A chemical nickel plating process for ultra-large diameter diamond surfaces

Abstract

This invention relates to the field of diamond raw material processing technology, and in particular to a chemical nickel plating process for ultra-large diameter diamonds. The process comprises the following steps: First, the diamond is subjected to alkaline degreasing → hydrochloric acid roughening → sensitization → activation → sodium hypophosphite reduction. For chemical nickel plating: a main chemical nickel plating solution is prepared using 25-35 g / L sodium citrate, 25-40 g / L sodium hypophosphite, 8-16 g / L lactic acid, 5-10 mL / L ammonia, and 40-55 mL / L nickel aminosulfonate. The pH is adjusted to 8.5-9.5 with ammonia. The pretreated diamond is then added, and the mixture is continuously stirred for 40-90 minutes using a non-contact electromagnetic stirrer. During stirring, the chemical nickel plating solution is replenished. Finally, the diamond is rinsed with water and dried. This invention uniformly deposits a dense and firmly bonded metal transition layer on the surface of large-particle diamonds, completely changing the inert characteristics of the diamond surface and significantly improving the adhesion of diamond to steel wire surfaces.

Description

Technical Field

[0001] This invention relates to the field of diamond raw material processing technology, and in particular to a chemical nickel plating process for ultra-large diameter diamond surfaces. Background Technology

[0002] Diamond wire saws are core tools for large-size cutting in photovoltaic, semiconductor, hard and brittle materials, and stone processing. As the industry moves towards thicker workpieces, higher cutting efficiency, and lower wire breakage rates, large-diameter diamond coarse wire saws have become a key research and development area. Large-diameter diamonds with a particle size of 200μm, due to their large cutting edge, excellent wear resistance, and strong load-bearing capacity, can significantly improve the cutting depth and operational stability of coarse wire saws, making them a key abrasive for upgrading coarse wire products. The diamonds require surface chemical nickel plating for metallization modification to improve the interfacial adhesion with the steel wire substrate and the metal coating, preventing premature abrasive failure during cutting.

[0003] Currently, existing electroless nickel plating processes for diamonds are mainly focused on small to medium-sized diamonds with a particle size ≤100μm. They are not suitable for electroless nickel plating of large-sized diamonds with a particle size of 200μm. The main reasons are: small specific surface area, dense surface crystal planes, and large self-settling inertia. Using traditional nickel plating processes has the following defects: 1) Extremely poor coating uniformity: The active sites on the surface of large particles are unevenly distributed, with thicker coatings at edges / corners and thinner or even missed coatings at planes / crystal planes, resulting in large thickness differences within the same particle and poor batch consistency; 2) Severe agglomeration and adhesion: The high weight of the particles and rapid settling make it difficult for traditional stirring / dispersion methods to prevent particle contact, easily forming "sugar-coated" adhered particles, directly causing problems with wire sawing. 3) Low pretreatment activation efficiency: Large-diameter diamonds have dense surfaces and high chemical stability. Conventional roughening / sensitization / palladium activation processes are difficult to form uniform and continuous catalytic cores, often resulting in localized areas without coating or peeling of the coating; 4) Insufficient coating adhesion: The interface contact area is relatively reduced. If the pretreatment is not in place or the plating solution parameters are not matched, the nickel layer is easy to peel off in whole pieces under stress or thermal cycling conditions, which seriously affects the service life of the wire saw; 5) It is difficult to accurately control the weight gain rate and coating thickness: Large-diameter diamonds have a small specific surface area. The weight gain rate corresponding to the same coating thickness is significantly lower than that of fine particles. The traditional weight gain-thickness conversion model based on fine particles is completely invalid and cannot guide process control.

[0004] In summary, existing traditional electroless nickel plating processes are prone to problems such as uneven surface activation, large differences in coating thickness, localized missed plating, particle agglomeration and adhesion, and insufficient adhesion between the coating and the diamond substrate. These issues make it difficult to meet the stringent requirements of coarse wire saws for uniformity, dispersion, holding power, and batch consistency of the abrasive coating. Therefore, the inventors have provided an electroless nickel plating process for ultra-large diameter diamond surfaces. Summary of the Invention

[0005] To address the problem that existing electroless nickel plating processes for diamond cannot be adapted to electroless nickel plating of large-diameter diamonds with a particle size of 200μm, this invention provides an electroless nickel plating process for ultra-large-diameter diamond surfaces.

[0006] The present invention provides a chemical nickel plating process for ultra-large diameter diamond surfaces, which is achieved through the following technical solution:

[0007] A chemical nickel plating process for ultra-large diameter diamond surfaces includes the following steps:

[0008] S1, alkaline degreasing: the concentration of alkaline solution is 65-85g / L, the mass ratio of alkaline solution to diamond is (5-10):7, and the alkaline degreasing treatment is carried out at 60±5℃ for at least 30±5min under ultrasonic dispersion conditions, followed by washing with water 3 to 5 times.

[0009] S2, hydrochloric acid roughening: The concentration of hydrochloric acid solution is 30-210 g / L, and the mass ratio of hydrochloric acid solution to diamond is (8-12):7. At room temperature, the hydrochloric acid roughening treatment is carried out for at least 20±5 min under ultrasonic dispersion conditions, followed by washing with water until neutral.

[0010] S3, Sensitization: The sensitization solution contains 50-200 g / L stannous chloride and 25-75 g / L hydrochloric acid. The mass ratio of the sensitization solution to diamond is (8-12):7. Sensitize at room temperature under ultrasonic dispersion for at least 10-15 min, then wash with water until neutral.

[0011] S4, Activation: The activation solution contains 50-180 mg / L of palladium chloride, and the mass ratio of the activation solution to diamond is (8-12):7. Sensitize at room temperature for at least 5-8 minutes under ultrasonic dispersion conditions, and then wash with water 3-5 times.

[0012] S5, sodium hypophosphite reduction: The concentration of sodium hypophosphite solution is 100-250 mg / L, and the mass ratio of sodium hypophosphite solution to diamond is (8-12):7. Sensitize at room temperature under ultrasonic dispersion for at least 3-5 min, and then wash with water 3-5 times.

[0013] S6, Electroless Nickel Plating: Prepare the main electroless nickel plating solution using 25-35 g / L sodium citrate, 25-40 g / L sodium hypophosphite, 6-12 mL / L lactic acid, 5-10 mL / L ammonia, and 40-55 mL / L nickel sulfamate. Adjust the pH of the main electroless nickel plating solution to 8.5-9.5 with ammonia. Add diamond that has been reduced by sodium hypophosphite in S5. The mass ratio of diamond to the main electroless nickel plating solution is (20-25):1. Use non-contact electromagnetic stirring and stir continuously for 40-90 minutes. During stirring, add more electroless nickel plating solution to maintain the concentration of the solution. Rinse with deionized water until neutral. After drying, the ultra-large diameter diamond with nickel plating is obtained.

[0014] Preferably, the specific process of alkaline degreasing in S1 is as follows: Dissolve 500g of sodium hydroxide or potassium hydroxide in 5.0L of deionized water to obtain an alkaline mother liquor. Take 300-500mL of the alkaline mother liquor and add deionized water to adjust it to 500-1000mL. Under ultrasonic stirring or ultrasonic stirring and non-contact electromagnetic stirring, heat the water bath to 60±5℃, add 700g of diamond, and maintain the alkaline degreasing treatment under ultrasonic dispersion conditions or ultrasonic stirring and non-contact electromagnetic stirring for 30±5min. Then filter and rinse with deionized water 3-5 times.

[0015] Preferably, the specific process of S2 hydrochloric acid roughening is as follows: Take 100-300 mL of industrial hydrochloric acid with a concentration of 30-36%, add deionized water to adjust to 800-1000 mL, add diamond obtained by alkaline degreasing treatment in S1 under room temperature and ultrasonic stirring or ultrasonic stirring and non-contact electromagnetic stirring, maintain ultrasonic dispersion conditions or ultrasonic stirring and non-contact electromagnetic stirring for hydrochloric acid roughening treatment for 15-25 min, then filter, rinse multiple times with deionized water until the pH value of the cleaning solution is 6.8-7.0, and the hydrochloric acid roughening treatment is completed.

[0016] Preferably, the specific sensitization process in S3 is as follows: Take 500 mL of concentrated hydrochloric acid, add 500 g of stannous chloride and mix evenly to obtain a sensitization mother solution. Take 100-300 mL of the sensitization mother solution, add deionized water to adjust to 1000-1200 mL, and add diamond obtained by hydrochloric acid roughening treatment in S2 under room temperature and / or ultrasonic stirring and non-contact electromagnetic stirring. Maintain ultrasonic dispersion conditions or ultrasonic stirring and non-contact electromagnetic stirring for hydrochloric acid roughening treatment for 10-15 min, then filter and rinse multiple times with deionized water until the pH value of the washing solution is 6.8-7.0, thus completing the sensitization treatment of diamond.

[0017] Preferably, the specific activation process of S4 is as follows: 3g of palladium chloride is added to 5L of deionized water and mixed evenly to obtain an activation mother liquor. 100-300mL of the activation mother liquor is taken and deionized water is added to adjust it to 1000-1200mL. Under room temperature and / or ultrasonic stirring and non-contact electromagnetic stirring, diamond obtained by S3 sensitization treatment is added. The activation treatment is maintained under ultrasonic dispersion conditions or ultrasonic stirring and non-contact electromagnetic stirring for 5-8 minutes. Then, the mixture is filtered and rinsed with deionized water 3-5 times to complete the activation treatment of the diamond.

[0018] Preferably, the specific process for sodium hypophosphite reduction in step S5 is as follows: dilute a 20-25% industrial sodium hypophosphite solution to a 10-12% sodium hypophosphite mother liquor. Take 10-30 mL of the sodium hypophosphite mother liquor, add deionized water to adjust to 1000-1200 mL, and add step S4 for activation treatment to obtain diamond under room temperature and / or ultrasonic stirring and non-contact electromagnetic stirring. Maintain ultrasonic dispersion conditions or ultrasonic stirring and non-contact electromagnetic stirring for activation treatment for 3-5 minutes, then filter and rinse with deionized water 3-5 times to complete the sodium hypophosphite reduction treatment of diamond.

[0019] Preferably, the specific process for S6, electroless nickel plating, is as follows:

[0020] S6.1, Prepare the main solution for electroless nickel plating: Take sodium citrate: 400-500g, sodium hypophosphite: 400-600g, lactic acid: 100-200mL, ammonia water with a concentration of 9.5-10.5%: 80-150mL, nickel aminosulfonate: 600-800mL, add deionized water to 15L, then add ammonia water with a concentration of 14.5-15.5% to adjust the pH value to 8.9-9.5, and adjust the temperature to 30-45℃ to obtain the main solution for electroless nickel plating;

[0021] S6.2, add S5 sodium hypophosphite to the electroless nickel plating main solution for reduction treatment to obtain diamond. Use non-contact electromagnetic stirring and stir continuously for 40-90 minutes. During the stirring process, add electroless nickel plating solution to maintain the concentration of the electroless plating solution. Then rinse with deionized water until neutral and dry after completion.

[0022] Preferably, in step S6.2, sodium hypophosphite (S5) is added to the electroless nickel plating main solution for reduction treatment to obtain diamond. The diamond is then pre-dispersed for 30-90 seconds at 30-45℃ with ultrasonic stirring at a frequency of 20-60kHz and a power of 400-900W. Afterward, non-contact electromagnetic stirring is used for continuous stirring for 40-90 minutes. During the stirring process, the electroless nickel plating solution is replenished to maintain the concentration of the electroless plating solution. The solution is then rinsed with deionized water until neutral. After the process is completed, the diamond is dried to obtain ultra-large diameter diamond with a nickel-plated surface.

[0023] Pre-ultrasonic stirring can disperse large diamond particles evenly, which helps improve the uniformity and density of the electroless nickel plating layer and greatly enhances the adhesion of diamond to the steel wire surface.

[0024] Preferably, the parameters of the non-contact electromagnetic stirring are as follows: the stirring rod is driven to rotate under the conditions of magnetic field frequency of 10-30Hz and magnetic induction intensity of 0.2-0.5T, and the rotation speed of the stirring rod is 100-300rpm.

[0025] Preferably, the preparation method of the electroless nickel plating replenishment solution is as follows: Take sodium citrate: 450-1200g, sodium hypophosphite: 450-1000g / L, lactic acid: 45-200mL / L, ammonia water: 450-1600mL / L, nickel aminosulfonate: 1500-3000mL / L, thiourea: 0.8-1.2mL, add deionized water to 15-20L, mix evenly to obtain the electroless nickel plating replenishment solution, wherein the replenishment amount of the electroless nickel plating replenishment solution is 15-20L.

[0026] In summary, the present invention has the following advantages:

[0027] 1. This invention utilizes a fully optimized chemical plating pretreatment process—degreasing, roughening, sensitization, activation, and reduction—specifically designed for large-diameter diamonds with a particle size of 200μm. This process uniformly deposits a dense and firmly bonded metal transition layer on the diamond surface, completely altering the inert characteristics of the diamond surface. This achieves a dual anchoring effect of chemical metallurgical bonding and physical interlocking between the diamond and the metal plating layer and the steel wire substrate, significantly improving the adhesion strength of the diamond to the steel wire surface and eliminating the problem of diamond shedding and detachment at its source.

[0028] 2. The large-diameter diamonds treated with the chemical nickel plating process provided by this invention adhere more evenly and are positioned more precisely on the steel wire surface. The plating layer provides stronger support for the diamonds, ensuring that the diamond crystals remain intact during cutting, preventing breakage and uneven wear. This allows the diamonds to maintain a sharp cutting edge. Compared to traditional bare powder wire, this patented product has stronger cutting penetration and more stable cutting efficiency. It is suitable for high-speed cutting of large-sized, high-hardness, and brittle materials, effectively avoiding defects such as wire marks, chipping, and cutting jams during the cutting process, and significantly improving the cutting yield and processing accuracy.

[0029] 3. Traditional bare powder-coated steel wire is prone to premature detachment and failure due to poor diamond adhesion, resulting in short product lifespan, high replacement frequency, and significantly increased consumable costs and downtime losses. This invention strengthens diamond adhesion through chemical plating, effectively reducing diamond loss and detachment, and fully utilizing the cutting performance of diamond. Under the same working conditions, the continuous service life of the diamond wire is greatly extended, reducing the frequency of consumable replacement, lowering user cutting production costs, and improving the continuity and economy of production operations.

[0030] 4. The process of this invention is suitable for large-scale production of large-diameter diamonds. The process is highly versatile and practical. The entire process adopts a standardized production mode of tank opening and quantitative replenishment. It is easy to operate and highly controllable. It can be directly adapted to industrial mass production and has extremely high industrial application value and promotion potential.

[0031] 5. The metal layer deposited on the diamond surface by the process of this invention has high density, low internal stress, wear resistance, and corrosion resistance. It can not only strengthen the bonding force of diamond, but also protect the diamond particles, preventing the diamond from being damaged by environmental erosion and external impact during storage, transportation, and cutting, and further improving the overall quality and durability of diamond steel wire. Attached Figure Description

[0032] Figure 1 This is an electron microscope image of the nickel-plated ultra-large diameter diamond prepared by the electroless nickel plating process in Example 1, with a scale bar of 500 μm.

[0033] Figure 2 This is an electron microscope image of the nickel-plated ultra-large diamond prepared by the electroless nickel plating process in Example 1, with a scale bar of 200 μm.

[0034] Figure 3 This is an electron microscope image of the nickel-plated ultra-large diamond prepared by the electroless nickel plating process in Example 2, with a scale bar of 500 μm.

[0035] Figure 4 This is an electron microscope image of the nickel-plated ultra-large diamond prepared by the electroless nickel plating process in Example 2, with a scale bar of 200 μm.

[0036] Figure 5 This is an electron microscope image of the nickel-plated ultra-large diamond prepared by the electroless nickel plating process in Example 3, with a scale bar of 500 μm.

[0037] Figure 6 This is an electron microscope image of the nickel-plated ultra-large diamond prepared by the electroless nickel plating process in Example 3, with a scale bar of 200 μm.

[0038] Figure 7 This is an electron microscope image of the nickel-plated ultra-large diameter diamond prepared by the electroless nickel plating process in Example 4, with a scale bar of 500 μm.

[0039] Figure 8 This is an electron microscope image of the nickel-plated ultra-large diamond prepared by the electroless nickel plating process in Example 4, with a scale bar of 200 μm.

[0040] Figure 9 This is an electron microscope image of the nickel-plated ultra-large diamond prepared by electroless nickel plating on the surface of ultra-large diamond in Comparative Example 1. The scale bar is 500 μm.

[0041] Figure 10This is an electron microscope image of the nickel-plated ultra-large diamond prepared by electroless nickel plating on the surface of ultra-large diamond in Comparative Example 1. The scale bar is 200 μm.

[0042] Figure 11 This is an electron microscope image of the nickel-plated ultra-large diamond prepared by electroless nickel plating on the surface of ultra-large diamond in Comparative Example 2. The scale bar is 500 μm.

[0043] Figure 12 This is an electron microscope image of the nickel-plated ultra-large diamond prepared by electroless nickel plating process on the surface of ultra-large diamond in Comparative Example 2. The scale bar is 200 μm. Detailed Implementation

[0044] To further understand the inventiveness and technical advancements of this invention, the preferred embodiments of this invention will be discussed in detail below with reference to examples and comparative examples.

[0045] Example: The steps of a chemical nickel plating process for ultra-large diameter diamond surfaces are as follows:

[0046] S1, alkaline degreasing: the concentration of alkaline solution is 65-85g / L, the mass ratio of alkaline solution to diamond is (5-10):7, and the alkaline degreasing treatment is carried out at 60±5℃ for at least 30±5min under ultrasonic dispersion conditions, followed by washing with water 3 to 5 times.

[0047] Specifically, S1, the alkaline degreasing process is as follows: Dissolve 500g of sodium hydroxide or potassium hydroxide in 5.0L of deionized water to obtain an alkaline mother liquor. Take 300-500mL of the alkaline mother liquor and add deionized water to adjust it to 500-1000mL. Under ultrasonic stirring or ultrasonic stirring and non-contact electromagnetic stirring, heat the water bath to 60±5℃, add 700g of diamond, and maintain the alkaline degreasing treatment under ultrasonic dispersion conditions or ultrasonic stirring and non-contact electromagnetic stirring for 30±5min. Then filter and rinse with deionized water 3-5 times.

[0048] S2, hydrochloric acid roughening: The concentration of hydrochloric acid solution is 30-210 g / L, and the mass ratio of hydrochloric acid solution to diamond is (8-12):7. At room temperature, the hydrochloric acid roughening treatment is carried out for at least 20±5 min under ultrasonic dispersion conditions, followed by washing with water until neutral.

[0049] Specifically, the S2 hydrochloric acid roughening process is as follows: Take 100-300 mL of industrial hydrochloric acid with a concentration of 30-36%, add deionized water to adjust to 800-1000 mL, add diamond obtained by S1 alkaline degreasing treatment under room temperature and ultrasonic stirring or ultrasonic stirring and non-contact electromagnetic stirring, maintain ultrasonic dispersion conditions or ultrasonic stirring and non-contact electromagnetic stirring for hydrochloric acid roughening treatment for 15-25 min, then filter, rinse multiple times with deionized water until the pH of the cleaning solution is 6.8-7.0, and the hydrochloric acid roughening treatment is completed;

[0050] S3, Sensitization: The sensitization solution contains 50-200 g / L stannous chloride and 25-75 g / L hydrochloric acid. The mass ratio of the sensitization solution to diamond is (8-12):7. Sensitize at room temperature under ultrasonic dispersion for at least 10-15 min, then wash with water until neutral.

[0051] Specifically, the S3 sensitization process is as follows: Take 500 mL of concentrated hydrochloric acid, add 500 g of stannous chloride and mix well to obtain a sensitization mother solution. Take 100-300 mL of the sensitization mother solution and add deionized water to adjust it to 1000-1200 mL. Under room temperature and / or ultrasonic stirring and non-contact electromagnetic stirring, add diamond obtained by S2 hydrochloric acid roughening treatment. Maintain ultrasonic dispersion conditions or ultrasonic stirring and non-contact electromagnetic stirring for hydrochloric acid roughening treatment for 10-15 min. Then filter and rinse multiple times with deionized water until the pH of the washing solution is 6.8-7.0. The sensitization treatment of diamond is then completed.

[0052] S4, Activation: The activation solution contains 50-180 mg / L of palladium chloride, and the mass ratio of the activation solution to diamond is (8-12):7. Sensitize at room temperature for at least 5-8 minutes under ultrasonic dispersion conditions, and then wash with water 3-5 times.

[0053] Specifically, the activation process for S4 is as follows: Add 3g of palladium chloride to 5L of deionized water and mix well to obtain an activation mother liquor. Take 100-300mL of the activation mother liquor and add deionized water to adjust it to 1000-1200mL. Add the diamond obtained after S3 sensitization treatment at room temperature and / or under ultrasonic stirring and non-contact electromagnetic stirring. Maintain ultrasonic dispersion conditions or under ultrasonic stirring and non-contact electromagnetic stirring for 5-8 minutes for activation treatment. Then filter and rinse with deionized water 3-5 times to complete the activation treatment of diamond.

[0054] S5, sodium hypophosphite reduction: The concentration of sodium hypophosphite solution is 100-250 mg / L, and the mass ratio of sodium hypophosphite solution to diamond is (8-12):7. Sensitize at room temperature under ultrasonic dispersion for at least 3-5 min, and then wash with water 3-5 times.

[0055] Specifically, the S5 sodium hypophosphite reduction process is as follows: Dilute the 20-25% industrial sodium hypophosphite solution to a 10-12% sodium hypophosphite mother liquor. Take 10-30 mL of the sodium hypophosphite mother liquor, add deionized water to adjust to 1000-1200 mL, and add S4 for activation treatment to obtain diamond under room temperature and / or ultrasonic stirring and non-contact electromagnetic stirring. Maintain ultrasonic dispersion conditions or activation treatment under ultrasonic stirring and non-contact electromagnetic stirring for 3-5 min, then filter and rinse with deionized water 3-5 times to complete the sodium hypophosphite reduction treatment of diamond.

[0056] S6, Electroless Nickel Plating: Prepare the main electroless nickel plating solution according to 25-35 g / L sodium citrate, 25-40 g / L sodium hypophosphite, 6-12 mL / L lactic acid, 5-10 mL / L ammonia, and 40-55 mL / L nickel sulfamate. Adjust the pH of the main electroless nickel plating solution to 8.5-9.5 with ammonia. Add diamond that has been reduced by sodium hypophosphite in S5. The mass ratio of diamond to the main electroless nickel plating solution is (20-25):1. Use non-contact electromagnetic stirring and stir continuously for 40-90 minutes. During the stirring process, add electroless nickel plating solution to maintain the concentration of the electroless plating solution. Then rinse with deionized water until neutral. After the process is completed, dry to obtain ultra-large diameter diamond with nickel plating on the surface.

[0057] Specifically, the S6 electroless nickel plating process is as follows:

[0058] S6.1, Prepare the main solution for electroless nickel plating: Take sodium citrate: 400-500g, sodium hypophosphite: 400-600g, lactic acid: 100-200mL, ammonia water with a concentration of 9.5-10.5%: 80-150mL, nickel aminosulfonate: 600-800mL, add deionized water to 15L, then add ammonia water with a concentration of 14.5-15.5% to adjust the pH value to 8.9-9.5, and adjust the temperature to 30-45℃ to obtain the main solution for electroless nickel plating;

[0059] Take sodium citrate: 450-1200g, sodium hypophosphite: 450-1000g / L, lactic acid: 45-200mL / L, ammonia water: 450-1600mL / L, nickel aminosulfonate: 1500-3000mL / L, thiourea: 0.8-1.2mL, add deionized water to 15-20L, mix well to obtain the chemical nickel plating replenishment solution;

[0060] S6.2, add S5 sodium hypophosphite to the electroless nickel plating main solution for reduction treatment to obtain diamond. Non-contact electromagnetic stirring is used, and the parameters of non-contact electromagnetic stirring are as follows: drive the stirring rod to rotate under the conditions of magnetic field frequency of 10-30Hz and magnetic induction intensity of 0.2-0.5T, the stirring rod speed is 100-300rpm, and stirring is continued for 40-90min. During the stirring process, the electroless nickel plating solution is added to maintain the concentration of the electroless nickel plating solution. The amount of electroless nickel plating solution added is 15-20L. After that, rinse with deionized water until neutral. After the end, dry to obtain ultra-large diameter diamond with nickel plating on the surface.

[0061] To improve the uniformity of diamond dispersion in electroless nickel plating solution, S5 sodium hypophosphite was added to the electroless nickel plating main solution for reduction treatment to obtain diamond. After obtaining diamond, it was pre-dispersed for 30-90s at 30-45℃ with ultrasonic stirring (ultrasonic frequency 20-60kHz, ultrasonic power 400-900W). Then, it was continuously stirred with non-contact electromagnetic stirring for 40-90min. During the stirring process, the electroless nickel plating solution was increased to maintain the concentration of the electroless plating solution. Afterwards, it was rinsed with deionized water until neutral. After the process was completed, it was dried to obtain ultra-large diamond particles with nickel plating on the surface.

[0062] Example 1: A chemical nickel plating process for ultra-large diameter diamond surfaces, the steps of which are as follows:

[0063] S1, Alkaline Degreasing: Dissolve 500g of sodium hydroxide or potassium hydroxide in 5.0L of deionized water to obtain an alkaline mother liquor. Take 300mL of the alkaline mother liquor and add deionized water to adjust it to 900mL. Under ultrasonic stirring, with an ultrasonic frequency of 40kHz and an ultrasonic power of 650W, heat the water bath to 60℃, add 700g of diamond with a particle size of 200μm, and maintain the ultrasonic dispersion (40kHz / 650W) for alkaline degreasing treatment for 30min. Then filter and rinse 5 times with deionized water.

[0064] S2, hydrochloric acid roughening: Take 200 mL of 36% industrial hydrochloric acid, add deionized water to adjust to 1000 mL, and under room temperature and ultrasonic stirring, ultrasonic frequency 40 kHz, ultrasonic power 650 W, add diamond obtained by S1 alkaline degreasing treatment, maintain ultrasonic dispersion (40 kHz / 650 W) for hydrochloric acid roughening treatment for 20 min, then filter, and rinse with deionized water eight times until the pH of the cleaning solution is 7.0, and the hydrochloric acid roughening treatment is completed;

[0065] S3, Sensitization: Take 500mL of concentrated hydrochloric acid, add 500g of stannous chloride and mix well to obtain a sensitization stock solution. Take 200mL of the sensitization stock solution, add deionized water to adjust to 1000mL, and add diamond obtained by S2 hydrochloric acid roughening treatment under room temperature and ultrasonic stirring at an ultrasonic frequency of 40kHz and an ultrasonic power of 650W. Maintain ultrasonic dispersion (40kHz / 650W) for hydrochloric acid roughening treatment for 12min, then filter and rinse with deionized water eight times until the pH of the washing solution is 7.0, thus completing the sensitization treatment of diamond.

[0066] S4, Activation: Add 3g of palladium chloride to 5L of deionized water and mix well to obtain an activation mother liquor. Take 150mL of the activation mother liquor and add deionized water to adjust it to 1200mL. Under room temperature and ultrasonic stirring, with an ultrasonic frequency of 40kHz and an ultrasonic power of 650W, add diamond obtained by S3 sensitization treatment. Maintain ultrasonic dispersion (40kHz / 650W) for 6min of activation treatment. Then filter and rinse 5 times with deionized water to complete the activation treatment of diamond.

[0067] S5, sodium hypophosphite reduction: Dilute the 24% industrial sodium hypophosphite solution to a 12% sodium hypophosphite mother liquor. Take 20 mL of the sodium hypophosphite mother liquor, add deionized water to adjust to 1000 mL, and add S4 for activation treatment at room temperature and ultrasonic stirring at an ultrasonic frequency of 40 kHz and an ultrasonic power of 650 W to obtain diamond. Maintain the ultrasonic dispersion conditions (40 kHz / 650 W) for activation treatment for 4 min, then filter and rinse with deionized water 5 times to complete the sodium hypophosphite reduction treatment of diamond.

[0068] The specific process for S6 electroless nickel plating is as follows:

[0069] S6.1, Prepare the main solution for electroless nickel plating: Take 480g of sodium citrate, 540g of sodium hypophosphite, 150mL of lactic acid, 100mL of 10% ammonia solution, and 720mL of nickel aminosulfonate. Add deionized water to 15.0L, then add 15.0% ammonia solution to adjust the pH to 9.2 and adjust the temperature to 40℃ to obtain the main solution for electroless nickel plating.

[0070] Take sodium citrate: 640g, sodium hypophosphite: 720g / L, lactic acid: 200mL / L, ammonia: 600mL / L, nickel aminosulfonate: 1600mL / L, thiourea: 1mL, add deionized water to 20L, mix well to obtain the chemical nickel plating replenishment solution;

[0071] S6.2, add S5 sodium hypophosphite to the electroless nickel plating solution for reduction treatment to obtain diamond. Pre-disperse the diamond for 90s at 40℃ with ultrasonic stirring (ultrasonic frequency 40kHz, ultrasonic power 650W), and then use non-contact electromagnetic stirring with the following parameters: drive the stirring rod to rotate at 120rpm under the conditions of magnetic field frequency 24Hz and magnetic induction intensity 0.5T, and continue stirring for 90min. During the stirring process, add electroless nickel plating solution to maintain the concentration of the electroless plating solution. The amount of electroless nickel plating solution added is 20L. Then rinse with deionized water until neutral. After the process, dry the diamond: vacuum dry at 120℃ for 6 hours and cool naturally to room temperature to obtain ultra-large diameter diamond with nickel plating on the surface.

[0072] The difference between Example 2 and Example 1 is as follows: S1, alkaline degreasing: 500g of sodium hydroxide or potassium hydroxide is dissolved in 5.0L of deionized water to obtain an alkaline mother liquor. 300mL of the alkaline mother liquor is taken, and deionized water is added to adjust it to 900mL. Under ultrasonic stirring and non-contact electromagnetic stirring, the ultrasonic stirring conditions are: ultrasonic frequency 40kHz, ultrasonic power 650W; the non-contact electromagnetic stirring conditions are: the stirring rod is driven to rotate under the conditions of magnetic field frequency 24Hz and magnetic induction intensity 0.5T, and the stirring rod speed is 120rpm; the water bath is heated to 60℃, 700g of diamond with a particle size of 200μm is added, and alkaline degreasing treatment is carried out for 30min under the condition of ultrasonic dispersion (40kHz / 650W), followed by filtration and rinsing with deionized water 5 times;

[0073] S2, Hydrochloric Acid Roughening: Take 200 mL of 36% industrial hydrochloric acid, add deionized water to adjust to 1000 mL, and stir at room temperature with ultrasonic stirring and non-contact electromagnetic stirring. Ultrasonic stirring conditions: ultrasonic frequency 40 kHz, ultrasonic power 650 W; non-contact electromagnetic stirring conditions: drive the stirring rod to rotate at a magnetic field frequency of 24 Hz and a magnetic induction intensity of 0.5 T, and the stirring rod speed is 120 rpm. Add diamond obtained by alkaline degreasing treatment in S1, and maintain ultrasonic dispersion (40 kHz / 650 W) for hydrochloric acid roughening treatment for 20 min. Then filter and rinse with deionized water eight times until the pH of the washing solution is 7.0 to complete the hydrochloric acid roughening treatment.

[0074] S3, Sensitization: Take 500mL of concentrated hydrochloric acid, add 500g of stannous chloride and mix well to obtain a sensitization mother solution. Take 200mL of the sensitization mother solution and add deionized water to adjust to 1000mL. Under room temperature ultrasonic stirring and non-contact electromagnetic stirring conditions: ultrasonic frequency 40kHz, ultrasonic power 650W; non-contact electromagnetic stirring conditions: drive the stirring rod to rotate under the conditions of magnetic field frequency 24Hz and magnetic induction intensity 0.5T, and the stirring rod speed is 120rpm. Add diamond obtained by S2 hydrochloric acid roughening treatment, maintain ultrasonic dispersion (40kHz / 650W) for hydrochloric acid roughening treatment for 12min, then filter, and rinse with deionized water eight times until the pH of the washing solution is 7.0, and the sensitization treatment of diamond is completed.

[0075] S4, Activation: Add 3g of palladium chloride to 5L of deionized water and mix well to obtain an activation mother liquor. Take 150mL of the activation mother liquor and add deionized water to adjust to 1200mL. Under room temperature ultrasonic stirring and non-contact electromagnetic stirring conditions: ultrasonic frequency 40kHz, ultrasonic power 650W; non-contact electromagnetic stirring conditions: drive the stirring rod to rotate under the conditions of magnetic field frequency 24Hz and magnetic induction intensity 0.5T, and the stirring rod speed is 120rpm. Add diamond obtained by S3 sensitization treatment and maintain ultrasonic dispersion (40kHz / 650W) for 6min activation treatment. Then filter and rinse 5 times with deionized water to complete the activation treatment of diamond.

[0076] S5, Sodium hypophosphite reduction: Dilute the 24% industrial sodium hypophosphite solution to a 12% sodium hypophosphite mother liquor. Take 20 mL of the sodium hypophosphite mother liquor and add deionized water to adjust to 1000 mL. Under room temperature and ultrasonic stirring and non-contact electromagnetic stirring conditions: ultrasonic frequency 40 kHz, ultrasonic power 650 W; non-contact electromagnetic stirring conditions: drive the stirring rod to rotate at a magnetic field frequency of 24 Hz and a magnetic induction intensity of 0.5 T, with a stirring rod speed of 120 rpm. Add S4 for activation treatment to obtain diamond. Maintain the activation treatment under ultrasonic dispersion conditions (40 kHz / 650 W) for 4 min, then filter and rinse with deionized water 5 times to complete the sodium hypophosphite reduction treatment of diamond. The remaining steps remain unchanged.

[0077] The difference between Example 3 and Example 1 is as follows: S5, sodium hypophosphite reduction: dilute the 24% concentration industrial sodium hypophosphite solution to a 10% concentration sodium hypophosphite mother liquor, take 10 mL of sodium hypophosphite mother liquor, add deionized water to adjust to 1200 mL, and under room temperature and ultrasonic stirring, ultrasonic frequency 40 kHz, ultrasonic power 650 W, add S4 activation treatment to obtain diamond, maintain ultrasonic dispersion conditions (40 kHz / 650 W) for activation treatment for 5 min, then filter, and rinse with deionized water 5 times to complete the sodium hypophosphite reduction treatment of diamond. The remaining steps are unchanged.

[0078] The difference between Example 4 and Example 1 is as follows: S5, sodium hypophosphite reduction: Dilute the 24% industrial sodium hypophosphite solution to a 12% sodium hypophosphite mother liquor. Take 30 mL of the sodium hypophosphite mother liquor, add deionized water to adjust to 1000 mL, and add it to the solution at room temperature and with ultrasonic stirring at a frequency of 40 kHz and an ultrasonic power of 650 W. Then add the solution to the activation treatment in S4 to obtain diamond. Maintain the activation treatment under ultrasonic dispersion conditions (40 kHz / 650 W) for 3 min, then filter and rinse with deionized water 5 times to complete the sodium hypophosphite reduction treatment of diamond. All other steps remain unchanged.

[0079] The difference between Comparative Example 1 and Example 1 lies in the chemical nickel plating process on the diamond surface, the steps of which are as follows:

[0080] S1, Alkaline Degreasing: Dissolve 500g of sodium hydroxide or potassium hydroxide in 5.0L of deionized water to obtain an alkaline mother liquor. Take 300mL of the alkaline mother liquor, add deionized water to adjust to 900mL, heat to 60℃ in a water bath with mechanical stirring at 100rpm, add 700g of diamond with a particle size of 200μm, maintain mechanical stirring for alkaline degreasing treatment for 30min, then filter and rinse 5 times with deionized water;

[0081] S2, hydrochloric acid roughening: Take 200 mL of 36% industrial hydrochloric acid, add deionized water to adjust to 1000 mL, add diamond obtained by S1 alkaline degreasing treatment under room temperature and mechanical stirring at 100 rpm, maintain mechanical stirring for hydrochloric acid roughening treatment for 20 min, then filter, rinse with deionized water eight times until the pH of the washing solution is 7.0, and the hydrochloric acid roughening treatment is completed;

[0082] S3, Sensitization: Take 500mL of concentrated hydrochloric acid, add 500g of stannous chloride and mix well to obtain a sensitization stock solution. Take 200mL of the sensitization stock solution, add deionized water to adjust to 1000mL, and add diamond obtained by S2 hydrochloric acid roughening treatment under room temperature and mechanical stirring at 100rpm. Maintain the mechanical stirring condition for hydrochloric acid roughening treatment for 12min, then filter and rinse with deionized water eight times until the pH of the washing solution is 7.0, and the sensitization treatment of diamond is completed.

[0083] S4, Activation: Add 3g of palladium chloride to 5L of deionized water and mix well to obtain an activation mother liquor. Take 150mL of the activation mother liquor and add deionized water to adjust it to 1200mL. Add diamond obtained by S3 sensitization treatment under mechanical stirring at 100rpm at room temperature. Maintain mechanical stirring for 6min of activation treatment. Then filter and rinse 5 times with deionized water to complete the activation treatment of diamond.

[0084] The specific process for S5 electroless nickel plating is as follows:

[0085] S5.1, Prepare the main solution for electroless nickel plating: Take 480g of sodium citrate, 540g of sodium hypophosphite, 150mL of lactic acid, 100mL of 10% ammonia solution, and 720mL of nickel aminosulfonate. Add deionized water to 15.0L, then add 15.0% ammonia solution to adjust the pH to 9.2 and adjust the temperature to 40℃ to obtain the main solution for electroless nickel plating.

[0086] Take sodium citrate: 640g, sodium hypophosphite: 720g / L, lactic acid: 200mL / L, ammonia: 600mL / L, nickel aminosulfonate: 1600mL / L, thiourea: 1mL, add deionized water to 20L, mix well to obtain the chemical nickel plating replenishment solution;

[0087] S5.2, add S4 to the electroless nickel plating main solution for activation treatment to obtain diamond. Stir continuously for 90 minutes with mechanical stirring at 100 rpm. During stirring, add electroless nickel plating solution to maintain the concentration of the electroless plating solution. The amount of electroless nickel plating solution added is 20L. Then rinse with deionized water until neutral. After completion, dry: vacuum dry at 120℃ for 6 hours, and cool naturally to room temperature to obtain ultra-large diameter diamond with nickel plating on the surface.

[0088] The difference between Comparative Example 2 and Example 1 lies in the chemical nickel plating process on the diamond surface, the steps of which are as follows:

[0089] S1, Alkaline Degreasing: Dissolve 500g of sodium hydroxide or potassium hydroxide in 5.0L of deionized water to obtain an alkaline mother liquor. Take 300mL of the alkaline mother liquor, add deionized water to adjust to 900mL, heat to 60℃ in a water bath with mechanical stirring at 100rpm, add 700g of diamond with a particle size of 200μm, maintain mechanical stirring for alkaline degreasing treatment for 30min, then filter and rinse 5 times with deionized water;

[0090] S2, hydrochloric acid roughening: Take 200 mL of 36% industrial hydrochloric acid, add deionized water to adjust to 1000 mL, add diamond obtained by S1 alkaline degreasing treatment under room temperature and mechanical stirring at 100 rpm, maintain mechanical stirring for hydrochloric acid roughening treatment for 20 min, then filter, rinse with deionized water eight times until the pH of the washing solution is 7.0, and the hydrochloric acid roughening treatment is completed;

[0091] S3, Sensitization: Take 500mL of concentrated hydrochloric acid, add 500g of stannous chloride and mix well to obtain a sensitization stock solution. Take 200mL of the sensitization stock solution, add deionized water to adjust to 1000mL, and add diamond obtained by S2 hydrochloric acid roughening treatment under room temperature and mechanical stirring at 100rpm. Maintain the mechanical stirring condition for hydrochloric acid roughening treatment for 12min, then filter and rinse with deionized water eight times until the pH of the washing solution is 7.0, and the sensitization treatment of diamond is completed.

[0092] S4, Activation: Add 3g of palladium chloride to 5L of deionized water and mix well to obtain an activation mother liquor. Take 150mL of the activation mother liquor and add deionized water to adjust it to 1200mL. Add diamond obtained by S3 sensitization treatment under mechanical stirring at 100rpm at room temperature. Maintain mechanical stirring for 6min of activation treatment. Then filter and rinse 5 times with deionized water to complete the activation treatment of diamond.

[0093] S5, sodium hypophosphite reduction: Dilute the 24% industrial sodium hypophosphite solution to a 12% sodium hypophosphite mother liquor. Take 20 mL of the sodium hypophosphite mother liquor, add deionized water to adjust to 1000 mL, add S4 activation treatment at room temperature and with mechanical stirring at 100 rpm to obtain diamond. Maintain mechanical stirring for 4 min of activation treatment, then filter and rinse with deionized water 5 times to complete the sodium hypophosphite reduction treatment of diamond.

[0094] The specific process for S6 electroless nickel plating is as follows:

[0095] S6.1, Prepare the main solution for electroless nickel plating: Take 480g of sodium citrate, 540g of sodium hypophosphite, 150mL of lactic acid, 100mL of 10% ammonia solution, and 720mL of nickel aminosulfonate. Add deionized water to 15.0L, then add 15.0% ammonia solution to adjust the pH to 9.2 and adjust the temperature to 40℃ to obtain the main solution for electroless nickel plating.

[0096] Take sodium citrate: 640g, sodium hypophosphite: 720g / L, lactic acid: 200mL / L, ammonia: 600mL / L, nickel aminosulfonate: 1600mL / L, thiourea: 1mL, add deionized water to 20L, mix well to obtain the chemical nickel plating replenishment solution;

[0097] S6.2, add S5 sodium hypophosphite to the electroless nickel plating main solution for reduction treatment to obtain diamond. Stir continuously for 90 minutes with mechanical stirring at 100 rpm. During the stirring process, add electroless nickel plating solution to maintain the concentration of the electroless plating solution. The amount of electroless nickel plating solution added is 20L. Then rinse with deionized water until neutral. After the process, dry: vacuum dry at 120℃ for 6 hours, and cool naturally to room temperature to obtain ultra-large diameter diamond with nickel plating on the surface.

[0098] Performance testing: The weight of electroless nickel-plated diamond was characterized and evaluated by the deposition rate, density, corrosion resistance, and electron micrographs of the electroless plating.

[0099] 1. Coating deposition rate: The mass m0 of diamond micropowder before electroless plating and the mass m1 after electroless plating are measured by an electronic balance. The plating time is t. The coating deposition rate is W. Coating deposition rate W = (m1 - m0) / t.

[0100] 2. The coating density is expressed as the mass of diamond coating per unit volume. Under a microscope, the shape of diamond microparticles is often irregular. For ease of calculation, this invention approximates the shape of the diamond particles as spherical. The equivalent volume particle size of the diamond microparticles before and after coating is measured using a laser particle size analyzer and taken as the average particle size r0 and r1. The diamond density is ρ0 (3.5 g / cm³). 3 In equation (2), n represents the number of particles in 3g of diamond powder, and the coating density ρ1 is calculated using equation (3).

[0101] Equation (2) ;

[0102] Equation (3) ;

[0103] 3. Coating acid corrosion resistance: 10g of coated diamond micro powder was soaked in 10wt% hydrochloric acid for 24h. The strength of the coating corrosion resistance was represented by the mass of the corroded coating. The greater the weight loss, the worse the acid corrosion resistance of the coating. The average particle size of the corroded diamond micro powder was r2, and the corrosion weight loss was m2, which was calculated using equation (4).

[0104] Equation (4) ;

[0105] Table 1: Test parameters of electroless nickel-plated diamond in Examples 1-4 and Comparative Examples 1-2

[0106] Example 1 <![CDATA[3.25*10 -3 ]]> 8.017 0.198 Example 2 <![CDATA[3.32*10 -3 ]]> 8.027 0.189 Example 3 <![CDATA[3.13*10 -3 ]]> 7.998 0.211 Example 4 <![CDATA[3.21*10 -3 ]]> 8.008 0.203 Comparative Example 1 <![CDATA[2.46*10 -3 ]]> 7.859 0.315 Comparative Example 2 <![CDATA[2.79*10 -3 ]]> 7.958 0.279

[0107] In conjunction with Example 1 and Comparative Example 1, and in conjunction with Table 1 and Figure 1-4 It is understood that the chemical nickel plating process provided in this invention uniformly deposits a dense and firmly bonded metal transition layer on the surface of large diamond particles, completely changing the inert characteristics of the diamond surface and greatly improving the adhesion of diamond to the steel wire surface.

[0108] In conjunction with Example 1 and Comparative Examples 1-2, and in conjunction with Table 1 and Figure 1-6 It is known that sodium hypophosphite reduction treatment during diamond pretreatment is beneficial to improving the density and uniformity of the metal transition layer. Therefore, sodium hypophosphite reduction treatment is a necessary condition for electroless nickel plating of large-particle-size diamonds.

[0109] Combining Examples 1 and 2 with Table 1, it can be seen that, compared with Example 1, the coating density in Example 2 is higher and the corrosion weight loss is smaller. Therefore, it can be seen that using ultrasonic stirring and non-contact electromagnetic stirring in diamond pretreatment S1-5 can achieve better surface modification effect and improve the quality of the final nickel plating layer.

[0110] It should be noted that this specific embodiment is merely an explanation of the technical solution of the present invention and is not intended to limit the present invention. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but as long as they are within the scope of the claims of the present invention, they are protected by patent law.

Claims

1. A chemical nickel plating process for ultra-large diameter diamond surfaces, characterized in that: The steps are as follows: S1, alkaline degreasing: the concentration of alkaline solution is 65-85g / L, the mass ratio of alkaline solution to diamond is (5-10):7, and the alkaline degreasing treatment is carried out at 60±5℃ for at least 30±5min under ultrasonic dispersion conditions, followed by washing with water 3 to 5 times. S2, hydrochloric acid roughening: The concentration of hydrochloric acid solution is 30-210 g / L, and the mass ratio of hydrochloric acid solution to diamond is (8-12):

7. At room temperature, the hydrochloric acid roughening treatment is carried out for at least 20±5 min under ultrasonic dispersion conditions, followed by washing with water until neutral. S3, Sensitization: The sensitization solution contains 50-200 g / L stannous chloride and 25-75 g / L hydrochloric acid. The mass ratio of the sensitization solution to diamond is (8-12):

7. Sensitize at room temperature under ultrasonic dispersion for at least 10-15 min, then wash with water until neutral. S4, Activation: The activation solution contains 50-180 mg / L of palladium chloride, and the mass ratio of the activation solution to diamond is (8-12):

7. Sensitize at room temperature for at least 5-8 minutes under ultrasonic dispersion conditions, and then wash with water 3-5 times. S5, sodium hypophosphite reduction: The concentration of sodium hypophosphite solution is 100-250 mg / L, and the mass ratio of sodium hypophosphite solution to diamond is (8-12):

7. Sensitize at room temperature under ultrasonic dispersion for at least 3-5 min, and then wash with water 3-5 times. S6, Electroless Nickel Plating: Prepare the main electroless nickel plating solution using 25-35 g / L sodium citrate, 25-40 g / L sodium hypophosphite, 6-12 mL / L lactic acid, 5-10 mL / L ammonia, and 40-55 mL / L nickel sulfamate. Adjust the pH of the main electroless nickel plating solution to 8.5-9.5 with ammonia. Add diamond that has been reduced by sodium hypophosphite in S5. The mass ratio of diamond to the main electroless nickel plating solution is (20-25):

1. Use non-contact electromagnetic stirring and stir continuously for 40-90 minutes. During stirring, add more electroless nickel plating solution to maintain the concentration of the solution. Rinse with deionized water until neutral. After drying, the ultra-large diameter diamond with nickel plating is obtained.

2. The electroless nickel plating process for ultra-large diameter diamond surfaces according to claim 1, characterized in that: The specific process for alkaline degreasing in S1 is as follows: Dissolve 500g of sodium hydroxide or potassium hydroxide in 5.0L of deionized water to obtain an alkaline mother liquor. Take 300-500mL of the alkaline mother liquor and add deionized water to adjust it to 500-1000mL. Under ultrasonic stirring or ultrasonic stirring and non-contact electromagnetic stirring, heat the water bath to 60±5℃, add 700g of diamond, and maintain the alkaline degreasing treatment under ultrasonic dispersion conditions or ultrasonic stirring and non-contact electromagnetic stirring for 30±5min. Then filter and rinse with deionized water 3-5 times.

3. The electroless nickel plating process for ultra-large diameter diamond surfaces according to claim 1, characterized in that: The specific process for S2 hydrochloric acid roughening is as follows: Take 100-300 mL of industrial hydrochloric acid with a concentration of 30-36%, add deionized water to adjust to 800-1000 mL, add diamond obtained by alkaline degreasing treatment in S1 at room temperature and under ultrasonic stirring or ultrasonic stirring and non-contact electromagnetic stirring, maintain ultrasonic dispersion conditions or ultrasonic stirring and non-contact electromagnetic stirring for hydrochloric acid roughening treatment for 15-25 min, then filter, rinse multiple times with deionized water until the pH value of the cleaning solution is 6.8-7.0, and the hydrochloric acid roughening treatment is completed.

4. The electroless nickel plating process for ultra-large diameter diamond surfaces according to claim 1, characterized in that: The specific sensitization process for S3 is as follows: Take 500 mL of concentrated hydrochloric acid, add 500 g of stannous chloride and mix evenly to obtain a sensitization mother solution. Take 100-300 mL of the sensitization mother solution, add deionized water to adjust to 1000-1200 mL, and add diamond obtained by hydrochloric acid roughening treatment in S2 under room temperature and / or ultrasonic stirring and non-contact electromagnetic stirring. Maintain ultrasonic dispersion conditions or ultrasonic stirring and non-contact electromagnetic stirring for hydrochloric acid roughening treatment for 10-15 min, then filter and rinse multiple times with deionized water until the pH value of the washing solution is 6.8-7.0, thus completing the sensitization treatment of diamond.

5. The electroless nickel plating process for ultra-large diameter diamond surfaces according to claim 1, characterized in that: The specific activation process for S4 is as follows: Add 3g of palladium chloride to 5L of deionized water and mix evenly to obtain an activation mother liquor. Take 100-300mL of the activation mother liquor and add deionized water to adjust it to 1000-1200mL. Add the diamond obtained after S3 sensitization treatment at room temperature and / or under ultrasonic stirring and non-contact electromagnetic stirring. Maintain ultrasonic dispersion conditions or ultrasonic stirring and non-contact electromagnetic stirring for 5-8 minutes for activation treatment. Then filter and rinse with deionized water 3-5 times to complete the activation treatment of diamond.

6. The electroless nickel plating process for ultra-large diameter diamond surfaces according to claim 1, characterized in that: The specific process for reducing sodium hypophosphite (S5) is as follows: Dilute the 20-25% industrial sodium hypophosphite solution to a 10-12% sodium hypophosphite mother liquor. Take 10-30 mL of the sodium hypophosphite mother liquor, add deionized water to adjust to 1000-1200 mL, and add S4 for activation treatment to obtain diamond under room temperature and / or ultrasonic stirring and non-contact electromagnetic stirring. Maintain ultrasonic dispersion conditions or ultrasonic stirring and non-contact electromagnetic stirring for 3-5 minutes for activation treatment. Then filter and rinse with deionized water 3-5 times to complete the sodium hypophosphite reduction treatment of diamond.

7. The electroless nickel plating process for ultra-large diameter diamond surfaces according to claim 1, characterized in that: The specific process for S6, electroless nickel plating, is as follows: S6.1, Prepare the main solution for electroless nickel plating: Take sodium citrate: 400-500g, sodium hypophosphite: 400-600g, lactic acid: 100-200mL, ammonia water with a concentration of 9.5-10.5%: 80-150mL, nickel aminosulfonate: 600-800mL, add deionized water to 15L, then add ammonia water with a concentration of 14.5-15.5% to adjust the pH value to 8.9-9.5, and adjust the temperature to 30-45℃ to obtain the main solution for electroless nickel plating; S6.2, add S5 sodium hypophosphite to the electroless nickel plating main solution for reduction treatment to obtain diamond. Use non-contact electromagnetic stirring and stir continuously for 40-90 minutes. During the stirring process, add electroless nickel plating solution to maintain the concentration of the electroless plating solution. Then rinse with deionized water until neutral and dry after completion.

8. The electroless nickel plating process for ultra-large diameter diamond surfaces according to claim 7, characterized in that: In step S6.2, sodium hypophosphite (S5) is added to the electroless nickel plating main solution for reduction treatment to obtain diamond. The diamond is then pre-dispersed for 30-90 seconds at 30-45℃ with ultrasonic stirring at a frequency of 20-60kHz and a power of 400-900W. Afterward, non-contact electromagnetic stirring is used for continuous stirring for 40-90 minutes. During the stirring process, the electroless nickel plating solution is replenished to maintain the concentration of the electroless plating solution. The solution is then rinsed with deionized water until neutral. After the process is completed, the diamond is dried to obtain ultra-large diameter diamond with a nickel-plated surface.

9. The electroless nickel plating process for ultra-large diameter diamond surfaces according to claim 7, characterized in that: The parameters of the non-contact electromagnetic stirring are as follows: the stirring rod is driven to rotate under the conditions of magnetic field frequency of 10-30Hz and magnetic induction intensity of 0.2-0.5T, and the rotation speed of the stirring rod is 100-300rpm.

10. The electroless nickel plating process for ultra-large diameter diamond surfaces according to claim 7, characterized in that: The preparation method of the electroless nickel plating replenishment solution is as follows: Take sodium citrate: 450-1200g, sodium hypophosphite: 450-1000g / L, lactic acid: 45-200mL / L, ammonia water: 450-1600mL / L, nickel aminosulfonate: 1500-3000mL / L, thiourea: 0.8-1.2mL, add deionized water to 15-20L, mix well to obtain the electroless nickel plating replenishment solution, and the replenishment amount of the electroless nickel plating replenishment solution is 15-20L.

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