CN112475311A - Quasi-spherical silver powder with accurately controllable particle size and preparation method thereof - Google Patents
Quasi-spherical silver powder with accurately controllable particle size and preparation method thereof Download PDFInfo
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Abstract
The invention provides quasi-spherical silver powder with accurately controllable particle size and a preparation method thereof, wherein the method comprises the following steps: (1) mixing nano-silver colloid and a dispersant solution to obtain a mixed solution, wherein silver particles in the nano-silver colloid are approximately spherical; (2) under the condition of stirring, dropwise adding the silver salt solution and the reducing agent solution into the mixed solution obtained in the step (1) in a cocurrent manner to react to obtain silver powder slurry; (3) and (3) carrying out solid-liquid separation, washing and drying on the silver powder slurry obtained in the step (2) to obtain the sphere-like silver powder. The silver salt solution and the reducing agent solution are dripped into the mixed solution of the dispersing agent and the crystal seed in a parallel flow manner to control the generation speed of the simple substance silver, so that the simple substance silver uniformly grows on the provided nano silver colloid crystal seed to obtain the sphere-like silver powder with accurately controllable particle size, and the method has the advantages of mild reaction conditions, normal temperature and pressure, simple equipment and process, short production period, easy amplification and industrial application; the prepared silver powder has uniform appearance, good dispersibility and high tap density.
Description
Technical Field
The invention relates to a preparation method of silver powder, in particular to quasi-spherical silver powder with accurately controllable particle size and a preparation method thereof.
Background
The silver powder has excellent electric and heat conducting performance and is widely applied to the field of electronic paste such as solar cell paste, conductive adhesive and the like. With the increasing exhaustion of non-renewable resources such as petroleum and coal and the enhancement of environmental awareness of people, the development of new energy is more and more emphasized by people, and especially the development and utilization of solar energy become hot spots. The silver powder is a conductive phase of the silver paste of the crystalline silicon solar cell, the mass ratio of the silver powder in the silver paste is about 90%, the rheological property and the printability of the paste are greatly influenced, and the silver powder plays a decisive role in the photoelectric conversion efficiency of the solar cell. With the market demand for the photoelectric conversion efficiency of the crystalline silicon solar cell becoming higher and higher, research on silver powder is more and more concerned by researchers. At present, the preparation method of the silver powder mainly comprises a gas phase method, a solid phase method and a liquid phase method. The gas phase method requires expensive equipment, large investment and low production efficiency; although the solid phase method is simple, the prepared silver powder has large and uncontrollable particle size; the liquid phase method has the advantages of simple required equipment and process, easy control of technical parameters and suitability for mass production.
The method for preparing silver powder by using a liquid phase chemical reduction method is the most widely applied method, silver particles are reduced from a complex of silver salt and silver by using a reducing agent, the reduction process comprises the processes of nucleation and growth, and the morphology and the particle size of the silver powder are adjusted by controlling the nucleation rate and the growth rate by generally using the reaction temperature, the pH value, the reactant concentration and the type of the reducing agent; however, in the process, part of the particles are long in growth time and part of the particles are short in growth time or do not grow, and the silver powder is inaccurate in particle size control and uneven in appearance.
Patent CN 104646683A discloses a method for preparing sphere-like silver powder with controllable particle size, which comprises the steps of firstly preparing nano-scale spherical silver powder as seed crystal by a hydrothermal method, then dropping a mixed solution of silver salt and a dispersing agent into a reducing agent and the seed crystal positively by the hydrothermal method, and inducing the silver seed crystal to grow uniformly by adopting precipitation reaction. The method has the advantages of long period, low crystallinity of the silver powder, uneven morphology, narrow particle size adjustable range, incapability of accurately controlling the particle size, complex operation, reaction completion in a certain pressure container and at high temperature, unsuitability for large-scale industrial production and certain operation risk.
Disclosure of Invention
In order to solve the technical problems, the silver salt solution and the reducing agent solution are dripped into the mixed solution of the dispersing agent and the nano-silver colloid in a parallel flow manner to control the generation speed of the simple substance silver, so that the simple substance silver uniformly grows on the provided nano-silver colloid, and the sphere-like silver powder with accurately controllable particle size is obtained.
The technical scheme adopted by the invention is as follows:
according to one aspect of the present application, there is provided a method for preparing a spheroidal silver powder having a precisely controllable particle size, the method comprising the steps of:
(1) mixing nano-silver colloid and a dispersant solution to obtain a mixed solution, wherein silver particles in the nano-silver colloid are approximately spherical;
(2) under the condition of stirring, simultaneously dropwise adding a silver salt solution and a reducing agent solution into the mixed solution obtained in the step (1) in a parallel-flow adding manner for reaction to obtain silver powder slurry;
(3) and (3) carrying out solid-liquid separation, washing and drying on the silver powder slurry obtained in the step (2) to obtain the sphere-like silver powder.
Further, in the step (1), the particle size of silver particles in the nano silver adhesive is 50-300 nm, the content of the silver particles is 0.5-4%, and the silver particles have hydrophilic surfaces.
Preferably, the particle size of the silver particles in the nano silver adhesive is 100-200 nm, the content of the silver particles is 1-3%, and the silver particles have hydrophilic surfaces. Preferably, the lower limit of the particle size of the silver particles in the nano-silver colloid is selected from 110nm, 120nm, 130nm, 140nm, 150nm, 160nm, 170nm, 180nm or 190nm, the upper limit of the particle size of the silver particles in the nano-silver colloid is selected from 110nm, 120nm, 130nm, 140nm, 150nm, 160nm, 170nm, 180nm or 190nm, the lower limit of the content of the silver particles is selected from 1.5%, 2% or 2.5%, and the upper limit of the content of the silver particles is selected from 1.5%, 2% or 2.5%.
Further, in the step (1), the nano silver colloid is obtained by the following preparation method:
firstly, silver nitrate reacts with a precipitator to form a silver precursor, and then the silver precursor is mixed with nano colloidal silver crystal seeds to generate silver-containing precursor precipitate;
and secondly, mixing the silver-containing precursor precipitate obtained in the step one with a reducing agent to obtain the nano silver colloid.
Further, in the step (2), the dripping time of the silver salt solution is 10-25 min, and the dripping time of the reducing agent solution is 8-20 min;
preferably, in the step (2), the dripping time of the silver salt solution is 12-20 min, and the dripping time of the reducing agent solution is 10-16 min; preferably, the lower limit of the dropping time of the silver salt solution is selected from 13min, 14min, 15min, 16min, 17min, 18min or 19min, and the upper limit of the dropping time of the silver salt solution is selected from 13min, 14min, 15min, 16min, 17min, 18min or 19 min; the lower limit value of the dropping time of the reducing agent solution is selected from 11min, 12min, 13min, 14min or 15min, and the upper limit value of the dropping time of the reducing agent solution is selected from 11min, 12min, 13min, 14min or 15 min.
Further, in the step (2), the stirring speed is 50-200 r/min, and/or the reaction temperature is 10-25 ℃.
Further, before the step (1), a step of preparing a silver salt solution, a reducing agent solution and a dispersing agent solution respectively is also included;
preferably, dissolving soluble silver salt in deionized water, adjusting the pH value of the solution to 0.5-3, and preparing a silver salt solution;
dissolving a reducing agent in deionized water, adjusting the pH of the solution to 1-6, and preparing to obtain a reducing agent solution; and/or
Dissolving a dispersing agent in deionized water to prepare a dispersing agent solution.
Further, the soluble silver salt is silver nitrate, and the reducing agent is at least one selected from glucose, sodium borohydride, formaldehyde, ascorbic acid, hydrazine hydrate, hydroquinone, alkanolamine and hydrogen peroxide; and/or the dispersant is selected from at least one of polyethylene glycol, polyvinyl alcohol, gelatin, sodium dodecylbenzenesulfonate, tween 80, polyvinylpyrrolidone and gum arabic.
Further, the concentration of silver ions in the silver salt solution is 0.2-3 mol/L, the concentration of a reducing agent in the reducing agent solution is 0.1-5 mol/L, and/or the concentration of a dispersing agent in the dispersing agent solution is 100-600 g/L.
Further, in the step (3), the drying temperature is 90-120 ℃, and the drying time is 5-20 min; preferably, the drying temperature is 95-105 ℃, and the drying time is 10-15 min.
According to another aspect of the application, the sphere-like silver powder with the accurately controllable particle size prepared by the preparation method is provided, the particle size of the sphere-like silver powder is 0.5-3.0 mu m, and the tap density is 5.0g/cm3The above.
Benefits of the present application include, but are not limited to:
(1) according to the preparation method of the sphere-like silver powder with the accurately controllable particle size, the silver salt solution and the reducing agent solution are dripped into the mixed solution of the dispersing agent and the nano-silver colloid in a parallel flow mode to control the generation speed of the simple substance silver, so that the simple substance silver uniformly grows on the provided nano-silver colloid crystal seed, the sphere-like silver powder with the accurately controllable particle size is obtained, the reaction condition is mild, the normal temperature and the normal pressure are realized, the equipment and the process are simple, the production period is short, and the sphere-like silver powder is easy to amplify and apply industrially.
(2) According to the preparation method of the sphere-like silver powder with the accurately controllable particle size, the particle size and the content of the silver particles in the nano silver colloid, the dropping flow rate of the silver salt solution and the reducing agent solution and the like are controlled, so that the accurate control of the silver powder crystal grains can be realized, and the error between the synthesized target particle size and the actually produced particle size is controlled within +/-0.1 mu m.
(3) The sphere-like silver powder has a wide controllable range of particle size, the particle size of the sphere-like silver powder is 0.5-3.0 mu m, and the tap density is 5.0g/cm3Silver prepared as aboveThe powder has uniform appearance, good dispersibility and high tap density, and can be used for preparing silver paste for solar cells and/or electrode paste for electronic components and the like.
Drawings
FIG. 1 is a scanning electron microscope image of a spheroidal silver powder prepared in example 1 of the present invention;
FIG. 2 is a scanning electron microscope image of the spheroidal silver powder obtained in example 2 of the present invention;
FIG. 3 is a scanning electron microscope image of the spheroidal silver powder obtained in example 3 of the present invention;
FIG. 4 is a scanning electron microscope image of the spheroidal silver powder obtained in example 4 of the present invention;
FIG. 5 is a scanning electron microscope image of the spheroidal silver powder obtained in example 5 of the present invention;
FIG. 6 is a scanning electron microscope image of the spheroidal silver powder obtained in example 6 of the present invention;
FIG. 7 is a scanning electron micrograph of a spheroidal silver powder prepared in comparative example 1 according to the present invention;
FIG. 8 is a scanning electron micrograph of a spheroidal silver powder obtained according to comparative example 2 of the present invention.
Detailed Description
The present invention is described in detail with reference to specific examples, which are provided to facilitate the understanding of the technical solutions of the present invention by those skilled in the art, and the implementation or use of the present invention is not limited by the description of the present invention.
In the present invention, the raw materials and equipment used are commercially available or commonly used in the art, if not specified. The methods in the examples are conventional in the art unless otherwise specified.
The nano silver colloid is used as the crystal seed, the particle size of silver particles in the nano silver colloid is 50-300 nm, the content of the silver particles is 0.5-4%, and the silver particles have hydrophilic surfaces. The nano silver colloid which meets the above conditions can be used as the seed crystal of the application. Specifically, the nano silver colloid used in the following examples is referred to patent CN102407342B, and the preparation method of the nano silver colloid specifically includes the following steps:
(1) preparation of seed crystals
The polymer is calculated by a monomer, firstly, dissolving a dispersing agent I and silver nitrate in water according to a molar ratio of 1-100: 1 to form a mixed solution I with the concentration of the silver nitrate being 0.01-20.0 mmol/L, then adding a solution of a reducing agent I under stirring, and continuing stirring to react to form nano-silver seed crystals;
wherein, the dispersant I is one or the combination of gelatin, polyvinyl alcohol, polyvinylpyrrolidone, polyethylene glycol, citric acid, trisodium citrate, sodium oleate and sodium dodecyl benzene sulfonate; the reducing agent I is one or a combination of sodium borohydride, hydrazine hydrate, ascorbic acid or hydrogen peroxide; the molar ratio of the reducing agent I to the silver nitrate is 0.2-3: 1;
(2) preparation of silver-containing precursor precipitate
Firstly, dissolving a complexing agent and silver nitrate in water to form a mixed solution II with the silver nitrate concentration of 0.1-2.0 mol/L; wherein the complexing agent is one or a combination of citric acid, trisodium citrate, sodium oleate, ammonia water, polyvinylpyrrolidone, formamide and polyacrylic acid; wherein the polymer is calculated by a monomer, and the molar ratio of the complexing agent to the silver nitrate is 0.1-10: 1;
secondly, dispersing agent II, precipitating agent and the seed crystal prepared in the step I are put into water to form mixed solution III;
the dispersant II is one or a combination of gelatin, polyvinyl alcohol, polyvinylpyrrolidone, polyethylene glycol, citric acid, trisodium citrate, sodium oleate and sodium dodecyl benzene sulfonate; the precipitant is one or combination of oxalic acid, sodium oxalate, ammonium bicarbonate, sodium carbonate, phosphoric acid, sodium phosphate, hydrochloric acid, sodium chloride, sodium hydroxide, sulfuric acid and ammonium sulfate;
thirdly, adding the mixed solution II into the mixed solution III under stirring, and stirring for reaction to form uniform silver-containing precursor precipitate;
(3) redox preparation of nano silver colloidal particles
Firstly, adding a dispersant III and a reducing agent II into water according to a molar ratio of 0.1-10: 1 to dissolve a polymer calculated by a monomer to form a mixed solution IV; the dispersant III is one or a combination of gelatin, polyvinyl alcohol, polyvinylpyrrolidone, polyethylene glycol, citric acid, trisodium citrate, sodium oleate and sodium dodecyl benzene sulfonate, and the reducing agent II is sodium borohydride, hydrazine hydrate, ascorbic acid or hydrogen peroxide;
dissolving a dispersant IV and a reaction speed control agent in water to form a mixed solution V; the dispersant IV is one or a combination of gelatin, polyvinyl alcohol, polyvinylpyrrolidone, polyethylene glycol, citric acid, trisodium citrate, sodium oleate and sodium dodecyl benzene sulfonate; the reaction speed control agent is ammonia water, nitric acid or sodium hydroxide; wherein the polymer is calculated by a monomer, and the molar ratio of the consumption of the dispersant IV to the reducing agent II in the mixed solution IV is 0.1-10: 1; the molar ratio of the using amount of the reaction speed control agent to the reducing agent II in the mixed solution IV is 0.1-10: 1; the concentration of the reaction rate control agent in the mixed solution V is 0.05-3.0 mol/L;
and thirdly, adding the mixed solution IV and the mixed solution V into the silver-containing precursor precipitate prepared in the step (2) at a constant speed, and stirring for reaction to generate nano silver colloid serving as seed crystals in the preparation method of the following embodiment.
According to the silver powder control synthesis method provided by the embodiment of the application, the crystal nucleus generation stage and the crystal growth stage can be separated, secondary nucleation in a reaction system can be effectively prevented, and the target particle size (theoretical particle size) of the silver powder can be calculated according to the crystal growth theory through the size and the number of the crystal nuclei (corresponding to the particle size of the added silver colloidal particles and the silver-containing quality) and the quality of silver uniformly coated outside the crystal nuclei in the crystal growth stage (corresponding to the silver-containing quality of the added silver salts), so that the accurate control synthesis of the particle size of the silver powder can be realized. Specifically, the calculation of the target particle size can be found in CRYSTAL GROWTH & DESIGN 2010, Vol.103378-3386,
wherein "D" is the target particle size; "d" is the particle size of the selected silver colloidal particles; "n" is the silver-containing mass of the added silver colloidal particles; "N" is the silver-containing mass of the added silver salt.
Example 1 preparation of spheroidal silver powder 1# with a target particle size D50 of 0.5 μm
The specific preparation method of the sphere-like silver powder comprises the following steps:
(1) weighing 4.5Kg of silver nitrate solid, preparing 1mol/L of silver nitrate solution A, adding nitric acid, and adjusting the pH value to 2; weighing 5Kg of ascorbic acid as a reducing agent, preparing a reducing agent solution B with the concentration of 1.5mol/L, and adding ammonia water to adjust the pH value to 5; 3.2Kg of polyvinylpyrrolidone was weighed out to prepare a dispersant solution C with a concentration of 250 g/L.
(2) 300g of the seed crystal with the particle size of 50nm (wherein the content of the silver particles is 1.0%, and the silver particles have hydrophilic surfaces) is weighed, added into the dispersant solution C and stirred uniformly, the temperature of the reaction kettle is kept at 15 ℃, the stirring speed is 200r/min, the silver nitrate solution A and the reducing agent solution B are respectively dripped into the dispersant solution C in a parallel flow feeding mode, and the dripping time is respectively 12min and 10 min.
(3) Washing with deionized water and ethanol, centrifuging, drying at 100 deg.C for 5min, and sieving with 800 mesh sieve to obtain silver powder.
The theoretical particle size of the silver powder obtained in this example was calculated according to the formula
The actual particle size D50 of the silver powder is 0.490 μm, and a scanning electron micrograph is shown in figure 1, as shown in figure 1, the silver powder has concentrated particle size distribution, uniform morphology and good dispersibility.
Example 2 preparation of spheroidal silver powder having a target particle size D50 of 0.8 μm No. 2
The specific preparation method of the sphere-like silver powder comprises the following steps:
(1) weighing 4.5Kg of silver nitrate solid, preparing 1mol/L of silver nitrate solution A, adding nitric acid, and adjusting the pH value to 2; weighing 5Kg of glucose as a reducing agent, preparing a reducing agent solution B with the concentration of 2mol/L, and adding sodium hydroxide to adjust the pH value to 5; 3.2Kg of polyvinylpyrrolidone was weighed out to prepare a dispersant solution C with a concentration of 250 g/L.
(2) 300g of the seed crystal with the particle size of 100nm (wherein the content of the silver particles is 1.5%, and the silver particles have hydrophilic surfaces) is weighed, added into the dispersant solution C and stirred uniformly, the temperature of the reaction kettle is kept at 20 ℃, the stirring speed is 200r/min, the silver nitrate solution A and the reducing agent solution B are respectively dripped into the dispersant solution C in a parallel flow feeding mode, and the dripping time is respectively 12min and 10 min.
(3) Washing with deionized water and ethanol, centrifuging, drying at 95 deg.C for 10min, and sieving with 625 mesh sieve to obtain silver powder.
The theoretical particle size of the silver powder obtained in this example was calculated according to the formula
The actual particle size D50 of the silver powder is 0.856 μm, and a scanning electron micrograph is shown in FIG. 2, as shown in FIG. 2, the silver powder has concentrated particle size distribution, uniform morphology and good dispersibility.
Example 3 preparation of spheroidal silver powder 3# with a target particle size D50 of 1.25 μm
The specific preparation method of the sphere-like silver powder comprises the following steps:
(1) weighing 4.5Kg of silver nitrate solid, preparing 1mol/L of silver nitrate solution A, adding nitric acid, and adjusting the pH value to 2; weighing 5Kg of ascorbic acid as a reducing agent, preparing a reducing agent solution B with the concentration of 1.5mol/L, and adding potassium hydroxide to adjust the pH value to 4; 3.2Kg of gum arabic was weighed out to prepare a dispersant solution C having a concentration of 250 g/L.
(2) Weighing 100g of the seed crystal with the particle size of 100nm (wherein the content of the silver particles is 1.5%, and the silver particles have hydrophilic surfaces), adding the seed crystal into the dispersant solution C, uniformly stirring, keeping the temperature of the reaction kettle at 20 ℃ and the stirring speed at 150r/min, and respectively dropwise adding the silver nitrate solution A and the reducing agent solution B into the dispersant solution C in a parallel-flow feeding manner for 12min and 10 min.
(3) Washing with deionized water and ethanol, centrifuging, drying at 90 deg.C for 20min, and sieving with 600 mesh sieve to obtain silver powder.
The theoretical particle size of the silver powder obtained in this example was calculated according to the formula
The actual particle size D50 of the silver powder is 1.291 mu m, and a scanning electron micrograph is shown in figure 3, as shown in figure 3, the silver powder has concentrated particle size distribution, uniform morphology and good dispersibility.
Example 4 preparation of spheroidal silver powder 4# having a target particle size D50 of 2.0. mu.m
The specific preparation method of the sphere-like silver powder comprises the following steps:
(1) weighing 4.5Kg of silver nitrate solid, preparing 1mol/L of silver nitrate solution A, adding nitric acid, and adjusting the pH value to 2; weighing 5Kg of ascorbic acid as a reducing agent, preparing a reducing agent solution B with the concentration of 1.5mol/L, and adding ammonia water to adjust the pH value to 4; 3.2Kg of polyvinylpyrrolidone was weighed out to prepare a dispersant solution C with a concentration of 250 g/L.
(2) 150g of the seed crystal with the particle size of 200nm (wherein the content of the silver particles is 2.0 percent, and the silver particles have hydrophilic surfaces) is weighed, added into the dispersant solution C and stirred uniformly, the temperature of the reaction kettle is kept at 15 ℃, the stirring speed is 150r/min, the silver nitrate solution A and the reducing agent solution B are respectively dripped into the dispersant solution C in a parallel flow feeding mode, and the dripping time is respectively 12min and 10 min.
(3) Washing with deionized water and ethanol, centrifuging, drying at 120 deg.C for 5min, and sieving with 400 mesh sieve to obtain silver powder.
The theoretical particle size of the silver powder obtained in this example was calculated according to the formula
The actual particle size D50 of the silver powder is 1.991 μm, and a scanning electron microscope picture is shown in FIG. 4, as shown in FIG. 4, the silver powder has concentrated particle size distribution, uniform morphology and good dispersibility.
Example 5 preparation of spheroidal silver powder 5# having a target particle size D50 of 2.5 μm
The specific preparation method of the sphere-like silver powder comprises the following steps:
(1) weighing 4.5Kg of silver nitrate solid, preparing 1mol/L of silver nitrate solution A, adding nitric acid, and adjusting the pH value to 2; weighing 5Kg of ascorbic acid as a reducing agent, preparing a reducing agent solution B with the concentration of 1.5mol/L, and adding ammonia water to adjust the pH value to 4; 3.2Kg of polyvinylpyrrolidone was weighed out to prepare a dispersant solution C with a concentration of 250 g/L.
(2) 200g of the crystal seeds with the particle size of 300nm (wherein the content of silver particles is 2.5%, and the silver particles have hydrophilic surfaces) are weighed and added into the dispersant solution C to be uniformly stirred, the temperature of the reaction kettle is kept at 20 ℃, the stirring speed is 150r/min, the silver nitrate solution A and the reducing agent solution B are respectively dripped into the dispersant solution C in a parallel flow feeding mode, and the dripping time is respectively 12min and 10 min.
(3) Washing with deionized water and ethanol, centrifuging, drying at 105 deg.C for 5min, and sieving with 600 mesh sieve to obtain silver powder.
The theoretical particle size of the silver powder obtained in this example was calculated according to the formula
The actual particle size D50 of the silver powder is 2.490 μm, and a scanning electron micrograph is shown in FIG. 5, as shown in FIG. 5, the silver powder has concentrated particle size distribution, uniform morphology and good dispersibility.
Example 6 preparation of spheroidal silver powder 6# with a target particle size D50 of 3.0 μm
The specific preparation method of the sphere-like silver powder comprises the following steps:
(1) weighing 9Kg of silver nitrate solid, preparing a silver nitrate solution A with the concentration of 2mol/L, adding nitric acid, and adjusting the pH value to 1; weighing 10Kg of ascorbic acid as a reducing agent, preparing a reducing agent solution B of 3mol/L, and adding ammonia water to adjust the pH value to 5; 6.4Kg of polyvinylpyrrolidone was weighed out to prepare a dispersant solution C with a concentration of 250 g/L.
(2) 200g of the crystal seeds with the particle size of 300nm (wherein the content of silver particles is 3 percent, and the silver particles have hydrophilic surfaces) are weighed and added into the dispersant solution C to be uniformly stirred, the temperature of the reaction kettle is kept at 20 ℃, the stirring speed is 150r/min, the silver nitrate solution A and the reducing agent solution B are respectively dripped into the dispersant solution C in a parallel-flow feeding mode, and the dripping time is respectively 20min and 16 min.
(3) Washing with deionized water and ethanol, centrifuging, drying at 100 deg.C for 10min, and sieving with 400 mesh sieve to obtain silver powder.
The theoretical particle size of the silver powder obtained in this example was calculated according to the formula
The actual particle size D50 of the silver powder is 3.091 mu m, and a scanning electron micrograph is shown in figure 6, as shown in figure 6, the silver powder has concentrated particle size distribution, uniform morphology and good dispersibility.
Comparative example 1 preparation of spheroidal silver powder D1#
The preparation method of the silver powder of the comparative example is basically the same as that of example 4, except that the feeding speed of the dropping reaction is increased and the dropping time is shortened, and the method specifically comprises the following steps:
(1) weighing 4.5Kg of silver nitrate solid, preparing 1mol/L of silver nitrate solution A, adding nitric acid, and adjusting the pH value to 2; weighing 5Kg of ascorbic acid as a reducing agent, preparing a reducing agent solution B with the concentration of 1.5mol/L, and adding ammonia water to adjust the pH value to 4; 3.2Kg of polyvinylpyrrolidone was weighed out to prepare a dispersant solution C with a concentration of 250 g/L.
(2) 150g of the seed crystal with the particle size of 200nm (wherein the content of the silver particles is 2.0 percent, and the silver particles have hydrophilic surfaces) is weighed, added into the dispersant solution C and stirred uniformly, the temperature of the reaction kettle is kept at 15 ℃, the stirring speed is 150r/min, the silver nitrate solution A and the reducing agent solution B are respectively dripped into the dispersant solution C in a parallel flow feeding mode, and the dripping time is respectively 5min and 4 min.
(3) Washing with deionized water and ethanol, centrifuging, drying at 120 deg.C for 5min, and sieving with 400 mesh sieve to obtain silver powder.
The theoretical particle size of the silver powder obtained by the comparative example is calculated according to a formula
The actual particle size D50 of the silver powder is 1.532 μm, and a scanning electron micrograph is shown in FIG. 7, as shown in FIG. 7, the silver powder has wide particle size distribution, uniform morphology and a small amount of aggregates.
Comparative example 2 preparation of spheroidal silver powder D2#
The preparation method of the comparative silver powder is basically the same as that of example 4, except that the selected seed crystal comes from an aladdin reagent platform (S110970, 200nm), and the method specifically comprises the following steps:
(1) weighing 4.5Kg of silver nitrate solid, preparing 1mol/L of silver nitrate solution A, adding nitric acid, and adjusting the pH value to 2; weighing 5Kg of ascorbic acid as a reducing agent, preparing a reducing agent solution B with the concentration of 1.5mol/L, and adding ammonia water to adjust the pH value to 4; 3.2Kg of polyvinylpyrrolidone was weighed out to prepare a dispersant solution C with a concentration of 250 g/L.
(2) Weighing 3g of superfine silver powder (aladdin, S110970, 200nm), mixing the superfine silver powder with 150ml of water in a beaker, then placing the mixture into an ultrasonic water bath for dispersing for 15min, taking the superfine silver powder dispersion as a seed crystal, adding the superfine silver powder dispersion into a dispersant solution C, uniformly stirring, keeping the temperature of a reaction kettle at 15 ℃ and the stirring speed at 150r/min, and respectively dripping a silver nitrate solution A and a reducing agent solution B into the dispersant solution C for 12min and 10 min.
(3) Washing with deionized water and ethanol, centrifuging, drying at 120 deg.C for 5min, and sieving with 400 mesh sieve to obtain silver powder.
The theoretical particle size of the silver powder obtained by the comparative example is calculated according to a formula
The actual particle diameter D50 of the silver powder is 2.649 μm, and a scanning electron micrograph is shown in figure 8, and as shown in figure 8, the silver powder particles have poor dispersibility and relatively obvious agglomeration.
TABLE 1 comparison of Performance parameters of silver powders obtained in examples and comparative examples
From the results in table 1, it can be seen that the feeding speed is too high during the preparation of the silver powder of comparative example D1# so that the reaction is too fast, the silver simple substance formed by the redox reaction does not reach the surface of the seed crystal until it is completely coated and grown, and therefore, small particles and agglomerates formed by secondary nucleation are generated, so that the obtained silver powder has poor dispersibility, uneven particle size distribution, relatively low tap density of the powder, large deviation between the actual particle size and the target particle size, and the synthesis cannot be controlled according to the theoretical calculation. The silver powder of comparative example No. D2 was prepared by using the purchased ultrafine silver powder as seed crystals after ultrasonic dispersion, and the obtained silver powder had poor dispersibility, significant agglomeration, low tap density of the powder, and large deviation between the actual particle size and the target particle size, and could not be synthesized under theoretical calculation due to the difference between the dispersibility and the surface activity of the seed crystals. The silver powder control synthesis method can separate two stages of crystal nucleus generation and crystal growth and effectively prevent secondary nucleation in a reaction system, silver simple substances generated by redox reaction can uniformly coat and grow on the surface of dispersed crystal nuclei, and control synthesis can be realized according to a crystal growth theory. In specific examples 1-6, the preparation of the spheroidal silver powder is sequentially controlled from a particle size range of 0.5-3.0 μm, the obtained silver powder has uniform particle morphology, good dispersion and high tap density, and the actual particle size obtained by designing and regulating process parameters, such as the size and number of the seed crystal, the addition speed and number of the reaction materials and the like, is basically consistent with the target particle size calculated theoretically, so that the precise control and synthesis of the particle size of the spheroidal silver powder can be realized.
The above description is only an example of the present application, and the protection scope of the present application is not limited by these specific examples, but is defined by the claims of the present application. Various modifications and changes may occur to those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the technical idea and principle of the present application should be included in the protection scope of the present application.
Claims (10)
1. A method for preparing spheroidal silver powder with accurately controllable particle size is characterized by comprising the following steps:
(1) mixing nano-silver colloid and a dispersant solution to obtain a mixed solution, wherein silver particles in the nano-silver colloid are approximately spherical;
(2) under the condition of stirring, simultaneously dropwise adding a silver salt solution and a reducing agent solution into the mixed solution obtained in the step (1) in a parallel-flow adding manner for reaction to obtain silver powder slurry;
(3) and (3) carrying out solid-liquid separation, washing and drying on the silver powder slurry obtained in the step (2) to obtain the sphere-like silver powder.
2. The preparation method according to claim 1, wherein in the step (1), the particle size of the silver particles in the nano silver adhesive is 50-300 nm, the content of the silver particles is 0.5-4%, and the silver particles have hydrophilic surfaces;
preferably, the particle size of the silver particles in the nano silver adhesive is 100-200 nm, the content of the silver particles is 1-3%, and the silver particles have hydrophilic surfaces.
3. The preparation method according to claim 1, wherein in the step (1), the nano silver colloid is obtained by the following preparation method:
firstly, silver nitrate reacts with a precipitator to form a silver precursor, and then the silver precursor is mixed with nano colloidal silver crystal seeds to generate silver-containing precursor precipitate;
and secondly, mixing the silver-containing precursor precipitate obtained in the step one with a reducing agent to obtain the nano silver colloid.
4. The method according to claim 1, wherein in the step (2), the dropping time of the silver salt solution is 10 to 25min, and the dropping time of the reducing agent solution is 8 to 20 min;
preferably, in the step (2), the dropping time of the silver salt solution is 12-20 min, and the dropping time of the reducing agent solution is 10-16 min.
5. The method according to claim 1, wherein in the step (2), the stirring speed is 50 to 200r/min, and/or
The reaction temperature is 10-25 ℃.
6. The method according to claim 1, characterized by further comprising, before the step (1), a step of preparing a silver salt solution, a reducing agent solution and a dispersing agent solution separately;
preferably, dissolving soluble silver salt in deionized water, adjusting the pH value of the solution to 0.5-3, and preparing a silver salt solution;
dissolving a reducing agent in deionized water, adjusting the pH of the solution to 1-6, and preparing to obtain a reducing agent solution; and/or
Dissolving a dispersing agent in deionized water to prepare a dispersing agent solution.
7. The method according to claim 6, wherein the soluble silver salt is silver nitrate,
the reducing agent is selected from at least one of glucose, sodium borohydride, formaldehyde, ascorbic acid, hydrazine hydrate, hydroquinone, alkanolamine and hydrogen peroxide; and/or
The dispersing agent is at least one selected from polyethylene glycol, polyvinyl alcohol, gelatin, sodium dodecyl benzene sulfonate, tween 80, polyvinylpyrrolidone and gum arabic.
8. The production method according to claim 6, wherein the silver ion concentration in the silver salt solution is 0.2 to 3mol/L,
the concentration of the reducing agent in the reducing agent solution is 0.1-5 mol/L, and/or
The concentration of the dispersing agent in the dispersing agent solution is 100-600 g/L.
9. The preparation method according to claim 1, wherein in the step (3), the drying temperature is 90-120 ℃ and the drying time is 5-20 min;
preferably, the drying temperature is 95-105 ℃, and the drying time is 10-15 min.
10. The spherical silver powder according to any one of claims 1 to 9, wherein the spherical silver powder has a particle diameter of 0.5 to 3.0 μm and a tap density of 5.0g/cm3The above.
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