Composite heat-conductive filler, graphene in-situ modified heat-conductive gel and preparation and application thereof

Abstract

The application discloses a kind of composite heat-conducting fillers, the composite heat-conducting filler is graphene oxide wraps aluminium oxide composite heat-conducting filler, wherein aluminium oxide is in situ grown on the surface of graphene oxide, then through special drying technique to form the microsphere structure of graphene oxide wrapping on the surface of aluminium oxide.The application also discloses a kind of graphene in-situ modified heat-conducting gel, containing the composite heat-conducting filler described above.The application also discloses its preparation and application.In the product prepared in the embodiment of the application, graphene is wrapped on the surface of aluminium oxide, and the two are mutually overlapped, mutually synergistic, form the special compounding effect of two-dimensional and zero-dimensional spherical, construct three-dimensional, extensive heat-conducting network structure, realize high thermal conductivity and high extrusion rate under lower filling amount.

Description

Composite thermally conductive fillers, graphene in-situ modified thermally conductive gels, their preparation and applications Technical Field

[0001] This invention relates to composite thermally conductive fillers, graphene in-situ modified thermally conductive gels, their preparation and applications. Background Technology

[0002] During device heat dissipation, heat needs to be transferred from the device's interior through the device packaging material and the heat sink interface, and then through the heat sink to the external environment. Because solid surfaces are rough and uneven at the microscale, even under contact pressures as high as 10 MPa, the actual contact area between two solid surfaces accounts for only 1-2% of the apparent contact area; the remainder consists of tiny air-filled pores. To reduce interfacial thermal resistance, thermally conductive interface materials have been developed. Filling the contact surfaces with these materials removes air from the pores at the interface, forming continuous thermally conductive channels across the entire interface and improving heat dissipation efficiency.

[0003] Thermally conductive gels are a novel type of thermally conductive interface material. Conventional thermally conductive gel materials are generally composite materials made by directly mixing thermally conductive particles into organic polymer materials such as silicone oil. The addition of a large amount of thermally conductive filler not only increases the cost and weight of the thermally conductive gel, but also reduces the interfacial wettability, increases viscosity, and increases hardness, while making it difficult to significantly improve thermal conductivity. Summary of the Invention

[0004] This invention was made to further improve the thermal conductivity of thermally conductive gels.

[0005] As one aspect of this invention, a composite thermally conductive filler is disclosed, which is a graphene oxide-encapsulated alumina composite thermally conductive filler, wherein the alumina is grown in situ on the graphene surface. Generally, in the implementation process of this invention, spherical alumina is first grown in situ on the surface of two-dimensional graphene oxide. During the in-situ growth process, the alumina exhibits a bias, tending to grow on one side of the graphene while growing less on the other side. Then, during the spray drying process, it curls up, forming a graphene oxide-encapsulated alumina morphology, mostly in the form of microspheres. In the final product, the alumina is primarily located on the inner surface of the graphene.

[0006] Preferably, the microspheres have a diameter of 5–20 μm and a specific surface area of ​​1–5 m². 2 / g.

[0007] Preferably, the graphene oxide is graphene modified with a coupling agent. In specific embodiments, the coupling agent is γ-aminopropyltriethoxysilane, a borate coupling agent, a titanate coupling agent, or an aluminate coupling agent.

[0008] As another aspect of the present invention, there is a graphene in-situ modified thermal conductive gel containing the above-mentioned graphene oxide-encapsulated aluminum oxide composite thermal conductive filler.

[0009] As another aspect of the present invention, a method for preparing the above-mentioned graphene oxide-encapsulated alumina composite thermally conductive filler includes:

[0010] 1) Preparation of graphene oxide dispersion:

[0011] Graphite oxide is dispersed in deionized water, and the pH is adjusted to between 4 and 7 (preferably 6 and 7) by adding ammonia water to prepare a graphite oxide suspension with a mass concentration of 1 to 20 g / L (preferably 5 to 10 g / L). The graphite oxide suspension is then exfoliated using a high-pressure homogenizer and homogenized (1 to 6 times) under a pressure of 30 to 80 MPa (preferably 40 to 60 MPa) to achieve single-layer exfoliation and a uniform and stable graphene oxide dispersion with a size of 5 to 20 μm.

[0012] 2) Preparation of graphene oxide-encapsulated alumina composite thermally conductive filler:

[0013] Aluminum salts were dissolved in the graphene oxide dispersion, wherein the amount of aluminum salts, calculated as aluminum, was 2 to 15 times the mass of the graphene oxide. The pH of the system was adjusted to between 8 and 12, allowing aluminum oxide particles to nucleate and grow in situ on the surface of the graphene oxide. The mixture was then spray-dried to obtain a particle size of 5–20 μm and a specific surface area of ​​1–5 m². 2 / g of graphene oxide-encapsulated alumina composite thermally conductive filler.

[0014] In a specific embodiment, in step 1), the pH is adjusted to between 6 and 7 to prepare a graphite oxide suspension with a mass concentration of 5 to 10 g / L, and homogenized under a pressure of 40 to 60 MPa.

[0015] In a specific embodiment, the aluminum salt is one of aluminum chloride, aluminum nitrate, aluminum sulfate, ammonium aluminum sulfate, and sodium aluminate.

[0016] In a specific embodiment, in step 2), before spray drying, a coupling agent is added at a mass ratio of 1:5 to 1 to the graphene oxide, and the reaction is carried out at 40 to 100°C for 0.5 to 10 hours. In a specific embodiment, the coupling agent is γ-aminopropyltriethoxysilane, a borate coupling agent, a titanate coupling agent, or an aluminate coupling agent.

[0017] In a specific embodiment, in step 2), the spray air pressure of the spray dryer ranges from 2 to 20 MPa, and the outlet temperature ranges from 80 to 110°C.

[0018] As another aspect of the present invention, a method for preparing the above-mentioned graphene in-situ modified thermally conductive gel is provided, comprising:

[0019] Platinum catalyst is dispersed in silicone oil matrix, with a mass percentage of 0.1-2.0% between platinum catalyst and silicone oil. The graphene-coated alumina composite thermally conductive filler is dispersed in the silicone oil matrix at a mass ratio of 10-15:1 (stirred at 1000-3000 rpm until homogeneous). Under vacuum conditions while maintaining mechanical stirring, the graphene oxide is heated for vulcanization, crosslinking, and reduction.

[0020] As another aspect of the present invention, the application of the above-mentioned composite thermally conductive filler in the preparation of graphene in-situ modified thermally conductive gel is involved.

[0021] As another aspect of the present invention, the application of the above-mentioned graphene in-situ modified thermal conductive gel in the preparation of electronic products (such as mobile phones, communication base stations, new energy battery vehicles, LED chips, IGBTs and other power modules, high-power semiconductors, aerospace, etc.).

[0022] As another aspect of the present invention, there is a relation to an electronic product comprising the graphene in-situ modified thermal conductive gel of claim 13.

[0023] In the products prepared according to the embodiments of this invention, graphene and alumina spheres are tightly coated. This invention achieves in-situ growth of alumina on the surface of graphene oxide by reacting aluminum salts with ammonia in a graphene oxide dispersion, effectively inhibiting graphene oxide agglomeration. During the drying stage, spray drying is used to achieve spherical composite thermally conductive fillers with graphene oxide encapsulating alumina oxide. Optimal droplet size is obtained by precisely controlling the spray air pressure and outlet temperature range. At lower spray pressures, the droplet size is too large, resulting in a final composite thermally conductive filler size exceeding 20 μm, making it difficult for graphene to completely encapsulate alumina oxide. This results in a thermally conductive gel with low thermal conductivity and high hardness. At higher spray pressures, alumina oxide detaches from the graphene oxide surface, leading to uneven composite composition of graphene and alumina oxide. The special spherical graphene structure effectively reduces the specific surface area of ​​graphene (1–5 m²). 2 / g), inhibiting the growth of large specific surface area graphene (theoretical specific capacity ~2600m³). 2 The problem of high adsorption capacity of silicone oil matrix ( / g).

[0024] In the product prepared in the embodiments of the present invention, graphene is wrapped on the surface of aluminum oxide. The two overlap and cooperate with each other to form a special composite effect of two-dimensional and zero-dimensional spheres, which constructs a three-dimensional and extensive thermally conductive network structure, achieving high thermal conductivity and high extrusion rate with low filling amount.

[0025] The thermal conductivity of the product prepared in this invention can reach 8-12 W / (m·K), and the extrusion rate exceeds 60 g / min. The process of this invention is simple and easy to implement, suitable for large-scale industrial production, and improves upon the technical defect that the thermal conductivity of graphene thermally conductive gel still does not reach 8 W / (m·K) after existing cumbersome preparation steps. Detailed Implementation

[0026] The inventors had prepared thermal conductive gels based on several prior art documents, including CN108148558A, CN110003438A, CN105754350A, and CN111471305A. However, the thermal conductivity of the prepared products could not exceed 8 W / (m·K), which did not meet the inventors' expectations. Through further research and development, the inventors came up with this invention. This invention develops a simple and easy-to-implement process suitable for large-scale industrial production, and the prepared high-performance graphene thermal conductive gel has a thermal conductivity of 8–12 W / (m·K).

[0027] The inventors attempted to mechanically mix graphene powder and alumina powder using existing technology. However, due to the huge difference between the density of graphene powder (0.003 g / mL) and the density of alumina (3.96 g / mL), it was difficult to mix graphene and alumina evenly. Graphene was prone to agglomeration and could not form an effective pathway in the thermally conductive gel.

[0028] Based on the above, the inventors conducted further research and development, and thus created this invention.

[0029] Source of raw materials or equipment:

[0030] Graphite oxide: The solid content of the graphite oxide paste used is 43±5wt%, pH value is 1.8-2.3, size ≤100μm, carbon content is 51±5wt%, sulfur content is ≤2wt%, and it is the product SE2430W-N of Changzhou Sixth Element Materials Technology Co., Ltd.

[0031] Evaluation and analysis methods: Test equipment—DRL thermal conductivity meter; Test method—ASTM D5470 thermal resistance and thermal conductivity test standard.

[0032] Example 1:

[0033] 1) Preparation of graphene oxide slurry

[0034] Graphene oxide was dispersed in deionized water to prepare a 1L graphene oxide suspension with a mass concentration of 10g / L. A certain amount of ammonia solution was added to adjust the pH to 5, and the mixture was stirred evenly to obtain a graphene oxide dispersion. The graphene oxide dispersion was homogenized once under a pressure of 80MPa to achieve monolayer exfoliation and obtain a uniform and stable graphene oxide dispersion with a graphene oxide size of 5μm.

[0035] 2) Preparation of graphene oxide-encapsulated alumina composite thermally conductive filler:

[0036] First, 100g of aluminum chloride was dissolved in 1L of graphene oxide dispersion with a mass concentration of 10g / L, and mechanically stirred until completely dissolved. Then, ammonia was added to adjust the pH to 9, allowing aluminum ions to combine with hydroxide ions, thus achieving nucleation and in-situ growth of aluminum oxide particles on the graphene oxide surface. Next, 2g of γ-aminopropyltriethoxysilane was added, and the mixture was reacted at 50°C for 5 hours to modify both aluminum oxide and graphene oxide. Finally, the mixture was dried using a spray drying method at a spray air pressure of 20MPa and an outlet temperature of 110°C, yielding a particle size of 5μm and a specific surface area of ​​5.1m². 2 / g of coupling agent modified graphene oxide-encapsulated alumina composite thermally conductive filler.

[0037] 3) Preparation of thermally conductive gel:

[0038] First, 0.1g of platinum catalyst was weighed and dispersed in 1g of vinyl silicone oil, and mechanically stirred until uniformly dispersed. Then, 10g of the graphene oxide-coated alumina composite thermally conductive filler prepared in step 2 was weighed and dispersed in vinyl silicone oil, and the filler was uniformly dispersed in vinyl silicone oil under high-speed stirring at 1000rpm / min. Finally, the system was transferred to a planetary mixer, and the mixture was evacuated to a vacuum at 40rpm / min and heated to 120℃ for 5h to obtain a high-performance thermally conductive gel. Tests showed that the thermal conductivity of the thermally conductive gel was 8.3W / (m·K), and the extrusion rate was 82g / min.

[0039] Example 2:

[0040] 1) Preparation of graphene oxide slurry

[0041] Graphene oxide was dispersed in deionized water to prepare a 1L graphene oxide suspension with a mass concentration of 10g / L. A certain amount of ammonia solution was added to adjust the pH to 5, and the mixture was stirred evenly to obtain a graphene oxide dispersion. The graphene oxide dispersion was homogenized once under a pressure of 80MPa to achieve monolayer exfoliation and obtain a uniform and stable graphene oxide dispersion with a graphene oxide size of 5μm.

[0042] 2) Preparation of graphene oxide-encapsulated alumina composite thermally conductive filler:

[0043] First, 100g of aluminum chloride was dissolved in 1L of graphene oxide dispersion with a mass concentration of 10g / L, and mechanically stirred until completely dissolved. Then, ammonia was added to adjust the pH to 9, allowing aluminum ions to combine with hydroxide ions, thus achieving nucleation and in-situ growth of aluminum oxide particles on the graphene oxide surface. Next, 2g of γ-aminopropyltriethoxysilane was added, and the mixture was reacted at 50°C for 5 hours to modify both aluminum oxide and graphene oxide. Finally, the mixture was dried using a spray drying method at a spray air pressure of 20MPa and an outlet temperature of 110°C, yielding a particle size of 5μm and a specific surface area of ​​5.1m². 2 / g of coupling agent modified graphene oxide-encapsulated alumina composite thermally conductive filler.

[0044] 3) Preparation of thermally conductive gel:

[0045] First, 2g of platinum catalyst was weighed and dispersed in 1g of dimethyl silicone oil, and mechanically stirred until uniformly dispersed. Then, 12g of the graphene oxide-coated alumina composite thermally conductive filler prepared in step 2 was weighed and dispersed in dimethyl silicone oil. The filler was uniformly dispersed in the dimethyl silicone oil under high-speed stirring at 2000rpm / min. Finally, the system was transferred to a planetary mixer, and the mixture was evacuated to a vacuum at 80rpm / min and heated to 200℃ for 0.5h to obtain a high-performance thermally conductive gel. Tests showed that the thermal conductivity of the gel was 9.5W / (m·K), and the extrusion rate was 72g / min.

[0046] Example 3:

[0047] 1) Preparation of graphene oxide slurry

[0048] Graphene oxide was dispersed in deionized water to prepare a 1L graphene oxide suspension with a mass concentration of 10g / L. A certain amount of ammonia solution was added to adjust the pH to 5, and the mixture was stirred evenly to obtain a graphene oxide dispersion. The graphene oxide dispersion was homogenized once under a pressure of 80MPa to achieve monolayer exfoliation and obtain a uniform and stable graphene oxide dispersion with a graphene oxide size of 5μm.

[0049] 2) Preparation of graphene oxide-encapsulated alumina composite thermally conductive filler:

[0050] First, 100g of aluminum chloride was dissolved in 1L of graphene oxide dispersion with a mass concentration of 10g / L, and mechanically stirred until completely dissolved. Then, ammonia was added to adjust the pH to 9, allowing aluminum ions to combine with hydroxide ions, thus achieving nucleation and in-situ growth of aluminum oxide particles on the graphene oxide surface. Next, 2g of γ-aminopropyltriethoxysilane was added, and the mixture was reacted at 50°C for 5 hours to modify both aluminum oxide and graphene oxide. Finally, the mixture was dried using a spray drying method at a spray air pressure of 20MPa and an outlet temperature of 110°C, yielding a particle size of 5μm and a specific surface area of ​​5.1m². 2 / g of coupling agent modified graphene oxide-encapsulated alumina composite thermally conductive filler.

[0051] 3) Preparation of thermally conductive gel:

[0052] First, 1g of platinum catalyst was weighed and dispersed in 1g of methylphenyl silicone oil, and mechanically stirred until uniformly dispersed. Then, 13g of the graphene oxide-coated alumina composite thermally conductive filler prepared in step 2 was weighed and dispersed in methylphenyl silicone oil. The filler was uniformly dispersed in the methylphenyl silicone oil under high-speed stirring at 3000rpm / min. Finally, the system was transferred to a planetary mixer, and the mixture was evacuated to a vacuum at 60rpm / min and heated to 160℃ for 2 hours to obtain a high-performance thermally conductive gel. Tests showed that the thermal conductivity of the gel was 10.6W / (m·K), and the extrusion rate was 69g / min.

[0053] Example 4:

[0054] 1) Preparation of graphene oxide slurry

[0055] Graphene oxide was dispersed in deionized water to prepare a 1L graphene oxide suspension with a mass concentration of 10g / L. A certain amount of ammonia solution was added to adjust the pH to 5, and the mixture was stirred evenly to obtain a graphene oxide dispersion. The graphene oxide dispersion was homogenized once under a pressure of 80MPa to achieve monolayer exfoliation and obtain a uniform and stable graphene oxide dispersion with a graphene oxide size of 5μm.

[0056] 2) Preparation of graphene oxide-encapsulated alumina composite thermally conductive filler:

[0057] First, 100g of aluminum chloride was dissolved in 1L of graphene oxide dispersion with a mass concentration of 10g / L, and mechanically stirred until completely dissolved. Then, ammonia was added to adjust the pH to 9, allowing aluminum ions to combine with hydroxide ions, thus achieving nucleation and in-situ growth of aluminum oxide particles on the graphene oxide surface. Next, 2g of γ-aminopropyltriethoxysilane was added, and the mixture was reacted at 50°C for 5 hours to modify both aluminum oxide and graphene oxide. Finally, the mixture was dried using a spray drying method at a spray air pressure of 20MPa and an outlet temperature of 110°C, yielding a particle size of 5μm and a specific surface area of ​​5.1m². 2 / g of coupling agent modified graphene oxide-encapsulated alumina composite thermally conductive filler.

[0058] 3) Preparation of thermally conductive gel:

[0059] First, 2g of platinum catalyst was weighed and dispersed in 1g of methylchlorophenyl silicone oil, and mechanically stirred until uniformly dispersed. Then, 15g of the graphene oxide-coated alumina composite thermally conductive filler prepared in step 2 was weighed and dispersed in methylchlorophenyl silicone oil. The filler was uniformly dispersed in the methylchlorophenyl silicone oil under high-speed stirring at 2000rpm / min. Finally, the system was transferred to a planetary mixer, and the mixture was evacuated to a vacuum at 80rpm / min and heated to 200℃ for 1 hour to obtain a high-performance thermally conductive gel. Tests showed that the thermal conductivity of the gel was 12.1W / (m·K), and the extrusion rate was 63g / min.

[0060] Example 5:

[0061] 1) Preparation of graphene oxide slurry

[0062] Graphene oxide was dispersed in deionized water to prepare a 1L graphene oxide suspension with a mass concentration of 10g / L. A certain amount of ammonia solution was added to adjust the pH to 5, and the mixture was stirred evenly to obtain a graphene oxide dispersion. The graphene oxide dispersion was homogenized once under a pressure of 80MPa to achieve monolayer exfoliation and obtain a uniform and stable graphene oxide dispersion with a graphene oxide size of 5μm.

[0063] 2) Preparation of graphene oxide-encapsulated alumina composite thermally conductive filler:

[0064] First, 100g of aluminum chloride was dissolved in 1L of graphene oxide dispersion with a mass concentration of 10g / L, and mechanically stirred until completely dissolved. Then, ammonia was added to adjust the pH to 9, allowing aluminum ions to combine with hydroxide ions, thus achieving nucleation and in-situ growth of aluminum oxide particles on the graphene oxide surface. Next, 2g of γ-aminopropyltriethoxysilane was added, and the mixture was reacted at 50°C for 5 hours to modify both aluminum oxide and graphene oxide. Finally, the mixture was dried using a spray drying method at a spray air pressure of 20MPa and an outlet temperature of 110°C, yielding a particle size of 5μm and a specific surface area of ​​5.1m². 2 / g of coupling agent modified graphene oxide-encapsulated alumina composite thermally conductive filler.

[0065] 3) Preparation of thermally conductive gel:

[0066] First, 0.1g of platinum catalyst was weighed and dispersed in 1g of vinyl silicone oil, and mechanically stirred until uniformly dispersed. Then, 15g of the graphene oxide-coated alumina composite thermally conductive filler prepared in step 2 was weighed and dispersed in vinyl silicone oil, and the filler was uniformly dispersed in vinyl silicone oil under high-speed stirring at 2000rpm / min. Finally, the system was transferred to a planetary mixer, and the mixture was evacuated to a vacuum at 10rpm / min and heated to 200℃ for 2h to obtain a high-performance thermally conductive gel. Tests showed that the thermal conductivity of the thermally conductive gel was 12.3W / (m·K), and the extrusion rate was 68g / min.

[0067] Example 6:

[0068] 1) Preparation of graphene oxide slurry

[0069] Graphene oxide was dispersed in deionized water to prepare a 1L graphene oxide suspension with a mass concentration of 10g / L. A certain amount of ammonia solution was added to adjust the pH to 5, and the mixture was stirred evenly to obtain a graphene oxide dispersion. The graphene oxide dispersion was homogenized once under a pressure of 80MPa to achieve monolayer exfoliation and obtain a uniform and stable graphene oxide dispersion with a graphene oxide size of 5μm.

[0070] 2) Preparation of graphene oxide-encapsulated alumina composite thermally conductive filler:

[0071] First, 100g of aluminum chloride was dissolved in 1L of graphene oxide dispersion with a mass concentration of 10g / L, and mechanically stirred until completely dissolved. Then, ammonia was added to adjust the pH to 9, allowing aluminum ions to combine with hydroxide ions, thus achieving nucleation and in-situ growth of aluminum oxide particles on the graphene oxide surface. Next, 2g of γ-aminopropyltriethoxysilane was added, and the mixture was reacted at 50°C for 5 hours to modify both aluminum oxide and graphene oxide. Finally, the mixture was dried using a spray drying method at a spray air pressure of 20MPa and an outlet temperature of 110°C, yielding a particle size of 5μm and a specific surface area of ​​5.1m². 2 / g of coupling agent modified graphene oxide-encapsulated alumina composite thermally conductive filler.

[0072] 3) Preparation of thermally conductive gel:

[0073] First, 0.2 g of platinum catalyst was weighed and dispersed in 1 g of vinyl silicone oil, and mechanically stirred until uniformly dispersed. Then, 15 g of the graphene oxide-coated alumina composite thermally conductive filler prepared in step 2 was weighed and dispersed in vinyl silicone oil, and the filler was uniformly dispersed in vinyl silicone oil under high-speed stirring at 2000 rpm / min. Finally, the system was transferred to a planetary mixer, and the mixture was evacuated to a vacuum at 10 rpm / min and heated to 200℃ for 2 h to obtain a high-performance thermally conductive gel. Tests showed that the thermal conductivity of the thermally conductive gel was 12.1 W / (m·K), and the extrusion rate was 65 g / min.

[0074] Example 7:

[0075] 1) Preparation of graphene oxide slurry

[0076] Graphene oxide was dispersed in deionized water to prepare a 1L graphene oxide suspension with a mass concentration of 10g / L. A certain amount of ammonia solution was added to adjust the pH to 5, and the mixture was stirred evenly to obtain a graphene oxide dispersion. The graphene oxide dispersion was homogenized once under a pressure of 80MPa to achieve monolayer exfoliation and obtain a uniform and stable graphene oxide dispersion with a graphene oxide size of 5μm.

[0077] 2) Preparation of graphene oxide-encapsulated alumina composite thermally conductive filler:

[0078] First, 100g of aluminum chloride was dissolved in 1L of graphene oxide dispersion with a mass concentration of 10g / L, and mechanically stirred until completely dissolved. Then, ammonia was added to adjust the pH to 9, allowing aluminum ions to combine with hydroxide ions, thus achieving nucleation and in-situ growth of aluminum oxide particles on the graphene oxide surface. Next, 2g of γ-aminopropyltriethoxysilane was added, and the mixture was reacted at 50°C for 5 hours to modify both aluminum oxide and graphene oxide. Finally, the mixture was dried using a spray drying method at a spray air pressure of 20MPa and an outlet temperature of 110°C, yielding a particle size of 5μm and a specific surface area of ​​5.1m². 2 / g of coupling agent modified graphene oxide-encapsulated alumina composite thermally conductive filler.

[0079] 3) Preparation of thermally conductive gel:

[0080] First, 0.3g of platinum catalyst was weighed and dispersed in 1g of vinyl silicone oil, and mechanically stirred until uniformly dispersed. Then, 15g of the graphene oxide-coated alumina composite thermally conductive filler prepared in step 2 was weighed and dispersed in vinyl silicone oil, and the filler was uniformly dispersed in vinyl silicone oil under high-speed stirring at 2000rpm / min. Finally, the system was transferred to a planetary mixer, and the mixture was evacuated to a vacuum at 10rpm / min and heated to 200℃ for 2h to obtain a high-performance thermally conductive gel. Tests showed that the thermal conductivity of the thermally conductive gel was 12.2W / (m·K), and the extrusion rate was 58g / min.

[0081] Example 8:

[0082] 1) Preparation of graphene oxide slurry

[0083] Graphene oxide was dispersed in deionized water to prepare a 1L graphene oxide suspension with a mass concentration of 10g / L. A certain amount of ammonia solution was added to adjust the pH to 5, and the mixture was stirred evenly to obtain a graphene oxide dispersion. The graphene oxide dispersion was homogenized once under a pressure of 80MPa to achieve monolayer exfoliation and obtain a uniform and stable graphene oxide dispersion with a graphene oxide size of 5μm.

[0084] 2) Preparation of graphene oxide-encapsulated alumina composite thermally conductive filler:

[0085] First, 100g of aluminum chloride was dissolved in 1L of graphene oxide dispersion with a mass concentration of 10g / L, and mechanically stirred until completely dissolved. Then, ammonia was added to adjust the pH to 9, allowing aluminum ions to combine with hydroxide ions, thus achieving nucleation and in-situ growth of aluminum oxide particles on the graphene oxide surface. Next, 2g of γ-aminopropyltriethoxysilane was added, and the mixture was reacted at 50°C for 5 hours to modify both aluminum oxide and graphene oxide. Finally, the mixture was dried using a spray drying method at a spray air pressure of 20MPa and an outlet temperature of 110°C, yielding a particle size of 5μm and a specific surface area of ​​5.1m². 2 / g of coupling agent modified graphene oxide-encapsulated alumina composite thermally conductive filler.

[0086] 3) Preparation of thermally conductive gel:

[0087] First, 0.5g of platinum catalyst was weighed and dispersed in 1g of vinyl silicone oil, and mechanically stirred until uniformly dispersed. Then, 15g of the graphene oxide-coated alumina composite thermally conductive filler prepared in step 2 was weighed and dispersed in vinyl silicone oil, and the filler was uniformly dispersed in vinyl silicone oil under high-speed stirring at 2000rpm / min. Finally, the system was transferred to a planetary mixer, and the mixture was evacuated to a vacuum at 10rpm / min and heated to 200℃ for 2h to obtain a high-performance thermally conductive gel. Tests showed that the thermal conductivity of the thermally conductive gel was 12.1W / (m·K), and the extrusion rate was 55g / min.

[0088] Example 9:

[0089] 1) Preparation of graphene oxide slurry

[0090] Graphite oxide was dispersed in deionized water to prepare a 5L graphite oxide suspension with a mass concentration of 1g / L. A certain amount of ammonia solution was added to adjust the pH to 7, and the mixture was stirred evenly to obtain a graphene oxide dispersion. The graphene oxide dispersion was homogenized three times under a pressure of 30MPa to achieve monolayer exfoliation and obtain a uniform and stable graphene oxide dispersion with a graphene oxide size of 10μm.

[0091] 2) Preparation of graphene oxide-encapsulated alumina composite thermally conductive filler:

[0092] First, 140g of aluminum sulfate was weighed and dissolved in 5L of graphene oxide dispersion with a mass concentration of 1g / L, and mechanically stirred until completely dissolved. Then, ammonia was added to adjust the pH to 12, allowing aluminum ions to combine with hydroxide ions, thus achieving nucleation and in-situ growth of aluminum oxide particles on the graphene oxide surface. Next, 5g of borate ester coupling agent was added, and the reaction was carried out at 90℃ for 0.5h to modify both aluminum oxide and graphene oxide. Finally, the mixture was dried using a spray drying method with a spray air pressure of 20MPa and an outlet temperature of 100℃, yielding a particle size of 5μm and a specific surface area of ​​4.9m². 2 / g of coupling agent modified graphene oxide-encapsulated alumina composite thermally conductive filler.

[0093] 3) Preparation of thermally conductive gel:

[0094] First, 0.1g of platinum catalyst was weighed and dispersed in 1g of vinyl silicone oil, and mechanically stirred until uniformly dispersed. Then, 15g of the graphene oxide-coated alumina composite thermally conductive filler prepared in step 2 was weighed and dispersed in vinyl silicone oil, and the filler was uniformly dispersed in vinyl silicone oil under high-speed stirring at 2000rpm / min. Finally, the system was transferred to a planetary mixer, and the mixture was evacuated to a vacuum at 10rpm / min and heated to 200℃ for 2h to obtain a high-performance thermally conductive gel. Tests showed that the thermal conductivity of the thermally conductive gel was 11.6W / (m·K), and the extrusion rate was 65g / min.

[0095] Example 10:

[0096] 1) Preparation of graphene oxide slurry

[0097] Graphene oxide was dispersed in deionized water to prepare a 5L suspension with a mass concentration of 2g / L. A certain amount of ammonia solution was added to adjust the pH to 6, and the mixture was stirred evenly to obtain a graphene oxide dispersion. The graphene oxide dispersion was homogenized once under a pressure of 60MPa to achieve monolayer exfoliation and obtain a uniform and stable graphene oxide dispersion with a graphene oxide size of 15μm.

[0098] 2) Preparation of graphene oxide-encapsulated alumina composite thermally conductive filler:

[0099] First, 300g of aluminum nitrate was dissolved in 5L of graphene oxide dispersion with a mass concentration of 2g / L, and mechanically stirred until completely dissolved. Then, ammonia was added to adjust the pH to 11, allowing aluminum ions to combine with hydroxide ions, thus achieving nucleation and in-situ growth of aluminum oxide particles on the graphene oxide surface. Next, 5g of titanate coupling agent was added, and the reaction was carried out at 80℃ for 1 hour to modify both aluminum oxide and graphene oxide. Finally, the mixture was dried using a spray drying method with a spray air pressure of 12MPa and an outlet temperature of 100℃, yielding a particle size of 10μm and a specific surface area of ​​2.3m². 2 / g of coupling agent modified graphene oxide-encapsulated alumina composite thermally conductive filler.

[0100] 3) Preparation of thermally conductive gel:

[0101] First, 0.1g of platinum catalyst was weighed and dispersed in 1g of vinyl silicone oil, and mechanically stirred until uniformly dispersed. Then, 15g of the graphene oxide-coated alumina composite thermally conductive filler prepared in step 2 was weighed and dispersed in vinyl silicone oil, and the filler was uniformly dispersed in vinyl silicone oil under high-speed stirring at 2000rpm / min. Finally, the system was transferred to a planetary mixer, and the mixture was evacuated to a vacuum at 10rpm / min and heated to 200℃ for 2h to obtain a high-performance thermally conductive gel. Tests showed that the thermal conductivity of the thermally conductive gel was 11.7W / (m·K), and the extrusion rate was 61g / min.

[0102] Example 11:

[0103] 1) Preparation of graphene oxide slurry

[0104] Graphite oxide was dispersed in deionized water to prepare a 5L graphite oxide suspension with a mass concentration of 4g / L. A certain amount of ammonia solution was added to adjust the pH to 7, and the mixture was stirred evenly to obtain a graphene oxide dispersion. The graphene oxide dispersion was homogenized once under a pressure of 50MPa to achieve monolayer exfoliation and obtain a uniform and stable graphene oxide dispersion with a graphene oxide size of 20μm.

[0105] 2) Preparation of graphene oxide-encapsulated alumina composite thermally conductive filler:

[0106] First, 400g of ammonium aluminum sulfate was dissolved in 5L of graphene oxide dispersion with a mass concentration of 4g / L, and mechanically stirred until completely dissolved. Then, ammonia was added to adjust the pH to 10, allowing aluminum ions to combine with hydroxide ions, thus achieving nucleation and in-situ growth of aluminum oxide particles on the graphene oxide surface. Next, 5g of aluminate coupling agent was added, and the mixture was reacted at 60℃ for 5 hours to modify both aluminum oxide and graphene oxide. Finally, the mixture was dried using a spray drying method with a spray air pressure of 2MPa and an outlet temperature of 80℃, yielding a particle size of 20μm and a specific surface area of ​​1m². 2 / g of coupling agent modified graphene oxide-encapsulated alumina composite thermally conductive filler.

[0107] 3) Preparation of thermally conductive gel:

[0108] First, 0.1g of platinum catalyst was weighed and dispersed in 1g of vinyl silicone oil, and mechanically stirred until uniformly dispersed. Then, 15g of the graphene oxide-coated alumina composite thermally conductive filler prepared in step 2 was weighed and dispersed in vinyl silicone oil, and the filler was uniformly dispersed in vinyl silicone oil under high-speed stirring at 2000rpm / min. Finally, the system was transferred to a planetary mixer, and the mixture was evacuated to a vacuum at 10rpm / min and heated to 200℃ for 2h to obtain a high-performance thermally conductive gel. Tests showed that the thermal conductivity of the thermally conductive gel was 11.9W / (m·K), and the extrusion rate was 63g / min.

[0109] Example 12:

[0110] 1) Preparation of graphene oxide slurry

[0111] Graphite oxide was dispersed in deionized water to prepare a 2L graphite oxide suspension with a mass concentration of 5g / L. A certain amount of ammonia solution was added to adjust the pH to 7, and the mixture was stirred evenly to obtain a graphene oxide dispersion. The graphene oxide dispersion was homogenized twice under a pressure of 30MPa to achieve monolayer exfoliation and obtain a uniform and stable graphene oxide dispersion with a graphene oxide size of 12μm.

[0112] 2) Preparation of graphene oxide-encapsulated alumina composite thermally conductive filler:

[0113] First, 300g of sodium aluminate was dissolved in 2L of graphene oxide dispersion with a mass concentration of 5g / L, and mechanically stirred until completely dissolved. Then, ammonia was added to adjust the pH to 12, allowing aluminum ions to combine with hydroxide ions, thus achieving nucleation and in-situ growth of alumina particles on the graphene oxide surface. Next, 5g of aluminate coupling agent was added, and the reaction was carried out at 50℃ for 5 hours to modify both alumina and graphene oxide. Finally, the mixture was dried using a spray drying method with a spray air pressure range of 12MPa and an outlet temperature of 90℃, yielding a particle size of 10μm and a specific surface area of ​​3.2m². 2 / g of coupling agent modified graphene oxide-encapsulated alumina composite thermally conductive filler.

[0114] 3) Preparation of thermally conductive gel:

[0115] First, 0.1g of platinum catalyst was weighed and dispersed in 1g of vinyl silicone oil, and mechanically stirred until uniformly dispersed. Then, 15g of the graphene oxide-coated alumina composite thermally conductive filler prepared in step 2 was weighed and dispersed in vinyl silicone oil, and the filler was uniformly dispersed in vinyl silicone oil under high-speed stirring at 2000rpm / min. Finally, the system was transferred to a planetary mixer, and the mixture was evacuated to a vacuum at 10rpm / min and heated to 200℃ for 2h to obtain a high-performance thermally conductive gel. Tests showed that the thermal conductivity of the thermally conductive gel was 11.7W / (m·K), and the extrusion rate was 65g / min.

[0116] Comparative Example 1

[0117] 3g of intercalated graphene powder, 400g of spherical alumina filler with an average particle size of 50μm, 50g of spherical alumina filler with an average particle size of 3μm, and 100g of alumina with a viscosity of 6000mm were mixed. 2 Dimethyl silicone oil was added to a ball mill jar and stirred at 100 rpm for 10 minutes. 200 g of zirconia balls were then added to the jar. The mixture was ball-milled at 500 rpm for 20 hours. After ball milling, the mixture was removed to obtain a graphene-containing thermally conductive gel composite material. Tests showed that the thermal conductivity of the gel was 5 W / (m·K), and the extrusion rate was not measured.

[0118] Comparative Example 2

[0119] 1) Preparation of graphene oxide slurry:

[0120] Graphite oxide was dispersed in deionized water to prepare a 5L graphite oxide suspension with a mass concentration of 4g / L. A certain amount of ammonia solution was added to adjust the pH to 7, and the mixture was stirred evenly to obtain a graphene oxide dispersion. The graphene oxide dispersion was homogenized once under a pressure of 50MPa to achieve monolayer exfoliation and obtain a uniform and stable graphene oxide dispersion with a graphene oxide size of 20μm.

[0121] 2) Preparation of graphene oxide-encapsulated alumina composite thermally conductive filler:

[0122] First, 400g of ammonium aluminum sulfate was dissolved in 5L of graphene oxide dispersion with a mass concentration of 4g / L, and mechanically stirred until completely dissolved. Then, ammonia was added to adjust the pH to 10, allowing aluminum ions to combine with hydroxide ions, thus achieving nucleation and in-situ growth of aluminum oxide particles on the graphene oxide surface. Next, 5g of aluminate coupling agent was added, and the mixture was reacted at 60℃ for 5 hours to modify both aluminum oxide and graphene oxide. Finally, the mixture was freeze-dried to obtain a specific surface area of ​​155m². 2 / g of sheet-like composite thermally conductive filler supported on graphene oxide.

[0123] 3) Preparation of thermally conductive gel:

[0124] First, 2g of platinum catalyst was weighed and dispersed in 1g of methylchlorophenyl silicone oil, and mechanically stirred until uniformly dispersed. Then, 15g of the alumina-supported graphene oxide sheet-like thermally conductive filler prepared in step 2 was weighed and dispersed in methylphenyl silicone oil. The filler was uniformly dispersed in the methylchlorophenyl silicone oil under high-speed stirring at 2000rpm / min. Finally, the system was transferred to a planetary mixer, and the mixture was evacuated to a vacuum at 80rpm / min and heated to 200℃ for 1 hour to obtain a thermally conductive gel. Tests showed that the thermal conductivity of the gel was 6W / (m·K), and the extrusion rate was 5g / min.

[0125] Comparative Example 3

[0126] 1) Preparation of graphene oxide slurry:

[0127] Graphite oxide was dispersed in deionized water to prepare a 5L graphite oxide suspension with a mass concentration of 4g / L. A certain amount of ammonia solution was added to adjust the pH to 7, and the mixture was stirred evenly to obtain a graphene oxide dispersion. The graphene oxide dispersion was homogenized once under a pressure of 50MPa to achieve monolayer exfoliation and obtain a uniform and stable graphene oxide dispersion with a graphene oxide size of 20μm.

[0128] 2) Preparation of graphene oxide-encapsulated alumina composite thermally conductive filler:

[0129] First, 400g of commercially available alumina spherical particles with a size of 5μm were weighed and dispersed in 5L of graphene oxide dispersion with a mass concentration of 4g / L, and mechanically stirred until uniformly dispersed. Then, 5g of aluminate coupling agent was added, and the mixture was reacted at 60℃ for 5h to modify the alumina and graphene oxide. Finally, the mixture was dried using a spray drying method with a spray air pressure of 2MPa and an outlet temperature of 80℃, yielding particles with a size of 20μm and a specific surface area of ​​63m². 2 / g of coupling agent modified graphene oxide-encapsulated alumina composite thermally conductive filler.

[0130] 3) Preparation of thermally conductive gel:

[0131] First, 2g of platinum catalyst was weighed and dispersed in 1g of methylchlorophenyl silicone oil, and mechanically stirred until uniformly dispersed. Then, 15g of the graphene oxide-coated alumina composite thermally conductive filler prepared in step 2 was weighed and dispersed in methylphenyl silicone oil. The filler was uniformly dispersed in the methylchlorophenyl silicone oil under high-speed stirring at 2000rpm / min. Finally, the system was transferred to a planetary mixer, and the mixture was evacuated to a vacuum at 80rpm / min and heated to 200℃ for 1 hour to obtain a thermally conductive gel. Tests showed that the thermal conductivity of the gel was 7W / (m·K), and the extrusion rate was 13g / min.

[0132] Comparative Example 4

[0133] 1) Preparation of graphene oxide slurry:

[0134] Graphite oxide was dispersed in deionized water to prepare a 5L graphite oxide suspension with a mass concentration of 4g / L. A certain amount of ammonia solution was added to adjust the pH to 7, and the mixture was stirred evenly to obtain a graphene oxide dispersion. The graphene oxide dispersion was homogenized once under a pressure of 50MPa to achieve monolayer exfoliation and obtain a uniform and stable graphene oxide dispersion with a graphene oxide size of 20μm.

[0135] 2) Preparation of graphene oxide-encapsulated alumina composite thermally conductive filler:

[0136] First, 400g of ammonium aluminum sulfate was dissolved in 5L of graphene oxide dispersion with a mass concentration of 4g / L, and mechanically stirred until completely dissolved. Then, ammonia was added to adjust the pH to 10, allowing aluminum ions to combine with hydroxide ions, thus achieving nucleation and in-situ growth of aluminum oxide particles on the graphene oxide surface. Finally, the mixture was dried using a spray drying method at a spray air pressure of 2MPa and an outlet temperature of 80℃, yielding particles with a size of 20μm and a specific surface area of ​​1.2m². 2 / g of coupling agent modified graphene oxide-encapsulated alumina composite thermally conductive filler.

[0137] 3) Preparation of thermally conductive gel:

[0138] First, 2g of platinum catalyst was weighed and dispersed in 1g of methylchlorophenyl silicone oil, and mechanically stirred until uniformly dispersed. Then, 15g of the graphene oxide-coated alumina composite thermally conductive filler prepared in step 2 was weighed and dispersed in methylphenyl silicone oil. The filler was uniformly dispersed in the methylchlorophenyl silicone oil under high-speed stirring at 2000rpm / min. Finally, the system was transferred to a planetary mixer, and the mixture was evacuated to a vacuum at 80rpm / min and heated to 200℃ for 1 hour to obtain a thermally conductive gel. Tests showed that the thermal conductivity of the gel was 3W / (m·K), and the extrusion rate was 11g / min.

[0139] Comparative Example 5

[0140] 1) Preparation of graphene oxide slurry:

[0141] Graphite oxide was dispersed in deionized water to prepare a 5L graphite oxide suspension with a mass concentration of 4g / L. A certain amount of ammonia solution was added to adjust the pH to 7, and the mixture was stirred evenly to obtain a graphene oxide dispersion. The graphene oxide dispersion was homogenized once under a pressure of 50MPa to achieve monolayer exfoliation and obtain a uniform and stable graphene oxide dispersion with a graphene oxide size of 20μm.

[0142] 2) Preparation of graphene oxide-encapsulated alumina composite thermally conductive filler:

[0143] First, 400g of ammonium aluminum sulfate was dissolved in 5L of graphene oxide dispersion with a mass concentration of 4g / L, and mechanically stirred until completely dissolved. Then, ammonia was added to adjust the pH to 10, allowing aluminum ions to combine with hydroxide ions, thus achieving nucleation and in-situ growth of aluminum oxide particles on the graphene oxide surface. Finally, the mixture was dried using a spray drying method at a spray air pressure of 2MPa and an outlet temperature of 80℃, yielding particles with a size of 20μm and a specific surface area of ​​1.2m². 2 / g of coupling agent modified graphene oxide-encapsulated alumina composite thermally conductive filler.

[0144] 3) Preparation of thermally conductive gel:

[0145] First, 2g of platinum catalyst was weighed and dispersed in 1g of methylchlorophenyl silicone oil, and mechanically stirred until uniformly dispersed. Then, 5g of aluminate coupling agent was added, and 15g of the graphene oxide-coated alumina composite thermally conductive filler prepared in step 2 was weighed and dispersed in methylphenyl silicone oil. The thermally conductive filler was uniformly dispersed in the methylchlorophenyl silicone oil under high-speed stirring at 2000rpm / min. Finally, the system was transferred to a planetary mixer, and the mixture was evacuated to a vacuum at 80rpm / min and heated to 200℃ for 1h to obtain a thermally conductive gel. Tests showed that the thermal conductivity of the thermally conductive gel was 4.1W / (m·K), and the extrusion rate was 26g / min.

[0146] Comparative Example 6

[0147] 1) Preparation of graphene oxide slurry:

[0148] Graphite oxide was dispersed in deionized water to prepare a 5L graphite oxide suspension with a mass concentration of 4g / L. A certain amount of ammonia solution was added to adjust the pH to 7, and the mixture was stirred evenly to obtain a graphene oxide dispersion. The graphene oxide dispersion was homogenized once under a pressure of 50MPa to achieve monolayer exfoliation and obtain a uniform and stable graphene oxide dispersion with a graphene oxide size of 20μm.

[0149] 2) Preparation of graphene oxide-encapsulated alumina composite thermally conductive filler:

[0150] First, 400g of ammonium aluminum sulfate was dissolved in 5L of graphene oxide dispersion with a mass concentration of 4g / L, and mechanically stirred until completely dissolved. Then, 5g of aluminate coupling agent was added and stirred until dissolved. Next, ammonia was added to adjust the pH to 10, allowing aluminum ions to combine with hydroxide ions, thus achieving nucleation and in-situ growth of aluminum oxide particles on the graphene oxide surface. Finally, the mixture was dried using a spray drying method at a spray air pressure of 2MPa and an outlet temperature of 80℃, yielding particles with a size of 20μm and a specific surface area of ​​1.2m². 2 / g of coupling agent modified graphene oxide-encapsulated alumina composite thermally conductive filler.

[0151] 3) Preparation of thermally conductive gel:

[0152] First, 2g of platinum catalyst was weighed and dispersed in 1g of methylchlorophenyl silicone oil, and mechanically stirred until uniformly dispersed. Then, 15g of the graphene oxide-coated alumina composite thermally conductive filler prepared in step 2 was weighed and dispersed in methylphenyl silicone oil. The filler was uniformly dispersed in the methylchlorophenyl silicone oil under high-speed stirring at 2000rpm / min. Finally, the system was transferred to a planetary mixer, and the mixture was evacuated to a vacuum at 80rpm / min and heated to 200℃ for 1 hour to obtain a thermally conductive gel. Tests showed that the thermal conductivity of the gel was 3.5W / (m·K), and the extrusion rate was 13g / min.

[0153] The properties of the graphene thermally conductive gels prepared in Examples 1-5 were compared with those prepared in Comparative Example 1. The thermal conductivity of the thermally conductive gel prepared in Example 4 reached 12 W / (m·K), which is much higher than that of Comparative Example 1 (5 W / (m·K). At the same time, the extrusion rate exceeded 60 g / min, and reached a maximum of 82 g / min.

[0154] The graphene thermally conductive gels prepared in Examples 1-5 were compared with those prepared in Comparative Example 2. The thermal conductivity of the gel prepared in Example 4 reached 12 W / (m·K), which is much higher than that of Comparative Example 2 (6 W / (m·K). Simultaneously, the extrusion rate exceeded 60 g / min, much higher than that of Comparative Example 2 (5 g / min). The main difference between Comparative Example 2 and the examples is that freeze-drying was used instead of spray drying. Freeze-drying freezes the system into a solid state and then utilizes the principle of ice sublimation under low pressure, perfectly preserving the two-dimensional sheet structure of graphene. Therefore, the specific surface area of ​​the alumina-supported graphene oxide composite filler obtained in Comparative Example 2 reached as high as 155 m². 2 / g, significantly higher than the 1.1m in Example 4. 2 With such a high specific surface area dispersed in methylphenyl silicone oil, the methylphenyl silicone oil will quickly adsorb onto the large-area graphene surface, making it difficult for the silicone oil to uniformly wet all the fillers and form a uniform and highly extruded thermally conductive gel.

[0155] The graphene thermally conductive gels prepared in Examples 1-5 were compared with those prepared in Comparative Example 3. The thermal conductivity of the gel prepared in Example 4 reached 12 W / (m·K), which is much higher than that of Comparative Example 3 (7 W / (m·K). Simultaneously, the extrusion rate exceeded 60 g / min, much higher than that of Comparative Example 2 (13 g / min). The main difference between Comparative Example 3 and the examples is the use of commercially available micron-sized alumina. Alumina has a high density of 3.96 g / mL, making it difficult to uniformly disperse in the graphene oxide dispersion through mechanical stirring. Therefore, it is difficult to uniformly disperse on the surface of the graphene oxide. In the composite filler obtained by spray drying, most of the alumina particles were not combined with the graphene. The graphene oxide was individually coated and dried into spherical shapes, while the alumina dried into powder in its initial state. Therefore, the specific surface area of ​​the composite filler is still as high as 63 m². 2 / g, which makes it difficult for silicone oil to evenly wet all fillers and form a uniform and highly extruded thermally conductive gel.

[0156] The graphene thermally conductive gels prepared in Examples 1-5 were compared with those prepared in Comparative Example 4. The thermal conductivity of the thermally conductive gel prepared in Example 4 reached 12 W / (m·K), which is much higher than the 3 W / (m·K) of Comparative Example 4. Simultaneously, the extrusion rate exceeded 60 g / min, which is much higher than the 11 g / min of Comparative Example 4. The main difference between Comparative Example 4 and the examples is that the composite thermally conductive filler was not modified with a coupling agent. This resulted in poor compatibility between the graphene-encapsulated alumina thermally conductive filler and the silicone oil during the preparation of the thermally conductive gel, making it difficult to disperse uniformly in the silicone oil. Therefore, it was difficult to form a thermally conductive network structure, resulting in lower thermal conductivity and a lower extrusion rate.

[0157] The properties of the graphene thermally conductive gels prepared in Examples 1-5 were compared with those prepared in Comparative Example 5. The thermal conductivity of the thermally conductive gel prepared in Example 4 reached 12 W / (m·K), which is much higher than that of Comparative Example 5 (4.1 W / (m·K). Simultaneously, the extrusion rate exceeded 60 g / min, which is much higher than that of Comparative Example 5 (26 g / min). The main difference between Comparative Example 5 and the examples is that the silane coupling agent was added during the preparation of the thermally conductive gel, simultaneously with the thermally conductive filler into the silicone oil matrix, without prior modification of the thermally conductive filler. Coupling agent modification requires a specific temperature to occur, while the mixing of the thermally conductive filler and silicone oil is carried out at room temperature. Therefore, the coupling agent is difficult to effectively adhere to the surface of the thermally conductive filler, resulting in poor compatibility between the thermally conductive filler and silicone oil, making it difficult to disperse uniformly in the silicone oil. Consequently, it is difficult to form a thermally conductive network structure, resulting in low thermal conductivity and a low extrusion rate.

[0158] The properties of the graphene thermally conductive gels prepared in Examples 1-5 were compared with those prepared in Comparative Example 5. The thermal conductivity of the thermally conductive gel prepared in Example 4 reached 12 W / (m·K), which is much higher than that of Comparative Example 6 (3.3 W / (m·K). Simultaneously, the extrusion rate exceeded 60 g / min, much higher than that of Comparative Example 6 (13 g / min). The main difference between Comparative Example 6 and the examples is that the silane coupling agent was added before the formation of alumina. The modification of the coupling agent requires a certain temperature to occur, and the subsequent preparation of alumina and graphene encapsulation did not involve a high-temperature process. Furthermore, during the subsequent drying process, the coupling agent partially adsorbed onto the alumina surface but not entirely onto the graphene surface. Therefore, the coupling agent was difficult to effectively graft onto the graphene surface, resulting in poor compatibility between the thermally conductive filler and silicone oil, making it difficult to disperse uniformly in the silicone oil. Consequently, it was difficult to form a thermally conductive network structure, resulting in low thermal conductivity and a low extrusion rate.

Claims

1. A method for preparing composite thermally conductive fillers, characterized in that, include: 1) Preparation of graphene oxide dispersion: Graphene oxide is dispersed in deionized water, and the pH is adjusted to between 4 and 7 to prepare a graphene oxide suspension with a mass concentration of 1-20 g / L. The graphene oxide suspension is exfoliated using a high-pressure homogenizer and homogenized at a pressure of 30-80 MPa to achieve a single-layer exfoliation and a uniform and stable graphene oxide dispersion with a size of 5-20 μm. 2) Preparation of graphene oxide-coated alumina composite thermally conductive filler: Aluminum salt is dissolved in the graphene oxide dispersion, wherein the amount of aluminum salt, calculated as aluminum, is 2-15 times the mass of the graphene oxide. The pH of the system is adjusted to between 8 and 12, allowing alumina particles to nucleate and grow in situ on the surface of the graphene oxide. A coupling agent is added at a mass ratio of 1:5-1 to the graphene oxide, and the reaction is carried out at 40-100 °C for 0.5-10 h. Spray drying is performed, with the spray air pressure ranging from 2 to 20 MPa. MPa, outlet temperature range 80~110 ℃; yielded particles with dimensions of 5~20 μm and a specific surface area of ​​1~5 m². 2 / g of graphene oxide-encapsulated alumina composite thermally conductive filler; wherein the alumina is grown in situ on the surface of the graphene oxide, and the composite thermally conductive filler is a microsphere of graphene oxide-encapsulated alumina composite thermally conductive filler.

2. The method according to claim 1, characterized in that, In step 1), the pH is adjusted to between 6 and 7 to prepare a graphite oxide suspension with a mass concentration of 5 to 10 g / L, and homogenized under a pressure of 40 to 60 MPa.

3. The method according to claim 1, characterized in that, The aluminum salt is one of aluminum chloride, aluminum nitrate, aluminum sulfate, ammonium aluminum sulfate, and sodium aluminate.

4. The method according to claim 1, characterized in that, The coupling agent is γ-aminopropyltriethoxysilane, borate coupling agent, titanate coupling agent, or aluminate coupling agent.

5. The thermally conductive filler prepared by any one of claims 1-4.

6. A method for preparing graphene-modified thermally conductive gel in situ, characterized in that, include: The platinum catalyst is dispersed in the silicone oil matrix, and the thermally conductive filler described in claim 5 is dispersed in the silicone oil matrix at a mass ratio of composite thermally conductive filler to silicone oil matrix of 10~15:1; under vacuum conditions while maintaining mechanical stirring, the graphene oxide is heated for vulcanization crosslinking and reduction.

7. The method according to claim 6, characterized in that, The mass percentage of platinum catalyst to silicone oil is 0.1~2.0%.

8. The graphene in-situ modified thermal conductive gel prepared by the method of any one of claims 6-7.

9. An electronic product, characterized in that, The electronic product includes the graphene in-situ modified thermal conductive gel of claim 8.