Study On Resistive-type Humidity Sensors Based On Several Kinds Of Mesoporous Materials

Humidity sensors have been used in an increasing number of applications in industrial processing and environmental control. According to the operation principle, humidity sensors can be divided into resistive-type or capacitive-type. In our experiments, we studied the humidity sensitive properties of resistive-type humidity sensor. Growing demands for controlling water vapor have led to considerable interest in the development of sensing materials. Many kinds of materials including inorganic ceramic, organic polymer and electrolyte have been selected in fabricating humidity sensors. Among these materials, ceramics have been extensively investigated at both room and elevated temperatures. But it may unstable when it absorbed acid atmosphere. Polymers can not work under high temperature and electrolyte may soluble in highly humidity environments. That means all of them exist some disadvantages.Since a family of novel mesoporous silica materials was synthesized by the scientists from Mobil Oil Corporation, mesoporous materials have been receiving wide attention from both the scientific and industry communities. In recent years, The development of material science accelerated the application in many fields. The large surface area created by mesoporous materials enables an improvement in the water adsorption properties of humidity sensor. In this paper, several functional mesoporous materials have been synthesized and their application property in humidity sensors has been studied.In chapterâ…¡, the author uses the mesoporous silica SBA-15 and SBA-16 as humidity sensing material. Mesoporous silica SBA-15 and SBA-16 are selected as the host material and LiCl is selected as humidity functional material. After loading optimized amount of LiCl, The humidity-sensitive properties were improved a lot. Except traditional LiCl, what about metal oxide semiconductor? Therefore, in chapterâ…¢, the author loaded metal oxide into the mesoporous SBA-15. We obtained MgO/SBA-15 and ZnO/SBA-15 composites by one-pot synthesizing method and fabricated resistive-type humidity sensor. After testing the humidity-sensitive response, the optimized mount of metal oxide was obtained. When the molar ratio of the metal oxide and SBA-15 was 1:1, the humidity sensors show best sensitivity. Test results show that the appropriate introduction of metal oxides improved the performance of the humidity-sensitive properties.Since we found that the humidity-sensitivity can be improved by introduction of metal-oxide semiconductor into mesoporous pore. We considered about that if traditional metal-oxide semiconductor can be provided with mesopore, the sensitivity will be improved a lot. In the fourth chapter, we use nanocasting method in preparing mesoporous In2O3 and WO3 mesoporous materials. Then, studied the humidity-sensitive property based on mesoporous In2O3 and WO3. The sensor fabricated by mesoporous In2O3 and WO3 show quite satisfactory results. Combined with the material structure analysis, we also studied the humidity-sensing mechanism based on mesoporous In2O3 and WO3.Chapter V studied the humidity-sensitivity of organic polymer materials PPY and a traditional ABO3-type ceramics oxide LaCO0.3Fe0.7O3 material. Conducting polymers have been extensively studied because of their remarkable mechanical and electrical properties. Compare with other conducting polymers, PPY has relative high conductivity and environmental stability. In the experiments, we synthesized PPY with different polymerization times, and studied the effect of polymerization time on the humidity-sensitive properties. At last, we found that the humidity-sensitive properties were improved greatly by extending the polymerization time to 96 hours. In order to improve the humidity-sensitive property further, we also encapsulated conducting polymer NiO-PPY into the channel of mesoporous silica SBA-15 to form host-guest material. After loading the PPY into the mesoporous material, the sensitivity of the humidity sensor was improved greatly. This method combined the advantage of conductive polymer and mesopore structure. In the same chapter, we also studied the humidity-sensitive property of traditional ABO3-type ceramics oxide LaCO0.3Fe0.7O3. ABO3-type ceramics oxide is one of the traditional humidity-sensitive materials. We provided nano-LaCO0.3Fe0.7O3 by sol-gel method. K+ was doped by adding to the precursor and the appropriate doping of K' improved the sensitivity of material in the low relative humidity.The author has employed different method in study the humidity-sensitive mechanism. For example, the polarization theory, complex impedance plots, the Direct-current method and so on. Finally, the conductive carriers were confirmed though the mechanism analysis.