受限空间中金属纳米线的熔化

发布时间：2018-01-30 20:04

本文关键词： 金属纳米线分子动力学熔化行为碳纳米管受限空间　出处：《山东大学》2015年硕士论文　论文类型：学位论文

【摘要】：过去的几十年间,以碳纳米管、纳米线为代表的一维纳米材料备受关注。其中,纳米线因其具有的独特的物理化学性能,在光电子器件、化学催化、生物科技、国防科技、能源储运、复合材料等领域具有受人瞩目的应用前景。在推广纳米线的实际应用过程中,维持其结构与物理化学性能的稳定性是首先要解决的问题。近年来,研究者发现将纳米线封装于受限空间中,不仅能够增加其结构稳定性,防止其与外界的氧气与水蒸气反应,还能够获得综合性能优异的碳纳米管-纳米线复合材料从而开拓新的研究领域。受限空间与纳米线原子的相互作用以及受限空间的结构和尺寸对内部纳米线的结构与性能具有非常显著的影响。研究受限空间中纳米线的熔化,对于丰富并完善纳米尺度下材料性能的研究、拓展纳米线及其复合材料的应用、发展先进的纳米材料制备与加工技术具有非常重要的科学意义和价值。本论文选取了两种典型的金属纳米线——Al纳米线与Fe纳米线,并采用分子动力学模拟方法对其在受限空间中的热稳定性和熔化过程进行了深入探讨。本论文首次发现了碳纳米管受限空间中Al纳米线具有三种熔化行为,分别为：(Ⅰ)熔化过程中不出现内层原子到外层的可视化扩散；(Ⅱ)熔化过程出现纳米线的回复现象；(Ⅲ)熔化后内层原子完全扩散到外层导致纳米线最终具有中空结构。这三种熔化行为由Al纳米线的直径和碳纳米管的长度共同决定。碳纳米管与纳米线各层原子之间的相互作用强弱差异以及碳纳米管中的范德华力势阱是引起其内部Al纳米线出现以上三种异常熔化行为的主要原因。沿不同晶向排布的Fe纳米线([100]、[110]和[111]Fe纳米线)的热稳定性明显不同。[111]Fe纳米线由于其具有的表面能最小以及表面的近邻原子数最多具有最好的结构稳定性和热稳定性,该模拟结果从理论角度验证了实验中自发生长的Fe纳米线多沿[111]晶向排布。当把Fe纳米线封装于虚拟墙受限空间中时,外界轴向压力的存在能够强化受限空间对于纳米线的束缚作用,从而使得纳米线的熔点随着轴向压力的增加而增加。但是,该轴向压力存在一个临界值,结果表明为3 GPa,在该压力值以下,虚拟墙中的Fe纳米线才能够维持自身结构稳定。本论文首次比较了两种相同形状、相同尺寸的受限空间,即虚拟墙和碳纳米管,对于内部Fe纳米线熔化行为和热稳定性的影响。结果表明,Fe纳米线在碳纳米管中的结构稳定性最强,碳纳米管对于其束缚作用更大。纳米线在这两种受限空间中的熔化行为也呈现出明显不同。该结果形象地说明了碳纳米管对于内部纳米线熔化行为的影响不仅仅局限于尺寸限制,其管壁的碳原子排布以及形成的碳纳米管内的范德华力势阱是影响内部原子结构与性能的重要原因。
[Abstract]:In the past decades, carbon nanotubes (CNTs) and nanowires (CNTs) have attracted much attention. Among them, nanowires have been widely used in photoelectron devices, chemical catalysis and biotechnology because of their unique physical and chemical properties. National defense science and technology, energy storage and transportation, composite materials and other fields have attracted great attention in the application of nanowires. In recent years, researchers have found that encapsulating nanowires in confined space can not only increase the structural stability of nanowires. Prevent it from reacting with oxygen and water vapor. Carbon nanotube-nanowire composites with excellent properties can also be obtained to open up new research fields. Interaction between confined space and nanowire atoms and junction of structure and size of confined space to internal nanowires. The structure and properties of nanowires in confined space are studied. To enrich and improve the properties of nanoscale materials, expand the application of nanowires and composites. It is of great scientific significance and value to develop advanced preparation and processing technology of nanomaterials. In this paper, two typical metal nanowires, Al nanowires and Fe nanowires, are selected. The thermal stability and melting process of Al nanowires in confined space were investigated by molecular dynamics simulation. In this paper, three kinds of melting behaviors of Al nanowires in confined space of carbon nanotubes were first found. There is no visible diffusion from the inner layer to the outer layer in the melting process. (II) recovery of nanowires in the melting process; (III). These three melting behaviors are determined by the diameter of Al nanowires and the length of carbon nanotubes. The differences in interaction and the van der Waals potential well in carbon nanotubes are the main reasons for the above three abnormal melting behaviors of Al nanowires in the carbon nanotubes. [100], [110] and. [The thermal stability of 111] Fe nanowires is obviously different. [111] Fe nanowires have the best structural stability and thermal stability due to their minimal surface energy and the maximum number of adjacent atoms on the surface. The simulation results demonstrate theoretically that the spontaneous growth of Fe nanowires in the experiment has multiple edges. [When Fe nanowires are encapsulated in the confined space of virtual wall, the existence of external axial pressure can strengthen the binding effect of confined space to nanowires. Therefore, the melting point of nanowires increases with the increase of axial pressure. However, there is a critical value of the axial pressure. The results show that the melting point of nanowires is 3 GPA below this pressure value. Only Fe nanowires in virtual walls can maintain their own structural stability. In this paper, two kinds of confined spaces of the same shape and size, namely virtual walls and carbon nanotubes, are compared for the first time. The results show that the structure stability of Fe nanowires is the strongest in carbon nanotubes. The melting behavior of nanowires in these two confined spaces is also obviously different. This result vividly shows that the effect of carbon nanotubes on the melting behavior of internal nanowires is more than just the effect of carbon nanotubes on the melting behavior of internal nanowires. Limited to the size limit. The arrangement of carbon atoms in the tube wall and the formation of van der Waals force trap in carbon nanotubes are the important factors affecting the structure and properties of the inner atoms.
【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB383.1

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