摘要
近年来氧等离子体技术在材料表面改性、激光产生、半导体制造、臭氧产生和环保等领域展现出了良好的应用前景。特别是应用氧等离子体技术处理船舶压载水,可快速杀灭压载水所携带的微生物,而对海洋环境无负面影响,对防治海洋外来生物入侵、保护近岸海域生态安全和生物多样性具有重要的科学意义和实际应用前景。但目前氧等离子体源在构建中存在理论基础薄弱、技术及工艺复杂、一次投入成本和维护成本高等诸多问题;由于多尺度结构效应,简单地放大小型等离子体源装置并不能取得预期效果,这些都限制了氧等离子体技术的规模化应用。针对构建大尺度氧等离子体源的需要,本文依托国家自然科学基金项目“气体电离放电治理外来微生物入侵性传播研究(60371035)”,对DBD氧等离子体源构建中的若干关键问题进行研究,内容涉及DBD电介质材料、等离子体源谐振及等离子体化学动力学三个方面。
根据DBD电介质材料性能要求,对搪瓷作为大尺度DBD氧等离子体源用电介质材料的适用性进行了探讨。通过优化釉料配方和搪烧工艺,制得了电性能、导热性能和机械性能良好,且可修复,成本低的搪瓷材料,该材料适合作为大尺度DBD氧等离子体源用电介质材料。
由于尺度放大,氧等离子体源各组件间会出现失配现象,直接导致系统性能差、能耗高、维护任务重。通过实验对DBD等离子体源与其激励电源之间的失配问题进行了研究,结果发现二者失配的根源在于系统谐振,谐振频率取决于激励电源变压器漏感与DBD电介质层等效电容。
以臭氧产生应用为例,对氧等离子体进行了微观化学动力学模拟研究。通过改变电子浓度、电子平均能量和本底气体温度,研究了等离子体内部参量对臭氧产率的影响。增加电子浓度和电子平均能量会极大地提高臭氧产生速率;若臭氧长时间地受到电子碰撞,其产率会急剧下降。根据DBD微流柱中电子时空分布不均匀性,可通过设置影响微流柱特性的一些参量来优化等离子体源,由此明确了大尺度氧等离子体源的构建设计方向。
In recent years, oxygen plasma technology has shown promising application prospects in materials surface modification, laser generation, semiconductor manufacturing, ozone generation and environmental fields, in particular, the oxygen plasma technology has been successfully employed to ship ballast water treatment, where organisms contained in ballast water are killed in a short time without any negative influence on marine environment. This application is a significant step in preventing invasive spread of marine organisms and protecting marine species diversity, offshore environment. However, the technology and crafts of oxygen plasma sources are very complex, their costs and maintenance are high, the theoretical basis for oxygen plasma source is not well developed, and moreover space-time multi-scale structure effect affects the efficiency of plasma source when it is enlarged in size. Due to the above limitations, scale application of oxygen plasma technology is restricted to few fields. This work aims at building large scale, high efficient oxygen plasma source with the support of National Natural Science Foundation of China "Treating invasive spread of exotic organism with gas discharge (60371035)". In this paper, key problems with regard to establishing large scale DBD oxygen plasma source are studied, main contents are divided into three parts as following: dielectric material for DBD, resonance phenomenon of plasma source, oxygen plasma chemical dynamics.Enamel material with excellent dielectric, heat conducting, and mechanical capabilities is prepared by optimizing ingredients of enamel and technology of enamel firing. This material, which is of low cost and reparable, fits into the requirements for large scale DBD oxygen plasma source.Owing to the enlarging of scale, components of plasma source no longer match with each other, resulting in performance descending, high energy cost and more frequent maintenance. It is found through experiment that the reason for mismatching between DBD plasma source and its exiting power supply lies in system resonance, frequency of resonance is determined by the leak inductance of voltage changer of power supply and the equivalent capacity of the dielectric layer in DBD device.
Micro-chemical dynamics simulation study on oxygen plasma generated by DBD plasma source is conducted, the influence of inner parameters of plasma on ozone yield is studied by varying electron density, electron mean energy and ambient gas temperature. It is found that rates of ozone generation increase greatly with increasing electron mean energy and electronic concentration. If ozone molecules are under electron impaction for a long time, ozone concentration will drop sharply. According to temporal and spatial non-homogeneous distribution of electrons in DBD microdischarges, we can optimize the plasma source by setting the parameters which affect microdischarge, such as input voltage, frequency or dielectric. The direction of building large-scale oxygen plasma source has been given by above research.
引文
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