The development of materials technology is divided into two aspects: production and application.

       research status of production technology

      There have been three main methods for preparing CNT: arc-discharge, laser ablation and chemical vapor deposition (CVD).

      Arc-discharge is one important method for preparing CNT on large scale. In this method, high purity and density flake graphite whose thickness is 10mm and diameter is about 30mm acts as cathode, while graphite rod whose diameter is about 6mm acts as anode. The whole system maintains the helium atmosphere in which the pressure is about 104 Pa, the discharge current is 50A and the discharge voltage is 20V. Through adjusting the feed speed of anode, the discharge end interval of two electrodes can be unchanged with the growth of anode, thus large area discrete distribution CNT is obtained. The characteristics of this method are: fast growth speed, easily controllable process parameters. But the growth temperature is relatively high and the preparation equipment is relatively complicated.

      In laser ablation method, laser is used to irradiate graphite target containing catalyst at a certain temperature. As a result, gaseous carbon and catalyst particle are taken to low temperature region from high temperature region by air flow and CNT forms under catalyst action. The characteristic of this method is the high quality but the yield is low. It is basically used to prepare singe-walled carbon nanotube.

      Chemical vapor deposition (CVD) is another commonly used method for preparing CNT. In this method, the substrate, dispersed with small metal catalysts such as iron particles, was sent into the hotspot of the furnace under a constant flow of hydrocarbon such as benzene and hydrogen and argon mixture gas. The temperature of the furnace was around 1000‿ and the fibrous materials grew on the surface of the substrate from the iron particle. The obtained fibrous carbon material had the carbon nanotube in the core, and deposited carbons on it. Due to low preparation temperature(usually between 500ﹿ00‿ high quality and quantity product, simple equipment demanded and easily controllable condition, CVD technology has a bright future for industrialization.

       research status of application

      Depending on the size and morphology of the fibrous carbons, the application varies a lot. When the diameter is large, they are used in energy devices such as fuel cells, lithium ion secondary batteries, and electric double-layer capacitors. Large fibers can also be used in composites as a filter material, for reinforcing the composites, and as a thermal conductor. As the diameter of fibrous carbon decreases, the application also scale down in size. Smaller fibrous carbons can be used as a filler of three-phase composites, such as the resin/large carbon fiber/small carbon nanotube composite. Nanotubes are used as field emitters and optical polarizers, as well. For the small carbon nanotubes, electronic devices, such as FETs, and interconnects are under development.

     (1)application in lithium battery

      The outstanding mechanical properties and the high surface-to-volume ratio(due to their small diameter) make carbon nanotube potentially useful as an anode material or an additive in lithium-ion battery systems. An SEM image of an electrode containing 10wt% carbon nanotube as the additive shows a homogenous distribution of nanotube in synthetic graphite reveals the cyclic efficiency of a synthetic graphite anode as a function of the weight percent of muti-walled carbon nanotube(MWNT). With increasing weight percent of carbon nanotube, the cyclic efficiency of the synthetic graphite battery anode increases continuously, and in particular, when 10wt% nanofibers/ nanotube were added, the cyclic efficiency was maintained at almost 100% up to 50cycles. At higher concentrations, the nanotube interconnect graphite powder particles together to form a continuous conductive network.

     (2)application in electric double-layer capacitor

      The advantage of the electric double-layer capacitor(EDLC) is considered to be its high discharge rate,thus making it application as a hydrid energy source for electric vehicles and protable electric devices. EDLC containing carbon nanotubes in the electrode exhibited relatively high capacitances resulting from the high surface area accessible to the electrolyte. On the other hand, the most important factor in commercial EDLC is considered to be the overall resistance on the cell system. In this contest, carbon nanotubes and nanofibers with enhanced electrical and mechanical properties can be applied as an electrical conductive additive in the electrode of EDLC. It has been demonstrated that the addition of carbon nanotubes results in an enhanced capacity at higher current densities, when compared with electrodes containing carbon blacks.

     (3)application in fuel cell

      Fuel cells have been considered as next-generation energy devices because such systems transform the chemical reaction energy from hydrogen and oxygen into electric energy. Carbon nsnotubes decorated with metal nanopaticles as an electrode has doubled the fuel cell performance due to the increased catalytic activity of nanotube-based electrodes. It is anticipated that carbon nanotube technology will contribute to the development of fuel cells, as a catalyst support, and also as a main component as bipolar systems.

     (4)application in field emission tube(plate display)

      Under special condition, carbon nanotubes can vertically growth and form array structure on the silica wafer plated with catalyst. The definition of the superhigh definition flat display made of this carbon nanotube can reach to several ten thousands lines. Also, carbon nanotubes can be form array structure on many materials such as nickel, titanium, chromium, graphite, tungsten so as to be used to produce various field emission tubes.

     (5)application in polymer composite

      It has been showed that carbon nanotubes could behave as the ultimate one-dimensional material with remarkable mechanical properties. The density-based modulus and strength of highly crystalline SWNTs are 19 and 56 times that of steel. On the basis of a continuum shell model, the armchair tube exhibits a large stress-stain response than the zigzag tube under tensile loading. Also highly improved mechanical properties are expected owing to the strong carbon-carbon covalent bond depending strongly upon the atmotic structure of nanotubes and the number of shells.
Moreover, carbon nanotubes exhibit enhanced electrical and thermal conducting properties; better than those of copper.

      Therefore, carbon nanotubes have been studied intensively as fillers in various matrices, especially polymers. The best ultization of the intrinsic properties of these fibrous nanocarbon-bons in polymer could be achieved by optimizing the interface interaction of the nanotube surface and the polymer. Therefore, surface treatments via oxidation in conjunction with the polymer or epoxy could be used in order to improve adhesion properties between the filler and the matrix. This results in a good stress transfer from the polymer to the nanotebe. There are various surface oxidative process, such as electrochemical, chemical and plasma techniques. In addition, the dispersion of nanotubes/nanofibers in the polymer should be uniform within the matrix.

      The smallest working composite gear has been prepared by mixing nanotubes into molten nylon and then injecting into a tiny mold. The diameter of this gear is as small as that of human hair. This piece exhibits high mechanical strength, high abrasion resistance and also good electrical and thermal conductivity.

      When cup-stacked-type carbon nanotubes are incorporated in polypropylene, the improvement in tensile strength with increasing the amount of nanotubes is really remarkable(up to 40%). This remarkable result can be explained by the particular morphology of cup-stacked-type carbon nanotubes. In other words, a large portion of edge sites on the outer surface of nanotubes migh act as nucleation sites and then higher crystallization of polypropylene, resulting in good adhesion between nanotubes and polymers, is achived. Recently, various studies on the nucleation effect of nanotubes on the crystallization of semi crystalline polymer have been reported.