Silver / graphene composite coating and preparation method thereof

Abstract

The invention discloses a silver / graphene composite coating and a preparation method thereof, and belongs to the technical field of electrolysis or electrophoresis production process methods of coatings. The preparation method comprises the following steps: (1) pretreating the surface of the base material; (2) pre-silver plating and electroplating; (3) electroplating a pure silver layer; and (4) silver / graphene composite electroplating. The invention provides a mode of carrying out composite electroplating at an intermittent stirring speed, a thin silver layer is electroplated in a pre-silver plating solution, then a silver layer is plated in a pure silver plating solution, and finally electroplating is carried out in a silver / graphene composite plating solution, so that the composite plating containing the pre-silver plating layer, the pure silver layer and the silver / graphene layer is obtained. Therefore, the performance of the silver plating layer is enhanced, and the binding force of the plating layer and a base material is greatly improved. The method has the advantages of being convenient to operate, mild in reaction, low in cost and uniform in coating. The prepared silver / graphene composite coating has excellent conductivity, hardness, corrosion resistance and wear resistance, and has a good application prospect under outdoor working conditions.

Description

Technical Field

[0001] The invention relates to the technical field of electrolysis or electrophoresis production process methods for coatings, and in particular to a silver / graphene composite coating and a preparation method thereof. Background Art

[0002] In the application of outdoor high-voltage disconnectors, the performance of electrical contact materials is crucial. For the high-temperature, high-humidity and high-salt environment outdoors, electrical contact materials need to have excellent electrical contact performance, as well as good wear resistance, corrosion resistance and chemical stability, to ensure the reliability and safety of high-voltage switchgear in various harsh environments.

[0003] As a material with high electrical and thermal conductivity, silver is often used as an electrical contact material. At present, the main material of electrical contacts for outdoor high-voltage disconnectors is a layer of silver plated on the surface of a pure copper substrate. However, pure silver has a low hardness and is easy to wear, resulting in increased contact resistance, which affects the performance and service life of the contact switch. In order to improve the corrosion resistance and wear resistance of silver, other materials are usually added to silver to make alloys or composite materials, such as silver-antimony, silver-tungsten, silver-graphite composite materials, etc., to improve its performance and life in high-voltage disconnectors.

[0004] As a new type of two-dimensional material, graphene has excellent mechanical strength, electrical conductivity and thermal conductivity, and has shown great potential in the research of electrical contact materials in recent years. Silver / graphene composite coating combines the high conductivity of silver with the high hardness and wear resistance of graphene, and is expected to provide better performance in outdoor high-voltage disconnectors.

[0005] For example, the Chinese invention patent with publication number CN107254696A discloses a silver / graphene composite silver plating solution, its preparation method and electrodeposition process. The silver / graphene composite silver plating solution includes the following components: 20-60 g / L of water-soluble silver-containing compound, 150-300 g / L of sodium thiosulfate, 20-60 g / L of potassium pyrosulfite, 20-30 g / L of ammonium acetate, 0.2-1 g / L of thiosemicarbazide, 5-10 g / L of graphene, and 5 mL / L of polyvinyl pyrrolidone. Its electrodeposition process uses the silver / graphene composite silver plating solution for processing, and the operating temperature can be directly carried out at room temperature, which solves the technical defect that graphene is not well combined into the silver / graphene composite coating. However, in practical applications, this process still has the problem of uneven coating.

[0006] There are many reasons for uneven coating. Graphene is a two-dimensional crystal composed of carbon atoms, each of which forms a hexagonal honeycomb lattice through sp2 hybrid orbitals. The huge specific surface area of ​​graphene means that its surface energy is very high. In a solution environment, substances tend to reduce surface energy, so graphene sheets tend to approach each other in the solution and re-aggregate into larger particles. This agglomeration will cause the graphene to be unable to be evenly distributed in the metal matrix during the electroplating process, thereby affecting the uniformity and overall performance of the coating. The van der Waals force between graphene sheets is very strong. This force comes from long-range dispersion interactions, which is particularly significant in two-dimensional materials. In solution, graphene sheets are easy to stack together to form a compact stacking structure. Even after ultrasonic dispersion or other physical treatments, if effective measures are not taken to prevent re-aggregation, graphene will still re-adhere in a short time, resulting in uneven coating.

[0007] In addition, if the active order of the matrix material (commonly used copper matrix in this field) is before copper, the substrate is prone to replacement reaction in the electroplated silver solution environment, and the anions are replaced to form a loose silver layer on the surface of the material, resulting in poor bonding between the subsequent electroplated silver layer and the substrate. For this situation, there is a scheme in the field to improve the density and bonding of the coating by depositing a silver-graphene layer after the silver-plated layer. For example, the Chinese invention patent with publication number CN116162910A provides a silver-graphene composite coating and its preparation method and application. The preparation method includes the following steps: step 1, preparing a nanosilver plating solution and a silver-graphene plating solution, and pretreating the substrate; step 2, using magnetron sputtering to plate a first nanosilver layer on the substrate; step 3, using a vacuum composite electrodeposition method to deposit a silver-graphene layer on the first nanosilver layer; step 4, using magnetron sputtering to plate a second nanosilver layer on the silver-graphene layer. However, as can be seen from its steps, the process uses magnetron sputtering and vacuum composite electrodeposition for preparation, which has high cost, low efficiency and high requirements on process conditions, all of which restrict its large-scale application in electrical contact materials.

[0008] In summary, providing a silver / graphene composite coating processing technology with convenient preparation, mild reaction and low cost, which can solve the problem of uneven coating and meet the use requirements of conductivity and mechanical properties, is of great significance for expanding the application of this material. Summary of the invention

[0009] In view of the above-mentioned defects of the prior art, in a first aspect of the present invention, a method for preparing a silver / graphene composite coating which is convenient, mild in reaction, low in cost and has uniform coating is provided, comprising the following steps: (1) Substrate surface pretreatment: Placing the substrate in an electrolytic degreasing solution to remove dirt and impurities on the substrate surface and activate the substrate to obtain a pretreated substrate; (2) Pre-silver plating: Placing the pretreated substrate in a pre-silver plating solution, and electroplating to obtain a material containing a pre-silver plating layer; (3) Pure silver layer plating: Placing the material containing the pre-silver coating in a pure silver plating solution and electroplating the material to obtain a composite material containing the pure silver coating; (4) Silver / graphene composite electroplating: Placing the composite material containing the pure silver coating in a silver / graphene composite plating solution and electroplating the composite material under intermittent stirring conditions to obtain a silver / graphene composite coating; Among them, the intermittent stirring rate is ≤800 rads / min; in a single stirring cycle, the stirring time is ≤10 min, and the stirring stop time is ≤5 min.

[0010] Preferably, in step (1), the electrolytic degreasing solution is an aqueous solution, and its components include: 3-15 g / L sodium tripolyphosphate, 12-50 g / L sodium hydroxide, 10-30 g / L sodium silicate, 2-10 g / L sodium gluconate, and 10-30 g / L sodium carbonate.

[0011] Preferably, in step (1), the substrate is used as the cathode, the electrolysis temperature is 40-80 °C, the stirring speed is 100-500 rads / min, and the current density is 0.5-5 A / dm 2 , the electrolysis time is 30-60 s.

[0012] Preferably, in step (1), activation is performed by treating with 3% to 18% by volume sulfuric acid for 30 to 60 seconds.

[0013] Preferably, in step (2), the pre-silver plating solution is an aqueous solution, and its components include: 20-50 g / L of a water-soluble silver-containing compound, 50-200 g / L of potassium cyanurate, 100-300 g / L of sodium sulfite, 10-50 g / L of tetrahydroxypropyl ethylenediamine, 0.5-10 g / L of potassium hydroxide, 0.5-5 g / L of naphthalenesulfonic acid formaldehyde polymer sodium salt, and 0.1-3 g / L of tetrasodium ethylenediaminetetraacetic acid.

[0014] Further preferably, the water-soluble silver-containing compound includes one of silver nitrate, silver fluoride and silver chlorate.

[0015] Preferably, in step (2), the pretreated substrate is used as the cathode, the electroplating temperature is 20-50 °C, the stirring speed is 100-800 rads / min, and the current density is 0.5-5 A / dm 2 , the electroplating time is 30-120 s.

[0016] Preferably, in step (3), the pure silver plating solution is an aqueous solution, and its components include: 20-50 g / L water-soluble silver-containing compound, 50-200 g / L potassium cyanurate, 100-300 g / L sodium sulfite, 10-50 g / L tetrahydroxypropyl ethylenediamine, 0.5-10 g / L potassium hydroxide, 0.5-5 g / L naphthalenesulfonic acid formaldehyde polymer sodium salt, and 0.1-3 g / L tetrasodium ethylenediaminetetraacetic acid; the pH of the pure silver plating solution is 8-11.

[0017] Further preferably, the water-soluble silver-containing compound includes one of silver nitrate, silver fluoride and silver chlorate.

[0018] Preferably, in step (3), the material containing the pre-silver coating is used as the cathode, the electroplating temperature is 20-50 °C, the stirring speed is 100-800 rads / min, and the current density is 0.5-5 A / dm 2 The electroplating time is 1-10 min.

[0019] During the electroplating process, the kinetic properties of the solution play a key role in the dispersion and deposition of graphene. Intermittent stirring can break the agglomeration structure of graphene through mechanical force and redisperse it in the solution. The shear force and impact force generated during the stirring process can overcome the van der Waals force between graphene, thereby preventing agglomeration. In addition, stirring can also promote the interaction between ions and graphene in the solution, so that graphene can be better adsorbed on the electrode surface to form a uniform composite coating. In addition, the chemical properties of the plating solution, the stirring speed, the temperature, and the stability of the plating solution are also important factors affecting the dispersion of graphene. If the plating solution is unstable, it may cause the graphene particles to settle or flocculate in the plating solution, thereby affecting its uniform distribution in the coating. Therefore, when preparing the composite plating solution, the present invention adopts a suitable formula and electroplating parameters to improve the stability of the plating solution, break the agglomeration structure of graphene, promote solution dynamics and optimize the interaction during the electroplating process, effectively prevent the problem of uneven coating caused by graphene agglomeration, and prevent graphene from settling at the bottom of the solution, thereby ensuring that graphene can be uniformly doped in the composite coating.

[0020] Preferably, in step (4), the silver / graphene composite plating solution is an aqueous solution, and its components include: 20-50 g / L water-soluble silver-containing compound, 50-200 g / L potassium cyanurate, 100-300 g / L sodium sulfite, 10-50 g / L tetrahydroxypropyl ethylenediamine, 0.5-10 g / L potassium hydroxide, 0.5-5 g / L naphthalenesulfonic acid formaldehyde polymer sodium salt, 0.1-3 g / L tetrasodium ethylenediaminetetraacetic acid, and 0.1-5 g / L graphene; the pH of the silver / graphene composite plating solution is 8-11.

[0021] Further preferably, the water-soluble silver-containing compound includes one of silver nitrate, silver fluoride and silver chlorate.

[0022] Further preferably, when the components of the silver / graphene composite plating solution are prepared, the graphene is dispersed at a stirring speed of 800-2000 rads / min, and the dispersion time is 30-120 min.

[0023] Further preferably, the number of layers of the graphene sheet is 10-80, and the median particle size is 0.5-5 μm.

[0024] Preferably, in step (4), the composite material containing the pure silver coating is used as the cathode, the electroplating temperature is 20-50°C, and the current density is 0.5-5 A / dm 2 The electroplating time is 10-60 min.

[0025] Those skilled in the art can select a suitable anode according to the type of cathode material for electrolysis or electroplating. As presented in one or more embodiments of the present invention, when the substrate is copper, the substrate surface pretreatment and pre-silver plating can use a stainless steel plate as the anode, and the pure silver layer electroplating and silver / graphene composite plating can use a pure silver plate as the anode.

[0026] In the second aspect of the present invention, there is provided a silver / graphene composite coating having good electrical conductivity, excellent hardness and excellent wear resistance, which is prepared by the preparation method provided by the first aspect of the present invention.

[0027] In order to obtain a uniformly dispersed silver / graphene composite coating, based on the above technical solution, the design concept and principle of the present invention is to propose a method of composite electroplating at an intermittent stirring speed, first electroplating a thin layer of silver in a pre-silver plating solution, then electroplating another layer of silver in a pure silver plating solution, and finally electroplating in a silver / graphene composite plating solution to obtain a composite coating containing a pre-silver plating layer-pure silver layer-silver / graphene layer. In this way, the performance of the silver plating layer is enhanced and the bonding force between the plating layer and the substrate is greatly improved.

[0028] In the process, graphene is first pre-dispersed in the composite plating solution at a relatively fast stirring speed, and then the silver / graphene composite layer is electroplated by intermittent stirring, so that the graphene can be evenly dispersed in the solution, effectively preventing the problem of uneven plating caused by graphene agglomeration, and preventing the technical problem that graphene is difficult to be doped in the composite plating layer due to long-term non-stirring, which causes the graphene to sink to the bottom of the solution. Therefore, the process also obtains good applicability, and intermittent stirring is conducive to the embedding of graphene in the silver layer. Compared with the prior art (such as CN111519232A) that selects the number of graphene sheets ≤3, the graphene layer selection range of the present invention is larger, and the raw material selection surface is wider.

[0029] Compared with the prior art, the present invention has the following advantages and beneficial effects: The invention provides a method for preparing a silver / graphene composite coating, which adopts an intermittent stirring speed to carry out a composite electroplating process, and has the advantages of convenient operation, mild reaction, low cost and uniform coating.

[0030] The present invention provides a silver / graphene composite coating, in which graphene is evenly distributed, the powder distribution blank rate is low, the composite coating has the advantages of good conductivity, excellent hardness and wear resistance, and has good application prospects in components such as disconnectors. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The microscopic morphology of the silver / graphene composite coating prepared in Examples 1-9 and Comparative Example 1; Figure 2 The macroscopic morphology of the fracture of the silver / graphene composite coating prepared in Example 5 after the bending test; Figure 3 This is the powder distribution blank rate of the silver / graphene composite coating prepared in Example 5. DETAILED DESCRIPTION

[0032] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples. The experimental methods in the following examples without specifying specific conditions are carried out according to conventional methods and conditions, or selected according to the product specifications.

[0033] Example 1 A method for preparing a silver / graphene composite coating, comprising the following steps: (1) Substrate surface pretreatment: The stainless steel plate was used as the anode and the copper sheet was used as the cathode to remove the oil stains on the substrate surface by cathode electrolysis. The electrolysis time was 5 min and the current density was 3 A / dm 2 , temperature is 60 °C, stirring speed is 300 rads / min, and washed with water; Activate with 5% by volume sulfuric acid, immerse the degreased substrate in the sulfuric acid, take it out after 60 seconds, and rinse it with deionized water to obtain a pretreated substrate; The preparation method of the electrolytic degreasing solution in this step is as follows: 8 g of sodium tripolyphosphate, 20 g of sodium hydroxide, 10 g of sodium silicate, 6 g of sodium gluconate and 25 g of sodium carbonate are added to 1 L of deionized water and stirred until completely dissolved; (2) Pre-silver plating: The pure silver plate was used as the anode and the treated copper substrate was used as the cathode. The silver plate was placed in the pre-silver plating solution and electroplated under constant stirring. The plating time was 120 s and the current density was 1 A / dm2 , the temperature is 30 °C, the stirring speed is 200 rads / min, and after the electroplating is completed, the test piece is taken out and washed with deionized water to obtain a material containing a pre-silver coating; The preparation method of the pre-silver plating solution in this step is as follows: 2 g of silver nitrate, 50 g of potassium cyanurate, 100 g of sodium sulfite, 10 g / L of tetrahydroxypropylethylenediamine, and 3 g / L of potassium hydroxide are added to deionized water to a volume of 1 L, and stirred until completely dissolved, and the pH value is 9 to obtain a pre-silver plating solution; (3) Pure silver layer plating: The pure silver plate was used as the anode and the pre-silvered substrate was used as the cathode. The substrate was placed in the pure silver plating solution and electroplated under constant stirring. The plating time was 5 min and the current density was 1 A / dm 2 , temperature 30 ℃, stirring speed 200 rads / min, after the electroplating is completed, the test piece is taken out and washed with deionized water, and dried to obtain a composite material containing a pure silver coating; The preparation method of the pure silver plating solution in this step is as follows: 40 g of silver nitrate, 50 g of potassium cyanurate, 200 g of sodium sulfite, 50 g of tetrahydroxypropylethylenediamine, 1 g of naphthalenesulfonic acid formaldehyde polymer sodium salt, 2 g of tetrasodium ethylenediaminetetraacetate, and 5 g of potassium hydroxide are added to deionized water to a volume of 1 L, and stirred until completely dissolved, and the pH value is 9 to obtain a pure silver plating solution; (4) Silver / graphene composite electroplating: The pure silver plate was used as the anode and the composite material containing the pure silver coating was used as the cathode. The silver / graphene composite plating solution was placed in the solution with a stirring speed of 600 rads / min. The stirring was continued for 1 min and then stopped for 1 min. There were 15 cycles with a total of 30 min. The current density was 1 A / dm 2 , the temperature is 30 ℃, after the electroplating is completed, the test piece is taken out and washed with deionized water, and dried to obtain a silver / graphene composite coating; The preparation method of the silver / graphene composite plating solution in this step is as follows: 40 g of silver nitrate, 50 g of potassium cyanurate, 200 g of sodium sulfite, 50 g of tetrahydroxypropylethylenediamine, 1 g of naphthalenesulfonic acid formaldehyde polymer sodium salt, 2 g of tetrasodium ethylenediaminetetraacetic acid, and 5 g of potassium hydroxide are added to deionized water to a volume of 1 L, and stirred until completely dissolved, the pH value is 9, 0.1 g of graphene is slowly added to the above solution, and magnetic stirring is carried out in a single direction at 1000 rads / min for 60 min to obtain a silver / graphene composite plating solution.

[0034] Example 2 This embodiment is basically the same as Embodiment 1, except that the steps of silver / graphene composite electroplating are as follows: The pure silver plate was used as the anode and the composite material containing the pure silver coating was used as the cathode. The silver / graphene composite plating solution was placed in the solution with a stirring speed of 400 rads / min. The stirring was continued for 1 min and then stopped for 1 min. There were 15 cycles with a total of 30 min. The current density was 1 A / dm 2 , the temperature is 30 ℃, and after the electroplating is completed, the test piece is taken out, washed with deionized water, and dried to obtain a silver / graphene composite coating.

[0035] Example 3 This embodiment is basically the same as Embodiment 1, except that the steps of silver / graphene composite electroplating are as follows: The pure silver plate was used as the anode and the composite material containing the pure silver coating was used as the cathode. The silver / graphene composite plating solution was placed in the solution with a stirring speed of 200 rads / min. The stirring was continued for 1 min and then stopped for 1 min. There were 15 cycles with a total of 30 min. The current density was 1 A / dm 2 , the temperature is 30 ℃, and after the electroplating is completed, the test piece is taken out, washed with deionized water, and dried to obtain a silver / graphene composite coating.

[0036] Example 4 This embodiment is basically the same as Embodiment 1, except that the steps of silver / graphene composite electroplating are as follows: The pure silver plate was used as the anode and the composite material containing the pure silver coating was used as the cathode. The silver / graphene composite plating solution was placed in the solution with a stirring speed of 600 rads / min. The stirring was continued for 1 min and then stopped for 2 min. There were 10 cycles with a total of 30 min. The current density was 1 A / dm 2 , the temperature is 30 ℃, and after the electroplating is completed, the test piece is taken out, washed with deionized water, and dried to obtain a silver / graphene composite coating.

[0037] Example 5 This embodiment is basically the same as Embodiment 1, except that the steps of silver / graphene composite electroplating are as follows: The pure silver plate was used as the anode and the composite material containing the pure silver coating was used as the cathode. The silver / graphene composite plating solution was placed in the solution with a stirring speed of 400 rads / min. The stirring was continued for 1 min and then stopped for 2 min. There were 10 cycles with a total of 30 min. The current density was 1 A / dm 2 , the temperature is 30 ℃, and after the electroplating is completed, the test piece is taken out, washed with deionized water, and dried to obtain a silver / graphene composite coating.

[0038] Example 6 This embodiment is basically the same as Embodiment 1, except that the steps of silver / graphene composite electroplating are as follows: The pure silver plate was used as the anode and the composite material containing the pure silver coating was used as the cathode. The silver / graphene composite plating solution was placed in the solution with a stirring speed of 200 rads / min. The stirring was continued for 1 min and then stopped for 2 min. There were 10 cycles with a total of 30 min. The current density was 1 A / dm 2 , the temperature is 30 ℃, and after the electroplating is completed, the test piece is taken out, washed with deionized water, and dried to obtain a silver / graphene composite coating.

[0039] Example 7 This embodiment is basically the same as Embodiment 1, except that the steps of silver / graphene composite electroplating are as follows: The pure silver plate was used as the anode and the composite material containing the pure silver coating was used as the cathode. The silver / graphene composite plating solution was placed in the solution with a stirring speed of 600 rads / min. The stirring was repeated for 2 min and then stopped for 1 min. The total number of cycles was 10 and the total time was 30 min. The current density was 1 A / dm 2 , the temperature is 30 ℃, and after the electroplating is completed, the test piece is taken out, washed with deionized water, and dried to obtain a silver / graphene composite coating.

[0040] Example 8 This embodiment is basically the same as Embodiment 1, except that the steps of silver / graphene composite electroplating are as follows: The pure silver plate was used as the anode and the composite material containing the pure silver coating was used as the cathode. The silver / graphene composite plating solution was placed in the solution with a stirring speed of 400 rads / min. The stirring was repeated for 2 min and then stopped for 1 min. The total number of cycles was 10 and the total time was 30 min. The current density was 1 A / dm 2 , the temperature is 30 ℃, and after the electroplating is completed, the test piece is taken out, washed with deionized water, and dried to obtain a silver / graphene composite coating.

[0041] Example 9 This embodiment is basically the same as Embodiment 1, except that the steps of silver / graphene composite electroplating are as follows: The pure silver plate was used as the anode and the composite material containing the pure silver coating was used as the cathode. The silver / graphene composite plating solution was placed in the solution with a stirring speed of 200 rads / min. The stirring was repeated for 2 min and then stopped for 1 min. The total number of cycles was 10 and the total time was 30 min. The current density was 1 A / dm 2 , the temperature is 30 ℃, and after the electroplating is completed, the test piece is taken out, washed with deionized water, and dried to obtain a silver / graphene composite coating.

[0042] Comparative Example 1 This comparative example is basically the same as Example 1, except that the steps of silver / graphene composite electroplating are as follows: The pure silver plate was used as the anode and the composite material containing the pure silver coating was used as the cathode. The silver / graphene composite plating solution was placed in the solution and electroplated without stirring. The plating time was 30 min and the current density was 1 A / dm 2 , the temperature is 30 ℃, and after the electroplating is completed, the test piece is taken out, washed with deionized water, and dried to obtain a silver / graphene composite coating.

[0043] The performance tests were performed on the silver / graphene composite coatings prepared in Examples 1-9 and Comparative Example 1. The test items and methods are as follows: 1) Hardness: The test process is carried out in accordance with the method specified in GB / T 4340.1 "Metallic Materials Vickers Hardness Test Part 1: Test Method". During the test, the test force is applied perpendicular to the test surface, and shock and vibration are avoided during the entire test process. The indenter descending speed is 35 μm / s, the test force is 25 g, and the holding time is 15 s.

[0044] 2) Friction coefficient: GCr15 steel ball was used as the grinding material, and the reciprocating sliding friction method was adopted. A constant load of 4 N was applied, the rotation speed was 300 r / min, the wear scar radius was 4 mm, and the operation time was 15 min.

[0045] 3) Coating resistance: Use DRM-40 micro-ohm meter to test the square resistance of the coating.

[0046] 4) Adhesion test: The test specimen was bent repeatedly 180° until it broke according to the method specified in GB / T 5270-2005 "Review of test methods for adhesion strength of electrodeposited and chemically deposited metal coatings on metal substrates". There was no peeling or shedding on the fracture surface.

[0047] 5) Micromorphology of coating: The micromorphology of coating was tested using a CM-33 metallographic microscope.

[0048] 6) Blank rate of graphene powder distribution: The microscopic morphology obtained by the test is gridded to obtain 100 small areas of 10×10, and observe whether there are areas without graphene. Blank rate = (area without graphene / 100) × 100%.

[0049] The experimental results of hardness, friction coefficient and coating resistance are shown in Table 1.

[0050] Table 1: Experimental results of hardness, friction coefficient and coating resistance of examples and comparative examples

[0051] The microscopic morphology of the silver / graphene composite coatings prepared in Examples 1-9 and Comparative Example 1 is as follows: Figure 1 As shown, according to Figure 1It can be seen from the microscopic morphology of each embodiment and comparative example that graphene exists, indicating that the present invention successfully prepares a silver / graphene oxide composite coating on a metal substrate. It can be seen from the microscopic morphology that there is some graphene agglomeration in the comparative example, while the graphene coatings of each embodiment prepared by intermittent stirring are not agglomerated, indicating that this method is beneficial to obtaining a composite coating with uniform dispersion of graphene. Combined with the test data in Table 1, in the above embodiments, the faster the intermittent stirring speed, the longer the stirring time, the shorter the stopping stirring time, the smaller the hardness of the coating. Compared with the comparative example, the coating hardness obtained after intermittent stirring during the electroplating process is greater, the friction coefficient is smaller, and the resistivity is basically the same. It shows that the uniform dispersion of graphene in the composite coating is beneficial to improving its mechanical properties.

[0052] The present invention successfully prepared silver / graphene composite coatings on metal substrates by adjusting the number and speed of electroplating stirring cycles. These coatings exhibited excellent conductivity, corrosion resistance and wear resistance. The bending test confirmed that the coating had a strong bonding force with the substrate and there was no peeling or shedding at the fracture (taking Example 5 as an example, see Figure 2 ) verified the performance of the silver / graphene composite coating. And under proper stirring, electroplating can make the graphene evenly distributed. Taking Example 5 as an example (see Figure 3 ), the powder distribution blank rate is 0; the highest powder distribution blank rate measured by other embodiments is only 2%, and the general preparation level has been achieved.

[0053] The above results show that compared with the traditional high-temperature thermal processing method for preparing composite coatings, the silver / graphene composite coating preparation method provided by the present invention can be carried out at room temperature, the requirements for production equipment are greatly reduced, the production cost is reduced, and it has the characteristics of simple process and low material loss.

[0054] The present invention first electroplates a thin silver layer in a pre-silver plating solution, then electroplates another silver layer in a pure silver plating solution, and finally electroplates in a silver / graphene composite plating solution to obtain a composite coating containing a pre-silver plating layer-pure silver layer-silver / graphene layer. The active order of silver metal is located after copper. Copper undergoes a replacement reaction in the silver solution, and anions are replaced to form a loose silver layer on the surface of the material, resulting in poor bonding between the subsequent electroplated silver layer and the copper substrate. The composite coating is prepared using this intermittent coating preparation method, first a thin silver layer is plated on the surface of the copper substrate, and then immersed in the composite plating solution for electroplating, which greatly improves the bonding between the coating and the substrate. According to the method specified in GB / T5270-2005, the sample is repeatedly bent 180 degrees until it breaks, and there is no peeling or shedding on the fracture.

[0055] In the present invention, graphene is pre-dispersed in the composite plating solution at a relatively fast stirring speed, and then the silver / graphene composite layer is electroplated by intermittent stirring, so that the graphene can be uniformly dispersed in the solution, effectively preventing the problem of uneven plating caused by graphene agglomeration, and preventing the graphene from sinking to the bottom of the solution due to long-term non-stirring, making it difficult for the graphene to be doped in the composite plating layer. In addition, the present invention also has good applicability, intermittent stirring is conducive to the embedding of graphene in the silver layer, the graphite layer has a larger selection range, and the raw material selection surface is wider.

[0056] The silver / graphene composite coating obtained by this process has uniform graphene distribution, and the powder distribution blank rate is only 0-2%. It also has the same conductivity as the silver coating, and effectively improves the hardness and wear resistance.

[0057] The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained by a person skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. A method for preparing a silver / graphene composite coating, characterized in that: The steps include: (1) Substrate surface pretreatment: The substrate is placed in an electrolytic degreasing solution to remove dirt and impurities on the surface of the substrate through electrolysis and activation to obtain a pretreated substrate; (2) Pre-silver plating: Placing the pretreated substrate in a pre-silver plating solution, and electroplating to obtain a material containing a pre-silver plating layer; (3) Pure silver layer plating: Placing the material containing the pre-silver coating in a pure silver plating solution and electroplating the material to obtain a composite material containing the pure silver coating; (4) Silver / graphene composite electroplating: Placing the composite material containing the pure silver coating in a silver / graphene composite plating solution and electroplating the composite material under intermittent stirring conditions to obtain a silver / graphene composite coating; Among them, the intermittent stirring rate is ≤800 rads / min; in a single stirring cycle, the stirring time is ≤10 min, and the stirring stop time is ≤5 min.

2. The method for preparing the silver / graphene composite coating according to claim 1, characterized in that: In the step (1), the electrolytic degreasing solution is an aqueous solution, and its components include: 3-15 g / L sodium tripolyphosphate, 12-50 g / L sodium hydroxide, 10-30 g / L sodium silicate, 2-10 g / L sodium gluconate, and 10-30 g / L sodium carbonate.

3. The method for preparing the silver / graphene composite coating according to claim 1, characterized in that: In the step (1), the substrate is used as the cathode, the electrolysis temperature is 40-80°C, the stirring speed is 100-500 rads / min, and the current density is 0.5-5 A / dm 2 The electrolysis time is 30-60 s; the activation is carried out by treating with 3%-18% sulfuric acid by volume for 30-60 s.

4. The method for preparing the silver / graphene composite coating according to claim 1, characterized in that: In the step (2), the pre-silver plating solution is an aqueous solution, and its components include: 20-50 g / L of a water-soluble silver-containing compound, 50-200 g / L of potassium cyanurate, 100-300 g / L of sodium sulfite, 10-50 g / L of tetrahydroxypropyl ethylenediamine, 0.5-10 g / L of potassium hydroxide, 0.5-5 g / L of naphthalenesulfonic acid formaldehyde polymer sodium salt, and 0.1-3 g / L of tetrasodium ethylenediaminetetraacetate; the water-soluble silver-containing compound includes one of silver nitrate, silver fluoride, and silver chlorate.

5. The method for preparing the silver / graphene composite coating according to claim 1, characterized in that: In the step (2), the pretreated substrate is used as the cathode, the electroplating temperature is 20-50 °C, the stirring speed is 100-800 rads / min, and the current density is 0.5-5 A / dm 2 , the electroplating time is 30-120 s.

6. The method for preparing the silver / graphene composite coating according to claim 1, characterized in that: In the step (3), the pure silver plating solution is an aqueous solution, and its components include: 20-50 g / L of a water-soluble silver-containing compound, 50-200 g / L of potassium cyanurate, 100-300 g / L of sodium sulfite, 10-50 g / L of tetrahydroxypropylethylenediamine, 0.5-10 g / L of potassium hydroxide, 0.5-5 g / L of naphthalenesulfonic acid formaldehyde polymer sodium salt, and 0.1-3 g / L of tetrasodium ethylenediaminetetraacetic acid; the pH of the pure silver plating solution is 8-11; the water-soluble silver-containing compound includes one of silver nitrate, silver fluoride, and silver chlorate.

7. The method for preparing the silver / graphene composite coating according to claim 1, characterized in that: In the step (3), the material containing the pre-silver coating is used as the cathode, the electroplating temperature is 20-50°C, the stirring speed is 100-800 rads / min, and the current density is 0.5-5 A / dm 2 The electroplating time is 1-10 min.

8. The method for preparing the silver / graphene composite coating according to claim 1, characterized in that: In step (4), the silver / graphene composite plating solution is an aqueous solution, and its components include: 20-50 g / L water-soluble silver-containing compound, 50-200 g / L potassium cyanurate, 100-300 g / L sodium sulfite, 10-50 g / L tetrahydroxypropyl ethylenediamine, 0.5-10 g / L potassium hydroxide, 0.5-5 g / L naphthalenesulfonic acid formaldehyde polymer sodium salt, 0.1-3 g / L tetrasodium ethylenediaminetetraacetic acid, and 0.1-5 g / L graphene; the pH value of the silver / graphene composite plating solution is 8-11; the water-soluble silver-containing compound includes one of silver nitrate, silver fluoride, and silver chlorate; when the components of the silver / graphene composite plating solution are prepared, the graphene is dispersed at a stirring speed of 800-2000 rads / min, and the dispersion time is 30-120 min; the number of graphene sheets is 10-80, and the median particle size is 0.5-5 μm.

9. The method for preparing the silver / graphene composite coating according to claim 1, characterized in that: In step (4), the composite material containing the pure silver coating is used as the cathode, the electroplating temperature is 20-50°C, and the current density is 0.5-5 A / dm 2 The electroplating time is 10-60 min.

10. A silver / graphene composite coating, characterized in that: The method is prepared according to any one of claims 1 to 9.

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