Preparation method of wide-distribution nano copper powder

Abstract

The invention relates to a preparation method of wide-distribution nano copper powder. The preparation method comprises the following steps: step 1, preparing a sodium hydroxide aqueous solution; 2, preparing an ascorbic acid aqueous solution; 3, preparing a copper sulfate aqueous solution; step 4, adding a sodium citrate protective agent; step 5, mixing an ascorbic acid reducing solution; step 6, adjusting the pH value of the solution; step 7, carrying out constant-temperature reduction reaction; step 8, washing, surface modification and solid-liquid separation; and step 9, vacuum drying. The method has the beneficial effects that 1, the method is environment-friendly, safe and high in purity; 2, the particle size distribution is wide and controllable; 3, the oxidation resistance is excellent; and 4, the industrial suitability is high.

Description

Technical Field

[0001] This invention relates to the field of metal nanomaterial preparation technology, specifically to a method for preparing broadly distributed nano-copper powder. Background Technology

[0002] Due to its excellent electrical and thermal conductivity and low-temperature sintering properties, nano-copper powder has irreplaceable application value in fields such as electronic pastes, chip interconnects, chip packaging, and conductive coatings. For example, in the field of electronic pastes, micro- and nano-composite copper powders can reduce the sintering temperature and increase the density of the sintered coating by tightly packing particles of different sizes. If a one-step reduction method can be used to prepare broadly distributed nano-copper powders similar to composite copper powders, it can avoid the problem of cracking that easily occurs during the sintering of single-size nano-copper powders and reduce the cost of use, which is of great significance for the promotion and application of nano-copper powders in the field of third-generation semiconductors.

[0003] Currently, the mainstream methods for preparing nano-copper powder include chemical reduction, hydrothermal methods, vapor deposition, and mechanical ball milling. Among these, chemical reduction has become the most widely used technical route for industrial applications due to its simplicity and low cost. However, existing chemical reduction methods still have the following key problems:

[0004] 1. Safety and purity issues of reducing agents: Traditional methods often use hydrazine hydrate, sodium borohydride, etc. as reducing agents. Hydrazine hydrate is toxic, and sodium borohydride has too strong reducing power, which can easily lead to uncontrolled reaction. Both of these will affect the purity of copper powder and production safety.

[0005] 2. Challenges in particle size distribution control: The lack of an efficient dispersion and protection system makes copper powder particles prone to agglomeration, which is difficult to meet the requirements of wide distribution (50nm~2μm) application scenarios;

[0006] 3. Insufficient antioxidant properties: The post-processing process did not design protective measures for the easy oxidation of copper powder, and the finished product is prone to forming an oxide layer on the surface during storage or use, resulting in loss of original properties;

[0007] 4. Poor industrial adaptability: Some processes require high temperature and high pressure conditions (such as hydrothermal method), rely on special equipment, or have complicated steps (such as multiple washing and purification), resulting in high production costs and low production efficiency, making it difficult to achieve large-scale mass production.

[0008] Therefore, developing a method for preparing wide-distribution nano-copper powder that is non-toxic, environmentally friendly, has controllable particle size distribution, excellent antioxidant properties, and is suitable for industrial production has become an important development direction for the production of nano-copper powder. Summary of the Invention

[0009] In summary, to overcome the shortcomings of the prior art, the technical problem to be solved by the present invention is to provide a method for preparing wide-distribution nano-copper powder, aiming to overcome the defects of existing chemical reduction methods for preparing nano-copper powder, such as "toxic reducing agent, narrow particle size distribution, poor antioxidant properties, and difficulty in industrialization", and to provide a method that is simple, environmentally friendly and safe, and can stably prepare wide-distribution and highly antioxidant nano-copper powder.

[0010] The technical solution of this invention to solve the above-mentioned technical problems is as follows: A method for preparing broadly distributed nano-copper powder, comprising the following steps:

[0011] Step 1: Add sodium hydroxide and distilled water to a mixing tank and stir at room temperature to accelerate dissolution, thus preparing a sodium hydroxide aqueous solution.

[0012] Step 2: Add ascorbic acid and distilled water to the reaction vessel, heat and stir to accelerate dissolution, and prepare an ascorbic acid aqueous solution;

[0013] Step 3: Add copper sulfate and distilled water to the reaction vessel, heat and stir to accelerate dissolution, and prepare a copper sulfate aqueous solution;

[0014] Step 4: Add sodium citrate powder, which serves as a protective agent in the reaction process, to the copper sulfate aqueous solution prepared in Step 3 to obtain the first mixed solution;

[0015] Step 5: Add the ascorbic acid aqueous solution prepared in step 2 to the first mixed solution prepared in step 4 to obtain the second mixed solution;

[0016] Step 6: Add the sodium hydroxide aqueous solution prepared in Step 1 to the second mixed solution prepared in Step 5 to obtain the third mixed solution, and adjust the pH of the third mixed solution.

[0017] Step 7: Heat the third mixed solution prepared in Step 6 to the target temperature and maintain it for a period of time until Cu 2+ Completely reduced to Cu 0 The fourth mixed solution was obtained;

[0018] Step 8: Transfer the fourth mixed solution after the reaction in Step 7 to the vacuum filtration system for washing, surface modification and solid-liquid separation;

[0019] Step 9: Transfer the copper powder separated in Step 8 to a vacuum drying oven to obtain the final product.

[0020] Based on the above technical solution, the present invention can be further improved as follows:

[0021] Furthermore, the concentration of the sodium hydroxide aqueous solution prepared in step 1 is 1–5 mol / L.

[0022] Furthermore, in step 2, the heating and holding temperature is 40–70°C, the stirring rate is 100–250 r / min, and the concentration of the prepared ascorbic acid solution is 1–12 mol / L.

[0023] Furthermore, in step 3, the heating and holding temperature is 40–60°C, the stirring rate inside the vessel is 100–300 r / min, and the concentration of the prepared copper sulfate aqueous solution is 0.1–3 mol / L.

[0024] Furthermore, in step 4, the concentration of sodium citrate powder protective agent is 0.2–5 mol / L.

[0025] Furthermore, in step 5, the rate at which ascorbic acid is added is 2–10 L / min.

[0026] Furthermore, in step 6, the pH of the third mixed solution is adjusted to 9–13.

[0027] Furthermore, in step 7, the target reaction temperature is 70–90°C, and the reaction time is 1–3 hours.

[0028] Furthermore, in step 8, the washing time is 30–90 min, the surface modifier mass is 1–15% of the copper powder mass, and the surface modification time is 10–60 min.

[0029] Furthermore, in step 9, the vacuum drying temperature is 30–80°C, and the drying time is 10–20 hours.

[0030] The beneficial effects of this invention are:

[0031] 1. Environmentally friendly, safe and high purity: Food-grade ascorbic acid is used as a reducing agent, which is non-toxic and leaves no residue. Combined with pressure filtration and washing to remove impurities, the purity of the finished copper powder is ≥99.8%, meeting the requirements of electronic applications.

[0032] 2. Wide and controllable particle size distribution: Through sodium citrate as a protective agent and precise temperature and pH control, a wide distribution of nano-copper powder particle size of 50nm to 2μm is achieved, which can adapt to the different particle size requirements of different fields.

[0033] 3. Excellent antioxidant properties: The double protective layer formed by the passivating agent modification ensures that the oxidation rate of copper powder is less than 1% after 6 months of storage in air, which is far superior to untreated copper powder (oxidation rate ≥15% after 1 month of storage).

[0034] 4. Strong industrial adaptability: It adopts conventional reaction kettles, filtration systems, vacuum drying ovens and other equipment. The operation steps are simple, easy to standardize, the production cycle is short, the cost is low, and it is suitable for large-scale mass production. Attached Figure Description

[0035] Figure 1This is a high-magnification SEM image of the nano-copper powder prepared in Example 1 of this invention;

[0036] Figure 2 This is a low-magnification SEM image of the nano-copper powder prepared in Example 1 of this invention;

[0037] Figure 3 This is a high-magnification SEM image of the nano-copper powder prepared in Example 2 of this invention;

[0038] Figure 4 This is a low-magnification SEM image of the nano-copper powder prepared in Example 2 of this invention. Detailed Implementation

[0039] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0040] A method for preparing broadly distributed nano-copper powder includes the following steps:

[0041] Step 1: Add sodium hydroxide (NaOH) and distilled water to a preparation vessel, stir at room temperature to accelerate dissolution, and prepare a sodium hydroxide aqueous solution with a concentration of 1-5 mol / L.

[0042] Sodium hydroxide is a strong electrolyte and ionizes when dissolved in water at room temperature (NaOH = Na₂O). + +OH - Stirring breaks the concentration gradient at dissolution equilibrium, accelerates ion diffusion, and ensures uniform solution concentration. This alkaline solution is subsequently used to adjust the pH of the reaction system, providing an alkaline environment for the reduction reaction.

[0043] Step 2: Add ascorbic acid (C6H8O6, reducing agent) and distilled water to the reaction vessel, heat to 40-70℃, stir at a rate of 100-250 r / min to accelerate dissolution and prepare an ascorbic acid aqueous solution with a concentration of 1-12 mol / L.

[0044] The solubility of ascorbic acid increases with increasing temperature; heating conditions of 40–70°C can improve its dissolution efficiency and prevent undissolved solids from affecting the homogeneity of subsequent reactions. A stirring rate controlled at 100–250 r / min ensures complete dissolution without causing splashing or localized overheating due to excessive stirring. As a reducing agent, ascorbic acid's hydroxyl group (-OH) in its molecule has reducing properties, which can subsequently reduce Cu. 2+ Reduced to Cu 0 .

[0045] Step 3: Add copper sulfate (CuSO4, copper source) and distilled water to the reaction vessel, heat to 40-60℃, stir at a rate of 100-300 r / min to accelerate dissolution and prepare a copper sulfate aqueous solution with a concentration of 0.1-3 mol / L.

[0046] A higher stirring rate (100–300 r / min) is appropriate for its solubility characteristics, ensuring uniform distribution of Cu²⁺ in the solution and avoiding excessively high local concentrations that could lead to subsequent particle agglomeration. This solution provides Cu²⁺ raw material for the reaction and serves as the metal ion source for the nano-copper powder.

[0047] Step 4: Add sodium citrate powder to the copper sulfate aqueous solution prepared in Step 3 to obtain the first mixed solution. Control the concentration of sodium citrate to be 0.2-5 mol / L. Sodium citrate powder is used as a protective agent.

[0048] Sodium citrate (C6H8O7) molecules contain multiple carboxyl groups (-COOH), which can react with Cu in solution. 2+ A complexation reaction occurs, forming a stable complex. At the same time, sodium citrate molecules adsorb onto the surface of the subsequently generated copper nanoparticles, preventing the particles from agglomerating through steric hindrance. This achieves the goal of "wide distribution" particle size control, avoiding the narrowing of the particle size distribution or the formation of large particles due to agglomeration.

[0049] Step 5: Add the ascorbic acid aqueous solution prepared in step 2 to the first mixed solution prepared in step 4 at a rate of 2-10 L / min to obtain the second mixed solution.

[0050] Controlling the addition rate (2–10 L / min) is to ensure a gentle reduction reaction: if added too quickly, the local ascorbic acid concentration will be too high, leading to Cu... 2+ Rapid reduction generates a large number of nanoparticles, which easily leads to aggregation; if added too slowly, the reaction efficiency is too low. Ascorbic acid and Cu 2+ The reduction reaction needs to be initiated in a homogeneous mixed system. This step creates a homogeneous reactant distribution environment for the subsequent reduction reaction.

[0051] Step 6: Add the sodium hydroxide aqueous solution prepared in Step 1 to the second mixed solution prepared in Step 5 to obtain the third mixed solution, and adjust the pH of the third mixed solution to 9-13.

[0052] An alkaline environment (pH 9–13) is crucial for the reduction reaction: on the one hand, OH- -It can promote the reduction activity of ascorbic acid (ascorbic acid loses electrons more easily under alkaline conditions); on the other hand, excessively high or low pH will affect the reaction equilibrium: when the pH is below 9, the reduction reaction rate slows down; when the pH is above 13, Cu(OH)2 precipitate may be formed instead of elemental copper nanoparticles. Sodium hydroxide, as a strong base, can quickly adjust the pH of the system to the optimal reaction range.

[0053] Step 7: Heat the third mixed solution prepared in step 6 to 70–90°C and maintain it for 1–3 hours until Cu… 2+ Completely reduced to Cu 0 The fourth mixed solution was obtained.

[0054] The target temperature of 70–90℃ represents the optimal kinetic conditions for the reduction reaction: if the temperature is too low (below 70℃), the reaction rate is slow, and Cu… 2+ Incomplete reduction; excessively high temperature (above 90℃) leads to excessively rapid growth of copper nanoparticles, resulting in easy agglomeration and uncontrolled particle size distribution. A reaction time of 1–3 hours ensures that all Cu nanoparticles are reduced. 2+ Reduced to Cu by ascorbic acid 0 (Core of the reaction equation: C6H8O7 + 2Cu) 2+ + 2OH - → C6H6O6+ 2Cu↓+ 2H2O), while the dispersing effect of sodium citrate continues to be effective, maintaining the wide distribution characteristics of the particles.

[0055] Step 8: Transfer the fourth mixed solution after the reaction in Step 7 to a vacuum filtration system, wash for 30-90 minutes, add 1-15% of copper powder by weight as a surface modifier, modify for 10-60 minutes, and then perform solid-liquid separation.

[0056] The purpose of washing (30–90 min) is to remove unreacted NaOH, sodium citrate, ascorbic acid oxidation products, and other impurities from the solution. Surface modifiers (1–15% of the copper powder mass) are applied to the surface of the nano-copper particles through physical adsorption or chemical bonding to further improve the dispersion stability and environmental adaptability (such as antioxidant properties) of the particles. The modification time is 10–60 min to ensure that the modifiers are fully adsorbed. The solid-liquid separation function of the filtration system quickly separates the nano-copper powder solids, preparing for subsequent drying.

[0057] Step 9: Transfer the copper powder separated in Step 8 to a vacuum drying oven and dry it at 30-80°C for 10-20 hours.

[0058] Vacuum drying is an ideal drying method for nanomaterials: the low temperature of 30-80℃ can avoid the oxidation of nano copper powder (nano copper is easily oxidized at room temperature); in a vacuum environment, the drying time of 10-20 hours ensures that the moisture is completely removed, and finally obtains dry, well-dispersed, and widely distributed nano copper powder.

[0059] The following specific examples illustrate the beneficial effects of the present invention.

[0060] Example 1

[0061] Step 1: Dissolve 8 kg of sodium hydroxide in 100 L of distilled water and stir to accelerate dissolution, thus obtaining an aqueous solution of sodium hydroxide.

[0062] Step 2: Dissolve 6160g of vitamin C powder in 25L of distilled water and stir well, while slowly heating to 45℃ to obtain solution A.

[0063] Step 3: Dissolve 3410g of copper sulfate in 25L of distilled water and stir until homogeneous, while slowly heating to 60℃ to obtain solution B.

[0064] Step 4: Add 3025g of sodium citrate powder to solution B, stir to dissolve, and obtain solution C.

[0065] Step 5: Add solution A to solution C at a flow rate of 5 L / min to obtain solution D.

[0066] Step 6: Add the sodium hydroxide aqueous solution obtained in Step 1 to solution D to adjust the pH to 13, thus obtaining solution E.

[0067] Step 7: Place solution E in a reaction vessel, then heat it to 90°C at a heating rate of 5°C / min, and react for 90 min to obtain a purple-red product.

[0068] Step 8: Place the purplish-red product obtained in Step 7 into a vacuum filtration system and wash it with distilled water for 30 min. Then add a surface modifier and wash for 15 min. Continue washing with distilled water for 10 min. Finally, place it in a vacuum drying oven and dry for 18 h to obtain a wide-distribution nano-copper powder with a particle size of 50-500 nm.

[0069] Figure 1 This is a high-magnification SEM image of the nano-copper powder prepared in Example 1. Figure 2 This is a low-magnification SEM image of the nano-copper powder prepared in Example 1. From... Figure 1 and Figure 2 As can be seen from the above, the copper powder prepared in Example 1, i.e., the present invention, is a nano- and submicron composite particle with a particle size distribution of 50-500 nm. The surface is clean and no obvious coating was found.

[0070] Example 2

[0071] Step 1: Dissolve 8 kg of sodium hydroxide in 100 L of distilled water and stir to accelerate dissolution, thus obtaining an aqueous solution of sodium hydroxide.

[0072] Step 2: Dissolve 6160g of vitamin C powder in 25L of distilled water and stir well, while slowly heating to 45℃ to obtain solution A.

[0073] Step 3: Dissolve 4000g of copper sulfate in 25L of distilled water and stir until homogeneous, while slowly heating to 60℃ to obtain solution B.

[0074] Step 4: Add 3100g of sodium citrate powder to solution B, stir to dissolve, and obtain solution C.

[0075] Step 5: Add solution A to solution C at a flow rate of 5 L / min to obtain solution D.

[0076] Step 6: Add the sodium hydroxide aqueous solution obtained in Step 1 to solution D to adjust the pH to 12.5, thus obtaining solution E.

[0077] Step 7: Place solution E in a reaction vessel, then heat it to 90°C at a heating rate of 5°C / min, and react for 2 hours to obtain a purple-red product.

[0078] Step 8: Place the purplish-red product obtained in Step 7 into a vacuum filtration system and wash it with distilled water for 30 min. Then add a surface modifier and wash for 15 min. Continue washing with distilled water for 10 min. Finally, place it in a vacuum drying oven and dry for 18 h to obtain a wide-distribution nano-copper powder with a particle size of 400 nm-1.3 μm.

[0079] Figure 3 This is a high-magnification SEM image of the nano-copper powder prepared in Example 2. Figure 4 This is a low-magnification SEM image of the nano-copper powder prepared in Example 2. From... Figure 3 and Figure 4 As can be seen from the above, the copper powder prepared in Example 2, i.e., the present invention, is a submicron composite particle with a particle size distribution of 400nm-1.3μm. The surface is clean and no obvious coating was found.

[0080] Chinese invention patent application number 202411373897.2 discloses an ultrafine copper powder, its preparation method, and its application. Compared to the aforementioned patent, this invention uses ascorbic acid as a reducing agent and copper chloride as a copper source, but the two differ fundamentally in reaction path design, control mechanism, and product formation mechanism. These differences directly lead to significant differences in the final product's particle size, distribution range, morphology, and antioxidant properties. This invention eliminates the complex intermediate control process of the two-step reduction method, pioneering a new integrated reaction path combining "one-step direct reduction with alkaline ascorbic acid" with "in-situ simultaneous protection with sodium citrate." This invention uses food-grade ascorbic acid and sodium citrate, eliminating the need for metal salt reducing agents such as ferrous sulfate, resulting in a cleaner process that meets green production requirements and reduces safety risks and environmental treatment costs. This invention employs "high-concentration ascorbic acid + strongly alkaline environment" to make Cu... 2+ The explosive nucleation and the timely adsorption and encapsulation of crystal nuclei by sodium citrate inhibit Ostwald ripening, making it difficult for the nuclei to continue growing. This significantly reduces the size of copper powder particles, focusing on nanoscale wide-distribution copper powder to meet the precision requirements of high-end electronics, clearly distinguishing it from the aforementioned patents that focus on micron-scale narrow-distribution copper powder to replace silver powder and reduce costs.

[0081] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a wide distribution of copper nanoparticles, characterized in that, It comprises the following steps: Step 1, take sodium hydroxide and distilled water into a preparation tank, accelerate dissolution by stirring at room temperature, and prepare a sodium hydroxide aqueous solution; Step 2, take ascorbic acid and distilled water into a reaction kettle, accelerate dissolution by heating and stirring, and prepare an ascorbic acid aqueous solution; Step 3, take copper sulfate and distilled water into a reaction kettle, accelerate dissolution by heating and stirring, and prepare a copper sulfate aqueous solution; Step 4, take sodium citrate powder as a protective agent in the reaction process into the copper sulfate aqueous solution prepared in step 3 to obtain a first mixed solution; Step 5, add the ascorbic acid aqueous solution prepared in step 2 into the first mixed solution prepared in step 4 to obtain a second mixed solution; Step 6, add the sodium hydroxide aqueous solution prepared in step 1 into the second mixed solution prepared in step 5 to obtain a third mixed solution, and adjust the pH of the third mixed solution; Step 7, the third mixed solution prepared in step 6 is warmed to a target temperature and kept for a period of time until Cu 2+ is completely reduced to Cu 0 , to obtain a fourth mixed solution; Step 8, transfer the fourth mixed solution after the reaction in step 7 to a filtration system for washing, surface modification, and solid-liquid separation; Step 9, transfer the copper powder separated in step 8 to a vacuum drying oven to obtain the product.

2. The method of claim 1, wherein the wide distribution of copper nanoparticles is prepared by the process of claim 1. The concentration of the sodium hydroxide aqueous solution prepared in step 1 is 1-5 mol / L.

3. The method of claim 1, wherein the copper nanoparticles have a wide distribution. The heating temperature in step 2 is 40-70℃, the stirring rate is 100-250 r / min, and the concentration of the prepared ascorbic acid solution is 1-12 mol / L.

4. The method of claim 1, wherein the copper nanoparticles have a wide distribution. The heating temperature in step 3 is 40-60℃, the stirring rate in the kettle is 100-300 r / min, and the concentration of the prepared copper sulfate aqueous solution is 0.1-3 mol / L.

5. The method of claim 1, wherein the copper nanoparticles have a wide distribution. The concentration of the sodium citrate powder protective agent in step 4 is 0.2-5 mol / L.

6. The method of claim 1, wherein the copper nanoparticles have a wide distribution. The addition rate of ascorbic acid in step 5 is 2-10 L / min.

7. The method of claim 1, wherein the copper nanoparticles have a wide distribution. The pH of the third mixed solution in step 6 is adjusted to 9-13.

8. The method of claim 1, wherein the copper nanoparticles have a wide distribution. The target reaction temperature in step 7 is 70-90℃, and the reaction time is 1-3 h.

9. The method of claim 1, wherein the copper nanoparticles have a wide distribution. The washing time in step 8 is 30-90 min, the mass of the surface modifier is 1-15% of the mass of the copper powder, and the surface modification time is 10-60 min.

10. The method of claim 1 to 9, wherein the method is characterized by, The vacuum drying temperature in step 9 is 30-80℃, and the drying time is 10-20 h.

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