Humidity Sensitivity Research Of 1-Dimension Nanomaterials

Humidity sensor, as an important field in chemical sensors, gains considerable attention driven by its practical applications in environment monitoring, industrial process control, and our daily life. In recent years, researchers have developed humidity sensors that use changes in capacitance, impedance, frequency and refractive index as sensing mechanisms. Many kinds of sensing materials including electrolyte, organic polymer and ceramic materials, have been employed to serve these applications. At present, the major goal in this field is to fabricate humidity sensors with excellent sensing characteristics such as high sensitivity, best linearity, good reliability and stability, rapid response and fast recovery, and small hysteresis. One-dimensional (1-D) nanomaterials as humidity sensing materials, have special points of superiority in improving the sensor performance due to its large surface to volume ratio and effective electron transport. In this dissertation, the properties of humidity element based on amorphous Al2O3 nanotubes and porous ZnAl2O4 spinel nanorods were investigated in details by Agilent 4284A Precision LCR meter.Firstly,1-D NH4Al(OH)2CO3 precursors were prepared by a simple coprecipitation method, and then various crystallographic phase Al2O3 were obtained by post-annealed at different temperatures. Pellet of amorphous Al2O3 powder was made and tested for its humidity performance. The impedance of the element decreases by about four orders of magnitude from 5×104 to 2 kΩwith increasing relative humidity from 11% to 95%. The hysteresis is about 6%RH. The response time is about 10s (from 11%RH to 95%RH), and the recovery time is about 20s. The sensing mechanism based on complex impedance plots was also discussed.Secondly, a large quantity of porous ZnAl2O4 spinel nanorods could be obtained easily through a transition of layered composite precursors at 900℃, which was synthesized by a facile homogenization coprecipitation method combined with surfactant assembly. Pellet of ZnAl2O4 powder was made and tested for its humidity performance. The impedance of the element decreases by about two orders of magnitude 7×103 to 70 kΩwith increasing relative humidity from 11% to 95%. The hysteresis is about 2% RH. The response time is about 15 s (from 11% RH to 95% RH), and the recovery time is about 30 s.It is believed that these humidity materials will gain practical applications in humidity sensors. The research results can provide experimental and theoretical guidance for further researching sensitivity characteristic of other 1-D nanomaterials. Meanwhile, it also provides a new method to improve performance of humidity sensor.