奈米碳管場發射特性對放電產生空氣負離子影響之研究

The effect of field emission traits of carbon-nanotubes on the generation of negative air ions

盧宣任(Shan-Jen Lu)

指導教授 ： 李慧梅

國立臺灣大學/工學院/環境工程學研究所/碩士(2009年)

https://doi.org/10.6342/NTU.2009.00259

摘要

本研究探討奈米碳管場發射特性應用在負極放電產生空氣負離子的影響，並且探討發展微型空氣清淨裝置的可行性。實驗主要探討包含奈米碳管長徑比、奈米碳管密度多寡、奈米碳管層數、金屬材質、金屬長徑比、金屬針尖曲率對放電電壓之影響、產生空氣負離子之穩定度和有效作用空間及監測可能產生之臭氧副產物。奈米碳管長徑比愈大，其場增強效應(enhanced field emission)愈大，所以放電電壓愈低。以長徑比1666.66~5000的多壁奈米碳管做為放電電極時極限電壓值僅需要0.5 kV，首次突破至1.0 kV以下。

奈米碳管陣列因規則排列能降低屏蔽效應(screening effect)，在碳管內部間距為碳管長度的十分之一(陣列碳管密度為1~2×109 CNTs/cm2)時會有最好的場發射效果。奈米碳管長徑比的影響大於奈米碳管層數之影響，長徑比較大的奈米碳管不論其層數，皆具有較低的放電電壓。在相同電壓下，奈米碳管長徑比愈大，負極放電產生空氣負離子濃度之穩定度愈好。

利用模擬脈衝放電產生空氣負離子的穩定度遠高於連續放電。關閉電場30sec後再重新開啟電場一分鐘的方式可讓空氣負離子濃度維持在4.0×105 ions/cm3以上超過30分鐘。空氣負離子濃度隨空間的增加並無明顯影響，對放電電壓幾乎不影響。在沾附奈米碳管的銅電極上，於電壓0.5 kV即可達至空氣負離子極限偵測範圍，並且無臭氧的產生，直到放電電壓為2.5 kV時，才開始產生臭氧增加濃度0.2 ppb，此數值遠低於室內空氣品質建議值0.03 ppm，故不會有臭氧污染問題。

關鍵字

空氣負離子 ； 場發射 ； 奈米碳管 ； 脈衝放電

並列摘要

This study investigated the traits of field emission effect of carbon-nanotubes (CNTs) on generation of negative air ions (NAIs) by negative electric discharging, and the feasibility of developing a microscale air cleaner. The research evaluated the effect of the aspect ratio of CNTs, density of the CNTs, single-wall and multi-wall CNTs and double-wall CNTs, metal material, metal aspect ratio, and metal needle-point curvature on the discharging voltage of CNTs. It also evaluated the stability and the effective space of the generation of NAIs by using CNTs with negative electric discharging, and studied the possible generation of ozone. The results show that enhanced field emission gets bigger when the aspect ratio of CNTs increased, so that discharging voltage gets lower. The limited voltage value of multi-wall CNTs(aspect ratio ranged from 1666.66 to 5000) required only 0.5 kV when they used as discharging electrode. That was the first time the value lower than 1.0 kV.

CNTs array can reduce screening effect because of regular alignment and also reduce discharging voltage effectively. The field emission from CNTs array could be optimized with the inter-tube distance of 10th of the height(CNTs array with density of 1~2×109 CNTs/cm2). No matter the number of layers of CNTs, the CNTs with greater aspect ratio have lower discharging voltage. At same discharging voltage, the stability of NAIs by negative electric discharging gets higher when the aspect ratio of CNTs increases.

And we find out that the stability of generate NAIs by imitate pulsed corona is much better than continued discharging. If we close the electric field for 30sec and restart it for 1 minutes. We could keep the concentration of NAIs over than 4.0×105ions/cm3 for 30minutes. The NAIs concentration did not change with increasing space. CNTs on copper electrode can reach detecting limit range of NAIs at discharging voltage of 0.5kV without generation of ozone. At discharging voltage of 2.5 kV, CNTs on copper electrode begin to generate ozone at 0.2 ppb, this value is much lower than the Indoor Air Quality value (0.03 ppm), so we don’t have to worry about the problem of ozone pollution.

並列關鍵字

negative air ions (NAIs) ； field emission ； carbon-0nanotubes ； pulsed corona

參考文獻

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