Preparation method of laminated structure high-thermal-conductivity copper graphite composite material

Abstract

The application discloses a preparation method of a laminated high-thermal-conductivity copper-graphite composite material, and comprises the following steps: (1) flake graphite pretreatment; (2) flake graphite chemical roughening treatment; (3) flake graphite sensitization treatment; (4) flake graphite activation treatment; (5) flake graphite surface copper plating treatment; (6) high-temperature reduction; (7) layered compression sintering of a powder sample; and (8) discharge plasma sintering. The copper plating on the surface of the flake graphite by the chemical copper plating improves the copper / graphite interface properties, improves the interface bonding strength, improves Cu / C wettability, improves the relative density, reduces the porosity, and enhances the strength of the composite material. The copper foil and the copper powder are introduced as the copper matrix, the layered compression makes the flake graphite and the copper matrix more closely combined, and the comprehensive performance of the composite material is more excellent. Finally, the discharge plasma sintering refines the alloy grain size, improves the density of the composite material, and further improves the thermal conductivity of the copper-graphite composite material.

Description

Technical Field

[0001] This invention belongs to the field of copper-based thermally conductive material preparation technology, specifically relating to a method for preparing a layered high thermal conductivity copper-graphite composite material. Background Technology

[0002] As the electronic information industry rapidly develops towards miniaturization, high power density, and integration, the heat flux density of electronic devices is increasing dramatically. Efficient thermal management has become a core bottleneck for improving the performance and ensuring the reliability of electronic devices. Traditional heat dissipation materials, such as pure copper and aluminum-based composite materials, cannot meet the requirements of high heat flux density scenarios due to insufficient thermal conductivity (TC) and mismatch in coefficient of thermal expansion (CTE).

[0003] Flake graphite, as a typical layered carbon-based functional material, has carbon atoms arranged in sp... 2 The hybridization process forms a stable honeycomb covalent bond network within the layer, resulting in minimal in-plane phonon transmission loss and an in-plane thermal conductivity of 1500~1800 W / (m·k). It also possesses an extremely low coefficient of thermal expansion, only 1.0~2.0 ppm / K, exhibiting excellent thermal expansion matching with silicon-based and silicon carbide-based semiconductor chips. Therefore, copper-graphite composite materials have become an ideal material choice for heat dissipation in electronic packaging.

[0004] The traditional method for preparing copper-graphite composite materials involves thoroughly mixing copper matrix powder and graphite, then loading them into a mold for high-temperature sintering. However, due to the weak interlayer bonding force of graphite, its poor mechanical properties, and insufficient wettability with copper, pores and defects easily form at the copper-graphite interface, limiting its application as a standalone heat dissipation material. Summary of the Invention

[0005] This invention provides a method for preparing a layered high thermal conductivity copper-graphite composite material. Copper is deposited on the surface of flake graphite, and then copper powder and copper foil are loaded into a mold in a stacked manner for spark plasma sintering. The orientation of graphite is controlled to improve the in-plane thermal conductivity and mechanical properties of the composite material.

[0006] The technical solution of this invention: A method for preparing a layered high thermal conductivity copper-graphite composite material specifically includes the following steps: (1) Pretreatment of flake graphite The flake graphite was ultrasonically cleaned in anhydrous ethanol to remove surface contaminants and oxides. After rinsing with deionized water, it was soaked in NaOH solution to remove acidic contaminants. It was then rinsed repeatedly with deionized water, soaked in HCl solution to remove alkalinity, rinsed repeatedly with deionized water, and dried. (2) Chemical roughening treatment of flake graphite Add HNO3 and deionized water to a beaker in a certain proportion, stir thoroughly, heat to 60 ℃, add pretreated flake graphite and soak for 20 min for chemical roughening, then rinse repeatedly with deionized water. (3) Sensitization treatment of flake graphite SnCl2, HCl and deionized water were added to a beaker in a certain proportion. After stirring thoroughly, the mixture was heated to 60 °C. Chemically roughened flake graphite was added and soaked for 15 min to introduce reducing sites. Then it was rinsed repeatedly with deionized water. (4) Activation treatment of flake graphite PdCl2, HCl and deionized water were added to a beaker in a certain proportion. After stirring thoroughly, the mixture was heated to 60 °C. Sensitized flake graphite was added and soaked for 15 min to construct the catalytic center. Then, it was rinsed repeatedly with deionized water. (5) Copper plating treatment on the surface of flake graphite In a beaker, deionized water, EDTA 2Na, potassium sodium tartrate, copper sulfate pentahydrate, and 2,2'-bipyridine were added sequentially in a certain proportion. The beaker was placed in a water bath and heated to 60 °C with magnetic stirring until homogeneous. The pH of the solution was adjusted to 12 by titration with prepared NaOH solution. Then, activated flake graphite was added to the solution, followed by the addition of HCHO to reduce the deposited Cu. 2+ During the reaction, the pH value of the solution was continuously measured to ensure that the pH value was 12 during the reaction. After the reaction was completed, the solution was repeatedly rinsed with deionized water, and the copper-plated flake graphite was sieved out and dried. (6) High-temperature reduction After the surface copper plating of the flake graphite in step (5) is evenly spread on a ceramic firing boat, it is placed in a tube furnace, and after setting the program, it is reduced in a hydrogen-argon mixed atmosphere to finally obtain copper-plated flake graphite. (7) Layered pressing and sintering powder samples Copper foil and an appropriate amount of copper powder were placed in the graphite mold in sequence, spread out and pre-compacted. Then, an appropriate amount of copper-plated flake graphite after high-temperature reduction in step (6) was weighed and pre-compacted in the graphite mold. Subsequently, an appropriate amount of copper powder and copper foil were placed in sequence, spread out and pre-compacted again. The operation was repeated four times to finally obtain a layered copper-graphite composite powder. (8) Spark plasma sintering The pretreated graphite mold from step (7) is placed in the furnace cavity of the spark plasma sintering furnace. After setting the program, the furnace cavity is vacuum-treated and then sintered. After sintering, copper-graphite composite material is obtained.

[0007] Preferably, the volume fraction of flake graphite in the laminated high thermal conductivity copper-graphite composite material is 35%; the copper foil is electrolytic copper foil, with a thickness of 30 mm and a diameter of 25 mm; the remainder is pure Cu powder, which is high-purity electrolytic Cu powder, in the form of grape bunches, with a purity of 99.999% and a particle size of 1-3 mm, and the flake graphite has a specification of 500 mm.

[0008] Preferably, the ultrasonic cleaner used in step (1) is a JK5200B ultrasonic cleaner with a cleaning time of 15 min, a power of 200 W, and a frequency of 40 KHz.

[0009] Preferably, the drying oven used in step (1) is model DHG-9000-9005, the drying temperature is 80-100 ℃, and the drying time is 12 h.

[0010] Preferably, the water bath used for water bath heating in step (5) is a TSGP10 model, the heating temperature is 60 ℃, and the concentration of the prepared NaOH solution is 4%.

[0011] Preferably, in step (6), the tubular furnace is model GSL-1200X, and the program is set as follows: heat from room temperature to 400 ℃ at 10 ℃ / min, hold for 2 h, and then cool down to room temperature with the furnace.

[0012] Preferably, in step (6), the ratio of hydrogen to argon mixture is 10% H2-90% Ar, and the flow rate is 300-350 ml / min.

[0013] Preferably, in step (7), the inner diameter of the graphite mold is 25 mm, the outer diameter is 60 mm, and the height is 70 mm. Carbon paper is used to separate the copper-graphite composite powder and copper foil from the graphite mold to facilitate sampling and demolding after sintering.

[0014] Preferably, the manual powder tablet press used in step (7) is model 769YP-40C, the pre-pressing pressure of copper powder is 10 MPa and the holding time is 12s; the pre-pressing pressure of copper-plated flake graphite is 5 MPa and the holding time is 6s.

[0015] Preferably, in step (8), the discharge plasma sintering furnace is a LaboxTM300 model, and thermocouple temperature measurement is used. The front end of the thermocouple is inserted into the temperature measuring hole of the graphite mold. The discharge plasma sintering setting program is as follows: the initial pressure is set to 10 MPa, the temperature is raised from room temperature to 600 ℃ at a rate of 100 ℃ / min, and held for 5 min; then the temperature is raised to 920~980 ℃ at a rate of 100 ℃ / min. During this process, the pressure is increased from 10 MPa to 50 MPa, held for 5 min, and then rapidly cooled.

[0016] The beneficial effects of this invention are as follows: This invention improves the interfacial properties of copper / graphite by electroless copper plating to deposit copper on the surface of flake graphite, thereby increasing the bonding strength between flake graphite and the copper matrix. This transforms the original weak van der Waals bond into a tight metallurgical interfacial bond, significantly improving the wettability of Cu / C, increasing the relative density, reducing the interfacial gap between copper and graphite, and effectively enhancing the thermal conductivity and mechanical properties of the copper-graphite composite material. Furthermore, this invention mixes Cu powder, copper foil, and copper-plated flake graphite using a layering and pressing method, directionally controlling the orientation of the flake graphite, further improving the thermal conductivity of the copper-graphite composite material. This ultimately produces a layered, high-thermal-conductivity copper-graphite composite material, solving the problems of poor copper / graphite interfacial bonding, high porosity, and random flake graphite orientation that limit the high thermal conductivity of the composite material in traditional processes. Attached Figure Description

[0017] Figure 1 Surface morphology diagram of pure copper powder; Figure 2 A surface morphology diagram of flake graphite; Figure 3 A surface morphology diagram of copper-plated flake graphite; Figure 4 XRD diffraction patterns of copper-plated flake graphite / copper composite materials in the XY plane at different sintering temperatures; Figure 5 The image shows the TEM interface morphology of copper-plated flake graphite / copper composite material sintered at 950 °C. Detailed Implementation

[0018] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0019] Example 1

[0020] The copper-graphite composite material in this embodiment was prepared by chemical deposition, high-temperature reduction, lamination and spark plasma sintering, wherein the volume fraction of flake graphite is 35%, and the remainder is copper foil and pure Cu powder.

[0021] The method for preparing the copper-graphite composite material in this embodiment is as follows: (1) Pretreatment of flake graphite Weigh 3.075g of flake graphite into a beaker, pour in 100ml of anhydrous ethanol, then place the beaker in an ice-water bath ultrasonic cleaner and sonicate for 15 min. Afterward, rinse repeatedly with deionized water, place it in a beaker containing 100ml of 0.5 mol / L NaOH solution and soak for 30 min. Afterward, rinse repeatedly with deionized water, place it in a beaker containing 100ml of 10% HCl solution and soak for 30 min. Afterward, rinse repeatedly with deionized water, and place it in a drying oven for drying at 80-100 ℃ for 12 h. (2) Chemical roughening treatment of flake graphite Pour 80 ml of deionized water and 20 ml of 65% nitric acid into a beaker, stir well, place it in a water bath, heat to 60 ℃, then pour in the dried flake graphite from step (1), soak for 20 min, and then rinse repeatedly with deionized water. (3) Sensitization treatment of flake graphite Pour 12g SnCl2, 12ml of 10% dilute hydrochloric acid and 88ml of deionized water into a beaker in sequence, stir thoroughly, place in a water bath, heat to 60℃, then pour in the flake graphite washed in step (2), soak for 15min, and then rinse repeatedly with deionized water. (4) Activation treatment of flake graphite Pour 0.3g PdCl2, 12 ml of 10% dilute hydrochloric acid and 88 ml of deionized water into a beaker in sequence, stir thoroughly, place in a water bath, heat to 60 ℃, then pour in the flake graphite washed in step (3), soak for 15 min, and then rinse repeatedly with deionized water. (5) Copper plating treatment on the surface of flake graphite Add 200 ml of deionized water, 14.375 g of EDTA 2Na, 8.05 g of potassium sodium tartrate, 14.375 g of copper sulfate pentahydrate, and 0.0115 g of 2,2'-bipyridine to a beaker in sequence. After stirring evenly, add deionized water to make up the volume to 950 ml. Prepare a 4% NaOH solution to adjust the pH value of the solution. Place the beaker in a water bath and heat it to 60 ℃ while stirring magnetically continuously. Test the pH value of the solution with a pH tester. Add the prepared NaOH solution to the solution by titration to adjust the pH value of the solution to 12. Then pour in the flake graphite washed in step (4), and then pour in 14.4 ml of 37% formaldehyde solution to reduce the deposited Cu. 2+During the reaction, the pH value of the solution was continuously measured to ensure that the pH value was 12 during the reaction. The reaction was completed when the solution color turned colorless. Then, the solution was repeatedly rinsed with deionized water, the copper-plated flake graphite was sieved out, and it was placed in a drying oven for drying at a temperature of 80-100 ℃ for 12 h. (6) High-temperature reduction After drying the copper-plated flake graphite in step (5), it was evenly spread on a ceramic firing boat and placed in a tube furnace. A reducing atmosphere was created by passing 10% H2-90% Ar gas through the furnace at a flow rate of 300-350 ml / min. The program was set to raise the temperature from room temperature to 400 ℃ at a rate of 10 ℃ / min and hold for 2 h. Then the furnace was cooled to room temperature, and finally 5.68 g of copper-plated flake graphite was obtained. (7) Layered pressing and sintering powder samples In a graphite mold (the inner diameter of the graphite mold is 25 mm, the outer diameter is 60 mm, and the height is 70 mm, and carbon paper is used to separate the copper-graphite composite powder from the graphite mold for easy sampling and demolding after sintering), a single layer of copper foil with a mass of 0.131 g is placed first. 2.35 g of copper powder is weighed and placed into the mold, spread flat, and pre-compacted with a pressure of 10 MPa for 12 s. Then, 1.136 g of copper-plated flake graphite obtained in step (6) is weighed and placed into the mold, spread flat, and pre-compacted with a pressure of 5 MPa for 6 s. Then, 2.35 g of copper powder is weighed and placed into the mold, spread flat, and pre-compacted with a pressure of 10 MPa for 12 s. Finally, a single layer of copper foil with a mass of 0.131 g is placed in the mold. This operation is repeated four times to ensure that the composite powder is a layered structure of copper foil + copper powder + copper-plated flake graphite + copper powder + copper foil. (8) Spark plasma sintering The pre-pressed graphite mold was placed in the furnace cavity of the spark plasma sintering furnace, and the tip of the thermocouple was inserted into the temperature measuring hole of the graphite mold. The furnace cavity door was closed for vacuum treatment. After the furnace cavity reached the vacuum level, sintering was carried out according to the set program as follows: the initial pressure was set to 10 MPa, the temperature was raised from room temperature to 600 ℃ at a rate of 100 ℃ / min, and held for 5 min; then the temperature was raised to 920 ℃ at a rate of 100 ℃ / min, during which the pressure was increased from 10 MPa to 50 MPa, held for 5 min, and then rapidly cooled.

[0022] Example 2

[0023] The copper-graphite composite material in this embodiment was prepared by chemical deposition, high-temperature reduction, lamination and spark plasma sintering, wherein the volume fraction of flake graphite is 35%, and the remainder is copper foil and pure Cu powder.

[0024] The method for preparing the copper-graphite composite material in this embodiment is as follows: (1) Pretreatment of flake graphite Weigh 3.075g of flake graphite into a beaker, pour in 100ml of anhydrous ethanol, then place the beaker in an ice-water bath ultrasonic cleaner and sonicate for 15 min. Afterward, rinse repeatedly with deionized water, place it in a beaker containing 100ml of 0.5 mol / L NaOH solution and soak for 30 min. Afterward, rinse repeatedly with deionized water, place it in a beaker containing 100ml of 10% HCl solution and soak for 30 min. Afterward, rinse repeatedly with deionized water, and place it in a drying oven for drying at 80-100 ℃ for 12 h. (2) Chemical roughening treatment of flake graphite Pour 80 ml of deionized water and 20 ml of 65% nitric acid into a beaker, stir well, place it in a water bath, heat to 60 ℃, then pour in the dried flake graphite from step (1), soak for 20 min, and then rinse repeatedly with deionized water. (3) Sensitization treatment of flake graphite Pour 12g SnCl2, 12ml of 10% dilute hydrochloric acid and 88ml of deionized water into a beaker in sequence, stir thoroughly, place in a water bath, heat to 60℃, then pour in the flake graphite washed in step (2), soak for 15min, and then rinse repeatedly with deionized water. (4) Activation treatment of flake graphite Pour 0.3g PdCl2, 12 ml of 10% dilute hydrochloric acid and 88 ml of deionized water into a beaker in sequence, stir thoroughly, place in a water bath, heat to 60 ℃, then pour in the flake graphite washed in step (3), soak for 15 min, and then rinse repeatedly with deionized water. (5) Copper plating treatment on the surface of flake graphite Add 200 ml of deionized water, 14.375 g of EDTA 2Na, 8.05 g of potassium sodium tartrate, 14.375 g of copper sulfate pentahydrate, and 0.0115 g of 2,2'-bipyridine to a beaker in sequence. After stirring evenly, add deionized water to make up the volume to 950 ml. Prepare a 4% NaOH solution to adjust the pH value of the solution. Place the beaker in a water bath and heat it to 60 ℃ while stirring magnetically continuously. Test the pH value of the solution with a pH tester. Add NaOH solution to the solution by titration to adjust the pH value of the solution to 12. Then pour in the flake graphite washed in step (4), and then pour in 14.4 ml of 37% formaldehyde solution to reduce the deposited Cu. 2+During the reaction, the pH value of the solution was continuously measured to ensure that the pH value was 12 during the reaction. The reaction was completed when the solution color turned colorless. Then, the solution was repeatedly rinsed with deionized water, the copper-plated flake graphite was sieved out, and it was placed in a drying oven for drying at a temperature of 80-100 ℃ for 12 h. (6) High-temperature reduction After drying the copper-plated flake graphite in step (5), it was evenly spread on a ceramic firing boat and placed in a tube furnace. A reducing atmosphere was created by passing 10% H2-90% Ar gas through the furnace at a flow rate of 300-350 ml / min. The program was set to raise the temperature from room temperature to 400 ℃ at a rate of 10 ℃ / min and hold for 2 h. Then the furnace was cooled to room temperature, and finally 5.68 g of copper-plated flake graphite was obtained. (7) Layered pressing and sintering powder samples In a graphite mold (the inner diameter of the graphite mold is 25 mm, the outer diameter is 60 mm, and the height is 70 mm, and carbon paper is used to separate the copper-graphite composite powder from the graphite mold for easy sampling and demolding after sintering), a single layer of copper foil with a mass of 0.131 g is placed first. 2.35 g of copper powder is weighed and placed into the mold, spread flat, and pre-compacted with a pressure of 10 MPa for 12 s. Then, 1.136 g of copper-plated flake graphite obtained in step (6) is weighed and placed into the mold, spread flat, and pre-compacted with a pressure of 5 MPa for 6 s. Then, 2.35 g of copper powder is weighed and placed into the mold, spread flat, and pre-compacted with a pressure of 10 MPa for 12 s. Finally, a single layer of copper foil with a mass of 0.131 g is placed in the mold. This operation is repeated four times to ensure that the composite powder is a layered structure of copper foil + copper powder + copper-plated flake graphite + copper powder + copper foil. (8) Spark plasma sintering The pre-pressed graphite mold was placed in the furnace cavity of the spark plasma sintering furnace, and the tip of the thermocouple was inserted into the temperature measuring hole of the graphite mold. The furnace cavity door was closed for vacuum treatment. After the furnace cavity reached the vacuum level, sintering was carried out according to the set program, which is as follows: the initial pressure was set to 10 MPa, the temperature was raised from room temperature to 600 ℃ at a rate of 100 ℃ / min, and held for 5 min; then the temperature was raised to 950 ℃ at a rate of 100 ℃ / min, during which the pressure was increased from 10 MPa to 50 MPa, held for 5 min, and then rapidly cooled.

[0025] Example 3

[0026] The copper-graphite composite material in this embodiment was prepared by chemical deposition, high-temperature reduction, lamination and spark plasma sintering, wherein the volume fraction of flake graphite is 35%, and the remainder is copper foil and pure Cu powder.

[0027] The method for preparing the copper-graphite composite material in this embodiment is as follows: (1) Pretreatment of flake graphite Weigh 3.075g of flake graphite into a beaker, pour in 100ml of anhydrous ethanol, then place the beaker in an ice-water bath ultrasonic cleaner and sonicate for 15 min. Afterward, rinse repeatedly with deionized water, place it in a beaker containing 100ml of 0.5 mol / L NaOH solution and soak for 30 min. Afterward, rinse repeatedly with deionized water, place it in a beaker containing 100ml of 10% HCl solution and soak for 30 min. Afterward, rinse repeatedly with deionized water, and place it in a drying oven for drying at 80-100 ℃ for 12 h. (2) Chemical roughening treatment of flake graphite Pour 80 ml of deionized water and 20 ml of 65% nitric acid into a beaker, stir well, place it in a water bath, heat to 60 ℃, then pour in the dried flake graphite from step (1), soak for 20 min, and then rinse repeatedly with deionized water. (3) Sensitization treatment of flake graphite Pour 12g SnCl2, 12ml of 10% dilute hydrochloric acid and 88ml of deionized water into a beaker in sequence, stir thoroughly, place in a water bath, heat to 60℃, then pour in the flake graphite washed in step (2), soak for 15min, and then rinse repeatedly with deionized water. (4) Activation treatment of flake graphite Pour 0.3g PdCl2, 12 ml of 10% dilute hydrochloric acid and 88 ml of deionized water into a beaker in sequence, stir thoroughly, place in a water bath, heat to 60 ℃, then pour in the flake graphite washed in step (3), soak for 15 min, and then rinse repeatedly with deionized water. (5) Copper plating treatment on the surface of flake graphite Add 200 ml of deionized water, 14.375 g of EDTA 2Na, 8.05 g of potassium sodium tartrate, 14.375 g of copper sulfate pentahydrate, and 0.0115 g of 2,2'-bipyridine to a beaker in sequence. After stirring evenly, add deionized water to make up the volume to 950 ml. Prepare a 4% NaOH solution to adjust the pH value of the solution. Place the beaker in a water bath and heat it to 60 ℃ while stirring magnetically continuously. Test the pH value of the solution with a pH tester. Add NaOH solution to the solution by titration to adjust the pH value of the solution to 12. Then pour in the flake graphite washed in step (4), and then pour in 14.4 ml of 37% formaldehyde solution to reduce the deposited Cu. 2+During the reaction, the pH value of the solution was continuously measured to ensure that the pH value was 12 during the reaction. The reaction was complete when the solution turned colorless. Then, the solution was repeatedly rinsed with deionized water, the copper-plated flake graphite was sieved out, and then placed in a drying oven for drying at 80-100 ℃ for 12 h. (6) High-temperature reduction After drying the copper-plated flake graphite in step (5), it was evenly spread on a ceramic firing boat and placed in a tube furnace. A reducing atmosphere was created by passing 10% H2-90% Ar gas through the furnace at a flow rate of 300-350 ml / min. The program was set to raise the temperature from room temperature to 400 ℃ at a rate of 10 ℃ / min and hold for 2 h. Then the furnace was cooled to room temperature, and finally 5.68 g of copper-plated flake graphite was obtained. (7) Layered pressing and sintering powder samples In a graphite mold (the inner diameter of the graphite mold is 25 mm, the outer diameter is 60 mm, and the height is 70 mm, and carbon paper is used to separate the copper-graphite composite powder from the graphite mold for easy sampling and demolding after sintering), a single layer of copper foil with a mass of 0.131 g is placed first. 2.35 g of copper powder is weighed and placed into the mold, spread flat, and pre-compacted with a pressure of 10 MPa for 12 s. Then, 1.136 g of copper-plated flake graphite obtained in step (6) is weighed and placed into the mold, spread flat, and pre-compacted with a pressure of 5 MPa for 6 s. Then, 2.35 g of copper powder is weighed and placed into the mold, spread flat, and pre-compacted with a pressure of 10 MPa for 12 s. Finally, a single layer of copper foil with a mass of 0.131 g is placed in the mold. This operation is repeated four times to ensure that the composite powder is a layered structure of copper foil + copper powder + copper-plated flake graphite + copper powder + copper foil. (8) Spark plasma sintering The pre-pressed graphite mold was placed in the furnace cavity of the spark plasma sintering furnace, and the tip of the thermocouple was inserted into the temperature measuring hole of the graphite mold. The furnace cavity door was closed for vacuum treatment. After the furnace cavity reached the vacuum level, sintering was carried out according to the set program as follows: the initial pressure was set to 10 MPa, the temperature was raised from room temperature to 600 ℃ at a rate of 100 ℃ / min, and held for 5 min; then the temperature was raised to 980 ℃ at a rate of 100 ℃ / min, during which the pressure was increased from 10 MPa to 50 MPa, held for 5 min, and then rapidly cooled.

[0028] Comparative Example 1 The copper-graphite composite material in this embodiment was prepared by lamination and spark plasma sintering, wherein the volume fraction of flake graphite was 35%, and the remainder was copper foil and pure Cu powder.

[0029] The method for preparing the copper-graphite composite material in this embodiment is as follows: (1) Pretreatment of flake graphite Weigh 3.075g of flake graphite into a beaker, pour in 100ml of anhydrous ethanol, then place the beaker in an ice-water bath ultrasonic cleaner and sonicate for 15 min. Afterward, rinse repeatedly with deionized water, place it in a beaker containing 100ml of 0.5 mol / L NaOH solution and soak for 30 min. Afterward, rinse repeatedly with deionized water, place it in a beaker containing 100ml of 10% HCl solution and soak for 30 min. Afterward, rinse repeatedly with deionized water, and place it in a drying oven for drying at 80-100 ℃ for 12 h. (2) Layered pressing and sintering powder samples In a graphite mold (the inner diameter of the graphite mold is 25 mm, the outer diameter is 60 mm, and the height is 70 mm, and carbon paper is used to separate the copper-graphite composite powder from the graphite mold for easy sampling and demolding after sintering), a single layer of copper foil with a mass of 0.131 g is placed first. 2.614 g of copper powder is weighed and placed into the mold, spread evenly, and pre-compacted with a pressure of 10 MPa for 12 s. Then, 0.615 g of flake graphite washed and dried in step (1) is weighed and placed into the mold, spread evenly, and pre-compacted with a pressure of 5 MPa for 6 s. Then, 2.614 g of copper powder is weighed and placed into the mold, spread evenly, and pre-compacted with a pressure of 10 MPa for 12 s. Finally, a single layer of copper foil with a mass of 0.131 g is placed in the mold. This operation is repeated four times to ensure that the composite powder is a layered structure of copper foil + copper powder + flake graphite + copper powder + copper foil. (3) Spark plasma sintering The pre-pressed graphite mold was placed in the furnace cavity of the spark plasma sintering furnace, and the tip of the thermocouple was inserted into the temperature measuring hole of the graphite mold. The furnace cavity door was closed for vacuum treatment. After the furnace cavity reached the vacuum level, sintering was carried out according to the set program, which is as follows: the initial pressure was set to 10 MPa, the temperature was raised from room temperature to 600 ℃ at a rate of 100 ℃ / min, and held for 5 min; then the temperature was raised to 950 ℃ at a rate of 100 ℃ / min, during which the pressure was increased from 10 MPa to 50 MPa, held for 5 min, and then rapidly cooled.

[0030] Comparative Example 2 The copper-graphite composite material in this embodiment was prepared by ball milling and spark plasma sintering, wherein the volume fraction of flake graphite was 35%, and the remainder was pure Cu powder.

[0031] The method for preparing the copper-graphite composite material in this embodiment is as follows: (1) High-energy ball milling mixing Weigh out 26.925g of high-purity Cu powder and 3.075g of flake graphite, and put them into a ball mill jar. Add cemented carbide balls at a ball-to-material ratio of 5:1. Place the ball mill jar in a vacuum glove box under an argon atmosphere for assembly. After assembly, take out the ball mill jar and fix it in a planetary ball mill. Set the speed to 200 rpm and mill for 8 hours. (2) Spark plasma sintering The ball-milled mixed powder from step (1) is loaded into a graphite mold (the inner diameter of the graphite mold is 25 mm, the outer diameter is 60 mm, and the height is 70 mm. Carbon paper is used to separate the copper-graphite composite powder from the graphite mold to facilitate sampling and demolding after sintering). After pre-pressing, the graphite mold is placed in the furnace cavity of the spark plasma sintering furnace, and the front end of the thermocouple is inserted into the temperature measuring hole of the graphite mold. The furnace cavity door is closed for vacuum treatment. After the furnace cavity reaches the vacuum level, sintering is carried out according to the set program. The program is as follows: the initial pressure is set to 10 MPa, the temperature is raised from room temperature to 600 ℃ at a rate of 100 ℃ / min, and held for 5 min; then the temperature is raised to 950 ℃ at a rate of 100 ℃ / min. During this process, the pressure is increased from 10 MPa to 50 MPa, held for 5 min, and then rapidly cooled.

[0032] The copper-graphite composite materials prepared in Examples 1 to 3 and Comparative Examples 1 to 2 were subjected to performance tests, and the test results are shown in Table 1: Table 1. Test results of various properties of the composite materials obtained in Examples 1-3 and Comparative Examples 1-2 from Figure 1 It can be seen that the pure copper powder is spherical with a particle size of 20-25 mm.

[0033] from Figure 2 As can be seen, the flake graphite is in the form of flakes, with a size of 500 mm.

[0034] from Figure 3 It can be seen that the surface of the flake graphite is completely coated with copper, proving that electroless copper plating can effectively deposit copper on the surface of flake graphite.

[0035] from Figure 4 It can be seen that after the composite material was sintered into a block by spark plasma, only characteristic diffraction peaks of Cu and GF were detected, and no obvious new impurity phase peaks were observed. This indicates that no new reaction products detectable by XRD were formed during the electroless copper plating and SPS sintering process under the experimental conditions. The diffraction peaks at 2θ values ​​of 26.44° and 54.78° correspond to the (002) and (004) crystal planes of GF, and the 2θ value is... , , The high diffraction peaks correspond to the (111), (200), and (220) crystal planes of the face-centered cubic Cu structure.

[0036] from Figure 5 It can be seen that the flake graphite and the copper matrix are well bonded. During the sintering process, element interdiffusion occurs, forming a tight metallurgical bond, which enhances the interfacial bonding strength between Cu and C and improves the thermodynamic properties of the composite material.

[0037] As shown in Table 1, compared with copper graphite without chemical copper plating and composite materials prepared by traditional ball milling, the composite material of flake graphite after chemical copper plating has significantly improved thermal conductivity and density, and its coefficient of thermal expansion has also decreased, exhibiting superior performance. This proves that the method of chemical copper plating on the surface of flake graphite and lamination can optimize the interfacial properties of copper graphite composite materials.

[0038] This invention improves the interfacial properties of copper / graphite by electroless copper plating to deposit copper on the surface of flake graphite, thereby increasing the bonding strength between flake graphite and the copper matrix. This transforms the original weak van der Waals bond into a tight metallurgical interfacial bond, significantly improving the wettability of Cu / C, increasing the relative density, reducing the interfacial gap between copper and graphite, and effectively enhancing the thermal conductivity and mechanical properties of the copper-graphite composite material. Furthermore, by mixing Cu powder, copper foil, and copper-plated flake graphite together using a layering and pressing method, the orientation of the flake graphite is directionally controlled, further improving the thermal conductivity of the copper-graphite composite material. Finally, a high thermal conductivity copper-graphite composite material with a layered structure is prepared.

[0039] The above embodiments are merely illustrative of specific implementations of this disclosure, but the implementations of this disclosure are not limited to the above content. Any changes, modifications, substitutions, combinations, or simplifications made without substantially departing from the spirit and principle of the inventive concept of this disclosure shall be considered equivalent substitutions and included within the scope of protection defined by the claims.

Claims

1. A method for preparing a layered high thermal conductivity copper-graphite composite material, specifically comprising the following steps: (1) Pretreatment of flake graphite The flake graphite was ultrasonically cleaned in anhydrous ethanol to remove surface contaminants and oxides. After rinsing with deionized water, it was soaked in NaOH solution to remove acidic contaminants. It was then rinsed repeatedly with deionized water, soaked in HCl solution to remove alkalinity, rinsed repeatedly with deionized water, and dried. (2) Chemical roughening treatment of flake graphite Add HNO3 and deionized water to a beaker in a certain proportion, stir thoroughly, heat to 60 ℃, add pretreated flake graphite and soak for 20 min for chemical roughening, then rinse repeatedly with deionized water. (3) Sensitization treatment of flake graphite SnCl2, HCl and deionized water were added to a beaker in a certain proportion. After stirring thoroughly, the mixture was heated to 60 °C. Chemically roughened flake graphite was added and soaked for 15 min to introduce reducing sites. Then it was rinsed repeatedly with deionized water. (4) Activation treatment of flake graphite PdCl2, HCl and deionized water were added to a beaker in a certain proportion. After stirring thoroughly, the mixture was heated to 60 °C. Sensitized flake graphite was added and soaked for 15 min to construct the catalytic center. Then, it was rinsed repeatedly with deionized water. (5) Copper plating treatment on the surface of flake graphite In a beaker, deionized water, EDTA 2Na, potassium sodium tartrate, copper sulfate pentahydrate, and 2,2'-bipyridine were added sequentially in a certain proportion. The beaker was placed in a water bath and heated to 60 °C with magnetic stirring until homogeneous. The pH of the solution was adjusted to 12 by titration with prepared NaOH solution. Then, activated flake graphite was added to the solution, followed by the addition of HCHO to reduce the deposited Cu. 2+ During the reaction, the pH value of the solution was continuously measured to ensure that the pH value was 12 during the reaction. After the reaction was completed, the solution was repeatedly rinsed with deionized water, and the copper-plated flake graphite was sieved out and dried. (6) High-temperature reduction After the surface copper plating of the flake graphite in step (5) is evenly spread on a ceramic firing boat, it is placed in a tube furnace, and after setting the program, it is reduced in a hydrogen-argon mixed atmosphere to finally obtain copper-plated flake graphite. (7) Layered pressing and sintering powder samples Copper foil and an appropriate amount of copper powder were placed in the graphite mold in sequence, spread out and pre-compacted. Then, an appropriate amount of copper-plated flake graphite after high-temperature reduction in step (6) was weighed and pre-compacted in the graphite mold. Subsequently, an appropriate amount of copper powder and copper foil were placed in sequence, spread out and pre-compacted again. The operation was repeated four times to finally obtain a layered copper-graphite composite powder. (8) Spark plasma sintering The pretreated graphite mold from step (7) is placed in the furnace cavity of the spark plasma sintering furnace. After setting the program, the furnace cavity is vacuum-treated and then sintered. After sintering, copper-graphite composite material is obtained.

2. The method for preparing a layered high thermal conductivity copper-graphite composite material as described in claim 1, characterized in that: The volume fraction of flake graphite in the laminated high thermal conductivity copper-graphite composite material is 35%; the copper foil is electrolytic copper foil, with a thickness of 30 mm and a diameter of 25 mm, forming a circular disc; the remainder is pure Cu powder, which is high-purity electrolytic Cu powder, in the form of grape bunches, with a purity of 99.999% and a particle size of 1-3 mm, and the flake graphite has a specification of 500 mm.

3. The method for preparing a layered high thermal conductivity copper-graphite composite material as described in claim 1, characterized in that: The ultrasonic cleaner used in step (1) is a JK5200B ultrasonic cleaner with a cleaning time of 15 minutes, a power of 200 W, and a frequency of 40 KHz.

4. The method for preparing a layered high thermal conductivity copper-graphite composite material as described in claim 1, characterized in that: The drying oven used in step (1) is model DHG-9000-9005, with a drying temperature of 80-100 ℃ and a drying time of 12h.

5. The method for preparing a layered high thermal conductivity copper-graphite composite material as described in claim 1, characterized in that: In step (5), the water bath used for heating is a TSGP10 model, the heating temperature is 60 ℃, and the concentration of the prepared NaOH solution is 4%.

6. The method for preparing a layered high thermal conductivity copper-graphite composite material as described in claim 1, characterized in that: In step (6), the tubular furnace model is GSL-1200X, and the program is set as follows: heat up from room temperature to 400 ℃ at a rate of 10 ℃ / min, hold for 2 h, and then cool down to room temperature with the furnace.

7. The method for preparing a layered high thermal conductivity copper-graphite composite material as described in claim 1, characterized in that: In step (6), the ratio of hydrogen to argon mixture is 10% H2-90% Ar, and the injection rate is 300-350 ml / min.

8. The method for preparing a layered high thermal conductivity copper-graphite composite material as described in claim 1, characterized in that: The manual powder tablet press used in step (7) is model 769YP-40C. The pre-compression pressure of copper powder is 10 MPa and the holding time is 12s. The pre-compression pressure of copper-plated flake graphite is 5 MPa and the holding time is 6s.

9. The method for preparing a layered high thermal conductivity copper-graphite composite material as described in claim 1, characterized in that: In step (8), the discharge plasma sintering furnace is a LaboxTM300 model. Thermocouple temperature measurement is used. The front end of the thermocouple is inserted into the temperature measuring hole of the graphite mold. The discharge plasma sintering setting program is as follows: the initial pressure is set to 10 MPa, the temperature is raised from room temperature to 600 ℃ at a rate of 100 ℃ / min, and held for 5 min; then the temperature is raised to 920~980 ℃ at a rate of 100 ℃ / min. During this process, the pressure is increased from 10 MPa to 50 MPa, held for 5 min, and then rapidly cooled.

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