Graphene composite kaolin powder, and preparation method and application thereof

Abstract

The application discloses graphene composite kaolin powder and a preparation method and application thereof. The preparation method is characterized in that firstly, the surface of kaolin powder is grafted and modified by using an amino silane coupling agent, so that the kaolin powder and graphene oxide present opposite electric properties within a certain pH range. When the pH is 2-3, the two can effectively self-assemble, the problem that the two kinds of materials with negative electricity, namely, graphene and kaolin powder, are difficult to mix uniformly and graphene is prone to agglomeration in the sintered ceramic body of kaolin powder is overcome, the micro-morphology of the graphene composite kaolin heat-conducting ceramic material is relatively dense, the porosity is low, graphene constructs a rapid heat conduction path in the ceramic, and the thermal diffusion coefficient and the thermal conductivity of the composite material are increased.

Description

Technical Field

[0001] This invention belongs to the field of thermally conductive ceramics technology, specifically relating to a graphene composite kaolin powder, its preparation method, and its application. Background Technology

[0002] Thermally conductive ceramic materials are ceramic materials with excellent thermal conductivity, widely used in heat sinks for electronic components, insulation layers for high-voltage cables, and other fields. Currently, commonly used thermally conductive ceramic materials are mostly alumina and silicon nitride. However, traditional thermally conductive ceramic materials suffer from high density, low mechanical strength, and fragility despite their high thermal conductivity. Therefore, finding a new type of thermally conductive ceramic material with both high thermal conductivity and high mechanical strength is of great significance. Graphene is a novel carbon material with excellent thermal and mechanical properties, and can be used to prepare thermally conductive ceramic materials. Kaolin is a common ceramic raw material with good high-temperature resistance and structural stability. Combining graphene and kaolin to prepare thermally conductive ceramic materials can fully utilize the advantages of both, improving the material's thermal conductivity and mechanical properties. For example, CN112707736A provides a method for preparing graphene-modified ceramic composite materials. In this method, ceramic powder and graphene nanosheet dispersion are mixed uniformly in the mold cavity of a pressure casting machine using the graphene nanosheet dispersion. The resulting composite material exhibits excellent fracture toughness and good thermal conductivity. Multiphase thermal storage ceramics typically possess excellent thermal shock resistance, high fracture toughness and strength, low thermal resistance, high thermal storage density, and good high-temperature thermal properties. Therefore, developing novel high-temperature, high-efficiency, and low-cost thermal storage ceramic materials is of great significance for improving the efficiency of thermal power generation and thermal utilization technologies. Kaolin is an important solid thermal storage material. Its main chemical components are SiO2 and Al2O3. Most kaolin also contains MgO and Fe2O3, and the high Fe2O3 content promotes the formation of the liquid phase, making the sample denser. Since high bulk density corresponds to high thermal storage density, this provides a new approach for using kaolin to prepare solar thermal storage materials.

[0003] Compared to traditional ceramics, graphene-composite kaolin thermally conductive ceramic materials offer advantages including improved heat conduction, thermal management efficiency, and potentially superior mechanical properties. These composite ceramic materials have wide applications in electronics, aerospace, and automotive fields, and hold particular promise for applications requiring highly efficient thermal management. Summary of the Invention

[0004] The purpose of this invention is to provide a graphene-composite kaolin powder, its preparation method, and its application. This graphene-composite kaolin powder can be used to sinter graphene-composite kaolin thermally conductive ceramic materials with good thermal conductivity and mechanical strength, and has broad application prospects.

[0005] The technical solution of the present invention is as follows:

[0006] A method for preparing graphene-composite kaolin powder includes the following steps:

[0007] (1) Kaolin powder is ultrasonically dispersed in an ethanol solution, then an aminosilane coupling agent is added, and after thorough mixing, the reaction is carried out. Then, the residual aminosilane coupling agent is washed away, and the powder is dried to obtain surface-modified kaolin powder. The reaction temperature is 73-83℃ and the reaction time is 19-29h.

[0008] The mass-to-volume ratio of the above-mentioned kaolin powder to the above-mentioned aminosilane coupling agent is 1-1.5 g : 10-15 mL; the reaction time after mixing is 24 h ± 5 h.

[0009] (2) Disperse the above surface-modified kaolin powder in deionized water and adjust the pH to 2-3 to obtain kaolin dispersion.

[0010] (3) Disperse graphene oxide aerogel in deionized water, adjust the pH to 2-3, then add the above kaolin dispersion, mix thoroughly and let stand until the system separates into layers, then take off the lower layer of slurry and centrifuge and wash until weakly acidic, and finally dry to obtain graphene oxide composite kaolin powder.

[0011] The mass ratio of the surface-modified kaolin powder to the graphene oxide aerogel in the above-mentioned kaolin dispersion is 100:2.5-10.

[0012] (4) The graphene oxide composite kaolin powder was reduced by hydrazine hydrate as a reducing agent to obtain graphene composite kaolin powder.

[0013] In some possible implementations, the preparation method of graphene oxide aerogel is as follows: Slowly pour concentrated sulfuric acid into graphite powder, then stir in an ice-water bath to fully mix the graphite powder and concentrated sulfuric acid. After the system temperature drops below 10°C, slowly add potassium permanganate powder, continue stirring and react at 45°C for 2 hours. After the reaction is completed, slowly add distilled water to the system and control the system temperature to not exceed 100°C. Then cool to room temperature, then add hydrogen peroxide dropwise until the system turns golden yellow. Seal and let stand until the system separates into layers. Then take off the lower layer precipitate, wash it until neutral, and then freeze-dry to obtain graphene oxide aerogel.

[0014] The mass-volume ratio of graphite powder, concentrated sulfuric acid, and distilled water is 1g:50mL:75mL, the mass ratio of graphite powder to potassium permanganate powder is 1:6, and the mass fraction of hydrogen peroxide is 30wt%.

[0015] In the above steps, the main functions of sealing are to prevent contamination, maintain reaction conditions such as temperature and humidity of the system, prevent splashing, reduce the release of harmful gases, and facilitate subsequent processing. For example, this can be achieved by covering the mouth of the reaction vessel with plastic wrap and then sealing it.

[0016] In some possible implementations, the specific operation of step (4) is as follows: the graphene oxide composite kaolin powder is dispersed in deionized water, hydrazine hydrate is added, and then the reaction is carried out at 90-95℃ for 80-100h to obtain a black precipitate. After washing and drying the black precipitate, the graphene composite kaolin powder is obtained.

[0017] The mass-to-volume ratio of graphene oxide composite kaolin powder to hydrazine hydrate is 0.5 g: 5 mL.

[0018] In some possible implementations, the size of the kaolin powder is 200 mesh, and the size of the graphite powder is 8000 mesh.

[0019] In some possible implementations, the aminosilane coupling agent is 3-aminopropylmethyldiethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyltrimethylsilane, or aminoethylaminopropyltrimethoxysilane.

[0020] A graphene-composite kaolin powder is prepared by the above-described preparation method.

[0021] A graphene-composite kaolin thermally conductive ceramic material is obtained by shaping and sintering the graphene-composite kaolin powder.

[0022] In some possible implementations, the sintering temperature is 1080-1400℃ and the sintering time is 180 min.

[0023] In some possible implementations, sintering is carried out under nitrogen or argon protection.

[0024] The application of the above-mentioned graphene-kaolin composite powder in the preparation of graphene-kaolin composite thermally conductive ceramic materials.

[0025] The present invention has at least the following beneficial effects:

[0026] 1. This invention first uses an aminosilane coupling agent to graft and modify the surface of kaolin powder, so that it exhibits opposite electrical properties to graphene oxide within a certain pH range. When the pH is 2-3, the two can effectively self-assemble, overcoming the problems that graphene and kaolin powder, two negatively charged materials, are difficult to mix evenly and that graphene is prone to agglomeration in the ceramic aggregate of sintered kaolin powder.

[0027] 2. In some possible implementations, this application uses the Hummers method to prepare graphene oxide aerogel, mixes it with surface-modified kaolin powder, and then performs a hydrazine hydrate reduction reaction to obtain graphene composite kaolin powder. After that, graphene composite kaolin thermally conductive ceramic material is obtained by high-temperature sintering. The whole production process is safe, efficient and easy to mass-produce.

[0028] 3. The graphene-kaolin composite thermally conductive ceramic material prepared by this invention has a relatively dense microstructure and low porosity. Graphene constructs a rapid heat conduction path inside the ceramic, increasing the thermal diffusivity and thermal conductivity of the ceramic material.

[0029] 4. Compared with pure phase kaolin ceramics, the graphene composite kaolin thermally conductive ceramic material prepared by this invention has better mechanical properties; at the optimal addition amount, the thermal diffusivity increases by 2.8 times and the thermal conductivity increases by 6 times. Attached Figure Description

[0030] Figure 1 The process diagrams for preparing graphene-composite kaolin thermally conductive ceramic materials in Examples 1-12 are shown.

[0031] Figure 2 This is the TG-DSC curve of Example 1;

[0032] Figure 3 These are scanning electron microscope images of the graphene-composite kaolin thermally conductive ceramic materials prepared in Examples 1-4; where (a) is Example 1, (b) is Example 2, (c) is Example 3, and (d) is Example 4.

[0033] Figure 4 These are XRD diffraction patterns of the graphene-composite kaolin thermally conductive ceramic materials prepared in Examples 5-8. Detailed Implementation

[0034] The technical solution of the present invention will be further explained and described below through specific embodiments.

[0035] In the following embodiments, the water used can be one or more of distilled water, purified water, and drinking water; unless otherwise specified, the detection methods in the following embodiments are conventional detection methods; unless otherwise specified, the reagents in the following embodiments are all purchased from commercial channels.

[0036] Example 1

[0037] (1) 200-mesh kaolin powder was dispersed in 200 mL of ethanol for 1 h using 200 W ultrasonication to separate thin sheets. Then, kaolin powder was added and ultrasonically dispersed in the ethanol solution at a mass ratio of 3-aminopropylmethyldiethoxysilane. The mixture was stirred at 500 rpm for 10 min to ensure thorough mixing. Afterward, the mixture was continuously stirred at 78 °C and refluxed for 24 h. After the reaction was completed, the product was washed with deionized water and ethanol by alternating centrifugation 3-5 times to remove excess 3-aminopropylmethyldiethoxysilane. The product was then dried at 60 °C for 6 h to obtain surface-modified kaolin powder.

[0038] (2) Disperse the above surface-modified kaolin powder in deionized water and adjust the pH to 2-3 to obtain kaolin dispersion.

[0039] (3) Weigh 1g of 8000 mesh graphite powder, slowly pour 50mL of concentrated sulfuric acid into it, and then perform magnetic stirring in an ice-water bath to fully mix the graphite powder and concentrated sulfuric acid. After the system temperature drops below 10℃, slowly add 6g of potassium permanganate powder, continue stirring and react at 45℃ for 2h. After the reaction is completed, slowly add 75mL of distilled water to the system and increase the magnetic stirring speed. During the reaction, control the system temperature to not exceed 100℃. Then cool to room temperature, and then add 30wt% hydrogen peroxide until the system turns golden yellow. Seal with plastic wrap and let stand for 24h. Then take off the lower layer precipitate and wash it with deionized water until neutral. Then freeze dry to obtain graphene oxide aerogel.

[0040] (4) The graphene oxide aerogel was ultrasonically dispersed for 2 hours to obtain a graphene oxide dispersion. The graphene oxide dispersion was then dispersed again in deionized water and the pH was adjusted to 3 with dilute hydrochloric acid. The dispersion was then added dropwise to the kaolin dispersion under ultrasonic vibration and ultrasonically mixed for 2 hours. The mixture was then allowed to stand until the system separated into layers. At this point, the upper layer was a clear and transparent liquid and the lower layer was a slurry. The lower slurry was taken and washed until the pH was weakly acidic. Finally, it was dried to obtain graphene oxide composite kaolin powder.

[0041] The mass ratio of the surface-modified kaolin powder to the graphene oxide aerogel in the above-mentioned kaolin dispersion is 100:2.5.

[0042] (5) Disperse the graphene oxide composite kaolin powder in deionized water, sonicate for 2 hours, add hydrazine hydrate, and then react at 90-95℃ for 80-100 hours to obtain a black precipitate. After washing and drying the black precipitate, obtain the graphene composite kaolin powder.

[0043] The mass-to-volume ratio of graphene oxide composite kaolin powder to hydrazine hydrate is 0.5 g: 5 mL.

[0044] (6) The above graphene composite kaolin powder is formed by hydraulic pressing with a mold to obtain a ceramic green body, which is then placed in a tube sintering furnace for sintering at a temperature of 1087℃ and held for 180 minutes to obtain a graphene composite kaolin thermally conductive ceramic material.

[0045] Thermogravimetric analysis was performed on Example 1, and the results are as follows: Figure 2 As shown, the graphene-kaolin composite thermally conductive ceramic material of Example 1 experienced a 20% weight loss during sintering.

[0046] Example 2

[0047] The difference between Example 2 and Example 1 is that the mass ratio of the surface-modified kaolin powder to the graphene oxide aerogel in step (4) is 100:5.

[0048] Example 3

[0049] The difference between Example 3 and Example 1 is that the mass ratio of the surface-modified kaolin powder to the graphene oxide aerogel in step (4) is 100:7.5.

[0050] Example 4

[0051] The difference between Example 4 and Example 1 is that the mass ratio of the surface-modified kaolin powder to the graphene oxide aerogel in step (4) is 100:10.

[0052] Scanning electron microscope (SEM) images of the graphene-kaolin composite thermally conductive ceramic materials prepared in Examples 1-4 are shown below. Figure 3 As shown, the graphene-composite kaolin thermally conductive ceramic material has a dense microstructure and low porosity. The graphite flakes are uniformly distributed in the matrix and wrapped around the grains, indicating that the addition of graphene enhances the microstructure of the sintered body.

[0053] Example 5

[0054] (1) 200-mesh kaolin powder was dispersed in 200 mL of ethanol for 2 h using 200 W ultrasonication to separate thin sheets. Then, kaolin powder was added and ultrasonically dispersed in the ethanol solution at a mass ratio of 3-aminopropyltriethoxysilane. The mixture was stirred at 500 rpm for 10 min to ensure thorough mixing. Afterward, the mixture was continuously stirred at 78 °C and refluxed for 24 h. After the reaction was completed, the product was washed with deionized water and ethanol alternately by centrifugation 3-5 times to remove excess 3-aminopropyltriethoxysilane. The product was then dried at 60 °C for 6 h to obtain surface-modified kaolin powder.

[0055] (2) Disperse the above surface-modified kaolin powder in deionized water and adjust the pH to 2-3 to obtain kaolin dispersion.

[0056] (3) Weigh 2g of 8000 mesh graphite powder, slowly pour 100mL of concentrated sulfuric acid into it, and then perform magnetic stirring in an ice-water bath to fully mix the graphite powder and concentrated sulfuric acid. After the system temperature drops below 10℃, slowly add 12g of potassium permanganate powder, continue stirring and react at 45℃ for 2h. After the reaction is completed, slowly add 75mL of distilled water to the system and increase the magnetic stirring speed. During the reaction, control the system temperature to not exceed 100℃. Then cool to room temperature, and then add 30wt% hydrogen peroxide until the system turns golden yellow. Seal with plastic wrap and let stand for 24h. Then take off the lower layer precipitate and wash it with deionized water until neutral. Then freeze dry to obtain graphene oxide aerogel.

[0057] (4) The graphene oxide aerogel was ultrasonically dispersed for 2 hours to obtain a graphene oxide dispersion. The graphene oxide dispersion was then dispersed again in deionized water and the pH was adjusted to 3 with dilute hydrochloric acid. The dispersion was then added dropwise to the kaolin dispersion under ultrasonic vibration and ultrasonically mixed for 2 hours. The mixture was then allowed to stand until the system separated into layers. At this point, the upper layer was a clear and transparent liquid and the lower layer was a slurry. The lower slurry was taken and washed until the pH was neutral. Finally, it was dried to obtain graphene oxide composite kaolin powder.

[0058] The mass ratio of the surface-modified kaolin powder to the graphene oxide aerogel in the above-mentioned kaolin dispersion is 100:2.5.

[0059] (5) Disperse the graphene oxide composite kaolin powder in deionized water, sonicate for 2 hours, add hydrazine hydrate, and then react at 90-95℃ for 80-100 hours to obtain a black precipitate. After washing and drying the black precipitate, obtain the graphene composite kaolin powder.

[0060] The mass-to-volume ratio of graphene oxide composite kaolin powder to hydrazine hydrate is 0.5 g: 5 mL.

[0061] (6) The above graphene composite kaolin powder is formed by hydraulic pressing with a mold to obtain a ceramic green body, which is then placed in a tube sintering furnace for sintering at a temperature of 1150℃ and held for 180 min to obtain a graphene composite kaolin thermally conductive ceramic material.

[0062] Example 6

[0063] The difference between Example 6 and Example 5 is that the mass ratio of the surface-modified kaolin powder to the graphene oxide aerogel in step (4) is 100:5.

[0064] Example 7

[0065] The difference between Example 7 and Example 5 is that the mass ratio of the surface-modified kaolin powder to the graphene oxide aerogel in step (4) is 100:7.5.

[0066] Example 8

[0067] The difference between Example 8 and Example 5 is that the mass ratio of the surface-modified kaolin powder to the graphene oxide aerogel in step (4) is 100:10.

[0068] The XRD diffraction patterns of the graphene-kaolin composite thermally conductive ceramic materials prepared in Examples 5-8 are shown below. Figure 4 As shown.

[0069] Example 9

[0070] (1) 200-mesh kaolin powder was dispersed in 200 mL of ethanol for 2 h using 200 W ultrasonication to separate thin sheets. Then, kaolin powder was added and ultrasonically dispersed in the ethanol solution at a mass ratio of 3-aminopropyltriethoxysilane. The mixture was stirred at 500 rpm for 10 min to ensure thorough mixing. Afterward, the mixture was continuously stirred at 78 °C and refluxed for 24 h. After the reaction was completed, the product was washed with deionized water and ethanol alternately by centrifugation 3-5 times to remove excess 3-aminopropyltriethoxysilane. The product was then dried at 60 °C for 6 h to obtain surface-modified kaolin powder.

[0071] (2) Disperse the above surface-modified kaolin powder in deionized water and adjust the pH to 2-3 to obtain kaolin dispersion.

[0072] (3) Weigh 2g of 8000 mesh graphite powder, slowly pour 100mL of concentrated sulfuric acid into it, and then perform magnetic stirring in an ice-water bath to fully mix the graphite powder and concentrated sulfuric acid. After the system temperature drops below 10℃, slowly add 12g of potassium permanganate powder, continue stirring and react at 45℃ for 2h. After the reaction is completed, slowly add 150mL of distilled water to the system and increase the magnetic stirring speed. During the reaction, control the system temperature to not exceed 100℃. Then cool to room temperature, and then add 30wt% hydrogen peroxide until the system turns golden yellow. Seal with plastic wrap and let stand for 24h. Then take off the lower layer precipitate and wash it with deionized water until neutral. Then freeze dry to obtain graphene oxide aerogel.

[0073] (4) The graphene oxide aerogel was ultrasonically dispersed for 2 hours to obtain a graphene oxide dispersion. The graphene oxide dispersion was then dispersed again in deionized water and the pH was adjusted to 3 with dilute hydrochloric acid. The dispersion was then added dropwise to the kaolin dispersion under ultrasonic vibration and ultrasonically mixed for 2 hours. The mixture was then allowed to stand until the system separated into layers. At this point, the upper layer was a clear and transparent liquid and the lower layer was a slurry. The lower slurry was taken and washed until the pH was neutral. Finally, it was dried to obtain graphene oxide composite kaolin powder.

[0074] The mass ratio of the surface-modified kaolin powder to the graphene oxide aerogel in the above-mentioned kaolin dispersion is 100:2.5.

[0075] (5) Disperse the graphene oxide composite kaolin powder in deionized water, sonicate for 2 hours, add hydrazine hydrate, and then react at 90-95℃ for 80-100 hours to obtain a black precipitate. After washing and drying the black precipitate, obtain the graphene composite kaolin powder.

[0076] The mass-to-volume ratio of graphene oxide composite kaolin powder to hydrazine hydrate is 0.5 g: 5 mL.

[0077] (6) The above graphene composite kaolin powder is formed by hydraulic pressing with a mold to obtain a ceramic green body, which is then placed in a tube sintering furnace for sintering at a temperature of 1087℃ and held for 180 minutes to obtain a graphene composite kaolin thermally conductive ceramic material.

[0078] Example 10

[0079] The difference between Example 10 and Example 9 is that the mass ratio of the surface-modified kaolin powder to the graphene oxide aerogel in step (4) is 100:5.

[0080] Example 11

[0081] The difference between Example 11 and Example 9 is that the mass ratio of the surface-modified kaolin powder to the graphene oxide aerogel in step (4) is 100:7.5.

[0082] Example 12

[0083] The difference between Example 12 and Example 9 is that the mass ratio of the surface-modified kaolin powder to the graphene oxide aerogel in step (4) is 100:10.

[0084] Comparative Example 1

[0085] The difference between Comparative Example 1 and Example 5 is that step (5) does not use hydrazine hydrate as a reducing agent to reduce the graphene oxide composite kaolin powder, but instead reduces the graphene oxide composite kaolin powder to graphene composite kaolin powder through high-temperature heat treatment.

[0086] The specific operation of high-temperature heat treatment is as follows: The graphene oxide composite kaolin powder is placed in a high-temperature tube furnace. The temperature and time are adjusted, and the heating rate is controlled between 5-10℃ / min to avoid thermal shock to the graphene oxide composite kaolin powder. The powder is slowly heated to 1000℃ and then held for 2 hours to ensure effective reduction of the graphene oxide. Afterward, the system is slowly cooled to room temperature to avoid the influence of rapid temperature changes on the sample.

[0087] Comparative Example 2

[0088] The difference between Comparative Example 2 and Comparative Example 1 is that the mass ratio of the surface-modified kaolin powder to the graphene oxide aerogel in step (4) is 100:5.

[0089] Comparative Example 3

[0090] The difference between Comparative Example 3 and Comparative Example 1 is that the mass ratio of the surface-modified kaolin powder to the graphene oxide aerogel in step (4) is 100:7.5.

[0091] Comparative Example 4

[0092] The difference between Comparative Example 4 and Comparative Example 1 is that the mass ratio of the surface-modified kaolin powder to the graphene oxide aerogel in step (4) is 100:10.

[0093] Comparative Example 5

[0094] The difference between Comparative Example 5 and Comparative Example 1 is that the sintering temperature in step (6) is 1400℃.

[0095] Comparative Example 6

[0096] The difference between Comparative Example 6 and Comparative Example 5 is that the mass ratio of the surface-modified kaolin powder to the graphene oxide aerogel in step (4) is 100:5.

[0097] Comparative Example 7

[0098] The difference between Comparative Example 7 and Comparative Example 5 is that the mass ratio of the surface-modified kaolin powder to the graphene oxide aerogel in step (4) is 100:7.5.

[0099] Comparative Example 8

[0100] The difference between Comparative Example 8 and Comparative Example 5 is that the mass ratio of the surface-modified kaolin powder to the graphene oxide aerogel in step (4) is 100:10.

[0101] Comparative Example 9

[0102] The difference between Comparative Example 9 and Example 5 is that the kaolin used was not surface modified (kaolin specifications: flake size 75±5μm) and no graphene aerogel was added in step (4), and the sintering temperature in step (6) was 1087℃.

[0103] Comparative Example 10

[0104] The difference between Comparative Example 10 and Comparative Example 9 is that the sintering temperature in step (6) is 1150℃.

[0105] Comparative Example 11

[0106] The difference between Comparative Example 11 and Example 9 is that the surface-modified kaolin powder obtained in step (1) is replaced with unmodified kaolin, and the mass ratio of unmodified kaolin to the above-mentioned graphene oxide aerogel is 100:2.5.

[0107] Comparative Example 12

[0108] The difference between Comparative Example 11 and Example 9 is that the kaolin used was not surface modified (kaolin specifications: flake size 75±5μm), and the mass ratio of unmodified kaolin to the above-mentioned graphene oxide aerogel was 100:5.

[0109] Comparative Example 13

[0110] The difference between Comparative Example 13 and Example 9 is that the kaolin used was not surface modified (kaolin specifications: flake size 75±5μm), and the mass ratio of unmodified kaolin to the above-mentioned graphene oxide aerogel was 100:7.5.

[0111] Comparative Example 14

[0112] The difference between Comparative Example 14 and Example 9 is that the kaolin used was not surface modified (kaolin specifications: flake size 75±5μm), and the mass ratio of unmodified kaolin to the above-mentioned graphene oxide aerogel was 100:10.

[0113] Performance testing

[0114] The thermal diffusivity and thermal conductivity in the following performance tests are all tested in the vertical direction.

[0115] (1) The thermal conductivity of Examples 5-12 and Comparative Examples 1-10 was tested at 25°C, and the results are shown in Table 1.

[0116] Table 1 Thermal conductivity of Examples 5-12 and Comparative Examples 1-10

[0117]

[0118]

[0119] As can be seen from Table 1, in Examples 5-12, by adding graphene aerogel to the raw materials of ceramic materials, the thermal diffusivity and thermal conductivity were improved by about 0.5-1 times compared to Comparative Examples 1-8, which reduced graphene oxide composite kaolin powder by high-temperature heat treatment; their thermal diffusivity and thermal conductivity were about twice that of Comparative Examples 11-14, which used unmodified kaolin; and compared to Comparative Examples 9 and 10, which only used unmodified kaolin and did not add graphene aerogel, the thermal diffusivity and thermal conductivity were significantly improved.

[0120] (2) The thermophysical properties of the graphene-kaolin composite thermally conductive ceramic material prepared in Example 9 (graphene aerogel: surface-modified kaolin powder = 2.5 wt%, sintering temperature 1087℃) were tested, and the results are shown in Table 2.

[0121] Table 2 Thermophysical properties of Example 9

[0122] Test temperature / ℃ <![CDATA[Specific heat capacity / (J·g -1 ·K -1 )]]> <![CDATA[Thermal diffusivity / (mm 2 / s)]]> Thermal conductivity (W / mK) 25 1.85 3.42 13.65 100 1.95 3.02 12.62 200 2.11 2.68 12.11

[0123] As can be seen from Table 2, as the temperature increases, the specific heat capacity of the graphene composite kaolin thermally conductive ceramic material prepared in Example 9 gradually increases, while the thermal diffusivity and thermal conductivity gradually decrease, but it still maintains good thermal conductivity at 200℃.

[0124] The above description is merely a preferred embodiment of the present invention, and therefore should not be construed as limiting the scope of the present invention. All equivalent changes and modifications made in accordance with the scope of the patent and the contents of the specification should still fall within the scope of the present invention.

Claims

1. A method for preparing graphene-composite kaolin powder, characterized in that, Includes the following steps: Kaolin powder was ultrasonically dispersed in an ethanol solution, then an aminosilane coupling agent was added, and the mixture was thoroughly mixed and reacted. The residual aminosilane coupling agent was then washed away, and the powder was dried to obtain surface-modified kaolin powder. The reaction temperature was 73-83℃ and the reaction time was 19-29h. The mass-to-volume ratio of the above-mentioned kaolin powder to the above-mentioned aminosilane coupling agent is 1-1.5g:10-15mL; the reaction time after mixing is 24±5h, and the aminosilane coupling agent is 3-aminopropylmethyldiethoxysilane, 3-aminopropyltriethoxysilane or aminoethylaminopropyltrimethoxysilane. The above-mentioned surface-modified kaolin powder was dispersed in deionized water, and the pH was adjusted to 2-3 to obtain a kaolin dispersion. Graphene oxide aerogel was dispersed in deionized water, the pH was adjusted to 2-3, and then the above kaolin dispersion was added. After thorough mixing, the mixture was allowed to stand until the system separated into layers. The lower layer of slurry was then removed and centrifuged and washed until it was weakly acidic. Finally, it was dried to obtain graphene oxide composite kaolin powder. The mass ratio of the surface-modified kaolin powder to the graphene oxide aerogel in the above-mentioned kaolin dispersion is 100:2.5-10. The graphene oxide composite kaolin powder was reduced with hydrazine hydrate as a reducing agent to obtain graphene composite kaolin powder. The preparation method of the graphene oxide aerogel is as follows: concentrated sulfuric acid is slowly poured into graphite powder, and then stirred in an ice-water bath to fully mix the graphite powder and the concentrated sulfuric acid. After the system temperature drops below 10°C, potassium permanganate powder is slowly added, and the mixture is continuously stirred and reacted at 45°C for 2 hours. After the reaction is completed, distilled water is slowly added to the system while controlling the system temperature to not exceed 100°C. Then, the system is cooled to room temperature, and hydrogen peroxide is added dropwise until the system turns golden yellow. The system is sealed and allowed to stand until it separates into layers. The lower layer of precipitate is then removed, washed until neutral, and then freeze-dried to obtain the graphene oxide aerogel. The graphite powder, concentrated sulfuric acid, and distilled water are in a mass-to-volume ratio of 1g:50mL:75mL, the graphite powder to potassium permanganate powder is in a mass ratio of 1:6, and the hydrogen peroxide has a mass fraction of 30wt%.

2. The preparation method according to claim 1, characterized in that, The specific reduction operation is as follows: the graphene oxide composite kaolin powder is dispersed in deionized water, hydrazine hydrate is added, and then the reaction is carried out at 90-95℃ for 80-100 min to obtain a black precipitate. The black precipitate is washed and dried to obtain the graphene composite kaolin powder. The mass-to-volume ratio of the graphene oxide composite kaolin powder to the hydrazine hydrate is 0.5 g: 5 mL.

3. The preparation method according to claim 2, characterized in that, The kaolin powder has a size of 200 mesh, and the graphite powder has a size of 8000 mesh.

4. A graphene-composite kaolin powder, characterized in that, It is prepared by the preparation method described in any one of claims 1-3.

5. A graphene-composite kaolin thermally conductive ceramic material, characterized in that, It is obtained by shaping and sintering the graphene composite kaolin powder as described in claim 4.

6. The graphene-composite kaolin thermally conductive ceramic material as described in claim 5, characterized in that, The sintering temperature is 1080-1400℃, and the sintering time is 180min.

7. The graphene-composite kaolin thermally conductive ceramic material as described in claim 6, characterized in that, The sintering is carried out under nitrogen or argon protection.

8. The application of the graphene-kaolin composite powder according to claim 4 in the preparation of graphene-kaolin composite thermally conductive ceramic materials.

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