Study On Properties On Resistive-type Humidity Sensor Based On Several Novel Materials

The resistive-type humidity sensor is a kind of the chemical sensors, which can be widely used in many fields. It plays a role through absorption effect of the sensing materials, in other words, the impedance of the resistive-type humidity sensor will change when the sensor is exposed in different water vapor. At present, the sensing materials used in the resistive-type humidity sensor are mainly dividing into there part: ceramic oxide, polymer materials and organic-inorganic hybrid materials. But there are a little disadvantage for them, which the humidity sensor based on polymer, has bad properties in high humidity situation, and the humidity sensor based on ceramic oxide has unstable impedance after it absorbed acid matter in air for a long time. The organic-inorganic hybrid materials overcome some disadvantages in some grade.In this paper, the author mainly studies on the two kind of sensing materials: polymerization polymer and mesoporous silica SBA-15 materials. According to the polymerization polymer material, the author mostly concentrates on making humidity sensor and testing the electrical properties. According to the mesoporous silica SBA-15 materials, the author prepares and characterizes all the samples and testes the electrical properties of the sensors. The author has applied the polarization theory of Dielectric Physics in the humidity sensor field to explain sensing mechanism of the humidity sensor. The final research results show that there are two kinds of particles to participate electric conduction in all humidity range. The domain carriers areions in high humidity. The electron and ion together take effect in middle humidity. The electron and polarization particles play a role more and more weakly, and ion plays a role more and more strongly for electric conduction when relative humidity increases from low to high. The obtained conclusion is identical to the Electron and Proton Theory, which is the theory to explain the humidity sensing mechanism currently.In this paper, the author uses the mesoporous silica SBA-15 as humidity sensing material for the first time. Mesoporous silica SBA-15 is synthesized by the sol-gel method, and different level of LiCl is doped into the material in order to modify the humidity sensing properties. According to the synthesizing processes, the materials are divided into two parts. Those are A-SBA-15 (as-synthesized SBA-15) and P-SBA-15 (pure SBA-15). The material which we named A-SBA-15 means that the material didn't remove the surfactant template. So the resultant we obtained has organic contains. The material which we named P-SBA-15 means that the material is removed the surfactant template at 550℃during the synthesizing processes. So the resultant we obtained don't have any organic contains.The author dopes different level of LiCl into A-SBA-15 and P-SBA-15, and then characters all the samples by IR,XRD and SEM. The relationship between the structure of the material and sensing properties of the different samples has been studied. The electrical properties are also studied seriously and the Cole-Cole plots in different humidity are obtained. The humidity sensor based on mesoporous silica SBA-15 wasn't covered before.According to the Cole-Cole plots, the author studies the sensing principle of these materials. The mesoporous silica material is insulator, so it is difficultto have free electron. The final research results show that there are two kinds of particles to participate electric conduction: the proton and the ion. According to the proton transport mode, we think H+ is the domain carriers in low humidity. When water molecules content is increased, ions become taking part in electrical conduction. That's why the sensing properties are modified after doping some LiCl. At last, we believe that the proton is the domain carriers in low humidity. The proton and the ion together take effect in middle humidity. The proton plays a role more and more weakly and the ion plays a role more and more strongly for electric conduction when relative humidity increases from low to high. The domain carriers are ions in high humidity.