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    Please use this identifier to cite or link to this item: http://ir.lib.ksu.edu.tw/handle/987654321/6236

    Title: 擴散火焰燃燒合成奈米碳簇之研究
    Authors: 侯順雄
    Date: 2008-07-31
    Issue Date: 2009-12-30
    Abstract: 本研究計畫之目的在於利用對沖流擴散火焰進行燃燒合成奈米碳簇的實驗分析,探討混合燃料、氧濃度、溫度場與沉積位置等參數對於火焰合成奈米碳結構之成長機制及其結構的影響。研究中以鎳網當作沉積基板和金屬催化物來合成奈米碳結構,並以掃描式電子顯微鏡(SEM)及穿透式電子顯微鏡(TEM和HR-TEM)觀察不同實驗條件下所生成奈米碳結構的形態及結構。本研究合成的奈米碳結構包含奈米碳管和奈米碳球兩大類。合成的奈米碳管有捲曲(curved)和螺旋型(helically coiled)兩種多壁碳管,而合成的奈米碳球為實心,且具有同心圓的石墨層結構。當下燃燒器供應空氣(即低氧氣濃度:21%),上燃燒器的乙烯濃度固定為5%,甲烷濃度由15%增加至45%時,發現只有在甲烷濃度為25%,溫度範圍在800~ 1000°C時,可以大量合成奈米碳管,其管徑約為20 ~ 25 nm。然而當下燃燒器的氧濃度增加至50%時,則只有奈米碳球可以被成功地合成;將甲烷濃度由15%逐漸增加至45%時,發現奈米碳球的產率和直徑亦隨著逐漸增加。甲烷濃度為15%、25%、35%和45%時,其對應的碳球直徑分別為5 nm、20 nm、40 nm和60 nm。顯而易見,氧氣濃度的高低對於火焰合成奈米碳結構有重大的影響。此外,為了探討混合燃料的影響,將上燃燒器中的乙烯調降為0%,而僅供應45%的甲烷濃度,結果發現並無法合成奈米碳球。然而,此時若將甲烷濃度提高至50%或55%時,則又可觀察到大量的奈米碳球,且其產率同樣隨甲烷濃度提高而增加。因此,本研究的重要結論為利用對沖流擴散火焰燃燒合成奈米碳球的關鍵參數為氧氣濃度,而非混合燃料。
    High-yield synthesis of carbon nanotubes (CNTs) and nano-onions (CNOs) on a catalytic nickel substrate using counterflow diffusion flames was investigated. With ethylene fixed at 5%, methane varied from 15% to 45% in the upper flow, and air supplied in the lower flow, only a moderate CH4 concentration (25%) could yield high-density CNTs. Curved and entangled tubular multi-walled CNTs were harvested, which had both typical straight tubular and bamboo-like structures. Besides curved CNTs, helically coiled tubular CNTs were also fabricated. However, when oxygen was increased to 50% in the lower flow, only CNOs were synthesized. An increase in methane concentration from 15% to 45% led to a higher yield and a greater diameter (ranging from 5 ~ 60 nm) of CNOs. To examine the role of mixed fuel, it was observed that as ethylene was removed and only 45% methane and nitrogen were supplied in the upper flow, no CNOs could be generated. While, as methane was increased to 50% or 55%, high-yield CNOs were synthesized and the yield increased with the methane concentration. The key parameter affecting the formation of CNOs using counterflow diffusion flames is the oxygen concentration, not the mixed fuel.
    Appears in Collections:[機械工程系所] 研究計畫

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