A silver-plated nickel powder, its industrial preparation method and application

Abstract

The present invention discloses a silver-plated nickel powder, an industrial preparation method thereof and an application thereof, relating to the technical fields of surface treatment of metal powders and preparation of composite powders. The industrial preparation method of the silver-plated nickel powder comprises the following steps: S1, surface treatment of nickel powder; S2, formation of active centers: uniformly dispersing negatively charged silver nanoparticles and a surfactant in a solvent, then adding the surface-treated nickel powder and a reducing agent, and adjusting the pH value of the system to be greater than 11 to obtain a reduction solution of nickel powder; S3, silver plating: dropping a silver ammonia complex solution into the reduction solution of nickel powder for reaction to obtain the silver-plated nickel powder. The silver-plated nickel powder of the present invention has a dense silver layer on the surface, low volume resistivity, good oxidation resistance, excellent comprehensive performance, and its preparation method has simple process, low cost and is easy to industrialize production.

Description

Technical Field:

[0001] The present invention relates to the technical fields of surface treatment of metal powders and preparation of composite powders, and particularly relates to a silver-plated nickel powder, an industrial preparation method thereof, and an application thereof. Background Art:

[0002] In electronics, electrical appliances, communications, modern electronic warfare, warships, and nuclear submarines, in order to prevent external electromagnetic interference and prevent the outward radiation of its own electromagnetic waves, effective shielding measures need to be adopted. At present, most of the problems of electromagnetic wave interference and shielding of electronic products are solved by using conductive pastes or conductive rubbers, and conductive pastes are also important components of electronic ceramic components and solar photovoltaic panels.

[0003] Replacing precious metals such as silver, gold, and palladium with base metals to prepare conductive pastes, conductive coatings, and conductive rubbers is the goal pursued by people, and has become an important trend and an inevitable trend in the future development of electronic industrial materials. Replacing precious metals with base metals can overcome some deficiencies of precious metal electronic pastes. At present, mainly metal powders of base metal nickel are used as fillers for conductive pastes. However, the following problems exist in use: First, since pure nickel powder is easily oxidized at high temperatures, it cannot be sintered in high-temperature air or an oxidizing atmosphere for a long time, otherwise it will be oxidized and lose its conductivity, affecting its use performance; therefore, it must be sintered in a protective atmosphere or a reducing atmosphere, but the sintering equipment is expensive and not suitable for use in an oxidizing atmosphere.

[0004] Base metal powders with good antioxidant properties are necessary as conductive phases. Therefore, to use base metal powders as conductive media, they must be subjected to antioxidant treatment. Combining base metal nickel and silver to make silver-plated nickel powder can greatly improve the antioxidant ability of nickel powder, broaden its temperature range of use, overcome the shortcomings of base metals to a great extent, and at the same time reduce the cost of silver powder. At present, scientific researchers have also conducted certain research on silver-plated nickel powder.

[0005] Patents CN1188544C, CN108284224B, and CN105880633B all adopt processes of surface cleaning, sensitization, activation, and then silver plating to prepare silver-plated nickel powder. The process is complex and difficult to control. At the same time, a large amount of waste liquid is generated during the production process, which is not conducive to industrial production; Patent CN102218533A uses a physical vapor deposition process to prepare silver-plated nickel powder, but the equipment requirements are high and the cost is large, making it difficult to industrialize production; Patent CN112643026A uses surface pickling and then directly chemical silver plating process. This process is simple, but there are no activation points on the surface of nickel powder, which is not conducive to the deposition of silver on the surface of nickel powder, resulting in an uneven silver layer on the surface of silver-plated nickel powder; Patent CN112935245A uses a method of first plating copper on the surface of nickel powder and then plating silver. The product contains a copper coating in the middle, and the antioxidant performance is reduced.

[0006] Therefore, it is highly necessary to provide a silver plating method suitable for industrialization, which is simple in method, environmentally friendly, low in cost and has a dense plating layer. Summary of the Invention:

[0007] The purpose of the present invention is to overcome the problems existing in the prior art, such as complex preparation process, high cost, and non-dense plating layer, which are not conducive to industrial production, and to provide a preparation method of silver-plated nickel powder with a simple process and a dense plating layer, which can realize industrial production.

[0008] In order to achieve the above purpose, one of the purposes of the present invention is to provide an industrial preparation method of silver-plated nickel powder, including the following steps:

[0009] S1. Surface treatment of nickel powder;

[0010] S2. Formation of active centers: Uniformly disperse negatively charged silver nanoparticles and a surfactant in a solvent, then add the surface-treated nickel powder and a reducing agent, and adjust the pH value of the system to be greater than 11 to obtain a reduction solution of nickel powder.

[0011] S3. Silver plating: Drop the silver ammonia complex solution into the reduction solution of nickel powder for reaction to obtain silver-plated nickel powder.

[0012] Another purpose of the present invention is to provide silver-plated nickel powder obtained by the aforementioned preparation method.

[0013] Another purpose of the present invention is to provide an application of the aforementioned silver-plated nickel powder in electromagnetic shielding.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] 1. The present invention uses a physical method to introduce silver activation points on the surface of nickel powder, and through conventional process control, the uniform distribution of silver activation points on the surface of nickel powder is realized. And due to the single particle size distribution of nano-silver particles, the sizes of the activation points are quite the same, which is conducive to the formation of a uniform and dense silver layer on the surface of nickel powder during the subsequent silver plating process.

[0016] 2. The present invention uses a one-step physical activation process to replace the current conventional sensitization and activation processes, which can not only shorten the process flow, improve the product quality, but also the preparation method is environmentally friendly and low in cost, especially suitable for industrial preparation of silver-plated nickel powder. Description of the Drawings:

[0017] Figure 1 SEM image of the silver-plated nickel powder obtained in Example 1;

[0018] Figure 2 SEM image of the silver-plated nickel powder obtained in Comparative Example 1;

[0019] Figure 3SEM image of the silver-plated nickel powder obtained in Example 5;

[0020] Figure 4 SEM image of the silver-plated nickel powder obtained in Example 6;

[0021] Figure 5 SEM image of the silver-plated nickel powder obtained in Comparative Example 4;

[0022] Figure 6 Thermogravimetric analysis diagram of the silver-plated nickel powder obtained in Example 1;

[0023] Figure 7 Thermogravimetric analysis diagram of the silver-plated nickel powder obtained in Example 5. Detailed implementation method:

[0024] In order to make the technical means, creative features, achieved purposes and effects of the present invention easy to understand, the present invention will be further described below in conjunction with specific embodiments and illustrations.

[0025] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of each range, between the endpoint values of each range and a single point value, and between single point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0026] The present invention provides an industrial preparation method of silver-plated nickel powder, which comprises the following steps:

[0027] S1. Surface treatment of nickel powder;

[0028] S2. Formation of active centers: Uniformly disperse negatively charged silver nanoparticles and a surfactant in a solvent, then add the surface-treated nickel powder and a reducing agent, and adjust the pH value of the system to be greater than 11 to obtain a reduction solution of nickel powder;

[0029] S3. Silver plating: Dropwise add a silver ammonia complex solution to the reduction solution of nickel powder for reaction to obtain silver-plated nickel powder.

[0030] According to the present invention, in step S1, the method for surface treatment of nickel powder includes: pickling nickel powder in an acidic solution. Specifically, the method for surface treatment of nickel powder includes: putting nickel powder into dilute acid for stirring, removing the oxide layer on the surface of nickel powder, and finally washing it clean with deionized water.

[0031] The method provided by the present invention is suitable for silver plating on the surface of nickel powders with different particle sizes. However, the particle size of the nickel powder should not be less than 1 μm. Because when the particle size of the nickel powder is too small, the nickel powder is difficult to disperse and may agglomerate during silver plating, resulting in the inability to form a complete and dense silver plating layer, and the performance of the silver-plated nickel powder deteriorates. Those skilled in the art can select the size of the nickel powder according to actual needs. Exemplarily, the median particle size of the nickel powder is greater than 1 μm, such as 1 μm, 2 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm or any value within the range formed by any two of the above values.

[0032] In the present invention, if the particle size of the negatively charged silver nanoparticles is too large, it may lead to a decrease in the adsorption stability on the surface of the nickel powder, resulting in an uneven silver layer and the appearance of pure silver particles in the silver layer. Under preferred conditions, the median particle size of the negatively charged silver nanoparticles is 1-30 nm. For example, it can be 1 nm, 2 nm, 5 nm, 8 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm or any value within the range formed by any two of the above values. The negatively charged silver nanoparticles can be self-made or commercially available.

[0033] In the present invention, only a trace amount of negatively charged silver nanoparticles needs to be added to form active centers on the surface of the nickel powder, realizing silver plating on the surface of the nickel powder. Under preferred conditions, the mass ratio of the negatively charged silver nanoparticles to the nickel powder is (2×10 -6 -1×10 -5 ):100.

[0034] In the present invention, in an alkaline environment, the surface of the nickel powder is positively charged. By adding an anionic surfactant, a double electric layer can be formed to improve the dispersion effect. Under preferred conditions, the surfactant is an anionic surfactant; preferably, the anionic surfactant is sodium linear alkyl benzene sulfonate and / or fatty alcohol sulfate. In some preferred embodiments of the present invention, the addition amount of the anionic surfactant is 0.5-3% of the mass of the nickel powder. For example, it can be 0.5%, 1%, 1.5%, 2%, 2.5%, 3% or any value within the range formed by any two of the above values.

[0035] According to the present invention, in step S2, the dispersion method is preferably ultrasonic dispersion to uniformly disperse the negatively charged silver nanoparticles and the surfactant in the solvent.

[0036] The inventors of the present invention have found that it is necessary to control the pH value of the reduction solution of nickel powder above 11. For example, it can be 12, 13, 14 or any value within the range formed by any two of the above values. If the pH value is too low, it will lead to a low reduction rate of silver during the silver plating process, a low silver content on the surface of the product silver-plated nickel powder, and further cause an increase in the volume resistivity and a decrease in the antioxidant property of the silver-plated nickel powder.

[0037] In the present invention, in order to improve the dissolution and dispersion effect of the surfactant, the solvent is preferably a mixed solvent of deionized water and ethanol. Further, the mass ratio of the deionized water to ethanol is 8:2 - 9:1.

[0038] In the present invention, the reducing agent includes but is not limited to at least one of sodium citrate, potassium sodium tartrate, glucose, formaldehyde, and ascorbic acid.

[0039] In the present invention, the preparation method of the silver ammonia complex solution can be known to those skilled in the art. Exemplarily, the preparation method of the silver ammonia complex solution includes: dissolving silver nitrate with deionized water, and then adding a complexing agent to obtain the silver ammonia complex solution; wherein, the complexing agent can be one of ammonia water, ethylenediamine, diethylenetriamine, and triethylenetetramine.

[0040] The present invention also provides a silver-plated nickel powder prepared by the above preparation method.

[0041] Under preferred conditions, the median particle size of the silver-plated nickel powder is 1 - 50 μm, and the surface silver content is 15 - 50%; further preferably, the volume resistivity of the silver-plated nickel powder < 1×10 -4 Ω·cm; more preferably, the antioxidant temperature of the silver-plated nickel powder > 500 °C.

[0042] Theoretically, the lower the volume resistivity of the silver-plated nickel powder, the better the product performance. Combining with experiments, it is found that the volume resistivity of the silver-plated nickel powder should be between (0.85 - 0.95)×10 -4 Ω·cm. When the volume resistivity is greater than 1×10 -4 Ω·cm, it does not meet the usage requirements; in addition, the denser the silver-plated layer in the silver-plated nickel powder, the more beneficial it is to reduce the volume resistivity of the silver-plated nickel powder and improve its antioxidant property. Combining with experiments, it is found that the antioxidant temperature of qualified products > 500 °C.

[0043] The present invention also provides the application of the above silver-plated nickel powder in electromagnetic shielding.

[0044] The present invention will be described in detail below through examples.

[0045] Example 1

[0046] S1. Surface treatment of nickel powder: Weigh 960 g of deionized water into a reaction kettle, slowly add 24 g of concentrated sulfuric acid, then add 480 g of nickel powder (median particle size is 30 μm), stir at a speed of 500 r / min for 30 min, remove the oxide layer on the surface of the nickel powder, and wash it clean with deionized water to obtain surface-treated nickel powder.

[0047] S2. Formation of active centers: Accurately weigh 0.05 mg of silver nanoparticles (purchased from Jiangsu Xianfeng Nanomaterials Technology Co., Ltd., median particle size is 5 nm), 6 g of sodium dodecylbenzenesulfonate, 3000 g of deionized water, and 300 g of ethanol, disperse them by ultrasonic and mechanical stirring for 30 min, then add 480 g of the surface-treated nickel powder obtained in step S1 to form a stable and uniform nickel powder dispersion; then add 160 g of potassium sodium tartrate, and adjust the pH value to 13.2 with sodium hydroxide to obtain a reduction solution of nickel powder.

[0048] S3. Silver plating: Dissolve 190 g of silver nitrate in 3000 g of deionized water, then add 101 g of diethylenetriamine to prepare a silver ammonia complex solution; then drop the silver ammonia complex solution into the reduction solution of nickel powder obtained in step S2, wash it with deionized water after reacting for 2 h, and dry it at 80 °C for 2 h to obtain 595 g of silver-plated nickel powder.

[0049] Figure 1 is the SEM image of the silver-plated nickel powder obtained in Example 1. From Figure 1 it can be seen that the silver-plated layer on the surface of the silver-plated nickel powder obtained in Example 1 has a high density and there are no silver particles on the surface of the silver-plated layer, indicating that a dense and highly uniform silver-plated layer can be prepared on the surface of nickel powder by the method of Example 1.

[0050] Figure 6 is the thermogravimetric analysis chart of the silver-plated nickel powder obtained in Example 1. From Figure 6 it can be seen that the product silver-plated nickel powder has good antioxidant performance (>500 °C).

[0051] Comparative Example 1

[0052] According to the method of Example 1, the difference is that negatively charged silver nanoparticles are not added.

[0053] Example 2 and Comparative Example 2

[0054] According to the method of Example 1, the difference is that the particle size of the silver nanoparticles is adjusted, as shown in Table 1 for details.

[0055] The performance test results of the silver-plated nickel powder obtained in Examples 1-2 and Comparative Examples 1-2 are shown in Table 1.

[0056] Table 1

[0057]

[0058] Figure 2 SEM image of the silver-plated nickel powder obtained in Comparative Example 1. From Table 1 in combination with Figure 1 and Figure 2 it can be seen that: Adding silver nanoparticles to provide activation centers can effectively improve the comprehensive performance of silver-plated nickel powder, but the size of the silver nanoparticles needs to be controlled. Without adding silver nanoparticles, there are very few activation points on the surface of the nickel powder, and the reduction rate of silver is relatively fast, so the product contains pure silver particles and the silver layer on the surface of the nickel powder is not dense; at the same time, as the particle size of the silver nanoparticles increases, their adsorption stability on the surface of the nickel powder decreases, resulting in silver nanoparticles in the solution, so pure silver particles also appear after silver plating.

[0059] Examples 3-4

[0060] According to the method of Example 2, the difference is that the amount of silver nanoparticles is adjusted, as shown in Table 2 specifically.

[0061] The performance test results of the silver-plated nickel powder obtained in Examples 3-4 are shown in Table 2.

[0062] Table 2

[0063]

[0064] As can be seen from Table 2, adjusting the addition amount of negatively charged silver nanoparticles has no obvious effect on the performance of the silver-plated nickel powder. Therefore, adding a small amount of silver nanoparticles can produce a dense silver-plated layer. Considering the production cost comprehensively, on the basis of stable product performance, the addition amount of silver nanoparticles should be reduced as much as possible.

[0065] Examples 5-6 and Comparative Example 3

[0066] According to the method of Example 1, the difference is that the particle size of the nickel powder is adjusted, as shown in Table 3 specifically.

[0067] The performance test results of the silver-plated nickel powder obtained in Examples 5-6 and Comparative Example 3 are shown in Table 3.

[0068] Table 3

[0069]

[0070] Figure 3 SEM image of the silver-plated nickel powder obtained in Example 5; Figure 4 SEM image of the silver-plated nickel powder obtained in Example 6. From Figure 3 and Figure 4 it can be seen that the silver-plated layer on the surface of the product silver-plated nickel powder is highly dense and there are no silver particles on the surface of the silver-plated layer.

[0071] Figure 7 Thermogravimetric analysis diagram of the silver-plated nickel powder obtained in Example 5. From Figure 7It can be seen that the product silver-plated nickel powder has good antioxidant properties (>500 °C).

[0072] As can be seen from Table 3, when using nickel powders with different particle sizes, the silver content required on the surface of the silver-plated nickel powder is also different. As the particle size of the nickel powder decreases, its specific surface area increases correspondingly, and the silver content required on the surface of the silver-plated nickel powder is higher. When the particle size of the nickel powder is less than 1 μm, it is difficult to disperse the nickel powder, and serious agglomeration occurs during silver plating, making it impossible to form a complete and dense silver coating, resulting in poor performance of the silver-plated nickel powder.

[0073] Comparative Example 4

[0074] According to the method of Example 1, the difference is that: during the mixing process of silver nanoparticles and sodium dodecylbenzenesulfonate in step S2, ultrasonic treatment was not carried out, and only mechanical stirring and dispersion were performed for 30 min.

[0075] The performance test results of the silver-plated nickel powder obtained in Comparative Example 4 are shown in Table 4.

[0076] Table 4

[0077]

[0078] Figure 5 is the SEM image of the silver-plated nickel powder obtained in Comparative Example 4. From Table 4 combined with Figure 1 and Figure 5 it can be seen that: the uniformity and density of the silver layer on the surface of the silver-plated nickel powder obtained by increasing ultrasonic dispersion are very high. The possible reason is that ultrasonic treatment can effectively improve the dispersion of silver nanoparticles in the solution, thereby improving their dispersion uniformity on the surface of the nickel powder.

[0079] Example 7 and Comparative Examples 5-6

[0080] According to the method of Example 1, the difference is that: the addition amount of the anionic surfactant sodium dodecylbenzenesulfonate (SDBS) was adjusted, as shown in Table 5 specifically.

[0081] The performance test results of the silver-plated nickel powder obtained in Example 7 and Comparative Examples 5-6 are shown in Table 5.

[0082] Table 5

[0083]

[0084] As can be seen from Table 5: Adding an anionic surfactant is beneficial to subsequent silver plating and improves the comprehensive performance of the silver-plated nickel powder. The possible reason is that the anionic surfactant can significantly improve the distribution uniformity of silver nanoparticles on the surface of the nickel powder and the dispersion of the nickel powder itself; however, as the addition amount of the anionic surfactant continues to increase, the coating layer on the surface of the nickel powder is too thick, which is not conducive to subsequent silver plating, resulting in the mixture of some pure silver particles in the product.

[0085] Example 8 and Comparative Example 7

[0086] According to the method of Example 1, the difference is that the pH value of the reducing solution of nickel powder in step S2 is adjusted, as shown in Table 6 specifically.

[0087] The performance test results of the silver-plated nickel powder obtained in Example 8 and Comparative Example 7 are shown in Table 6.

[0088] Table 6

[0089]

[0090] It can be seen from Table 6 that when the pH value of the nickel reducing solution is 11, the reduction rate of the silver source is low during the silver plating process, the silver content on the surface of the product silver-plated nickel powder is low, the volume resistivity increases, and the antioxidant property decreases; when the pH value reaches above 12, the silver content on the surface of the nickel powder increases, and the comprehensive performance of the product silver-plated nickel powder is excellent.

[0091] Comparative Examples 8 - 9

[0092] According to the method of Example 1, the difference is that the type of surfactant is adjusted, as shown in Table 7 specifically.

[0093] The performance test results of the silver-plated nickel powder obtained in Example 1 and Comparative Examples 8 - 9 are shown in Table 7.

[0094] Table 7

[0095]

[0096] It can be seen from Table 7 that adding an anionic surfactant is beneficial to subsequent silver plating, while adding cationic and non-ionic surfactants shows poor silver plating effects; the reason may be that the surface of the nickel powder is positively charged, and the anionic surfactant is beneficial to form an electric double layer on the surface of the nickel powder, which is beneficial to the dispersion of the nickel powder and the uniform adsorption of nano silver particles on the surface of the nickel powder; although the non-ionic surfactant and cation have no effect on the silver content on the surface of the nickel powder, due to the uneven dispersion of the nickel powder, the silver layer on the surface of the nickel powder is not dense, and free pure silver particles will be formed.

[0097] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification only illustrates the principle of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. An industrial preparation method of silver-plated nickel powder, characterized in that, the industrial preparation method comprises the following steps: S1. Surface treatment of nickel powder; S2. Formation of active centers: Uniformly disperse negatively charged silver nanoparticles and an anionic surfactant in a solvent, then add the surface-treated nickel powder and a reducing agent, and adjust the pH value of the system to be greater than 11 to obtain a reduction solution of nickel powder; The anionic surfactant is sodium linear alkyl benzene sulfonate and / or fatty alcohol sulfate, and the addition amount of the anionic surfactant is 0.5-3% of the mass of the nickel powder; S3. Silver plating: Dropwise add a silver ammonia complex solution to the reduction solution of nickel powder for reaction to obtain silver-plated nickel powder; The method for surface treatment of nickel powder includes: pickling nickel powder in an acidic solution; The median particle size of the nickel powder is greater than 1 μm; The median particle size of the negatively charged silver nanoparticles is 1-30 nm; The mass ratio of the negatively charged silver nanoparticles to the nickel powder is (2×10 -6 -1×10 -5 ): 100; The reducing agent is selected from at least one of sodium citrate, potassium sodium tartrate, glucose, formaldehyde, and ascorbic acid.

2. The silver-plated nickel powder prepared by the preparation method according to claim 1.

3. The silver-plated nickel powder according to claim 2, characterized in that: the surface silver content of the silver-plated nickel powder is 15-50%.

4. The silver-plated nickel powder according to claim 3, characterized in that: The volume resistivity of the silver-plated nickel powder < 1×10 -4 Ω·cm.

5. The silver-plated nickel powder according to claim 3, characterized in that: the oxidation resistance temperature of the silver-plated nickel powder > 500 °C.

6. Application of the silver-plated nickel powder according to any one of claims 2 to 5 in electromagnetic shielding.

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