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    Please use this identifier to cite or link to this item: http://ir.lib.ksu.edu.tw/handle/987654321/9146


    Title: 使用混合燃料反置擴散火焰合成奈米碳結構
    其他題名: A Study on Carbon Nano-Structures in Inverse Diffusion Flames of Mixed Fuels
    Authors: 郭文智
    Kuo, Wen-Chih
    指導教授: 侯順雄
    Keywords: 反置擴散火焰
    Carbon Nano-Structures
    奈米碳結構
    奈米碳管
    奈米碳球
    火焰合成
    Flame Synthesis
    Inverse Diffusion Flame
    Carbon Nanocapsule
    Carbon Nanotubes
    Date: 2007-06-29
    Issue Date: 2010-03-06 18:09:48 (UTC+8)
    Abstract: 本研究之目的在於利用反置同軸噴流擴散火焰,探討混合燃料之比例、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結構之成長機制及其結構的影響。研究中首先針對內管/外環流速比、氧氣濃度和混合燃料比例等參數對火焰臨界特性的影響。結果顯示,提高流速比會減弱富碳環境,抑制黃焰生成,使其黃焰生成之臨界甲烷濃度增高;然而增加氧氣濃度、甲烷濃度及乙烯濃度,則會增加火焰高度及黃焰分布範圍,使得黃焰生成之臨界濃度降低。
    其次,使用鎳格網當作沉積基板來合成奈米碳結構,以掃描式及穿透式電子顯微鏡(SEM、TEM和HR-TEM)觀察不同實驗條件下所生成之奈米碳結構的形態。基板上沉積之奈米碳結構以奈米碳管與奈米碳球為主。以奈米碳管的生成情形來看,甲烷濃度10%的生成範圍及數量都優於甲烷濃度5%,而奈米碳球大部分都生成於甲烷濃度30%下沾附硝酸鎳之鎳格網。此外,並發現在遠離火焰處不易觀察到奈米碳結構,而火焰面或者貼近火焰面處則是奈米碳結構生成最多的地方。利用HR-TEM觀察奈米碳管發現其為多壁奈米碳管,且所生成之奈米碳管有直管及類竹兩類,其頂端及轉折處均有粒狀物。而奈米碳球的內部有粒狀物,可能為填充金屬奈米碳球。在鎳格網上沾附硝酸鎳溶液後,其合成奈米碳結構的數量較未沾附硝酸鎳之鎳格網多且範圍更廣、長度更長,顯示沾附硝酸鎳溶液的鎳格網有助於奈米碳結構生成。
    The formation and growth of carbon nano-structures including carbon nanotubes (CNTs) and carbon nanocapsules in inverse co-flowing diffusion flames of mixed fuel were experimentally studied. The influences of volumetric methane concentrations in ethylene/nitrogen mixture from the outer jet, sampling position and substrate (uncoated or coated with Ni(NO3)2-36.4% by weight) upon the yield of carbon nano-structures were particularly emphasized. The flame appearance, flame structure, and flame stability under the influences of inner/outer velocity ratios, volumetric oxygen concentrations in nitrogen of the inner jet and methane concentrations in ethylene/nitrogen mixture of the outer jet were firstly studied using image processing techniques. The results showed that increasing the injection velocity of oxygen/nitrogen mixture, the sooty zone becomes narrower, leading to an increase in the critical methane concentration require for the occurrence of yellow flame (sooty zone). However, raising oxygen concentration of inner jet or fuel (methane or ethylene) concentration of outer jet resulted in an increase in flame height and a wider range of sooty zone, and in turn a decrease in the critical fuel concentration required for the occurrence of yellow flame.
    Thereafter, we employed a sampling Ni grid as the catalytic metal substrate for the carbon nano-structures growth. The sampler was mounted on a two-dimensional micro-positioner with the plane normal to the burner axis. The sampling time of the substrate inside the flame was kept at 120 sec. The SEM and TEM images showed that carbon nano-structures depositted on the substrates were mainly CNTs and carbon nanocapsule. Curved and entangled tubular multi-walled CNTs (MWCNTs) were harvested, which had both typical straight tubular and bamboo-like structures. Besides curved CNTs, carbon nanocapsules were also synthesized, inside which metal particles were encapsulated. It is of interest to note that only MWCNTs were generated when the mixture of 5% methane/5% ethylene/90% nitrogen and the mixture of 10% methane/5% ethylene/85% nitrogen were separately used as the fuel. Both the growth range and yield of CNTs of the former are smaller than those of the latter. However, carbon nanocapsules synthesized on Ni(NO3)2-coated substrates were found when the methane concentration of outer fuel jet was equal to 30% (i.e. 30% methane/5% ethylene/65% nitrogen). Furthermore, for the same sampling approach, the sampling positions on or near the flame front had a greater carbon nano-structures harvest than those far from the flame front. Using Ni(NO3)2-coated substrates had advantages over uncoated Ni(NO3)2 substrates, which can increase the range, quantity and length of carbon nano-structures.
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