A post-treatment method for improving the oxidation resistance of flaky silver powder

Abstract

The application relates to the technical field of metal powder material surface treatment, and discloses a post-treatment method for improving the oxidation resistance of flaky silver powder, which comprises the following steps: dispersing the flaky silver powder in an organic solvent containing a surfactant and nano silver seeds to form a suspension, and performing surface activation treatment by introducing ozone; adding a composite antioxidant containing a mercapto functional group and an amino functional group into the suspension to perform a surface modification reaction; adding a reducing passivator and an organic chelating agent to perform passivation treatment; performing solid-liquid separation and washing; and performing vacuum drying, and applying ultraviolet light irradiation in the early stage of drying. The nano silver seeds are used as bridging sites to improve the grafting density of the antioxidant, the mercapto chemical adsorption and the amino hydrogen bond network are used to cooperatively construct a molecular assembly layer, the reducing passivator is combined to fill active sites, the organic chelating agent is combined to remove metal impurity ions, and ultraviolet light-induced crosslinking is combined to form a three-dimensional network protection layer, so that the oxidation resistance of the flaky silver powder is effectively improved.

Description

Technical Field

[0001] This invention relates to the field of surface treatment technology for metal powder materials, specifically a post-treatment method for improving the oxidation resistance of flake silver powder. Background Technology

[0002] Flake silver powder is widely used as a conductive filler in conductive pastes due to its high conductivity and low contact resistance. It has important applications in electronic packaging, photovoltaic cells, flexible circuits and other fields. However, flake silver powder has a large specific surface area and its surface atoms have high surface energy. It is easy to react with oxygen in the air to form a silver oxide layer, which leads to the deterioration of its conductivity and thus affects the reliability and service life of the conductive paste.

[0003] In the prior art, common methods to improve the oxidation resistance of silver powder include coating the surface of the silver powder with organic protective agents or performing chemical plating treatment. For example, silver powder is soaked in a silver protective agent under heating conditions, so that the protective agent molecules are adsorbed on the surface of the silver powder to form a protective layer. However, this type of method has the following drawbacks: during the ball milling process, a large number of lattice defects and highly active crystal faces are generated on the surface of the silver powder. These active sites have a strong adsorption capacity for oxygen and become the preferred areas for oxidation reactions. Existing coating treatment methods are difficult to selectively passivate these microscopic active sites, resulting in insufficient protection at the active sites even though the protective layer covers the surface of the silver powder. Under high temperature and high humidity conditions, the silver powder is still prone to oxidation and discoloration. Summary of the Invention

[0004] The purpose of this invention is to provide a post-processing method for improving the antioxidant properties of flake silver powder, so as to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a post-treatment method for improving the antioxidant properties of flake silver powder, comprising the following steps: S1: Disperse the flake silver powder to be treated in an organic solvent containing a surfactant, and simultaneously add nano-silver seeds to the organic solvent. The particle size of the nano-silver seeds is 10nm to 50nm, and the amount added is 0.01% to 0.1% of the mass of the flake silver powder. Stir to form a flake silver powder suspension. The nano-silver seeds are uniformly dispersed in the suspension with the assistance of the surfactant. Ozone is introduced into the suspension for surface activation treatment. The ozone volume concentration is 10ppm to 100ppm, and the activation treatment time is 5 minutes to 30 minutes. S2: Add a composite antioxidant containing thiol and amino functional groups to the suspension and carry out a surface modification reaction under stirring conditions. The composite antioxidant binds to the surface of silver powder through the chemical adsorption of thiol groups. At the same time, the amino functional groups form a hydrogen bond network on the surface of silver powder. The nano-silver seeds serve as bridging sites for the chemical adsorption of thiol functional groups and silver powder. S3: Add a reducing passivating agent and an organic chelating agent to the suspension after surface modification, adjust the temperature of the suspension to 40℃~80℃, and continue stirring to carry out passivation treatment. The reducing passivating agent fills the active sites remaining on the surface of the silver powder, and the organic chelating agent captures free metal impurity ions in the suspension. S4: Separate the passivated suspension into solid and liquid components, collect the solid products, and wash the solid products with anhydrous ethanol after separation. S5: Dry the washed solid product in a vacuum environment at a temperature of 40℃~80℃ and a vacuum degree below -0.08MPa for 2 hours to 8 hours. Apply ultraviolet light irradiation at the initial stage of drying, with a wavelength of 254nm or 365nm and an intensity of 5mW / cm². 2 ~20mW / cm 2 The ultraviolet light irradiation time is 30 to 60 minutes.

[0006] As a preferred embodiment of the present invention, step S1 involves the following steps to disperse the flake-shaped silver powder in an organic solvent: The first step involves adding the surfactant to an organic solvent and stirring at room temperature for 5 to 15 minutes at a stirring speed of 300 to 500 rpm to obtain a surfactant solution. The surfactant is selected from at least one of polyvinylpyrrolidone, sodium dodecyl sulfate, and hexadecyltrimethylammonium bromide. The mass concentration of the surfactant in the organic solvent is 0.5 g / L to 5 g / L. The organic solvent is selected from at least one of anhydrous ethanol, isopropanol, and acetone. The second step is to add nano-silver seed crystals to the surfactant solution and ultrasonically disperse them for 2 to 5 minutes at an ultrasonic frequency of 40 kHz to 80 kHz. The third step is to degas the surfactant solution by bubbling nitrogen gas through it for 10 to 20 minutes before adding the flake silver powder. The fourth step involves adding the flake silver powder into the degassed solution and stirring for 10 to 40 minutes at a stirring speed of 200 to 600 rpm to obtain a flake silver powder suspension.

[0007] As a preferred embodiment of the present invention, the composite antioxidant in S2 is composed of an organic compound containing a thiol functional group and an auxiliary modifier containing an amino functional group. The organic compound containing a thiol functional group is selected from at least one of mercaptoacetic acid, mercaptoethanol, mercaptopropyltrimethoxysilane, and cysteine, and the mass percentage of the organic compound containing a thiol functional group in the composite antioxidant is 70% to 95%. The auxiliary modifier containing an amino functional group is selected from at least one of ethylenediamine, triethanolamine, and hexamethylenediamine, and the mass percentage of the auxiliary modifier in the composite antioxidant is 5% to 30%. The molar ratio of thiol functional group to amino functional group in the composite antioxidant is 1:0.1 to 1:0.5. The following steps are used in S2 to achieve the premixing and addition of the composite antioxidant: The first step involves mixing an organic compound containing a thiol functional group and an auxiliary modifier containing an amino functional group at a mass ratio of 4:1 to 19:1 to obtain a composite antioxidant. The second step is to dissolve the composite antioxidant in anhydrous ethanol for 5 to 10 minutes under stirring at a speed of 200 to 400 rpm to obtain a premixed solution. The mass concentration of the composite antioxidant in the premixed solution is 1 g / L to 10 g / L. The third step is to add the premixed solution to the suspension dropwise at a rate of 0.5 mL / min to 2 mL / min, while maintaining a stirring speed of 100 rpm to 400 rpm during the dropwise addition. Fourth step: After the premixed liquid is added, continue stirring for 5 to 10 minutes to ensure that the composite antioxidant is evenly distributed in the suspension.

[0008] As a preferred embodiment of the present invention, the surface modification reaction in S2 is carried out under the dual protection of a constant temperature water bath and an inert gas, specifically employing the following steps: The first step is to place the suspension after adding the composite antioxidant in a constant temperature water bath. The water bath temperature is set to 20℃~60℃, and the water bath temperature fluctuation range is ±1℃. The second step is to introduce an inert gas, either nitrogen or argon, into the container containing the suspension. The inert gas flow rate is 0.1 L / min to 1 L / min, and the aeration time is 5 to 10 minutes to remove air from the container. The third step involves continuously stirring the suspension under inert gas protection at a speed of 100 rpm to 400 rpm for a reaction time of 30 to 120 minutes. Fourth step: After the reaction is complete, stop stirring and let the suspension stand for 10 to 30 minutes to allow the composite antioxidant to spread fully on the surface of the silver powder. Fifth step: After settling, start stirring again at a speed of 50 to 100 rpm for 2 to 5 minutes to resuspend the settled silver powder.

[0009] As a preferred embodiment of the present invention, the reducing passivating agent in S3 is selected from at least one of sodium borohydride, ascorbic acid, and sodium hypophosphite, and the amount of the reducing passivating agent added is 0.1% to 1% of the mass of the flake silver powder; the organic chelating agent in S3 is selected from at least one of ethylenediaminetetraacetic acid, citric acid, and tartaric acid, and the amount of the organic chelating agent added is 5% to 20% of the mass of the reducing passivating agent; The mixed solution is prepared and added in S3 using the following steps: The first step involves mixing the reducing passivating agent and the organic chelating agent at a mass ratio of 5:1 to 20:1 and then adding them to deionized water. The mixture is then dissolved for 5 to 15 minutes under stirring at a speed of 200 to 500 rpm to obtain a mixed solution. The mass concentration of the reducing passivating agent in the mixed solution is 0.5 g / L to 5 g / L. The second step is to adjust the pH of the mixed solution to 4.0–6.0 using dilute hydrochloric acid or dilute sulfuric acid. The third step is to add the mixed solution to the surface-modified suspension by dropping it at a rate of 0.5 mL / min to 2 mL / min, while maintaining the stirring speed of the suspension at 200 rpm to 400 rpm during the dropping process. Fourth step: After the mixed solution has been added dropwise, adjust the stirring speed to 100 rpm to 200 rpm and continue stirring for 2 to 5 minutes.

[0010] As a preferred embodiment of the present invention, the passivation treatment in S3 is performed using a gradient heating method, specifically including the following steps: The first step is to bubble nitrogen gas into the suspension after the mixed solution has been added to remove oxygen. The nitrogen flow rate is 0.5 L / min to 2 L / min, and the bubbling time is 5 minutes to 15 minutes. The second step involves raising the temperature of the suspension from room temperature to 40°C using a water bath heating method at a rate of 2°C / min to 3°C / min. The suspension is then stirred at 40°C for 10 to 15 minutes at a stirring speed of 300 to 500 rpm. The third step is to raise the temperature of the suspension from 40°C to 60°C at a rate of 1°C / min to 2°C / min, and maintain stirring at 60°C for 15 to 25 minutes at a stirring speed of 200 to 400 rpm. The fourth step is to raise the temperature of the suspension from 60°C to 80°C at a rate of 1°C / min, and maintain stirring at 80°C for 10 to 20 minutes at a stirring speed of 100 to 200 rpm.

[0011] As a preferred embodiment of the present invention, pH adjustment is performed after the passivation treatment in step S3 using the following steps: The first step is to prepare a pH adjustment solution with a mass concentration of 1% to 10%. The pH adjustment agent is selected from at least one of dilute hydrochloric acid, dilute sulfuric acid, dilute nitric acid, and ammonia water. The second step is to use a pH meter to monitor the pH value of the suspension. The pH meter electrode is calibrated with a standard buffer solution before use. The third step is to add a pH adjusting agent solution to the suspension dropwise under stirring conditions at a rate of 0.2 mL / min to 1 mL / min, and adjust the pH value of the suspension to 6.5 to 7.5. Fourth step: After the pH value is adjusted, continue stirring for 5 to 15 minutes at a stirring speed of 200 to 400 rpm to make the pH value of the suspension system uniform and stable. Fifth step: After the pH value stabilizes, stop stirring and let the suspension stand for 5 to 10 minutes.

[0012] As a preferred embodiment of the present invention, step S4 involves solid-liquid separation and washing of the passivated suspension using a vacuum filtration method, specifically including the following steps: The first step is to pour the passivated suspension into a vacuum filtration device, place filter paper with a pore size of 0.22μm to 0.45μm in the vacuum filtration device, start the vacuum filtration, control the vacuum degree of the vacuum filtration to -0.06MPa to -0.09MPa, and collect the filter cake. The second step is to add anhydrous ethanol to the filter cake. The volume of anhydrous ethanol should be 2 to 5 times the mass of the filter cake. Stir for 2 to 5 minutes to redisperse the filter cake in the anhydrous ethanol. The third step is to start the vacuum filtration to separate the washing liquid and collect the washed filter cake. Fourth, repeat steps two and three 1 to 3 times, using fresh anhydrous ethanol for each wash; Fifth step: After the final washing is completed, maintain the filtration vacuum at -0.06MPa to -0.09MPa and continue filtration for 5 to 10 minutes to fully remove the residual washing liquid from the filter cake. The sixth step is to remove the filtered cake from the filter paper and transfer it to a clean glass dish.

[0013] As a preferred embodiment of the present invention, step S4 involves centrifugal separation and washing of the passivated suspension, specifically including the following steps: The first step is to transfer the passivated suspension to a centrifuge tube and centrifuge it in a centrifuge at a speed of 3000 rpm to 8000 rpm for 5 to 20 minutes. After centrifugation, discard the supernatant and collect the precipitate. The second step is to add anhydrous ethanol to the precipitate and ultrasonically disperse it for 1 to 3 minutes at a frequency of 40 kHz to 80 kHz, so that the precipitate is redispersed in anhydrous ethanol. The third step is to place the dispersed suspension in a centrifuge again for centrifugation at a speed of 3000 rpm to 8000 rpm for 5 to 20 minutes. After centrifugation, discard the supernatant and collect the precipitate. Fourth, repeat steps two and three 1 to 3 times, using fresh anhydrous ethanol for each wash; Fifth step: After the final centrifugation, place the precipitate in a fume hood at room temperature to air dry naturally for 5 to 10 minutes to allow the residual ethanol in the precipitate to evaporate. Step 6: Transfer the dried sediment to a clean glass dish.

[0014] As a preferred embodiment of the present invention, after the solid-liquid separation is completed in step S4, the filtrate is recycled using the following steps: The first step is to collect the filtrate generated during the solid-liquid separation process and filter the filtrate through a microporous membrane with a pore size of 0.22 μm to 0.45 μm. The second step is to measure the volume of the filtrate after filtration and add fresh organic solvent to the initial volume. The third step is to add surfactant to the initial concentration according to the volume of organic solvent to be added. The fourth step is to return the treated filtrate to S1 for use as an organic solvent. The filtrate is recycled 3 to 8 times. Fifth, after the filtrate has been recycled 8 times, discard the filtrate and prepare a new organic solvent.

[0015] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention introduces nano-silver seeds as bridging sites in the surface modification step, forming a lattice-matched interface between the nano-silver seeds and the flake silver powder matrix, providing more chemical adsorption attachment sites for thiol functional groups, thereby increasing the grafting density of the composite antioxidant on the silver powder surface and improving the uniformity and density of the surface modification layer.

[0016] 2. The invention employs a composite antioxidant containing thiol and amino functional groups. The thiol groups form chemical adsorption bonds with the surface of silver powder, while the amino functional groups form a hydrogen bond network. The two types of functional groups work synergistically to construct a molecular assembly layer on the surface of silver powder. The chemical anchoring effect of the thiol groups ensures a strong bond between the antioxidant and the silver powder matrix, while the intermolecular forces of the hydrogen bond network enhance the structural stability of the protective layer.

[0017] 3. The present invention fills the residual active sites on the surface of silver powder with a reducing passivating agent. The reducing passivating agent reduces the silver oxide that may exist at the active sites to elemental silver and adsorbs at the active sites to play a sealing role, thereby reducing the adsorption and diffusion channels of oxygen molecules on the surface of silver powder.

[0018] 4. This invention captures free metal impurity ions in the suspension using an organic chelating agent, preventing these impurity ions from catalyzing the oxidation reaction of silver powder during subsequent drying, thus reducing the possibility of forming electrochemical corrosion micro-batteries.

[0019] 5. This invention induces a photo-crosslinking reaction of the composite antioxidants remaining on the surface of silver powder by ultraviolet light irradiation, forming a three-dimensional network protective layer on the surface of the silver powder. This further improves the structural integrity and density of the protective layer, enabling the treated flake silver powder to maintain good antioxidant performance in high temperature and high humidity environments. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the overall process of a post-processing method for improving the antioxidant properties of flake silver powder according to the present invention. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Example 1 A post-processing method for improving the antioxidant properties of flake silver powder includes the following steps: S1: Disperse the flake silver powder to be treated in an organic solvent containing a surfactant, and simultaneously add nano-silver seeds to the organic solvent. The particle size of the nano-silver seeds is 10nm to 50nm, and the amount added is 0.01% to 0.1% of the mass of the flake silver powder. Stir to form a flake silver powder suspension. The nano-silver seeds are uniformly dispersed in the suspension with the assistance of the surfactant. Ozone is introduced into the suspension for surface activation treatment. The ozone volume concentration is 10ppm to 100ppm, and the activation treatment time is 5 minutes to 30 minutes. S2: Add a composite antioxidant containing thiol and amino functional groups to the suspension and carry out a surface modification reaction under stirring conditions. The composite antioxidant binds to the surface of silver powder through the chemical adsorption of thiol groups. At the same time, the amino functional groups form a hydrogen bond network on the surface of silver powder. The nano-silver seeds serve as bridging sites for the chemical adsorption of thiol functional groups and silver powder. S3: Add a reducing passivating agent and an organic chelating agent to the suspension after surface modification, adjust the temperature of the suspension to 40℃~80℃, and continue stirring to carry out passivation treatment. The reducing passivating agent fills the active sites remaining on the surface of the silver powder, and the organic chelating agent captures free metal impurity ions in the suspension. S4: Separate the passivated suspension into solid and liquid components, collect the solid products, and wash the solid products with anhydrous ethanol after separation. S5: Dry the washed solid product in a vacuum environment at a temperature of 40℃~80℃ and a vacuum degree below -0.08MPa for 2 hours to 8 hours. Apply ultraviolet light irradiation at the initial stage of drying, with a wavelength of 254nm or 365nm and an intensity of 5mW / cm². 2 ~20mW / cm 2 The ultraviolet light irradiation time is 30 to 60 minutes.

[0023] Furthermore, in S1, the following steps are used to disperse the flake silver powder in the organic solvent: The first step involves adding the surfactant to an organic solvent and stirring at room temperature for 5 to 15 minutes at a stirring speed of 300 to 500 rpm to obtain a surfactant solution. The surfactant is selected from at least one of polyvinylpyrrolidone, sodium dodecyl sulfate, and hexadecyltrimethylammonium bromide. The mass concentration of the surfactant in the organic solvent is 0.5 g / L to 5 g / L. The organic solvent is selected from at least one of anhydrous ethanol, isopropanol, and acetone. The second step is to add nano-silver seed crystals to the surfactant solution and ultrasonically disperse them for 2 to 5 minutes at an ultrasonic frequency of 40 kHz to 80 kHz. The third step is to degas the surfactant solution by bubbling nitrogen gas through it for 10 to 20 minutes before adding the flake silver powder. The fourth step involves adding the flake silver powder into the degassed solution and stirring for 10 to 40 minutes at a stirring speed of 200 to 600 rpm to obtain a flake silver powder suspension.

[0024] Furthermore, the composite antioxidant in S2 is composed of an organic compound containing a thiol functional group and an auxiliary modifier containing an amino functional group. The organic compound containing a thiol functional group is selected from at least one of mercaptoacetic acid, mercaptoethanol, mercaptopropyltrimethoxysilane, and cysteine, and the mass percentage of the organic compound containing a thiol functional group in the composite antioxidant is 70% to 95%. The auxiliary modifier containing an amino functional group is selected from at least one of ethylenediamine, triethanolamine, and hexamethylenediamine, and the mass percentage of the auxiliary modifier in the composite antioxidant is 5% to 30%. The molar ratio of thiol functional group to amino functional group in the composite antioxidant is 1:0.1 to 1:0.5. The following steps are used in S2 to achieve the premixing and addition of the composite antioxidant: The first step involves mixing an organic compound containing a thiol functional group and an auxiliary modifier containing an amino functional group at a mass ratio of 4:1 to 19:1 to obtain a composite antioxidant. The second step is to dissolve the composite antioxidant in anhydrous ethanol for 5 to 10 minutes under stirring at a speed of 200 to 400 rpm to obtain a premixed solution. The mass concentration of the composite antioxidant in the premixed solution is 1 g / L to 10 g / L. The third step is to add the premixed solution to the suspension dropwise at a rate of 0.5 mL / min to 2 mL / min, while maintaining a stirring speed of 100 rpm to 400 rpm during the dropwise addition. Fourth step: After the premixed liquid is added, continue stirring for 5 to 10 minutes to ensure that the composite antioxidant is evenly distributed in the suspension.

[0025] Furthermore, the surface modification reaction in S2 is carried out under dual protection conditions of a constant temperature water bath and an inert gas, specifically using the following steps: The first step is to place the suspension after adding the composite antioxidant in a constant temperature water bath. The water bath temperature is set to 20℃~60℃, and the water bath temperature fluctuation range is ±1℃. The second step is to introduce an inert gas, either nitrogen or argon, into the container containing the suspension. The inert gas flow rate is 0.1 L / min to 1 L / min, and the aeration time is 5 to 10 minutes to remove air from the container. The third step involves continuously stirring the suspension under inert gas protection at a speed of 100 rpm to 400 rpm for a reaction time of 30 to 120 minutes. Fourth step: After the reaction is complete, stop stirring and let the suspension stand for 10 to 30 minutes to allow the composite antioxidant to spread fully on the surface of the silver powder. Fifth step: After settling, start stirring again at a speed of 50 to 100 rpm for 2 to 5 minutes to resuspend the settled silver powder.

[0026] Furthermore, the reducing passivating agent in S3 is selected from at least one of sodium borohydride, ascorbic acid, and sodium hypophosphite, and the amount of the reducing passivating agent added is 0.1% to 1% of the mass of the flake silver powder; the organic chelating agent in S3 is selected from at least one of ethylenediaminetetraacetic acid, citric acid, and tartaric acid, and the amount of the organic chelating agent added is 5% to 20% of the mass of the reducing passivating agent. The mixed solution is prepared and added in S3 using the following steps: The first step involves mixing the reducing passivating agent and the organic chelating agent at a mass ratio of 5:1 to 20:1 and then adding them to deionized water. The mixture is then dissolved for 5 to 15 minutes under stirring at a speed of 200 to 500 rpm to obtain a mixed solution. The mass concentration of the reducing passivating agent in the mixed solution is 0.5 g / L to 5 g / L. The second step is to adjust the pH of the mixed solution to 4.0–6.0 using dilute hydrochloric acid or dilute sulfuric acid. The third step is to add the mixed solution to the surface-modified suspension by dropping it at a rate of 0.5 mL / min to 2 mL / min, while maintaining the stirring speed of the suspension at 200 rpm to 400 rpm during the dropping process. Fourth step: After the mixed solution has been added dropwise, adjust the stirring speed to 100 rpm to 200 rpm and continue stirring for 2 to 5 minutes.

[0027] Furthermore, the passivation process in S3 is performed using a gradient temperature increase method, specifically including the following steps: The first step is to bubble nitrogen gas into the suspension after the mixed solution has been added to remove oxygen. The nitrogen flow rate is 0.5 L / min to 2 L / min, and the bubbling time is 5 minutes to 15 minutes. The second step involves raising the temperature of the suspension from room temperature to 40°C using a water bath heating method at a rate of 2°C / min to 3°C / min. The suspension is then stirred at 40°C for 10 to 15 minutes at a stirring speed of 300 to 500 rpm. The third step is to raise the temperature of the suspension from 40°C to 60°C at a rate of 1°C / min to 2°C / min, and maintain stirring at 60°C for 15 to 25 minutes at a stirring speed of 200 to 400 rpm. The fourth step is to raise the temperature of the suspension from 60°C to 80°C at a rate of 1°C / min, and maintain stirring at 80°C for 10 to 20 minutes at a stirring speed of 100 to 200 rpm.

[0028] Furthermore, after the passivation treatment in S3 is completed, the pH is adjusted using the following steps: The first step is to prepare a pH adjustment solution with a mass concentration of 1% to 10%. The pH adjustment agent is selected from at least one of dilute hydrochloric acid, dilute sulfuric acid, dilute nitric acid, and ammonia water. The second step is to use a pH meter to monitor the pH value of the suspension. The pH meter electrode is calibrated with a standard buffer solution before use. The third step is to add a pH adjusting agent solution to the suspension dropwise under stirring conditions at a rate of 0.2 mL / min to 1 mL / min, and adjust the pH value of the suspension to 6.5 to 7.5. Fourth step: After the pH value is adjusted, continue stirring for 5 to 15 minutes at a stirring speed of 200 to 400 rpm to make the pH value of the suspension system uniform and stable. Fifth step: After the pH value stabilizes, stop stirring and let the suspension stand for 5 to 10 minutes.

[0029] Furthermore, in step S4, the passivated suspension is subjected to solid-liquid separation and washing using a vacuum filtration method, specifically including the following steps: The first step is to pour the passivated suspension into a vacuum filtration device, place filter paper with a pore size of 0.22μm to 0.45μm in the vacuum filtration device, start the vacuum filtration, control the vacuum degree of the vacuum filtration to -0.06MPa to -0.09MPa, and collect the filter cake. The second step is to add anhydrous ethanol to the filter cake. The volume of anhydrous ethanol should be 2 to 5 times the mass of the filter cake. Stir for 2 to 5 minutes to redisperse the filter cake in the anhydrous ethanol. The third step is to start the vacuum filtration to separate the washing liquid and collect the washed filter cake. Fourth, repeat steps two and three 1 to 3 times, using fresh anhydrous ethanol for each wash; Fifth step: After the final washing is completed, maintain the filtration vacuum at -0.06MPa to -0.09MPa and continue filtration for 5 to 10 minutes to fully remove the residual washing liquid from the filter cake. The sixth step is to remove the filtered cake from the filter paper and transfer it to a clean glass dish.

[0030] Furthermore, in step S4, centrifugation is used to separate the passivated suspension into solid and liquid components and to wash it. Specifically, this includes the following steps: The first step is to transfer the passivated suspension to a centrifuge tube and centrifuge it in a centrifuge at a speed of 3000 rpm to 8000 rpm for 5 to 20 minutes. After centrifugation, discard the supernatant and collect the precipitate. The second step is to add anhydrous ethanol to the precipitate and ultrasonically disperse it for 1 to 3 minutes at a frequency of 40 kHz to 80 kHz, so that the precipitate is redispersed in anhydrous ethanol. The third step is to place the dispersed suspension in a centrifuge again for centrifugation at a speed of 3000 rpm to 8000 rpm for 5 to 20 minutes. After centrifugation, discard the supernatant and collect the precipitate. Fourth, repeat steps two and three 1 to 3 times, using fresh anhydrous ethanol for each wash; Fifth step: After the final centrifugation, place the precipitate in a fume hood at room temperature to air dry naturally for 5 to 10 minutes to allow the residual ethanol in the precipitate to evaporate. Step 6: Transfer the dried sediment to a clean glass dish.

[0031] Furthermore, after solid-liquid separation in S4 is completed, the filtrate is recycled using the following steps: The first step is to collect the filtrate generated during the solid-liquid separation process and filter the filtrate through a microporous membrane with a pore size of 0.22 μm to 0.45 μm. The second step is to measure the volume of the filtrate after filtration and add fresh organic solvent to the initial volume. The third step is to add surfactant to the initial concentration according to the volume of organic solvent to be added. The fourth step is to return the treated filtrate to S1 for use as an organic solvent. The filtrate is recycled 3 to 8 times. Fifth, after the filtrate has been recycled 8 times, discard the filtrate and prepare a new organic solvent.

[0032] Example 2 In this embodiment, step S2 uses mercaptoacetic acid as an organic compound containing thiol functional groups and ethylenediamine as an auxiliary modifier containing amino functional groups. The mass ratio of mercaptoacetic acid to ethylenediamine is 9:1, and the molar ratio of thiol functional groups to amino functional groups in the composite antioxidant is 1:0.2.

[0033] The specific steps are as follows: In step S1, the surfactant polyvinylpyrrolidone was added to anhydrous ethanol and stirred at room temperature for 10 min at a stirring speed of 400 r / min. The mass concentration of polyvinylpyrrolidone in anhydrous ethanol was 2 g / L. Nano-silver seeds with an average particle size of 30 nm were added to the obtained surfactant solution at an amount of 0.05% of the mass of the flake silver powder to be treated. The solution was ultrasonically dispersed for 3 min at a frequency of 60 kHz. Nitrogen gas was bubbled into the surfactant solution for 15 min for degassing. The flake silver powder to be treated with an average particle size of 6 μm and an aspect ratio of 40:1 was added to the degassed solution. The solution was stirred at a stirring speed of 400 r / min for 25 min to form a flake silver powder suspension. Ozone was introduced into the suspension for surface activation treatment at a volume concentration of 50 ppm for 15 min.

[0034] In S2, mercaptoacetic acid and ethylenediamine are mixed at a mass ratio of 9:1 to obtain a composite antioxidant. The composite antioxidant is dissolved in anhydrous ethanol and stirred for 8 minutes at a stirring speed of 300 r / min to obtain a premixed solution. The mass concentration of the composite antioxidant in the premixed solution is 5 g / L. The premixed solution is added to the suspension dropwise at a dropping rate of 1 mL / min, while maintaining a stirring speed of 250 r / min during the dropwise addition. The amount of composite antioxidant added is 2.5% of the mass of the flake silver powder. After the premixed solution is completely added, stirring is continued for 8 minutes.

[0035] The suspension after adding the composite antioxidant was placed in a constant temperature water bath at 40°C with a temperature fluctuation range of ±1°C. Nitrogen gas was introduced into the container containing the suspension at a flow rate of 0.5 L / min for 8 min. The suspension was continuously stirred under nitrogen protection at a stirring speed of 250 r / min for 75 min. After the reaction was completed, stirring was stopped, and the suspension was allowed to stand for 20 min. After standing, stirring was restarted at a stirring speed of 80 r / min for 3 min.

[0036] In S3, ascorbic acid was selected as the reducing passivating agent, and its addition amount was 0.5% of the mass of the flake silver powder; citric acid was selected as the organic chelating agent, and its addition amount was 12% of the mass of ascorbic acid. Ascorbic acid and citric acid were mixed at a mass ratio of 8:1 and added to deionized water. The mixture was dissolved for 10 minutes under stirring at a stirring speed of 350 r / min to obtain a mixed solution with a mass concentration of 2.5 g / L of ascorbic acid. The pH of the mixed solution was adjusted to 5.0 using dilute hydrochloric acid. The mixed solution was added dropwise to the surface-modified suspension at a dropping rate of 1 mL / min. During the dropping process, the stirring speed of the suspension was maintained at 300 r / min. After the mixed solution was added dropwise, the stirring speed was adjusted to 150 r / min and stirring was continued for 3 minutes.

[0037] Nitrogen gas was bubbled into the suspension after the mixed solution was added to remove oxygen. The nitrogen flow rate was 1 L / min and the bubbling time was 10 min. The temperature of the suspension was raised from room temperature to 40°C using a water bath heating method at a heating rate of 2.5°C / min. The suspension was stirred at 40°C for 12 min at a stirring speed of 400 r / min. The temperature of the suspension was then raised from 40°C to 60°C at a heating rate of 1.5°C / min. The suspension was stirred at 60°C for 20 min at a stirring speed of 300 r / min. The temperature of the suspension was then raised from 60°C to 80°C at a heating rate of 1°C / min. The suspension was stirred at 80°C for 15 min at a stirring speed of 150 r / min.

[0038] After passivation treatment, a 5% ammonia solution was prepared as a pH adjuster. The pH value of the suspension was monitored using a pH meter. The pH meter electrode was calibrated with a standard buffer solution before use. The ammonia solution was added dropwise to the suspension under stirring at a rate of 0.5 mL / min to adjust the pH value of the suspension to 7.0. After the pH value was adjusted, stirring was continued for 10 min at a stirring speed of 300 r / min. After the pH value stabilized, stirring was stopped, and the suspension was allowed to stand for 8 min.

[0039] In step S4, the passivated suspension is separated into solid and liquid components and washed using vacuum filtration. The passivated suspension is poured into a vacuum filtration device, and filter paper with a pore size of 0.22 μm is placed in the device. Vacuum filtration is started, and the vacuum degree is controlled at -0.08 MPa. The filter cake is collected, and anhydrous ethanol is added to it. The volume of anhydrous ethanol is three times the mass of the filter cake. The mixture is stirred for 3 minutes to redisperse the filter cake in the anhydrous ethanol. Vacuum filtration is started again, and the washing liquid is separated by vacuum filtration. The washed filter cake is collected. The washing operation is repeated twice, using fresh anhydrous ethanol each time. After the last washing, the vacuum degree is maintained at -0.08 MPa and filtration continues for 8 minutes. The filtered filter cake is removed from the filter paper and transferred to a clean glass dish.

[0040] In step S5, the washed solid product was dried in a vacuum environment at a temperature of 60°C and a vacuum degree of -0.09 MPa for 5 hours. Ultraviolet (UV) light irradiation was applied at the beginning of the drying process, with a wavelength of 254 nm and an intensity of 12 mW / cm². 2 The ultraviolet light irradiation time was 45 minutes.

[0041] In the above steps, the composite antioxidant binds to the silver powder surface through the chemical adsorption of thiol groups. At the same time, amino functional groups form a hydrogen bond network on the silver powder surface. The Ag-S bonds formed between thiol groups and the silver surface anchor the antioxidant molecules to the silver powder surface. The hydrogen bond network between amino functional groups and between amino groups and the oxidation activation layer on the silver powder surface constructs a molecular assembly layer on the silver powder surface. The nano-silver seeds serve as bridging sites for the chemical adsorption of thiol functional groups and the silver powder surface, thereby increasing the grafting density of antioxidants per unit area.

[0042] The reducing passivating agent fills the active sites remaining on the surface of silver powder under heating conditions. Ascorbic acid reduces the silver oxide present at the active sites to elemental silver. The dehydroascorbic acid molecules formed after oxidation of ascorbic acid are adsorbed at the active sites. The carboxyl and hydroxyl groups in the citric acid molecule form chelates with the free metal impurity ions in the suspension, removing the impurity ions from the suspension.

[0043] In the gradient temperature passivation treatment, surface adsorption and preliminary reduction reactions are carried out at a low temperature of 40℃; at 60℃, passivating agent molecules penetrate into the microscopic active sites on the surface of silver powder; at 80℃, the passivation reaction tends to be complete; ultraviolet light irradiation in the early stage of drying causes the residual composite antioxidant on the surface of silver powder to undergo photo-induced cross-linking reaction; mercaptoacetic acid molecules undergo oxidative coupling reaction under ultraviolet light irradiation to form disulfide bonds; and the amino groups in ethylenediamine molecules undergo amidation reaction with the carboxyl groups in mercaptoacetic acid molecules to form a three-dimensional network protective layer on the surface of silver powder.

[0044] Example 3 In this embodiment, step S2 uses mercaptopropyltrimethoxysilane as an organic compound containing thiol functional groups and triethanolamine as an auxiliary modifier containing amino functional groups. The mass ratio of mercaptopropyltrimethoxysilane to triethanolamine is 15:1, and the molar ratio of thiol functional groups to amino functional groups in the composite antioxidant is 1:0.4.

[0045] The specific steps are as follows: In step S1, sodium dodecyl sulfate, a surfactant, was added to isopropanol and stirred at room temperature for 6 minutes at a stirring speed of 450 r / min. The mass concentration of sodium dodecyl sulfate in isopropanol was 4 g / L. Nano-silver seeds with an average particle size of 20 nm were added to the resulting surfactant solution at an addition amount of 0.08% of the mass of the flake silver powder to be treated. The solution was ultrasonically dispersed for 4 minutes at a frequency of 50 kHz. Nitrogen gas was bubbled into the surfactant solution for 12 minutes for degassing. The flake silver powder to be treated with an average particle size of 4 μm and an aspect ratio of 60:1 was added to the degassed solution. The solution was stirred at a stirring speed of 500 r / min for 15 minutes to form a flake silver powder suspension. Ozone was introduced into the suspension for surface activation treatment at a volume concentration of 80 ppm for 10 minutes.

[0046] In S2, mercaptopropyltrimethoxysilane and triethanolamine are mixed at a mass ratio of 15:1 to obtain a composite antioxidant. The composite antioxidant is dissolved in anhydrous ethanol and stirred for 6 minutes at a stirring speed of 350 r / min to obtain a premixed solution. The mass concentration of the composite antioxidant in the premixed solution is 8 g / L. The premixed solution is added to the suspension dropwise at a dropping rate of 1.5 mL / min, while maintaining a stirring speed of 300 r / min during the dropwise addition. The amount of composite antioxidant added is 4% of the mass of the flake silver powder. After the premixed solution is completely added, stirring is continued for 6 minutes.

[0047] The suspension after adding the composite antioxidant was placed in a constant temperature water bath at 50°C with a temperature fluctuation range of ±1°C. Argon gas was introduced into the container containing the suspension at a flow rate of 0.8 L / min for 6 min. The suspension was continuously stirred under argon protection at a stirring speed of 300 r / min for 90 min. After the reaction was completed, stirring was stopped, and the suspension was allowed to stand for 25 min. After standing, stirring was restarted at a stirring speed of 60 r / min for 4 min.

[0048] In S3, sodium borohydride was selected as the reducing passivating agent, and its addition amount was 0.8% of the mass of the flake silver powder; ethylenediaminetetraacetic acid (EDTA) was selected as the organic chelating agent, and its addition amount was 18% of the mass of sodium borohydride. Sodium borohydride and EDTA were mixed at a mass ratio of 15:1 and added to deionized water. The mixture was dissolved for 12 minutes under stirring at a stirring speed of 400 r / min to obtain a mixed solution. The mass concentration of sodium borohydride in the mixed solution was 4 g / L. The pH of the mixed solution was adjusted to 4.5 using dilute sulfuric acid. The mixed solution was added dropwise to the surface-modified suspension at a dropping rate of 1.5 mL / min. During the dropping process, the stirring speed of the suspension was maintained at 350 r / min. After the mixed solution was added dropwise, the stirring speed was adjusted to 180 r / min and stirring was continued for 4 minutes.

[0049] Nitrogen gas was bubbled into the suspension after the mixed solution was added to remove oxygen. The nitrogen flow rate was 1.5 L / min and the bubbling time was 8 min. The temperature of the suspension was raised from room temperature to 40°C using a water bath heating method at a heating rate of 2°C / min. The suspension was stirred at 40°C for 14 min at a stirring speed of 450 r / min. The temperature of the suspension was then raised from 40°C to 60°C at a heating rate of 1.8°C / min. The suspension was stirred at 60°C for 18 min at a stirring speed of 350 r / min. The temperature of the suspension was then raised from 60°C to 80°C at a heating rate of 1°C / min. The suspension was stirred at 80°C for 12 min at a stirring speed of 180 r / min.

[0050] After passivation treatment, a 3% (w / w) dilute nitric acid solution was prepared as a pH adjuster. The pH value of the suspension was monitored using a pH meter. The pH meter electrode was calibrated with a standard buffer solution before use. The dilute nitric acid solution was added dropwise to the suspension under stirring at a rate of 0.8 mL / min to adjust the pH value of the suspension to 6.8. After the pH value was adjusted, stirring was continued for 8 min at a stirring speed of 350 r / min. After the pH value stabilized, stirring was stopped, and the suspension was allowed to stand for 6 min.

[0051] In step S4, centrifugation is used to separate the passivated suspension into solid and liquid components and wash it. The passivated suspension is transferred to a centrifuge tube and centrifuged at 5000 rpm for 10 minutes. After centrifugation, the supernatant is discarded, and the precipitate is collected. Anhydrous ethanol is added to the precipitate, and the mixture is ultrasonically dispersed for 2 minutes at a frequency of 60 kHz to redisperse the precipitate in anhydrous ethanol. The dispersed suspension is then centrifuged again at 5000 rpm for 10 minutes. After centrifugation, the supernatant is discarded, and the precipitate is collected. The washing operation is repeated twice, using fresh anhydrous ethanol each time. After the final centrifugation, the precipitate is air-dried at room temperature in a fume hood for 8 minutes. The dried precipitate is then transferred to a clean glass dish.

[0052] In step S5, the washed solid product was dried in a vacuum environment at a temperature of 70°C and a vacuum degree of -0.085 MPa for 3 hours. Ultraviolet (UV) light irradiation was applied at the beginning of the drying process, with a wavelength of 365 nm and an intensity of 15 mW / cm². 2 The ultraviolet light irradiation time was 35 minutes.

[0053] In the above steps, the methoxy groups in the mercaptopropyltrimethoxysilane molecule undergo hydrolysis and condensation reaction under the action of residual moisture on the silver powder surface, forming a siloxane network structure. The siloxane network structure and the chemisorption layer of mercapto groups on the silver powder surface constitute a double-layer protective structure: the inner layer is the chemisorption layer of mercapto groups on the silver surface, and the outer layer is the siloxane polymer network layer. The hydroxyl groups in the triethanolamine molecule participate in the formation of the hydrogen bond network, and the tertiary amine structure in the triethanolamine molecule regulates the local microenvironment on the silver powder surface.

[0054] Sodium borohydride reduces silver oxide at the active sites on the surface of silver powder in a temperature range of 40℃ to 80℃. The reduction product of sodium borohydride, sodium metaborate, is removed during the washing process. Ethylenediaminetetraacetic acid forms a chelate ring structure with the metal impurity ions in the suspension, thereby removing the impurity ions from the suspension.

[0055] During centrifugation, the flake-shaped silver powder settles under the action of centrifugal force. The ultrasonic dispersion step breaks up the soft agglomeration between silver powder particles during washing, allowing the silver powder particles to disperse in the washing liquid. Ultraviolet light irradiation triggers the cross-linking reaction between mercaptopropyltrimethoxysilane molecules in the early stage of drying. The mercapto groups are oxidized under ultraviolet light to form disulfide bonds, forming intermolecular covalent cross-links between adjacent antioxidant molecules on the surface of the silver powder. The silanol groups formed by the hydrolysis of methoxy groups undergo a condensation reaction, further enhancing the compactness of the outer protective layer.

[0056] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A post-processing method for improving the antioxidant properties of flake silver powder, characterized in that, Includes the following steps: S1: Disperse the flake silver powder to be treated in an organic solvent containing a surfactant, and simultaneously add nano-silver seeds to the organic solvent. The particle size of the nano-silver seeds is 10nm to 50nm, and the amount added is 0.01% to 0.1% of the mass of the flake silver powder. Stir to form a flake silver powder suspension. The nano-silver seeds are uniformly dispersed in the suspension with the assistance of the surfactant. Ozone is introduced into the suspension for surface activation treatment. The ozone volume concentration is 10ppm to 100ppm, and the activation treatment time is 5 minutes to 30 minutes. S2: Add a composite antioxidant containing thiol and amino functional groups to the suspension and carry out a surface modification reaction under stirring conditions. The composite antioxidant binds to the surface of silver powder through the chemical adsorption of thiol groups. At the same time, the amino functional groups form a hydrogen bond network on the surface of silver powder. The nano-silver seeds serve as bridging sites for the chemical adsorption of thiol functional groups and silver powder. S3: Add a reducing passivating agent and an organic chelating agent to the suspension after surface modification, adjust the temperature of the suspension to 40℃~80℃, and continue stirring to carry out passivation treatment. The reducing passivating agent fills the active sites remaining on the surface of the silver powder, and the organic chelating agent captures free metal impurity ions in the suspension. S4: Separate the passivated suspension into solid and liquid components, collect the solid products, and wash the solid products with anhydrous ethanol after separation. S5: Dry the washed solid product in a vacuum environment at a temperature of 40℃~80℃ and a vacuum degree below -0.08MPa for 2 hours to 8 hours. Apply ultraviolet light irradiation at the initial stage of drying, with a wavelength of 254nm or 365nm and an intensity of 5mW / cm². 2 ~20mW / cm 2 The ultraviolet light irradiation time is 30 to 60 minutes.

2. The method according to claim 1, characterized in that, The following steps are used in step S1 to disperse the flake-shaped silver powder in the organic solvent: The first step involves adding the surfactant to an organic solvent and stirring at room temperature for 5 to 15 minutes at a stirring speed of 300 to 500 rpm to obtain a surfactant solution. The surfactant is selected from at least one of polyvinylpyrrolidone, sodium dodecyl sulfate, and hexadecyltrimethylammonium bromide. The mass concentration of the surfactant in the organic solvent is 0.5 g / L to 5 g / L. The organic solvent is selected from at least one of anhydrous ethanol, isopropanol, and acetone. The second step is to add nano-silver seed crystals to the surfactant solution and ultrasonically disperse them for 2 to 5 minutes at an ultrasonic frequency of 40 kHz to 80 kHz. The third step is to degas the surfactant solution by bubbling nitrogen gas through it for 10 to 20 minutes before adding the flake silver powder. The fourth step involves adding the flake silver powder into the degassed solution and stirring for 10 to 40 minutes at a stirring speed of 200 to 600 rpm to obtain a flake silver powder suspension.

3. The method according to claim 1, characterized in that, The composite antioxidant in S2 is composed of an organic compound containing a thiol functional group and an auxiliary modifier containing an amino functional group. The organic compound containing a thiol functional group is selected from at least one of mercaptoacetic acid, mercaptoethanol, mercaptopropyltrimethoxysilane, and cysteine, and the mass percentage of the organic compound containing a thiol functional group in the composite antioxidant is 70% to 95%. The auxiliary modifier containing an amino functional group is selected from at least one of ethylenediamine, triethanolamine, and hexamethylenediamine, and the mass percentage of the auxiliary modifier in the composite antioxidant is 5% to 30%. The molar ratio of thiol functional group to amino functional group in the composite antioxidant is 1:0.1 to 1:0.

5. The following steps are used in S2 to achieve the premixing and addition of the composite antioxidant: The first step involves mixing an organic compound containing a thiol functional group and an auxiliary modifier containing an amino functional group at a mass ratio of 4:1 to 19:1 to obtain a composite antioxidant. The second step is to dissolve the composite antioxidant in anhydrous ethanol for 5 to 10 minutes under stirring at a speed of 200 to 400 rpm to obtain a premixed solution. The mass concentration of the composite antioxidant in the premixed solution is 1 g / L to 10 g / L. The third step is to add the premixed solution to the suspension dropwise at a rate of 0.5 mL / min to 2 mL / min, while maintaining a stirring speed of 100 rpm to 400 rpm during the dropwise addition. Fourth step: After the premixed liquid is added, continue stirring for 5 to 10 minutes to ensure that the composite antioxidant is evenly distributed in the suspension.

4. The method according to claim 1, characterized in that, The surface modification reaction in S2 is carried out under the dual protection of a constant temperature water bath and an inert gas, specifically using the following steps: The first step is to place the suspension after adding the composite antioxidant in a constant temperature water bath. The water bath temperature is set to 20℃~60℃, and the water bath temperature fluctuation range is ±1℃. The second step is to introduce an inert gas, either nitrogen or argon, into the container containing the suspension. The inert gas flow rate is 0.1 L / min to 1 L / min, and the aeration time is 5 to 10 minutes to remove air from the container. The third step involves continuously stirring the suspension under inert gas protection at a speed of 100 rpm to 400 rpm for a reaction time of 30 to 120 minutes. Fourth step: After the reaction is complete, stop stirring and let the suspension stand for 10 to 30 minutes to allow the composite antioxidant to spread fully on the surface of the silver powder. Fifth step: After settling, start stirring again at a speed of 50 to 100 rpm for 2 to 5 minutes to resuspend the settled silver powder.

5. The method according to claim 1, characterized in that, The reducing passivating agent in S3 is selected from at least one of sodium borohydride, ascorbic acid, and sodium hypophosphite, and the amount of the reducing passivating agent added is 0.1% to 1% of the mass of the flake silver powder; the organic chelating agent in S3 is selected from at least one of ethylenediaminetetraacetic acid, citric acid, and tartaric acid, and the amount of the organic chelating agent added is 5% to 20% of the mass of the reducing passivating agent. The mixed solution is prepared and added in S3 using the following steps: The first step involves mixing the reducing passivating agent and the organic chelating agent at a mass ratio of 5:1 to 20:1 and then adding them to deionized water. The mixture is then dissolved for 5 to 15 minutes under stirring at a speed of 200 to 500 rpm to obtain a mixed solution. The mass concentration of the reducing passivating agent in the mixed solution is 0.5 g / L to 5 g / L. The second step is to adjust the pH of the mixed solution to 4.0–6.0 using dilute hydrochloric acid or dilute sulfuric acid. The third step is to add the mixed solution to the surface-modified suspension by dropping it at a rate of 0.5 mL / min to 2 mL / min, while maintaining the stirring speed of the suspension at 200 rpm to 400 rpm during the dropping process. Fourth step: After the mixed solution has been added dropwise, adjust the stirring speed to 100 rpm to 200 rpm and continue stirring for 2 to 5 minutes.

6. The method according to claim 1, characterized in that, The passivation process in S3 is performed using a gradient heating method, specifically including the following steps: The first step is to bubble nitrogen gas into the suspension after the mixed solution has been added to remove oxygen. The nitrogen flow rate is 0.5 L / min to 2 L / min, and the bubbling time is 5 minutes to 15 minutes. The second step involves raising the temperature of the suspension from room temperature to 40°C using a water bath heating method at a rate of 2°C / min to 3°C / min. The suspension is then stirred at 40°C for 10 to 15 minutes at a stirring speed of 300 to 500 rpm. The third step is to raise the temperature of the suspension from 40°C to 60°C at a rate of 1°C / min to 2°C / min, and maintain stirring at 60°C for 15 to 25 minutes at a stirring speed of 200 to 400 rpm. The fourth step is to raise the temperature of the suspension from 60°C to 80°C at a rate of 1°C / min, and maintain stirring at 80°C for 10 to 20 minutes at a speed of 100 to 200 rpm.

7. The method according to claim 1, characterized in that, After the passivation treatment in S3 is completed, the pH is adjusted using the following steps: The first step is to prepare a pH adjustment solution with a mass concentration of 1% to 10%. The pH adjustment agent is selected from at least one of dilute hydrochloric acid, dilute sulfuric acid, dilute nitric acid, and ammonia water. The second step is to use a pH meter to monitor the pH value of the suspension. The pH meter electrode is calibrated with a standard buffer solution before use. The third step is to add a pH adjusting agent solution to the suspension dropwise under stirring conditions at a rate of 0.2 mL / min to 1 mL / min, and adjust the pH value of the suspension to 6.5 to 7.

5. Fourth step: After the pH value is adjusted, continue stirring for 5 to 15 minutes at a stirring speed of 200 to 400 rpm to make the pH value of the suspension system uniform and stable. Fifth step: After the pH value stabilizes, stop stirring and let the suspension stand for 5 to 10 minutes.

8. The method according to claim 1, characterized in that, In step S4, the passivated suspension is separated into solid and liquid components and washed using a vacuum filtration method, specifically including the following steps: The first step is to pour the passivated suspension into a vacuum filtration device, place filter paper with a pore size of 0.22μm to 0.45μm in the vacuum filtration device, start the vacuum filtration, control the vacuum degree of the vacuum filtration to -0.06MPa to -0.09MPa, and collect the filter cake. The second step is to add anhydrous ethanol to the filter cake. The volume of anhydrous ethanol should be 2 to 5 times the mass of the filter cake. Stir for 2 to 5 minutes to redisperse the filter cake in the anhydrous ethanol. The third step is to start the vacuum filtration to separate the washing liquid and collect the washed filter cake. Fourth, repeat steps two and three 1 to 3 times, using fresh anhydrous ethanol for each wash; Fifth step: After the final washing is completed, maintain the filtration vacuum at -0.06MPa to -0.09MPa and continue filtration for 5 to 10 minutes to fully remove the residual washing liquid from the filter cake. The sixth step is to remove the filtered cake from the filter paper and transfer it to a clean glass dish.

9. The method according to claim 1, characterized in that, In step S4, centrifugation is used to separate the passivated suspension into solid and liquid components and wash it. Specifically, this includes the following steps: The first step is to transfer the passivated suspension to a centrifuge tube and centrifuge it in a centrifuge at a speed of 3000 rpm to 8000 rpm for 5 to 20 minutes. After centrifugation, discard the supernatant and collect the precipitate. The second step is to add anhydrous ethanol to the precipitate and ultrasonically disperse it for 1 to 3 minutes at a frequency of 40 kHz to 80 kHz, so that the precipitate is redispersed in anhydrous ethanol. The third step is to place the dispersed suspension in a centrifuge again for centrifugation at a speed of 3000 rpm to 8000 rpm for 5 to 20 minutes. After centrifugation, discard the supernatant and collect the precipitate. Fourth, repeat steps two and three 1 to 3 times, using fresh anhydrous ethanol for each wash; Fifth step: After the final centrifugation, place the precipitate in a fume hood at room temperature to air dry naturally for 5 to 10 minutes to allow the residual ethanol in the precipitate to evaporate. Step 6: Transfer the dried sediment to a clean glass dish.

10. The method according to claim 1, characterized in that, After the solid-liquid separation in step S4 is completed, the filtrate is recycled using the following steps: The first step is to collect the filtrate generated during the solid-liquid separation process and filter the filtrate through a microporous membrane with a pore size of 0.22 μm to 0.45 μm. The second step is to measure the volume of the filtrate after filtration and add fresh organic solvent to the initial volume. The third step is to add surfactant to the initial concentration according to the volume of organic solvent to be added. The fourth step is to return the treated filtrate to S1 for use as an organic solvent. The filtrate is recycled 3 to 8 times. Fifth, after the filtrate has been recycled 8 times, discard the filtrate and prepare a new organic solvent.

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