Study On In₂O₃-based Formaldehyde Gas Sensors

It is important for semiconductor formaldehyde gas sensor to improve their properties of response sensitivity, selectivity and stability. While the above mentioned improvements of traditional Metal-Oxide-Semiconductor materials were researched, like SnO2, ZnO and so on, people continiously researched other materials. It has been reported that the In2O3-based gas sensor has lower operating temperature and response to high concentration of formaldehyde.The paper is mainly about the study on improving response of In2O3-based gas sensors to formaldehyde in low concentration and selectivity. The composite materials based on In2O3 were prepared and characterized by several methods. The gas sensing properties of composite materials were also researched.The paper introduced the synthesis of In2O3 using method of coprecipitation, microemulsion and hydrothermal synthesis method, respectively. The tokens including TG-DTA, XRD, SEM and TEM were also done to the prepared material. The coprecipitation method is convinent and easy to do, but the grain size of In2O3 prepared by this method is bigger. The grain size of granuliform In2O3 prepared by microemulsion is relatively smaller at the same calcining temperature, the smallest grain size is about 7.4nm. Hydrothermal synthesis method is fit for preparing different shapes of In2O3 material. In this paper, nanosheet In2O3, nanoball In2O3 and flower-like In2O3 were separately synthesized. New materials containing Indium, such as In3CrTi2O10 and SrCd2In2Ti2O10-x were also researched and synthesized.The heater-type gas sensors were prepared by using In2O3 and composite materials. The gas sensors were detected in the static state distribution system. The gas sensing materials includes:In2O3 materials prepared by several methods, In2O3 materials doped separately with Ag and Pd, In2O3/CdO composite materials, In2O3/ZrO2/Y2O3(molar rate is 1.75:9:1) composite material, SrCd2In2Ti2O10-x, In3CrTi2O10 and so on.The test results indicated that In2O3 in small grain size had better gas sensing properties to formaldehyde than big grain size. The gas sensor prepared by In2O3 doped CdO in 1:1 molar ratio showed high response to formaldehyde. The gas sensor made by nanoball In2O3 doped CdO had excellent selectivity to formaldehyde when the interference gases included methanol, alcohol, methylbenzene and acetone. The gas sensor prepared by flower-like In2O3 doped CdO had higher response to low concentration formaldehyde, and the response to 0.05 ppm formaldehyde was 1.45, the result reached the national standard. The gas sensor prepared by nanosheet In2O3 doped CdO had higher response to high concentration formaldehyde, and the response to 50 ppm formaldehyde was more than 600. The gas sensing property of SrCd2In2Ti2O10-x gas sensor was better than In3CrTi2O10 in new materials containing Indium.The research about In2O3 formation of different shapes was carried, the main reasons are fixed direction attachment mechanism, the shape matching principle in the gathering process and crystal grew in small nanoparticles therory. The gas sensing mechanism about In2O3 synthesized by various methods was also studied. Particle size, specific surface, pore canal, adsorption, heterojunction were analysized.