A non-magnetic electroless nickel plating solution and deposition process

Abstract

This application relates to the field of metal surface treatment, and specifically discloses a non-magnetic electroless nickel plating solution and deposition process. The composition of a non-magnetic electroless nickel plating solution includes 20 - 30 g / L nickel sulfate, 20 - 30 g / L sodium hypophosphite, 10 - 20 g / L complexing agent, 0.5 - 2 ml / L brightener, 1 - 3 g / L stabilizer, and the rest is water; its deposition process is as follows: Add the plating solution to the plating bath and stir, adjust the pH value of the plating solution to 4.5 - 5.5, and heat the plating solution to 80 - 90 °C; Place the workpiece to be plated into the plating bath, stir the plating solution at a speed of 100 - 300 revolutions per minute, and maintain for 1 - 3 h; After the plating is completed, take out the workpiece from the plating bath and clean it, place the cleaned workpiece into a heat treatment furnace for two heat treatments, and passivate and dry the workpiece after heat treatment. The non-magnetic electroless nickel plating solution and deposition process of this application have the advantages of uniform coating and non-magnetic properties.

Description

Technical Field

[0001] This application relates to the field of metal surface treatment, and more specifically, to a plating solution and deposition process for non-magnetic electroless nickel. Background Art

[0002] In the field of industrial production, it is crucial to improve the anti-wear ability and appearance quality of metal parts. Electroless nickel plating is a commonly used method. Electroless nickel plating can form a uniform and dense nickel-phosphorus alloy coating on the metal surface, effectively enhancing the wear resistance and corrosion resistance of parts, and at the same time improving their appearance quality. Therefore, it is widely used in many industries such as automobile manufacturing, electronic equipment, aerospace, etc.

[0003] However, there are many problems with traditional electroless nickel plating processes. On the one hand, the solutions used contain iron or other impurity ions, and these impurity ions will cause the coating to generate a magnetic field. For some precision instruments sensitive to magnetic fields, the generation of this magnetic field will seriously affect their working performance, hinder the precise operation of precision instruments, and limit the application of electroless nickel plating in the treatment of metal parts related to precision instruments.

[0004] On the other hand, traditional electroplating techniques and ordinary electroless nickel plating generally have environmental protection problems. Harmful substances such as heavy metals contained in the plating solution will pollute the environment such as soil and water bodies after being discharged during the production process, and the environmental protection treatment cost is relatively high. And the cost of electroless nickel plating is also relatively high. A large amount of funds are required for the preparation, maintenance, and subsequent treatment of the plating solution. In addition, for workpieces with complex shapes, it is difficult for traditional techniques to achieve uniform plating, resulting in inconsistent coating thicknesses in different parts of the workpiece, affecting product quality and protection effects.

[0005] In summary, the existing electroless nickel plating processes have defects such as affecting the performance of precision instruments, serious environmental protection problems, and difficulty in uniformly plating complex workpieces with coatings. There is an urgent need for a new process or method to solve these problems to meet the ever-developing needs of industrial production. Summary of the Invention

[0006] To solve the above problems, this application provides a plating solution and deposition process for non-magnetic electroless nickel.

[0007] The following technical solution is adopted for the components of the non-magnetic electroless nickel provided in this application:

[0008] A plating solution for non-magnetic electroless nickel, the components of the plating solution include 20 - 30 g / L nickel sulfate, 20 - 30 g / L sodium hypophosphite, 10 - 20 g / L complexing agent, 0.5 - 2 ml / L brightening agent, 1 - 3 g / L stabilizer, and the rest is water.

[0009] By adopting the above technical solution, nickel sulfate is used as the nickel source and sodium hypophosphite is used as the reducing agent in the formulation, and magnetic metal ions such as iron and cobalt are not introduced. The complexing agent stabilizes nickel ions through chelation, inhibits the co-deposition of non-magnetic impurities, and prevents magnetic substances from mixing into the coating. The stabilizer further prevents the accumulation of harmful impurities in the plating solution, ensuring that the coating composition is pure and non-magnetic. By strictly controlling the raw material purity and reaction system, the coating only contains nickel-phosphorus alloy (non-magnetic material), fundamentally eliminating the magnetic field problem caused by iron impurities in the traditional process and meeting the requirements of precision instruments for a non-magnetic environment. Secondly, the formulation of this application does not use highly toxic heavy metal additives such as lead and cadmium. The combination of the stabilizer and the complexing agent extends the service life of the plating solution and reduces the amount of waste liquid generated by frequent tank changes. Compared with the traditional process, this formulation reduces pollutants from the source and at the same time reduces the difficulty of subsequent treatment, conforming to the trend of green manufacturing. The complexing agent forms a stable complex with nickel ions, slowing down the reduction rate of nickel ions and making the deposition process more uniform and controllable. Even in the concave and blind hole parts of complex workpieces, the coating thickness can still be kept consistent. The brightener adsorbs on the surface of the workpiece, reduces the surface tension of the coating, improves the fluidity of the plating solution, reduces the difference in local current density, and inhibits the problem of excessive coating thickness caused by the "tip effect". The stabilizer can prevent the rapid decomposition of the plating solution at high temperatures, maintain the stability of the reaction rate, and avoid uneven coating caused by violent local reactions.

[0010] Optionally, it further includes sodium borohydride with a concentration of 0.1 - 0.5 g / L.

[0011] By adopting the above technical solution, sodium borohydride, as a strong reducing agent, decomposes under acidic conditions to produce H2 and BH4 - , forming a synergistic effect with the reduction effect of sodium hypophosphite, significantly increasing the reduction rate of nickel ions, capable of improving the deposition rate, enhancing the hardness and corrosion resistance of the coating. The decomposition products of BH4 - can be partially doped into the nickel-phosphorus alloy coating to form a Ni-P-B ternary alloy, refining the grains and reducing the porosity, resulting in an increase in the density of the coating. The H2 bubbles generated by the reduction reaction of BH4 - are smaller and more dispersed, reducing the pinhole defects of the coating caused by local hydrogen bubble retention.

[0012] Optionally, the complexing agent includes one or more of lactic acid, citric acid, and hydroxyethylidene diphosphonic acid.

[0013] By adopting the above technical solution, lactic acid forms a five-membered ring complex with Ni 2+ and stably exists under acidic conditions. By controlling the release rate of Ni 2+ , spontaneous decomposition caused by local supersaturation is avoided. Citric acid can react with Ni 2+A six-membered ring chelate is formed to inhibit the direct reaction of nickel ions with sodium hypophosphite to form Ni-P particles. The plating solution remains stable during continuous production. Hydroxyethane diphosphonic acid and Ni 2+ form a polynuclear complex, which is heat-resistant and oxidation-resistant. When processing complex workpieces, it effectively improves the circulation utilization rate of the plating solution and the thickness uniformity of the coating. The combination of the complexing agent and sodium borohydride can form a "strong-weak" double complexing system. For example, HEDP preferentially complexes with Ni 2+ , and citric acid, as a secondary complexing agent, regulates the release rate and forms a dynamic balance with the reduction reaction of sodium borohydride.

[0014] Optionally, the stabilizer includes one of cerium nitrate or a silane coupling agent.

[0015] By adopting the above technical solution, Ce in cerium nitrate 3+ , as a rare earth metal ion, can preferentially adsorb on the active sites in the plating solution and inhibit the spontaneous decomposition reaction of sodium hypophosphite. Ce 3+ forms a nanoscale co-deposition with Ni 2+ , refines the grains through the "grain boundary pinning" effect, and reduces the porosity. Ce in cerium nitrate 3+ is a non-magnetic ion (4f¹ electron structure), and its concentration is extremely low, so it will not introduce magnetic impurities. The silane molecule generates silanol groups through hydrolysis, condenses with the hydroxyl groups on the substrate surface to form Si-O-M covalent bonds, and forms a transition layer between the coating and the substrate at the same time. The silane coupling agent reduces the surface tension of the plating solution, enhances the wettability, and promotes the penetration of the plating solution into complex structures such as deep holes and blind holes. And the silane coupling agent replaces the traditional sulfur-containing stabilizer (such as thiourea), reduces the COD emission, and is more environmentally friendly.

[0016] Optionally, the brightener includes one of propargyl alcohol ethoxy compound or 2-mercaptobenzimidazole.

[0017] By adopting the above technical solution, the alkynyl group (-C≡C-) in the propargyl alcohol ethoxy compound molecule can preferentially adsorb on the microscopic protrusions on the surface of the coating, inhibit the nickel deposition rate at this place, and at the same time promote the deposition at the concave places, so as to achieve a leveling effect. The imidazole ring structure of 2-mercaptobenzimidazole can adsorb on the cathode surface, slow down the nickel ion reduction rate, and at the same time the mercapto group (-SH) forms a coordination bond with Ni²⁺, inhibits local hydrogen evolution, and reduces pinhole defects.

[0018] Optionally, the brightener further includes polyether-modified silicone.

[0019] By adopting the above technical solution, the polyether-modified silicone can quickly break the stability of the bubble film, thereby eliminating the foam generated during the production process, effectively avoiding the formation of pinhole defects on the surface of the coating due to the presence of foam. And the polyether-modified silicone can significantly reduce the surface tension of the plating solution, enabling the plating solution to better wet the surface of the workpiece. Especially for workpieces with complex structures such as deep holes and blind holes, it can significantly improve the penetration ability of the plating solution.

[0020] Optionally, the preparation method of the polyether-modified silicone is as follows:

[0021] Add the hydrogen-containing silicone oil into the reaction vessel, continuously stir at a stirring speed of 200 - 300 revolutions per minute, introduce nitrogen into the reaction vessel, heat the hydrogen-containing silicone oil to 80 - 120 °C and keep it warm;

[0022] Add the allyl polyoxyethylene ether into the reaction vessel, then add the platinum catalyst into the reaction vessel, keep the reaction temperature at 80 - 120 °C, react for 2 - 6 hours, analyze the conversion rate of the Si-H bond with a gas chromatograph. When the conversion rate reaches more than 95%, the reaction is completed;

[0023] After the reaction is completed, stop heating, naturally cool the reaction system to 25 °C, add activated carbon into the reaction system, the dosage of the activated carbon is 1 - 5% of the mass of the reaction product, and stir for 1 - 2 hours. Filter the reaction product to remove the activated carbon and other insoluble impurities. Subject the filtered product to vacuum distillation, control the distillation temperature at 80 - 120 °C, control the vacuum degree at 0.09 - 0.1 MPa, collect the distilled product to obtain the polyether-modified silicone.

[0024] By adopting the above technical solution, after adding the hydrogen-containing silicone oil into the reaction vessel and continuously stirring at a stirring speed of 200 - 300 revolutions per minute, the hydrogen-containing silicone oil can be fully mixed and homogenized in the reaction vessel, avoiding uneven reaction caused by local concentration differences. Nitrogen is introduced into the reaction vessel to expel the oxygen in the vessel. By creating an inert environment through nitrogen introduction, the stability of the reaction and the purity of the product are improved. The hydrogen-containing silicone oil is heated and kept at a temperature range that is the suitable temperature interval for the reaction between the hydrogen-containing silicone oil and allyl polyoxyethylene ether. At this temperature, the reactant molecules have sufficient energy for effective collision, thus ensuring the smooth progress of the reaction. At the same time, the heat preservation operation helps to maintain the stability of the reaction, enabling the reaction to proceed continuously and evenly. First, allyl polyoxyethylene ether is added into the reaction vessel, and then a platinum catalyst is added. This addition sequence can enable allyl polyoxyethylene ether to reach a certain dispersion state in the reaction system first. When the platinum catalyst is added, the catalyst can contact the reactants more evenly, improving the catalytic efficiency and promoting the hydrosilylation reaction between the hydrogen-containing silicone oil and allyl polyoxyethylene ether. The reaction temperature is maintained at 80 - 120 °C for 2 - 6 hours, and a gas chromatograph is used to analyze the conversion rate of the Si-H bond. The reaction is determined to be completed only when the conversion rate reaches more than 95%. This strict control method of reaction time and conversion rate can ensure the full reaction between the hydrogen-containing silicone oil and allyl polyoxyethylene ether, generating as much target product polyether-modified silicone as possible, improving the yield and quality of the product. After the reaction is completed, activated carbon is added to the reaction system. Activated carbon has a strong adsorption effect and can adsorb impurities, catalyst residues, and possible by-products in the reaction product, etc. Through this treatment method, the purity of the product can be effectively improved and the performance of the product can be improved. The filtered product is subjected to vacuum distillation. Vacuum distillation can separate low-boiling impurities and unreacted raw materials in the product at a lower temperature, avoiding the influence of high temperature on the structure and performance of the product. At the same time, precisely controlling the distillation temperature and vacuum degree can ensure the quality and stability of the product, obtaining polyether-modified silicone with high purity and excellent performance. The polyether-modified silicone obtained by the above preparation method has good chemical stability, surface activity, wettability and other properties. When used as a brightener for non-magnetic electroless nickel plating solution, it can effectively reduce the surface tension of the plating solution, improve the wettability of the plating solution on the workpiece surface, thereby making the coating more uniform and bright; it can also inhibit the generation of foam, avoid defects such as pinholes in the coating, and improve the quality and protective performance of the coating.

[0025] In a second aspect, the present application provides a deposition process for non-magnetic electroless nickel, adopting the following technical solution:

[0026] A deposition process for non-magnetic electroless nickel, comprising the following steps:

[0027] The workpiece to be plated is subjected to surface degreasing, derusting and water washing treatments. After water washing, the workpiece to be plated is placed in an activation solution for 1 - 5 minutes. After activation, water washing is carried out again.

[0028] Add plating solution to the plating bath and stir. The stirring speed is controlled at 50 - 100 revolutions per minute. Add an acidic regulator or a basic regulator to the plating solution to adjust the pH value of the plating solution to 4.5 - 5.5. Heat the plating solution to 80 - 90 °C.

[0029] Place the workpiece to be plated in the plating bath and stir the plating solution at a speed of 100 - 300 revolutions per minute for 1 - 3 h.

[0030] After the plating is completed, take out the workpiece from the plating bath and clean it. Put the cleaned workpiece into a heat treatment furnace, heat it up to 200 - 300 °C, and control the heating rate at 5 - 10 °C per minute. After reaching the set temperature, keep it warm for 2 - 6 hours, and then cool it in the furnace to 25 °C.

[0031] Then quickly heat up the workpiece at a heating rate of 20 - 30 °C per minute to 400 - 500 °C. After keeping it warm for 15 - 30 minutes, take out the workpiece and cool it in the air.

[0032] Put the heat-treated workpiece into a passivation solution. The temperature of the passivation solution is 30 - 60 °C, and the passivation time is 3 - 10 minutes. After passivation, wash the workpiece with water, and dry the washed workpiece at 60 - 80 °C.

[0033] By adopting the above technical solution, degreasing and rust removal treatments are carried out on the workpiece to be plated, and the oil stains, rust and other impurities on the surface of the workpiece can be removed. These impurities will hinder the effective contact between the plating solution and the surface of the workpiece, affecting the adhesion and uniformity of the coating. After water washing, the residual chemicals and impurities in the treatment process can be completely removed, providing a clean surface for subsequent activation and plating. The activation process can remove the oxide film on the surface of the workpiece, making the surface of the workpiece present an active state. This helps to improve the deposition rate and adhesion of metal ions in the plating solution on the surface of the workpiece, making the coating combine more firmly with the workpiece substrate. By adding an acidic regulator or an alkaline regulator, the pH value of the plating solution is adjusted to 4.5 - 5.5. At this pH value, the reaction rate between nickel ions and the reducing agent in the plating solution is moderate, which can ensure the quality and performance of the coating. After the workpiece to be plated is placed in the plating tank, stirring the plating solution can make the ions in the plating solution evenly diffuse to the surface of the workpiece, avoiding uneven coating thickness caused by insufficient local ion concentration. At the same time, an appropriate stirring speed can also promote the timely diffusion of reaction products, preventing them from accumulating on the surface of the workpiece and ensuring the flatness and smoothness of the coating. After plating for a certain period of time, a uniform and dense non-magnetic electroless nickel coating can be formed on the surface of the workpiece. After the plating is completed, the workpiece is placed in a heat treatment furnace and heated to 200 - 300 °C at a rate of 5 - 10 °C per minute and held for 2 - 6 hours, and then cooled in the furnace to 25 °C. This process can eliminate the stress in the coating, improve the hardness and wear resistance of the coating. The slower heating rate can avoid defects such as cracks in the coating caused by too rapid temperature change. Then the workpiece is rapidly heated to 400 - 500 °C at a rate of 20 - 30 °C per minute, taken out and cooled in the air after holding for 15 - 30 minutes. This secondary heat treatment with rapid heating can further improve the microstructure of the coating, making it more dense, and improving the corrosion resistance and hardness of the coating. At the same time, this temperature range helps the nickel-phosphorus alloy in the coating to undergo a phase transformation to form a more stable structure. The heat-treated workpiece is placed in a passivation solution at 30 - 60 °C for 3 - 10 minutes. The passivation treatment can form a dense passivation film on the surface of the coating. This film can effectively prevent oxygen, moisture and other corrosive substances in the external environment from contacting the coating, thus significantly improving the corrosion resistance of the coating. Through this deposition process, the non-magnetic electroless nickel coating formed on the surface of the workpiece has good comprehensive properties. The coating combines firmly with the workpiece substrate, has high hardness, high wear resistance and excellent corrosion resistance. At the same time, due to the strict control of various parameters in the process, the uniformity and stability of the coating can be ensured, meeting the requirements of precision instruments, etc. for a non-magnetic environment and high-quality coatings, and improving the service life and reliability of the workpiece in different working environments.

[0034] Optionally, the activation solution comprises an aqueous solution of methanesulfonic acid with a mass concentration of 2 - 5%.

[0035] Optionally, the passivation solution comprises a molybdate solution with a concentration of 5 - 15 g / L.

[0036] In summary, the present application has the following beneficial effects:

[0037] 1. Since the present application uses nickel sulfate as the nickel source and sodium hypophosphite as the reducing agent, combined with a complexing agent to chelate nickel ions and inhibit the co-deposition of impurities, and a stabilizer to prevent the accumulation of harmful impurities, ensuring that the coating contains only non-magnetic nickel-phosphorus alloy, eliminating magnetic field interference from the source and meeting the strict requirements of precision instruments for a non-magnetic environment; no highly toxic heavy metal additives are used, and the service life of the plating solution is extended and waste liquid discharge is reduced through the complexing agent and stabilizer, reducing the environmental protection treatment cost and conforming to the trend of green manufacturing; the complexing agent regulates the release rate of nickel ions, the brightener improves the leveling property of the plating solution, and the stabilizer maintains the reaction stability, and the three work together to achieve uniform plating on the surface of complex workpieces.

[0038] 2. In the present application, lactic acid, citric acid, and HEDP are preferably used as complexing agents to chelate nickel ions and inhibit the co-deposition of impurities, combined with cerium nitrate / silane coupling agent stabilizers to inhibit the decomposition of the plating solution, refine the grains, and enhance the interfacial adhesion. At the same time, propargyl alcohol ethoxy compound / 2-mercaptobenzimidazole brighteners are used to level the coating and reduce pinholes, and polyether-modified silicone is innovatively introduced to further defoam, reduce the surface tension, improve the coating uniformity of complex workpieces, and reduce the porosity.

[0039] 3. The method of the present application ensures the cleanliness and activity of the substrate through surface pretreatment, and promotes the uniform deposition of complex workpieces by combining the control of the pH and temperature of the plating solution; the innovative two-stage heat treatment improves the hardness of the coating and reduces the porosity, and at the same time forms a stable Ni-P-B structure through phase transformation. Detailed Embodiments

[0040] The following further elaborates on the present application in conjunction with embodiments. It should be specifically noted that: for those not specifying specific conditions in the following embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. Except for special instructions, the raw materials used in the following embodiments can all be obtained from ordinary commercial sources.

[0041] Preparation Example of Polyether-Modified Silicone

[0042] Preparation Example 1

[0043] A preparation method of polyether-modified silicone:

[0044] Material preparation: The hydrogen-containing silicone oil is industrial grade with a hydrogen content of 0.15%; the relative molecular mass of allyl polyoxyethylene ether is 1000; the platinum catalyst is a chloroplatinic acid-isopropanol solution with a platinum content of 2%; the activated carbon is of analytical grade;

[0045] Add 5 kg of hydrogen-containing silicone oil into a sealed container. Turn on the stirrer and set the stirring speed to 200 revolutions per minute to fully mix the hydrogen-containing silicone oil evenly.

[0046] Introduce nitrogen into the reaction vessel to displace all the air inside the vessel to create an inert reaction environment. Meanwhile, turn on the heating device, heat the hydrogen-containing silicone oil to 90 °C, and maintain this temperature.

[0047] Weigh 3 kg of allyl polyoxyethylene ether, slowly add it to the reaction vessel, then add 0.05 kg of platinum catalyst, and continue to maintain the reaction temperature at 90 °C. The reaction lasts for 6 hours. During this period, analyze the conversion rate of the Si-H bond using a gas chromatograph every 1 hour. When the conversion rate of the Si-H bond reaches over 95%, the reaction is determined to be complete.

[0048] Stop heating and let the reaction system cool naturally to 25 °C.

[0049] Add 0.1 kg of activated carbon to the reaction system, adjust the stirring speed to 100 revolutions per minute, and stir for 2 hours to allow the activated carbon to fully adsorb impurities.

[0050] Filter the reaction product using a sintered glass funnel to remove the activated carbon and other insoluble impurities.

[0051] Transfer the filtered product to a vacuum distillation device, control the distillation temperature at 100 °C and the vacuum degree at 0.09 MPa, carry out vacuum distillation, collect the distilled product, and obtain polyether-modified silicone.

[0052] Example 1

[0053] A deposition process for non-magnetic electroless nickel:

[0054] Treat the workpiece to be plated with an alkaline degreaser containing 50 g / L NaOH, 30 g / L sodium carbonate, and 5 g / L surfactant at a temperature of 65 °C for 10 minutes of workpiece immersion. Then, use a 15% hydrochloric acid solution by mass to clean the rust on the workpiece surface. After rust removal, wash the workpiece with water. Place the workpiece to be plated after water washing into a 4% methanesulfonic acid activation solution by mass concentration for 3 minutes of activation. After activation, carry out water washing again;

[0055] Add the plating solution to the plating bath and stir it with a stirrer. Control the stirring speed at 80 revolutions per minute. Add a 10% sulfuric acid solution or a 20% ammonia water solution by mass concentration to the plating solution to adjust the pH value of the plating solution within the range of 4.5 - 5.5, and heat the plating solution to 85 °C;

[0056] Nickel sulfate, sodium hypophosphite, complexing agent, brightening agent, and stabilizer were successively added to deionized water. After stirring and mixing evenly, a plating solution was obtained. The concentrations of each component in the plating solution were as follows: nickel sulfate 20 g / L, sodium hypophosphite 20 g / L, complexing agent 10 g / L, brightening agent 0.5 ml / L, stabilizer 1 g / L; among them, lactic acid was selected as the complexing agent, cerium nitrate was selected as the stabilizer, and propargyl alcohol ethoxy compound (purchased from Macklin Reagent, model P831321) was selected as the brightening agent;

[0057] The workpiece to be plated was placed in the plating bath, and the stirrer stirred the plating solution at a speed of 200 revolutions per minute for 1 - 3 h to deposit a coating on the workpiece;

[0058] After the plating was completed, the workpiece was taken out of the plating bath and washed with water. The washed workpiece was placed in a heat treatment furnace. Starting from room temperature of 25 °C, the workpiece was heated to 250 ± 5 °C at a heating rate of 8 ± 2 °C per minute. After reaching the set temperature, it was kept warm for 4 hours, and then cooled in the furnace to 25 °C;

[0059] Then the workpiece was quickly heated to 450 °C at a heating rate of 25 °C per minute, taken out after holding for 20 minutes, and naturally cooled to 25 °C in the air;

[0060] The heat-treated workpiece was placed in a passivation solution. The passivation solution was a 10 g / L molybdate solution. The temperature of the passivation solution was 45 °C, and the passivation time was 5 minutes. After passivation, the workpiece was washed with water, and the washed workpiece was placed in a drying device and dried at a low temperature of 70 °C.

[0061] Example 2

[0062] A deposition process for non-magnetic electroless nickel: The difference from Example 1 is that the concentrations of each component in the plating solution are as follows: nickel sulfate 30 g / L, sodium hypophosphite 30 g / L, complexing agent 20 g / L, brightening agent 2 ml / L, stabilizer 3 g / L.

[0063] Example 3

[0064] A deposition process for non-magnetic electroless nickel: The difference from Example 1 is that the concentrations of each component in the plating solution are as follows: nickel sulfate 25 g / L, sodium hypophosphite 27 g / L, complexing agent 13 g / L, brightening agent 1.2 ml / L, stabilizer 2.2 g / L.

[0065] Example 4

[0066] A deposition process for non-magnetic electroless nickel: The difference from Example 3 is that citric acid is selected as the complexing agent.

[0067] Example 5

[0068] A deposition process of non-magnetic electroless nickel: The difference from Example 3 is that the complexing agent is hydroxyethylidene diphosphonic acid.

[0069] Example 6

[0070] A deposition process of non-magnetic electroless nickel: The difference from Example 3 is that the complexing agent is a mixture of lactic acid and hydroxyethylidene diphosphonic acid with a mass ratio of 1:1.

[0071] Example 7

[0072] A deposition process of non-magnetic electroless nickel: The difference from Example 3 is that the stabilizer is a silane coupling agent (Macklin reagent, model A800524).

[0073] Example 8

[0074] A deposition process of non-magnetic electroless nickel: The difference from Example 3 is that the brightener is 2-mercaptobenzimidazole.

[0075] Example 9

[0076] A deposition process of non-magnetic electroless nickel: The difference from Example 3 is that the brightener is polyether-modified silicone, and the polyether-modified silicone is prepared by Preparation Example 1.

[0077] Example 10

[0078] A deposition process of non-magnetic electroless nickel: The difference from Example 3 is that the concentrations of each component in the plating solution are as follows: nickel sulfate 25 g / L, sodium hypophosphite 27 g / L, complexing agent 13 g / L, brightener 1.2 ml / L, stabilizer 2.2 g / L, sodium borohydride 0.3 g / L.

[0079] Example 11

[0080] A deposition process of non-magnetic electroless nickel: The difference from Example 10 is that the concentrations of each component in the plating solution are as follows: nickel sulfate 25 g / L, sodium hypophosphite 27 g / L, complexing agent 13 g / L, brightener 1.2 ml / L, stabilizer 2.2 g / L, sodium borohydride 0.1 g / L.

[0081] Example 12

[0082] A deposition process of non-magnetic electroless nickel: The difference from Example 10 is that the concentrations of each component in the plating solution are as follows: nickel sulfate 25 g / L, sodium hypophosphite 27 g / L, complexing agent 13 g / L, brightener 1.2 ml / L, stabilizer 2.2 g / L, sodium borohydride 0.5 g / L.

[0083] Example 13

[0084] A deposition process of non-magnetic electroless nickel: The difference from Example 3 is that the activation solution includes a dilute sulfuric acid solution with a mass concentration of 4%.

[0085] Example 14

[0086] A deposition process of non-magnetic electroless nickel: The difference from Example 3 is that the passivation solution includes a phytic acid solution with a concentration of 10 g / L.

[0087] Comparative Example 1

[0088] A deposition process of non-magnetic electroless nickel: The difference from Example 3 is that the concentrations of each component in the plating solution are as follows: nickel sulfate 15 g / L, sodium hypophosphite 15 g / L, complexing agent 5 g / L, brightener 0.1 ml / L, stabilizer 0.5 g / L.

[0089] Comparative Example 2

[0090] A deposition process of non-magnetic electroless nickel: The difference from Example 3 is that the concentrations of each component in the plating solution are as follows: nickel sulfate 35 g / L, sodium hypophosphite 35 g / L, complexing agent 25 g / L, brightener 2.5 ml / L, stabilizer 3.5 g / L.

[0091] Comparative Example 3

[0092] A deposition process of non-magnetic electroless nickel: The difference from Example 3 is that no heat treatment operation is performed after the plating is completed.

[0093] Comparative Example 4

[0094] A deposition process of non-magnetic electroless nickel: The difference from Example 3 is that after the plating is completed, the workpiece is taken out of the plating bath and washed with water. The washed workpiece is put into a heat treatment furnace. Starting from room temperature of 25 °C, the workpiece is heated to 250 ± 5 °C at a heating rate of 8 ± 2 °C / minute. After reaching the set temperature, it is kept warm for 4 hours, and then cooled in the furnace to 25 °C. Immediately, it enters the passivation step without performing the second heat treatment;

[0095] The heat-treated workpiece is put into a passivation solution. The passivation solution is a molybdate solution with a concentration of 10 g / L. The temperature of the passivation solution is 45 °C, and the passivation time is 5 minutes. After the passivation is completed, the workpiece is washed with water, and the washed workpiece is put into a drying device for low-temperature drying at 70 °C.

[0096] Performance detection test

[0097] In Examples 1-14 and Comparative Examples 1-2 of this application, a vibrating sample magnetometer (VSM) was used to detect the coating. When the saturation magnetization intensity ≤ 0.1 emu / g, it indicates that it will not interfere with the performance of precision instruments.

[0098] Place the plated workpiece on the sample stage of an X-ray fluorescence spectrometer. Select 10 different measurement points on the coating surface of the workpiece. The measurement points are evenly distributed on the coating surface, including positions such as the edges, corners, and center of the workpiece. Use the X-ray fluorescence spectrometer to measure each measurement point and obtain the coating thickness data at that point. Calculate the standard deviation of the coating thicknesses of the multiple measured points.

[0099] Table 1 Detection Data

[0100] Saturation magnetization / emu / g Standard deviation of coating thickness / μm Example 1 0.0638 0.68 Example 2 0.0646 0.62 Example 3 0.0620 0.58 Example 4 0.0728 0.77 Example 5 0.0627 0.64 Example 6 0.0433 0.53 Example 7 0.0739 0.67 Example 8 0.0874 0.60 Example 9 0.0599 0.50 Example 10 0.0369 0.48 Example 11 0.0394 0.51 Example 12 0.0380 0.49 Example 13 0.0708 0.80 Example 14 0.0855 0.82 Comparative Example 1 0.1881 1.94 Comparative Example 2 0.1369 1.97 Comparative Example 3 0.0976 1.32 Comparative Example 4 0.0859 1.67

[0101] Combining Example 3 and Comparative Examples 1-2 and referring to Table 1, it can be seen that in Comparative Example 1, the nickel ions and sodium hypophosphite are insufficient, resulting in residual iron impurities in the coating (the saturation magnetization intensity exceeds the standard), slow deposition rate, and uneven thickness. In Comparative Example 2, the viscosity of the plating solution increases, the mass transfer efficiency decreases, and local supersaturation triggers spontaneous decomposition, forming coarse grains (the thickness standard deviation increases). The concentration range of this application ensures non-magnetic properties and uniformity by balancing the reaction rate and impurity control.

[0102] Combining Example 3 and Comparative Examples 3-4 and referring to Table 1, it can be seen that the first-stage heat treatment eliminates the internal stress in the coating. However, if the second stage is missing, there are still amorphous defects in the coating, resulting in an increase in magnetization intensity. The second-stage heat treatment promotes the formation of the Ni3P phase, refines the grains, reduces the porosity, and at the same time releases the residual stress, improving the uniformity. The two-stage heat treatment ensures non-magnetic properties and structural stability through the synergistic effect of phase transformation and stress regulation.

[0103] Combining Examples 1-3 and referring to Table 1, it can be seen that the molar ratio of nickel sulfate to sodium hypophosphite in Example 3 is close to 1:2, which promotes the synchronous consumption of Ni 2+ and H 2 PO2 - , reducing residual impurities. The optimized ratio of the complexing agent and the stabilizer enhances the complexing stability of Ni 2+ and inhibits the co-deposition of non-magnetic impurities.

[0104] Combining Examples 3-9 and referring to Table 1, it can be seen that lactic acid and HEDP form a gradient complexing system, and the release rate of Ni 2+ is more uniform, inhibiting the co-deposition of magnetic impurities. In Example 9, the polyether-modified silicone reduces the surface tension to 28 mN / m, promotes deep-hole penetration, and the thickness standard deviation drops to 0.50 μm. Although the silane coupling agent enhances the bonding force, cerium nitrate is superior in inhibiting the decomposition of the plating solution and refining the grains.

[0105] Combining Example 3 and Examples 10-12 and referring to Table 1, it can be seen that the role of sodium borohydride: as the second reducing agent, it synergistically with sodium hypophosphite to increase Ni 2+Reduction rate, forming a ternary Ni-P-B alloy, inhibiting the adsorption of iron impurities (significantly reducing the saturation magnetization). The concentration of 0.3 g / L is the best. Excessive concentration leads to violent reaction, increased local hydrogen evolution, and affects the uniformity.

[0106] Combining Example 3 with Examples 13 - 14 and Table 1, it can be seen that methanesulfonic acid has lower corrosivity to the substrate than sulfuric acid, reducing iron ion pollution. The passivation film formed by molybdate is denser than that formed by phytic acid, and has better corrosion resistance.

[0107] This specific embodiment is only an interpretation of the present application, and it does not limit the present application. After reading this specification, those skilled in the art can make modifications to this embodiment without creative contributions as needed, but as long as it is within the scope of the claims of the present application, it is protected by the patent law.

Claims

1. A deposition process for non-magnetic electroless nickel, characterized in that, It includes the following steps: Degrease, derust and wash the surface of the workpiece to be plated. Put the washed workpiece to be plated into the activation solution for 1 - 5 minutes of activation. After activation, wash it again; Add plating solution to the plating bath and stir. Control the stirring speed at 50 - 100 revolutions per minute. Add an acidic regulator or a basic regulator to the plating solution to adjust the pH value of the plating solution to 4.5 - 5.

5. Heat the plating solution to 80 - 90 °C; Put the workpiece to be plated into the plating bath and stir the plating solution at a speed of 100 - 300 revolutions per minute for 1 - 3 h; After the plating is completed, take out the workpiece from the plating bath and wash it. Put the washed workpiece into the heat treatment furnace, heat it up to 200 - 300 °C, and control the heating rate at 5 - 10 °C per minute. After reaching the set temperature, keep it warm for 2 - 6 hours, and then cool it in the furnace to 25 °C; Then quickly heat up the workpiece at a heating rate of 20 - 30 °C per minute to 400 - 500 °C. After keeping it warm for 15 - 30 minutes, take out the workpiece and cool it in the air; Put the heat-treated workpiece into the passivation solution. The temperature of the passivation solution is 30 - 60 °C, and the passivation time is 3 - 10 minutes. After passivation, wash the workpiece, and dry the washed workpiece at 60 - 80 °C; The composition of the plating solution includes 20 - 30 g / L of nickel sulfate, 20 - 30 g / L of sodium hypophosphite, 10 - 20 g / L of complexing agent, 0.5 - 2 ml / L of brightener, 1 - 3 g / L of stabilizer, 0.1 - 0.5 g / L of sodium borohydride, and the rest is water; The complexing agent includes one or more of lactic acid, citric acid, and hydroxyethylidene diphosphonic acid; The brightener includes polyether-modified silicone. The preparation method of the polyether-modified silicone is: Add hydrogen-containing silicone oil to the reaction vessel and continuously stir at a stirring speed of 200 - 300 revolutions per minute. Pass nitrogen into the reaction vessel, heat the hydrogen-containing silicone oil to 80 - 120 °C and keep it warm; Add allyl polyoxyethylene ether into the reaction vessel, and then add a platinum catalyst into the reaction vessel. Keep the reaction temperature at 80 - 120 °C and react for 2 - 6 hours. Analyze the conversion rate of Si-H bonds with a gas chromatograph. When the conversion rate reaches more than 95%, the reaction is completed; After the reaction is completed, stop heating, let the reaction system cool naturally to 25 °C. Add activated carbon to the reaction system. The dosage of activated carbon is 1 - 5% of the mass of the reaction product, and stir for 1 - 2 hours. Filter the reaction product to remove activated carbon and other insoluble impurities. Subject the filtered product to vacuum distillation. Control the distillation temperature at 80 - 120 °C and the vacuum degree at 0.09 - 0.1 MPa. Collect the distilled product to obtain polyether-modified silicone.

2. The deposition process of non-magnetic electroless nickel according to claim 1, characterized in that: The stabilizer includes one of cerium nitrate or silane coupling agent.

3. The deposition process of non-magnetic electroless nickel according to claim 1, characterized in that: The brightener also includes one of propargyl alcohol ethoxy compound or 2-mercaptobenzimidazole.

4. The deposition process of non-magnetic electroless nickel according to claim 1, characterized in that: The activation solution includes an aqueous solution of methanesulfonic acid with a mass concentration of 2 - 5%.

5. The deposition process of non-magnetic electroless nickel according to claim 1, wherein: The passivation solution includes a molybdate solution with a concentration of 5 - 15 g / L.