A method and apparatus for preparing horizontally arrayed carbon nanotubes
By employing an upper and lower electrode structure and magnet-assisted catalyst distribution in the arc discharge method, the problems of uneven catalyst diffusion and electrode ablation were solved, and the efficient preparation of horizontal array carbon nanotubes was achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- HEILONGJIANG GUANGSHENGDA NEW MATERIAL TECH CO LTD
- Filing Date
- 2023-06-07
- Publication Date
- 2026-05-26
AI Technical Summary
When preparing horizontal array carbon nanotubes by arc discharge method, the catalyst is difficult to diffuse to all reaction sites, resulting in reduced conversion and selectivity, while the electrode is severely eroded.
The catalyst powder is magnetically attracted to the bottom of the upper electrode by the electrodes arranged opposite each other. The catalyst powder comes into contact with the gaseous carbon source through a rotating electric arc and is vaporized to generate transition metal vapor. The magnetic field provided by the magnet ensures that the catalyst is evenly distributed, and the directional growth of carbon nanotubes is promoted by the airflow directional method.
This improved the diffusion range and utilization rate of the catalyst, reduced electrode erosion, and enhanced reaction efficiency and conversion rate.
Smart Images
Figure CN116654904B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of carbon nanotube technology, and in particular to a method and apparatus for preparing horizontally arrayed carbon nanotubes. Background Technology
[0002] Carbon nanotubes are a special type of carbon, which can be viewed as graphene rolled into a tubular shape. They possess various unique properties and play an important role in many fields. Horizontally arrayed carbon nanotubes are a type of carbon nanotube in which the carbon nanotubes are generally oriented in the same direction.
[0003] The electric arc discharge method is a commonly used method for preparing horizontally arrayed carbon nanotubes, developed by S. Lijima et al. in 1993. Its key feature is the use of transition metal vapor as a catalyst. Gas-phase carbon-containing reactants generate free carbon atoms under the action of an electric arc, which then rearrange into carbon nanotubes under the catalysis of the transition metal vapor. An airflow within the reaction vessel assists in the directional growth of the carbon nanotubes.
[0004] In the arc discharge method, transition metal vapor is generated by the evaporation of a transition metal loaded on an electrode under the action of an electric arc. The transition metal is placed in a groove or empty tube of an electrode, and after being struck by the electric arc, it first liquefies and then vaporizes to produce transition metal vapor. However, this brings a problem: the generation of transition metal vapor is limited to a single point on the electrode with the transition metal, and the transition metal vapor itself cannot diffuse very far. Over long distances, it recondenses or even adheres to the walls of the reaction vessel. Most of the reaction vessel is without catalyst. In areas without catalyst, the proportion of amorphous carbon in the rearrangement products of free carbon atoms increases significantly, resulting in a significant decrease in reaction conversion and selectivity. CN1958442A, a carbon nanotube preparation apparatus and method, proposes an improved method, namely, setting up an additional catalyst evaporation chamber. The catalyst is generated in this chamber and then mixed with carbon-containing reactants before entering the reaction vessel. This ensures that the reactants enter the reaction vessel already doped with catalyst. However, this results in significant catalyst loss before entering the reaction vessel, leading to a very thin catalyst layer in the reaction vessel, although the catalyst layer is uniform.
[0005] Another problem with the arc discharge method is that the electrode erosion is quite severe. So much so that in the preparation method of controllable diameter single-walled carbon nanotubes (CN101905880A), this electrode erosion is utilized to directly make a graphite electrode by using catalyst powder and carbon powder together, and the eroded electrode releases transition metal vapor. Summary of the Invention
[0006] This invention provides a method and apparatus for preparing horizontally arrayed carbon nanotubes.
[0007] The technical problem to be solved is that when preparing horizontal array carbon nanotubes using the arc discharge method, the catalyst is difficult to diffuse to all the reaction sites, and the electrode is severely eroded.
[0008] To solve the above technical problems, the present invention adopts the following technical solution: a method for preparing horizontal array carbon nanotubes, using a gaseous carbon source as a reactant, using transition metal vapor as a catalyst, and preparing by an electric arc discharge method. The electric arc used in the preparation is located between two energized electrodes in a reaction vessel. The two electrodes are arranged vertically opposite each other, with the upper electrode referred to as the upper electrode and the lower electrode referred to as the lower electrode.
[0009] The transition metal vapor is generated by electric arc vaporization of catalyst raw material powder, wherein the catalyst raw material powder is a transition metal element and / or oxide, and the catalyst raw material powder is a magnetic material and is magnetically attracted to the bottom of the upper electrode.
[0010] The electric arc rotates around the vertical central axis and comes into contact with the gaseous carbon source and the catalyst powder. The catalyst powder in contact with the electric arc loses its magnetism and falls down. During the falling process, it is vaporized by the electric arc into transition metal vapor. The gaseous carbon source is plasma-ionized and rearranged into carbon nanotubes under the catalytic action of the transition metal vapor.
[0011] Furthermore, an airflow directional method is used to promote the directional growth of carbon nanotubes, with arc-initiating gas containing a gaseous carbon source flowing vertically from top to bottom through the reaction vessel.
[0012] Furthermore, the arc-igniting gas is argon, and the gaseous carbon source is methane.
[0013] Furthermore, a magnet for magnetically attracting the catalyst powder is provided on the upper part of the upper electrode, and the magnetic field lines of the magnet radiate downwards from the upper electrode and pass through the reaction vessel.
[0014] Furthermore, the catalyst precursor powder is iron powder or iron oxide powder.
[0015] Furthermore, both the upper and lower electrodes are graphite electrodes, with the upper electrode being the cathode.
[0016] Furthermore, the bottom of the upper electrode is hemispherical.
[0017] Furthermore, the lower electrode has a groove at its top, which is opposite to the upper electrode, for receiving incompletely vaporized catalyst powder, and the downward projection of the upper electrode falls completely into the groove.
[0018] An apparatus for preparing horizontally arrayed carbon nanotubes, used to implement the above-described method for preparing horizontally arrayed carbon nanotubes, includes a cylindrical reaction vessel with a vertically oriented central axis, an upper electrode and a lower electrode disposed within the reaction vessel, gas flow openings at the top and bottom of the reaction vessel, and a magnet disposed outside the reaction vessel.
[0019] The upper and lower electrodes are positioned on the central axis of the reaction vessel. The gas flow openings at the top and bottom of the reaction vessel are positioned opposite each other and avoid the upper and lower electrodes. The magnet is positioned above the upper electrode.
[0020] Furthermore, the magnet is a ring-shaped permanent magnet or electromagnet, and the central axis of the magnet is located on the central axis of the reaction vessel.
[0021] Compared with existing technologies, the method and apparatus for preparing horizontally arrayed carbon nanotubes of this invention have the following advantages:
[0022] In this invention, two electrodes for generating an electric arc are arranged opposite each other, with the catalyst powder magnetically attracted to the bottom of the upper electrode. The catalyst powder struck by the electric arc heats up, loses its magnetism, and falls down, coming into contact with the electric arc in the air and being vaporized. This not only allows for more thorough contact with the electric arc to generate more transition metal vapor, but also changes the location of transition metal vapor generation from a single point on the electrode to the entire electric arc. The location where the reaction occurs (i.e., along the electric arc path) completely coincides with the location where transition metal vapor is generated, thereby overcoming the problem of some reaction locations lacking catalyst.
[0023] In this invention, a magnetic field is introduced into the reaction vessel by a magnet used to adsorb the original catalyst powder, causing the electric arc to rotate within the magnetic field. This prevents the two ends of the arc from continuously striking the same position on the electrode, thus overcoming the electrode erosion problem. Simultaneously, the rotating arc has a larger contact area with the reactants, improving reaction efficiency; the rotating arc also ensures that more original catalyst powder is dislodged. Attached Figure Description
[0024] Figure 1 This is a schematic diagram of the structure of a horizontal array carbon nanotube fabrication device according to the present invention;
[0025] Figure 2 Electron micrographs of the product;
[0026] In the diagram, 1-upper electrode, 2-lower electrode, 3-electric arc, 4-magnet, 5-magnetic field lines, 6-catalyst powder, 7-reaction vessel. Detailed Implementation
[0027] A method for preparing horizontal array carbon nanotubes uses a gaseous carbon source as a reactant and a transition metal vapor as a catalyst. The preparation is carried out by an electric arc 3 discharge method. The electric arc 3 used in the preparation is located between two energized electrodes in a reaction vessel 7. The two electrodes are arranged vertically opposite each other. The electrode located above is referred to as the upper electrode 1, and the electrode located below is referred to as the lower electrode 2.
[0028] The transition metal vapor is generated by the vaporization of catalyst powder 6 by electric arc 3. The catalyst powder 6 is a transition metal element and / or oxide. The catalyst powder 6 is a magnetic material (soft or hard magnetic) and is magnetically attracted to the bottom of the upper electrode 1. The electric arc 3 rotates around the vertical central axis and comes into contact with the gaseous carbon source and the catalyst powder 6. The catalyst powder 6 in contact with the electric arc 3 loses its magnetism and falls down. During the falling process, it is vaporized into transition metal vapor by the electric arc 3.
[0029] Here, because the catalyst powder 6 is a powder, its falling speed is very slow, while the electric arc 3 itself is a gas with very little weight and rotates extremely fast in the magnetic field. The rotating electric arc 3 can repeatedly come into contact with the catalyst powder 6. If a small amount of catalyst powder 6 fails to come into contact with the electric arc 3 during multiple rotations, it will gradually cool and regain its magnetism during its fall, thus being attracted back to the magnet 4.
[0030] After being plasma-ionized, the gaseous carbon source rearranges into carbon nanotubes under the catalysis of transition metal vapor. A portion of the product can be collected on the wall of reaction vessel 7, and another portion can be collected on the gas-solid separation vessel connected downstream of reaction vessel 7.
[0031] A gas-directed airflow method is used to promote the directional growth of carbon nanotubes. The arc-igniting gas, containing a gaseous carbon source, flows vertically from top to bottom through the reaction vessel 7. This is a conventional approach. The difference in this embodiment is that the electric arc 3 is parallel to the airflow direction. In conventional methods, the electric arc 3 is perpendicular to the airflow direction to ensure sufficient contact between the arc 3 and the airflow. However, this has a problem: it effectively extinguishes the arc with gas, leading to an increase in the current and voltage required to maintain the arc 3, thus increasing energy consumption and hazard. In this embodiment, because the electric arc 3 rotates, it can still make sufficient contact with the airflow even if it is not perpendicular to the airflow direction.
[0032] In this embodiment, the ignition gas is argon, and the gaseous carbon source is methane. Methane is added to reaction vessel 7 at 13.33 kPa, and argon is added to reaction vessel 7 at 53.32 Pa. Reaction vessel 7 is evacuated before gas is introduced. After gas is introduced, the arc is ignited and the reaction begins. After arc 3 is generated, the current is maintained at 200 A, and the voltage is maintained at 20 V.
[0033] Of course, other types of reactants, arc-initiating gases, and reaction parameters are also acceptable, as long as the electric arc 3 is stably present and the reaction proceeds stably. The reactants, arc-initiating gas, and reaction parameters in this embodiment contribute to the generation of horizontally arrayed carbon nanotubes; a photograph of the product can be found in [link to product image]. Figure 2 The spacing between electrodes does not affect the arrangement of carbon nanotubes. Therefore, while ensuring the stable existence of arc 3, the spacing between electrodes should be as large as possible to ensure a large reaction space.
[0034] A magnet 4 for magnetically attracting the catalyst powder 6 is provided on the upper part of the upper electrode 1. The magnetic field lines 5 of the magnet 4 radiate downwards from the upper electrode 1 and pass through the reaction vessel 7. The arrangement of the magnetic field lines 5 here is to ensure that the electric arc 3 can rotate around a vertical central axis. The magnetic field lines 5 can radiate outwards from the upper electrode 1 or converge into the upper electrode 1. Changing the direction of the magnetic field lines 5 will cause the rotation direction of the electric arc 3 to change, but the clockwise or counterclockwise rotation of the electric arc 3 does not affect its use.
[0035] The catalyst powder 6 is either iron powder or iron(III) oxide powder. Both of these powders are easily adsorbed by magnet 4. Although iron(III) oxide powder is not elemental iron, it will immediately become elemental iron under the high temperature of electric arc 3 and the reducing atmosphere in reaction vessel 7.
[0036] Both the upper electrode 1 and the lower electrode 2 are graphite electrodes, with the upper electrode 1 serving as the cathode. In this embodiment, the catalyst is composed of iron powder. Although iron powder has a weaker magnetic attraction effect than iron oxide powder, it is conductive. If adsorbed onto the cathode, electrons can enter the iron powder. Simultaneously, the magnetically attracted powder tends to form raised structures, and the electric arc 3 tends to strike these charge-rich raised structures (i.e., tip discharge), making it easier to maintain the electric arc 3 and resulting in less electrode ablation.
[0037] The bottom of the upper electrode 1 is hemispherical. The hemispherical shape is designed to accommodate the rotation of the electric arc 3. At the same time, the hemispherical shape has no sharp points, so the electric arc 3 will not tend to remain in the position with sharp points due to the phenomenon of point discharge.
[0038] The lower electrode 2 has a groove on its top, opposite to the upper electrode 1, for receiving the incompletely vaporized catalyst powder 6. The downward projection of the upper electrode 1 falls completely into the groove. This groove should also be as smooth, flat, continuous, and without any sharp points as possible.
[0039] The magnetic field strength provided by magnet 4 must be sufficient to attract the catalyst powder 6 that has fallen into the groove to the bottom of the upper electrode 1. Therefore, magnet 4 needs to be a small but strong magnet, such as a neodymium magnet or an electromagnet. Of course, if it doesn't attract the catalyst powder 6, it won't affect the use, but it will shorten the continuous operating time of the device in this invention.
[0040] like Figure 1 As shown, a fabrication apparatus for horizontal array carbon nanotubes is used to implement the above-described fabrication method for horizontal array carbon nanotubes. It includes a cylindrical reaction vessel 7 with its central axis vertically arranged, an upper electrode 1 and a lower electrode 2 disposed inside the reaction vessel 7, gas flow openings at the top and bottom of the reaction vessel 7, and a magnet 4 disposed outside the reaction vessel 7.
[0041] The upper electrode 1 and the lower electrode 2 are positioned on the central axis of the reaction vessel 7. The gas flow openings at the top and bottom of the reaction vessel 7 are positioned opposite each other and avoid the upper electrode 1 and the lower electrode 2. The magnet 4 is positioned above the upper electrode 1.
[0042] Magnet 4 is a ring-shaped permanent magnet or electromagnet, and its central axis is located on the central axis of the reaction vessel 7. Magnet 4 is slightly smaller than the downward projection of the upper electrode 1; otherwise, much of the catalyst powder 6 would be attracted to the top of the reaction vessel 7 instead of the bottom of the upper electrode 1.
[0043] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.
Claims
1. A method for producing a horizontal array of carbon nanotubes, using a gaseous carbon source as a reactant, using a transition metal vapor as a catalyst, by means of an electric arc (3) discharge method, the electric arc (3) used for the production being located between two electrodes that are electrically connected in a reaction vessel (7), characterized in that: Two electrodes are set up opposite each other, with the upper electrode being called the upper electrode (1) and the lower electrode being called the lower electrode (2). The transition metal vapor is generated by the gasification of catalyst raw material powder (6) by electric arc (3). The catalyst raw material powder (6) is a transition metal element and / or oxide. The catalyst raw material powder (6) is a magnetic material and is magnetically attracted to the bottom of the upper electrode (1). The electric arc (3) rotates around the vertical central axis and comes into contact with the gaseous carbon source and the catalyst powder (6). The catalyst powder (6) in contact with the electric arc (3) loses its magnetism and falls down. During the falling process, it is vaporized by the electric arc (3) into transition metal vapor. After being plasmaized, the gaseous carbon source rearranges into carbon nanotubes under the catalytic action of the transition metal vapor.
2. The method of claim 1, wherein: The directional growth of carbon nanotubes is promoted by airflow orientation method, and the arc-initiating gas containing gaseous carbon source flows vertically from top to bottom through the reaction vessel (7).
3. The method of claim 2, wherein the horizontal array of carbon nanotubes is formed by the steps of: The arc-igniting gas is argon, and the gaseous carbon source is methane. 4. The method for preparing horizontally arrayed carbon nanotubes according to claim 1, characterized in that: The upper electrode (1) is provided with a magnet (4) for magnetically attracting the catalyst raw material powder (6). The magnetic field lines (5) of the magnet (4) radiate downwards from the upper electrode (1) and pass through the reaction vessel (7).
5. The method for preparing a horizontal array of carbon nanotubes according to claim 1, characterized in that: The catalyst precursor powder (6) is iron powder or iron oxide powder.
6. The method for preparing a horizontal array of carbon nanotubes according to claim 1, characterized in that: Both the upper electrode (1) and the lower electrode (2) are graphite electrodes, with the upper electrode (1) being the cathode.
7. The method for preparing a horizontal array of carbon nanotubes according to claim 6, characterized in that: The bottom of the upper electrode (1) is hemispherical.
8. The method for preparing a horizontal array of carbon nanotubes according to claim 7, characterized in that: The lower electrode (2) has a groove on its top that is opposite to the upper electrode (1) and is used to receive the incompletely vaporized catalyst raw material powder (6). The downward projection of the upper electrode (1) falls completely into the groove.
9. An apparatus for preparing horizontally arrayed carbon nanotubes, characterized in that: The method for preparing a horizontal array of carbon nanotubes as described in claim 2 includes a cylindrical reaction container (7) with its central axis vertically arranged, an upper electrode (1) and a lower electrode (2) disposed inside the reaction container (7), gas flow openings at the top and bottom of the reaction container (7), and a magnet (4) disposed outside the reaction container (7). The upper electrode (1) and the lower electrode (2) are positioned on the central axis of the reaction vessel (7). The gas flow openings at the top and bottom of the reaction vessel (7) are positioned opposite each other and avoid the upper electrode (1) and the lower electrode (2). The magnet (4) is positioned above the upper electrode (1).
10. The apparatus for preparing horizontally arrayed carbon nanotubes according to claim 9, characterized in that: The magnet (4) is a ring-shaped permanent magnet or electromagnet, and the central axis of the magnet (4) is located on the central axis of the reaction vessel (7).