Filament carbon nanotube assemblies, apparatuses and methods for making same

Abstract

The application discloses a filament carbon nanotube assembly, a preparation device and a preparation method thereof. The preparation device comprises a growth tube cavity for floating vapor phase deposition growth and an activator releasing structure arranged in the cavity; the growth tube cavity is divided into a continuous injection section, a growth initial section, a growth later section and an output section; the activator releasing structure is arranged in the growth later section and can inject the activator into the atmosphere of the growth later section; and the activator can react with amorphous carbon to remove the amorphous carbon. The preparation device and the preparation method provided by the application inject the activator into the growth later section, and the etching effect of the activator on the amorphous carbon can realize the secondary activation of the catalyst particles floating in the gas phase in the floating vapor phase deposition process, so that the catalyst particles can continue to catalyze the growth of the carbon nanotubes; the length of the carbon nanotubes in the carbon nanotube assembly composed of the carbon nanotubes obtained finally is significantly prolonged; and the physical properties of the obtained carbon nanotube assembly are significantly improved.

Description

Technical Field

[0001] This invention relates to the field of inorganic carbon material preparation technology, and in particular to a long-filament carbon nanotube assembly, its preparation apparatus and method. Background Technology

[0002] In carbon nanotube assemblies, such as carbon nanotube fibers, the length of the carbon nanotubes that make up the fiber is a key factor determining the fiber's mechanical properties. The longer the carbon nanotubes, the stronger the interaction between them, and the higher the fiber's mechanical properties. Floating catalytic CVD is one of the main methods for preparing continuous carbon nanotube fibers, with advantages such as low cost and good continuity. However, using floating catalytic CVD to prepare carbon nanotube fibers makes it difficult to fully utilize the high strength characteristics of individual carbon nanotube "molecules".

[0003] To achieve the preparation of long carbon nanotube fibers, existing technical solutions propose a two-step process of array growth and dry spinning. Although this method can produce carbon nanotube arrays with adjustable lengths and obtain carbon nanotube fibers with longer lengths and higher strength, the process is more complex. At the same time, when the length of the carbon nanotube array is too large, the spinnability of the fiber will be affected, the spinning difficulty will increase, and it is almost impossible to have a prospect of mass production.

[0004] Therefore, efficiently and inexpensively preparing long carbon nanotube assemblies using floating catalytic CVD is an important approach to achieving industrial applications. The inventors of this invention have discovered that during the floating catalytic growth of carbon nanotubes, the catalyst particles move with the carrier gas while simultaneously undergoing catalytic growth. As growth progresses, the catalyst particles are gradually coated with byproducts and impurities such as amorphous carbon, leading to gradual deactivation. Thus, the effective lifespan of the catalyst is a key factor affecting the length of the carbon nanotubes and, consequently, the strength of the carbon nanotube fibers. The technical challenge is how to specifically improve the effective lifespan of the catalyst without affecting other reaction processes. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a long-filament carbon nanotube assembly, its preparation apparatus, and its method.

[0006] To achieve the aforementioned objectives, the technical solution adopted by this invention includes:

[0007] In a first aspect, the present invention provides an apparatus for preparing a carbon nanotube assembly, comprising a growth chamber for growing carbon nanotubes by floating vapor deposition and an activator release structure disposed in the growth chamber; along the process direction, the growth chamber is divided into a continuous injection section, a growth initiation section, a growth post-growth section, and an output section; the activator release structure is disposed in the growth post-growth section and is capable of injecting an activator into the atmosphere of the growth post-growth section, and the activator is capable of reacting with amorphous carbon to remove the amorphous carbon.

[0008] Secondly, the present invention also provides a method for preparing a long-filament carbon nanotube assembly, comprising:

[0009] Carbon nanotubes were continuously grown using a floating vapor deposition method within a growth cavity.

[0010] An activator is injected into the atmosphere of the later stage of the growth chamber. The activator can react with the amorphous carbon attached to the surface of the catalyst particles during the growth process of the floating vapor deposition to remove the amorphous carbon.

[0011] Secondly, the present invention also provides a carbon nanotube assembly prepared by the above preparation method, wherein the length of the carbon nanotubes in the carbon nanotube assembly is greater than 100 μm.

[0012] Based on the above technical solution, compared with the prior art, the beneficial effects of the present invention include at least the following:

[0013] The preparation equipment and method provided by the present invention employs an activator injection method in the later stage of growth. The activator etches the amorphous carbon, thereby reactivating the catalyst particles floating in the gas phase during the floating vapor deposition process, enabling them to continue catalyzing the growth of carbon nanotubes. This results in a significant increase in the length of carbon nanotubes in the final carbon nanotube assembly, which in turn significantly improves the various physical properties of the obtained carbon nanotube assembly.

[0014] The above description is merely an overview of the technical solution of the present invention. In order to enable those skilled in the art to better understand the technical means of this application and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described below in conjunction with detailed drawings. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the preparation apparatus provided in a typical embodiment of the present invention;

[0016] Figure 2a This is an electron microscope image of the end face of carbon nanotube fiber half-length test provided in a typical comparative case of the present invention.

[0017] Figure 2bThis is an electron microscope image of the end face of carbon nanotube fiber half-length test provided in a typical embodiment of the present invention.

[0018] Figure 3 These are test diagrams of the multi-point mechanical properties of carbon nanotube fibers provided in the typical comparison and implementation cases of this invention.

[0019] Explanation of reference numerals in the attached drawings: 1. Injection pump; 2. First carrier gas; 3. Sealing flange; 4. Growth chamber; 5. High-temperature furnace; 6. Carbon nanotube intermediate product; 7. Activator release structure; 8. Tail gas outlet; 9. Water seal box with exhaust; 10. Water tank; 11. Roller; 12. Carbon nanotube fiber; 13. Winding and collecting device; 14. Second carrier gas; 15. Bubbling tank; 16. Activator; 17. Heating and temperature control component; 18. Spray nozzle. Detailed Implementation

[0020] In view of the shortcomings of the prior art, the inventors of this invention, through long-term research and extensive practice, have proposed the technical solution of this invention. The following will further explain and illustrate this technical solution, its implementation process, and its principles.

[0021] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0022] Moreover, relational terms such as “first” and “second” are used merely to distinguish one component or method step from another that has the same name, and do not necessarily require or imply any such actual relationship or order between these components or method steps.

[0023] This invention provides an apparatus for preparing a long-filament carbon nanotube assembly, comprising a growth cavity for growing carbon nanotubes by floating vapor deposition and an activator release structure disposed in the growth cavity; along the process direction, the growth cavity is divided into a continuous injection section, a growth initiation section, a growth post-growth section, and an output section; the activator release structure is disposed in the growth post-growth section and can inject an activator into the atmosphere of the growth post-growth section, and the activator can react with amorphous carbon to remove the amorphous carbon.

[0024] Based on the above overall technical concept, the key points of the present invention are (1) providing a catalyst secondary activation device and method for preparing long carbon nanotube fibers by floating catalytic CVD, including the supply, transportation and release of the secondary activator in a high-temperature furnace tube, and more importantly, the specific release location.

[0025] Regarding how to extend the length of carbon nanotubes, the inventors of this invention and prior art workers have made numerous attempts. Some of the prior art and the research work of this invention involve directly introducing a trace amount of etching agent as an activator (e.g., water). Some technical solutions involve adding a small amount of water to the carbon source and catalyst precursor. Some technical solutions involve directly introducing water in the injection section through carrier gas, etc. However, none of them have achieved a good technical effect in extending the length of the filament.

[0026] The inventors of this invention even attempted to customize and lengthen the furnace tube to increase the length of the carbon nanotubes by extending the growth time, but this also failed to achieve good results. The inventors believe that the reason for this is that in the later stages of growth, although the temperature and atmosphere are sufficient to meet the growth requirements, the catalyst particles in the later stages have already become deactivated. At this point, even if the furnace tube length is extended indefinitely to prolong the time, it will not be of any use.

[0027] Based on the above findings and analysis, the inventors proposed the technical solution of this invention, which involves introducing an activator at a specific location to reactivate the catalyst particles and further extend the filament length. The timing of the activator introduction is crucial. As described above, introducing the activator at the initial injection stage often fails to achieve the desired effect. This is because premature introduction not only leads to early consumption but also interferes with the decomposition of the carbon source and catalyst precursor, chemical reactions, and the initial carbon nanotube growth process in the injection stage, thus hindering effective carbon nanotube extension. However, through extensive practice, this invention has found that the activator should be introduced later in the growth process. At this stage, a small amount of fresh activator can both reactivate the catalyst particles and avoid affecting the growth process. The combined effect of these factors is what achieves the desired result.

[0028] Regarding the specific location of the growth stage, in some embodiments, during the floating vapor deposition growth, the temperature of the injection stage and the output stage are both lower than that of the initial growth stage and the growth stage, and the temperature range of the growth stage is 1100℃-1300℃; or in some embodiments, the growth stage is a section of tube between 1 / 2 and 3 / 4 (or other values) of the total length of the growth tube along the process direction.

[0029] Typically, the temperature of the later growth stage is the same as that of the initial growth stage, but there are slight differences. In some common cases, the temperature of the later growth stage will be about 50°C lower than that of the initial growth stage. If we refer to the above method of segmenting according to the total length, then we can generally consider 0-1 / 4 of the entire growth tube as the injection stage, 1 / 4-1 / 2 as the initial growth stage, 1 / 2-3 / 4 as the later growth stage, and the rest as the output stage. However, strict segmentation is not limited to any one of the above conditions or a combination of the above conditions. For example, when the position of the furnace body that heats the growth tube is adjusted, the corresponding positions of each segment will also be adjusted. In some cases, the high temperature range covered by the heating furnace body can be simply used as the growth stage, with the first half of the entire temperature range being the initial growth stage and the second half being the later growth stage.

[0030] Of course, the specific location of the growth stage may be adjusted and exceed the numerical range summarized by long-term experience for different specific situations. Essentially, the growth stage is defined as the location where the carbon nanotubes significantly stop increasing in length, as tested by various technical means. The significant characteristic of this growth stage is that most of the carbon nanotubes have stopped growing in this stage, but there is still a relatively high ambient temperature (e.g., above 1100°C, preferably above 1200°C), which meets the temperature and atmosphere conditions for floating gas phase growth of carbon nanotubes. The characterization method can refer to existing technologies, such as sampling and analyzing at different locations in the tube cavity, to analyze where the carbon nanotube sample will enter the plateau period of length growth. This invention will not elaborate on this further.

[0031] Regarding the specific shape of the activator release structure, in some embodiments, the activator release structure may include, for example, an annular injector with multiple nozzles arranged around its circumference, the nozzles being directed toward the axis of the injector.

[0032] In some preferred embodiments, the injector is preferably coaxially arranged with the growth cavity and as close as possible to the cavity wall. This is a preferred solution to avoid airflow instability as much as possible. Of course, even if it is not strictly coaxial, some slight offset is still within the scope of the present invention as long as it does not significantly affect the airflow and is still protected by the present invention.

[0033] Furthermore, the activator release structure may also include a delivery conduit for supplying the activator to the injector; more preferably, in some embodiments, the delivery conduit extends from the injector toward the output section until it extends beyond the port of the output section. The above solution, by extending the delivery conduit at the outlet end, can minimize the impact on the injection and initial growth stages of the growth reaction. However, placing it in the later stage, since the carbon nanotubes have already aggregated and formed intermediate carbon nanotube products, and to some extent contracted towards the axis and away from the tube wall, the delivery conduit positioned close to or adjacent to the tube wall has less impact on the intermediate carbon nanotube products, making it a more effective implementation overall.

[0034] It should be noted that the above method is only a preferred method and does not mean that the present invention can only be implemented in this way. Under the guidance of the overall technical concept of the present invention, those skilled in the art can use the same overall concept to inject the activator by making an opening at the corresponding position on the tube wall, or to deliver the activator from the direction of the injection section. All these methods are within the feasible and protection scope of the present invention.

[0035] Regarding how the activator is supplied, in some embodiments, the delivery line extends to an activator supply unit, which is used to supply the activator using a carrier gas.

[0036] More specifically, in some embodiments, the activator supply unit includes a bubbling tank capable of holding a liquid containing the activator, and the carrier gas flows through the bubbling tank in a bubbling manner to carry the activator.

[0037] More specifically, the activator supply unit may also include other devices that can realize the vaporization of the activator and its mixing with the carrier gas, including microwave heating vaporization, ultrasonic vaporization, etc., and can adjust the supply speed of the activator.

[0038] In addition, regarding other components of the growth apparatus, in some embodiments, the fabrication apparatus may further include: a growth supply unit, a temperature control unit, and a collection unit; the growth supply unit is used to supply the gas, catalyst precursor, and carbon source required for the floating vapor deposition growth of carbon nanotubes into the growth chamber; the temperature control unit is used to regulate the temperature of the growth chamber; and the collection unit is used to collect carbon nanotubes from the outlet of the output section to form a carbon nanotube assembly.

[0039] For details on the relevant components and functions, please refer to the guidelines of many existing technologies. This invention will not elaborate further.

[0040] As a typical application example of the above-mentioned technical solution, this invention discloses a method and apparatus for preparing long-filament carbon nanotube fibers. The apparatus includes a raw material injection component, a sealed high-temperature tubular furnace component, a water-sealed collection box with exhaust gas, a catalyst secondary activator release component, and a carbon nanotube fiber winding and collection component, etc. The catalyst secondary activator introduction component further includes a sealed liquid container with a bubbling design, a heating device, a conveying pipeline, and a secondary activator release structure. The secondary activator is introduced through heating and bubbling, entering the rear section of the floating catalytic carbon nanotube growth zone. This etches away amorphous carbon and other impurities on the catalyst surface, thereby reactivating the catalyst and continuing to catalyze the increase in carbon nanotube length, achieving the preparation of long-filament carbon nanotube fibers (carbon nanotube length greater than 100 μm).

[0041] Corresponding to the above-described preparation apparatus, a second aspect of the present invention also provides a method for preparing a long-filament carbon nanotube assembly, comprising the following steps:

[0042] Carbon nanotubes were continuously grown using a floating vapor deposition method within a growth cavity.

[0043] An activator is injected into the atmosphere of the later stage of the growth chamber. The activator can react with the amorphous carbon attached to the surface of the catalyst particles during the growth process of the floating vapor deposition to remove the amorphous carbon.

[0044] Regarding the specific selection of the activator, in some embodiments, the activator includes, for example, any one or a combination of two or more of water, hydrogen peroxide, formic acid, and formaldehyde. However, it is not limited to this; the selection of the activator described above is a limited selection obtained by the inventors through experimentation. However, this does not preclude the possibility that other substances with similar molecular properties may not produce a secondary activation effect. It is understood that the commonality of the above-mentioned activators is that they are all small molecules (inorganic substances or organic acids) containing oxygen.

[0045] In some specific implementation schemes, the preparation method includes the following steps:

[0046] A first carrier gas, a carbon source, and a catalyst precursor are continuously introduced into the injection section of the growth tube. Driven by the first carrier gas, the catalyst travels along the growth tube and catalyzes growth to form a carbon nanotube aerogel, which is continuously output from the outlet section of the growth tube.

[0047] The activator is carried by a second carrier gas and injected into the atmosphere from the rear section of the growth tube.

[0048] Regarding specific growth and preparation conditions, in some implementations, the preferred flow ratio of the second carrier gas to the first carrier gas can be 1:25 to 1:5.

[0049] In some embodiments, the preferred volume fraction of the activator in the mixture with the second carrier gas may be 2%-10%.

[0050] The optimal conditions are as follows: the flow rate ratio of the second carrier gas to the first carrier gas is approximately 1:10, for example, 1:8-12; and the proportion of the activator in the second carrier gas mixture is approximately 5%, for example, 4-6%. Through long-term experiments, the inventors of this invention have discovered that the above-mentioned optimal process conditions can bring about a sufficient secondary activation effect, while also avoiding adverse effects on the growth and formation of carbon nanotubes.

[0051] Based on the above technical solution, a third aspect of the present invention also provides a carbon nanotube assembly prepared by the above preparation method, wherein the length of the carbon nanotubes in the carbon nanotube assembly is greater than 100 μm.

[0052] In some embodiments, the carbon nanotube assembly includes any one of carbon nanotube aerogel, carbon nanotube fiber, carbon nanotube narrow strip, carbon nanotube film, and carbon nanotube composite material. The following examples use carbon nanotube fiber, a more common form, but this does not mean that the technical solution provided by this invention can only be used to prepare carbon nanotube fiber. Preparing fibers, films, narrow strips, or even directly combining them with polymers to prepare composite materials using floating vapor deposition are all existing technologies. The difference lies only in the collection method. For example, narrow strips or fibers can be obtained through densification treatment in a water tank; multilayer aerogels can be formed by winding them onto a roller, and then densified to obtain films; in some cases, aerogels output from the nozzle can even be directly collected for experiments or other applications, and so on.

[0053] The technical solution of the present invention will be further described in detail below through several embodiments and in conjunction with the accompanying drawings. However, the selected embodiments are only for illustrating the present invention and do not limit the scope of the present invention.

[0054] Example 1

[0055] This embodiment illustrates a device for preparing a long-filament carbon nanotube assembly. The specific technical process and principle are as follows:

[0056] like Figure 1 As shown, a micro-injection pump 1 injects a liquid carbon source / catalyst solution into the growth chamber 4 of a high-temperature reactor at a set flow rate, where it evaporates and vaporizes at the top of the reactor. Simultaneously, a first carrier gas 2 enters the growth chamber 4 at a set flow rate, and the vaporized material, carried by the first carrier gas 2, enters a region with a higher temperature. In the high-temperature reaction zone, the gaseous carbon source / catalyst undergoes decomposition and catalytic growth reactions to generate carbon nanotube intermediate product 6.

[0057] During the catalytic growth of carbon nanotubes, a weakly oxidizing secondary activator 16 (water) is bubbled in a sealed bubbling tank 15 with a bubbling device. This mixture is then transported along a pipeline into the rear section of the growth zone of the growth chamber 4 and released through the inner nozzle 18 of the annular secondary activator release structure 7. The activator release structure 7 is preferably made of high-temperature resistant materials such as quartz or corundum ceramic. The H2O content in the mixed gas is controlled by the heating and temperature control component 17 and the flow rate of the second carrier gas 14. After secondary activation, the catalyst in the carbon nanotube intermediate product 6 can continue to grow carbon nanotubes. The carbon nanotube product shrinks and densifies in the water tank 10, forming carbon nanotube fibers 12, which are ultimately collected by the fiber winding and collecting device 13.

[0058] The purpose of the preparation apparatus provided in this embodiment is to introduce a secondary activator H2O during the floating catalytic CVD carbon nanotube growth process to remove amorphous carbon impurities that cause catalyst failure, thereby improving the effective lifespan of the catalyst and preparing long-filament carbon nanotube fibers.

[0059] Example 2

[0060] This embodiment demonstrates the preparation of carbon nanotube fibers using the preparation apparatus provided in Example 1, as shown below:

[0061] Basic process conditions: In the liquid reaction solution, the mass ratio of carbon source (ethanol) / catalyst (ferrocene) / co-catalyst (thiophene) is 100:1:2; the injection rate of the reaction solution is 0.5 mL / min; the first carrier gas is a mixture of hydrogen and argon in a 1:1 ratio, and the first carrier gas flow rate is 4 L / min; the temperature of the initial and later stages of the high-temperature growth zone is set at 1200℃; and the carbon nanotube fiber collection rate is 5 m / min.

[0062] Secondary activation conditions: The total length of the furnace tube is 1m, the injection position is 0.7m from top to bottom in the furnace tube, the second carrier gas is argon, the flow rate is 400mL / min (the flow rate ratio with the first carrier gas is 1:10), and the water content in the mixed gas is 5%.

[0063] Continuous carbon nanotube fibers were prepared based on the above process conditions.

[0064] Comparative Example 1

[0065] This comparative example is largely the same as Example 2, with the main difference being:

[0066] The secondary activation component was eliminated, and carbon nanotube fibers were prepared using the same basic conditions.

[0067] Finally, the tensile cross-sectional morphologies of the carbon nanotube fibers prepared in Comparative Example 1 and Example 2 are as follows: Figure 2aand Figure 2b As shown, the carbon nanotubes grown in this invention have a longer length when pulled out of the fiber cross-section, indicating that the carbon nanotubes in the fiber have a greater length. According to the tensile fracture model of carbon nanotube fibers in the literature (Vilatela et al., ACS Nano, 2011, 5, 1921), the carbon nanotube length in the carbon nanotube fibers of this invention can reach 120 μm, while the carbon nanotube length in carbon nanotube fibers grown with conventional equipment is about 60 μm. This shows that the secondary activation device introduced in this invention can effectively improve the catalyst lifetime, thereby increasing the length of the grown carbon nanotubes.

[0068] Figure 3 The mechanical tensile curves of carbon nanotube fibers grown by the conventional floating catalytic CVD equipment and method in Comparative Example 1 and the floating catalytic CVD equipment in Example 2 are shown. It can be seen that the tensile strength of the filament carbon nanotube fibers provided in Example 2 reaches 2.6 GPa, which is significantly higher than that of the carbon nanotube fibers grown by the conventional equipment in Comparative Example 1 (1.5 GPa). This shows that the secondary activation device introduced in this invention can realize the preparation of filament carbon nanotube fibers, thereby effectively improving the mechanical properties of the fibers.

[0069] Comparative Example 2

[0070] This comparative example is largely the same as Example 2, with the main difference being:

[0071] A complete set of secondary activation components is retained, and the same flow rate of second carrier gas is maintained, but no more activator water is introduced.

[0072] The carbon nanotube length and mechanical properties of the obtained fibers were no different from those of Comparative Example 1.

[0073] This indicates that the technical effect achieved by the present invention is due to the introduction of the secondary activator, and is not significantly related to the corresponding hardware structure or the introduction of the secondary carrier gas.

[0074] Comparative Example 3

[0075] This comparative example is largely the same as Example 2, with the main difference being:

[0076] The position of the activator release structure is moved upwards to the initial growth stage (0.3m from top to bottom).

[0077] At this point, because the activator water directly participates in the nucleation and growth reactions in the initial stage of growth, it reacts prematurely with the catalyst (containing iron) and carbon elements and is excessively consumed. Furthermore, the introduction of the second carrier gas will also interfere with the growth process in the initial stage.

[0078] Therefore, the length of the carbon nanotubes in the obtained fibers not only did not increase, but actually decreased to some extent (40μm~50μm). At the same time, due to the premature consumption of the carbon source, the grown carbon nanotube fibers became thinner, and the tensile strength also decreased to some extent (1.2GPa).

[0079] Comparative Example 4

[0080] This comparative example is largely the same as Example 2, with the main difference being:

[0081] An equal dose of activator water is introduced directly by the first carrier gas at the sealing flange.

[0082] At this point, because the activator water directly participates in the decomposition and initial nucleation of the injection section, as well as the nucleation and growth reaction of the initial growth section, it reacts prematurely with the catalyst (containing iron) and carbon elements and is excessively consumed, and it also interferes with the growth process of the injection section and the initial growth section.

[0083] Therefore, the length of the carbon nanotubes in the obtained fibers not only did not increase, but actually decreased to some extent. The same was true for the tensile strength. The grown carbon nanotube fibers also became thinner, and the tensile strength also decreased to some extent (1.0 GPa). The overall effect was similar to that of Comparative Example 3.

[0084] Comparative Example 5

[0085] This comparative example is largely the same as Example 2, with the main difference being:

[0086] The position of the activator release structure was moved downwards, to a position beyond the later stage of growth (0.2m from bottom to top).

[0087] At this point, the activator release point is close to the furnace tube outlet, and the temperature in this area is significantly lower than that in the later growth stage. Even if the amorphous carbon impurities on the catalyst surface are removed at this time, the catalyst particles cannot support the continued growth of carbon nanotubes at low temperatures, and the growth process of carbon nanotubes basically stops.

[0088] Therefore, the secondary activator did not achieve the effect of continuing the growth of carbon nanotubes, and the length of the carbon nanotubes and the mechanical properties of the obtained fibers were no different from those of Comparative Example 1.

[0089] Comparative Example 6

[0090] This comparative example is largely the same as Example 2, with the main difference being:

[0091] An excessive amount of secondary activator was introduced, with the water content of the secondary activator reaching 12% in the second carrier gas.

[0092] At this point, the excessive amount of secondary activator not only removes amorphous carbon impurities from the catalyst surface, but also consumes a large amount of carbon source used for the continuous growth of carbon nanotubes, causing the growth process of carbon nanotubes to essentially stop.

[0093] Therefore, the excessive amount of secondary activator did not achieve the effect of continuing the growth of carbon nanotubes, and the length of carbon nanotubes and mechanical properties of the obtained fibers were no different from those of Comparative Example 1.

[0094] Comparative Example 7

[0095] This comparative example is largely the same as Example 2, with the main difference being:

[0096] An excessively high proportion of the second carrier gas flow rate is introduced, with the ratio of the second carrier gas flow rate to the first carrier gas flow rate being 1:4, reaching 1L / min.

[0097] At this point, an excessively high second carrier gas flow rate will disrupt the airflow of the first carrier gas in the later stage of growth, interfere with the continued growth of carbon nanotubes, and destroy the formation of carbon nanotube aerogel intermediates. This results in the collected carbon nanotube fibers having poor microstructure and low performance. At the same time, the uniformity and continuity of the carbon nanotube fibers will also be adversely affected, resulting in only discontinuous carbon nanotube fibers being obtained, rather than continuous and long carbon nanotube fibers.

[0098] Excessive second carrier gas flow rate will damage the structure of the carbon nanotube assembly, resulting in a decrease in the tensile strength of the prepared carbon nanotube fibers (1.0 GPa).

[0099] Example 3

[0100] This embodiment is largely the same as Embodiment 2, with the main difference being:

[0101] By changing the basic conditions, the ratio of carbon source (ethanol) / catalyst (ferrocene) / co-catalyst (thiophene) in the liquid reaction solution was 200:1:2, the injection rate of the reaction solution was 0.4 mL / min, the first carrier gas was a mixture of hydrogen and argon in a 1:1 ratio, the first carrier gas flow rate was 5 L / min, the temperature of the initial and later stages of the high-temperature growth zone was set at 1300℃, and the carbon nanotube fiber collection rate was 10 m / min.

[0102] It is still possible to obtain carbon nanotube fibers with a length of more than 100μm.

[0103] Example 4

[0104] This embodiment is largely the same as Embodiment 2, with the main difference being:

[0105] The secondary activation conditions were changed. The total length of the furnace tube was 1m, the injection position was 0.6m from top to bottom in the furnace tube, the second carrier gas was argon, the flow rate was 600mL / min (the flow rate ratio with the first carrier gas was 3:20), and the water content in the mixed gas was 6%.

[0106] It is still possible to obtain carbon nanotube fibers with a length of more than 100μm.

[0107] Example 5

[0108] This embodiment is largely the same as Embodiment 2, with the main difference being:

[0109] The choice of activator was changed to hydrogen peroxide. Since its oxidizing power is greater than that of water, the volume fraction of the activator in the second carrier gas was 1% to avoid excessive oxidizing power that could damage the carbon nanotube structure.

[0110] It is still possible to obtain carbon nanotube fibers with a length of more than 100μm.

[0111] Example 6

[0112] This embodiment is largely the same as Embodiment 2, with the main difference being:

[0113] The collection conditions were changed by introducing an electrically driven roller collection device at the furnace tube outlet to collect the aerogel intermediates. The collection speed was 3 m / min and the translation speed was 1 m / min. The collected multilayer aerogel was then densified.

[0114] It is still possible to obtain carbon nanotube films with a length of more than 100 μm.

[0115] Based on the above embodiments and comparative examples, it is clear that the embodiments of the present invention improve the length of carbon nanotubes in the preparation of carbon nanotube fibers by floating catalytic CVD. The key lies in the design of the catalyst secondary activation device. This device can uniformly introduce a secondary activator in the high-temperature furnace tube in the later stage of carbon nanotube growth and fully contact it with the catalyst, thereby etching away impurities such as amorphous carbon on the catalyst surface. The deactivated catalyst can continue to catalytically grow carbon nanotubes after being reactivated, ultimately obtaining carbon nanotubes of greater length and carbon nanotube fibers assembled from them, and obtaining excellent physical properties such as mechanical strength.

[0116] It should be understood that the above embodiments are merely illustrative of the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a long-filament carbon nanotube assembly, characterized in that, include: Carbon nanotubes are continuously grown using floating vapor deposition in a growth cavity. Along the process direction, the growth cavity is divided into a continuous injection section, an initial growth section, a post-growth section, and an output section. The post-growth section is a segment between 1 / 2 and 3 / 4 of the total length of the growth cavity along the process direction. An activator is injected into the atmosphere of the growth section of the growth chamber using an activator release structure disposed in the growth section. The activator reacts with amorphous carbon adhering to the surface of the catalyst particles during the growth process of the floating vapor deposition to remove the amorphous carbon. The activator includes any one or a combination of two or more of water, hydrogen peroxide, formic acid, and formaldehyde.

2. The preparation method according to claim 1, characterized in that, During the floating vapor deposition growth, the temperatures of the injection section and the output section are lower than those of the initial growth section and the later growth section, with the temperature range of the later growth section being 1100℃-1300℃.

3. The preparation method according to claim 1, characterized in that, The activator release structure includes an annular injector with multiple nozzles around its circumference. The nozzles spray in the direction of their sprays towards the axis of the injector, and the injector is coaxially arranged with the growth chamber.

4. The preparation method according to claim 3, characterized in that, The activator release structure further includes a delivery conduit for supplying the activator to the injector, the delivery conduit extending from the injector toward the output section until it extends out of a port of the output section.

5. The preparation method according to claim 4, characterized in that, The delivery pipeline extends to an activator supply unit, which provides the activator using a carrier gas. The activator supply unit includes a bubbling tank capable of holding a liquid containing the activator, and the carrier gas flows through the bubbling tank in a bubbling manner to carry the activator.

6. The preparation method according to claim 1, characterized in that, The preparation apparatus used in the preparation method includes: a growth supply unit, a temperature control unit, and a collection unit; The growth supply unit is used to supply the gas, catalyst precursor and carbon source required for the floating vapor deposition growth of carbon nanotubes into the growth cavity; the temperature control unit is used to regulate the temperature of the growth cavity; the collection unit is used to collect carbon nanotubes from the outlet of the output section to form a carbon nanotube assembly.

7. The preparation method according to claim 1, characterized in that, Specifically, it includes: A first carrier gas, a carbon source, and a catalyst precursor are continuously introduced into the injection section of the growth tube. Under the drive of the first carrier gas, the catalyst travels along the growth tube and catalyzes growth to form a carbon nanotube aerogel, which is continuously output from the outlet section of the growth tube. The activator is carried by a second carrier gas and injected into the atmosphere from the rear section of the growth tube. The flow rate ratio of the second carrier gas to the first carrier gas is 1:25-1:5, and the volume fraction of the activator in the mixture formed with the second carrier gas is 2%-10%.

8. The preparation method according to claim 7, characterized in that, The flow rate ratio of the second carrier gas to the first carrier gas is 1:8-12, and the volume fraction of the activator in the mixed gas is 4-6%.

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