A method for preparing a graphene heat-conducting film

Abstract

The application provides a preparation method of a graphene heat-conducting film, which uses low-cost and easily-obtained coal-based graphite as raw material, prepares coal-based graphene oxide through a chemical oxidation method, controls the in-plane size of the coal-based graphene oxide through process conditions, adjusts the concentration and system composition of the graphene oxide solution, prepares a graphene oxide film through a suction filtration method, and obtains the graphene heat-conducting film through steps of low-temperature reduction, high-temperature graphitization and cold pressing. The application successfully breaks through the process flow of preparing the graphene heat-conducting film by taking the coal-based graphite as the main raw material, has low cost, and the obtained graphene heat-conducting film has thin thickness and high heat conduction coefficient.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of industrial heat dissipation materials, and in particular to a preparation method of a graphene heat conduction film. BACKGROUND

[0002] At present, metals and their composite materials are recognized as heat dissipation materials by most people, but the metals have large density and thermal expansion coefficient, are prone to oxidation, and have problems such as the purity affecting the heat conduction performance, and therefore cannot meet the requirements of new heat dissipation materials, so it is urgent to develop a new heat dissipation material which is light in quality and good in heat conduction performance.

[0003] Due to excellent heat conduction and good mechanical strength, graphene thin films are considered to be an ideal choice for heat dissipation materials (HDM) and thermal interface materials (TIM) in electronic devices. At present, graphene thin films are mostly prepared by the CVD method, but the method is complex and high in cost; secondly, flake graphite is mostly used as raw material to prepare graphene thin films, but the yield of flake graphite is limited; and coal has a similar structure to flake graphite, and coal can obtain coal-based graphite under certain conditions. However, since the aromatic ring structure of coal-based graphite is relatively small compared with flake graphite, whether coal-based graphite can be prepared into coal-based graphene heat conduction film like flake graphite, there is no related technical solution at present.

[0004] CN116445856A discloses a preparation method of a graphene thin film. The method mainly uses a mixed gas of acetylene, acetone and argon as a carbon source to grow a graphene thin film on a substrate, but the method can only prepare a super-thin film at present, is high in cost, and the heat conduction performance of the graphene is not mentioned.

[0005] CN111471292A discloses a preparation method of a graphene heat dissipation film. The method uses graphite powder as raw material to prepare a graphene slurry, and then prepares a graphene heat dissipation film through film scraping and directional treatment, but the graphite powder used is one or more of expanded graphite, flake graphite or natural graphite sheet. SUMMARY

[0006] The application provides a preparation method of a graphene heat conduction film, successfully breaks through the process flow of preparing a graphene heat conduction film by taking coal-based graphite as main raw material, is low in cost, and the obtained graphene heat conduction film is thin in thickness and high in heat conduction coefficient.

[0007] In order to achieve the purpose, the application provides the following technical scheme:

[0008] The application provides a preparation method of a graphene heat conduction film, which comprises the following steps:

[0009] 1) coal-based graphite is obtained by graphitizing treatment of pulverized coal, wherein the particle size of the pulverized coal needs to meet D97 of 5-75 μm (for example, 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) sulfuric acid and sodium nitrate are mixed in an ice water bath to obtain a mixed solution 1, and then the coal-based graphite is added to obtain a mixed solution 2;

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

[0012] 4) the mixed solution 3 in step 3) is raised to 95-100 °C (for example, 96 °C, 97 °C, 98 °C, 99 °C, etc.), water is added, and the reaction is continuously stirred until the solution is brownish yellow, and then hydrogen peroxide is added to obtain a mixed solution 4;

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

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

[0015] 7) the coal-based graphene oxide slurry obtained in step 6) is taken, the concentration is adjusted to 3-8 mg / mL (for example, 4 mg / mL, 5 mg / mL, 6 mg / mL, 7 mg / mL, etc.), and then a graphite-based graphene oxide slurry is added, and 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.; uniformly dispersed, suction filtered, dried and demolded to obtain a graphene oxide film;

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

[0017] 9) the graphene film obtained in step 8) is subjected to graphitization treatment, cold-pressed to obtain the graphene heat-conducting film.

[0018] In some embodiments of the preparation method of the present application, in step 1), the conditions of the graphitization treatment include: a temperature of 2800-3200℃ (e.g. 2900℃, 3000℃, 3100℃, 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, semi-coke coal, preferably anthracite. In this context, other conditions of the graphitization treatment are well known to those skilled in the art and can be reasonably selected, except for the conditions specifically emphasized, such as the graphite crucible and graphite furnace and other apparatuses and the need for the graphitization treatment to be carried out under the protection of an inert atmosphere (such as argon).

[0019] In some embodiments of the preparation method of the present application, 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 with a mass concentration of not less than 95% (e.g. 96%, 97%, 98%, etc.); and / or, the solid-liquid ratio of the coal-based graphite to the mixed solution 1 is 1:(25-40) g / ml (e.g. 1:30 g / ml, 1:35 g / ml, etc.); and / or, after the coal-based graphite is added, the stirring is uniform to obtain the 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 application, 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, the potassium permanganate is slowly and uniformly added 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.) to continuously add the potassium permanganate; and / or, after the addition of the potassium permanganate is completed, the stirring is uniform, and the stirring is continuously performed during the reaction.

[0021] In some embodiments of the preparation method of the present application, in step 4), the hydrogen peroxide is 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 process of adding water and adding hydrogen peroxide is independently dropwise.

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

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

[0024] In some embodiments of the preparation method of the present application, 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 any range formed by any two of the above-mentioned end values); and / or, ultrasonic treatment is used to uniformly disperse the slurry; and / or, filter paper is used for suction filtration; and / or, the drying temperature is room temperature, and the drying time is 8-20h (for example, 10h, 15h, etc.); and / or, the diameter of the graphene oxide film is 2-8cm (for example, 3cm, 4cm, 5cm, 6cm, 7cm, etc.).

[0025] In some embodiments of the preparation method of the present application, in step 8), the reduction conditions include: the mixed gas of H2:inert gas is 1:(7-12) (for example, 1:9), the heating rate is 2-8℃ / min (for example, 4℃ / min, 6℃ / min, etc.), after maintaining at 300-600℃ (for example, 400℃, 500℃, etc.) for 40-100min (for example, 60min, 80min), natural cooling to room temperature, and the flow rate of the mixed gas is maintained at 100-300mL / min (for example, 200mL / min) during the period; preferably, the inert gas is argon.

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

[0027] The present application provides a preparation method of graphene heat-conducting film, which uses low-cost and easily available coal-based graphite as raw material, prepares coal-based graphene oxide by chemical oxidation method, controls the in-plane size of coal-based graphene oxide through specific process conditions, adjusts the concentration and system composition of graphene oxide solution, prepares graphene oxide film through suction filtration method, and obtains coal-based graphene film through low-temperature reduction, high-temperature graphitization and cold pressing.

[0028] The technical scheme provided by the present application has the following beneficial effects:

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

[0030] 2) The aromatic ring structure of coal-based graphite is relatively small compared to flake graphite, and there is no mature process for preparing graphene heat-conducting film using coal-based graphite as the main raw material in the prior art, and the present application successfully solves this problem.

[0031] 3) The graphene heat-conducting film prepared by the preparation method has a small thickness and a high thermal conductivity. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 A flowchart of the preparation method of the present application is shown.

[0033] Figure 2 An example diagram of the preparation of graphene oxide film by filtering the mixed solution of coal-based graphene oxide and graphite-based graphene oxide in the preparation method of the present application is shown. DETAILED DESCRIPTION

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

[0035] If the specific experimental steps or conditions are not specified in the examples, the corresponding conventional experimental steps or conditions can be used. If the reagents or instruments used are not specified by the manufacturer, they are conventional products that can be obtained by purchase. The method for measuring the thermal conductivity is referred to GB / T 22588-2008 flash method for measuring thermal diffusivity or thermal conductivity.

[0036] Example 1

[0037] 1) Coal-based graphite was obtained by graphitizing coal powder (Taixi anthracite) with a D97 of 62 μm (3000℃, 3h).

[0038] 2) Coal-based graphite was added to a mixed solution 1 of concentrated sulfuric acid (concentration 98%) and sodium nitrate (solid-liquid ratio of sodium nitrate to concentrated sulfuric acid 1:40 g / ml, mixed in an ice bath), stirred for 30 min to mix uniformly, the solid-liquid ratio of coal-based graphite to mixed solution 1 was 1:30 g / ml, and a mixed solution 2 was obtained.

[0039] 3) Potassium permanganate (5 times the mass of coal-based graphite) was slowly and uniformly added (added continuously at a feeding rate of about 0.1 g / min) to the mixed solution 2 of step 2), after the addition was completed and stirred uniformly, the temperature was raised to 35℃ and reacted for 4h, and the stirring was continued during the reaction, and a mixed solution 3 was obtained.

[0040] 4) The mixture 3 in step 3) is warmed to 98℃, and deionized water is added dropwise, the reaction is continuously stirred until the solution is brownish yellow, then 30wt% hydrogen peroxide is added dropwise, the ratio of hydrogen peroxide to potassium permanganate is 1:0.8ml / g, to obtain mixture 4.

[0041] 5) The mixture 4 in step 4) is filtered, and the solid product is washed with dilute hydrochloric acid with a mass ratio of hydrochloric acid to water of 1:10, then washed with a large amount of deionized water until the separated washing water is neutral, to obtain coal-based graphite oxide.

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

[0043] 7) The coal-based graphene oxide slurry obtained in step 6) is taken and deionized water is added to adjust the concentration to 4mg / mL, then graphite-based graphene oxide (particle size within 40-120 microns) slurry is added, the mass ratio of coal-based graphene oxide to graphite-based graphene oxide is 1:0.2, ultrasonic dispersion is uniform, and the graphene oxide film is obtained by suction filtration with acetic acid fiber membrane filter paper, and dried at room temperature for 12h, the diameter is about 5cm.

[0044] 8) The graphene oxide film obtained in step 7) is reduced, a mixed gas of H2:Ar is 1:9, the heating rate is 5℃ / min, maintained at 400℃ for 60min, and then naturally cooled to room temperature, during which the mixed gas of H2:Ar is maintained at 200mL / min. The graphene film is obtained by taking out the sample.

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

[0046] The specific preparation method in the example can also refer to Figure 1 and Figure 2 , wherein, Figure 1 relates to an exemplary flowchart of the preparation method, Figure 2 relates to an exemplary diagram of the process of preparing graphene oxide film by suction filtration of the mixture of coal-based graphene oxide and graphite-based graphene oxide in the preparation method.

[0047] Example 2

[0048] Refer to Example 1, the difference is that in step 7) the mass ratio of coal-based graphene oxide to graphite-based graphene oxide is 1:0.25. The thickness of the obtained graphene heat conduction film is about 27 microns, and the thermal conductivity coefficient is about 1184w / mk.

[0049] Example 3

[0050] Referring to Example 1, except that the raw coal powder size D97 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 heat-conducting film has a thickness of about 26 microns and a thermal conductivity of about 1247 w / mk.

[0051] Comparative Example 1

[0052] Referring to Example 1, except that in step 7), the concentration of the coal-based graphene oxide slurry is adjusted to 2.5 mg / mL, and no graphite-based graphene oxide slurry is added. The obtained film is brittle and completely cracked, and no complete film can be obtained, i.e., the film cannot be formed.

[0053] Comparative Example 2

[0054] Referring to Example 1, except that in step 7), the concentration of the coal-based graphene oxide slurry is adjusted to 2.5 mg / mL. The obtained film has cracks, and the obtained film is not complete, i.e., the film cannot be formed.

[0055] Comparative Example 3

[0056] Referring to Example 1, except that in step 7), no graphite-based graphene oxide slurry is added. The obtained film has cracks and is brittle, and no complete film can be obtained, i.e., the film cannot be formed.

[0057] Comparative Example 4

[0058] Referring to Example 1, except that the mass ratio of coal-based graphene oxide to graphite-based graphene oxide is 1:0.05. The obtained film is brittle and cannot be formed.

[0059] It is easily understood that the above examples are only examples for clearly illustrating the present application, and do not mean that the present application is limited to this. Based on the above description, other different forms of changes or variations can be made by those skilled in the art. Here, it is not necessary and impossible to exhaust all the embodiments. The obvious changes or variations derived therefrom are still within the protection scope of the present application.

Claims

1. A method for preparing a graphene thermally conductive film, comprising the following steps: 1) Graphitize pulverized coal to obtain coal-based graphite, wherein the particle size of the pulverized coal must meet the requirement that D97 is 5-75 μm; 2) Mix sulfuric acid and sodium nitrate in an ice-water bath to obtain mixture 1, and then add the coal-based graphite to obtain mixture 2; 3) Slowly and evenly add potassium permanganate to the mixture 2 from step 2), then heat to 30-40℃ and react for 3-5 hours to obtain mixture 3; 4) Heat the mixture 3 from step 3) to 95-100℃, add water, and continue stirring until the solution turns brownish-yellow. Then add hydrogen peroxide to obtain mixture 4. 5) Filter the mixture 4 from step 4), wash the solid product with hydrochloric acid solution, and then wash with water until the separated wash water is neutral to obtain coal-based graphite oxide. 6) The coal-based graphene oxide is dispersed in water and subjected to ultrasonic treatment to obtain a coal-based graphene oxide slurry; 7) Take the coal-based graphene oxide slurry obtained in step 6), adjust the concentration to 3-8 mg / mL, and then add graphene oxide slurry. The mass ratio of coal-based graphene oxide to graphene oxide is 1:(0.1-0.4). Disperse evenly, filter, dry and remove the film to obtain a graphene oxide film. 8) Reduce 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, characterized in that, In step 1), the graphitization treatment conditions include: a temperature of 2800-3200℃ and a time of 2-4 hours; and / or, the pulverized coal is selected from one or more of anthracite, bituminous coal, and semi-coking coal.

3. The preparation method according to claim 1, characterized in that, In step 1), the pulverized coal is anthracite.

4. The preparation method according to claim 1, characterized in that, In step 2), the solid-liquid ratio of sodium nitrate to sulfuric acid is 1:(30-50) g / ml; and / or, the solid-liquid ratio of coal-based graphite to mixture 1 is 1:(25-40) g / ml; and / or, after adding the coal-based graphite, the mixture is stirred evenly to obtain mixture 2, and the stirring time is 20-60 min.

5. The preparation method according to claim 1, characterized in that, In step 2), the sulfuric acid is concentrated sulfuric acid with a mass concentration of not less than 95%.

6. The preparation method according to claim 1, 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 uniformly at a feeding rate of 0.05-0.15 g / min; and / or, after the potassium permanganate is added, the mixture is stirred evenly and continuously stirred during the reaction.

7. The preparation method according to claim 1, characterized in that, In step 4), the hydrogen peroxide is hydrogen peroxide with a mass concentration of 20-40%; and / or, the process of adding water and adding hydrogen peroxide is independently dropwise.

8. The preparation method according to claim 1, characterized in that, In step 4), the ratio of the amount of hydrogen peroxide used to the amount of potassium permanganate used in step 3) is 1:0.6-2 ml / g.

9. The preparation method according to any one of claims 1-8, characterized in that, In step 5), the mass ratio of hydrochloric acid to water in the hydrochloric acid solution is 1:(6-12).

10. The preparation method according to any one of claims 1-8, characterized in that, In step 6), the ultrasonic treatment power is 600-1000W and the ultrasonic time is 4-10h.

11. The preparation method according to any one of claims 1-8, characterized in that, In step 7), the particle size of the graphite-based graphene oxide is 20-160 micrometers; and / or, ultrasonic treatment is used to disperse the slurry evenly; and / or, filtration is performed using cellulose acetate membrane filter paper; 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.

12. The preparation method according to any one of claims 1-8, characterized in that, In step 8), the reduction conditions include: introducing a mixture of H2 and inert gas in a ratio of 1:(7-12), heating at a rate of 2-8℃ / min, maintaining at 300-600℃ for 40-100min, and then naturally cooling to room temperature, while maintaining the flow rate of the mixture at 100-300mL / min.

13. The preparation method according to claim 12, characterized in that, The inert gas is argon.

14. The preparation method according to any one of claims 1-8, characterized in that, In step 9), the graphitization conditions include: a temperature of 2800-3200℃, a time of 0.5-2h; and / or, a cold pressing pressure of 10-50MPa.

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