【作者】 李永峰；

【导师】 邱介山；

【作者基本信息】 大连理工大学 ， 化学工艺， 2004， 博士

【摘要】 发现于上世纪末的富勒烯和碳纳米管是炭素材料家族的新成员,在力学和电学等诸多方面展示出奇特的性质,是当今纳米材料和炭素材料研究领域的前沿和热点课题。目前,纳米炭素材料的研究在材料的制备及其物理化学性质的研究等方面已经取得了很大进展,但纳米炭材料昂贵的价格仍然是限制其大规模化应用的主要瓶颈之一。本文以廉价碳源-煤炭为原料,采用等离子电弧放电法较系统地开展了煤基纳米炭素材料的制备研究,成功制备得到了富勒烯和多种结构形态的碳纳米管,其中包括高碳富勒烯、多壁碳纳米管、竹节形碳纳米管、Y形碳纳米管、单壁碳纳米管和双壁碳纳米管;研究了煤基炭纳米材料的微观形貌及其生长机理,同时探讨了在催化剂和等离子体电弧辅助条件下热解烃类气体,以煤基炭棒为基体制备微米炭材料的技术途径。通过优化实验条件和控制实验参数,可以在一定程度上实现不同形态的炭微米材料的选择性可控制备。主要的研究结果如下:以煤为原料实现了煤基富勒烯的大量制备。激光时间飞行质谱的检测发现,煤基富勒烯烟灰中含有多种高碳富勒烯如C72、 C82、 C102、 C106及C120等;煤种是影响富勒烯产率的主要因素之一,新疆无烟煤和太西无烟煤是电弧放电法制备富勒烯的理想碳源,在最佳实验条件下粗富勒烯的产率可达6. 77Wt%(与烟灰的重量比),而由扎赉诺尔褐煤得到的粗富勒烯产率仅为1. 43Wt%;富勒烯副产物的成分分析显示它们中含有大量碳氢化合物,表明煤基富勒烯的形成机理与石墨基富勒烯的形成机理不同,大尺寸的芳香碎片可能是形成煤基富勒烯的主要前驱体来源之一。制备得到了多种不同形态的煤基多壁碳纳米管。由不同变质程度的煤种制备得到的碳纳米管在产率上有很大差异,顺序如下:无烟煤>烟煤>褐煤;在最佳实验条件下煤基多壁碳纳米管的产率可达9. 16Wt%(以消耗的煤基炭棒为基准);电弧放电状态和催化剂对于碳纳米管的形成至关重要,控制电弧放电状态可以制备出宏观量的竹节形碳纳米管,其含量在60%以上(根据电镜观察结果估计);催化剂是影响纳米碳管形态和结构的一个重要因素,以铁粉为催化剂(10-20Wt%,占整个炭棒的重量比),不仅得到了竹节形碳纳米管,同时还得到了一种巨型富勒烯,其外径分布为50-70 nm,内径分布为40-50 nm;添加硫化亚铁能显著促进Y形碳纳米管的形成,得到的Y形碳纳米管之含量可以高达40%以上(根据电镜观察结果估计)。实验结果表明,影响碳纳米管形态和产率的主要因素包括煤基炭棒的结构、催化剂和电弧的放电状态等数个方面。以煤为原料,利用电弧放电技术制备得到了高纯度的单壁碳纳米管。在本文实验条件下,以无烟煤为原料制备单壁碳纳米管的产率最高,烟煤次之,褐煤最差;以La一Ni为催化剂获得的单壁碳纳米管的产率较高(1.67wt%,以消耗的煤基炭棒为基准);由不同催化剂得到的单壁碳纳米管之直径大小顺序为:Fe>Ni>La一Ni。 在低真空条件下,用电弧放电方法以煤为原料制备出双壁碳纳米管,产率和纯度均较高:得到的双壁管的直径均匀,大约70%左右的煤基双壁碳纳米管的直径分布在4.0一4.snln之间。 通过在煤中添加催化剂,电弧放电条件下,以煤为起始原料获得了一种外形新颖的球形炭,其直径分布在10一20协m,炭球之间的结合形态有链状、平板状、链状及树状等,EDX、XRI)及拉曼光谱的表征结果证实得到的煤基炭微球的碳含量超过99%,且具有较高的石墨化程度。 实验发现,在缓冲气体中有烃类气体(乙炔和甲烷)存在条件下,用电弧放电技术方法可以制备新型的炭微米材料。分别以煤基炭棒、石墨棒及碳化硅棒为阳极,制得了形态各异的炭微米材料,包括:微米树、生物形态微米炭、花形微米炭等;初步认为影响微米炭材料的因素有:电(阳)极的结构和性质、缓冲气体中烃类气体的混合比例、所用催化剂的性质等;用发射光谱(OES)技术对电弧等离子体进行了原位诊断研究,结果表明反应体系中存在的C:自由基可能形成炭微米材料的主要中间体之一。关键词:煤;电弧等离子体技术;炭纳米材料;炭微米材料;制备方法更多还原

【Abstract】 Fullerene and carbon nanotubes (CNTs) are new family members in carbon materials since their first discovery in the late 20th century. Due to their spectacular mechanical and electronic properties, fullerenes and CNTs are found to be of great use both in theoretical study and in applications in a wide range, which have been the frontiers in the research field of nanocarbon science. Though much progress has been made in synthesis of various carbon nanomaterials and in study on their chemical and physical properties, the high-cost for producing nanocarbons is still one of the key issues that need to be considered for the commercial applications.Coal is a cheap carbon source in nature, and has long been considered to be a good starting materials for value-added carbons. In this paper, the potential of using coal as precursor for making novel nanocarbons and microcarbons has been explored systematically. Various forms of nanocarbons including higher fullerenes, multi-walled CNTs (MWNTs), bamboo-shaped CNTs (BCNTs), Y-junction CNTs (YCNTs), single-walled CNTs (SWNTs) and double-walled CNTs (DWNTs) have been successfully synthesized from coal by arc plasma, which depends on the arc discharge conditions and other parameters including coal type and/or whether catalysts are used or not. The morphologies of the obtained nanocarbons and the mechanisms involved in the their formation process are studied. In addition, the possibility of producing microcarbons with coal-based carbon rods as substrate via arc discharge technique in a mixture gas of helium and hydrocarbons such as CH4 or C2H2 is also explored and highlighted. It has been found that several micro-sized carbons with novel morphologies can be prepared after optimizing the experimental conditions. The main results are summarized as follows.Fullerenes can be obtained from coal in high yield by arc discharge method, and the crude fullerenes were analyzed using laser desorption time-of-flight mass spectrometer. The results show that in addition to C60 and C70 fullerenes, higher fullerenes such as C72, C82, C102, C106 and C120 are present in the coal-based crude fullerenes in relative high content. The yield of coal-based crude fullerenes depends on coal rank to a great degree. Of the coals tested, Taixi anthracite is the best one in terms of fullerenes yield, from which a yield of 6.77 wt% is obtained. While in the case of Zhalainuoer lignite, the yield of crude fullerenes is only 1.43 wt%. The by-products of coal-based fullerenes were analyzed using GC-MS, showing the presence of aromatic hydrocarbons, which implies that carbon fragments released from the coal-based carbon rods during the arcing process may function as one of the main intermediate precursors and get involved in the formation process of coal-based fullerenes.It has been found that the yield of coal-based CNTs is greatly affected by the coal rank, and the highest yield of CNTs (9.16 wt%) could be obtained from Taixi anthracite under theoptimized conditions. The results show that the arcing conditions and catalysts are the key factors for the formation of bamboo-shaped CNTs (BCNTs), and over 60% of well-developed BCNTs in the products is obtained from coal-based carbon when iron powder is added as catalyst; at the same time, a novel carbon nano-capsules or giant fullerenes with uniform outer diameters of 50-70 nm and inner diameter of 40-50 nm is also obtained as the by-products of BCNTs when a high content of iron powder (10~20wt%) is used as catalyst. Moreover, YCNTs could be prepared in high yield when FeS powder is added into the iron group catalysts. It has been estimated according to the TEM examination that the content of YCNTs in the final products is over 40% under some conditions.High purity SWNTs is successfully prepared from coal. The yield of SWNTs is closely related to coal rank, which follows an order: anthracite > bituminous coal > lignite. The SWNTs synthesized with iron as catalyst have a diameter distribution range of 1.24-2.19 nm, while SWNTs prepared with nickel or lanthanum-nickel as ca更多还原