Study On Properties Of Humidity Sensor Based On Polypyrrole Novel Materials

Sensor technology is one of the three core technologies of the modern information technology. Because it was in the forefront of information acquisition system, its performance will directly affect how the whole system working conditions and quality. Nowadays application, research and development of sensor and sensor technology is the necessary requirement of this information era. Resistance-type humidity sensor is a kind of chemical sensors which has a wider use. Its work is based on the principle of adsorption and desorption humidity water molecules induced changes in the resistance of materials, which leading to changes in the output signal components to characterize the environment and humidity changes. In recent years, the hot humidity-sensitive material mainly organic polymer materials, ceramic oxide materials, inorganic nano-materials, as well as organic and inorganic composite materials, each material has its own advantages and disadvantages. With the rapid development of materials science in recent years, conductive polymers as a new type of material which has been humidity, become another hotspot materials. In this paper, a major study of the humidity properties of the series of polypyrrole (PPY) materials was showed.Polypyrrole materials were prepared by using chemical method at different polymerization times. The different polymerization time was 4, 24, or 96 h. Their structure and morphology were characterized through X-Ray powder diffraction (XRD), IR, and scanning electron microscope (SEM). Resistive-type humidity sensors were fabricated based on the polypyrrole materials of different polymerization time by a coating membrane method. The humidity sensing properties of the PPY-x films (the letter'x'denotes the polymerization time and it was 4, 24, or 96 h) were studied. It was found that the humidity sensing properties of PPY could be improved greatly by extending the polymerization time. Some basic humidity properties such as frequency property, hysteresis property, response and recovery property and capacitance property were studied based on materials of PPY-96. Through the test of the basic characteristics of the materials, the shortcomings of the hysteresis property and response and recovery property were found. The humidity-sensing mechanism of the PPY-96 materials was discussed in terms of complex impedance, direct current and dielectric loss properties. The discussion on the sensing mechanism indicated that not only electrons or ions but also dipoles contributed to the conduction in the whole relative humidity range. It was the first time that applied the direct current and dielectric loss method for analysis the sensing mechanism, and this was not covered before.Because of the shortcoming of the hysteresis property and response and recovery property, some adulterations were added into the pure polypyrrole materials to improve the humidity property. Firstly was the Fe2+ adulterate. The detailed description of method of materials preparation, basic chemistry characterizes and electric property test were showed in this part. It was found that after the doping of FeCl2·2H2O, the humidity sensitive property of PPY has been greatly improved, the hysteresis was reduced and the response and recovery times were shortened. A possible mechanism was provided to explain the humidity sensitive properties of mixed materials through analysis the complex impedance spectra at different relative humidity. It was found that the conduct particles of Fe2+ adulterate material were electrons and ions, but include a metal ion of whole ions. It was the same as the pure PPY-96 material through contrast the complex impedance spectra of the two kinds of materials. Then were the NiO/ SBA-15 adulterate. The detailed description of method of materials preparation, basic chemistry characterizes and electric property test were showed. The humidity sensitive properties were studied seriously. It was found that the humidity sensitive properties were improved very much by encapsulating NiO/SBA-15 into PPY-96. At last the sensing mechanism was discussed by analysis the complex impedance spectra at different relative humidity. Though contrast the complex impedance spectra of the pure PPY-96 and Fe2+ adulterate materials, the conduct particles were electrons and ions (include a metal ion) were concluded. It was also found that different metal ions corresponding to the different slope of curves at high humidity areas through the contrast.A new type of ceramic humidity material of LaCo0.3Fe0.7O3 was studied at the last part of this paper. The material of LaCo0.3Fe0.7O3 was prepared by citrate method, and characterized by XRD and SEM. The XRD indicated that when the sintering temperature was further increased to 600 ?C, the stable perovskite nanocrystallite could be obtained. The SEM indicated that there are many sample size uniform mesoporous on the surface of the materials. It was found that pure LaCo0.3Fe0.7O3 showed sensitivity only in the relative humidity (RH) above 54%. Therefore, the appropriate amounts of K2CO3 were doped into the pure material. A series of other electric tests shows that K+ ion-doped material is a good ceramic oxide humidity-sensitive material. Finally the sensitive mechanism was analyzed by the complex impedance spectra at different relative humidity, based on the traditional conductive ceramic materials theory. It was found that the conduct particles of this material are electrons, protons and ions. The electrons and protons were contributed to the conduction at all relative humidity range, while the ions only contributed at high relative humidity range.