【作者】 计道珺；

【导师】 汪厚植；

【作者基本信息】 武汉科技大学 ， 材料学， 2005， 博士

【摘要】 碳纳米管由于具有一系列优异的性能,从1991年被发现以来,受到物理学家、化学家和材料学家的广泛关注。目前碳纳米管的应用及产业化过程还存在诸多问题,碳纳米管的规模化制备技术尚未成熟。本论文以日产公斤级多壁碳纳米管为目标,利用溶胶-凝胶和超临界流体干燥技术制备的复合气凝胶NiO/SiO₂为催化剂,用催化气相裂解法制备了不同形貌和结构的多壁碳纳米管,系统地研究了裂解反应温度、催化剂的化学组分、反应时间、气体流量等工艺条件对多壁碳纳米管的收得率、形貌和结构的影响,探讨了不同的纯化处理工艺对多壁碳纳米管表面特性和内部结构的影响,并比较由不同碳源气制备的碳纳米管的形貌和结构。在实验室研究的基础上,对多壁碳纳米管的规模化制备进行设计研究,设计出一条多壁碳纳米管规模化制备生产线,制得的多壁碳纳米管纯度高,成本低,具有竞争优势。得到以下结论: 1.以正硅酸乙酯和硝酸镍为原料,通过合理调变溶胶-凝胶和超临界流体干燥法的制备条件,获得了比表面积在500～1400m²/g范围内,并具有中孔和微孔结构的二元气凝胶——NiO/SiO₂。 2.对各工艺参数的研究结果表明:反应温度、催化剂的化学组分、反应时间、气体流量均对多壁碳纳米管的形貌、结构和收得率有重要影响。 （1）反应温度直接影响着多壁碳纳米管的形貌和收得率。适宜的温度有利于碳纳米管的形成,600～740℃是多壁碳纳米管的适宜生长温度区间,温度过高或过低均使收得率大大降低,在680℃左右,收得率最高（8.6）。温度过低多壁碳纳米管生长不完全,长径比很小,而温度过高合成的产物中含有大量杂质。 （2）催化剂的化学组分是影响多壁碳纳米管的收得率的关键因素。以n_（Ni）:n_（Si）值不同的气凝胶NiO/SiO₂为催化剂,制各出的多壁碳纳米管收得率差异较大,当气凝胶中n_（Ni）:n_（Si）=4:6时,收得率最高。 （3）反应时间对多壁碳纳米管的收得率有重要影响,对碳纳米管的形貌影响相对较小。在180min内,随反应时间延长,多壁碳纳米管的收得率呈增长趋势,多壁碳纳米管的长径比增加,而直径的变化不大。超过180min,多壁碳纳米管的收得率增长很慢,最终保持在一个最大值。 （4）碳纳米管的形貌和收得率随气体流量的变化而变化。CH₄与H₂的流量比例为2:1更多还原

【Abstract】 Since their discovery in 1991, carbon nanotubes （CNTs） have attracted many scientists to study them due to their excellent properties. At present, many problems about application and industrialization of CNTs need to be solved, and the technology of large-scale preparation of CNTs has not been well developed. In this dissertation, in order to prepare multi-walled carbon nanotubes （MWNTs） at least one kilogram every day, MWNTs with different morphologies and microstructures were prepared by using composite aerogel NiO/SiO₂ as catalyst, which was synthesized using sol-gel and supercritical fluid drying technology. It was studied that how the aerogel component, decomposition temperature, time and gas flow rate affect the yield, morphology and microstructure, and the influence of purifying process of MWNTs was discussed. On the basis of laboratory work, the author designed a set of product line for large-scale preparing MWNTs. Resultant MWNTs have high purity, low cost and competitive advantage. Some conclusions were draw as below:1. By using tetraethoxysilane, nickel nitrate as starting materials, NiO/SiO₂ aerogel, with high specific surface area in the range of 500¹400m²/g, having micropore and mesopore structure, was synthesized by sol-gel and supercritical fluid drying method. The microstructure and aerogel component could be controlled by adjusting preparing conditions.2. The experimental results indicate that parameters, including decomposition temperature, aerogel component, decomposition time and gas flow rate, directly influence morphology, microstructure and yield of resultant MWNTs.（1） The decomposition temperature influences morphology and yield of MWNTs directly. Proper temperature is helpful for MWNTs’ growth. MWNTs prepared at lower temperature can not grow enough and have a low aspect ratio, but MWNTs prepared at higher temperature have much impurity. The yield of MWNTs will be reduced much at too high or low temperature. The temperature range, from 600 to 740℃, is suitable for MWNTs growth, and the yield of MWNTs prepared at 680℃ is the highest （8.6）.（2） Aerogel Component is the key factor to influence yield of MWNTs. The yield of MWNTs varies greatly with the different value of n_Ni:in_Si in NiO/SiO₂ aerogel. If value ofri（Ni）:n（si） equals 4:6, the yield of MWNTs is the highest.（3） Decomposition time plays an important role on the yield of MWNTs, but little on their morphology. The yield of MWNTs increases with decomposition time within 180min. The length increases but the diameter changes little. MWNTs grow slowly after 180min, and the yield remains constant.（4） The morphology and yield of MWNTs vary with gas flow rate. The MWNTs with good morphology and large aspect ratio can be prepared while the flow rate of CH4 is twice that of H2, and the yield is high. The yield of MWNTs increases with the total gas flow rate, but above 300ml/min, the yield of MWNTs will be constant.（5） Purifying process can remove impurity in MWNTs, enhance their purity and influence their microstructure. Introducing 129Xe NMR to characterization of CNTs for the first time, the experimental results indicate that it is an effective technique to explore microstructure and surface condition of CNTs.3. Possibility of searching for other gas as carbon source is explored. The experimental results show that morphology and structure of MWNTS vary greatly with different carbon sources. MWNTs prepared from CH4 have a large aspect ratio, smooth wall and regular morphology; those from C3H6 have a little amorphous matter, rough wall, and some wrinkle, which means a lower oriented order of carbon atoms. Compared with from CH4, MWNTs prepared from C3H6 have a higher yield and a lower conversion.4. On the basis of above research, the author designed a set of safe, efficient and convenient product line for preparing MWNTs in large scale. The solid distributing style for catalyst can make an area over lm2. At the help of Pd-carbon fiber deoxy catalyst, tittle oxygen in industrial nitrogen can react with hydrogen at low temperature and produce water, and it can be absorbed by zeolite. Flowing route of gases can be prolonged by disturbing tube in pyrolysis furnace, and CH4 and H2 are utilized efficiently by using gas recycling equipment. According to the relationship among distribution area of catalyst, quartz tube volume and gas flow rate in laboratory catalytic decomposition, gas flow rate in large-scale preparation can be calculated. By comparing yield and microstructure of MWNTs, the processing parameters are optimized, and the practical cost of high quality MWNTs is no more than 1.5 yuan RMB.更多还原