass production in industry.The foothold of scientific research should be the practical applications in everyday life. In this work, the STF35 oxygen sensors and the WO₃/SnO₂ double-layer NOX sensors have the potential to come into pragmatic. Therefore, we redesigned the structure and standardized the preparation process of the oxygen sensor according to the request of industry to make it suitable for practical use and manufactured a batch of oxygen sensors based on the industrialized mode of production. This batch of oxygen sensors exhibited good sensing properties, much better stability, repeatability and consistency. Moreover, SO₂ protection device was designed and show excellent protective effect. Based on the structure and preparation process of the oxygen sensors, we manufactured NOX sensors and the test their sensing properties. The WO₃/SnO₂ double-layer NOX sensors also show great performances.