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    Please use this identifier to cite or link to this item: http://ir.lib.ksu.edu.tw/handle/987654321/6352

    Title: 旋轉對沖流擴散火焰燃燒合成奈米碳管之研究
    Combustion Synthesis of Carbon Nanotubes via Diffusion Flames in Rotating Opposed-Jet Flow
    Authors: 侯順雄
    Keywords: 火焰合成
    Flame Synthesis
    Carbon Nanotubes
    Rotating Counterflow
    Diffusion flame
    Date: 2007-07-31
    Issue Date: 2009-12-30 10:45:17 (UTC+8)
    Abstract: 奈米碳管的合成須具備碳源、熱源和金屬觸媒顆粒三大要件。在各種合成方法中,燃燒合成法具有成本低、穩定性高且能大量產出的絕佳優勢,因此發展潛力十足。本研究之目的係利用旋轉對沖流擴散火焰來進行燃燒合成奈米碳管的分析。對沖流擴散火焰可提供較大面積和較佳的沉積物收集方式,而旋轉流的新方法可增進不飽和自由基於高溫流場的滯留時間,有助於奈米碳管的合成,使燃燒合成法更具經濟效益。實驗中,上燃燒器通入體積百分比14%乙烯和86%氮氣之混合氣,下燃燒器通入空氣形成乙烯/空氣旋轉對沖流擴散火焰,以探討不同旋轉角速度、溫度場、沉積取樣位置和硝酸鎳(催化劑)對奈米碳管生成的影響。本計畫利用鎳網格當做金屬基板,將不塗佈或塗佈重量百分比濃度36.4%之硝酸鎳溶液的鎳網格,置於火焰面上方不同軸向位置,沉積取樣2分鐘,以蒐集碳奈米材料(carbon nanomaterials),然後進行SEM、TEM分析。研究結果顯示,較高的旋轉角速度將使乙烯火焰承受較小的火焰拉伸,使得火焰強度增強,最高溫度提高。而更重要的是由於增大旋轉角速度可增進不飽和自由基於高溫流場的滯留時間,提供有助於火焰合成奈米碳管的碳源濃度。火焰合成的捲曲糾纏型(curved and entangled)多壁奈米碳管結構有中空直管狀(straight tubular)和管內具分隔蓋的類竹狀(bamboo-like)兩種。除了捲曲狀奈米碳管外,亦發現螺旋型(helically coiled)多壁奈米碳管的結構。本計畫之最主要貢獻為證明旋轉流的作用,不但可改變火焰位置、火焰強度和拉伸率,也可提升燃料和氧於流場之滯留時間,有利於碳煙區的形成,亦即更有助於奈米碳管的燃燒合成。若金屬基板塗佈硝酸鎳,則合成的奈米碳管,其長度和數量均有增加的趨勢。此外,本研究利用低燃料濃度(14%乙烯濃度)和低氧濃度(空氣)的對沖流擴散火焰成功合成奈米碳管,而非先前文獻中燃料濃度為100%,且氧濃度必須超過50%才可合成奈米碳管的門檻條件。
    The synthesis of carbon nanotubes (CNTs) on a catalytic nickel substrate using rotating counterflow diffusion flames was investigated. A diffusion flame at high angular velocity (low strain rate) is stronger than a weak flame at low angular velocity (high strain rate) and produces more carbon sources because of the longer residence time of the flow. Even though both the fuel and oxygen concentrations are quite low (using 86% N2-diluted C2H4 as the fuel and air as the oxidizer), CNTs can be successfully produced. This opens the possibility that CNTs can be synthesized in simple non-sooting fuel-air diffusion flames under the influence of flow rotation with a quite low fuel concentration and without a threshold oxygen concentration. Curved and entangled tubular multi-walled CNTs are harvested, which have both typical straight tubular and bamboo-like structures. Besides curved CNTs, helically coiled tubular CNTs are also synthesized. It is verified that flow rotation associated with strain rate plays an important role in the synthesis of CNTs. Using a Ni(NO3)2-coated substrate has advantages over uncoated Ni substrates.
    Appears in Collections:[Graduate School and Department of Mechhanical Engineering] Research Projects

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