A CF-Si3N4@CNTs / EP thermally conductive composite material and its preparation method

Abstract

This invention discloses a CF-Si3N4@CNTs / EP thermally conductive composite material and its preparation method. Using cotton fibers as a skeleton, silicon nitride and cobalt nitrate hexahydrate are loaded onto the surface of the cotton fibers through ultrasonic impregnation. Under high-temperature conditions, carbon-containing gas generated from urea pyrolysis is used to reduce cobalt ions to metallic cobalt, which then serves as a catalytic site for the high-temperature pyrolysis growth of carbon nanotubes. The cotton fibers are then carbonized to obtain the CF-Si3N4@CNTs composite skeleton. This composite skeleton is then vacuum impregnated and cured with epoxy resin to obtain the CF-Si3N4@CNTs / EP thermally conductive composite material. This invention effectively reduces the interfacial contact thermal resistance between the filler, fiber skeleton, and matrix by constructing a multi-level continuous thermally conductive network, significantly improving the thermal conductivity of the composite material. The process is simple, environmentally friendly, and has good application prospects.

Description

Technical Field

[0001] This invention belongs to the field of thermally conductive polymer composite materials technology, specifically relating to a CF-Si3N4@CNTs / EP thermally conductive composite material and its preparation method. Background Technology

[0002] With the continuous increase in power density and integration of electronic devices, small electronic devices are prone to heat accumulation during operation. Long-term heat accumulation significantly shortens the lifespan of electronic devices, making efficient thermal management technology a critical issue that urgently needs to be addressed in the field of electronic devices. Polymer composite materials, with their excellent comprehensive properties, have broad application prospects in thermal management fields such as thermal interface materials and heat dissipation elements. Among them, epoxy resin, due to its advantages of being lightweight, corrosion-resistant, and easy to process, has become the preferred matrix material in this field. However, the inherent low thermal conductivity of epoxy resin makes it difficult to directly apply to scenarios with high heat transfer efficiency requirements, such as heat sinks. Therefore, it is usually necessary to add high thermal conductivity fillers to the epoxy resin matrix to improve the overall thermal conductivity of the composite material.

[0003] Currently, silicon nitride (Si3N4) and carbon nanotubes (CNTs) are the most widely used high thermal conductivity fillers in thermally conductive polymer composites: silicon nitride possesses high thermal conductivity, low coefficient of thermal expansion, high melting point, excellent mechanical properties, and good chemical stability; carbon nanotubes, on the other hand, combine ultra-high thermal conductivity and electrical conductivity, and are also relatively inexpensive and easy to process. However, both have significant shortcomings when used alone: ​​silicon nitride powder is prone to agglomeration, making it difficult to construct long-range ordered heat transfer paths in the matrix; and significant interfacial thermal resistance exists between carbon nanotubes, which severely restricts further improvement in the thermal conductivity of composite materials and fails to meet the thermal management requirements of high-end electronic devices.

[0004] Therefore, developing a preparation technology that can solve the above-mentioned defects in filler application and significantly improve the thermal conductivity of epoxy resin-based composite materials has important practical application value and research significance. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a CF-Si3N4@CNTs / EP thermally conductive composite material and its preparation method. This invention uses cotton fibers as a skeleton, loads silicon nitride on its surface, and catalytically grows carbon nanotubes through high-temperature pyrolysis. The fiber skeleton is then subjected to high-temperature carbonization treatment to obtain the CF-Si3N4@CNTs composite skeleton. This constructs a continuous, low-interfacial-thermal-resistance thermally conductive pathway within the epoxy resin matrix, significantly improving the thermal conductivity of the composite material and solving problems such as filler agglomeration, discontinuous thermally conductive pathways, and high interfacial thermal resistance in the prior art.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a CF-Si3N4@CNTs / EP thermally conductive composite material is characterized by: using cotton fibers as a skeleton, ultrasonically impregnating and loading silicon nitride (Si3N4) and cobalt nitrate hexahydrate (Co(NO3)2·6H2O) onto the surface of the cotton fibers; placing the treated cotton fibers in a tube furnace, using urea as a carbon source, and utilizing the carbon-containing gas generated by urea pyrolysis at high temperature to reduce cobalt ions to metallic cobalt, which then serves as a catalytic site for growing carbon nanotubes (CNTs); subsequently carbonizing the cotton fibers to obtain the CF-Si3N4@CNTs composite skeleton; and then vacuum impregnating and curing the CF-Si3N4@CNTs composite skeleton with epoxy resin EP to obtain the CF-Si3N4@CNTs / EP thermally conductive composite material. Specifically, the method includes the following steps: Step 1: Preparation of CF-Si3N4@Co Add 0.8-1 g of silicon nitride to 30-40 mL of deionized water and ultrasonically disperse to obtain a suspension. Add 0.5-0.6 g of cobalt nitrate hexahydrate to the suspension and ultrasonically treat for 20-30 min at 25-35 °C to obtain a mixture. Immerse cotton cloth in the mixture and ultrasonically treat to promote the penetration of Si3N4 powder and cobalt ions into the fiber pores of the cotton cloth. Remove the cotton cloth, dry it in an oven at 80-100 °C, then roll it into a cylinder and place it in a mold to shape it, thus obtaining cotton cloth with silicon nitride and cobalt nitrate adhering to its surface, denoted as CF-Si3N4@Co. Step 2: Preparation of CF-Si3N4@CNTs The CF-Si3N4@Co obtained in step 1 was placed in a tube furnace, and urea was placed at the front end of the furnace. The furnace was then heat-treated at 850~950 °C for 2~3 h under an Ar atmosphere to pyrolyze the urea into C2N2. + C3N2 + and C3N3 + Reducing gas, the reducing gas containing Co 2+ The fiber was reduced to metallic cobalt and CNTs were generated using metallic cobalt as a catalytic site. Then, the temperature was raised to 1050~1150 ℃ to carbonize the cotton fiber, resulting in a CF-Si3N4@CNTs composite framework. Step 3: Preparation of CF-Si3N4@CNTs / EP Weigh methyl hexahydrophthalic anhydride (MeHHPA, curing agent), epoxy resin EP (862), and 2,4,6-tris(dimethylaminomethyl)phenol (TAP, catalyst) in a mass ratio of 1:1:0.05, mix and stir until all components are fully miscible to form a homogeneous and transparent resin system; add the CF-Si3N4@CNTs composite skeleton obtained in step 2 into the resin system, impregnate in a vacuum environment for 1-2 h, and then place it in an oven at 90-120 ℃ for 4-6 h to obtain the CF-Si3N4@CNTs / EP thermally conductive composite material.

[0007] Preferably, in step 3, the CF-Si3N4@CNTs composite skeleton is used as a filler, and its mass fraction in the thermally conductive composite material is 16~20 wt%.

[0008] The beneficial effects of this invention are reflected in: This invention employs a green preparation strategy using cotton fabric templates, employing natural cotton fibers as a three-dimensional continuous thermally conductive framework. Silicon nitride is loaded onto the fiber surface and carbon nanotubes are grown through high-temperature pyrolysis. This achieves a synergistic effect across multiple components: First, carbon nanotubes effectively suppress the aggregation of silicon nitride particles, ensuring uniform dispersion of silicon nitride on the fiber surface and laying the foundation for constructing a continuous thermally conductive pathway. Second, carbon nanotubes act as interfacial bridges between silicon nitride and cotton fibers, and between cotton fibers and the epoxy resin matrix, significantly reducing interfacial thermal resistance between components and minimizing heat loss during transfer. Third, high-temperature carbonization further enhances the thermal conductivity of the cotton fiber framework, forming a multi-level continuous thermally conductive network of "fiber framework-silicon nitride-carbon nanotubes." The synergistic effect of these three components significantly improves the thermal conductivity of the composite material, solving the problems of poor thermal conductivity caused by the agglomeration of single fillers, discontinuous thermal pathways, and high interfacial thermal resistance in existing technologies. Meanwhile, the use of cotton fabric templates has the advantages of being green and environmentally friendly, and low in cost. The preparation process is simple and controllable, and it is easy to promote industrialization. Attached Figure Description

[0009] Figure 1 This is a SEM image of Si3N4 in Embodiment 1 of the present invention; Figure 2 This is a SEM image of the CF used in Embodiment 1 of the present invention; Figure 3 This is a SEM image of CF-Si3N4@CNTs obtained in Example 1 of the present invention; Figure 4 This is a cross-sectional SEM image of CF-Si3N4@CNTs / EP obtained in Example 1 of the present invention; Figure 5 This is a comparison chart of the thermal conductivity coefficients of the samples obtained in Examples 1 and 2 and Comparative Examples 1 and 2 of the present invention. Detailed Implementation

[0010] The embodiments of the present invention are described in detail below. These embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiments.

[0011] Example 1 In this embodiment, the CF-Si3N4@CNTs / EP thermally conductive composite material was prepared according to the following steps: Step 1: Preparation of CF-Si3N4@Co 0.8 g of silicon nitride was added to 30 mL of deionized water and ultrasonically dispersed to obtain a suspension. 0.5 g of cobalt nitrate hexahydrate was added to the suspension and ultrasonically treated at 25 °C for 30 min to obtain a mixture. A clean strip of cotton cloth measuring 1.5 cm × 150 cm was cut, immersed in the mixture, and ultrasonically treated to promote the penetration of Si3N4 powder and cobalt ions into the pores of the cotton cloth fibers. The cotton cloth was removed, dried in an oven at 80 °C, and then rolled into a cylinder (base dimensions 20 × 20 mm, height 15 mm). The cylinder was then placed in a mold at room temperature for 24 h to set, resulting in a cotton cloth with silicon nitride and cobalt nitrate adhering to its surface, denoted as CF-Si3N4@Co.

[0012] Step 2: Preparation of CF-Si3N4@CNTs The CF-Si3N4@Co obtained in step 1 was placed in a tube furnace, and 5 g of urea was placed in the boat at the front end of the furnace. Under an argon atmosphere, the temperature was increased to 850 °C at a heating rate of 5 °C / min and held for 2 h to allow the urea to pyrolyze into C2N2. + C3N2 + and C3N3 + Reducing gases, these reducing gases will reduce Co 2+ The material is reduced to metallic cobalt and CNTs are generated using metallic cobalt as a catalytic site. Subsequently, the temperature is raised to 1050 °C to carbonize the cotton fiber skeleton, resulting in a CF-Si3N4@CNTs composite skeleton.

[0013] Step 3: Preparation of CF-Si3N4@CNTs / EP Methylhexahydrophthalic anhydride, epoxy resin EP (862), and 2,4,6-tris(dimethylaminomethyl)phenol were weighed out in a mass ratio of 1:1:0.05 and mixed until all components were fully miscible to form a homogeneous and transparent resin system. 1.28 g of the CF-Si3N4@CNTs composite skeleton obtained in step 2 was added to 20.5 g of the resin system and impregnated under vacuum for 1 h, followed by curing in a 90 ℃ oven for 4 h to obtain the CF-Si3N4@CNTs / EP thermally conductive composite material. After removing excess resin by sanding, the mass was 8 g. In this embodiment, CF-Si3N4@CNTs was used as a filler, with a mass fraction of 16 wt% in the composite material, which was designated as CF-Si3N4@CNTs-16 / EP.

[0014] Figure 1 The image shows the SEM image of the silicon nitride used in Example 1. It can be observed that the silicon nitride powder is well dispersed and there is no obvious agglomeration, which lays the foundation for the subsequent construction of an efficient heat-conducting network. Figure 2 The image shows a SEM image of the cotton fabric raw material used in Example 1. It can be seen that the raw cotton fabric fibers are arranged in a regular and complete manner, forming a continuous three-dimensional network skeleton, which can provide a stable pathway for subsequent heat transfer. Figure 3 The image shows the SEM image of the CF-Si3N4@CNTs composite skeleton obtained in Example 1. It can be clearly seen that the surface of the carbonized cotton fiber is uniformly covered by a dense nanoscale material with no obvious exposed areas. A large number of tubular structures (i.e., CNTs grown by high-temperature pyrolysis catalysis) are interwoven and distributed, and CNTs are also successfully grown on the surface of silicon nitride. These CNTs are uniformly dispersed on the surface of the cotton fiber, forming a multi-level continuous thermally conductive network of "fiber skeleton-Si3N4-CNTs". Figure 4 The image shows a cross-sectional SEM image of the CF-Si3N4@CNTs / EP composite material obtained in Example 1. It can be seen that the composite material has a distinct vertical orientation structure. This orientation structure can reduce path loss during heat transfer and is beneficial to significantly improve the out-of-plane thermal conductivity of the composite material.

[0015] Example 2 This embodiment prepares the CF-Si3N4@CNTs / EP thermally conductive composite material using the same method as in Example 1, except that in step 1, the mass of silicon nitride is increased to 1 g. In step 3, 1.53 g of the CF-Si3N4@CNTs obtained in step 2 is added to a 20.5 g resin system. After curing, the excess resin on the surface is removed by polishing, resulting in a mass of 7.65 g. The mass fraction of CF-Si3N4@CNTs in the resulting composite material is 20 wt%, and this composite material is designated as CF-Si3N4@CNTs-20 / EP.

[0016] Comparative Example 1 In this comparative example, CF-Si3N4 / EP composite materials were prepared according to the following steps: Step 1: Add 0.8 g of silicon nitride to 30 mL of deionized water and ultrasonically disperse it evenly to obtain a suspension; cut a clean strip of cotton cloth measuring 1.5 cm × 150 cm, immerse it in the above suspension, and ultrasonically treat it to promote the penetration of Si3N4 powder in the mixture into the pores of the cotton cloth fibers; take out the cotton cloth, dry it in an oven at 80 ℃, roll it into a cylinder, and place it in a mold to set for 24 h to obtain cotton cloth with silicon nitride attached to the surface.

[0017] Step 2: Place the cotton obtained in Step 1 in a tube furnace and heat it to 850 ℃ at a heating rate of 5 ℃ / min under an argon atmosphere. Hold it at this temperature for 2 h for high-temperature heat treatment. Then heat it to 1050 ℃ to carbonize the cotton fiber skeleton to obtain CF-Si3N4.

[0018] Step 3: Weigh out methylhexahydrophthalic anhydride, epoxy resin, and 2,4,6-tris(dimethylaminomethyl)phenol in a mass ratio of 1:1:0.05, and mix and stir until all components are fully miscible to form a homogeneous and transparent resin system. Add 1.04 g of CF-Si3N4 obtained in Step 2 to 20.5 g of the resin system, impregnate under vacuum for 1 h, and then cure in a 90 ℃ oven for 4 h. After curing, polish to remove excess resin from the surface, yielding 8 g of the CF-Si3N4 / EP thermally conductive composite material. In this embodiment, CF-Si3N4 is used as a filler, with a mass fraction of 13 wt% in the composite material.

[0019] Comparative Example 2 In this comparative example, CF@CNTs / EP composite materials were prepared according to the following steps: Step 1: Preparation of CF@Co 0.5 g of cobalt nitrate hexahydrate was added to 30 mL of deionized water and ultrasonically dispersed to obtain a suspension. A clean strip of cotton cloth measuring 1.5 cm × 150 cm was cut and immersed in the above suspension mixture. The cloth was ultrasonically treated to promote the penetration of cobalt ions in the mixture into the pores of the cotton cloth fibers. The cotton cloth was removed, dried in an oven at 80 ℃, rolled into a cylinder, and placed in a mold for 24 h to set. The resulting cotton cloth with cobalt nitrate adhering to its surface was denoted as CF@Co.

[0020] Step 2, Preparation of CF@CNTs The CF@Co obtained in step 1 was placed in a tube furnace, and 5 g of urea was placed in the boat at the front end of the furnace. Under an argon atmosphere, the temperature was increased to 850 °C at a heating rate of 5 °C / min and held for 2 h for high-temperature heat treatment, so that the urea was pyrolyzed into C2N2. + C3N2 + and C3N3+ Reducing gases, these reducing gases will reduce Co 2+ The material is reduced to metallic cobalt and CNTs are generated using metallic cobalt as a catalytic site. Subsequently, the temperature is raised to 1050 °C to carbonize the cotton fiber skeleton, yielding CF@CNTs.

[0021] Step 3: Preparation of CF@CNTs / EP Methylhexahydrophthalic anhydride, epoxy resin, and 2,4,6-tris(dimethylaminomethyl)phenol were weighed out in a mass ratio of 1:1:0.05 and mixed until all components were fully miscible to form a homogeneous and transparent resin system. 0.24 g of the CF@CNTs obtained in step 2 was added to 20.5 g of the resin system, and the mixture was impregnated under vacuum for 1 h. Then, it was cured in a 90 ℃ oven for 4 h. After curing, the excess resin on the surface was removed by sanding, yielding 8 g of the resulting CF@CNTs / EP thermally conductive composite material. In this embodiment, CF-CNTs were used as a filler, with a mass fraction of 3 wt% in the composite material.

[0022] Comparative Example 3 This comparative example prepared pure EP samples according to the following steps: Methylhexahydrophthalic anhydride, epoxy resin, and 2,4,6-tris(dimethylaminomethyl)phenol were weighed out in a mass ratio of 1:1:0.05, mixed and stirred until all components were fully miscible to form a homogeneous and transparent resin system. The mixture was allowed to stand in a vacuum environment for 1 h, and then placed in a 90 ℃ oven for 4 h to cure, thus obtaining the EP sample.

[0023] The thermal conductivity of the samples obtained in Examples 1 and 2 and Comparative Examples 1, 2 and 3 are shown in Table 1 and Table 2. Figure 5 As shown.

[0024] Table 1. Thermal conductivity coefficients of samples obtained from each embodiment and comparative example

[0025] From Table 1 and Figure 5 It can be seen that the thermal conductivity of samples in Examples 1 and 2 is significantly improved compared with that of Comparative Examples 1 and 2. The comparison shows that the composite sample loaded with silicon nitride and CNTs grown by high-temperature pyrolysis exhibits far superior thermal conductivity compared to the comparative sample loaded with only a single filler. This is because a multi-level continuous thermally conductive network of "fiber skeleton-Si3N4-CNTs" is constructed, and the grown CNTs act as interfacial bridges between silicon nitride and fibers, and between fibers and the matrix, forming a three-dimensional interconnected structure. This effectively reduces interfacial contact thermal resistance, thereby significantly improving the thermal conductivity of the composite material.

[0026] The above are merely exemplary embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a CF-Si3N4@CNTs / EP thermally conductive composite material, characterized in that: Using cotton fibers as a skeleton, silicon nitride (Si3N4) and cobalt nitrate hexahydrate (Co(NO3)2·6H2O) were loaded onto the surface of the cotton fibers through ultrasonic impregnation. The treated cotton fibers were then placed in a tube furnace, and urea was used as a carbon source. Under high temperature conditions, the carbon-containing gas generated by the pyrolysis of urea was used to reduce cobalt ions to metallic cobalt, which served as catalytic sites for the growth of carbon nanotubes (CNTs). The cotton fibers were then carbonized to obtain a CF-Si3N4@CNTs composite skeleton. The CF-Si3N4@CNTs composite skeleton was then vacuum impregnated and cured with epoxy resin (EP) to obtain a CF-Si3N4@CNTs / EP thermally conductive composite material.

2. The preparation method according to claim 1, characterized in that, Includes the following steps: Step 1: Preparation of CF-Si3N4@Co 0.8-1 g of silicon nitride was added to 30-40 mL of deionized water and ultrasonically dispersed to obtain a suspension. 0.5-0.6 g of cobalt nitrate hexahydrate was added to the suspension and ultrasonically treated at 25-35 °C for 20-30 min to obtain a mixture. Cotton cloth was immersed in the mixture and ultrasonically treated to promote the penetration of Si3N4 powder and cobalt ions into the fiber pores of the cotton cloth. The cotton cloth was removed, dried in an oven at 80-100 °C, then rolled into a cylinder, placed in a mold for shaping, resulting in cotton cloth with a surface loaded with silicon nitride and cobalt nitrate, denoted as CF-Si3N4@Co. Step 2: Preparation of CF-Si3N4@CNTs The CF-Si3N4@Co obtained in step 1 was placed in a tube furnace, and urea was placed at the front end of the furnace. The furnace was then heat-treated at 850~950 °C for 2~3 h under an Ar atmosphere to pyrolyze the urea into C2N2. + C3N2 + and C3N3 + Reducing gas, the reducing gas containing Co 2+ The fiber is reduced to metallic cobalt and CNTs are generated using metallic cobalt as a catalytic site. Then, the temperature is raised to 1050~1150 ℃ to carbonize the cotton fiber to obtain the CF-Si3N4@CNTs composite framework. Step 3: Preparation of CF-Si3N4@CNTs / EP Weigh out the curing agent methylhexahydrophthalic anhydride MeHHPA, epoxy resin EP, and catalyst 2,4,6-tris(dimethylaminomethyl)phenol TAP, mix and stir until all components are fully miscible to form a homogeneous and transparent resin system; add the CF-Si3N4@CNTs composite skeleton obtained in step 2 into the resin system, impregnate in a vacuum environment for 1-2 h, and then place it in an oven at 90-120 ℃ for 4-6 h to cure, thereby obtaining the CF-Si3N4@CNTs / EP thermally conductive composite material.

3. The preparation method according to claim 2, characterized in that: In step 3, the CF-Si3N4@CNTs composite skeleton is used as a filler, and its mass fraction in the thermally conductive composite material is 16~20 wt%.

4. A CF-Si3N4@CNTs / EP thermally conductive composite material obtained by the preparation method according to any one of claims 1 to 4.

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