Preparation method of nano-copper powder with controllable morphology and particle size and application thereof

Abstract

The application relates to a preparation method of nano copper powder with controllable morphology and particle size and application thereof, and belongs to the technical field of metal nano material preparation, and comprises the following steps: S1, preparation of a precursor complex solution; S2, construction of a gradient reduction system: formation of a cuprous ion solution; S3, variable-temperature and variable-speed nucleation and growth: formation of copper element; S4, composite passivation and coating: solid-liquid separation to obtain a copper powder filter cake, redispersion of the copper powder filter cake in an organic solvent to form slurry, addition of a composite antioxidant, and heating coating treatment in an inert atmosphere; and S5, gradient dehydration and airflow drying: nano copper powder is obtained. The preparation method of the nano copper powder with controllable morphology and particle size and application thereof are prepared through a "precursor complexation-gradient reduction-variable-temperature and variable-speed nucleation" multistage synergistic regulation mechanism, the nucleation and growth process are decoupled in kinetics, the product particle size is mainly determined by the supersaturation condition of the nucleation stage, and the problem of uncontrollable particle size in the amplification process of a traditional process is fundamentally overcome.

Description

Technical Field

[0001] This invention relates to the field of metal nanomaterial preparation technology, specifically to a method for preparing nano-copper powder with controllable morphology and particle size and its application in electronic pastes, conductive inks, MLCC internal electrodes, and other fields. Background Technology

[0002] With the miniaturization, high-frequency, and integration of electronic components, and the urgent need for low-cost, high-efficiency conductive materials in the photovoltaic industry, nano-copper powder, as an ideal substitute for silver powder, has shown great application potential in fields such as internal electrodes of multilayer ceramic capacitors (MLCCs), silver paste additives for the front side of photovoltaic cells, conductive inks, and 3D printed electronic devices due to its excellent conductivity, thermal conductivity, good sintering activity, and significant cost advantages. The liquid-phase reduction method has become the mainstream technical route for preparing nano-copper powder due to its advantages such as mild reaction conditions, simple equipment, strong controllability of product morphology and particle size, and ease of industrial scale-up.

[0003] However, the existing liquid-phase reduction method for preparing nano-copper powder still faces the following technical bottlenecks: (1) It is difficult to accurately control the particle size and morphology. The nucleation and growth process of nano-copper powder is affected by multiple factors. The traditional "one-step method" or simple sequential feeding is difficult to achieve independent control of nucleation and growth, which easily leads to a wide particle size distribution, poor morphological uniformity, and a significant increase in particle size when the reaction system is scaled up. (2) The hard agglomeration and oxidation problems during the drying process are serious. Nano-copper powder has a large specific surface area and high surface energy, and is very easy to undergo irreversible hard agglomeration due to the capillary action of liquid phase surface tension. Conventional oven drying is also accompanied by surface oxidation, resulting in high oxygen content and decreased conductivity of the product. (3) The function of a single surface control system is limited. Existing surfactants or dispersants have a single function and cannot simultaneously meet the multiple requirements of morphology control, dispersion stability and anti-oxidation, thus limiting the comprehensive performance of the product.

[0004] Therefore, there is an urgent need for a method for preparing nano-copper powder that can achieve precise particle size control, diverse and controllable morphology, high dispersibility, high oxidation resistance, and is easy to scale up. This invention aims to provide a method for preparing nano-copper powder and its application, which solves the problems of difficult precise control of particle size and morphology, severe drying agglomeration and oxidation, and poor overall product performance in existing technologies through a multi-stage synergistic control system of "precursor complexation-gradient reduction-temperature and speed nucleation-composite passivation-gradient dehydration and airflow dispersion drying". Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for preparing nano-copper powder with controllable morphology and particle size, and its application. It has the advantages of precise control over particle size and morphology, good stability during decoupling and scale-up of nucleation and growth processes, synergistic elimination of hard agglomeration by gradient dehydration and airflow drying, and significant improvement in antioxidant properties by composite passivation coating. It solves the problems of difficulty in precisely controlling particle size and morphology, uncontrollable particle size after reaction scale-up, easy occurrence of hard agglomeration and surface oxidation during the drying process leading to poor dispersibility and high oxygen content when preparing nano-copper powder by existing liquid phase reduction methods.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing nano-copper powder with controllable morphology and particle size includes the following steps: S1. Preparation of precursor complex solution: Dissolve copper salt in solvent, add first surface modifier to carry out complexation reaction to form copper-organic ligand complex precursor solution; the first surface modifier is a compound of sulfur-containing amino acid and natural polymer; S2. Construction of the gradient reduction system: Add a second surface modifier and a reducing agent solution to the solution obtained in step S1 to form a cuprous ion solution; the second surface modifier is a mixture of a nonionic polymer and a cationic-nonionic composite surfactant; S3. Temperature- and speed-dependent nucleation and growth: pH adjuster is added in a segmented speed-dependent manner to adjust the pH value of the system to alkaline. At the same time, the temperature is heated to 70-90℃ and held at that temperature to carry out the reduction reaction and form elemental copper. S4. Composite passivation and coating: Copper powder filter cake is obtained by solid-liquid separation, redispersed in an organic solvent to form a slurry, a composite antioxidant is added, and a coating treatment is carried out under an inert atmosphere with heating; the composite antioxidant includes an organic corrosion inhibitor and reducing sugars; S5. Gradient dehydration and airflow drying: After coating, solid-liquid separation is performed again. The filter cake is washed with organic solvents with decreasing surface tension gradients, and then dried by airflow pulverizer to obtain nano copper powder.

[0007] Furthermore, in S1, the sulfur-containing amino acid is methionine or cysteine, the natural polymer is gum arabic or gelatin, and the mass ratio of the sulfur-containing amino acid to the natural polymer is 1:2 to 1:5.

[0008] Furthermore, in S2, the nonionic polymer is polyvinylpyrrolidone or polyvinyl alcohol, and the cationic-nonionic composite surfactant is a compound of hexadecyltrimethylammonium bromide and polyethylene glycol, with a molar ratio of 1:1 to 1:3.

[0009] Furthermore, in S3, the segmented variable-speed alkali addition method is as follows: in the first stage, the pH is adjusted from acidic to 5.0-7.0 at a relatively fast speed, and in the second stage, the pH is adjusted to 9.0-12.0 at a relatively slow speed; the programmed temperature rise method is as follows: in the first stage, the temperature is increased to 40-60℃ at 5-10℃ / min, and in the second stage, the temperature is increased to 70-90℃ at 2-5℃ / min.

[0010] Furthermore, in step S4, the organic corrosion inhibitor is benzotriazole or mercaptobenzothiazole, and the reducing sugar is sorbitol or glucose, with a mass ratio of 1:1 to 1:4; the coating temperature is 50 to 80°C, and the time is 0.5 to 2 hours.

[0011] Furthermore, in S5, the gradient dehydration pretreatment involves sequentially washing the filter cake with anhydrous ethanol, acetone, and n-hexane; the inlet air temperature of the airflow pulverizer drying is 100–150°C, the outlet air temperature is 50–70°C, and the feeding rate is 5–20 kg / h.

[0012] Furthermore, the reducing agent is one or more of ascorbic acid, glucose, or hydrazine hydrate; the pH adjusting agent is a sodium hydroxide solution or a potassium hydroxide solution.

[0013] Furthermore, the particle size of the nano-copper powder is adjustable from 100 to 1000 nm, and its morphology is controllable as spherical, near-spherical, or polyhedral.

[0014] Furthermore, the tap density of the nano-copper powder is 2.5–4.5 g / cm³. 3 Oxygen content ≤0.5 wt.%, specific surface area 2–8 m² 2 / g.

[0015] The present invention also provides an application of nano-copper powder with controllable morphology and particle size, wherein the nano-copper powder is used in the internal electrode paste of multilayer ceramic capacitors, conductive paste of photovoltaic cells, conductive ink, or 3D printed electronic materials.

[0016] Compared with the prior art, the present invention provides a method for preparing nano-copper powder with controllable morphology and particle size and its application, which has the following beneficial effects: 1. The preparation method and application of morphology- and particle size-controllable nano-copper powder utilizes a multi-level synergistic regulation mechanism of "precursor complexation-gradient reduction-variable temperature and speed nucleation" to kinetically decouple the nucleation and growth processes. This allows the product particle size to be primarily determined by the supersaturation conditions during the nucleation stage, fundamentally overcoming the problem of uncontrollable particle size during the scale-up process of traditional methods. Experiments show that customized particle size control can be achieved within the range of 100–1000 nm, and the particle size deviation can be controlled within ±15% from a 5L pilot-scale test to a 50L pilot-scale test.

[0017] 2. The preparation method and application of nano-copper powder with controllable morphology and particle size: By combining the complexation effect of the first surface regulator with the crystal facet selective adsorption of the second surface regulator, and using a variable temperature and speed strategy, nano-copper powders with various morphologies such as spherical, near-spherical, and polyhedral can be prepared according to application requirements. Gradient dehydration pretreatment effectively reduces the drying capillary force, and airflow pulverization drying achieves integrated drying and dispersion. The resulting powder has no hard agglomerates, the tap density is increased by 20-35%, the specific surface area is reduced by 15-25%, and the flowability is significantly improved.

[0018] 3. The preparation method and application of this morphology and particle size controllable nano-copper powder: By employing a composite antioxidant consisting of an organic corrosion inhibitor and reducing sugars, a dual-layer protective structure of "chemical passivation + physical barrier" is constructed on the surface of the copper powder, resulting in an oxygen content of less than 0.5 wt.% in the nano-copper powder. The overall performance of the product is as follows: particle size adjustable from 100 to 1000 nm, tap density 2.5 to 4.5 g / cm³. 3 Specific surface area 2–8 m² 2 / g, can be widely used in MLCC internal electrode paste, photovoltaic cell conductive paste, conductive ink, 3D printing electronic materials and other fields, and is expected to achieve an industrial breakthrough in replacing silver with copper. Attached Figure Description

[0019] Figure 1 This is a process flow diagram of a method for preparing nano-copper powder with controllable morphology and particle size according to the present invention.

[0020] Figure 2 This is a SEM image of the 200nm spherical copper nanoparticles obtained in Example 1 of this invention.

[0021] Figure 3 This is a SEM image of the 500nm polyhedral copper nanoparticles obtained in Example 2 of the present invention.

[0022] Figure 4 This is a SEM image of the 800nm ​​near-spherical copper nanoparticles obtained in Example 3 of the present invention. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Please see Figures 1 to 4 .

[0025] Example 1: Preparation of 200nm spherical copper nanopowder S1. Preparation of precursor complexing solution: Weigh 170g of copper chloride dihydrate and dissolve it in 2L of deionized water. Stir and dissolve at a constant temperature of 30℃. Add the first surface modifier (composed of 5g of methionine and 15g of gum arabic, in a mass ratio of 1:3), and stir for 30 minutes to obtain a clear copper-organic ligand complex precursor solution.

[0026] S2, Construction of the gradient reduction system: Add the second surface modifier (a compound of 10g PVP-K30 and 5g CTAB and PEG-400, with a CTAB:PEG-400 molar ratio of 1:2) to the above solution and stir to dissolve. Add 1L of reducing agent solution containing 150g ascorbic acid and stir until homogeneous. At this point, the pH of the system is approximately 2.5.

[0027] S3, variable-temperature-variable-speed nucleation and growth: Start stirring and add 3 mol / L NaOH solution in stages using a variable-rate method. First stage: Add NaOH at a rate of 50 mL / min until pH = 6.0 (approximately 2 minutes), while simultaneously increasing the temperature to 50°C at a rate of 8°C / min. Second stage: Adjust the alkali addition rate to 15 mL / min and continue adding NaOH until the final pH = 10.5 (approximately 8 minutes), while simultaneously adjusting the heating rate to 3°C / min and continuing to heat to 85°C. Maintain the reaction temperature for 1 hour.

[0028] S4. Composite passivation and coating: After the reaction was completed, copper powder filter cake was obtained by vacuum filtration. The filter cake was put into a reaction vessel containing 2L of anhydrous ethanol and stirred to disperse it into a slurry. A composite antioxidant (composed of 5g BTA and 10g sorbitol, with a mass ratio of 1:2) was added, nitrogen gas was introduced for protection, and the temperature was raised to 65℃ and stirred for 1.5 hours for coating.

[0029] S5. Gradient dehydration and airflow drying: After coating, the filter cake was filtered, and then washed twice with anhydrous ethanol, twice with acetone, and once with n-hexane. The pretreated filter cake was then dried using an air jet mill-dryer with an inlet air temperature of 120°C, an outlet air temperature of 60°C, and a feed rate of 10 kg / h.

[0030] Performance testing: The obtained product is spherical nano-copper powder with an average particle size of 210 nm and a tap density of 3.8 g / cm³. 3 Oxygen content 0.32 wt.%, specific surface area 4.5 m² 2 / g.

[0031] Example 2: Preparation of 500nm polyhedral copper nanopowder S1, precursor complexing solution: Dissolve 170g of copper chloride dihydrate in 2L of water. Add the first surface modifier: 4g of cysteine ​​+ 16g of gelatin (mass ratio 1:4). React for 30 minutes.

[0032] S2, Gradient Reduction: Second surface regulator: 12g PVA + 6g compound of dodecyltrimethylammonium bromide and PEG-600 (molar ratio 1:1.5); reducing agent: 200g glucose dissolved in 1L water; system pH≈2.0.

[0033] S3, Variable Temperature and Variable Speed: First stage: Add alkali at a rate of 60 mL / min until pH=5.5, and raise the temperature at a rate of 10℃ / min until 45℃; Second stage: Add alkali at a rate of 10 mL / min until pH=11.0, and raise the temperature at a rate of 2℃ / min until 80℃; Hold for 1.5h.

[0034] S4, Composite Passivation: Compound antioxidant: MBT 6g + glucose 12g (1:2), coated at 70℃ for 1h.

[0035] S5. Gradient dehydration and drying: The material is replaced sequentially with ethanol, acetone, and n-hexane. The airflow drying process involves an inlet temperature of 130°C, an outlet temperature of 65°C, and a feed rate of 12 kg / h.

[0036] Properties: Polyhedral shape, average particle size 530 nm, tap density 4.2 g / cm³ 3 Oxygen content 0.28 wt.%, specific surface area 3.2 m² 2 / g.

[0037] Example 3: Preparation of 800nm ​​near-spherical copper nanopowder S1, precursor complexing solution: Dissolve 170g of copper chloride dihydrate in 2L of water. First surface modifier: 3g of methionine + 12g of gum arabic (1:4). React for 30 minutes.

[0038] S2, Gradient Reduction: Second surface regulator: 8g PVP-K90 + 4g CTAB and PEG-400 compound (1:3); reducing agent: 1L mixed solution of 120g ascorbic acid and 80g glucose; pH≈2.8.

[0039] S3, Variable Temperature and Variable Speed: First stage: Add alkali at 40 mL / min until pH=6.5, and raise the temperature at 6℃ / min to 55℃; Second stage: Add alkali at 8 mL / min until pH=10.0, and raise the temperature at 2℃ / min to 75℃; keep warm for 2 hours.

[0040] S4, Composite Passivation: Compound antioxidant: BTA 4g + sorbitol 16g (1:4), coated at 60℃ for 2h.

[0041] S5. Gradient dehydration and drying: Same as in Example 1, with airflow drying inlet temperature of 110°C, outlet temperature of 55°C, and feed rate of 8 kg / h.

[0042] Properties: Spherical shape, average particle size 820 nm, tap density 4.5 g / cm³ 3 Oxygen content 0.35 wt.%, specific surface area 2.5 m² 2 / g.

[0043] Comparative Example 1: (Traditional one-step method, without multi-level coordinated regulation) The nano-copper powder was prepared using a conventional liquid-phase reduction method, and the steps are as follows: Precursor solution preparation: Weigh 170g of copper chloride dihydrate, dissolve it in 2L of deionized water, stir to dissolve, and do not add the first surface conditioner.

[0044] Construction of the reduction system: Add 10g of PVP-K30 as a dispersant to the copper salt solution, stir to dissolve, and then add 1L of reducing agent solution containing 150g of ascorbic acid.

[0045] Nucleation and growth: Under stirring conditions, 3 mol / L NaOH solution was added at once to adjust the pH of the system to 10.5, and the temperature was raised to 85℃ and kept at this temperature for 1 hour.

[0046] Post-processing: After the reaction was completed, the filter cake was filtered and washed three times with anhydrous ethanol. The filter cake was then placed in a vacuum drying oven and dried under vacuum at 50°C for 8 hours to obtain nano-copper powder.

[0047] Performance testing: The product has a wide particle size distribution (200–800 nm), irregular morphology (mostly amorphous particles), and a tap density of 2.1 g / cm³. 3 It has an oxygen content of 1.2 wt.%, exhibits severe hard agglomeration, poor dispersibility, and poor flowability.

[0048] Comparative conclusion: Compared with Examples 1-3 of the present invention, the traditional one-step method lacks key steps such as precursor complexation regulation, variable temperature and speed nucleation growth control, composite passivation coating, and gradient dehydration-airflow drying. As a result, the obtained nano-copper powder is significantly inferior to the product of the present invention in terms of particle size uniformity, morphological regularity, dispersibility, tap density, and antioxidant properties.

[0049] Comparative Example 2: (Drying with a gradient-free dehydration airflow) S1-S4 of Example 1 were used, but S5 was dried in a conventional oven at 50°C under vacuum.

[0050] Performance: The product has a particle size of approximately 220 nm, but exhibits significant hard agglomeration; the tap density is 2.8 g / cm³. 3 It has an oxygen content of 0.45 wt.% and poor dispersibility.

[0051] Application example: Preparation of conductive paste The nano-copper powder obtained in Example 1 was mixed with an organic carrier (terpineol and ethyl cellulose) at a mass ratio of 70:30 and dispersed using a three-roll mill to prepare a conductive paste. This paste was screen-printed onto a ceramic substrate and sintered at 250°C for 30 minutes under a nitrogen atmosphere. The sheet resistance was measured to be 15 mΩ / □, indicating good adhesion. This paste can replace silver paste for the internal electrodes of MLCCs.

[0052] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0053] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing nano-copper powder with controllable morphology and particle size, characterized in that, Includes the following steps: S1. Preparation of precursor complex solution: Dissolve copper salt in solvent, add first surface modifier to carry out complexation reaction to form copper-organic ligand complex precursor solution; the first surface modifier is a compound of sulfur-containing amino acid and natural polymer; S2. Construction of the gradient reduction system: Add a second surface modifier and a reducing agent solution to the solution obtained in step S1 to form a cuprous ion solution; the second surface modifier is a mixture of a nonionic polymer and a cationic-nonionic composite surfactant; S3. Temperature- and speed-dependent nucleation and growth: pH adjuster is added in a segmented speed-dependent manner to adjust the pH value of the system to alkaline. At the same time, the temperature is heated to 70-90℃ and held at that temperature to carry out the reduction reaction and form elemental copper. S4. Composite passivation and coating: Copper powder filter cake is obtained by solid-liquid separation, redispersed in an organic solvent to form a slurry, a composite antioxidant is added, and a coating treatment is carried out under an inert atmosphere with heating; the composite antioxidant includes an organic corrosion inhibitor and reducing sugars; S5. Gradient dehydration and airflow drying: After coating, solid-liquid separation is performed again. The filter cake is washed with organic solvents with decreasing surface tension gradients, and then dried by airflow pulverizer to obtain nano copper powder.

2. The method for preparing nano-copper powder with controllable morphology and particle size according to claim 1, characterized in that, In S1, the sulfur-containing amino acid is methionine or cysteine, and the natural polymer is gum arabic or gelatin. The mass ratio of the sulfur-containing amino acid to the natural polymer is 1:2 to 1:

5.

3. The method for preparing nano-copper powder with controllable morphology and particle size according to claim 1, characterized in that, In S2, the nonionic polymer is polyvinylpyrrolidone or polyvinyl alcohol, and the cationic-nonionic composite surfactant is a compound of hexadecyltrimethylammonium bromide and polyethylene glycol, with a molar ratio of 1:1 to 1:

3.

4. The method for preparing nano-copper powder with controllable morphology and particle size according to claim 1, characterized in that, In S3, the segmented variable-speed alkali addition method is as follows: in the first stage, the pH is adjusted from acidic to 5.0-7.0 at a relatively fast speed, and in the second stage, the pH is adjusted to 9.0-12.0 at a relatively slow speed; the programmed temperature increase method is as follows: in the first stage, the temperature is increased to 40-60℃ at 5-10℃ / min, and in the second stage, the temperature is increased to 70-90℃ at 2-5℃ / min.

5. The method for preparing nano-copper powder with controllable morphology and particle size according to claim 1, characterized in that, In step S4, the organic corrosion inhibitor is benzotriazole or mercaptobenzothiazole, and the reducing sugar is sorbitol or glucose, with a mass ratio of 1:1 to 1:4; the coating temperature is 50 to 80°C, and the coating time is 0.5 to 2 hours.

6. The method for preparing nano-copper powder with controllable morphology and particle size according to claim 1, characterized in that, In step S5, the gradient dehydration pretreatment involves sequentially washing the filter cake with anhydrous ethanol, acetone, and n-hexane; the inlet air temperature of the airflow pulverizer is 100–150°C, the outlet air temperature is 50–70°C, and the feeding rate is 5–20 kg / h.

7. The method for preparing nano-copper powder with controllable morphology and particle size according to claim 1, characterized in that, The reducing agent is one or more of ascorbic acid, glucose, or hydrazine hydrate; the pH adjusting agent is a sodium hydroxide solution or a potassium hydroxide solution.

8. The method for preparing nano-copper powder with controllable morphology and particle size according to claim 1, characterized in that, The particle size of the nano-copper powder is adjustable from 100 to 1000 nm, and its morphology is controllable as spherical, near-spherical, or polyhedral.

9. The method for preparing nano-copper powder with controllable morphology and particle size according to claim 1, characterized in that, The tap density of the nano-copper powder is 2.5–4.5 g / cm³. 3 Oxygen content ≤0.5 wt.%, specific surface area 2–8 m² 2 / g.

10. The application of the nano-copper powder prepared by any one of claims 1-9 in the electrode paste of multilayer ceramic capacitors, conductive paste of photovoltaic cells, conductive ink, or 3D printed electronic materials.

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