Preparation method of sphere-like silver powder with holes

Abstract

The invention belongs to the technical field of silver powder preparation, and particularly relates to a preparation method of sphere-like porous silver powder, which comprises the following steps: (1) dissolving silver nitrate in deionized water to obtain a silver-containing solution A; (2) adding a surface treating agent into a water-soluble organic ester solvent, adding deionized water while stirring, and adding ascorbic acid to obtain a reaction base solution B; (3) diluting the aqueous solution of hydrazine hydrate with deionized water, and adding a pH value regulator to obtain a reducing agent solution C; (4) adding the silver-containing solution A and the reducing agent solution C into the reaction base solution B for reaction; and (5) after the reaction is finished, the reaction liquid in the step (4) is subjected to centrifugal separation, washing and drying, and then the sphere-like silver powder with holes is obtained. The method has the beneficial effects that ascorbic acid serving as a reducing agent is added into the reaction base solution B, hydrazine hydrate serving as a reducing agent solution C and the silver-containing solution A are added at the same time, and the silver powder generates a porous structure under the state that the silver powder is kept in a sphere-like state.

Description

Technical Field

[0001] The invention belongs to the technical field of silver powder preparation, and particularly relates to a method for preparing spherical silver powder with holes. Background Art

[0002] At present, most of the silver powder used in conductive silver paste is ultrafine silver powder, and its morphology is generally spherical silver powder, quasi-spherical silver powder and flaky silver powder. Spherical silver powder and quasi-spherical silver powder have a high degree of sphericity, and the prepared silver paste has good fluidity and can pass through the positive electrode fine grid line well. Spherical silver powder and quasi-spherical silver powder are used in solar slurry to form a good dense stacking. After screen printing and sintering, it can effectively reduce the porosity, increase the opening voltage and filling of solar cells, and thus effectively improve the photoelectric conversion efficiency of the battery.

[0003] The market demand for conductive silver paste that can be sintered at low temperatures is growing, so silver powder is required to be suitable for sintering at low temperatures. When the silver powder used in the conductive silver paste has holes, compared with the silver powder with a nearly solid structure, the silver powder with holes has a larger specific surface area, which increases the adsorption of organic matter. During sintering, more organic matter is separated from the silver powder, making the silver powder suitable for sintering at low temperatures. Therefore, how to prepare spherical silver powder with holes has become an urgent problem to be solved. Summary of the invention

[0004] The purpose of the present invention is to solve the above problems and provide a method for preparing spherical porous silver powder.

[0005] The present invention relates to a method for preparing spherical porous silver powder, comprising the following steps: (1) Preparing a silver-containing solution A: dissolving silver nitrate in deionized water to obtain a silver-containing solution A; (2) preparing reaction base liquid B: adding the surface treatment agent to a water-soluble organic ester solvent, adding deionized water under stirring, and adding ascorbic acid to obtain reaction base liquid B; (3) preparing reducing agent solution C: diluting the aqueous solution of hydrazine hydrate with deionized water, and adding a pH adjuster to obtain reducing agent solution C; (4) adding the silver-containing solution A and the reducing agent solution C to the reaction base solution B for reaction; (5) After the reaction is completed, the reaction solution in step (4) is centrifuged, washed and dried to obtain spherical porous silver powder.

[0006] Preferably, the molar concentration of silver nitrate in the silver-containing solution A is 3.5-4.5 mol / L.

[0007] Preferably, the volume of the deionized water in the reaction base solution B is 2 to 3 times that of the deionized water in the silver-containing solution A.

[0008] Preferably, the surface treatment agent in the reaction base liquid B is at least one of octanoic acid, dodecanoic acid, stearic acid and oleic acid; the amount of the surface treatment agent added to the reaction base liquid B is 3.0 to 5.0 wt % relative to the amount of silver in the silver-containing solution A.

[0009] Preferably, the organic ester solvent in the reaction base liquid B is at least one of a dibasic acid ester mixture, propylene glycol methyl ether acetate and ethylene glycol diacetate; the dibasic acid ester mixture includes dimethyl succinate, dimethyl glutarate and dimethyl adipate; the volume of the organic ester solvent in the reaction base liquid B is 0.25 to 0.35 times the volume of the deionized water in the reaction base liquid B.

[0010] Preferably, the amount of ascorbic acid added to the reaction base solution B is 1.0 to 1.5 molar equivalents relative to the amount of silver in the silver-containing solution A.

[0011] Preferably, the amount of hydrazine hydrate added to the reducing agent solution C is 1.0 to 1.5 molar equivalents relative to the amount of silver in the silver-containing solution A; and the molar concentration of hydrazine hydrate in the reducing agent solution C is 1.5 to 2.5 mol / L.

[0012] Preferably, the pH regulator in the reducing agent solution C is at least one of ammonia water, sodium hydroxide and potassium hydroxide; the amount of the pH regulator added in the reducing agent solution C is 1.0 to 1.5 molar equivalents relative to the amount of silver in the silver-containing solution A.

[0013] Preferably, in the step (4), before adding the silver-containing solution A and the reducing agent solution C, the temperature of the reaction base solution B is controlled to be 10-20°C; after starting to add the silver-containing solution A and the reducing agent solution C, the temperature of the reaction solution is controlled to be 10-35°C.

[0014] Preferably, in step (4), the silver-containing solution A and the reducing agent solution C are added simultaneously, the adding time of the silver-containing solution A is controlled within 30 to 40 minutes, and the adding speed ratio of the silver-containing solution A to the reducing agent solution C is 1:(1.05 to 1.30).

[0015] Compared with the prior art, the advantages and positive effects of the present invention are: Compared with the prior art, the preparation method of the quasi-spherical porous silver powder of the present invention is (1) The preparation method of this type of spherical porous silver powder does not require the addition of a dispersant during the entire reaction process, thereby reducing the cost of silver powder preparation; (2) The preparation method of this type of spherical porous silver powder includes adding a water-soluble organic ester solvent to the reaction base liquid B, which can effectively disperse the organic surface treatment agent, avoid agglomeration of the silver powder, and increase the dispersibility of the silver powder; (3) The preparation method of this type of spherical porous silver powder uses ascorbic acid as a reducing agent added to the reaction base solution B, and hydrazine hydrate is added simultaneously as a reducing agent solution C and a silver-containing solution A, so that the silver powder can generate a porous structure while maintaining a spherical state, thereby not affecting the printing performance, and the spherical porous silver powder has a high specific surface area and higher sintering activity; (4) The preparation method of this type of spherical porous silver powder reuses the centrifugal separation mother liquor as the reaction bottom liquid B. The entire preparation process has little hazardous waste and is suitable for large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solution of the embodiment of the present invention, the following briefly introduces the drawings required for describing the embodiment. Figure 1 This is a scanning electron microscope image of the spherical porous silver powder provided in Example 1; Figure 2 This is a scanning electron microscope image of the spherical porous silver powder provided in Example 2; Figure 3 This is a scanning electron microscope image of the silver powder provided for Comparative Example 2. DETAILED DESCRIPTION

[0017] In order to more clearly understand the above-mentioned objects, features and advantages of the present invention, the present invention is further described below with reference to the accompanying drawings and embodiments.

[0018] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways than those described herein. Therefore, the present invention is not limited to the specific embodiments of the following disclosure.

[0019] Example 1 A method for preparing spherical porous silver powder comprises the following steps: (1) Preparation of silver-containing solution A: 585 g of silver nitrate was added into 850 ml of deionized water and stirred to dissolve to obtain silver-containing solution A with a concentration of about 4.0 mol / L.

[0020] (2) Preparation of reaction base liquid B: 11 g of oleic acid (3.0 wt% relative to silver) was added to 425 ml of the dibasic acid ester mixture, and 1700 ml of deionized water was added under stirring. 606 g of ascorbic acid (1.0 molar equivalent relative to silver) was added and stirred until completely dissolved to obtain reaction base liquid B.

[0021] (3) Preparation of reducing agent solution C: 215 g of 80% by mass hydrazine hydrate aqueous solution (1.0 molar equivalent relative to silver) was diluted with 1800 ml of deionized water, and 250 g of ammonia water (1.2 molar equivalent relative to silver) was added to obtain reducing agent solution C.

[0022] (4) The temperature of the reaction base liquid B is controlled at 15° C. The silver-containing solution A and the reducing agent solution C are simultaneously added to the stirred reaction base liquid B for reaction. The silver-containing solution A is added at a rate of 27 ml / min, and the reducing agent solution C is added at a rate of 33 ml / min. The reaction temperature is controlled at 25° C.

[0023] (5) After the reaction is completed, the reaction solution in step (4) is centrifuged, washed and dried to obtain spherical silver powder with holes. The obtained silver powder is as follows Figure 1 shown.

[0024] Example 2 The difference between this embodiment and embodiment 1 is that: The organic ester solvent in the reaction base solution B is ethylene glycol diacetate, and the obtained spherical porous silver powder is as follows Figure 2 shown.

[0025] Example 3 The difference between this embodiment and embodiment 1 is that: 727 g of ascorbic acid (1.2 molar equivalents relative to silver) was added to the reaction base solution B; 322 g of 80% by mass hydrazine hydrate aqueous solution (1.5 molar equivalents relative to silver) was added to the reducing agent solution C.

[0026] Example 4 The difference between this embodiment and embodiment 1 is that: 2500 ml of the centrifuged mother liquor was added to the reaction base liquid B, without adding oleic acid, dibasic acid ester mixture and deionized water.

[0027] Comparative Example 1 The dibasic acid ester mixture in the reaction base solution B was replaced with ethanol.

[0028] Comparative Example 2 The hydrazine hydrate in the reducing agent solution C is replaced with ascorbic acid, and the obtained silver powder is as follows Figure 3 shown.

[0029] Comparative Example 3 727 g of ascorbic acid (1.2 molar equivalents relative to silver) was added to the reaction base solution B; 322 g of 80% by mass hydrazine hydrate aqueous solution (2.0 molar equivalents relative to silver) was added to the reducing agent solution C.

[0030] Performance Testing 1) The silver powder prepared in Examples 1, 2 and Comparative Example 2 was observed by scanning electron microscope. Figure 1-3 The silver powders prepared in Examples 1 to 4 and Comparative Examples 1 to 3 were tested for particle size distribution, specific surface area, ignition loss, and tap density. The test results are shown in Table 1.

[0031] Table 1 From Table 1 and Figures 1 to 3 It can be seen that compared with Example 2 using a single ascorbic acid reducing agent, Example 1 using a mixed reducing agent of ascorbic acid and hydrazine hydrate, the silver powder obtained in Example 1 is a quasi-spherical porous structure, and the silver powder obtained in Comparative Example 2 is a spherical silver powder. For silver powders with similar particle size distribution, the silver powder obtained in Example 1 has a higher specific surface area and a higher ignition loss, indicating that the silver powder obtained in Example 1 has better surface activity and sintering activity. Compared with Example 1 using ethanol as a solvent, Comparative Example 1 uses ethanol as a solvent. Compared with the embodiment using a water-soluble organic ester solvent, the particle size D90 value of the obtained silver powder is significantly increased, and the silver powder has agglomeration phenomenon, indicating that after using a mixed reducing agent of ascorbic acid and hydrazine hydrate, the hydrazine hydrate has stronger reducibility, but the water-soluble organic ester solvent can ensure the dispersibility of the silver powder. Compared with Example 1, Comparative Example 3 increases the amount of hydrazine hydrate reducing agent, and the reduction reaction is faster, but causes the silver powder particle size D90 value to increase significantly, and the silver powder has agglomeration phenomenon.

[0032] Compared with Example 1, in Example 2, the solvent in the reaction base liquid B is replaced with ethylene glycol diacetate, and the obtained silver powder has no obvious difference in various indicators; in Example 3, the molar equivalent of the reducing agent ascorbic acid and hydrazine hydrate relative to silver in the reaction base liquid B is increased compared with Example 1, the reduction reaction rate is accelerated, and it can be seen that the particle size, specific surface area and ignition loss are slightly increased; in Example 4, compared with Example 1, the reaction base liquid B is replaced with centrifuged mother liquor. Oleic acid, dibasic acid ester mixture and deionized water, and the obtained silver powder has no obvious difference in various indicators.

[0033] 2) The silver powder prepared in Examples 1 to 2 and Comparative Example 2 was measured by thermogravimetric-differential thermal analysis to obtain the 90% weight loss temperature (the temperature at which the weight change is 90% of the maximum weight loss when the silver powder is heated from room temperature to 400°C at a heating rate of 10°C / min). The test results are shown in Table 2.

[0034] Table 2 The results of thermogravimetric-differential thermal analysis show that the 90% weight loss temperature is 355°C in Comparative Example 2, 265°C in Example 1, and 270°C in Example 2, and the 90% weight loss temperature of Examples 1 and 2 is lower. Compared with Comparative Example 2, the organic components contained in the quasi-spherical porous silver powder prepared in Examples 1 and 2 are easy to leak out at one time, indicating a lower sintering temperature.

[0035] 3) The silver powders prepared in Examples 1 to 4 and Comparative Example 2 were used to prepare silver pastes in the same proportion and carrier, and the viscosity of the silver pastes was tested.

[0036] The preparation method of the silver paste is as follows: 90wt% of silver powder and 10wt% of a carrier are uniformly mixed, and the silver paste is obtained by three-roll rolling. The carrier formula is as follows: 5wt% of ethyl cellulose, 10wt% of JH180 thixotropic agent, 20wt% of dibutyl phthalate, 20wt% of diethylene glycol butyl ether acetate, 20wt% of diethylene glycol butyl ether, 15wt% of pine alcohol and 10wt% of dodecyl alcohol ester.

[0037] Viscosity test: The test temperature is 25°C, the speeds are 10 rpm, 30 rpm, 50 rpm and 100 rpm, and the test time is 1 min. The viscosity test results are shown in Table 3.

[0038] Table 3 It can be seen from Table 3 that the slurry viscosity of the silver powder using Examples 1 to 4 is slightly higher than that of the silver powder using Comparative Example 2, which confirms that the spherical porous silver powder of the present invention has a high specific surface area and high sintering activity, and its slurry printing performance is equivalent to that of the spherical silver powder in the comparative example.

[0039] The above description is only a preferred embodiment of the present invention and does not limit the present invention in other forms. Any technician familiar with the profession may use the technical content disclosed above to change or modify it into an equivalent embodiment with equivalent changes for application in other fields. However, any simple modification or equivalent change made to the above embodiment based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing spherical porous silver powder, characterized in that: The following steps are involved: (1) Preparing a silver-containing solution A: dissolving silver nitrate in deionized water to obtain a silver-containing solution A; (2) preparing reaction base liquid B: adding the surface treatment agent to a water-soluble organic ester solvent, adding deionized water under stirring, and adding ascorbic acid to obtain reaction base liquid B; (3) preparing reducing agent solution C: diluting the aqueous solution of hydrazine hydrate with deionized water, and adding a pH adjuster to obtain reducing agent solution C; (4) adding the silver-containing solution A and the reducing agent solution C to the reaction base solution B for reaction; (5) After the reaction is completed, the reaction solution in step (4) is centrifuged, washed and dried to obtain spherical porous silver powder.

2. The method for preparing spherical porous silver powder according to claim 1, characterized in that: The molar concentration of silver nitrate in the silver-containing solution A is 3.5-4.5 mol / L.

3. The method for preparing spherical porous silver powder according to claim 2, characterized in that: The volume of the deionized water in the reaction base solution B is 2 to 3 times that of the deionized water in the silver-containing solution A.

4. The method for preparing spherical porous silver powder according to claim 3, characterized in that: The surface treatment agent in the reaction base liquid B is at least one of octanoic acid, dodecanoic acid, stearic acid and oleic acid; the amount of the surface treatment agent added to the reaction base liquid B is 3.0-5.0wt% relative to the amount of silver in the silver-containing solution A.

5. The method for preparing spherical porous silver powder according to claim 4, characterized in that: The organic ester solvent in the reaction base liquid B is at least one of a dibasic acid ester mixture, propylene glycol methyl ether acetate and ethylene glycol diacetate; the dibasic acid ester mixture includes dimethyl succinate, dimethyl glutarate and dimethyl adipate; the volume of the organic ester solvent in the reaction base liquid B is 0.25 to 0.35 times the volume of the deionized water in the reaction base liquid B.

6. The method for preparing spherical porous silver powder according to claim 5, characterized in that: The amount of ascorbic acid added to the reaction base solution B is 1.0 to 1.5 molar equivalents relative to the amount of silver in the silver-containing solution A.

7. The method for preparing spherical porous silver powder according to claim 6, characterized in that: The amount of hydrazine hydrate added to the reducing agent solution C is 1.0 to 1.5 molar equivalents relative to the amount of silver in the silver-containing solution A; the molar concentration of hydrazine hydrate in the reducing agent solution C is 1.5 to 2.5 mol / L.

8. The method for preparing spherical porous silver powder according to claim 7, characterized in that: The pH regulator in the reducing agent solution C is at least one of ammonia water, sodium hydroxide and potassium hydroxide; the amount of the pH regulator added in the reducing agent solution C is 1.0 to 1.5 molar equivalents relative to the amount of silver in the silver-containing solution A.

9. The method for preparing spherical porous silver powder according to claim 8, characterized in that: In the step (4), before adding the silver-containing solution A and the reducing agent solution C, the temperature of the reaction base solution B is controlled to be 10-20° C.; after starting to add the silver-containing solution A and the reducing agent solution C, the temperature of the reaction solution is controlled to be 10-35° C.

10. The method for preparing spherical porous silver powder according to claim 9, characterized in that: In the step (4), the silver-containing solution A and the reducing agent solution C are added simultaneously, the adding time of the silver-containing solution A is controlled within 30 to 40 minutes, and the adding speed ratio of the silver-containing solution A to the reducing agent solution C is 1:(1.05 to 1.30).

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