Study On Flame Synthesis Of Carbon Nanotubes And Synthetic Mechanism

In order to realize industrialization synthesis of carbon nanotubes which is large scale, continuous, and low cost, a pyramid shaped reactor and experiment method were designed first. Then systematically studied the influence of process parameters on product and analyzed the synthesis mechanism of carbon nanotubes, and made the preliminary purification processing in the last.In this experiment, the main product is muiti-walled carbon nanotubes, single-walled carbon nanotubes also was synthesized. Pyramid shaped reactor can preclude the reactant from meeting the air. By adjusting the distance between the pyrolysis area and synthesis area, pyrolysis and synthesis do not affect each other can realized, and the temperature of pyrolysis and synthesis is at the best situation. Carbon sources too much (or too less) and catalyst too little (or excessive) are similar, all show that the catalyst is packaged by carbon source or catalyst deactive rapidly. Too much or too little hydrogen and helium show purging too strong which can bring about that carbon can not adsorb on catalyst or too weak which can not cleanse tubes and catalyst particles. In addition, hydrogen can make catalyst active, helium has local dilution and cooling effect, since the helium also carry catalyst into reactor which affect the supply speed of catalyst. There were not carbon nanotubes synthesized at first 60s of sampling time, only tube shape buds around particle group at 70s. The reason is that when the sampling time is short, the temperature of substrate is so low that catalyst particles and carbon atom clusters will be cooled as soon as they reached. With the increases of sampling time, the temperature of substrate rise, catalyst particles are no longer be cooled to a lower molten degree when they reach the substrate and with the catalytic activity. Experiments also conclude that carbon nanotubes grow thick with the time from the research on sampling time. Before carbon nanotubes can synthesis, the accumulation which coated on the surface of substrate is the mixture of carbon atom clusters, catalyst particles, and nanocapsules which carbon packaged catalyst particles forming. The accumulation covering the entire substrate also proved that the substrate can not participate in catalytic synthesis of carbon nanotubes. Pyrolysis temperature mainly influence the pyrolysis of carbon monoxide, and little to iron pentacarbonyl because iron pentacarbonyl can rapidly decompose at low temperature. Too high synthesis temperature easily gasify the carbon atom clusters from the surface of catalyst, and burn the synthesized tubes if some can. At low temperature, the molten degree of catalyst is too low to allow carbon atom clusters to dissolve into, or diffuse slowly. Small droplets iron pentacarbonyl as catalyst source are suitable to catalyse synthesis of carbon nanotubes at relative low temperature, while Fe-Al-O and Fe-Al-Mo-O compound are opposite. By the different sample carrier, products were difference. It is concluded that the influences is the capability of the carrier itself rather than material elements directly involved in to catalyse synthesis of carbon nanotubes. The influences of sampling location to synthesis of carbon nanotubes are mainly reflected in the synthesis temperature. Physical, chemical and comprehensive methods were used to purify carbon nanotubes. Only physical or chemical method can not remove all of the impurity, even if comprehensive method can not easily remove the nanocapsules. Sampling at pyrolysis area is a improvement of the traditional chemical vapor deposition which can realize continuous production and get small diameter carbon nanotubes. And further proved that iron pentacarbonyl as raw materials is not suitable in a relatively high temperature while Fe-Al-0 and Fe-Al-Mo-O compound can. In this paper, the synthesis mechanism of carbon nanotubes also be discussed. It is concluded that synthesis mechanism of carbon nanotubes accord with the traditional" solution-diffusion-precipitation " theory, but the difference is that the carbon source has decomposed at high temperatures before contact with the catalyst particles. Carbon nanotubes are also being thicker while growing, and their being thicker is not limited to the outermost, some of the most inside tube layers also increase. The synthesis mechanism of some special structure carbon nanotubes also be analyzed, that the main reason is the non-optimal conditions. Carbon nanofibers, carbon nanoonions, and nanocapsules also be produced at experiment.