Graphene nanosheet / carbon nanotube heterostructure and preparation method and application thereof

Abstract

The invention discloses a graphene nanosheet / carbon nanotube heterostructure as well as a preparation method and application thereof, a graphene nanosheet is taken as a substrate, a carbon nanotube is grown at the surface defect or edge of the graphene nanosheet, and the graphene nanosheet and the carbon nanotube are seamlessly connected through covalent bonding, the connection is tight, and the growth position is accurate. The preparation method comprises the following steps: firstly adsorbing Co < 2 + > at a defect position, then fixing Co < 2 + > at the defect position by adopting ZIF-67, cleaning free Co < 2 + >, and then reducing again, so that accurate growth of a carbon nanotube at the defect or vacancy of a graphene nanosheet is realized, and the graphene nanosheet / carbon nanotube heterostructure is prepared. When the prepared structure is doped into the composite explosive, the mechanical property and the heat-conducting property of the composite explosive can be synergistically improved, the mechanical property can be improved by 30% on the basis that the heat-conducting property is improved by 90%, and the industrial problem that the mechanical property and the heat-conducting property of the composite explosive are difficult to be greatly improved at the same time is solved; the method has important application value in the fields of weaponry and the like.

Description

Technical Field

[0001] This invention relates to the field of thermally conductive filler technology for explosives, specifically to a graphene nanosheet / carbon nanotube heterostructure, its preparation method, and its application. Background Technology

[0002] The statements in this section provide only background information relevant to the disclosure of this application and may not constitute prior art.

[0003] Hybrid explosives are a type of composite material primarily composed of high-energy explosive crystals, coated and bonded together with a small amount of polymer binder. They retain high explosive performance while possessing excellent molding and processing characteristics, demonstrating wide applicability in both civilian and military fields. Hybrid explosives face complex thermophysical environments during long-term transportation and storage, placing high demands on their environmental adaptability. However, due to the inherently low thermal conductivity of the explosive crystals and binder, the internal heat of the hybrid explosive is difficult to dissipate rapidly during rapid temperature changes, resulting in severe thermal stress. Furthermore, the high filling characteristics of the explosive crystals and the large number of interfaces result in lower strength and toughness of the hybrid explosive components. Consequently, the thermal stress induced by temperature differences can easily exceed the mechanical strength of the hybrid explosive, causing cracking or damage, threatening its reliability and safety in practical applications. Therefore, synergistically improving the mechanical and thermal conductivity properties of hybrid explosives is of great significance for enhancing the environmental adaptability of explosive components.

[0004] To enhance the mechanical and thermal conductivity properties of hybrid explosives, the most direct and effective strategy is to introduce high-strength / thermally conductive fillers. Graphene, with its ultra-high in-plane intrinsic thermal conductivity and huge specific surface area, has been proven to improve the thermal conductivity and mechanical properties of hybrid explosives to a certain extent. For example, patent (CN107759427A, 2018) invented an alternating microlayered thermally conductive hybrid explosive and its preparation method, mainly based on the efficient dispersion of fillers such as graphene nanosheets and carbon nanotubes in the hybrid explosive to improve its thermal conductivity. Literature (Composites Part B, 2020, 203: 108447) achieved a significant improvement in thermal conductivity by constructing a continuous thermally conductive network in the hybrid explosive using graphene nanosheets. However, the high interfacial thermal resistance between graphene layers results in a low out-of-plane thermal conductivity, which is a key bottleneck hindering its efficiency in enhancing thermal conductivity. Patents (CN107805179A, 2018) and literature (Composites Part A, 2021, 148:106492) reduce interfacial thermal resistance by loading metal nanoparticles / nanowires onto the surface of graphene nanosheets, thereby further improving thermal conductivity. However, this strategy relies on non-bonding forces (van der Waals forces, electrostatic adsorption), resulting in insufficient interfacial bonding strength and limited phonon coupling efficiency. Therefore, the improvement in the out-of-plane thermal conductivity of graphene remains unsatisfactory. Furthermore, while the graphene fillers introduced in the aforementioned patents or literature improve the mechanical properties of hybrid explosives to some extent, the stacking defects and weak interlayer van der Waals forces of graphene limit stress transfer efficiency, thus limiting the improvement in the mechanical properties of hybrid explosives. Therefore, how to design and construct high-strength / high-thermal-conductivity graphene hybrid fillers, and synergistically improve the thermal conductivity and mechanical properties of hybrid explosives through strong interfacial bonding and low interfacial thermal resistance between fillers, is a major technical bottleneck in this research field.

[0005] Currently, there is another method to directly construct a three-dimensional graphene thermally conductive network on plastic bonded explosives (PBX), which is to directly coat the surface of the molding powder particles to construct a three-dimensional isolated thermally conductive structure. This strategy can indeed significantly improve the thermal conductivity of PBX at low content. However, due to the large accumulation of graphene at the interface, rigid stress concentration points are formed, which leads to a decrease in the mechanical properties of PBX, making it difficult to achieve a synergistic improvement in mechanical and thermal properties. Summary of the Invention

[0006] The purpose of this invention is to address the current problem of simultaneously achieving good mechanical and thermal conductivity properties in mixed explosives, as well as the low thermal conductivity of fillers. This invention provides a graphene nanosheet / carbon nanotube heterostructure, its preparation method, and its applications. The prepared heterostructure uses graphene nanosheets as a substrate, with carbon nanotubes grown in situ at surface defects or edges. The carbon nanotubes between the graphene nanosheets are seamlessly connected by covalent bonding. This significantly reduces the interfacial thermal resistance between fillers, and the unique structure improves stress transfer efficiency. When added to mixed explosives, it achieves a synergistic breakthrough in both mechanical properties (20%-40% increase in Brazilian tensile fracture strength; 20%-40% increase in strain) and thermal conductivity (40%-125% increase in thermal conductivity).

[0007] The technical solution of the present invention is as follows: The present invention provides a graphene nanosheet / carbon nanotube heterostructure, which uses graphene nanosheets as a substrate and has carbon nanotubes at its surface defects or edges, and the carbon nanotubes between the graphene nanosheets are seamlessly connected by covalent bonding.

[0008] This invention provides a method for preparing a graphene nanosheet / carbon nanotube heterostructure, comprising the following steps: Step (1): A certain mass of graphene nanosheets, water-soluble cobalt salt, and hexadecyltrimethylammonium bromide are dispersed in deionized water and mixed evenly. After standing, the Co... 2+ Selective adsorption at defect sites on graphene nanosheets, followed by cleaning to remove free Co. 2+ Then, an excess of 2-methylimidazole solution was added, and after stirring evenly, a hydrothermal reaction was carried out to obtain graphene nanosheets loaded with ZIF-67 at the defect sites. Step (2): Place the graphene nanosheets loaded with ZIF-67 in a tube furnace and heat them in an inert gas / hydrogen atmosphere to reduce ZIF-67 at high temperature to obtain graphene nanosheets loaded with cobalt nanoparticles; then switch the gas to an inert gas / carbon source gas to catalyze the growth of carbon nanotubes and obtain a covalently bonded graphene nanosheet / carbon nanotube heterostructure.

[0009] According to a preferred embodiment, in step (1), the mass ratio of graphene nanosheets to water-soluble cobalt salt is 1:(0.1-1), controlling the total amount of cobalt salt to prevent oversaturation, and allowing it to stand for a short time to allow the Co to settle. 2+ It preferentially occupies highly active defect sites (edges, vacancies, etc.) and inhibits random surface deposition; the amount of hexadecyltrimethylammonium bromide added is such that the mass ratio of hexadecyltrimethylammonium bromide to graphene nanosheets is 1:100-300. Preferably, the standing time is 0.5h.

[0010] According to a preferred embodiment, in step (1), the method of uniform mixing is ultrasound-assisted.

[0011] According to a preferred embodiment, in step (1), the amount of 2-methylimidazole solution added is such that the molar ratio of 2-methylimidazole to water-soluble cobalt salt is 55:1. This utilizes the excess ligand ratio to suppress spontaneous nucleation of ZIF-67 in the bulk solution, forcing the reaction to preferentially occur at defect-anchored Co. 2+ Site occurrence.

[0012] According to a preferred embodiment, in step (1), the hydrothermal reaction temperature is 80-100℃, and the reaction time is 3-5 hours. This low-temperature hydrothermal reaction utilizes the localized high concentration of Co at the defect site. 2+ Induced preferential nucleation.

[0013] According to a preferred embodiment, in step (1), the water-soluble cobalt salt is at least one of cobalt nitrate hexahydrate, cobalt sulfate heptahydrate, and cobalt chloride hexahydrate.

[0014] According to a preferred embodiment, in step (2), the inert gas is at least one of argon, nitrogen, or helium; the carbon source gas is at least one of methane, acetylene, ethylene, or ethanol vapor. The suitable temperature for catalytic growth of carbon nanotubes is set according to the type of carbon source gas: 850-950°C for methane, 700-800°C for acetylene, 750-850°C for ethylene, and 600-750°C for ethanol vapor.

[0015] According to a preferred embodiment, in step (2), the inert gas flow rate during the high-temperature reduction process is 60-90 sccm, the hydrogen flow rate is 10-40 sccm, the high-temperature reduction time is 1 h, and the heating rate is 10 ℃ / min. During the carbon nanotube growth process, the inert gas flow rate is 60-90 sccm, the carbon source gas flow rate is 10-40 sccm, and the high-temperature growth time is 0.5-2 h.

[0016] According to a preferred embodiment, the graphene nanosheet / carbon nanotube heterostructure prepared by the method described above is used as a thermally conductive filler in the preparation of mixed explosives.

[0017] Another aspect of the present invention provides a method for synergistically improving the mechanical and thermal conductivity properties of a mixed explosive, comprising the following steps: Step (1): Take a graphene nanosheet / carbon nanotube heterostructure as described above or prepare a covalently bonded graphene nanosheet / carbon nanotube heterostructure material according to the preparation method of a graphene nanosheet / carbon nanotube heterostructure as described above. Step (2): Disperse and uniformly mix the graphene nanosheets / carbon nanotubes with the polymer binder solution; the mass percentage of the graphene nanosheets / carbon nanotubes is 0.5wt%~2wt%; the mass percentage of the polymer binder is 3wt%~4.5wt%. Step (3): Add the mixture obtained in step (2) to explosives with a mass percentage of 95 wt%, obtain explosive molding powder by water suspension method, filter, wash, dry, and press into explosive columns to obtain mixed explosive parts with synergistic improvement in mechanical and thermal conductivity.

[0018] According to a preferred embodiment, the explosive can be one of hexanitrohexaazapentazine (CL-20), octogen (HMX), rexogen (RDX), 1,3,5-triamino-2,4,6-trinitrobenzene (TATB), 1-oxo-diamino-3,5-dinitropyrazine (LLM-105), or 1,1-diamino-2,2-dinitroethylene explosive (FOX-7); the polymer binder can be one of fluororubber, polyurethane, or vinyl acetate cellulose.

[0019] Compared with existing technologies, the advantages of this invention are: 1. A graphene nanosheet / carbon nanotube heterostructure, which precisely addresses the defects and vacancies in the graphene nanosheets and grows carbon nanotubes at the corresponding locations, thereby precisely compensating for the decreased thermal conductivity at the defect sites of the graphene nanosheets and specifically improving the thermal conductivity of the graphene nanosheets. Compared with the traditional method of randomly growing carbon nanotubes on the surface of graphene nanosheets, the carbon nanotubes grown in this application are more precise and uniform, and less prone to Co generation. 2+ Accumulation and aggregation can ensure stable heat conduction efficiency; 2. A graphene nanosheet / carbon nanotube heterostructure and its preparation method, utilizing the high surface energy of defect sites during the static stage to drive Co 2+ Selective enrichment, through precise control of Co 2+ The amount added should be controlled to regulate the degree of reaction and avoid Co. 2+ Accumulation and aggregation; subsequently, by adding an excess of the ligand 2-methylimidazole, free Co was rapidly consumed. 2+ And preferentially in areas where Co has been adsorbed 2+ In this method, ZIF-67 crystals are generated in situ at the defect sites, and the spatial confinement effect of ZIF-67 "locks" cobalt atoms at the defect locations. Finally, ZIF-67 is decomposed at high temperature, allowing the reduced cobalt nanoparticles to inherit the anchoring sites of ZIF-67, thus achieving precise growth of carbon nanotubes at the defect sites. Existing techniques skip ZIF-67 conversion and directly reduce cobalt ions, which rely solely on weak physical adsorption for random distribution. These ions are prone to migration and aggregation at high temperatures, making precise positioning of defect sites impossible.

[0020] 3. An application of a graphene nanosheet / carbon nanotube heterostructure: This application's heterostructure, which precisely grows carbon nanotubes at defect locations, overcomes the thermal conductivity defects of traditional graphene nanosheets. Through covalent bonding, it enhances phonon coupling at the interface between graphene nanosheets and carbon nanotubes, thereby significantly reducing the interfacial thermal resistance between fillers. The unique "sheet-rod" three-dimensional structure of the graphene nanosheet / carbon nanotube material forms a mechanically interlocked structure with the polymer binder, thus improving stress transfer efficiency. The prepared graphene nanosheet / carbon nanotube heterostructure material is still a carbon nanomaterial. When added to explosives, it simultaneously improves the thermal conductivity and mechanical properties of the explosives, achieving a 40%-125% increase in thermal conductivity and a more than 30% increase in mechanical properties; effectively suppressing thermal stress damage; the improvement in both mechanical properties and thermal conductivity surpasses existing technologies; while in traditional preparation methods, Co... 2+ The catalyst is adsorbed onto the surface of graphene nanosheets via physical adsorption. However, the catalyst tends to aggregate at high temperatures, and Co... 2+ Excessive content of certain substances will reduce the thermal conductivity of graphene nanosheets. Attached Figure Description

[0021] Figure 1 This is a flowchart of a method for preparing a graphene nanosheet / carbon nanotube heterostructure. Figure 2 A scanning electron microscope image of a covalently bonded graphene nanosheet / carbon nanotube heterostructure material provided in Example 1 of this invention; the image shows graphene nanosheets / carbon nanotubes magnified 25,000 times, scale bar 400 nm. Figure 3 The thermal conductivity of the mixed explosives with different carbon nanofillers in Example 1 of the present invention varies with the filler content; Figure 4 The thermal conductivity of the mixed explosive varies with the cobalt nanoparticle content in the filler when the total filler content is 1 wt%. Figure 5 The Brazilian stress-strain curves of mixed explosives with different carbon nanofillers added at the same filler content (0.5 wt%) in Example 1 of the present invention. Detailed Implementation

[0022] The specific embodiments listed in this invention are merely examples, and the invention is not limited to the specific embodiments described below. For those skilled in the art, any equivalent modifications and substitutions to the embodiments described below are also within the scope of this invention. Therefore, all equivalent transformations and modifications made without departing from the spirit and scope of this invention should be covered within its scope. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. All reagents or instruments whose manufacturers are not specified are commercially available conventional products. To better illustrate this invention, numerous specific details are provided in the following detailed embodiments. Those skilled in the art should understand that this invention can be practiced even without certain specific details. In other embodiments, methods, means, equipment, and steps well known to those skilled in the art are not described in detail in order to highlight the main points of this invention.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art. Unless otherwise specified, all units used in this specification are International Standard Units (SI), and all numerical values ​​and ranges appearing in this invention should be understood to include systematic errors unavoidable in industrial production.

[0024] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0025] Example 1 Reference Figure 1 The illustrated flowchart illustrates the preparation of a graphene nanosheet / carbon nanotube heterostructure: Step (1): First, disperse 0.3g graphene nanosheets, 0.029g cobalt nitrate hexahydrate, and 1mg cetyltrimethylammonium bromide in 100ml deionized water, sonicate (90Hz) for 1 h, and let stand for 0.5 h to allow the Co to settle. 2+ Selective adsorption of ZIF-67 was achieved at defect sites on graphene nanosheets. Subsequently, 0.451 g of 2-methylimidazole was dissolved in 50 mL of deionized water and added to the mixture. After stirring thoroughly at room temperature, the mixture was transferred to a polytetrafluoroethylene-lined hydrothermal reactor and reacted at 90°C for 4 h. After the reaction was completed, the product was washed alternately with ethanol and deionized water until the filtrate was clear. Finally, ZIF-67-loaded graphene nanosheets were obtained by freeze-drying at -60°C for 72 h.

[0026] Step (2): Place the ZIF-67-loaded graphene nanosheets in a tubular furnace quartz boat, and introduce an argon / hydrogen mixture (argon flow rate of 90 sccm, hydrogen flow rate of 10 sccm) at 10°C for 1 min. -1The heating rate was increased to 900°C, and the catalyst reduction was completed after holding at this temperature for 1 hour, yielding graphene nanosheets loaded with cobalt nanoparticles. Subsequently, an argon / methane mixture (argon flow rate of 80 sccm, methane flow rate of 20 sccm) was switched, and carbon nanotubes were grown at 900°C for 0.5 hours. After the reaction was completed, the furnace was cooled to room temperature to obtain a graphene nanosheet / carbon nanotube heterostructure material. The scanning electron microscope image of the prepared graphene nanosheet / carbon nanotube heterostructure material is shown below. Figure 2 As shown, from Figure 2 It is evident that carbon nanotubes grow at the vacancies or defects of graphene nanosheets, which specifically overcomes the edge thermal conductivity defects of graphene nanosheets and significantly improves the thermal conductivity.

[0027] Step (3): Weigh 0.25g of the filler prepared in step (2) and add it to a polymer solution containing 2.25g of polyurethane. Disperse the solution using ultrasound at 100kHz for 10 minutes to obtain a binder solution containing the filler for use. Weigh 47.5g of TATB explosive and add 50g of water. Stir and disperse to form an explosive suspension. Heat to 60℃ and start adding the binder solution containing the filler. At the same time, apply vacuum to remove the organic solvent. After the solvent evaporates, obtain the explosive molding powder. After filtration, washing with water, drying, and pressing into explosive columns, a mixed explosive with synergistically improved mechanical and thermal conductivity properties can be obtained. Through mechanical and thermal conductivity tests, the results show that compared with the pure mixed explosive, the tensile fracture strength and strain of the mixed explosive obtained in this embodiment are increased by 35% and 40%, respectively, and the thermal conductivity is increased by 43%.

[0028] Example 2 Reference Figure 1 The illustrated flowchart illustrates the preparation of a graphene nanosheet / carbon nanotube heterostructure: Step (1): First, disperse 0.6g graphene nanosheets, 0.19g cobalt chloride hexahydrate, and 2mg cetyltrimethylammonium bromide in 200ml deionized water, sonicate for 1 h, and let stand for 0.5 h to allow the Co to settle. 2+ Selective adsorption was performed at defect sites on graphene nanosheets. Subsequently, 3.612 g of 2-methylimidazole was dissolved in 50 mL of deionized water and added to the above mixture. After stirring evenly at room temperature, the mixture was transferred to a polytetrafluoroethylene-lined hydrothermal reactor and reacted at 90°C for 4 h. After the reaction was completed, the product was washed alternately with ethanol and deionized water until the filtrate was clear. Finally, the ZIF-67-loaded graphene nanosheets were obtained by freeze-drying for 72 h.

[0029] Step (2): Place the ZIF-67-loaded graphene nanosheets in a tubular furnace quartz boat, and introduce a nitrogen / hydrogen mixture (nitrogen flow rate of 80 sccm, hydrogen flow rate of 20 sccm) at 10°C for 1 min. -1The temperature was increased to 800°C and held for 1 hour to complete catalyst reduction, yielding graphene nanosheets loaded with cobalt nanoparticles. Subsequently, a nitrogen / ethylene mixed gas was switched (nitrogen flow rate 90 sccm, ethylene flow rate 10 sccm), and carbon nanotubes were grown at 800°C for 1 hour. After the reaction, the furnace was cooled to room temperature to obtain a graphene nanosheet / carbon nanotube heterostructure material.

[0030] Step (3): Weigh 0.5g of the filler prepared in step (2) and add it to a polymer solution containing 2g of fluororubber. Disperse the solution using ultrasound at 100kHz for 10 minutes to obtain a binder solution containing the filler for use. Weigh 47.5g of HMX explosive and add 50g of water. Stir and disperse to form an explosive suspension. Heat to 60℃ and start adding the binder solution containing the filler. At the same time, apply vacuum to remove the organic solvent. After the solvent evaporates, obtain the explosive molding powder. After filtration, washing with water, drying, and pressing into explosive columns, a mixed explosive with synergistically improved mechanical and thermal conductivity properties can be obtained. Through mechanical and thermal conductivity tests, the results show that compared with the pure mixed explosive, the tensile fracture strength and strain of the mixed explosive obtained in this embodiment are increased by 28% and 30%, respectively, and the thermal conductivity is increased by 72%.

[0031] Example 3 Reference Figure 1 The illustrated flowchart illustrates the preparation of a graphene nanosheet / carbon nanotube heterostructure: Step (1): First, disperse 0.6g of graphene nanosheets, 0.34g of cobalt sulfate heptahydrate, and 2mg of hexadecyltrimethylammonium bromide in 200ml of deionized water, sonicate for 1 h, and let stand for 0.5 h to allow the Co to settle. 2+ Selective adsorption was achieved at defect sites on graphene nanosheets. Subsequently, 5.418 g of 2-methylimidazole was dissolved in 50 mL of deionized water and added to the above mixture. After stirring evenly at room temperature, the mixture was transferred to a polytetrafluoroethylene-lined hydrothermal reactor and reacted at 90°C for 4 h. After the reaction was completed, the product was washed alternately with ethanol and deionized water until the filtrate was clear. Finally, the ZIF-67-loaded graphene nanosheets were obtained by freeze-drying for 72 h.

[0032] Step (2): Place the ZIF-67-loaded graphene nanosheets in a tubular furnace quartz boat, and introduce a helium / hydrogen mixture (helium flow rate of 70 sccm, hydrogen flow rate of 30 sccm) at 10°C for 1 min. -1The heating rate was increased to 750°C, and the catalyst reduction was completed after holding at this temperature for 1 hour, yielding graphene nanosheets loaded with cobalt nanoparticles. Subsequently, a helium / acetylene mixture (helium flow rate of 80 sccm, acetylene flow rate of 20 sccm) was switched to grow carbon nanotubes at 750°C for 1.5 hours. After the reaction was completed, the furnace was cooled to room temperature to obtain a graphene nanosheet / carbon nanotube heterojunction material.

[0033] Step (3): Weigh 0.75g of the filler prepared in step (2) and add it to a polymer solution containing 1.75g ​​of vinyl acetate cellulose. Disperse the solution using ultrasound at 100kHz for 10 minutes to obtain a binder solution containing the filler for use. Weigh 47.5g of CL-20 explosive and add 50g of water. Stir and disperse to form an explosive suspension. Heat the solution to 60℃ and begin adding the binder solution containing the filler. Simultaneously, apply vacuum to remove the organic solvent. After the solvent evaporates, obtain the explosive molding powder. Filter, wash with water, dry, and press into explosive columns to obtain a mixed explosive with synergistically improved mechanical and thermal conductivity properties. Through mechanical and thermal conductivity tests, the results show that compared with the pure mixed explosive, the tensile fracture strength and strain of the mixed explosive obtained in this embodiment are increased by 27% and 24%, respectively, and the thermal conductivity is increased by 93%.

[0034] Example 4 Reference Figure 1 The illustrated flowchart illustrates the preparation of a graphene nanosheet / carbon nanotube heterostructure: Step (1): First, disperse 0.3g of graphene nanosheets, 0.291g of cobalt nitrate hexahydrate, and 1mg of cetyltrimethylammonium bromide in 100ml of deionized water, sonicate for 1 h, and let stand for 0.5 h to allow the Co to settle. 2+ Selective adsorption was achieved at defect sites on graphene nanosheets. Subsequently, 4.516 g of 2-methylimidazole was dissolved in 50 mL of deionized water and added to the above mixture. After stirring evenly at room temperature, the mixture was transferred to a polytetrafluoroethylene-lined hydrothermal reactor and reacted at 90°C for 4 h. After the reaction was completed, the product was washed alternately with ethanol and deionized water until the filtrate was clear. Finally, the ZIF-67-loaded graphene nanosheets were obtained by freeze-drying for 72 h.

[0035] Step (2): Place the ZIF-67-loaded graphene nanosheets in a tubular furnace quartz boat, and introduce a nitrogen / hydrogen mixture (nitrogen flow rate 60 sccm, hydrogen flow rate 40 sccm), at 10°C min. -1The temperature was increased to 650°C and held for 1 hour to complete catalyst reduction, yielding graphene nanosheets loaded with cobalt nanoparticles. Subsequently, a nitrogen / ethanol vapor mixture was switched (nitrogen flow rate 70 sccm, ethanol vapor flow rate 30 sccm), and carbon nanotubes were grown at 650°C for 2 hours. After the reaction, the furnace was cooled to room temperature to obtain a graphene nanosheet / carbon nanotube heterostructure material.

[0036] Step (3): Weigh 2g of the filler prepared in step (2) and add it to a polymer solution containing 3g of fluororubber. Disperse the solution using ultrasound at a frequency of 100kHz for 10 minutes to obtain a binder solution containing the filler for use. Weigh 95g of LLM-105 explosive and add 100g of water. Stir and disperse to form an explosive suspension. Heat to 60℃ and start adding the binder solution containing the filler. At the same time, apply vacuum to remove the organic solvent. After the solvent evaporates, obtain the explosive molding powder. After filtration, water washing, drying, and pressing into explosive columns, a mixed explosive with synergistically improved mechanical and thermal conductivity properties can be obtained. Through mechanical and thermal conductivity tests, the results show that compared with the pure mixed explosive, the tensile fracture strength and strain of the mixed explosive obtained in this embodiment are increased by 22% and 18%, respectively, and the thermal conductivity is increased by 125%.

[0037] Example 5 Reference Figure 1 The illustrated flowchart illustrates the preparation of a graphene nanosheet / carbon nanotube heterostructure: Step (1): First, disperse 0.9g of graphene nanosheets, 0.547g of cobalt chloride hexahydrate, and 3mg of cetyltrimethylammonium bromide in 300ml of deionized water, sonicate for 1 h, and let stand for 0.5 h to allow the Co to settle. 2+ Selective adsorption was achieved at defect sites on graphene nanosheets. Subsequently, 10.385 g of 2-methylimidazole was dissolved in 50 mL of deionized water and added to the above mixture. After stirring evenly at room temperature, the mixture was transferred to a polytetrafluoroethylene-lined hydrothermal reactor and reacted at 90°C for 4 h. After the reaction was completed, the product was washed alternately with ethanol and deionized water until the filtrate was clear. Finally, the ZIF-67-loaded graphene nanosheets were obtained by freeze-drying for 72 h.

[0038] Step (2): Place the ZIF-67-loaded graphene nanosheets in a tubular furnace quartz boat, and introduce an argon / hydrogen mixture (argon flow rate of 70 sccm, hydrogen flow rate of 30 sccm) at 10°C for 1 min. -1The temperature was increased to 800°C and held for 1 hour to complete catalyst reduction, yielding graphene nanosheets loaded with cobalt nanoparticles. Subsequently, an argon / ethylene mixture (argon flow rate of 80 sccm and ethylene flow rate of 20 sccm) was used to grow carbon nanotubes at 800°C for 0.5 hours. After the reaction, the furnace was cooled to room temperature to obtain a graphene nanosheet / carbon nanotube heterostructure material.

[0039] Step (3): Weigh 1g of the filler prepared in step (2) and add it to a polymer solution containing 4g of polyurethane. Disperse the solution using ultrasound at 100kHz for 10 minutes to obtain a binder solution containing the filler for use. Weigh 95g of RDX explosive and add 100g of water. Stir and disperse to form an explosive suspension. Heat to 60℃ and start adding the binder solution containing the filler. At the same time, apply vacuum to remove the organic solvent. After the solvent evaporates, obtain the explosive molding powder. After filtration, washing with water, drying, and pressing into explosive columns, a mixed explosive with synergistically improved mechanical and thermal conductivity properties can be obtained. Through mechanical and thermal conductivity tests, the results show that compared with the pure mixed explosive, the tensile fracture strength and strain of the mixed explosive obtained in this embodiment are increased by 24% and 33%, respectively, and the thermal conductivity is increased by 96%.

[0040] Example 6 Reference Figure 1 The illustrated flowchart illustrates the preparation of a graphene nanosheet / carbon nanotube heterostructure: Step (1): First, disperse 0.3g of graphene nanosheets, 0.14g of cobalt sulfate heptahydrate, and 1mg of hexadecyltrimethylammonium bromide in 100ml of deionized water, sonicate for 1 h, and let stand for 0.5 h to allow the Co to settle. 2+ Selective adsorption was achieved at defect sites on graphene nanosheets. Subsequently, 2.257 g of 2-methylimidazole was dissolved in 50 mL of deionized water and added to the above mixture. After stirring evenly at room temperature, the mixture was transferred to a polytetrafluoroethylene-lined hydrothermal reactor and reacted at 90°C for 4 h. After the reaction was completed, the product was washed alternately with ethanol and deionized water until the filtrate was clear. Finally, the ZIF-67-loaded graphene nanosheets were obtained by freeze-drying for 72 h.

[0041] Step (2): Place the ZIF-67-loaded graphene nanosheets in a tubular furnace quartz boat, and introduce a helium / hydrogen mixture (helium flow rate of 80 sccm, hydrogen flow rate of 20 sccm) at 10°C for 1 min. -1The temperature was increased to 900°C and held for 1 hour to complete catalyst reduction, yielding graphene nanosheets loaded with cobalt nanoparticles. Subsequently, a helium / methane mixture (helium flow rate of 60 sccm, methane flow rate of 40 sccm) was used to grow carbon nanotubes at 900°C for 1 hour. After the reaction, the furnace was cooled to room temperature to obtain a graphene nanosheet / carbon nanotube heterostructure material.

[0042] Step (3): Weigh 0.5g of the filler prepared in step (2) and add it to a polymer solution containing 4.5g of polyurethane. Disperse the solution using ultrasound at 100kHz for 10 minutes to obtain a binder solution containing the filler for use. Weigh 95g of FOX-7 explosive and add 100g of water. Stir and disperse to form an explosive suspension. Heat to 60℃ and start adding the binder solution containing the filler. At the same time, apply vacuum to remove the organic solvent. After the solvent evaporates, obtain the explosive molding powder. After filtration, washing with water, drying, and pressing into explosive columns, a mixed explosive with synergistically improved mechanical and thermal conductivity properties can be obtained. Through mechanical and thermal conductivity tests, the results show that compared with the pure mixed explosive, the tensile fracture strength and strain of the mixed explosive obtained in this embodiment are increased by 38% and 40%, respectively, and the thermal conductivity is increased by 52%.

[0043] Example 7: Differences in the Influence of Different Carbon Nanoparticle Fillers on the Performance of Hybrid Explosives Reference Figure 1 The illustrated flowchart illustrates the preparation of a graphene nanosheet / carbon nanotube heterostructure: like Figure 3 The figure shows the effects of adding carbon nanotube filler, adding graphene nanosheet filler, adding a physical mixture of graphene nanosheets and carbon nanotubes filler, and adding a graphene nanosheet / carbon nanotube heterojunction material on the thermal conductivity of the mixed explosive at different filler contents (0 wt%, 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%). Figure 3 As can be seen, the thermal conductivity of the mixed explosive with graphene nanosheets / carbon nanotube heterojunction fillers was significantly improved compared to other fillers at different filler contents. The explosive used was 1,3,5-triamino-2,4,6-trinitrobenzene (content 95 wt%), and the polymer binder used was fluororubber (content 5 wt%, 4.5 wt%, 4 wt%, 3.5 wt%, 3 wt%).

[0044] like Figure 4 The figure shows the change in thermal conductivity of the mixed explosive as a function of the cobalt nanoparticle content in the filler when the total filler content (referring to the heterostructure prepared by the method of this application, which contains a small amount of cobalt nanoparticles) is 1 wt%. Figure 4It is evident that an excessive amount of cobalt nanoparticles can negatively impact the thermal conductivity enhancement efficiency of the filler. Furthermore, the uncontrollability of conventional random, non-selective loading of fillers can lead to excessive loading and aggregation of cobalt nanoparticles, thus affecting the thermal conductivity and mechanical properties of the prepared filler for explosives.

[0045] like Figure 5 The figures show the effects of adding carbon nanotubes, graphene nanosheets, a physical mixture of graphene nanosheets and carbon nanotubes, and a graphene nanosheet / carbon nanotube heterojunction material on the mechanical properties of the mixed explosive at the same filler content (0.5 wt%). Figure 5 As can be seen, the Brazilian tensile strength and strain of the mixed explosive with graphene nanosheets / carbon nanotube heterojunction fillers are higher than those of other fillers; in particular, its Brazilian tensile fracture strength is consistently higher than that of the physical mixture of graphene nanosheets and carbon nanotubes. The explosive used is 1,3,5-triamino-2,4,6-trinitrobenzene (content 95 wt%), and the polymer binder used is fluororubber (content 4.5 wt%).

[0046] The embodiments described above merely illustrate specific implementation methods of this application, and while the descriptions are detailed and specific, they should not be construed as limiting the scope of protection of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the technical solution of this application, and these modifications and improvements all fall within the scope of protection of this application.

Claims

1. A graphene nanosheet / carbon nanotube heterostructure, characterized in that, Using graphene nanosheets as a substrate, carbon nanotubes are present at their surface defects or edges, and the carbon nanotubes between the graphene nanosheets are seamlessly connected by covalent bonding.

2. The method for preparing a graphene nanosheet / carbon nanotube heterostructure as described in claim 1, characterized in that, The specific steps include the following: Step (1): A certain mass of graphene nanosheets, water-soluble cobalt salt, and hexadecyltrimethylammonium bromide are dispersed in deionized water and mixed evenly. After standing, the Co... 2+ Selective adsorption at defect sites on graphene nanosheets, followed by cleaning to remove free Co. 2+ Then, an excess of 2-methylimidazole solution was added, and after stirring evenly, a hydrothermal reaction was carried out to obtain graphene nanosheets loaded with ZIF-67 at the defect sites. Step (2): Place the graphene nanosheets loaded with ZIF-67 in a tube furnace and heat them in an inert gas / hydrogen atmosphere to reduce ZIF-67 at high temperature to obtain graphene nanosheets loaded with cobalt nanoparticles at the defect sites; then switch the gas to an inert gas / carbon source gas to catalyze the growth of carbon nanotubes at the defect sites to obtain a covalently bonded graphene nanosheet / carbon nanotube heterostructure.

3. The method for preparing a graphene nanosheet / carbon nanotube heterostructure according to claim 2, characterized in that, In step (1), the mass ratio of graphene nanosheets to water-soluble cobalt salt is 1:(0.1-1), and the mass ratio of hexadecyltrimethylammonium bromide to graphene nanosheets is 1:100-300.

4. The method for preparing a graphene nanosheet / carbon nanotube heterostructure according to claim 2, characterized in that, In step (1), an excess of 2-methylimidazole solution is added, and the molar ratio of 2-methylimidazole to water-soluble cobalt salt is 55:

1.

5. The method for preparing a graphene nanosheet / carbon nanotube heterostructure according to claim 2, characterized in that, In step (1), the temperature of the hydrothermal reaction is 80-100℃ and the reaction time is 3-5h.

6. The method for preparing a graphene nanosheet / carbon nanotube heterostructure according to claim 2, characterized in that, In step (1), the water-soluble cobalt salt is at least one of cobalt nitrate hexahydrate, cobalt sulfate heptahydrate, and cobalt chloride hexahydrate.

7. The method for preparing a graphene nanosheet / carbon nanotube heterostructure according to claim 2, characterized in that, The inert carrier gas mentioned in step (2) is at least one of argon, nitrogen or helium, and the carbon source gas is at least one of methane, acetylene, ethylene or ethanol vapor.

8. The method for preparing a graphene nanosheet / carbon nanotube heterostructure according to claim 2, characterized in that, In step (2), the inert gas flow rate during the high-temperature growth of carbon nanotubes is 60-90 sccm, the carbon source gas flow rate is 10-40 sccm, and the high-temperature growth time is 0.5-2 h.

9. The application of the graphene nanosheet / carbon nanotube heterostructure prepared by the method of any one of claims 2-8 as a thermally conductive filler in the preparation of mixed explosives.

10. A method for synergistically improving the mechanical and thermal conductivity properties of a mixed explosive, characterized in that, Includes the following steps: Step (1): Take the graphene nanosheet / carbon nanotube heterostructure as described in claim 1 or prepare a covalently bonded graphene nanosheet / carbon nanotube heterostructure material according to the preparation method of the graphene nanosheet / carbon nanotube heterostructure as described in any one of claims 2-8. Step (2): Disperse the graphene nanosheets / carbon nanotubes material and the polymer binder solution to mix them evenly; The mass percentage of the graphene nanosheet / carbon nanotube heteromaterial is 0.5wt%~2wt%; the mass percentage of the polymer binder is 3wt%~4.5wt%. Step (3): Add the mixture obtained in step (2) to explosives with a mass percentage of 95 wt%, obtain explosive molding powder by water suspension method, filter, wash, dry, and press into explosive columns to obtain mixed explosive parts with synergistic improvement in mechanical and thermal conductivity.

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