激光液相辐照法合成纳米金刚石机理及其影响因素研究

发布时间：2018-02-13 11:25

本文关键词： 激光液相辐照法纳米金刚石石墨烯纳米带生长机理影响因素　出处：《江苏大学》2017年硕士论文　论文类型：学位论文

【摘要】：与宏观金刚石相比,纳米金刚石具有特殊机械、光电、热、磁性能,在各领域都有广泛的应用价值。与传统制备方法相比,激光液相辐照法绿色无污染、操作灵活、参数可控,在新型纳米材料的制备方面效果显著。本文以传统碳材料(鳞片石墨)为研究对象,采用高能脉冲激光辐照石墨悬浮液实验研究,讨论了纳米金刚石、石墨烯纳米带的形成机理及其产率的影响因素。论文的主要研究内容和结论如下:(1)高功率密度(109~1011W/cm2)、短脉冲(10ns)的激光辐照循环流动的石墨悬浮液后,石墨转变成不同的纳米结构:纳米金刚石、石墨烯纳米带、球状无定型纳米碳团簇、类碳纳米管状物、乱层碳组织团簇。在石墨粒度相同而能量不同的情况下,石墨烯结构层数各不相同,层数范围在单层到14层之间。在激光热应力和冲击波的复合作用下,少数层的短而有序的石墨烯片段也会单独从石墨表层剥离开来。随着能量的增加,石墨烯纳米带的层数越多,且无序度也越来越高。(2)脉冲激光液相辐照法连续合成了纳米金刚石,并对其晶体学形态、微观组织结构、微应力及各类缺陷进行了分析。实验发现粒度相同而激光能量不同的情况下,随着能量的增加,金刚石产量并没有明显的变化,表面形貌基本呈现球状或椭圆状,尺寸在2~10nm,平均尺寸在5nm左右。与宏观金刚石相比,生成物发生了细化,并且晶粒内部有残余应力,Raman光谱中的金刚石特征峰发生了宽化并向低频段位移。(3)从热力学和动力学角度提出了纳米金刚石的生长机理:在石墨颗粒升温过程中,石墨表面形成的等离子体溃灭形成液态碳液滴,此时液态碳液滴在热力学条件下进入石墨亚稳定金刚石稳定区域,碳原子开始重组形成金刚石晶核并迅速长大。结合碳的温度-压力相图,在等离子体冷却降温过程中,逼近三相共存点,由互相缠绕的带状石墨烯纳米管状物形成封闭的纳米级空间,金刚石可能在其内部形核长大。石墨的相变过程遵循固态-气态-液态-固态和固态-气态-等离子体态-液态-三相共存态-固态路径发展。总结了金刚石纳米晶尺寸细小的原因:从金刚石纳米晶的生长限制机制角度考虑,高的过冷度及短暂的生长时间制约了纳米金刚石的长大。(4)在激光能量相同而粒度不同的情况下,小粒径(2μm、5μm)石墨更易于相变形成纳米金刚石,小粒径石墨的形成热大于大粒径石墨,更不稳定,更易发生金刚石相变。通过优化改进实验装置,在双光束脉冲激光的共同作用下,增加了激光与石墨的作用面积,大大提高了纳米金刚石的合成效率。此时石墨的相变过程遵循固态-气态-等离子体态-液态-三相共存态-固态及固态-液态-固态两种路径生长,另外非晶碳团簇内部及乱层碳团簇边缘发现了金刚石相的存在,进一步证明了纳米金刚石的形成遵循液化机制。纳米尺寸效应导致的熔点降低是合成超细纳米金刚石的另一机制也是纳米金刚石表层自发重组形成类似Bucky-diamond的形状的重要原因。
[Abstract]:Compared with the macro nano diamond, diamond has special mechanical, optical, thermal and magnetic properties, are widely used in various fields. Compared with the traditional preparation method, laser irradiation method, liquid green pollution-free, flexible operation, controllable parameters, significant effect in the preparation of new nano materials based on the traditional. Carbon materials (graphite) as the research object, using the graphite suspension irradiated by laser experiment of high energy pulse, discusses the factors influencing the formation mechanism of nano diamond, and the yield of the graphene nanoribbons. The main research contents and conclusions are as follows: (1) high power density (109~1011W/cm2), short pulse (10ns) graphite suspension flow after laser irradiation, graphite into different nanostructures: nano diamond, graphene nanoribbons, spherical amorphous carbon clusters, carbon nano tube, disordered carbon clusters in the organization. The same energy while the graphite particle size under the condition of different graphene layers vary in scope of layers to 14 layers. Between the monolayer composite action force and impact wave in laser heat, a layer of short fragments will be ordered graphene from graphite surface alone to peel off. With the increase of the energy, the more layers of the graphene nanoribbons, and the degree of disorder is more and more high. (2) pulsed laser irradiation of continuous liquid phase synthesis of nano diamond, and the crystal morphology, microstructure, micro stress and all kinds of defects are analyzed. The experimental results showed that the same size and different laser energy situation, with the the increase of the energy, diamond production and no significant change in surface morphology showed spherical or oval shape, size in 2~10nm, the average size is about 5nm. Compared with the macro diamond, the refinement of product, and the grains Residual stress, characteristic of Diamond Peak in the Raman spectrum are broadened and shifted to low frequency. (3) the growth mechanism of nano diamond is put forward from the view of thermodynamics and dynamics: the graphite particles in the heating process, the formation of graphite surface plasma collapse to form liquid carbon droplets, the liquid droplets in the thermodynamics of carbon under the condition of graphite into the metastable diamond stable region, carbon atoms begin to recombine to form diamond nucleation and grow rapidly. The carbon temperature pressure phase diagram in the plasma cooling process approximation of three phase coexistence, to form a closed space by nano tube shaped graphene nano diamond may be intertwined, grew up in the the internal phase change process of graphite nucleation. Follow the solid - gas - liquid - solid and solid - liquid - gas - plasma - three-phase coexistence of solid gold total node development path. The reason of diamond nanocrystal size: from small diamond nanocrystal growth limiting mechanism into consideration, the undercooling and the short time high growth restricted grow the nanodiamond. (4) in the same laser energy and particle size under the condition of different particle size (2 m, 5 m) graphite more easily the formation of nano diamond phase transition, the formation of more heat than large size graphite particle size of graphite, more unstable, more prone to diamond. Through the improvement of device optimization, interaction of the double beam pulse laser, laser and graphite increases the area of effect, greatly improve the efficiency of the synthesis of nano diamond. The phase change follow the process of graphite solid gas - liquid phase plasma - coexistence of solid and solid - liquid - solid - two growth path, another non internal amorphous carbon clusters and turbostratic carbon cluster edge found the diamond phase into existence One step proves that the formation of nanocrystalline diamond follows the liquefaction mechanism. The reduction of melting point caused by nanometer size effect is another mechanism of synthesizing ultrafine nano diamond. It is also an important reason for the formation of Bucky-diamond like diamond on the surface of nano diamond.

【学位授予单位】：江苏大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TQ163;TB383.1

【相似文献】