Spherical-like gold nanopowder and method for preparing the same

Abstract

The application provides a preparation method of spherical-like nano gold powder and relates to the technical field of nano material preparation. The preparation method pre-mixes gold source precursor and low-concentration dispersant polyethylene glycol-400 to play a pre-coating role, and the low-concentration and low-molecular-weight weak coordination dispersant polyethylene glycol-400 enables the formation of gold-ether complex in the gold source precursor solution; then, under the protection of high-concentration dispersant, a reduction reaction is carried out to generate nano gold powder with good dispersity; a functional surface coating agent is added to the solution after the reaction, ligand exchange is carried out on the surface of the nano gold powder through the strong coordination ability functional groups of the surface coating agent, stable chemical bonds are formed on the surface of the gold powder, and thus a uniform coating film is formed, the compatibility and wettability of the nano gold powder with common solvents or organic carriers are improved, the low-temperature sintering performance of the nano gold powder is improved, low-temperature sintering can be realized, and the dispersity and stability of the prepared nano gold powder are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of nanomaterial preparation, and in particular to a kind of spherical-like nanometer gold powder and a preparation method thereof. BACKGROUND

[0002] As a key functional material, nanometer gold powder plays an irreplaceable role in electronic conductive paste. Conductive gold paste has excellent chemical stability, conductivity and other excellent properties such as no electron migration in harsh environment and can be used in complex application environment. The demand for advanced electronic components in the fields of 5G communication, radar electronics, aerospace and military is showing explosive growth. These high-end applications have put forward more stringent requirements for gold powder materials in gold paste. Particle size uniformity, morphology regularity and dispersion stability directly determine the performance reliability of the final product.

[0003] At present, the particle size of gold powder for conductive paste on the market is generally concentrated in 1-3 μm, which is relatively large. Higher temperature and time are required to melt large particle size gold powder during sintering, and the layer film formed after sintering is not dense enough, which greatly affects the application effect of subsequent paste printing, packaging materials and the like.

[0004] In the prior art, patent application No. CN 114799198 A provides a preparation method of high-dispersibility nanometer gold powder. The preparation method completes the reaction in an organic phase, and the preparation process requires 3 hours of heating reflux. The reaction temperature is too high, and the reaction time is too long. The reaction conditions are not conducive to large-scale production, and long-time high-temperature reaction can cause gold powder to agglomerate, thereby affecting the application effect.

[0005] Therefore, it is necessary to develop a new preparation method of nanometer gold powder to solve the above problems. SUMMARY

[0006] In view of the defects of the above prior art, the purpose of the present application is to provide a preparation method of spherical-like nanometer gold powder with high dispersibility, regular morphology, high sintering activity and suitable for low-temperature rapid sintering. The method uses low-concentration and low-molecular-weight weakly coordinated dispersant polyethylene glycol-400 to form gold-ether complex in the gold source precursor solution. At the same time, under the protection of a higher concentration of dispersant, a reduction reaction is carried out to generate nanometer gold powder with good dispersibility. A functional surface coating agent is added to the solution after the reaction. The strong coordination ability functional groups of the surface coating agent exchange ligands on the surface of the nanometer gold powder, form stable chemical bonds on the surface of the gold powder, and thus form a uniform coating film. The compatibility and wettability of the nanometer gold powder with common solvents or organic carriers are improved, the low-temperature sintering performance of the nanometer gold powder is improved, low-temperature sintering can be realized, and the nanometer gold powder can be applied in the field of low-temperature sintering gold paste.

[0007] To achieve the above object, the application provides a preparation method of spherical-like gold nanopowder, comprising the following steps:

[0008] S1, preparing a first dispersant solution with a first concentration and a second dispersant solution with a second concentration respectively by using ultrapure water as a solvent; the first dispersant and the second dispersant are both polyethylene glycol-400;

[0009] S2, dissolving solid chloroauric acid in the first dispersant solution to obtain a gold source precursor mixed solution A;

[0010] S3, dissolving a reducing agent in the second dispersant solution to obtain a reducing agent mixed solution B;

[0011] S4, dropping the gold source precursor mixed solution A into the reducing agent mixed solution B at 25-40 DEG C, reacting for 2-5 min, adding a functional surface coating agent into the solution after reaction, and continuing to react for 5-15 min; after standing, separation, washing and low-temperature freeze drying, the spherical-like gold nanopowder is obtained.

[0012] Further, in step S2, the molar ratio of chloroauric acid to the first dispersant is 1: (1-2.5).

[0013] Further, in step S3, the reducing agent is ascorbic acid; and the molar ratio of the reducing agent to the second dispersant is 1: (1-3).

[0014] Further, the functional surface coating agent is one or a mixture of more than one of oleic acid, ricinoleic acid, stearic acid, lauric acid, n-hexanoic acid, n-octanoic acid, hydrogenated rosin, Tween 20, Tween 40, Tween 80, octylamine, dodecylamine and hexadecylamine.

[0015] Further, in step S4, the amount of the functional surface coating agent is 0.2-4 wt% of the mass of chloroauric acid.

[0016] Further, the first concentration is 0.1-0.4 mol / L, and the second concentration is 0.5-1.5 mol / L.

[0017] Further, in step S4, the washing mode is that water and 0.1 mol / L Na2CO3 are used to wash alternately for 3-5 times until the conductivity of supernatant is less than 5 μs / cm.

[0018] Further, in step S4, the low-temperature freeze drying refers to vacuum drying at-40 ~ -50 DEG C for 10-15 h.

[0019] Further, the dropping speed of the gold source precursor mixed solution A into the reducing agent mixed solution B is 20-50 mL / min.

[0020] The application also provides the quasi-spherical gold nanopowder prepared by the preparation method, the particle size of the quasi-spherical gold nanopowder is 100-500 nm, the morphology is a single-dispersed quasi-spherical morphology, and the quasi-spherical gold nanopowder is suitable for low-temperature sintering at 200-300 DEG C.

[0021] The application has the following beneficial effects:

[0022] 1. The preparation method of the quasi-spherical gold nanopowder provided by the application, the gold source precursor is pre-mixed with low-concentration dispersant polyethylene glycol-400, which plays a pre-coating role, the weak coordination dispersant polyethylene glycol-400 with low concentration and low molecular weight enables the formation of a gold-ether complex in the gold source precursor solution; then, under the protection of a dispersant with a higher concentration, a reduction reaction is carried out to generate a well-dispersed gold nanopowder; a functional surface coating agent is added to the solution after the reaction, and the strong coordination ability functional groups of the surface coating agent are used to exchange ligands on the surface of the gold nanopowder, so that a stable chemical bond is formed on the surface of the gold powder, thereby forming a uniform coating film, which can improve the compatibility and wettability of the gold nanopowder with common solvents or organic carriers, improve the low-temperature sintering performance of the gold nanopowder, and realize low-temperature sintering, so that the preparation method can be applied to the field of low-temperature sintering gold slurry and improve the dispersibility and stability of the prepared gold nanopowder.

[0023] 2. The preparation method of the quasi-spherical gold nanopowder provided by the application can adjust the particle size of the prepared gold nanopowder by adjusting the molar ratio of the gold source precursor and the low-concentration dispersant polyethylene glycol-400 during pre-mixing.

[0024] 3. The application uses a low-temperature freeze-drying method instead of a traditional high-temperature drying method, so that the gold nanopowder maintains good dispersibility. The problem of agglomeration caused by the small particle size and the excessively large surface energy of the gold nanopowder in the prior art is avoided, the Brownian motion between particles is intensified with the increase of temperature, and the agglomeration between particles is accelerated. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 The scanning electron microscope image of the gold nanopowder prepared in Example 1.

[0026] Figure 2 The scanning electron microscope image of the gold nanopowder prepared in Example 1 after low-temperature sintering.

[0027] Figure 3 The scanning electron microscope image of the gold nanopowder prepared in Comparative Example 1.

[0028] Figure 4 The scanning electron microscope image of the gold nanopowder prepared in Comparative Example 1 after low-temperature sintering.

[0029] Figure 5 The scanning electron microscope image of the gold nanopowder prepared in Comparative Example 2.

[0030] Figure 6 A scanning electron microscope image of the dried nanogold powder in Comparative Example 3.

[0031] Figure 7 A scanning electron microscope image of the nanogold powder prepared in Example 2.

[0032] Figure 8 A scanning electron microscope image of the nanogold powder prepared in Example 3.

[0033] Figure 9 A scanning electron microscope image of the nanogold powder prepared in Example 4 after low-temperature sintering. DETAILED DESCRIPTION

[0034] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be described in detail below with reference to the accompanying drawings and specific examples.

[0035] It should also be noted here that, in order to avoid the present application being obscured by unnecessary details, only structures and / or processing steps closely related to the solutions of the present application are shown in the accompanying drawings, and other details not closely related to the present application are omitted.

[0036] It should also be noted that the terms "comprise", "contain" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such a process, method, article or device.

[0037] In the prior art, the particle size of the gold powder used in the conductive paste is generally concentrated in 1-3 μm, which is relatively large. High temperature (>1000℃) and long time (>5h) are required to melt the large particle size gold powder during sintering, and the layer film formed after sintering is not dense enough, which greatly affects the subsequent application effects of paste printing, packaging materials, etc. Therefore, a nanogold powder with high sintering activity and suitable for low-temperature rapid sintering is needed to solve this problem.

[0038] The application provides a preparation method of spherical-like nanometer gold powder, and the gold-ether complex is formed in a gold source precursor solution by using a low-concentration and low-molecular-weight weak coordination dispersant polyethylene glycol-400, and a reduction reaction is carried out under the protection of a high-concentration dispersant to generate nanometer gold powder with good dispersity; a functional surface coating agent is added into the solution after the reaction, ligand exchange is carried out on the surface of the nanometer gold powder by using the strong coordination ability functional groups of the surface coating agent, stable chemical bonds are formed on the surface of the gold powder, and thus a uniform coating film is formed, the compatibility and wettability of the nanometer gold powder with common solvents or organic carriers are improved, the low-temperature sintering performance of the nanometer gold powder is improved, and low-temperature sintering can be realized, and the nanometer gold powder can be applied to the field of low-temperature sintering gold slurry.

[0039] The application provides a preparation method of spherical-like nanometer gold powder, and the gold-ether complex is formed in a gold source precursor solution by using a low-concentration and low-molecular-weight weak coordination dispersant polyethylene glycol-400, and a reduction reaction is carried out under the protection of a high-concentration dispersant to generate nanometer gold powder with good dispersity; a functional surface coating agent is added into the solution after the reaction, ligand exchange is carried out on the surface of the nanometer gold powder by using the strong coordination ability functional groups of the surface coating agent, stable chemical bonds are formed on the surface of the gold powder, and thus a uniform coating film is formed, the compatibility and wettability of the nanometer gold powder with common solvents or organic carriers are improved, the low-temperature sintering performance of the nanometer gold powder is improved, and low-temperature sintering can be realized, and the nanometer gold powder can be applied to the field of low-temperature sintering gold slurry.

[0040] S1, a first dispersant solution with a first concentration and a second dispersant solution with a second concentration are respectively prepared by using ultrapure water as a solvent; the first dispersant and the second dispersant are both polyethylene glycol-400;

[0041] The first concentration is 0.1-0.4 mol / L, and the second concentration is 0.5-1.5 mol / L.

[0042] S2, solid chloroauric acid is dissolved in the first dispersant solution to obtain a gold source precursor mixed solution A;

[0043] The molar ratio of chloroauric acid to the first dispersant is 1: (1-2.5).

[0044] S3, a reducing agent is dissolved in the second dispersant solution to obtain a reducing agent mixed solution B;

[0045] The reducing agent is ascorbic acid; the molar ratio of the reducing agent to the second dispersant is 1: (1-3).

[0046] S4, the gold source precursor mixed solution A is dropped into the reducing agent mixed solution B at 25-40 DEG C, and reacts for 2-5 min; a functional surface coating agent is added into the solution after the reaction, and continues to react for 5-15 min; after standing, settling, separation, washing and low-temperature freeze drying, the spherical-like nanometer gold powder is obtained.

[0047] The dropping speed of the gold source precursor mixed solution A into the reducing agent mixed solution B is 20-50 mL / min.

[0048] The functional surface coating agent is one or a mixture of more than one of oleic acid, ricinoleic acid, stearic acid, lauric acid, n-hexanoic acid, n-octanoic acid, hydrogenated rosin, Tween 20, Tween 40, Tween 80, octylamine, dodecylamine and hexadecylamine.

[0049] The functional surface coating agent is used in an amount of 0.2-4wt% of the mass of chloroauric acid.

[0050] The washing method is: using water and 0.1mol / L Na2CO3 to clean alternately for 3-5 times until the conductivity of the supernatant is <5 μs / cm.

[0051] The low-temperature freeze drying refers to vacuum drying for 10-15h at-40 ~ -50℃.

[0052] The application further provides a kind of spherical gold nano powder, the particle size of the gold nano powder is 100-500nm, the morphology is monodisperse spherical morphology, and is suitable for 200-300℃ low-temperature sintering.

[0053] The preparation method of the spherical gold nano powder provided by the application will be described below in combination with specific examples. Unless otherwise specified, the raw materials and reagents in the examples of the application are purchased through commercial channels.

[0054] Example 1

[0055] The embodiment provides a preparation method of a spherical gold nano powder, which specifically comprises the following steps:

[0056] S1, 30mL of 0.4mol / L polyethylene glycol-400 solution is prepared as a first dispersant solution with ultrapure water as a solvent; 50mL of 0.75mol / L polyethylene glycol-400 solution is prepared as a second dispersant solution;

[0057] S2, preparation of gold source precursor mixed solution A: 2g of solid chloroauric acid is dissolved in the first dispersant solution to form solution A.

[0058] S3, preparation of reducing agent mixed solution B: 2.6g of ascorbic acid is dissolved in the second dispersant solution to form solution B.

[0059] S4, preparation of gold nano powder: under the condition of constant temperature at 30℃, solution A is dropped into solution B at a dropping speed of 40mL / min, and the reaction is continued for 3min; 0.005g of Span 80 and hydrogenated rosin 1:1 mixture is added to the solution after reaction, and the reaction is continued for 10min under sufficient stirring. After standing, separation, and cleaning with water and 0.1mol / L Na2CO3 solution alternately until the conductivity is <5 μs / cm, the spherical gold nano powder is obtained through low-temperature freeze drying.

[0060] The SEM image of the gold nano powder prepared in Example 1 is shown in Figure 1 It can be seen that the particle size range is about 200-300nm, the morphology is regular spherical morphology, and the dispersion is good without agglomeration.

[0061] Low-temperature sintering can be achieved under constant temperature conditions at 200°C, and the SEM image of the gold powder after sintering is shown in Figure 2 .

[0062] Comparative Example 1

[0063] Comparative Example 1 provides a preparation method of nano-gold powder, which is mainly different from Example 1 in that the first dispersant and the second dispersant used are both high-molecular-weight polyvinylpyrrolidone. The specific steps are as follows:

[0064] S1, preparation of dispersant solution: 30 mL of 0.001 mol / L polyvinylpyrrolidone as the first dispersant solution was prepared with ultrapure water as the solvent; 50 mL of 0.003 mol / L polyvinylpyrrolidone as the second dispersant solution was prepared;

[0065] S2, preparation of gold source precursor mixed solution A: 2 g of solid chloroauric acid was dissolved in the first dispersant solution to form solution A;

[0066] S3, preparation of reducing agent mixed solution B: 2.6 g of ascorbic acid was dissolved in the second dispersant solution to form solution B;

[0067] S4, preparation of nano-gold powder: under constant temperature conditions at 30°C, solution A was added to solution B at a drop rate of 40 mL / min, 0.005 g of a 1:1 mixture of Span 80 and hydrogenated rosin was added to the reaction solution, and the reaction was continued for 10 min under sufficient stirring. After standing, separation, and washing with water and 0.1 mol / L Na2CO3 solution alternately until the conductivity was <10 μs / cm, low-temperature freeze-drying was performed to obtain spherical nano-gold powder.

[0068] The SEM image of the nano-gold powder obtained in Comparative Example 1 is shown in Figure 3 , and the particle size range is about 200-300 nm.

[0069] Under constant temperature conditions at 200°C, the SEM image of the sintered gold powder is shown in Figure 4 .

[0070] It can be seen that the sintered gold powder is still granular, and no sintering neck is generated. Since polyvinylpyrrolidone is used as a nanometer gold powder dispersant, even if the amount of polyethylene glycol-400 is less than that of polyvinylpyrrolidone, the nitrogen element in polyvinylpyrrolidone can form a strong coordination chemical bond Au-N with the surface of gold. The subsequent addition of a functional surface coating agent cannot replace the polyvinylpyrrolidone on the surface of the gold powder, which greatly affects the sintering performance. In addition, due to the strong intermolecular coordination of Au-N, the cleaning process is very difficult, and the same cleaning method and cleaning times cannot reduce the conductivity of the gold powder to less than 5 μs / cm. The residual polyvinylpyrrolidone also has a great influence on the sintering performance.

[0071] Comparative Example 2

[0072] Comparative Example 2 provides a preparation method of nanometer gold powder, which is mainly different from Example 1 in that the entire amount of dispersant is added to the reducing agent, and the dispersant is not pre-mixed with chloroauric acid. The specific steps are as follows:

[0073] S1, preparation of dispersant solution: 50 mL of 0.99 mol / L polyethylene glycol-400 is prepared as a dispersant with ultrapure water as a solvent;

[0074] S2, preparation of gold source precursor solution A: 2 g of solid chloroauric acid is dissolved in 30 mL of ultrapure water to form solution A;

[0075] S3, preparation of reducing agent mixed solution B: 2.6 g of ascorbic acid is dissolved in the dispersant to form solution B;

[0076] S4, preparation of nanometer gold powder: under the condition of constant temperature at 30°C, solution A is added to solution B at a drop rate of 40 mL / min, 0.005 g of a mixture of Span 80 and hydrogenated rosin at a ratio of 1:1 is added to the solution after the reaction, and the reaction is continued for 10 min under sufficient stirring. After standing, separation, and cleaning with water and 0.1 mol / L Na2CO3 solution alternately until the conductivity is <5 μs / cm, the spherical nanometer gold powder is obtained by low-temperature freeze drying.

[0077] The SEM image of the nanometer gold powder obtained in Comparative Example 2 is shown in Figure 5 The particle size range is about 200-300 nm, and there is agglomeration between the particles. It can be seen that the pre-mixing of chloroauric acid and dispersant can achieve the pre-coating of the dispersant on the surface of chloroauric acid, which can increase the dispersibility and stability of the nanometer gold powder in the subsequent reaction process.

[0078] Comparative Example 3

[0079] Comparative Example 3 provides a preparation method of the spherical gold nanopowder, which is different from Example 1 in that, in step S4, the low-temperature freeze-drying method is replaced by the 80℃ air-drying method. The rest is basically the same as Example 1, which is not described here.

[0080] Figure 6 The SEM image of the gold powder after drying in Comparative Example 3 can be seen that there is obvious agglomeration between the particles. Due to the excessively high surface energy of the gold nanopowder, high drying temperature will intensify the collision movement between the particles, thus producing irreversible agglomeration phenomenon, which greatly affects the sintering performance.

[0081] Example 2-3

[0082] Example 2-3 provides a preparation method of the spherical gold nanopowder, which is different from Example 1 in that, in step S2, the molar ratio of chloroauric acid to the first dispersant is different. The specific values are shown in the following table. The rest is basically the same as Example 1, which is not described here.

[0083]

[0084] Figure 7 The SEM image of the gold nanopowder prepared in Example 2 can be seen that the particle size range of the gold nanopowder is about 300-500nm.

[0085] Figure 8 The SEM image of the gold nanopowder prepared in Example 3 can be seen that the particle size range of the gold nanopowder is about 100-200nm.

[0086] From the above table, it can be seen that as the molar ratio of chloroauric acid to the first dispersant increases, the particle size of the prepared gold nanopowder increases.

[0087] Example 4

[0088] Example 4 provides a preparation method of the spherical gold nanopowder, which is different from Example 1 mainly in that the type and amount of the functional surface dispersant in step S4 are changed. The other experimental parameters are basically the same as Example 1, which is not described here.

[0089] Specifically, the 0.005g Tween 80 and hydrogenated rosin 1:1 mixture in Example 1 is replaced by 0.01g n-octanoic acid and Tween 20 1:1 mixture.

[0090] The gold nanopowder obtained in Example 4 can realize low-temperature sintering under the condition of constant temperature at 200℃, and the SEM image of the sintered gold powder is shown in Figure 9

[0091] ​It should be noted that the functional surface coating agent can be one or more of oleic acid, ricinoleic acid, stearic acid, lauric acid, n-hexanoic acid, n-octanoic acid, hydrogenated rosin, Tween 20, Tween 40, Tween 80, octylamine, dodecylamine, hexadecylamine, or a mixture thereof.

[0092] The above examples are only used to illustrate the technical solutions of the present application and are not limiting. Although the present application has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solutions of the present application can be modified or replaced equivalently without departing from the spirit and scope of the technical solutions of the present application.

Claims

1. A method for preparing a spheroid-like gold nanopowder, characterized by, Includes the following steps: S1, using ultrapure water as a solvent, prepare a first dispersant solution of a first concentration and a second dispersant solution of a second concentration; both the first and second dispersants are polyethylene glycol-400; the first concentration is 0.1-0.4 mol / L, and the second concentration is 0.5-1.5 mol / L; S2, dissolve solid chloroauric acid in the first dispersant solution to obtain a gold source precursor mixed solution A; S3, dissolve the reducing agent in the second dispersant solution to obtain a reducing agent mixed solution B; S4. At 25-40℃, the gold source precursor mixed solution A is added dropwise to the reducing agent mixed solution B, and the reaction is carried out for 2-5 minutes. A functional surface coating agent is added to the solution after the reaction, and the reaction is continued for 5-15 minutes. After standing and settling, separation, washing, and low-temperature freeze drying, spherical gold nanoparticles are obtained.

2. The method of claim 1, wherein the method is characterized by: In step S2, the molar ratio of chloroauric acid to the first dispersant is 1:(1-2.5).

3. The method of claim 1, wherein the method is characterized by: In step S3, the reducing agent is ascorbic acid; the molar ratio of the reducing agent to the second dispersant is 1:(1-3).

4. The method of claim 1, wherein the method is characterized by: The functional surface coating agent is one or more of the following: oleic acid, ricinoleic acid, stearic acid, lauric acid, hexanoic acid, octanoic acid, hydrogenated rosin, Tween 20, Tween 40, Tween 80, octylamine, dodecylamine, and hexadecylamine.

5. The method for preparing near-spherical gold nanopowder according to claim 1, characterized in that: In step S4, the amount of the functional surface coating agent is 0.2-4 wt% of the mass of chloroauric acid.

6. The method for preparing near-spherical gold nanopowder according to claim 1, characterized in that: In step S4, the washing method is as follows: wash with water and 0.1 mol / L Na2CO3 alternately 3-5 times until the conductivity of the supernatant is <5 μs / cm.

7. The method for preparing near-spherical gold nanopowder according to claim 1, characterized in that: In step S4, the low-temperature freeze drying refers to vacuum drying at -40 ~ -50℃ for 10-15 hours.

8. The method for preparing near-spherical gold nanopowder according to claim 1, characterized in that: The dropping rate of the Jinyuan precursor mixed solution A into the reducing agent mixed solution B is 20-50 mL / min.

9. A quasi-spherical gold nanopowder, characterized in that: The spherical gold nanoparticles are prepared by the preparation method described in any one of claims 1-8. The particle size of the nanoparticles is 100-500 nm, and the morphology is monodisperse and spherical. They are suitable for low-temperature sintering at 200-300℃.

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