电弧法无催化剂控制制备碳纳米管

IMR OpenIR

	电弧法无催化剂控制制备碳纳米管
	蔡兴科
学位类型	硕士
导师	丛洪涛
	2012
学位授予单位	中国科学院金属研究所
学位授予地点	北京
学位专业	材料学
关键词	电弧无催化剂可控制备碳纳米管 Arc Discharge Without a Catalyst Controllable Synthesis Carbon Nanotube
摘要	" 一般情况下，催化剂是碳纳米管制备必不可少的，常用催化剂为过渡金属Fe/Co/Ni。产物中金属催化剂的残留会直接影响对碳纳米管化学、电学、磁学和热学性质的研究。也会阻碍了其在纳电子器件、催化剂载体、生物医学等领域内的实际应用。无催化剂污染高纯度、宏量、控制合成碳纳米管始终是该研究领域的重点和难点，也是制约其应用的“瓶径”问题之一。电弧放电法是大量制备碳纳米管的方法之一。相比于其它方法，电弧放电法制备的碳纳米管具有石墨化程度高、结构完整、缺陷少和稳定性高等优点。电弧放电法也是唯一不需要催化剂宏量制备碳纳米管的方法。然而，因电弧放电过程是局域超高温、超高温度梯度的远离平衡态，故电弧法的制备条件难以控制。本文围绕改进电弧放电法在不加催化剂的条件下对碳纳米管的取向、形貌和直径的调控开展工作，取得主要研究成果如下：（1）氢电弧放电法自催化调控取向生长垂直碳纳米管阵列。改进氢电弧放电法，在不加催化剂条件下，通过扩大阳极区的尺寸和在阳极表面施加垂直电场等方法，制备出垂直于阳极表面的碳纳米管阵列。研究表明：碳纳米管阵列的长度可达30 um，直径20-120 nm，碳纳米管形貌为类竹节状；氢自由基的活化作用、适宜的温度场和电场力是影响碳纳米管阵列生长的主要因素。（2）优化生长条件调控碳纳米管直径。分别采用氢、氦、氩和氮等不同种类的等离子电弧法，在不加催化剂的条件下，研究电极尺寸、气体种类对碳纳米管直径和长度的影响，在分析氢、氦、氩或氮等不同种类气体热导率、比热容等热物理特性对电弧温度场作用的基础上，通过优化电弧温度场、实现碳纳米管直径在10-15 nm，长度在1-2.5 μm 范围内的大致可控。特别是采用小阳极（直径为2 mm）的氢电弧法在不加催化剂的条件下成功制备出单壁碳纳米管。为无催化剂污染、宏量制备单壁碳纳米管探索了可行性。（3）研究建立了一种半连续大量制备单壁碳纳米角的氮电弧法。研究表明：单壁碳纳米角的产量随放电电流增加而提高，单位产量的能耗也有所降低。电流为420 A时，产量可达100 g/h。XPS分析表明:单壁碳纳米角有约0.3%氮掺杂。在此基础上，用氮化取代氧化，在600-1000℃高温下，建立了一种单壁碳纳米角开口处理的方法。研究表明：单壁碳纳米角开口处理是氨气刻蚀和高温退火共同作用的过程。随着处理温度的提高，单壁碳纳米角的比表面积和孔体积都增加。经1000℃/1h小时热处理，单壁碳纳米角的比表面积（BET）可达1245 m2/g,孔体积为1.30 cm3/g。这种单壁碳纳米角可望在超级电容器、锂离子电池等有广泛的应用前景。"
其他摘要	Catalysts are usually necessary for the growth of carbon nanotubes (CNTs), and usually they are metals, such as Fe, Co and Ni. However, the residual catalysts will directly influence the property characterization of CNTs, such as chemical property, electrical property, magnetic property and thermal property. Moreover, it will also impede the potential applications of CNTs in many fields, such as electric devices, catalysts supports and biological medicine. Controlled synthesis of CNTs without the contamination of catalysts in large quantities has always been the key and difficult problem in the CNT field, and the “bottle neck” that restrict the application of CNTs. Arc discharge is one of the methods that can produce carbon nanotubes in large quantities. Compared with products by chemical vapor deposition, the products by arc discharge have higher degree of graphitization, complete structure, fewer defects and better stability. What’s more, arc discharge is the only method that could produce CNTs in large quantities without a catalyst. However, it is very difficult to control the synthesis by this method, since the arc discharge process is a non-equilibrium process which has local high temperature, high temperature gradient. In this dissertion, we focus on controlling the direction, morphology and diameter of CNTs by arc discharge without a catalyst. The main results obtained are as follows: (1) Synthesis of vertically-aligned CNTs by hydrogen arc discharge without a catalyst. Vertically-aligned CNTs were prepared by hydrogen arc discharge, using pure graphite powder as carbon source without catalysts added. Scanning and transmission electron microscopy characterizations show that the aligned CNTs have a bamboo-like structure, and their lengths and diameters are about 30 μm and 40–60 nm, respectively. No metallic impurities can be detected in the samples by careful X-ray photoelectron spectroscopy detection. The activation of hydrogen radicals, the heating effect of the arc, and the electric ﬁeld surrounding the arc column area are considered to play important roles for the non-catalyst growth of the CNTs. (2) Control the diameter and length by optimizing the growth condition. The diameters and lengths of CNTs can be adjusted among 10-15 nm and 0.5-2.5 μm, respectively, by arc discharge without a catalyst, through adjusting the anode graphitic rod size, cathode graphitic rod size and the growth atmosphere. SWCNTs were synthesized by arc discharge without a catalyst, when the anode size is 2 mm under hydrogen atmosphere. Retention time, carbon source concentration in the arc column area, and active species are considered to be important factors to influence the diameters of CNTs. What’s more, this provides a way to obtain SWCNTs in large quantities without a catalyst. (3) Semi-continous synthesis of single-walled carbon nanohorns (SWCNHs) in large quantities by arc discharge and open it without oxidation. The productivity of SWCNHs by nitrogen arc discharge will increase as the discharge current increases, while energy consumption per gram will decrease as the discharge current decreases. When the current is 420 A, the productivity can reach 100 g/h. The XPS analysis shows the nitrogen content of SWCNHs is about 0.3% by nitrogen arc discharge. And a new opening method without oxidation using NH3 treatment under high temperature is invented, which is an NH3 etching and high temperature annealing process. As the treating temperature under NH3 atmosphere increases, the BET specific surface area and pore volume will increase. When the synthesized SWCNHs was treated at 1000 ℃ for 1 h under NH3 atmosphere, the BET reaches 1245 m2/g, and the pore volume reaches 1.3 cm3/g. This kind of material may find its potential application in supercapacitors, lithium ion batteries and so on.
文献类型	学位论文
条目标识符	http://ir.imr.ac.cn/handle/321006/64511
专题	中国科学院金属研究所
推荐引用方式 GB/T 7714	蔡兴科. 电弧法无催化剂控制制备碳纳米管[D]. 北京. 中国科学院金属研究所,2012.