Preparationtin Dioxide Coatings And Studying On The Gas Sensor Properties

Tin dioxide (SnO2), is a suitable material for gas sensors application because ofits low cost, high sensitivity and fast response. The characteristics of the gas sensors areinfluenced by many factors, such as grain size, porosity, texture, faceting, grain network,etc. There are important factors for improving gas-sensing characteristics of tin dioxideresistive (conducto-metric) type sensors. So optimizing the preparation parameters andresearch on the relationships between the preparation parameters, micro-structure,morphology and sensitive properties are essential for the application of tin dioxide.In this dissertation, a sol-gel process starting with the tin tetrachloride andethylene glycol as precursors is successfully used to prepare nano-structured tin dioxidecoatings. The molecular structure evolution during the process has been identified usingFourier Transform infrared spectroscopy (FTIR). Compared to a sol-gel process usingmetal alkoxides or water"route"as precursors, this process is not only cost-effective butalso simple to control; the sol solution is extremely stable even in the presence of highconcentration of hydrochloride and the kinetics of the gelation process is not susceptibleto chloride ions. Further, conversions of xerogel to tin dioxide are studied using ThermoGravimetric Analysis-Differential Scanning Calorimeter (TG-DSC) and FTIR. It isfound that tin dioxide begins to form at a temperature as low as 179℃when organicsbegin to burn off. However, the tin dioxide coatings are formed only after the completecrystallization at about 430℃. As shown by X-Ray Diffraction (XRD), tin dioxidecoatings are prepared using ultrasonic spray pyrolysis and spin coating technology, themicro-structure and morphology are characterized by XRD, Raman Spectroscopy (RS)and Scanning Electron Microscopy (SEM). Porous tin dioxide coatings, made up ofballs (300~500nm in diameter) with 30~50nm micro-pores are successfully prepared.The resistance changes with concentration, the resistivity changes with coatingnumbers and the thermal stability of the resistance about the tin dioxide coatings underdifferent operation temperature are characterized by LCR meters (E4980A, Aglient). The optimum preparation parameters for lowest resistance and uniform tin dioxidecoatings are obtained. The sensor properties are measured by WS-60A test system withethanol and acetone as the target gases. There is an optimum heating voltage for ethanoland acetone, 4.5V and 5.0V respectively, and for the coating prepared, there is a bettersensitivity and selectivity for ethanol with the heating voltage in the range from 4.0 to4.75V.