| SnO2 is a kind of surface-control sensing material, and have high sensitivity to combustible and dangerous gases, such as CO, hydrocarbons ,ethanol etc. One of the disadvantages of present gas sensor is the long-term stability. When the element was exposed to environment, the resistance of sensor will be effect drasticly by the temperature and humidity of circumstance, which limited the veracity and area of sensor's application . This paper began with the synthesization of SnO2 material ,and discussed many means to improve the property of gas sensors, for example La0.7Sr0.3FeO3 doping and thiourea surface modification . A new kind of sensing material SnO2(0.9)Fe2O3(0.1) was prepared by citrate method. Furthermore by measuring the temperature of some key points on heating thread, earthenware pipe and dope surface layer, the distributing characteristic of their temperature field has been analysed.SnO2 material was prepared by sol-gel method. First was the hydrolysis of SnCl4 with ammonium hydroxide solution. The tin oxide hydrate was dried at certain temperature and then calcined in temperatures of 500℃ to obtain SnO2 crystallites. Subsequently XRD,TEM was used to character the structure and grain size of the resulting materials. The result indicates that by controlling the PH value and sinter temperature pure SnO2 nanocrystalline can be prepared.The main part of the thesis was focused on improving the property of gas sensors by using dopant materials and surface modification. The resulting SnO2 material was impregnated with 3wt% La0.7Sr0.3FeO3. The result indicates that the gas sensor's long-term stability and sensitivity to CO can be improved by doping the SnO2 with La0.7Sr0.3FeO3. After energizing for ten days, change of the sensor's resistance value was between ±10% in 90 days. The effect of thiourea surface modification on the stability and gas-sensing properties of SnO2 nanocrystalline material was also discussed in this paper. From XRD pattern of the samples we can draw a conclusion thiourea surface modification has no markedly effect on the material structure and grain size. In order to understand the nature of the species on the modified SnO2 surfaces, the Thermal gravimetric & differential thermal analyzer (TG-DTA) were taken. The results indicated that thiourea modification can enhance the stability of oxygen groups absorbed on SnO2 crystal surface and reduce the amount of surface hudroxyl groups. And It is widely accept that the oxygen groups absorption or desorption and amount of surface hudroxyl groups greatly influence the resistance stability of gas sensor. Ferrite and the compound oxide of iron and other metals were becoming important gas sensing materials recently. While such elements have the satisfied long-term stability, they must work under high temperature and the sensitivity of them were low. In this thesis, we try to do some experiment on preparing SnO2(0.9)-Fe2O3(0.1) gas sensing materials by means of citrate method and the SnO2(0.9)-Fe2O3(0.1) based gas sensors with high sensitivity and low working temperature were made. The result colloid was sintered in temperature of 500℃ -1000℃.The XRD patterns of sample indicated that SnO2(0.9)-Fe2O3(0.1) can be prepared at 700℃. The prominent virtue of this kind of material was its high resistance stability and satisfied sensitivity to CO and CH5OH. From the test of gas sensing test ,it can been seen that at 70mA the sensor had the max sensitivity to CO, and at 90mA the sensor got the max sensitivity to C2H5OH. The value of sensitivity was about 5.5 and 14.0 respectively. At the same time such elements have high long-term stability. SnO2 gas sensor can only work effectively at center temperature( 80 ℃—300℃ ). So it is necessary to investigate the distributing characteristic of the element's temperature field for finding some new design, which can provide reference to optimization for side-heating gas sensing elements. The temperature of some key points on heating thread, earthenware pipe and dope surface...
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