應用單脈衝放電生成奈米碳管之研究

Abstract

隨著奈米碳管應用的方式與目的不同，使得碳管在多元的應用上被賦予相當多的期待，目前最常製備奈米碳管的方法，分別是:電弧法、化學氣相沉積法與雷射蒸發法。然而在生成上需配合高電流、真空腔、特殊氣體、催化劑與長的反應時間來營造出碳管生成氣氛，使得奈米碳管的製程條件複雜與缺乏擇區生長的彈性。因此，本論文提出一種新的奈米碳管製程技術，將藉由微放電加工的方式，期待符合奈米碳管多元應用之需求，另一方面可擴展微放電加工技術至奈米碳管製程產業中。 本研究創新提出以放電加工的方法，在大氣下生成奈米碳管，更特別的是本製程並不需高電流與催化劑來營造生成氣氛。在研究中，自行製作了一套單脈衝放電迴路與機構，並以放電電流與放電幅寬為製程的主要參數。由奈米碳管生成的形貌與趨勢，歸納出本製程技術之奈米碳管生成參數範圍，成功的生成多壁與尖狀的奈米碳管。研究結果顯示，製程中提供過大的電流量與放電幅寬時，雖然可產生較多的碳源，但電極尖端的消耗亦隨之增加，而引發電弧的不穩定，使得放電坑內的碳濃度反而下降，而並未能有碳管長成。另一方面，當電流量與放電幅寬過小時，放電坑內卻又無足夠的碳源與持續的溫度場，給予成核點吸附碳源，同樣的亦無碳管的長成。這意味著碳管的生成與電流、放電幅寬有關，但並無比例的關係。由一次性單脈衝放電 Ip=4A,τ=1200μs的條件所製得的奈米碳管叢中發現，其碳管的頭型為尖型，這將有利於場發射電極的應用，其碳管的生長率更高達22.5mm/min。 綜觀上述本研究的製程與分析，我們已成功的在無催化劑、大氣下生及無操作腔體限制之環境下生成奈米碳管，藉由微放電的製程確實可為奈米碳管的生成提供更簡易、快速與可擇區的製程。

The principal methods for producing CNTs have arc discharge method, chemical vapor deposition (CVD) method and laser ablation. Owing to the different applications of CNTs, many methods are created to meet this purpose. The application of CNTs in many fields is hopefully expected. In this research we will offer a new fabrication technology for CNTs by micro electro-discharge machining (MEDM). This method not only can comply with different applications of CNTs but also extend the MEDM method to the CNTs industry. In contrast to the typical CNT preparation method, the current micro-electro discharge method can be used to prepare CNTs under atmospheric environment without the necessity of expensive vacuum system. In this study, a self-design micro electro discharge-system was used to prepare carbon nanotubes. The effect of processing parameters including the applied peak current and pulse duration were investigated. The results reveal that the carbon concentration in the hole is decreased while high current and widen arc width are used, so no CNTs can be obtained. On the other hand, insufficient carbon source and temperature field can provide the energy for CNT growth under low current and narrow arc with. Therefore, the current and arc width play important roles for the CNT growth but no proportional relationship between the parameters and production is observed. The CNTs with tape tip can be prepared under Ip=4A,τ=1200μs under single-pulse discharge, which is benefit for the field emission application. The growth rate is up to 22.5mm/min。 It is concluded that the CNTs can be produced by using MEDM even without any protection gas, cooling system, special preparation and cavity. Furthermore, using this simplified equipments and preparation process of MEDM, as another beneficial option, can be applied to producing CNTs in the near future.