A method for preparing ultrafine silver powder

Abstract

The invention discloses a method for preparing ultrafine silver powder. The method comprises the following steps: using a silver plate as a silver source, inserting two silver plates and an auxiliary electrode into an electrolyte; heating the electrolyte to 20-40°C; connecting the silver plate to a positive electrode of a constant current power supply, connecting an auxiliary electrode to a negative electrode of the constant current power supply, passing direct current, and preparing ultrafine silver powder on the surface of the auxiliary electrode; taking out the auxiliary electrode, scraping off the silver powder attached to the surface, washing, filtering, and vacuum drying, and obtaining ultrafine silver powder with a particle size of micrometer level; the method is simple to operate, has good consistency, and has a current efficiency of not less than 70%, and a current consumption of not more than 5kw·h / kg of silver powder; using a pure silver plate instead of silver nitrate as a silver source, the electrolyte and the auxiliary electrode can be reused, has good economic efficiency, is green and environmentally friendly, and has no pollution in the whole process; and the method can control the particle size of the silver powder by adjusting the current density, the electrolyte component, the electrolyte temperature, and the relative distance between the electrode pieces, so as to facilitate the production of silver powders of different specifications.

Description

Technical Field

[0001] The invention belongs to the technical field of materials, and in particular relates to a method for preparing ultrafine silver powder. Background Art

[0002] Ultrafine silver powder is an important industrial raw material with huge market demand. It is widely used in coatings, printing, solar cells, textiles and other fields, and different industries have different requirements for silver powder particle size.

[0003] At present, the mainstream methods for preparing silver powder are mainly the following:

[0004] Wet reduction method: Use silver nitrate solution and ammonia water to make a silver ammonia complex aqueous solution, and add an organic reducing agent to the solution to prepare silver powder.

[0005] Dry reduction method: Use ammonium acetate solution to titrate silver nitrate solution to produce silver acetate precipitate, and sinter the silver acetate solid in a high-temperature furnace to prepare silver powder.

[0006] Atomization method: Use distilled water or treated pure water as the atomization medium to form a high-pressure water jet to impact the molten pure silver liquid flow, atomizing it into irregularly shaped silver powder, and then obtain high-purity ultrafine silver powder through heat treatment and mechanical treatment.

[0007] These methods have the disadvantages of high initial equipment investment, complicated and sophisticated procedures, environmental pollution during the production process, and high safety requirements. Summary of the invention

[0008] The present invention aims to provide a method for preparing ultrafine silver powder, which has the characteristics of good economy, simple process and environmental friendliness, and can produce silver powder with different particle size specifications by changing the electrolysis process conditions.

[0009] In order to achieve the above purpose, the technical solutions adopted are as follows:

[0010] A method for preparing ultrafine silver powder comprises the following steps:

[0011] (1) Using silver plates as silver sources, insert two silver plates and an auxiliary electrode into an electrolyte; heating the electrolyte to 20°C to 40°C;

[0012] (2) connecting the silver plate to the positive electrode of a constant current power supply, connecting the auxiliary electrode to the negative electrode of the constant current power supply, passing direct current, and preparing ultrafine silver powder on the surface of the auxiliary electrode;

[0013] (3) The auxiliary electrode is removed, the silver powder attached to the surface is scraped off, and ultrafine silver powder with a particle size of micrometer level is obtained through washing, filtering and vacuum drying.

[0014] According to the above scheme, the auxiliary electrode is one of nickel plate, silver plate, titanium plate, copper plate, steel plate, lead plate, zinc plate or a composite of the above metals.

[0015] According to the above scheme, the auxiliary electrode is sandwiched between two silver plates, and the distance between the auxiliary electrode and the silver plates is 4 cm to 20 cm.

[0016] According to the above scheme, the current density of the direct current is 0.02A / cm 2 ~0.1A / cm 2 .

[0017] According to the above scheme, the electrolyte is composed of deionized water, silver nitrate, and auxiliary materials; the concentration of silver nitrate is 0.051mol / L~2mol / L; the auxiliary materials are one or more of nitric acid, sodium nitrate, potassium nitrate, ammonium nitrate, glycerol, and ethylene glycol; the auxiliary material content is less than 1.5wt% of the electrolyte.

[0018] According to the above scheme, silver powders with different particle sizes are obtained by controlling the current density; as the current density increases, the particle size of the silver powder first decreases and then increases.

[0019] According to the above scheme, silver powders with different particle sizes are obtained by controlling the electrolyte temperature; as the electrolyte temperature increases, the silver powder particle size first decreases and then increases.

[0020] According to the above scheme, silver powders with different particle sizes are obtained by controlling the relative distance between the pole pieces; as the relative distance increases, the particle size of the silver powder decreases.

[0021] According to the above scheme, silver powders with different particle sizes are obtained by controlling the electrolyte components; as the concentration of silver nitrate increases, the particle size of the silver powder first decreases and then increases;

[0022] According to the above scheme, silver powders of different particle sizes can be obtained by controlling the voltage; an increased voltage is conducive to obtaining silver powder grains with small particle sizes.

[0023] According to the above scheme, the addition of polyols into the electrolyte improves the sphericity of the silver powder grains.

[0024] The present invention inserts two silver plates and an auxiliary electrode plate into an electrolyte, with the silver plate serving as an anode and the auxiliary electrode plate serving as a cathode, and heats the electrolyte to a specified temperature. The output current of the constant current source is adjusted according to the current density, and the electrodes are energized to generate silver powder with uniform particle size on the surface of the auxiliary electrode plate. This process consumes the silver plates but does not consume the electrolyte. After a period of power-on, the constant current source is turned off, the auxiliary electrode is taken out, and the floating powder on the surface of the electrode is scraped into a plastic basin filled with a large amount of clean water with a plastic plate. After filtering and rinsing, high-purity ultrafine silver powder is obtained by vacuum drying at 70°C to 90°C.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The invention has the advantages of simple operation, good consistency, current efficiency not less than 70%, and current consumption not more than 5kw·h / kg silver powder.

[0027] The present invention uses a pure silver plate instead of silver nitrate as a silver source, the electrolyte and the auxiliary electrode can be reused, the economic efficiency is good, the environment is green and the whole process is pollution-free.

[0028] The present invention can control the particle size of silver powder by adjusting current density, electrolyte composition, electrolyte temperature and the relative distance between pole pieces, so as to facilitate the production of silver powder of different specifications. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 : Schematic diagram of the electrolytic preparation device of ultrafine silver powder of the present invention.

[0030] Figure 2 : SEM image of the silver powder prepared in Example 1 of the present invention.

[0031] Figure 3 : SEM image of the silver powder prepared in Example 2 of the present invention.

[0032] Figure 4 : SEM image of silver powder prepared in Example 3.

[0033] Figure 5 : SEM image of silver powder prepared in Example 4.

[0034] Figure 6 : SEM image of silver powder prepared in Example 5. DETAILED DESCRIPTION

[0035] The following examples further illustrate the technical solution of the present invention, but are not intended to limit the scope of protection of the present invention.

[0036] The specific embodiment provides a method for preparing ultrafine silver powder:

[0037] (1) Using silver plates as silver sources, insert two silver plates and an auxiliary electrode into an electrolyte; raise the temperature of the electrolyte to 20°C to 40°C. The auxiliary electrode is one of nickel plates, silver plates, titanium plates, copper plates, steel plates, lead plates, and zinc plates, or a composite of the above metals. The auxiliary electrode is sandwiched between the two silver plates, and the distance between the auxiliary electrode and the silver plates is 4 cm to 20 cm. See Figure 1.

[0038] (2) Connect the silver plate to the positive electrode of the constant current power supply, connect the auxiliary electrode to the negative electrode of the constant current power supply, pass direct current, and prepare ultrafine silver powder on the surface of the auxiliary electrode. The current density of the direct current is 0.02A / cm 2 ~0.1A / cm2 The electrolyte is composed of deionized water, silver nitrate and auxiliary materials; the concentration of silver nitrate is 0.05mol / L to 2mol / L; the auxiliary materials are one or more of nitric acid, sodium nitrate, potassium nitrate, ammonium nitrate, glycerol and ethylene glycol; the content of the auxiliary materials is less than 1.5wt% of the electrolyte.

[0039] The present invention can adjust the output current of the constant current source according to the current density, energize the electrode, and generate silver powder with uniform particle size on the surface of the auxiliary electrode plate. This process will consume the silver plate but will not consume the electrolyte.

[0040] (3) After the preparation is completed, the auxiliary electrode is taken out, and the silver powder attached to the surface is scraped off with a plastic plate. After washing, filtering, and vacuum drying, ultrafine silver powder with a particle size of micrometer level is obtained.

[0041] The present invention can control the particle size of silver powder by adjusting current density, electrolyte composition, electrolyte temperature and the relative distance between pole pieces, so as to facilitate the production of silver powder of different specifications.

[0042] Specifically, silver powders of different particle sizes are obtained by controlling the current density; as the current density increases, the silver powder particle size first decreases and then increases, and the current density is one of the main factors affecting the particle size. Silver powders of different particle sizes are obtained by controlling the electrolyte temperature; as the electrolyte temperature increases, the silver powder particle size first decreases and then increases, and the temperature can be suitable as needed. Silver powders of different particle sizes are obtained by controlling the relative distance between the pole pieces; as the relative distance increases, the silver powder particle size decreases, the voltage increases, and the distance can be suitable as needed. Silver powders of different particle sizes are obtained by controlling the electrolyte components; the concentration of silver nitrate in the electrolyte is one of the main factors affecting the particle size, and as the concentration of silver nitrate increases, the silver powder particle size first decreases and then increases; the concentration of nitric acid and nitrate in the auxiliary material has a greater influence on the electrolysis voltage, and a higher voltage is conducive to obtaining small-sized silver powder crystals, and the silver powder particle size is controlled by controlling its concentration; the addition of polyols in the auxiliary material can improve the sphericity of the crystals.

[0043] The invention is easy to operate, has good consistency, current efficiency is not less than 70%, and current consumption is not higher than 5kw·h / kg silver powder. The invention uses pure silver plate instead of silver nitrate as the silver source, the electrolyte and the auxiliary electrode can be reused, the economy is good, green and environmentally friendly, and the whole process is pollution-free.

[0044] Example 1

[0045] A method for preparing ultrafine silver powder comprises the following steps:

[0046] Two silver plates and one nickel plate are inserted into the electrolyte, the silver plate is connected to the negative electrode of the constant current source, and the nickel plate is connected to the negative electrode of the constant current source. The size of the silver plate and the nickel plate are both 300mm×50mm×0.5mm, and the distance between the silver plate and the nickel plate is 10cm; the electrolyte is a 0.1mol / L silver nitrate solution containing 1wt% nitric acid, and the electrolyte is heated to 30°C;

[0047] A 9A direct current was applied to the electrode plate for 1 hour, and the voltage during the electrolysis period was 14V to 15V. After completion, the auxiliary electrode was taken out, and the floating powder on the surface of the electrode was scraped into a plastic basin filled with a large amount of clean water with a plastic plate. After suction filtration and rinsing, it was vacuum dried at 70℃ to 90℃ for 2 hours to obtain 29.7g of silver powder product with a particle size of about 0.5μm to 1μm. The SEM image of the silver powder prepared in this embodiment is shown in the attached Figure 2 shown.

[0048] Example 2

[0049] A method for preparing ultrafine silver powder comprises the following steps:

[0050] Insert three silver plates side by side into the electrolyte, connect the two silver plates on both sides to the negative electrode of the constant current source, and connect the middle silver plate to the negative electrode of the constant current source. The size of the silver plates is 300mm×50mm×0.5mm, and the distance between the silver plates is 5cm. The electrolyte is a 0.5mol / L silver nitrate solution containing 1wt% potassium nitrate and 0.5wt% ethylene glycol. Heat the electrolyte to 35°C.

[0051] A 15A direct current was applied to the electrode plate for 1 hour, and the voltage during the electrolysis period was 18V to 20V. After completion, the auxiliary electrode was taken out, and the floating powder on the surface of the electrode was scraped into a plastic basin filled with a large amount of clean water with a plastic plate. After suction filtration and rinsing, it was vacuum dried at 70℃ to 90℃ for 2 hours to obtain 47.2g of silver powder product with a particle size of about 5μm to 15μm. The SEM image of the silver powder prepared in this embodiment is shown in the attached figure. Figure 3 shown.

[0052] Example 3

[0053] A method for preparing ultrafine silver powder comprises the following steps:

[0054] Insert three silver plates side by side into the electrolyte, connect the two silver plates on both sides to the negative electrode of the constant current source, connect the middle silver plate to the negative electrode of the constant current source, the size of the silver plates is 300mm×50mm×0.5mm, and the distance between the silver plates is 5cm; the electrolyte is a 0.1mol / L silver nitrate solution containing 1wt% nitric acid and 0.2wt% glycerol, and heat the electrolyte to 40°C;

[0055] A 2A direct current was applied to the electrode plate for 1 hour, and the voltage during the electrolysis period was 2V to 3V. After completion, the auxiliary electrode was taken out, and the floating powder on the surface of the electrode was scraped into a plastic basin filled with a large amount of clean water with a plastic plate. After suction filtration and rinsing, it was vacuum dried at 70℃ to 90℃ for 2 hours to obtain 7.8g of silver powder product with a particle size of about 20μm to 40μm. The SEM image of the silver powder prepared in this embodiment is shown in the attached figure. Figure 4 shown.

[0056] Example 4

[0057] A method for preparing ultrafine silver powder comprises the following steps:

[0058] Insert three silver plates side by side into the electrolyte, connect the two silver plates on both sides to the negative electrode of the constant current source, connect the middle silver plate to the negative electrode of the constant current source, the size of the silver plates is 300mm×50mm×0.5mm, and the distance between the silver plates is 10cm; the electrolyte is a 0.1mol / L silver nitrate solution containing 1wt% nitric acid and 0.2wt% glycerol, and heat the electrolyte to 30°C;

[0059] A 2A direct current was applied to the electrode plate for 1 hour, and the voltage during the electrolysis period was 4V to 5V. After completion, the auxiliary electrode was taken out, and the floating powder on the surface of the electrode was scraped into a plastic basin filled with a large amount of clean water with a plastic plate. After suction filtration and rinsing, it was vacuum dried at 70℃ to 90℃ for 2 hours to obtain 7.6g of silver powder product with a particle size of about 10μm to 15μm. The SEM image of the silver powder prepared in this embodiment is shown in the attached Figure 5 shown.

[0060] Example 5

[0061] A method for preparing ultrafine silver powder comprises the following steps:

[0062] Insert three silver plates side by side into the electrolyte, connect the two silver plates on both sides to the negative electrode of the constant current source, connect the middle silver plate to the negative electrode of the constant current source, the size of the silver plates is 300mm×50mm×0.5mm, and the distance between the silver plates is 10cm; the electrolyte is a 0.1mol / L silver nitrate solution containing 1wt% nitric acid and 0.1wt% ethylene glycol, and heat the electrolyte to 30°C;

[0063] A 9A direct current was applied to the electrode plate for 1 hour, and the voltage during electrolysis was 14V to 15V. After completion, the auxiliary electrode was taken out, and the floating powder on the surface of the electrode was scraped into a plastic basin filled with a large amount of clean water with a plastic plate. After suction filtration and rinsing, it was vacuum dried at 70℃ to 90℃ for 2 hours to obtain 29.9g of silver powder product with a particle size of about 0.5μm to 1μm. The SEM image of the silver powder prepared in this embodiment is shown in the attached figure. Figure 6 shown.

Claims

1. A method for preparing ultrafine silver powder, characterized in that The following steps are involved: (1) Using silver plates as silver sources, insert two silver plates and an auxiliary electrode into an electrolyte; raise the temperature of the electrolyte to 20°C to 40°C; the electrolyte and the corresponding voltage used are one of the following three situations: 0.5 mol / L silver nitrate solution containing 1 wt% potassium nitrate and 0.5 wt% ethylene glycol, with a voltage of 18 V to 20 V during electrolysis; 0.1 mol / L silver nitrate solution containing 1 wt% nitric acid and 0.2 wt% glycerol, with a voltage of 2V to 3V during electrolysis; 0.1 mol / L silver nitrate solution containing 1 wt% nitric acid and 0.2 wt% glycerol, with a voltage of 4V to 5V during electrolysis; (2) Connecting the silver plate to the positive electrode of a constant current power supply, connecting the auxiliary electrode to the negative electrode of the constant current power supply, passing direct current, and preparing ultrafine silver powder on the surface of the auxiliary electrode; (3) Take out the auxiliary electrode, scrape off the silver powder attached to the surface, wash, filter and vacuum dry to obtain ultrafine silver powder with a particle size of micrometer level.

2. The method for preparing ultrafine silver powder according to claim 1, characterized in that The auxiliary electrode is one of nickel plate, silver plate, titanium plate, copper plate, steel plate, lead plate and zinc plate, or a composite of the above metals.

3. The method for preparing ultrafine silver powder according to claim 1, characterized in that The auxiliary electrode is sandwiched between two silver plates, and the distance between the auxiliary electrode and the silver plates is 4 cm to 20 cm.

4. The method for preparing ultrafine silver powder according to claim 1, characterized in that The current density of the direct current is 0.02A / cm 2 ~0.1A / cm 2 .

5. The method for preparing ultrafine silver powder according to claim 1, characterized in that Silver powders with different particle sizes are obtained by controlling the current density; as the current density increases, the particle size of the silver powder first decreases and then increases.

6. The method for preparing ultrafine silver powder according to claim 1, characterized in that Silver powders with different particle sizes are obtained by controlling the electrolyte temperature; as the electrolyte temperature increases, the silver powder particle size first decreases and then increases.

7. The method for preparing ultrafine silver powder according to claim 1, characterized in that Silver powders with different particle sizes are obtained by controlling the relative distance between the electrodes; as the relative distance increases, the particle size of the silver powder decreases.

8. The method for preparing ultrafine silver powder according to claim 1, characterized in that Silver powders with different particle sizes are obtained by controlling the electrolyte composition; as the concentration of silver nitrate increases, the particle size of the silver powder first decreases and then increases.

9. The method for preparing ultrafine silver powder according to claim 1, characterized in that Increasing the voltage results in smaller silver powder grains.

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