A method for preparing graphene-coated copper powder

Abstract

The application discloses a preparation method of graphene-coated copper powder, which combines a hydrothermal method and an in-situ cracking method to uniformly coat graphene on the surface of copper powder by using a low-cost organic carbon source, so that the prepared graphene-coated copper powder has excellent conductivity and oxidation resistance. In the application, the high-temperature and high-pressure environment of the hydrothermal reaction promotes the partial decomposition or oxidation of the organic carbon source, generates oxygen-containing functional groups, and combines the oxygen-containing functional groups with the surface of the copper powder through hydrogen bonds or chemical bonds to form a pre-coating layer, so that the number of chemical bonds to be broken in the in-situ cracking stage is reduced, and the temperature required for cracking is reduced. In addition, the hydrothermal reaction also promotes the uniform dispersion and close coating of the organic carbon source on the surface of the copper powder, reduces the diffusion distance of carbon atoms during cracking, avoids the local aggregation and defects of graphene during cracking, so that the graphene can uniformly coat the surface of the copper powder after cracking, and the conductivity and oxidation resistance of the copper powder are ensured.

Description

Technical Field

[0001] This invention belongs to the field of conductive powder material preparation, specifically relating to a method for preparing graphene-coated copper powder. Background Technology

[0002] Copper possesses excellent electrical conductivity (second only to silver), thermal conductivity, and chemical stability, and its relatively low cost makes it widely used in fields such as power transmission and the electronics industry. However, copper also has the following disadvantages: low mechanical strength, low hardness, susceptibility to oxidation and corrosion, and a high resistivity at high temperatures that leads to a decrease in its electrical conductivity.

[0003] Graphene is composed of carbon atoms arranged in sp... 2 Hexagonal honeycomb planar network crystal materials formed by orbital hybridization exhibit excellent electrical conductivity (carrier mobility of 15000 cm⁻¹). 2 ·V -1 ·S -1 Thermal conductivity (thermal conductivity is 5000 W·m) -1 ·K -1 Graphene possesses excellent properties such as high mechanical strength (elastic modulus of approximately 1 TPa and strength approximately 200 times that of steel). These superior properties make graphene an ideal material reinforcing agent. However, due to its extremely large specific surface area and interlayer van der Waals forces, graphene is extremely prone to aggregation and difficult to disperse uniformly. In addition, graphene has poor wettability with metals (the wetting angle between graphene and copper is approximately 140°), resulting in weak interfacial bonding.

[0004] Graphene-coated copper powder not only retains the electrical conductivity of copper and the mechanical properties of graphene, but also enhances the thermal stability and oxidation resistance of copper, thus greatly improving the overall performance of graphene / copper composite materials.

[0005] There are several methods for preparing graphene / copper composites, including mechanical mixing, layered composite, molecular-level mixing, and in-situ growth. Mechanical mixing can achieve uniform dispersion of graphene and copper powder under certain conditions, but prolonged mechanical mixing can affect the uniformity of graphene coating on copper powder and the structural integrity of graphene, thus impacting the overall performance of the composite. Layered composite uses techniques such as chemical vapor deposition to prepare graphene-metal layered structures in the composite material through alternating deposition, thereby obtaining graphene-metal matrix composites with significant reinforcing effects. The layered composite method has a complex preparation process, requires sophisticated equipment, and is not suitable for composite graphene on copper powder surfaces. Molecular-level mixing avoids the problems of uneven graphene dispersion and easy agglomeration during preparation, but it requires high-quality graphene oxide and reduced graphene oxide; otherwise, the conductivity of the composite cannot be guaranteed. In-situ growth (in-situ pyrolysis) of graphene on copper surfaces mainly relies on the catalytic activity of the copper surface. In-situ growth can produce graphene / copper composites with intact graphene structures, fewer defects, and tight bonding between graphene and copper. However, the in-situ growth method alone requires high temperatures (usually 800–1000 °C) to prepare graphene / copper composites, and copper powder is prone to sticking at high temperatures. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing graphene-coated copper powder. This method utilizes a low-cost organic carbon source and combines hydrothermal and in-situ pyrolysis methods to uniformly coat the surface of copper powder with graphene, resulting in graphene-coated copper powder with excellent electrical conductivity and oxidation resistance. Furthermore, this method, by combining hydrothermal and in-situ pyrolysis methods, effectively reduces the temperature required for in-situ graphene growth, thereby lowering energy consumption.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: copper powder is pretreated and then mixed with an organic carbon source solution. The resulting mixture is transferred to a reaction vessel and hydrothermally reacted at 150–200 °C for 8–24 h. The powder obtained after hydrothermal reaction is filtered, washed, and freeze-dried, and then in-situ pyrolyzed at 350–550 °C for 0.5–12 h in a mixed atmosphere of nitrogen and hydrogen to obtain graphene-coated copper powder.

[0008] The above-mentioned organic carbon source solution is composed of an organic carbon source and a solvent. The organic carbon source is any one or more of ascorbic acid, citric acid, α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin, glucose, acetylsalicylic acid, and salicylic acid. The solvent is any one or a mixture of two of water and ethanol.

[0009] The copper powder mentioned above is spherical or flake-shaped powder with an average particle size of 0.5–5 μm and a purity of ≥99.9%.

[0010] Furthermore, in the above preparation method, the copper powder pretreatment method is as follows: the copper powder is stirred and soaked in a 15-20 mol / L formic acid aqueous solution for 20-30 min at a stirring speed of 400-500 rpm, then the copper powder is washed with deionized water and filtered; the mass ratio of copper powder to formic acid aqueous solution is 1:1.5-2. The purpose of formic acid washing is to remove impurities from the surface of commercial copper powder, making the copper powder surface clean to obtain good catalytic effect.

[0011] Furthermore, in the above preparation method, the preferred mass ratio of the organic carbon source to copper powder is 1:150 to 250.

[0012] Furthermore, in the above preparation method, it is preferable to pretreat the copper powder and then emulsify and mix it with the organic carbon source solution using an emulsifier for 3 to 10 minutes, with the emulsifier speed being 8000 to 12000 rpm.

[0013] Furthermore, in the above preparation method, it is preferable to carry out the hydrothermal reaction at 150–180 °C for 8–12 h.

[0014] Furthermore, in the above preparation method, it is preferable to filter the powder obtained after hydrothermal reaction, wash it with deionized water until the resistivity of the washing solution is ≥18 MΩ, and freeze-dry it at -40 to -50 ℃ for 10 to 12 h under a vacuum of 0.05 to 0.15 Pa.

[0015] Furthermore, in the above preparation method, it is preferable to perform in-situ pyrolysis at 400–500 °C for 4–8 h in a mixed atmosphere of nitrogen and hydrogen.

[0016] Furthermore, in the above preparation method, the volume fraction of hydrogen in the nitrogen and hydrogen mixture is preferably 2% to 4%, and the flow rate of the mixture is 200 to 300 mL / min; the heating rate of the in-situ pyrolysis is 5 to 15 °C / min.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0018] This invention combines hydrothermal and in-situ pyrolysis methods. A low-cost organic carbon source is uniformly coated onto the surface of acid-treated copper powder via a hydrothermal reaction. This uniform coating ensures that the copper powder produced by subsequent in-situ pyrolysis is uniformly coated with graphene. Furthermore, the hydrothermal reaction effectively reduces the temperature required for subsequent in-situ pyrolysis, thus reducing energy consumption. The high-temperature, high-pressure environment of the hydrothermal reaction promotes partial decomposition or oxidation of the organic carbon source, generating oxygen-containing functional groups that bond with the copper powder surface via hydrogen bonds or chemical bonds to form a pre-coating layer. This reduces the number of chemical bonds that need to be broken in the subsequent in-situ pyrolysis stage, thereby lowering the pyrolysis temperature. This tight bond between the pre-coating layer and the copper powder also effectively prevents oxidation of the copper powder. The application of the hydrothermal method in the early stage results in a pyrolysis temperature of 350–550 °C, significantly lower than that of in-situ pyrolysis alone. In addition, the hydrothermal reaction can complete the pyrolysis and carbonization of the organic carbon source to a certain extent, allowing the carbon source to transition from a long chain to an ordered carbon structure, thereby reducing the activation energy required for pyrolysis. In addition, the hydrothermal reaction can promote the uniform dispersion and tight coating of organic carbon sources on the surface of copper powder under high pressure, reducing the diffusion distance of carbon atoms during pyrolysis and avoiding local agglomeration and defects of graphene during pyrolysis. This ensures that the graphene can be uniformly coated on the surface of copper powder after pyrolysis, guaranteeing the conductivity and antioxidant properties of the copper powder. The hydrogen bonds and oxygen-containing groups on the surface of the copper powder also enhance the interfacial bonding force, allowing oxygen atoms to be removed at lower temperatures during in-situ pyrolysis, promoting the formation of graphene sp. 2 The formation of carbon structures. Attached Figure Description

[0019] Figure 1 This is a scanning electron microscope image of the graphene-coated copper powder prepared in Example 1.

[0020] Figure 2 This is the Raman spectrum of the graphene-coated copper powder prepared in Example 1.

[0021] Figure 3 This is a scanning electron microscope image of the graphene-coated copper powder prepared in Example 4.

[0022] Figure 4 This is a scanning electron microscope image of the graphene-coated copper powder prepared in Example 11. Detailed Implementation

[0023] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments. It should be noted that the described embodiments are only some embodiments of the present invention, and not all embodiments. These embodiments are only for a better understanding of the present invention, and not for limiting the scope of protection of the present invention.

[0024] Unless otherwise specified, all reagents and raw materials used in this invention are commercially available products or products that can be prepared by known methods. Example 1

[0025] 90 g of spherical copper powder with an average particle size of 1 μm was added to 135 g of 18 mol / L formic acid aqueous solution and stirred and soaked at 500 rpm for 30 min. The copper powder was then washed with deionized water and filtered to obtain acid-treated copper powder. 0.45 g of ascorbic acid was dissolved in 90 mL of deionized water and added to the aforementioned acid-treated copper powder. The mixture was emulsified and mixed at 10000 rpm for 5 min using an emulsifier. The resulting mixture was transferred to a hydrothermal reactor and hydrothermally reacted at 150 ℃ for 8 h under sealed conditions. After the reaction was completed, the mixture was naturally cooled to room temperature. The hydrothermally reacted powder was filtered and washed with deionized water until the resistivity of the washing solution was ≥18 MΩ. Then, it was freeze-dried at -50 ℃ under a vacuum of 0.1 Pa for 12 h. The freeze-dried powder was placed in a mixed atmosphere of nitrogen and hydrogen, with hydrogen comprising 2% and a flow rate of 250 mL / min. The temperature was increased to 400 °C at a rate of 5 °C / min, and the powder was in situ pyrolyzed for 4 h to obtain graphene-coated copper powder.

[0026] Depend on Figure 1 It can be seen that the surface of the copper powder is uniformly coated with graphene with obvious wrinkles. Figure 2 Display, I D / I G The ratio of 0.74 indicates that the graphene coated on the copper powder surface has a low degree of disorder and few defects. Example 2

[0027] 90 g of spherical copper powder with an average particle size of 1 μm was added to 135 g of 18 mol / L formic acid aqueous solution and stirred and soaked at 500 rpm for 30 min. The copper powder was then washed with deionized water and filtered to obtain acid-treated copper powder. 0.45 g of citric acid was dissolved in 90 mL of deionized water and added to the aforementioned acid-treated copper powder. The mixture was emulsified and mixed at 10000 rpm for 5 min using an emulsifier. The resulting mixture was transferred to a hydrothermal reactor and hydrothermally reacted at 180 ℃ for 16 h under sealed conditions. After the reaction was completed, the mixture was naturally cooled to room temperature. The hydrothermally reacted powder was filtered and washed with deionized water until the resistivity of the washing solution was ≥18 MΩ. Then, it was freeze-dried at -50 ℃ under a vacuum of 0.1 Pa for 12 h. The freeze-dried powder was placed in a mixed atmosphere of nitrogen and hydrogen, with hydrogen comprising 2% and a flow rate of 250 mL / min. The temperature was increased to 400 °C at a rate of 5 °C / min, and the powder was in situ pyrolyzed for 1 h to obtain graphene-coated copper powder. Example 3

[0028] 90 g of spherical copper powder with an average particle size of 1 μm was added to 135 g of 18 mol / L formic acid aqueous solution and stirred and soaked at 500 rpm for 30 min. The copper powder was then washed with deionized water and filtered to obtain acid-treated copper powder. 0.45 g of acetylsalicylic acid was dissolved in a 1:1 mixture of deionized water and anhydrous ethanol. The acid-treated copper powder was added to the mixture and emulsified and mixed at 10,000 rpm for 5 min using an emulsifier. The resulting mixture was transferred to a hydrothermal reactor and hydrothermally reacted at 150 ℃ for 8 h under sealed conditions. After the reaction was complete, the mixture was naturally cooled to room temperature. The hydrothermally reacted powder was filtered, washed with deionized water until the resistivity of the washing solution was ≥18 MΩ, and then freeze-dried at -50 ℃ under a vacuum of 0.1 Pa for 12 h. The freeze-dried powder was placed in a mixed atmosphere of nitrogen and hydrogen, with hydrogen comprising 2% of the total gas volume and a flow rate of 250 mL / min. The temperature was increased to 350 °C at a rate of 5 °C / min, and the powder was in situ pyrolyzed for 4 h to obtain graphene-coated copper powder. Example 4

[0029] 90 g of spherical copper powder with an average particle size of 1 μm was added to 135 g of 18 mol / L formic acid aqueous solution and stirred and soaked at 500 rpm for 30 min. The copper powder was then washed with deionized water and filtered to obtain acid-treated copper powder. 0.45 g of α-cyclodextrin was dissolved in 90 mL of deionized water and added to the aforementioned acid-treated copper powder. The mixture was emulsified and mixed at 10000 rpm for 5 min using an emulsifier. The resulting mixture was transferred to a hydrothermal reactor and hydrothermally reacted at 200 ℃ for 24 h under sealed conditions. After the reaction was completed, the mixture was naturally cooled to room temperature. The hydrothermally reacted powder was filtered, washed with deionized water until the resistivity of the washing solution was ≥18 MΩ, and then freeze-dried at -50 ℃ under a vacuum of 0.1 Pa for 12 h. The freeze-dried powder was placed in a mixed atmosphere of nitrogen and hydrogen, with hydrogen comprising 2% of the total gas volume and a flow rate of 250 mL / min. The temperature was increased to 550 °C at a rate of 10 °C / min, and the mixture was in-situ pyrolyzed for 4 h to obtain graphene-coated copper powder (see...). Figure 3 ). Example 5

[0030] In this embodiment, the temperature was increased to 400 ℃ at a heating rate of 5 ℃ / min, and in-situ pyrolysis was performed for 8 h. Other steps were the same as in Example 1 to obtain graphene-coated copper powder. Example 6

[0031] In this embodiment, the temperature was increased to 400 ℃ at a heating rate of 5 ℃ / min, and in-situ pyrolysis was performed for 12 h. Other steps were the same as in Example 1 to obtain graphene-coated copper powder. Example 7

[0032] In this embodiment, the temperature was increased to 500 ℃ at a heating rate of 5 ℃ / min, and in-situ pyrolysis was performed for 4 h. Other steps were the same as in Example 1 to obtain graphene-coated copper powder. Example 8

[0033] 90 g of flaky copper powder with an average particle size of 4 μm was added to 135 g of 18 mol / L formic acid aqueous solution and stirred and soaked at 500 rpm for 30 min. The copper powder was then washed with deionized water and filtered to obtain acid-treated copper powder. 0.45 g of ascorbic acid was dissolved in 90 mL of deionized water and added to the aforementioned acid-treated copper powder. The mixture was emulsified and mixed at 10000 rpm for 5 min using an emulsifier. The resulting mixture was transferred to a hydrothermal reactor and hydrothermally reacted at 150 ℃ for 16 h under sealed conditions. After the reaction was completed, the mixture was naturally cooled to room temperature. The hydrothermally reacted powder was filtered and washed with deionized water until the resistivity of the washing solution was ≥18 MΩ. Then, it was freeze-dried at -50 ℃ under a vacuum of 0.1 Pa for 12 h. The freeze-dried powder was placed in a mixed atmosphere of nitrogen and hydrogen, with hydrogen comprising 2% of the total gas volume and a flow rate of 250 mL / min. The temperature was increased to 500 °C at a rate of 10 °C / min, and the powder was in situ pyrolyzed for 2 h to obtain graphene-coated copper powder. Example 9

[0034] 90 g of flaky copper powder with an average particle size of 4 μm was added to 135 g of 18 mol / L formic acid aqueous solution and stirred and soaked at 500 rpm for 30 min. The copper powder was then washed with deionized water and filtered to obtain acid-treated copper powder. 0.45 g of citric acid was dissolved in 90 mL of anhydrous ethanol, and the aforementioned acid-treated copper powder was added. The mixture was emulsified and mixed at 10000 rpm for 5 min using an emulsifier. The resulting mixture was transferred to a hydrothermal reactor and hydrothermally reacted at 150 ℃ for 8 h under sealed conditions. After the reaction was completed, the mixture was naturally cooled to room temperature. The hydrothermally reacted powder was filtered, washed with deionized water until the resistivity of the washing solution was ≥18 MΩ, and then freeze-dried at -50 ℃ under a vacuum of 0.1 Pa for 12 h. The freeze-dried powder was placed in a mixed atmosphere of nitrogen and hydrogen, with hydrogen comprising 2% and a flow rate of 250 mL / min. The temperature was increased to 400 °C at a rate of 5 °C / min, and the powder was in situ pyrolyzed for 0.5 h to obtain graphene-coated copper powder. Example 10

[0035] 90 g of flaky copper powder with an average particle size of 4 μm was added to 135 g of 18 mol / L formic acid aqueous solution and stirred and soaked at 500 rpm for 30 min. The copper powder was then washed with deionized water and filtered to obtain acid-treated copper powder. 0.45 g of glucose was dissolved in a 3:7 mixture of deionized water and anhydrous ethanol in 90 mL. The aforementioned acid-treated copper powder was added and emulsified and mixed at 10,000 rpm for 5 min using an emulsifier. The resulting mixture was transferred to a hydrothermal reactor and hydrothermally reacted at 150 ℃ for 8 h under sealed conditions. After the reaction was complete, the mixture was naturally cooled to room temperature. The hydrothermally reacted powder was filtered, washed with deionized water until the resistivity of the washing solution was ≥18 MΩ, and then freeze-dried at -50 ℃ under a vacuum of 0.1 Pa for 12 h. The freeze-dried powder was placed in a mixed atmosphere of nitrogen and hydrogen, with hydrogen comprising 2% and a flow rate of 250 mL / min. The temperature was increased to 400 °C at a rate of 15 °C / min, and the powder was in situ pyrolyzed for 4 h to obtain graphene-coated copper powder. Example 11

[0036] 90 g of spherical copper powder with an average particle size of 0.5 μm was added to 135 g of 18 mol / L formic acid aqueous solution and stirred and soaked at 500 rpm for 30 min. The copper powder was then washed with deionized water and filtered to obtain acid-treated copper powder. 0.45 g of ascorbic acid was dissolved in 90 mL of deionized water and added to the aforementioned acid-treated copper powder. The mixture was emulsified and mixed at 10000 rpm for 5 min using an emulsifier. The resulting mixture was transferred to a hydrothermal reactor and hydrothermally reacted at 150 ℃ for 8 h under sealed conditions. After the reaction was completed, the mixture was naturally cooled to room temperature. The hydrothermally reacted powder was filtered and washed with deionized water until the resistivity of the washing solution was ≥18 MΩ. Then, it was freeze-dried at -50 ℃ under a vacuum of 0.1 Pa for 12 h. The freeze-dried powder was placed in a mixed atmosphere of nitrogen and hydrogen, with hydrogen comprising 2% of the total gas volume and a flow rate of 250 mL / min. The temperature was increased to 350 °C at a rate of 5 °C / min, and the mixture was in-situ pyrolyzed for 1 h to obtain graphene-coated copper powder (see [link to article]). Figure 4 ). Example 12

[0037] 90 g of spherical copper powder with an average particle size of 5 μm was added to 135 g of 18 mol / L formic acid aqueous solution and stirred and soaked at 500 rpm for 30 min. The copper powder was then washed with deionized water and filtered to obtain acid-treated copper powder. 0.45 g of citric acid was dissolved in 90 mL of deionized water and added to the aforementioned acid-treated copper powder. The mixture was emulsified and mixed at 10000 rpm for 5 min using an emulsifier. The resulting mixture was transferred to a hydrothermal reactor and hydrothermally reacted at 150 ℃ for 16 h under sealed conditions. After the reaction was completed, the mixture was naturally cooled to room temperature. The hydrothermally reacted powder was filtered and washed with deionized water until the resistivity of the washing solution was ≥18 MΩ. Then, it was freeze-dried at -50 ℃ under a vacuum of 0.1 Pa for 12 h. The freeze-dried powder was placed in a mixed atmosphere of nitrogen and hydrogen, with hydrogen comprising 2% and a flow rate of 250 mL / min. The temperature was increased to 400 °C at a rate of 15 °C / min, and the powder was in situ pyrolyzed for 4 h to obtain graphene-coated copper powder. Example 13

[0038] 90 g of flaky copper powder with an average particle size of 2 μm was added to 135 g of 18 mol / L formic acid aqueous solution and stirred and soaked at 500 rpm for 30 min. The copper powder was then washed with deionized water and filtered to obtain acid-treated copper powder. 0.45 g of citric acid was dissolved in 90 mL of deionized water and added to the aforementioned acid-treated copper powder. The mixture was emulsified and mixed at 10000 rpm for 5 min using an emulsifier. The resulting mixture was transferred to a hydrothermal reactor and hydrothermally reacted at 150 ℃ for 8 h under sealed conditions. After the reaction was completed, the mixture was naturally cooled to room temperature. The hydrothermally reacted powder was filtered and washed with deionized water until the resistivity of the washing solution was ≥18 MΩ. Then, it was freeze-dried at -50 ℃ under a vacuum of 0.1 Pa for 12 h. The freeze-dried powder was placed in a mixed atmosphere of nitrogen and hydrogen, with hydrogen comprising 2% and a flow rate of 250 mL / min. The temperature was increased to 450 °C at a rate of 10 °C / min, and the powder was in situ pyrolyzed for 4 h to obtain graphene-coated copper powder.

[0039] Comparative Example 1

[0040] 90 g of spherical copper powder with an average particle size of 1 μm (without acid treatment or hydrothermal reaction) was placed in a mixed atmosphere of nitrogen and hydrogen, with hydrogen as the integral of 2% and the flow rate of the mixed gas being 250 mL / min. The temperature was increased to 400 °C at a heating rate of 5 °C / min, and in-situ pyrolysis was carried out for 4 h.

[0041] Comparative Example 2

[0042] Compared with Comparative Example 1, the difference is that spherical copper powder with an average particle size of 1 μm was replaced with flake copper powder (without acid treatment and hydrothermal reaction) with an average particle size of 4 μm. The other steps are the same as those in Comparative Example 1.

[0043] Comparative Example 3

[0044] 90 g of spherical copper powder with an average particle size of 1 μm was added to 135 g of 18 mol / L formic acid aqueous solution and stirred and soaked at 500 rpm for 30 min. The copper powder was then washed with deionized water and filtered to obtain acid-treated copper powder. 0.45 g of ascorbic acid was dissolved in 90 mL of deionized water, and the acid-treated copper powder was added. The mixture was emulsified and mixed at 10000 rpm for 5 min using an emulsifier, and then freeze-dried at -50 ℃ under vacuum of 0.1 Pa for 12 h. The freeze-dried powder was placed in a mixed atmosphere of nitrogen and hydrogen, with hydrogen comprising 2% and a flow rate of 250 mL / min, and heated to 400 ℃ at a heating rate of 5 ℃ / min. In-situ pyrolysis was performed for 4 h to obtain graphene-coated copper powder.

[0045] Comparative Example 4

[0046] Compared with Comparative Example 3, the difference is that flake copper powder with an average particle size of 4 μm was used instead of spherical copper powder with an average particle size of 1 μm, while the other steps are the same as those in Comparative Example 3.

[0047] The resistivity and Tg weight gain of the powders obtained in Examples 1 to 13 and Comparative Examples 1 to 4 were tested according to the following method, and the results are shown in Table 1.

[0048] Resistivity: Weigh 1.5 ± 0.1 g of sample and place it in a cylindrical mold with a diameter of 6 mm and a height of 10 mm. Press the sample under a pressure of 5 MPa for 1 min. Measure its resistance using a four-wire resistance instrument and calculate its resistivity according to formula (1).

[0049] (1)

[0050] In the formula, ρ Here, is the resistivity in Ω•cm; R is the resistance in Ω; h is the sample height in cm; d is the sample base diameter in cm; and π is pi. Generally, a lower resistivity is desirable for the sample.

[0051] Tg weight gain: Weigh 0.1 ± 0.01 g of sample and place it in a 0.4 mL alumina crucible. Heat the sample from room temperature to 200 °C at a rate of 5 °C / min under air atmosphere, then hold at this temperature for 60 min. Calculate the sample weight gain rate. Generally, a lower weight gain rate indicates better antioxidant properties.

[0052] Table 1

[0053]

[0054] As shown in Table 1, the copper powders of Examples 1-13 that were coated with organic carbon sources by hydrothermal method and then subjected to in-situ pyrolysis have significantly better resistivity and oxidation resistance than the copper powders of Comparative Examples 1 and 2 that were directly subjected to in-situ pyrolysis, and the copper powders of Comparative Examples 3 and 4 that were directly coated (without hydrothermal coating) and then subjected to in-situ pyrolysis.

[0055] The embodiments and comparative examples described above are merely some embodiments and comparative examples of the present invention, and not all embodiments and comparative examples. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A method for preparing graphene-coated copper powder, characterized in that: Copper powder was pretreated and then mixed with an organic carbon source solution. The resulting mixture was transferred to a reaction vessel and hydrothermally reacted at 150–200 °C for 8–24 h. The powder obtained after hydrothermal reaction was filtered, washed, and freeze-dried, and then in-situ pyrolyzed at 350–550 °C for 0.5–12 h in a mixed atmosphere of nitrogen and hydrogen to obtain graphene-coated copper powder. The mass ratio of organic carbon source to copper powder is 1:150 to 250; The organic carbon source solution is composed of an organic carbon source and a solvent, wherein the organic carbon source is any one or more of ascorbic acid, citric acid, α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin, glucose, acetylsalicylic acid, and salicylic acid.

2. The method for preparing graphene-coated copper powder according to claim 1, characterized in that: The copper powder is spherical or flake-shaped, with an average particle size of 0.5–5 μm and a purity of ≥99.9%.

3. The method for preparing graphene-coated copper powder according to claim 1, characterized in that: The method for pretreatment of copper powder is as follows: copper powder is stirred and soaked in a 15-20 mol / L formic acid aqueous solution for 20-30 min at a stirring speed of 400-500 rpm, and then the copper powder is washed with deionized water and filtered; the mass ratio of copper powder to formic acid aqueous solution is 1:1.5-2.

4. The method for preparing graphene-coated copper powder according to claim 1, characterized in that: The solvent is any one or a mixture of two of water and ethanol.

5. The method for preparing graphene-coated copper powder according to claim 1, characterized in that: After pretreatment, copper powder is emulsified and mixed with organic carbon source solution using an emulsifier for 3 to 10 minutes at a speed of 8000 to 12000 rpm.

6. The method for preparing graphene-coated copper powder according to claim 1, characterized in that: The hydrothermal reaction was carried out at 150–180℃ for 8–12 h.

7. The method for preparing graphene-coated copper powder according to claim 1 or 6, characterized in that: The powder obtained after hydrothermal reaction was filtered, washed with deionized water until the resistivity of the washing solution was ≥18 MΩ, and then freeze-dried at -40 to -50 ℃ for 10 to 12 h under a vacuum of 0.05 to 0.15 Pa.

8. The method for preparing graphene-coated copper powder according to claim 1, characterized in that: In-situ pyrolysis was performed at 400–500 °C for 4–8 h under a mixed atmosphere of nitrogen and hydrogen.

9. The method for preparing graphene-coated copper powder according to claim 1 or 8, characterized in that: The volume fraction of hydrogen in the nitrogen and hydrogen mixture is 2% to 4%, and the flow rate of the mixture is 200 to 300 mL / min; the heating rate of the in-situ pyrolysis is 5 to 15 °C / min.

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