Preparation method of smooth spherical gold powder with narrow particle size distribution and low organic residue rate

Abstract

The present invention relates to the technical field of precious metal powders, and provides a method for preparing smooth spherical gold powder with a narrow particle size distribution and a low organic residue rate. The present invention uses a water-n-propanol mixed solvent system to prepare gold powder, which can appropriately increase the solution viscosity, reduce the ion diffusion rate, slow down the reaction rate, and promote the uniform growth of the formed gold crystal nuclei, resulting in gold powder with a relatively uniform particle size distribution. At the same time, the present invention disperses the gold-containing precipitate obtained by the reduction reaction in a treatment liquid with strong oxidizing properties, and removes the organic matter remaining on the surface of the gold powder particles through ultrasonic treatment. The gold powder prepared by the present invention has a low organic residue rate, a smooth surface without attachments, a uniform and controllable particle size, high dispersibility, and high sphericity. It can be used to prepare gold conductor pastes, and the preparation process is simple, the batch repetition stability is high, and large-scale production can be carried out.

Description

Technical Field

[0001] The present invention relates to the technical field of precious metal powders, and particularly to a method for preparing smooth spherical gold powder with a narrow particle size distribution and a low organic residue rate. Background Art

[0002] With the high-quality and rapid development of the electronic information industry, electronic products are developing towards miniaturization, integration, and high frequency, and the requirements for thick film integrated circuits, which are relatively widely used in them, are also increasing. Therefore, the quality requirements for thick film paste technology are beyond doubt. Gold conductor paste is widely used in military devices, automotive electronic components, aerospace and other fields due to its excellent conductivity, stability, and high reliability. However, as the application conditions become more and more stringent, the performance of gold conductor paste also needs to be continuously improved to meet the application requirements.

[0003] The particle size, morphology, and the organic residue rate on the particle surface of gold powder have crucial effects on the performance of the gold conductor paste film layer. A low organic residue rate can avoid the blistering problem of the sintered film layer. The smooth spherical particles without surface adsorption have good fluidity between them, which is convenient for the infiltration of glass, beneficial to the densification of gold paste sintering, and further promotes the improvement of conductivity. Moreover, using gold powder particles within a suitable particle size range as the conductive phase to prepare gold paste is also beneficial to the improvement of the adhesion of gold conductor paste. Existing practices have proved that the conductive phase that is relatively useful in the application of gold conductor paste is gold powder particles with no adsorption on the particle surface, a narrow particle size distribution, and different particle sizes based on the narrow particle size distribution. In the prior art, the liquid-phase chemical reduction method is mostly used to prepare gold powder. This method has a simple process flow and is easy to operate, but the obtained gold powder has a high organic residue rate, resulting in problems such as blistering and incomplete sintering in the subsequent gold paste film layer, and the morphology and particle size of the gold powder are not easy to control, causing poor batch stability in the production process. To address the problem of high organic residue rate, some researchers use ozone oxidation treatment techniques to treat prefabricated gold powder to obtain spherical gold powder without organic substances and with better sintering reaction activity, but it is not easy to produce in large quantities.

[0004] In summary, the current gold powder preparation methods have problems such as high organic residue rate, difficult control of morphology and particle size, poor batch stability, and are not conducive to mass production. There is an urgent need to provide a new preparation method to solve the above problems and meet the application requirements of gold conductor paste. Summary of the Invention

[0005] In view of this, the present invention provides a method for preparing smooth spherical gold powder with a narrow particle size distribution and a low organic residue rate. The gold powder prepared by the preparation method provided by the present invention has a low organic residue rate, a narrow particle size distribution, a smooth surface without adsorbed substances, good dispersibility, a high sphericity, and is simple to operate, with high batch repeat stability, and can achieve mass production, effectively solving the problems of high organic residue rate, difficult control of morphology and particle size, and poor batch stability in the preparation of gold powder.

[0006] In order to achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0007] A method for preparing smooth spherical gold powder with a narrow particle size distribution and a low organic residue rate, comprising the following steps:

[0008] Mix a chloroauric acid solution and a water-n-propanol mixed solvent, and adjust the pH value of the obtained mixed solution to 3-6 to obtain a reaction gold source solution;

[0009] Mix a surfactant solution and the reaction gold source solution to obtain a pre-reaction solution;

[0010] Mix a reducing agent solution and the pre-reaction solution to carry out a reduction reaction, and sequentially carry out aging and solid-liquid separation on the obtained reaction solution to obtain a gold-containing precipitate;

[0011] Perform ultrasonic treatment on the gold-containing precipitate in a treatment solution, and then sequentially carry out solid-liquid separation and drying to obtain the smooth spherical gold powder with a narrow particle size distribution and a low organic residue rate; the solute in the treatment solution includes one or more of hydrogen peroxide, potassium permanganate, and sodium hypochlorite.

[0012] Preferably, the mass concentration of gold ions in the chloroauric acid solution is 50 wt%; the concentration of gold ions in the reaction gold source solution is 10-50 g / L; the mixing of the chloroauric acid solution and the water-n-propanol mixed solvent is carried out under water bath and stirring conditions, the temperature of the water bath is 20-50 °C, and the stirring rate is 200-500 rpm.

[0013] Preferably, the surfactant includes one or more of glucose, gum arabic, polyvinylpyrrolidone, sodium polyacrylate, and dopamine; the mass ratio of the surfactant to gold ions in the reaction gold source solution is 0.03-0.3:1; the solvent of the surfactant solution is water or n-propanol.

[0014] Preferably, the reducing agent includes one or more of hydrazine hydrate, sodium citrate, ascorbic acid, and sodium phosphite; the solvent of the reducing agent solution is water; the molar ratio of the reducing agent to gold ions in the reaction gold source solution is 3-6:1; the volume ratio of the water-n-propanol mixed solvent to the solvent in the reducing agent solution is 10:1-30:1.

[0015] Preferably, the reducing agent solution is prepared by adding a reducing agent to water, stirring and dissolving it under a water bath condition, and then cooling to obtain the reducing agent solution; the temperature of the water bath is 50-80°C.

[0016] Preferably, in the system obtained by mixing the reducing agent solution and the pre-reaction solution, the volume ratio of water to n-propanol is 999:1-1:5;

[0017] The reducing agent solution is added dropwise to the pre-reaction solution for a reduction reaction, and the dropping rate is 1-4 mL / s.

[0018] Preferably, when the solute in the treatment solution includes hydrogen peroxide, the concentration of hydrogen peroxide in the treatment solution is 1-20 wt%; when the solute in the treatment solution includes potassium permanganate, the concentration of potassium permanganate in the treatment solution is 0.005-0.1 wt%; when the solute in the treatment solution includes sodium hypochlorite, the concentration of sodium hypochlorite in the treatment solution is 0.1-3 wt%.

[0019] Preferably, the temperature of the reduction reaction is 20-50°C, and the reaction time is 1-2 h.

[0020] Preferably, the temperature of the aging is room temperature, and the time is 10-120 min.

[0021] Preferably, the organic residue rate of the smooth spherical gold powder with a narrow particle size distribution and a low organic residue rate is ≤1.6‰, and the difference between the D90 particle size and the D10 particle size is ≤0.75 μm.

[0022] The present invention provides a method for preparing smooth spherical gold powder with a narrow particle size distribution and a low organic residue rate, comprising the following steps: mixing a chloroauric acid solution and a water-n-propanol mixed solvent, adjusting the pH value of the obtained mixed solution to 3-6 to obtain a reaction gold source solution; mixing a surfactant solution and the reaction gold source solution to obtain a pre-reaction solution; mixing a reducing agent solution and the pre-reaction solution for a reduction reaction, subjecting the obtained reaction solution to aging and solid-liquid separation in sequence to obtain a gold-containing precipitate; performing ultrasonic treatment on the gold-containing precipitate in a treatment solution, and then performing solid-liquid separation and drying in sequence to obtain the smooth spherical gold powder with a narrow particle size distribution and a low organic residue rate; the solute in the treatment solution includes one or more of hydrogen peroxide, potassium permanganate, and sodium hypochlorite. Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] 1. The solvent system of the present invention uses a water-n-propanol mixed solvent, which can appropriately increase the solution viscosity, reduce the ion diffusion rate, slow down the reaction rate, and the change of crystal nuclei is very slow after reaching supersaturation. Subsequently, more gold ions are reduced for the growth of crystal nuclei, promoting the uniform growth of grains and obtaining gold powder particles with a relatively uniform particle size distribution. Thus, the uniformity and dispersibility of gold powder particles are significantly improved, effectively promoting the densification of the sintered film layer. Further, by adjusting the ratio of water to alcohol in the mixed solvent, the viscosity of the solvent system can be adjusted, indirectly adjusting the ion diffusion rate in the solution, and then achieving good control of the particle size of gold powder particles, and the obtained gold powder has a relatively uniform particle size distribution.

[0024] 2. The treatment liquid used in the present invention has strong oxidizing property. Ultrasonic dispersing the preliminarily prepared gold powder precipitate in the treatment liquid can remove the organic matter on the surface of gold powder by oxidation, reduce the organic matter residue rate of gold powder, obtain gold powder particles with a smooth surface and no organic matter adsorption, and improve the foaming problem caused by incomplete removal of organic matter on the surface of gold powder particles during the sintering process of gold conductor paste.

[0025] 3. Further, the present invention prepares gold powder by adding a small amount of reducing agent solution to a large amount of pre-reaction liquid, reducing the change of the reaction environment brought by the introduction of a large amount of additional solution, ensuring that the growth environment of gold crystal nuclei is as consistent as possible during the formation and growth process, so as to obtain particles with the same particle size.

[0026] In summary, the present invention uses the liquid-phase chemical reduction method to prepare gold powder. The obtained gold powder has a low organic residue rate, a narrow particle size distribution, a smooth surface without adsorbents, good dispersibility, high sphericity, and controllable particle size. The results of the examples show that the organic residue rate of the spherical gold powder prepared by the present invention can be as low as 0.73‰, and the difference between D90 and D10 can reach 0.25 μm; the gold powder prepared by the present invention can be formulated into a gold conductor paste with excellent printing performance, sintering performance and electrical conductivity; at the same time, the preparation method provided by the present invention has a simple process, convenient operation, good batch repeat stability of the prepared gold powder, and can achieve large-scale production. Description of the Drawings

[0027] Figure 1 SEM image of the gold powder obtained in Example 1;

[0028] Figure 2 Thermogravimetric curve of the gold powder obtained in Example 1;

[0029] Figure 3 Particle size distribution diagram of the gold powder obtained in Example 1;

[0030] Figure 4 Particle size distribution diagram of the gold powder obtained in Example 2;

[0031] Figure 5SEM image of the gold powder obtained in Comparative Example 2;

[0032] Figure 6 Particle size distribution diagram of the gold powder obtained in Comparative Example 2;

[0033] Figure 7 SEM image of the gold powder obtained in Comparative Example 3;

[0034] Figure 8 Particle size distribution diagram of the gold powder obtained in Comparative Example 3. Detailed implementation mode

[0035] The present invention provides a preparation method of smooth spherical gold powder with a narrow particle size distribution and a low organic residue rate, comprising the following steps:

[0036] Mix a chloroauric acid solution and a water - n - propanol mixed solvent, and adjust the pH value of the obtained mixed solution to 3 - 6 to obtain a reaction source solution;

[0037] Mix a surfactant solution and the reaction source solution to obtain a pre - reaction solution;

[0038] Mix a reducing agent solution and the pre - reaction solution for a reduction reaction, and subject the obtained reaction solution to aging and solid - liquid separation in sequence to obtain a gold - containing precipitate;

[0039] Perform ultrasonic treatment on the gold - containing precipitate in a treatment solution, and then perform solid - liquid separation and drying in sequence to obtain the smooth spherical gold powder with a narrow particle size distribution and a low organic residue rate; the solute in the treatment solution includes one or more of hydrogen peroxide, potassium permanganate, and sodium hypochlorite.

[0040] The present invention mixes a chloroauric acid solution and a water - n - propanol mixed solvent, and adjusts the pH value of the obtained mixed solution to 3 - 6 to obtain a reaction source solution. In the present invention, the mass concentration of gold ions in the chloroauric acid solution is preferably 30 - 60 wt%, more preferably 50 wt%, and the solvent of the chloroauric acid solution is water.

[0041] In the present invention, the mixing of the chloroauric acid solution and the water - n - propanol mixed solvent is carried out under water - bath and stirring conditions. The temperature of the water - bath is preferably 20 - 50 °C, the stirring rate is preferably 200 - 500 rpm, the concentration of gold ions in the reaction source solution is preferably 10 - 50 g / L, more preferably 10 - 20 g / L; the reagent used to adjust the pH value of the mixed solution is preferably a weak alkaline solution, more preferably ammonia water; the present invention preferably adjusts the pH value of the mixed solution to 4.

[0042] After obtaining the reaction gold source solution, the present invention mixes the surfactant solution and the reaction gold source solution to obtain a pre-reaction solution. In the present invention, the surfactant preferably includes one or more of glucose, gum arabic, polyvinylpyrrolidone, sodium polyacrylate, and dopamine; the mass ratio of the surfactant to the gold ions in the reaction gold source solution is preferably 0.03-0.3:1, more preferably 0.05-0.2:1; the solvent of the surfactant solution is preferably water or alcohol, and the alcohol is preferably n-propanol; the concentration of the surfactant solution is preferably 40-50 g / L, more preferably 40 g / L; the volume ratio of the water-n-propanol mixed solvent to the solvent in the surfactant solution is preferably 10:1-30:1, more preferably 15:1-25:1.

[0043] After obtaining the pre-reaction solution, the present invention mixes the reducing agent solution and the pre-reaction solution to carry out a reduction reaction, and the obtained reaction solution is subjected to aging and solid-liquid separation in sequence to obtain a gold-containing precipitate. In the present invention, the reducing agent preferably includes one or more of hydrazine hydrate, sodium citrate, ascorbic acid, and sodium phosphite; the solvent of the reducing agent solution is preferably water; the molar ratio of the reducing agent to the gold ions in the reaction gold source solution is 3-6:1; the volume ratio of the water-n-propanol mixed solvent to the solvent in the reducing agent solution is preferably 10:1-30:1, more preferably 15:1-25:1; the preparation method of the reducing agent solution is preferably: adding the reducing agent to water, stirring and dissolving under a water bath condition, and then cooling to obtain the reducing agent solution; the temperature of the water bath is preferably 50-80 °C.

[0044] In the present invention, in the system obtained by mixing the reducing agent solution and the pre-reaction solution, the volume ratio of water to n-propanol is preferably 999:1-1:5, more preferably 100:1-1:5, further preferably 10:1-1:5, and even more preferably 1:1 or 3:7 (that is, the volume ratio of the two is calculated based on the total amount of water or n-propanol used in the water-n-propanol mixed solvent, the surfactant solution, and the reducing agent solution); the volume ratio of water to n-propanol in the water-n-propanol mixed solvent used for preparing the reaction gold source solution can be calculated according to the volume ratio of water to n-propanol in the target mixed system, the volume of the solvent in the reduction solution, and the volume of the solvent in the surfactant solution. The present invention uses a water-n-propanol mixed solvent as the reaction system solvent, which causes a slight increase in the solution viscosity, slows down the ion diffusion rate, slows down the crystal nucleation rate, and more gold ions are used for crystal nucleus growth after reduction, promoting the uniform growth of grains, improving the uniformity of particle distribution, and effectively promoting the densification of the sintered film layer. When the solvent system is a single solvent water, the ion diffusion rate is fast, the crystal nucleation rate is fast, and grains are continuously growing while crystal nuclei are continuously generated, so the phenomenon of uneven particle size distribution appears.

[0045] In the present invention, it is preferred to drop the reducing agent solution into the pre-reaction solution for the reduction reaction. The dropping rate is preferably 1-4 mL / s, more preferably 1.6-3 mL / s; the temperature of the reduction reaction is preferably 20-50 °C. In the specific embodiments of the present invention, the reduction reaction is preferably carried out at 40 °C; the time of the reduction reaction is preferably 1-2 h, more preferably 1 h, and the time of the reduction reaction is counted from the completion of the dropping of the reducing agent solution.

[0046] In the present invention, the temperature of the aging is preferably room temperature, and the time is preferably 10-120 min, more preferably 15 min; the method of solid-liquid separation is preferably centrifugation, and the solid obtained by centrifugation is the gold-containing precipitate.

[0047] After obtaining the gold-containing precipitate, the present invention performs ultrasonic treatment on the gold-containing precipitate in the treatment solution, followed by solid-liquid separation and drying in sequence to obtain the smooth spherical gold powder with a narrow particle size distribution and a low organic residue rate. In the present invention, the solute in the treatment solution includes one or more of hydrogen peroxide, potassium permanganate, and sodium hypochlorite. When the solute in the treatment solution includes hydrogen peroxide, the concentration of hydrogen peroxide in the treatment solution is preferably 1-20 wt%, more preferably 2-8 wt%; when the solute in the treatment solution includes potassium permanganate, the concentration of potassium permanganate in the treatment solution is preferably 0.005-0.1 wt%, more preferably 0.006-0.01 wt%; when the solute in the treatment solution includes sodium hypochlorite, the concentration of sodium hypochlorite in the treatment solution is preferably 0.1-3 wt%, more preferably 0.5-2.5 wt%. In the specific embodiments of the present invention, the treatment solution is preferably a hydrogen peroxide solution or preferably a hydrogen peroxide-potassium permanganate mixed solution. The concentration of the hydrogen peroxide solution is preferably 1-20 wt%, and the concentration of hydrogen peroxide in the hydrogen peroxide-potassium permanganate mixed solution is preferably 1-20 wt%, and the concentration of potassium permanganate is preferably 0.005-0.1 wt%. In the present invention, when a hydrogen peroxide-potassium permanganate mixed solution is used as the treatment solution, hydrogen peroxide and potassium permanganate will react to a certain extent, generating a small amount of MnO2 as a catalyst to accelerate the reaction process, with higher treatment efficiency and shorter required time.

[0048] In the present invention, the power of the ultrasonic treatment is preferably 700-900 W, and the time is preferably 30-60 min; the ultrasonic treatment is preferably carried out in an ultrasonic cleaner; in the specific embodiments of the present invention, it is preferably taken out after the solution boils during ultrasonic treatment. After the temperature drops and the solution becomes clear and transparent, the supernatant is removed. The remaining precipitate is washed and dried to obtain the smooth spherical gold powder with a narrow particle size distribution and a low organic residue rate; the washing is preferably centrifugal washing with deionized water and ethanol three times respectively; the drying temperature is preferably 70 °C, and the drying is preferably carried out in a forced-air drying oven.

[0049] In the present invention, the organic residue rate of the smooth spherical gold powder with a narrow particle size distribution and low organic residue rate is ≤1.6‰, preferably 0.73‰ - 1.6‰, the difference between D90 and D10 is ≤0.75μm, more preferably ≤0.25μm; in a specific embodiment of the present invention, the D50 particle size of the smooth spherical gold powder with a narrow particle size distribution and low organic residue rate is preferably 1.83 - 2.61μm.

[0050] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0051] Example 1 Use water - n - propanol (volume ratio 1:1, this volume ratio is the volume ratio of water and alcohol in the finally mixed reaction system, and will not be repeated hereinafter) as the solvent, and the gold powder after post - treatment

[0052] S1. Weigh 40g of chloroauric acid solution (concentration in terms of gold is 50wt%), dilute it with 900mL of water - n - propanol mixed solvent with a volume ratio of 1:1, place it in a constant temperature water bath at 40°C, stir evenly at a stirring rate of 250rpm, and then adjust the pH value of the solution to 4.0 by dropping concentrated ammonia water to obtain the reaction source solution;

[0053] S2. Weigh 2g of the surfactant polyvinylpyrrolidone and dissolve it in 50mL of n - propanol solvent, and then add the obtained surfactant solution to the reaction source solution obtained in step S1 to obtain the pre - reaction solution;

[0054] S3. Weigh 70g of the reducing agent ascorbic acid, add it to 50mL of deionized water, stir and dissolve it in a constant temperature water bath at 60°C, cool to obtain the reducing agent solution, and then add it to the pre - reaction solution at a dropping rate of 1.6mL / s for reaction for 1h. After the reaction is completed, age the obtained golden turbid liquid for 15min, and then centrifuge and wash it twice with deionized water to obtain the gold - containing precipitate;

[0055] S4. Measure 33mL of hydrogen peroxide solution with a mass concentration of 30%, weigh 0.012g of potassium permanganate and dissolve it in 20mL of deionized water. Pour the two solutions into a beaker containing 147mL of deionized water in sequence to prepare 200mL of hydrogen peroxide - potassium permanganate treatment solution. Disperse the gold - containing precipitate obtained in step S3 in the treatment solution, put it into an ultrasonic cleaner for ultrasonic treatment, take it out after the solution boils, and remove the supernatant after the temperature of the beaker drops and the solution becomes clear and transparent. Centrifuge and wash it three times with deionized water and ethanol respectively, and then dry it in a forced - air drying oven at 70°C to obtain the required gold powder.

[0056] Example 2 uses water - n - propanol (volume ratio 3:7) as the solvent, and the post - treated gold powder

[0057] S1. Weigh 40 g of chloroauric acid solution (concentration of gold is 50 wt%) into a beaker, dilute it with 900 mL of water - n - propanol mixed solvent with a volume ratio of 5:13, place it in a constant - temperature water bath at 40 °C and stir evenly at a stirring rate of 250 rpm. Then adjust the pH value of the solution to 4.0 by drop - adding concentrated ammonia water to obtain the reaction source solution;

[0058] S2. Weigh 2 g of the surfactant polyvinylpyrrolidone and dissolve it in 50 mL of n - propanol solvent, and then add the obtained surfactant solution to the reaction source solution obtained in step S1 to obtain the pre - reaction solution;

[0059] S3. Weigh 70 g of the reducing agent ascorbic acid and add it to 50 mL of deionized water, stir and dissolve it in a constant - temperature water bath at 60 °C. After cooling, obtain the reducing agent solution, and then add it to the pre - reaction solution at a dropping rate of 1.6 mL / s for reaction for 1 h. After the reaction ends, age the obtained golden - yellow turbid liquid for 15 min, and then centrifuge and wash it twice with deionized water to obtain the gold - containing precipitate;

[0060] S4. Measure 33 mL of hydrogen peroxide solution with a mass concentration of 30%, weigh 0.012 g of potassium permanganate and dissolve it in 20 mL of deionized water. Pour the two solutions into a beaker containing 147 mL of deionized water in sequence to prepare 200 mL of hydrogen peroxide - potassium permanganate treatment solution. Disperse the gold - containing precipitate obtained in step S3 in the treatment solution, put it into an ultrasonic cleaner for ultrasonic treatment. Take it out after the solution boils. After the temperature of the beaker drops and the solution becomes clear and transparent, remove the supernatant, centrifuge and wash it three times with deionized water and ethanol respectively, and then dry it in a forced - air drying oven at 70 °C to obtain the required gold powder.

[0061] Example 3 uses water - n - propanol (volume ratio 1:1) as the solvent, and the post - treated gold powder

[0062] S1. Weigh 40 g of chloroauric acid solution (concentration of gold is 50 wt%) into a beaker, dilute it with 900 mL of water - n - propanol mixed solvent with a volume ratio of 1:1, place it in a constant - temperature water bath at 40 °C and stir evenly at a stirring rate of 250 rpm / min. Then adjust the pH value of the solution to 4.0 by drop - adding concentrated ammonia water to obtain the reaction source solution;

[0063] S2. Weigh 2 g of the surfactant polyvinylpyrrolidone and dissolve it in 50 mL of n - propanol solvent, and then add the obtained surfactant solution to the reaction source solution obtained in step S1 to obtain the pre - reaction solution;

[0064] S3. Weigh 70 g of the reducing agent ascorbic acid and add it to 50 mL of deionized water. Stir and dissolve it in a constant temperature water bath at 60 °C. After cooling, a reducing agent solution is obtained. Then, add it to the pre-reaction solution at a dropping rate of 1.6 mL / s and react for 1 h. After the reaction is completed, age the resulting golden turbid liquid for 15 min, and then centrifuge and wash it twice with deionized water to obtain a gold-containing precipitate.

[0065] S4. Measure 33 mL of hydrogen peroxide solution with a mass concentration of 30%. Pour it into a beaker and add deionized water to prepare 200 mL of hydrogen peroxide treatment solution. Disperse the gold-containing precipitate obtained in step S3 in the treatment solution, put it into an ultrasonic cleaner for ultrasonic treatment. Take it out after the solution boils. After the temperature of the beaker drops and the solution becomes clear and transparent, remove the supernatant. Centrifuge and wash it three times with deionized water and ethanol respectively, and then dry it in a forced air drying oven at 70 °C to obtain the required gold powder.

[0066] In Comparative Example 1, water - n-propanol (volume ratio 1:1) was used as the solvent, and the gold powder without post-treatment

[0067] S1. Weigh 40 g of chloroauric acid solution (with a gold concentration of 50 wt%) in a beaker, dilute it with 900 mL of a water - n-propanol mixed solvent with a volume ratio of 1:1, place it in a constant temperature water bath at 40 °C, and stir evenly at a stirring rate of 250 rpm / min. Then, adjust the pH value of the solution to 4.0 by dropping concentrated ammonia water to obtain a reaction gold source solution.

[0068] S2. Weigh 2 g of the surfactant polyvinylpyrrolidone and dissolve it in 50 mL of n-propanol solvent. Then, add the obtained surfactant solution to the reaction gold source solution obtained in step S1 to obtain a pre-reaction solution.

[0069] S3. Weigh 70 g of the reducing agent ascorbic acid and add it to 50 mL of deionized water. Stir and dissolve it in a constant temperature water bath at 60 °C. After cooling, a reducing agent solution is obtained. Then, add it to the pre-reaction solution at a dropping rate of 1.6 mL / s and react for 1 h. After the reaction is completed, age the resulting golden turbid liquid for 15 min, remove the supernatant, centrifuge and wash it three times with deionized water and ethanol respectively, and then dry it in a forced air drying oven at 70 °C to obtain the required gold powder.

[0070] In Comparative Example 2, water - ethylene glycol (volume ratio 1:1) was used as the solvent, and the gold powder with post-treatment

[0071] S1. Weigh 40 g of chloroauric acid solution (with a gold concentration of 50 wt%) in a beaker, dilute it with 900 mL of a water - ethylene glycol mixed solvent with a volume ratio of 1:1, place it in a constant temperature water bath at 40 °C, and stir evenly at a stirring rate of 250 rpm / min. Then, adjust the pH value of the solution to 4.0 by dropping concentrated ammonia water to obtain a reaction gold source solution.

[0072] S2. Weigh 2 g of the surfactant polyvinylpyrrolidone and dissolve it in 50 mL of ethylene glycol solvent. Then add the obtained surfactant solution to the reaction source solution obtained in step S1 to obtain a pre-reaction solution;

[0073] S3. Weigh 70 g of the reducing agent ascorbic acid and add it to 50 mL of deionized water. Stir and dissolve it in a constant temperature water bath at 60 °C. After cooling, obtain a reducing agent solution, and then add it to the pre-reaction solution at a dropping rate of 1.6 mL / s for reaction for 1 h. After the reaction is completed, age the obtained golden turbid liquid for 15 min, and then centrifuge and wash it twice with deionized water to obtain a gold-containing precipitate;

[0074] S4. Measure 33 mL of hydrogen peroxide solution with a mass concentration of 30%. Weigh 0.012 g of potassium permanganate and dissolve it in 20 mL of deionized water. Pour the two solutions into a beaker containing 147 mL of deionized water in sequence to prepare 200 mL of hydrogen peroxide-potassium permanganate treatment solution. Disperse the gold-containing precipitate obtained in step S3 in the treatment solution, place it in an ultrasonic cleaner for ultrasonic treatment. After the solution boils, take it out. After the temperature of the beaker drops and the solution becomes clear and transparent, remove the supernatant. Centrifuge and wash it three times with deionized water and ethanol respectively, and then dry it in a forced air drying oven at 70 °C to obtain the required gold powder.

[0075] Comparative Example 3 uses water as a solvent, and the gold powder after post-treatment

[0076] S1. Weigh 40 g of chloroauric acid solution (with a gold concentration of 50 wt%) in a beaker, dilute it with 900 mL of deionized water, place it in a constant temperature water bath at 40 °C, and stir evenly at a stirring rate of 250 rpm / min. Then adjust the pH value of the solution to 4.0 by dropping concentrated ammonia water to obtain a reaction source solution;

[0077] S2. Weigh 2 g of the surfactant polyvinylpyrrolidone and dissolve it in 50 mL of deionized water. Then add the obtained surfactant solution to the reaction source solution obtained in step S1 to obtain a pre-reaction solution;

[0078] S3. Weigh 70 g of the reducing agent ascorbic acid and add it to 50 mL of deionized water. Stir and dissolve it in a constant temperature water bath at 60 °C. After cooling, obtain a reducing agent solution, and then add it to the pre-reaction solution at a dropping rate of 1.6 mL / s for reaction for 1 h. After the reaction is completed, age the obtained golden turbid liquid for 15 min, and then centrifuge and wash it twice with deionized water to obtain a gold-containing precipitate;

[0079] S4. Measure 33 mL of hydrogen peroxide solution with a mass concentration of 30%, weigh 0.012 g of potassium permanganate and dissolve it in 20 mL of deionized water. Pour the two solutions into a beaker containing 147 mL of deionized water in sequence to prepare 200 mL of hydrogen peroxide - potassium permanganate treatment solution. Disperse the gold precipitate obtained in step S3 in the treatment solution, put it into an ultrasonic cleaner for ultrasonic treatment, take it out after the solution boils, wait for the temperature of the beaker to drop, and remove the supernatant after the solution becomes clear and transparent. Centrifuge and wash it 3 times with deionized water and ethanol respectively, and then dry it in a blast drying oven at 70 °C to obtain the required gold powder.

[0080] Comparative Example 4 uses water as a solvent and the gold powder without post - treatment

[0081] S1. Weigh 40 g of chloroauric acid solution (with a gold concentration of 50 wt%) in a beaker, dilute it with 900 mL of deionized water, place it in a constant temperature water bath at 40 °C, and stir evenly at a stirring rate of 250 rpm / min. Then adjust the pH value of the solution to 4.0 by dropping concentrated ammonia water to obtain the reaction source solution.

[0082] S2. Weigh 2 g of the surfactant polyvinylpyrrolidone and dissolve it in 50 mL of deionized water, and then add the obtained surfactant solution to the reaction source solution obtained in step S1 to obtain the pre - reaction solution.

[0083] S3. Weigh 70 g of the reducing agent ascorbic acid and add it to 50 mL of deionized water, stir and dissolve it in a constant temperature water bath at 60 °C, cool it to obtain the reducing agent solution, and then add it to the pre - reaction solution at a dropping rate of 1.6 mL / s for reaction for 1 h. After the reaction is completed, age the obtained golden turbid liquid for 15 min, remove the supernatant, centrifuge and wash it 3 times with deionized water and ethanol respectively, and then dry it in a blast drying oven at 70 °C to obtain the required gold powder.

[0084] Performance test

[0085] Figure 1 is the SEM image of the gold powder obtained in Example 1, Figure 2 is the thermogravimetric curve of the gold powder obtained in Example 1; Figure 3 is the particle size distribution diagram of the gold powder obtained in Example 1. According to Figures 1 to 3 It can be seen that the gold powder prepared by using the water - n - propanol mixed solvent as the reaction solvent has a uniform particle size distribution, single dispersion, and low organic residue rate.

[0086] Figure 4 is the particle size distribution diagram of the gold powder obtained in Example 2. According to Figure 4 It can be seen that the gold powder prepared in Example 2 also has the characteristic of narrow particle size distribution. At the same time, combined with Figure 3 it can be known that by adjusting the ratio of water and alcohol in the solvent system, good control of the particle size of the gold powder can be achieved.

[0087] Figure 5 SEM image of the gold powder obtained in Comparative Example 2 Figure 6 Particle size distribution diagram of the gold powder obtained in Comparative Example 2. According to Figures 5 to 6 It can be seen that when water-ethylene glycol is used as the solvent to prepare gold powder, the particle size distribution shows a polarization phenomenon. This may be because the viscosity of the ethylene glycol solvent is relatively high, and the dispersant coating is uneven during the nucleation-growth stage of the gold powder particles, resulting in the polarized growth of the gold powder particles.

[0088] Figure 7 SEM image of the gold powder obtained in Comparative Example 3 Figure 8 Particle size distribution diagram of the gold powder obtained in Comparative Example 3. According to Figures 7 to 8 It can be seen that when only water is used as the solvent, small particles are generated during the preparation of gold powder, and the small particles adsorb on the surface of the large particles, and the dispersibility is average.

[0089] Organic residue rate test: The gold powders prepared in Examples 1 to 3 and Comparative Examples 1 to 4 were calcined at 600 °C for 3 h, and the loss rate (i.e., the organic residue rate) was measured. The results are shown in Table 1.

[0090] Table 1 Loss rates of the gold powders obtained in Examples 1 to 3 and Comparative Examples 1 to 4

[0091]

[0092] According to the data in Table 1, by comparing the organic residue rates of the post-treated gold powder and the non-post-treated gold powder, it can be found that the loss rates of the two differ by one order of magnitude, indicating that the post-treatment of the preliminarily prepared gold powder can effectively reduce the organic residue rate on the particle surface.

[0093] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing smooth spherical gold powder with low organic residue rate and narrow particle size distribution, characterized in that: The following steps are involved: Mixing chloroauric acid solution and water-n-propanol mixed solvent, and adjusting the pH value of the resulting mixed solution to 3-6 to obtain a reaction gold source solution; Mixing the surfactant solution and the reaction gold source solution to obtain a pre-reaction solution; Mixing the reducing agent solution and the pre-reaction liquid to perform a reduction reaction, and sequentially performing aging and solid-liquid separation on the obtained reaction liquid to obtain a gold-containing precipitate; The gold-containing precipitate is ultrasonically treated in a treatment liquid, and then solid-liquid separation and drying are performed in sequence to obtain the smooth spherical gold powder with low organic residue rate and narrow particle size distribution; the solute in the treatment liquid includes one or more of hydrogen peroxide, potassium permanganate and sodium hypochlorite.

2. The preparation method according to claim 1, characterized in that The mass concentration of gold ions in the chloroauric acid solution is 30-60wt%; the concentration of gold ions in the reaction gold source solution is 10-50g / L; the mixing of the chloroauric acid solution and the water-n-propanol mixed solvent is carried out in a water bath and under stirring conditions, the temperature of the water bath is 20-50°C, and the stirring rate is 200-500rpm.

3. The preparation method according to claim 1, characterized in that The surfactant includes one or more of glucose, gum arabic, polyvinyl pyrrolidone, sodium polyacrylate and dopamine; the mass ratio of the surfactant to the gold ions in the reaction gold source solution is 0.03 to 0.3:1; and the solvent of the surfactant solution is water or n-propanol.

4. The preparation method according to claim 1, characterized in that The reducing agent includes one or more of hydrazine hydrate, sodium citrate, ascorbic acid and sodium phosphite; the solvent of the reducing agent solution is water; the molar ratio of the reducing agent to the gold ions in the reaction gold source solution is 3 to 6:1; and the ratio of the volume of the water-n-propanol mixed solvent to the volume of the solvent in the reducing agent solution is 10:1 to 30:

1.

5. The preparation method according to claim 1 or 4, characterized in that The reducing agent solution is prepared by adding the reducing agent into water, stirring and dissolving the reducing agent in a water bath, and then cooling the reducing agent solution; the temperature of the water bath is 50-80°C.

6. The preparation method according to claim 1, 3 or 4, characterized in that: In the system obtained by mixing the reducing agent solution and the pre-reaction solution, the volume ratio of water to n-propanol is 999:1 to 1:5; The reducing agent solution is added dropwise to the pre-reaction solution to perform a reduction reaction, and the rate of the addition is 1 to 4 mL / s.

7. The preparation method according to claim 1, characterized in that When the solute in the treatment liquid includes hydrogen peroxide, the concentration of hydrogen peroxide in the treatment liquid is 1 to 20 wt %; when the solute in the treatment liquid includes potassium permanganate, the concentration of potassium permanganate in the treatment liquid is 0.005 to 0.1 wt %; when the solute in the treatment liquid includes sodium hypochlorite, the concentration of sodium hypochlorite in the treatment liquid is 0.1 to 3 wt %.

8. The preparation method according to claim 1, characterized in that The temperature of the reduction reaction is 20-50° C., and the reaction time is 1-2 hours.

9. The preparation method according to claim 1, characterized in that The aging temperature is room temperature, and the aging time is 10 to 120 minutes.

10. The preparation method according to claim 1, characterized in that The smooth spherical gold powder with low organic residue rate and narrow particle size distribution has an organic residue rate of ≤1.6‰, and a difference between the D90 particle size and the D10 particle size of ≤0.75 μm.

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