Spherical gold powder and preparation method thereof

Abstract

The present invention provides a kind of spherical gold powder and preparation method thereof, relate to the technical field of precious metal powder preparation, the preparation method uses aqua regia to prepare chloroauric acid solution, and uses concentrated hydrochloric acid to adjust pH to 1.5-2, then adds ammonia water to adjust pH to 7-9, stirs 20-60s, then adds concentrated hydrochloric acid to adjust pH to 1.2-2 again, obtains mixed solution B;Then, the first dispersant solution is poured into the aforementioned mixed solution B, after stirring evenly, the mixed solution A of the second dispersant and the reducing agent is quickly added, after stirring reaction, sedimentation, post-treatment, obtains spherical gold powder. Wherein, spherical gold powder of different sizes with a particle size within the range of 0.3-4 μm can be prepared by adjusting pH twice, and adding two different dispersants in a specific order of addition can make the prepared spherical gold powder uniform in particle size, good in dispersibility, regular in shape and smooth in surface. The preparation method reacts rapidly, the process is short and stable, and it has been stably expanded to 500g, which can realize large-scale industrial 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] In electronic fields such as aerospace, military engineering, medical equipment, computers and satellite communications, electronic gold paste is often used to prepare components. Among them, gold powder plays a very important role in conductive paste and requires high electrical and thermal conductivity. In industrial production, high-end electronic components have more stringent requirements on gold powder. Therefore, it is very necessary to produce gold powder that meets the requirements, has uniform and controllable particle size, smooth surface, good dispersibility, and high compatibility with electronic paste. However, in the prior art, the spherical gold powder prepared by traditional physical methods is difficult to control in size, and the particle size distribution is wide, making it difficult to obtain spherical gold powder with uniform particle size; the spherical gold powder prepared by chemical reduction method has a narrow size control range, and the product is relatively single, which is difficult to meet production needs.

[0003] 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 a solution A, and then slowly drips an aqueous solution of chloroauric acid into the solution A at 5°C-15°C, and after dripping a certain volume, starts to drip a second dispersant solution synchronously 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. The method uses a seed method to synthesize gold powder, and 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, and there are limitations on the regulation of particle size, and only gold powder with a size in the range of 80-200nm can be prepared.

[0004] 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.

[0005] 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

[0006] The object of the present invention is to provide a spherical gold powder and a preparation method thereof. The preparation method has a simple process, adopts a chemical reduction method, and adjusts the pH value twice with hydrochloric acid to achieve a controllable gold powder particle size between 0.3 and 4 μm. A first dispersant is first added for pre-coating, and then a mixed solution of a second dispersant and a reducing agent is added. Under the synergistic effect of the two different dispersants, the prepared gold powder has a uniform particle size, good dispersibility, a regular shape and a smooth surface.

[0007] To achieve the above object, the present invention provides a method for preparing spherical gold powder, comprising the following steps:

[0008] 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;

[0009] S2, preparing a first dispersant solution, and then preparing a mixed solution A of a second dispersant and a reducing agent, wherein the first dispersant solution is a polyvinyl pyrrolidone solution, the second dispersant is polyvinyl alcohol, and the reducing agent is ascorbic acid;

[0010] S3, taking the chloroauric acid solution prepared in step S1 and diluting it, adjusting the pH to 1.5-2 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 mixed solution B;

[0011] S4, pouring the polyvinyl pyrrolidone solution into the mixed solution B in step S3, stirring evenly, and then quickly adding the mixed solution A, stirring for sufficient reaction, and settling to obtain a precipitate;

[0012] S5, taking the reaction precipitate prepared in step S4 and performing post-treatment to obtain spherical gold powder.

[0013] As a further improvement of the present invention, in step S2, the polyvinyl pyrrolidone solution is prepared by dissolving polyvinyl pyrrolidone in deionized water, and the concentration of the polyvinyl pyrrolidone solution is 0.05 g / mL.

[0014] As a further improvement of the present invention, in step S2, the preparation method of the mixed solution A is to use deionized water as a solvent, first prepare an ascorbic acid solution with a concentration of 0.18g / mL-0.2g / mL and a polyvinyl alcohol solution with a concentration of 0.05g / mL, and then mix the ascorbic acid solution with the polyvinyl alcohol solution to obtain a mixed solution A.

[0015] As a further improvement of the present invention, in step S4, the mass ratio of the polyvinyl pyrrolidone to the gold in the chloroauric acid solution is (0.1-0.15):1, the mass ratio of the polyvinyl alcohol to the gold in the chloroauric acid solution is (0.1-0.15):1, and the mass ratio of the ascorbic acid to the gold in the chloroauric acid solution is (1.8-2.4):1.

[0016] 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-10 g / L.

[0017] As a further improvement of the present invention, in step S4, the dropping speed of the mixed solution A is 140-160 mL / min.

[0018] As a further improvement of the present invention, in step S5, the post-treatment is washing, surface coating, drying, and screening; the surface coating agent used is one of oleic acid, gelatin, and Tween-80, or a mixture of two of them, and the amount used is 0.2%-2% of the mass of the gold powder.

[0019] To achieve the above-mentioned purpose, the present invention also provides a spherical gold powder, which is prepared by the preparation method described in any of the technical schemes in the aforementioned technical schemes. The particle size of the spherical gold powder is 0.3-4μm, and is used in aerospace, military engineering, medical equipment, computer and satellite communication electronics fields.

[0020] The beneficial effects of the present invention are:

[0021] The present invention provides a method for preparing spherical gold powder. The preparation method adopts a chemical reduction method. By adjusting the pH with hydrochloric acid twice, the particle size of the spherical gold powder can be controlled between 0.3-4 μm. At the same time, through the synergistic effect of two different dispersants, the prepared spherical gold powder has uniform particle size, good dispersibility, regular shape and smooth surface. The spherical gold powder can be used in aerospace, military engineering, medical equipment, computers, satellite communications and other electronic fields. The preparation method proposed by the present invention has rapid response, simple operation, high reproducibility, low requirements for experimental conditions and equipment, and has been stably expanded to 500g, which can achieve large-scale industrial production;

[0022] (1) In step S3, by adjusting the pH value for the first time, on the one hand, the concentration of chloride ions 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 fulminate gold complex more complete; on the other hand, the pH value is fine-tuned within the range of 1.5-2 to change the concentration of the gold complex, which can adjust the particle size of the spherical gold powder, and the higher the pH value, the smaller the size of the spherical gold powder;

[0023] (2) In step S3, by adjusting the pH value for the second time, the reaction rate can be controlled to make the gold powder uniform in particle size, regular in shape and smooth in surface. Through the synergistic effect of adjusting the pH value twice, spherical gold powder with a controllable particle size within the range of 0.3-4 μm and good morphology can be prepared;

[0024] (3) In step S4, the present invention uses two dispersants. After the first dispersant is used to preferentially encapsulate chloroauric acid, a mixed solution A of a second dispersant and a reducing agent is quickly added to react to obtain spherical gold powder. The first dispersant is polyvinyl pyrrolidone, which has a large molecular weight and is conducive to increasing the dispersibility of the spherical gold powder and making the size of the gold powder more uniform; the second dispersant is polyvinyl alcohol, which contains a large number of hydroxyl groups in its molecules. While playing a dispersing role, it can also increase the hydrophilicity of the spherical gold powder, further improve the dispersion effect, and improve the compatibility of the spherical gold powder in the subsequent gold paste;

[0025] (4) In step S4, the order of adding the first dispersant and the second dispersant is limited and cannot be changed. This is because polyvinyl pyrrolidone is used as the first dispersant, which has a better coating effect on the spherical gold powder and can make the gold powder more dispersed during the formation process; polyvinyl alcohol is used as the second dispersant for re-coating, which can make the hydroxyl groups in the molecular chain free on the surface of the formed gold powder, which is beneficial to increase the hydrophilicity of the spherical gold powder and its compatibility in the subsequent gold paste. Through the synergistic effect of the first dispersant and the second dispersant, the particle size distribution of the prepared spherical gold powder can be made more uniform, so as to solve the problem that the powder is prone to agglomeration when it is smaller in size. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is the scanning electron microscopy result of the spherical gold powder prepared in Example 1.

[0027] Figure 2 This is the scanning electron microscopy result of the spherical gold powder prepared in Example 2.

[0028] Figure 3 This is the scanning electron microscopy result of the spherical gold powder prepared in Example 3.

[0029] Figure 4 This is the scanning electron microscopy result of the spherical gold powder prepared in Example 4.

[0030] Figure 5 This is the scanning electron microscopy result of the spherical gold powder prepared in Example 5.

[0031] Figure 6 This is the scanning electron microscopy result of the spherical gold powder prepared in Example 6.

[0032] Figure 7 This is the scanning electron microscopy result of the spherical gold powder prepared in Comparative Example 1.

[0033] Figure 8 This is the scanning electron microscopy result of the spherical gold powder prepared in Comparative Example 2.

[0034] Fig. 9 This is the scanning electron microscopy result of the spherical gold powder prepared in Comparative Example 3.

[0035] Fig.10 This is the scanning electron microscopy result of the spherical gold powder prepared in Comparative Example 4. DETAILED DESCRIPTION

[0036] 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.

[0037] 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.

[0038] 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.

[0039] The present invention provides a method for preparing spherical gold powder, comprising the following steps:

[0040] 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;

[0041] Specifically, the purity of gold is 99.9%, and the concentration of chloroauric acid solution is 4.17g / L-10g / L.

[0042] S2, preparing a first dispersant solution, and then preparing a mixed solution A of a second dispersant and a reducing agent, wherein the first dispersant solution is a polyvinyl pyrrolidone solution, the second dispersant is polyvinyl alcohol, and the reducing agent is ascorbic acid;

[0043] Specifically, the polyvinyl pyrrolidone solution is prepared by dissolving polyvinyl pyrrolidone in deionized water, the concentration of the polyvinyl pyrrolidone solution is 0.05 g / mL, and the mass ratio of polyvinyl pyrrolidone to gold in the chloroauric acid solution is (0.1-0.15):1.

[0044] The preparation method of mixed solution A is as follows: using deionized water as a solvent, first preparing an ascorbic acid solution with a concentration of 0.18 g / mL-0.2 g / mL and a polyvinyl alcohol solution with a concentration of 0.05 g / mL, and then mixing the ascorbic acid solution with the polyvinyl alcohol solution to obtain mixed solution A; the mass ratio of polyvinyl alcohol to gold in the chloroauric acid solution is (0.1-0.15):1, and the mass ratio of ascorbic acid to gold in the chloroauric acid solution is (1.8-2.4):1.

[0045] S3, taking the chloroauric acid solution prepared in step S1 and diluting it, adjusting the pH to 1.5-2 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 mixed solution B;

[0046] 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 333 times with deionized water.

[0047] The concentration of ammonia water is 25%-28%.

[0048] The concentration of concentrated hydrochloric acid used in step S1 and step S3 is 36%-38%.

[0049] By adjusting the pH value for the first time, on the one hand, the chloride ion concentration in the chloroauric acid reaction system can be increased, which is beneficial to the formation of a trivalent gold-ammonia-chlorine system and makes the generated fulminate gold complex more complete; on the other hand, by fine-tuning the pH value within the range of 1.5-2 to change the concentration of the gold complex, the particle size of the spherical gold powder can be adjusted, and the higher the pH value, the smaller the size of the spherical gold powder.

[0050] By adjusting the pH value for the second time, the reaction rate can be controlled to make the gold powder uniform in particle size, regular in shape and smooth in surface. Through the synergistic effect of adjusting the pH value twice, spherical gold powder with a controllable particle size within the range of 0.3-4 μm and good morphology can be prepared.

[0051] S4, pouring the polyvinyl pyrrolidone solution into the mixed solution B in step S3, stirring evenly, and then quickly adding the mixed solution A, stirring for sufficient reaction, and settling to obtain a precipitate;

[0052] The drop rate of the mixed solution A was 140-160 mL / min. In the 500 g scale-up test, the drop rate of the mixed solution A was 7.5-8.5 L / min.

[0053] The first dispersant, polyvinyl pyrrolidone, has a large molecular weight, which is beneficial to increasing the dispersibility of the spherical gold powder and making the size of the gold powder more uniform; the second dispersant, polyvinyl alcohol, contains a large number of hydroxyl groups in its molecules, which can increase the hydrophilicity of the spherical gold powder while playing a dispersing role, further improving the dispersion effect and improving the compatibility of the spherical gold powder in the subsequent gold paste.

[0054] The order of adding the first dispersant and the second dispersant cannot be changed, that is, the order of adding polyvinyl pyrrolidone and polyvinyl alcohol cannot be changed. This is because polyvinyl pyrrolidone has a better coating effect on spherical gold powder, which can make the gold powder more dispersed during the formation process; and using polyvinyl alcohol for re-coating can make the hydroxyl groups in the molecular chain free on the surface of the formed gold powder, which is beneficial to increase the hydrophilicity of the spherical gold powder and its compatibility in the subsequent gold slurry. Through the synergistic effect of the first dispersant and the second dispersant, the particle size distribution of the prepared spherical gold powder can be made more uniform, so as to solve the problem that the powder is prone to agglomeration when it is smaller in size.

[0055] S5, taking the reaction precipitate prepared in step S4 and performing post-treatment to obtain spherical gold powder.

[0056] Specifically, the post-treatment is washing, surface coating, drying and screening the reaction precipitate. The surface coating agent used for surface coating is one of oleic acid, gelatin and Tween-80 or a mixture of two of them, and the amount of the surface coating agent is 0.2%-2% of the mass of the gold powder.

[0057] The preparation method of the spherical gold powder provided by the present invention is described below with reference to specific embodiments.

[0058] Example 1

[0059] This embodiment provides a method for preparing spherical gold powder, comprising the following steps:

[0060] 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. After 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, and heat to concentrate the solution to a volume of 10mL;

[0061] S2, take 0.5g polyvinyl pyrrolidone and dissolve it in 5mL deionized water to prepare a first dispersant solution with a concentration of 0.05g / mL. Take 9g ascorbic acid and dissolve it in 42mL deionized water to prepare a reducing agent solution with a concentration of 0.18g / mL. Take 0.5g polyvinyl alcohol and dissolve it in 5mL deionized water to prepare a second dispersant solution with a concentration of 0.05g / mL. Mix the reducing agent solution and the second dispersant solution to obtain solution A.

[0062] S3, dilute the chloroauric acid solution prepared in step S1 to 1.2 L with deionized water, add concentrated hydrochloric acid dropwise, adjust the pH value of the solution to 2, add concentrated ammonia water (concentration of 25%-28%), adjust the pH value of the solution to 7.6, and stir for 30 seconds to allow the solution to fully generate fulminate gold complex, and add concentrated hydrochloric acid again to adjust the pH to 1.28 to obtain solution B.

[0063] S4, after pouring the first dispersant solution into the solution B prepared in step S3, the mixed solution A is quickly added dropwise using a peristaltic pump with the dropping rate set to 150 mL / min, and the mixture is stirred for 30 min, and finally settled to obtain a reaction precipitate.

[0064] S5, take the reaction precipitate prepared in step S4, wash it with water three times, wash it with ethanol three times, weigh 1g oleic acid + 4g Tween and mix it in 20ml ethanol, extract 400uL of the mixed solution for surface coating, wash it with ethanol twice, dry it, and sieve it with a 200-mesh sieve to obtain spherical gold powder.

[0065] See also Figure 1 As shown, the spherical gold powder prepared in Example 1 has a size of about 300 nm, and is uniform in size and has a smooth surface.

[0066] Example 2

[0067] 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 1.9, 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.

[0068] See also Figure 2 As shown, the spherical gold powder prepared in Example 2 has a size of about 800 nm, and is uniform in size and has a smooth surface.

[0069] Example 3

[0070] 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 1.8, 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 those in Example 1 and will not be repeated here.

[0071] See also Figure 3 As shown, the spherical gold powder prepared in Example 3 has a size of about 1.8 μm, and has uniform size and a smooth surface.

[0072] Example 4

[0073] The main difference between Example 4 and Example 1 is that in step S3, concentrated hydrochloric acid is added for the first time to adjust the pH to 1.7, 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.

[0074] See also Figure 4 As shown, the spherical gold powder prepared in Example 4 has a size of about 2.5 μm, and has uniform size and a smooth surface.

[0075] Example 5

[0076] The main difference between Example 5 and Example 1 is that in step S3, concentrated hydrochloric acid is added for the first time to adjust the pH to 1.6, 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.

[0077] See also Figure 5 As shown, the spherical gold powder prepared in Example 5 has a size of about 3.5 μm, and has uniform size and a smooth surface.

[0078] Example 6

[0079] Example 6 provides an amplified test of a method for preparing spherical gold powder, comprising the following steps:

[0080] S1, put 500g gold bar (purity is 99.9%) and 150mL pure water into a 500mL beaker, heat the mixture in the beaker with a constant temperature heating table, and add 25mL of prepared aqua regia to the beaker in batches. After 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, and then heat and concentrate the solution to a volume of 150mL;

[0081] S2, take 75g of polyvinyl pyrrolidone and dissolve it in 750mL of deionized water to prepare a first dispersant solution with a concentration of 0.05g / mL. Take 1200g of ascorbic acid and dissolve it in 6L of deionized water to prepare a reducing agent solution with a concentration of 0.2g / mL. Take 75g of polyvinyl alcohol and dissolve it in 750mL of deionized water to prepare a second dispersant solution with a concentration of 0.05g / mL. Mix the reducing agent solution and the second dispersant solution to obtain solution A.

[0082] S3, dilute the chloroauric acid solution prepared in step S1 to 50 L with deionized water, add concentrated hydrochloric acid dropwise, adjust the pH value of the solution to 1.7, add concentrated ammonia water (concentration of 25%-28%), adjust the pH value of the solution to 7.6, and stir for 30 seconds to allow the solution to fully generate a fulminate gold complex, and add concentrated hydrochloric acid again to adjust the pH to 1.28 to obtain solution B.

[0083] S4, after pouring the first dispersant solution into the solution B prepared in step S3, the mixed solution A is quickly added dropwise using a peristaltic pump with the dropping rate set to 8 L / min, and the mixture is stirred for 30 minutes, and finally settled to obtain a reaction precipitate.

[0084] S5, take the reaction precipitate prepared in step S4, wash it with water three times, wash it with ethanol three times, weigh 1g oleic acid + 4g Tween and mix it in 20ml ethanol, extract 8mL of the mixed solution for surface coating, wash it with ethanol twice, dry it, and sieve it with a 200-mesh sieve to obtain spherical gold powder.

[0085] See also Figure 6 As shown, the size of the spherical gold powder prepared in Example 6 is about 2.5 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 500 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.

[0086] Comparative Example 1

[0087] Comparative Example 1 provides a method for preparing spherical gold powder, which is different from Example 4 in that: in step S4, the first dispersant polyvinyl pyrrolidone is not used, and a mixed solution of a reducing agent and a second dispersant polyvinyl alcohol is directly added. The other contents are substantially the same as those of Example 4 and are not described here.

[0088] See also Figure 7 As shown, the spherical gold powder prepared in Comparative Example 1 is unevenly distributed in size, difficult to control in shape, severely agglomerated, and partially connected and grown into sheets.

[0089] Comparative Example 2

[0090] Comparative Example 2 provides a method for preparing spherical gold powder, which is different from Example 4 in that: in step S4, the first dispersant is polyvinyl pyrrolidone, the reducing agent is directly added, and the second dispersant polyvinyl alcohol is not used. The other contents are substantially the same as those in Example 4 and will not be repeated here.

[0091] See also Figure 8 As shown, the size of the spherical gold powder prepared in Comparative Example 2 is about 1 μm, and obvious agglomeration occurs.

[0092] Comparative Example 3

[0093] Comparative Example 3 provides a method for preparing spherical gold powder, which is different from Example 4 in that: in step S4, the first dispersant is polyvinyl pyrrolidone, and the second dispersant is polyvinyl pyrrolidone. The other contents are substantially the same as those in Example 4 and will not be described in detail here.

[0094] See also Fig. 9 As shown, the spherical gold powder prepared in Comparative Example 3 has a size between 1-3 μm and a smooth surface. However, in the subsequent process of using the spherical gold powder to prepare gold paste, the gold paste shows obvious stratification, indicating that the spherical gold powder has poor compatibility with the gold paste.

[0095] Comparative Example 4

[0096] Comparative Example 4 provides a method for preparing spherical gold powder, which is different from Example 4 in that: in step S4, the first dispersant is polyvinyl alcohol, and the second dispersant is polyvinyl alcohol. The other contents are substantially the same as those in Example 4 and will not be described in detail here.

[0097] See also Fig.10 As shown, the size of the spherical gold powder prepared in Comparative Example 4 is between 1-2 μm, the size distribution is relatively uneven, and there is partial agglomeration. This shows that the dispersion effect of using single polyvinyl alcohol as a dispersant is poor.

[0098] Those skilled in the art should understand that the size of the spherical gold powder prepared in Example 4 is the most commonly used, so a comparative example is set with reference to Example 4 for comparison.

[0099] The tap density of the spherical gold powder prepared in Example 4 and Comparative Examples 1-4 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. Then, 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 by the formula ρ = m / V. The results are shown in the following table.

[0100]

[0101] Please refer to the above table. By comparison, it can be seen that the spherical gold powder prepared in Example 4 has the highest tap density, indicating that it has the best dispersion effect. However, the spherical gold powders prepared in other comparative examples have poor dispersion effects and low tap densities due to problems such as agglomeration and uneven size distribution.

[0102] In summary, polyvinyl pyrrolidone is used as the first dispersant, which has a better coating effect on spherical gold powder and can make the gold powder more dispersed during the formation process; polyvinyl alcohol is used as the second dispersant for re-coating, which can make the hydroxyl groups in the molecular chain free on the surface of the formed gold powder, which is beneficial to increase the hydrophilicity of the spherical gold powder and its compatibility in the subsequent gold paste. The synergistic effect of the first dispersant and the second dispersant can make the particle size distribution of the prepared spherical gold powder more uniform, so as to solve the problem that the powder is prone to agglomeration when it is smaller in size.

[0103] 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, preparing a first dispersant solution, and then preparing a mixed solution A of a second dispersant and a reducing agent, wherein the first dispersant solution is a polyvinyl pyrrolidone solution, the second dispersant is polyvinyl alcohol, and the reducing agent is ascorbic acid; S3, taking the chloroauric acid solution prepared in step S1 and diluting it, adjusting the pH to 1.5-2 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 mixed solution B; S4, pouring the polyvinyl pyrrolidone solution into the mixed solution B in step S3, stirring evenly, and then quickly adding the mixed solution A, stirring for sufficient reaction, and 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 S2, the polyvinyl pyrrolidone solution is prepared by dissolving polyvinyl pyrrolidone in deionized water, and the concentration of the polyvinyl pyrrolidone solution is 0.05 g / mL.

3. The method for preparing spherical gold powder according to claim 2, characterized in that: In step S2, the preparation method of the mixed solution A is to use deionized water as a solvent, first prepare an ascorbic acid solution with a concentration of 0.18g / mL-0.2g / mL and a polyvinyl alcohol solution with a concentration of 0.05g / mL, and then mix the ascorbic acid solution with the polyvinyl alcohol solution to obtain a mixed solution A.

4. The method for preparing spherical gold powder according to claim 3, characterized in that: In step S4, the mass ratio of the polyvinyl pyrrolidone to the gold in the chloroauric acid solution is (0.1-0.15):1, the mass ratio of the polyvinyl alcohol to the gold in the chloroauric acid solution is (0.1-0.15):1, and the mass ratio of the ascorbic acid to the gold in the chloroauric acid solution is (1.8-2.4):

1.

5. 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-10 g / L.

6. The method for preparing spherical gold powder according to claim 1, characterized in that: In step S4, the dropping speed of the mixed solution A is 140-160 mL / min.

7. The method for preparing spherical gold powder according to claim 1, characterized in that: In step S5, the post-treatment is washing, surface coating, drying and screening; the surface coating agent used is one of oleic acid, gelatin and Tween-80 or a mixture of two of them, and the amount used is 0.2%-2% of the mass of the gold powder.

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