High-tap-density and high-crystallinity gold powder and preparation method thereof

Abstract

The invention relates to the technical field of metal powder preparation, in particular to high-tap-density and high-crystallinity gold powder and a preparation method thereof. The preparation method comprises the following steps: preparing a seed crystal solution, preparing a gold salt solution from chloroauric acid and a complexing agent, preparing a mixed solution of a reducing agent and a dispersing agent, and dropwise adding the gold salt solution and the reducing agent solution into the seed crystal solution at a certain rate, so that the seed crystal gradually grows into micron-sized particles. According to the method, small-size gold particles serve as seed crystals, the nucleation process and the growth process in a liquid phase method can be separated, and the prepared gold particles are uniform in particle size; meanwhile, the complexing agent and the dispersing agent are added, the reaction rate in the growth process can be reduced, and the crystallinity of the gold particles is improved. The preparation method is simple and convenient, the grain size of the gold powder is controllable, the tap density of the prepared gold powder is larger than or equal to 9.0 g / cm < 3 >, the crystallinity is high, the grain size distribution is narrow, the dispersity is good, and the requirement of the gold powder for high-performance electronic paste can be met.

Description

Technical Field

[0001] The invention relates to the technical field of metal powder preparation, and in particular to a gold powder with high tap density and high crystallinity and a preparation method thereof. Background Art

[0002] With the rapid development of advanced manufacturing industries such as 5G communications, radar electronics, and smart cars in the electronic information industry, the market demand for electronic components such as hybrid multi-chip modules (MCM-C / D), microwave hybrid integrated circuits, and high-power micro-assembly chips has also exploded. Since gold has electrical conductivity second only to silver and copper, excellent corrosion resistance and oxidation resistance, and gold usually has no electromigration, these points together determine the inherent advantages of gold as a functional phase of electronic paste conductors for the preparation of high-frequency, low-loss, and long-life electronic components. Therefore, gold conductor paste has become an important basic material that is indispensable for the development direction of "miniaturization, integration, and high frequency" in the electronic information industry.

[0003] Gold powder is the functional phase of gold conductor slurry, and its tap density has an important influence on the conductivity, welding performance and co-firing matching of gold conductor slurry. The crystallinity, particle size distribution and dispersibility of gold powder particles will have a great influence on the tap density of powder.

[0004] In the prior art, Chinese patent CN106112005A discloses a method for preparing monodisperse flaky gold powder, using ascorbic acid as a reducing agent and linear polyethyleneimine as an auxiliary agent to prepare flaky gold powder. This preparation method can obtain highly crystalline submicron-grade 500-800nm ​​irregular polygonal granular gold powder, but the main product is 4-6μm flaky gold powder; Chinese patent CN117123791A discloses a gold powder for matching low-temperature co-fired ceramics, using amino acids as gold ion complexing agents, using small molecule organic matter containing imidazole functional groups as reducing agents, and preparing submicron gold powder with irregular morphology and size of 200-900nm; CN109622985A discloses a method for preparing highly dispersed gold powder, the gold powder particle size distribution is 0.3-1.2μm, but the tap density is relatively low at 3.5-6.0g / cm 3 .

[0005] The tap density of gold powder in existing patents cannot meet the needs of high-performance electronic pastes. Therefore, the preparation of high tap density and high crystallinity gold powder is a key technology that urgently needs to be broken through. Summary of the invention

[0006] In order to solve the problems in the prior art, the present invention provides a method for preparing gold powder with high tap density and high crystallinity, comprising the following steps: S1. preparing a seed solution: quickly adding a reducing agent solution to a chloroauric acid solution to generate nano seed crystals, then adding polyvinyl pyrrolidone to protect the seed crystals, and adding deionized water to obtain a seed solution, wherein the concentration of gold in the seed solution is 0.04-0.42 mM, and the concentration of polyvinyl pyrrolidone is 3-20 g / L; the absorption characteristic peak of the ultraviolet visible spectrum of the obtained gold seed solution is between 520-650 nm; S2. preparing a gold salt solution: preparing a 5-100 mM chloroauric acid solution, then slowly adding a complexing agent into the chloroauric acid solution, stirring evenly to form a uniform solution, and standing for not less than 24 hours to obtain a gold salt solution, wherein the solubility of the complexing agent in the gold salt solution is 5-150 g / L; S3, preparing a reducing agent solution: fully dissolving a reducing agent and a dispersant in deionized water to prepare a 10-250 mM reducing agent solution, wherein the concentration of the dispersant in the reducing agent solution is 10-100 g / L; S4, preparing gold powder: under stirring, dripping the gold salt solution and the reducing agent solution into the seed crystal solution simultaneously by a peristaltic pump to form a reaction solution, the addition rate of the peristaltic pump is 1-50mL / min, and the amount ratio of the gold salt to the reducing agent dripped into the reaction solution is 1:(1-5), so that the seed crystal gradually grows to D50≥0.5μm; S5, post-processing: after the reaction in S4 is completed, solid-liquid separation is performed, the solid gold powder is washed until the conductivity of the washing liquid is ≤20us / cm, and vacuum dried to obtain a gold powder product.

[0007] Furthermore, the ratio of the amount of the reducing agent added in step S1 to the amount of chloroauric acid is 1:(0.5-5), and the temperature is maintained at 20-150° C. during the reaction.

[0008] Furthermore, the concentration of the chloroauric acid solution in step S1 is 2.5 mM.

[0009] Furthermore, the reducing agent in step S1 and / or step S3 is one or more of sodium borohydride, ascorbic acid, formic acid, oxalic acid, hydrazine hydrate, and ethylene glycol.

[0010] Furthermore, in step S2, the complexing agent is one or more of 1-methylhydantoin, 5,5-dimethylhydantoin, 1,5,5-trimethylhydantoin, citric acid or potassium citrate.

[0011] Furthermore, in step S3, the dispersant is one or more of polyvinyl pyrrolidone, polyvinyl alcohol, gum arabic or polyethylene glycol.

[0012] Furthermore, in step S4, the temperature is maintained at 20-150° C. during the reaction.

[0013] The high tap density and high crystallinity gold powder prepared by the above method has a tap density of ≥9.0g / cm 3 , particle size D50 is 0.5-3.5μm.

[0014] The beneficial effects of the present invention are: (1) The gold powder preparation method of the present invention uses small-sized gold particles as seeds, which can separate the nucleation and growth processes in the liquid phase method, prepare gold particles with more uniform particle sizes, and can prepare gold particles of different particle sizes by simply adjusting the number of seeds and the gold salt used for regrowth; (2) Adding a complexing agent to the chloroauric acid solution can significantly reduce the reaction rate during the growth process, improve the crystallinity of the gold particles, and prepare gold powder with high tap density and high crystallinity. The tap density of the prepared gold powder is ≥9.0g / cm 3 . BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The embodiments of the present invention are further described below with reference to the accompanying drawings, in which: Figure 1 The preparation method flow chart of the present invention is shown; Figure 2 The SEM image of the micron gold powder prepared in Example 1 of the present invention is shown; Figure 3 The XRD spectrum of the micron gold powder prepared in Example 1 of the present invention is shown. DETAILED DESCRIPTION

[0016] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below through specific embodiments in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0017] A method for preparing gold powder with high tap density and high crystallinity comprises the following steps: S1. Prepare a seed solution: quickly add a reducing agent solution to a chloroauric acid solution, wherein the molar ratio of the added reducing agent to the chloroauric acid is 1:(0.5-5), and the concentration of the chloroauric acid solution is preferably 2.5 mM. The temperature is maintained at 20-150°C during the reaction to generate nano seed crystals, and then polyvinyl pyrrolidone is added to protect the seed crystals. Deionized water is added to obtain a seed solution, wherein the concentration of gold (including the generated nano gold seed crystals and the unreacted chloroauric acid) in the seed solution is 0.04-0.42 mM, where mM is the concentration unit, i.e., mmol / L, and the concentration of polyvinyl pyrrolidone is 3-20 g / L. The absorption characteristic peak of the ultraviolet-visible spectrum of the obtained gold seed solution is between 520-650 nm.

[0018] S2. preparing a gold salt solution: preparing a 5-100 mM chloroauric acid solution, then slowly adding a complexing agent into the chloroauric acid solution, stirring evenly to form a uniform solution, and standing for not less than 24 hours to obtain a gold salt solution, wherein the solubility of the complexing agent in the gold salt solution is 5-150 g / L; the complexing agent is one or more of 1-methylhydantoin, 5,5-dimethylhydantoin, 1,5,5-trimethylhydantoin, citric acid or potassium citrate.

[0019] S3. Prepare reducing agent solution: fully dissolve the reducing agent and dispersant in deionized water to prepare a 10-250 mM reducing agent solution, wherein the concentration of the dispersant in the reducing agent solution is 10-100 g / L; the dispersant is one or more of polyvinyl pyrrolidone, polyvinyl alcohol, gum arabic or polyethylene glycol.

[0020] S4. Preparation of gold powder: The temperature is maintained at 20-150°C during the reaction under stirring, and the gold salt solution and the reducing agent solution are simultaneously dripped into the seed solution by a peristaltic pump to form a reaction solution. The addition rate of the peristaltic pump is 1-50 mL / min, and the molar ratio of the gold salt and the reducing agent dripped into the reaction solution is 1:(1-5), so that the seed crystals gradually grow again to D50 ≥ 0.5 μm.

[0021] S5, post-processing: after the reaction in S4 is completed, solid-liquid separation is performed, the solid gold powder is washed until the conductivity of the washing liquid is ≤20us / cm, and vacuum dried to obtain a gold powder product.

[0022] The reducing agent in step S1 and / or step S3 is one or more of sodium borohydride, ascorbic acid, formic acid, oxalic acid, hydrazine hydrate, and ethylene glycol.

[0023] The high tap density and high crystallinity gold powder prepared by the above method has a tap density of ≥9.0g / cm 3 , particle size D50 is 0.5-3.5μm.

[0024] Example 1 S1. Quickly add 5 mL of 2.5 mM sodium borohydride solution to 10 mL of 2.5 mM chloroauric acid solution at 30°C to generate nano seed crystals, add 2 g of polyvinyl pyrrolidone to protect the seed crystals, and add 500 mL of ionized water to obtain a seed crystal solution; S2, prepare 100 mL of 25 mM chloroauric acid solution, add 5 g of 1-methylhydantoin to the chloroauric acid solution, stir evenly to form a uniform solution, and let stand for 24 h to obtain a gold salt solution; S3, prepare 100 mL of 50 mM ascorbic acid solution, and add 1 g of polyvinyl pyrrolidone to fully dissolve to prepare a reducing agent solution; S4. At 30°C and under stirring, the prepared gold salt solution and reducing agent solution were respectively dripped into the nanocrystal seed solution through a peristaltic pump at a feeding rate of 5 mL / min. After the addition was completed, the solution was stirred for 1 h for sufficient reaction; S5. After the reaction is completed, the solid and liquid are separated, and the gold powder is washed with deionized water and ethanol respectively until the conductivity of the washing liquid is ≤20us / cm, and then vacuum dried to obtain gold powder. The particle size D50 of the gold powder is 1.5μm, and the tap density is 10.5g / cm 3 .

[0025] Example 2 S1. At 20°C, 40 mL of 2.5 mM sodium borohydride solution was quickly added to 50 mL of 2.5 mM chloroauric acid solution to generate nanocrystalline seeds, 10 g of polyvinyl pyrrolidone was added to protect the seeds, and 500 mL of ionized water was added to obtain a seed solution; S2, prepare 200 mL of 100 mM chloroauric acid solution, add 10 g of 5,5-dimethylhydantoin to the chloroauric acid solution, stir evenly to form a uniform solution, and let stand for 24 hours to obtain a gold salt solution; S3, prepare 200 mL of 250 mM ascorbic acid solution, and add 5 g of polyvinyl pyrrolidone to fully dissolve to prepare a reducing agent solution; S4, at 20°C, under stirring, the prepared gold salt solution and reducing agent solution were respectively dripped into the nanocrystal seed solution through a peristaltic pump at a feeding rate of 2 mL / min, and stirred for 1 h to fully react after the addition was completed; S5. After the reaction is completed, the solid and liquid are separated, and the gold powder is washed with deionized water and ethanol respectively until the conductivity of the washing liquid is ≤20us / cm, and then vacuum dried to obtain gold powder. The particle size D50 of the gold powder is 1.0μm, and the tap density is 9.5g / cm 3 .

[0026] Example 3 S1. At 25°C, 3 mL of 5 mM hydrazine hydrate solution was quickly added to 10 mL of 2.5 mM chloroauric acid solution to generate nanocrystalline seeds, 2 g of polyvinyl pyrrolidone was added to protect the seeds, and 500 mL of ionized water was added to obtain a seed solution; S2, prepare 150 mL of 25 mM chloroauric acid solution, add 8 g of 1,5,5-trimethylhydantoin to the chloroauric acid solution, stir evenly to form a uniform solution, and let stand for 24 hours to obtain a gold salt solution; S3, prepare 150 mL of 75 mM formic acid solution, and add 5 g of polyvinyl pyrrolidone to fully dissolve to prepare a reducing agent solution; S4, at 80°C, under stirring, the prepared gold salt solution and reducing agent solution were respectively dripped into the nanocrystal seed solution through a peristaltic pump at a feeding rate of 3 mL / min, and stirred for 1 h to fully react after the addition was completed; S5. After the reaction is completed, the solid and liquid are separated, and the gold powder is washed with deionized water and ethanol respectively until the conductivity of the washing liquid is ≤20us / cm, and then vacuum dried to obtain gold powder. The particle size D50 of the gold powder is 2.1μm, and the tap density is 9.8g / cm 3 .

[0027] Example 4 S1. At 25°C, 6 mL of 5 mM hydrazine hydrate solution was quickly added to 20 mL of 2.5 mM chloroauric acid solution to generate nanocrystalline seeds, 2 g of polyvinyl pyrrolidone was added to protect the seeds, and 200 mL of ionized water was added to obtain a seed solution; S2, prepare 100 mL of 25 mM chloroauric acid solution, add 15 g of citric acid to the chloroauric acid solution, stir evenly to form a uniform solution, and let stand for 24 hours to obtain a gold salt solution; S3, prepare 100 mL of 25 mM hydrazine hydrate solution, and add 2 g of polyvinyl pyrrolidone to fully dissolve to prepare a reducing agent solution; S4. At 25°C and under stirring, the prepared gold salt solution and reducing agent solution were respectively dripped into the nanocrystal seed solution through a peristaltic pump at a feeding rate of 5 mL / min. After the addition was completed, the solution was stirred for 1 h for full reaction; S5. After the reaction is completed, the solid and liquid are separated, and the gold powder is washed with deionized water and ethanol respectively until the conductivity of the washing liquid is ≤20us / cm, and then vacuum dried to obtain gold powder. The particle size D50 of the gold powder is 0.5μm, and the tap density is 9.2g / cm 3 .

[0028] Example 5 S1. At 30°C, 7 mL of 2.5 mM sodium borohydride solution was quickly added to 10 mL of 2.5 mM chloroauric acid solution to generate nanocrystal seeds, 2 g of polyvinyl pyrrolidone was added to protect the seeds, and 100 mL of ionized water was added to obtain a seed solution; S2. Prepare 200 mL of 50 mM chloroauric acid solution, add 5 g of potassium citrate to the chloroauric acid solution, stir evenly to form a uniform solution, and let stand for 24 hours; S3, prepare 200 mL of 150 mM ascorbic acid solution, and add 2 g of polyvinyl pyrrolidone to fully dissolve to prepare a reducing agent solution; S4, at 30°C, under stirring, the prepared gold salt solution and reducing agent solution were respectively dripped into the nanocrystal seed solution through a peristaltic pump at a feeding rate of 20 mL / min, and stirred for 1 h to fully react after the addition was completed; S5. After the reaction is completed, the solid and liquid are separated, and the gold powder is washed with deionized water and ethanol respectively until the conductivity of the washing liquid is ≤20us / cm, and then vacuum dried to obtain gold powder. The particle size D50 of the gold powder is 3.5μm, and the tap density is 10.2g / cm 3 .

[0029] Comparative Example 1 S1. Quickly add 10 mL of 2.5 mM sodium borohydride solution to 10 mL of 2.5 mM chloroauric acid solution to generate nano seed crystals, add 2 g of polyvinyl pyrrolidone to protect the seed crystals, and add 500 mL of ionized water to obtain a seed crystal solution; S2, prepare 100 mL of 25 mM chloroauric acid solution as the gold salt solution; S3, prepare 100 mL of 50 mM ascorbic acid solution, and add 1 g of polyvinyl pyrrolidone to fully dissolve to prepare a reducing agent solution; S4, at 30°C and under stirring, the prepared gold salt solution and reducing agent solution were respectively dripped into the nanocrystal seed solution through a peristaltic pump at a feeding rate of 5 mL / min, and stirred for 1 h to fully react after the addition was completed; S5. After the reaction is completed, the solid and liquid are separated, and the gold powder is washed with deionized water and ethanol respectively until the conductivity of the washing liquid is ≤20us / cm, and vacuum dried to obtain gold powder. The surface of the gold powder is rough, the crystallinity is average, the particle size D50 of the gold powder is 2.5μm, and the tap density is 8.0g / cm 3 .

[0030] Comparative Example 2 S1. Prepare 100 mL of 25 mM chloroauric acid solution, add 10 g of 5,5-dimethylhydantoin to the chloroauric acid solution, stir evenly to form a uniform solution, and let stand for 24 hours; S2, prepare 100 mL of 50 mM ascorbic acid solution, and add 1 g of polyvinyl pyrrolidone to fully dissolve to prepare a reducing agent solution; S3. At 20°C and under stirring, the prepared gold salt solution and reducing agent solution were respectively dripped into a beaker filled with deionized water through a peristaltic pump at a feeding rate of 2 mL / min. After the addition was completed, the solution was stirred for 1 h to fully react. S4. After the reaction is completed, the solid and liquid are separated, and the gold powder is washed with deionized water and ethanol respectively until the conductivity of the washing liquid is ≤20us / cm, and then vacuum dried to obtain gold powder. The particle size D50 of the gold powder is 1.5μm, and the tap density is 6.5g / cm 3 This indicates that using small-sized particles as seeds can produce gold powder with controllable particle size, narrow particle size span, and higher tap density.

[0031] Table 1 Particle size and tap density of gold powder in the examples and comparative examples

[0032] Based on the above results and the attached Figure 3 It can be seen from the XRD spectrum in the figure that the gold powder prepared by the method of the present invention has high crystallinity, narrow particle size distribution, and a tap density of up to 9g / cm 3 The above can meet the demand for gold powder for high-performance electronic paste.

[0033] Some exemplary embodiments of the present invention are described above. It can be understood that the above embodiments are only used to explain the present invention and do not constitute a limitation on the protection scope of the present invention. The features in these embodiments can be recombined in a suitable manner, and the scheme obtained thereby is still within the protection scope required by the present invention. Based on the above embodiments, all other embodiments obtained by those skilled in the art without making creative work, that is, all modifications, equivalent substitutions and improvements made within the spirit and principles of this application, fall within the protection scope required by the present invention.

Claims

1. A method for preparing gold powder with high tap density and high crystallinity, characterized in that: The following steps are involved: S1. preparing a seed solution: quickly adding a reducing agent solution to a chloroauric acid solution to generate nano seed crystals, then adding polyvinyl pyrrolidone to protect the seed crystals, and adding deionized water to obtain a seed solution, wherein the concentration of gold in the seed solution is 0.04-0.42 mM, and the concentration of polyvinyl pyrrolidone is 3-20 g / L; S2. preparing a gold salt solution: preparing a 5-100 mM chloroauric acid solution, then slowly adding a complexing agent into the chloroauric acid solution, stirring evenly to form a uniform solution, and standing for not less than 24 hours to obtain a gold salt solution, wherein the solubility of the complexing agent in the gold salt solution is 5-150 g / L; S3, preparing a reducing agent solution: fully dissolving a reducing agent and a dispersant in deionized water to prepare a 10-250 mM reducing agent solution, wherein the concentration of the dispersant in the reducing agent solution is 10-100 g / L; S4, preparing gold powder: under stirring, dripping the gold salt solution and the reducing agent solution into the seed crystal solution simultaneously by a peristaltic pump to form a reaction solution, the addition rate of the peristaltic pump is 1-50mL / min, and the amount ratio of the gold salt and the reducing agent dripped into the reaction solution is 1:1-5, so that the seed crystal gradually grows to D50≥0.5μm; S5, post-processing: after the reaction in S4 is completed, solid-liquid separation is performed, the solid gold powder is washed until the conductivity of the washing liquid is ≤20us / cm, and vacuum dried to obtain a gold powder product.

2. The method for preparing a gold powder with high tap density and high crystallinity according to claim 1, characterized in that: The molar ratio of the reducing agent and chloroauric acid added in step S1 is 1:0.5-5, and the temperature is maintained at 20-150° C. during the reaction.

3. The method for preparing a gold powder with high tap density and high crystallinity according to claim 2, characterized in that: The concentration of the chloroauric acid solution in step S1 is 2.5 mM.

4. The method for preparing a gold powder with high tap density and high crystallinity according to claim 1, characterized in that: The reducing agent in step S1 and / or step S3 is one or more of sodium borohydride, ascorbic acid, formic acid, oxalic acid, hydrazine hydrate, and ethylene glycol.

5. The method for preparing a gold powder with high tap density and high crystallinity according to claim 1, characterized in that: In step S2, the complexing agent is one or more of 1-methylhydantoin, 5,5-dimethylhydantoin, 1,5,5-trimethylhydantoin, citric acid or potassium citrate.

6. The method for preparing a gold powder with high tap density and high crystallinity according to claim 1, characterized in that: In step S3, the dispersant is one or more of polyvinyl pyrrolidone, polyvinyl alcohol, gum arabic or polyethylene glycol.

7. The method for preparing a gold powder with high tap density and high crystallinity according to claim 1, characterized in that: In step S4, the temperature is maintained at 20-150° C. during the reaction.

8. A gold powder with high tap density and high crystallinity prepared by the method according to any one of claims 1 to 7, characterized in that: The tap density of the gold powder is ≥9.0g / cm 3 , particle size D50 is 0.5-3.5μm.

Images