A method for continuously preparing narrow-distribution sub-micron spherical gold powder by microfluid

Abstract

The application provides a method for continuously preparing narrow-distribution sub-micron spherical gold powder in a microflow, and relates to the technical field of metal powder preparation. In the preparation method, a gold precursor solution and a dispersant solution are continuously fed into a mixing module at the same flow rate for pre-mixing to generate a reaction intermediate; the generated pre-mixing solution and a reducing agent solution are continuously fed into a reaction module at the same flow rate for a reduction reaction, and the narrow-distribution sub-micron spherical gold powder is obtained after solid-liquid separation. By controlling the molar ratio of the reducing agent to the gold precursor and the concentration ratio of the dispersant solution to the gold precursor solution, the application realizes accurate regulation of the gold atom nucleation and growth process, and the prepared sub-micron spherical gold powder has a particle size accurately locked in the range of 300-800 nm, a narrow particle size distribution, a regular spherical morphology, a sphericity of >0.95, a smooth particle surface, no obvious edges and corners, and no obvious agglomeration phenomenon.

Description

Technical Field

[0001] This invention relates to the field of metal powder preparation technology, and in particular to a method for preparing narrowly distributed submicron spherical gold powder using continuous microfluidics. Background Technology

[0002] Submicron spherical gold powder is a key conductive phase material in electronic pastes (especially thick film conductor pastes and LTCC pastes). Its particle size distribution, sphericity, and purity directly affect the printing performance, sintering density, and conductivity of the paste.

[0003] Currently, the main methods for preparing submicron gold powder include polyol reduction, plasma reduction, and chemical reduction. The polyol method is simple and low-cost, but suffers from wide particle size distribution and irregular particle morphology. While the plasma method can produce spherical particles, the equipment is expensive, energy-intensive, and prone to oxidation. Traditional chemical reduction methods (using a stirred tank) suffer from uneven mixing, wide particle size distribution, and poor batch-to-batch repeatability.

[0004] In recent years, microfluidic technology has shown unique advantages in the field of nanomaterial preparation, enabling rapid and uniform mixing of reactants, precise control of reaction time and temperature, and excellent mass and heat transfer performance. However, existing microfluidic methods mainly produce gold particles at the nanoscale (<100 nm), and there is currently a lack of effective technical solutions for the continuous preparation of submicron-scale (300~800 nm) spherical gold powder.

[0005] Therefore, developing a method for continuously preparing narrowly distributed, highly spherical submicron spherical gold powder is of great significance for meeting the application requirements of high-end electronic pastes. Summary of the Invention

[0006] In view of this, the purpose of this invention is to provide a method for preparing narrow-distribution submicron spherical gold powder using continuous microfluidics. The method of this invention can prepare gold powder with a submicron scale of 300-800 nm, exhibiting a narrow particle size distribution and high sphericity.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing narrowly distributed submicron spherical gold powder using continuous microfluidics, comprising the following steps: The gold precursor solution and the dispersant solution are continuously fed into the mixing module at the same flow rate for premixing to generate a reaction intermediate; the premixed liquid and the reducing agent solution are continuously fed into the reaction module at the same flow rate for reduction reaction; the resulting reaction product is subjected to solid-liquid separation to obtain the submicron spherical gold powder with a particle size of 300~800 nm. Both the mixing module and the reaction module are microchannel reactors; The dispersant solution is a mixture of dispersant, ammonia, and water; the volume fraction of ammonia in the dispersant solution is 3-6%; the mass concentration ratio of the dispersant in the dispersant solution to that of gold in the gold precursor solution is (0.25-0.5):1; and the molar ratio of the reducing agent to that of gold in the gold precursor solution is (2.5-5):1.

[0008] Preferably, the gold precursor solution is an aqueous solution of chloroauric acid.

[0009] Preferably, the dispersant comprises one or more of polyvinylpyrrolidone, polyethylene glycol, and sodium polyacrylate.

[0010] Preferably, the reducing agent includes one or more of ascorbic acid, oxalic acid, hydroquinone, and ferrous sulfate.

[0011] Preferably, the concentration of the gold precursor solution, calculated as gold, is 25 g / L.

[0012] Preferably, the temperature of the reduction reaction is 20~80℃.

[0013] Preferably, the flow rate of the gold precursor solution and the dispersant solution is 10~40 mL / min; the flow rate of the reducing agent solution is 20~80 mL / min.

[0014] Preferably, the reduction reaction takes 8 to 34 seconds.

[0015] Preferably, the solid-liquid separation process further includes washing and drying the resulting solid.

[0016] Compared with the prior art, the present invention has the following advantages: This invention achieves precise control over the nucleation and growth process of gold atoms by controlling parameters such as the concentration of reducing agent and dispersant, the amount of ammonia added, and the flow rate.

[0017] This invention enables the continuous preparation of gold powder. The prepared submicron spherical gold powder has a particle size distribution in the range of 300~800 nm, a narrow particle size distribution, a regular spherical morphology, a sphericity >0.95, a smooth particle surface, no obvious sharp edges, and no obvious agglomeration. Attached Figure Description

[0018] Figure 1 SEM image of the gold powder prepared in Example 1; Figure 2 SEM image of the gold powder prepared in Example 2; Figure 3 SEM image of the gold powder prepared in Example 3; Figure 4 SEM image of the gold powder prepared in Comparative Example 1; Figure 5 A photograph of the supernatant in Comparative Example 1; Figure 6 SEM image of the gold powder prepared in Comparative Example 2; Figure 7 The image shows the SEM image of the gold powder prepared in Comparative Example 3. Detailed Implementation

[0019] This invention provides a method for preparing narrow-distribution submicron spherical gold powder using continuous microfluidics, comprising the following steps: continuously feeding a gold precursor solution and a dispersant solution into a mixing module at the same flow rate for premixing to generate a reaction intermediate; The premixed solution and reducing agent solution are continuously fed into the reaction module at the same flow rate to carry out the reduction reaction. The resulting reaction product is then subjected to solid-liquid separation to obtain the narrowly distributed submicron spherical gold powder.

[0020] In this invention, unless otherwise specified, all raw materials and equipment used are commercially available products well known in the art.

[0021] In this invention, a gold precursor solution and a dispersant solution are fed into a microchannel mixer at the same flow rate for premixing to generate a reaction intermediate.

[0022] In this invention, the gold precursor solution is preferably an aqueous solution of chloroauric acid; the concentration of the gold precursor solution, calculated as gold, is preferably 25 g / L.

[0023] In this invention, the dispersant solution is a mixture of dispersant, ammonia, and water; the volume fraction of ammonia in the dispersant solution is 3-6%, and in specific embodiments it can be 3%, 4%, 5%, or 6%. In this invention, the dispersant preferably includes one or more of polyvinylpyrrolidone (PVP), polyethylene glycol, and sodium polyacrylate, more preferably PVP. In this invention, the mass concentration ratio of the dispersant in the dispersant solution to the gold in the gold precursor solution is (0.25-0.5):1, and in specific embodiments it can be 0.25:1, 0.3:1, or 0.35:1. By controlling the ratio of the concentrations of the dispersant solution and the gold precursor solution, as well as the molar ratio of the reducing agent to the gold precursor, this invention can control the nucleation and growth process of gold atoms, thereby obtaining gold powder with a narrow particle size distribution and high sphericity at a target size (300-800 nm).

[0024] In this invention, the flow rates of the gold precursor solution and the dispersant solution are preferably 10-40 mL / min, and in specific embodiments, they can be 10, 15, 20, 25, 30, 35, or 40 mL / min. Preferably, the gold precursor solution and the dispersant solution are continuously delivered to the mixing module separately using independent plunger pumps. This invention first mixes the gold precursor solution and the dispersant solution, ensuring the dispersion of gold nanoparticles on one hand, and allowing the dispersant to react with the gold precursor to form a reaction intermediate (gold fulminate intermediate), which facilitates subsequent reduction.

[0025] In this invention, the mixing module is a microchannel reactor. The residence time of the gold precursor solution and the dispersant solution in the mixing module is preferably 4-17 s, and in specific embodiments, it can be 4, 6, 8, 10, 12, 15, or 17 s. In an embodiment of this invention, the mixing module is specifically a microchannel heart-shaped reactor; the microchannel heart-shaped reactor comprises three glass plates connected in series, and in this invention, the first plate is used as the mixing module, and the other two plates are used as the reaction module. In an embodiment of this invention, the inner diameter of the microchannels in the mixing module is 1.6 mm.

[0026] After premixing to form a premixed liquid, the present invention continuously delivers the premixed liquid and the reducing agent solution to the reaction module at the same flow rate for reduction reaction, and performs solid-liquid separation on the resulting reaction product to obtain the narrow-distribution submicron spherical gold powder.

[0027] In this invention, the reducing agent solution is preferably an aqueous solution of a reducing agent; the reducing agent preferably includes one or more of ascorbic acid, oxalic acid, hydroquinone, and ferrous sulfate, more preferably ascorbic acid. In this invention, the molar ratio of the reducing agent to gold entering the microchannel reactor is (2.5~5):1, and in specific embodiments it can be 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, or 5:1.

[0028] In this invention, the flow rate of the reducing agent solution is preferably 20-80 mL / min, and in specific embodiments, it can be 20, 30, 40, 50, 60, 70, or 80 mL / min. In this invention, the premixed solution and the reducing agent solution are delivered to the reaction module at the same flow rate, which is beneficial for the stable and uniform progress of the reduction reaction. Preferably, this invention uses an independently controlled plunger pump to deliver the reducing agent solution to the reaction module, which has the advantage of stable flow rate.

[0029] Before delivery, the microchannel reactor is preferably heated to the target temperature, i.e., the temperature of the reduction reaction. In this invention, the temperature of the reduction reaction is preferably 20-80°C, and in specific embodiments, it can be 20, 30, 40, 50, 60, 70, or 80°C; the time of the reduction reaction (i.e., the residence time of the raw material liquid in the reaction module) is preferably 8-34 s, and in specific embodiments, it can be 8, 10, 12, 15, 20, 25, 30, or 34 s. During the reduction reaction, the gold precursor is reduced to gold atoms by the reducing agent. Under the dispersion protection of the dispersant, the gold atoms nucleate and grow, ultimately forming spherical gold particles of 300-800 nm submicron size.

[0030] The present invention does not have any special requirements for the solid-liquid separation method; any solid-liquid separation method well known in the art is acceptable, such as centrifugation.

[0031] After solid-liquid separation, the resulting solid is preferably washed and dried to obtain the submicron spherical gold powder. In this invention, the washing method is preferably repeated washing with anhydrous ethanol and deionized water sequentially. In this invention, the drying temperature is preferably 40-60°C, and the drying time is preferably 6-12 hours.

[0032] This invention achieves precise control over the nucleation and growth process of gold atoms by controlling the molar ratio of the reducing agent to the gold precursor and the concentration ratio of the dispersant solution to the gold precursor solution, through their synergistic effect. The prepared submicron spherical gold powder has a particle size distribution in the range of 300~800 nm, with uniform particle size distribution, regular spherical morphology, smooth particle surface, no obvious sharp edges, and no obvious agglomeration.

[0033] The following detailed description of the method for preparing narrowly distributed submicron spherical gold powder using continuous microfluidics provided by the present invention, with reference to specific embodiments, should not be construed as limiting the scope of protection of the present invention.

[0034] The preparation steps of submicron spherical gold powder in the following embodiments are as follows: S1, using ultrapure water as a solvent, prepare gold precursor solution, dispersant solution and reducing agent solution respectively; S2, set the equipment temperature and start heating; S3. After the temperature reaches the expected temperature, set the flow rate and use a plunger pump to continuously deliver the gold precursor solution and dispersant solution to the mixing module (actually the first plate of the microchannel heart-shaped reactor, with an inner diameter of 1.6 mm and a liquid holding capacity of 8.2 mL) at the same flow rate for premixing to generate the reaction intermediate. S4. While the two solutions in S3 are being mixed, a plunger pump is used to continuously deliver the reducing agent solution to the reaction module (composed of a second and a third plate connected in series, with an inner diameter of 1.6 mm and a liquid holding capacity of 8.2 mL per plate) at the same flow rate as the premixed solution, and the reduction reaction is carried out in the reaction module. S5. After the reduction reaction is completed, the product flows out from the outlet and enters the collection container. The collected mixture is centrifuged and the supernatant is discarded. The obtained gold powder is washed repeatedly with anhydrous ethanol and deionized water 3 to 5 times to remove residues. The washed gold powder is dried at 50°C for 10 h to obtain submicron spherical gold powder.

[0035] Example 1 The molar ratio of gold in the aqueous solutions of ascorbic acid and chloroauric acid is 2.5:1; The mass concentration ratio of gold in the PVP aqueous solution and the chloroauric acid aqueous solution is 0.3:1; (1) Raw materials: Gold precursor solution: chloroauric acid aqueous solution, gold concentration 25 g / L; Reducing agent solution: ascorbic acid aqueous solution, concentration 28 g / L; Dispersant solution: PVP aqueous solution, concentration 7.5 g / L, ammonia water volume fraction 3%; (2) Process parameters: Gold precursor solution flow rate: 40 mL / min; Dispersant solution flow rate: 40 mL / min; Flow rate of reducing agent solution: 80 mL / min; Reduction reaction time: 8.6 s; Reaction temperature: 40℃; SEM image of the gold powder prepared in Example 1 is shown below. Figure 1 As shown. Figure 1 The obtained gold powder was spherical with no obvious agglomeration, and the average particle size was 350 nm. 10 =287 nm, D 50 =350 nm, D 90 =476 nm, with a narrow particle size distribution.

[0036] Example 2 The molar ratio of gold in the aqueous solutions of ascorbic acid and chloroauric acid is 2.5:1; The mass concentration ratio of gold in the PVP aqueous solution and the chloroauric acid aqueous solution is 0.3:1; (1) Raw materials: Gold precursor solution: chloroauric acid aqueous solution, gold concentration 25 g / L; Reducing agent solution: ascorbic acid aqueous solution, concentration 28 g / L; Dispersant solution: PVP aqueous solution, concentration 7.5 g / L, ammonia water volume fraction 3.5%; (2) Process parameters: Gold precursor solution flow rate: 20 mL / min; Dispersant solution flow rate: 20 mL / min; Flow rate of reducing agent solution: 40 mL / min; Reduction reaction time: 16.6 s; Reaction temperature: 40℃; SEM image of the gold powder prepared in Example 2 is shown below. Figure 2 As shown, the obtained gold powder is spherical with no obvious agglomeration, and the average particle size is 530 nm. 10 =443 nm, D 50 =509 nm, D 90 =582 nm, with a narrow particle size distribution.

[0037] Example 3 The molar ratio of gold in the aqueous solutions of ascorbic acid and chloroauric acid is 3:1; The mass concentration ratio of gold in the PVP aqueous solution and the chloroauric acid aqueous solution is 0.3:1; (1) Raw materials: Gold precursor solution: chloroauric acid aqueous solution, gold concentration 25 g / L; Reducing agent solution: ascorbic acid aqueous solution, concentration 33.5 g / L; Dispersant solution: PVP aqueous solution, concentration 7.5 g / L, ammonia water volume fraction 6%; (2) Process parameters: Gold precursor solution flow rate: 35 mL / min; Dispersant solution flow rate: 35 mL / min; Flow rate of reducing agent solution: 70 mL / min; Reduction reaction time: 10 s; Reaction temperature: 40℃; SEM image of the gold powder prepared in Example 3 is shown below. Figure 3 As shown. Figure 3 The obtained gold powder was spherical with no obvious agglomeration, and the average particle size was 780 nm. 10 =536 nm, D 50 =761 nm, D 90 =783 nm, with a narrow particle size distribution.

[0038] Comparative Example 1 The only difference from Example 1 is that the concentration of the ascorbic acid aqueous solution is adjusted from 28 g / L to 21 g / L, so that the molar ratio of gold in the ascorbic acid and chloroauric acid aqueous solutions is 2:1; the rest is the same as in Example 1.

[0039] SEM image of the gold powder prepared in Comparative Example 1 is shown below. Figure 4 As shown, when the reducing agent concentration is too low, the gold precursor cannot be completely reduced, the reaction is incomplete, and the supernatant is yellow (see...). Figure 5 ).

[0040] Comparative Example 2 The only difference from Example 2 is that the concentration of the PVP aqueous solution is adjusted from 7.5 g / L to 5 g / L, so that the mass concentration ratio of PVP to gold is 0.2:1. The rest is the same as Example 2.

[0041] SEM image of the gold powder prepared in Comparative Example 2 is shown below. Figure 6 As shown. Figure 6 The results showed that when the dispersant concentration was too low, the prepared gold powder exhibited obvious agglomeration, forming large, irregular aggregates.

[0042] Comparative Example 3 The only difference from Example 3 is the amount of ammonia added when preparing the dispersant solution, so that the volume fraction of ammonia is 2.85%. The rest is the same as Example 3.

[0043] SEM image of the gold powder prepared in Comparative Example 3 is shown below. Figure 7 As shown, when the amount of ammonia is not appropriate, the prepared gold powder particles stick together and have poor sphericity.

[0044] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing narrowly distributed submicron spherical gold powder using continuous microfluidics, characterized in that, Includes the following steps: The gold precursor solution and dispersant solution are continuously pumped into the mixing module at the same flow rate by independent pumps for premixing to generate a reaction intermediate. The premixed solution and the reducing agent solution are continuously pumped into the reaction module at the same flow rate for reduction reaction. The resulting reaction product is subjected to solid-liquid separation to obtain the submicron spherical gold powder with a particle size of 300~800 nm. Both the mixing module and the reaction module are microchannel reactors; The dispersant solution is a mixture of dispersant, ammonia, and water; the volume fraction of ammonia in the dispersant solution is 3-6%; the mass concentration ratio of the dispersant in the dispersant solution to that of gold in the gold precursor solution is (0.25-0.5):1; and the molar ratio of the reducing agent to that of gold in the gold precursor solution is (2.5-5):

1.

2. The method according to claim 1, characterized in that, The gold precursor solution is an aqueous solution of chloroauric acid.

3. The method according to claim 1, characterized in that, The dispersant includes one or more of polyvinylpyrrolidone, polyethylene glycol, and sodium polyacrylate.

4. The method according to claim 1, characterized in that, The reducing agent includes one or more of ascorbic acid, oxalic acid, hydroquinone, and ferrous sulfate.

5. The method according to claim 1 or 2, characterized in that, The concentration of the gold precursor solution, calculated as gold, is 25 g / L.

6. The method according to claim 1, characterized in that, The reduction reaction is carried out at a temperature of 20~80℃.

7. The method according to claim 1, characterized in that, The flow rate of the gold precursor solution and the dispersant solution is 10-40 mL / min; the flow rate of the reducing agent solution is 20-80 mL / min.

8. The method according to claim 1, characterized in that, The reduction reaction takes 8 to 34 seconds.

9. The method according to claim 1, characterized in that, The solid-liquid separation process also includes washing and drying the resulting solid.

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