Preparation And Humidity Sensing Properties Of Eucryptite Thick Film Humidity Sensor

Being more concerned about environmental humidity in working and living, people require more about the monitoring and control of environmental humidity. So humidity sensor is paid more and more attention. In this paper,takes eucryptite as humidity sensor material, uses eucryptite sol as binder, adopts thick-film technology to produce humidity sensor material and uses X-Ray diffraction(XRD), scanning electron microscope(SEM) and other equipments to characterize the phase and microstructure of the samples. Using the impedance analyzer to study humidity properties of eucryptite componentsEucryptite sol binder can generate eucryptite after heating in the temperature of 650℃,750℃and 850℃.Heat humidity sensor materials in 650℃,750℃and 850℃and then test the microscopic structure characterization and humidity properties of the samples separately. The results show that eucryptite particles in humidity properties become bigger as the temperature rising, and particles change from edge-shaped to oval-shaped. Compared with other samples, the particles of 650℃sample has smaller shape, high porosity, large superficial area and high humidity sensitivity, so 650℃is the best heating temperature. The length of heating has little influence to humidity properties.Take 10 percent eucryptite sol and 90 percent powder of pure eucryptite, pure eucryptite sol binder and heated eucryptite with sol as sample and test its microstructure observation and humidity properties. Pure eucryptite sample shaped as particle accumulation, the sample is a bumpy 3D mesh structure consisted of many particles, while the pure sol sample has a smooth 3D mesh structure. The result of humidity properties measurement shows the humidity properties of pure eucryptite powder sample are close to that of 10% sol and 90% powder sample. But during the process of heating pure eucryptite powder sample is found to be poor in mechanics and easy to be destroyed. Thus the best ingredient for sensor material is 10 percent sol and 90 percent eucryptite powder. Through testing the moderate sensor property of eucryptite samples for different particles, the sizes of particles has less influence to sensitivity, but bigger particles can shorten the responding time.Adopt thin-layer coated and thick-layer coated to make the samples. Compared with thick-layer coated sample, thin-layer coated sample acts more sensitive and takes less time to response and it is a better coating process.Use 1000Hz 10v alternating current to ageing the sample under the environment of 98%RH high humidity. With the increase of ageing time, eucryptite humidity sensors become more sensitive, better linear. So maturing is a key process to optimize eucryptite humidity sensor.