Graphite foam copper-silver gradient metal composite material and preparation method thereof

Abstract

The invention provides a graphite foam copper-silver gradient metal composite material and a preparation method thereof. The preparation method comprises the steps that a graphite foam base body is cleaned, and surface pollutants are removed; electroplating a copper conductive layer on the surface of the treated graphite foam matrix by adopting a copper electroplating process to form a copper-coated graphite foam composite material; soaking the copper-coated graphite foam composite material in the chemical silvering presoaking liquid or wetting the copper-coated graphite foam composite material by using the chemical silvering presoaking liquid; and the treated copper-coated graphite foam composite material is put into a chemical silver plating solution, chemical silver plating treatment is conducted on the surface of the copper-coated graphite foam composite material, and the graphite foam copper-silver gradient metal composite material is prepared. According to the invention, a plating layer can be flat, uniform and controllable in thickness, and has bright white metal luster, meanwhile, the original high thermal conductivity of graphite foam can be maintained, and the oxidation resistance and the mechanical strength of the graphite foam are remarkably improved, so that the urgent demand of the high thermal conductivity field on a high-performance composite material is met.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high-thermal-conductivity composite material preparation, and particularly relates to a graphite foam copper-silver gradient metal composite material and a preparation method thereof. BACKGROUND

[0002] As a high-performance composite material, copper-coated graphite foam integrates light weight, high strength, high thermal conductivity, and metal weldability, and can significantly improve the comprehensive performance of the composite material by fully exerting the respective advantages of graphite foam and the copper layer. It has shown broad application potential in many fields. However, although the copper layer gives the graphite foam high strength and easy weldability, the treated copper surface is easily oxidized in air, which limits its application range to some extent. Silver is an ideal choice for surface oxidation-resistant process due to its excellent electrical conductivity, thermal conductivity, and stable physical and chemical properties. The chemical silver plating technology is widely used in silver plating treatment on the surface of metal and non-metal materials due to its high stability and strong anti-silver discoloration ability. It not only effectively protects the copper surface from pollution and corrosion, but also provides excellent weldability to ensure the reliability and durability of the material in complex environments.

[0003] Although the related technology such as patent CN112409947A discloses a method for chemical silver plating on the surface of graphite powder, which uses dopamine deposition to replace the traditional pretreatment methods of oil removal, roughening, and sensitization, and can avoid the generation of heavy metal waste liquid, but there is still room for optimization in terms of the concentration and pH value of dopamine solution, and it is difficult to directly deposit a silver plating layer with high electrical conductivity on the surface of graphite. Another patent CN113061948A discloses a method for electrochemical silver plating on a copper substrate, which performs oil removal, palladium plating, silver plating, and other process treatments on the surface of the copper substrate, but does not optimize the current density, reaction time control, and plating solution composition, making it difficult to obtain a uniform and dense silver plating layer. In addition, due to the rough and uneven surface of graphite foam and poor electrical conductivity, direct electroplating is difficult, and the bonding force between the metal layer and the graphite non-metal layer is weak, making it difficult to form a uniform silver plating layer on the surface.

[0004] The existing technology has the defect that it is difficult to form a uniform, dense, high-brightness, and excellent oxidation-resistant metal plating layer on the rough surface of graphite foam, which limits the further expansion of graphite foam composite materials in high-performance application fields. SUMMARY

[0005] (I) Technical problems to be solved

[0006] The present application provides a graphite foam copper-silver gradient metal composite material and a preparation method thereof to solve the technical problems of forming a uniform plating layer directly on the surface of graphite foam and improving the brightness of the silver plating layer of graphite foam.

[0007] (II) Technical Solution

[0008] To solve the above technical problems, the present application provides a preparation method of graphite foam copper-silver gradient metal composite, which comprises the following steps:

[0009] S1. Base pretreatment: clean the graphite foam base to remove surface contaminants;

[0010] S2. Copper electroplating: use copper electroplating process to electroplate a copper conductive layer on the surface of the graphite foam base treated in step S1, forming a copper-coated graphite foam composite material;

[0011] S3. Pre-dipping treatment: immerse the copper-coated graphite foam composite material in a chemical silver plating pre-dipping solution or wet the copper-coated graphite foam composite material with the chemical silver plating pre-dipping solution;

[0012] S4. Chemical silver plating: place the copper-coated graphite foam composite material treated in step S3 into a chemical silver plating solution to perform chemical silver plating treatment on the surface of the copper-coated graphite foam composite material, thereby preparing a graphite foam copper-silver gradient metal composite material.

[0013] Further, in step S1, the density of the graphite foam base is 0.3-0.6 g / cm 3 .

[0014] Further, in step S2, in the copper electroplating process, an electroplating solution containing copper sulfate, sulfuric acid, and sodium chloride is used, the pH value of the electroplating solution is 1.5-2.5, the current density is 6-8 A / dm 2 , the electroplating temperature is 20-30℃, and the electroplating time is 10-20 minutes.

[0015] Further, in step S3, the chemical silver plating pre-dipping solution contains nitric acid and a chelating agent, wherein the concentration of the nitric acid is 0.2-0.4 mol / L, the chelating agent is EDTA or its salt, and the concentration is 0.02-0.04 mol / L; the pre-dipping treatment temperature is 30-40℃, and the immersion time is 20-30 seconds.

[0016] Further, in step S4, the chemical silver plating solution comprises the following components:

[0017] Main salt: silver nitrate or silver sulfate, concentration 0.8-1.5 g / L;

[0018] Accelerator: nitric acid or methyl sulfonic acid, concentration 0.4-0.6 mol / L;

[0019] Anti-discoloration agent: fatty acid or benzimidazole derivative, concentration 0.5-1%;

[0020] Surfactant: isomeric decanol polyoxyethylene ether or block polyether, concentration is 1-5%;

[0021] Complexing agent: EDTA or its salt, concentration is 0.02-0.04 mol / L;

[0022] Reducing agent: formaldehyde or sodium hypophosphite, amount is 1-50 times of the molar number of the main salt;

[0023] The temperature of the chemical silver plating treatment is 30-50 DEG C, the time is 45-90 seconds, and the thickness of the obtained silver layer is 0.3-0.5 mu m.

[0024] Further, in the step S4, DNS is further added in the chemical silver plating solution as an oxidizing agent, and the concentration is 0.05-0.1%.

[0025] Further, after the step S4, a post-treatment step is further included: the graphite foam copper-silver gradient metal composite material is subjected to ultrasonic water washing, the temperature is 40-60 DEG C, repeated for 3 times, and then subjected to drying treatment.

[0026] In addition, the application further provides a graphite foam copper-silver gradient metal composite material prepared by the above method.

[0027] Further, the density of the graphite foam copper-silver gradient metal composite material is 0.5-2 g / cm 3 , the thermal conductivity is 30-60 W / (m*K), and the tensile strength is greater than or equal to 4.2 MPa.

[0028] Further, the surface of the silver plating layer of the graphite foam copper-silver gradient metal composite material is bright and has no discoloration, and the peeling area of the plating layer after the adhesion test is less than or equal to 5%.

[0029] (Three) beneficial effects

[0030] The application provides a graphite foam copper-silver gradient metal composite material and a preparation method thereof, and the preparation method comprises the following steps: cleaning a graphite foam substrate to remove surface contaminants; adopting a copper electroplating process to electroplate a copper conductive layer on the surface of the treated graphite foam substrate to form a copper-coated graphite foam composite material; immersing the copper-coated graphite foam composite material in a chemical silver plating pre-impregnation solution or wetting the copper-coated graphite foam composite material with the chemical silver plating pre-impregnation solution; and placing the treated copper-coated graphite foam composite material into a chemical silver plating solution to perform chemical silver plating treatment on the surface of the copper-coated graphite foam composite material to prepare the graphite foam copper-silver gradient metal composite material.

[0031] The present application can not only realize uniform and controllable thickness of the plating layer, but also has bright white metal luster, can maintain the original high thermal conductivity of the graphite foam, and significantly improve the oxidation resistance and mechanical strength, thereby meeting the urgent needs of high-performance composite materials in the high-thermal-conductivity field, and is especially suitable for forming a uniform, dense, strong-bonding and oxidation-resistant copper-silver composite plating layer on the rough surface of the graphite foam.

[0032] Compared with the prior art, the present application has the following beneficial effects:

[0033] 1. The present application adopts gradient metallization design, and through the gradient process of "electroplating copper-chemical plating silver", a copper bottom layer is first electroplated on the surface of the graphite foam, and then silver is chemically plated, so that a uniform, dense, strong-bonding and oxidation-resistant metal plating layer can be formed on the surface of the graphite foam, and the problem that it is difficult to directly form a uniform plating layer on the surface of the graphite foam in the prior art can be solved.

[0034] 2. The present application can significantly improve the brightness of the silver plating layer by optimizing the component selection and concentration ratio of the chemical silver plating solution, and solve the problem of poor brightness of the silver plating layer of the graphite foam obtained in the prior art.

[0035] 3. The silver plating layer obtained in the present application has excellent electrical conductivity, thermal conductivity and mechanical strength, and the density of the copper-silver gradient metal composite material of the graphite foam is 0.5-2 g / cm 3 , the thermal conductivity coefficient is 30-60 W / (m·K), and the tensile strength is greater than or equal to 4.2 MPa, which can meet the urgent needs of high-performance composite materials in the high-thermal-conductivity field.

[0036] 4. The preparation method of the present application is simple in process and high in operation simplicity, does not need complex pretreatment process, can avoid the generation of heavy metal waste liquid, and has the advantages of environmental friendliness. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 The micrograph of the graphite foam used for Example 1;

[0038] Figure 2 The SEM graph of the graphite foam used for Example 1;

[0039] Figure 3 The micrograph of the copper-coated graphite foam composite material prepared in Example 1;

[0040] Figure 4 The micrograph of the graphite foam copper-silver gradient metallization composite material prepared in Example 1;

[0041] Figure 5 The SEM graph of the metal plating layer of the graphite foam copper-silver gradient metallization composite material prepared in Example 1;

[0042] Figure 6SEM image of the silver layer on the surface of the graphite foam copper-silver gradient metalized composite prepared in Example 1. DETAILED DESCRIPTION

[0043] In order to make the objectives, contents and advantages of the present application clearer, the specific embodiments of the present application are described in further detail below in combination with the drawings and examples.

[0044] Example 1

[0045] The present embodiment proposes a preparation method of a graphite foam copper-silver gradient metal composite, which specifically comprises the following steps:

[0046] S1. Substrate pretreatment: Select high-thermal-conductivity graphite foam with a density of 0.55 g / cm 3 as the substrate, the microscopic photograph of the high-thermal-conductivity graphite foam is shown in Figure 1 , and the SEM image of the surface morphology is shown in Figure 2 ; clean the graphite foam substrate to remove surface impurities and contaminants.

[0047] S2. Copper electroplating: adopt copper electroplating process to electroplate a copper conductive layer on the surface of the graphite foam substrate treated in step S1, to form a copper-coated graphite foam composite, as shown in Figure 3 , which has good electrical conductivity and mechanical properties.

[0048] In the copper electroplating process, an electroplating solution containing 180 g / L copper sulfate, 50 g / L sulfuric acid and 30 mg / L sodium chloride is adopted, the pH value of the electroplating solution is 1.5, the current density is 6 A / dm 2 , the electroplating temperature is 20℃, and the electroplating time is 10 minutes.

[0049] S3. Pre-dipping treatment: immerse the copper-coated graphite foam composite treated in step S2 in a chemical silver plating pre-dipping solution composed of 0.2 mol / L nitric acid and 0.02 mol / L chelating agent EDTA, control the temperature of the pre-dipping solution to be 30℃, and the immersion time to be 20 seconds.

[0050] S4. Chemical silver plating: transfer the copper-coated graphite foam composite treated in step S3 to a chemical silver plating solution prepared from 1.0 g / L silver nitrate, 0.4 mol / L nitric acid, 0.7% anti-tarnish agent (fatty acid, benzimidazole and its derivatives), 0.07% DNS, 3% isomeric decanol polyoxyethylene ether, 0.02 mol / L EDTA, 1 times the molar number of formaldehyde (main salt) and deionized water, control the temperature of the silver plating solution to be 30℃, the immersion time to be 45 seconds, and the thickness of the deposited silver layer to be 0.3 μm; then perform 3 times of ultrasonic water washing with the water washing temperature being 45℃, and obtain the graphite foam copper-silver gradient metal composite with a uniform surface after drying, as shown inFigure 5 and 6 The density is 1.22 g / cm 3 , and the thermal conductivity is 56.40 W / (m·K).

[0051] Example 2

[0052] The embodiment provides a preparation method of a graphite foam copper-silver gradient metal composite material, and the preparation method specifically comprises the following steps:

[0053] S1. Base pretreatment: high-thermal-conductivity graphite foam with a density of 0.57 g / cm 3 is selected as a base; the graphite foam base is cleaned to remove surface impurities and pollutants.

[0054] S2. Copper electroplating: a copper electroplating process is adopted to electroplate a copper conductive layer on the surface of the graphite foam base treated in step S1, so as to form a copper-coated graphite foam composite material.

[0055] In the copper electroplating process, an electroplating solution containing 200 g / L copper sulfate, 60 g / L sulfuric acid and 40 mg / L sodium chloride is adopted, the pH value of the electroplating solution is 2, the current density is 7 A / dm 2 , the electroplating temperature is 25 DEG C, and the electroplating time is 15 minutes.

[0056] S3. Pre-impregnation treatment: the copper-coated graphite foam composite material treated in step S2 is soaked in a chemical silver plating pre-impregnation solution composed of 0.3 mol / L nitric acid and 0.03 mol / L chelating agent EDTA, the temperature of the pre-impregnation solution is controlled to be 35 DEG C, and the soaking time is 45 seconds.

[0057] S4. Chemical silver plating: the copper-coated graphite foam composite material treated in step S3 is transferred to a chemical silver plating solution prepared from 0.9 g / L silver nitrate, 0.5 mol / L nitric acid, 0.6 % anti-tarnish agent (fatty acid, benzimidazole and derivatives thereof), 0.06 % DNS, 2 % isomeric decanol polyoxyethylene ether, 0.03 mol / L EDTA, sodium hypophosphite (reducing agent, the amount is 25 times the molar amount of the main salt) and deionized water, the temperature of the silver plating solution is controlled to be 40 DEG C, the soaking time is 120 seconds, and the thickness of the deposited silver layer is 0.4 μm; then the graphite foam copper-silver gradient metal composite material with a uniform surface is obtained through three times of ultrasonic water washing with a water washing temperature of 50 DEG C and drying, the density is 1.16 g / cm 3 , and the thermal conductivity is 56.13 W / (m·K).

[0058] Example 3

[0059] The embodiment provides a preparation method of a graphite foam copper-silver gradient metal composite material, and the preparation method specifically comprises the following steps:

[0060] S1. Base pretreatment: Select high thermal conductivity graphite foam with a density of 0.55 g / cm 3 2 as the base; soak the graphite foam base in 10% hydrochloric acid for 8 minutes, wash with water until neutral, dry at 80°C, and remove surface impurities and pollutants.

[0061] S2. Copper plating: adopt copper plating process to form copper-coated graphite foam composite material on the surface of the graphite foam base treated in step S1.

[0062] In the copper plating process, an electroplating solution containing 220 g / L copper sulfate, 60 g / L sulfuric acid and 10.3 g / L sodium chloride is used, the pH value of the electroplating solution is 2.5, the current density is 8.0 A / dm 2 , the plating temperature is 30°C, and the plating time is 20 minutes.

[0063] S3. Pre-impregnation treatment: immerse the copper-coated graphite foam composite material treated in step S2 in a chemical silver plating pre-impregnation solution composed of 0.4 mol / L nitric acid and 0.03 mol / L chelating agent EDTA, control the temperature of the pre-impregnation solution at 40°C, and the soaking time is 30 seconds.

[0064] S4. Chemical silver plating: transfer the copper-coated graphite foam composite material treated in step S3 to a chemical silver plating solution prepared from 1.5 g / L silver nitrate, 0.6 mol / L nitric acid, 1% anti-tarnish agent (fatty acid), 0.1% DNS, 5% isomeric decanol polyoxyethylene ether, 0.04 mol / L EDTA and formaldehyde (50 times the molar number of silver nitrate), the pH value is 2.0, the temperature of the silver plating solution is controlled at 50°C, the soaking time is 90 seconds, and the thickness of the deposited silver layer is 5 μm; then wash with water for 3 times, the water washing temperature is 60, and after drying, a graphite foam copper-silver gradient metal composite material with a uniform surface is obtained, the density is 1.18 g / cm 3 , and the thermal conductivity is 55.90 W / (m·K).

[0065] The chemical silver plating pre-impregnation solution used in the application has chelating effect: EDTA chelates free copper ions, which can prevent them from competing with silver ions for deposition, so that the silver layer uniformly nucleates on the copper surface, and the silver layer coverage reaches 99%.

[0066] The anti-oxidation performance of the application is significantly improved, and the anti-tarnish agent has a synergistic effect: fatty acid forms a dense organic film on the surface of the silver layer, and benzimidazole derivative coordinates with silver atoms, which inhibits oxidation through a double mechanism.

[0067] The first heavy mechanism: the fatty acid type anti-tarnish agent in the electroless silver plating solution forms a uniform and dense organic film on the surface of the silver layer after deposition. The film can physically isolate the silver layer from oxygen, water vapor and other corrosive media in the air, prevent the reaction of silver atoms with external oxidizing factors, and inhibit the oxidation and discoloration of the silver layer from the physical barrier level.

[0068] The second heavy mechanism: the benzimidazole derivative in the anti-tarnish agent can form a stable coordination bond with the silver atoms on the surface of the silver layer. The active groups (such as nitrogen atoms) in the molecular structure of the benzimidazole derivative can form a stable coordination bond with the silver atoms on the surface of the silver layer, change the surface electronic structure of the silver atoms, and reduce the chemical activity of the silver atoms being oxidized. This chemical coordination modification can weaken the oxidation tendency of silver from the atomic level, further improving the oxidation resistance and stability of the silver layer. The above two mechanisms work together to inhibit the oxidation of the silver layer from the physical isolation and chemical modification dimensions.

[0069] In the graphite foam copper-silver gradient metal composite prepared by the application, the copper-silver gradient structure forms a continuous heat conduction path, the thermal conductivity of the composite material reaches 30-60 W / (m·K), and the tensile strength is greater than or equal to 4.2 MPa, which can meet the anti-vibration requirements of electronic devices.

[0070] The process of the application is simplified, and the traditional sensitization (SnCl2) and activation (PdCl2) steps are omitted, reducing the discharge of heavy metal waste liquid.

[0071] The EDTA complexing agent used in the application can reduce the ineffective consumption of silver ions, and the electroless silver plating solution can be recycled for 5-8 times, reducing the cost by 30%.

[0072] The method of the application is simple, and a uniform, dense, strong and oxidation-resistant silver plating layer is successfully prepared by combining electroplating and electroless plating, thereby obtaining a graphite foam copper-silver gradient metallized composite material with excellent performance. The obtained silver plating layer is bright and anti-tarnish, and the interface performance is stable, the thermal conductivity reaches 30-60 W / (m·K), and the mechanical performance of the composite material is improved, which can meet the urgent needs of high thermal conductivity field for high-performance composite materials. The application not only expands the application field of graphite foam material, but also improves its reliability and durability in complex environment, and provides a new technical approach for the surface metallization treatment of graphite foam material.

[0073] The above only describes the preferred embodiments of the application, and it should be pointed out that for ordinary skilled persons in the art, some improvements and modifications can be made without departing from the technical principles of the application, and these improvements and modifications should also be considered as the protection scope of the application.

Claims

1. A method for preparing a graphite foam copper-silver gradient metal composite material, characterized in that, The preparation method includes the following steps: S1. Matrix pretreatment: Clean the graphite foam matrix to remove surface contaminants; S2. Copper plating: A copper conductive layer is electroplated onto the surface of the graphite foam substrate after step S1 to form a copper-clad graphite foam composite material. S3. Pre-impregnation treatment: Immerse the copper-clad graphite foam composite material in chemical silver plating pre-impregnation solution or wet the copper-clad graphite foam composite material with chemical silver plating pre-impregnation solution; S4. Chemical silver plating: The copper-coated graphite foam composite material treated in step S3 is placed in a chemical silver plating solution, and chemical silver plating is performed on the surface of the copper-coated graphite foam composite material to prepare a graphite foam copper-silver gradient metal composite material.

2. The method for preparing graphite foam copper-silver gradient metal composite material as described in claim 1, characterized in that, In step S1, the density of the graphite foam matrix is ​​0.3–0.6 g / cm³. 3 .

3. The method for preparing graphite foam copper-silver gradient metal composite material as described in claim 1, characterized in that, In step S2, the copper electroplating process uses an electroplating solution containing copper sulfate, sulfuric acid, and sodium chloride. The pH value of the electroplating solution is 1.5–2.5, and the current density is 6–8 A / dm³. 2 The electroplating temperature is 20-30℃, and the electroplating time is 10-20 minutes.

4. The method for preparing graphite foam copper-silver gradient metal composite material as described in claim 1, characterized in that, In step S3, the electroless silver plating pre-immersion solution contains nitric acid and a chelating agent, wherein the concentration of nitric acid is 0.2-0.4 mol / L, and the chelating agent is EDTA or its salts, with a concentration of 0.02-0.04 mol / L; the pre-immersion treatment temperature is 30-40℃, and the immersion time is 20-30 seconds.

5. The method for preparing graphite foam copper-silver gradient metal composite material as described in claim 1, characterized in that, In step S4, the electroless silver plating solution includes the following components: Main salt: silver nitrate or silver sulfate, concentration of 0.8–1.5 g / L; Accelerator: Nitric acid or methanesulfonic acid, concentration of 0.4–0.6 mol / L; Anti-discoloration agent: fatty acid or benzimidazole derivative, at a concentration of 0.5-1%; Surfactant: Isomeric decacarbonyl alcohol polyoxyethylene ether or block polyether, concentration of 1-5%; Complexing agent: EDTA or its salts, at a concentration of 0.02–0.04 mol / L; Reducing agent: formaldehyde or sodium hypophosphite, in amounts of 1 to 50 times the molar number of the main salt; The chemical silver plating process is performed at a temperature of 30–50°C for 45–90 seconds, resulting in a silver layer thickness of 0.3–0.5 μm.

6. The method for preparing graphite foam copper-silver gradient metal composite material as described in claim 1, characterized in that, In step S4, DNS is further added to the chemical silver plating solution as an oxidant at a concentration of 0.05-0.1%.

7. The method for preparing graphite foam copper-silver gradient metal composite material as described in claim 1, characterized in that, After step S4, a post-processing step is further included: ultrasonically washing the graphite foam copper-silver gradient metal composite material at a temperature of 40-60℃, repeating 3 times, and then drying it.

8. A graphite foam copper-silver gradient metal composite material, characterized in that, The graphite foam copper-silver gradient metal composite material is prepared by the method described in any one of claims 1 to 7.

9. The graphite foam copper-silver gradient metal composite material as described in claim 8, characterized in that, The density of the graphite foam copper-silver gradient metal composite material is 0.5–2 g / cm³. 3 It has a thermal conductivity of 30–60 W / (m·K) and a tensile strength of ≥4.2 MPa.

10. The graphite foam copper-silver gradient metal composite material as described in claim 8, characterized in that, The silver plating surface of the graphite foam copper-silver gradient metal composite material is bright and does not change color, and the area of ​​plating peeling off after adhesion test is ≤5%.

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