A method for continuously preparing low-residual spherical gold powder on a large scale

Abstract

The present application relates to precious metal powder preparation technical field, especially to a kind of method for large-scale continuous preparation of low residual spherical gold powder.The present application adopts two-stage microflow continuous reaction to combine coil dynamic ripening process, constructs full-closed dynamic continuous preparation system, generates gold fulminate intermediate by microflow mixing unit online complexation, continuously reduces and prepares gold powder suspension by microflow reaction unit, is prepared finished product after coil ripening, dynamic collection and post-processing.The present application breaks through the technical defects of intermittent kettle process material static stockpiling, cannot continuously mass-produce, batch fluctuation is big, poor safety, need high additive addition.Process can be stably enlarged to 8L scale production, and uninterrupted steady-state production can be realized by continuous feeding.Meanwhile, relying on continuous fluid dynamic shearing and interface scouring effect, particle agglomeration can be effectively inhibited under low dispersant condition, and the obtained gold powder is spherical and complete, and the particle size is uniform, suitable for high-end electronic components field with strict requirements on precision and reliability.

Description

Technical Field

[0001] This invention relates to the field of precious metal powder preparation technology, and in particular to a method for large-scale continuous preparation of low-residue spherical gold powder. Background Technology

[0002] Currently, the microelectronics industry is continuously expanding its production capacity in thick-film conductive pastes, LTCC ceramic electrodes, and semiconductor precision packaging, leading to a sustained increase in market demand for spherical gold powder. Downstream manufacturers prioritize the continuity of material supply, as the ability to achieve uninterrupted large-scale production directly impacts supply assurance capabilities. Furthermore, they have stringent standards for the cleanliness of the gold powder surface, as the level of organic residue in the powder significantly affects the sintering effect and conductivity of components, ultimately determining the yield of end products.

[0003] Currently, the mainstream industrial production of spherical gold powder mostly adopts a batch reactor process. Due to equipment structure limitations, it is difficult to support long-term uninterrupted output, which severely restricts the release of large-scale production capacity. The batch process requires batch feeding, settling and maturation, opening the lid for discharge and reactor cleaning. There are obvious downtime gaps between batches, making it impossible to achieve 24-hour continuous stable production. The equipment utilization rate is low, making it difficult to meet the demand for large-volume supply. At the same time, this process has several drawbacks: First, the gold fulminate precursor generated in the reactor needs a settling time to fully react, but the intermediate is subject to decomposition and explosion risks due to temperature and vibration. Stringent safety control requirements further limit the long-term uninterrupted operation of the equipment. Second, in order to inhibit particle agglomeration, the batch reactor system can only increase the amount of organic dispersant added. A large amount of organic matter is adsorbed on the surface of the gold powder. The cleaning process is cumbersome and time-consuming. In fact, the cleaning agent used may corrode the surface of the gold powder sphericals and introduce by-product impurities, making it difficult to guarantee the cleanliness of the powder. Third, material concentration stratification is prone to occur in the reactor, and high-density gold particles are very easy to settle and clump, resulting in poor uniformity of powder in the same batch; each batch requires manual adjustment of reaction parameters, the process repeatability is poor, and the produced powder needs to be crushed, sieved and shaped, the process is complicated, and the yield of precious metal products, loss and waste liquid treatment costs increase simultaneously.

[0004] In summary, the current mainstream preparation process for spherical gold powder has drawbacks such as inability to achieve long-term continuous mass production, high safety risks of intermediates, high organic residues in the powder, poor batch consistency, and high overall mass production costs. There is an urgent need to provide a new continuous flow preparation process to solve the above-mentioned industrialization pain points and meet the application requirements of large-scale and stable supply of high-end microelectronic conductive powders. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a method for the large-scale continuous preparation of low-residue spherical gold powder. This invention achieves long-term continuous mass production of spherical gold powder with low organic residue, eliminates the need for precise manual control of grain size, produces powder with intact spherical shape and minimal batch-to-batch variation, significantly improves production efficiency, and eliminates production safety issues caused by the accumulation of explosive intermediates at the source.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for scalable and continuous preparation of low-residue spherical gold powder, comprising the following steps: continuously and synchronously mixing an aqueous solution of chloroauric acid and a composite dispersion through a microfluidic mixing unit to complete the complexation reaction online and generate a gold fulminate intermediate mixture; The gold fulminate intermediate mixture from the microfluidic mixing unit directly enters the microfluidic reaction unit, and a reducing solution is simultaneously introduced into the microfluidic reaction unit to carry out a continuous reduction reaction, thereby generating a spherical gold powder suspension online. The spherical gold powder suspension from the microfluidic reaction unit directly enters the closed delay coil for continuous flow maturation. The matured suspension is dynamically collected in a stirring system, and after solid-liquid separation, water washing, alcohol washing and drying, low-residue spherical gold powder is obtained; The composite dispersion is composed of a dispersant, ammonia, and water; the dispersant is gelatin and gum arabic; the mass ratio of gum arabic to gelatin is 1:(0.5~1.5); the mass ratio of the dispersant to gold ions introduced into the microfluidic mixing unit is (0.02~0.15):1; The volumetric flow rate ratio of the chloroauric acid aqueous solution, the composite dispersion, and the reducing solution is 1:1:2.

[0007] Preferably, the concentration of gold ions in the chloroauric acid aqueous solution is 20~60 g / L.

[0008] Preferably, the flow rate of the chloroauric acid aqueous solution is 20~60 mL / min.

[0009] Preferably, the mass fraction of the ammonia water is 25-28%, and the mass ratio of ammonia water to gold ions introduced into the microfluidic mixing unit is 1.1:1.

[0010] Preferably, the reducing solution is an aqueous solution of ascorbic acid; the molar ratio of gold ions in the aqueous solution of ascorbic acid and chloroauric acid is (1.5~5):1.

[0011] Preferably, the flow maturation time of the spherical gold powder suspension in the delay coil is 0.5~5 min.

[0012] Preferably, the stirring speed of the stirring system is 200~700 r / min.

[0013] Preferably, the reaction temperatures in the microfluidic mixing unit, the microfluidic reaction unit, and the sealed coil are independently 20~60℃.

[0014] Preferably, the microchannel length of the microfluidic mixing unit and the microfluidic reaction unit is 8~18m, and the inner diameter of the microchannel is 1.6mm.

[0015] Preferably, the length of the delay coil is 10~200m and the inner diameter is 1.6mm or 3.2mm.

[0016] This invention abandons the traditional static batch preparation mode in batch reactors and adopts a fully enclosed pipeline continuous flow reaction architecture. It completes the complexation and reduction sequential reactions stepwise through two independent microfluidic units, coupled with a post-delayed coil for dynamic ripening and a dynamic continuous collection method at the end. This ensures the immediate reaction of gold fulminate intermediates throughout the process, eliminating the risk of explosive intermediate accumulation from the source. The continuous fluid system can form a dynamically updated solid-liquid interface. Combined with the low-addition dispersion system of gelatin and gum arabic and the self-cleaning properties of the fluid dynamic flushing, it effectively inhibits particle agglomeration while significantly reducing powder content. The adsorption of organic additives on the surface of the powder allows for powder purification through water washing and alcohol washing alone, simplifying post-processing steps. This invention incorporates a dynamic stirring mechanism at the pipeline outlet, which, in conjunction with a microfluidic pipeline dynamic maturation process, replaces the static maturation process of a kettle. This continuously agitates the fluid state of the system, avoiding the defects of material stratification and particle sedimentation and agglomeration. The resulting powder has a narrow original particle size distribution, complete sphericity, and small batch-to-batch variation, eliminating the need for manual batch-by-batch parameter adjustment and subsequent crushing and screening processes. The entire system constructs a constant ratio and constant flow fully automatic three-way material conveying system, eliminating the discrete manual intervention required for intermittent processes. It can achieve 24-hour uninterrupted steady-state discharge and long-cycle closed-loop continuous operation, significantly improving process stability and meeting the needs of industrial-scale continuous mass production of spherical gold powder.

[0017] Compared with the prior art, the present invention has the following beneficial effects: (1) The process is continuous and stable, and the consistency of powder batches is excellent: The present invention adopts a fully enclosed continuous closed-loop process to avoid process deviations caused by intermittent production batch start-up and shutdown and manual operation. It can achieve continuous preparation for a long time without interruption. The performance indicators of gold powder fluctuate little, which can meet the requirements of large-scale stable supply of high-end microelectronic components.

[0018] (2) Low organic residue in powder and simplified and efficient purification process: Relying on the self-cleaning effect of compound dispersion system and fluid dynamic interface, the amount of organic matter adsorbed on the powder surface is effectively reduced; the powder can be purified by water washing and alcohol washing, without the need for additional cleaning agent soaking to remove impurities, shortening the powder post-processing cycle, and the obtained spherical gold powder has excellent sphericity, sintering consistency and good conductivity.

[0019] (3) Significantly improved inherent safety in production: The entire process operates in a closed, continuous, and dynamic manner. After the gold fulminate intermediate is generated, it quickly participates in the reaction. There is no static accumulation or open storage conditions, which eliminates the risk of intermediate decomposition and explosion from the source and makes it easier to meet the safety control requirements of continuous industrial production.

[0020] (4) Lower industrial production cost and less precious metal loss: The resulting powder has a narrow particle size distribution, eliminating the need for crushing, sieving and shaping, thus reducing precious metal powder processing loss; the process system does not require additional cleaning agents, reducing waste liquid generation and post-treatment costs, and has good prospects for industrial application. Attached Figure Description

[0021] Figure 1 SEM image of the gold powder prepared in Example 1; Figure 2 The particle size distribution diagram is shown for the gold powder prepared in Example 1. Figure 3 SEM image of the gold powder prepared in Example 2; Figure 4 This is a particle size distribution diagram of the gold powder prepared in Example 2; Figure 5 A comparison diagram of the D10, D50, and D90 particle size changes of gold powder prepared in Example 1 and Example 3; Figure 6 SEM morphology of gold powder prepared by batch reactor process in Comparative Example 1; Figure 7 SEM image of the gold powder prepared in Comparative Example 2; Figure 8 This is a comparison chart of the thermogravimetric curves of gold powder obtained in Examples 1-3 and Comparative Examples 1-2; Figure 9 The image shows the SEM morphology of the gold powder prepared in Comparative Example 3. Detailed Implementation

[0022] This invention provides a method for scalable and continuous preparation of low-residue spherical gold powder, comprising the following steps: continuously and synchronously mixing an aqueous solution of chloroauric acid and a composite dispersion through a microfluidic mixing unit to complete the complexation reaction online and generate a gold fulminate intermediate mixture; The gold fulminate intermediate mixture from the microfluidic mixing unit directly enters the microfluidic reaction unit, and a reducing solution is simultaneously introduced into the microfluidic reaction unit to carry out a continuous reduction reaction, thereby generating a spherical gold powder suspension online. The spherical gold powder suspension from the microfluidic reaction unit directly enters the closed delay coil for continuous flow maturation. The matured suspension is dynamically collected in a stirring system, and after solid-liquid separation, water washing, alcohol washing and drying, low-residue spherical gold powder is obtained.

[0023] In this invention, unless otherwise specified, all raw materials and equipment used are commercially available products well known in the art.

[0024] This invention involves continuously and synchronously mixing an aqueous solution of chloroauric acid and a composite dispersion through a microfluidic mixing unit to complete the complexation reaction online, thereby generating a fulminate intermediate mixture.

[0025] In this invention, the concentration of gold ions in the chloroauric acid aqueous solution is preferably 20~60 g / L, and in specific embodiments it can be 20, 30, 40, 50 or 60 g / L, with the most preferred concentration being 40 g / L.

[0026] In this invention, the composite dispersion is composed of a dispersant, ammonia, and water; the dispersant is gelatin and gum arabic; the mass ratio of gum arabic to gelatin is 1:(0.5~1.5), and in specific embodiments it can be 1:0.5, 1:0.8, 1:1, 1:1.2, or 1:1.5; the mass ratio of dispersant to gold ions introduced into the microfluidic mixing unit is (0.02~0.15):1, and in specific embodiments it can be 0.05:1, 0.08:1, 0.1:1, 0.13:1, or 0.15:1. This invention uses a blend of gum arabic and gelatin as a dispersant, which has a good dispersing effect. Combining the good dispersibility of gelatin and the relatively easy cleaning of gum arabic, the amount of dispersant used can be significantly reduced. Combined with the self-cleaning characteristics of continuous fluid dynamic scouring, the dispersant load is greatly reduced while ensuring that the powder does not agglomerate, thus simplifying the powder post-processing process. Most organic impurities on the powder surface can be removed by water washing and alcohol washing alone. In the traditional batch reaction mode of intermittent reactor, a large amount of organic dispersant needs to be added to suppress particle agglomeration, resulting in high organic residue and cumbersome cleaning process.

[0027] In this invention, the mass fraction of the ammonia water is 25-28%, and the mass ratio of the ammonia water to gold ions introduced into the microfluidic mixing unit is preferably 1.1:1.

[0028] In this invention, the volumetric flow rate ratio of the chloroauric acid aqueous solution and the composite dispersion is 1:1; the flow rate of the chloroauric acid aqueous solution is preferably 20~60 mL / min, and in specific embodiments it can be 20, 30, 40, 50 or 60 mL / min, with the most preferred being 30 mL / min.

[0029] In this invention, the length of the microchannel of the microfluidic mixing unit is preferably 8 to 18 m, and in specific embodiments it can be 9, 10, 11, 13, 15, 16, 17 or 18 m, and the inner diameter is preferably 1.6 mm.

[0030] In this invention, the reaction temperature within the microfluidic mixing unit is preferably 20~60℃, and in specific embodiments, it can be 20, 25, 30, 35, 40, 45, 50, 55, or 60℃. In this invention, the complexation reaction is completed online in the microfluidic mixing unit to generate a gold fulminate intermediate mixture.

[0031] In this invention, the gold fulminate intermediate mixture from the microfluidic mixing unit directly enters the microfluidic reaction unit, and a reducing solution is simultaneously introduced into the microfluidic reaction unit to carry out a continuous reduction reaction.

[0032] In this invention, the reducing solution is preferably an aqueous solution of ascorbic acid; the molar ratio of gold ions in the aqueous solution of ascorbic acid and chloroauric acid is preferably (1.5~5):1, and in specific embodiments it can be 2:1, 2.5:1, 3:1, 4:1 or 5:1.

[0033] In this invention, the volumetric flow rate ratio of the gold fulminate intermediate mixture from the microfluidic mixing unit to the reducing liquid is 1:1, that is, the volumetric flow rate ratio of the chloroauric acid aqueous solution, the composite dispersion, and the reducing liquid is 1:1:2.

[0034] In this invention, the specifications of the microfluidic reaction unit are the same as those of the microfluidic mixing unit, and the reaction temperature in the microfluidic reaction unit is consistent with the reaction temperature in the microfluidic mixing unit, which will not be elaborated here.

[0035] This invention generates spherical gold powder suspensions online within a microfluidic reaction unit.

[0036] In this invention, the spherical gold powder suspension from the microfluidic reaction unit directly enters a sealed delay coil for continuous flow curing.

[0037] In this invention, the flow curing time of the spherical gold powder suspension in the delay coil is preferably 0.5~5 min, and in specific embodiments it can be 1, 2, 3, 4 or 5 min, with 4 min being the most preferred. The length of the delay coil is preferably 10~200 m, and in specific embodiments it can be 20, 60, 80, 100, 120, 150, 170 or 200 m; the inner diameter is preferably 1.6 mm or 3.2 mm.

[0038] In this invention, the reaction temperature inside the delay coil is consistent with the reaction temperature inside the microfluidic mixing unit, which will not be elaborated here.

[0039] The present invention allows the spherical gold powder suspension to undergo continuous dynamic maturation after being fed into the delay coil. It relies on the dynamic shearing action of continuous fluid to inhibit particle agglomeration and improve the residual reduction reaction, with no static accumulation of materials throughout the process.

[0040] In this invention, the matured suspension is dynamically collected in a stirring system, and after solid-liquid separation, water washing, alcohol washing and drying, low-residue spherical gold powder is obtained.

[0041] In this invention, the stirring system can be a conventional stirring system capable of stirring materials; the stirring speed is preferably 200~700 r / min, and in specific embodiments it can be 200, 300, 400, 500, 550, 600, 650 or 700 r / min. This invention prevents gold powder particles from settling and accumulating at the bottom, thus avoiding clumping, through the stirring system. In this invention, the stirring system is pre-filled with water, ethanol or a water-ethanol mixture. This invention does not specifically limit the solid-liquid separation method; any solid-liquid separation method well-known in the art can be used, such as vacuum filtration. In this invention, the number of water washing and alcohol washing cycles is preferably 2~4 times independently. In this invention, the drying temperature is preferably 60℃.

[0042] This invention utilizes microfluidic pipelines and delayed coils for dynamic curing to replace static curing in a batch. Combined with end-of-pipe dynamic collection, it can eliminate material stratification, sedimentation, and agglomeration problems, eliminate the need for manual batch-by-batch parameter adjustment, significantly improve process stability, and eliminate the need for subsequent crushing and screening, thereby increasing production efficiency.

[0043] In this invention, the organic residue rate of the low-residue spherical gold powder is less than 0.6%; the low-residue spherical gold powder is intact in shape.

[0044] The following detailed description of the method for scalable and continuous preparation of low-residue spherical gold powder provided by the present invention, with reference to the embodiments, should not be construed as limiting the scope of protection of the present invention.

[0045] In the following examples and comparative examples, the microfluidic mixing unit used for primary microfluidic complexation and the microfluidic reaction unit used for secondary microfluidic reduction both have a channel length of 11m and a microchannel inner diameter of 1.6mm; the delay coil used for coil dynamic curing has a length of 60m and an inner diameter of 1.6mm.

[0046] Example 1 (Continuous Flow Steady-State Pilot-Scale Process) S1. Preparation of gold source solution: Weigh chloroauric acid with a gold content of 47.8% and dissolve it in 100mL of deionized water to prepare an aqueous solution of chloroauric acid with a gold ion concentration of 40 g / L. S2. Preparation of composite dispersion: Weigh 0.2g of gum arabic and 0.2g of gelatin and dissolve them in 100mL of deionized water, then add 4.4g of ammonia water with a mass fraction of 25~28% to obtain composite dispersion; S3. Preparation of reducing solution: Dissolve 10g of ascorbic acid in 200mL of deionized water and stir until completely dissolved to obtain a homogeneous reducing solution; S4. First-stage microfluidic complexation: The gold source solution and the composite dispersion are continuously and synchronously mixed in the microfluidic unit at a flow rate of 30 mL / min to complete the complexation reaction online. The complexation temperature is 40℃ to generate a uniform gold fulminate intermediate mixture. S5. Secondary microfluidic reduction: The gold fulminate intermediate mixture and the reducing solution at a flow rate of 60 mL / min are continuously fed into the microfluidic reaction unit for continuous reduction reaction at a reaction temperature of 40℃, generating a spherical gold powder suspension online; S6. Dynamic curing of the coil: The reduced gold powder suspension is continuously flowed and cured in a closed delay coil for 4 minutes at a curing temperature of 40℃. S7. Dynamic collection and post-processing: The matured suspension is collected in a water-ethanol system stirred at 500 r / min, filtered, washed twice with water, washed twice with alcohol, and dried at 60℃ to obtain spherical gold powder.

[0047] Test results: The process in this embodiment is stable. Under low dispersant addition conditions, the obtained gold powder spherical shape is intact and the dispersion is uniform (e.g., Figure 1 (As shown in the SEM image), narrow particle size distribution (see...) Figure 2 The particle size distribution diagram shows that the organic residue on the powder surface is low (residual rate is 0.59%), with no agglomeration or sedimentation, and the batch quality consistency is excellent.

[0048] Example 2 (Process with changed dispersant ratio) Completely consistent with Example 1, except that the compound dispersant ratio was adjusted, and the mass ratio of gelatin to gum arabic was adjusted to 1:1.5, that is, 0.16g and 0.24g respectively.

[0049] Test results show that after adjusting the dispersant compound ratio, the process can still operate stably and continuously, and the obtained gold powder still maintains a regular spherical morphology and good dispersibility, with no significant deviation in particle size (see...). Figure 3 and Figure 4 This demonstrates that the dispersion system of the present invention has a wide process window, strong parameter tolerance, and a wide range of adaptability. In this embodiment, the organic residue rate on the powder surface is 0.56%.

[0050] Example 3 (Scal-up Steady-State Verification of 8L System) The process parameters, proportions, and operations are the same as in Example 1, except that the material in S1 is increased to 2L, the material in S2 is increased to 2L, and the material in S3 is increased to 4L.

[0051] The results of the large-scale production show that the process is smooth and stable, without problems such as pipeline blockage, material accumulation, or process fluctuation. The morphology, particle size, and organic residue of the gold powder obtained from the mass production are very similar to those of the 400mL small-scale sample (the residue rate is 0.61%). The batch performance fluctuation is small, which proves that the process of this invention can be stably scaled up across scales. Moreover, the continuous flow system has no fixed batch volume limit, and long-term uninterrupted mass production can be achieved by continuous feeding. Figure 5 Table 1 shows a comparison of the D10, D50, and D90 particle size changes of gold powder prepared in Example 1 (small-scale process) and Example 3 (8L large-scale production process).

[0052] Table 1. D10, D50, and D90 particle sizes of gold powders prepared in Examples 1 and 3

[0053] Comparative Example 1 (Traditional batch reactor process) S1. Weigh 41.67g of chloroauric acid (concentration of 48wt% based on gold) into a beaker, dissolve it in 900mL of deionized water, place it in a 40℃ constant temperature water bath and stir at a stirring speed of 250rpm until homogeneous. Then adjust the pH of the solution to 4.0 by adding concentrated ammonia dropwise to obtain the gold source solution. S2. Weigh 2.5g of gum arabic and 2.5g of gelatin and dissolve them in 50mL of deionized water, then add them to the reaction gold source solution obtained in step S1 to obtain a pre-reaction solution; S3. Weigh 50g of reducing agent ascorbic acid and dissolve it in 50mL of deionized water to obtain a reducing agent solution. Then add it to the pre-reaction solution at a dropping rate of 1.6mL / s and react for 1h. After the reaction is completed, age the resulting golden yellow turbid liquid for 1h, then filter it, wash it twice with deionized water and ethanol, and then dry it in an oven at 60℃ to obtain the desired gold powder.

[0054] Figure 6 SEM images of gold powder prepared by batch reactor process are shown. The results show that the mass ratio of dispersant to gold in the batch reactor static system must be increased to 0.25:1 to obtain spherical gold powder with relatively uniform particle size. Under low addition conditions, problems such as agglomeration and large particle size will occur. Even with a high dispersant addition, there are still problems of material stratification and particle sedimentation, poor powder uniformity, high organic residue (residue rate of 1.05%), and long-term static accumulation of gold fulminate intermediate poses significant safety hazards. The process cannot be continuously produced and has large batch fluctuations.

[0055] Comparative Example 2 (High Addition Dispersant System) Similar to Example 1, the mass ratio of dispersant to gold was increased to 0.25:1, i.e., 0.5g gum arabic and 0.5g gelatin.

[0056] The results show that in continuous flow systems, excessive addition of dispersant does not improve sphericity and reduces powder particle size (see...). Figure 7 The amount of organic adsorption on the powder surface increased significantly, and the organic residue increased significantly (the residue rate was 0.84%), which increased the cleaning burden. This proves that the low addition amount formulation of the present invention with a ratio of 0.1:1 combined with the dynamic fluid mechanism is the preferred solution that takes into account both high sphericity and low residue.

[0057] Figure 8 This is a comparison of the thermogravimetric curves of the gold powder obtained in Examples 1-3 and Comparative Examples 1-2. Figure 8 It can be seen that the organic residue rate of the gold powder obtained in Example 1 was 0.59%, the organic residue rate of the gold powder in Example 2 was 0.56%, the organic residue rate of the gold powder in Example 3 was 0.61%, the organic residue rate of the gold powder obtained in Comparative Example 1 was 1.05%, and the organic residue rate of the gold powder obtained in Comparative Example 2 was 0.84%. Under the same dispersant dosage, the organic residue of the gold powder obtained by the continuous flow technology was lower than that of the gold powder obtained by the batch process. This proves that the scouring effect and shearing action of the continuous fluid flow can reduce the amount of organic adsorption on the gold powder surface. At the same time, compared with the batch process, the amount of dispersant used can be greatly reduced to obtain powder of the corresponding particle size, thereby significantly reducing the organic residue on the gold powder surface.

[0058] Comparative Example 3 (No Delay Coil) Same as in Example 1, but with the subsequent delay coil removed.

[0059] Test results show that after canceling the delayed coil dynamic curing, the residual reduction reaction in the system cannot be fully completed, resulting in uneven powder formation, an increase in fine powder and trace agglomerates, a wider particle size distribution, and a significant decrease in sphericity (see...). Figure 9 This demonstrates that the post-delay coil dynamic curing structure of the present invention is a core and essential structure for ensuring high uniformity and high sphericity of gold powder.

[0060] 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 scalable and continuous preparation of low-residue spherical gold powder, characterized in that, The process includes the following steps: continuously and synchronously mixing an aqueous solution of chloroauric acid and a composite dispersion through a microfluidic mixing unit to complete the complexation reaction online, thereby generating a mixture of gold fulminate intermediates; The gold fulminate intermediate mixture from the microfluidic mixing unit directly enters the microfluidic reaction unit, and a reducing solution is simultaneously introduced into the microfluidic reaction unit to carry out a continuous reduction reaction, thereby generating a spherical gold powder suspension online. The spherical gold powder suspension from the microfluidic reaction unit directly enters the closed delay coil for continuous flow maturation. The matured suspension is dynamically collected in a stirring system, and after solid-liquid separation, water washing, alcohol washing and drying, low-residue spherical gold powder is obtained; The composite dispersion is composed of a dispersant, ammonia, and water; the dispersant is gelatin and gum arabic; the mass ratio of gum arabic to gelatin is 1:(0.5~1.5); the mass ratio of the dispersant to gold ions introduced into the microfluidic mixing unit is (0.02~0.15):1; The volumetric flow rate ratio of the chloroauric acid aqueous solution, the composite dispersion, and the reducing solution is 1:1:

2.

2. The method according to claim 1, characterized in that, The concentration of gold ions in the chloroauric acid aqueous solution is 20~60 g / L.

3. The method according to claim 1 or 2, characterized in that, The flow rate of the chloroauric acid aqueous solution is 20~60 mL / min.

4. The method according to claim 1, characterized in that, The ammonia water has a mass fraction of 25-28%, and the mass ratio of ammonia water to gold ions introduced into the microfluidic mixing unit is 1.1:

1.

5. The method according to claim 1, characterized in that, The reducing solution is an aqueous solution of ascorbic acid; the molar ratio of gold ions in the aqueous solution of ascorbic acid and chloroauric acid is (1.5~5):

1.

6. The method according to claim 1, characterized in that, The flow maturation time of the spherical gold powder suspension in the delay coil is 0.5~5 minutes.

7. The method according to claim 1, characterized in that, The stirring system operates at a speed of 200~700 r / min.

8. The method according to claim 1, characterized in that, The reaction temperatures in the microfluidic mixing unit, the microfluidic reaction unit, and the sealed coil are independently 20~60℃.

9. The method according to claim 1, characterized in that, The microchannels of the microfluidic mixing unit and the microfluidic reaction unit have a length of 8-18 m and an inner diameter of 1.6 mm.

10. The method according to claim 1 or 2, characterized in that, The delay coil has a length of 10~200m and an inner diameter of 1.6mm or 3.2mm.

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