KR102812801B1 - Method and apparatus for synthesizing carbon nanotube using thermal plasma - Google Patents

Abstract

The present invention relates to a method and apparatus for synthesizing carbon nanotubes using thermal plasma, wherein a carbon source-containing gas is injected from all directions of 360° into a vaporized metal catalyst that is dispersed in all directions of 360°, thereby minimizing unreacted metal catalyst and allowing the carbon source-containing gas to be thermally decomposed by the metal catalyst without being decomposed in advance at high temperatures.

Description

Method and Apparatus for Synthesizing Carbon Nanotubes Using Thermal Plasma {METHOD AND APPARATUS FOR SYNTHESIZING CARBON NANOTUBE USING THERMAL PLASMA}

The present invention relates to a method and apparatus for synthesizing carbon nanotubes using thermal plasma in which a plasma jet is generated by an arc discharge between electrodes.

Carbon nanotubes (CNTs) are polymeric carbon isotopes in which carbon atoms are interconnected in a hexagonal honeycomb pattern. Depending on the number of carbon walls, they can be classified into single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs). Representative methods for synthesizing these carbon nanotubes (CNTs) include the arc discharge method and the CVD (Chemical Vapor Deposition) method.

The synthesis method using thermal plasma, which is one of the above arc discharge methods, has the advantage of being able to synthesize carbon nanotubes with high crystallinity and excellent electrical properties. However, this method has the disadvantages of a short electrode life and low synthesis efficiency of carbon nanotubes.

Specifically, the conventional synthesis method using thermal plasma introduces a hydrocarbon gas or a mixture of hydrocarbon gas and gases such as Ar, _N2 , _H2 , and He as a gas for forming plasma into the thermal plasma torch pipe (gas flow channel) where the electrode is located. At this time, carbide is formed on the electrode due to the carbon component derived from the introduced gas, thereby shortening the life of the electrode. To solve this problem, a method has been proposed in which a hole is made in the positive charging (Anode) and gas for forming plasma and source gas (gas containing a carbon source) are injected together. However, this method has a problem in that the source gas is cooled by cooling water that is flowed to protect the thermal plasma torch device, and when the cooled source gas comes into contact with the metal catalyst, the metal catalyst is quenched, preventing smooth synthesis of carbon nanotubes.

In addition, when using thermal plasma, there is also a problem that the source gas is exposed to a thermal plasma flame of several thousand degrees or more and decomposes before meeting the metal catalyst, causing side reactions (free carbon generation, carbon encapsulation, etc.).

In addition, since the source gas is injected by connecting a pipe to the wall of the reaction chamber, the source gas flows in one direction, so a large amount of metal catalyst that does not meet it exists as unreacted catalyst (unable to synthesize CNT and surrounded by a carbon shell), which reduces the purity of the carbon nanotube and also reduces the carbon conversion efficiency.

Republic of Korea Publication Patent No. 2021-0016102 (2021.02.15)

The present invention aims to provide a method and apparatus for synthesizing carbon nanotubes, which can minimize the amount of unreacted metal catalyst while controlling side reactions that occur during the process of synthesizing carbon nanotubes using thermal plasma.

In order to solve the above problem, the present invention provides a method for synthesizing carbon nanotubes, including the steps of: supplying a metal catalyst into a crucible accommodated in a reaction chamber; generating a plasma jet in a plasma jet generating unit; spraying the plasma jet onto the metal catalyst to vaporize the metal catalyst; and supplying a gas containing a carbon source to the vaporized metal catalyst to react the vaporized metal catalyst with the carbon source.

In addition, the present invention provides a carbon nanotube synthesized by the method for synthesizing the carbon nanotube.

In addition, the present invention provides a carbon nanotube synthesis device including a plasma jet generating unit that generates a plasma jet; a crucible containing a metal catalyst vaporized by the plasma jet; a reaction chamber that accommodates the crucible; and a capturing unit that captures carbon nanotubes synthesized by a reaction between the vaporized metal catalyst and a carbon source contained in a carbon source-containing gas.

According to the present invention, since the synthesis environment of carbon nanotubes is controlled so that a gas containing a carbon source is not decomposed in advance in a high synthesis temperature environment of 1,500°C or higher and thermal decomposition is performed by a metal catalyst, carbon nanotubes exhibiting high purity can be synthesized while minimizing side reactions (free carbon generation, carbon encapsulation, etc.) occurring during the synthesis process.

In particular, according to the present invention, since a gas containing a carbon source can be supplied in all directions of 360° to correspond to a vaporized metal catalyst scattered in all directions of 360° during a synthesis process, the carbon conversion rate can be maximized, and unreacted metal catalyst can be minimized, thereby obtaining carbon nanotubes exhibiting high purity.

Figure 1 is a schematic diagram showing a carbon nanotube synthesis device according to one embodiment of the present invention.
Figure 2 is an image of a carbon nanotube synthesized in Example 2 of the present invention, confirmed by a transmission electron microscope.

Hereinafter, the present invention will be described in detail. Herein, the present invention is not limited to the contents disclosed below, and may be modified in various forms as long as the gist of the invention is not changed.

The word “comprising” or “including” as used herein is intended to specify particular features, regions, steps, processes, elements and/or components, and does not exclude the presence or addition of other features, regions, steps, processes, elements and/or components, unless specifically stated otherwise.

In this specification, the description that one component is connected or coupled with another component includes both direct connection or coupling between these components, or indirect connection or coupling through another component.

In this specification, singular expressions are interpreted to include the singular or plural as interpreted by the context, unless otherwise specified.

All numbers and expressions indicating the amounts of ingredients, reaction conditions, etc. described in this specification can be modified by the term "about" in all cases unless otherwise specified.

The terms first, second, etc., used in this specification are used to describe various components, and the components should not be limited by the terms, and the terms are used only for the purpose of distinguishing one component from another.

Method for synthesizing carbon nanotubes

The present invention is characterized by supplying a gas containing a carbon source to the omnidirectional region to react the metal catalyst with the carbon source before the flight distance of the metal catalyst, which is vaporized and scattered (flies) in a 360° omnidirectional region, becomes too far, thereby minimizing the amount of unreacted metal catalyst and enabling the synthesis of carbon nanotubes with excellent physical properties with high efficiency (high yield).

Specifically, the method for synthesizing carbon nanotubes according to the present invention includes the steps of (S-1) supplying a metal catalyst into a crucible accommodated in a reaction chamber; (S-2) generating a plasma jet in a plasma jet generating unit; (S-3) spraying the plasma jet onto the metal catalyst to vaporize the metal catalyst; and (S-4) supplying a gas containing a carbon source to the vaporized metal catalyst to react the vaporized metal catalyst with the carbon source, which will be specifically described as follows.

S-1: Metal catalyst supply

The above S-1 step is a step of supplying a metal catalyst (e.g., metal catalyst powder) into a crucible accommodated in a reaction chamber. Specifically, the metal catalyst is supplied so that the metal catalyst is contained inside the crucible. At this time, the method of supplying the metal catalyst can be carried out by a commonly known method.

The material of the above crucible is not particularly limited, but may be a carbon material or ceramic material with excellent durability and heat resistance.

The above metal catalyst is not particularly limited, but may include technetium (Tc), cobalt (Co), tungsten (W), manganese (Mn), copper (Cu), vanadium (V), chromium (Cr), scandium (Sc), titanium (Ti), yttrium (Y), nickel (Ni), zirconium (Zr), niobium (Nb), molybdenum (Mo), iron (Fe), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), hafnium (Hf), tantalum (Ta), rhenium (Re), osmium (Os), iridium (Ir), platinum (Pt), gold (Au), actinium (Ac), zinc (Zn), germanium (Ge), beryllium (Be), aluminum (Al), calcium (Ca), magnesium (Mg), bismuth (Bi), cadmium (Cd), lead (Pb), tin (Sn), thallium (Tl), indium (In), It may be a metal catalyst comprising at least one element selected from the group consisting of sodium (Na), lithium (Li), potassium (K), rubidium (Rb), gallium (Ga), cesium (Cs), strontium (Sr), barium (Ba), radium (Ra), tellurium (Te), silicon (Si), and phosphorus (P). Specifically, the metal catalyst may be a sulfide, a chloride, a hydroxide, a nitride, or an organometallic compound comprising at least one element, or a mixture thereof.

For example, the metal catalyst may be technetium (Tc), cobalt (Co), tungsten (W), manganese (Mn), copper (Cu), vanadium (V), chromium (Cr), scandium (Sc), titanium (Ti), yttrium (Y), nickel (Ni), zirconium (Zr), niobium (Nb), molybdenum (Mo), iron (Fe), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), hafnium (Hf), tantalum (Ta), rhenium (Re), osmium (Os), iridium (Ir), platinum (Pt), gold (Au), actinium (Ac), zinc (Zn), germanium (Ge), beryllium (Be), aluminum (Al), calcium (Ca), magnesium (Mg), bismuth (Bi), cadmium (Cd), lead (Pb), tin (Sn), thallium (Tl), indium (In), It may include two or more elements selected from the group consisting of sodium (Na), lithium (Li), potassium (K), rubidium (Rb), gallium (Ga), cesium (Cs), strontium (Sr), barium (Ba), radium (Ra), tellurium (Te), silicon (Si), and phosphorus (P). Specifically, the metal catalyst may include two or more elements selected from the group consisting of cobalt (Co), nickel (Ni), and iron (Fe), but is not limited thereto.

S-2: Plasma jet generation

The above S-2 step is a step of generating a plasma jet from a plasma jet generating unit to melt the metal catalyst supplied to the crucible. The generation of the plasma jet can be accomplished through a transferred type or a non-transferred type via the plasma jet generating unit.

Specifically, according to the present invention, the step of generating the plasma jet includes the step (S-2a) of injecting plasma generation gas into a plasma jet generating unit having an anode and a cathode therein; the step (S-2b) of supplying power to the plasma jet generating unit; and the step (S-2c) of generating a plasma arc region on the anode side, whereby the plasma jet can be generated in a non-transport manner. Since the plasma jet is generated in a non-transport manner, a non-conductive metal compound (oxide, chloride, nitride, etc.) that does not conduct electricity outside the plasma jet generating unit can be utilized as a metal catalyst, and the distance between the molten metal catalyst and the plasma jet generating unit can be freely adjusted, and the plasma jet can be generated more stably than in a transport manner.

The above S-2a step may be a step of injecting plasma generation gas into the plasma jet generating unit so that plasma can be generated. At this time, the flow rate at which the plasma generation gas is injected may be 10 to 100 SLPM, specifically 15 to 60 SLPM, or 20 to 40 SLPM, but is not limited thereto. When the flow rate is within the above range, the plasma generation efficiency and the carbon nanotube synthesis yield can be increased.

The above S-2b step may be a step of supplying power to the plasma jet generator to generate thermal energy (high electric field) for plasma formation. At this time, the power supplied to the plasma jet generator may be 5 to 100 kW, specifically 6 to 50 kW, or 7 to 25 kW, but is not limited thereto. As the power is supplied within the above range, thermal energy can be stably generated.

The plasma generating gas is not particularly limited, but may be a gas including at least one selected from the group consisting of argon (Ar), hydrogen (H ₂ ), nitrogen (N ₂ ), carbon monoxide (CO), helium (He), and a hydrocarbon (C _x H _y ). Specifically, the plasma generating gas may be a mixed gas comprising argon (Ar) and at least one gas selected from the group consisting of hydrogen (H ₂ ), nitrogen (N ₂ ), carbon monoxide (CO), helium (He), and a hydrocarbon (C _x H _y ). More specifically, the plasma generating gas may be a mixed gas of argon (Ar) and hydrogen (H ₂ ), or a mixed gas of argon (Ar) and nitrogen (N ₂ ), but is not limited thereto. Since the plasma generating gas is the mixed gas, the thermal energy for plasma generation is increased (the ionization voltage is increased and thus the output is high), so that the synthesis yield of carbon nanotubes can be significantly increased.

The above S-2c step is a step in which the plasma generating gas receives thermal energy to generate plasma, and the density of the generated plasma increases, thereby generating a plasma arc region (arc point) on the anode side provided inside the plasma jet generating unit.

By going through the above S-2b and S-2c steps, the generated plasma can be ejected in the form of a plasma jet from the plasma jet generating unit by the plasma arc region.

The center temperature of the plasma jet generated from the plasma jet generating unit may be 10,000 K or higher, 18,000 K or higher, or 30,000 K or higher (e.g., 10,000 to 40,000 K). When the temperature is within the above range, the vaporization of the metal catalyst can occur smoothly.

S-3: Metal catalyst vaporization

The above S-3 step is a step of spraying the plasma jet generated from the plasma jet generator onto the metal catalyst contained inside the crucible to vaporize the metal catalyst. Specifically, through the S-3 step, a metal catalyst that is vaporized and scattered in the form of particles (floating metal catalyst) can be formed. That is, when the plasma jet begins to be sprayed onto the metal catalyst, the metal catalyst melts to form a molten metal catalyst, and then, as the plasma jet continues to be sprayed, a metal catalyst that is vaporized in the form of particles from the molten metal catalyst can be formed.

In order to better vaporize the metal catalyst, the plasma jet may be sprayed vertically onto the metal catalyst.

Vaporization of the above metal catalyst can be carried out until all of the metal catalyst present inside the crucible is vaporized, and the time required for this is affected by the injection flow rate of plasma generation gas, the amount of power supplied to the plasma jet generator, the distance between the metal catalyst and the plasma jet, etc. Therefore, by appropriately setting these and controlling the required time, the synthesis yield of carbon nanotubes can be optimized.

S-4: Reaction of vaporized metal catalyst with carbon source

The above S-4 step is a step for supplying a carbon source-containing gas to the vaporized metal catalyst to react the vaporized metal catalyst with the carbon source. In this S-4 step, the supply path of the carbon source-containing gas, the reaction conditions of the carbon source and the metal catalyst, etc. are controlled, thereby minimizing the amount of unreacted metal catalyst while synthesizing carbon nanotubes with excellent properties.

Specifically, according to the present invention, the carbon source-containing gas can be supplied through at least one of the first conduit provided in the plasma jet generating unit, the second conduit provided in the crucible, and the third conduit provided in the reaction chamber. By supplying the carbon source-containing gas through at least one of the first to third conduit, the carbon source-containing gas can be supplied to the metal catalyst in all directions (up and down and left and right), thereby greatly increasing the amount of reaction with the metal catalyst in the form of particles flying in all directions. That is, since the carbon source and the metal catalyst meet and react in various directions, the amount of unreacted metal catalyst is minimized and the amount of carbon nanotubes synthesized is significantly increased. In addition, since the carbon source is not decomposed in advance before meeting the metal catalyst but is decomposed by the heat of the metal catalyst, side reactions (free carbon generation, carbon encapsulation, etc.) that occur during the synthesis of carbon nanotubes can also be minimized.

Meanwhile, the reaction of the vaporized metal catalyst and the carbon source can be controlled to occur before the average particle diameter of the vaporized metal catalyst exceeds 20 nm. By allowing the reaction to occur before the average particle diameter of the vaporized metal catalyst exceeds 20 nm, carbon nanotubes having excellent physical properties (e.g., electrical conductivity, purity, etc.) can be synthesized.

That is, the vaporized metal catalyst is dispersed in the form of particles, and at this time, if the concentration of the dispersed metal catalyst is high or the flight time is long, nuclear growth occurs due to migration between the metal catalysts, which increases the average particle size. Here, if the metal catalyst with an average particle size that is too large reacts with a carbon source, carbon nanotubes may not grow, which may significantly reduce the synthesis yield of carbon nanotubes. In addition, carbon nanotubes obtained through the reaction of the metal catalyst with an average particle size that is too large with the carbon source may have poor crystallinity and straightness, and thus low electrical conductivity. Accordingly, the present invention controls the reaction between the metal catalyst having an average particle size that does not exceed 20 nm (for example, the metal catalyst having an average particle size of 1 to 10 nm) and the carbon source before the average particle size of the metal catalyst becomes too large, thereby allowing the synthesis of carbon nanotubes with excellent physical properties.

In addition, the reaction of the vaporized metal catalyst and the carbon source occurs in the space between one end of the plasma jet generating unit and the metal catalyst inside the crucible. At this time, the distance between one end (tip) of the plasma jet generating unit and the metal catalyst (the vertical distance from the plasma jet torch nozzle of the plasma jet generating unit to the surface of the metal catalyst) can be controlled so that the reaction occurs within a range of 10 to 100 mm (specifically, 15 to 90 mm, or 25 to 80 mm). By allowing the reaction of the vaporized metal catalyst and the carbon source to occur within the range of the distance, carbon nanotubes having excellent physical properties can be synthesized.

In addition, the reaction of the vaporized metal catalyst and the carbon source can be controlled to occur at a temperature of 600° C. or higher. Specifically, the reaction of the vaporized metal catalyst and the carbon source can occur at a temperature of 600 to 2000° C., or 900 to 1200° C., thereby synthesizing carbon nanotubes with excellent physical properties.

Meanwhile, the carbon source-containing gas may include, but is not limited to, a carbon source and a carrier gas.

The carbon source may be a hydrocarbon gas, a solid carbon body, or a liquid carbon body. Specifically, the carbon source may include at least one selected from _{the group consisting of methane (CH 4 ), acetylene (C 2 H 2 ) , ethylene} (C ₂ H ₄ ), ethane (C ₂ H ₆ ), propane (C ₃ H ₈ ), butane (C 4 H 10 ), and pentane (C ₅ H ₁₂ ), but is not limited thereto.

The carrier gas is included in the carbon source-containing gas and acts as a mobile phase. The carrier gas may specifically include at least one selected from the group consisting of argon (Ar), nitrogen (N ₂ ), hydrogen (H ₂ ), and helium (He), but is not limited thereto.

carbon nanotube

The carbon nanotube according to the present invention can exhibit excellent electrical properties and high purity as it is obtained by the above-described synthesis method. The carbon nanotube may be a single-wall carbon nanotube (SWCNT) or a multi-wall carbon nanotube (MWCNT), and specifically, may be a single-wall carbon nanotube (SWCNT).

The above carbon nanotube may have an electrical conductivity of 500 S/cm or more, 700 S/cm or more, or 900 S/cm or more, specifically, 600 to 1500 S/cm, 750 to 1300 S/cm, or 900 to 1250 S/cm, but is not limited thereto.

In addition, the carbon nanotube may have a carbon purity of 80% or higher and a synthesis yield of 500% or higher. Specifically, the carbon nanotube may have a carbon purity of 80 to 99.9%, 85 to 99%, or 90 to 98%, and a synthesis yield of 700 to 2500%, 900 to 2300%, or 1000 to 2000%, but is not limited thereto.

In addition, the carbon nanotube may have a G/D ratio of 45 or more, 50 or more, 55 or more, or 60 or more, specifically 45 to 90, 48 to 85, 50 to 80, or 55 to 80, as measured by Raman spectroscopy, based on single-walled carbon nanotubes (SWCNTs).

Carbon nanotube synthesis device

The present invention provides a carbon nanotube synthesis device capable of supplying a carbon source-containing gas in all directions (multi-directionally) so as to minimize the unreacted amount of a metal catalyst that is scattered in all directions. Specifically, the carbon nanotube synthesis device according to the present invention includes a plasma jet generating unit that generates a plasma jet; a crucible containing a metal catalyst vaporized by the plasma jet; a reaction chamber that accommodates the crucible; and a capturing unit that captures carbon nanotubes synthesized by a reaction between the vaporized metal catalyst and a carbon source contained in the carbon source-containing gas.

In addition, the carbon nanotube synthesis device further includes at least one conduit among a first conduit provided in the plasma jet generating unit; a second conduit provided in the crucible; and a third conduit provided in the reaction chamber, and the carbon source-containing gas is supplied to the vaporized metal catalyst through at least one conduit among the first conduit, the second conduit, and the third conduit.

This is explained in detail with reference to Fig. 1 as follows.

Plasma jet generator (10)

The plasma jet generating unit (10) above generates a plasma jet. Specifically, the plasma jet generating unit (10) may generate a plasma jet in a non-transport manner by including an anode and a cathode that receive plasma generating gas to form a plasma arc region; a housing that accommodates the anode and the cathode; and a plasma jet torch nozzle provided at one end of the housing, but is not limited thereto.

The anode (11) and cathode (12) included in the plasma jet generating unit (10) receive plasma generating gas from the plasma generating gas supply unit (80) to form a plasma arc region (Arc). Specifically, the plasma arc region (Arc) can be formed on the anode (11) side. The anode (11) and cathode (12) can be made of a commonly known material.

The housing (13) included in the above plasma jet generating unit (10) accommodates the anode (11) and the cathode (12). This housing (13) may be made of a commonly known metal material, and its structure is not particularly limited as long as it is a structure capable of accommodating the anode (11) and the cathode (12).

The plasma jet torch nozzle (14) included in the above plasma jet generating unit (10) is provided at one end (tip) of the housing (13), through which the plasma jet (D1) is sprayed. This plasma jet torch nozzle (14) can be made of commonly known materials and structures.

The plasma jet generating unit (10) may be positioned vertically on the crucible (20) described below. When the plasma jet generating unit (10) is positioned vertically on the crucible (20), the plasma jet (D1) generated from the plasma jet generating unit (10) is intensively sprayed onto the metal catalyst contained inside the crucible (20), so that vaporization of the metal catalyst can be efficiently achieved.

Meanwhile, the plasma jet generating unit (10) may be equipped with a first conduit (50) that allows the carbon source-containing gas to be supplied to the vaporized metal catalyst. The number of the first conduits (50) may be 1 or more, and the structure thereof is not particularly limited as long as the carbon source-containing gas can be smoothly supplied. The first conduit (50) may be connected to a carbon source-containing gas supply unit (90) so that the carbon source-containing gas can be supplied to the vaporized metal catalyst, and the carbon source-containing gas can be supplied to the vaporized metal catalyst from above through the first conduit (50).

Crucible (20)

The above crucible (20) contains a metal catalyst that is vaporized by the plasma jet. Specifically, when a solid metal catalyst is contained in the crucible (20) and the metal catalyst is melted and vaporized by the plasma jet, a molten metal catalyst (D2) is contained in the crucible (20). This crucible (20) can be made of a commonly known material and structure.

The crucible (20) may be provided with a second conduit (60) that allows the carbon source-containing gas to be supplied to the vaporized metal catalyst. The number of the second conduits (60) may be 1 or more, and the structure thereof is not particularly limited as long as the carbon source-containing gas can be smoothly supplied. The second conduit (60) may be connected to a carbon source-containing gas supply unit (90) so that the carbon source-containing gas can be supplied to the vaporized metal catalyst, and the carbon source-containing gas can be supplied to the vaporized metal catalyst from below through the second conduit (60).

Reaction chamber (30)

The above reaction chamber (30) accommodates the crucible (20). The reaction chamber (30) may have a volume and structure that allow the reaction between the vaporized metal catalyst and the carbon source to occur smoothly while accommodating the crucible (20). In addition, the operating pressure of the reaction chamber (30) is not particularly limited, but may be atmospheric pressure (e.g., 1 atm).

The reaction chamber (30) may be provided with a third conduit (70) that allows the carbon source-containing gas to be supplied to the vaporized metal catalyst. The number of the third conduits (70) may be 1 or more, and the structure thereof is not particularly limited as long as the carbon source-containing gas can be smoothly supplied. The third conduit (70) may be connected to a carbon source-containing gas supply unit (90) so that the carbon source-containing gas can be supplied to the vaporized metal catalyst, and the carbon source-containing gas can be supplied to the vaporized metal catalyst in a horizontal direction through the third conduit (70).

Capture Unit (40)

The above-mentioned capturing unit (40) captures carbon nanotubes synthesized by the reaction of the vaporized metal catalyst and the carbon source. This capturing unit (40) may be formed of a structure and material capable of collecting the synthesized carbon nanotubes without damage. In addition, the position of the capturing unit (40) may be appropriately changed, and a process of purifying the carbon nanotubes may be performed within the capturing unit (40).

The present invention is described more specifically through the following examples. However, the scope of the present invention is not limited to these examples.

Example 1

100 g of a metal catalyst (composition: Fe 1 mol + Co 1 mol + Ni 1 mol, purity 99%) was supplied inside the crucible.

A non-transferred type plasma jet generator was positioned on the crucible so as to be 30 mm away from the metal catalyst inside the crucible. Next, argon (Ar) as a plasma generating gas was injected into the plasma jet generator at 30 SLPM using a mass flow controller (MFC). At this time, the power supplied to the plasma jet generator was 7 kW (350 A × 20 V), and the internal pressure of the reaction chamber with a volume of 0.3 ㎥ containing the crucible was set to normal pressure.

Next, the plasma jet (flame) generated from the plasma jet generator was sprayed vertically onto the metal catalyst inside the crucible to vaporize the metal catalyst.

While spraying the plasma jet, pure methane (CH ₄ , 99.9% or more) as a carbon source and hydrogen (H ₂ ) as a carrier gas were simultaneously injected into the first conduit provided in the plasma jet generator at 1 SLPM and 2 SPLM, respectively, utilizing the MFC, and a gas (process gas) in which the methane and hydrogen were mixed was supplied to the vaporized metal catalyst through the first conduit to synthesize single-walled carbon nanotubes (SWCNT). At this time, the metal catalyst supplied to the crucible during the synthesis process was completely evaporated within 30 minutes.

Example 2

Single-walled carbon nanotubes (SWCNTs) were synthesized through the same process as Example 1, except that the distance between the plasma jet generator and the metal catalyst inside the crucible was adjusted to 40 mm, a mixture of argon (Ar) and hydrogen (H ₂ ) was used as the plasma generating gas, and the power supplied to the plasma jet generator was controlled to 10 kW (350 A × 29 V). At this time, the metal catalyst supplied to the crucible during the synthesis process was completely evaporated within 25 minutes.

Example 3

Single-walled carbon nanotubes (SWCNTs) were synthesized through the same process as Example 1, except that the distance between the plasma jet generator and the metal catalyst inside the crucible was adjusted to 70 mm, a mixture of argon (Ar) and nitrogen (N ₂ ) was used as the plasma generating gas, and the power supplied to the plasma jet generator was controlled to 18 kW (350 A × 50 V). At this time, the metal catalyst supplied to the crucible during the synthesis process was completely evaporated within 10 minutes.

Example 4

Single-wall carbon nanotubes (SWCNTs) were synthesized through the same process as Example 2, except that methane as a carbon source and hydrogen (H ₂ ) as a carrier gas were injected into the first conduit equipped in the plasma jet generator, the second conduit equipped in the crucible, and the third conduit equipped in the reaction chamber, and the gas (process gas) was supplied to the vaporized metal catalyst through the first to third conduit.

Example 5

Single-wall carbon nanotubes (SWCNTs) were synthesized through the same process as Example 2, except that methane as a carbon source and hydrogen (H ₂ ) as a carrier gas were injected into the first conduit equipped in the plasma jet generator and the second conduit equipped in the crucible, respectively, and gas (process gas) was supplied to the vaporized metal catalyst through the first conduit and the second conduit.

Example 6

Single-wall carbon nanotubes (SWCNTs) were synthesized through the same process as Example 2, except that methane as a carbon source and hydrogen (H ₂ ) as a carrier gas were injected into the second conduit equipped in the crucible and the third conduit equipped in the reaction chamber, respectively, and gas (process gas) was supplied to the vaporized metal catalyst through the second conduit and the third conduit.

Example 7

Single-wall carbon nanotubes (SWCNTs) were synthesized through the same process as Example 2, except that methane as a carbon source and hydrogen (H ₂ ) as a carrier gas were injected into the first conduit equipped in the plasma jet generator and the third conduit equipped in the reaction chamber, respectively, and gas (process gas) was supplied to the vaporized metal catalyst through the first conduit and the third conduit.

Example 8

Single-wall carbon nanotubes (SWCNTs) were synthesized through the same process as Example 2, except that methane as a carbon source and hydrogen (H ₂ ) as a carrier gas were injected into the second conduit equipped in the crucible and the gas (process gas) was supplied to the vaporized metal catalyst through the second conduit.

Example 9

Single-wall carbon nanotubes (SWCNTs) were synthesized through the same process as Example 2, except that methane as a carbon source and hydrogen (H ₂ ) as a carrier gas were injected into the third conduit provided in the reaction chamber and the gas (process gas) was supplied to the vaporized metal catalyst through the third conduit.

Comparative Example 1

Multi-walled carbon nanotubes (MWCNT) were synthesized in an 8 ㎥ continuous fixed-bed reactor using a metal catalyst containing Fe/Co/Al in a molar ratio of 1:0.5:1. Specifically, the metal catalyst oxide manufactured by the hydration reaction method was placed in a carbon container, and hydrogen gas and ethylene gas maintained at 670 ℃ were flowed at flow rates of 1 SLM and 3 SLM, respectively, to allow the reaction to take place for 1 hour, thereby synthesizing multi-walled carbon nanotubes (MWCNT).

Comparative Example 2

A first catalyst composition was prepared by mixing 60 g of graphite powder (particle size: 20 ㎍, purity: 99.9%) and 4 g, 14 g, and 8 g of Fe, Co, and Ni powders (purity: 99.9%), respectively, and then grinding them. The first catalyst composition was put into a carbon rod with a circular hole inside (outer diameter: 15 mm, inner diameter: 7.5 mm, depth: 200 mm, length: 300 mm), which was then mounted in an arc discharge chamber, and arc plasma was generated at a discharge voltage of 20 V and a discharge current of 250 A to synthesize single-walled carbon nanotubes (SWCNTs) for 1 hour.

Test Example 1. Checking the Synthesis Results

The carbon nanotubes synthesized in Example 2 were confirmed using a transmission electron microscope, and the results are shown in Fig. 2.

Referring to Figure 2, it can be confirmed that single-wall carbon nanotubes (SWCNTs) are well formed.

Test Example 2. Determination of crystallinity

The crystallinity of each synthesized carbon nanotube in the Examples and Comparative Examples was analyzed through the RBM (radial breathing mode) of Raman spectroscopy, and the results are shown in Table 1 below. Specifically, the crystallinity was defined as the value obtained by dividing the G-peak (Graphite mode) at approximately 1,593 cm ^-1 , which is a unique characteristic of carbon nanotubes and graphite, by the D-peak (Disorder mode) observed at approximately 1,330 cm ^-1 .

Test Example 3. Carbon Purity Measurement

The carbon purity of each synthesized carbon nanotube in the Examples and Comparative Examples was analyzed by thermogravimetric analysis, and the results are shown in Table 1 below. Specifically, the carbon nanotubes were loaded at a minimum of 5 mg in an oxygen atmosphere (100 ml/min) and oxidized up to 1000°C, and the weight percentage of the remaining residue (Ash; metal catalyst) was defined as the carbon purity of the carbon nanotubes.

Test Example 4. Measurement of Synthesis Yield

The synthesis yield of carbon nanotubes was calculated according to Equation 1 below, and the results are shown in Table 1 below.

[Formula 1]

Synthesized carbon yield = {(total amount of carbon obtained - total amount of metal catalyst) / total amount of carbon obtained} × 100

Test Example 5. Electrical Conductivity Measurement

In each of the examples and comparative examples, 0.1 to 0.2 g of the synthesized carbon nanotubes were measured for resistance to a load (force) from 100 kgf to 2,000 kgf at intervals of 100 kgf, and this was converted into electrical conductivity. The results at a load of 2,000 kgf are shown in Table 1 below.

division catalyst
furtherance process
electrical energy
(kW) Plasma
generated gas
(SLPM) process
gas
(SLPM) process
gas
Supply pipeline carbon
water
(%) synthesis
transference number
(%) Decision CNT types electricity
conductivity
(S/cm) Example 1 Fe/Co/Ni 7 Ar 30 CH ₄ 1
H ₂ 2 1st pipeline 90 1000 54 SWCNT 864 Example 2 10 Ar+H ₂ 30 1st pipeline 93 1430 73 SWCNT 917 Example 3 18 Ar+N ₂ 30 1st pipeline 90 1000 79 SWCNT 952 Example 4 10 Ar+H ₂ 30 Pipelines 1 to 3 95 2000 72 SWCNT 1107 Example 5 10 Ar+H ₂ 30 1st and 2nd pipelines 95 2000 68 SWCNT 1132 Example 6 10 Ar+H ₂ 30 2nd and 3rd pipelines 95 2000 73 SWCNT 1164 Example 7 10 Ar+H ₂ 30 1st and 3rd pipelines 94 1670 72 SWCNT 1059 Example 8 10 Ar+H ₂ 30 Second pipeline 95 2000 74 SWCNT 1201 Example 9 10 Ar+H ₂ 30 3rd pipeline 92 1250 71 SWCNT 1088 Comparative Example 1 CVD process 95 2000 4 MWCNT 8 Comparative Example 2 ARC Process 50 200 88 SWCNT 721

Referring to Table 1 above, it can be confirmed that in Examples 1 to 9 in which carbon nanotubes were synthesized by controlling the generation conditions of the plasma jet, the supply path of the carbon source-containing gas (process gas), etc. as in the present invention, carbon nanotubes with high purity, crystallinity, and electrical conductivity were synthesized in a high yield.

Specifically, in Examples 2 and 3, where a mixed gas of argon (Ar) and hydrogen (H ₂ ) or nitrogen (N ₂ ) was used and the power supply was increased, it was confirmed that the crystallinity of carbon nanotubes and the synthesis yield of carbon nanotubes increased as the plasma jet generation energy increased compared to Example 1, where argon (Ar) was used alone as a plasma generating gas.

In addition, it can be confirmed that the crystallinity and the synthesis yield of carbon nanotubes are controlled as the carbon source-containing gas (process gas) is supplied through each of the first, second and third pipelines, or through two or more of these pipelines.

10: Plasma jet generator
11: Bipolar
12: Negative
13: Housing
14: Plasma jet torch nozzle
20: The Crucible
30: Reaction chamber
40: Capture Department
50: 1st pipeline
60: Second pipeline
70: Third pipeline
80: Plasma generation gas supply unit
90: Carbon source containing gas supply section
D1: Plasma Jet
D2: Metal catalyst melt

Claims (17)

A step of supplying a metal catalyst into a crucible accommodated in a reaction chamber;
A step of generating a plasma jet in a plasma jet generating unit;
A step of vaporizing the metal catalyst by spraying the plasma jet onto the metal catalyst; and
It comprises a step of supplying a gas containing a carbon source to the vaporized metal catalyst and reacting the vaporized metal catalyst with the carbon source.
The above carbon source containing gas is,
A first conduit provided in the above plasma jet generating unit;
A second conduit provided in the above crucible; and
A method for synthesizing carbon nanotubes, wherein the carbon nanotubes are supplied through at least one of the third conduits provided in the above reaction chamber.
delete In paragraph 1,
A method for synthesizing carbon nanotubes, wherein a reaction between the vaporized metal catalyst and the carbon source occurs before the average particle diameter of the vaporized metal catalyst exceeds 20 nm.
In paragraph 1,
The distance between one end of the plasma jet generating unit and the metal catalyst inside the crucible is 10 to 100 mm,
A method for synthesizing carbon nanotubes, wherein a reaction between the vaporized metal catalyst and the carbon source occurs within the above-mentioned distance range.
In paragraph 1,
A method for synthesizing carbon nanotubes, wherein the reaction of the vaporized metal catalyst and the carbon source occurs at a temperature of 600°C or higher.
In paragraph 1,
The step of generating the above plasma jet is:
A step of injecting plasma generation gas into a plasma jet generating unit having an anode and cathode inside;
A step of supplying power to the plasma jet generating unit; and
A method for synthesizing carbon nanotubes, comprising a step of generating a plasma arc region on the anode side.
In paragraph 6,
A method for synthesizing carbon nanotubes, wherein the plasma generating gas comprises at least one selected from the group consisting of argon (Ar), hydrogen (H ₂ ), nitrogen (N ₂ ), carbon monoxide (CO), helium (He), and hydrocarbons.
In paragraph 6,
A method for synthesizing carbon nanotubes, wherein the above plasma generating gas is injected at 10 to 100 SLPM.
In paragraph 6,
A method for synthesizing carbon nanotubes, wherein the power supplied to the plasma jet generator is 5 to 100 kW.
In paragraph 1,
A method for synthesizing a carbon nanotube, wherein the carbon source comprises at least one selected from _the group consisting of methane (CH ₄ ), acetylene (C ₂ H _{2 )} , ethylene (C ₂ H ₄ ), ethane (C ₂ H ₆ ), propane (C ₃ H ₈ ), butane (C 4 H 10 ), and pentane (C ₅ H ₁₂ ).
In paragraph 1,
The above metal catalyst is technetium (Tc), cobalt (Co), tungsten (W), manganese (Mn), copper (Cu), vanadium (V), chromium (Cr), scandium (Sc), titanium (Ti), yttrium (Y), nickel (Ni), zirconium (Zr), niobium (Nb), molybdenum (Mo), iron (Fe), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), hafnium (Hf), tantalum (Ta), rhenium (Re), osmium (Os), iridium (Ir), platinum (Pt), gold (Au), actinium (Ac), zinc (Zn), germanium (Ge), beryllium (Be), aluminum (Al), calcium (Ca), magnesium (Mg), bismuth (Bi), cadmium (Cd), lead (Pb), tin (Sn), thallium (Tl), indium (In), sodium (Na), A method for synthesizing a carbon nanotube, comprising at least one selected from the group consisting of lithium (Li), potassium (K), rubidium (Rb), gallium (Ga), cesium (Cs), strontium (Sr), barium (Ba), radium (Ra), tellurium (Te), silicon (Si), and phosphorus (P).
Synthesized by the method for synthesizing carbon nanotubes of Article 1,
A carbon nanotube having an electrical conductivity of 500 S/cm or more, a carbon purity of 80% or more, and a synthesis yield of 500% or more.
delete A plasma jet generating unit that generates a plasma jet;
A crucible containing a metal catalyst vaporized by the plasma jet;
A reaction chamber accommodating the above crucible; and
It includes a capturing unit that captures carbon nanotubes synthesized by the reaction between the vaporized metal catalyst and the carbon source contained in the carbon source-containing gas,
It further includes at least one of the first conduit provided in the plasma jet generating unit; the second conduit provided in the crucible; and the third conduit provided in the reaction chamber.
A carbon nanotube synthesis device, wherein the carbon source-containing gas is supplied to the vaporized metal catalyst through at least one of the first conduit, the second conduit, and the third conduit.
delete In Article 14,
A carbon nanotube synthesis device, wherein the plasma jet generating unit is positioned vertically on the crucible.
In Article 14,
The above plasma jet generating unit is,
An anode and a cathode that receive plasma generating gas and form a plasma arc region;
a housing accommodating the positive and negative electrodes; and
A carbon nanotube synthesis device comprising a plasma jet torch nozzle provided at one end of the above housing.