Study On Properties Of Humidity Sensor Based On Sodium Titanate

In the rapid development of technology and living standards, humidity sensors havemore and more development and innovation in various fields nowadays. When it comes tothe reformation of humidity sensors, it’s important to optimize sensing materials and novelsensors with different functions, principles or structures, whose purpose is to improveevery parameter and property. The way of water molecules adsorbing on the surfaceincludes chemical and physical adsorption, and the whole impedance change largelydepends on surface conductivity of the material. Therefore, more attention is paid tocharacteristic of surface as for humidity sensing material, i.e. a large specific surface areaproviding more space, more metal point, defects and tip providing more electrostaticdriving force, porosity characteristics or one-dimensional structure making it easier forwater adsorption and diffusion. Research on one-dimensional nanomaterials has become ahot issue currently. This paper mainly focuses on the humidity properties of sodiumtitanium with a one-dimensional structure and aluminum phosphate molecular sieves witha pore structure.In the second and third chapters, Na2Ti3O7nanowires, Na2Ti3O7nanotubes, Na2Ti6O13nanorods were synthesized by a hydrothermal method and then characterized. By comparingthree different structures of sodium titanate, three similar but different results were obtained.The minimum impedance changing range of Na2Ti3O7nanowire is four orders of magnitudeand that of Na2Ti3O7nanotubes and Na2Ti6O13nanorods are both5orders. The linearrelationship on characteristic curve of Na2Ti6O13nanorods presented best results. Thehysteresis loops of Na2Ti3O7nanotubes and Na2Ti6O13nanorods were better(less than3%).Na2Ti6O13nanorods showed best response and recovery characteristics, response and recoverytimes both were less than2s. While response and recovery times Na2Ti3O7nanowire were4~5s, and that of Na2Ti3O7nanotubes were5s and2s. By contrast, we found that humiditysensing characteristics of Na2Ti6O13nanorods were best. In addition, we analyzed the sensingmechanism in example of Na2Ti6O13nanorods through six complex impedance curves in theway of dielectric polarization and equivalent circuit. The types of polarization and conductive particles are:①low humidity stages: H+hopping conductivity;②medium humiditystages: H3O+;③high humidity stages: ions of sodium and H+under the proton conductiveof Grothuss mechanisms; while polarized electron and ion displacement polarization ofmaterial itself exist in all stages, that is to say, electric dipoles of material itself involved in allstages.In the fourth chapter, AlPO4-5zeolite was synthesized by a hydrothermal method. Theresults is that the impedance variation range is three orders of magnitude, hysteresis loop lessthan3%, and response and recovery time2~3s, which shows a promising humidity sensor.Finally, a brief analysis of sensing mechanism was presented: water molecules adsorbing intoAlPO4-5zeolite pores first enter into six-membered ring, and12-membered ring, and gatherand form two helical structures in the12-membered ring under high humidity conditionsthrough " capillary condensation ", whose structure is similar to the structure of ice.