【作者】 王竹仪；

【导师】 吴凤清；

【作者基本信息】 吉林大学 ， 物理化学， 2009， 博士

【摘要】 湿度监测、控制在工业、农业、日常生活、科学研究等方面受到越来越多重视,电阻式湿度传感器是有着广泛应用的一类化学传感器,它是基于湿敏材料的吸附作用来工作的,即湿敏材料吸附和脱附水分子后能引起材料的阻抗发生变化,从而引起元件输出信号发生变化。在本论文中作者合成并表征了两类湿敏材料,研究了基于这两类功能材料的电阻型湿度敏感元件的电学特性及敏感机理。将柠檬酸法制备的具有不同X值的LaCo_xFe_1-xO₃纳米粉体材料用作厚膜技术制备敏感器件的敏感浆料,对其进行湿敏性能参数测试,结果显示敏感性能相对最佳的材料为LaCo_0.3Fe_0.7O₃。对此材料进行碱金属的物理掺杂、化学掺杂改性,有效地降低了材料的电阻,使该材料的湿敏元件能够在整个湿度量程内工作,元件的感湿灵敏度大大提高。以钛酸四丁酯为前驱物,在溶胶凝胶法合成样品的过程中添加正硅酸乙酯后HF处理制得的TiO₂的比表面积大大提高,显著改善了传统方法制备的TiO2在低湿区灵敏度差的现象,湿敏元件在整个湿度区对湿度的变化都有很好的响应。将电介质物理的理论用于解释这两类材料的湿敏元件的敏感机理,根据实验,得到了元件在不同的湿度环境下的复阻抗谱图,设计了直流瞬时极性反转实验得到了湿敏元件在不同的湿度环境下的具体导电粒子。认为这两类湿敏材料在整个湿度量程中均由两类粒子参与导电,即电子和离子。随着湿度的不断增大,电子参与导电的作用逐渐减弱,而离子参与导电的作用逐渐增强,实验得到的结果与目前较为流行的电子-离子导电理论相吻合。这些研究为寻找新型的湿敏材料和对当前一些湿敏材料的改性研究有一定的意义。更多还原

【Abstract】 Monitoring and controlling humidity are more and more emphasized on industry, agriculture, daily life, science research etc. The resistance-type humidity sensor is a kind of the chemical sensors, which can be widely used in many fields. It plays a role through adsorption effect of the sensing materials, in other words, the impedance of the resistance-type humidity sensor will change when the sensor is exposed in different water vapor. In this paper, the author has prepared and characterized two kinds of materials sensitive to humidity, and the electrical properties and sensing mechanism to humidity of the two resistance-type humidity sensors based on the two materials have been investigated.In the first chapter, the concept of humidity sensors, the development process, and the direction of current research was introduced comprehensively. At the end of this chapter, we pointed out the significance of our work and summarized the important results obtained.Perovskite-type oxides LaCo_xFe_1-xO₃ was mainly applied in these areas such as solid oxide fuel cells, chemical sensors for the detection of alcohol and oxygen, methane oxidation catalysis. There were reports about the magnetism of this material. But the humidity sensitive properties of this material were rarely reported. In the second chapter, the nanocrystalline LaCo_xFe_1-xO₃ prepared by citrate method was ground to form the humidity sensing paste, and the paste was then screen printed on ceramic substrates with interdigitated electrodes to obtain the humidity sensitive thick films. The humidity response of LaCo_xFe_1-xO₃ showed that LaCo_0.3Fe_0.7O₃ has the highest sensitivity to change in humidity when compared with the other samples, and the optimal calcination temperature is 600°C.In view of the past, many reports have showed that the addition of alkali ions was effective in improving the performance of many different kinds of materials, the alkali ion can be dissolved in water to become the conduction carrier, and play a major role in improving the humidity properties of materials. In the third chapter, the doping of alkali cation was considered to improve the humidity-sensitive properties of material, the results showed that the optimal dopant was K+, the resistance of material reduced after alkali cation was doped into it, the humidity sensor based on it had good response in the whole humidity range, and the sensitivity was enhanced significantly. The shortage of this method was time-consuming and laborious, and the uniformity of doping was limited, moreover, the recovery characteristic of humidity sensor was poor.In the fourth chapter, the K+ was doped by adding to precursor prepared by sol-gel method. The appropriate doping of K⁺ improved the sensitivity of material in the low relative humidity. The resistance of material reduced after K⁺ was doped into it, the humidity sensor based on it had good response in the whole humidity range, and the sensitivity was enhanced significantly. The advantages of this method are saving time and manpower, and easy to achieve uniform doping. At the same time, the recovery characteristic of humidity sensor has also been greatly improved.TiO₂ possess good properties such as chemical and physical stability, good humidity sensitivity and wide sources. Pure TiO2 is an intrinsic semiconductor, the humidity sensor based on the pure TiO2 have high intrinsic resistance, and bring some difficulties to accurate measure. In the past research, the humidity sensitive properties of TiO₂ were usually improved by doping or mixing with other compounds, which was called as TiO₂-based humidity sensitive material, and have been widely investigated. For the material sensitive to humidity, when the other factors about surface of material is roughly same, the greater the surface area, the more the center for absorption of water, and the material possess better humidity sensitive properties. In the fifth chapter, we try to prepared TiO₂ with larger surface area and pore volume by adding tetraethyl orthosilicate to precursor, followed by HF treatment. The sensitivity of synthesized TiO₂ in the low RH was improved significantly, and the humidity sensor had good response to change in humidity in the whole humidity range with little hysteresis and quick response and recovery.The theory of Dielectric Physics was applied to explain the sensing mechanism of the humidity sensors based on the two materials. The complex impedance was obtained, and a circuit was designed to do an experiment named ITIC （the isothermal transient ionic current） to deduce which kinds of the carriers of the sensing materials are domain in different humidity environment. The final results showed that there are two kinds of particles to participate electric conduction in all humidity range, i.e. electron and ion. The electron plays a role more and more weakly, and ion plays a role more and more strongly for electron conduction when relative humidity increases from low to high. The obtained conclusion is identical to the Electron and Proton （Ion） Theory, which is popular currently to explain the humidity sensing mechanism.更多还原