A method for preparing a spheroidal copper powder

Abstract

The application relates to the technical field of metal powder preparation, in particular to a preparation method of spherical copper powder, which comprises the following steps: stirring a copper-containing substance and a dispersing agent in deionized water to form an A solution; stirring silver nitrate in deionized water to form a B solution; stirring a weak reducing agent in deionized water to form a C solution; stirring a strong reducing agent in deionized water to form a D solution; adding the B solution into the A solution and stirring to form a mixed solution; adding the C solution into the mixed solution to react and form silver nanocrystal nuclei; heating the silver nanocrystal nuclei and quickly pouring them into the D solution to react; after the reaction is completed, the obtained copper powder slurry is filtered and cleaned until the conductivity of waste water is less than or equal to 20 muS / cm, and then the copper powder slurry is subjected to dispersion, filtration and drying to form the spherical copper powder. The application adjusts the nucleation and growth process by selecting reducing agents with different reducing properties, first forms silver nanocrystal nuclei, and then generates copper powder on the silver nanocrystal nuclei, so that the spherical copper powder with high purity and uniform particle size is prepared.

Description

Technical Field

[0001] This application relates to the field of metal powder preparation technology, and in particular to a method for preparing spherical copper powder. Background Technology

[0002] With the development of the electronics industry, base metals, represented by copper, have become a trend in replacing precious metals such as silver and palladium. The main reason is that copper powder has excellent electrical conductivity similar to silver (silver's volume resistivity is 1.59 × 10⁻⁶). -6 The volume resistivity of copper is 1.72 × 10⁻⁶ Ω·cm. -6 The copper content is 1 Ω·cm, and the price of copper is only 1 / 20th that of silver. However, copper is extremely prone to oxidation, so using silver-coated copper powder to replace silver powder in the preparation of conductive paste for HJT solar cells has become a mainstream approach, thereby significantly reducing the manufacturing cost of the cells. Among them, high-purity copper powder is the basic raw material for preparing silver-coated copper powder.

[0003] The most widely used technology in the present field is the production of spherical copper powder by atomization. The disadvantages of this method are: large investment in equipment, high manufacturing cost, high equipment requirements, high energy consumption, wide range of product particle size distribution, high dependence on operator experience, and poor reproducibility between batches. These factors make the preparation method difficult and the quality of the prepared copper powder unstable, which is prone to producing copper oxide, cuprous oxide or a mixture of the two.

[0004] Therefore, providing a copper powder with a simple preparation method and high purity is of great significance to the development of conductive pastes. Summary of the Invention

[0005] In order to develop a copper powder with a simple preparation method and high purity, this application provides a method for preparing spherical copper powder.

[0006] This application provides a method for preparing near-spherical copper powder, using the following technical solution:

[0007] A method for preparing near-spherical copper powder includes the following steps:

[0008] S1, copper sulfate pentahydrate and dispersant in a mass ratio of (100-120):(3-8) are stirred in deionized water at 20-40℃ until completely dissolved, and acid is added to adjust the pH to 0.7-1.5 to form solution A;

[0009] S2, dissolve 0.01-2g of silver nitrate in 0.1L of deionized water at 20-40℃ to form solution B; dissolve 1.5-2.5g of a weak reducing agent in 0.2L of deionized water at 20-40℃ to form solution C; dissolve 24-48g of a strong reducing agent in 1.5L of deionized water at 20-40℃ to form solution D.

[0010] S3, add solution B to solution A and stir to form a mixture; add solution C to the mixture to react and form nano-silver crystal nuclei;

[0011] S4, the nano-silver crystal nuclei are heated and an alkaline solution is added to adjust the pH to 8-12. The solution is then rapidly poured into solution D over a feeding time of 3-10 seconds to react. After the reaction is complete, the resulting copper powder slurry is filtered, washed with deionized water and ethanol until the conductivity of the wastewater is ≤20 μS / cm, and then dispersed, filtered and dried to form spherical copper powder.

[0012] By adopting the above technical solution, this application first uses a weak reducing agent to reduce silver nitrate solution under low temperature and acidic conditions to form nano-silver crystal nuclei, taking advantage that copper ions do not participate in the reaction. This forms nano-silver crystal nuclei for subsequent copper powder growth. Combined with the control of a strong reducing agent, high-purity, uniformly sized spherical copper powder is formed on the nano-silver crystal nuclei. The preparation method of this type of spherical copper powder is simple, and no intermediates such as copper oxide and cuprous oxide are generated during the preparation process.

[0013] In one specific implementation scheme, in S1, the copper-containing substance is one or more of copper sulfate pentahydrate, copper nitrate hydrate, and copper chloride hydrate, and more preferably copper sulfate pentahydrate.

[0014] By adopting the above technical solution, copper sulfate pentahydrate exhibits good stability at room temperature and pressure, and does not deliquesce; furthermore, it can ionize Cu in aqueous solution. 2+ It is reduced by the reducing agent to form elemental copper.

[0015] In one specific implementation, in S1, the dispersant is one or more of polyvinyl alcohol, polyethylene glycol, polyvinylpyrrolidone, gelatin, gum arabic, and Tween; more preferably, gelatin.

[0016] By adopting the above technical solution, during the silver crystal nucleus production process, agglomeration is easily formed due to excessively high surface energy during the crystal nucleus formation period. By adding a certain amount of gelatin to protect the surface of the crystal nucleus, the size of the generated copper powder particles can be effectively controlled.

[0017] In one specific implementation scheme, in S1, the acid solution is one or more of nitric acid, sulfuric acid, ammonia, sodium hydroxide, sodium bicarbonate, and sodium carbonate; more preferably, it is sulfuric acid.

[0018] By employing the above technical solution and adjusting the pH value of the reaction system, the prepared copper powder exhibits a high tap density. When the pH value of the reaction solution is low, the H+ in the system... +A higher pH level hinders the reduction reaction, reducing the supersaturation and nucleation rate of silver in the solution. At lower supersaturation, once silver nuclei form, the resulting copper grows on these nuclei, promoting growth and resulting in coarse, agglomerated copper powder. When the pH is high, the OH- ions in the system... - A higher concentration of small crystal nuclei hinders the reaction from proceeding towards oxidation, accelerates the nucleation rate, and causes severe aggregation of the resulting small crystal nuclei due to instability, resulting in poor dispersibility.

[0019] In one specific implementation scheme, in S2, the weak reducing agent is one or more of ascorbic acid, hydroxylamine sulfate, ethylene glycol, ethanol, and methanol, and more preferably ascorbic acid; the strong reducing agent is one or more of sodium borohydride, hydrazine hydrate, formaldehyde, acetaldehyde, and formic acid, and more preferably hydrazine hydrate.

[0020] By employing the above technical solution, ascorbic acid, acting as a reducing agent of moderate strength, allows silver ions to attack the oxygen atoms in ascorbic acid, thus initiating a redox reaction. Simultaneously, the hydroxyl groups in the enol structure of ascorbic acid can ionize to release hydrogen ions, which react with silver ions. Ultimately, ascorbic acid is oxidized to dehydroascorbic acid, and silver ions are reduced to elemental silver. After the silver ions react with ascorbic acid, the reduced silver adsorbs around the dehydroascorbic acid, which can reduce the aggregation of silver particles to some extent, thus having a dispersing effect.

[0021] Hydrazine hydrate is the strongest reducing agent, which can reduce copper ions from the ionic state to generate elemental copper. It can also effectively control the reaction process, ensuring that the resulting aerated particles have a controllable and uniform size and a narrow particle size distribution range, and have good single-particle dispersibility.

[0022] This application uses reducing agents with different reducing properties to regulate the nucleation of silver crystals and the growth process of copper powder, thereby preparing high-purity, uniformly sized spherical copper powder.

[0023] In one specific implementation, during S1 and S2, when solutions A, B, C, and D are formed, the stirring speed used for dissolution is 300-500 rpm.

[0024] By adopting the above technical solution, if the stirring speed is too low, it may lead to insufficient mixing, thereby affecting the subsequent reaction rate and results; conversely, if the stirring speed is too high, it may cause splashing or other adverse effects, reducing the mixing effect.

[0025] In one specific implementation scheme, in step S4, the alkaline solution is one or more of ammonia, sodium hydroxide, potassium hydroxide, sodium carbonate, and sodium bicarbonate; more preferably, it is ammonia.

[0026] By employing the above technical solution, the reducing agent reduces copper ions from their ionic state to generate elemental copper and an acid. However, once the acid accumulates to a certain level, the reaction enters a dynamic equilibrium. To break this equilibrium, a certain amount of alkaline substance needs to be added for neutralization. After adding alkali, copper ions and hydroxide ions will react simultaneously in the presence of the reducing agent to generate cuprous hydroxide and water. The reducing agent will then further reduce the copper in the cuprous hydroxide from the solution. Simultaneously, ammonia water has a relatively weak alkalinity, making it less likely to cause significant pH changes when adjusting the pH, thus allowing the solution pH to be easily controlled within the desired range.

[0027] In one specific implementation, in step S4, the dispersion is carried out using a 2% (by weight) lauric acid ethanol solution of copper powder.

[0028] By adopting the above technical solution, using an appropriate amount of dispersant can effectively further disperse copper powder, prevent copper powder agglomeration, increase the tap density of copper powder, and accelerate the subsequent filtration efficiency of copper powder, thereby improving the preparation efficiency. Meanwhile, lauric acid is used as the dispersant; through its hydrophilic head group and hydrophobic tail group structure, it reduces the surface tension of copper powder and enhances its dispersibility.

[0029] In one specific implementation, in step S4, the drying temperature is 40-60°C and the time is 7-9 hours.

[0030] By adopting the above technical solution, the obtained product is dried to obtain copper powder with high purity. At the same time, by optimizing the temperature and time during drying, the efficiency of copper powder preparation is improved.

[0031] In summary, this application includes at least one of the following beneficial technical effects:

[0032] 1. This application utilizes reducing agents with different reducing properties to first synthesize silver crystal nuclei, and then uses the silver crystal nuclei as crystal nuclei to prepare high-purity, uniformly sized spherical copper powder. The preparation method is simple, and no intermediates such as copper oxide, cuprous oxide, or cuprous hydroxide are generated during the preparation process. At the same time, it has a high tap density, making it very suitable for preparing conductive pastes for solar cells with good flowability and high printability.

[0033] 2. In this application, lauric acid ethanol solution is used as a dispersant in the subsequent preparation process of copper powder, which reduces the surface tension of copper powder and enhances the dispersibility of copper powder;

[0034] 3. The preparation method of this application is simple, and spherical copper powder can be prepared with simple raw materials and equipment, which is suitable for large-scale industrial production and has good usability. Attached Figure Description

[0035] Figure 1 This is a SEM image of the silver powder prepared in Example 1 of this application.

[0036] Figure 2 The image shows the XRD pattern of the silver powder prepared in Example 1 of this application.

[0037] Figure 3 This is a SEM image of the silver powder prepared in Comparative Example 1 of this application.

[0038] Figure 4 The image shows the XRD pattern of the silver powder prepared in Comparative Example 1 of this application. Implementation

[0039] The following examples and appendices Figure 1-4 This application will be described in further detail.

[0040] All raw materials used in the examples are commercially available. Example 1

[0041] This embodiment discloses a method for preparing near-spherical copper powder, including the following steps:

[0042] S1, Dissolve 399.6g of copper sulfate pentahydrate and 20.16g of gelatin in 3.6L of deionized water at 30℃, and mix thoroughly at 400rpm to form solution A;

[0043] S2, dissolve 2g of silver nitrate in 0.1L of deionized water at 30℃, stirring at 400rpm until completely dissolved and mixed thoroughly to form solution B; dissolve 1.8g of ascorbic acid in 0.2L of deionized water at 30℃, stirring at 400rpm until completely dissolved and mixed thoroughly to form solution C; dissolve 40.5g of hydrazine hydrate in 1.5L of deionized water at 30℃, stirring at 400rpm until completely dissolved and mixed thoroughly to form solution D.

[0044] S3, adjust the pH of the above solution A to 1.1 with sulfuric acid, add solution B to solution A, stir and mix for 1 min to form a mixed solution, then add solution C to the mixed solution, react for 2 min to form nano-silver crystal nuclei;

[0045] S4. The nano-silver crystal nuclei were heated to 80℃, and the pH was adjusted to 10 with ammonia water. The nuclei were then rapidly added to solution D over a 5-second feeding period. The reaction was allowed to proceed for 30 minutes. After the reaction, the resulting copper powder slurry was filtered and washed with deionized water and ethanol until the conductivity of the wastewater was ≤20 μS / cm. Then, a 2% (w / w) lauric acid ethanol solution was prepared, and the slurry was dispersed at a high speed of 1800 rpm and filtered again. Finally, it was filtered once more and dried at 50℃ for 8 hours to obtain spherical copper powder. The lauric acid solution was prepared by dissolving 17.2 g of lauric acid in 500 ml of ethanol to form a 5 wt% lauric acid ethanol solution. Example 2

[0046] This embodiment is basically the same as embodiment 1, except that in S1, 360g of copper sulfate pentahydrate and 10.8g of gelatin are dissolved in 3.6L of deionized water at 30°C and mixed evenly at a stirring speed of 400rpm to form solution A. Example 3

[0047] This embodiment is basically the same as Embodiment 1, except that in S1, 432g of copper sulfate pentahydrate and 28.8g of gelatin are dissolved in 3.6L of deionized water at 30°C and mixed evenly at a stirring speed of 400rpm to form solution A. Example 4

[0048] This embodiment is basically the same as Embodiment 1, except that in S2, 0.01g of silver nitrate is dissolved in 0.1L of deionized water at 30°C and stirred at 400rpm until completely dissolved and mixed evenly to form solution B; 1.5g of ascorbic acid is dissolved in 0.2L of deionized water at 30°C and stirred at 400rpm until completely dissolved and mixed evenly to form solution C; 24g of hydrazine hydrate is dissolved in 1.5L of deionized water at 30°C and stirred at 400rpm until completely dissolved and mixed evenly to form solution D. Example 5

[0049] This embodiment is basically the same as Embodiment 1, except that in S2, 0.1g of silver nitrate is dissolved in 0.1L of deionized water at 30°C and stirred at 400rpm until completely dissolved and mixed evenly to form solution B; 2.5g of ascorbic acid is dissolved in 0.2L of deionized water at 30°C and stirred at 400rpm until completely dissolved and mixed evenly to form solution C; 48g of hydrazine hydrate is dissolved in 1.5L of deionized water at 30°C and stirred at 400rpm until completely dissolved and mixed evenly to form solution D. Example 6

[0050] This embodiment discloses a method for preparing near-spherical copper powder, including the following steps:

[0051] S1, Dissolve 399.6g of copper sulfate pentahydrate and 20.16g of gelatin in 3.6L of deionized water at 20℃, and mix evenly at 500rpm to form solution A;

[0052] S2, dissolve 2g of silver nitrate in 0.1L of deionized water at 20℃, stirring at 500rpm until completely dissolved and mixed thoroughly to form solution B; dissolve 1.8g of ascorbic acid in 0.2L of deionized water at 20℃, stirring at 500rpm until completely dissolved and mixed thoroughly to form solution C; dissolve 40.5g of hydrazine hydrate in 1.5L of deionized water at 20℃, stirring at 500rpm until completely dissolved and mixed thoroughly to form solution D.

[0053] S3, adjust the pH of the above solution A to 0.7 with sulfuric acid, add solution B to solution A, stir and mix for 1 min to form a mixed solution, then add solution C to the mixed solution, react for 2 min to form nano-silver crystal nuclei;

[0054] S4. The nano-silver crystal nuclei were heated to 80℃, and the pH was adjusted to 8 with ammonia water. The nuclei were then rapidly added to solution D over a 3-second feeding period. The reaction was allowed to proceed for 30 minutes. After the reaction, the resulting copper powder slurry was filtered and washed with deionized water and ethanol until the conductivity of the wastewater was ≤20 μS / cm. Then, a 2% (w / w) lauric acid ethanol solution was prepared, and the slurry was dispersed at a high speed of 1800 rpm and filtered again. Finally, it was filtered once more and dried at 40℃ for 9 hours to obtain spherical copper powder. The lauric acid solution was prepared by dissolving 17.2 g of lauric acid in 500 ml of ethanol to form a 5 wt% lauric acid ethanol solution. Example 7

[0055] This embodiment discloses a method for preparing near-spherical copper powder, including the following steps:

[0056] S1, Dissolve 399.6g of copper sulfate pentahydrate and 20.16g of gelatin in 3.6L of deionized water at 40℃, and mix thoroughly at 300rpm to form solution A;

[0057] S2, dissolve 2g of silver nitrate in 0.1L of deionized water at 40℃, stirring at 300rpm until completely dissolved and mixed thoroughly to form solution B; dissolve 1.8g of ascorbic acid in 0.2L of deionized water at 40℃, stirring at 300rpm until completely dissolved and mixed thoroughly to form solution C; dissolve 40.5g of hydrazine hydrate in 1.5L of deionized water at 40℃, stirring at 300rpm until completely dissolved and mixed thoroughly to form solution D.

[0058] S3, adjust the pH of the above solution A to 1.5 with sulfuric acid, add solution B to solution A, stir and mix for 1 min to form a mixed solution, then add solution C to the mixed solution, react for 2 min to form nano-silver crystal nuclei;

[0059] S4. The nano-silver crystal nuclei were heated to 80℃, and the pH was adjusted to 12 with ammonia. The nuclei were then rapidly added to solution D over a 10-second feeding period. The reaction was allowed to proceed for 30 minutes. After the reaction, the resulting copper powder slurry was filtered and washed with deionized water and ethanol until the conductivity of the wastewater was ≤20 μS / cm. Then, a 2% (w / w) lauric acid ethanol solution was prepared, and the slurry was dispersed at 1800 rpm and filtered again. Finally, it was filtered once more and dried at 60℃ for 7 hours to obtain spherical copper powder. The lauric acid solution was prepared by dissolving 17.2 g of lauric acid in 500 ml of ethanol to form a 5 wt% lauric acid ethanol solution.

[0060] Comparative Example 1

[0061] This embodiment discloses a method for preparing near-spherical copper powder, including the following steps:

[0062] S1, Dissolve 399.6g of copper sulfate pentahydrate and 20.16g of gelatin in 3.6L of deionized water at 30℃, and mix thoroughly at 400rpm to form solution A;

[0063] S2, Dissolve 1.8g of ascorbic acid in 0.2L of deionized water at 30℃, and stir at 4300rpm until completely dissolved and mixed evenly to form solution C; Dissolve 40.5g of hydrazine hydrate in 1.5L of deionized water at 30℃, and stir at 4300rpm until completely dissolved and mixed evenly to form solution D.

[0064] S3. Add solution C to solution A and heat to 80℃. Adjust the pH to 10 with ammonia. Quickly pour the solution into solution D over a 5-second addition period. React for 30 minutes. After the reaction, filter the resulting copper powder slurry and wash with deionized water and ethanol until the conductivity of the wastewater is ≤20μS / cm. Then, prepare a 2% (w / w) lauric acid ethanol solution of copper powder, disperse it at high speed of 1800 rpm, filter again, and finally filter again. Dry at 50℃ for 8 hours to obtain spherical copper powder. The lauric acid solution is a 5wt% lauric acid ethanol solution formed by dissolving 17.2g of lauric acid in 500ml of ethanol.

[0065] 1. Particle size detection

[0066] The silver powder in each example and comparative example was detected using a Malvern laser particle size analyzer. The diameters corresponding to 10%, 50%, 90% and 100% of the cumulative distribution of silver powder particle size were measured and denoted as D (0.1), D (0.5), D (0.9) and D (1.0), respectively.

[0067] 2. Tap density test

[0068] The tap density of the silver powder in each embodiment and comparative example was measured using a tap density tester.

[0069] 3. Liquidity Detection

[0070] The tap density of the silver powder in each embodiment and comparative example was measured using a loose density tester.

[0071] Table 1 Performance test data of Examples 1-7 and Comparative Example 1

[0072]

[0073] Refer to Table 1 and combine with Figure 1 and Figure 3 By comparing Examples 1-7 and Comparative Example 1, it can be seen that the copper powder prepared in Example 1 has a more uniform particle size and smaller particle size compared to the copper powder prepared in Comparative Example 1; Figure 2 and Figure 4 It can be seen that the copper powder prepared in Example 1 has a purity of 100%, while the copper powder prepared in Comparative Example 1 is 80% copper + 19% cuprous oxide.

[0074] This application utilizes reducing agents with different reducing properties to first form nano-silver crystal nuclei, and then uses the silver crystal nuclei as the crystal nuclei to prepare copper powder. Compared with copper powder directly prepared without preparing silver crystal nuclei, the copper powder prepared has the advantages of high purity and uniform particle size. At the same time, the prepared copper powder has high tap density and good flowability, which is very suitable for preparing conductive pastes for solar cells with high printing performance.

[0075] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for preparing spherical copper powder, characterized in that: Includes the following steps: S1. Dissolve a copper-containing substance and a dispersant in a mass ratio of (100-120):(3-8) in 3.6L of deionized water at 20-40℃ until completely dissolved. Adjust the pH to 0.7-1.5 with acid to form solution A. S2. Dissolve 0.01-2g of silver nitrate in 0.1L of deionized water at 20-40℃ to form solution B. Dissolve 1.5-2.5g of a weak reducing agent in 0.2L of deionized water at 20-40℃ to form solution C. Dissolve 24-48g of a strong reducing agent in 1.5L of deionized water at 20-40℃ to form solution D. S3. Add solution B to solution A and stir to form a mixture. Add solution C to the mixture to react and form nano-silver crystal nuclei. S4, the nano-silver crystal nuclei are heated and an alkaline solution is added to adjust the pH to 8-12. The solution is then rapidly poured into solution D over a feeding time of 3-10 seconds for reaction. After the reaction is complete, the resulting copper powder slurry is filtered, washed with deionized water and ethanol until the conductivity of the wastewater is ≤20μS / cm, and then dispersed, filtered, and dried to form spherical copper powder. In S2, the weak reducing agent is one or more of ascorbic acid, hydroxylamine sulfate, ethylene glycol, ethanol, and methanol; the strong reducing agent is one or more of sodium borohydride, hydrazine hydrate, formaldehyde, acetaldehyde, and formic acid.

2. The method for preparing spherical copper powder according to claim 1, characterized in that: In S1, the copper-containing substance is one or more of copper sulfate pentahydrate, copper nitrate hydrate, and copper chloride hydrate.

3. The method for preparing spherical copper powder according to claim 1, characterized in that: In S1, the dispersant is one or more of polyvinyl alcohol, polyethylene glycol, polyvinylpyrrolidone, gelatin, gum arabic, and Tween.

4. The method for preparing spherical copper powder according to claim 1, characterized in that: In S1, the acid solution is either nitric acid or sulfuric acid.

5. The method for preparing spherical copper powder according to claim 1, characterized in that: In S1 and S2, when solutions A, B, C, and D are formed, the stirring speed used for dissolution is 300-500 rpm.

6. The method for preparing spherical copper powder according to claim 1, characterized in that: In step S4, the alkaline solution is one or more of ammonia, sodium hydroxide, potassium hydroxide, sodium carbonate, and sodium bicarbonate.

7. The method for preparing spherical copper powder according to claim 1, characterized in that: In step S4, the dispersion is carried out using a 2% copper powder mass lauric acid ethanol solution.

8. The method for preparing spherical copper powder according to claim 1, characterized in that: In step S4, the drying temperature is 40-60℃ and the time is 7-9 hours.

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