Monodisperse nano spherical copper powder, liquid phase reduction preparation method and application

Abstract

The invention belongs to the technical field of metal powder, and particularly relates to monodisperse nanometer spherical copper powder and a liquid phase reduction preparation method and application. According to the liquid-phase reduction preparation method of the monodisperse nano spherical copper powder, the silver salt and the copper salt are introduced at the same time, so that the nano spherical copper powder with the small particle size can be rapidly synthesized by taking the pre-reduced silver crystal nucleus as the core in the constant-temperature reduction reaction; meanwhile, by controlling the proportion of the silver salt, the copper salt and the dispersing agent, the probability that the nano spherical copper powder is gathered together due to collision is reduced, so that a subsequent separation step is not needed, the production process of the nano spherical copper powder is simplified, and the technical problem that an efficient synthesis method of the nano spherical copper powder is lacked in the prior art is solved.

Description

Technical Field

[0001] The present application belongs to the technical field of metal powders, and in particular relates to a monodisperse nano-spherical copper powder and a liquid phase reduction preparation method and application. Background Art

[0002] Nano copper powder is a fine spherical powder with good electrical conductivity, thermal conductivity and chemical stability, and is widely used in the field of electronic components. Multilayer ceramic capacitors (MLCC) are one of the main passive chip components in electronic devices, including internal and external electrodes and ceramic layers. The internal electrodes are mainly nickel electrodes, and the external electrodes are mainly copper electrodes. MLCC electrodes use nano spherical copper powder, but nano spherical copper powder has high surface activity and is very easy to agglomerate and oxidize, resulting in high technical requirements for its production, preparation and storage. At present, domestic MLCC electrode nano spherical copper powder mainly relies on imports; therefore, it is of great value to develop a synthesis method for highly dispersible and anti-oxidative nano spherical copper powder.

[0003] At present, nano-spherical copper powder for MLCC electrodes can be synthesized by solid phase method, gas phase method and liquid phase method. The solid phase method mainly uses physical crushing and other methods, and uses hard media for stirring and grinding. The metal copper powder is crushed and ground to reduce the particle size, thereby obtaining nano-spherical copper powder. The gas phase method refers to a method in which the reaction gas undergoes a chemical reaction under the action of heat, laser, reducing gas, etc. to generate nano-spherical copper powder. For example, copper acetylacetonate is deposited in the pores as a reaction precursor, and then the reducing gas hydrogen is introduced into the pores to continuously reduce the precursor to generate nano-spherical copper. Powder; the liquid phase method mainly refers to the precipitation of nano-spherical copper powder from a metal cation solution under the action of a reducing agent by controlling certain reaction conditions; since nano-spherical copper powder is easy to aggregate during the solid phase grinding process, it is difficult to control the dispersion of nano-spherical copper powder during the preparation process, and the gas phase method usually requires specific equipment to generate heat, laser, and reducing gas, the cost of the preparation process is high, and it is difficult to industrialize mass production; while the liquid phase reduction process is not easy to aggregate nano-spherical copper powder, the production cost is low, and it is suitable for mass production and has attracted much attention, and has a good prospect for industrial development.

[0004] However, in the process of preparing nano spherical copper powder by liquid phase reduction method, due to the weak ability of copper ions to obtain electrons, the reduction speed to obtain nano spherical copper powder is slow, and nano spherical copper powder with larger particle size is easily generated; therefore, the current liquid phase reduction preparation method of nano spherical copper powder has poor effect, and it is difficult to prepare nano spherical copper powder efficiently, and there is a need for a new synthesis method of nano spherical copper powder. Summary of the invention

[0005] In view of this, the present application provides a monodisperse nano-spherical copper powder and a liquid phase reduction preparation method and application, which are used to solve the technical problem of the lack of an efficient synthesis method of nano-spherical copper powder in the prior art.

[0006] In a first aspect, the present application provides a method for preparing monodisperse nano-spherical copper powder by liquid phase reduction, the preparation method comprising the steps of:

[0007] Step S1, mixing a solution containing a reducing agent and a dispersant, a copper salt solution, and a silver salt solution to obtain a mixed solution;

[0008] Step S2, adding an alkaline solution to the mixed solution to adjust the pH and then perform a constant temperature reduction reaction to obtain a nano-spherical copper-coated silver powder suspension;

[0009] Step S3, adding the coating agent solution into the nano-spherical copper-coated silver powder suspension to carry out a constant temperature coating reaction to obtain a monodisperse nano-spherical copper powder suspension;

[0010] Step S4, sequentially subjecting the monodisperse nanometer spherical copper powder suspension to solid-liquid separation, washing, and drying to obtain monodisperse nanometer spherical copper powder.

[0011] Preferably, in step S1, the molar ratio of the dispersant, the copper ions in the copper salt solution, and the silver ions in the silver salt solution is 775:750:0.45-3.21.

[0012] Preferably, in step S1, the reducing agent is selected from at least one of ascorbic acid, isoascorbic acid, and sodium thiosulfate;

[0013] The dispersant is selected from at least one of sodium citrate, polyvinyl pyrrolidone, polyacrylamide, polyvinyl alcohol, and polyethyleneimine;

[0014] The solute in the copper salt solution is selected from at least one of copper sulfate pentahydrate, copper chloride, copper nitrate and copper acetate, and the solvent is water;

[0015] The solute in the silver salt solution is selected from at least one of silver sulfate, silver nitrate and silver chloride, and the solvent is ammonia water.

[0016] Preferably, in step S1, the dispersant is sodium citrate, the solute in the copper salt solution is copper sulfate pentahydrate, and the solute in the silver salt solution is silver sulfate;

[0017] The mass ratio of the sodium citrate, copper sulfate pentahydrate and silver sulfate is 200:187.5:0.14~1.

[0018] Preferably, in step S2, the alkaline solution is at least one of aqueous ammonia, sodium hydroxide solution, potassium hydroxide solution, ammonium carbonate solution, and urea solution.

[0019] Preferably, in step S3, the solute in the coating agent solution is benzotriazole and the solvent is water.

[0020] Preferably, in step S2, the pH is adjusted to 8-10;

[0021] The temperature of the isothermal reduction reaction is 60-80° C. and the time is 1-3 hours.

[0022] Preferably, in step S3, the temperature of the isothermal coating reaction is 60-80° C., and the time is 5-20 min.

[0023] Preferably, in step S4, the solid-liquid separation is performed by suction filtration or centrifugation;

[0024] The washing method is to wash with pure water 2 to 5 times;

[0025] The drying method is to dry in a vacuum drying oven at 70-90° C. for 2-4 hours.

[0026] The second aspect of the present application provides a monodisperse nano-spherical copper powder, which is prepared by the liquid phase reduction preparation method described in the first aspect.

[0027] The third aspect of the present application provides the use of the monodisperse nano-spherical copper powder described in the second aspect in the preparation of multilayer chip ceramic capacitor electrodes.

[0028] Compared with the prior art, the liquid phase reduction preparation method of monodisperse nano-spherical copper powder provided by the present application has at least the following beneficial technical effects:

[0029] 1. The liquid phase reduction preparation method provided in the present application introduces silver salt, which can be pre-reduced as the core of copper generation in the isothermal reduction reaction stage, thereby quickly synthesizing small-particle-size monodisperse nano-spherical copper powder; the yield of monodisperse nano-spherical copper powder prepared by the liquid phase reduction preparation method is improved and the particle size is reduced.

[0030] 2. The liquid phase reduction preparation method provided in the present application controls the ratio of silver salt, copper salt and dispersant, reduces the probability of nano-spherical copper powder agglomerating due to collision, simplifies the production process of nano-spherical copper powder, and can directly synthesize monodisperse nano-spherical copper powder.

[0031] 3. The reaction raw materials used in the liquid phase reduction preparation method provided in the present application are easy to obtain and meet the requirements of large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the specific implementation methods of the present application or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0033] Figure 1 This is an electron microscope image of the monodisperse nano-spherical copper powder prepared by the liquid phase reduction preparation method provided in Example 1 of the present application;

[0034] Figure 2 This is an electron microscope image of the monodisperse nano-spherical copper powder prepared by the liquid phase reduction preparation method provided in Example 2 of the present application;

[0035] Figure 3 This is an electron microscope image of the monodisperse nano-spherical copper powder prepared by the liquid phase reduction preparation method provided in Example 3 of the present application;

[0036] Figure 4 This is an electron microscope image of the monodisperse nano-spherical copper powder prepared by the liquid phase reduction preparation method provided in Example 4 of the present application;

[0037] Figure 5 This is an electron microscope image of the monodisperse nano-spherical copper powder prepared by the liquid phase reduction preparation method provided in Example 5 of the present application;

[0038] Figure 6 This is an electron microscope image of nano-spherical copper powder prepared by the liquid phase reduction preparation method provided in Example 6 of the present application. DETAILED DESCRIPTION

[0039] The present application provides a monodisperse nanometer spherical copper powder and a liquid phase reduction preparation method and application thereof, which are used to solve the technical problem of the lack of an efficient synthesis method of nanometer spherical copper powder in the prior art.

[0040] The technical solution of the present application will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present application.

[0041] In view of the defect that the current liquid phase reduction preparation method cannot efficiently synthesize nano spherical copper powder, the present application provides a liquid phase reduction preparation method for monodisperse nano spherical copper powder; the synthesis method comprises: firstly mixing a solution containing a reducing agent and a dispersant, a copper salt solution, and a silver salt solution to obtain a mixed solution; then adding an alkaline solution to adjust the pH of the mixed solution and then performing a constant temperature reduction reaction to obtain a nano spherical copper-coated silver powder suspension; then adding a coating agent to the nano spherical copper-coated silver powder suspension to perform a constant temperature coating reaction, and then performing solid-liquid reaction, washing, drying and other steps to obtain a monodisperse nano spherical copper powder.

[0042] In a liquid phase reduction preparation method for monodisperse nano-spherical copper powder provided by the present application, at the stage of isothermal reduction reaction; the ability of silver ions in the mixed solution to obtain electrons is stronger than that of copper ions, so that the silver ions will first obtain electrons and be reduced to generate a large number of silver crystal nuclei, and then the reduced copper ions will attach to the silver crystal nuclei and grow rapidly to obtain nano-spherical copper-coated silver powder, and the use of silver crystal nuclei shortens the time of copper powder synthesis reaction, and the silver crystal nuclei also reduce agglomeration, which is conducive to the generation of small-particle copper powder; and in the coating reaction stage after the isothermal reduction reaction, the copper powder is coated with a coating agent to improve the oxidation resistance of the copper powder, thereby overcoming the defects of the current slow reduction speed of nano-spherical copper powder, easy generation of spherical copper powder with larger particle size, and inability to efficiently synthesize nano-spherical copper powder.

[0043] As a preferred technical solution, in a liquid phase reduction preparation method for a monodisperse nano-spherical copper powder provided by the present application, in the process of generating silver crystal nuclei in the isothermal reduction reaction, when the amount of silver crystal nuclei generated is too much and the amount of dispersant is insufficient, the probability of the silver crystal nuclei colliding and aggregating will increase, and the generated nano-spherical copper powder will be close to each other, and it will need to be separated by mechanical means such as grinding to obtain dispersed nano-spherical copper powder; therefore, in order to reduce the subsequent cumbersome steps and simplify the process, the present application also controls the ratio of dispersant, copper and silver. Calculated by molar ratio, the molar ratio of the dispersant, the copper ions in the copper salt solution, and the silver ions in the silver salt solution is 775:750:0.45~3.21, and calculated by mass, the mass ratio of the dispersant sodium citrate, the copper source copper sulfate pentahydrate and the silver source silver sulfate is 200:187.5:0.14~1.

[0044] At the same time, in the reactants used in the liquid phase reduction preparation method of a monodisperse nano-spherical copper powder provided by the present application, the reducing agent is selected from at least one of ascorbic acid, isoascorbic acid, and sodium thiosulfate;

[0045] The dispersant is selected from at least one of sodium citrate, polyvinyl pyrrolidone and polyacrylamide; the solute in the copper salt solution is selected from at least one of copper sulfate pentahydrate, copper chloride, copper nitrate and copper acetate, and the solvent is water; the solute in the silver salt solution is selected from at least one of silver sulfate, silver nitrate and silver chloride, and the solvent is ammonia water; the alkaline solution is at least one of ammonia water, sodium hydroxide solution and potassium hydroxide solution; the solute in the coating agent solution is benzotriazole, and the solvent is water; it can be seen that the reducing agent, dispersant, copper salt, silver salt, alkaline solution and coating agent in the reactants used are all safe reaction reagents with low cost, which is conducive to the mass production of monodisperse nano spherical copper powder.

[0046] The following is a detailed description of the liquid phase reduction preparation method of a monodisperse nano-spherical copper powder provided by the present application in combination with embodiments and experimental examples.

[0047] Example 1

[0048] Example 1 of the present application provides a liquid phase reduction preparation method for monodisperse nano-spherical copper powder, the preparation method comprising the steps of preparing a reaction solution, a isothermal reduction reaction, a isothermal coating reaction, and a post-treatment step.

[0049] The steps of preparing the reaction solution include: uniformly mixing 218.35g of ascorbic acid, 200g of sodium citrate and 2kg of pure water to obtain a solution containing a reducing agent and a dispersant; uniformly mixing 187.5g of copper sulfate pentahydrate and 500g of water to obtain a copper salt solution; uniformly mixing 0.14g of silver sulfate and 100g of ammonia water to obtain a silver salt solution; uniformly mixing 1g of benzotriazole and 50g of water to obtain a coating agent solution; and respectively heating the solution containing the reducing agent and the dispersant, the copper salt solution, the silver salt solution and the coating agent solution to 70°C and then keeping them warm for standby use.

[0050] The steps of the isothermal reduction reaction include: installing a reaction container in a water bath, setting the temperature to 70°C, turning on a stirring device, and controlling the stirring speed at 300rpm; then adding a solution containing a reducing agent and a dispersant, a copper salt solution, and a silver salt solution into the reaction container, adding ammonia water to adjust the pH to 9, and then maintaining the temperature at 70°C for 2 hours to obtain a nano-spherical copper-coated silver powder suspension.

[0051] The step of isothermal coating reaction comprises: adding coating agent solution into nano spherical copper-coated silver powder suspension, maintaining 70° C. and continuing the reaction for 10 minutes to obtain monodisperse nano spherical copper powder suspension.

[0052] The post-treatment steps include: turning off the agitator and the constant temperature water bath, taking out the reaction container; separating the mixture in the reaction container into solid and liquid by centrifugal separation, and then washing the monodisperse nano spherical copper powder with pure water for 3 to 4 times until the conductivity of the supernatant is ≤10µs / cm; then putting the monodisperse nano spherical copper powder into a vacuum drying oven, setting the temperature to 80°C, and drying for 3 hours to obtain dry monodisperse nano spherical copper powder.

[0053] Example 2

[0054] Example 2 of the present application provides a liquid phase reduction preparation method for monodisperse nano-spherical copper powder, the preparation method comprising the steps of preparing a reaction solution, a isothermal reduction reaction, a isothermal coating reaction, and a post-treatment step.

[0055] The steps of preparing the reaction solution include: uniformly mixing 218.35g of ascorbic acid, 200g of sodium citrate and 2kg of pure water to obtain a solution containing a reducing agent and a dispersant; uniformly mixing 187.5g of copper sulfate pentahydrate and 500g of water to obtain a copper salt solution; uniformly mixing 0.5g of silver sulfate and 100g of ammonia water to obtain a silver salt solution; uniformly mixing 1g of benzotriazole and 50g of water to obtain a coating agent solution; and respectively heating the solution containing the reducing agent and the dispersant, the copper salt solution, the silver salt solution and the coating agent solution to 70°C and then keeping them warm for standby use.

[0056] The steps of the isothermal reduction reaction include: installing a reaction container in a water bath, setting the temperature to 70°C, turning on a stirring device, and controlling the stirring speed at 300rpm; then adding a solution containing a reducing agent and a dispersant, a copper salt solution, and a silver salt solution into the reaction container, adding ammonia water to adjust the pH to 9, and then maintaining the temperature at 70°C for 2 hours to obtain a nano-spherical copper-coated silver powder suspension.

[0057] The step of isothermal coating reaction comprises: adding coating agent solution into nano spherical copper-coated silver powder suspension, maintaining 70° C. and continuing the reaction for 10 minutes to obtain monodisperse nano spherical copper powder suspension.

[0058] The post-treatment steps include: turning off the agitator and the constant temperature water bath, taking out the reaction container; separating the mixture in the reaction container into solid and liquid by centrifugal separation, and then washing the monodisperse nano spherical copper powder with pure water for 3 to 4 times until the conductivity of the supernatant is ≤10µs / cm; then putting the monodisperse nano spherical copper powder into a vacuum drying oven, setting the temperature to 80°C, and drying for 3 hours to obtain dry monodisperse nano spherical copper powder.

[0059] Example 3

[0060] Example 3 of the present application provides a liquid phase reduction preparation method for monodisperse nano-spherical copper powder, the preparation method comprising the steps of preparing a reaction solution, a isothermal reduction reaction, a isothermal coating reaction, and a post-treatment step.

[0061] The steps of preparing the reaction solution include: uniformly mixing 218.35g of ascorbic acid, 200g of sodium citrate and 2kg of pure water to obtain a solution containing a reducing agent and a dispersant; uniformly mixing 187.5g of copper sulfate pentahydrate and 500g of water to obtain a copper salt solution; uniformly mixing 0.8g of silver sulfate and 100g of ammonia water to obtain a silver salt solution; uniformly mixing 1g of benzotriazole and 50g of water to obtain a coating agent solution; and respectively heating the solution containing the reducing agent and the dispersant, the copper salt solution, the silver salt solution and the coating agent solution to 70°C and then keeping them warm for standby use.

[0062] The steps of the isothermal reduction reaction include: installing a reaction container in a water bath, setting the temperature to 70°C, turning on a stirring device, and controlling the stirring speed at 300rpm; then adding a solution containing a reducing agent and a dispersant, a copper salt solution, and a silver salt solution into the reaction container, adding ammonia water to adjust the pH to 9, and then maintaining the temperature at 70°C for 2 hours to obtain a nano-spherical copper-coated silver powder suspension.

[0063] The step of isothermal coating reaction comprises: adding coating agent solution into nano spherical copper-coated silver powder suspension, maintaining 70° C. and continuing the reaction for 10 minutes to obtain monodisperse nano spherical copper powder suspension.

[0064] The post-treatment steps include: turning off the agitator and the constant temperature water bath, taking out the reaction container; separating the mixture in the reaction container into solid and liquid by centrifugal separation, and then washing the monodisperse nano spherical copper powder with pure water for 3 to 4 times until the conductivity of the supernatant is ≤10µs / cm; then putting the monodisperse nano spherical copper powder into a vacuum drying oven, setting the temperature to 80°C, and drying for 3 hours to obtain dry monodisperse nano spherical copper powder.

[0065] Example 4

[0066] Example 4 of the present application provides a liquid phase reduction preparation method for monodisperse nano-spherical copper powder, the preparation method comprising the steps of preparing a reaction solution, a isothermal reduction reaction, a isothermal coating reaction, and a post-treatment step.

[0067] The steps of preparing the reaction solution include: uniformly mixing 218.35g of ascorbic acid, 200g of sodium citrate and 2kg of pure water to obtain a solution containing a reducing agent and a dispersant; uniformly mixing 187.5g of copper sulfate pentahydrate and 500g of water to obtain a copper salt solution; uniformly mixing 1.0g of silver sulfate and 100g of ammonia water to obtain a silver salt solution; uniformly mixing 1g of benzotriazole and 50g of water to obtain a coating agent solution; and respectively heating the solution containing the reducing agent and the dispersant, the copper salt solution, the silver salt solution and the coating agent solution to 70°C and then keeping them warm for standby use.

[0068] The steps of the isothermal reduction reaction include: installing a reaction container in a water bath, setting the temperature to 70°C, turning on a stirring device, and controlling the stirring speed at 300rpm; then adding a solution containing a reducing agent and a dispersant, a copper salt solution, and a silver salt solution into the reaction container, adding ammonia water to adjust the pH to 9, and then maintaining the temperature at 70°C for 2h to obtain a nano-spherical copper-coated silver powder suspension.

[0069] The step of isothermal coating reaction comprises: adding coating agent solution into nano spherical copper-coated silver powder suspension, maintaining 70° C. and continuing the reaction for 10 minutes to obtain monodisperse nano spherical copper powder suspension.

[0070] The post-treatment steps include: turning off the agitator and the constant temperature water bath, taking out the reaction container; separating the mixture in the reaction container into solid and liquid by centrifugal separation, and then washing the monodisperse nano spherical copper powder with pure water for 3 to 4 times until the conductivity of the supernatant is ≤10µs / cm; then putting the monodisperse nano spherical copper powder into a vacuum drying oven, setting the temperature to 80°C, and drying for 3 hours to obtain dry monodisperse nano spherical copper powder.

[0071] Example 5

[0072] Example 5 of the present application provides a liquid phase reduction preparation method for monodisperse nano-spherical copper powder. As the first comparative example, the preparation method includes the steps of preparing a reaction solution, a isothermal reduction reaction, a isothermal coating reaction, and a post-treatment step.

[0073] The steps of preparing the reaction solution include: uniformly mixing 218.35g of ascorbic acid, 200g of sodium citrate and 2kg of pure water to obtain a solution containing a reducing agent and a dispersant; uniformly mixing 187.5g of copper sulfate pentahydrate and 500g of water to obtain a copper salt solution; preparing 100g of ammonia water as an alkali solution component; uniformly mixing 1g of benzotriazole and 50g of water to obtain a coating agent solution; and heating the solution containing the reducing agent and the dispersant, the copper salt solution, the alkali solution component and the coating agent solution to 70°C respectively and then keeping them warm for standby use.

[0074] The steps of the isothermal reduction reaction include: installing a reaction container in a water bath, setting the temperature to 70°C, turning on a stirring device, and controlling the stirring speed at 300rpm; then adding a solution containing a reducing agent and a dispersant, a copper salt solution, and an alkali solution component into the reaction container, adding ammonia water to adjust the pH to 9, and then maintaining the temperature at 70°C for 2h to obtain a nano-spherical copper powder suspension.

[0075] The step of isothermal coating reaction comprises: adding coating agent solution into nano spherical copper powder suspension, maintaining 70° C. and continuing the reaction for 10 minutes to obtain monodisperse nano spherical copper powder suspension.

[0076] The post-treatment steps include: turning off the agitator and the constant temperature water bath, taking out the reaction container; separating the mixture in the reaction container into solid and liquid by centrifugal separation, and then washing the monodisperse nano spherical copper powder with pure water for 3 to 4 times until the conductivity of the supernatant is ≤10µs / cm; then putting the monodisperse nano spherical copper powder into a vacuum drying oven, setting the temperature to 80°C, and drying for 3 hours to obtain dry monodisperse nano spherical copper powder.

[0077] Example 6

[0078] Example 6 of the present application provides a liquid phase reduction preparation method for nano-spherical copper powder. As a second comparative example, the preparation method includes the steps of preparing a reaction solution, a isothermal reduction reaction, a isothermal coating reaction, and a post-treatment step.

[0079] The steps of preparing the reaction solution include: uniformly mixing 218.35g of ascorbic acid, 200g of sodium citrate and 2kg of pure water to obtain a solution containing a reducing agent and a dispersant; uniformly mixing 187.5g of copper sulfate pentahydrate and 500g of water to obtain a copper salt solution; uniformly mixing 1.4g of silver sulfate and 100g of ammonia water to obtain a silver salt solution; uniformly mixing 1g of benzotriazole and 50g of water to obtain a coating agent solution; and respectively heating the solution containing the reducing agent and the dispersant, the copper salt solution, the silver salt solution and the coating agent solution to 70°C and then keeping them warm for standby use.

[0080] The steps of the isothermal reduction reaction include: installing a reaction container in a water bath, setting the temperature to 70°C, turning on a stirring device, and controlling the stirring speed at 300rpm; then adding a solution containing a reducing agent and a dispersant, a copper salt solution, and a silver salt solution into the reaction container, adding ammonia water to adjust the pH to 9, and then maintaining the temperature at 70°C for 2 hours to obtain a nano-spherical copper-coated silver powder suspension.

[0081] The step of isothermal coating reaction comprises: adding coating agent solution into nano spherical copper-coated silver powder suspension, maintaining 70° C. and continuing the reaction for 10 minutes to obtain nano spherical copper powder suspension.

[0082] The post-treatment steps include: turning off the agitator and the constant temperature water bath, taking out the reaction container; separating the mixture in the reaction container from solid and liquid by centrifugation, and then washing the nano spherical copper powder with pure water for 3 to 4 times until the conductivity of the supernatant is ≤10µs / cm; then putting the nano spherical copper powder into a vacuum drying oven, setting the temperature to 80°C, and drying for 3 hours to obtain dry nano spherical copper powder.

[0083] Experimental Example 1

[0084] This experimental example analyzes the monodisperse nano-spherical copper powder or nano-spherical copper powder prepared by the liquid phase reduction preparation method provided in Examples 1-6; wherein the morphology structure analyzed by scanning electron microscopy is as follows Figure 1-6 The D50 results of the particle size analyzer analysis, the oxygen content results of the infrared absorption analysis and the yield results are shown in Table 1.

[0085] Table 1: Particle size, oxygen content and yield analysis results

[0086]

[0087] As can be seen from Table 1, the liquid phase reduction preparation method provided in Example 5 can directly prepare monodisperse nano spherical copper powder, but the yield of preparing monodisperse nano spherical copper powder is low, with only 84.8% yield in the isothermal reduction reaction for 2 hours (120 min), and more than half of the copper powder particles in the prepared monodisperse nano spherical copper powder are above 2.355 microns, and the average particle size of the copper powder will be larger; while the preparation method provided in Examples 1-4 of the present application has a higher yield of 95.8~98.6% for the prepared monodisperse nano spherical copper powder, and more than half of the copper powder particles do not exceed 0.861~1.972 microns, and the average particle size of the copper powder will be smaller; this shows that the present application introduces silver salt into the reactant, and in the isothermal reduction reaction stage, the pre-reduced silver crystal nucleus is used as the core, and small-particle-size copper powder can be quickly synthesized. The liquid phase reduction preparation method provided in Examples 1-4 of the present application can efficiently prepare monodisperse nano spherical copper powder.

[0088] It can be further seen from Table 1 that the liquid-phase reduction preparation method provided in Example 5 can also quickly synthesize copper powder with a high yield. However, due to the excessive number of silver crystal nuclei generated in the isothermal reduction reaction stage, the nano-spherical copper powder collides and aggregates together, and the copper powder particle size cannot be measured, and subsequent steps are required to separate the nano-spherical copper powder. In the liquid-phase reduction preparation method provided in Examples 1-4 of the present application, by controlling the ratio of dispersant, copper and silver, the silver crystal nuclei are moderate, the nano-spherical copper powder is difficult to collide and aggregate together, and monodisperse nano-spherical copper powder can be directly synthesized.

[0089] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some or all of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing monodisperse nano-spherical copper powder by liquid phase reduction, characterized in that: Includes steps: Step S1, mixing a solution containing a reducing agent and a dispersant, a copper salt solution, and a silver salt solution to obtain a mixed solution; Step S2, adding an alkaline solution to the mixed solution to adjust the pH and then perform a constant temperature reduction reaction to obtain a nano-spherical copper-coated silver powder suspension; Step S3, adding the coating agent solution into the nano-spherical copper-coated silver powder suspension to carry out a constant temperature coating reaction to obtain a monodisperse nano-spherical copper powder suspension; Step S4, sequentially subjecting the monodisperse nanometer spherical copper powder suspension to solid-liquid separation, washing, and drying to obtain monodisperse nanometer spherical copper powder.

2. The method for preparing monodisperse nano-spherical copper powder by liquid phase reduction according to claim 1, characterized in that: In step S1, the molar ratio of the dispersant, the copper ions in the copper salt solution, and the silver ions in the silver salt solution is 775:750:0.45-3.

21.

3. The method for preparing monodisperse nano-spherical copper powder by liquid phase reduction according to claim 1, characterized in that: In step S1, the dispersant is sodium citrate, the solute in the copper salt solution is copper sulfate pentahydrate, and the solute in the silver salt solution is silver sulfate; The mass ratio of the sodium citrate, copper sulfate pentahydrate and silver sulfate is 200:187.5:0.14~1.

4. The method for preparing monodisperse nano-spherical copper powder by liquid phase reduction according to claim 1, characterized in that: In step S2, the pH is adjusted to 8-10; The temperature of the isothermal reduction reaction is 60-80° C. and the time is 1-3 hours.

5. The method for preparing monodisperse nano-spherical copper powder by liquid phase reduction according to claim 1, characterized in that: In step S3, the temperature of the isothermal coating reaction is 60-80° C. and the time is 5-20 min.

6. The method for preparing monodisperse nano-spherical copper powder by liquid phase reduction according to claim 1, characterized in that: In step S4, the solid-liquid separation method is suction filtration or centrifugation; The washing method is to wash with pure water 2 to 5 times; The drying method is to dry in a vacuum drying oven at 70-90° C. for 2-4 hours.

7. The method for preparing monodisperse nano-spherical copper powder by liquid phase reduction according to claim 1, characterized in that: The reducing agent is selected from at least one of ascorbic acid, isoascorbic acid, and sodium thiosulfate; The dispersant is selected from at least one of sodium citrate, polyvinyl pyrrolidone, polyacrylamide, polyvinyl alcohol, and polyethyleneimine; The solute in the copper salt solution is selected from at least one of copper sulfate pentahydrate, copper chloride, copper nitrate and copper acetate, and the solvent is water; The solute in the silver salt solution is selected from at least one of silver sulfate, silver nitrate and silver chloride, and the solvent is aqueous ammonia; The alkaline solution is at least one of aqueous ammonia, sodium hydroxide solution, potassium hydroxide solution, ammonium carbonate solution, and urea solution; The solute in the coating agent solution is benzotriazole, and the solvent is water.

8. A monodisperse nano-spherical copper powder, characterized in that: The product is prepared by the liquid phase reduction preparation method according to any one of claims 1 to 7.

9. Use of the monodisperse nano-spherical copper powder according to claim 8 in preparing multi-layer ceramic capacitor electrodes.

10. A multilayer ceramic capacitor, characterized in that: It comprises an inner electrode, a ceramic layer and an outer electrode; the outer electrode comprises the monodisperse nano-spherical copper powder as claimed in claim 8.

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