| The contact combustion-type gas sensor is an important class of gas sensors; it has a good sensitivity of flammable gas. Therefore it is generally used in the areas where regularly contact with combustible gas, such as mine tunnels, petrochemical, and kitchen bathroom, and it is specially critical in the application of Low-density mine gas alarm. In 1920s, people started to use the bare platinum coil as contact combustion-type gas sensor. And then, the contact combustion-type gas sensor, which was made by using the platinum catalyst material to coat on the surface of the platinum coil, had been put in broad application. Relying on traditional methods, this paper used several different methods to prepare the catalyst materials of the contact combustion-type gas sensor, and obtain the catalyst materials with uniform doping and big BET by means of improving the methods of preparation, to improve the sensor's gas-sensing properties.First, this paper prepared the catalyst material of Pd/Al2O3 by the traditional co precipitation method. To melt the solutions of Al2(SO4)3 and Na2CO3, and make them react with each other, the Al2O3 carrier materials had been obtained. Then, by means of reduced pressure distillation, we used Pd(NO3)2 as Pd source, loaded Pd on the carrier material, to obtained the catalyst material of Pd/Al2O3. Having changed different carrier sintering temperature and concentrations of Pd doping and combined some characterization methods, such as XRD and nitrogen adsorption, we want to discuss the compact of sintering temperature on the crystal style and BET of the carrier material, as well as the influences of concentrations of Pd doping on the final sensitivity of the materials.Subsequently, we had prepared the catalyst material of Pd/Al2O3 by the means of hydrothermal method. Use Al(NO3)3 and Pd(NO3)2 as the raw materials,By setting the appropriate reaction temperature and time, Pd/Al2O3 catalyst materials were obtained by using three different solvents——water, ethanol and ethylene glycol. Through some characterization methods, such as XRD, SEM and TEM, we could found that along with the variation of the solvents, the surface properties of the catalyst had greatly changed, in which ethylene glycol solvent, with a strong reducibility, had prepared the material with smaller particles and more gaps. The materials obtained by this method also have a characteristic of good doping uniformity.At last, we had synthesized the material of SBA-15 by the means of template method. We use TEOS as silica source, P123 as surfactant,and make them react with each other in an acidic condition, then we doped Pd to the SBA-15 materials through the ion exchange method, where the used Pd source is PdCl2. Through XRD characterize the SBA-15 materials, we could confirm that this material had mesoporous structure and large BET.In The second part of the experiment, we build a gas test system to test methane sensitivity of the material. We coat the obtained several materials to get corresponding contact combustion-type sensor, through matching the resistance of sensing and referencing components, to package them as a complete device. Through the test of the device sensitivity and acceleration, we compared the advantages and disadvantages of several methods. The results show that the different percent of Pd doped has little effect on the sensitivity of the device, however, in the aspects of the long-term work, larger percent of Pd doped could slow down the reduce of device sensitivity. For improve the sensitivity of device, doping uniformity and BET are the two important acts. The device coated with material obtained by hydrothermal method shows high gas sensitivity due to the doping uniformity of Pd. Moreover, the device coated with SBA-15 material obtained by template method also shows higher gas sensitivity compared to the material obtained by the traditional method, which approve the large BET will improve the sensitivity of the device. |
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