Preparation method of graphene heat-conducting film

Abstract

The invention provides a preparation method of a graphene heat-conducting film, which comprises the following steps: preparing coal-based graphene oxide by using low-cost and easily available coal-based graphite as a raw material through a chemical oxidation method, controlling the in-plane size of the coal-based graphene oxide through process conditions, adjusting the concentration and system composition of a graphene oxide solution, and preparing a graphene oxide film through a suction filtration method. The graphene heat-conducting film is obtained through the steps of low-temperature reduction, high-temperature graphitization, cold pressing and the like. The method successfully breaks through the technological process of preparing the graphene heat conduction film with coal-based graphite as the main raw material, the cost is low, and the obtained graphene heat conduction film is thin in thickness and high in heat conduction coefficient.

Description

Technical Field

[0001] The invention relates to the technical field of industrial heat dissipation materials, and in particular to a method for preparing a graphene heat-conducting film. Background Art

[0002] Currently, metals and their composite materials have been recognized by most people as heat dissipation materials. However, metals have high density and thermal expansion coefficient, are easily oxidized, and their purity affects thermal conductivity. They no longer meet the requirements of new heat dissipation materials. Therefore, it is urgent to develop a new, lighter and more thermally conductive heat dissipation material.

[0003] Due to its excellent thermal conductivity and good mechanical strength, graphene film is considered to be an ideal choice for heat dissipation materials (HDM) and thermal interface materials (TIM) in electronic devices. Current research mostly uses the CVD method to prepare graphene film, but this method has complex steps and high costs; secondly, graphene film is mostly prepared using flake graphite as raw material, but the output of flake graphite is limited; coal has a structure similar to flake graphite, and coal can be used to obtain coal-based graphite under certain conditions. However, since the aromatic ring structure of coal-based graphite is smaller than that of flake graphite, there is currently no relevant technical solution for whether coal-based graphite can be used to prepare coal-based graphene thermal conductive film like flake graphite.

[0004] CN116445856A discloses a method for preparing a graphene film. The method mainly uses a mixed gas of acetylene, acetone and argon as a carbon source to grow a graphene film on a substrate, but the method can only prepare ultra-thin films at present, the cost is high, and the thermal conductivity of graphene is not mentioned.

[0005] CN111471292A discloses a method for preparing a graphene heat dissipation film, wherein the graphene slurry is prepared from graphite powder as a raw material, and then the graphene heat dissipation film is prepared by scraping and directional treatment, wherein the graphite powder used is one or more of expanded graphite, flake graphite or natural graphite flakes. Summary of the invention

[0006] The present invention provides a method for preparing a graphene thermally conductive film, which successfully opens up a process flow for preparing the graphene thermally conductive film using coal-based graphite as a main raw material, has low cost, and the obtained graphene thermally conductive film has a thin thickness and a high thermal conductivity coefficient.

[0007] To achieve the purpose, the present invention provides the following technical solutions:

[0008] The present invention provides a method for preparing a graphene thermal conductive film, which comprises the following steps:

[0009] 1) Graphitizing pulverized coal to obtain coal-based graphite, wherein the particle size of the pulverized coal needs to satisfy D97 of 5-75 μm (e.g., 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, etc.);

[0010] 2) mixing sulfuric acid and sodium nitrate in an ice water bath to obtain a mixed solution 1, and then adding the coal-based graphite to obtain a mixed solution 2;

[0011] 3) potassium permanganate is slowly and evenly added to the mixed solution 2 of step 2), and then the temperature is raised to 30-40° C. (e.g., 32° C., 34° C., 36° C., 38° C., etc.) and reacted for 3-5 h (e.g., 3.5 h, 4.0 h, 4.5 h, etc.) to obtain a mixed solution 3;

[0012] 4) heating the mixed solution 3 in step 3) to 95-100° C. (e.g., 96° C., 97° C., 98° C., 99° C., etc.), adding water, and continuously stirring the reaction until the solution turns brown-yellow, and then adding hydrogen peroxide to obtain a mixed solution 4;

[0013] 5) filtering the mixed solution 4 of step 4), washing the solid product with a hydrochloric acid solution, and then washing with water until the separated washing water is neutral, to obtain coal-based graphite oxide;

[0014] 6) dispersing the coal-based graphite oxide in water and performing ultrasonic treatment to obtain a coal-based graphene oxide slurry;

[0015] 7) taking the coal-based graphene oxide slurry obtained in step 6), adjusting the concentration to 3-8 mg / mL (e.g., 4 mg / mL, 5 mg / mL, 6 mg / mL, 7 mg / mL, etc.), and then adding graphite-based graphene oxide slurry, the mass ratio of coal-based graphene oxide to graphite-based graphene oxide is 1:(0.1-0.4), for example, 1:0.15, 1:0.20, 1:0.25, 1:0.30, 1:0.35, etc.; dispersing evenly, filtering, drying and stripping to obtain a graphene oxide film;

[0016] 8) reducing the graphene oxide film obtained in step 7) to obtain a graphene film;

[0017] 9) The graphene film obtained in step 8) is graphitized and cold pressed to obtain the graphene thermal conductive film.

[0018] In some embodiments of the preparation method of the present invention, in step 1), the conditions of graphitization treatment include: a temperature of 2800-3200°C (e.g., 2900°C, 3000°C, 3100°C, etc.), a time of 2-4h (e.g., 2.5h, 3.0h, 3.5h, etc.); and / or, the pulverized coal is selected from one or more of anthracite, bituminous coal, and semi-coke, preferably anthracite. In this article, except for the conditions particularly emphasized, other conditions of graphitization treatment are well known to those skilled in the art and can be reasonably selected, such as graphite crucibles and graphitization furnaces and other equipment, and the graphitization treatment needs to be carried out under the protection of an inert atmosphere (e.g., argon).

[0019] In some embodiments of the preparation method of the present invention, in step 2), the solid-liquid ratio of sodium nitrate to sulfuric acid is 1: (30-50) g / ml (e.g., 1: 35 g / ml, 1: 40 g / ml, 1: 45 g / ml, etc.), and the sulfuric acid is preferably concentrated sulfuric acid having a mass concentration of not less than 95% (e.g., 96%, 97%, 98%, etc.); and / or, the solid-liquid ratio of coal-based graphite to mixed solution 1 is 1: (25-40) g / ml (e.g., 1: 30 g / ml, 1: 35 g / ml, etc.); and / or, after adding the coal-based graphite, stirring is performed uniformly to obtain a mixed solution 2, and the stirring time is 20-60 min (e.g., 30 min, 40 min, 50 min, etc.).

[0020] In some embodiments of the preparation method of the present invention, in step 3), the mass ratio of potassium permanganate to coal-based graphite is (2-8): 1 g / g (e.g., 3: 1 g / g, 4: 1 g / g, 5: 1 g / g, 6: 1 g / g, 7: 1 g / g, etc.); and / or, potassium permanganate is added slowly and evenly by continuously adding potassium permanganate at a feeding rate of 0.05-0.15 g / min (e.g., 0.075 g / min, 0.10 g / min, 0.125 g / min, etc.); and / or, potassium permanganate is stirred evenly after addition is completed, and stirring is continued during the reaction.

[0021] In some embodiments of the preparation method of the present invention, in step 4), the hydrogen peroxide is a hydrogen peroxide with a mass concentration of 20-40% (e.g., 30%); and / or, the ratio of the amount of the hydrogen peroxide to the potassium permanganate used in step 3) is preferably 1:0.6-2 ml / g (1:0.8 ml / g, 1:1.0 ml / g, 1:1.5 ml / g, etc.); and / or, the processes of adding water and adding hydrogen peroxide are independently added dropwise.

[0022] In some embodiments of the preparation method of the present invention, in step 5), the mass ratio of hydrochloric acid to water in the hydrochloric acid solution is 1:(6-12), for example, 1:7, 1:8, 1:9, 1:10, 1:11, etc.

[0023] In some embodiments of the preparation method of the present invention, in step 6), the power of ultrasonic treatment is 600-1000 W (eg, 700 W, 800 W, 900 W, etc.), and the ultrasonic time is 4-10 h (eg, 6 h, 8 h, etc.).

[0024] In some embodiments of the preparation method of the present invention, in step 7), the particle size of the graphite-based graphene oxide is 20-160 microns (for example, the particle size is about 20 microns, 40 microns, 60 microns, 80 microns, 100 microns, 120 microns, 140 microns and 160 microns, and within the range formed by any two endpoint values ​​above); and / or, ultrasonic treatment is used to disperse the slurry evenly; and / or, cellulose acetate membrane filter paper is used for suction filtration; and / or, the drying temperature is room temperature, and the drying time is 8-20 hours (for example, 10 hours, 15 hours, etc.); and / or, the diameter of the graphene oxide film is 2-8 cm (for example, 3 cm, 4 cm, 5 cm, 6 cm, 7 cm, etc.).

[0025] In some embodiments of the preparation method of the present invention, in step 8), the reduction conditions include: introducing H 2 : The inert gas is a mixed gas of 1:(7-12) (for example, 1:9), the heating rate is 2-8°C / min (for example, 4°C / min, 6°C / min, etc.), after maintaining at 300-600°C (for example, 400°C, 500°C, etc.) for 40-100min (for example, 60min, 80min), it is naturally cooled to room temperature, during which the flow rate of the mixed gas is maintained at 100-300mL / min (for example, 200mL / min); preferably, the inert gas is argon.

[0026] In some embodiments of the preparation method of the present invention, in step 9), the conditions of the graphitization treatment include: a temperature of 2800-3200°C (e.g., 2900°C, 3000°C, 3100°C, etc.), a time of 0.5-2h (e.g., 1.0h, 1.5h, etc.); and / or a cold pressing pressure of 10-50Mpa (e.g., 20Mpa, 30Mpa, 40Mpa, etc.).

[0027] The invention provides a method for preparing a graphene thermal conductive film. Coal-based graphite, which is easily available and of low cost, is used as a raw material. Coal-based graphene oxide is prepared by a chemical oxidation method. The in-plane size of the coal-based graphene oxide is controlled by specific process conditions. The concentration and system composition of the graphene oxide solution are adjusted. A graphene oxide film is prepared by a suction filtration method. The coal-based graphene film is obtained by low-temperature reduction, high-temperature graphitization, cold pressing and other steps.

[0028] The technical solution provided by the present invention has the following beneficial effects:

[0029] 1) Coal-based graphite is used as the main raw material, with low cost;

[0030] 2) The aromatic ring structure of coal-based graphite is smaller than that of flake graphite. There is no mature process for preparing graphene thermal conductive film using coal-based graphite as the main raw material in the prior art, and the present invention successfully solves this problem;

[0031] 3) The graphene thermal conductive film obtained by the preparation method of the present invention has a thin thickness and a high thermal conductivity coefficient. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is an exemplary flow chart of the preparation method of the present invention;

[0033] Figure 2 This is an exemplary diagram of preparing a graphene oxide film by filtration of a mixed solution of coal-based graphene oxide and graphite-based graphene oxide in the preparation method of the present invention. DETAILED DESCRIPTION

[0034] In order to facilitate the understanding of the present invention, the present invention will be further described below in conjunction with examples. It should be understood that the following examples are only for a better understanding of the present invention and do not mean that the present invention is limited to the following examples.

[0035] Where specific experimental steps or conditions are not specified in the embodiments, the corresponding conventional experimental steps or conditions in the art can be used. The reagents or instruments used without indicating the manufacturer are all conventional products that can be obtained commercially. The thermal conductivity coefficient is determined by referring to GB / T 22588-2008 flash method for measuring thermal diffusion coefficient or thermal conductivity.

[0036] Example 1

[0037] 1) Pulverized coal (Taixi anthracite) with a D97 of 62 μm was graphitized (3000°C, 3 h) to obtain coal-based graphite.

[0038] 2) adding coal-based graphite to a mixed solution 1 of concentrated sulfuric acid (concentration of 98%) and sodium nitrate (the solid-liquid ratio of sodium nitrate to concentrated sulfuric acid is 1:40 g / ml, mixed in an ice bath), stirring for 30 minutes to mix them evenly, the solid-liquid ratio of coal-based graphite to mixed solution 1 is 1:30 g / ml, and mixed solution 2 is obtained.

[0039] 3) Slowly and evenly add potassium permanganate (5 times the mass of coal-based graphite) (continuously add at a feeding rate of about 0.1 g / min) to the mixed solution 2 of step 2). After the addition is completed and stirred evenly, the temperature is raised to 35° C. and reacted for 4 hours, during which stirring is continued to obtain a mixed solution 3.

[0040] 4) The mixed solution 3 of step 3) was heated to 98° C., and deionized water was added dropwise, and the reaction was continued with stirring until the solution turned brown-yellow, and then 30 wt % hydrogen peroxide was added dropwise, with the ratio of hydrogen peroxide to potassium permanganate being 1:0.8 ml / g, to obtain a mixed solution 4.

[0041] 5) filtering the mixed solution 4 of step 4), washing the solid product with dilute hydrochloric acid having a mass ratio of hydrochloric acid to water of 1:10, and then washing with a large amount of deionized water until the separated washing water is neutral, thereby obtaining coal-based graphite oxide.

[0042] 6) The coal-based graphite oxide is dispersed in distilled water, and ultrasonically dispersed at a power of 700 W for 6 h to obtain a coal-based graphene oxide slurry.

[0043] 7) Add deionized water to the coal-based graphene oxide slurry obtained in step 6) to adjust the concentration to 4 mg / mL, and then add graphite-based graphene oxide slurry (particle size within 40-120 microns), the mass ratio of coal-based graphene oxide to graphite-based graphene oxide is 1:0.2, ultrasonically dispersed uniformly, filtered with cellulose acetate membrane filter paper, and dried at room temperature for 12 hours to obtain a graphene oxide film with a diameter of about 5 cm.

[0044] 8) The graphene oxide film obtained in step 7) is reduced by introducing H 2 :Ar is a 1:9 mixed gas, the heating rate is 5℃ / min, after maintaining at 400℃ for 60min, it is naturally cooled to room temperature, during which H 2 The mixed gas of Ar:Ar is 1:9 at 200 mL / min. The sample is taken out to obtain a graphene film.

[0045] 9) The graphene film obtained in step 8) is graphitized (2800° C., 1 h), and then cold pressed (pressure is 15 MPa) to obtain a graphene thermal conductive film. The obtained graphene thermal conductive film has a thickness of about 24 microns and a thermal conductivity of about 1200 w / mk.

[0046] The specific preparation method in the embodiment can also be referred to Figure 1 and Figure 2 ,in, Figure 1 An exemplary flow chart of a preparation method is provided, Figure 2 An example diagram of the process of preparing a graphene oxide film by filtering a mixed solution of coal-based graphene oxide and graphite-based graphene oxide in a preparation method.

[0047] Example 2

[0048] The method is carried out in accordance with Example 1, except that the mass ratio of coal-based graphene oxide to graphite-based graphene oxide in step 7) is 1:0.25. The obtained graphene thermal conductive film has a thickness of about 27 microns and a thermal conductivity of about 1184 W / mk.

[0049] Example 3

[0050] The method is carried out in accordance with Example 1, except that the size D97 of the raw material pulverized coal is 40 μm, and the mass ratio of coal-based graphene oxide to graphite-based graphene oxide in step 7) is 1:0.3. The obtained graphene thermal conductive film has a thickness of about 26 μm and a thermal conductivity of about 1247 W / mk.

[0051] Comparative Example 1

[0052] The method was carried out in accordance with Example 1, except that in step 7), the concentration of the coal-based graphene oxide slurry was adjusted to 2.5 mg / mL, and no graphite-based graphene oxide slurry was added. The obtained film was brittle and completely cracked, and no complete film was obtained, that is, no film could be formed.

[0053] Comparative Example 2

[0054] The method was carried out in accordance with Example 1, except that in step 7), the concentration of the coal-based graphene oxide slurry was adjusted to 2.5 mg / mL. The obtained film had cracks and was incomplete, that is, it could not be formed into a film.

[0055] Comparative Example 3

[0056] The method was carried out in accordance with Example 1, except that in step 7), no graphite-based graphene oxide slurry was added. The obtained film had cracks and was relatively brittle, and a complete film could not be obtained, that is, a film could not be formed.

[0057] Comparative Example 4

[0058] The method was carried out in accordance with Example 1, except that the mass ratio of coal-based graphene oxide to graphite-based graphene oxide was 1:0.05. The obtained film was brittle and could not be separated from the film.

[0059] It is easy to understand that the above embodiments are only examples for clear explanation and do not mean that the present invention is limited thereto. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from this are still within the protection scope of the present invention.

Claims

1. A method for preparing a graphene thermally conductive film, wherein The following steps are involved: 1) Graphitizing pulverized coal to obtain coal-based graphite, wherein the particle size of the pulverized coal must satisfy D97 of 5-75 μm; 2) mixing sulfuric acid and sodium nitrate in an ice water bath to obtain a mixed solution 1, and then adding the coal-based graphite to obtain a mixed solution 2; 3) potassium permanganate is slowly and evenly added to the mixed solution 2 of step 2), and then the temperature is raised to 30-40° C. and reacted for 3-5 hours to obtain a mixed solution 3; 4) heating the mixed solution 3 in step 3) to 95-100° C., adding water, and continuously stirring the mixture to react until the solution turns brown-yellow, and then adding hydrogen peroxide to obtain a mixed solution 4; 5) filtering the mixed solution 4 of step 4), washing the solid product with a hydrochloric acid solution, and then washing with water until the separated washing water is neutral, to obtain coal-based graphite oxide; 6) dispersing the coal-based graphite oxide in water and performing ultrasonic treatment to obtain a coal-based graphene oxide slurry; 7) taking the coal-based graphene oxide slurry obtained in step 6), adjusting the concentration to 3-8 mg / mL, and then adding the graphite-based graphene oxide slurry, the mass ratio of coal-based graphene oxide to graphite-based graphene oxide is 1:(0.1-0.4); dispersing evenly, filtering, drying and stripping to obtain a graphene oxide film; 8) reducing the graphene oxide film obtained in step 7) to obtain a graphene film; 9) The graphene film obtained in step 8) is graphitized and cold pressed to obtain the graphene thermal conductive film.

2. The preparation method according to claim 1, It is characterized in that In step 1), the conditions for graphitization treatment include: a temperature of 2800-3200° C. and a time of 2-4 hours; and / or, the pulverized coal is selected from one or more of anthracite, bituminous coal, and semi-coke, preferably anthracite.

3. The preparation method according to claim 1, It is characterized in that In step 2), the solid-liquid ratio of sodium nitrate to sulfuric acid is 1:(30-50) g / ml, and the sulfuric acid is preferably concentrated sulfuric acid with a mass concentration of not less than 95%; and / or, the solid-liquid ratio of coal-based graphite to mixed solution 1 is 1:(25-40) g / ml; and / or, after adding the coal-based graphite, stirring is uniform to obtain mixed solution 2, and the stirring time is 20-60 min.

4. The preparation method according to claim 1, It is characterized in that In step 3), the mass ratio of potassium permanganate to coal-based graphite is (2-8): 1 g / g; and / or, potassium permanganate is added slowly and evenly by continuously adding potassium permanganate at a feeding rate of 0.05-0.15 g / min; and / or, potassium permanganate is stirred evenly after addition is completed, and stirring is continued during the reaction.

5. The preparation method according to claim 1, It is characterized in that In step 4), the hydrogen peroxide is a hydrogen peroxide with a mass concentration of 20-40%; and / or, the ratio of the amount of the hydrogen peroxide to the potassium permanganate used in step 3) is preferably 1:0.6-2 ml / g; and / or, the process of adding water and adding hydrogen peroxide is independently added dropwise.

6. The preparation method according to any one of claims 1 to 6, It is characterized in that In step 5), the mass ratio of hydrochloric acid to water in the hydrochloric acid solution is 1:(6-12).

7. The preparation method according to any one of claims 1 to 6, It is characterized in that In step 6), the power of ultrasonic treatment is 600-1000 W, and the ultrasonic time is 4-10 h.

8. The preparation method according to any one of claims 1 to 6, It is characterized in that In step 7), the particle size of the graphite-based graphene oxide is 20-160 microns; and / or, ultrasonic treatment is used to make the slurry evenly dispersed; and / or, cellulose acetate membrane filter paper is used for suction filtration; and / or, the drying temperature is room temperature and the drying time is 8-20 hours; and / or, the diameter of the graphene oxide film is 2-8 cm.

9. The preparation method according to any one of claims 1 to 6, It is characterized in that In step 8), the reduction conditions include: introducing H 2 : The inert gas is a mixed gas of 1:(7-12), the heating rate is 2-8°C / min, and after maintaining at 300-600°C for 40-100min, it is naturally cooled to room temperature, during which the flow rate of the mixed gas is maintained at 100-300mL / min; preferably, the inert gas is argon.

10. The preparation method according to any one of claims 1 to 6, It is characterized in that In step 9), the conditions of graphitization treatment include: a temperature of 2800-3200° C. and a time of 0.5-2 h; and / or a cold pressing pressure of 10-50 MPa.

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