【作者】 巫华龙；

【导师】 刘晓初；

【作者基本信息】 广州大学 ， 机械设计及理论， 2010， 硕士

【摘要】 在当前水资源日益短缺情况下,推广节水灌溉已成为世界各国为缓解水资源危机和实现农业现代化的必然选择。要改变传统的灌溉方式,推行现代精准农业,没有稳定、可靠的土壤干湿探头就无法保证智能化节水灌溉的实施。然而,由于土壤干湿探头长期工作在耕作层土壤中,很易发生腐蚀和钝化,从而引起土壤湿度探测的失灵,进而导致过灌而浪费水资源或缺灌而旱坏农作物和植物。本文对太阳能自动节水灌溉控制器土壤干湿探头抗钝化技术进行理论和实验研究,研发了石墨胶凝材料的抗钝化探头。采用了压力实验、化学实验、电化学实验、直流探针压降法和扫描电镜等方法和手段,对探头的形状和表面微结构及其设计与制造方法进行了深入的研究,对不同环境和使用条件的土壤干湿探头的导电性能、力学性能、耐腐蚀性能和抗钝化性能进行了对比分析。研究结果表明:(1)电阻值变化与接触面积并不呈线性关系,在接触面积较小时,探头两端电阻值随接触面积的增大而迅速减小,当接触面积增加到一定程度时,探头两端电阻值随着接触面积增大而减小的速率变慢,但探头和土壤之间的接触面积与探头两端电阻值并没有必然的联系。如内“W”形探头插入深度为3mm时与矩形探头插入深度为15mm时相比,不但接触面积较小而且其检测到的电阻值也比较小。(2)土壤在由湿变干的过程中,有轻微收缩,致使探头与土壤接触由紧变松,导致测量值与实际值发生偏差,土壤越干,偏差越大。合理的形状和表面微结构设计能有效减小这种偏差,其中内“W”型土壤干湿探头和表面微齿结构土壤干湿探头效果最为明显。(3)在酸、碱、盐环境下进行测试,石墨胶凝材料探头都能保持良好的导电性能,稳定性和可靠性明显高于金属探头。酸性和盐分含量高的环境对石墨胶凝材料探头有一定的侵蚀作用,其中盐含量高的工作环境对石墨胶凝材料探头的腐蚀性最大,但都不影响使用效果,也未见发生钝化,而碱性环境下对石墨胶凝材料探头的基本没有影响。(4)土壤干湿探头插入土壤后,其两端电阻值在初期阶段并不是很快稳定下来的,而是呈现出不断增大的变化规律。其中金属探头初值很小,其两端电阻值迅速增大,相比而言,石墨胶凝材料探头所测电阻值较稳定,其增速并不明显。(5)用SEM对四个在相同环境下使用了不同时间的铜镀镍探头横截面进行拍照分析可知,随时间越久,钝化膜层越厚,但膜层厚度与时间并不呈线性关系,膜层生长速度随着时间的增长而减小。更多还原

【Abstract】 Nowadays, with the increasingly shortage of the water resources, promoting water-saving irrigation has became the inevitable choice to ease the water crisis. To change the traditional irrigation methods to promote the modern water-saving agriculture, it has to develop a reliable, stable, soil moisture probe to support the implementation of Water-saving irrigation technology. However, corrosion and passivation are serious problems to soil moisture probe as it must have been working in surface soil. It will lead to the failure of soil humidity detection system, thus cause crops bad because of drought or a waste of water.In this paper, anti-passivation technology of soil moisture probe of solar-powered intelligent water-saving irrigation controller has been studied on. We developed the graphite-cementitious materials probe, and design and manufacture the shape and surface micro-structure of soil moisture probe. Different environments and application conditions affecting conductivity, mechanical, properties, corrosion resistance and anti-passivation of soil moisture probe have been studied by means of compressive strength test, chemical experiment, electrochemical test, DC probe voltage drop method and SEM.Such conclusions can be drawn in our study.(1) As the increase of the contact area between soil moisture probes and soil, the voltage of probes slightly drops and the resistance decreases, but the change of resistance and the contact area is not a linear relationship. The resistance of probes drops rapidly when the contact area increases as the contact area is small, but as the contact area is larger, the resistance of probes drops slowly when the contact area increases.(2) A slight contraction of the soil when it from wet to dry. It makes the contact area between soil moisture probes and soil slightly smaller. This will result in measured value of resistance is larger than actual value. This measurement error can be reduced by reasonable design of shape and surface micro-structure of soil moisture probe. The "W"-shaped probe and the probe of micro tooth structure have excellent performance in reducing this type of measurement error.(3) The reliability and stability of graphite-cementitious materials probe is significantly higher than metal probe, because it can maintain original conductivity in acid, alkali, salt environment. The acid and the salt environment can erode the graphite-cementitious materials probe,but don’t affect its application effect. The graphite-cementitious materials probe was most serious eroded when it works in the environment contained high salt, but Alkaline do not almost affect the graphite-cementitious materials probe.(4) When the soil moisture probes ere inserted into the soil, the resistance of the probes is not stabilized in initial stage, but continuously increases. Initial value of the resistance of metal probes is small, but it increases rapidly. In comparison, initial value of the resistance of graphite-cementitious materials probes is bigger, but its increase is obviously slower. The stability of the graphite-cementitious materials probes is better than metal probes.(5) In the same environment at different times, cross sections of the four probes made of copper coated nickel have been observed with SEM. It can be drawn that the longer, the thicker passive film is. Growth rate of passive film and the time is not a linear relationship. The growth rate of passive film decreases as time increase.更多还原