A high-purity single-walled carbon nanotube, its preparation method and system

Abstract

This invention belongs to the field of new materials technology, and specifically relates to a high-purity single-walled carbon nanotube, its preparation method, and system. The method utilizes the high-temperature conditions of a plasma arc to evaporate catalyst material floating on the surface of a liquid anode, forming fine catalyst particles. These particles combine with simultaneously decomposed organic carbon sources, catalytically growing into single-walled carbon nanotubes. The particles are then discharged from the reactor with the exhaust gas, yielding the final product. This method effectively avoids the shortcomings of insufficient graphite crucible lifespan, catalyst metal contamination, and uncontrollable catalyst concentration during the reaction, significantly improving product purity and preparation efficiency. It is an effective means for the large-scale preparation of high-quality single-walled carbon nanotubes and has significant economic value.

Description

Technical Field

[0001] This invention belongs to the field of new materials technology, and specifically relates to a high-purity single-walled carbon nanotube, its preparation method, and system. Background Technology

[0002] Single-walled carbon nanotubes (SUVs) are hollow, tubular, one-dimensional nanomaterials composed of sp2-hybridized C-C covalent bonds. Due to their high crystallinity and large surface curvature, the potential barriers to their fabrication and growth are much higher than those for multi-walled carbon nanotubes, making their large-scale, efficient fabrication a significant challenge. Existing fabrication methods include arc ablation, laser ablation, chemical vapor deposition (CVD), and plasma ablation. Among these, laser ablation, plasma ablation, and arc ablation, based on high-temperature technology, produce SUVs with higher crystallinity than CVD. However, due to the complexity and high energy consumption of the equipment systems, most high-temperature SUV fabrication technologies remain at the laboratory level.

[0003] The arc method uses a graphite rod filled with a mixture of Y / Ni, FeS, and carbon powder as the anode, initiating an arc between the cathode and anode. The high temperature of the arc evaporates and consumes the solid components of the anode, while simultaneously generating single-walled carbon nanotubes during outward diffusion. Since most of the product deposits on the inner wall of the reaction chamber, the anode is continuously consumed, limiting preparation to intermittent processes. Although many studies have overcome this limitation by continuously replenishing the anode rod, large-scale continuous preparation remains challenging. The plasma method involves passing the carbon source and catalyst through the center of a plasma torch, rapidly passing through a high-temperature zone, and generating carbon nanotubes during the downward flow of the gas. In the plasma method, a plasma arc is generated inside the electrode gun, which is then blown out by a high-speed gas flow, and a high-power cooling zone ensures electrode lifespan. However, the biggest constraint to the industrialization of this method is still electrode lifespan; rapid anode burn-out makes continuous operation difficult and increases costs. Existing technologies utilize plasma arc evaporation to generate catalyst nanoparticles from a catalyst metal placed in a graphite crucible, which simultaneously combine with the decomposed carbon source to generate single-walled carbon nanotubes. This method places catalyst preparation and carbon nanotube growth in the same reaction chamber, utilizing the ultra-high heat source of plasma arc for evaporation, pyrolysis, and plasma activation to achieve efficient preparation. However, this anode structure has significant shortcomings. First, at high temperatures, the iron and graphite used as catalysts cause carbon to dissolve and diffuse into the molten iron, leading to continuous erosion of the graphite crucible by the molten iron, which not only reduces the lifespan of the anode crucible but also contaminates the catalyst. Second, placing a large amount of catalyst in the graphite crucible will cause a large amount of catalyst metal to evaporate, which is not conducive to the formation of ultrafine catalyst nanoparticles and easily forms a large number of large particles during collisions, which is not conducive to the formation of single-walled carbon nanotubes. Third, the large amount of molten iron also has a certain dissolving capacity for carbon pyrolyzed in the atmosphere, which will lead to a decrease in the utilization rate of gaseous carbon source. Summary of the Invention

[0004] This invention discloses a high-purity single-walled carbon nanotube, its preparation method, and a system to solve any of the above-mentioned technical problems and other potential problems in the prior art.

[0005] To solve the above problems, the technical solution of the present invention is: a method for preparing high-purity single-walled carbon nanotubes. The method utilizes the high-temperature conditions of plasma arc to evaporate the catalyst material floating on the surface of the liquid anode to form fine catalyst particles, which combine with the simultaneously cracked organic carbon source to catalytically grow into single-walled carbon nanotubes. The grown single-walled carbon nanotubes are discharged from the reactor along with the exhaust gas, thus obtaining high-purity single-walled carbon nanotubes.

[0006] Furthermore, the preparation method specifically includes the following steps:

[0007] S1) Under the protection of inert gas, plasma arc gas is introduced into the cathode of the plasma arc furnace, and plasma arc is generated by energizing, which melts the anode metal placed in the graphite crucible into a liquid state, and continues to heat up to the set temperature.

[0008] S2) First, the catalyst metal powder is transported to the surface of the liquid anode metal to form a catalyst metal layer on the surface of the liquid anode metal;

[0009] S3) The carbon source gas, co-catalyst and carrier gas are mixed and then introduced into the plasma arc furnace. The cracked organic carbon source combines with the catalyst particles formed by evaporation to catalyze the growth into single-walled carbon nanotubes. The grown single-walled carbon nanotubes are continuously discharged from the reactor with the tail gas to obtain high-purity single-walled carbon nanotubes.

[0010] Furthermore, the flow rate of the plasma arc gas in S1) is 1L / min-200L / min;

[0011] The plasma arc furnace has a power of 10-500kW, a current of 100-10000A, and a voltage of 1-200V.

[0012] The set temperature is 700-1800℃;

[0013] The anode metal is copper or a copper-iron alloy.

[0014] Furthermore, the inert gas in S1) is any one of nitrogen, argon, and helium;

[0015] The plasma arc gas is any one, two, or three of nitrogen, argon, helium, hydrogen, and water vapor in any mixing ratio.

[0016] The copper-iron alloy has an iron content of 1-5 wt%, and the anode metal layer has a height of 5-35 cm and a diameter of 30-200 cm.

[0017] Furthermore, in S2), the particle size of the catalyst metal powder is 50-350 mesh, and the input flow rate is 0.5-200 g / min; the thickness of the catalyst on the surface of the liquid anode metal is maintained at 0.01-5 mm, and the diameter is not greater than 200 cm.

[0018] Furthermore, the catalyst metal powder is iron, cobalt, nickel powder or an alloy powder formed by iron, cobalt, nickel powder and high-melting-point metals such as molybdenum, tungsten, tantalum, niobium, hafnium, chromium, vanadium, and zirconium.

[0019] Furthermore, the carbon source gas in S3) occupies 5-30% of the volume;

[0020] The carrier gas includes hydrogen and an inert gas, wherein hydrogen accounts for 0.1-50% of the volume, and the remainder is an inert gas;

[0021] The flow rates of the carbon source gas and the carrier gas are 1 L / min to 500 L / min;

[0022] The molar ratio of the co-catalyst and the catalyst metal powder is 20:1 to 1:1.

[0023] Furthermore, the co-catalyst is any one of sulfur powder, selenium powder, thiophene, or hydrogen sulfide;

[0024] The carbon source gas is any one of methane, ethylene, acetylene, propylene, or propane;

[0025] The inert gas is one or more of nitrogen, argon, or helium.

[0026] Another object of the present invention is to provide a system for implementing the above-described preparation method, the system comprising: a plasma arc furnace body, a graphite crucible, a plasma arc furnace cathode, and an anode metal;

[0027] The anode metal is placed inside the graphite crucible, which is located at the bottom of the plasma arc furnace body, and the plasma arc furnace cathode is positioned vertically above the graphite crucible.

[0028] The plasma arc furnace body has a reaction gas inlet and a catalyst inlet on one side wall and a discharge outlet on the other side wall, and the reaction gas inlet, catalyst inlet and discharge outlet are all located above the graphite crucible.

[0029] Furthermore, the inner diameter of the graphite crucible is not less than four-fifths of the inner diameter of the plasma arc furnace.

[0030] A high-purity single-walled carbon nanotube is prepared using the above-described preparation method.

[0031] The beneficial effects of the present invention are as follows: By adopting the above technical solution, the preparation method of the present invention sets up structural parameters such as the current and voltage parameters of the plasma arc, the composition and flow rate of the arc to regulate the arc length, so as to realize the control of the impact force of the arc on the liquid anode, effectively avoiding the liquid metal anode being impacted and splashed onto the upper end of the catalyst layer and evaporated by the arc, which would lead to catalyst contamination, reduced catalyst activity and product quality.

[0032] Because the density of the anode metal is greater than that of the catalyst metal, it melts at the high temperature of the plasma arc to form a two-phase immiscible liquid metal, causing the catalyst metal to float on the anode metal and form a uniform thin layer of catalyst. This not only helps to make the anode surface smooth and improve the stability of the plasma arc, but also avoids the dissolution of a large amount of catalyst on the gaseous carbon source cracking products, thus improving the carbon source utilization rate.

[0033] Simultaneously, at the high temperature of plasma arc formation, the liquid anode metal floats on the surface of the molten metal anode, isolating the catalyst metal from contact with the graphite crucible. This prevents mutual diffusion and dissolution between graphite and catalyst metal, as well as erosion of the graphite crucible by the molten catalyst and contamination of the catalyst metal by graphite. Furthermore, the anode metal exhibits no significant dissolution or alloying with either graphite or catalyst metal, causing no corrosion to the graphite crucible and no significant contamination of the catalyst metal. It maintains good conductivity, ensuring stable operation of the plasma anode and significantly extending the system's lifespan, which can reach 10 days.

[0034] Based on this structure, the catalyst can be continuously, quantitatively, and controllably added through the powder feed inlet, effectively controlling the amount of catalyst and the amount of evaporation, avoiding large-scale evaporation that leads to particle collision and aggregation, forming large particles, improving catalyst activity and utilization, and significantly improving product purity, up to 80%. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the structure of a high-purity single-walled carbon nanotube preparation system according to the present invention.

[0036] Figure 2 This is a scanning electron microscope image of the single-walled carbon nanotubes prepared in Example 1 of the present invention.

[0037] Figure 3 The image shows the Raman spectrum of the single-walled carbon nanotubes prepared in Example 1 of this invention.

[0038] Figure 4 The thermogravimetric analysis curve of the single-walled carbon nanotubes prepared in Example 1 of this invention.

[0039] Figure 5 This is a scanning electron microscope image of the single-walled carbon nanotubes prepared in Comparative Example 1.

[0040] Figure 6 The image shows the Raman spectrum of the single-walled carbon nanotubes prepared in Comparative Example 1.

[0041] Figure 7 The thermogravimetric analysis curves of the single-walled carbon nanotubes prepared in Comparative Example 1 are shown.

[0042] In the picture:

[0043] 1. Graphite crucible; 2. Anode metal; 3. Catalyst metal; 4. Reactant gas inlet; 5. Catalyst feed inlet; 6. Plasma arc furnace body; 7. Plasma arc furnace cathode; 8. Thermal insulation layer; 9. Discharge port. Detailed Implementation

[0044] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0045] like Figure 1 As shown, the present invention discloses a preparation system for high-purity single-walled carbon nanotubes, the system comprising: a plasma arc furnace body 6, a graphite crucible 1, a plasma arc furnace cathode 7, and an anode metal 2;

[0046] The anode metal 2 is placed inside the graphite crucible 1, which is located at the bottom of the plasma arc furnace body 6, and the plasma arc furnace cathode 7 is positioned vertically above the graphite crucible 1.

[0047] The plasma arc furnace body 6 has a reaction gas inlet 4 and a catalyst inlet 5 on one side wall, and a discharge outlet 9 on the other side wall. The reaction gas inlet 4, the catalyst inlet 5 and the discharge outlet 9 are all located above the graphite crucible 1. The top of the plasma arc furnace body 6 is provided with a heat insulation layer 8.

[0048] Furthermore, the inner diameter of the graphite crucible 1 is not less than four-fifths of the inner diameter of the plasma arc furnace body 6.

[0049] The preparation method using the above-mentioned high-purity single-walled carbon nanotube preparation system specifically includes the following steps:

[0050] S1) Under the protection of inert gas, plasma arc gas is introduced through the cathode 7 of the plasma arc furnace. The flow rate of the plasma arc gas is 1L / min-200L / min. When the power is applied, a plasma arc is generated, which melts the anode metal 2 placed in the graphite crucible 1 into a liquid state and continues to heat up to 700-1800℃.

[0051] The plasma arc furnace has a power of 10-500kW, a current of 100-10000A, and a voltage of 1-200V.

[0052] S2) First, the catalyst metal 3 powder is transported to the surface of the liquid anode metal 2 to form a catalyst metal layer on the surface of the liquid anode metal 2;

[0053] The particle size of the catalyst metal powder is 50-350 mesh, and the input flow rate is 0.5-200 g / min; the thickness of the catalyst on the surface of the liquid anode metal is maintained at 0.01-5 mm, and the diameter is not greater than 200 cm;

[0054] S3) The carbon source gas, co-catalyst and carrier gas are mixed and then introduced into the plasma arc furnace. The cracked organic carbon source combines with the catalyst particles formed by evaporation to catalyze the growth into single-walled carbon nanotubes. The grown single-walled carbon nanotubes are continuously discharged from the reactor with the tail gas to obtain high-purity single-walled carbon nanotubes.

[0055] The anode metal has no significant miscibility or alloying effect with graphite and catalyst metal at high temperatures, and the density of the catalyst metal is less than that of the anode metal. It can be gold, platinum, silver, copper, or copper-iron alloy, preferably copper or copper-iron alloy. The iron content of the copper-iron alloy is 1-5%, and the height of the anode metal layer is 5-35 cm, and the diameter is 30-200 cm.

[0056] The catalyst metal powder can be iron, cobalt, nickel powder, or alloy powder formed with high-melting-point metals such as molybdenum, tungsten, tantalum, niobium, hafnium, chromium, vanadium, and zirconium, preferably iron powder and iron-molybdenum alloy powder, with a particle size of 50-350 mesh and an input flow rate of 0.5-200 g / min; the thickness of the catalyst on the surface of the liquid anode metal is maintained at 0.01-5 mm, and the diameter is not greater than 200 cm.

[0057] The carbon source gas is any one of methane, ethylene, acetylene, propylene, or propane; the carrier gas is a mixture of nitrogen, argon, helium, and hydrogen.

[0058] The carbon source gas accounts for 5-30% of the volume; hydrogen accounts for 0.1-50% of the volume, and the remainder is inert gas, with a flow rate of 1L / min-500L / min.

[0059] The co-catalyst is any one of sulfur powder, selenium powder, thiophene, hydrogen sulfide, etc., and the molar ratio of catalyst to co-catalyst is 1:1 to 20:1.

[0060] Example 1

[0061] The plasma arc furnace used has a power of 50kW, a current of 1000A, and a voltage of 50V. Under argon protection, argon gas at a rate of 5L / min is introduced into the cathode of the plasma arc furnace to generate a plasma arc, which melts the anode metal copper-4% iron alloy placed in a graphite crucible into a liquid state, and raises the furnace temperature to 1200℃. Then, catalyst metal powder, which is iron-molybdenum alloy powder with a particle size of 100 mesh and a powder feeding flow rate of 5g / min, is fed to the surface of the liquid anode metal. Subsequently, a mixture of carbon source gas, co-catalyst, and carrier gas is introduced, with a composition of 10% methane, 20% hydrogen, and 70% argon, and a total gas flow rate of 20L / min. The co-catalyst is hydrogen sulfide, and the molar ratio of catalyst metal to co-catalyst is 10:1. The reaction continues in the arc furnace, and the product is collected at the outlet with the tail gas to obtain the final single-walled carbon nanotube product. Figure 2 The image shown is a scanning electron microscope image of the prepared product; Figure 3 To obtain the Raman spectrum of the product; Figure 4 Thermogravimetric analysis curves of the obtained product were prepared.

[0062] Example 2

[0063] The plasma arc furnace used has a power of 500kW, a current of 10000A, and a voltage of 50V. Under argon protection, argon gas at a rate of 200L / min is introduced into the cathode of the plasma arc furnace to generate a plasma arc, which melts the anode copper metal placed in the graphite crucible into a liquid state and raises the furnace temperature to 1800℃. Then, catalyst metal powder, which is iron powder with a particle size of 50 mesh and a powder feeding flow rate of 200g / min, is fed to the surface of the liquid anode metal. Subsequently, a mixture of carbon source gas, co-catalyst, and carrier gas is introduced, with a composition of 30% methane, 50% hydrogen, and 20% argon, and a total gas flow rate of 200L / min. The co-catalyst is sulfur powder, and the molar ratio of catalyst metal to co-catalyst is 20:1. The reaction continues in the arc furnace, and the product is collected at the outlet with the tail gas to obtain the final single-walled carbon nanotube product.

[0064] Example 3

[0065] The plasma arc furnace used has a power of 10kW, a current of 100A, and a voltage of 100V. Under argon protection, argon gas at a rate of 1L / min is introduced into the cathode of the plasma arc furnace to generate a plasma arc, which melts the anode metal copper-4% iron alloy placed in a graphite crucible into a liquid state, and raises the furnace temperature to 700℃. Then, catalyst metal powder, which is iron powder with a particle size of 350 mesh and a powder feeding flow rate of 0.5g / min, is fed to the surface of the liquid anode metal. Subsequently, a mixture of carbon source gas, co-catalyst, and carrier gas is introduced, with a composition of 5% methane, 0.1% hydrogen, and 94.9% argon, and a total gas flow rate of 1L / min. The co-catalyst is thiophene, and the molar ratio of catalyst metal to co-catalyst is 15:1. The reaction continues in the arc furnace, and the product is collected at the outlet with the tail gas to obtain the final single-walled carbon nanotube product.

[0066] Comparative Example 1

[0067] The basic process parameters of Comparative Example 1 are basically the same as those of Example 1, except that the catalyst feeding device is eliminated and the anode metal is directly replaced by the catalyst metal, so that the catalyst metal is placed directly in the graphite crucible.

[0068] The plasma arc furnace used had a power of 50kW, a current of 1000A, and a voltage of 50V. Under argon protection, argon gas was introduced into the cathode of the plasma arc furnace at a rate of 5L / min. The plasma arc was generated by energizing the furnace, melting the iron-molybdenum alloy catalyst placed in the graphite crucible into a liquid state and raising the furnace temperature to 1200℃. Subsequently, a mixture of carbon source gas, co-catalyst, and carrier gas was introduced, with a composition of 10% methane, 20% hydrogen, and 70% argon, and a total gas flow rate of 20L / min. The co-catalyst was hydrogen sulfide, with the same flow rate as in Example 1. The reaction continued in the arc furnace, and the product was collected at the outlet along with the tail gas to obtain the final single-walled carbon nanotube product. Figure 5 The image shown is a scanning electron microscope image of the prepared product; Figure 6 To obtain the Raman spectrum of the product; Figure 7 Thermogravimetric analysis curves of the obtained product were prepared.

[0069] Data Result Comparison

[0070]

[0071]

[0072] The above provides a detailed description of a high-purity single-walled carbon nanotube, its preparation method, and the system provided in the embodiments of this application. The descriptions of the embodiments above are merely for the purpose of helping to understand the method and its core ideas; furthermore, those skilled in the art will recognize that, based on the ideas of this application, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this application.

[0073] Certain terms are used in the specification and claims to refer to specific components. Those skilled in the art will understand that hardware manufacturers may use different names to refer to the same component. This specification and claims do not distinguish components based on differences in name, but rather on differences in function. The terms "comprising" and "including" used throughout the specification and claims are open-ended and should be interpreted as "comprising / including but not limited to". "Approximately" means that within an acceptable margin of error, those skilled in the art can solve the technical problem and substantially achieve the technical effect within a certain margin of error. The following descriptions in the specification are preferred embodiments for carrying out this application; however, these descriptions are for the purpose of illustrating the general principles of this application and are not intended to limit the scope of this application. The scope of protection of this application shall be determined by the appended claims.

[0074] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a product or system comprising a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a product or system. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the product or system that includes said element.

[0075] It should be understood that the term "and / or" used in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this article generally indicates that the preceding and following related objects have an "or" relationship.

[0076] The foregoing description illustrates and describes several preferred embodiments of this application. However, as previously stated, it should be understood that this application is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the application concept described herein through the foregoing teachings or techniques or knowledge in related fields. Any modifications and variations made by those skilled in the art that do not depart from the spirit and scope of this application should be within the protection scope of the appended claims.

Claims

1. A method for preparing high-purity single-walled carbon nanotubes, characterized in that: This preparation method utilizes the high-temperature conditions of a plasma arc to evaporate catalyst material floating on the surface of a liquid anode, forming fine catalyst particles. These particles combine with simultaneously pyrolyzed organic carbon sources to catalytically grow single-walled carbon nanotubes. The grown single-walled carbon nanotubes are then discharged from the reactor along with the exhaust gas, yielding high-purity single-walled carbon nanotubes. The specific preparation method includes the following steps: S1) Under the protection of inert gas, plasma arc gas is introduced into the cathode of the plasma arc furnace, and plasma arc is generated by energizing, which melts the anode metal placed in the graphite crucible into a liquid state, and continues to heat up to the set temperature. The anode metal is copper or a copper-iron alloy; The copper-iron alloy has an iron content of 1-5 wt%, and the anode metal layer has a height of 5-35 cm and a diameter of 30-200 cm. S2) First, the catalyst metal powder is transported to the surface of the liquid anode metal to form a catalyst metal layer on the surface of the liquid anode metal; The catalyst metal powder has a particle size of 50-350 mesh and an input flow rate of 0.5-200 g / min; the thickness of the catalyst on the liquid anode metal surface is maintained at 0.01-5 mm, and the diameter is not greater than 200 cm; The catalyst metal powder is iron, cobalt, nickel powder or an alloy powder formed by iron, cobalt, nickel powder and high-melting-point metals such as molybdenum, tungsten, tantalum, niobium, hafnium, chromium, vanadium, and zirconium; S3) The carbon source gas, co-catalyst and carrier gas are mixed and then introduced into the plasma arc furnace. The cracked organic carbon source combines with the catalyst particles formed by evaporation to catalyze the growth into single-walled carbon nanotubes. The grown single-walled carbon nanotubes are continuously discharged from the reactor with the tail gas to obtain high-purity single-walled carbon nanotubes.

2. The preparation method according to claim 1, characterized in that, The flow rate of the plasma arc gas in S1) is 1 L / min-200 L / min; The plasma electric arc furnace has a power of 10-500 kW, a current of 100-10000 A, and a voltage of 1-200 V; The set temperature is 700-1800℃.

3. The preparation method according to claim 2, characterized in that, The inert gas in S1) is any one of nitrogen, argon and helium; The plasma arc gas is any one, two, or three of nitrogen, argon, helium, hydrogen, and water vapor in any mixing ratio.

4. The preparation method according to claim 1, characterized in that, The carbon source gas in S3) occupies 5-30% of the volume; The carrier gas includes hydrogen and an inert gas, wherein hydrogen accounts for 0.1-50% by volume and the remainder is an inert gas; The flow rates of the carbon source gas and the carrier gas are 1 L / min to 500 L / min; The molar ratio of the co-catalyst and the catalyst metal powder is 20:1 to 1:

1.

5. The preparation method according to claim 4, characterized in that, The co-catalyst is any one of sulfur powder, selenium powder, thiophene, or hydrogen sulfide. The carbon source gas is any one of methane, ethylene, acetylene, propylene, or propane; The inert gas is one or more of nitrogen, argon, or helium.

6. A system for implementing the preparation method according to any one of claims 1-5, characterized in that, The system includes: a plasma arc furnace body, a graphite crucible, a plasma arc furnace cathode, and an anode metal; The anode metal is placed inside the graphite crucible, which is located at the bottom of the plasma arc furnace body, and the plasma arc furnace cathode is positioned vertically above the graphite crucible. The plasma arc furnace body has a reaction gas inlet and a catalyst inlet on one side wall and a discharge outlet on the other side wall, and the reaction gas inlet, catalyst inlet and discharge outlet are all located above the graphite crucible. Furthermore, the inner diameter of the graphite crucible is not less than four-fifths of the inner diameter of the plasma arc furnace.

7. A high-purity single-walled carbon nanotube, characterized in that, The high-purity single-walled carbon nanotubes were prepared using the preparation method described in any one of claims 1-5.

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