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The Study of Preparation, Characterization and Properties of Helical Carbon Nanotubes

Author: ZhangYang
Tutor: DuYouWei；TangNuJiang
School: Nanjing University
Course: Condensed Matter Physics
Keywords: Carbon nanotubes Nanoparticles Nanomaterials Characterization Colloid chemistry method Core-shell structure Catalyst component Microwave absorption properties Hydrogen reduction Graphite structure Silica Hollow tubular Sol Particle size Soft magnetic properties Nano-scale HRTEM Chemically inert Electromagnetic wave absorption Controllable synthesis
CLC: TB383.1
Type: Master's thesis
Year: 2011
Downloads: 96
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Abstract

With the deepening of the understanding of the people nanomaterials and rich, its research also gradually starting from the simple preparation of nanoparticles to design and controlled synthesis of specific performance nanocomposites prepared conducive to the unique properties of the research material structural transition. As colloid chemistry method has a reaction was carried out in the liquid phase, the mild reaction conditions and uniformly controllable conditions, etc., has been widely used in the preparation of various types having a complicated microstructure nanomaterials. Nanoscale synthesis, preparation of composite nanomaterials is one of the current research focus. Having a core / shell structure of the composite nano-material is a typical form of such a composite material. Nanomaterials with core / shell structure has a series the regulation of excellent nature, so much attention. Magnetic metal nanoparticles size, large surface area, easy to aggregate, the difference between the oxidation resistance of its application is very limited. The carbon and silicon dioxide are chemically inert material has highly stable in aqueous solution, the advantages of using it as a protective shell has been proven effective in protecting the core particles are not oxidized. Meanwhile, the use of silica, and the thickness of the carbon layer to change the control particles interval can effectively reduce the agglomeration of the particles during the heat treatment. In addition, along with the discovery of carbon nanotubes magnetic and electromagnetic wave absorption performance, caused great concern of the magnetic academic electromagnetic properties and microwave absorption properties of carbon nanotubes. And helical carbon nanotubes has been theoretically and experimentally proved due to its unique morphology and microstructure, compared with traditional carbon material has a lot of unique and superior performance. The main work of this paper is based on colloid chemistry method based on sol - gel combined hydrogen reduction of the prepared catalysts prepared with high purity helical carbon nanotubes and has a knot on the iron structure and uniform attachment by acetylene pyrolysis method nanoparticles of silica core-shell structure of carbon nanotubes, and structural characterization, and then study their magnetic and microwave absorption properties. Mainly include the following two parts: preparation, characterization and properties of Fe/SiO2 core / shell nanoparticles, carbon nanotubes, uniform adhesion. By the hydrogen reduction of nickel chloride, ferrous chloride, citric acid and ethanol as a raw material, a non-aqueous sol-gel combination prepared nickel-iron core-shell structure mixing nano-particles, and through the nano-particles at a relatively low temperature (475 ℃) without any doping gas pyrolysis of acetylene preparation twinning higher even attached to the iron core-shell structure nanoparticles carbon nanotubes. XRD diffraction and Raman spectra show the sample to the growth of the nickel nanoparticles defective graphite structure, no other impurity phase. By FE-SEM and HR-TEM sample characterization know the carbon nano helically into a tubular structure, accompanied by defects, the presence of twinning structure, uniform size and diameter. The preliminary study found that the magnetic properties of the resulting samples and comparison of pure carbon nanotubes by adding the soft magnetic properties of the samples after the iron core-shell nanoparticles greatly improve. The microwave absorbing study found that the resulting sample displayed in the high frequency performance of a good microwave absorption, in the low frequency absorption is not ideal, it may be caused by the unevenness due to the particle content is not high and adhered. We can spiral carbon nanotubes by using better methods to load more magnetic nanoparticles to greatly improve the performance of its absorption. Second, the preparation of high purity helical carbon nanotubes, characterization and performance. Ni nanoparticles were prepared by the sol - gel combined hydrogen reduction method, and such nickel nanoparticles as a catalyst, by the catalytic cracking of acetylene was prepared at 425 ℃ spiral high and was symmetric spiral growth carbon nanotubes. The results show that this method is a simple, convenient and low-cost, environmentally friendly preparation of high purity helical carbon nanotubes. The field emission scanning electron microscope (FE-SEM), and high-resolution transmission electron microscopy (HR-TEM) picture shows the general case opposite to the spiral of two chiral carbon nanotubes are grown in a catalyst particle, and this nano spiral form of a hollow tubular . X-ray diffraction and Raman spectroscopy show that the resulting sample components is defective graphite structure and nickel polycrystalline and found no other impurity phase. In addition, samples of prepared state magnetic and microwave absorption properties were studied.

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