Carbon has a strange physical and chemical properties, such as metal or semiconductor unique electrical conductivity, high mechanical strength, hydrogen storage capacity of absorption capacity and strong ability to absorb microwave, 90 first found by the immediate physical, chemical Materials and the scientific community as well as the high-tech industry sector great importance. Application studies have shown that carbon nanotubes can be used for a variety of high-tech fields.
If it is used as a reinforcing agent and the agent can be conductive to create high-performance car parts protection; use it as a catalyst carrier to significantly improve the catalytic activity and selectivity; microwave absorption of carbon nanotubes strong performance, it can be used as absorbent preparation Stealth materials, electromagnetic shielding material or absorbing materials such as the darkroom.
Carbon is considered to be a new type of high-performance structural materials and functional materials throughout the world in the preparation and application of substantial investment in research and development strength, look forward to occupying the high ground in the field of technology.
I was launched in 1996 and the preparation of carbon nanotubes, president of the Chinese Academy of Sciences in 1998 to be a special fund to support, then participated in the national innovation projects for major projects, “carbon nanotubes and other nanomaterials,” the research.
Has been made to the current phase of a series of results, such as carbon nanotubes to create a boiling bed and moving bed catalytic cracking technology preparation for large-scale preparation of a new way out of carbon nanotubes; to explore the carbon nanotubes used as catalyst support, lithium-ion Battery anode materials for electric double-layer capacitors and the possibility of electrode materials; for the first time will be used as a microwave absorbent carbon nanotubes, carbon nanotubes and found that the broadband microwave absorption characteristics; in the preparation of the design size of the carbon nanotubes have also been active Progress.
First, mass Preparation of carbon nanotubes
To achieve the industrial application of carbon nanotubes, carbon nanotubes must first resolve the problem of preparation of a large number of low-cost. Since carbon nanotubes were found in 1991, its preparation has been extensively studied. At present, there are three main methods of preparation, that is, the arc discharge method, laser ablation and fixed-bed catalytic cracking method. Arc discharge and laser ablation was the product of the rule of law, are carbon nanotubes and other forms of carbon product of co-existence, the separation and purification difficulties, low yield and difficult to scale. A third fixed-bed catalytic cracking method of natural gas from the preparation process of carbon nanotubes with simple, low cost and easy to control the size of the nanotube, length, the higher the yield, and other advantages, there are important research value, but the method can only be a catalyst to The thin-layer form, will have good results, otherwise the catalyst on the low utilization rate and therefore difficult to raise output.
Boiling-bed catalytic cracking technology of gas-solid reactions contact well suited to handle a large number of particles of solid catalyst, by boiling bed catalytic cracking method in place of solid-bed catalytic cracking method can substantially increase the amount of carbon nanotube preparation.
In the boiling-bed catalytic cracking reactor, the raw material to a certain degree of gas flow rate through the gas distribution plate, gas distribution will be a catalyst for the activation of on-board “blowing” as “boiling” state. Catalyst particles has been in a campaign, the catalyst particles than the distance between the fixed bed catalyst particles in the distance between the much larger catalyst on the surface easy to grow straight out of carbon nanotubes, catalyst particles due to the collision between the , Carbon nanotubes easily emerge from the catalyst surface. This is the result of both direct and guaranteed the opening of the high rate of the formation of carbon nanotubes. At the same time, in boiling bed catalyst can be a significant increase in the volume of raw materials and gases can still have full access to the surface of the catalyst, a catalyst to ensure high utilization rate.
Despite the boiling-bed catalytic cracking in the mass production of carbon nanotubes have a larger break, but all of the carbon nanotubes with the existing methods of preparation, only intermittent operation is not conducive to high-volume low-cost carbon nanotube preparation.
To achieve high-volume preparation of carbon nanotubes, we must first solve the problem and put a catalyst for a catalyst and a product export in a timely manner. This study had shown that the adoption of a special response unit and the process of carbon nanotubes can be prepared in a row, so as to achieve high-volume low-cost preparation of carbon nanotubes.
Preparation of carbon nanotubes in a row through the process to achieve the following: the closure of the mobile-bed catalytic cracking reactor, after a deal to restore the nano-catalysts in a row evenly through the nozzle onto cloth to a mobile bed, moving bed to a certain speed of movement. Catalyst temperature in the area of the residence time can be controlled through the movement of the bed to adjust the speed of movement. The feed gas flow with the direction of movement of bed in the same direction could be the opposite.
Raw gas in the catalyst cracking formation on the surface of carbon nanotubes. When the catalyst in moving the bed to reach the residence time settings, together with the catalyst in the formation of carbon nanotubes on the move from the bed into the traps away from the limitations of the reaction through the exhaust gas emissions. Use of mobile-bed catalytic cracking reactor can be designed to achieve the size of carbon nanotubes for manufacturing, is expected to substantially reduce the cost of production for industrial applications of carbon nanotubes to provide a guarantee.
Second, the application of carbon nanotubes
1Ã¯Â¼Â? Due to the special structure and dielectric properties, carbon nanotubes (CNTs) to show strong broadband microwave absorption properties, it also has a light weight, adjustable variable electrical conductivity, high temperature oxidation resistance strong and good stability, Is a promising ideal microwave absorbent, it is possible for the stealth materials, electromagnetic shielding material or chamber absorbing materials.
2Ã¯Â¼Â? Nano-materials than the large surface area, surface atoms large percentage (about 50% of the number of atoms), so that the system of electronic structure and crystal structure changed significantly, showing a special electronic effects and surface effects. If the gas through the proliferation of carbon nanotubes through the speed of conventional catalyst particles thousands of times, Supported catalyst after a great catalyst to improve the activity and selectivity.
Carbon nanomaterials as a new member of the family, its special structure and surface characteristics, excellent storage capability Semiconductor and metal and electrical conductivity, in its hydrogenation, dehydrogenation and-choose, such as catalytic reaction is very Potential applications. Once the carbon nanotubes to obtain the catalytic applications, is expected to greatly increase the activity and selectivity, resulting in huge economic benefits.
3Ã¯Â¼Â? (1) lithium-ion battery anode materials. CNTs layer of the pitch to 0.34nm, slightly larger than the graphite layer spacing 0.335nm, which is conducive to Li + ions into and moved out, it’s a special cylinder-shaped configuration allows not only Li + from the outer wall and inner wall into two , But will also prevent solvent as a result of Li + ions embedded in the graphite layer caused by the spin-off caused damage to the negative electrode materials. Graphite-doped CNTs can increase the electrical conductivity of the graphite anode, the elimination of polarization. Experiments showed that CNTs as a separate additive or used as a lithium-ion battery anode materials can significantly improve the negative electrode materials of Li + embedded capacity and stability.
( (2) most electric double-layer capacitor materials. Electrical power is also a two-tier energy storage device. In addition to the capacity of the smaller (usually the second nickel-cadmium battery of 1%), electric double-layer capacitors and other integrated performance much better than the rechargeable battery, such as high current charging and discharging almost no charge and discharge over-voltage, the cycle of life Up to tens of thousands of times, wide temperature range, and so on. Electric double-layer capacitors in the audio-video equipment, tuner, such as telephone and fax communications equipment and household appliances in a variety of widely used. As the electric double-layer capacitor electrode materials requiring a high degree of crystalline materials, electrical conductivity, specific surface area, pore size concentrated in a certain range.
At present, which tends to be used for porous carbon electrode material, not only the distribution of micro-kuan (storage of energy contributing less than 30% of the hole), and low crystallinity, poor electrical conductivity, resulting in a small capacity. Does not have the right material is to limit the electric double-layer capacitors in a wider range of use is an important reason.
Carbon surface area, crystallinity, electrical conductivity, and pore size can be controlled synthesis, which could become an ideal electrode materials. Hyperion Catalysis International Co., Ltd. of the United States is reported to the catalytic cracking Preparation of carbon nanotubes (diameter pipe about 8nm) for the electrode material, in order to 38wt% H 2 SO 4 as the electrolyte, will be greater than 113F / g electrical capacity, Than the current capacity of porous carbon than 2 times. We have to 30nm diameter of carbon nanotubes as the electrode material, in order to PVDF for the binder to 1MN (C 2 H 5) 4 BF 4 / PC electrolyte for electric double-layer capacitors pose, the electrodes measured electrical capacity of carbon nanotubes 89F / g.
At present, carbon nanotubes as the electrode material to the electric double-layer capacitors, and its power-to-weight ratio more than 8kw/kg, it is possible to start the electric vehicle as the use of power. Once these steps are followed then the production can be raised to higher levels that will make commercial production practical.