Preparation method of heterogeneous coating material and application of heterogeneous coating material

Abstract

The application discloses a preparation method of heterogeneous coating material and application of the heterogeneous coating material and belongs to the technical field of heterogeneous coating powder material preparation. The method comprises the following steps: performing surface magnetization treatment on the surface of a material to be plated to obtain a material to be plated containing a magnetization layer; and placing the material to be plated containing the magnetization layer in an electroplating solution to perform magnetohydrodynamic electroplating treatment, thereby obtaining the heterogeneous coating material. The magnetohydrodynamic electroplating treatment is performed in a cyclic alternating environment of a magnetic field and a flow field, the single holding time of the magnetic field is 10-200s, the magnetic field is always applied on the cathode side, and the single fluidization time of the flow field is 3-50s. The method realizes low-cost and large-batch pre-magnetization treatment of non-magnetic powder by depositing a magnetic coating on the surface of the material to be plated through single chemical plating; and then through magnetohydrodynamic electroplating treatment, the synergistic effect of the magnetic field force and the flow field force is utilized to realize the large-scale and continuous coating of the material to be plated, thereby obtaining a metal-coated powder with a uniform and dense plating layer and low cost.

Description

Technical Field

[0001] This invention relates to a method for preparing heterogeneous coating materials and the application of heterogeneous coating materials, belonging to the field of heterogeneous coating powder material preparation technology. Background Technology

[0002] Metal-coated composite powders combine the advantages of both metals and matrix materials, such as electrical conductivity, thermal conductivity, and corrosion resistance, making them widely used in communications, electronics, aerospace, and powder metallurgy. Despite numerous preparation methods, pressurized hydrogen reduction and electroless plating remain the mainstream technologies, considering both coating quality and industrial applicability. However, both technologies rely on intermittent "one-pot" operations, whose inherent limitations have become bottlenecks restricting development. Limited by reaction kinetics and mass transfer efficiency, the feed rate in a single-pot reaction is strictly compressed to ensure coating uniformity, making it difficult to directly meet the demands of large-scale production. To achieve production targets, multiple batches must be repeated, leading to a significant increase in wastewater discharge with each batch. This not only creates enormous environmental pressure but also significantly increases production costs due to frequent bath changes, high energy consumption, and labor input.

[0003] Chinese patent document (publication number CN116479489A) discloses a nickel-coated graphite powder, an additive, an electroplating solution, and an electroplating process thereof. The additive is a particulate electroplating nano-nickel additive, which contains a complexing agent, a current dispersant, a low-potential deposition promoter, and a lubricant. The mass ratio of the complexing agent, the current dispersant, and the low-potential deposition promoter is 40~100:10:1. Electroplating within this ratio can form a large number of micro crystal nuclei, but their growth is inhibited, thereby obtaining a finely crystalline nano-nickel electroplated layer.

[0004] Chinese patent document (CN219808020U) discloses an electroplating apparatus for particulate matter. The electroplating apparatus includes a support mechanism with a base and a bracket mounted on the base; a roller with one open end inclined upward and rotatably mounted on the bracket, the bottom of which is mounted on the base via a rotating seat; a blocking strip is provided on the inner side wall of the roller; an anode cylinder is mounted on the bracket and located inside the roller for adding anode material; and a rotary motor is mounted on the base, its working end connected to the bottom of the roller, which can drive the roller to rotate on the base and the bracket.

[0005] However, the two methods mentioned above mainly employ barrel plating, whose core limitation lies in the low cathode current density caused by the special cathode structure, and their reliance primarily on contact charging mechanisms. This makes the deposition process highly sensitive to current parameters: too low a current cannot drive electrons to penetrate the powder deposit layer, resulting in uneven coating and excessively long plating times (up to 80 hours); too high a current causes localized overheating and "burning" due to the contact resistance between powder particles. Furthermore, because it mainly relies on gravity, this process is difficult to effectively deposit low-density or small-particle-size powders, limiting its applicability. Summary of the Invention

[0006] The purpose of this invention is to address the problems of traditional one-pot preparation processes (such as electroless plating and pressurized hydrogen reduction) in the preparation of metal coatings on the surface of materials to be plated, which are limited in single-batch processing capacity, require multiple batches of repeated plating, resulting in large amounts of wastewater, high production costs, and difficulty in continuous production. The purpose of this invention is to provide a method for preparing heterogeneous coating materials. This method first deposits a magnetic coating on the surface of the material to be plated through a single electroless plating process, achieving low-cost, large-scale pre-magnetization of non-magnetic powders. Then, through magnetofluidic electroplating, the synergistic effect of magnetic field force and fluid field force is used to achieve large-scale, continuous coating of the material to be plated, obtaining a uniform, dense, and low-cost metal-coated powder. The core coating of this heterogeneous coating material is uniform, dense, and linearly adjustable in thickness, and can be continuously prepared.

[0007] The second objective of this invention is to provide applications of heterogeneous coating materials in electrical contact elements, electromagnetic shielding and wave absorption, high-temperature lubrication, electronic heat dissipation, thermal spray coatings, aerospace, precision molds and cutting tools, electronic packaging, or the manufacture of high-temperature industrial components.

[0008] To achieve the above objectives, a first aspect of the present invention provides a method for preparing a heterogeneous coating material, the method comprising:

[0009] (1) Perform surface magnetization treatment on the surface of the material to be plated to obtain a material containing a magnetized layer;

[0010] (2) The material to be plated containing the magnetized layer is placed in the electroplating solution for magnetic fluidization electroplating treatment to obtain a heterogeneous coating material; the material of the material to be plated in the heterogeneous coating material is different from the material of the electroplating layer, and the electroplating layer is a metal layer.

[0011] The magnetofluidized electroplating process is carried out in a cyclical alternation of magnetic field and flow field, and the magnetic field is maintained for 10~200s at a time, and the magnetic field is always applied on the cathode side. The flow field is fluidized for 3~50s at a time. The power supply for the magnetofluidized electroplating process has a reversing function, with a reversing frequency of 10min~3h / time and a reversing duration of 10min~3h / time.

[0012] The inventors have innovatively discovered a magnetofluidized electroplating technology that effectively solves common problems in powder electrodeposition, such as poor contact and easy agglomeration, by utilizing the synergy of magnetic and fluid fields. However, for non-conductive and non-magnetic substrates, magnetofluidized electroplating technology cannot be directly applied and requires prior magnetization. To address this, this invention proposes a novel composite process of "magnetization-magnetofluidized electroplating," which constructs a new path of "pretreatment-continuous deposition," breaking through the constraints of the traditional "one-pot" method. First, a nanoscale thin layer (magnetized layer) is deposited on the surface of the material to be plated, imparting only magnetic response without contributing to thickness. This avoids the high cost and pollution caused by repeated plating for thickness enhancement in traditional processes. This step allows for the mass production of powders. Furthermore, minimal waste liquid is generated. Subsequently, magnetofluidic electroplating technology is used to prepare the core coating. By applying an external magnetic field, the magnetized powder to be plated is adsorbed onto the cathode surface to complete coating deposition. After the magnetic field is removed, the powder detaches from the cathode and undergoes fluidization renewal within the reactor. Further, the magnetofluidic electroplating power supply also has a reversing function. Through periodic reversal of the cathode and anode, the metal coating on the cathode plate is periodically removed, preventing excessive metal coating from affecting the powder electrodeposition efficiency. Simultaneously, it cleans the powder deposited on the cathode plate due to factors such as current density during long-term electroplating. This invention, through alternating cyclic control of the "magnetic deposition-demagnetization fluidization" process, combined with the synergistic effect of magnetic field force, fluid field force, and the reversing function, achieves efficient contact between the powder and the cathode. This not only significantly improves the electroplating rate but also greatly enhances the coating uniformity, ultimately achieving continuous and controllable preparation of a uniform, dense, and linearly adjustable core coating.

[0013] In this invention, the electroplating process is carried out in a cyclical alternation of magnetic field and flow field, which means that during the electroplating process, the flow field is closed when the magnetic field is turned on, and the magnetic field is closed when the flow field is turned on, that is, the flow field or magnetic field is always present.

[0014] As a preferred option, the reversal frequency is 15~45 min / time, and the reversal duration is 15~45 min / time.

[0015] In this invention, the reversal frequency refers to the reversal performed after a certain period of electroplating, and the reversal duration refers to the time for reverse electroplating under the reversal condition. For example, the reversal frequency is 20 min / time, and the reversal duration is 20 min / time, which means that the reversal is performed after 20 min of electroplating, and then reverse electroplating is performed for 20 min under the reversal condition.

[0016] As a preferred embodiment, in the material to be plated containing the magnetized layer, the mass ratio of the magnetized layer to the mass of the material to be plated is ≥5wt%. Experiments have shown that under this preferred condition, the subsequent magnetofluidization electroplating process can be guaranteed to proceed smoothly. If the amount of the magnetized layer is less than 5wt%, the subsequent magnetofluidization electroplating process cannot be performed, or the resulting heterogeneous coating material coating layer is uneven.

[0017] As a preferred embodiment, the mass ratio of the magnetizing layer to the material to be plated is 5-30 wt%. Experiments have shown that under this preferred condition, resource utilization can be maximized, thereby significantly reducing costs and wastewater volume.

[0018] As a preferred embodiment, the particle size of the material to be plated is less than or equal to 500 μm, preferably 10 μm to 300 μm.

[0019] As a preferred embodiment, the material to be plated is non-magnetic and is a carbonaceous material and / or a ceramic material.

[0020] As a preferred embodiment, the carbonaceous material is selected from at least one of carbonaceous materials such as graphite, diamond, and carbon nanotubes.

[0021] As a preferred embodiment, the ceramic material is selected from at least one of the following ceramic materials: silicon nitride, silicon carbide, alumina, zirconium oxide, tungsten carbide, tin dioxide, chromium oxide, and molybdenum sulfide.

[0022] It should be noted that the shape of the material to be plated is not particularly required in this invention; it can be spherical, sheet-like, strip-like, irregular, or other shapes.

[0023] As a preferred embodiment, the material of the magnetizing layer is selected from at least one of iron, cobalt, and nickel. Experiments have shown that these magnetizing layers possess both electrical conductivity and magnetism, enabling the formation of a complete conductive layer on the powder surface while ensuring magnetic properties. This is beneficial for producing a uniform and dense coating during subsequent powder electroplating processes.

[0024] As a preferred solution, a single-pass electroless plating method is used for surface magnetization. By depositing a nanoscale thin layer on the surface of the material in a single electroless plating process, the function of electroless plating is limited to depositing a nanoscale thin layer, imparting only a magnetic response to the powder, without contributing to thickening. This step requires only a single reaction to complete the pretreatment of large batches of powder, without involving further deposition, completely avoiding the high pollution and high cost problems caused by repeated plating for thickening in traditional processes, thus achieving emission reduction and cost reduction at the source.

[0025] As a preferred embodiment, the single-pass electroless plating method includes: first activating the material to be plated, and then placing it in an electroless plating solution for electroless plating to obtain a material containing a magnetic layer.

[0026] The activation treatment method is either scheme A or scheme B;

[0027] Scheme A: (a1) After calcining the material to be plated, it is immersed in a nickel source solution and then dried to obtain an intermediate material to be plated;

[0028] (a2) The intermediate material to be plated is reduced with hydrogen and then fluidized in a mixture of nitrogen and hydrogen.

[0029] Option B: After the material to be plated is degreased by alkaline washing, it is immersed in an acid solution for treatment II, and then sensitized in a sensitization solution and activated in an activation solution in sequence.

[0030] As a preferred embodiment, in embodiment A, the calcination treatment is carried out at a temperature of 300~600℃ for a time of 1~4h;

[0031] The solid-liquid ratio of the nickel source solution to the material to be plated is 3~30g / 100mL;

[0032] The nickel source solution is a nickel chloride solution with a concentration of 100~600 g / L;

[0033] The impregnation treatment I is performed at a temperature of 30~80℃ for a time of 0.5~5 hours.

[0034] The hydrogen reduction is carried out at a temperature of 250~350℃ for a time of 20~50 min;

[0035] In the nitrogen and hydrogen mixture, the flow rates of nitrogen and hydrogen are each independently 0.2~1.2 L / min;

[0036] or,

[0037] In scheme B, the sensitizing solution is a tin-containing solution; the sensitization time is 10~90 min;

[0038] The activation solution is a palladium-containing solution; the activation time is 10~90 min.

[0039] As a preferred embodiment, in embodiment A, the impregnation treatment I is carried out under stirring conditions, and the stirring rate is 100~500 r / min.

[0040] As a preferred embodiment, in embodiment A, the drying process is carried out at a temperature of 50-100°C for a duration of 2-6 hours.

[0041] As a preferred embodiment, in embodiment B, the sensitizing solution is a mixture of tin dichloride and hydrochloric acid. This invention does not have special requirements regarding the ratio of tin dichloride to hydrochloric acid; any solution known in the art can be used.

[0042] As a preferred embodiment, in embodiment B, the activation solution is a mixture of palladium dichloride and hydrochloric acid. This invention does not have special requirements regarding the ratio of palladium dichloride to hydrochloric acid; any ratio known in the art is acceptable.

[0043] It should be noted that in Scheme B, the present invention does not have any special requirements for the solid-liquid ratio of the material to be plated to the sensitization solution and the activation solution, and any ratio known in the art can be used.

[0044] By using the method of Scheme A or Scheme B provided by the present invention for surface magnetization treatment, the magnetization layer can achieve a high coverage rate of the material to be plated and a more uniform coating.

[0045] As a preferred embodiment, the electroless plating solution contains: 10-50 g / L of water-soluble metal salt, 5-80 g / L of reducing agent, 5-60 g / L of complexing agent, 5-50 g / L of buffer, 0-10 g / L of stabilizer, and 0-5 g / L of brightener / surfactant.

[0046] As a preferred embodiment, the water-soluble metal salt is selected from at least one of water-soluble nickel salt, water-soluble iron salt, and water-soluble cobalt salt. The water-soluble nickel salt is selected from at least one of nickel nitrate, nickel chloride, and nickel sulfate; the water-soluble iron salt is selected from at least one of ferric nitrate, ferric chloride, and ferric sulfate; and the water-soluble cobalt salt is selected from at least one of cobalt nitrate, cobalt chloride, and cobalt sulfate.

[0047] As a preferred embodiment, the reducing agent is selected from at least one of hydrazine hydrate, sodium hypophosphite, and sodium borohydride.

[0048] As a preferred embodiment, the complexing agent is selected from at least one of citric acid and its salts, tartaric acid and its salts, lactic acid, pyrophosphate, and EDTA and its disodium salt.

[0049] As a preferred embodiment, the buffer is selected from at least one of boric acid, acetic acid, sodium acetate, citric acid, sodium citrate, ammonium chloride, glycine, tartaric acid, and sodium carbonate.

[0050] As a preferred embodiment, the brightener / surfactant is selected from at least one of sodium dodecyl sulfate, polyethylene glycol and its derivatives, thiourea and its derivatives, 1,4-butynediol, sodium saccharin and thioglycolic acid.

[0051] As a preferred embodiment, the electroless plating temperature is 50~95℃ and the stirring speed is 100~400 r·min. -1 .

[0052] As a preferred embodiment, the current density of the magnetofluidization electroplating treatment is 10~500 mA·cm. -2 The powder loading is 5~100 g·L -1 The electroplating treatment time is 0.1~30h; the single magnetic field holding time is 10~100s; the single fluidization time of the flow field is 3~30s; and the fluidization velocity is 0.05~5 m·s. -1 Powder loading refers to the amount of material to be plated containing the magnetizing layer. By controlling parameters such as fluidization rate, current density, and magnetic field time in fluidized bed electroplating, a more uniform coating and a larger coating amount can be achieved, with a shorter coating time compared to traditional electrodeposition. Furthermore, compared to existing barrel plating technology with low current (0.01~0.5 mA·cm⁻¹), this method also achieves better results. -2 This invention can employ ultra-high current (e.g., 200 mA·cm). -2 Magnetorheological electroplating can rapidly coat the material with an electroplating layer, significantly improving plating efficiency. Furthermore, by controlling the current density, the crystal structure of the electroplated metal can be manipulated to prepare crystalline / amorphous metal coatings.

[0053] As a more preferred embodiment, the current density of the magnetofluidization electroplating treatment is 60~300 mA·cm. -2 The fluidization velocity is 0.1~1 m·s. -1 The single magnetic field holding time is 15-50 s, and the single fluidization time of the flow field is 4-10 s. Furthermore, excessive current density can cause powder to agglomerate due to rapid deposition, while insufficient current density leads to low efficiency and affects production progress. Simultaneously, insufficient fluidization velocity causes powder to accumulate at the bottom of the reactor, preventing electrodeposition, while excessive current density results in excessive liquid pressure drop within the reactor, affecting ion transport and powder fluidization. Moreover, excessively long single magnetic field holding times can easily cause powder to be directly fixed to the cathode plate along with the deposited metal, while insufficient holding time results in inadequate deposition time, affecting deposition efficiency.

[0054] It should be noted that this invention does not have special requirements for the composition of the electroplating solution; conventional electroplating solutions in the art can be used. For example, when the material of the electroplated layer is nickel, a standard Watt-type nickel plating electrolyte is used; when the material of the electroplated layer is copper, an acidic sulfate copper plating electrolyte or a cyanide-free pyrophosphate copper plating electrolyte is used. When different materials need to be electroplated, the electrolyte can be replaced with the corresponding commonly used electrolyte.

[0055] As a preferred embodiment, the material of the electroplated layer is selected from at least one of copper, nickel, zinc, chromium, tin, silver, gold, iron, cobalt, lead, and cadmium.

[0056] As a preferred embodiment, the magnetic field generating device for the magnetofluidized electroplating treatment is selected from at least one of an electromagnet and a permanent magnet. The electromagnet is selected from at least one of a Helmholtz coil, a lifting electromagnet, and an electromagnetic chuck, and the permanent magnet is selected from at least one of a permanent magnet separator, a permanent magnet separator, and a neodymium iron boron permanent magnet.

[0057] As a preferred embodiment, the fluidization method of the magnetofluidized electroplating process is liquid-solid fluidization or gas-liquid-solid three-phase fluidization. In liquid-solid fluidization, the fluidizing liquid is an electrolyte, and in gas-liquid-solid three-phase fluidization, the fluidizing gas is selected from an inert gas and / or air. The inert gas is selected from at least one of argon, nitrogen, and helium.

[0058] As a preferred embodiment, the magnetofluidized electroplating process first activates the flow field and then the magnetic field. Activating the flow field first fluidizes the powder to be plated, and then activating the power supply and magnetic field initiates the electroplating process.

[0059] The second aspect of the present invention is to provide the application of the heterogeneous coating material prepared by the method described in the first aspect above in electrical contact elements, electromagnetic shielding and wave absorption, high-temperature lubrication, electronic heat dissipation, thermal spray coating, aerospace, precision molds and cutting tools, electronic packaging, or the preparation of high-temperature industrial components.

[0060] When the material to be plated is a carbonaceous material, the prepared metal-coated carbon powder has the advantages of combining electrical and thermal conductivity, wear resistance and lubrication, and can be used in electrical contact components, electromagnetic shielding and wave absorption, high-temperature lubrication or electronic heat dissipation. When the material to be plated is a ceramic material, the prepared metal-coated ceramic powder has the combination of ceramic high temperature resistance, high hardness and corrosion resistance and metal strength and toughness, and can be widely used in thermal spray coating, aerospace, precision mold and tool, electronic packaging or preparation of high-temperature industrial components.

[0061] Compared with the prior art, the present invention has at least the following advantages:

[0062] (1) Significantly reduces production costs and environmental pressure, breaking through the bottleneck of the traditional "one-pot" process. Existing chemical plating or pressurized hydrogen reduction methods are limited by the reaction kinetics and mass transfer efficiency of a single pot. To ensure the uniformity of the coating, the amount of material fed at one time is extremely low, and multiple batches of repeated plating are often required to achieve the target thickness. This vicious cycle of "capacity demand - repeated batches - cost and environmental burden" leads to a significant increase in wastewater discharge and high costs for raw materials and wastewater treatment. This invention innovatively constructs a "magnetization-magnetic fluidized electroplating treatment" composite process, which strictly limits the function of chemical plating to depositing nanoscale thin layers to only impart magnetic response to the powder, without undertaking the function of thickening. This step only requires a single reaction to complete the pretreatment of a large number of powders, completely avoiding the high pollution and high cost problems caused by repeated plating for thickening in traditional processes, and achieving source emission reduction and cost reduction.

[0063] (2) Continuous production of the coating process has been achieved, significantly improving preparation efficiency and production capacity. Addressing the shortcomings of traditional one-pot methods in achieving continuous production, the pre-magnetized powder of this invention forms a dynamically stable fluidized state on the cathode surface, achieving efficient and sufficient contact between the powder and the cathode. This not only solves the common problems of poor contact and easy agglomeration in conventional powder electrodeposition, but also allows for linear and precise control of the coating thickness through deposition time, supporting continuous and large-scale preparation of metal-coated powders and significantly shortening the production cycle.

[0064] (3) The product has excellent quality, with a uniform, dense coating and strong adhesion. Utilizing the excellent dispersibility of the magnetic fluidized bed, the material to be coated remains in an independent suspension state throughout the fluidization process, avoiding particle adhesion and agglomeration, and ensuring the uniformity of the coating distribution on the powder surface. The metal-coated powder prepared in this way has a continuous, complete, and uniform coating thickness with high density, significantly improving the comprehensive performance of the composite powder in terms of electrical conductivity, thermal conductivity, and corrosion resistance.

[0065] (4) The process is highly versatile and has broad application prospects. The technical solution proposed in this invention is not limited to the single system of nickel-coated graphite. By adjusting the type of metal pre-magnetized by chemical plating (such as iron, cobalt, and nickel) and the composition of the electrodeposition solution, it can be widely applied to the metal coating of various non-magnetic matrix powders such as alumina and silicon dioxide, providing a general technical path for the green, low-cost, and large-scale preparation of heterogeneous coating materials. Attached Figure Description

[0066] Figure 1 This is a secondary electron scanning image of the surface morphology of the magnetized nickel-coated graphite prepared by chemical plating in Example 1. As can be seen from the image, after chemical plating, there is a thin metal coating on the graphite surface.

[0067] Figure 2This is a secondary electron scanning image of the surface morphology of nickel-coated graphite prepared by magnetofluidization electroplating in Example 1. As can be seen from the image, the nickel-coated graphite treated by magnetofluidization electroplating has a smooth and flat surface, a uniform and dense coating, and no loose or porous phenomena.

[0068] Figure 3 This is a secondary electron scanning image of the cross-sectional morphology of the magnetic nickel-coated graphite prepared by chemical plating in Example 1. As can be seen from the image, the magnetic nickel-coated graphite after chemical plating has a coating thickness of about 0.5 μm and is discontinuous.

[0069] Figure 4 This is a secondary electron scanning image of the cross-sectional morphology of nickel-coated graphite prepared by magnetofluidization electroplating in Example 1. As can be seen from the image, the nickel-coated graphite treated by magnetofluidization electroplating has a coating thickness of about 1 μm, which is significantly thicker than that of magnetized nickel-coated graphite. The coating is also uniform and dense, and tightly bonded to the substrate.

[0070] Figure 5 This is a secondary electron scanning image of the surface morphology of nickel-coated graphite prepared by magnetofluidization electroplating (without reversing function) in Comparative Example 8. As can be seen from the image, the powder surface is rough and uneven with obvious granular protrusions, and the plating quality is poor. Detailed Implementation

[0071] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0072] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments. Obviously, the embodiments described below are only a part of the embodiments, and all other embodiments obtained by those skilled in the art without creative effort are still within the scope of protection of the present invention.

[0073] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0074] Example 1

[0075] Step 1: Irregular graphite particles with a particle size between 75μm and 150μm are selected by crushing and sieving. The graphite particles are then placed in a muffle furnace and calcined at 500℃ in air atmosphere for 2 hours.

[0076] Step 2: Dissolve NiCl2·6H2O in deionized water to prepare a 400 g / L NiCl2·6H2O solution. Place the calcined graphite particles into an Erlenmeyer flask containing the NiCl2 solution (5 g / 100 ml), and place the flask in a constant temperature water bath shaker. Immerse the particles at 50 °C and 180 r / min for 1 h. Separate the loaded graphite particles from the solution by suction filtration, and place them in a forced-air drying oven to dry at 70 °C for 6 h.

[0077] Step 3: Place some of the successfully loaded precursor graphite particles in a gas-solid fluidized bed and reduce them with hydrogen at 300℃ for 30 min. Fluidization is performed using a mixture of H2 and N2 at a gas velocity of 0.5 L / min to obtain activated graphite particles.

[0078] Step 4: First, raise the temperature of the chemical plating solution to 85℃ in a water bath. Add the activated graphite particles (loading amount 20g / L) to the chemical plating solution and stir at a speed of 200 r / min until the reaction is completed, to obtain magnetic nickel-coated graphite with a magnetic layer to plating material mass ratio of 20wt%.

[0079] The composition of the chemical plating solution is as follows: NiCl2·6H2O (30g / L), NaH2PO2·H2O (60g / L), Na3C6H5O7·H2O (30g / L), NH4Cl (30g / L), and NaOH (20g / L).

[0080] Step 5: First, prepare the electroplating solution. Weigh out specific amounts of nickel sulfate hexahydrate, nickel chloride hexahydrate, and boric acid and dissolve them in deionized water to achieve concentrations of 200 g / L, 40 g / L, and 30 g / L, respectively. Place the surface-magnetized nickel-coated graphite particles into the electrolyte solution for magnetofluidized electroplating. First, activate the flow field to fluidize the powder, setting the current density to 60 mA·cm². -2 The magnetic field was maintained for 20 seconds at a time, the fluidization time of the flow field was 5 seconds at a time, and the fluidization velocity was 0.1 m / s. -1 The loading of surface-magnetized nickel-coated graphite particles was 8 g / L, the electroplating treatment time was 60 min, and the power supply for the magnetofluidized electroplating treatment had a reversing function with a reversing frequency of 15 min / time and a reversing duration of 15 min / time. After the magnetofluidized electroplating treatment, the powder was washed three times with deionized water, placed in a vacuum oven, and dried at 80℃ for 6 h to obtain nickel-coated graphite.

[0081] Example 2

[0082] This embodiment is carried out using a method similar to that of Embodiment 1, except that the powder loading in step five is adjusted to 30 g / L and the electroplating treatment time is 90 min.

[0083] Example 3

[0084] This embodiment follows a similar method to Embodiment 1, except that the single-time magnetic field maintenance time in step five is set to 12 s, the single-time fluidization time of the flow field is set to 3 s, and the fluidization velocity is adjusted to 1.5 m·s⁻¹. -1 .

[0085] Example 4

[0086] Step 1: First, dissolve NaOH and OP-10 emulsifier in deionized water to concentrations of 200 g / L and 10 g / L, respectively. Then, place graphite particles in the solution (20 g / L) and stir at 90 °C for 0.5 h. Wash the treated graphite powder with deionized water until neutral and filter. Dry it in a 60 °C oven for 6 h to remove the grease from the graphite surface. Place the alkaline-washed and degreased graphite particles in a 65% nitric acid solution (200 g / L), sonicate for 30 min, wash with deionized water until neutral and filter. Dry it in a 60 °C oven for 6 h to increase the roughness of the graphite surface.

[0087] Step 2: First, sensitize the pretreated graphite particles in a sensitizing solution (30 g / L) for 75 min, then activate them in an activation solution (30 g / L) for 75 min. Next, wash the graphite particles with deionized water and filter them, then place them at 60°C. o The sample was dried in an oven at C for 6 h. The sensitization solution consisted of 20 g / L SnCl2·2H2O and 40 mL / L HCl; the activation solution consisted of 0.25 g / L PdCl2 and 2.5 mL / L HCl.

[0088] Step 3: First, raise the temperature of the chemical plating solution to 85℃ in a water bath. Add the activated graphite particles (loading amount 20g / L) to the chemical plating solution and stir at a speed of 200 r / min until the reaction is completed, to obtain magnetic nickel-coated graphite with a magnetic layer to plating material mass ratio of 20wt%.

[0089] The composition of the chemical plating solution is as follows: NiCl2·6H2O (30g / L), NaH2PO2·H2O (60g / L), Na3C6H5O7·H2O (30g / L), NH4Cl (30g / L), and NaOH (20g / L).

[0090] Step 4: First, prepare the electroplating solution. Weigh out measured amounts of nickel sulfate hexahydrate, nickel chloride hexahydrate, and boric acid and dissolve them in deionized water to achieve concentrations of 200 g / L, 40 g / L, and 30 g / L, respectively. Place the surface-magnetized nickel-coated graphite particles into the electrolyte solution for magnetofluidized electroplating. First, activate the flow field to fluidize the powder, setting the current density to 60 mA·cm². -2 The magnetic field was maintained for 20 seconds at a time, the fluidization time of the flow field was 5 seconds at a time, and the fluidization velocity was 0.1 m / s. -1 The loading of surface-magnetized nickel-coated graphite particles was 10 g / L, the electroplating time was 60 min, and the power supply for the magnetofluidized electroplating treatment had a reversing function with a reversing frequency of 30 min / time and a reversing duration of 30 min / time. After the magnetofluidized electroplating treatment, the powder was washed three times with deionized water, placed in a vacuum oven, and dried at 80℃ for 6 h to obtain nickel-coated graphite.

[0091] Example 5

[0092] This embodiment is carried out using a method similar to that of Embodiment 1, except that the composition of the electroplating solution is adjusted to: the concentrations of nickel aminosulfonate, nickel chloride hexahydrate, and boric acid are 150 g / L, 10 g / L, and 30 g / L, respectively.

[0093] Example 6

[0094] This embodiment follows a similar method to Example 4 to prepare nickel-coated carbon nanotubes. The difference is that the material to be coated is changed to carbon nanotubes, and the current density in "Step Four" is changed to 50 mA·cm⁻¹. -2 The powder loading amount was changed to 5g / L, and the single magnetic field maintenance time was changed to 15s.

[0095] Example 7

[0096] This embodiment follows a similar method to Example 4 to prepare nickel-coated alumina powder. The difference is that the material to be plated is changed to alumina powder, and "Step 1" is modified as follows: the alumina powder is mixed with anhydrous ethanol, ultrasonically treated using an ultrasonic cleaner to remove surface impurities, and then washed and filtered with water. Furthermore, the current density in "Step 4" is set to 80 mA·cm⁻¹. -2 The powder loading rate was changed to 20 g / L, the single magnetic field holding time was changed to 30 s, and the fluidization velocity was changed to 0.15 m·s. -1 .

[0097] Example 8

[0098] This embodiment follows a similar method to Example 4 to prepare nickel-coated zirconium oxide powder. The difference is that the material to be plated is replaced with zirconium oxide powder, and "Step 1" is changed to: mixing the zirconium oxide powder with anhydrous ethanol, performing ultrasonic treatment using an ultrasonic cleaner to remove surface impurities, and then washing and filtering with water. Secondly, the current density in "Step 4" is set to 80 mA·cm⁻¹. -2 The powder loading rate was changed to 30 g / L, the single magnetic field holding time was changed to 30 s, and the fluidization velocity was changed to 0.2 m·s. -1 .

[0099] Example 9

[0100] This embodiment is performed using a method similar to that of Embodiment 1, except that the current density in step five is adjusted to 200 mA·cm⁻¹. -2 .

[0101] Example 10

[0102] This embodiment is carried out using a method similar to that of Embodiment 1, except that the reversal frequency in step five is changed to 50 min / time, the reversal duration is 20 min / time, and the electroplating treatment time is 90 min.

[0103] Comparative Example 1

[0104] This comparative example was performed using a method similar to that of Example 1, except that the current density in "Step 5" was adjusted to 50 mA·cm. -2 The single-cycle duration of the magnetic field is 8 s, the single-cycle fluidization time of the flow field is 2 s, and the fluidization velocity is 0.174 m·s. -1 The powder loading rate was 10 g / L, and the electroplating treatment time was 90 min.

[0105] Comparative Example 2

[0106] This comparative example is performed using a method similar to that of Example 1, except that steps two, three, and four are omitted. The graphite particles obtained in step one are directly subjected to magnetofluidization electroplating treatment, and the parameters for magnetofluidization electroplating treatment are the same as in Example 1.

[0107] In this comparative example, the graphite powder itself is conductive and has not been magnetized, which affects its contact with the cathode plate. The graphite powder cannot be pulled to the cathode by the magnetic field, but it can still collide and contact with the cathode plate. As the electroplating time increases, a coating will form, but the surface quality of the electroplated layer is extremely poor.

[0108] Comparative Example 3

[0109] This comparative example is carried out using a method similar to that of Example 1, except that "Step 3" is omitted, and the graphite particles obtained in "Step 2" are directly subjected to chemical plating (Step 4) and magnetofluidization electroplating treatment (Step 5). Steps 4 and 5 are the same as in Example 1.

[0110] Comparative Example 4

[0111] This comparative example was carried out using a method similar to that of Example 1, except that "step four" was omitted. Instead, the activated graphite particles (with weak magnetism) obtained in "step three" were directly subjected to magnetofluidization electroplating treatment, and the mass ratio of the magnetized layer (nickel layer) to the material to be plated (graphite particles) was approximately 0.1 wt%.

[0112] Comparative Example 5

[0113] This comparative example was carried out using a method similar to that of Example 4, except that "Step 2" was omitted, and the graphite particles obtained in "Step 1" were directly subjected to chemical plating (Step 3) and magnetofluidization electroplating treatment (Step 4).

[0114] Comparative Example 6

[0115] This comparative example was carried out using a method similar to that of Example 8, except that "Step Two" and "Step Three" were omitted, and the alumina powder obtained in "Step One" was directly subjected to magnetofluidization electroplating.

[0116] Comparative Example 7

[0117] This comparative example was carried out using a method similar to that of Example 9, except that "Step Two" and "Step Three" were omitted, and the zirconium oxide powder obtained in "Step One" was directly subjected to magnetofluidization electroplating.

[0118] Comparative Example 8

[0119] This comparative example was performed using a method similar to that of Example 4, except that the reverse polarity function was turned off, i.e., the frequency was 0 times.

[0120] Comparative Example 9

[0121] This comparative example was carried out using a method similar to that of Example 1, except that the loading amount of graphite particles in step four was adjusted to 100 g / L, so that the mass ratio of the magnetized nickel-coated graphite magnetized layer (nickel layer) to the mass of the material to be plated (graphite particles) was 3wt.

[0122] Comparative Example 10

[0123] This comparative example is carried out using a method similar to that of Example 4, except that the single-time magnetic field maintenance time in "Step 4" is changed to 3 s and the single-time fluidization time of the flow field is changed to 2 s.

[0124] The powder quality of the heterogeneous coated materials prepared in the above examples is shown in Table 1.

[0125] Table 1

[0126]

[0127] In the table, “Excellent,” “Good,” “Poor,” and “Very Poor” refer to:

[0128] Excellent: The powder surface is smooth and flat, without obvious undulations or rough particles; the coating is 100% continuous and complete, without any missed plating, pinholes, pitting, or cracks, and without free self-nucleated metal particles. Figure 2 The cross-section shows that the coating thickness is uniform and consistent, the core-shell interface is clear and sharp, the bonding is tight, and there are no gaps, voids or peeling. The boundary between the core and shell materials is clear, and the entire powder cross-section is completely covered by the uniform coating without any dead corners. Figure 4 ).

[0129] Good: The powder surface is basically flat with only a very small number of minor undulations. The coating is continuous with no visible gaps and no obvious free euhedral metal particles. The cross-section shows that the coating thickness is basically uniform, the core-shell interface is well bonded, there are only a very small number of minor gaps and no local peeling. All powder sections are completely covered by the coating.

[0130] Poor: The powder surface is rough and uneven, with obvious pits and granular protrusions, a small number of local uncoated areas, a small number of free euhedral metal particles, and slight adhesion of the powder; the cross-section shows uneven coating thickness, poor core-shell interface bonding, many gaps and local peeling areas, and discontinuous coating in some powder cross-sections.

[0131] Extremely poor: The powder surface is uneven, the coating is distributed in island or cluster shape, there is a large area of ​​uncoated areas, the coating is discontinuous and has a large number of cracks and holes, there are a large number of free euhedral metal particles, and the powder is severely agglomerated; the cross-section shows that the coating thickness is extremely uneven, and most powder sections have only local coating or no coating at all.

[0132] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing a heterogeneous coating material, characterized in that: The method includes: (1) Perform surface magnetization treatment on the surface of the material to be plated to obtain a material containing a magnetized layer; (2) The material to be plated containing the magnetized layer is placed in the electroplating solution for magnetic fluidization electroplating treatment to obtain a heterogeneous coating material; the material of the material to be plated in the heterogeneous coating material is different from the material of the electroplating layer, and the electroplating layer is a metal layer. The magnetofluidized electroplating process is carried out in a cyclical alternation of magnetic field and flow field, and the magnetic field is maintained for 10~200s at a time, and the magnetic field is always applied on the cathode side. The flow field is fluidized for 3~50s at a time. The power supply for the magnetofluidized electroplating process has a reversing function, with a reversing frequency of 10min~3h / time and a reversing duration of 10min~3h / time.

2. The method for preparing a heterogeneous coating material according to claim 1, characterized in that: In the material to be plated containing the magnetizing layer, the mass ratio of the magnetizing layer to the mass of the material to be plated is ≥5wt%; And / or, the reversal frequency is 15~45 min / time, and the reversal duration is 15~45 min / time.

3. The method for preparing a heterogeneous coating material according to claim 2, characterized in that: In the material to be plated containing the magnetizing layer, the mass ratio of the magnetizing layer to the mass of the material to be plated is 5~30wt%.

4. A method for preparing a heterogeneous coating material according to claim 1 or 2, characterized in that: The material of the magnetizing layer is selected from at least one of iron, cobalt and nickel; And / or, surface magnetization is performed using a single chemical plating method.

5. The method for preparing a heterogeneous coating material according to claim 4, characterized in that: The single-pass electroless plating method includes: first activating the material to be plated, then placing it in an electroless plating solution for electroless plating to obtain a material containing a magnetic layer. The activation treatment method is either Scheme A or Scheme B; Scheme A: (a1) After calcining the material to be plated, it is immersed in a nickel source solution and then dried to obtain an intermediate material to be plated; (a2) The intermediate material to be plated is reduced with hydrogen and then fluidized in a mixture of nitrogen and hydrogen. Option B: After the material to be plated is degreased by alkaline washing, it is immersed in an acid solution for treatment II, and then sensitized in a sensitization solution and activated in an activation solution in sequence.

6. The method for preparing a heterogeneous coating material according to claim 5, characterized in that: In Scheme A, the calcination treatment is carried out at a temperature of 300~600℃ for 1~4 hours; The solid-liquid ratio of the nickel source solution to the material to be plated is 3~30g / 100mL; The nickel source solution is a nickel chloride solution with a concentration of 100~600 g / L; The immersion treatment I is performed at a temperature of 30~80℃ for a time of 0.5~5h. The hydrogen reduction is carried out at a temperature of 250~350℃ for a time of 20~50 min; In the nitrogen and hydrogen mixture, the flow rates of nitrogen and hydrogen are each independently 0.2~1.2 L / min; or, In scheme B, the sensitizing solution is a tin-containing solution; the sensitization time is 10~90 min; The activation solution is a palladium-containing solution; the activation time is 10~90 min.

7. A method for preparing a heterogeneous coating material according to claim 1 or 2, characterized in that: The material of the electroplating layer is selected from at least one of copper, nickel, zinc, chromium, tin, silver, gold, iron, cobalt, lead, and cadmium; And / or, the material to be plated is non-magnetic; and the material to be plated is a carbonaceous material and / or a ceramic material.

8. The method for preparing a heterogeneous coating material according to claim 7, characterized in that: The carbonaceous material is selected from at least one of graphite, diamond, and carbon nanotubes; And / or, the ceramic material is selected from at least one of silicon nitride, silicon carbide, alumina, zirconium oxide, tungsten carbide, tin dioxide, chromium oxide, and molybdenum sulfide.

9. A method for preparing a heterogeneous coating material according to claim 1 or 2, characterized in that: The current density of the magnetofluidized electroplating treatment is 10~500 mA·cm. -2 The powder loading is 5~100 g·L -1 The electroplating treatment time is 0.1~30h; the single magnetic field holding time is 10~100s; the single fluidization time of the flow field is 3~30s; and the fluidization velocity is 0.05~5m·s. -1 ; Preferably, the current density of the magnetofluidization electroplating treatment is 60~300 mA·cm. -2 The fluidization velocity is 0.1~1 m·s. -1 The magnetic field is held for 15-50 seconds at a time, and the fluidization time of the flow field is 4-10 seconds at a time.

10. The heterogeneous coating material prepared by the preparation method according to any one of claims 1 to 9 is used in electrical contact elements, electromagnetic shielding and wave absorption, high-temperature lubrication, electronic heat dissipation, thermal spray coating, aerospace, precision molds and cutting tools, electronic packaging, or in the preparation of high-temperature industrial components.

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