以火焰合成奈米碳管的方法具有成本低、穩定性高且能大量產出的絕佳優勢，因此頗具有發展的潛力。目前探討奈米碳管火焰合成技術是一個在國際上正開始競爭追逐的熱門研究重點，然而國內相關的基礎研究則尚付之闕如，因此建立火焰合成奈米碳管的技術和分析能力是刻不容緩的重要課題。本研究之目的在於利用反置同軸噴流擴散火焰，探討不同的燃料濃度、距離火焰遠近、沉積方式、沉積位置以及金屬觸媒催化方式等參數對燃燒合成奈米碳管之成長機制及其結構的影響。
　　研究中首先探討兩環和三環同軸噴流之出口流速、內外管流速比、氧氣濃度和燃料濃度等參數對火焰臨界特性的影響。結果顯示，增加氧氣濃度、燃料濃度以及燃料流速會增加火焰強度、火焰高度及黃焰分布範圍，使得黃焰生成之臨界濃度降低；然而提高氧氣之流速(或流速比)則會減弱富碳環境，抑制黃焰生成，使其黃焰生成之臨界燃料濃度增高。
　　其次，利用三環同軸噴流反置擴散火焰，使用鎳網當作沉積基板和金屬催化物來合成奈米碳管，以穿透式電子顯微鏡(TEM和HR-TEM)及掃描式電子顯微鏡(SEM)觀察不同實驗條件下所生成之奈米碳管的形態及結構。結果指出，在黃焰生成之臨界燃料濃度(高和低沉積位置)下或高燃料濃度且低沉積位置時，垂直沉積之方式可增加碳原子滯留時間，使碳原子滯留在基板上的數量增多，故垂直沉積生成之奈米碳管的數量與長度優於水平沉積。然而在高燃料濃度且高沉積位置時，使用垂直沉積之方式會使得滯留之碳原子數量過多，反而易生成碳顆粒，使得奈米碳管生成量銳減，故在高燃料濃度且高沉積位置時，水平沉積效果反而較垂直沉積為佳。比較同一沉積基板上奈米碳管生成之數量，發現在遠離火
焰端不易觀察到奈米碳管，而基板上靠近火焰端則是奈米碳管生成最多的地方。利用HR-TEM觀察奈米碳管發現其管壁為多壁結構是為多壁奈米碳管(MWNTs)，且所生成之奈米碳管有直管(straight-tubular)及類竹(bamboo-like)兩類。在TEM及SEM的相片中，奈米碳管之頂端、底部及轉折處均有粒狀物，推測奈米碳管係利用火焰中的熱源與碳源，以及金屬觸媒(鎳)所燃燒合成。在鎳格網上沾附硝酸鎳溶液後，其合成奈米碳管的數量較未沾附硝酸鎳的鎳格網多且範圍更廣、長度更長，代表在不同金屬觸媒催化方式中，沾附硝酸鎳溶液的鎳格網，更有助於火焰合成奈米碳管。

　　Flames have great potential for synthesis of carbon nanotubes in large quantities at considerably lower cost in comparison with other currently available methods. This experimental study is aimed at investigating the formation and growth of carbon nanotubes by using inverse co-flowing diffusion flames with different concentrations of fuel and oxidant.
　　The flame appearance, flame structure, and flame stability under the influences of oxidizer and fuel concentrations, stream velocities and inner/outer velocity ratios were firstly studied using image processing techniques. The results showed that raising the concentration of oxygen or fuel, or the velocity of fuel/nitrogen mixture increase the flame intensity, the flame height and the range of yellow flame (sooty zone), and in turn decrease the critical fuel concentrations for the occurrence of yellow flame. However, with increasing the velocity of oxygen/nitrogen mixture, the sooty zone became narrower, leading to the increase of the critical fuel concentration where yellow flame took place.
　　Thereafter, we employed a sampling grid (Ni) used for transmission electron microscopy as the catalytic metal substrate for the nanotube growth. The sampler was mounted on a two-dimensional micro-positioner with the plane normal or parallel to the burner axis. The residence time of the sampling grid inserted into the flame was 120 sec. Synthesis of canbon nanotubes was successfully found from laminar co-flowing oxygen-enriched ethylene diffusion flames. The horizontal sampling approach (with the grid plane normal to the burner axis) to collect deposited materials, carbon nanotubes grew much more and longer than the horizontal sampling approach (with the grid plane parallel to the burner axis) at the critical concentration where yellow flame occured. However, at the fuel concentration higher than the critical concentration where yellow flame took place, there were higher radical concentrations as the grid was placed at a higher position. Therefore, at this condition using the horizontal sampling approach to collect deposited materials was superior to the vertical sampling approach. Furthermore, for the same sampling approach, the position near the flame front had a greater carbon nanotube harvest than that far from the flame front. Straight and bamboo-like carbon nanotubes were observed in the HR-TEM images. The SEM-EDS showed that the particles in the carbon nanotubes are nickel oxide. It is evidenced that carbon nanotubes are produced by the heat source and carbon source in the inverse diffusion flame with the metal catalyst (Ni).

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