A method for passivating an electroplated silver layer

Abstract

This invention relates to a passivation method for electroplated silver layers and its application. The method includes steps such as cleaning the workpiece, chemical passivation, constant-voltage electrolytic passivation, boiling water immersion, and constant-temperature drying. This method uses environmentally friendly molybdate instead of dichromate for chemical passivation, and uses molybdate, aluminum hydroxide, and sodium carbonate instead of dichromate for electrolytic passivation. This allows for the preparation of a silver plating passivation layer with strong corrosion resistance without using chromium-containing substances or cyanides, reducing environmental pollution and improving operational safety. Through the chemical + electrolytic passivation treatment in this method, the corrosion resistance of the silver plating layer is significantly improved, meeting the requirements for anti-discoloration. Electrochemical impedance spectroscopy and Tafel curve measurements show that the corrosion resistance of the passivated samples is significantly improved, the corrosion current density is significantly reduced, and pitting corrosion is less likely to occur. This method has significant practical and industrialization value.

Description

Technical Field

[0001] This invention belongs to the field of metal material surface protection technology, and particularly relates to a method for passivating electroplated silver layers and its application. Background Technology

[0002] To date, cyanide silver plating technology remains widely used in China. This is partly because the quality of cyanide-plated silver layers is far superior to that of cyanide-free silver plating, and partly because cyanide plating solutions exhibit significantly higher stability compared to cyanide-free solutions. However, due to environmental pressures, many silver-plated products are prohibited from using chromium-containing substances for passivation. Since traditional chemical and electrolytic passivation methods contain chromium, many manufacturers have resorted to organic passivation to protect their silver plating layers. However, the protective ability of organic passivation is extremely limited. Organically passivated silver plating layers exposed to air typically discolor within 3 to 6 months, thus failing to meet practical application requirements. Summary of the Invention

[0003] To avoid the adverse environmental impact of traditional chromium-containing passivation processes, overcome the shortcomings of poor protective effects of organic passivation processes, enhance the corrosion resistance of electroplated silver layers, and extend their service life, the inventors, based on years of practical experience and professional knowledge accumulated in metal coating research and production, have developed an electroplated silver passivation method after design and repeated verification. This method can effectively overcome the aforementioned shortcomings of existing technologies, and prepares an electroplated silver passivation layer with strong corrosion resistance without using hexavalent chromium, trivalent chromium, or cyanide, thus possessing significant practical and industrialization value.

[0004] To achieve the above objectives, the present invention provides a method for passivating an electroplated silver layer, the passivation method comprising the following steps:

[0005] S1. Cleaning: Rinse the workpiece with running water to clean the silver-plated layer;

[0006] S2. Chemical passivation: Place the workpiece in a chemical passivation solution, treat for 1 minute, then remove it and rinse the workpiece with running water.

[0007] S3. Electrolytic passivation: Place the workpiece in the electrolytic passivation solution, with the workpiece as the cathode, and treat it using a constant voltage method for 1 to 3 minutes. Then remove the workpiece and rinse it with running water.

[0008] S4. Boiling water immersion: Place the workpiece in boiling pure water and immerse it for 1 minute before removing it;

[0009] S5. Drying: Place the workpiece in an oven and dry it at a constant temperature of 45-60℃.

[0010] Furthermore, the chemical passivation solution in the passivation method S2 of the present invention is composed of the following components:

[0011] Molybdate 27-57g,

[0012] 10-15 mL of nitric acid

[0013] Add pure water to 1L.

[0014] Furthermore, the molybdate mentioned in the above passivation method is one or more of sodium molybdate, ammonium molybdate, phosphomolybdic acid, and lithium molybdate in any proportion.

[0015] Furthermore, the electrolytic passivation solution in passivation method S3 of the present invention is composed of the following components:

[0016] 45-55g of molybdate

[0017] Aluminum hydroxide 0.5–0.6 g,

[0018] 10-20g of sodium carbonate

[0019] Add pure water to 1L.

[0020] Furthermore, the molybdate mentioned in the above passivation method is one or more of sodium molybdate, ammonium molybdate, phosphomolybdic acid, and lithium molybdate in any proportion.

[0021] Furthermore, the constant voltage method described in passivation method S3 of the present invention operates at a voltage of 2 to 4.5V.

[0022] Furthermore, the present invention also relates to the use of the above-described electroplated silver layer passivation method in metal plating passivation operations.

[0023] On the other hand, the present invention also provides a chemical passivation solution for passivating electroplated silver layers, the chemical passivation solution being composed of the following components:

[0024] Molybdate 27-57g,

[0025] 10-15 mL of nitric acid

[0026] Add pure water to 1L;

[0027] The molybdate is one or more of sodium molybdate, ammonium molybdate, phosphomolybdic acid, and lithium molybdate in any proportion.

[0028] Similarly, the present invention also provides an electrolytic passivation solution for passivating electroplated silver layers, the electrolytic passivation solution being composed of the following components:

[0029] 45-55g of molybdate

[0030] Aluminum hydroxide 0.5–0.6 g,

[0031] 10-20g of sodium carbonate

[0032] Add pure water to 1L;

[0033] The molybdate is one or more of sodium molybdate, ammonium molybdate, phosphomolybdic acid, and lithium molybdate in any proportion.

[0034] In summary, the passivation method for electroplated silver layer of the present invention has the following characteristics:

[0035] (1) This method can passivate the electroplated silver layer without using chromium-containing substances and cyanide, which greatly reduces the adverse impact on the environment.

[0036] (2) Using environmentally friendly molybdate instead of dichromate for chemical passivation reduces environmental pollution and improves operational safety.

[0037] (3) Use environmentally friendly molybdate, aluminum hydroxide, and sodium carbonate instead of dichromate for electrolytic passivation treatment. The electrolytic passivation solution is alkaline and has little environmental pollution.

[0038] (4) The chemical + electrolytic passivation treatment in this method greatly improves the corrosion resistance of the silver plating layer, enabling it to meet the discoloration resistance requirements in CB / T 3764 "Series of Thicknesses and Quality Requirements for Metallic Coatings and Chemical Coatings". Electrochemical impedance spectroscopy and Tafel curve measurements show that the passivated sample exhibits significantly improved corrosion resistance, and the corrosion current density of the sample decreases significantly (from 3.69 × 10⁻⁶). -5 Reduced to 1.58×10 -6 A / cm 2 It is also not prone to pitting and breakdown. Attached Figure Description

[0039] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments are briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention, and not all embodiments. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0040] Figure 1 This is a schematic diagram illustrating the implementation process of the electroplated silver layer passivation method of the present invention.

[0041] Figure 2 This is a schematic diagram of the electroplating silver layer and passivation production process according to an embodiment of the present invention.

[0042] Figure 3 This is a sample image of an electroplated silver layer after immersion in sodium sulfide for 30 minutes, according to an embodiment of the present invention.

[0043] Figure 4This is a sample image of a silver-plated layer after being cross-cut according to an embodiment of the present invention.

[0044] Figure 5 Electrochemical impedance spectroscopy (3.5 wt.% NaCl) of an unpassivated silver plating layer, a chemically passivated silver plating layer, and a chemically passivated + electrolytically passivated silver plating layer according to an embodiment of the present invention.

[0045] Figure 6 Tafel curves (3.5 wt.% NaCl) of an unpassivated silver plating layer, a chemically passivated silver plating layer, and a chemically passivated + electrolytically passivated silver plating layer according to an embodiment of the present invention. Detailed Implementation

[0046] The technical solution of the present invention will be clearly and completely described below through specific examples. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Those skilled in the art can easily understand other advantages and functions of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0047] Before further describing specific embodiments of the present invention, it should be understood that the scope of protection of the present invention is not limited to the specific embodiments described below; it should also be understood that the terminology used in the embodiments of the present invention is for describing specific embodiments and not for limiting the scope of protection of the present invention.

[0048] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in this invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical terms used in this invention have the same meaning as commonly understood by those skilled in the art. In addition to the specific methods, devices, and materials used in the embodiments, based on the knowledge of those skilled in the art and the description of this invention, any prior art methods, devices, and materials similar to or equivalent to those described, used, and materials in the embodiments of this invention may be used to implement this invention.

[0049] In this invention, unless otherwise specified, all parts and percentages are by weight. Unless otherwise stated, all equipment and raw materials are commercially available or commonly used in the industry. The methods in the following embodiments are conventional methods in the art, unless otherwise specified.

[0050] Example 1

[0051] See Figure 1 and Figure 2Taking a 0.3×0.4×0.05dmT2 material sample as an example, its electroplating silver layer and passivation method include the following steps:

[0052] Step 1: Degreasing. Use No. 120 solvent oil to brush the surface of the workpiece to remove all oil stains.

[0053] Step 2: Chemical degreasing. Place the workpiece in a chemical degreasing solution for ultrasonic degreasing. The chemical degreasing solution formula is: sodium phosphate 40g / L, sodium silicate 5g / L, sodium carbonate 25g / L, sodium hydroxide 5g / L, and add pure water to make up to 1L. The chemical degreasing temperature is 80℃, and the degreasing time is 10min.

[0054] Step 3: Water washing. Rinse the workpiece with hot water at 60℃ and running tap water. The surface of the cleaned workpiece should be wetted and have a continuous water film. The workpiece is considered qualified if the water film does not break after 30 seconds.

[0055] Step 4: Pickling. Place the workpiece in the pickling solution. The pickling solution formula is: sodium nitrate 160g / L, nitric acid 100mL / L, sulfuric acid 400mL / L, and add pure water to make up to 1L; the pickling time is 1min; then take out the workpiece and rinse it clean with running water.

[0056] Step 5: Gloss immersion. Place the workpiece in the gloss immersion solution, which has the following formula: glacial acetic acid 300 mL / L, phosphoric acid 399.9 mL / L, nitric acid 300 mL / L, and hydrochloric acid 0.1 mL / L. The gloss immersion time is 1 minute. Then, remove the workpiece and rinse it with running water.

[0057] Step 6: Silver immersion. Place the workpiece in the silver immersion solution. The silver immersion solution formula is: silver nitrate 15g / L, thiourea 220g / L, copper sulfate 0.3g / L, add pure water to make up to 1L, use hydrochloric acid to adjust the pH of the solution to 3, the silver immersion time is 2min, and then take out the workpiece and rinse it clean with running water.

[0058] Step 7: Remove thiourea. Place the workpiece in a thiourea removal solution (5% nitric acid solution) and immerse for 1 minute. Then remove the workpiece and rinse it with running water.

[0059] Step 8: Silver plating. Place the workpiece in the silver plating solution. The silver plating solution formula is as follows: The main salt is one or both of silver nitrate or silver sulfamate, 12-32 g / L based on silver (in this example, silver nitrate is used at 20 g / L based on silver); the complexing agent is a mixture of two or more of the following: ammonium iminodisulfonate, nicotinic acid, ammonia, sodium thiosulfate, potassium sodium tartrate, succinimide, thiourea, sodium thiosulfate, and sodium citrate, totaling 150-300 g / L (in this example, nicotinic acid is used at 105 g / L and ammonia at 18 g / L). 0 g / L, sodium thiosulfate 10 g / L); pH stabilizer is one or more of glacial acetic acid, sodium carbonate, potassium carbonate, and sodium bicarbonate, totaling 140–200 g / L (80 g / L glacial acetic acid and 60 g / L sodium carbonate are used in this example); the prepared solution is adjusted to pH greater than 8 using potassium hydroxide (9 in this example); the anode to cathode area ratio is greater than 1, the workpiece is used as the cathode, and the pure silver plate is used as the anode, the silver plate purity is ≥99.9%, and the current density is 0.05–0.5 A / dm³. 2 (In this embodiment, the current density is 0.05 A / dm) 2 The plating time is determined based on specific requirements. The current efficiency of this formula is comparable to that of cyanide silver plating, approaching 100%. (When applied at 0.5 A / dm²...) 2 During the plating process, it takes about 3.2 minutes to plate 1μm of silver, and the plating time is 1 hour. After that, the workpiece is removed and rinsed clean with running water.

[0060]

[0061] Step 9: Chemical passivation. Place the workpiece in a chemical passivation solution. The chemical passivation solution formula is 27 g / L lithium molybdate, 15 mL / L nitric acid, and pure water to 1 L. After treatment for 1 min, remove the workpiece and rinse it with running water.

[0062] Step 10: Electrolytic passivation. Place the workpiece in the electrolytic passivation solution. The electrolytic passivation solution formula is: sodium molybdate 55g / L, aluminum hydroxide 0.6g / L, sodium carbonate 20g / L, and pure water to 1L. Treat with constant voltage method for 1min at a voltage of 4.5V. Remove and rinse the workpiece with running water.

[0063] Step 11: Boiling water immersion. Place the workpiece in boiling pure water and immerse it for 1 minute before removing it.

[0064] Step 12: Drying. Place the workpiece in an oven and dry it at a constant temperature of 50°C until there is no moisture.

[0065] After electroplating and passivation treatment, the silver layer adhesion of the samples was tested using the cross-cut test according to the standard "Review of Test Methods for Adhesion Strength of Electrodeposited and Chemically Deposited Metallic Coatings on Metallic Substrates" (GB / T). The tested samples are shown below. Figure 4After immersing in a 1% sodium sulfide solution (calculated as Na2S) for 30 minutes according to the standard "CB / T3764 Series and Quality Requirements for Thickness of Metallic Coatings and Chemical Coatings", no obvious color change was observed. See the test results below. Figure 3 .

[0066] Example 2

[0067] See Figure 1 and Figure 2 Taking a 0.3×0.4×0.05dmT2 material sample as an example, its electroplating silver layer and passivation method include the following steps:

[0068] Step 1: Degreasing. Use No. 120 solvent oil to brush the surface of the workpiece to remove all oil stains.

[0069] Step 2: Chemical degreasing. Place the workpiece in a chemical degreasing solution for ultrasonic degreasing. The chemical degreasing solution formula is: sodium phosphate 40g / L, sodium silicate 5g / L, sodium carbonate 25g / L, sodium hydroxide 5g / L, and add pure water to make up to 1L. The chemical degreasing temperature is 80℃, and the degreasing time is 10min.

[0070] Step 3: Water washing. Rinse the workpiece with hot water at 60℃ and running tap water. The surface of the cleaned workpiece should be wetted and have a continuous water film. The workpiece is considered qualified if the water film does not break after 30 seconds.

[0071] Step 4: Pickling. Place the workpiece in the pickling solution. The pickling solution formula is: sodium nitrate 160g / L, nitric acid 100mL / L, sulfuric acid 400mL / L, and add pure water to make up to 1L; the pickling time is 1min; then take out the workpiece and rinse it clean with running water.

[0072] Step 5: Gloss immersion. Place the workpiece in the gloss immersion solution, which has the following formula: glacial acetic acid 300 mL / L, phosphoric acid 399.9 mL / L, nitric acid 300 mL / L, and hydrochloric acid 0.1 mL / L. The gloss immersion time is 1 minute. Then, remove the workpiece and rinse it with running water.

[0073] Step 6: Silver immersion. Place the workpiece in the silver immersion solution. The silver immersion solution formula is: silver nitrate 15g / L, thiourea 220g / L, copper sulfate 0.3g / L, add pure water to make up to 1L, use hydrochloric acid to adjust the pH of the solution to 3, the silver immersion time is 2min, and then take out the workpiece and rinse it clean with running water.

[0074] Step 7: Remove thiourea. Place the workpiece in a thiourea removal solution (5% nitric acid solution) and immerse for 1 minute. Then remove the workpiece and rinse it with running water.

[0075] Step 8: Silver plating. Place the workpiece in the silver plating solution. The silver plating solution formula is as follows: The main salt is one or both of silver nitrate or silver sulfamate, 12-32 g / L based on silver (in this example, silver nitrate is used at 20 g / L based on silver); the complexing agent is a mixture of two or more of the following: ammonium iminodisulfonate, nicotinic acid, ammonia, sodium thiosulfate, potassium sodium tartrate, succinimide, thiourea, sodium thiosulfate, and sodium citrate, totaling 150-300 g / L (in this example, nicotinic acid is used at 105 g / L and ammonia at 18 g / L). 0 g / L, sodium thiosulfate 10 g / L); pH stabilizer is one or more of glacial acetic acid, sodium carbonate, potassium carbonate, and sodium bicarbonate, totaling 140–200 g / L (80 g / L glacial acetic acid and 60 g / L sodium carbonate are used in this example); the prepared solution is adjusted to pH greater than 8 using potassium hydroxide (9 in this example); the anode to cathode area ratio is greater than 1, the workpiece is used as the cathode, and the pure silver plate is used as the anode, the silver plate purity is ≥99.9%, and the current density is 0.05–0.5 A / dm³. 2 (In this embodiment, the current density is 0.05 A / dm) 2 The plating time is determined based on specific requirements. The current efficiency of this formula is comparable to that of cyanide silver plating, approaching 100%. (When applied at 0.5 A / dm²...) 2 When plating, it takes about 3.2 minutes to plate 1μm of silver, and 40 minutes for the entire plating process. Then, remove the workpiece and rinse it clean with running water.

[0076]

[0077] Step 9: Chemical passivation. Place the workpiece in a chemical passivation solution. The chemical passivation solution formula is 57g / L sodium molybdate, 10mL / L nitric acid, and pure water to 1L. After treatment for 1 minute, remove the workpiece and rinse it clean with running water.

[0078] Step 10: Electrolytic passivation. Place the workpiece in the electrolytic passivation solution. The electrolytic passivation solution formula is: sodium molybdate 45g / L, aluminum hydroxide 0.5g / L, sodium carbonate 10g / L, and add pure water to 1L. Treat with constant voltage method for 1min, voltage is 2.5V. Take out and rinse the workpiece with running water.

[0079] Step 11: Boiling water immersion. Place the workpiece in boiling pure water and immerse it for 1 minute before removing it.

[0080] Step 12: Drying. Place the workpiece in an oven and dry it at a constant temperature of 50°C until there is no moisture.

[0081] Three samples were taken: silver-plated, silver-plated followed by chemical passivation only, and silver-plated followed by chemical passivation and electrolytic passivation. Corrosion tests were performed on these samples. Tafel curves and electrochemical impedance spectroscopy (EIS) of the samples in a 3.5 wt.% sodium chloride solution were measured using a CHI660E electrochemical workstation. The Tafel curve testing conditions were as follows: a three-electrode system, with a 10 mm × 10 mm effective sample area as the working electrode, a platinum sheet as the counter electrode, and a saturated calomel electrode (SCE) as the reference electrode. The sample was first immersed in the sodium chloride solution for 30 min before testing, with a scan rate of 0.01 V / s. The EIS testing conditions were: initial potential -0.08 V, amplitude 0.005 V, electrolyte 3.5 wt.% sodium chloride, and a three-electrode working system. The EIS results are shown below. Figure 5 According to the impedance diagram, the diameter of the capacitive arc at the high-frequency end is equal to the resistance value of the electrochemical reaction. The resistance values ​​are: chemical passivation + electrolytic passivation after silver plating > chemical passivation only after silver plating > silver plating. This indicates that the corrosion resistance of the sample is significantly improved after chemical passivation + electrolytic passivation. The Tafel curve is shown below. Figure 6 The relevant corrosion parameters are shown in Table 1 below. It can be seen that the corrosion current density is: silver plating > silver plating followed by chemical passivation only > silver plating followed by chemical passivation + electrolytic passivation. This indicates that the sample exhibits the best corrosion resistance after chemical passivation + electrolytic passivation. Furthermore, from... Figure 6 As can be seen, the electroplated silver sample experienced pitting breakdown at a potential of 0.12V (vs. SCE), while the passivated film did not experience pitting breakdown in the range of -1 to 1V (vs. SCE), indicating that the passivation of the sample also significantly improved the resistance to pitting breakdown.

[0082] Table 1 Corrosion parameters of silver plating, chemical passivation silver plating, and chemical passivation + electrolytic passivation silver plating

[0083] Handling method <![CDATA[Φ corr (vs.SCE) / V]]> <![CDATA[J corr (A / cm 2 )]]> Chemical passivation + electrolytic passivation -0.305 <![CDATA[1.58×10 -6 ]]> Chemical passivation -0.278 <![CDATA[2.16×10 -5 ]]> Unpassivated silver plating -0.276 <![CDATA[3.69×10 -5 ]]>

[0084] The above description is merely an embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, substitutions, etc., made within the spirit and principle of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for passivating an electroplated silver layer, characterized in that, The passivation method includes the following steps: S1. Cleaning: Rinse the workpiece with running water to remove the silver plating layer; S2. Chemical passivation: Place the workpiece in a chemical passivation solution, treat for 1 minute, then remove and rinse the workpiece with running water. S3. Electrolytic passivation: The workpiece is placed in the electrolytic passivation solution, with the workpiece serving as the cathode. After treatment using a constant voltage method for 1–3 minutes, the workpiece is removed and rinsed clean with running water. The electrolytic passivation solution consists of the following components: 45-55g of molybdate Aluminum hydroxide 0.5–0.6 g, 10-20g of sodium carbonate Add pure water to 1 L; S4. Boiling water immersion: Place the workpiece in boiling pure water and immerse it for 1 minute before removing it; S5. Drying: Place the workpiece in an oven and dry it at a constant temperature of 45-60℃.

2. The passivation method for electroplated silver layer according to claim 1, characterized in that, The chemical passivation solution described in S2 consists of the following components: Molybdate 27-57g, 10-15 mL of nitric acid Add pure water to 1 L.

3. The passivation method for electroplated silver layer according to claim 2, characterized in that, The molybdate is one or more of sodium molybdate, ammonium molybdate, and lithium molybdate in any proportion.

4. The passivation method for electroplated silver layer according to claim 1, characterized in that, The molybdate is one or more of sodium molybdate, ammonium molybdate, and lithium molybdate in any proportion.

5. The passivation method for electroplated silver layer according to claim 1, characterized in that, The constant voltage method described in S3 operates at a voltage of 2–4.5V.

6. The use of the electroplated silver passivation method according to any one of claims 1-5 in metal plating passivation operations.

7. An electrolytic passivation solution for passivating electroplated silver layers, characterized in that, The electrolytic passivation solution is composed of the following components: 45-55g of molybdate Aluminum hydroxide 0.5–0.6 g, 10-20g of sodium carbonate Add pure water to 1 L; The molybdate is one or more of sodium molybdate, ammonium molybdate, and lithium molybdate in any proportion.

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