The Research Of QCM Humidity Sensors Based On Zeolite Films

Moisture in the air causes the storage quality deterioration, which affect theoperation stability of the instrument and moisture is also one of the main causes ofmaterial corrosion, hydrolysis and aging. Humidity sensor used to test the water vaporcontent in the gas, translates it into output signals, and it has great significance tocontrol the humidity. Quartz Crystal microbalance (QCM) received wide attention forits high sensitivity, simple structure, and low price. In addition, A-type zeolite issensitive to the changes of water vapor in the air, especially in low humidityenvironment. This project combined the character of QCM to mass and A-type zeolite tohumidity. The author did some research work on the QCM humidity sensors based onzeolite film.The zeolite powder was prepared by the method of low-temperature hydrothermalprocess. The effect of raw materials selection and the Si/Al ratio setting on the finalproducts was explored, and the influence of crystallization conditions, for instance,crystallization temperature and crystallization time, was studied. Characterizationmethods such as XRD, SEM, EDS, IR analysis were employed to analysis the phasestructure, morphology and IR adsorption peaks of the product, respectively. Andgranularity analysis and adsorption/desorption curve was used to calculate the particlesize of the prepared NaA zeolite. Finally, the optimum technological conditions wasdetermined: silicon-sol was used as source of silicon,, silica alumina ratio was set as1:2,crystallization temperature was60℃, and crystallization reaction time was24h. Inthis way, the average grain size of NaA was about700nm and the size uniformity of theparticles was great. Its XRD spectrum and IR absorption spectrum were in goodagreement with the standard feature spectrum reported. The N2adsorption isothermcurve indicated that the pore of the zeolite prepared was micropore.Prepared zeolite film was coated on the surface of QCM by method of physicalspin coating. QCM wafer with zeolite film coated was connected to the measuringcircuit, and the characteristic of humidity under different environment was test. Basedon the measuring and analyzing result of sensitivity, repeatability and hysteresis loop toanalyze, application potential of QCM-zeolite film system was evaluated. At the sametime, effect of temperature on humidity measurement was tested, proving theimportance of temperature compensation in practical application.Besides, considering the pore size of KA zeolite is more closed to water moleculeand KA zeolite is sensitive to water molecule only. Then Potassium was used to replaceNa in NaA zeolite. Properties of humidity sensors based on KA zeolite were estimated by the aspects of moisture characteristic curve, wet-hysteresis curve and repeatability.Compared with NaA zeolite, it can be concluded that KA zeolite has better feature insensitivity and linearity, while it has larger wet delay compared with NaA zeolite, whichis harmful to application.