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研究生:鄭啟煇
研究生(外文):Cheng, Chi-Hui
論文名稱:用電弧法在甲烷與氦氣混合氣體中合成石墨包裹奈米鎳晶粒的初步結果
論文名稱(外文):Preliminary Results of the Synthesis of Graphite Encapsulated Nickel Nanoparticles by Tungsten Arc Method in Methane/Helium Atmosphere
指導教授:鄧茂華鄧茂華引用關係
指導教授(外文):Teng, Mao-Hua
學位類別:碩士
校院名稱:國立臺灣大學
系所名稱:地質科學研究所
學門:自然科學學門
學類:地球科學學類
論文種類:學術論文
論文出版年:2002
畢業學年度:90
語文別:中文
論文頁數:69
中文關鍵詞:奈米材料電弧石墨包裹甲烷
外文關鍵詞:nanoparticlesarcgraphitecarbonencapsulatednickelmethane
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石墨包裹奈米晶粒是一種粒徑為1~100 奈米(nm)的球狀複合材料,其內核為金屬,外層為石墨。最早於1993年利用碳碳電弧法(Krätschmer-Huffman method)製造碳60的衍生材料的實驗中發現(Tomita et al., 1993, Ruoff et al., 1993)。當時有許多人想要在碳60中間的空位中塞入其他的金屬,卻意外的在實驗產物中發現少量的石墨包裹奈米晶粒。不過此法所製造出來的產物量極少(約幾百粒),根本無法進行科學的基礎研究。1995年Teng et al.與Dravid et al.提出以鎢電極為陰極,以石墨坩堝為陽極,並將電極以垂直配置新方法以取代水平配置的舊方法。此改良式鎢電弧法的優點為:穩定性高、實驗時間長且產生的雜質較少;但因金屬的比例過大所以能用來包裹的碳之來源相對不足,無法有效率地將所有金屬顆粒包覆,造成產物在經純化分離的過程後僅能回收少量的純石墨包裹奈米晶粒。
對於碳含量不足的問題,林春長(2002)提出在純化分離的步驟之前加入真空熱處理的程序,使初產物之金屬顆粒可以被石墨包覆的更完整,進而減少其中的碳雜質。本研究則嘗試另一個增加碳含量的方法,在鎢電弧法的製程之中加入甲烷氣體,經由甲烷的分解,提供石墨原料之外的碳來源,以解決碳含量不足的問題。
實驗的結果發現,在氦氣中摻入少量甲烷,對回收率的增加有非常顯著之效果;於低電流變因的實驗條件下,回收率可以高達60%左右,而在高電流的情況下也有約30%左右。相對於純氦氣的實驗,不論是高電流或是低電流,回收率都不到5%。對於甲烷可以提昇回收率的原因推測有三:第一、甲烷在高溫下分解產生的碳,經由二步驟機制中的催化效應,可以使未包裹完整的顆粒外層包覆的更完整。第二、甲烷分解產生的氫原子在電弧區附近結合,放出的熱有助維持電弧區附近的高溫。第三、經甲烷分解的氫原子可接在石墨邊緣的懸吊鍵(dangling bonds)上,有助於石墨的分解,對一開始加進坩堝的石墨原料,可令其以更小片的形式分散在金屬之中,因而有助於石墨的蒸發。至於高電流條件下回收率會較低,猜測是因為金屬蒸氣量會較低電流時來的多,但碳的蒸氣量並沒有相對增加。對於總產量來說,以摻入甲烷的高電流變因之實驗結果較佳,但是因為其回收率較差,所以此實驗條件組合較易造成鎳金屬原料的浪費。若將裝置改善為以一恰當比例的甲烷/氦氣持續的在實驗進行的過程中流通,應該可以改善高電流實驗產物的回收率。
Graphite encapsulated nanoparticle is a new composite material with a core/shell structure. The core may be pure elements or carbides, and the shell is graphite or amorphous carbon. This new material has great potential in various applications, not only because its nanocrystalline spherical structure, but also because the shell can protect the core material from sever environmental reactions such as oxidation, hydrolysis, or acid erosion.
Graphite encapsulated nanoparticles were first found in 1993 by two groups, one is Saito et al. in Japan, and the other is Subramoney et al. in USA. They used Krätschmer-Huffman method to synthesize the particles, but the very low production rate and the high percentage carbonaceous debris were the two major problems of this method. To improve the Krätschmer-Huffman method, Dravid et al. developed a new tungsten arc method in 1995. The new method uses tungsten rods as cathode, and graphite crucible with metal source materials as anode. The tungsten arc method raises the production rate and greatly decreases the amount of carbonaceous debris in the product, however, it is still suffer from low recovery ratio after acid wash procedure due to relatively low carbon content.
To increase the recovery ratio of the initial product, Lin (2002) has demonstrated that a heat treatment process prior to the acid bath procedure can effectively increase the recovery ratio. In this research, we introduce some methane into the chamber atmosphere during the arcing process, so as to provide additional carbon sources that may facilitate the encapsulation process of the particles.
The results show that the new methane procedure can greatly increase the recovery ratio of initial products. The ratio has been raised to 30~60%, comparing to less then 5% if we use helium only. There are three possible reasons for this result: 1. the carbon coming from the decomposing methane may provide additional carbon sources that makes the particles to be encapsulated easier. 2. some of the hydrogen atoms coming form the decomposing methane may reunite into molecules after passing through the arc, and therefore may release additional heat to maintain the required high temperature around the arc, effectively prolong the reaction time of the particles. 3. the hydrogen atoms may also help to etch the graphite into small pieces of polycyclic aromatic hydrocarbon and be separated in the melting nickel pool more easily.
The equipment now can only take up to 40 Torr methane with 200 Torr helium atmosphere in order to have a steady arc. If we can introduce low ratio CH4/He gas continuously during the experiment, the recovery ratio can be higher. In the future, we’ll set up a continuous flow of methane/helium mixed gas with various mixing ratios and total pressures. Hopefully the new setup can greatly increase the recovery ratio of the desired nanoparticles.
致謝……………………………………………………………………I
摘要……………………………………………………………………II
Abstract………………………………………………………………IV
目錄……………………………………………………………………VI
表目錄………………………………………………………………VIII
圖目錄…………………………………………………………………IX
第一章 前言……………………………………………………………1
第二章 文獻回顧………………………………………………………3
2-1奈米材料……………………………………………………………3
2-1.1奈米材料的製造方法…………………………………………3
2-1.2電漿加熱蒸發法………………………………………………4
2-2石墨包裹奈米晶粒…………………………………………………6
2-2.1顆粒的結構與型態……………………………………………6
2-2.2石墨包裹奈米晶粒的形成機制………………………………10
2-2.3各元素與碳進行作用的狀態…………………………………12
2-2.4以電弧法製造石墨包裹奈米晶粒之製程演進………………15
2-2.5石墨包裹奈米鎳晶粒的磁性質………………………………18
第三章 實驗方法與儀器分析………………………………………22
3-1實驗裝置……………………………………………………………22
3-2實驗流程……………………………………………………………24
3-3分析儀器……………………………………………………………27
第四章 實驗結果與討論……………………………………………33
4-1儀器分析結果………………………………………………………33
4-2各變因的控制與影響討論…………………………………………50
4-2.1坩堝內的配置…………………………………………………50
4-2.2電弧所使用之電壓……………………………………………52
4-2.3艙內氣壓………………………………………………………54
4-2.4甲烷分壓………………………………………………………54
4-2.5電弧所使用電流………………………………………………56
第五章 結論…………………………………………………………58
參考文獻………………………………………………………………60
中文部分………………………………………………………………60
英文部分………………………………………………………………61
附錄一…………………………………………………………………64
附錄二…………………………………………………………………67
附錄三…………………………………………………………………68
中文部分
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