碳纳米管及其限域体系的高压结构相变和超硬相研究

发布时间：2018-04-08 16:06

本文选题：金刚石对顶砧　切入点：高压　出处：《吉林大学》2017年博士论文

【摘要】：碳纳米管作为一维纳米材料的典型代表,其中空的一维纳米孔道为研究纳米限域体系提供了理想的模板。限域环境下碳纳米管内部的分子会展示出不同于体材料的新结构和新性质。高压可以有效的调控原子间距离,从而影响其相互作用及成键形式,进而导致物质结构、性质的变化,是合成新材料、发现新现象的重要手段。将碳纳米管及其限域体系与高压手段相结合开展实验研究,不仅有助于丰富和深化我们对碳材料新特性及其主客体之间相互作用的认识,揭示它们高压相变的物理机制,而且为我们构筑具有新型结构和性质的碳材料提供了新的思路和途径。目前关于碳纳米管及其限域富勒烯和纳米带体系在高压下的结构转变机制和性质变化还不清楚,以碳纳米管作为初始碳源去构筑新碳结构的研究还很少。针对这一问题,本文对多壁碳纳米管阵列(MWNTAs)、C70 peapod(C70@SWCNTs)、石墨烯纳米带掺杂的单壁碳纳米管(GNRs@SWCNTs)和碳纳米管纤维这几种材料开展高压研究,得到如下结果:1.利用高压偏振拉曼光谱对多壁碳纳米管阵列(MWNTAs)进行了研究,针对高压下MWNTs阵列中的压制管间相互作用变化、结构相变及键连行为等问题进行了分析。发现多壁碳纳米管阵列在常压条件下D峰和G峰的强度随偏振角度的改变呈现规律性的变化,表现出明显的偏振依赖性:在VV情况下,G峰的拉曼峰强度在0o达到最强,90o达到最小;VH时,45o达到最强,0o/90o达到最小。高压下,G峰的强度随着压力的增加偏振依赖性逐渐减弱,当压力高于20GPa后,偏振依赖性消失。对22GPa卸压后的样品进行表征发现压力处理后,阵列中碳纳米管的排布更为紧凑,但多壁碳纳米管的结构并没有被破坏。这种偏振性的减弱是由于压力下增强的管间相互作用导致电子态离域,降低了材料的偏振依赖性,使其行为趋向体材料所引起的。另一方面,随着压力进一步增加,MWNTAs出现的偏振依赖性消失可以归因于压力诱导管间相互作用增强导致碳管发生结构相变,管间或层间形成共价键。我们的结果说明偏振拉曼技术能够在高压下用于判断MWNTs阵列中压力诱导的管间相互作用变化和结构相变的行为。这也解决了长期以来在高压下研究碳管管间聚合课题上存在的争议,为碳纳米管的压致转变研究提供了重要的思路。2.对C70@SWNTs材料开展了原位超高压研究,获得了可常压截获的新型超硬碳结构。利用透射电镜、Raman光谱及X射线衍射(XRD)等实验手段对几个不同压力卸压的C70 peapod样品分别进行了表征。发现从最高压力卸压后的C70 peapod样品的XRD具有很多清晰可辨的衍射峰,这些衍射峰不属于以往报道的任何碳结构。理论模拟进一步预测了一个新的全sp3碳的、具有C2/m对称性的V carbon结构。所有的碳原子完全以化方式成键。计算表明V carbon在0-100GPa的压力范围是稳定的,它的能量仅略高于金刚石,而低于以往报道的其他碳结构。此外,V carbon具有与金刚石相媲美的的硬度和体弹模量,这很好的解释了实验中金刚石砧面上留下的环形压痕。V carbon模拟的XRD谱与实验数据吻合的很好,说明我们实验产生的新碳结构指认为V carbon是合理的。同样重要的是,我们给出了从初始C70 peapod材料向V carbon转变的物理图像。该转变过程中,含奇数碳环的C70 peapod作为基本构筑单元起到了重要作用,这为设计合成新碳结构提供了一种新的策略,强调了初始碳源的重要性。该结果对人们构筑碳结构提供了新的思路,将启发人们利用、设计含有奇数碳环的peapod前驱物作为基本单元去构筑新碳结构。3.对限域于碳纳米管内的石墨烯纳米带(GNRs@SWNTs)开展了常压和高压结构研究,揭示了温度对限域纳米带生长的影响及高压下结构相变行为。研究发现限域于碳纳米管内部的二萘嵌苯分子在高温退火后能形成限域的纳米带,且纳米带的长度受退火温度影响。高压进一步调控主客体之间的相互作用,发现碳纳米管在7GPa左右开始发生坍塌,内部的纳米带受到破坏,限域的石墨烯纳米带作为“探针”反映碳纳米管在高压下的结构相变。对比研究了高压下空的和填充的碳纳米管的结构塌缩压力,发现填充纳米带后的碳纳米管塌缩压力明显降低,这种现象是由于纳米带分子的非均匀填充碳纳米管,带来了应力分布不均匀所致。理论计算进一步支持我们的实验结果。该结果有助于我们更深入理解限域空间纳米带的高压变化行为以及纳米带与碳纳米管之间相互作用。4.利用激光加热在金刚石对顶砧内对碳纳米管纤维进行了高温高压研究研究。发现15GPa,2000K条件下,碳纳米管纤维转变形成纳米金刚石结构,同时产物中可能还含有少量的“n-diamond”结构。
[Abstract]:Carbon nanotubes as a typical one-dimensional nano materials, including one-dimensional nano pore space of nano confinement system provides an ideal template. The molecular carbon nanotubes within the domain environment will show new structures and new properties different from bulk materials. High pressure can effectively control the distance between atoms, thus affecting their mutual the role and bonding form, resulting in material structure, the nature of the change is the synthesis of new materials, an important means to discover new phenomena. The carbon nanotube and its confinement system and high pressure by means of combining experiments, not only helps to enrich and deepen our understanding of the interaction between the new characteristics of carbon material and its main object they reveal the physical mechanism, high pressure phase transition, and the formation of the carbon materials with novel structure and properties and provides a new way for us. At present on carbon nanotubes and its limit The domain of fullerenes and nanoribbons structure transition mechanism and properties under high pressure change is not clear, using carbon nanotubes as the initial carbon source to build on new carbon structure are rare. In order to solve this problem, the array of multi walled carbon nanotubes (MWNTAs), C70 Peapod (C70@ SWCNTs), graphene nanoribbons doped single-walled carbon nanotubes (GNRs@SWCNTs) and carbon nanotube fibers of high pressure to carry out this research of several materials, the results are as follows: 1. using high polarization Raman spectra of multi walled carbon nanotubes array (MWNTAs) was studied, the interaction between the change in the tube pressing under high pressure in MWNTs array, phase transformation and bonding behavior of structure the problem is analyzed. That change strength of multiwalled carbon nanotube array under atmospheric conditions D and G peaks with the polarization angle of the obvious polarization dependent: in the case of VV, G peak The intensity of Raman peak reached its maximum at 0o, 90o VH, 45o reached the minimum; the strongest, 0o/90o minimum. Under high pressure, the intensity of G peak with the increase of pressure polarization dependence gradually weakened, when the pressure is higher than 20GPa, the polarization dependence of the samples disappeared. After unloading for 22GPa. The results showed that the pressure after treatment, the carbon nanotube array arrangement is more compact, but the structure of multi walled carbon nanotubes and has not been destroyed. This is due to the reduced polarization pressure enhanced tube interaction leads to electronic delocalization, reduces material polarization dependent, the behavior body caused by the materials. On the other hand, with the further increase of pressure, the polarization dependence of MWNTAs disappeared can be attributed to the pressure induced by the interaction between tubes led to the increase of carbon nanotube structure transformation, the formation of a covalent bond between layers of Guan Jianhuo. Our results show that polarization pull Manchester technology under high pressure is used to determine the phase transition pressure induced tube interaction and structural changes in the MWNTs array. This behavior has been solved under high pressure of carbon tubes are polymerization on the subject of controversy,.2. provides a way for C70@SWNTs material to carry out in situ high pressure on carbon nanotubes the pressure induced change research, the new super hard carbon structure can be obtained. The atmospheric interception by transmission electron microscopy, Raman spectroscopy and X ray diffraction (XRD) C70 Peapod sample experiments on several different pressure were characterized. C70 Peapod samples from the highest pressure after the XRD has many the clarity of the diffraction peaks, the diffraction peak of carbon structure does not belong to any previously reported. Further predicted a new SP3 carbon simulation theory, V carbon structure with C2/m symmetry of all. Carbon atoms entirely in way of bonding. The calculation shows that V carbon is stable in the pressure range of 0-100GPa, its energy is only slightly higher than the diamond, but lower than the other carbon structure reported previously. In addition, V carbon has comparable with diamond hardness and bulk modulus, which is a good explanation of the annular indentation.V carbon left on the surface of the diamond anvil experiment simulation of XRD spectra agree well with the experimental data well, indicating that the new structure of our carbon produced by the experiments that think V carbon is reasonable. It is also important that we give the physical image is transformed from the initial C70 to V carbon Peapod materials. The process of change with odd carbon ring C70 Peapod as the basic building unit has played an important role, which provides a new strategy for the design and synthesis of new carbon structure, stressed the importance of the initial carbon source. The result of the formation of the carbon structure for people New ideas will inspire people to use and design of Peapod precursors containing odd carbon ring as the basic unit to build a new structure of graphene nano carbon.3. confined inside carbon nanotubes (GNRs@SWNTs) were studied with normal pressure and high pressure structure, reveals the influence of temperature on the structure phase transition behavior of nano confinement with growth and under high pressure. The study found that confined in carbon nanotubes within two rylene molecules can form nano confinement zone after annealing at high temperature and nano belt length affected by the annealing temperature. The interaction between the main object of high pressure further regulation, the discovery of carbon nanotubes to collapse around 7GPa, internal nano with the destruction of the graphene nano domain as "structural transformation" probe reflects the carbon nanotubes under high pressure. A comparative study of the structure collapse under high pressure and air filled carbon nanotubes reduced pressure, hair Is filled with carbon nanotubes nanoribbons after collapse shrinkage pressure decreased obviously, this phenomenon is due to the non uniformly filled carbon nanotubes with molecular, brings stress distribution is not uniform. The theoretical calculation further supports our experimental results. The results will help us to further understand the pressure change behavior between the nano domain space with the nanoribbons and carbon nanotubes and the interaction of.4. with laser heating in the diamond anvil cell of carbon nanotube fibers was studied under high temperature and high pressure. The discovery of 15GPa, 2000K, carbon nanotube fibers transformed into nano diamond structure, while the product may also contain a small amount of "n-Diamond" structure.

【学位授予单位】：吉林大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O613.71;TB383.1

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