Preparation method of superfine nanometer silver powder

Abstract

This invention discloses a method for preparing ultrafine nano-silver powder. This method prepares ultrafine nano-silver powder without the use of dispersants or wetting agents, ensuring that the silver powder does not contain organic matter, thus meeting the requirements for silver powder with high carbon content and broadening the application range of this silver powder. Simultaneously, a high-pressure water crushing method is used to break silver chloride to nanoscale size, which is then reacted with a reducing agent through a pipeline mixer. Since each silver chloride nanoparticle is an independent crystal nucleus, there are no silver ions in the solution, preventing the growth of silver ions on pre-formed crystal nuclei that occurs in ordinary liquid-phase reduction methods, thus ensuring the nanoscale size of the generated silver powder. Low-temperature vacuum drying is used during drying, effectively preventing high-temperature aggregation of the silver powder, ultimately yielding ultrafine nano-sized silver powder.

Description

Technical Field

[0001] This invention belongs to the field of precious metal metallurgy, specifically relating to a method for preparing ultrafine nano silver powder. Background Technology

[0002] Silver possesses the best electrical and thermal conductivity among all metals, along with excellent corrosion resistance and biocompatibility in air. Furthermore, it is the most inexpensive of the precious metals, making it widely used in various electrical and thermal conductivity applications in air. Powdered elemental silver is called silver powder, and its morphology mainly includes dendritic, triangular, flake, spherical, linear, polygonal, and flocculent forms.

[0003] Ultrafine silver powder (average particle size 0.1–5 μm) has a small average particle size, large specific surface area, and high sintering activity, enabling it to achieve high electrical conductivity at relatively low sintering temperatures. Therefore, conductive pastes using ultrafine silver powder as filler exhibit excellent comprehensive performance and are widely used in photovoltaic power generation, ceramic capacitors, conductive inks, electromagnetic shielding, and other fields. Among these, conductive pastes for the front side of silicon solar cells have the largest usage, and with the rapid expansion of the industry, photovoltaics has become the industrial sector consuming the largest amount of silver resources. Furthermore, due to the macroscopic quantum tunneling effect and surface effect of nanoparticles, the surface activity of ultrafine silver powder is significantly increased, giving it special catalytic and bactericidal functions, thus finding wide application in health, environmental protection, and catalysis fields.

[0004] In conventional liquid-phase reduction methods for producing silver powder, the silver ions that appear tend to grow on the pre-formed crystal nuclei, making it impossible to guarantee the nanoscale size of the silver powder. Adding dispersants, wetting agents, or other organic reagents to reduce the silver powder particle size results in residual organic matter in the final silver powder. For example, the invention patent with application number CN202210254041.8 discloses a method for preparing highly dispersed micron-sized silver powder for electrical contacts. While this method effectively prevents silver powder agglomeration by adding a dispersant, the resulting silver powder easily retains organic matter, failing to meet the requirements for high carbon content silver powder and limiting its application range. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings and deficiencies of the existing technology and to provide a method for preparing ultrafine nano silver powder.

[0006] To achieve the above objectives, the technical solution of the present invention includes the following steps:

[0007] S1. Silver nitrate is dissolved in water and precipitated with sodium chloride to obtain silver chloride;

[0008] S2. Dry the silver chloride obtained in step S1;

[0009] S3. The silver chloride is crushed under high pressure. After crushing, the precipitate is formed. The upper colloidal liquid is extracted to obtain silver chloride colloid. The lower precipitate is centrifuged and then crushed.

[0010] S4. After mixing the reducing agent with the silver chloride colloid, add the mixture to the reduction vessel and continue stirring;

[0011] S5. The ultrafine silver powder obtained in S4 is washed, filtered, and dried under low temperature vacuum to obtain the finished product.

[0012] A further step is to use a hanging bag centrifuge in S2 to spin-dry the silver chloride.

[0013] A further step is to use a high-pressure water gun in S3 to break up the silver chloride inside the hanging bag.

[0014] Further settings include a high-pressure water gun with a pressure of 30kg-100kg.

[0015] A further setting is that the reducing agent described in S4 is a mixture of sodium hydroxide and hydrazine hydrate.

[0016] A further step involves mixing the reducing agent and silver chloride colloid in S4 via a metering pump and a pipeline mixer before pumping it into the reduction reactor.

[0017] A further setting is that the low-temperature drying temperature in S5 is less than 50℃.

[0018] The beneficial effects of this invention are:

[0019] This method prepares ultrafine nano silver powder without the use of dispersants or wetting agents, ensuring that the silver powder does not contain organic matter, thus meeting the requirements for the use of silver powder with high carbon content, broadening the application range of the silver powder and reducing production costs.

[0020] Meanwhile, high-pressure water crushing is used to break silver chloride down to nanoscale size, and then it reacts with a reducing agent through a pipeline mixer. Since each silver chloride nanoparticle is an individual crystal nucleus, there are no silver ions in the solution, and the situation of silver ions growing on the pre-generated crystal nuclei, which occurs in the ordinary liquid-phase reduction method for producing silver powder, is not observed, thus ensuring the nanoscale size of the produced silver powder. Low-temperature vacuum drying is used during drying, which effectively prevents the high-temperature aggregation of silver powder, and finally, ultrafine nanoscale silver powder is obtained. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, obtaining other drawings based on these drawings without creative effort still falls within the scope of the present invention.

[0022] Figure 1 The process flow diagram of this invention;

[0023] Figure 2 The images are scanning electron microscope (SEM) images of the finished products obtained by the methods in Examples 1-3 and Comparative Example 2. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings.

[0025] Example 1

[0026] (1) Dissolve 100 kg of silver nitrate in water, precipitate with silver chloride, adjust the speed of the hanging bag centrifuge to 40 Hz to dehydrate the silver chloride, hoist the hanging bag centrifuge into a special equipment, start stirring, adjust the pressure of the high-pressure pump to 3 MPa to start water crushing, observe that all the silver chloride falls off the cloth bag, then turn off the stirring, let stand for 12 hours, pump the upper layer of silver chloride colloid into a temporary storage tank totaling 965 kg, and pump the lower layer of silver chloride precipitate into the centrifuge again for centrifugation and dehydration, high-pressure crushing, for use in the next reduction. Mix 100 L of liquid alkali (30%) with 10 L of hydrazine hydrate (50%), set the silver chloride colloid addition rate to 30 L / min, and the liquid alkali and hydrazine hydrate mixture addition rate to 3.4 L / min, and simultaneously use a metering pump to pump into the reduction kettle through a pipeline mixer, then stir for 15 minutes, wash and filter the silver powder obtained from the reduction, and finally dry it under vacuum at 40℃ to obtain 50.285 kg of finished product, with a one-time yield of 66.81%. Figure 2 As shown in (a), the average particle size of the resulting product ranges from 500 nm to 800 nm.

[0027] Example 2

[0028] (1) Dissolve 100 kg of silver nitrate in water, precipitate with silver chloride, adjust the speed of the hanging bag centrifuge to 40 Hz to dehydrate the silver chloride, hoist the hanging bag centrifuge into a special equipment, start stirring, adjust the pressure of the high-pressure pump to 6 MPa to start water crushing, observe that all the silver chloride has fallen from the cloth bag, then turn off the stirring, let stand for 12 hours, pump the upper layer of silver chloride colloid into a temporary storage tank totaling 925 kg, and pump the lower layer of silver chloride precipitate into the centrifuge again for centrifugation and dehydration, high-pressure crushing, for use in the next reduction. Mix 120 L of liquid alkali (30%) with 12 L of hydrazine hydrate (50%), set the silver chloride colloid addition rate to 30 L / min, and the liquid alkali and hydrazine hydrate mixture addition rate to 3.89 L / min, and simultaneously use a metering pump to pump into the reduction kettle through a pipeline mixer, then stir for 15 minutes, wash and filter the silver powder obtained from the reduction, and finally vacuum dry at 40℃ to obtain 61.556 kg of finished product, with a one-time yield of 81.79%. Figure 2 As shown in (b), the average particle size of the resulting product ranges from 300 nm to 600 nm.

[0029] Example 3

[0030] (1) Dissolve 100 kg of silver nitrate in water, precipitate with silver chloride, adjust the speed of the hanging bag centrifuge to 40 Hz to dehydrate the silver chloride, hoist the hanging bag centrifuge into a special equipment, start stirring, adjust the pressure of the high-pressure pump to 10 MPa to start water crushing, observe that all the silver chloride has fallen from the cloth bag, then turn off the stirring, let stand for 12 hours, pump the upper layer of silver chloride colloid into a temporary storage tank totaling 805 kg, and pump the lower layer of silver chloride precipitate into the centrifuge again for centrifugation and dehydration, high-pressure crushing, for use in the next reduction. Mix 120 L of liquid alkali (30%) with 12 L of hydrazine hydrate (50%), set the silver chloride colloid addition rate to 30 L / min, and the liquid alkali and hydrazine hydrate mixture addition rate to 3.89 L / min, and simultaneously use a metering pump to pump into the reduction kettle through a pipeline mixer, then stir for 15 minutes, wash and filter the silver powder obtained from the reduction, and finally vacuum dry at 40℃ to obtain 69.825 kg of finished product, with a one-time yield of 92.78%. Figure 2 As shown in (c), the average particle size of the resulting product ranges from 100 nm to 400 nm.

[0031] Comparative Example 1

[0032] (1) Dissolve 100kg of silver nitrate in water, precipitate with silver chloride, adjust the speed of the hanging bag centrifuge to 40 Hz to dehydrate the silver chloride, hoist the hanging bag centrifuge into the special equipment, start stirring, adjust the pressure of the high pressure pump to 1 MPa to start water crushing, and after crushing for 120 minutes, there is still a lot of silver chloride on the cloth bag. The yield and efficiency are too low and it is not suitable for production.

[0033] Comparative Example 2

[0034] (1) Dissolve 100 kg of silver nitrate in water, precipitate with silver chloride, adjust the speed of the hanging bag centrifuge to 40 Hz to dehydrate the silver chloride, hoist the hanging bag centrifuge into a special equipment, start stirring, adjust the pressure of the high-pressure pump to 10 MPa to start water crushing, observe that all the silver chloride has fallen from the cloth bag, then turn off the stirring, let stand for 12 hours, pump the upper layer of silver chloride colloid into a temporary storage tank totaling 785 kg, and pump the lower layer of silver chloride precipitate into the centrifuge again for centrifugation and dehydration, high-pressure crushing, for use in the next reduction. Mix 120 L of liquid alkali (30%) with 12 L of hydrazine hydrate (50%), set the silver chloride colloid addition rate to 30 L / min, and the liquid alkali and hydrazine hydrate mixture addition rate to 3.89 L / min, and simultaneously use a metering pump to pump into the reduction kettle through a pipeline mixer, then stir for 15 minutes, wash and filter the silver powder obtained from the reduction, and finally vacuum dry at 120℃ to obtain 68.0218 kg of finished product, with a one-time yield of 90.7%. Figure 2 As shown in (d), the average particle size of the obtained product ranges from 1000nm to 2000nm.

[0035] Through comparative analysis of Examples 1-3 and Comparative Examples 1-2, the following conclusions are drawn: 1. The high-pressure water pressure for crushing should not be too low. Too low a crushing pressure results in low crushing efficiency and is unsuitable for industrial production. Conversely, due to equipment limitations, excessively high water pressure cannot be used. 2. The drying temperature should not be too high. Excessively high drying temperatures will cause silver powder to aggregate and grow, increasing particle size.

[0036] The above description discloses only preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. Therefore, equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A method for preparing ultrafine nano silver powder, characterized in that Includes the following steps: S1. Silver nitrate is dissolved in water and precipitated with sodium chloride to obtain silver chloride; S2. Dry the silver chloride obtained in step S1; S3. The silver chloride is crushed under high pressure. After crushing, the precipitate is formed. The upper colloidal liquid is extracted to obtain silver chloride colloid. The lower precipitate is centrifuged and then crushed. S4. After mixing the reducing agent with the silver chloride colloid, add the mixture to the reduction vessel and continue stirring; S5. The ultrafine silver powder obtained in S4 is washed, filtered, and dried under low temperature vacuum to obtain the finished product. In step S2, silver chloride is spun dry using a hanging bag centrifuge; in step S3, silver chloride in the hanging bag is broken up using a high-pressure water gun with a pressure of 30 kg to 100 kg; in step S4, the reducing agent is a mixture of sodium hydroxide and hydrazine hydrate; in step S4, the reducing agent and silver chloride colloid are mixed by a metering pump through a pipeline mixer and then pumped into the reduction reactor; in step S5, the low-temperature drying temperature is less than 50°C.

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