Spherical gold powder and preparation method thereof

Abstract

The present invention provides a kind of spherical gold powder and preparation method thereof, and relates to the technical field of precious metal powder preparation. The present invention uses aqua regia to prepare chloroauric acid solution, and first adds concentrated hydrochloric acid to the solution to adjust pH to 0.5-1.5, then adds ammonia to adjust pH to 7-9, stirs 20-60s, then adds concentrated hydrochloric acid to adjust pH to 1.2-2 again, obtains the solution to be reacted;Finally, dispersant solution and reducing agent solution are added to the solution to be reacted in order, and after sedimentation, washing, dry coating, drying, screening and other post-treatments, a large-particle size spherical gold powder with smooth surface is obtained. The present invention forms a trivalent gold-ammonia-chlorine system by increasing the chloride ion concentration in chloroauric acid, so that the generated fulminate gold complex is more complete, thereby promoting the growth of spherical gold powder, and the particle size of the prepared spherical gold powder is controllable between 4-8 μm by the synergistic effect of adjusting pH twice, and the particle size is uniform and has good dispersibility. The present invention has simple process, rapid reaction, and can realize large-scale production.

Description

Technical Field

[0001] The invention relates to the technical field of precious metal powder preparation, and in particular to spherical gold powder and a preparation method thereof. Background Art

[0002] Gold has stable chemical properties, low resistivity, high thermal conductivity and other characteristics, and is widely used in aerospace, military engineering, medical equipment, computers, satellite communications and other electronic fields. Among them, gold is prepared into large-sized spherical gold powder, which can also be used in surface decoration, ceramics, utensils and Buddha statues in the gold-plating process, and the demand is relatively high. However, the size, surface morphology, particle size distribution and dispersibility of domestically produced gold powder are difficult to meet production requirements, and most of them need to be imported from abroad.

[0003] At present, the size of large-sized spherical gold powder prepared by traditional physical methods is difficult to control, and the particle size distribution is wide, making it difficult to obtain spherical gold powder with uniform particle size; while the spherical gold powder prepared by chemical reduction method has a narrow size control range and a relatively single product.

[0004] In the prior art, a method for preparing micron-sized spherical gold powder for decoration is proposed in a patent document with publication number CN1772422A. The method first dissolves gold in aqua regia, and adjusts the pH value of the gold solution to 3-5, then adds ferrous sulfate solution to react, and finally post-treats the reaction tail liquid to prepare spherical gold powder with a particle size between 4-8 μm, but its morphology is not regular enough and the particle size distribution is uneven.

[0005] In the prior art, a patent document with publication number CN117300147B proposes an ultrafine gold powder and a preparation method thereof. The preparation method mixes a first dispersant solution with an ascorbic acid aqueous solution to obtain solution A, then slowly drips an aqueous solution of chloroauric acid into solution A at 5°C-15°C, and starts to drip a second dispersant solution synchronously after a certain volume is dripped to prepare uniformly dispersed gold seeds, and continuously deposits gold particles on the gold seeds at an appropriate rate, and finally obtains nano-scale ultrafine gold powder. This method uses a seed method to synthesize gold powder. The reaction needs to be carried out under low temperature conditions. The conditions are harsh, the seeds are difficult to control, and agglomeration is easy to occur. There are limitations on the regulation of particle size, and only gold powder with a size range of 80-200nm can be prepared.

[0006] In the prior art, a patent document with publication number CN116652204B proposes a spherical gold powder and a preparation method thereof. The preparation method uses hydrochloric acid and hydrogen peroxide to dissolve gold and filter. The obtained chloroauric acid solution is diluted and first adjusted to pH 7-8 with ammonia water, and then adjusted to pH below 1.8 with hydrochloric acid, and then subsequent reactions and post-treatments are performed. This method uses hydrogen peroxide to dissolve gold, which not only takes a long time to dissolve gold, but also causes loss of chloroauric acid during filtration, which is not conducive to large-scale production. In addition, this method has limitations on the regulation of particle size, and can only prepare gold powder with a size range of 1-3 μm.

[0007] In view of this, it is necessary to design a spherical gold powder and a preparation method thereof to solve the above problems. Summary of the invention

[0008] The object of the present invention is to provide a spherical gold powder and a preparation method thereof. The preparation method adopts a chemical reduction method and adjusts the pH value with hydrochloric acid twice to achieve a controllable gold powder particle size between 4 and 8 μm. The method is simple in process and the prepared large-size spherical gold powder has uniform particle size, good dispersibility, regular shape and smooth surface.

[0009] To achieve the above object, the present invention provides a method for preparing spherical gold powder, comprising the following steps:

[0010] S1, adding gold and aqua regia to deionized water, heating until the gold is completely dissolved, then dropping concentrated hydrochloric acid to remove nitric acid, concentrating, and preparing a chloroauric acid solution;

[0011] S2, using deionized water as solvent to prepare a dispersant solution and a reducing agent solution;

[0012] S3, taking the chloroauric acid solution prepared in step S1 and diluting it, adjusting the pH to 0.5-1.5 with concentrated hydrochloric acid, adding ammonia water until the pH of the solution is 7-9 to generate a fulminate gold complex, stirring for 20-60 seconds, and adjusting the pH to 1.2-2 with concentrated hydrochloric acid again to obtain a solution to be reacted;

[0013] S4, pouring the dispersant solution into the solution to be reacted in step S3, stirring evenly, and then rapidly dropping the reducing agent solution, stirring for reaction, and then settling to obtain a precipitate;

[0014] S5, taking the reaction precipitate prepared in step S4 and performing post-treatment to obtain spherical gold powder.

[0015] As a further improvement of the present invention, in step S1, the purity of the gold is 99.9%, and the concentration of the chloroauric acid solution is 4.17 g / L-6.67 g / L.

[0016] As a further improvement of the present invention, in step S5, the post-treatment is three water washes, three alcohol washes, the surface coating agent is dissolved, and evenly sprayed on the surface of the gold powder, and after drying at 50-90°C, sieving is performed using a 200-mesh sieve.

[0017] As a further improvement of the present invention, the surface coating agent is 3-mercaptopropionic acid, and the amount used is 0.2%-2% of the mass of the gold powder after alcohol washing.

[0018] As a further improvement of the present invention, in step S2, the concentration of the dispersant solution is 0.08-0.12 g / mL, and the concentration of the reducing agent solution is 0.18 g / mL-0.2 g / mL.

[0019] As a further improvement of the present invention, the mass ratio of the dispersant to the gold in the chloroauric acid solution is (1-3.33):5, and the mass ratio of the reducing agent to the gold in the chloroauric acid solution is (1.8-2.4):1.

[0020] As a further improvement of the present invention, in step S2, the dispersant is gum arabic, polyvinyl pyrrolidone, gelatin or polyvinyl alcohol, and the reducing agent is ascorbic acid.

[0021] As a further improvement of the present invention, in step S1 and step S3, the concentration of the concentrated hydrochloric acid used is 36%-38%.

[0022] As a further improvement of the present invention, in step S4, the dropping speed of the reducing agent is 140-160 mL / min.

[0023] To achieve the above-mentioned purpose, the present invention also provides a spherical gold powder, which is prepared by the preparation method of the spherical gold powder described in any of the technical schemes in the aforementioned technical schemes. The spherical gold powder has a particle size of 4-8 μm and is used in the fields of surface decoration, ceramics, utensils, and gold plating of Buddha statues.

[0024] The beneficial effects of the present invention are:

[0025] The invention adopts a chemical reduction method to prepare a large-sized spherical gold powder, and by adjusting the pH with hydrochloric acid twice, the particle size of the spherical gold powder can be controlled between 4 and 8 μm, and 3-mercaptopropionic acid is used to dry-coat the prepared gold powder. The prepared gold powder has uniform particle size and good dispersibility, and can be applied to the fields of surface decoration, ceramics, utensils, and gold plating of Buddha statues. The invention adopts a simple process, has a rapid reaction, and can realize large-scale production.

[0026] (1) In the process of adjusting pH, the first adjustment of pH value can increase the concentration of chloride ions in the chloroauric acid reaction system, which is conducive to the formation of a trivalent gold-ammonia-chlorine system, making the generated fulminate gold complex more complete, thereby promoting the growth of spherical gold powder; the second adjustment of pH value can control the reaction rate, making the gold powder uniform in size, regular in shape and smooth in surface. Through the synergistic effect of the two pH adjustments, the particle size of the spherical gold powder can be controlled between 4-8μm.

[0027] (2) In post-treatment, the prepared gold powder is dry coated with 3-mercaptopropionic acid to enhance the dispersibility and affinity of the spherical gold powder. The mercapto group at one end of the carbon chain of 3-mercaptopropionic acid forms an Au-S covalent bond with the gold surface, making the organic coating effect better and the gold powder dispersibility better, while the carboxyl group at the other end of the carbon chain can increase the affinity of the gold powder, thereby increasing the compatibility with the gold paste in subsequent applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a scanning electron microscope image of the spherical gold powder prepared in Example 1.

[0029] Figure 2 This is a scanning electron microscope image of the spherical gold powder prepared in Example 2.

[0030] Figure 3 This is a scanning electron microscope image of the spherical gold powder prepared in Example 3.

[0031] Figure 4 This is a scanning electron microscope image of the spherical gold powder prepared in Example 4.

[0032] Figure 5 This is a scanning electron microscope image of the spherical gold powder prepared in Comparative Example 1.

[0033] Figure 6 This is a scanning electron microscope image of the spherical gold powder prepared in Comparative Example 2.

[0034] Figure 7 This is a scanning electron microscope image of the spherical gold powder prepared in Comparative Example 3. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0036] It should also be noted that, in order to avoid obscuring the present invention due to unnecessary details, only structures and / or processing steps closely related to the scheme of the present invention are shown in the drawings, while other details that are not closely related to the present invention are omitted.

[0037] In addition, it should be noted that the terms "comprises", "includes" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or apparatus.

[0038] See also Figure 1 As shown, the present invention provides a method for preparing spherical gold powder, comprising the following steps:

[0039] S1, adding gold and aqua regia to deionized water, heating until the gold is completely dissolved, then dropping concentrated hydrochloric acid to remove nitric acid, concentrating, and preparing a chloroauric acid solution;

[0040] Specifically, the purity of gold is 99.9%, and the concentration of chloroauric acid solution is 4.17g / L-6.67g / L.

[0041] S2, using deionized water as solvent to prepare a dispersant solution and a reducing agent solution;

[0042] Specifically, the dispersant is gum arabic, polyvinyl pyrrolidone, gelatin or polyvinyl alcohol, and the reducing agent is ascorbic acid. The mass ratio of the dispersant to the gold in the chloroauric acid solution is (1-3.33):5, and the mass ratio of the reducing agent to the gold in the chloroauric acid solution is (1.8-2.4):1. The concentration of the dispersant solution is 0.08-0.12 g / mL, and the concentration of the reducing agent solution is 0.18 g / mL-0.2 g / mL.

[0043] S3, taking the chloroauric acid solution prepared in step S1 and diluting it, adjusting the pH to 0.5-1.5 with concentrated hydrochloric acid, adding ammonia water until the pH of the solution is 7-9 to generate a fulminate gold complex, stirring for 20-60 seconds, and adjusting the pH to 1.2-2 with concentrated hydrochloric acid again to obtain a solution to be reacted;

[0044] The chloroauric acid solution was diluted 120 times with deionized water and stirred thoroughly. In the scale-up test, the chloroauric acid solution was diluted 150 times with deionized water.

[0045] The concentration of ammonia water is 25%-28%.

[0046] The concentration of concentrated hydrochloric acid used in step S1 and step S3 is 36%-38%.

[0047] In the process of adjusting pH, the first adjustment of pH value can increase the concentration of chloride ions in the chloroauric acid reaction system, which is conducive to the formation of trivalent gold-ammonia-chlorine system, making the generated fulminate gold complex more complete, thereby promoting the growth of spherical gold powder; the second adjustment of pH value can control the reaction rate, making the gold powder uniform in size, regular in shape and smooth in surface. Through the synergistic effect of the two pH adjustments, the particle size of the spherical gold powder can be controlled between 4-8μm.

[0048] S4, pouring the dispersant solution into the solution to be reacted in step S3, stirring evenly, then quickly adding the reducing agent solution dropwise, stirring for 30 minutes, and then settling to obtain a precipitate;

[0049] The reducing agent was added at a rate of 140-160 mL / min. In the scale-up test, the reducing agent was added at a rate of 1.9-2.1 L / min.

[0050] S5, post-treating the reaction precipitate prepared in step S4 to obtain spherical gold powder.

[0051] Specifically, after three water washes and three alcohol washes, the surface coating agent is dissolved in ethanol and sprayed evenly on the surface of the gold powder. After drying at 50-90°C, the gold powder is sieved using a 200-mesh sieve.

[0052] The surface coating agent is 3-mercaptopropionic acid, and the dosage is 0.2%-2% of the mass of the gold powder after alcohol washing.

[0053] In the post-treatment, 3-mercaptopropionic acid is used to dry-coat the prepared gold powder, which can enhance the dispersibility and affinity of the spherical gold powder. The mercapto group at one end of the carbon chain of 3-mercaptopropionic acid forms an Au-S covalent bond with the gold surface, making the organic coating effect better and the gold powder more dispersible, while the carboxyl group at the other end of the carbon chain can increase the affinity of the gold powder, thereby increasing the compatibility with the gold paste in subsequent applications.

[0054] The spherical gold powder and the preparation method thereof provided by the present invention are described below in conjunction with specific embodiments.

[0055] Example 1

[0056] This embodiment provides a spherical gold powder and a preparation method thereof, comprising the following steps:

[0057] S1, put 5g gold bar (purity is 99.9%) and 20mL pure water into a 100mL beaker, heat the mixture in the beaker with a constant temperature heating table, and add 10mL of prepared aqua regia to the beaker in batches, wait until the gold bar is completely dissolved, add concentrated hydrochloric acid (concentration is 36%-38%) to the beaker to remove nitric acid, until no yellow smoke comes out, heat and concentrate to a solution volume of 10mL;

[0058] S2, dissolve 1g of polyvinyl pyrrolidone in deionized water to prepare a dispersant solution with a concentration of 0.1g / mL. Dissolve 9g of ascorbic acid in deionized water to prepare a reducing agent solution with a concentration of 0.18g / mL;

[0059] S3, diluting the chloroauric acid solution prepared in step S1 with deionized water to 1200 mL, adding concentrated hydrochloric acid dropwise, adjusting the pH value of the solution to 1.5, adding concentrated ammonia (concentration of 25%-28%), adjusting the pH value of the solution to 7.6, and stirring for 30 seconds to allow the solution to fully generate a fulminate gold complex, and adding concentrated hydrochloric acid again to adjust the pH to 1.28 to obtain a solution to be reacted;

[0060] S4, pour 10 mL of dispersant solution into the reaction solution prepared in step S3, quickly add 42 mL of reducing agent solution to the mixed solution by using a peristaltic pump, set the dripping rate to 150 mL / min, stir thoroughly for 30 min, and finally settle to obtain a reaction precipitate;

[0061] S5, taking the reaction precipitate prepared in step S4, washing it three times with water, and then washing it three times with ethanol. Then, dissolving 25 mg of 3-mercaptopropionic acid in 10 mL of ethanol to prepare a surface coating agent with a concentration of 2.5 g / L, spraying it evenly on the surface of the gold powder, stirring the gold powder while spraying, drying it at 70°C, and sieving it with a 200-mesh sieve to obtain spherical gold powder.

[0062] See also Figure 1 As shown, the spherical gold powder prepared in Example 1 has a size of about 4.5 μm, and has uniform size and a smooth surface.

[0063] Example 2

[0064] The main difference between Example 2 and Example 1 is that in step S3, concentrated hydrochloric acid is added for the first time to adjust the pH to 0.8, and concentrated hydrochloric acid is added for the second time to adjust the pH to 1.28. The other contents are roughly the same as Example 1 and will not be repeated here.

[0065] See also Figure 2 As shown, the spherical gold powder prepared in Example 2 has a size of about 6.5 μm, and has uniform size and a smooth surface.

[0066] Example 3

[0067] The main difference between Example 3 and Example 1 is that in step S3, concentrated hydrochloric acid is added for the first time to adjust the pH to 0.52, and concentrated hydrochloric acid is added for the second time to adjust the pH to 1.28. The other contents are roughly the same as those in Example 1 and will not be repeated here.

[0068] See also Figure 3As shown, the spherical gold powder prepared in Example 3 has a size of about 7.5 μm, and has uniform size and a smooth surface.

[0069] Example 4

[0070] Example 4 provides an amplified test of spherical gold powder and a preparation method thereof, comprising the following steps:

[0071] S1, put 100g gold bar (purity is 99.9%) and 100mL pure water into a 500mL beaker, heat the mixture in the beaker with a constant temperature heating table, and add 25mL of the prepared aqua regia to the beaker in batches, and add concentrated hydrochloric acid (concentration is 36%-38%) to the beaker to remove nitric acid until no yellow smoke comes out, and heat and concentrate the solution to a volume of 100mL;

[0072] S2, dissolving 30 g of polyvinyl pyrrolidone in deionized water to prepare a dispersant solution with a concentration of 0.1 g / mL. Dissolving 240 g of ascorbic acid in deionized water to prepare a reducing agent solution with a concentration of 0.2 g / mL;

[0073] S3, diluting the chloroauric acid solution prepared in step S1 to 15 L with deionized water, adding concentrated hydrochloric acid dropwise, adjusting the pH value of the solution to 1.5, adding concentrated ammonia water (concentration of 25%-28%), adjusting the pH value of the solution to 7.6, and stirring for 30 seconds to allow the solution to fully generate a fulminate gold complex, and adding concentrated hydrochloric acid again to adjust the pH to 1.28 to obtain a solution to be reacted;

[0074] S4, pour 300 mL of dispersant solution into the reaction solution prepared in step S3, quickly add 1200 mL of reducing agent solution to the mixed solution by a peristaltic pump, set the dripping rate to 2 L / min, stir thoroughly for 30 min, and finally settle to obtain a reaction precipitate;

[0075] S5, taking the reaction precipitate prepared in step S4, washing it three times with water, and then washing it three times with ethanol. Then, dissolving 500 mg of 3-mercaptopropionic acid in 100 mL of ethanol to prepare a surface coating agent with a concentration of 5 g / L, spraying it evenly on the surface of the gold powder, stirring the gold powder while spraying, drying it at 70°C, and sieving it with a 200-mesh sieve to obtain spherical gold powder.

[0076] See also Figure 4 As shown, the size of the spherical gold powder prepared in Example 4 is about 4.5 μm, and the size is uniform and the surface is smooth. It can be seen that the preparation method of the spherical gold powder proposed in the present invention has been successfully expanded to 100 g, and the morphology, size, uniformity, etc. of the prepared spherical gold powder remain stable. It can be seen that the preparation method is stable and suitable for industrial production.

[0077] Comparative Example 1

[0078] Comparative Example 1 provides a spherical gold powder and a preparation method thereof. Compared with Example 1, the difference lies in that in step S4, the order of adding the dispersant solution and the reducing agent solution is changed.

[0079] Specifically, 42 mL of reducing agent solution was first added dropwise to the reaction solution prepared in step S3 using a peristaltic pump, the dripping rate of the peristaltic pump was set to 150 mL / min, and the mixture was stirred evenly to obtain a mixed solution, and then 10 mL of dispersant solution was quickly poured into the mixed solution, and the mixture was stirred for 30 min, and finally the reaction precipitate was obtained by sedimentation. The other contents are substantially the same as those in Example 1, and will not be repeated here.

[0080] See also Figure 5 As shown, the size of the spherical gold powder prepared in Comparative Example 1 is about 2 μm, the gold powder morphology is irregular, and the agglomeration is serious.

[0081] Comparative Example 2

[0082] Comparative Example 2 provides a spherical gold powder and a preparation method thereof. Compared with Example 1, the difference is that in step S3, the pH of the chloroauric acid solution is not adjusted, and ammonia water is directly added thereto to react to prepare a fulminate gold complex, and then the pH is adjusted to 1.28 with concentrated hydrochloric acid.

[0083] Specifically, the chloroauric acid solution prepared in step S1 was diluted to 1200 mL with deionized water, concentrated aqueous ammonia (concentration of 25%-28%) was added, the pH value of the solution was adjusted to 7.6, and stirred for 30 seconds to allow the solution to fully generate a fulminate gold complex, and concentrated hydrochloric acid was added again to adjust the pH to 1.28 to obtain a solution to be reacted. The other contents are substantially the same as those in Example 1 and will not be repeated here.

[0084] See also Figure 6 As shown, the spherical gold powder prepared in Comparative Example 2 is relatively small in size, and as it grows continuously, the gold powder agglomerates into clusters in a flower ball shape. The gold powder has this morphology because, firstly, in step S3, there is a lack of the step of adjusting the pH value of the solution with hydrochloric acid for the first time before adding ammonia water to the chloroauric acid solution, resulting in incomplete fulminate gold complex generated in the reaction, and then the spherical gold powder generated subsequently is too small in size, and it is difficult to stably exist in the solution, and can only agglomerate together with continuous growth to form a cluster of flower balls; secondly, after adding ammonia water, the pH value of the fulminate gold complex solution is adjusted with hydrochloric acid, so that the acidity of the reaction system is enhanced, the reduction potential is reduced, and then the reducing ability of the reducing agent in the reaction system is enhanced, the reaction rate is increased, and while agglomeration occurs, the gold powder grows stably and the growth rate is consistent, and finally a flower ball-shaped gold powder of uniform size is obtained.

[0085] Comparative Example 3

[0086] Comparative Example 3 provides a spherical gold powder and a preparation method thereof. Compared with Example 1, the difference is that in step S3, hydrochloric acid is used for the second time to adjust the pH to 2.5.

[0087] Specifically, the chloroauric acid solution prepared in step S1 is diluted to 1200 mL with deionized water, concentrated hydrochloric acid is added dropwise, the pH value of the solution is adjusted to 1.5, concentrated ammonia water (concentration is 25%-28%) is added, the pH value of the solution is adjusted to 7.6, and stirred for 30 seconds to allow the solution to fully generate a fulminate gold complex, and concentrated hydrochloric acid is added again to adjust the pH to 2.5 to obtain a solution to be reacted.

[0088] See also Figure 7 As shown, the size of the spherical gold powder prepared in Comparative Example 3 is between 1.5 and 5 μm. It can be seen that the size of the gold powder becomes uneven and the particle size distribution is wide. This is because the pH value of the reaction solution is too high due to the second adjustment with hydrochloric acid, the acidity of the reaction system is weakened, the reduction potential is increased, and the reducing ability of the reducing agent in the reaction system is weakened, the reaction rate is reduced, and the growth rate of the gold powder is inconsistent, and finally spherical gold powder of uneven size is obtained.

[0089] Comparative Examples 4-5

[0090] Comparative Example 4-5 provides a spherical gold powder and a preparation method thereof. Compared with Example 1, the difference is that in step S5, Comparative Example 4 uses oleic acid to form a surface coating agent with a concentration of 2.5 g / L, and Comparative Example 5 uses stearic acid to form a surface coating agent with a concentration of 2.5 g / L. The other contents are substantially the same as those in Example 1 and will not be repeated here.

[0091] The tap density of the spherical gold powder prepared in Example 1 and Comparative Examples 4-5 was tested. The specific method was as follows: the sample was placed in a measuring cylinder, and the surface of the powder was kept horizontal. Subsequently, the measuring cylinder was placed on a vibrating device, and vibrated until the volume of the powder no longer decreased. The volume was recorded, and the tap density was calculated using the formula ρ=m / V. The results are shown in the following table.

[0092] <![CDATA[Tap density (g / cm 3 )]]> Example 1 7.21 Comparative Example 4 6.94 Comparative Example 5 6.86

[0093] Please refer to the table above. Compared with Comparative Examples 4-5, the spherical gold powder prepared in Example 1 has a higher tap density and better dispersibility, indicating that the surface coating agent 3-mercaptopropionic acid has the best coating effect. This is because the mercapto group at one end of the carbon chain of 3-mercaptopropionic acid can form an Au-S covalent bond with the gold surface, so that the organic matter is tightly wrapped on the surface of the gold powder, thereby making the gold powder more dispersible and having a higher tap density; the carboxyl group at the other end of the carbon chain can increase the affinity of the gold powder and make the gold powder more fluid. Conventional organic coating agents can only be simply coated on the surface of the gold powder without forming corresponding chemical bonds, and the dispersion effect is relatively poor.

[0094] In summary, by adjusting the pH value of the solution for the first time, the chloride ion concentration in the chloroauric acid reaction system can be increased, which is conducive to the formation of a trivalent gold-ammonia-chlorine system and makes the generated gold fulminate complex more complete, thereby promoting the growth of spherical gold powder; the second adjustment of the pH value can control the reaction rate and make the gold powder particle size uniform. Through the synergistic effect of the two pH adjustments, the particle size of the spherical gold powder can be controlled between 4-8μm, and the morphology is regular and the size is uniform.

[0095] In the post-treatment, 3-mercaptopropionic acid is used to dry-coat the prepared gold powder, which can enhance the dispersibility and affinity of the spherical gold powder. The mercapto group at one end of the carbon chain of 3-mercaptopropionic acid forms an Au-S covalent bond with the gold surface, making the organic coating effect better and the gold powder more dispersible, while the carboxyl group at the other end of the carbon chain can increase the affinity of the gold powder, thereby increasing the compatibility with the gold paste in subsequent applications.

[0096] The above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for preparing spherical gold powder, characterized in that: The following steps are involved: S1, adding gold and aqua regia to deionized water, heating until the gold is completely dissolved, then dropping concentrated hydrochloric acid to remove nitric acid, concentrating, and preparing a chloroauric acid solution; S2, using deionized water as solvent to prepare a dispersant solution and a reducing agent solution; S3, taking the chloroauric acid solution prepared in step S1 and diluting it, adjusting the pH to 0.5-1.5 with concentrated hydrochloric acid, adding ammonia water until the pH of the solution is 7-9 to generate a fulminate gold complex, stirring for 20-60 seconds, and adjusting the pH to 1.2-2 with concentrated hydrochloric acid again to obtain a solution to be reacted; S4, pouring the dispersant solution into the solution to be reacted in step S3, stirring evenly, and then rapidly dropping the reducing agent solution, stirring for reaction, and then settling to obtain a precipitate; S5, taking the reaction precipitate prepared in step S4 and performing post-treatment to obtain spherical gold powder.

2. The method for preparing spherical gold powder according to claim 1, characterized in that: In step S1, the purity of gold is 99.9%, and the concentration of chloroauric acid solution is 4.17 g / L-6.67 g / L.

3. The method for preparing spherical gold powder according to claim 1, characterized in that: In step S5, the post-treatment is three water washes and three alcohol washes, the surface coating agent is dissolved and evenly sprayed on the surface of the gold powder, and after drying at 50-90°C, sieving is performed using a 200-mesh screen.

4. The method for preparing spherical gold powder according to claim 3, characterized in that: The surface coating agent is 3-mercaptopropionic acid, and the amount used is 0.2%-2% of the mass of the gold powder after alcohol washing.

5. The method for preparing spherical gold powder according to claim 1, characterized in that: In step S2, the concentration of the dispersant solution is 0.08-0.12 g / mL, and the concentration of the reducing agent solution is 0.18 g / mL-0.2 g / mL.

6. The method for preparing spherical gold powder according to claim 5, characterized in that: The mass ratio of the dispersant to the gold in the chloroauric acid solution is (1-3.33):5, and the mass ratio of the reducing agent to the gold in the chloroauric acid solution is (1.8-2.4):

1.

7. The method for preparing spherical gold powder according to claim 5, characterized in that: In step S2, the dispersant is gum arabic, polyvinyl pyrrolidone, gelatin or polyvinyl alcohol, and the reducing agent is ascorbic acid.

8. The method for preparing spherical gold powder according to claim 1, characterized in that: In step S1 and step S3, the concentration of concentrated hydrochloric acid used is 36%-38%.

9. The method for preparing spherical gold powder according to claim 1, characterized in that: In step S4, the reducing agent is added at a rate of 140-160 mL / min.

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