Device and method for preparing carbon nanotubes
The preparation of carbon nanotubes by direct pyrolysis of methane by microwave plasma chemical vapor deposition under catalyst-free conditions, solving the problem of poor crystallization of amorphous carbon and tube walls in traditional methods, and improving the performance of carbon nanotubes.
Patent Information
- Application Number
- CN202510311220.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-17
- Publication Date
- 2025-05-13
AI Technical Summary
When mass production of carbon nanotubes by chemical vapor deposition method, more amorphous carbon is often generated, resulting in a decrease in the performance of the carbon nanotubes and the degree of crystallization of the tube wall is poor, affecting its electrical, mechanical, thermal stability and other properties.
The microwave plasma chemical vapor deposition method is used to prepare carbon nanotubes by direct pyrolysis of methane under catalyst-free conditions, and heat it with a microwave resonant cavity, rinse the quartz tubes with nitrogen, and pass the mixed gas of methane and nitrogen for reaction.
The efficient and environmentally friendly preparation of carbon nanotubes is achieved, improving their electrical, mechanical and thermal stability properties, and avoiding performance reductions compared with traditional methods.
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Abstract
Description
Technical Field
[0001] The invention relates to the technical field of nano material preparation, and in particular to a method for preparing carbon nano tubes. Background Art
[0002] Carbon nanotubes are a new member of the carbon family. Their excellent mechanical properties, good electrical properties, hollow layered structure, large specific surface area, good chemical stability and thermal stability make them have important application value as composite material reinforcement, nanoelectronic devices, adsorption materials and chemical catalysis.
[0003] Carbon nanotubes are crystalline carbon, but when using chemical vapor deposition to mass produce carbon nanotubes, more amorphous carbon is often produced. These amorphous carbons do not show the properties of graphite crystals, which will reduce the performance of carbon nanotubes. In addition, the degree of crystallization of the carbon nanotube wall is often poor. These two factors greatly affect the electrical, mechanical, thermal stability and other properties of carbon nanotubes, thereby limiting the practical application of carbon nanotubes. Summary of the invention
[0004] The technical problem to be solved by the present invention is to use microwave energy to directly couple with materials to achieve the purpose of rapid annealing in an extremely simple way. The preparation method and device proposed in the present invention can enable energy to accumulate rapidly inside the material. More importantly, there is no direct contact between the heat source and the material, thereby effectively avoiding problems such as pollution.
[0005] The present invention provides a method for preparing carbon nanotubes, characterized in that the device used comprises: A microwave resonant cavity; a gas inlet is provided at one end of the microwave resonant cavity, and a gas outlet is provided at the other end, the gas inlet and the gas outlet are located at corresponding positions, and a quartz tube is provided between the gas inlet and the gas outlet; a microwave absorbing material is provided in the quartz tube; The preparation method comprises the following steps: A. Microwave heating is performed in the microwave resonant cavity. During the heating process, nitrogen flows into the gas inlet and flows out of the gas outlet, and the quartz tube is flushed with nitrogen; B. When the temperature reaches 1000-1100°C, a mixed gas of methane and nitrogen is introduced at this temperature, and the reaction time is 50-70 minutes; C. After completion, stop heating and continue to introduce nitrogen until the microwave cavity cools to room temperature.
[0006] Wherein: the microwave absorbing material is carbon felt.
[0007] The conditions for microwave heating in step A are: frequency of 2.45 GHz and power of 6 kW.
[0008] The volume ratio of methane to nitrogen in the mixed gas of methane and nitrogen in step B is 1:4.
[0009] The volume flow rate of the mixed gas of methane and nitrogen introduced in step B is 60-80 sccm.
[0010] The prepared carbon nanotubes are deposited on the surface of the quartz tube.
[0011] The technical solution of the present invention has the following advantages: The present invention adopts microwave plasma chemical vapor deposition method to prepare carbon nanotubes by direct pyrolysis of methane without catalyst, which is highly efficient and environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS
[0012] In order to more clearly illustrate the specific implementation of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation or the prior art description will be briefly introduced below. Obviously, the drawings described below are some implementations of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. Figure 1 It is a schematic diagram of the overall structure of the present invention; Figure 2 This is a morphology diagram of the carbon nanotubes prepared in the present invention. DETAILED DESCRIPTION
[0013] The following examples are provided for a better understanding of the present invention, but are not intended to limit the best mode of implementation, nor to limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior arts shall fall within the protection scope of the present invention.
[0014] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in the field can be used. If no manufacturer is specified for the reagents or instruments used, they are all conventional reagent products that can be obtained commercially.
[0015] Reference Figure 1 FIG. 1 is a schematic diagram of the overall structure of a carbon nanotube preparation device of the present invention. The preparation device of the present invention comprises: A microwave resonant cavity, wherein the microwave resonant cavity is preferably a rectangular parallelepiped structure, and microwave heating can be performed inside, wherein the heating frequency is 2.45 GHz and the power is 6 kW; a gas inlet is provided at one end of the microwave resonant cavity, and a gas outlet is provided at the other end, and the positions of the gas inlet and the gas outlet correspond to each other.
[0016] Preferably, the gas inlet and the gas outlet may be located at a central position or other positions without specific limitation.
[0017] A quartz tube is provided between the gas inlet and the gas outlet; The quartz tubes are parallel strips with a length of 30 cm and a width of 8 cm. The distance between one end of the quartz tube and the gas inlet is 5 cm, and the distance between the other end of the quartz tube and the gas outlet is 5 cm.
[0018] The quartz tube is equipped with microwave absorbing material: Microwave absorbing materials can be: carbon cloth, carbon felt, (function: microwave absorber) Most preferably, the microwave absorbing material is carbon felt.
[0019] The preparation method comprises the following steps: A. Microwave heating is performed in the microwave resonant cavity. During the heating process, nitrogen flows into the gas inlet and flows out of the gas outlet, and the quartz tube is flushed with nitrogen; B. When the temperature reaches 1000-1100°C, a mixed gas of methane and nitrogen is introduced at this temperature, and the reaction time is 50-70 minutes; C. After completion, stop heating and continue to introduce nitrogen until the microwave cavity cools to room temperature.
[0020] In step A: nitrogen is introduced at the gas inlet and outlet, and the quartz tube is flushed with nitrogen to remove oxygen (usually nitrogen is introduced for more than half an hour, or vacuum is drawn with a vacuum pump, and nitrogen is introduced, and repeated several times, the oxygen will be completely removed).
[0021] In step B: the temperature in the microwave resonant cavity is heated to 1000-1100°C, which can be 1000°C, 1010°C, 1020°C, 1050°C, 1070°C, 1080°C, 1100°C, or any temperature in the range of 1000-1100°C; preferably 1100°C.
[0022] While maintaining this temperature, a mixed gas of methane and nitrogen is introduced, wherein the volume ratio of methane to nitrogen in the mixed gas is 1:4; the volume flow rate of the mixed gas is 60-80 sccm; it can be 60 sccm, 61 sccm, 62 sccm, 65 sccm, 69 sccm, 70 sccm, 72 sccm, 74 sccm, 75 sccm, 77 sccm, 80 sccm or a volume flow rate between 60 and 80 sccm; preferably 75 sccm.
[0023] The reaction time is 50-70 min, and can be 50 min, 52 min, 55 min, 57 min, 60 min, 62 min, 65 min, 68 min, 70 min, or any temperature between 50-70°C, preferably 60°C.
[0024] Embodiment 1 The present invention provides a method for preparing carbon nanotubes, the device used comprises: a microwave resonant cavity; a gas inlet is arranged at one end of the microwave resonant cavity, and a gas outlet is arranged at the other end, the gas inlet and the gas outlet are located at corresponding positions, and a quartz tube is arranged between the gas inlet and the gas outlet; carbon felt is arranged in the quartz tube; The preparation method comprises the following steps: A. Microwave heating is performed in the microwave resonant cavity at a heating frequency of 2.45 GHz and a power of 6 kW. During the heating process, nitrogen flows in from the gas inlet and flows out from the gas outlet, and the quartz tube is flushed with nitrogen; B. When the heating temperature reaches 1100°C, a mixed gas of methane and nitrogen (the volume ratio of methane to nitrogen is 1:4) is introduced at this temperature, and the reaction time is 70 minutes; C. After completion, stop heating and continue to introduce nitrogen until the microwave cavity cools to room temperature.
[0025] Embodiment 2 The present invention provides a method for preparing carbon nanotubes, the device used comprises: a microwave resonant cavity; a gas inlet is arranged at one end of the microwave resonant cavity, and a gas outlet is arranged at the other end, the gas inlet and the gas outlet are located at corresponding positions, and a quartz tube is arranged between the gas inlet and the gas outlet; carbon felt is arranged in the quartz tube; The preparation method comprises the following steps: A. Microwave heating is performed in the microwave resonant cavity at a heating frequency of 2.45 GHz and a power of 6 kW. During the heating process, nitrogen flows in from the gas inlet and flows out from the gas outlet, and the quartz tube is flushed with nitrogen; B. When the heating temperature reaches 1000°C, a mixed gas of methane and nitrogen (the volume ratio of methane to nitrogen is 1:4) is introduced at this temperature, and the reaction time is 60 minutes; C. After completion, stop heating and continue to introduce nitrogen until the microwave cavity cools to room temperature.
[0026] The carbon nanotubes prepared in Example 1 and Example 2 were scraped off, and the test data are shown in the table: Embodiment 1 Embodiment 2 Carbon nanotube content 10.8 mg 11.1 mg According to the preparation method and device of this embodiment, the final prepared sediment (carbon nanotube) is attached to the wall of the quartz tube, and the test morphology (SEM) is as follows: Figure 2 shown.
[0027] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.
Claims
1. A method for preparing carbon nanotubes, characterized in that: The devices used include: A microwave resonant cavity; a gas inlet is provided at one end of the microwave resonant cavity, and a gas outlet is provided at the other end, the gas inlet and the gas outlet are located at corresponding positions, and a quartz tube is provided between the gas inlet and the gas outlet; a microwave absorbing material is provided in the quartz tube; The preparation method comprises the following steps: A. Microwave heating is performed in the microwave resonant cavity. During the heating process, nitrogen flows into the gas inlet and flows out of the gas outlet, and the quartz tube is flushed with nitrogen; B. When the heating temperature reaches 1000-1100°C, a mixed gas of methane and nitrogen is introduced at this temperature, and the reaction time is 50-70 minutes; C. After completion, stop heating and continue to introduce nitrogen until the microwave cavity cools to room temperature.
2. The method for preparing carbon nanotubes according to claim 1, characterized in that: The microwave absorbing material is carbon felt.
3. The method for preparing carbon nanotubes according to claim 1, characterized in that: The conditions for microwave heating in step A are: frequency of 2.45 GHz and power of 6 kW.
4. The method for preparing carbon nanotubes according to claim 1, characterized in that: The volume ratio of methane to nitrogen in the mixed gas of methane and nitrogen in step B is 1:
4.
5. The method for preparing carbon nanotubes according to claim 1, characterized in that: The volume flow rate of the mixed gas of methane and nitrogen introduced in step B is 60-80 sccm.
6. The method for preparing carbon nanotubes according to claim 1, characterized in that: The prepared carbon nanotubes are deposited on the surface of the quartz tube.