Superfine copper powder and preparation method and application thereof

Abstract

The invention provides superfine copper powder and a preparation method and application thereof, according to the preparation method of the superfine copper powder, a two-step liquid phase reduction method is used for preparing the superfine copper powder, process conditions are improved, and a dropwise adding mode is adopted. In the first step, an alkaline ascorbic acid solution is used for reducing copper chloride into cuprous chloride with narrow particle size distribution; in the second step, ferrous sulfate and sodium citrate are used as a mixed reducing agent, meanwhile, sodium citrate can also be used as a complexing agent, and cuprous chloride can be secondarily reduced into the superfine copper powder which is similar to a sphere and is good in dispersity and uniform in particle size distribution. Meanwhile, the used raw materials are easy to obtain, the reaction process is mild, organic solvents and toxic and dangerous reagents such as sodium borohydride and hydrazine hydrate do not need to be used, and the preparation process has cost benefits, is environmentally friendly and is suitable for industrial production.

Description

Technical Field

[0001] The invention relates to the technical field of precious metal powder materials, and in particular to an ultrafine copper powder and a preparation method and application thereof. Background Art

[0002] Nowadays, conductive paste has been widely used in microelectronics industries such as conductive adhesives and ceramic capacitors. The extremely important conductive phase in conductive paste is mainly precious metals with good conductivity, oxidation resistance and ductility, such as silver powder and gold powder. The prices of these metals are getting higher and higher, and there is silver ion migration in electronic silver paste, which makes electronic devices have the risk of short circuit failure. Metal copper powder can greatly reduce industrial costs and has more market advantages due to its high conductivity, low price, low electrochemical migration, good adhesion and solderability. In addition, the surface interface effect, quantum tunneling effect and oxidative stress effect of ultrafine copper powder make it also have potential application value in the fields of catalysis and medicine.

[0003] At present, the preparation methods of ultrafine copper powder are divided into physical method and chemical method. The physical method refers to crushing large pieces of copper into fine copper powder under physical force, including high-energy ball milling method, magnetron sputtering method, etc. The physical method for preparing copper powder has high requirements for equipment and technology, low production efficiency, and the morphology and particle size of the prepared copper powder are uncontrollable. The chemical method is to generate copper molecules through redox reaction or decomposition reaction, and obtain ultrafine copper powder through nucleation growth, including thermal decomposition method, electrochemical method, liquid phase reduction method, polyol method, microemulsion method, etc. Among them, the liquid phase reduction method has the advantages of short process flow, low manufacturing cost, high yield, controllable powder morphology and particle size, and has more industrial application prospects. The liquid phase reduction method is to control the reaction conditions, and the metal cation solution gradually generates micron or nanometer metal powder under the action of the reducing agent. However, in the preparation process of ultrafine copper powder, the reducing agents commonly used are formaldehyde, sodium hypophosphite, sodium borohydride, hydrazine hydrate, etc., which are often environmentally unfriendly.

[0004] Therefore, it is urgent to develop a cost-effective and environmentally friendly process to prepare ultrafine copper powder with regular particle size distribution and good dispersibility to meet client application needs. Summary of the invention

[0005] The purpose of the present invention is to solve the technical problems in the existing silver powder preparation process that the sphericity is difficult to ensure and the particle size is difficult to control.

[0006] In order to solve the above technical problems, the present invention first provides a method for preparing ultrafine copper powder, comprising the following steps: S1, adding the cupric chloride solution and the alkaline ascorbic acid solution dropwise to deionized water containing a dispersant simultaneously, stirring, and heating in a water bath at 30° C. to 80° C., and removing the supernatant after the reaction is completed to obtain a suspension containing cuprous chloride precipitate; S2, adding a mixed solution containing ferrous sulfate and sodium citrate dropwise into the suspension, performing solid-liquid separation after the reaction to obtain a precipitate, and then washing and drying the precipitate to obtain ultrafine copper powder.

[0007] Preferably, step S1 specifically includes: S11, adding copper chloride to deionized water and stirring to dissolve, to obtain a copper chloride solution; S12, dissolving ascorbic acid in water and adding sodium hydroxide to obtain an alkaline ascorbic acid solution; S13, adding the cupric chloride solution and the alkaline ascorbic acid solution dropwise to the deionized water containing the dispersant simultaneously, and performing a water bath heating treatment at 30-80°C.

[0008] Preferably, in step S11: the copper chloride concentration of the copper chloride solution is 0.1 mol / L to 4.0 mol / L.

[0009] Preferably, in step S12: the ascorbic acid concentration of the alkaline ascorbic acid solution is 0.1 mol / L to 1.8 mol / L, and the pH value of the alkaline ascorbic acid solution is 7.5 to 11.5.

[0010] Preferably, in step S1, the molar ratio of the cupric chloride solution to the alkaline ascorbic acid solution is 1:(1-1.2).

[0011] Preferably, in step S1: the dispersant is at least one of glycerol, polyethylene glycol, gelatin, gum arabic, polyvinyl pyrrolidone and Tween-80; and the mass content of the dispersant is greater than 0 and less than or equal to 5.0wt% based on the theoretical mass of the ultrafine copper powder as 100wt%.

[0012] Preferably, in step S2: the molar ratio of ferrous sulfate in the mixed solution to cupric chloride in the cupric chloride solution is 1:(1.5-3); the molar ratio of sodium citrate in the mixed solution to cupric chloride in the cupric chloride solution is 1:(1.5-3).

[0013] Preferably, the dropping time in step S1 is 1 min to 30 min, the stirring speed is 100 rad / min to 600 rad / min; the dropping time in step S2 is 1 min to 30 min, the stirring speed is 100 rad / min to 600 rad / min, and the reaction temperature is 30°C to 80°C.

[0014] Correspondingly, the present invention also provides an ultrafine copper powder prepared by any of the above methods for preparing ultrafine copper powder; wherein the ultrafine copper powder has a particle size of 1 μm to 2 μm and a tap density of 3.7 g / ml to 3.9 g / ml.

[0015] Correspondingly, the present invention further provides a use of the above ultrafine copper powder in preparing a conductive paste.

[0016] The beneficial effects of the present invention are as follows: Different from the prior art, the present invention provides an ultrafine copper powder and a preparation method and application thereof. The preparation method of the ultrafine copper powder uses a two-step liquid phase reduction method to prepare the ultrafine copper powder, improves the process conditions, and adopts a dripping feeding method. In the first step, alkaline ascorbic acid solution is used to reduce cupric chloride to cuprous chloride with a narrow particle size distribution; in the second step, ferrous sulfate and sodium citrate are used as mixed reducing agents, and sodium citrate can also be used as a complexing agent, which helps to reduce cuprous chloride to a spherical ultrafine copper powder with good dispersibility and uniform particle size distribution. At the same time, the raw materials used in the present invention are easy to obtain, the reaction process is mild, and there is no need to use organic solvents and toxic and hazardous reagents, such as sodium borohydride and hydrazine hydrate, etc. The preparation process is cost-effective, environmentally friendly, and suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A flow chart of a method for preparing ultrafine copper powder provided by an embodiment of the present invention; Figure 2 This is a SEM image of the ultrafine copper powder prepared in Example 1 of the present invention; Figure 3 This is a SEM image of the ultrafine copper powder prepared in Example 2 of the present invention; Figure 4 This is a SEM image of the ultrafine copper powder prepared in Example 3 of the present invention. DETAILED DESCRIPTION

[0018] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0019] Aiming at the technical problem that the reducing agent used in the process of preparing ultrafine copper powder by liquid phase reduction method is not environmentally friendly, the present invention aims to provide an ultrafine copper powder and a preparation method and application thereof, which mainly prepares spherical ultrafine copper powder with good dispersibility and uniform particle size distribution by improving the process conditions on the basis of the two-step liquid phase reduction method. This method is safe and environmentally friendly, has mild reaction conditions, and is suitable for industrial production.

[0020] In order to achieve the above technical objectives, this application adopts the following technical solutions: In a first aspect, the present invention first provides a method for preparing ultrafine copper powder.

[0021] See also Figure 1 , Figure 1 A flow chart of a method for preparing ultrafine copper powder provided by an embodiment of the present invention; wherein the above-mentioned preparation method specifically comprises: S1, adding the cupric chloride solution and the alkaline ascorbic acid solution simultaneously to deionized water containing a dispersant, stirring, and heating in a water bath at 30° C. to 80° C., removing the supernatant after the reaction is completed, and obtaining a suspension containing cuprous chloride precipitate.

[0022] Specifically, step S1 also includes: S11, adding copper chloride to deionized water and stirring to dissolve, to obtain a copper chloride solution; S12, dissolving ascorbic acid in water and adding sodium hydroxide to obtain an alkaline ascorbic acid solution; S13, adding the cupric chloride solution and the alkaline ascorbic acid solution dropwise to the deionized water containing the dispersant simultaneously, and performing a water bath heating treatment at 30-80°C.

[0023] In step S11: the copper chloride concentration of the copper chloride solution is 0.1 mol / L to 4.0 mol / L.

[0024] In step S12: the ascorbic acid concentration of the alkaline ascorbic acid solution is 0.1 mol / L~1.8 mol / L, and the pH value of the alkaline ascorbic acid solution is 7.5~11.5; wherein, the use of the alkaline ascorbic acid solution can reduce cupric chloride to cuprous chloride with a narrow particle size distribution.

[0025] Specifically, the molar ratio of the cupric chloride solution to the alkaline ascorbic acid solution is 1: (1-1.2); wherein, ascorbic acid is used as a reducing agent, and a proper excess can ensure that the cupric chloride is fully reduced to cuprous chloride, thereby improving the conversion rate of the reaction. If the amount of ascorbic acid is insufficient, the cupric chloride may not react completely. A slightly excessive amount of ascorbic acid helps to reduce the occurrence of side reactions and avoid the generation of other unnecessary impurities, thereby improving the purity of the cuprous chloride product. Although an excess of ascorbic acid is beneficial to the reaction, too much excess will increase the cost. By controlling the ratio to 1: (1-1.2), while ensuring the reaction effect, it can also better control costs and improve efficiency.

[0026] In step S1: the dispersant is at least one of glycerol, polyethylene glycol, gelatin, gum arabic, polyvinyl pyrrolidone and Tween-80; wherein the role of the dispersant is mainly reflected in preventing the agglomeration of silver powder particles, improving the dispersibility of particles, controlling the particle morphology and stabilizing the solution system. By selecting a suitable dispersant, the quality, uniformity and processing performance of copper powder can be significantly improved, thereby optimizing its application effect in photovoltaic, electronic and other fields.

[0027] Specifically, based on 100wt% of the theoretical mass of the ultrafine copper powder, the mass content of the dispersant is greater than 0 and less than or equal to 5.0wt%; wherein, if the mass content of the dispersant is too low, the dispersant may not fully play its role, resulting in poor dispersion of the copper powder particles; at the same time, too much dispersant may have an adverse effect on other aspects of the reaction system, such as affecting the purity of the product, changing the physicochemical properties of the solution, or causing additional difficulties in subsequent processing.

[0028] Preferably, the dropping time in step S1 is 1 min to 30 min, and the stirring speed is 100 rad / min to 600 rad / min.

[0029] Specifically, a longer drop time (such as 30 minutes) can make the reactants mix more evenly, help the reaction proceed smoothly, and reduce uneven reactions caused by local concentrations that are too high or too low. A shorter drop time (such as 1 minute) may be suitable for situations where the reaction speed is required to be high or the reactant concentration is low, so as to complete the reaction as quickly as possible. By adjusting the drop time, the reaction rate can be controlled to a certain extent, avoiding the reaction being too intense or too slow, which is beneficial to the formation of the product and controlling its properties.

[0030] Specifically, a lower stirring speed (such as 100 rad / min) may be sufficient to achieve uniform mixing when the reactant concentration is low or the reaction is mild. A higher stirring speed (such as 600 rad / min) can ensure that the components in the solution are quickly and fully contacted and promote the reaction when the reactant concentration is high or more intense mixing is required. The appropriate stirring speed helps the transfer of reactants and products in the solution, avoids the formation of concentration gradients, and thus improves the efficiency and consistency of the reaction.

[0031] S2, adding a mixed solution containing ferrous sulfate and sodium citrate dropwise into the suspension, performing solid-liquid separation after the reaction to obtain a precipitate, and then washing and drying the precipitate to obtain ultrafine copper powder.

[0032] Specifically, step S2 also includes: A mixed solution containing ferrous sulfate and sodium citrate is added dropwise to the suspension, the reaction temperature is 30°C to 80°C, and after the reaction is completed, solid-liquid separation is performed to obtain a precipitate, and then the precipitate is cleaned and dried to obtain ultrafine copper powder.

[0033] Specifically, in step S2: the molar ratio of ferrous sulfate in the mixed solution to cupric chloride in the cupric chloride solution is 1:(1.5-3); the molar ratio of sodium citrate in the mixed solution to cupric chloride in the cupric chloride solution is 1:(1.5-3); wherein ferrous sulfate and sodium citrate are used as mixed reducing agents, and sodium citrate can also be used as a complexing agent, which helps to secondary reduce cuprous chloride into ultrafine copper powder with spherical shape, good dispersibility and uniform particle size distribution.

[0034] Furthermore, if the amount of ferrous sulfate is too much, the cost may be increased and some unnecessary side reactions may be induced; and if the amount of ferrous sulfate is too little, sufficient reduction cannot be achieved.

[0035] Furthermore, sodium citrate may form a complex with certain ions in the solution, which can stabilize the solution system, control the reaction rate and improve the product performance. A larger amount can better exert this complexing and stabilizing effect. An appropriate excess of sodium citrate helps to suppress possible impurities and improve the purity of the product.

[0036] Furthermore, the reaction temperature of 30°C to 80°C helps to control the crystallization and growth process of the copper powder, thereby affecting its particle size, morphology and properties.

[0037] Preferably, the dropping time in step S2 is 1 min to 30 min, and the stirring speed is 100 rad / min to 600 rad / min.

[0038] Correspondingly, the present invention also provides an ultrafine copper powder prepared by any of the above methods for preparing ultrafine copper powder; wherein the ultrafine copper powder has a particle size of 1 μm to 2 μm and a tap density of 3.7 g / ml to 3.9 g / ml.

[0039] Correspondingly, the present invention further provides a use of the above ultrafine copper powder in preparing a conductive paste.

[0040] The technical solution of the present invention is now further described in conjunction with specific embodiments.

[0041] Embodiment 1: This embodiment 1 provides a method for preparing ultrafine copper powder, and the specific preparation steps are as follows: Step 1: weigh 19 g of copper chloride and add it to 250 mL of deionized water and stir to dissolve; Step 2, dissolving 30 g of ascorbic acid in 250 mL of water, adding 7.1 g of sodium hydroxide to adjust the solution, to obtain a first reduction solution; Step 3: In a 50° C. constant temperature water bath, 0.1 g of glycerol was added to 100 mL of deionized water, and the cupric chloride solution in step 1 and the first reducing solution in step 2 were simultaneously added dropwise to the water containing glycerol by a peristaltic pump. The addition time was 30 min, and the stirring rate was 550 rad / min. After the reaction was completed, the mixture was allowed to stand for 5 min, and the supernatant was removed to obtain a cuprous chloride suspension containing white cuprous chloride precipitates; Step 4, dissolving 27g of ferrous sulfate and 73g of sodium citrate in 300mL of deionized water to prepare a second reducing solution; adding the second reducing solution dropwise to the cuprous chloride suspension, the dropping time is controlled to be 30min, and the reaction temperature is 50°C; after the reaction is completed, solid-liquid separation is performed, and the ultrafine copper powder is obtained by washing multiple times and drying.

[0042] Embodiment 2: This embodiment 2 provides a method for preparing ultrafine copper powder, and the specific preparation steps are as follows: Step 1: weigh 15 g of copper chloride and add it to 200 mL of deionized water and stir to dissolve; Step 2, dissolving 24 g of ascorbic acid in 200 mL of water, adding 5.7 g of sodium hydroxide to adjust the solution, to obtain a first reduction solution; Step 3, at room temperature, the cupric chloride solution in step 1 and the first reducing solution in step 2 are simultaneously added dropwise to 100 mL of deionized water by a peristaltic pump, the dropping time is 30 min, the stirring rate is 550 rad / min, after the reaction is completed, the reaction is allowed to stand for 5 min, and the supernatant is removed to obtain a cuprous chloride suspension containing white cuprous chloride precipitates; Step 4, dissolving 25.2g of ferrous sulfate and 42.6g of sodium citrate in 200mL of deionized water to prepare a second reducing solution; adding the second reducing solution dropwise to the cuprous chloride suspension, the dropping time is controlled to be 1min, and the reaction temperature is 25°C; after the reaction is completed, solid-liquid separation is performed, and the ultrafine copper powder is obtained by washing multiple times and drying.

[0043] Embodiment 3: This embodiment 3 provides a method for preparing ultrafine copper powder, and the specific preparation steps are as follows: Step 1: weigh 19 g of copper chloride and add it to 250 mL of deionized water and stir to dissolve; Step 2, dissolving 30 g of ascorbic acid in 250 mL of water, adding 7.1 g of sodium hydroxide to adjust the solution, to obtain a first reduction solution; Step 3, in a 50°C constant temperature water bath, the cupric chloride solution in step 1 and the first reducing solution in step 2 are simultaneously added dropwise to 100 mL of deionized water by a peristaltic pump, the dropping time is 30 min, the stirring rate is 550 rad / min, after the reaction is completed, the reaction is allowed to stand for 5 min, and the supernatant is removed to obtain a cuprous chloride suspension containing white cuprous chloride precipitates; Step 4, dissolving 27g of ferrous sulfate and 73g of sodium citrate in 300mL of deionized water to prepare a second reducing solution; adding the second reducing solution dropwise to the cuprous chloride suspension, the dropping time is controlled to be 30min, and the reaction temperature is 50°C; after the reaction is completed, solid-liquid separation is performed, and the ultrafine copper powder is obtained by washing multiple times and drying.

[0044] See also Figure 2 , Figure 2 This is a SEM (scanning electron microscope) image of the ultrafine copper powder prepared in Example 1 of the present invention; Figure 2 It can be seen that the ultrafine copper powder prepared in Example 1 of the present invention is spherical, has a smooth powder surface, high crystallinity, a relatively uniform particle size distribution, an average particle size of about 1.5 μm, good dispersion performance, no agglomeration phenomenon, and a tap density of up to 3.9 g / ml.

[0045] See also Figure 3 , Figure 3 This is a SEM image of the ultrafine copper powder prepared in Example 2 of the present invention; Figure 3 It can be seen that the average particle size of the ultrafine copper powder prepared in Example 2 of the present invention is about 1 μm, the particle size distribution is narrow, the crystals are dense, and the tap density reaches 3.7 g / ml. See also Figure 4 , Figure 4 This is a SEM image of the ultrafine copper powder prepared in Example 3 of the present invention; Figure 4 It can be seen that in the absence of a dispersant and when the feed is added slowly, the particle size uniformity of the ultrafine copper powder prepared in Example 3 of the present invention deteriorates, two particle size distributions (2 μm and 1 μm) appear, and small particle crystals agglomerate.

[0046] In summary, different from the prior art, the present invention provides an ultrafine copper powder and a preparation method and application thereof, wherein the preparation method of the ultrafine copper powder uses a two-step liquid phase reduction method to prepare the ultrafine copper powder, improves the process conditions, and adopts a drip feeding method. In the first step, alkaline ascorbic acid solution is used to reduce cupric chloride to cuprous chloride with a narrow particle size distribution; ferrous sulfate and sodium citrate are used as mixed reducing agents in the second step, and sodium citrate can also be used as a complexing agent, which helps to reduce cuprous chloride to a spherical shape, good dispersibility, and uniform particle size distribution. Ultrafine copper powder. At the same time, the raw materials used in the present invention are easy to obtain, the reaction process is mild, and there is no need to use organic solvents and toxic and hazardous reagents, such as sodium borohydride and hydrazine hydrate, etc. The preparation process is cost-effective, environmentally friendly, suitable for industrial production, and can further promote its commercial development.

[0047] The raw materials listed in the present invention, as well as the upper and lower limits and interval values ​​of the raw materials of the present invention, and the upper and lower limits and interval values ​​of the process parameters (such as temperature, time, etc.) can all realize the present invention, and the embodiments are not listed one by one here.

[0048] It should be noted that the above embodiments all belong to the same inventive concept, and the description of each embodiment has its own focus. For matters that are not described in detail in some embodiments, reference may be made to the description in other embodiments.

[0049] The above embodiments only express the implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for those of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for preparing ultrafine copper powder, characterized in that: The steps include: S1, adding the cupric chloride solution and the alkaline ascorbic acid solution dropwise to deionized water containing a dispersant simultaneously, stirring, and heating in a water bath at 30° C. to 80° C., and removing the supernatant after the reaction is completed to obtain a suspension containing cuprous chloride precipitate; S2, adding a mixed solution containing ferrous sulfate and sodium citrate dropwise into the suspension, performing solid-liquid separation after the reaction to obtain a precipitate, and then washing and drying the precipitate to obtain ultrafine copper powder.

2. The method for preparing ultrafine copper powder according to claim 1, characterized in that: The S1 step specifically includes: S11, adding copper chloride to deionized water and stirring to dissolve, to obtain the copper chloride solution; S12, dissolving ascorbic acid in water and adding sodium hydroxide to obtain the alkaline ascorbic acid solution; S13, simultaneously adding the cupric chloride solution and the alkaline ascorbic acid solution dropwise into deionized water containing a dispersant, and performing a water bath heating treatment at 30-80° C.

3. The method for preparing ultrafine copper powder according to claim 2, characterized in that: In the step S11: the cupric chloride concentration of the cupric chloride solution is 0.1 mol / L to 4.0 mol / L.

4. The method for preparing ultrafine copper powder according to claim 2, characterized in that: In the step S12: the ascorbic acid concentration of the alkaline ascorbic acid solution is 0.1 mol / L to 1.8 mol / L, and the pH value of the alkaline ascorbic acid solution is 7.5 to 11.

5.

5. The method for preparing ultrafine copper powder according to claim 1, characterized in that: In the step S1: the molar ratio of the cupric chloride solution to the alkaline ascorbic acid solution is 1:(1-1.2).

6. The method for preparing ultrafine copper powder according to claim 1, characterized in that: In the step S1, the dispersant is at least one of glycerol, polyethylene glycol, gelatin, gum arabic, polyvinyl pyrrolidone and Tween-80; based on the theoretical mass of the ultrafine copper powder as 100wt%, the mass content of the dispersant is greater than 0 and less than or equal to 5.0wt%.

7. The method for preparing ultrafine copper powder according to claim 1, characterized in that: In the step S2: the molar ratio of ferrous sulfate in the mixed solution to cupric chloride in the cupric chloride solution is 1:(1.5-3); the molar ratio of sodium citrate in the mixed solution to cupric chloride in the cupric chloride solution is 1:(1.5-3).

8. The method for preparing ultrafine copper powder according to claim 1, characterized in that: The dropping time in step S1 is 1 min to 30 min, the stirring speed is 100 rad / min to 600 rad / min; the dropping time in step S2 is 1 min to 30 min, the stirring speed is 100 rad / min to 600 rad / min, and the reaction temperature is 30° C. to 80° C.

9. An ultrafine copper powder, characterized in that: The ultrafine copper powder is prepared by the preparation method of the ultrafine copper powder according to any one of claims 1 to 8; wherein the particle size of the ultrafine copper powder is 1 μm to 2 μm, and the tap density is 3.7 g / ml to 3.9 g / ml.

10. Use of the ultrafine copper powder according to claim 9 in preparing conductive slurry.

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