【作者】 温斌；

【导师】 李廷举； 赵纪军；

【作者基本信息】 大连理工大学 ， 材料加工工程， 2006， 博士

【摘要】 纳米金刚石由于其具有一系列特殊的结构和功能,倍受人们关注。然而其制备过程产量较低、不易实现连续化生产。1991年,日本学者Hirai等在研究金刚石的形成机理时发现了一种新的碳同素异构体——新金刚石。由于许多实验所获得的新金刚石样品量都比较少,且新金刚石的颗粒尺寸都很小（小于100nm）,对新金刚石结构的研究只能采用电子衍射的办法,从而制约了对新金刚石晶体结构及其物性的研究。在理论研究方面,纳米碳颗粒之间的相对稳定性问题是理解碳纳米材料形成机理的关键,但由于以前计算条件的限制,对该问题的研究仍然有许多的不足。 本文针对新金刚石产量低、纳米金刚石粉生产困难及理论研究方面的现状,提出了具有自主知识产权的催化法（炭黑催化法和催化碳纳米管法）制备纳米金刚石和新金刚石的构想。并在催化法大量制备纳米金刚石和新金刚石的基础上,对其合成机理、新金刚石的晶体结构、纳米金刚石的尺寸和形状对其稳定性、电子结构和声子振动的影响进行了系统的研究,同时,对炭黑催化产物在吸波材料方面的应用做了系统的研究。 以纳米铁为催化剂,炭黑为碳源,在常压和1100℃下保温成功地制备出了纳米金刚石和新金刚石,并用X射线衍射（XRD）、透射电镜（TEM）和拉曼光谱（Raman）对制备的样品粉末进行表征。结果表明,样品粉末是由纳米金刚石粉和石墨包覆新金刚石纳米颗粒组成,纳米金刚石粉的大小为20nm,石墨包覆新金刚石的大小为100nm。 在常压和100℃下,通过水热处理新金刚石和纳米金刚石的混合粉末,制备出了透明的碳薄片。利用扫描电镜（SEM）、TEM、电子探针（EPMA）和傅立叶变换红外吸收光谱（FTIR）对该薄片的相结构和形貌进行表征。结果表明,该碳薄片是具有sp³电子杂化类型的无定型碳,且其并不是纳米金刚石粉末的简单聚集体,而是一种新的水热处理产物。 依据不同温度下的炭黑催化法实验和催化碳纳米管实验结果,提出了催化法制备纳米金刚石和新金刚石的唯像机理。随着温度的增加和碳在铁中的扩散,催化剂Fe在反应过程中经历的相变化顺序是:Fe（OH）₃→Fe₂O₃→Fe₃O₄→α-Fe→γ-Fe→Fe-Calloy（liquid）→γ-Fe→α-Fe,碳通过在铁液中的扩散和溶解并以石墨和纳米金刚石的形式析出,并在铁处于γ-Fe阶段时,碳以新金刚石的形式析出,最后碳以石墨、纳米金刚石和新金刚石的形式保留了下来。 新金刚石的热稳定性实验结果表明,当其加热到150℃时开始相转变,并在400℃转变结束,而且该相转变反应为放热反应。通过XRD对不同时间时效处理新金刚石样更多还原

【Abstract】 The microstructure, mechanical, and electrical properties of nanocrystalline diamond offer many opportunities for application, therefor the study of nanocrystalline diamond was the research forcus recently. Whereas the synthesis of nanocrystalline diamond was very difficult, the yield was limited. In order to understand formation mechanisms of diamond, a unique procedure was designed by Hirai and Kondo in 1991, and found a new kind of possible allotrope of carbon. In their original paper, this new phase was referred to as "n-diamond" (new-diamond). For 77-diamond, despite the successful synthesis of n-diamond using different approaches, the crystal structure and properties of n-diamond is still unclear yet, mainly due to the small amount of n-diamond samples and the tiny crystalline size (typically less than 100 nm) in previous experiments. Hence, only transmission microscopy (TEM) and electron diffraction were feasible for structural analysis of n-diamond in the previous experiments. For theoretical part of nanocrystalline carbon particles, the relative stability of different forms of carbon at nanoscale is the key point to understand the formation mechanism of carbon phase at nanoscale, and then there are many insufficiencies as a result of calculational condition now.In order to solve the aboved-mentioned problems for nanocrystalline diamond and n-diamond, a method to synthesize nanocrystalline diamond and n-diamond by nano-sized Fe catalyzed carbon black or carbon nanotubes was suggested in this paper. Based on the larger output of n-diamond powders from the method of catalyzed carbon black, the formation mechanism of nanocrystalline diamond and n-diamond from catalyzed carbon black, and the crystal structure of n-diamond were studied. In addition, the effect of size and shape of nanocrystalline diamond on the stability, electron structure and phonon structure of nanocrystalline diamond were studied by the first principle. Finally, the electromagnetic wave absorption properties of carbon powder from catalyzed carbon black were studied by experiments and theory.With carbon black as carbon source and nano-sized Fe as catalyst, nanocrystalline diamond and n-diamond particles have been synthesized at atmospheric pressure and at 1100 ℃. X-Ray diffraction (XRD), Raman, TEM, and electron-probe microanalyzer (EPMA) were emploied to analyze the samples. The results indicated that the final product consists of two types of particles: spherical nanocrystalline diamond and graphite coated n-diamond particles,and the average size of the nanocrystalline diamond is about 20nm, and that of the graphite-coated ^-diamond particles is about 100 nm.With admixture of ^-diamond and nanocrystalline diamond from catalyzed carbon black as carbon source, transparent wafers have been synthesized by hydrothermal process at 100°C and atmosphere pressure. Scanning electron microscopy (SEM). XRD, Raman spectroscopy, TEM and EPMA were used to analyze those transparent wafers, and the results indicated that the transparent wafers were amorphous sp3-banding carbon wafer, and it also indicated that the wafers weren’t aggregate of nanocrystalline diamond from the carbon source, and that the wafers were a new kind of reaction product by hydrothermal treatment.A series of catalyzed carbon black or carbon nanotubes experiments at different temperatures were designed and the final products were studied by XRD, thermal gravimetric analysis (TGA) and differential thermal analysis (DTA). Based on the results of XRD, TGA and DTA, a formation mechanism was proposed to explain the phase transformation from carbon black or carbon nanotubes to nanocrystalline diamond and ^-diamond. With the increase of temperature and hence the carbon diffusion in iron, the phase sequence is from Fe(OH)3 into Fe2C>3, oc-Fe, y-Fe, then liquid iron. When carbon in the liquid iron is saturated, nanocrystalline diamond or graphite is separated out of the liquid iron. With the decrease of temperature, the carbon in y-Fe is separated out- and ^-diamond nuclei are formed and grow up.The thermal stability of /7-diamond was investigated with XRD, TGA and DTA. The results indicated that the phase transformation of w-diamond begins at 150°C and is complete at 400°C, and this phase transformation of ^-diamond was an exothermic reaction. The crystal structure of the ^-diamond after various aging-treatment times was investigated by XRD. The XRD indicated that the ^-diamond was a metastable phase, and crystal structure of the ^-diamond changed with the aging-treatment times at room temperature.Based on the XRD analysis and simulated XRD pattern, two kinds of crystal model for ^-diamond are suggested, and one is "defeciive diamond" model with fractional occupation site, and the other one is "mislayered diamond" model. With the "defective diamond" model, the zero occupancy corresponds to a face-central cubic (fee) crystal, while full occupation leads to a perfect diamond. In this model, a density functional theory computation further confirms the trend of increasing stability during the evolution from fee to diamond structure. Therefore, it was suggested that ^-diamond is indeed an intermediate state between the fee structure and diamond structure. With the "mislayered diamond" model, the crystal structure model of ^-diamond was considered to be R3 space group with cell angle a=90° and lattice parameter ao=3.58O9 A. An equilibrium lattice constant for this ’"mislayered diamond" model was obtained by the first-principles calculations, and that is close to the measured value. Itwas assumed mat n-diamond was a transition state between rhombohedral graphite and diamond. The electronic structures of n-diamond further investigated, and it was indiacted that the n-diamond is a good conductor with substantial density of state at Fermi level.Three kinds of nanocrystalline diamond in different shape and a high symmetrically graphene sheet were modeled at different size. The effect of size and shape of nanocrystalline diamond on the stability, electron structure and phonon structure of nanocrystalline diamond were studied by the first principle, and the following conclusions were obtained. 1. By comparing the heat of formation, it was found that the octahedron nanocrystalline diamond was the steadiest one among the three kind of nanocrystalline diamond with different shape. When the number of carbon atom was less than 330, the nanocrystalline diamond was steadier than graphene sheet. 2. The effect of shape of nanocrystalline diamond on the HOMO-LUMO energy gaps Egap, ionization potential IE and electron affinity EA were lesser, the function between energy gaps Egap, ionization potential IE, electron affinity EA and reciprocal of the size of nanocrystalline diamond d’1 was accord with a linear equation. 3. For the three kinds of nanocrystalline diamond in different shape studied in this paper, all of the values of electron affinity of nanocrystalline diamond were negative. With decreasing size of nanocrystalline diamond, the values of electron affinity of nanocrystalline diamond decrease. The negative electron affinity was directly related with the property of electron emission of nanocrystalline diamond.Using a refection/transmission technique, the complex relative permittivity and permeability of the carbon powder from catalyzed carbon black (CPCCB) were measured in X and Ku band. It was indicated that the real part e’ of permittivity for CPCCB decreases monotonously from 26 to 15, and the imaginary part s" of permittivity decreases monotonously from 41 to 23, and both the real part s’ and the imaginary part s" of permittivity for CPCCB show significant variation with the frequency and the magnitude of both parts decrease with increasing frequency. The real part n’ of permeability for CPCCB was 1.0, whereas the imaginary part fx " of it is about zero and nearly remains constant during the frequency region studied. Those results demonstrate that the CPCCB hardly has diamagnetism and magnetic loss. The reflection loss and percentage absorption of the CPCCB/paraffin wax composite were obtained by the arc reflecting method. For the sample with 3 vol. % lossy fillers content, it has a higher absorption value (absorption percentage larger than 70 %) in the X band (8 to 12.4 GHz). For the sample with 6 vol. % lossy fillers content, it has a higher absorption value (absorption percentage larger than 70 %) in the Ku band (12.4 to 18 GHz).The calculational results indicated that with increasing thickness, the absorption of the composite increases. For the sample with the CPCCB content of 3vol%, a broad absorptionpeak appears when the thicknesses reach 8 mm. For the sample with the CPCCB content of 6vol%, a broad absorption peak appears when the thicknesses reach 4 mm, whereas the frequency position of the broad absorption peak is different for the composites with different thickness.更多还原