| Controlling the growth of carbon nanotubes for controlling the preparation of various array structured orientation carbon nanotube films is a matter of importance to realize the practical application of carbon nanotubes.The vertically aligned carbon nanotube arrays can be used as ultra-black absorbent materials to eliminate the stray light generated by the optical path transmission process in a space camera,and have a good application prospect in high resolution space camera.In this paper,two aspects of work have been carried out.One is to use the organic metal-compound chemical vapor deposition(MOCVD)process to prepare the nano meter iron particle catalyst,which can be used to realize the controllable preparation of carbon nanotube array.Secondly,the preparation process of carbon nanotube arrays by CVD method was studied.At present,the main periodical research results are as follows.The MOCVD process can control the particle size and particle spacing of iron nano-particles by controlling the concentration of ferrocene vapor phase deposition temperature and deposition time.With the increase of deposition time from 1min to8 min,the spacing of particles decreases,and the particle size increases from 5.2±2.4 to44.3±10.7nmand the dispersion of particle size increases.The deposition temperature study shows that the particle size of the catalyst increases from 21.6nm to 37 nm with the increase of reaction temperature form 650℃ to 800℃.When the concentration of gas phase increases from 0.007 to 0.014,the particle size also increases,and the inter-particle spacing is small.In addition,a simple method to reduce the carbon content in the catalyst,water assisted metal-organic compound chemical vapor deposition,was put forward.By introducing water vapor into the deposition process,the main phase of the catalyst is ferrous oxide,and the carbon content reduces from 15.94at% to 1.25 at%.The decomposition reaction model of ferrocene in the MOCVD process was simulated by two dimensional CFD software FLUENT.Two phase diffusion,space chemical reaction and particle surface chemical reaction were used to analyze the particle size and concentration distribution in the reaction chamber under different gas phase concentration and reaction temperature.The results show that the particle density increases and the particle collision frequency increases with the increase of gas phase concentration.The increase of temperature accelerates the reaction rate,increases the number of particles.All of those lead to the greatly improvement of particles collision frequency and the particle size.The growth process of carbon nanotube arrays is affected by catalyst,growth temperature and the ratio of carbon to hydrogen.Through a series of studies,it is found that the diameter of carbon nanotubes can be effectively controlled by adjusting theparticle size,distribution and composition structure of Fe nano-particles grown by MOCVD.When the temperature of MOCVD is 700 ℃,the concentration of ferrocene is 0.007,and the reaction time is 3min,the carbon nanotube arrays prepared by the catalyst of Fe nano-particles have the highest height of 550.6 μ m.The influence of deposition temperature and the ratio of carbon to hydrogen on the growth stage of carbon nanotubes is mainly reflected in the balance between the supply and consumption of carbon atoms.If the carbon source ratio is too high or the temperature is too high,the oversupply of carbon atoms will make the large carbon atoms unable to crystallize,which will affect the catalytic effect.The experiment results show that the carbon nanotube arrays with good morphology can be catalyzed by the 3:4 mixture of hydrocarbon and hydrogen at 800℃.The minimum light reflectance of carbon nanotube array with a length of 550.6μm was measured to be 0.0046 in the spectral range of 200-2500 nm irradiated at a fixed incident angle.It exhibits excellent light absorption in the near-infrared band.The light reflectance in the visible range is about 0.073. |
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