摘要:電暈放電(Corona discharge)是一種能夠產生高濃度單一極性離子的離子產生現象,經常使用在靜電集塵器內,使微粒帶電。除此之外,文獻還指出電暈放電會產生微粒,並且微粒產生之粒徑與分布會受到電暈放電的特性所影響。而此現象的產生主要是經由兩種途徑,第一種途徑為電場內的離子獲得足夠動能後與放電極撞擊所產生的,另一種途徑為電暈放電所產生的臭氧與空氣中的氮化物所反應生成的。大部分的研究皆是探討如何減少微粒的產生以避免污染,而本計劃將利用此特性發展一奈米微粒產生器。對於奈米研究來說,一個良好的奈米微粒產生器是不可或缺的,目前已知產生奈米微粒的方法不外乎使用雷射、化學沉積、火焰燃燒、高溫氣化以及電噴灑法。這些奈米微粒產生法雖然可以產生出特定的奈米微粒分布,但仍然有其缺點,例如能量耗費過多、穩定時間長、易生成氧化物以及微粒濃度不足等問題。而電暈放電具有產生原理簡單、維修簡便、成本便宜與調整濃度容易等特點,作為一產生器可謂相當具有優勢,唯目前對其產生原理了解並不多,需花費更多時間研究。將在實驗室中架設一板線型電暈放電系統,並且以微粒電移動度分析儀與微粒電流計來量測奈米微粒分布以及帶電量並同時監測其臭氧產生量。電暈放電所產生的微粒將會利用能量散佈分析儀(EDX)與穿透式電子顯微鏡(TEM)確認其大小以及成分。而實驗過後的放電極也將使用電子顯微鏡(SEM)觀察其表面特性。實驗中將改變電暈放電的電極形狀與材料、風量與風速、載運氣體組成、供給電壓與電流、以及電極極性來探討各種影響產生微粒之因素。本實驗最終目的為釐清產生原理、探討影響因子,最後將根據電暈放電特性設計出一可長時間穩定、可控制微粒產生分佈以及濃度之奈米微粒產生器。整體架構可區分成4個部分:(1) 從靜電集塵到產生奈米微粒機制轉換研究(2) 電暈放電奈米微粒產生機制探討(3) 電暈放電產生奈米微粒影響因子探討(4) 可控制粒徑分佈奈米產生氣得研發
Abstract: A reliable nanoparticle generator is essential for nano-technology studies. Currently available generators use various methods to produce nanoparticles, including laser ablation, chemical vapor deposition, gas phase condensation, spark deposition, electro-spray, and liquid flame spray. Although these methods can generate specific particle distributions, they still are not perfected. Some of these generators waste energy, have a lengthy stabilization time, generate a low nanoparticle number concentration, and oxide the particles. In addition to the above-mentioned aerosol generators, electrostatic precipitators (ESP) have long been found to release more particles than the challenge exhaust air, especially when under extremely high electric field. The ESP nanoparticle production has a high correlation with the corona discharge of the device. The size distribution and number concentration were affected by the applied voltage, current and other parameters which can affect the corona discharge. Although the principle of this mechanism is still not clear, it is a workable way to generate nanoparticles.This proposal is to design and construct laboratory-sized corona discharge aerosol generation systems that can be used to evaluate the characteristics of aerosol generation. A scanning mobility particle spectrometer or a fast mobility particle sizer will be used to measure the nanoparticle number concentration and size distribution. An electrometer will be used to measure the number of particle charges, and a watt gauge will be used to measure the energy consumption. Variable air flow rate will be controlled by a mass flow controller to study the flow dependency. A PID controlled heating unit will be used to condition the carrier gas (or air) up to 80 degree Celsius. Particles generated by corona discharge will be collected by filters to analyze their size, morphology, chemical and physical characteristics by using SEM, TEM, AFM and EDX. An ozone meter will be used to measure the ozone concentration. In order to study the factors affecting particle generation, parameters will include the shape and material of electrodes, carrier gas flow rate and gas velocity, composition of carrier gas, applied voltage and current, and polarity of electrodes. Depending on the particle charge density and aerosol number concentration, a neutralizer (Am241) will be used to neutralize the aerosol output to the Boltzmann charge equilibrium right downstream of the aerosol generation section.This proposed corona discharge aerosol generation system is expected to be simple in principle, stable to operate, easy to use and has low energy consumption. An ideal nanoparticle generator should be stable for a long period of time, and capable of producing desired size distribution. Therefore, the ultimate goal of this proposed study is to develop a universal size–distribution nanoparticle generator based on corona discharge. The generator may be useful in the research fields of basic aerosol technology, material science, and aerosol medicine. The whole project can be divided into several sequential phases:Phase 1: Mechanism transmission from electrostatic precipitator to nanoparticle generator.Phase 2: Mechanism of corona discharge nanoparticle generation.Phase 3: Factors affecting corona discharge nanoparticle generation.Phase 4: A universal size-distribution corona discharge nanoparticle generator.