A palladium submicron spherical silver powder and its preparation method

Abstract

The present invention provides a palladium submicron spherical silver powder and a preparation method thereof, belonging to the technical field of silver powder. The preparation method comprises: adding a silver nitrate solution to ammonia water, dissolving it, and then heating it to obtain a first solution; dissolving an emulsifier and a strong reducing agent in water, then adding a weak reducing agent such as an aldehyde, mixing them uniformly, and then heating it to obtain a second solution; mixing a fatty amine, an emulsifier, a palladium chloride ethylene glycol solution, and water, and then keeping the mixture warm to obtain a third solution; adding the third solution to a water bath stirred kettle, stirring, alternately adding the first solution and the second solution, then adding water, and aging to obtain a silver powder-containing slurry; washing the silver powder-containing slurry until the conductivity of the filtrate is less than 10 microsiemens, obtaining a silver powder filter cake, and then drying, sieving, and shaping it in sequence to obtain palladium-containing submicron spherical silver powder. The palladium submicron spherical silver powder of the present invention has the characteristics of uniform morphology, good dispersibility, high tap density, and regular sphericity.

Description

Technical Field

[0001] The invention belongs to the technical field of silver powder, and in particular relates to palladium submicron spherical silver powder and a preparation method thereof. Background Art

[0002] The thick film prepared from silver-palladium composite powder has low silver ion mobility after sintering, and the sintered alloyed silver film has a higher resistance to solder corrosion than pure silver, which significantly improves the reliability and weather resistance of thick-film circuit boards. Therefore, how to prepare silver-palladium alloy powder with good filling capacity, high tap density and good dispersibility has become a research goal in the industry.

[0003] Micron-sized spherical silver-palladium alloy powder is a commonly used silver-palladium alloy powder form. Its silver-palladium content is proportional to the liquid-phase chemical reduction process: silver ions and palladium ions react with reducing agent molecules to form silver atoms. When the silver atom concentration in the reduction system reaches a certain level, the silver and palladium atoms spontaneously form small clusters, which then form larger clusters. When the cluster size reaches a critical value, a crystal nucleus is formed. Before the formation of the crystal nucleus, the reduction system remains a homogeneous process (liquid-phase reaction). After the formation of the crystal nucleus, the silver atom concentration in the reduction system rapidly decreases, and the silver powder growth process begins (liquid-solid reaction, i.e., reaction point). The silver-palladium powder grows through diffusion and aggregation mechanisms, ultimately yielding secondary particles. After aging (ripening), the final silver-palladium powder product is obtained. The combination of reducing agents with different reducing powers, organic dispersants with different hydrophilic-lipophilic balances, metal salt precursors, reaction method, temperature, and stirring speed can affect the silver-palladium powder morphology, particle size, internal structure, and dispersion and density. Generally, the shorter the growth cycle of silver palladium powder, the finer the particle size. The longer the growth cycle, the larger the silver palladium powder particle size and the more likely it is to agglomerate. The appropriate reducing agent, dispersant, silver source, and operating conditions for the silver powder reduction reaction should be selected by comprehensively considering factors such as the applicability, economics, production cycle, solid-liquid separation equipment conditions, and reaction yield.

[0004] Due to the difference in the redox standard electrode potentials of silver and palladium (silver's redox potential is 0.799V, palladium's redox potential is 0.915V), chemical reduction deposition usually only produces silver-palladium composite powder, not alloy powder. Methods for preparing silver-palladium alloy powder include chemical co-precipitation without alloy formation, followed by heat treatment to allow silver atoms to migrate to palladium for alloying; spray-thermal decomposition to prepare silver-palladium alloy powder; and precipitation of a silver and palladium nitrate solution by adjusting its pH to 5.0 using carbonate to form a precursor carbonate precipitate, which is then reduced with hydrazine hydrate at room temperature.

[0005] Chinese Patent Publication No. CN115041698A discloses a method for preparing silver-palladium alloy powder. Silver nitrate and palladium nitrate are combined to form an oxidation mother liquor with a total metal concentration (Ag + Pd ions) of 20-60 g / L. A water-based organic polymer dispersant (such as polyvinyl pyrrolidone, polyvinyl alcohol, polyethylene glycol, or gum arabic) is used as the dispersant. The oxidation mother liquor is then mixed with TX-100, Span, and fatty alcohol polyoxyethylene ether in silicone oil. Surfactants include ethanol, propanol, or isopropanol to form a water-in-oil "reactor." One or more of glucose, ascorbic acid, and sodium citrate are used as reducing agents. The reducing agent is added dropwise to the solution, then heated to above 100°C to complete the reduction reaction. The reaction proceeds through a water-in-oil microreactor, where heating completes the reduction, aging, demulsification, and silver-palladium alloying. The silver powder exhibits excellent dispersibility. The resulting silver powder is a submicron silver-palladium alloy powder with a particle size range of 200-500nm and a silver-palladium mass ratio of 7:3. However, because palladium has a higher electrode potential than silver, palladium is reduced before silver, resulting in the early-formed palladium atoms and atomic clusters serving as crystal nuclei. However, palladium has a significantly different atomic number and lattice structure from silver, making it difficult for palladium to serve as seeds for the subsequent silver reduction. As a result, the resulting silver-palladium composite powder is actually polycrystalline particles composed of nano-palladium and nano-silver. The distribution of silver and palladium elements during the sintering process is random, resulting in a reduced ability to resist silver migration after film formation. Furthermore, the resulting particles are all amorphous microcrystalline powders, and monodisperse, nearly spherical silver-palladium alloy powders are not yet available. Summary of the Invention

[0006] In order to solve the above technical problems, one of the objectives of the present invention is to provide a method for preparing palladium submicron spherical silver powder. The palladium submicron spherical silver powder prepared by this preparation method has the characteristics of uniform morphology, good dispersibility, high tap density and regular sphericity.

[0007] A second object of the present invention is to provide a palladium submicron spherical silver powder.

[0008] In order to achieve one of the above purposes, the present invention adopts the following technical solutions:

[0009] A method for preparing palladium submicron spherical silver powder, the preparation method comprising the following steps:

[0010] Step S1, adding silver nitrate solution to ammonia water to dissolve it, and then heating it to 40°C to 45°C to obtain a first solution;

[0011] Step S2, dissolving an emulsifier and a strong reducing agent in water, adding a weak reducing agent of an aldehyde containing an aldehyde group, mixing evenly, and heating to 40° C. to 45° C. to obtain a second solution;

[0012] Step S3, mixing the fatty amine, the emulsifier, the palladium chloride ethylene glycol solution and water, and then heating the mixture to 40° C. to 45° C. to obtain a third solution;

[0013] Step S4, adding the third solution to a water bath stirred tank, setting the water jacket temperature to 45°C and the stirring tank speed to 60-70 rpm, alternately adding the first solution and the second solution, stirring for 2-5 minutes, then adding water at 20-25°C, aging for 10-20 minutes, to obtain a slurry containing silver powder;

[0014] Step S5: washing the silver powder slurry until the conductivity of the filtrate is less than 10 micro-Siemens, obtaining a silver powder filter cake, and then drying, sieving and shaping it in sequence to obtain palladium-containing submicron spherical silver powder.

[0015] Furthermore, in step S1, the mass ratio of the silver nitrate solution to the ammonia water is 4.5 to 19:1;

[0016] The mass volume concentration of the silver nitrate solution is 50-210 g / L; the mass concentration of the ammonia water is 25%.

[0017] Furthermore, in step S2, the mass ratio of the strong reducing agent, the weak reducing agent, the emulsifier, and the water is 1:0.1-0.3:0.4-0.5:90-100.

[0018] Furthermore, the strong reducing agent includes one or both of hydrazine hydrate and hydroxylamine sulfate; the mass concentration of the hydrazine hydrate is 75-85%;

[0019] The emulsifier includes one or more of monoethanolamine, diethanolamine and triethanolamine;

[0020] The weak reducing agent is formaldehyde.

[0021] Furthermore, in the step S3, the mass ratio of the fatty amine, the emulsifier, the palladium chloride ethylene glycol solution and the water is 1:17-50:5-10:1500-1600;

[0022] The number of carbon atoms in the fatty amine is 6 to 18;

[0023] The mass volume concentration of the palladium chloride ethylene glycol solution is 0.5 g / L.

[0024] Furthermore, the emulsifier includes one or more of monoethanolamine, diethanolamine and triethanolamine;

[0025] The fatty amines include n-heptylamine, n-decylamine, n-octylamine, isooctylamine, hexadecylamine, dodecylamine, and oleylamine.

[0026] Furthermore, in step S4, the mass ratio of the first solution, the second solution and the third solution is 1.6-5.5:2.5-2.9:1.

[0027] Furthermore, in the step S5, the dispersion time is 5 to 15 minutes; and the drying time is 10 to 20 hours.

[0028] The process of alternately adding the first solution and the second solution in step S4 of this embodiment is: the first solution and the second solution are divided into 8 to 12 equal parts and then added alternately until all the first solution and the second solution are added, and the number of equal parts of the first solution and the second solution is the same.

[0029] In order to achieve the second of the above objectives, the present invention adopts the following technical solutions:

[0030] A palladium submicron spherical silver powder is prepared by the above-mentioned preparation method.

[0031] In summary, the solution proposed in the present invention has the following technical effects:

[0032] The invention uses a first solution (i.e., a silver ammonia precursor mother solution) prepared from a silver nitrate solution and ammonia water as a mother solution, a second solution prepared from an emulsifier, a strong reducing agent, a weak reducing agent of an aldehyde containing an aldehyde group, and water as a reducing solution, and a third solution prepared from a fatty amine, an emulsifier, a palladium chloride ethylene glycol solution, and water as a dispersing solution. The first solution, the second solution, and the third solution are mixed and aged to obtain a silver powder slurry, which is then washed, filtered, dried, sieved, and shaped. The silver powder slurry is prepared by mixing the fatty amine dispersant, the organic alcohol amine emulsifier, the palladium chloride growth regulator, the strong reducing agent, and the weak reducing agent. The method of combining, alternately adding materials, and adding aged pure water to dilute the ligand in the reaction process regulates the nucleation and growth of silver powder, so that the silver powder precipitates in large quantities in a short time, ensures that the silver and palladium elements are evenly distributed inside the particles, and produces submicron-level monodispersed palladium-containing silver powder with consistent silver and palladium components inside the particles. After sintering, the powder has uniform composition and good and consistent shrinkage. The submicron-level palladium-containing silver powder of the present invention has the characteristics of uniform morphology, good dispersibility, high tap density, and regular sphericity. The present invention uses alkaline fatty amine as a reducing dispersion liquid component and fatty acid as an outer layer coating during secondary dispersion. DETAILED DESCRIPTION

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0034] Example 1:

[0035] 1. Weigh 500 g of silver nitrate, dissolve it in 4300 g of pure water, stir and dissolve it clearly, add 666 g of commercially available ammonia water with a mass concentration of 25%, adjust the temperature to 40°C, and obtain a first solution (silver ammonia precursor mother liquor) with a silver ion concentration of 100 g / L.

[0036] 2. Weigh 25 g of monoethanolamine, dissolve it in 5025 g of room temperature pure water, add 67 g of 75% mass concentration of hydrazine hydrate solution, stir evenly, add 14.48 g of 37% formaldehyde solution, adjust the temperature of the reducing solution to 43°C, and obtain a second solution (reducing solution).

[0037] 3. Weigh 21.44 g of triethanolamine and dissolve it in 1900 g of pure water. Add 1.2 g of dodecylamine and stir to dissolve until the solution is clear. Then add 12 g of 0.5 g / L palladium chloride ethylene glycol solution and stir evenly. Use a water bath to adjust the temperature to 40°C to obtain a third solution (dispersion solution).

[0038] 4. Add the third solution (dispersed solution) into a 100 L barrel, adjust the stirring speed to 60 rpm, divide the first solution (silver ammonia precursor mother solution) and the second solution (reduced solution) into ten parts by weight, and alternately add the first solution (silver ammonia precursor mother solution) and the second solution (reduced solution) to the third solution (dispersed solution) using a jet pump. Continue stirring for 2 minutes, then add 15 L of 20 ° C pure water, continue stirring for 8 minutes, and complete the reaction after observing the precipitation of silver powder to obtain a slurry containing silver powder;

[0039] 5. Add the silver powder slurry into the Büchner funnel in batches for filtration and washing. Use pure water to wash repeatedly until the conductivity reaches 7 micro-Siemens, then filter to obtain a silver powder filter cake. Transfer the silver powder filter cake to a stainless steel plate and place it in a blast oven to dry for 10 hours. Then, sieve and crush it to obtain a gray silver powder.

[0040] The particle size distribution of the silver powder of this embodiment was measured using a Dandong Beiter laser particle size distribution instrument, the specific surface area was measured using a nitrogen adsorption instrument, and the bulk and tap density of the silver powder were measured using a bulk and tap density instrument.

[0041] Example 2:

[0042] 1. Weigh 7500g of silver nitrate, dissolve it in 36000g of pure water and stir to dissolve it clearly, add 10000g of commercially available ammonia water with a mass concentration of 25%, adjust the temperature to 43°C, and obtain a first solution (silver ammonia precursor mother liquor) with a silver ion concentration of 150g / L.

[0043] 2. Weigh 360 g of diethanolamine, dissolve it in 80,000 g of room-temperature pure water, add 1,000 g of 85% hydrazine hydrate solution, stir evenly, then add 400 g of 40% glyoxal solution, adjust the temperature of the reducing solution to 45° C., and obtain a second solution (reducing solution).

[0044] 3. Weigh 340 g of diethanolamine and dissolve it in 32,000 g of pure water. Add 20 g of n-octylamine and stir to dissolve until the solution is clear. Then add 100 g of 0.5 g / L palladium chloride ethylene glycol solution and stir evenly. Use a water bath to adjust the temperature to 43° C. to obtain a third solution (dispersed solution).

[0045] 4. Add the third solution (dispersed solution) to a 1000L reactor, adjust the stirring speed to 70 rpm, divide the first solution (silver-ammonia precursor mother liquor) and the second solution (reduced solution) into twelve parts by weight, and alternately add the first solution (silver-ammonia precursor mother liquor) and the second solution (reduced solution) to the third solution (dispersed solution) using a jet pump. Continue stirring for 5 minutes, then add 150,000 g of 22°C pure water and continue stirring for 15 minutes. After observing the precipitation of silver powder, the reaction is completed.

[0046] 5. Add the silver powder slurry into the Büchner funnel in batches for filtration and washing. Use pure water to wash repeatedly until the conductivity reaches 9 micro-Siemens, then filter to obtain a silver powder filter cake. Transfer the silver powder filter cake to a stainless steel plate and place it in a blast oven to dry for 15 hours. Then, sieve and crush it to obtain a gray silver powder.

[0047] The particle size distribution of the silver powder was determined using a Dandong Beiter laser particle size distribution analyzer, the specific surface area was determined using a nitrogen adsorption analyzer, and the bulk and tap density of the silver powder were determined using a bulk and tap density analyzer.

[0048] Example 3:

[0049] 1. Weigh 5000g of silver nitrate, dissolve it in 92000g of pure water and stir to dissolve it clearly, add 6700g of commercially available ammonia water with a mass concentration of 25%, adjust the temperature to 45°C, and obtain a first solution (silver ammonia precursor mother liquor) with a silver ion concentration of 50g / L.

[0050] 2. Weigh 268 g of triethanolamine, dissolve it in 53600 g of room temperature pure water, add 670 g of 80% hydrazine hydrate solution, stir evenly, then add 428 g of 37.5% formaldehyde solution, adjust the temperature of the reducing solution to 40°C, and obtain a second solution (reducing solution).

[0051] 3. Weigh 600 g of triethanolamine and dissolve it in 18600 g of pure water. Add 12 g of oleylamine and stir to dissolve until the solution is clear. Then add 120 g of 0.5 g / L palladium chloride ethylene glycol solution and stir evenly. Use a water bath to adjust the temperature to 45°C to obtain a third solution (dispersed solution).

[0052] 4. The obtained third solution (dispersed solution) was added to a reactor with a volume of 1000 L, and the stirring speed was adjusted to 65 rpm. The first solution (silver-ammonia precursor mother liquor) and the second solution (reduced solution) were divided into 8 parts by weight, and the first solution (silver-ammonia precursor mother liquor) and the second solution (reduced solution) were alternately added to the third solution (dispersed solution) using a jet pump, and the mixture was stirred for 4 minutes. After that, 140,000 g of 25° C. pure water was added and stirred for 6 minutes. After the precipitation of silver powder was observed, the reaction was completed to obtain a slurry containing silver powder;

[0053] 5. Add the silver powder slurry into the Büchner funnel in batches for filtration and washing. Use pure water to wash repeatedly until the conductivity reaches 8 micro-Siemens, then filter to obtain a silver powder filter cake. Transfer the silver powder filter cake to a stainless steel plate and place it in a blast oven to dry for 20 hours. Then sieve and crush it to obtain a gray silver powder.

[0054] The particle size distribution of the silver powder of this embodiment was measured using a Dandong Beiter laser particle size distribution instrument, the specific surface area was measured using a nitrogen adsorption instrument, and the bulk and tap density of the silver powder were measured using a bulk and tap density instrument.

[0055] The silver powder particle size distribution, specific surface area, bulk density and tap density of the palladium submicron spherical silver powder of Examples 1 to 3 are shown in the following table:

[0056]

[0057] Please note that the technical features of the above embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification. The above embodiments only express several implementation methods of the present application. The description is relatively specific and detailed, but it cannot be understood as a limitation on the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, without departing from the concept of this application, several variations and improvements can be made, which all fall within the scope of protection of this application. Therefore, the scope of protection of the patent in this application shall be based on the attached claims.

Claims

1. A method for preparing palladium submicron spherical silver powder, characterized in that: The preparation method comprises the following steps: Step S1, adding silver nitrate solution to ammonia water to dissolve it, and then heating it to 40° C. to 45° C. to obtain a first solution; Step S2: dissolving an emulsifier and a strong reducing agent in water, adding a weak reducing agent such as an aldehyde, mixing well, and heating the mixture to 40° C. to 45° C. to obtain a second solution; In step S2, the mass ratio of the strong reducing agent, the weak reducing agent, the emulsifier and water is 1:0.1-0.3:0.4-0.5:90-100; Step S3, mixing the fatty amine, the emulsifier, the palladium chloride ethylene glycol solution and water, and then heating the mixture to 40° C. to 45° C. to obtain a third solution; In step S3, the mass ratio of the fatty amine, the emulsifier, the palladium chloride ethylene glycol solution and water is 1:17-50:5-10:1500-1600; Step S4, adding the third solution to a water bath stirred tank, setting the water jacket temperature to 45°C and the stirring tank speed to 60-70 rpm, alternately adding the first solution and the second solution, stirring for 2-5 minutes, then adding water at 20°C-25°C, aging for 10-20 minutes, to obtain a slurry containing silver powder; The process of alternately adding the first solution and the second solution in step S4 is as follows: the first solution and the second solution are divided into 8 to 12 equal portions respectively and then added alternately until all the first solution and the second solution are added, and the number of equal portions of the first solution and the second solution is the same; Step S5: washing the silver powder slurry until the conductivity of the filtrate is less than 10 micro-Siemens, obtaining a silver powder filter cake, and then drying, sieving and shaping it in sequence to obtain palladium-containing submicron spherical silver powder.

2. The preparation method according to claim 1, characterized in that In step S1, the mass ratio of the silver nitrate solution to the ammonia water is 4.5-19:1; The mass volume concentration of the silver nitrate solution is 50-210 g / L; the mass concentration of the ammonia water is 25%.

3. The preparation method according to claim 2, characterized in that The strong reducing agent includes one or both of hydrazine hydrate and hydroxylamine sulfate; the mass concentration of the hydrazine hydrate is 75-85%; The emulsifier includes one or more of monoethanolamine, diethanolamine and triethanolamine; The weak reducing agents are formaldehyde and glyoxal.

4. The preparation method according to any one of claims 1 to 3, characterized in that In step S3, the number of carbon atoms in the fatty amine is 6 to 18; The mass volume concentration of the palladium chloride ethylene glycol solution is 0.5 g / L.

5. The preparation method according to claim 4, characterized in that The emulsifier includes one or more of monoethanolamine, diethanolamine and triethanolamine; The fatty amines include n-heptylamine, n-decylamine, n-octylamine, isooctylamine, hexadecylamine, dodecylamine, and oleylamine.

6. The preparation method according to claim 5, characterized in that In step S4, the mass ratio of the first solution, the second solution and the third solution is 1.6-5.5:2.5-2.9:

1.

7. The preparation method according to claim 6, characterized in that In step S5, the drying time is 10 to 20 hours.

8. A palladium submicron spherical silver powder, characterized in that: The palladium submicron spherical silver powder is prepared by the preparation method according to any one of claims 1 to 7.

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