A cyanide-free brush plating Ag-W alloy plating solution system and its preparation method and application

Abstract

The present invention belongs to the technical field of brush plating, and specifically relates to a cyanide-free brush plating Ag-W alloy plating solution system and its preparation method and application. The plating solution system includes the following components: 10-40g / L silver nitrate, 1-10g / L soluble nickel salt, 10-60g / L tungstate, 80-150g / L 5,5-dimethylhydantoin, 20-60g / L sodium citrate, 10-50g / L ammonium acetate and 0.1-1g / L 2,2′-bipyridine, and the solvent is water. The present invention adds nickel ions and tungstate ions to the electroplating silver plating solution, combines pulse reverse plating technology, deposits silver at a positive potential, deposits tungstate ions at a reverse potential, reduces metallic tungsten, and realizes the co-precipitation of Ag-W alloy; a coating mainly composed of nano-silver can be obtained, and the hardness is better than that of a traditional direct current silver plating coating. The present invention can significantly refine the grain size of the silver plating layer by adding a small amount of tungsten.

Description

Technical Field

[0001] The invention belongs to the technical field of brush plating, and in particular relates to a cyanide-free brush plating Ag-W alloy plating solution system and a preparation method and application thereof. Background Art

[0002] Silver has good electrical and thermal conductivity, and it has the best electrical conductivity among all metals. In addition, metallic silver also has high chemical stability and corrosion resistance, and has good chemical stability in most organic acids, strong bases and salt solutions. Based on these excellent properties of silver, the preparation of silver coatings occupies a very important position in coating production.

[0003] Silver plating is a widely used conductive metal plating. Conventional silver plating uses cyanide complexing agents. However, for environmental protection and to meet the requirements of field applications, a cyanide-free plating solution system is the current goal. However, compared with the plating prepared by the cyanide plating solution, the coating prepared by the cyanide-free plating solution has the disadvantages of low hardness, insufficient wear resistance, and poor ablation resistance. If a nanosilver coating containing tungsten is obtained by adjusting the composition and process of the electroplating solution, not only the hardness of the coating can be improved, but also the wear resistance and ablation resistance can be greatly improved. It will have important application prospects in the field of conductive coating preparation.

[0004] The brush plating process is a branch of electroplating. Compared with continuous DC plating, it has some special advantages. For example, during the brush plating process, the mechanical movement of the brush head can break up the continuous growth process of the grains, thus having a stronger grain refinement effect and even obtaining a nanocrystalline coating.

[0005] Since silver itself has a very high potential (+0.799V) and other metals have lower potentials, such as (-1.05V for tungsten and -0.22V for molybdenum), the co-deposition of silver with tungsten, molybdenum, etc. is very challenging. On the one hand, elements such as tungsten cannot be directly deposited by electroplating, but can only be achieved by co-deposition of iron group elements (Fe, Ni, Co). In addition, due to the high potential of silver, it is easy to cause fast deposition and it is not easy to obtain nanocrystals. Therefore, how to use brush plating to obtain a silver-tungsten alloy coating with a nanostructure requires not only a suitable complexing system, but also a suitable brush plating process.

[0006] At present, most of the relevant reports focus on the process and method of single silver plating method. For example, Patent 200510023573, Patent 200710009207, Patent 20010009208 all involve different cyanide-free silver plating process methods, and Patent CN103540978A involves a method of alkaline cyanide-free electroplating of Ag-Ni alloy. Based on current research, there are few technologies involving the use of brush plating to prepare Ag-W alloy coatings. Summary of the invention

[0007] In view of the problems existing in the prior art, the present invention provides a cyanide-free brush plating Ag-W alloy plating solution system.

[0008] The invention also provides a method for preparing the cyanide-free brush plating Ag-W alloy plating solution system.

[0009] Another object of the present invention is to provide an application of the above-mentioned cyanide-free brush plating Ag-W alloy plating solution system, by introducing a pulse reverse plating process, to achieve a nano silver-tungsten alloy coating by a brush plating method.

[0010] The technical solution adopted by the present invention to achieve the above-mentioned purpose is:

[0011] The invention provides a cyanide-free brush plating Ag-W alloy plating solution system, which comprises the following components: 10-40 g / L silver nitrate, 1-10 g / L soluble nickel salt, 10-60 g / L tungstate, 80-150 g / L 5,5-dimethylhydantoin, 20-60 g / L sodium citrate, 10-50 g / L ammonium acetate and 0.1-1 g / L 2,2′-bipyridine, and the solvent is water.

[0012] Furthermore, the pH of the Ag-W alloy plating solution system is 7-9; and the pH is adjusted using ammonia water or nitric acid.

[0013] The present invention also provides a method for preparing a cyanide-free brush plating Ag-W alloy plating solution system, comprising the following steps: weighing silver nitrate, nickel sulfate, sodium tungstate, 5,5-dimethylhydantoin, sodium citrate, ammonium acetate and 2,2′-bipyridine, preparing a solution with deionized water, and adjusting the pH with ammonia water and nitric acid.

[0014] The invention also provides an application of a plating solution system in cyanide-free brush plating of Ag-W alloy, characterized in that the brush-plated substrate is copper.

[0015] The specific process of the pulse reverse plating process provided by the present invention is:

[0016] (1) Use copper as the substrate and clean it for later use;

[0017] (2) Prepare plating solution for standby use;

[0018] (3) The pulse reverse plating process is used for brush plating of Ag-W alloy.

[0019] Furthermore, the parameters of the pulse reverse plating process are: voltage is ±2V, pulse working width forward voltage working time is 500-2000μs, reverse voltage working time is 200-500μs, and plating pen speed is 6-10m / min.

[0020] In the plating solution system provided by the present invention, the main function of silver nitrate is to be the main salt of the plating solution, providing silver ions during the deposition process. The soluble nickel salt serves as an auxiliary salt to provide a small amount of nickel precipitation, and nickel can promote the co-precipitation of tungsten. 5,5-Dimethylhydantoin is the main complex of silver ions in the plating solution. It can form a stable complex with silver ions, causing the precipitation potential of silver ions to shift significantly negative, thereby reducing the deposition rate and facilitating the formation of nanocrystals. Dimethylhydantoin can be used as a chelating agent for tungsten, and sodium citrate is an auxiliary chelating agent. Tungstates can be selected from sodium tungstate, ammonium tungstate, etc., mainly to provide a tungsten source during the brush plating process. 2,2′-Bipyridine is used as a brightener. The schematic diagram of brush plating is shown in FIG. Figure 1 shown.

[0021] The pulse reverse plating waveform used is as follows: Figure 2 As shown, U C and U A Represent the positive and negative loading voltages respectively. Through periodic changes, the deposition of silver ions and tungsten ions can be achieved. C and T A The deposition content of different elements can be controlled by adjusting the deposition time, so as to obtain the effect of tungsten grain boundary segregation inhibiting the growth of silver grains. The present invention realizes the co-precipitation of Ag-W alloy by controlling the content of each component, such as the concentration of the main salt and the content of the complexing agent, and coordinating and regulating the process parameters such as the plating voltage and pulse parameters.

[0022] The beneficial effects of the present invention are:

[0023] (1) The present invention adds nickel ions and tungstate ions to the silver electroplating solution, combines the pulse reverse plating technology, deposits silver at a positive potential, deposits tungstate ions at a reverse potential, reduces metallic tungsten, and realizes the co-precipitation of Ag-W alloy;

[0024] (2) The present invention utilizes a pulse reverse plating process to promote the deposition of W. The precipitation of W further promotes the formation of nanosilver due to the grain boundary segregation effect, and a nanosilver-based coating can be obtained. The hardness and wear resistance are better than those of the traditional direct current silver plating coating.

[0025] (3) The present invention can significantly refine the grain size of the silver-plated layer by adding a small amount of tungsten. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A schematic diagram of the pulse brush plating provided by the present invention.

[0027] Figure 2 Schematic diagram of pulse reverse plating waveform.

[0028] Figure 3 This is the XRD pattern of the coating prepared in Example 1.

[0029] Figure 4 This is the SEM image of the coating prepared in Example 1. DETAILED DESCRIPTION

[0030] The technical solution of the present invention is further explained and illustrated by means of specific embodiments below.

[0031] Example 1

[0032] (1) Use copper as the substrate and clean it after removing the oxide film;

[0033] (2) The plating solution composition is: 20 g / L silver nitrate, 10 g / L nickel sulfate, 30 g / L sodium tungstate, 120 g / L 5,5-dimethylhydantoin, 40 g / L sodium citrate, 40 g / L ammonium acetate and 0.2 g / L 2,2′-bipyridine. The solution is prepared with deionized water and the pH value is adjusted to 7 with ammonia and nitric acid.

[0034] (3) Pulse reverse plating process: voltage is ±2V, pulse working width forward voltage working time is 500μs, reverse voltage working time is 200μs, and plating pen speed is 6m / min.

[0035] The XRD results of the coating obtained in Example 1 are as follows: Figure 3 As shown in Figure 2, the calculated average grain size is 44 nanometers, and the SEM image is shown in Figure 2. Figure 4 As shown in the figure, the tungsten content obtained by EDS analysis is 0.8wt.%. The hardness of the nanoindentation test is 2.1GPa.

[0036] Example 2

[0037] (1) Use copper as the substrate and clean it after removing the oxide film;

[0038] (2) The plating solution composition is: 20 g / L silver nitrate, 20 g / L nickel chloride, 60 g / L ammonium tungstate, 150 g / L 5,5-dimethylhydantoin, 30 g / L sodium citrate, 20 g / L ammonium acetate and 0.5 g / L 2,2′-bipyridine. The solution is prepared with deionized water and the pH value is adjusted to 9.

[0039] (3) Pulse reverse plating process: voltage is ±2V, pulse working width forward voltage working time is 2000μs, reverse voltage working time is 500μs, and plating pen speed is 10m / min.

[0040] The grain size of the silver coating prepared in Example 2 was 34 nanometers, and the tungsten content was 1.3 wt.%. The nano-indentation hardness of the coating reached 2.4 GPa.

[0041] Comparative Example 1

[0042] (1) Use copper as the substrate and clean it after removing the oxide film;

[0043] (2) The plating solution composition is: 20 g / L silver nitrate, 150 g / L 5,5-dimethylhydantoin, 30 g / L sodium citrate, 20 g / L ammonium acetate and 0.5 g / L 2,2′-bipyridine. The solution is prepared with deionized water and the pH value is adjusted to 7 with ammonia and nitric acid.

[0044] (3) Pulse reverse plating process: voltage is ±2V, pulse working width forward voltage working time is 1000μs, reverse voltage working time is 500μs, and plating pen speed is 10m / min.

[0045] The grain size of the silver coating prepared in Comparative Example 1 is 180 nanometers, the coating does not contain tungsten, and the nanoindentation hardness is 1.3 GPa.

[0046] Comparative Example 2

[0047] (1) Use copper as the substrate and clean it after removing the oxide film;

[0048] (2) The composition of the plating solution is the same as that of Example 1;

[0049] (3) Instead of using pulse reverse plating process, conventional electroplating process is used: voltage is 2V, and the plating pen speed is 6m / min.

[0050] The grain size of the silver coating prepared in Comparative Example 2 is 670 nanometers and does not contain tungsten. The nanoindentation hardness of the coating is 1.1 GPa.

[0051] It can be seen from the results of the embodiments and comparative examples that adding tungstate to the plating solution and adopting the pulse reverse plating technology are necessary to obtain the Ag-W coating. When the appropriate plating solution composition and pulse reverse plating process as described in this embodiment are adopted, the obtained coating contains a certain amount of tungsten element and the grain size is significantly refined. Compared with traditional DC electroplating, the grain size is reduced by an order of magnitude and the nanoindentation hardness is increased by two times.

Claims

1. Application of a plating solution system in cyanide-free brush plating of Ag-W alloy, characterized in that: The plating solution system includes the following components: 10-40 g / L silver nitrate, 1-10 g / L soluble nickel salt, 10-60 g / L tungstate, 80-150 g / L 5,5-dimethylhydantoin, 20-60 g / L sodium citrate, 10-50 g / L ammonium acetate and 0.1-1 g / L 2,2′-bipyridine, and the solvent is water; The preparation process is: (1) Use copper as the substrate and clean it for later use; (2) Prepare plating solution for standby use; (3) Brush plating of Ag-W alloy using pulse reverse plating process; The parameters of the pulse reverse plating process are: voltage is ±2V, pulse working width forward voltage working time is 500-2000μs, reverse voltage working time is 200-500μs, and plating pen speed is 6-10m / min.

2. The use according to claim 1, characterized in that: The pH of the plating solution system is 7-9; ammonia water or nitric acid is used to adjust the pH.

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