Silver-coated aluminum powder and preparation method thereof

Abstract

The invention belongs to the technical field of preparation of silver-coated aluminum powder, and particularly relates to silver-coated aluminum powder and a preparation method thereof.The preparation method comprises the following steps that 1, aluminum powder, a dispersing agent and ethyl alcohol are mixed and subjected to homogeneous dispersion, and an aluminum powder system A is prepared; (2) preparing silver nitrate into a silver-ammonia solution to obtain a solution B; (3) under a homogeneous dispersion condition, adding the solution B into the aluminum powder system A in the step (1), uniformly mixing, heating to 35-40 DEG C, and adding a pH regulator until the pH value is 10-11 to obtain an aluminum powder system C; (4) dropwise adding a reducing agent into the aluminum powder system C in the step (3); and (5) the reactant obtained in the step (4) is subjected to surface treatment, solid-liquid separation, washing and drying, and the silver-coated aluminum powder is obtained. The silver-coated aluminum powder has the beneficial effects that the silver-coated aluminum powder is narrow in particle size distribution and good in dispersity, the surface of the aluminum powder is completely coated with silver and is not exposed, and a silver layer on the surface is uniform and compact.

Description

Technical Field

[0001] The invention belongs to the technical field of preparation of silver-coated aluminum powder, and particularly relates to silver-coated aluminum powder and a preparation method thereof. Background Art

[0002] Metallic silver has excellent physical and chemical properties, such as electrical conductivity, thermal conductivity and antioxidant properties. It is widely used in antibacterial materials, medical materials, electronic pastes, decorative materials and catalysts. However, it is prone to electromigration under hot and humid conditions and DC conductive conditions, resulting in short circuits. In addition, pure silver is expensive. These shortcomings limit the development and application of silver in the field of conductive materials.

[0003] The conductivity of aluminum powder is second only to silver and copper, its density is only one-fourth of silver, and its price is low. However, pure aluminum powder has high surface activity and is extremely unstable in the air. It easily forms a dense aluminum oxide film on the surface. Since aluminum oxide itself is not conductive, the application of aluminum powder is greatly limited.

[0004] By coating the surface of aluminum powder with a silver layer to prevent oxidation of aluminum powder, the advantages of aluminum powder can be maintained while further improving its conductivity. As a commonly used conductive material, it has been widely used in emerging materials such as electromagnetic shielding materials, antistatic materials and wave absorbing materials. At present, the traditional preparation process of silver-coated aluminum powder is mainly chemical reduction and replacement. The chemical reduction method is to add a reducing agent to the solution to reduce the metallic silver ions in the solution and deposit them on the surface of the aluminum powder to form a silver layer. The aluminum powder is required to have a certain catalytic activity for the reduction and deposition reaction of silver. Before the aluminum powder is formally reacted, it needs to undergo a series of pre-treatments, including cleaning and impurity removal, coarsening to improve binding force, sensitization to promote reaction, activation to form catalytic centers, etc. Due to the complicated pre-treatment steps, the complexity of the process is increased, and the process is difficult to control. There are problems such as unstable performance of the composite powder, high cost, and difficulty in wastewater treatment; the replacement method is to put a metal with strong reducing properties such as aluminum into a metal salt solution with strong oxidizing properties, such as copper salt and silver salt. The metal with strong reducing properties is a reducing agent. The electrons released by it are accepted by the metal ions to form a metal coating on the aluminum surface. The coating coverage is high but the thickness is thin, and the upper limit of the performance of the composite powder is low. The replacement method also has the problems of cumbersome pre-treatment steps, complex process, poor process stability and high cost, which brings great difficulties to industrial implementation. Therefore, a preparation method of silver-coated aluminum powder with a simple process and the ability to control the thickness and uniformity of the silver layer on the surface of the aluminum powder is particularly important. Summary of the invention

[0005] The purpose of the present invention is to solve the above problems and provide a silver-coated aluminum powder and a preparation method thereof.

[0006] The present invention relates to a method for preparing silver-coated aluminum powder, comprising the following steps: (1) Aluminum powder, a dispersant and ethanol are mixed and uniformly dispersed to prepare an aluminum powder system A; (2) preparing silver nitrate into a silver ammonia solution to obtain solution B; (3) under homogeneous dispersion conditions, adding solution B to the aluminum powder system A of step (1) and mixing evenly, heating to 35-40° C., adding a pH adjuster to a pH value of 10-11, and obtaining an aluminum powder system C; (4) adding a reducing agent dropwise to the aluminum powder system C in step (3); (5) The reactant obtained in step (4) is subjected to surface treatment, solid-liquid separation, washing and drying to obtain silver-coated aluminum powder.

[0007] Preferably, the homogeneous dispersion is carried out using an emulsifier or a high-speed disperser.

[0008] Preferably, in step (1), the mass ratio of the aluminum powder, the dispersant and the ethanol is 1:0.2-0.8:5-8.

[0009] Preferably, in step (1), the dispersant is selected from at least one of polyvinyl pyrrolidone, polyethylene glycol and polyvinyl alcohol.

[0010] Preferably, in step (2), the amount of silver nitrate used is 10% to 45% of the mass of the generated silver-coated aluminum powder.

[0011] Preferably, in step (3), the pH adjuster is selected from at least one of aqueous ammonia, sodium hydroxide, potassium hydroxide and sodium carbonate.

[0012] Preferably, in step (4), the reducing agent is selected from at least one of sodium borohydride, ascorbic acid, glucose and hydrogen peroxide; and the molar ratio of the reducing agent to silver nitrate is 0.5 to 1:1.

[0013] Preferably, the dropping speed of the reducing agent is 2 to 30 ml / min, and the dropping time of the reducing agent is controlled within 3 to 10 min.

[0014] Preferably, in step (5), the surface treatment agent is at least one of oleic acid and stearic acid, and the amount of the surface treatment agent is 1% to 3% of the mass of the silver-coated aluminum powder.

[0015] The present invention also relates to a silver-coated aluminum powder, characterized in that it is prepared by the preparation method of the silver-coated aluminum powder according to any one of claims 1 to 9, the silver-coated aluminum powder has a spherical or quasi-spherical morphology, a particle size of 1.5 to 6.0 μm, and a specific surface area of ​​3 to 5 m2 / g.

[0016] Compared with the prior art, the advantages and positive effects of the present invention are: Compared with the prior art, the silver-coated aluminum powder and the preparation method thereof of the present invention can (1) The preparation method of the silver-coated aluminum powder controls the conditions such as pH, reaction temperature and feeding time, and in the process of homogenizing and dispersing the reaction using an emulsifier or a high-speed disperser, the nano silver crystal nuclei will uniformly grow and coat the surface of the aluminum powder; at the same time, the thickness of the silver layer on the surface of the aluminum powder is controlled by adjusting the ratio of the silver ammonia solution; (2) The preparation method of the silver-coated aluminum powder adopts a one-step synthesis in a liquid phase redox system. The method directly performs chemical in-situ growth coating on the surface of the aluminum powder, and the pH value of the reaction system makes the lattice of the surface silver shell smaller and more active; (3) The silver-coated aluminum powder has a narrow particle size distribution and good dispersibility. The surface of the aluminum powder has been completely coated with silver without any exposure, and the silver layer on the surface is uniform and dense. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solution of the embodiment of the present invention, the following briefly introduces the drawings required for describing the embodiment. Figure 1 A scanning electron microscope image of the aluminum powder provided in Example 1; Figure 2 This is a scanning electron microscope image of the silver-coated aluminum powder provided in Example 1; Figure 3 A scanning electron microscope image of the aluminum powder provided in Example 2; Figure 4 This is a scanning electron microscope image of the silver-coated aluminum powder provided in Example 2; Figure 5 A scanning electron microscope image of the aluminum powder provided in Example 3; Figure 6 This is a scanning electron microscope image of the silver-coated aluminum powder provided in Example 3; Figure 7 The scanning electron microscope image of the silver-coated aluminum powder provided in Comparative Example 1; Figure 8 The scanning electron microscope image of the silver-coated aluminum powder provided in Comparative Example 2; Fig. 9 The scanning electron microscope image of the silver-coated aluminum powder provided in Comparative Example 3; Fig.10 Thermogravimetric analysis diagram of the aluminum powder provided in Example 1; Fig.11 Thermogravimetric analysis diagram of the silver-coated aluminum powder provided in Example 1; Fig.12 This is the thermogravimetric analysis diagram of commercially available silver-coated aluminum powder. DETAILED DESCRIPTION

[0018] In order to more clearly understand the above-mentioned objects, features and advantages of the present invention, the present invention is further described below with reference to the accompanying drawings and embodiments.

[0019] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways than those described herein. Therefore, the present invention is not limited to the specific embodiments of the following disclosure.

[0020] Example 1 A method for preparing silver-coated aluminum powder comprises the following steps: (1) Liquid preparation Aluminum powder system A: Add 600g ethanol, 40g dispersant and 80g aluminum powder with a particle size of 1.5 to 2 microns into a beaker and disperse with an emulsifier for 5 minutes; the mass ratio of aluminum powder, dispersant and ethanol is 1:0.5:7.5.

[0021] Silver ammonia solution B: Dissolve 14g of silver nitrate in 11.5g of deionized water, then add 14g of ammonia water and stir evenly. The amount of silver nitrate used is 15% of the mass of the silver-coated aluminum powder generated.

[0022] Aluminum powder system C: Add silver ammonia solution B to aluminum powder system A, add 3 g of ammonia water, continue to disperse with an emulsifier, heat to 35°C and keep warm for 5 minutes; at this time, the pH value of the reaction solution is 11.

[0023] (2) 10.4 ml of hydrogen peroxide was added to the aluminum powder system C at a flow rate of 2.3 ml / min. The temperature was controlled at 25°C. The addition time was 4.5 minutes. The temperature was then raised to 35°C and kept warm for 5 minutes.

[0024] (3) 1.8 g of oleic acid was added to step (2), and the mixture was dispersed at 35° C. for 10 minutes. The reactants were subjected to surface treatment, solid-liquid separation, washing and drying to obtain 88.6 g of silver-coated aluminum powder.

[0025] Example 2 A method for preparing silver-coated aluminum powder comprises the following steps: (1) Liquid preparation Aluminum powder system A: Add 1200g ethanol, 80g dispersant and 160g aluminum powder with a particle size of 3-4 microns into a beaker and disperse with an emulsifier for 5 minutes; the mass ratio of aluminum powder, dispersant and ethanol is 1:0.5:7.5.

[0026] Silver ammonia solution B: Dissolve 64g of silver nitrate in 52.5g of deionized water, then add 64g of aqueous ammonia and stir evenly. The amount of silver nitrate used is 28.5% of the mass of the silver-coated aluminum powder produced.

[0027] Aluminum powder system C: Add silver ammonia solution B to aluminum powder system A, add 7g of ammonia water, continue to disperse with an emulsifier, heat to 35°C and keep warm for 5 minutes; at this time, the solution pH is 11.

[0028] (2) Add 47.5 ml of hydrogen peroxide to the aluminum powder system C at a flow rate of 10.5 ml / min. The temperature is controlled at 25°C. The addition time is 4.5 minutes. Then the temperature is raised to 35°C and kept for reaction for 5 minutes.

[0029] (3) Add 3.9 g of oleic acid to step (2), keep warm and disperse at 35° C. for 10 minutes, and subject the reactants to surface treatment, solid-liquid separation, washing and drying to obtain 200 g of silver-coated aluminum powder.

[0030] Example 3 A method for preparing silver-coated aluminum powder comprises the following steps: (1) Liquid preparation Aluminum powder system A: Add 1500g ethanol, 100g dispersant, and 250g raw aluminum powder with a particle size of 5-6 microns into the reactor, and disperse it with an emulsifier for 5 minutes. The mass ratio of aluminum powder, dispersant and ethanol is 1:0.5:7.5.

[0031] Silver ammonia solution B: Dissolve 170g of silver nitrate in 140g of deionized water, then add 170g of aqueous ammonia and stir evenly. The amount of silver nitrate used is 40.5% of the mass of the silver-coated aluminum powder.

[0032] Aluminum powder system C: Add silver ammonia solution B to aluminum powder system A, add 14 g of ammonia water, continue to disperse with an emulsifier, heat to 40°C and keep warm for 5 minutes; at this time, the solution pH is 11.

[0033] (2) Add 126 ml of hydrogen peroxide to the aluminum powder system C at a flow rate of 28 ml / min. The temperature is controlled at 25°C. The addition time is 4.5 minutes. The reaction is kept at 40°C for 5 minutes.

[0034] (3) Add 7.2 g of oleic acid to step (2), keep the mixture dispersed at 40° C. for 10 minutes, and subject the reactants to surface treatment, solid-liquid separation, washing and drying to obtain 357 g of silver-coated aluminum powder.

[0035] Comparative Example 1 The difference between this comparative example and Example 1 is that: Aluminum powder system C: Add silver ammonia solution B to silver powder system A, add 7g of ammonia water, continue to disperse and heat to 25°C using an emulsifier and keep warm for 5 minutes; at this time, the pH of the solution is 12.5.

[0036] Comparative Example 2 The difference between this comparative example and Example 1 is that: No ammonia water was added to the aluminum powder system C to adjust the pH value, and the pH value of the solution was 9.

[0037] Comparative Example 3 The difference between this comparative example and Example 1 is that: The temperature was controlled at 20°C during the reaction.

[0038] Performance Testing (1) The aluminum powder and silver-coated aluminum powder of Examples 1-3 and the silver-coated aluminum powder of Comparative Examples 1-3 were observed by scanning electron microscope. Figure 1-9 .

[0039] from Figure 1-6 It is concluded that the silver-coated aluminum powder prepared in Examples 1-3 has good dispersibility, a uniform and dense surface silver layer, and the aluminum powder is completely coated; Figure 7 It is concluded that the silver-coated aluminum powder prepared in Comparative Example 1 has agglomeration phenomenon, and the surface silver layer is extremely uneven; Figure 8 It was found that there were many free silver particles in the silver-coated aluminum powder prepared in Comparative Example 2, and many aluminum powder surfaces were exposed without silver coating. Fig. 9 It is concluded that there are many free silver particles in the silver-coated aluminum powder prepared in Comparative Example 3, and many aluminum powder surfaces are exposed. Therefore, the silver-coated aluminum powder prepared by the preparation method of the present invention has excellent dispersibility, the aluminum powder is completely coated, and the silver layer on the surface of the aluminum powder is uniform and dense.

[0040] (2) The aluminum powder and silver-coated aluminum powder of Examples 1-3 and the silver-coated aluminum powder of Comparative Examples 1-3 were tested for particle size and specific surface area, and thermogravimetric analysis was performed. The results are shown in Table 1. The thermogravimetric analysis curves of the aluminum powder, silver-coated aluminum powder, and commercially available silver-coated aluminum powder of Example 1 are shown in Table 1. Figure 10-12 shown.

[0041] Table 1 From Table 1 and Figure 10-12 It was concluded that: compared with comparative examples 1-3, the particle size of the silver-coated aluminum powder prepared in examples 1-3 was slightly increased, the particle size distribution was narrower, the burn-in loss had changed from weight gain before coating to weight loss, and the value was equivalent to the burn-in loss of normal commercially available silver powder, indicating that the surface of the aluminum powder had been completely coated with silver without being exposed, and the coating thickness was controllable.

[0042] The above description is only a preferred embodiment of the present invention and does not limit the present invention in other forms. Any technician familiar with the profession may use the technical content disclosed above to change or modify it into an equivalent embodiment with equivalent changes for application in other fields. However, any simple modification or equivalent change made to the above embodiment based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing silver-coated aluminum powder, characterized in that: The following steps are involved: (1) Aluminum powder, a dispersant and ethanol are mixed and uniformly dispersed to prepare an aluminum powder system A; (2) preparing silver nitrate into a silver ammonia solution to obtain solution B; (3) under homogeneous dispersion conditions, adding solution B to the aluminum powder system A of step (1) and mixing evenly, heating to 35-40° C., adding a pH adjuster to a pH value of 10-11, and obtaining an aluminum powder system C; (4) adding a reducing agent dropwise to the aluminum powder system C in step (3); (5) The reactant obtained in step (4) is subjected to surface treatment, solid-liquid separation, washing and drying to obtain silver-coated aluminum powder.

2. The method for preparing silver-coated aluminum powder according to claim 1, characterized in that: The homogeneous dispersion is carried out by using an emulsifier or a high-speed disperser.

3. The method for preparing silver-coated aluminum powder according to claim 2, characterized in that: In the step (1), the mass ratio of the aluminum powder, the dispersant and the ethanol is 1:0.2-0.8:5-8.

4. The method for preparing silver-coated aluminum powder according to claim 3, characterized in that: In the step (1), the dispersant is selected from at least one of polyvinyl pyrrolidone, polyethylene glycol and polyvinyl alcohol.

5. The method for preparing silver-coated aluminum powder according to claim 4, characterized in that: In the step (2), the amount of silver nitrate used is 10% to 45% of the mass of the generated silver-coated aluminum powder.

6. The method for preparing silver-coated aluminum powder according to claim 5, characterized in that: In the step (3), the pH adjuster is selected from at least one of aqueous ammonia, sodium hydroxide, potassium hydroxide and sodium carbonate.

7. The method for preparing silver-coated aluminum powder according to claim 6, characterized in that: In the step (4), the reducing agent is selected from at least one of sodium borohydride, ascorbic acid, glucose and hydrogen peroxide; and the molar ratio of the reducing agent to silver nitrate is 0.5 to 1:

1.

8. The method for preparing silver-coated aluminum powder according to claim 7, characterized in that: The dropping speed of the reducing agent is 2-30 ml / min, and the dropping time of the reducing agent is controlled within 3-10 min.

9. The method for preparing silver-coated aluminum powder according to claim 8, characterized in that: In the step (5), the surface treatment agent is at least one of oleic acid and stearic acid, and the amount of the surface treatment agent is 1% to 3% of the mass of the silver-coated aluminum powder.

10. A silver-coated aluminum powder, characterized in that: The silver-coated aluminum powder is prepared by the preparation method of any one of claims 1 to 9, wherein the silver-coated aluminum powder has a spherical or quasi-spherical shape, a particle size of 1.5 to 6.0 μm, and a specific surface area of ​​3 to 5 m2 / g.

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