Silver powder morphology regulation and control method and silver powder

Abstract

The invention provides a silver powder morphology regulation and control method and silver powder. The silver powder morphology regulation and control method comprises the steps that a seed crystal solution, a silver-containing solution, a first reducing solution and a neutralizing solution are prepared; adding the seed crystal solution into the neutralization solution to obtain a first reaction solution; adding a pH regulator into the first reduction solution to regulate the pH value of the first reduction solution to obtain a second reduction solution, and adding the silver-containing solution and the second reduction solution into the first reaction solution according to a preset feeding mode to obtain a second reaction solution; uniformly mixing a surfactant with an ethanol solution to prepare an active agent solution; and adding the active agent solution into the second reaction solution to obtain silver powder slurry, and cleaning the silver powder slurry to obtain the silver powder. According to the silver powder morphology regulation and control method, under the condition that other reagents are not introduced or the solution ratio is not changed, the morphology of the silver powder is regulated and controlled by changing the feeding modes of different solutions, and preparation is simple; and the prepared silver powder is large in specific surface area and high in sintering activity.

Description

Technical Field

[0001] The present application relates to the technical field of preparation of new precious metal materials, and in particular to a method for regulating the morphology of silver powder and silver powder. Background Art

[0002] Silver powder material is a key material for solar cell electrodes, accounting for more than 85% of the silver paste. Its particle size, morphology, unit cell size, etc. will affect the sintering activity of silver powder. The sintering activity of silver powder directly determines the open circuit voltage, which in turn affects the photoelectric conversion efficiency of crystalline silicon solar cells. Therefore, the development of silver powder with high sintering activity is of great significance to improve the photoelectric conversion efficiency.

[0003] In order to improve the sintering activity of silver powder on the market, most of them start from the surface roughness of silver powder. By introducing new dispersants, crystal disruptors or other reagents, the growth mode of silver powder is regulated to make it have a rough surface. However, the use of new reagents requires major adjustments to the original formula, such as concentration ratio, time and temperature, and even the water loss may not meet the standards. Summary of the invention

[0004] The purpose of the present application is to provide a method for regulating the morphology of silver powder and silver powder. The morphology of the silver powder can be regulated by changing the feeding method of the solution without introducing other reagents or changing the solution ratio. The preparation is simple; and the prepared silver powder has a large specific surface area and high sintering activity.

[0005] In a first aspect, the present application provides a method for regulating the morphology of silver powder, comprising:

[0006] preparing a seed solution, a silver-containing solution, a first reducing solution and a neutralizing solution respectively;

[0007] adding the seed solution to the neutralization solution to obtain a first reaction solution;

[0008] Adding a pH adjuster to the first reducing solution to adjust the pH value of the first reducing solution to obtain a second reducing solution, and adding the silver-containing solution and the second reducing solution to the first reaction solution according to a preset adding method to obtain a second reaction solution;

[0009] The surfactant and the ethanol solution are mixed evenly to prepare an active agent solution;

[0010] The active agent solution is added to the second reaction solution to obtain a silver powder slurry, and the silver powder slurry is washed to obtain silver powder.

[0011] In some possible embodiments, the first reaction liquid is loaded in a reaction tank; and the silver-containing solution and the second reducing solution are added to the first reaction liquid according to a preset feeding method to obtain the second reaction liquid, comprising:

[0012] Adding the silver-containing solution into the first reaction solution in a dot-shaped or spraying manner, and the discharge port of the silver-containing solution is located at the center of the reaction tank;

[0013] The second reducing solution is added to the first reaction solution in a dot-shaped or spraying manner, and the discharge port of the silver-containing solution is located at the center of the reaction tank or at the edge of the tank body.

[0014] In some possible embodiments, adding a pH regulator to the first reducing solution to adjust the pH value of the first reducing solution includes:

[0015] A pH adjuster is added to the first reducing solution to adjust the pH value of the first reducing solution to 8-10.

[0016] In some possible embodiments, the pH adjuster is one or more of ammonia water, sodium hydroxide, and sodium bicarbonate.

[0017] In some possible embodiments, the step of washing the silver powder slurry to obtain silver powder includes:

[0018] Washing the silver powder slurry with ultrapure water to obtain a silver powder solution;

[0019] Drying the silver powder solution at a preset drying temperature for a preset time to obtain a silver powder mixture;

[0020] The silver powder mixture is classified to obtain a variety of silver powders with different morphologies.

[0021] In some possible embodiments, the temperature of the prepared silver-containing solution, the first reducing solution and the second reducing solution is 5-25°C.

[0022] In some possible embodiments, the first reducing solution includes a reducing agent, and the reducing agent is one or more of glucose, ascorbic acid, hydrazine hydrate, hydrogen peroxide, formaldehyde or acetaldehyde;

[0023] The neutralization solution includes a dispersant, and the dispersant is one or more of polyvinyl alcohol, polyvinyl pyrrolidone, polyethylene glycol, gum arabic, gelatin or Tween.

[0024] In some possible embodiments, the surfactant is one or more of caprylic acid, oleic acid, stearic acid, palmitic acid, lauric acid, dodecylamine, tetradecylamine, hexadecylamine or oleylamine.

[0025] In some possible embodiments, the particle size of the prepared silver powder is 1.5-2.5 μm, and the specific surface area is not less than 0.36 m 2 / g, tap density not less than 5.4g / cm 3 .

[0026] In a second aspect, an embodiment of the present application provides a silver powder, which is prepared by the method for controlling the morphology of silver powder as described in any of the above items.

[0027] The present application provides a method for regulating the morphology of silver powder and silver powder, including preparing a seed solution, a silver-containing solution, a first reducing solution and a neutralizing solution respectively; adding the seed solution to the neutralizing solution to obtain a first reaction solution; adding a pH regulator to the first reducing solution to adjust the pH value of the first reducing solution to obtain a second reducing solution, and adding the silver-containing solution and the second reducing solution to the first reaction solution according to a preset feeding method to obtain a second reaction solution; mixing a surfactant and an ethanol solution evenly to prepare an active agent solution; adding the active agent solution to the second reaction solution to obtain a silver powder slurry, and washing the silver powder slurry to obtain silver powder. The method for regulating the morphology of silver powder provided in the present application regulates the morphology of silver powder by changing the feeding method of different solutions without introducing other reagents or changing the solution ratio, and the preparation is simple; and the prepared silver powder has a large specific surface area and high sintering activity. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The technical solution and other beneficial effects of the present application will be made apparent by describing in detail the specific implementation methods of the present application in conjunction with the accompanying drawings.

[0029] Figure 1 It is a schematic diagram of the process of the method for regulating the silver powder morphology provided in the embodiment of the present application;

[0030] Figure 2 This is a schematic diagram of an embodiment of the process of separating silver powder provided in the embodiment of the present application;

[0031] Figure 3 This is a SEM image of the silver powder prepared in Example 1 of the method of the present invention;

[0032] Figure 4 This is a SEM image of the silver powder prepared in Example 1 of the method of the present invention;

[0033] Figure 5 This is a SEM image of the silver powder prepared in Example 1 of the method of the present invention. DETAILED DESCRIPTION

[0034] The present application is further described in detail below in conjunction with the accompanying drawings and examples. It is particularly noted that the following examples are only used to illustrate the present application, but are not intended to limit the scope of the present application. Similarly, the following examples are only some embodiments of the present application rather than all embodiments, and all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of this application.

[0035] In the following description of the present application, reference is made to “some embodiments”, which describe a subset of all possible embodiments, but it can be understood that “some embodiments” may be the same subset or different subsets of all possible embodiments and may be combined with each other without conflict.

[0036] In the following description of the present application, the terms "first\second\third" involved are merely used to distinguish similar objects and do not represent a specific ordering of the objects. It can be understood that "first\second\third" can be interchanged with a specific order or sequence where permitted, so that the embodiments of the present application described here can be implemented in an order other than that illustrated or described here.

[0037] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein are only for the purpose of describing the embodiments of this application and are not intended to limit this application.

[0038] The following is a detailed description with reference to specific embodiments. It should be noted that the serial numbers of the following embodiments are not intended to limit the preferred order of the embodiments.

[0039] The method for regulating the silver powder morphology provided in the present application also utilizes an oxidation-reduction reaction to convert silver ions into silver powder particles. However, unlike the method for regulating the silver powder morphology in the prior art, the present application improves the specific steps of the method for regulating the silver powder morphology, which is described in detail below.

[0040] See also Figure 1 , Figure 1 : is a schematic diagram of the process of the method for regulating the silver powder morphology provided in the embodiment of the present application. The specific process of the method for regulating the silver powder morphology can be as follows:

[0041] 11. Prepare a seed solution, a silver-containing solution, a first reducing solution and a neutralizing solution.

[0042] Specifically, it is necessary to prepare a seed solution, a silver-containing solution, a first reducing solution and a neutralizing solution respectively. Among them, the seed solution is mainly used to provide seeds, so that the reduced silver powder particles gather on the surface of the seeds to obtain larger silver powder particles; in some embodiments, the first mass of the initial seed solution can be weighed, and the second mass of ultrapure water can be added to the initial seed solution for mixing, and ultrasonic dispersion is performed for a certain period of time to ensure that the initial seed solution and the ultrapure water are fully mixed, so as to obtain a diluted and dispersed seed solution. At the same time, in an embodiment of the present application, the seeds in the initial seed solution can be obtained by mixing a variety of different materials, such as nanocrystal seeds are prepared by mixing one or more of Tween solution, gelatin solution, gum arabic solution, starch aqueous solution, polyvinyl pyrrolidone solution, polyethylene glycol solution and sodium citrate solution. The mass ratio of the initial seed solution and ultrapure water can be selected according to actual needs, and is not limited here.

[0043] The silver-containing solution is mainly used to provide silver ions and obtain silver powder particles through redox reaction. In the embodiment of the present application, silver nitrate can be dissolved in ultrapure water to prepare a silver nitrate solution, that is, a silver-containing solution. The mass of the dissolved silver nitrate can be selected according to actual needs and is not limited here. The first reducing solution is mainly used to carry out redox reaction to promote the conversion of silver ions into silver powder particles. In the embodiment of the present application, the reducing agent can be mixed with ultrapure water, stirred and dissolved to obtain the first reducing solution; the specific preparation process and ratio can refer to the prior art and are not limited here. The neutralizing solution mainly provides a place for chemical reaction and neutralizes the reaction solution; in some embodiments, a dispersant and a reducing agent can be added to ultrapure water, and the solvent can be stirred to obtain a neutralizing solution. In some embodiments, the reducing agent can be one or more of glucose, ascorbic acid, hydrazine hydrate, hydrogen peroxide, formaldehyde or acetaldehyde; the dispersant can be one or more of polyvinyl alcohol, polyvinyl pyrrolidone, polyethylene glycol, gum arabic, gelatin or Tween.

[0044] 12. Add the seed solution to the neutralization solution to obtain a first reaction solution.

[0045] 13. Add a pH regulator to the first reducing solution to adjust the pH value of the first reducing solution to obtain a second reducing solution, and add the silver-containing solution and the second reducing solution to the first reaction solution according to a preset adding method to obtain a second reaction solution.

[0046] 14. Evenly mix the surfactant and the ethanol solution to prepare an active agent solution.

[0047] 15. Add the activator solution to the second reaction solution to obtain a silver powder slurry, and wash the silver powder slurry to obtain silver powder.

[0048] After preparing the seed solution, the silver-containing solution, the first reducing solution and the neutralizing solution respectively, it is necessary to prepare the silver powder by different adding methods. Specifically, in the embodiment of the present application, the seed solution needs to be added to the neutralizing solution first, and the first reaction solution is obtained after stirring and mixing thoroughly; at the same time, a pH adjusting agent needs to be added to the first reducing solution to adjust the pH value of the first reducing solution to obtain a second reducing solution. In some embodiments, a pH adjusting agent can be added to the first reducing solution to adjust the pH value of the first reducing solution to 8-10; and the pH adjusting agent can be one or more of ammonia water, sodium hydroxide, and sodium bicarbonate.

[0049] Then, the silver-containing solution and the second reducing solution are added to the first reaction solution according to a preset feeding method to obtain the second reaction solution. The seed solution and the reducing solution will undergo an oxidation-reduction reaction in the neutralizing solution to obtain silver powder. It is also necessary to stir and mix the surfactant and ethanol evenly to obtain an activator solution; and the activator solution is added to the second reaction solution to obtain a silver powder slurry. Among them, the activator solution is mainly used to control the uniform dispersion of the silver powder particles obtained through the oxidation-reduction reaction; the silver powder slurry needs to be cleaned later to obtain the desired silver powder.

[0050] In the above embodiments, different feeding methods will affect the morphology of silver powder, so it is necessary to add the silver-containing solution and the second reducing liquid to the first reaction liquid according to the preset feeding method. Specifically, the first reaction liquid is usually loaded in a reaction tank, and the silver-containing solution and the second reducing liquid need to be added to the reaction tank containing the first reaction liquid; and the silver-containing solution and the second reducing liquid are usually loaded in different containers and added to the reaction tank through their respective discharge ports. In the embodiment of the present application, the discharge port of the silver-containing solution can be set at the center of the reaction tank, and the silver-containing solution can be added to the first reaction liquid in the form of point feeding or spraying; and the discharge port of the second reducing liquid is set at the center of the reaction tank or at the edge of the tank body of the reaction tank, and the second reducing liquid is added to the first reaction liquid in the form of point feeding or spraying. The detailed feeding method is described in detail in the subsequent embodiments and is not limited here.

[0051] After the redox reaction, the silver powder particles need to be separated from the second reaction solution. Figure 2 As shown, a schematic diagram of an embodiment of separating silver powder provided in an embodiment of the present application may include:

[0052] 21. Add the activator solution into the second reaction solution to obtain a silver powder slurry.

[0053] 22. Use ultrapure water to wash the silver powder slurry to obtain a silver powder solution.

[0054] 23. Dry the silver powder solution at a preset drying temperature for a preset time to obtain a silver powder mixture.

[0055] 24. Classify the silver powder mixture to obtain a variety of silver powders with different morphologies.

[0056] Specifically, first, the active agent solution needs to be added to the second reaction liquid so that the silver powder is evenly dispersed to obtain a silver powder slurry; then the silver powder slurry is washed with ultrapure water to obtain a silver powder solution free of impurities; finally, the silver powder solution is dried to obtain a mixture of silver powders of various different morphologies. Among them, the silver powder solution can be dried for a preset time at a preset drying temperature to obtain a silver powder mixture; the silver powder mixture also needs to be classified to distinguish silver powders of different morphologies. Specifically, the baked silver powder can be treated with a powdering machine, and the powdered silver powder can be sieved with a 500-mesh sieve. In some embodiments, the drying temperature can be 40 to 60°C, and the drying time is 60 to 120 minutes.

[0057] This application does not adjust the morphology of the silver powder by introducing other reagents or changing the solution ratio, but by changing the feeding method of the solution, which is simple to operate; and the average particle size of the prepared silver powder is between 1.5 and 2.5 μm, the specific surface area is above 0.36 m2 / g, and the tap density is above 5.4 g / cm3. The prepared silver powder has a rough surface, a large specific surface area, and high sintering activity, which is beneficial to improving the open circuit voltage of crystalline silicon solar cells. The following is a detailed description of how different feeding methods change the morphology of silver powder. Figure 3 Shown is a SEM image of silver powder prepared in Example 1 using the method of the present invention.

[0058] First, take 1g of seed solution and mix it with 30mL of ultrapure water, and then ultrasonically disperse it for 5 minutes to obtain the desired seed solution. Weigh 50kg of silver nitrate solid and prepare a silver nitrate solution with a mass fraction of 25% to obtain a silver-containing solution; weigh 17kg of ascorbic acid solid and mix it with ultrapure water to prepare a first reducing solution with a mass fraction of 15%. Then weigh 10kg of ascorbic acid solid and prepare a solution with a mass concentration of 3%, then add 5kg of polyvinyl pyrrolidone as a dispersant, and stir until completely dissolved to obtain a neutralized solution.

[0059] Then, add the dispersed seed solution to the neutralization solution, stir evenly, and obtain the first reaction solution; weigh 350g of lauric acid and 1kg of ethanol solution, stir and dissolve them by ultrasonic stirring to obtain an active agent solution; add ammonia water to the first reduced solution to adjust the pH of the first reduced solution to about 9.5, and obtain the second reduced solution. At this time, the discharge port of the silver-containing solution is a long straight tube, and the discharge port is located at the center of the reaction tank; the discharge port of the second reduced solution is a shower-shaped, and the discharge port is located at the edge of the tank body of the reaction tank. Under the premise of stirring the first reaction liquid, the silver-containing solution and the second reduced liquid are added to the first reaction liquid at the same time for reaction; the silver-containing solution is discharged in a point-like manner, and the second reduced liquid is discharged in a spray-like manner, and the discharge positions of the two are different. The silver-containing solution and the second reducing solution are all added to the first reaction solution within 4 minutes and 30 seconds; after the reaction continues for a period of time, the activator solution and 10 kg of ammonia water are added to the first reaction solution for surface treatment, and the silver powder slurry is obtained after stirring for 10 minutes; the silver powder slurry is washed with ultrapure water, separated, and placed in a 60°C oven for 120 minutes to obtain the target silver powder. In the above embodiment, the temperature of the silver-containing solution, the first reducing solution, and the second reaction solution is controlled at about 15°C.

[0060] like Figure 4 The figure shows a SEM image of silver powder prepared in Example 2 of the method of the present invention. This embodiment is basically the same as Example 1, except that the discharge ports of the silver-containing solution and the second reducing solution in Example 2 are both in the shape of a shower; both are sprayed, but the discharge positions are different. The activator solution and 10 kg of ammonia water are added to the second reaction solution for surface treatment, and the silver powder slurry is obtained after stirring for 10 minutes; the silver powder slurry is washed with ultrapure water, separated and dried to obtain the target silver powder.

[0061] like Figure 5 The figure shows a SEM image of silver powder prepared by Example 3 of the method of the present invention. This embodiment is basically the same as Example 1, except that the discharge ports of the silver-containing solution and the second reducing solution in Example 3 are both long straight tubes, and both are point-shaped discharges and the discharge positions are the same. Add the activator solution and 10 kg of ammonia water to the second reaction solution for surface treatment, stir for 10 minutes to obtain a silver powder slurry; wash the silver powder slurry with ultrapure water, separate and dry to obtain the target silver powder.

[0062] The silver powder in the embodiment and the comparative example was tested using a Better laser particle size analyzer to measure the particle size of the silver powder; the silver powder in the embodiment and the comparative example was tested using a Better tap density meter to measure the tap density of the silver powder. The silver powder performance data table in the following table can be obtained:

[0063]

[0064] Referring to the above table, in combination with Examples 1-3 and Figure 3-5It can be seen that under the same formula, the morphology of the silver powder prepared by different feeding methods has great differences. Compared with Example 1 and 3, the silver-containing solution and the second reducing solution in Example 3 are both point-feeded through a long straight tube, and the degree of mixing between the two is low, but the feeding positions of the two are the same; therefore, there may be a situation where the local concentration is higher; and the growth rate of the silver powder at the position with higher concentration is faster, resulting in lower crystallinity and forming a rough structure with slight protrusions on the surface of the silver powder. Compared with Example 1 and 2, the morphology and growth conditions are very similar. Both are sprayed and fed through a shower structure and the feeding positions are different; this makes the mixing degree of the two higher, so the obtained silver powder has a slightly higher crystallinity and a slightly larger unit cell. The silver-containing solution in Example 1 is point-fed through a long straight tube, which is similar to the situation in Example 3, but the second reducing solution is sprayed and fed through a shower, and the feeding positions of the two are different. Since the feeding position of the second reducing solution is close to the edge of the tank body of the reaction tank, the closer to the edge of the tank body, the farther the feeding positions of the silver-containing solution and the second reducing solution are, and the more uniform the mixing of the two is, which is similar to the situation in Example 2. Therefore, the morphology of Example 1 is also between Examples 2 and 3, with both block structures with larger crystallinity and micro-convex structures with smaller crystallinity.

[0065] In other embodiments, the silver-containing solution can also be sprayed through a showerhead, while the second reducing solution is dotted through a long straight tube; and the locations of the two can be the same or different. That is, in the embodiments of the present application, the specific feeding method and feeding location of the silver-containing solution and the second reducing solution can be selected according to actual needs; and different feeding methods and feeding locations will produce silver powders with different morphologies, so as to achieve the preparation of multi-morphological silver powders without introducing other reagents or changing the solution ratio.

[0066] It can be seen that the present application discloses a simple method for regulating the morphology of silver powder. Silver powders with different morphologies can be prepared by different adding methods. The prepared silver powder has a higher specific surface area and higher sintering activity, and has broad application prospects in the field of photovoltaic silver paste.

[0067] The present application also provides a silver powder, which is prepared by adopting the method for controlling the silver powder morphology provided in any of the above embodiments, and thus has all the same beneficial effects, and this embodiment will not be described in detail here.

[0068] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0069] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application shall be included in the protection scope of the present application. The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for regulating the morphology of silver powder, characterized in that: include: preparing a seed solution, a silver-containing solution, a first reducing solution and a neutralizing solution respectively; adding the seed solution to the neutralization solution to obtain a first reaction solution; Adding a pH adjuster to the first reducing solution to adjust the pH value of the first reducing solution to obtain a second reducing solution, and adding the silver-containing solution and the second reducing solution to the first reaction solution according to a preset adding method to obtain a second reaction solution; The surfactant and the ethanol solution are mixed evenly to prepare an active agent solution; The active agent solution is added to the second reaction solution to obtain a silver powder slurry, and the silver powder slurry is washed to obtain silver powder.

2. The method for controlling the silver powder morphology according to claim 1, characterized in that: The first reaction liquid is loaded in a reaction tank; The step of adding the silver-containing solution and the second reducing solution into the first reaction solution in a preset manner to obtain the second reaction solution comprises: Adding the silver-containing solution into the first reaction solution in a dot-shaped or spraying manner, and the discharge port of the silver-containing solution is located at the center of the reaction tank; The second reducing solution is added to the first reaction solution in a dot-shaped or spraying manner, and the discharge port of the silver-containing solution is located at the center of the reaction tank or at the edge of the tank body.

3. The method for controlling the silver powder morphology according to claim 1, characterized in that: The step of adding a pH adjusting agent to the first reducing solution to adjust the pH value of the first reducing solution comprises: A pH adjuster is added to the first reducing solution to adjust the pH value of the first reducing solution to 8-10.

4. The method for controlling the silver powder morphology according to claim 1, characterized in that: The pH regulator is one or more of ammonia water, sodium hydroxide and sodium bicarbonate.

5. The method for controlling the silver powder morphology according to claim 1, characterized in that: The step of washing the silver powder slurry to obtain silver powder comprises: Washing the silver powder slurry with ultrapure water to obtain a silver powder solution; Drying the silver powder solution at a preset drying temperature for a preset time to obtain a silver powder mixture; The silver powder mixture is classified to obtain a variety of silver powders with different morphologies.

6. The method for controlling the silver powder morphology according to claim 1, characterized in that: The temperatures of the prepared silver-containing solution, the first reducing solution and the second reducing solution are 5-25°C.

7. The method for controlling the silver powder morphology according to claim 1, characterized in that: The first reducing solution includes a reducing agent, and the reducing agent is one or more of glucose, ascorbic acid, hydrazine hydrate, hydrogen peroxide, formaldehyde or acetaldehyde; The neutralization solution includes a dispersant, and the dispersant is one or more of polyvinyl alcohol, polyvinyl pyrrolidone, polyethylene glycol, gum arabic, gelatin or Tween.

8. The method for controlling the silver powder morphology according to claim 1, characterized in that: The surfactant is one or more of caprylic acid, oleic acid, stearic acid, palmitic acid, lauric acid, dodecylamine, tetradecylamine, hexadecylamine or oleylamine.

9. The method for controlling the silver powder morphology according to claim 1, characterized in that: The particle size of the prepared silver powder is 1.5-2.5 μm, and the specific surface area is not less than 0.36 m 2 / g, tap density is not less than 5.4g / cm3.

10. A silver powder, characterized in that: The silver powder is prepared by the method for controlling the silver powder morphology according to any one of claims 1 to 9.

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