A method for preparing three-dimensional graphite thermal conductive filler assisted by graphene oxide

Abstract

This invention proposes for the first time a method for preparing three-dimensional graphite thermally conductive fillers using graphene oxide-assisted molding. By adding a small amount of graphene oxide and utilizing the gas generated during the reaction between graphene oxide and hydrazine hydrate, abundant voids are introduced into the graphite film, resulting in the preparation of a graphite thermally conductive filler with a continuous three-dimensional structure. By adjusting the amount of graphene oxide added, the diameter of the graphite flakes, and the conditions for introducing voids, the structure of the thermally conductive filler can be regulated, resulting in fillers with varying densities and thermal conductivities. Furthermore, this method features a simple preparation process, widely available and inexpensive raw materials, and a stable product structure, facilitating the industrialization of thermally conductive fillers.

Description

Technical Field

[0001] The present invention belongs to the technical field of functional materials, and in particular relates to a method for preparing a three-dimensional graphite thermal conductive filler with the assistance of graphene oxide. Background Art

[0002] In response to the rapid advancements in information technology, new-generation electronic devices are rapidly developing towards highly integrated and high-power devices. This significantly increases the amount of heat generated during device operation, making rapid and efficient heat dissipation a key factor in maintaining stable device operation. This places higher demands on the thermally conductive materials used in conjunction with these materials. Currently, the most widely used thermally conductive materials are based on polymers, with thermally conductive fillers such as carbon black, alumina, graphene, carbon nanotubes, and boron nitride added to form composite materials.

[0003] A key factor in improving the thermal conductivity of such materials is the formation of a continuous and stable thermal conductivity path by thermally conductive fillers. Commonly used thermal conductive main materials include zero-dimensional granular fillers, one-dimensional rod-shaped fillers, and two-dimensional flake fillers. These fillers have difficulty establishing a continuous and stable thermal conductivity path in the matrix material when added in low amounts. When added in larger amounts, the fillers cannot be evenly dispersed in the matrix material, and the stiffness of the composite material also increases, which reduces the overall processability of the composite material. These problems limit further improvements in the material's thermal conductivity.

[0004] Graphite is abundant in both storage and production, making it a cheap and readily available raw material for thermal conductivity. Natural flake graphite, with its low density and excellent thermal conductivity, has been widely used in thermal conductivity applications. However, current methods of using it as a thermally conductive filler typically involve direct dispersion within a matrix, limiting the amount of filler and failing to fully utilize graphite's high thermal conductivity. Furthermore, the weak interaction between graphite flakes prevents them from maintaining a stable, continuous three-dimensional structure, further limiting their application in high-thermal-conductivity composite materials.

[0005] The information disclosed in this background technology section is only intended to enhance understanding of the overall background of the invention and should not be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art. Summary of the Invention

[0006] The present invention aims to address the current difficulty in forming graphite sheets into a highly stable three-dimensional continuous structure. The present invention provides a method for preparing a three-dimensional graphite thermally conductive filler with the assistance of graphene oxide. The method primarily utilizes the gas-generating property of the reaction between graphene oxide and hydrazine hydrate. With the assistance of graphene oxide, abundant gaps are introduced between the graphite sheets. Simultaneously, the reduced graphene oxide coats the connecting nodes of the three-dimensional graphite skeleton, thereby improving the overall mechanical stability. Consequently, a three-dimensional continuous graphite thermally conductive filler with high thermal conductivity and stable structure is successfully obtained.

[0007] To achieve the above objectives, the present invention provides a method for preparing a three-dimensional graphite thermal conductive filler with the assistance of graphene oxide, and the specific implementation method is as follows:

[0008] 1) uniformly mixing the graphene oxide dispersion and graphite in a certain proportion to obtain a slurry;

[0009] 2) obtaining a wet film by a confined tape casting method or a blade coating method, and drying at normal pressure to obtain a graphite film containing 5% to 30% by mass of graphene oxide;

[0010] 3) immersing the graphite film in a hydrazine hydrate solution dissolved in a polar solvent, and using the gas generated by the reaction of graphene oxide and hydrazine hydrate to introduce gaps between the graphite sheets;

[0011] 4) Solvent replacement is performed, and after drying at room temperature and pressure, chemical reduction, carbonization and graphitization processes, a graphite thermal conductive filler with a continuous three-dimensional structure is obtained.

[0012] Further, in step (1), the graphite is natural flake graphite, and sheet diameter is between 10-300 μm. The solvent of the graphene oxide dispersion includes but is not limited to water, DMF, DMSO, DMAC, NMP, and solid content is between 5-25 mg / g, and graphene oxide sheet diameter is between 2-60 μm. In the present invention, graphene oxide reacts with hydrazine hydrate to produce gas, on the one hand, a large amount of gaps are introduced between flake graphite, and the two-dimensional structure of conventional dense stacking is converted into a three-dimensional structure with abundant pores, on the other hand, after reduction and graphitization treatment, the graphene sheets concentrated on the edge of the graphite sheet play a certain overlapping effect between the graphite sheets, increase the stability of the overall structure and the continuity of the heat conduction path, and form a three-dimensional continuous heat-conducting structure. If the graphite flakes are too small, they cannot form overlapping three-dimensional structures. If they are too large, it will be difficult to form a uniform and stable slurry with the graphene oxide dispersion. Furthermore, if the graphite flakes are too large, a small amount of graphene oxide will not be able to maintain the stability of the overall structure, and they will easily crack and collapse during the drying process after solvent replacement. The graphene oxide concentration is limited to obtain a uniform graphene oxide / graphite composite film. If the graphene oxide flakes are too small, they will not be able to effectively coat the overlapping nodes of the three-dimensional graphite skeleton, resulting in structural instability. The upper limit of the size is the maximum size of conventional commercially available graphene oxide products.

[0013] Furthermore, in step (2), the thickness of the wet film is 1-6 mm, and this thickness range is to ensure the uniformity and continuity of the graphite film obtained after drying. The drying temperature is 20-65 ° C to avoid premature removal of oxygen-containing groups due to excessively high temperature drying. Generally, in a system with a small amount of nanomaterials such as graphene added, during the process of normal pressure drying, the nanomaterials will preferentially gather at the skeleton nodes. Similarly, during the normal pressure drying process of the graphite film, the graphene oxide sheets will preferentially gather at the overlap of the edges of the graphite sheets and coat the overlap, playing a stabilizing role in the graphite structure during the subsequent reaction shaping, drying and further graphitization process, and can maintain the continuity of the three-dimensional structure when subjected to external pressure. In contrast, during freeze drying, the graphene oxide sheets will stack with the graphite sheets under the pressure of ice crystal growth, which may make it difficult to effectively connect the graphite sheets, and there are also problems of high energy consumption and low efficiency.

[0014] Tape casting and doctor blade coating are gentle processes that don't disrupt the relationship between the graphite flakes and graphene oxide in the uniformly mixed slurry. For confined tape casting, the process involves placing a 1-6mm frame on the substrate and pouring an appropriate amount of the graphite and graphene oxide slurry into the frame, ensuring the slurry level is flush with the top edge of the frame.

[0015] The doctor blade coating method involves adjusting the distance between the scraper and the substrate to 1-6 mm, pouring the graphite and graphene oxide slurry onto one side of the scraper, and then moving the scraper at a constant speed to evenly spread the slurry onto the substrate. The substrate can be made of polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE), polypropylene (PP), or glass.

[0016] Furthermore, in step (3), the concentration of the hydrazine hydrate solution can be 5-80wt%. The role of hydrazine hydrate is to react with the oxygen-containing functional groups on the surface of graphene oxide, and the generated gas can generate gaps between the graphite sheets to form a three-dimensional continuous structure. The polar solvent includes water, polar organic solvents and combinations thereof; the organic solvent can be anhydrous ethanol, DMF, DMAC, isopropyl alcohol, etc. The polar solvent plays a role in plasticizing and intercalating the graphite film, which can reduce the interaction between the graphite sheets and the graphene oxide sheets. At the same time, it can allow the hydrazine hydrate molecules to be inserted between the graphene oxide sheets and fully contact them, facilitating the smooth progress of the subsequent gap introduction process. The hydrazine hydrate reaction temperature is 25°C-90°C, and the reaction time is 2-60min.

[0017] Furthermore, in step (4), the solvent replacement is to repeatedly immerse the reaction-fixed membrane in one or more combinations of water, ethanol, and n-hexane until the hydrazine hydrate in the membrane is removed.

[0018] Furthermore, in step (4), the chemical reduction is to fumigate the sample with a mixture of hydroiodic acid and glacial acetic acid at 90-100°C for 12-18h, wherein the volume proportion of glacial acetic acid is 0-3 / 4. The purpose of chemical reduction is to further remove the oxygen-containing functional groups in the membrane to avoid the generation of gas during intense heat treatment to destroy the three-dimensional structure. The carbonization temperature is 1000-1600°C. The graphitization temperature is 2000-3000°C. After graphitization, graphene oxide is converted into graphene, which further plays a role in constructing and stabilizing the heat conduction path, thereby obtaining a three-dimensional heat conduction network with a full graphite structure.

[0019] The density of the graphite thermal conductive filler prepared according to the above method is not more than 450 mg / cm 3 Too high a filler density means too few effective voids, which is not conducive to subsequent compounding with other materials.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) This patent provides a simple preparation method that can, under relatively mild conditions, utilize the property of graphene oxide to generate gas by reacting with hydrazine hydrate to introduce abundant voids between graphite sheets to construct a graphite thermal conductive filler with a continuous three-dimensional structure.

[0022] (2) The content of graphene oxide used can be as low as 5 wt.%. The gas generated by the reaction of a small amount of graphene oxide with hydrazine hydrate can effectively overcome the weak interaction force between the graphite sheets, while introducing gaps between the graphite sheets and forming a stable overlapping structure between the graphite sheets, further improving and stabilizing the thermal conductivity of the thermally conductive filler, while also having certain cost advantages.

[0023] (3) Compared to the conventional method of directly adding graphite sheets, the method of introducing voids to construct a three-dimensional network expands the graphite sheets to form more longitudinal heat conduction paths, making it possible to produce a thermally conductive filler material that combines the advantages of high vertical thermal conductivity, low density, and low filling volume. In addition, graphite thermal conductive fillers can be compressed to a certain extent, and the thermal conductivity and composite ratio can be further adjusted according to actual needs, which has the advantage of flexibility and controllability. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a scanning electron microscope (SEM) photograph of the graphite three-dimensional thermally conductive filler obtained in Example 1.

[0025] Figure 2 This is a partially enlarged scanning electron microscope (SEM) photograph of the graphite three-dimensional thermally conductive filler obtained in Example 1.

[0026] Figure 3 This is a scanning electron microscope (SEM) photograph of the graphite three-dimensional thermally conductive filler obtained in Example 2.

[0027] Figure 4 This is a scanning electron microscope (SEM) photograph of the graphite three-dimensional thermally conductive filler obtained in Example 3.

[0028] Figure 5 This is a scanning electron microscope (SEM) photograph of the graphite three-dimensional thermally conductive filler obtained in Example 4. DETAILED DESCRIPTION

[0029] The present invention is further described below with reference to the following examples, but the scope of protection of the present invention is not limited thereto.

[0030] Example 1

[0031] (1) 70 g of a 10 mg / g aqueous dispersion of graphene oxide was mixed with 2.8 g of natural flake graphite with a sheet diameter of 100 μm to form a slurry, wherein the graphite content was 80 wt % and the graphene oxide sheet diameter was 2-10 μm;

[0032] (2) A wet film with a thickness of 3 mm was obtained by blade coating and dried at 20°C under normal pressure;

[0033] (3) Immerse the obtained graphite film in a 20 wt% hydrazine hydrate aqueous solution and keep it at 80°C for 30 min. Then transfer the sample to anhydrous ethanol and soak it for 3 h. Repeat this three times. Then transfer the sample to n-hexane and soak it for 3 h. Repeat this three times and dry it at room temperature and atmospheric pressure.

[0034] (4) The dried sample was fumigated with hydroiodic acid at 100°C for 12 h, then carbonized at 1000°C and graphitized at 3000°C to obtain a graphite thermal conductive filler with a continuous three-dimensional structure.

[0035] The microstructure of graphite thermal conductive filler is as follows: Figure 1 As shown in the figure, it can be seen that the overall structure of the graphite thermal conductive filler is continuous and there is no rigid unstable contact at the edge of the graphite sheet. Figure 2 As shown in the figure, graphene almost completely covers the overlap of graphite sheets, improving the stability of the three-dimensional graphite structure. Its density is about 34.9 mg / cm 3 , thermal conductivity is 2.6W / mk. After vertical compression, the deformation is about 80%, the pore size of the graphite filler is compressed, and the density is increased to 173mg / cm 3 As the density increases, its thermal conductivity also increases to 10.2W / mk, proving that the filler is still a three-dimensional continuous structure, and the overlap within the skeleton can still basically maintain a continuous state under a highly compressed state.

[0036] Example 2

[0037] (1) 60 g of a 10 mg / g aqueous dispersion of graphene oxide was mixed with 11.4 g of natural flake graphite with a sheet diameter of 45 μm to form a slurry with a graphite content of 95 wt% and a graphene oxide sheet diameter of 2-10 μm;

[0038] (2) A wet film with a thickness of 3 mm was obtained by blade coating and dried at 20°C under normal pressure;

[0039] (3) Immerse the obtained graphite film in a 30 wt% hydrazine hydrate aqueous solution at 60°C for 30 min, then transfer the sample to anhydrous ethanol and soak for 3 h. Repeat this three times, then transfer the sample to n-hexane and soak for 3 h. Repeat this three times, and then dry it at room temperature and normal pressure.

[0040] (4) The dried sample was fumigated with a mixed solution of hydroiodic acid and glacial acetic acid (volume ratio 1:2) at 95°C for 12 h, then carbonized at 1000°C and graphitized at 2800°C to obtain a graphite thermal conductive filler with a continuous three-dimensional structure.

[0041] The microstructure of graphite thermal conductive filler is as follows: Figure 3 As shown in the figure, it can be seen that the overall structure of the graphite thermal conductive filler is continuous, and there is no rigid unstable contact at the edge of the graphite sheet. Its density is about 414.4 mg / cm 3 , thermal conductivity 2.1W / mk.

[0042] Example 3

[0043] (1) 70 g of a 15 mg / g aqueous dispersion of graphene oxide was mixed with 2.5 g of natural flake graphite with a sheet diameter of 300 μm to form a slurry, wherein the graphite content was 70 wt % and the graphene oxide sheet diameter was 50-60 μm;

[0044] (2) A wet film with a thickness of 3 mm was obtained by blade coating and dried at 20°C under normal pressure;

[0045] (3) Immerse the obtained graphite film in a 20 wt% hydrazine hydrate aqueous solution and keep it at 80°C for 30 min. Then transfer the sample to anhydrous ethanol and soak it for 3 h. Repeat this three times. Then transfer the sample to n-hexane and soak it for 3 h. Repeat this three times and dry it at room temperature and atmospheric pressure.

[0046] (4) The dried sample was fumigated with a mixed solution of hydroiodic acid and glacial acetic acid (volume ratio 1:3) at 95°C for 12 h, and then carbonized at 1000°C and graphitized at 3000°C to obtain a graphite thermal conductive filler with a continuous three-dimensional structure.

[0047] The microstructure of graphite thermal conductive filler is as follows: Figure 4As shown in the figure, it can be seen that the overall structure of the graphite thermal conductive filler is continuous, and there is no rigid unstable contact at the edge of the graphite sheet. Its density is about 18.5mg / cm 3 , thermal conductivity 2.2W / mk.

[0048] Example 4

[0049] (1) 24 g of a 25 mg / g aqueous dispersion of graphene oxide was mixed with 1.4 g of natural flake graphite with a sheet diameter of 45 μm to form a slurry, wherein the graphite content was 70 wt % and the graphene oxide sheet diameter was 2-10 μm;

[0050] (2) A wet film with a thickness of 1 mm was obtained by confined casting and dried at 20 °C under normal pressure;

[0051] (3) The obtained graphite film was immersed in a 5 wt% hydrazine hydrate solution, the solvent was a mixed solvent of water and ethanol (mass ratio 1:1), and kept warm at 25 ° C for 60 min. The sample was then transferred to anhydrous ethanol and soaked for 3 h. After repeating three times, the sample was transferred to n-hexane and soaked for 3 h. After repeating three times, the sample was dried at room temperature and atmospheric pressure.

[0052] (4) The dried sample was fumigated with a mixed solution of hydroiodic acid and glacial acetic acid (volume ratio 1:3) at 95°C for 12 h, then carbonized at 1000°C and graphitized at 2000°C to obtain a graphite thermal conductive filler with a continuous three-dimensional structure.

[0053] The microstructure of graphite thermal conductive filler is as follows: Figure 5 As shown in the figure, it can be seen that the overall structure of the graphite thermal conductive filler is continuous, and there is no rigid unstable contact at the edge of the graphite sheet. Its density is about 18.2mg / cm 3 , thermal conductivity 1.6W / mk. After vertical compression, the deformation is about 70%, the pore size of the graphite filler is compressed, and the density is increased to 60.6mg / cm 3 As the density increases, its thermal conductivity also increases to 5.3W / mk, proving that the filler is still a three-dimensional continuous structure, and the overlap within the skeleton can still basically maintain a continuous state under a highly compressed state.

[0054] Example 5

[0055] (1) 60 g of a 5 mg / g graphene oxide NMP dispersion was mixed with 0.7 g of natural flake graphite with a sheet diameter of 10 μm to form a slurry, wherein the graphite content was 70 wt % and the graphene oxide sheet diameter was 2-10 μm;

[0056] (2) A wet film with a thickness of 6 mm was obtained by blade coating and dried at 65°C under normal pressure;

[0057] (3) Immerse the obtained graphite film in a hydrazine hydrate solution with a concentration of 80 vol%, keep it at 90 ° C for 2 minutes, then transfer the sample to anhydrous ethanol and soak it for 3 hours. After repeating three times, transfer the sample to n-hexane and soak it for 3 hours. After repeating three times, dry it at room temperature and atmospheric pressure.

[0058] (4) The dried sample was fumigated with hydroiodic acid at 90°C for 18 h, then carbonized at 1600°C and graphitized at 2800°C to obtain a graphite thermal conductive filler with a continuous three-dimensional structure.

[0059] The density of the graphite thermal conductive filler is about 31.2 mg / cm 3 , thermal conductivity 1.9W / mk. After vertical compression, the deformation is about 80%, the pore size of the graphite filler is compressed, and the density is increased to 150.4mg / cm 3 As the density increases, its thermal conductivity also increases to 9.3W / mk, proving that the filler is still a three-dimensional continuous structure, and the overlap within the skeleton can still basically maintain a continuous state under a highly compressed state.

[0060] Comparative Example 1

[0061] (1) Add 10 g of natural flake graphite with a flake diameter of 45 μm to 8 g of deionized water. To ensure uniform dispersion of the graphite flakes in the water, add 1.8 g of a 10 wt.% surfactant (sodium lauryl sulfate). Mix thoroughly to form a slurry.

[0062] (2) A wet film with a thickness of 2 mm was obtained by confined casting and dried at 20°C under normal pressure.

[0063] (3) After the dried graphite film is immersed in deionized water, the graphite film decomposes rapidly, making it impossible to achieve reaction finalization and subsequent processing steps.

[0064] Comparative Example 2

[0065] (1) Add 15 g of natural flake graphite with a flake diameter of 100 μm to 10 g of deionized water. To ensure uniform dispersion of the graphite flakes in the water, add 2.5 g of a 10 wt.% surfactant (sodium lauryl sulfate). Mix thoroughly to form a slurry.

[0066] (2) A wet film with a thickness of 3 mm was obtained by confined casting.

[0067] (3) After freeze-drying for 24 h, a block-shaped graphite film was obtained.

[0068] (4) When slightly squeezed with a force of 5N, the graphite film breaks and collapses, making subsequent testing and characterization impossible.

[0069] It can be seen from the above embodiments and comparative examples that the present invention introduces graphite oxide to the overlap of flake graphite and realizes effective coating support for the overlap by a series of gentle operation processes such as mixing, casting film, blade coating, drying at room temperature and pressure, and introducing reaction-generated gas into the gap. While utilizing graphene oxide to react with hydrazine hydrate to generate gas for pore formation, the obtained three-dimensional graphite thermal conductive filler always maintains a relatively stable continuous structure. When subjected to external pressure, the overlap can still remain continuous and stable. After chemical reduction, carbonization and graphitization, graphene oxide is converted into highly thermally conductive graphene, further providing a stable heat conduction path for the graphite filler. The finally obtained three-dimensional graphite thermal conductive filler has efficient and stable thermal conductivity.

Claims

1. A method for preparing a three-dimensional graphite thermal conductive filler assisted by graphene oxide, characterized in that: The method involves immersing a graphite film containing 5% to 30% graphene oxide by mass into a hydrazine hydrate solution dissolved in a polar solvent. The gas generated by the reaction of graphene oxide and hydrazine hydrate is used to introduce gaps between the graphite sheets. Subsequently, solvent replacement is performed, and a graphite thermal conductive filler with a continuous three-dimensional structure is obtained through drying at room temperature and pressure, chemical reduction, carbonization, and graphitization. The graphite film is obtained by preparing a wet film from a mixed slurry of natural flake graphite and graphene oxide dispersion by a doctor blade method or a confined casting method, and then drying at normal pressure; the flake diameter of the natural flake graphite is 10-300 μm; the solid content of the graphene oxide dispersion is 5-25 mg / g, and the graphene oxide flake diameter is 2-60 μm.

2. The method according to claim 1, characterized in that The thickness of the wet film is 1-6 mm, and the drying temperature is 20-65°C.

3. The method according to claim 1, characterized in that The solvents of the mixed slurry of natural flake graphite and graphene oxide dispersion are water, DMF, DMSO, DMAC, and NMP.

4. The preparation method according to claim 1, characterized in that The concentration of the hydrazine hydrate solution is 5-80 wt %, the polar solvent is water, a polar organic solvent, or a combination of water and a polar organic solvent, the reaction temperature is 25° C.-90° C., and the reaction time is 2-60 min.

5. The preparation method according to claim 4, characterized in that The polar organic solvent is anhydrous ethanol, DMF, DMAC, or isopropyl alcohol.

6. The preparation method according to claim 1, characterized in that The solvent replacement is to soak the reaction-fixed membrane in one or more combinations of ethanol and n-hexane for multiple times until the hydrazine hydrate in the membrane is removed.

7. The preparation method according to claim 1, characterized in that The chemical reduction is a fumigation reduction using a reducing gas, wherein the reducing gas is a mixture of 0.25 to 1 parts by volume of hydroiodic acid and 0 to 0.75 parts by volume of glacial acetic acid formed at 90 to 100° C., and the fumigation reduction time is 12 to 18 hours. The carbonization temperature is 1000 to 1600° C., and the graphitization temperature is 2000 to 3000° C. Both carbonization and graphitization are carried out under the protection of an inert gas.

8. The preparation method according to claim 1, characterized in that The density of the graphite thermal conductive filler is not greater than 450 mg / cm 3 .

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