Patent Application
20080226535
The present invention relates to a method and apparatus for manufacturing a carbon nano tube, and more particularly, to a method and apparatus for manufacturing a carbon nano tube by which a carbon nano tube having a uniform property and high purity can be manufactured by uniformly raising a temperature of reaction gas, which includes a gaseous transition metal catalyst precursor compound and gaseous carbon compound contained in a hermetically closed reaction space, to the Boudouard reaction temperature.
In general, a carbon nano tube (CNT) is one of the four known forms of solid carbon, the other three being diamond, C60, and graphite, and is in a tabular form. CNTs have many properties that can potentially be exploited for various worthwhile purposes.
The general principle of CNT formation is well known in the art. In general, CNT is produced when carbon-bearing gas molecules such as carbon monoxide (CO) collide against a surface of a metal catalyst such as iron (Fe) at an elevated temperature. In order for the produced CNTs to have uniform characteristics (i.e., diameter, length, and molecular structure, etc), the size of catalyst should be uniform and the temperature and pressure of the carbon-bearing gas should be spatially uniform. Further, in order to produce CNTs in a large quantity, the number of metal catalysts per unit volume should be large and the frequency of collision of the carbon-bearing molecules with the metal catalysts should be high. A condition suitable for mass production of CNTs can be found through a variety of test performed while changing the temperature and pressure.
A vapor phase growth method using a catalyst among the methods of manufacturing carbon nano tubes is composed of two mechanisms, i.e. a process of producing a metal catalyst and a process of producing a carbon nano tube. The metal catalyst can be obtained by thermally decompose metal-bearing gas such as Fe(CO)5 at high pressure. When the metal-bearing gas such as Fe(CO)5 is heated, it is dissociated to generate a metal atom such as Fe, as expressed in the following formula (I). The dissociated metal atoms are combined together to form a large spherical body composed of several hundreds of metal atoms, which is referred to as a cluster, as expressed in the following formula (II).
Fe(CO)5→Fe+5CO (I)
nFe→Fen, where 10<n<1000 (II)
Then, the carbon-bearing gas such as carbon monoxide (CO) is brought into contact with the produced metal cluster at a high temperature. At this time, as shown in
CO+Fen→CNT+½O2+Fen (III)
The mass production of the carbon nano tube that succeeded for the first time is a HiPco process (High Pressure carbon monoxide process) developed by Bronikowski et al. using such an apparatus as schematically shown in
When CNTs produced through the aforementioned process is used, it is preferred that CNTs have uniform properties, i.e. uniform diameter, length and molecular structure. To manufacture CNTs having a uniform property, metal catalysts must have a uniform diameter. As it can be understood from
The reaction rate in the formula (I) and (II) is a function of a reaction temperature and a concentration of gas species participating in the reaction. In the conventional process of manufacturing a carbon nano tube such as the HiPco process, the reaction gas is heated and cooled by heating and cooling a wall of a reactor. That is, when the heating or cooling is performed, heat is conducted through the reactor wall and reaction gas. At this time, since a heat conduction rate is proportional to a temperature gradient, the heat can be transferred to the reaction gas only if there is a temperature gradient in the gas. This means that the temperature of the reaction gas is not spatially uniform. According to the analysis of Gokcen and Dateo, the temperature of the reaction gas in the reactor varies between 300 K to 1300 K in the HiPco process.
As described above, since the process of manufacturing a carbon nano tube according to a method for heating reaction gas through heat transfer due to the temperature gradient, such as the HiPco process, is premised on inevitable non-uniformity of the reaction gas temperature, non-uniform metal catalyst is produced due to the non-uniform temperature distribution in the reactor. There is a limitation on the manufacture of a carbon nano tube having a uniform property.
An object of the present invention is to provide a method for manufacturing a carbon nano tube having a uniform property and high purity by spatially uniformly raising the temperature of the reaction gas comprising gaseous carbon compound and gaseous transition metal catalyst precursor compound.
Another object of the present invention is to provide an apparatus capable of manufacturing a carbon nano tube having a uniform property and high purity using the aforementioned manufacturing method.
A further object of the present invention is to provide a carbon nano tube which has a uniform property and high purity and is manufactured by the aforementioned manufacturing method.
By “adiabatic” used herein is meant that reaction gas is not intentionally heated or cooled using a heat source when the reaction gas is compressed or expanded. That is, the word “adiabatic” used herein has a different meaning from the conventional meaning of adiabatic that natural heat transfer to the surroundings through a reaction vessel is intentionally completely prevented, and actually has such a meaning that medium of consideration is not intentionally heated or cooled using a heat source (i.e., there is no heat transfer to the medium of consideration).
According to an aspect of the present invention, there is provided a method for manufacturing a carbon nano tube, comprising the steps of preparing a reaction vessel including a substantially hermetic and compressible reaction space; supplying the reaction space with carbon nano tube reaction gas containing a gaseous carbon compound and a gaseous transition metal catalyst precursor compound; and producing suspension gas with carbon nano tube products suspended therein by compressing the reaction gas in the reaction space until a temperature of the carbon nano tube reaction gas supplied to the reaction space reaches a temperature equal to or greater than a temperature at which the transition metal catalyst precursor compound is thermally decomposed and a minimum starting temperature of the Boudouard reaction. In addition, the method for manufacturing a carbon nano tube according to the present invention may further comprise the step of preheating the carbon nano tube reaction gas at a temperature below the thermal decomposition temperature of the catalyst precursor compound before supplying the reaction space with the carbon nano tube reaction gas.
Furthermore, according to the present invention, instead of performing the metal catalyst cluster generation process and the carbon nano tube growth process simultaneously, the process of generating metal catalyst clusters and the process of growing carbon nano tubes can be separated and independently performed. Therefore, a carbon nano tube having a uniform property and high purity can be produced.
According the present invention, there is provided a method for manufacturing a carbon nano tube, comprising the steps of preparing a reaction vessel including a substantially hermetic and compressible reaction space; supplying the reaction space with metal nanoparticles; supplying the reaction space with a gaseous carbon compound; and producing suspension gas with carbon nano tube products suspended therein by compressing the gaseous carbon compound in the reaction space until a temperature of the gaseous carbon compound in the reaction space reaches a temperature equal to or greater than a minimum starting temperature of the Boudouard reaction. Further, the step of supplying the reaction space with the metal nanoparticles may comprise the steps of supplying the reaction space with thermally decomposable reaction gas containing a gaseous transition metal catalyst precursor compound and generating a cluster of transition metal dissociated by compressing the reaction gas in the reaction space such that a temperature of the thermally decomposable reaction gas becomes a temperature equal to or greater than a temperature at which the gaseous transition metal catalyst precursor compound is thermally decomposed.
Furthermore, the present invention provides a method for manufacturing a carbon nano tube in which the reaction gas can be instantaneously compressed and heated at a spatially uniform temperature by using shock waves instead of using a cylinder and a piston for compressing the reaction gas.
According to the present invention, there is provided a method for manufacturing a carbon nano tube, comprising the steps of preparing a reaction vessel including a substantially hermetic reaction space; supplying the reaction space with carbon nano tube reaction gas containing a gaseous carbon compound and a gaseous transition metal catalyst precursor compound; and producing suspension gas with carbon nano tube products suspended therein by applying shock waves to the carbon nano tube reaction gas such that a temperature of the carbon nano tube reaction gas supplied to the reaction space reaches a temperature equal to or greater than a temperature at which the transition metal catalyst precursor compound is thermally decomposed and a minimum starting temperature of the Boudouard reaction. Further, the shock waves may be generated either by exploding gunpowder or by supplying the hermetic reaction space with a certain amount of high-pressure gas.
According to another aspect of the present invention, there is provided an apparatus for manufacturing a carbon nano tube, comprising a reaction vessel including a reaction gas supply port, a reaction gas discharge port and a reaction space; a first valve for opening/closing the supply port; a second valve for opening/closing the discharge port; reaction gas supply means for mixing reaction gas containing a gaseous carbon compound and/or transition metal catalyst precursor compound and supplying the mixed gas to the reaction vessel through the first valve; reaction gas compression means for producing suspension gas with carbon nano tube products suspended therein by compressing the reaction gas contained in the reaction space in a state where the first and second valves are closed such that a temperature of the reaction gas contained in the reaction vessel reaches a temperature equal to or greater than a temperature at which the transition metal catalyst precursor compound is thermally decomposed and a minimum starting temperature of the Boudouard reaction; and gas/solid separation means for separating the carbon nano tube products from the suspension gas discharged from the discharge port. Preferably, a cylinder having a closed end and an opposite open end is used as the reaction vessel, and the compression means includes a piston slidingly installed at the opposite open end and driving means for pushing the piston to compress the reaction gas contained in the reaction space. Further, the reaction gas supply means may comprise heating means for preheating the reaction gas at a temperature below the thermal decomposition temperature of the catalyst precursor compound and/or the minimum starting temperature of the Boudouard reaction before supplying the reaction space with the reaction gas.
According to a further aspect of the present invention, there is provided a carbon nano tube having a uniform property and high purity, which is produced by the manufacturing method of the present invention.
The most significant difference between a method for manufacturing a carbon nano tube according to the present invention and a method for manufacturing a carbon nano tube according to the prior art is that a heat transfer based on a temperature gradient is not be intentionally used when a temperature of reaction gas is raised to a temperature at which a metal cluster catalyst is produced or a starting temperature of Boudouard reaction at which a carbon nano tube grows in a vapor phase growth method. The heating method of the present invention employs a compression heating method by which mechanical energy can be directly transferred throughout the reaction gas, and more preferably employs an adiabatic compression heating method. This heating method due to adiabatic compression allows the reaction gas to be spatially uniformly heated. Further, in a case where it is necessary to cool the reaction gas in a process of manufacturing a carbon nano tube, an expansion cooling method by which the whole reaction gas can be simultaneously cooled using mechanical energy, and more preferably, an adiabatic cooling method may be employed. It is well known from the first law of thermodynamics that a gas temperature is increased by means of the adiabatic (meaning that there is no heat transfer to media) compression while a gas temperature is decreased by means of the adiabatic expansion. That is, according to the first law of thermodynamics, when work is adiabatically applied to gas, internal energy of the gas is increased proportionately. On the other hand, when work is adiabatically extracted from gas, internal energy is decreased proportionately.
T/T
o=(V/Vo)−(r−1)=(p/po)(r−1)/r, (1)
where T, V and p are temperature, volume and pressure of the reaction gas, respectively; r is a heat insulation coefficient (in such a case, approximately 1.4), and a subscript “o” means an initial value. As the volume of the reaction gas is reduced due to the compression, the temperature of the reaction gas is raised according to the equation (1), by which a dissociation reaction (Formula (I)) in which iron pentacarbonyl is thermally decomposed occurs in the reaction gas. It is known that the thermal decomposition of the iron pentacarbonyl (Fe(CO)5) occurs at a temperature of 250° C. or more. Iron atoms thermally decomposed at this time are combined together to produce a metal catalyst cluster (Formula (II)). If the piston is then pushed to compress the reaction gas, the temperature of the reaction gas is raised to be equal to or greater than a starting temperature of the Boudouard reaction in which a carbon nano tube grows on a surface of the metal catalyst cluster, while the pressure of the reaction gas is also suitable for the growth of carbon nano tube. At this time, the reaction in which the carbon nano tube grows on the surface of the metal catalyst cluster (Formula (III)) occurs, and thus, the carbon nano tube grows accordingly. It is known that the growth reaction of the carbon nano tube occurs at about 500° C., but a higher temperature is preferred.
The manufacturing principle of the carbon nano tube shown in
Further, referring to
In fact, the piston shown in
The method for manufacturing the carbon nano tube using shock waves will be explained with reference to
Although either the method for compressing/expanding the reaction gas through an isentropic process to heat/cool the reaction gas using the piston as shown in
In a case where the carbon nano tube is manufactured using the shock tube, all the reactions expressed in the formula (I), (II) and (III) preferably occur when the first shock wave propagates through the reaction gas. If the reaction gas is preheated to a suitable temperature below the thermal decomposition temperature and the starting temperature of the Boudouard reaction, the foregoing can be achieved. If the reactions expressed in the formula (I), (II) and (III) occur almost simultaneously, the catalyst clusters are combined with each other at a proper size and the growth of the carbon nano tube starts at the same time. Thus, it is advantageous in the growth of the carbon nano tube. Further, it is preferred that the temperature in the reaction vessel after the reflected shock wave has propagated through the vessel not be unnecessarily high. If the temperature is unnecessarily high, the catalyst is evaporated and the growth of the carbon nano tube may thus be hindered. If the reaction gas is cooled by means of the expansion process after a long period of time sufficient to occur the reaction expressed in the formula (III), the carbon nano tube produced on the surface of the uniform metal catalyst cluster will also have a uniform property.
To verify the technical spirit of the present invention, the shock wave test illustrated in
In a case where a shock tube test is performed under the conditions listed in the table 1, the pressure of the reaction gas measured at the end wall in the low-pressure driven region according to time is plotted in the graph shown in
After the dynamic process has been completed in the shock tube, the shock tube is opened to collect powder materials adhering to the end wall of the low-pressure driven region. Then, the collected powder materials were inspected using a scanning electron microscope (SEM).
As shown in
A process of manufacturing a carbon nano tube using the apparatus so configured will be explained. Referring to
In this embodiment of the present invention, the reaction vessel 100 is a cylinder having a closed end and an opposite open end. Further, the compression means includes a piston 110 slidingly installed at the opposite open end, and a pneumatic cylinder 210 for pushing the piston to compress the reaction gas contained in the reaction space. An end of a rod 230 of the pneumatic cylinder 210 is connected to the piston 110 used for compressing the reaction gas. A piston 220 of the pneumatic cylinder 210 according to this embodiment has a diameter greater than that of the piston 110 for compressing the reaction gas, such that it can provide a compression force capable of compressing the reaction gas at a sufficient rate. Supply valves 241 and 242 through which compressed air is supplied to move forward and rearward the rod 230 are installed at opposite ends of the pneumatic cylinder 210. Further, drain valves 243 and 244 through which the air is discharged when the rod 230 moves forward and rearward are installed at the opposite ends of the pneumatic cylinder 210. Reference numeral 250, which has not yet explained, designates a source for supplying high-pressure compressed air.
The apparatus 500 of the embodiment employs a pneumatic cylinder as compression means. However, a hydraulic cylinder may be used as compression means, and a connecting rod and crankshaft may be used for allowing the piston to continuously perform the compression and expansion process, if desired.
The reaction gas supply means 300 includes a tank 310 in which carbon monoxide is stored, and an evaporator 320 in which an organic metal compound such as iron pentacarbonyl Fe(CO)5 is dissolved. The carbon monoxide stored in the tank 310 is supplied to the reaction space via pipes 312 and 321. Further, the carbon monoxide stored in the tank 310 is also supplied to the evaporator 320 via a pipe 311 such that it is used for evaporating the liquid Fe(CO)5 and supplying the reaction space with the evaporated Fe(CO)5. The gaseous Fe(CO)5 evaporated in the evaporator is supplied to the reaction space 103 via the pipe 321. Reference numerals 340 and 350, which have not yet explained, designate flow regulators used to adjust a ratio of the carbon monoxide and iron pentacarbonyl supplied to the reaction space 103. In this embodiment, the carbon monoxide has been used as a source gas for evaporating the Fe(CO)5 dissolved in the evaporator 320. However, inert gas such as argon may be used as a source gas and the gaseous carbon compound may also be provided directly to the reaction space.
The apparatus 500 of the embodiment includes heating means 330 which is installed to the pipe 321 to preheat the reaction gas at a temperature below the thermal decomposition temperature of the catalyst precursor compound and the minimum starting temperature of the Boudouard reaction before supplying the reaction space 103 with the reaction gas. A heater may be used as the heating means 330. In addition, the apparatus of the embodiment further includes a heater 140 installed to preheat the reaction gas supplied to the reaction vessel 100.
The process for manufacturing a carbon nano tube will be described in connection with the apparatus 500 of the embodiment shown in
In this embodiment, the other end of the cylinder 610 is opened. If the other end is closed and the high-pressure driving gas is supplied, the apparatus becomes an apparatus conceptually identical to the shock tube shown in
It is intended that the embodiments of the present invention described above and illustrated in the drawings should not be construed as limiting the technical spirit of the present invention. The scope of the present invention is not limited to the embodiments but should be defined only by the appended claims. It is apparent to those skilled in the art that various changes and modifications can be made thereto without departing from the technical spirit of the present invention. Therefore, various changes and modifications fall within the scope of the present invention so far as they are obvious to those skilled in the art.
According to the present invention, there is provided a method and apparatus for manufacturing a carbon nano tube, wherein a carbon nano tube reaction gas containing a gaseous carbon compound and a gaseous transition metal catalyst precursor compound is uniformly heated though compression. The carbon nano tube produced by the method and apparatus of the present invention has a uniform property since it grows on the surface of a metal cluster with a uniform size produced in an atmosphere spatially uniformly heated.
Further, according to the present invention, there is provided a method and apparatus for manufacturing a carbon nano tube, by which a carbon nano tube with a uniform property can be mass-produced. The present invention provides an apparatus similar to a four-stroke internal combustion engine having a cylinder and a piston. The apparatus can mass-produce a carbon nano tube with a uniform property by repeatedly performing a cycle in which reaction gas is sucked, compressed, expanded and discharged.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2004-0035931 | May 2004 | KR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/KR05/01469 | 5/19/2005 | WO | 00 | 12/27/2007 |
