Research status and development prospect of carbon nanotubes Abstract:Carbon nanotubes due to their unique structure and excellent physical and chemical properties, and has wide application prospect and huge commercial value. This paper reviewed the methods for preparing carbon nanotubes, structural properties, application and development trend of carbon nanotubes.Keywords: carbon nanotubes; preparation; antistatic; stealth; radar absorbing coatingNanometer material because of its size in the transition region junction of atomic clusters and macroscopic objects, with the quantum size effect, small size effect, surface effect and the macroscopic quantum tunnel effect and other characteristics, exhibit many unique physical and chemical properties. Nanometer material nineteen eighties early after the formation of the concept, the world have paid great attention. It has unique properties, physical, chemical, material research, biology, medicine and other fields with meters of new opportunities.1, carbon nanotube preparation, structure and properties1.1, the preparation of carbon nanotubes1.1. 1 arc methodGraphite arc method is carbon nanotube synthesis method is the most typical of the earliest. The principle of arc chamber filled with inert gas protection, two rod of graphite electrode near, pull up the arc, and then opened, in order to maintain stable arc (1). The relatively high temperature cathode anode discharge process, so the graphite anode is consumed continuously, at the same time deposit containing carbon nanotubes product [2] on graphite cathode. This method has the characteristics of simple and fast, carbon nanotubes can maximize the graphitization, tube less defects. But there are disadvantages are: arc discharge violently, difficult to control the process and product, composition of carbon nanoparticles, amorphous carbon or graphite debris, impurities, so it is difficult to separate. After years of study, researchers have improved on the method, such as Takizawa et al. Discharge by arc, by changing the catalyst of nickel and yttrium ratio, the diameter distribution control product objective. Colbert[3] et al. General cathode (Boulder graphite electrode) into a cooled copper electrode and graphite electrode, in the above, morphology and structure. This product, the arc discharge method have rejuvenated.1.1.2 catalytic pyrolysis methodCatalytic pyrolysis method, chemical vapor deposition, by hydrocarbons or carbon oxide cracking in catalytic. The basic principle of the organic gas (such as acetylene, ethylene) mixed with a certain proportion of nitrogen as the suppression of gas, prior to removing the oxygen into the quartz tube, at a certain temperature, the formation of carbon on the catalyst surface cracking, carbon source through the catalyst diffusion in the catalyst surface, after long carbon nanotubes, at the same time pushing forward [4] small catalyst particles. Until the catalyst particles are coated with a layer of graphite, carbon nanotube growth end. The advantages of this method are: easy to control the reaction process, simple equipment, low cost of raw materials, large-scale production, higher yield. Disadvantages are: low reaction temperature, carbon nanotube layer number, the degree of graphitization is poor, and there are many crystal defects, mechanical properties and physical and chemical properties of carbon nanotubes may have adverse effects.1.1.3 ion or laser evaporation methodThe 1996 Nobel Prize for chemistry, carbon nanotubes were synthesized to obtain one of the Smally team for the first time using laser evaporation method. Since then, laser evaporation method is an effective method for preparing single-walled carbon nanotubes of [5]. This method in Ar atmosphere, with the double pulsed laser evaporation containing Fe/ Ni (Co / Ni) carbon target preparation method of a diameter distribution van lost in single-walled carbon nanotubes in 0.81 - 1.51 nnl. The preparation of carbon nanotube purity reached to 70% ~ 90%, basic does not require purification, but its sophisticated equipment, high energy consumption, high investment cost.1.1.4 Other synthesis methodIn recent years, researchers in the traditional preparation technology and improvement, explore and study the preparation technology of a new series of carbon nanotubes, including hydrothermal method, flame method, supercritical fluid technology, water arc method, solid-phase pyrolysis method, energy method. A typical example: in 1996 Yamamoto et al. In Taka Shinzora (5.33 ×10-3Pa) method by argon ion beam irradiation on amorphous carbon is obtained by pure sodiumCarbon nanotube. Chemozatonskii et al by electron beam evaporation coating on Si substrate preparation of graphite carbon regularly arranged pipe. Feldman et al. Preparation of diameter of 30 ～multi-walled carbon 50 nm tube by using the method of electrolysis of alkali metal halides. Carbon nanotubes in the process of industrialization, Japan and the United States of America has been in a leading position. At present, carbon nanotube production technology in China also has certain advantages in the world, such as Shenzhen nano port public scraping withboiling production technology and device of catalytic pyrolysis method with fully independent intellectual property rights, Tsinghua University and the Chinese Academy of Sciences and other scientific research institutes have formed a certain scale of production conditions.1.2, the structure of carbon nanotubesCarbon nanotubes are seamless, hollow nanotubes by monolayer or multilayer graphene sheet around the center in a certain angle (made up of atomic arrangement structure shown in Figure 1.).According to the different number of containing graphite, carbon nanotubes can be divided into single wall carbon nanotubes (Single - walled nanotubes, SWNTs) and multi-walled carbon nanotubes (Multi - walled nanotubes, MWNTs). Among them, SWNTs is composed of a layer of graphite sheet; MWNTs made of layers of graphene sheet, shape similarity and coaxial cable.1.3, the performance of carbon nanotubesCarbon nanotubes because of the molecular structure of the small size effect and unique, has excellent physical and chemical properties. One-dimensional molecular materials and hexagonal perfect connection structure make CNTs have the characteristics of light weight, high strength; large length to diameter ratio of SP2, SP3 hybrid probability of different carbon nanotubes have good elasticity; differences in diameter, spiral angle and the interaction between layers of the carbon nano tube has the characteristics of both conductors and semiconductors; absorbing materials spiral unique molecular structure of carbon nanotube structures than the average absorption material has much higher absorption rate. In addition, carbon nanotubes have unique optical properties, good thermal conductivity, acid, alkaline and thermal stability of high.2, the application of carbon nanotubesBecause of the unique structure of CNTs, which has electrical properties and mechanical properties, so it is widely used in the development of CNTs, electronic component, CNTs nano composite material, surface strengthening etc..2.1, electrical applicationsBecause CNTs has good electrical properties, especially after high temperature anneal eliminate defects after CNTs, conductivity is higher,the application of CNTs Ts in the electronic field itself has the end structure characteristics of small radius of curvature, so instead of molybdenum needle for field emission electrode, with excitation voltage is low, and has self repair function, can greatly improve the efficiency and function of visual display system. Through the control of the production process, the Pentagon heptagon carbon / carbon ring in the ring CNTs concentrated in the central pipe body, conductive properties can change the CNTs, which has characteristics of semiconductor, can be used for the production of CNTs electronic switch [6] and CNTs diode. 2.2, the field of composite materialsCarbon nanotubes with will be more conducive to play [7] high strength, low thermal expansion, good electric conductivity and thermal conductivity and wear properties of the composite material. Carbon Nanotubes reinforced copper matrix composite materials with better properties of antifriction and wear resistance, wear process of the composites containing the running-in stage and steady wear stage, in the steady wear stage oxidation wear occurs mainly, simultaneously also has the abrasive wear; carbon nanotube volume fraction is between 12% and 15%, the better the lubrication and inhibition of substrate oxidation effect of composite material, so the friction and wear properties of optimal [8].Surface chemical nickel plating2.3, carbon nanotubesSince the carbon nanotube itself does not have a catalytic surface, can not direct nickel plating on the surface, it is bound to the surface treatment, the purified carbon nanotubes (100K) sensitization and activation, in order to improve the carbon nanotube surface activity. After the pretreatment of carbon nanotubes has good surface activity, can be directly carried out chemical nickel plating in alkaline conditions, using nickel sulfate as main component of plating solution, potassium citrate (K3C6H5O7) as a complexing agent, sodium hypophosphite (NaH2PO2) as a reducing agent for chemical nickel plating on the surface of carbon nanotubes [9]. The Tsinghua University will carbon nanotubes for nodular cast iron laser surface cladding made some surface strengthening effect.2.4, carbon nanotubes on MWPCVD process to enhance diamond nucleationFor matrix MWPCVD process (silicon) through the surface of carbon nanotubes could obtain high diamond nucleation density, SP3 bonded carbon nanotube has promoted the diamond nucleation of MWPCVD, at the same time in the deposition process improves the surface carbon concentration so as to accelerate the growth process of diamond (film). The enhanced treatment of diamond Tong nuclear alsohas no damage to the surface of the matrix, can use quartz bell jar type MWPCVD equipment conditions, and simple, and easy [10].3, the latest domestic and foreign research situation and Prospect At present, countries in the experimental study of carbon nanotube be just unfolding, and have made some achievements, the United States invented the nanometer scale, Japan made the platinum filled carbon nanotubes, Germany prepared LNM diameter carbon nanotubes. Our country individual achievements while walking in the forefront of the world, such as the synthesis of hydrogen storage in carbon nanotubes, the longest in the world of high quality carbon nanotubes, but the overall level and the United States and Japan in the field of nano science and technology is compared, there is still a big gap between.Countries facing two common problems, so that the carbon nanotubes are not truly industrial application. How to realize the continuous industrial production of high quality carbon nanotubes. Preparation of carbon nanotubes status is roughly: multi-walled carbon nanotubes can be mass production, single wall carbon nanotubes most in the laboratory research stage, some preparation methods of carbon nanotubes growth mechanism is not clear, the structure of carbon nanotubes (diameter, length, helicity, wall thickness, pipe surface graphite crystallinity etc.) can not be arbitrary regulation and control,influencing factors on yield, quality and yield of carbon nanotubes too much (such as the size of the catalyst particles, carbon sources, temperature, mixture gas species and ratio), the prepared carbon nanotube has disadvantages of high yield, low impurities, there is no method purification of carbon nanotubes and efficient. ② to more in-depth study of the problem of the application of carbon nanotubes. For example, at normal temperature and pressure, how to parse the hydrogen and accelerate the hydrogen storage speed. How to improve the stability and sensitivity of adsorption pressure adsorption capacity of carbon nanotubes. Moreover, how to prepare the performance more carbon nanotubes composite materials with excellent properties can be expected or. To solve these common problems, requires researchers breakthroughs in key technologies, the further research and development of new, low cost, suitable for mass production of carbon nanotube technology, to strengthen the study on growth phenomena and mechanism by modeling and simulation; in-depth study of its application to continue on the other hand, the carbon nanotubes with various fields together give full play to its own characteristics, excellent.In addition, the recent carbon nanotubes and the emergence of a new research direction, namely the wettability of carbon nanotube films, many scholars have made a lot of research on its wettability. Jiang [11] lithography and plasma etching technique combined with specialmorphology, silicon substrate were prepared, and the chemical vapor deposition method with three-dimensional anisotropic microstructure array carbon nanotube films deposited on top. Research shows that, without changing the chemical composition of the surface film case, simply changing the structure parameters, the film can change from hydrophilic to hydrophobic, this phenomenon is caused by the coexistence of horizontal and vertical carbon nanotube array structure is three-dimensional anisotropic microstructure. Provide the hydrophobic contribution of carbon nanotube array longitudinal, and provides a hydrophilic contribution of carbon nanotube array lateral, and has spread to water. The horizontal and vertical carbon nanotube array Column combination of change in wettability properties of the film special. Lau [12] PECVD method is used to obtain the alignment growth of carbon nanotube forests, and then through the method of HF - CVD PTFE to modify the surface, the stability of the superhydrophobic surface, droplet can be above the free jump until detachment. Li [13] with phthalocyanine complexes as raw material, preparation method by pyrolysis of carbon nanotube films were prepared with arrays, a uniform length and diameter of the research shows that, without the array of carbon nanotubes film processing is super hydrophobic and lipophilic, after fluoride modified (FAS) after carbon nanotube films exhibit properties both hydrophobic and oleophobic nano structure, it is caused by the presence ofsuper-hydrophobic properties of the surface. This finding provides new ideas for the interface of hydrophobic and oleophobic surface / materials.We should see, more carbon nanotube defects at present have been, and not easy to disperse, which greatly limits the properties and applications of carbon nanotubes. Research on the preparation of carbon nanotubes method is particularly important. In addition, the measurement method of nanometer size must further strengthen. In short, with the deepening of research of carbon nanotubes and the rapid development of nanotechnology, nanometer carbon materials will have a major impact on the world of science and economy.Reference[1]G.B.Adams, O.F.Sankey, J.B.Page, et, al.[J].Science, 1992256:1792[2]Journet C. Maser W K, Bernier P, et al Large scale produced of single walled.Carbon nanotubes by the electric are technique [J].Nature, 1997388:756[3]Colbert D T, Zhang J, McClure S M, et al and sintering of fullere. Growth nanotubes[J].Science, 1994266:1218[4] Zhu Shaowen, Jia Zhijie, Li Zhongze, et al. Carbon nanotubes and application prospect of [J] science and technology review, 1999, 12:7 9[5]M.J.Yacaman, M.M.Yoshida, L.Rendon.Catalytic growth of carbon microtubules with fullerene structure, [J].Appl.Phys.Lett., 1993,62:202-204[6] Liang Yong, ke-tao Zhan. 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Journal of Hangzhou Insitute of Electronic and Technology, 2000 (3): 63-66.[10] carbon nanotubes on MWPCVD enhanced [J]. new technology and new process of diamond nucleation, 2000 (6): 56-59.[11]COCHON J L, GAVILLET J, CHAPELLE D L, et al.Acontinuous wave CO2 laser reactor for nanotubes synthesis[C].France:chatillon 92322[12]ALVAREZ L, GUILLARD T, OLALED G, et rge scale solar production of fullerenes and carbon nonatubes[J].Synth Met, 1999103 (1-3): 2476-2477.[13] Sishen Xie, Li Wenzhi, Wang Chaoying, et al. The preparation of mesoporous materials of carbon nanotube morphology, structure and Raman scattering studies (J). Science in China (series A), 1997, 27 (7): 631-635。
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