本研究之目的在於使用混合燃料之標準噴流擴散火焰合成奈米碳結構，分析奈米碳結構的生成範圍與溫度的條件，進而了解奈米碳結構的生長機制。
研究中首先對以甲烷為燃料之標準擴散火焰進行特性分析，結果發現，內外管速度比越大，火焰的熄滅極限會稍微提早發生，火焰較不穩定。當內外管速度比為1的情況，在以甲烷為單一燃料的實驗中發現，固定氧氣濃度，持續減少甲烷濃度會使黃焰消失，再繼續減少甲烷濃度則會造成上飄火焰，繼續降低甲烷濃度則會達到熄滅極限，火焰就會飄離管口並熄滅；若固定甲烷濃度，增加氧氣濃度會造成火焰長度變短，及黃焰分布範圍變小。在使用甲烷與乙烯5 %的混合燃料的情況下，固定氧氣濃度，持續減少甲烷濃度會使黃焰分布範圍變小，但不會消失，且無論甲烷濃度如何降低火焰都不會熄滅；若固定甲烷濃度，氧氣濃度增加會造成火焰長度變短，及黃焰分布範圍變小。比較兩者的碳顆粒生成範圍方面，加入乙烯5 %可大幅增加黃焰分布範圍，且所需的甲烷濃度可降低；而氧氣濃度過低易使火焰變長，造成火焰易受外界環境的影響，且也可能造成火焰熄滅極限提前發生。若氧氣濃度過高，則會使火焰長度變短及黃焰範圍減少。
本研究沉積取樣的火焰條件，固定燃料管出口速度20 cm/s、內外管速度比1、氧氣濃度30 %、乙烯濃度5 %，但改變甲烷濃度分別為5 %、10 %和30 %，在不同軸向位置沿徑向位置進行取樣，探討甲烷濃度與取樣位置對合成奈米碳結構的影響。為了瞭解奈米碳結構的生成機制與溫度範圍，亦進行溫度場量測。由沉積物取樣的觀察結果可以發現，奈米碳結構只能生長於黃焰範圍之內，且黃焰太多或太少都不利於生成奈米碳結構。在三個甲烷濃度中，以10 %及30 %高取樣位置的奈米碳管沉積效果較好，隨著取樣高度降低，奈米碳管的生成範圍有向火焰面接近的趨勢，數量隨著徑向距離越大而漸減少，接近火焰面奈米碳管的生成數量又再增多。只有在甲烷濃度30%發現奈米碳球，其合成溫度範圍約1000℃與1300~1400℃兩個區間，且在兩個奈米碳球的生成區間夾著奈米碳管的生長區域，溫度約1100℃。本研究利用火焰合成之奈米碳管有捲曲和螺旋狀兩大類。有趣的是螺旋狀奈米碳管之生成位置離黃焰約1.5~2 mm，且溫度約1048~1082℃。在各種甲烷濃度情況下，加入硝酸鎳在大部份的實驗條件可以促進合成奈米碳管。

In the present study, we aim at investigating the synthesis of carbon nano-structures including carbon nanotubes (CNTs) and carbon nano-spheres on a catalytic nickel substrate using normal jet diffusion flames, with particular emphasis on the influence of mixed fuel (methane and ethylene) on carbon nanomaterials growth. The flame appearance, flame structure, flame stability, and soot layer are experimentally observed using image processing techniques. Meanwhile, the temperature distributions at various axial and radial positions are measured by using an R-type thermocouple. Moreover, we employ the bare nickel substrate or Ni(NO3)2-coated nickel substrate to collect deposit materials. Finally, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy are utilized to characterize the morphology and microstructure of condensed carbon deposits and their formation mechanism in the combustion environment.
The SEM, TEM, HR-TEM and EDS images show that carbon nanotubes and carbon nano-spheres are successfully synthesized at suitable operating conditions. Many carbon nanotubes are harvested in the soot zone of flame whose temperature range is about 750~1250℃. Curved and entangled tubular multi-walled canbon nanotubes are found, which have only typical straight tubular structures. In addition to curved CNTs, a small amount of helically coiled tubular CNTs are also synthesized when the sampling position is located at a distance of 1.5~2 mm from the soot zone where the temperature is about 1048~1082℃. However, carbon nano-spheres can be observed only at higher height above of burner (i.e. 15 and 10 mm) and higher methane concentration, 30%, for fixed ethylene concentration, 5%. The temperature range of carbon nano-spheres formation is around 1000℃ and 1300~1400℃. It is of interests to note that the formation zones of carbon nanotubes and carbon nano-spheres are different although they can be synthesized at the same operating conditions.

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