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Preparation of Nanosized Carbon Materials by Detonation Technique and the Corresponding Research on Mechanism

Author: SunGuiLei
Tutor: LiXiaoJie;LiBaoYuan
School: Dalian University of Technology
Course: Engineering Mechanics
Keywords: Detonation Technique Nanosized Graphite Sheets Nanosized Carbon Materials Cleavage Mechanism Analysis Carbon Encapsulated Metal Nanoparticles
CLC: TB383.1
Type: PhD thesis
Year: 2008
Downloads: 273
Quote: 1
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Abstract


The research fever in carbon materials was caused by the discovery of fullerenes in 1985, carbon nanotubes in 1991 and carbon encapsulated metal nanoparticles in 1993. Afterwards, lots of synthesis methods were used for preparing carbon materials which resulted in the old but novel material being developed immensely. Among these methods, detonation technique has the advantage of low-cost, effective and convenient so that it can be used in many nanomaterials preparation or synthesis. Detonation technique is used in this paper to prepare nanosized carbon materials which mainly include nanodiamond, micro/nanographite and carbon encapsulated metal nanoparticles. Meanwhile, the corresponding mechanism research is also been carried out. The main content and the featured research results contain:1. The commonly used methods to prepare nanodiamond at present were analyzed in this paper. Nanodiamond was synthesized by detonation technique and the purification technology was also studied. With the help of X-ray diffraction (XRD), transmission electron microscope (TEM) and Raman spectra, the detonation soot and the purified powders were characterized systemically. The results indicated that the synthesized nanodiamonds were polycrystalline.2. The present techniques of preparing graphite nanopowders were synthetically described and divided into two categories by the used raw material. One was preparing graphite nanopowders from natural graphite and the other was synthesizing from rich carbon material. A method for preparing graphite micron powders by detonating the mixture of explosive and expandable graphite was proposed in this paper. The detonation soot was characterized by XRD, scanning electron microscope (SEM), specific surface area and porosity analysis. The results indicated that the detonation soot was made up of high purity graphite powders of which the diameter distributed between 1 and 10μm. Moreover, the specific surface area of the detonation soot was more than 5 times of natural graphite. A method for preparing graphite nanosheets by detonating natural graphite was also proposed. Here, strong oxidative acid was added into the natural graphite to form stable graphite intercalation compounds (GICs). Subsequently, an explosive was added in with a special ratio and then the mixture was detonated. The detonation soot was characterized by XRD, TEM, Raman spectra, specific surface area and porosity analysis. The results indicated that the thickness of the as-prepared graphite nanosheets distributed between 5 and 200 nm and varied with the stage number of GICs. In the detonation soot, the amount of pores that the diameters distributed between 3 and 8 nm were increased greatly. Meanwhile, the amount of the pore diameters that distributed at about 4 nm reached the maximum value. In addition, the pores of which the diameter distributed below 3 nm had the tendency to be reduced. The specific surface area of these detonation soot enlarged to 79 times of the natural graphite.3. The expression of force constant k, which reflected the interlayer force between carbon atoms in adjacent graphite layers, was derived out with Thomas-Fermi (TF) equation reference to Gaite’s "one-electron model". After comparison with the force constant values from experiments, the calculated value was satisfactory. Unit structure model and unit volume model of HNO3 GICs were built. According to the analysis of GICs decomposition process, we put forward two explosive models. Then we can nonlinear fit six parameters of JWL equation of state according to a simple P-V relationship of explosion products. With these parameters, the simulation to graphite layer movement was done by LS-DYNA program and the layer distance-time curve was obtained.4. Carbon encapsulated metal nanoparticles were synthesized by detonation technique in the vacuum detonation vessel. The nanoparticles were thoroughly characterized with XRD, TEM, Raman spectroscopy and magnetometer. The results indicated that the nanoparticles showed the properties of superparamagnetism and soft magnetic. The coating structure nanoparticles were complete though treated with concentrated hydrochloric acid. Moreover, the higher the detonation pressure the better the crystallinity of iron and the higher the vacuum degree the better the encapsulated structure. Furthermore, carbon transformed to amorphous carbon with the increase of oxygen content. In addition, when the detonation was initiated on the condition of vacuum, Fe could act as catalyst in producing fullerenes while Co and Ni could not.

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