【作者】 杨永珍；

【导师】 许并社； 刘旭光；

【作者基本信息】 太原理工大学 ， 材料学， 2007， 博士

【摘要】 碳材料是与人类文明进步息息相关的重要材料之一，各种不同形态的碳单质以及碳化合物在人类发展中做出了巨大的贡献。气相生长碳纤维（VGCFs）、碳微球（CMBs）、碳纳米管（CNTs）、纳米洋葱状富勒烯（NOLFs）和碳包覆金属等新型碳功能材料以其优异的特性，使它们在众多领域获得了广泛的应用。重油残渣（即脱油沥青）是重油加工过程中的副产物、一种富碳的复杂混合物，热解可产生CH₄、CO、H₂、N₂、H₂S等气体和低烃类化合物。依赖这些热解气体的综合作用，可以进行气相生长碳材料的合成研究，其裂解后的残余焦经过高温处理、电弧放电等技术也可以转化为石墨类产品。因此，可以说重油残渣是大规模工业化生产碳功能材料的来源之一。从重油残渣中获得高附加值产品，可为扩展传统石油加工过程的产品链并实现资源的综合利用提供新的途径。本论文提出以重油残渣为原料，采用化学气相沉积（CVD）、共炭化、微波等离子体法定向制备VGCFs、CMBs、CNTs、内包铁NOLFs、内包碳化铁碳微粒以及定向碳纳米薄膜等各种高附加值碳功能材料，对产物结构及反应机理进行了系统的分析，研究了各种反应条件下碳功能材料的形成规律，重点讨论了VGCFs的生长过程，提出了其可能的生长机理。并对提纯前后VGCFs的热稳定性和储氢性能进行了初步探讨。基于重油残渣和煤焦油沥青性质的异同点，在本文中也以煤焦油沥青为原料，借助于重油残渣制备气相生长碳材料的方法，采用CVD法合成了VGCFs、CMBs、CNTs及内包金属碳纳米颗粒等碳功能材料，并对二者制备的气相生长碳材料进行了比较。研究的主要内容和结果如下：1、以重油残渣为原料、二茂铁为催化剂前驱体，采用CVD法制备出VGCFs；考察了二茂铁含量、反应温度、反应时间及氩气流量对产物产量和结构的影响。通过场发射扫描电子显微术（FESEM）、高分辨透射电子显微术（HRTEM）、X-射线衍射（XRD）和拉曼（Raman）光谱等技术对产物的形貌和微观结构进行了细致的观察和分析，探讨了VGCFs的生长机理，并对提纯前后VGCFs的热稳定性和储氢性能进行了初步探讨。结果表明：利用重油残渣热解气体的综合作用，按照“颗粒-管-纤维”的过程形成，即直径很小的催化剂颗粒重组成大直径的催化剂颗粒，同时，气体碳源在金属颗粒上吸附、分解、扩散和析出形成细而短的CNTs，再通过CNTs的自催化效应形成VGCFs。通过改变不同的工艺参数制得可控的高质量VGCFs，直径主要分布在100nm～1.2μm之间；其断口呈树木年轮状，具有中空结构，壁是由两种不同结构的碳组成：内层是结晶比较好的石墨片层形成的多壁CNTs结构，外层是沉积在其上的热解碳层；当没有催化剂参与反应时，形成了纯度高的CMBs；定向生长碳纤维、碳树和二次生长碳纤维在其适合的工艺参数时也可形成。并解释了一些特殊结构的VGCFs的形成机理（分叉结构、竹节状和核-壳结构VGCFs）。与传统沥青基碳纤维相比，直接由重油残渣分解所得VGCFs的制备工艺简单、成本低廉，且生产出的碳纤维结构不同于沥青基碳纤维，各种性能也优越，为碳纤维的大量应用和碳纤维工业的进一步发展创造了有利条件。2、以重油残渣为碳源、二茂铁为催化剂前驱体、氩气和氢气的混合气氛为载气，利用CVD法，综合考察了反应温度和氢气流量对CNTs生长的影响，采用FESEM、HRTEM、EDS、XRD和Raman光谱等技术表征和分析产物的形貌和微观结构，提出适合CNTs生长的条件。结果表明：选用催化剂含量为10wt.％的二茂铁，在氩气流量为150ml／min、氢气流量为150ml／min的混合气氛中，当反应温度为1000℃、反应时间为30min时，制备出直径约35nm、弯曲缠绕且纯度高的CNTs，CNTs晶化程度较高但其表面有缺陷存在；CNTs的生长也是取决于重油残渣热解气体的综合协调作用，符合气-液-固的生长机制，其顶部有金属颗粒，属于顶部生长方式。3、以重油残渣为原料，采用CVD法制备了高纯的CMBs，且详细分析了反应温度、氩气流量和反应区域对CMBs的产量和结构的影响，通过改变工艺参数制备了直径可控的高纯CMBs。采用FESEM、EDS、HRTEM、XRD和Raman光谱对CMBs的形态和超微观结构进行了表征和分析；基于实验结果，探讨了其生长机理。结果表明：所制备的可控CMBs直径主要分布在100nm～1μm之间，为规则的球状颗粒，直径分布均匀，纯度很高，但碳球石墨化程度较低。4、以重油残渣为原料、二茂铁为催化剂，在反应温度900℃、反应时间30min、氩气气流150ml／min时，采用CVD法制备出内包铁NOLFs。通过FESEM、HRTEM、EDS、XRD和Raman光谱等技术对产物的形貌和微观结构进行了表征和分析，结果表明：出气口的产物为内包纯铁的洋葱状富勒烯，且颗粒大小比较均匀（直径约3～5nm），洋葱状富勒烯石墨化程度不高。内包铁NOLFs的生长本质上仍遵循气-液-固生长机制，碳层是由碳化铁中碳原子的析出而形成的。5、以重油残渣为碳源、二茂铁为催化剂前驱体，通过热解共炭化反应合成纳米金属颗粒分散的碳基复合材料，然后再经高温热处理合成了内包碳化铁碳微米颗粒，并对其进行了HRTEM和XRD表征分析，结果表明：重油残渣／二茂铁首先经450℃、3h的脱氢缩聚反应合成了直径大约为3nm的金属颗粒分散在无定形碳中的铁／碳复合材料；然后再经2000℃、2h高温热处理，形成了石墨化程度高的内包碳化铁的碳微米颗粒，其外径约300nm，粒径约260nm的金属颗粒被20nm的碳层包覆着，碳层的石墨化程度高，层间距约0.34nm，内包金属为Fe₃C；同时，产物中也发现有未充满的、中空的碳微米颗粒和中空碳纤维生成。6、以重油残渣为原料，采用微波等离子体法制备了一种新颖结构的定向纳米碳薄膜材料，对其进行了FESEM和HRTEM表征和分析。生成的这种定向排列的纳米碳薄膜材料纯度高，无其它形貌的纳米碳材料伴随生成，外观呈条状麦穗形，各条状物平行排列形成定向阵列，最大宽度约为65nm，长度则达到900nm左右；麦穗的主干表层和穗片晶化程度比较好，层与层之间清晰可见，而其中心部位则为非晶态，可能是产物经历了由外向内的生长过程，在目前的反应时间内还未使其内部完全晶化，重油残渣中的重金属Ni、Fe等对其生长起了一定的催化作用。7、以煤焦油沥青为原料，采用CVD法来直接合成VGCFs、CMBs、CNTs及内包金属碳纳米颗粒等碳功能材料；详细分析了催化剂二茂铁含量、反应温度、反应时间、氩气流量、载气种类和产物的生长区域对气相生长碳材料的产量和结构的影响。通过FESEM、HRTEM、XRD和Raman光谱等技术对产物的形貌和微观结构进行了表征和分析，结果表明：当无催化剂参与反应时，合成了高纯的、直径平均为560nm的均匀CMBs；当催化剂二茂铁参与反应时，在高温区依据不同的工艺参数可以制备出直径分别大约为100nm、115nm、320nm和890nm的高质量VGCFs；在载气为氢气（150ml／min）和氩气（150ml／min）的混合气氛时，由于适量氢气的加入，形成了平均直径40nm且弯曲缠绕的CNTs，这与重油残渣生成CNTs的结果和机理是一致的；同样的工艺条件下，在低温区形成了碳内包金属纳米颗粒，与重油残渣在低温区生成的产物相似。并指出，由于重油残渣和煤焦油沥青的元素组成和性质的差别，工艺参数对重油残渣和煤焦油沥青基气相生长碳材料的影响规律有所不同。总之，重油残渣和煤焦油沥青是具有应用前景的新型碳功能材料前驱体，通过采用不同的合成方法调整工艺参数，可以选择性地合成不同形貌和结构的新型碳功能材料。本研究有助于促进石油化工、煤化工和新型碳功能材料的有机融合，不仅为扩展传统石油加工和煤化工过程的产品链、实现资源的综合利用开辟了新的路线，而且也为碳功能材料的研究开辟了新的途径，丰富和发展了碳材料科学。更多还原

【Abstract】 Carbon materials, which have a close relationship with advancement of human civilization, have been one of the most important materials. The various carbon and their compounds have done a great contribution during human progress. Advanced carbon functional materials, such as vapor grown carbon fibers （VGCFs）, carbon microbeads （CMBs）, carbon nanotubes （CNTs）, carbon nano onion-like fullerenes （NOLFs） and metal-encapsulating carbon particles, have achieved extensive application in many areas because of their excellent properties.Deoiled asphalt （DOA） is a carbon-rich by-product of petroleum industry. Vapor grown carbon materials can be synthesized from synergic effects of gaseous species, including CH₄, CO, H₂, N₂, H₂S and low molecular hydrocarbons, which are released during by the pyrolysis of DOA. Furthermore, the residue coke from DOA can be converted into graphitie-like products by heat-treatment or arc-discharge method. Therefore, it is suggested that DOA is a favorable option as a carbon source for large-scale synthetic process of advanced carbon materials. Utilization of DOA of such kind can provide a new approach for expansion of product chains of petroleum processing and comprehensive utilization of petroleum resource.In this paper, the preparation of carbon materials with high added value was achieved from DOA by chemical vapor deposition （CVD）, co-carbonization and microwave plasma methods, including VGCFs, CMBs, CNTs, Fe-encapsulating NOLFs, Fe₃C-containing carbon microparticles and aligned carbon film. The structures and growth mechanisms of the products were investigated systematically with special emphasis on growth model of VGCFs. The thermal stability and H₂ storage performance of VGCFs were also explored. Based on similarities and differences between DOA and coal tar pitch （CTP）, carbon materials, such as VGCFs, CMBs, CNTs and metal-encapsulating carbon nanoparticles, were also prepared from CTP by CVD.The main contents and conclusions are as follows:1. VGCFs were synthesized by CVD in argon atmosphere, using deoiled asphalt as carbon source and ferrocene as catalyst precursor. The influences of different experimental parameters, such as ferrocene content, reaction temperature, reaction time and argon flow rate, were investigated, with respect to the morphology and product yield of VGCFs. The morphologies and structures of products were characterized by field emission scanning electron microscopy （FESEM）, high resolution transmission electron microscopy （HRTEM）, X-ray diffraction （XRD） and Raman spectroscopy. The formation mechanism of VGCFs was discussed in detail. The thermal stability and H₂ storage performance of VGCFs were also explored. The results revealed as follows:The synthesis of VGCFs was found to be dependent on the synergic effects of gaseous species from thermal cracking of DOA and following a growth mechanism of particle-tube-fiber: catalyst nanoparticles first agglomerate and assemble into larger nanoparticles, onto which gasous carbon species are absorbed and converted into CNTs through diffusion and precipitation of gaseous carbon species, and CNTs finally develop into VGCFs by a self-catalysis behavior. An effective mass production of controllable and pure VGCFs, with diameters ranging from 100nm to 1.2μm, was achieved under optimized preparation parameters. The VGCFs exhibited a tree annual ring type of structure and had a hollow core. Their walls can be divided into two different kinds of structures, that is, the high-graphitized inner layer shells and low-graphitized outer layer shells. CMBs were produced in the absence of catalyst. Oriented VGCFs, carbon trees and secondary VGCFs were obtained under appropriate conditions. The VGCFs with special structures （branched, bamboo-shaped and core-shell structure） were also discussed.VGCFs from direct pyrolysis of DOA are distinctively different from traditional pitch-derived carbon fibers in their simple and low-cost fabrication, unique structure and excellent properties. This new approach to VGCFs should be of potential in the production of carbon fibers in large scale.2. CNTs were prepared by CVD using DOA as carbon source and ferrocene as catalyst precursor in an atmosphere of hydrogen and argon. The influences of reaction temperature and hydrogen flow rate on CNTs growth were investigated. The optimum technological parameters for the preparation of CNTs were determined through CNTs characterization by FESEM, HRTEM, EDS, XRD and Raman spectroscopy. The result revealed that high purity and uniform CNTs, with diameter of about 35nm, were grown from DOA by CVD using ferrocene content of 10wt.% at 1000℃for 30min in an atmosphere of hydrogen （150ml/min） and argon （150ml/min）. The as-synthesized CNTs were randomly oriented and tangled with each other and had good crystallinity with some defects on their surface layers. The formation of CNTs depended on the joining effects of pyrolysis gases from DOA and followed vapor-liquid-solid growth model. The metal particles observed on tube tips suggested that the main growth mode followed a tip-growth mechanism.3. A series of size-controllable CMBs were grown from DOA by CVD, with the emphasis on the influences of experimental parameters, including reaction temperature, argon flow rate and reaction zone. The products were characterized by FESEM, HRTEM, EDS, XRD and Raman spectroscopy. The formation mechanism of CMBs was discussed based on experimental results. The results showed an effective mass production of size-controllable CMBs, with diameters ranging from 100nm to 1μm, was achieved. The obtained high purity CMBs were spherical with uniform size and amorphous structure.4. Fe-encapsulating NOLFs were obtained by CVD using DOA as carbon source and ferrocene as catalyst precursor in an argon flow of 150ml/min at 900℃for 30min. FESEM, HRTEM, EDS, XRD and Raman spectroscopy were used to characterize morphologies and microstructures of the products. The results showed that Fe-encapsulated NOLFs in the outlet of quartz tube had core/shell structures with sizes ranging from 3 to 5nm and their outer shells were composed of poorly crystallized graphitic layers. Their growth mode followed vapor-liquid-solid growth mechanism and all atoms in the graphite sheets arose from carbon atoms in the Fe-carbide particles.5. DOA as carbon source and ferrocene as catalyst precursor were chosen to synthesize an Fe/C composite, in which iron nanoparticles were dispersed uniformly in carbon via co-carbonization. The resulting samples were heat treated to synthesize Fe₃C-containing carbon microparticles by high-temperature heat treatment in vacuum. All products were examined by HRTEM and XRD. The results showed that large numbers of metal particles with～3nm in size were dispersed in carbon by co-carbonization products at the temperature of about 450℃for 3h and the degree of graphitization of the products was greatly improved after high-temperature heat treatment at 2000℃for 2h. An Fe₃C microparticle with～260nm in diameter was completely coated with 20 perfect graphitic carbon layers and the spacing of the lattice fringers was about 0.34nm. Besides, partially-filled and hollow carbon microparticles and hollow carbon fibers were obtained by this method.6. Aligned carbon film with novel structure was synthesised from DOA by microwave plasma method, the high pure products were formed orientedly in the shape of strip-like wheat head. Their out-layers possessed a higher degree of graphization, the maximum width was about 65nm and the length was about 900nm, but their center parts were amorphous. It was suggested that the products experienced an outer to inner growth. In addition, some metals in DOA, such as Ni and Fe, which might play the roles of catalyst for the growth of the aligned carbon film, were in favor of the formation of carbon nanomaterials. 7. The direct synthesis of carbon materials, including VGCFs, CMBs, CNTs and metal-encapsulating carbon nanoparticles, was achieved by the pyrolysis of CTP by CVD. The influences of the process parameters, including catalyst content and species, reaction temperature and time, species and flow rate of carrier gas, the growth zone of the products, were studied in detail. The morphologies and structures of the products were characterized and analyzed by FESEM, HRTEM, XRD and Raman spectroscopy. The experimental results demonstrated that pure CMBs with about 560nm in diameter were obtained in the absence of catalyst, and VGCFs, with the diameters of about 100nm, 115nm, 320nm and 890nm, respectively, were obtained, the curl and tangled CNTs with diameter of about 40nm were produced in mixed atmosphere of argon and hydrogen, metal-encapsulating carbon nanoparticles were obtained in the outlet of quartz tube, similar to DOA-based carbon materials. However, the different elemental composition and quality between DOA and CTP resulted in the different rules of influences on vapor grown carbon materials.In brief, DOA and CTP are good precursors for preparing advanced carbon functional materials with great prospect for wide application. Appropriate selection of processing conditions can realize the controllable conversion of DOA and CTP to various advanced carbon functional materials. This research can promote the combination of chemical industry of petroleum and coal with advanced carbon functional material so as to expand product chains in process of petroleum, realize comprehensive utilization of resource, provide a new route for research of carbon nanomaterials, and contribute to the science of carbon materials.更多还原