Composite powder with core-shell structure and preparation method thereof

Abstract

The application discloses a kind of composite powder of core-shell structure and its preparation method, and the preparation method includes pretreatment, titanium dioxide coating treatment, plating solution treatment, silver coating treatment.Titanium dioxide coating treatment includes: after ultrasonic stirring with butyl titanate, anhydrous ethanol, dilute acid is added to prepare reaction solution;Nickel powder is added to the reaction solution for constant temperature reaction, and titanium dioxide coated nickel powder is obtained after reaction;Plating solution treatment includes: after ultrasonic stirring with titanium dioxide coated nickel powder, solvent, dispersing agent, constant temperature stirring is carried out, and reducing agent, sodium hydroxide solution is added, and dispersed solution is obtained after reaction;Silver coating treatment includes: after ultrasonic stirring dispersion with silver nitrate and deionized water, complexing agent is added to carry out complexing reaction;Then pour into dispersed solution under stirring state, and composite powder is obtained after reaction.The application can effectively improve the stability of nickel powder and the compactness of coating layer in the preparation process of composite powder, and then improve the conductivity of composite powder.

Description

Technical Field

[0001] The present invention relates to the technical field of metal composite materials, and in particular to a composite powder with a core-shell structure and a preparation method thereof. Background Art

[0002] Multilayer ceramic capacitors (MLCCs), also known as chip capacitors, multilayer capacitors, and stacked capacitors, are the most widely used capacitor in modern electronic devices. MLCCs are formed by stacking ceramic dielectric diaphragms with printed electrodes (inner electrodes) in an interlaced pattern. This is then sintered at high temperature to form a ceramic block, which is then sealed with a metal layer (outer electrodes) at both ends. During the inner electrode manufacturing process, metal particles are first mixed with a glass phase, a dispersant, and other ingredients to form a slurry. During this process, poor metal particle uniformity can affect the thickness uniformity of the electrodes after subsequent printing and sintering. If the metal particles interact with each other or with other particles, causing them to agglomerate, breakdown can occur during the lamination process.

[0003] Nickel, the primary material currently used in this field, must be co-fired with the electrolyte material (barium titanate) at high temperatures to form the electrode and dielectric layers. However, nickel readily oxidizes in air at high temperatures, so sintering must be performed in a reducing atmosphere. However, conventional barium titanate materials are prone to forming oxygen vacancies in a reducing atmosphere, resulting in a loose coating and poor density. Consequently, improving the stability of nickel powder during the preparation process and the density of the coating are key research areas for MLCC applications. Summary of the Invention

[0004] In order to overcome the above shortcomings, the purpose of the present invention is to provide a core-shell structured composite powder and a preparation method thereof, which can effectively improve the stability of nickel powder and the density of the coating layer during the preparation process of the composite powder, thereby helping to improve the electrical conductivity of the composite powder.

[0005] In order to achieve the above objectives, one of the technical solutions adopted by the present invention is: a method for preparing a core-shell structure composite powder, comprising sequentially performing pretreatment, titanium dioxide coating, plating treatment, and silver coating on nickel powder, wherein:

[0006] The titanium dioxide coating treatment comprises: sequentially adding butyl titanate and anhydrous ethanol into a reaction container, stirring and dispersing with ultrasonic stirring, and then adding dilute acid to prepare a reaction solution; adding the pretreated nickel powder into the reaction solution to carry out a constant temperature reaction, and then sequentially performing solid-liquid separation, washing, and drying to obtain titanium dioxide-coated nickel powder after the reaction;

[0007] The plating solution treatment comprises: sequentially adding titanium dioxide coated nickel powder, solvent and dispersant in a reaction container, and then performing ultrasonic stirring and dispersion, and then moving to an oil bath for constant temperature stirring, and then adding a reducing agent and sodium hydroxide solution during the constant temperature stirring, and then obtaining a dispersion solution after reaction;

[0008] The silver coating treatment comprises: taking another reaction container, adding silver nitrate and deionized water, and then performing ultrasonic stirring and dispersion, and then adding a complexing agent for complexing reaction, and then slowly adding the complexed silver source reaction solution into the dispersion solution for reaction under stirring, and then obtaining a composite powder after solid-liquid separation, washing and drying.

[0009] The preparation method of the core-shell structure composite powder has the following advantages:

[0010] 1. The nickel powder is first pretreated to remove impurities on the surface of the nickel powder, so that the nickel powder is more pure for subsequent treatment, and then the titanium dioxide coating treatment is performed to coat a layer of titanium dioxide on the surface of the nickel powder, so that the titanium dioxide coated nickel powder has the dual performance of titanium dioxide and nickel, and then the plating solution treatment is performed to enable the titanium dioxide coated nickel powder to participate in the subsequent silver coating treatment in the form of chemical plating, so as to realize the deposition of silver atoms on the surface of the titanium dioxide coated nickel powder, and due to the coating of silver atoms on the titanium dioxide coated nickel powder, the oxygen vacancies on the surface of the titanium dioxide coating layer can be filled by the deposition of silver atoms on the surface of the titanium dioxide coating layer, so as to improve the density of the coating layer, and the resistivity and high-temperature oxidation resistance of the composite powder are reduced by using the good conductivity of silver atoms.

[0011] 2. In the silver coating treatment, the addition of the complexing agent can slow down the deposition rate of silver atoms, so that the silver atoms are better coated on the surface of the titanium dioxide coated nickel powder, and in the plating solution treatment, the pH value of the dispersion solution can be adjusted by adding sodium hydroxide solution, so as to reduce the phenomenon of hindering silver deposition coating caused by the adsorption of complex ions on the surface of the particles in the silver coating treatment, and by using titanium dioxide as an intermediate transition layer between nickel and silver, the probability of deformation of the composite powder during high-temperature sintering can be reduced by using the low high-temperature expansion coefficient of titanium dioxide, and the thickness of the intermediate transition layer of titanium dioxide can be adjusted by changing the amount of tetrabutyl titanate added, so that the uniformity of the titanium dioxide coating is better, which is beneficial to the subsequent silver coating.

[0012] 3. The preparation method of the present application has low cost, simple process and easy operation, and the prepared composite powder can have the performance of nickel, titanium dioxide and silver, which is better applied in the field of MLCC.

[0013] Further, the pretreatment includes oil removal treatment, roughening treatment and activation treatment in sequence, the oil removal treatment includes adding nickel powder and surface cleaning agent in a reaction container, after ultrasonic stirring, standing and settling for solid-liquid separation, using deionized water to wash the settled nickel powder for multiple times; the roughening treatment includes adding the oil removal treated nickel powder, dilute acid in a reaction container in sequence, after ultrasonic stirring, standing and settling for solid-liquid separation, using deionized water to wash the settled nickel powder for multiple times; the activation treatment includes adding the roughening treated nickel powder, deionized water, surfactant in a reaction container in sequence, constant temperature stirring until the reaction is completed, standing and settling for solid-liquid separation, using deionized water to wash the settled nickel powder for multiple times. The oil removal treatment can remove the oil stains on the surface of the nickel powder, the roughening treatment can remove the oxide layer on the surface of the nickel powder, and the activation treatment can improve the activation performance of the nickel powder, which is beneficial to the coating of titanium dioxide on the surface of the nickel powder particles.

[0014] Further, in the oil removal treatment, the surface cleaning agent is at least one of citric acid, dodecyl phenol polyoxyethylene ether, anhydrous ethanol, lauric acid alkylamine phosphate, fatty alcohol ether sodium sulfate, and the mass ratio of the surface cleaning agent to the nickel powder is 0.01 ~ 1:1.

[0015] Further, in the roughening treatment, the dilute acid is one of dilute sulfuric acid, dilute acetic acid and dilute hydrochloric acid, and the mass ratio of the dilute acid to the oil removal treated nickel powder is 5 ~ 15:1.

[0016] Further, in the activation treatment, the surfactant is a silane coupling agent, and the mass ratio of the surfactant to the roughening treated nickel powder is 0.01 ~ 1:1.

[0017] Further, in the titanium dioxide coating treatment, the mass ratio of the dilute acid to butyl titanate is 0.1 ~ 1:1, and the temperature of the constant temperature reaction is 20 ~ 80℃.

[0018] Further, in the plating solution treatment, the solvent is at least one of deionized water, anhydrous ethanol, ethylene glycol and glycerol, the dispersant is at least one of polyvinylpyrrolidone, polyethylene glycol, sodium dodecyl sulfate and ammonium citrate, and the reducing agent is at least one of glucose, L-ascorbic acid, hydrazine hydrate and sodium hypophosphite.

[0019] Further, in the plating solution treatment, the addition amount of the sodium hydroxide solution is to keep the pH value of the dispersion solution between 12 and 13.

[0020] Furthermore, during the silver coating treatment, the complexing agent is at least one of ammonia water, ethylenediaminetetraacetic acid, disodium ethylenediaminetetraacetate, diethylenetriamine, and triethylenetetramine, and the mass ratio of the complexing agent to silver nitrate is 1 to 50:1.

[0021] The second technical solution employed by the present invention is a core-shell composite powder produced using any of the aforementioned preparation methods. Through double coating (one with titanium dioxide and one with silver), the composite powder of the present invention combines the reduction resistance of titanium dioxide with the high conductivity of silver on the basis of nickel powder, making the composite powder more suitable for use in conductive pastes and MLCC applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a scanning electron microscope image of the composite powder of Example 1 of the present invention;

[0023] Figure 2 This is a scanning electron microscope image of the composite powder of Example 2 of the present invention;

[0024] Figure 3 This is a scanning electron microscope image of the composite powder of Example 3 of the present invention;

[0025] Figure 4 This is a scanning electron microscope image of the composite powder of Comparative Example 1 of the present invention;

[0026] Figure 5 This is a scanning electron microscope image of the composite powder of Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0027] The preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making a clearer and more precise definition of the protection scope of the present invention.

[0028] Example

[0029] The present invention provides a method for preparing a composite powder with a core-shell structure, comprising sequentially performing pretreatment, titanium dioxide coating, plating treatment, and silver coating on nickel powder. Specifically,

[0030] The pretreatment process includes degreasing, roughening, and activation, performed sequentially. The degreasing process involves adding nickel powder and a surface cleaning agent to a reaction vessel (e.g., a beaker), ultrasonically agitating the reaction vessel, then allowing the reaction vessel to settle for solid-liquid separation, and washing the settled nickel powder multiple times with deionized water. Furthermore, the surface cleaning agent is at least one of citric acid, dodecylphenol polyoxyethylene ether (OP-10), anhydrous ethanol, lauric acid alkylamine phosphate, and sodium fatty alcohol ether sulfate, with a surface cleaning agent to nickel powder mass ratio of 0.01 to 1:1. Exemplarily, the surface cleaning agent to nickel powder mass ratio can be 0.01:1, 0.05:1, 0.1:1, 0.2:1, 0.4:1, 0.8:1, or 1:1.

[0031] The roughening treatment includes adding degreased nickel powder and dilute acid to a reaction vessel, stirring ultrasonically, and then allowing the mixture to settle for solid-liquid separation. The settled nickel powder is washed multiple times with deionized water until the pH of the washing solution is neutral. Furthermore, the dilute acid is selected from the group consisting of dilute sulfuric acid, dilute acetic acid, and dilute hydrochloric acid, with the mass ratio of the dilute acid to the degreased nickel powder being 5 to 15:1. For example, the mass ratio of the dilute acid to the nickel powder can be 5:1, 7:1, 9:1, 10:1, 11:1, 13:1, or 15:1.

[0032] The activation treatment includes adding the roughened nickel powder, deionized water, and a surfactant to a reaction vessel, stirring at a constant temperature until the reaction is completed, allowing the nickel powder to settle for solid-liquid separation, and washing the settled nickel powder multiple times with deionized water. Furthermore, the surfactant is at least one of silane coupling agent KH550, silane coupling agent KH560, silane coupling agent KH570, and silane coupling agent KH590. The mass ratio of the surfactant to the roughened nickel powder is 0.01 to 1:1. Exemplarily, the mass ratio of the surfactant to the nickel powder can be 0.01:1, 0.05:1, 0.1:1, 0.2:1, 0.4:1, 0.8:1, or 1:1.

[0033] The titanium dioxide coating treatment includes: adding butyl titanate and anhydrous ethanol to a separate reaction vessel (e.g., a beaker), sequentially adding butyl titanate and anhydrous ethanol to the reaction vessel, ultrasonically stirring and dispersing the mixture, and then adding dilute acid to produce a reaction solution; adding the pretreated nickel powder to the reaction solution for a constant temperature reaction; and after the reaction is completed, allowing the powder to settle for solid-liquid separation. The powder is then washed with anhydrous ethanol and dried in a high-temperature drying oven to obtain titanium dioxide-coated nickel powder. Furthermore, the dilute acid can be one of dilute sulfuric acid, dilute acetic acid, and dilute hydrochloric acid, with a mass ratio of dilute acid to butyl titanate of 0.1 to 1:1, for example, 0.1:1, 0.3:1, 0.5:1, 0.8:1, or 1:1. The constant temperature reaction temperature is 20 to 80°C, for example, 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, or 80°C.

[0034] The plating solution treatment includes sequentially adding titanium dioxide-coated nickel powder, a solvent, and a dispersant into a reaction container, dispersing the solution by ultrasonic stirring, and then moving the solution into an oil bath for constant temperature stirring. During the constant temperature stirring process, a reducing agent is added, and a sodium hydroxide solution is added to adjust the pH value of the solution, and a dispersed solution is obtained after the reaction.

[0035] The solvent is at least one of deionized water, anhydrous ethanol, ethylene glycol, and glycerol. The mass ratio of the solvent to the nickel in the titanium dioxide-coated nickel powder is 10 to 100:1, for example, 10:1, 20:1, 30:1, 40:1, 50:1, 75:1, or 100:1.

[0036] The dispersant is at least one of polyvinyl pyrrolidone, polyethylene glycol 200, polyethylene glycol 2000, sodium lauryl sulfate, and ammonium citrate. The mass ratio of the dispersant to the nickel in the titanium dioxide-coated nickel powder is 0.001 to 1:1, for example, 0.001:1, 0.01:1, 0.1:1, 0.2:1, 0.5:1, 0.8:1, or 1:1.

[0037] The reducing agent is at least one of glucose, L-ascorbic acid, hydrazine hydrate, and sodium hypophosphite. The mass ratio of the reducing agent to silver nitrate is 0.1 to 10:1, for example, 0.1:1, 0.2:1, 0.5:1, 1:1, 2:1, 5:1, or 10:1.

[0038] Furthermore, the amount of sodium hydroxide solution added is such that the pH value of the dispersed solution is maintained between 12 and 13, so as to reduce the adsorption of nickel ammonia complex ions and silver ammonia complex ions on the particle surface during the subsequent complexation reaction between the dispersed solution and silver nitrate and the complexing agent, thereby affecting the deposition and coating of silver atoms.

[0039] The silver coating treatment includes: taking another reaction container (such as a beaker), adding silver nitrate and deionized water into the reaction container, and after ultrasonic stirring and dispersion, adding a complexing agent to carry out a complexing reaction; then slowly adding the complexed silver source reaction solution to the dispersed solution under stirring. After the reaction is completed, the solution is allowed to settle to separate the solid and liquid, and the solution is washed with deionized water until it is clear, and then washed twice with anhydrous ethanol and dried in a 60°C forced air drying oven for 3 to 6 hours to obtain a composite powder.

[0040] The complexing agent is at least one of ammonia water, ethylenediaminetetraacetic acid, disodium ethylenediaminetetraacetate, diethylenetriamine, and triethylenetetramine, and the mass ratio of the complexing agent to silver nitrate is 1 to 50:1, for example, 1:1, 5:1, 10:1, 20:1, 30:1, 40:1 or 50:1.

[0041] The present invention performs pretreatment to remove oil, remove oxide layer and activate the surface of nickel powder at one time, so that titanium dioxide is coated on the surface of nickel powder particles. Then, silver is deposited on the surface of the titanium dioxide-coated nickel powder by chemical plating, so as to reduce oxygen vacancies on the titanium dioxide surface by doping with silver metal, inhibit the crystallization of titanium dioxide and other phases, and improve the electrical conductivity of the composite powder.

[0042] Example 1

[0043] The composite powder 1 was prepared by the following steps:

[0044] Step 1: Add 1g of citric acid and 1000mL of deionized water to a beaker in sequence, stir to dissolve, add 10g of nickel powder to the citric acid solution, stir ultrasonically, and then let it stand for sedimentation. Then, wash it twice with anhydrous ethanol and three times with deionized water for use.

[0045] Step 2: Add 1000 mL of deionized water and 10 g of 98.3% sulfuric acid to a beaker in sequence and stir to mix. Then add the nickel powder treated in step 1 and perform ultrasonic stirring for 30 minutes (the frequency of the ultrasonic cleaning machine is 50 kHz). Then let it stand and settle for solid-liquid separation. Wash with deionized water until the solution is neutral for later use.

[0046] Step 3: Add 1000 mL of deionized water and 1 g of silane coupling agent KH550 to a beaker in sequence and stir to mix. Then add the nickel powder cleaned in step 2 and stir at a constant temperature of 40 ° C for 5 hours. After the reaction is completed, let it stand and settle for solid-liquid separation, and wash with anhydrous ethanol 3-5 times and then use deionized water to wash until the solution is clear for use.

[0047] Step 4: Add 10 g of butyl titanate and 1000 mL of anhydrous ethanol to a beaker, stir to mix, then add 10 g of 36.5% dilute acetic acid and the nickel powder cleaned in step 3 in sequence and stir at 500 rpm, add 50 g of deionized water at a rate of 1 ml / min, continue the reaction for 2 h after the addition is completed, let it stand and settle for solid-liquid separation and wash with ethanol 3-5 times. The washed wet powder is placed in a high-temperature drying oven and dried at 60 °C to obtain titanium dioxide-coated nickel powder.

[0048] Step 5: Add the titanium dioxide-coated nickel powder obtained in step 4, 1000 mL of deionized water, and 1 g of ammonium citrate to a beaker in sequence and stir for 30 minutes. Then move the mixture to an oil bath, add 4 g of glucose, and stir at 80°C to prepare a dispersed solution. Add sodium hydroxide solution in the middle to adjust the pH value of the solution to 12-13.

[0049] Step 6: Take another beaker, add 10 g of silver nitrate and 1000 mL of deionized water into the beaker and stir ultrasonically, then add 20 g of ethylenediaminetetraacetic acid and stir for 30 min, add the complexed silver source to the dispersed solution in step 5 and stir at 80 ° C at a speed of 300 rpm to react, after the reaction is completed, settle and perform solid-liquid separation, wash the solution with deionized water until it is clear, then wash twice with anhydrous ethanol and place it in a 60 ° C forced drying oven for 6 h to obtain the following Figure 1 The composite powder 1 shown.

[0050] Example 2

[0051] Step 1: Add 1g of citric acid and 1000mL of deionized water to a beaker in sequence, stir to dissolve, add 10g of nickel powder to the citric acid solution, stir ultrasonically, and then let it stand for sedimentation. Then, wash it twice with anhydrous ethanol and three times with deionized water for use.

[0052] Step 2: Add 1000 mL of deionized water and 10 g of 98.3% sulfuric acid to a beaker in sequence and stir to mix. Then add the nickel powder treated in step 1 and perform ultrasonic stirring for 30 minutes (the frequency of the ultrasonic cleaning machine is 50 kHz). Then let it stand and settle for solid-liquid separation. Wash with deionized water until the solution is neutral for later use.

[0053] Step 3: Add 1000 mL of deionized water and 0.5 g of silane coupling agent KH550 to a beaker in sequence and stir to mix. Then add the nickel powder cleaned in step 2 and stir at 40 ° C for 5 hours. After the reaction is completed, let it stand and settle for solid-liquid separation, and wash with anhydrous ethanol 3-5 times and then use deionized water to wash until the solution is clear for use.

[0054] Step 4: Add 50 g of butyl titanate and 1000 mL of anhydrous ethanol to a beaker, stir to mix, then add 50 g of 36.5% dilute acetic acid and the nickel powder cleaned in step 3 in sequence and stir at 500 rpm, add 50 g of deionized water at a rate of 1 ml / min, continue the reaction for 5 h after the addition is completed, let it stand and settle for solid-liquid separation and wash with ethanol 3-5 times. The washed wet powder is placed in a high-temperature drying oven and dried at 60 °C to obtain titanium dioxide-coated nickel powder.

[0055] Step 5: Add the titanium dioxide-coated nickel powder obtained in step 4, 1000 mL of deionized water, and 10 g of ammonium citrate to a beaker in sequence and stir for 30 min. Then move the mixture to an oil bath, add 40 g of L-ascorbic acid, and stir at 80°C to prepare a dispersed solution. Add sodium hydroxide solution midway to adjust the pH value of the solution to 12-13.

[0056] Step 6: Take another beaker, add 10 g of silver nitrate and 1000 mL of deionized water into the beaker and stir ultrasonically, then add 20 g of ethylenediaminetetraacetic acid and stir for 30 min, add the complexed silver source to the dispersed solution in step 5 and stir at 40 ° C at a speed of 300 rpm to react, after the reaction is completed, settle and perform solid-liquid separation, wash the solution with deionized water until it is clear, then wash twice with anhydrous ethanol and place it in a 60 ° C forced drying oven for 4 h to obtain the following Figure 2 The composite powder 2 shown.

[0057] Example 3

[0058] Step 1: Add 3g OP-10 and 1000mL deionized water to a beaker in sequence, stir to dissolve, add 10g nickel powder to the OP-10 solution, stir ultrasonically, and then let it stand for sedimentation. Then, wash it twice with anhydrous ethanol and three times with deionized water before use.

[0059] Step 2: Add 1000 mL of deionized water and 10 g of 98.3% sulfuric acid to a beaker in sequence and stir to mix. Then add the nickel powder treated in step 1 and perform ultrasonic stirring for 30 minutes (the frequency of the ultrasonic cleaning machine is 50 kHz). Then let it stand and settle for solid-liquid separation. Wash with deionized water until the solution is neutral for later use.

[0060] Step 3: Add 1000 mL of deionized water and 0.5 g of silane coupling agent KH550 to a beaker and stir to mix. Then add the nickel powder cleaned in step 2 and stir at 40 ° C for 5 hours. After the reaction is completed, let it stand and settle for solid-liquid separation, and wash with anhydrous ethanol 3-5 times and then use deionized water to wash until the solution is clear for use.

[0061] Step 4: Add 50 g of butyl titanate and 1000 mL of anhydrous ethanol to a beaker, stir to mix, then add 25 g of 36.5% dilute acetic acid and the nickel powder cleaned in step 3 in sequence and stir at 500 rpm, add 25 g of deionized water at a rate of 1 ml / min, continue the reaction for 5 hours after the addition is completed, let it stand and settle for solid-liquid separation and wash with ethanol 3-5 times. The washed wet powder is placed in a high-temperature drying oven and dried at 60 ° C to obtain titanium dioxide-coated nickel powder.

[0062] Step 5: Add the titanium dioxide-coated nickel powder obtained in step 4, 1000 mL of deionized water and 5 g of polyvinylpyrrolidone to a beaker in sequence and stir for 30 minutes. Then move the mixture to an oil bath, add 40 g of L-ascorbic acid and stir at 40°C to prepare a dispersed solution. Add sodium hydroxide solution in the middle to adjust the pH value of the solution to 12-13.

[0063] Step 6: Take another beaker, add 10 g of silver nitrate and 1000 mL of deionized water into the beaker and stir ultrasonically, then add 20 g of ethylenediaminetetraacetic acid and stir for 30 min, add the complexed silver source to the dispersion in step 5 and stir at 40 ° C at a speed of 300 rpm to react, after the reaction is completed, settle to separate the solid and liquid, and wash the solution with deionized water until it is clear, then wash twice with anhydrous ethanol and place it in a 60 ° C forced drying oven for 6 h to obtain the following Figure 3 The composite powder 3 shown.

[0064] Comparative Example 1

[0065] Prepare as Figure 4 The composite powder 4 shown in FIG. 4 is prepared in the same manner as in Example 1, and the only difference between the preparation steps is that the addition of sodium hydroxide is omitted in step five.

[0066] Comparative Example 2

[0067] Prepare as Figure 5 The composite powder 5 shown in FIG. 5 is prepared in the same manner as in Example 1 except that step 4 and step 5 are omitted.

[0068] The resistance of the composite powders prepared in Examples 1-3 and Comparative Examples 1-2 was tested, and the test data are shown in Table 1.

[0069] Table 1

[0070]

[0071] from Figure 1-5 And Table 1 shows that:

[0072] 1. In the SEM images of Examples 1-3, the particles are well adhered, while in the SEM images of Comparative Example 1-2, the particles are distributed in a dotted manner, and there is no obvious adhesion between the particles. It can be seen that the composite powders (Examples 1-3) prepared by the preparation method of the present invention have better coverage and coating smoothness, among which Example 1 has the best coverage.

[0073] 2. The resistivity and high-temperature oxidation resistance of Examples 1-3 are significantly lower than those of Comparative Examples 1-2. Lower resistivity indicates higher coverage, while lower high-temperature oxidation resistance indicates lower levels of over-oxidation of the nickel surface by gases in high-temperature atmospheres. This demonstrates that the composite powders prepared using the present method exhibit excellent coating density, effectively preventing oxidation of the nickel surface by gases passing through the gaps in the coating layer.

[0074] The above embodiments are only for illustrating the technical concept and features of the present invention. Its purpose is to enable people familiar with this technology to understand the content of the present invention and implement it. It cannot be used to limit the scope of protection of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a composite powder with a core-shell structure, characterized in that: The method includes sequentially performing pretreatment, titanium dioxide coating, plating solution treatment, and silver coating treatment on nickel powder, wherein: The titanium dioxide coating treatment comprises: sequentially adding butyl titanate and anhydrous ethanol into a reaction container, stirring and dispersing with ultrasonic stirring, and then adding dilute acid to prepare a reaction solution; adding the pretreated nickel powder into the reaction solution to carry out a constant temperature reaction, and then sequentially performing solid-liquid separation, washing, and drying to obtain titanium dioxide-coated nickel powder after the reaction; The plating solution treatment comprises: sequentially adding titanium dioxide-coated nickel powder, a solvent, and a dispersant into a reaction container, dispersing by ultrasonic stirring, and then transferring to an oil bath for constant temperature stirring; adding a reducing agent and a sodium hydroxide solution during the constant temperature stirring process, and obtaining a dispersed solution after reaction; The solvent is at least one of deionized water, anhydrous ethanol, ethylene glycol, and glycerol, and the mass ratio of the solvent to the nickel in the titanium dioxide-coated nickel powder is 10-100:1; The dispersant is at least one of polyvinyl pyrrolidone, polyethylene glycol, sodium lauryl sulfate, and ammonium citrate, and the mass ratio of the dispersant to the nickel in the titanium dioxide-coated nickel powder is 0.001 to 1:1; The silver coating treatment comprises: adding silver nitrate and deionized water to another reaction container, dispersing them with ultrasonic stirring, and then adding a complexing agent to carry out a complexing reaction; slowly adding the complexed reaction liquid to the dispersed solution under stirring to react, and after the reaction, sequentially performing solid-liquid separation, washing, and drying to obtain a composite powder; The reducing agent is at least one of glucose, L-ascorbic acid, hydrazine hydrate, and sodium hypophosphite, and the mass ratio of the reducing agent to silver nitrate is 0.1 to 10:1; The complexing agent is at least one of ammonia water, ethylenediaminetetraacetic acid, disodium ethylenediaminetetraacetate, diethylenetriamine, and triethylenetetramine, and the mass ratio of the complexing agent to silver nitrate is 1 to 50:1; The pretreatment includes degreasing treatment, coarsening treatment and activation treatment performed in sequence. The degreasing treatment includes adding nickel powder and a surface cleaning agent into a reaction container, ultrasonically stirring, allowing the mixture to settle for solid-liquid separation, and washing the settled nickel powder multiple times with deionized water. The coarsening treatment includes sequentially adding degreasing nickel powder and dilute acid into a reaction container, ultrasonically stirring, allowing the mixture to settle for solid-liquid separation, and washing the settled nickel powder multiple times with deionized water. The activation treatment includes sequentially adding coarsening nickel powder, deionized water and a surfactant into a reaction container, stirring at a constant temperature until the reaction is completed, allowing the mixture to settle for solid-liquid separation, and washing the settled nickel powder multiple times with deionized water.

2. The preparation method according to claim 1, characterized in that During the degreasing treatment, the surface cleaning agent is at least one of citric acid, dodecylphenol polyoxyethylene ether, anhydrous ethanol, and sodium fatty alcohol ether sulfate, and the mass ratio of the surface cleaning agent to the nickel powder is 0.01 to 1:

1.

3. The preparation method according to claim 1, characterized in that During the roughening treatment, the dilute acid is one of dilute sulfuric acid, dilute acetic acid, and dilute hydrochloric acid, and the mass ratio of the dilute acid to the deoiled nickel powder is 5 to 15:

1.

4. The preparation method according to claim 1, characterized in that During the activation treatment, the surfactant is a silane coupling agent, and the mass ratio of the surfactant to the nickel powder after the roughening treatment is 0.01 to 1:

1.

5. The preparation method according to claim 1, characterized in that During the titanium dioxide coating treatment, the mass ratio of the dilute acid to butyl titanate is 0.1 to 1:1, and the constant temperature reaction temperature is 20 to 80°C.

6. The preparation method according to claim 1, characterized in that During the plating solution treatment, the amount of sodium hydroxide solution added is such that the pH value of the dispersed solution is maintained between 12 and 13.

7. A composite powder with a core-shell structure, characterized in that: The method is prepared by any one of claims 1 to 6.

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