High tap density alkaline spherical silver powder based on low-temperature controllable reduction and preparation method thereof

Abstract

The application provides high-tapped alkaline spherical silver powder based on low-temperature controllable reduction and a preparation method thereof, and belongs to the technical field of metal powder preparation. The preparation method comprises the following steps: mixing silver nitrate solution and a pH regulator under constant temperature, controlling the pH to be 6-8, adding a complexing agent and stearic acid to obtain an activated silver source solution, and the constant temperature is 25-55 DEG C; then, an alkaline reducing agent is added into the activated silver source solution to react for 1-10 min, thereby obtaining high-tapped alkaline spherical silver powder, and the particle size of the silver powder is between 200-800 nm. The preparation method is in-situ coated during the reaction process, and the complicated post-surface coating modification step is omitted, thereby reducing the cost. The prepared silver powder has the characteristics of narrow particle size distribution, high sphericity and high tap density (usually up to 4.5 g / cm 3 The prepared silver powder has good low-temperature sintering activity and is suitable for high-end electronic paste.

Description

Technical Field

[0001] This application relates to the field of metal powder preparation technology, specifically to a high-tapping alkaline spherical silver powder based on low-temperature controllable reduction and its preparation method. Background Technology

[0002] Silver powder, as an indispensable key functional material in the electronics industry, directly determines the conductivity and reliability of electronic components such as thick-film circuits, conductive adhesives, and electrode pastes. Among them, spherical silver powder, due to its excellent dispersibility, flowability, and high tap density, has become an ideal raw material for preparing high-end electronic pastes. Ideal silver powder for electronic pastes needs to possess high sphericity, narrow particle size distribution, high tap density, and a clean surface to ensure close packing and a good conductive network in the paste.

[0003] Currently, the preparation of spherical silver powder mostly employs chemical reduction methods, but existing technologies still have many shortcomings. Firstly, traditional methods often involve liquid-phase reduction of silver nitrate, during which the nucleation and growth of silver particles are difficult to control precisely, easily leading to problems such as excessively wide particle size distribution and irregular morphology, resulting in low tap density, which is insufficient for high-end applications. Secondly, to prevent oxidation and agglomeration of silver powder during storage and application, complex surface coating steps are often required after preparation, such as coating with surface modifiers using organic solvents. This subsequent process is not only cumbersome and costly, but may also introduce impurities, affecting the surface cleanliness and low-temperature sintering activity of the silver powder. Furthermore, some methods suffer from excessively long reaction times, complex processes, or high equipment requirements, hindering their industrial production and application.

[0004] Therefore, it is of great significance to develop a simple, rapid, controllable morphology and particle size preparation method for alkaline silver powder that requires no post-processing or coating and is environmentally friendly. Summary of the Invention

[0005] In view of the technical problems existing in the background art, this application provides a high-tapping alkaline spherical silver powder based on low-temperature controllable reduction and its preparation method. The preparation method is simple, fast, and does not require post-processing coating. Moreover, the silver powder obtained has a narrow particle size distribution and high tap density.

[0006] In a first aspect, embodiments of this application provide a method for preparing high-taper alkaline spherical silver powder based on low-temperature controllable reduction, the specific steps of which are as follows:

[0007] S1, under constant temperature conditions, silver nitrate solution is mixed with pH adjuster to control pH to 6-8, and then complexing agent and stearic acid are added to obtain activated silver source solution, with constant temperature of 25-55℃;

[0008] S2, under stirring, add the alkaline reducing agent to the activated silver source solution and react for 1-10 minutes. Stop stirring, let it stand and settle, then remove the supernatant, collect the settled silver powder, wash and dry the silver powder to obtain high-taper alkaline spherical silver powder based on low-temperature controllable reduction. The particle size of the silver powder is between 200-800 nm.

[0009] In some embodiments, the amount of stearic acid used is 0.25-0.42% of the mass of silver nitrate.

[0010] In some embodiments, the alkaline reducing agent is hydrazine carbonate or sodium borohydride, with a concentration of 30-40 g / L.

[0011] In some embodiments, the molar ratio of the alkaline reducing agent to silver nitrate is (1-5):4.

[0012] In some embodiments, in step S1, the concentration of the silver nitrate solution is 10-20 g / L.

[0013] In some embodiments, the pH adjuster is one of sodium hydroxide and sodium carbonate.

[0014] In some embodiments, the complexing agent is one of ammonia, ethylenediamine, and EDTA.

[0015] In some embodiments, in step S2, the stirring speed is 300-800 rpm / min.

[0016] Secondly, embodiments of this application provide a high-tapping basic spherical silver powder based on low-temperature controllable reduction. The high-tapping basic spherical silver powder is prepared according to any one of the foregoing technical solutions. The D50 particle size of the high-tapping basic spherical silver powder is 200-800 nm, and the tap density is ≥4.5 g / cm³. 3 .

[0017] The beneficial effects of this application are:

[0018] This application provides a method for preparing high-tap alkaline spherical silver powder based on low-temperature controllable reduction. The entire reduction process of this method is within 10 minutes, resulting in rapid reaction and high production efficiency. The process is simple, the operation steps are convenient, the equipment requirements are low, and it is easy to industrialize. This preparation method performs in-situ coating during the reaction, eliminating the cumbersome subsequent surface coating modification steps and reducing costs. The prepared silver powder has a narrow particle size distribution, high sphericity, and high tap density (typically up to 4.5 g / cm³). 3 With the above characteristics, it has excellent performance; the prepared silver powder has a clean surface and regular morphology, and has good low-temperature sintering activity, making it suitable for high-end electronic pastes.

[0019] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0021] Figure 1 SEM image of the high-tapered alkaline spherical silver powder prepared in Example 1 based on low-temperature controllable reduction;

[0022] Figure 2 SEM image of the high-tapered alkaline spherical silver powder prepared in Example 2 based on low-temperature controllable reduction;

[0023] Figure 3 SEM image of the high-tapered alkaline spherical silver powder prepared in Example 3 based on low-temperature controllable reduction;

[0024] Figure 4 The image shows a SEM image of the silver powder prepared in Comparative Example 1.

[0025] Figure 5 The image shows the SEM image of the silver powder prepared in Comparative Example 2.

[0026] Figure 6 The image shows the SEM image of the silver powder prepared in Comparative Example 4.

[0027] Figure 7 The image shows a SEM image of the silver powder prepared in Comparative Example 5.

[0028] Figure 8 The image shows a SEM image of the silver powder prepared in Comparative Example 6.

[0029] Figure 9 The image shows a SEM image of the silver powder prepared in Comparative Example 7.

[0030] Figure 10 The image shows the SEM image of the silver powder prepared in Comparative Example 8.

[0031] Figure 11 The image shows the SEM image of the silver powder prepared in Comparative Example 9.

[0032] Figure 12 SEM image of the silver powder prepared in Comparative Example 10. Detailed Implementation

[0033] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0035] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0036] In the description of the embodiments of this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0037] In a first aspect, embodiments of this application provide a method for preparing high-taper alkaline spherical silver powder based on low-temperature controllable reduction, the specific steps of which are as follows:

[0038] S1, under constant temperature conditions, silver nitrate solution is mixed with pH adjuster to control pH to 6-8, and then complexing agent and stearic acid are added to obtain activated silver source solution, with constant temperature of 25-55℃;

[0039] The concentration of the silver nitrate solution is 10-20 g / L. If the concentration is below this range, the production efficiency will be low; if the concentration is above this range, the concentration of silver crystal nuclei generated in situ in the reaction system will be too high, which will easily lead to particle agglomeration and a widening of the particle size distribution, making it difficult to control the sphericity and particle size.

[0040] The pH adjuster is either sodium hydroxide or sodium carbonate, with a concentration of 100~200g / L.

[0041] The role of pH adjusters is to regulate and maintain the pH value of the reaction system within a suitable range. This environment is not only conducive to the conversion of silver ions, but also a necessary condition for alkaline reducing agents to exert their optimal reducing activity.

[0042] The complexing agent is one of ammonia, ethylenediamine, or EDTA. The molar ratio of the complexing agent to the silver nitrate is (3-4.5):1.

[0043] In this application, the complexing agent forms a stable complex with silver ions (e.g., [Ag(NH3)2)). + Complexation can effectively reduce the concentration of free silver ions, thereby controlling the kinetics of the reduction reaction, slowing down the nucleation rate, and promoting the formation of spherical particles with uniform size and regular morphology.

[0044] In this application, silver nitrate solution is first mixed with a pH adjuster to pre-form an intermediate that is more active and more soluble in the complexing agent. Then, a complexing agent and a surface coating agent, stearic acid, are added, and finally a reducing agent is added to react, which can prepare silver powder with stable morphology.

[0045] Experiments show that if the reducing agent is added first and then the surface coating agent stearic acid is added, the prepared silver powder will agglomerate after being left for 4 hours. The reagents must be added one by one in the order specified in this application.

[0046] The amount of stearic acid used is 0.25-0.42% of the mass of silver nitrate. Stearic acid is the key component for achieving "no post-treatment coating required". In this application, stearic acid is added at the initial stage of the reaction. Stearic acid can be pre-adsorbed on the surface of silver complex ion clusters or initially formed crystal nuclei, exerting a dual function of steric stabilization and morphology guidance. It in situ restricts the excessive growth and aggregation of silver crystal nuclei, guides them to grow into spherical shapes, and directly forms a protective film. This eliminates the cumbersome post-reaction coating process.

[0047] In this application, the temperature is controlled at a constant range of 25-55℃, which can ensure the necessary reaction rate and avoid excessive growth of silver particles or failure of the surface coating agent stearic acid due to excessive temperature.

[0048] S2, under stirring, add the alkaline reducing agent to the activated silver source solution and react for 1-10 minutes. Stop stirring, filter the obtained product to obtain a solid, wash with water and ethanol respectively, and dry to obtain high-taper alkaline spherical silver powder based on low-temperature controllable reduction. The particle size of the silver powder obtained is between 200-800 nm.

[0049] The alkaline reducing agent is either hydrazine carbonate or sodium borohydride, with a concentration of 30-40 g / L. This concentration ensures the driving force for the reduction reaction, allowing it to proceed rapidly and completely.

[0050] The molar ratio of alkaline reducing agent to silver nitrate is (1-5):4. If the amount of alkaline reducing agent is too small, the silver nitrate reaction will be incomplete; if the amount is too large, it will greatly increase the cost.

[0051] The stirring speed is 300-800 rpm / min. This stirring speed ensures that the reducing agent is instantly and uniformly dispersed in the system, avoiding explosive nucleation caused by excessively high local concentrations, thus obtaining silver powder with a narrow particle size distribution.

[0052] Secondly, this application also provides a high-tap basic spherical silver powder based on low-temperature controllable reduction. This high-tap basic spherical silver powder is prepared by the preparation method described in any of the aforementioned technical solutions. The D50 particle size of this high-tap basic spherical silver powder is 200-800 nm, and the tap density is ≥4.5 g / cm³. 3 .

[0053] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0054] Example 1

[0055] Example 1 provides a method for preparing high-taper alkaline spherical silver powder based on low-temperature controllable reduction, comprising the following steps:

[0056] S1. At a constant temperature of 50℃, first mix 2.6L of silver nitrate solution with a concentration of 14g / L and 3mL of sodium carbonate solution with a concentration of 160g / L, control the pH to 6.5, then add 60mL of concentrated ammonia water (concentration of 25%), followed by 0.675g of stearic acid solution (concentration of 15.5%), stir and mix evenly to obtain the activated silver source solution.

[0057] S2, under stirring (stirring speed of 500 rpm / min), 512 mL of hydrazine carbonate solution with a concentration of 38 g / L was added to the activated silver source solution to carry out the reaction for 5 min.

[0058] The obtained product was filtered to obtain a solid, which was washed with water until the conductivity was ≤5μS / cm. Then it was washed three times with ethanol and dried in an oven at 60℃ to obtain the target silver powder (high tap alkaline spherical silver powder based on low temperature controllable reduction).

[0059] SEM image of the high-tapered alkaline spherical silver powder prepared in Example 1 based on low-temperature controllable reduction is shown below. Figure 1 As shown.

[0060] As can be seen, the silver powder prepared in this embodiment exhibits high sphericity, good dispersibility and uniformity, with a particle size of approximately 400 nm. Tests show that the tap density of the silver powder prepared in this embodiment is 5.2 g / cm³. 2 .

[0061] Example 2

[0062] Example 2 provides a method for preparing high-taper alkaline spherical silver powder based on low-temperature controllable reduction, comprising the following steps:

[0063] S1. At a constant temperature of 25℃, first mix 2.6L of silver nitrate solution with a concentration of 10g / L and 3mL of sodium carbonate solution with a concentration of 100g / L, control the pH to 6.4, then add 50mL of concentrated ammonia water (concentration of 25%), followed by 0.532g of stearic acid solution (concentration of 15.5%), stir and mix evenly to obtain the activated silver source solution.

[0064] S2, under stirring (stirring speed 300 rpm / min), 675 mL of hydrazine carbonate solution with a concentration of 30 g / L was added to the activated silver source solution to carry out the reaction for 1 min.

[0065] The obtained product was filtered to obtain a solid, which was washed with water until the conductivity was ≤5μS / cm. Then it was washed three times with ethanol and dried in an oven at 60℃ to obtain the target silver powder (high tap alkaline spherical silver powder based on low temperature controllable reduction).

[0066] SEM image of the high-tapered alkaline spherical silver powder prepared in Example 2 based on low-temperature controllable reduction is shown below. Figure 2 As shown.

[0067] As can be seen, the silver powder prepared in this embodiment exhibits high sphericity, good dispersibility and uniformity, with a particle size of approximately 500 nm. Tests show that the tap density of the silver powder prepared in this embodiment is 5.5 g / cm³. 2 .

[0068] Example 3

[0069] Example 3 provides a method for preparing high-taper alkaline spherical silver powder based on low-temperature controllable reduction, comprising the following steps:

[0070] S1. At a constant temperature of 55℃, first mix 2.8L of silver nitrate solution with a concentration of 20g / L and 3mL of sodium carbonate solution with a concentration of 200g / L, control the pH to 6.7, then add 80mL of concentrated ammonia water (concentration of 25%), followed by 1.01g of stearic acid solution (concentration of 15.5%), stir and mix evenly to obtain the activated silver source solution.

[0071] S2, under stirring (stirring speed of 800 rpm / min), 780 mL of hydrazine carbonate solution with a concentration of 40 g / L was added to the activated silver source solution to carry out the reaction for 10 min.

[0072] The obtained product was filtered to obtain a solid, which was washed with water until the conductivity was ≤5μS / cm. Then it was washed three times with ethanol and dried in an oven at 60℃ to obtain the target silver powder (high tap alkaline spherical silver powder based on low temperature controllable reduction).

[0073] SEM image of the high-tapered alkaline spherical silver powder prepared in Example 3 based on low-temperature controllable reduction is shown below. Figure 3 As shown.

[0074] As can be seen, the silver powder prepared in this embodiment exhibits high sphericity, good dispersibility and uniformity, with a particle size of approximately 300 nm. Tests show that the tap density of the silver powder prepared in this embodiment is 4.9 g / cm³. 2 .

[0075] Comparative Example 1

[0076] The difference between Comparative Example 1 and Example 1 is that the reaction was carried out at 80°C. The other contents are roughly the same as those in Example 1, and will not be repeated here.

[0077] SEM image of the silver powder prepared in Comparative Example 1 is shown below. Figure 4 As shown.

[0078] As can be seen, the particle size distribution of the obtained silver powder becomes wider, with some irregularly shaped particles and particles sintered together, and the sphericity decreases.

[0079] Comparative Examples 2-3

[0080] The difference between Comparative Examples 2-3 and Example 1 is that the amount of ammonia solution was changed, as shown in Table 1; the other contents are roughly the same as Example 1, and will not be repeated here.

[0081] Table 1

[0082]

[0083] SEM image of the silver powder prepared in Comparative Example 2 is shown below. Figure 5 As shown, the silver powder has low sphericity, insufficient particle dispersion, and irregular morphology.

[0084] The experiment showed that in Comparative Example 3, due to the excess ammonia, a stable silver ammonia complex was formed, which affected the subsequent reduction process and almost no silver powder was generated. Therefore, no sample was taken for electron microscopy testing.

[0085] Comparative Example 4

[0086] The difference between Comparative Example 4 and Example 1 is that sodium carbonate solution, a pH adjuster, was not used. Otherwise, the contents are largely the same as those in Example 1 and will not be repeated here.

[0087] SEM image of the silver powder prepared in Comparative Example 4 is shown below. Figure 6 As shown.

[0088] As can be seen, the generated silver powder is irregular. This is because the pH adjuster can form an intermediate reaction state with silver nitrate, which can construct a solid-phase reaction template, thereby effectively controlling the nucleation and growth kinetics of silver microcrystals. Without the use of a pH adjuster, the reaction will turn into a homogeneous rapid reduction, resulting in irregular silver powder.

[0089] Comparative Example 5

[0090] The difference between Comparative Example 5 and Example 1 is that ammonia solution was not used. Other contents are roughly the same as Example 1, and will not be repeated here.

[0091] SEM image of the silver powder prepared in Comparative Example 5 is shown below. Figure 7 As shown.

[0092] As can be seen, amorphous aggregates were formed. This is because ammonia reacts with silver nitrate to form silver ammonium complex ions, allowing for precise control of the release rate of free silver ions, thus achieving a slow and controllable reduction process. This avoids explosive nucleation and severe agglomeration of the silver powder, and ensures that stearic acid can function effectively, ultimately resulting in silver powder with good dispersibility, high sphericity, and high tap density. Without ammonia, the reaction would run away with the flow, forming amorphous aggregates.

[0093] The particle size and tap density of the silver powders obtained in Examples 1-3 and Comparative Examples 1-2 and 4-5 are shown in Table 2.

[0094] Table 2

[0095]

[0096] Comparative Examples 6-9

[0097] The difference between Comparative Examples 6-9 and Example 1 is that stearic acid is replaced with one of polyvinylpyrrolidone (PVP, K30), methylcellulose, 1-dodecylamine acetate, or octadecylamine acetate. See Table 3 for details; other aspects are largely the same as in Example 1 and will not be repeated here.

[0098] Table 3. Types of surface coating agents and silver powder particle size and morphology in Comparative Examples 6-9

[0099]

[0100] SEM images of the silver powders prepared in Comparative Examples 6-9 are shown below. Figure 8-11 As shown.

[0101] As can be seen, when using PVP, due to its strong steric hindrance, it selectively adsorbs onto the crystal surface, thus forming fluffy small nanospheres, such as... Figure 8 As shown.

[0102] When using methylcellulose, due to its weak steric hindrance and weak crystal plane selectivity, it forms irregular spherical shapes, such as... Figure 9 As shown. When using 1-dodecylamine acetate, due to electrostatic stability, micelles are formed, thus creating nanoclusters. The primary particles are small but easily aggregate into submicron spheres, such as... Figure 10 As shown. When using octadecaneamine acetate, due to its electrostatic stability and strong hydrophobic effect, it exhibits severe agglomeration, resulting in uncontrolled particle size and morphology, making dispersion difficult, such as... Figure 11 As shown.

[0103] Comparative Example 10

[0104] The difference between Comparative Example 10 and Example 1 is that stearic acid was not added. The other contents are roughly the same as those in Example 1, and will not be repeated here.

[0105] SEM image of the silver powder prepared in Comparative Example 10 is shown below. Figure 12 As shown.

[0106] Experiments show that the freshly generated silver powder appears to be agglomerated to the naked eye, but its morphology and particle size are normal under an electron microscope. After 4 hours, agglomeration was observed, indicating that the surface coating agent plays an important role in stabilizing the morphology of the silver powder.

[0107] Comparative Example 11

[0108] The difference between Comparative Example 11 and Example 1 is that 0.675g of stearic acid solution was replaced with 5g of stearic acid solution. The other contents are roughly the same as those in Example 1, and will not be repeated here.

[0109] Experiments show that when stearic acid is in excess and coats the silver ammonia complex, it affects the contact between the silver source and the reducing agent, thus affecting the subsequent reduction process and resulting in no silver powder being generated.

[0110] It is evident that stearic acid plays a crucial role in the experiment, contributing to the formation of high-taper silver powder with good sphericity and narrow particle size distribution.

[0111] In summary, this invention can effectively control the particle size and morphology of silver powder by controlling the reaction temperature and the concentration of each substance. Among them, the role of stearic acid is particularly important. Without the addition of stearic acid, the morphology of the generated silver powder will agglomerate and deform over time. The addition of an appropriate amount of stearic acid can effectively increase the dispersibility of silver powder, improve its morphology and particle size, and enhance its stability. Excessive stearic acid will affect the contact between the reducing agent and the silver source, ultimately affecting the reaction and resulting in no silver powder formation.

[0112] The silver powder prepared by this invention is particularly suitable for preparing electronic materials such as solar cell electrode paste, MLCC internal electrode paste, conductive adhesive, and thermally conductive adhesive, and has broad application prospects.

[0113] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for preparing high tap density alkaline spherical silver powder based on low temperature controllable reduction, characterized in that, It comprises the following steps: S1, in a constant temperature state, mixing silver nitrate solution with pH regulator, controlling pH to be 6-8, then adding complexing agent, and subsequently adding stearic acid to obtain activated silver source solution, constant temperature being 25-55℃; the amount of stearic acid being 0.25-0.42% of the mass of silver nitrate; the concentration of silver nitrate solution being 10-20g / L; the complexing agent being one of ammonia, ethylenediamine and EDTA; the molar ratio of the amount of complexing agent to the amount of silver nitrate being (3-4.5):1; S2, in a stirring state, adding alkaline reducing agent into the activated silver source solution to react for 1-10min, stopping stirring, standing and settling, and subsequently removing supernatant to collect settled silver powder, washing and drying the silver powder to obtain high tap density alkaline spherical silver powder based on low-temperature controllable reduction, the particle size of the silver powder being between 200-800nm; wherein the stirring speed is 300-800rpm / min; the alkaline reducing agent being hydrazine carbonate or sodium borohydride, the concentration being 30-40g / L.

2. The method for preparing high tap density alkaline silver powder based on low-temperature controllable reduction according to claim 1, characterized in that, The molar ratio of the alkaline reducing agent to silver nitrate is (1-5):

4.

3. The method of claim 1, wherein the low-temperature controllable reduction-based preparation method of high-tapped alkaline spherical silver powder is characterized by, The pH regulator is one of sodium hydroxide and sodium carbonate.

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