- 學位論文
以流體化床反應器合成奈米碳纖/碳管之特性研究
Synthesis and Characterization of Carbon Nanofibers/Nanotubes by Fluidized-Bed Reactor
摘要
觸媒催化化學氣相沉積法(catalytic chemical vapor deposition, CCVD)是合成奈米碳管(carbon nanotubes, CNTs)的方法之一，也是最適合於大規模合成多壁奈米碳管(multi-walled carbon nanotubes, MWNTs)的方法。本實驗不同於以往傳統CVD法，我們將觸媒放入一直立式流體化床反應器(fluidized bed reactor)爐體中，通入碳源氣體(acetylene)合成奈米碳管產物，其結果以ASAP、SEM、TEM、HRTEM及XRD儀器來作各種分析。 我們並探討各種過渡金屬觸媒在不同反應溫度(700 °C~850 °C)下對於奈米碳管合成之熱力學行為。利用Arrhenius plot可以計算出其個別反應活化能，並且比較其觸媒活性的不同。由ASAP分析之結果得知所得到的奈米碳管產物均為中孔洞材料，其BET表面積介於100 m2/g 至 213 m2/g 之間。由TEM分析產物之外觀形態(morphology)，發現純化後之產物均為多壁奈米碳管而且都具有相當好的石墨層結構。此結果也可以由XRD分析得到證明。利用Debye-Scherrer equation及Bragg’s equation求出奈米碳管之石墨層間距(d002)以及c方向之晶格常數(Lc,)，探討溫度變化對碳管生成所造成的影響。藉由改變反應碳源氣體的分壓比例來推論其反應級數，推論其為一階反應。 本實驗使用具有較佳熱傳及質傳效應等優點的流體化床反應器合成奈米碳管。也提出了一種新型態觸媒載體的選擇，可以輕易的被去除而留下較純的奈米碳管產物，有助於量化奈米碳管的生產。
並列摘要
Catalytic chemical vapor deposition (CCVD) is one of the methods use for large scale production of carbon nanotubes (CNTs). In these results of our experiments, different from others, we synthesize CNTs by acetylene decomposition on supported catalysts in a fluidized bed reactor. The as-grown CNTs products were characterized by N2 adsorption isotherms (BET surface area), scanning electron microscopy (SEM), transmission electron spectroscope (TEM) and X-ray diffraction (XRD). We investigate the thermodynamic behavior in the synthesis of CNTs at different reaction temperature (i.e. 700°C-850°C). According to Arrhenius plots, the apparent activation energies for growth of CNTs were calculated. N2 adsorption showed that the CNTs products have a mainly mesoporosity, and their specific surface areas range from 100 m2/g to 213 m2/g. The morphology of the as-grown products was characterized by TEM, the multi-layered type products composed in perfect graphene layers after purification. This could be confirmed by the clear characteristic peaks after X-ray diffraction analysis. The interlayer distance, d002 and the mean crystalline size along the c axis Lc, could be obtained by using Bragg’s equation and the Debye-Scherrer’s equation. By varying the introduction of acetylene into the CVD reactor, the reaction was shown to be first order. In this present work, we represented the reactor with improved thermal transfer transferability and the catalyst supported material which can be removed easily. These results favored the large-scale production of CNTs with uniformity at low cost.
參考文獻
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