CN111790918A - Preparation method of silver powder with low thermal shrinkage - Google Patents
Preparation method of silver powder with low thermal shrinkage Download PDFInfo
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- CN111790918A CN111790918A CN202010925462.XA CN202010925462A CN111790918A CN 111790918 A CN111790918 A CN 111790918A CN 202010925462 A CN202010925462 A CN 202010925462A CN 111790918 A CN111790918 A CN 111790918A
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- B—PERFORMING OPERATIONS; TRANSPORTING
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- B22F9/00—Making metallic powder or suspensions thereof
- B22F9/16—Making metallic powder or suspensions thereof using chemical processes
- B22F9/18—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds
- B22F9/24—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds starting from liquid metal compounds, e.g. solutions
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- B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
- B22F1/14—Treatment of metallic powder
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- B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
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Abstract
The invention provides a preparation method of silver powder with low thermal shrinkage, which comprises the steps of adding a silver nitrate aqueous solution and a reducing agent solution into a dispersant aqueous solution simultaneously to obtain silver powder particles, coating a surfactant on the surface of the silver powder, utilizing high-speed airflow to enable the silver powder particles to generate mutual impact, collision and friction shearing to realize smooth and dispersed treatment on the surface of the silver powder, and finally utilizing high-energy pulse current to provide high energy in a very short time to promote the silver powder to recrystallize at a lower temperature in a faster mode, improve the crystal defects of the silver powder and prevent the silver powder particles from agglomerating. The silver powder prepared by the invention has the advantages that the thermal shrinkage rate at 700 ℃ is not more than 5%, the silver powder has good sphericity and dispersibility, the particle size D100 is not more than 5 mu m, and the tap density is not less than 4g/cm3And the method has wide application prospect in the field of miniaturized high-reliability circuits.
Description
Technical Field
The invention belongs to the technical field of metal powder manufacturing, and particularly relates to a preparation method of silver powder with low thermal shrinkage rate for electronic paste.
Background
The electronic paste is a system in which solid particles composed of a powdery conductive metal suspended in an organic carrier, an inorganic or polymeric binder, and an organic liquid are mixed. The fluid material is applied to electronic components in a printing mode and the like to form a module with a specific electrical function, and is a basic material of various electronic components.
The electronic paste can be classified into a low-temperature curing type and a high-temperature sintering type according to the sintering temperature. The low-temperature curing type slurry ensures circuit conduction by shrinking and crimping the conductive filler through curing of the resin; the high-temperature sintering type slurry volatilizes organic components by high-temperature sintering, and the conductive filler and the inorganic binder are sintered, thereby ensuring circuit conduction.
Silver powder is widely applied to electronic paste as a conductive phase and is a main functional material of the electronic paste. With the miniaturization development of electronic components, electronic paste is required to realize a finer line width and higher reliability. In order to meet the use requirements of the electronic paste, the existing silver powder preparation method is generally realized by reducing the particle size of the silver powder. However, the single pursuit of the reduction in the particle size of silver powder leads to a problem that the electronic paste prepared therefrom undergoes a large shrinkage during sintering, thereby lowering the reliability of the circuit. Therefore, the preparation of silver powder with low shrinkage and controllable particle size distribution has become the key to solve the above technical problems.
As a method for preparing silver powder with low shrinkage, the prior art prepares silver by a liquid phase reduction method or an atomization methodAnd (3) pulverizing. For example: chinese patent CN1709619 discloses a spherical silver powder, which is prepared by adding an aqueous solution containing a reducing agent into an aqueous reaction system containing silver ions to reduce and separate out silver particles, wherein the thermal shrinkage rate of the spherical silver powder is 5-15% at 500 ℃, 10-20% at 600 ℃, the average particle diameter D50 is less than 5 mu m, and the tap density is 2g/cm3Above, a BET specific surface area of 5m2The ratio of the carbon atoms to the carbon atoms is less than g. Chinese patent CN108349009A discloses a silver powder having a small average particle size and a small thermal shrinkage rate and a method for producing the same. The silver powder is powdered by rapidly solidifying the silver melt by spraying high-pressure water while dropping the silver melt heated to 330 to 730 ℃ higher than the melting point of the silver, and the silver powder is obtained, wherein the average particle diameter is 1 to 6 [ mu ] m, the shrinkage at 500 ℃ is 8% or less, and the product of the average particle diameter and the shrinkage at 500 ℃ is 1 to 11 [ mu ] m.
The reported methods for preparing low-shrinkage silver powder have the particle size D100 of the silver powder being more than 5 μm and the thermal shrinkage rate at 700 ℃ being more than 5%, and the silver powder can not be well applied to miniaturized high-reliability circuits.
Disclosure of Invention
The invention aims to overcome the defects of large particle size and low thermal shrinkage rate of the silver powder prepared by the prior art, and provides a preparation method of the silver powder with controllable particle size distribution and low thermal shrinkage rate.
Aiming at the purposes, the technical scheme adopted by the invention comprises the following steps:
step 1: under the action of stirring and ultrasound, simultaneously adding a silver nitrate aqueous solution and a reducing agent solution with the pH of 2-8 into a dispersing agent aqueous solution, continuing stirring and continuing ultrasound for 15-30 min after the silver nitrate aqueous solution and the reducing agent solution are added, and filtering and washing the obtained silver powder particles by using deionized water until the conductivity of filtrate is less than 30 us/cm.
Step 2: adding the filtered and washed silver powder into a surfactant solution under the stirring action, and keeping stirring for 10-30 min; then, fully drying the silver powder coated with the surfactant, and screening the dried silver powder; wherein the surfactant solution is prepared by dissolving a surfactant in an organic solvent.
And step 3: and (3) taking high-speed airflow as a carrier, and bringing the silver powder screened in the step (2) into a stainless steel spiral tubular channel with zirconia as an inner wall to perform surface smoothing and dispersion treatment.
And 4, step 4: putting the silver powder treated in the step 3 into a glass tube and compacting, applying high-energy pulse current at two ends of the glass tube, and adjusting the crystal structure of the silver powder to obtain the silver powder with the thermal shrinkage rate not more than 5%, the particle size D100 not more than 5 mu m and the tap density not less than 4g/cm at 700 DEG C3The silver powder of (1); the high-energy pulse current has an output current of 20-120A, an output voltage of 220V, an alternating of positive and negative output polarities, an output current wave of 8/20us, a discharge frequency of 100-500 times, and an interval time of 30 s.
In the step 1, the concentration of silver nitrate in the silver nitrate aqueous solution is 300-800 g/L, and the temperature of the silver nitrate aqueous solution is 25-60 ℃.
In the step 1, the reducing agent solution with the pH of 2-8 is prepared by adding a reducing agent into deionized water and adjusting the pH to 2-8 by using sodium hydroxide or nitric acid, wherein the reducing agent is any one or more of sodium hypophosphite, sodium formate, ethylene glycol, ascorbic acid, triethanolamine, hydroquinone and sodium citrate, and the temperature of the reducing agent solution is 25-60 ℃.
In the step 1, the dispersant is any one or more of gum arabic, polyvinyl alcohol, polyethylene glycol, polyacrylic acid and polyvinylpyrrolidone, and the temperature of the dispersant aqueous solution is 25-60 ℃.
In the step 1, the molar ratio of the silver nitrate to the reducing agent is 1: 0.5-3, and the mass ratio of the silver nitrate to the dispersing agent is 1: 0.005-0.05.
In the step 1, the rotating speed of stirring is 50-300 r/min, and the ultrasonic frequency is 33-38 kHz.
In the step 2, the surfactant is any one or more of oleic acid, oleylamine and palmitic acid; the organic solvent is one or more of absolute ethyl alcohol, ethylene glycol and isopropanol; the mass ratio of the surfactant to the silver nitrate is 0.001-0.01: 1.
In the step 2, the rotating speed of stirring is 3000-5000 r/min; the drying is vacuum drying, the drying temperature is 85-145 ℃, and the drying time is 24-48 h; the screen used for screening is an 80-mesh standard screen.
In the step 3, the high-speed airflow is 300-500 m/s of compressed air, and the amount of silver powder entering the stainless steel spiral tubular channel with the zirconia as the inner wall is 1-10 kg/h.
In the step 4, the parameters of the high-energy pulse current are preferably output current 30-80A, output voltage 220V, alternating of positive and negative of output polarity once respectively, output current wave 8/20us, discharge frequency setting 100-300 times, and interval time setting 30 s.
Compared with the prior art, the invention has the following beneficial effects:
1. the traditional process for preparing silver powder by a liquid phase reduction method is to directly mix silver nitrate or silver intermediate solution and reducing agent solution and carry out reduction reaction under certain process conditions to prepare the silver powder. The invention optimizes the process for preparing the silver powder by the traditional liquid phase reduction method, and adopts a mode of simultaneously adding silver nitrate and a reducing agent solution into a dispersant solution in the silver powder reduction process to carry out reduction reaction to prepare the silver powder. Compared with the traditional process for preparing the silver powder by the liquid phase reduction method, the method effectively reduces the introduction of impurities in the formation process of silver powder particles, particularly the inclusion of an organic reducing agent in the silver powder particles; has obvious effects on reducing the burning loss of the silver powder and improving the crystallinity of the silver powder. Compared with the traditional process, the method is easier to control the instantaneous excess ratio of the silver nitrate and the reducing agent in the chemical reaction process, and can effectively improve the batch stability in the silver powder production process.
2. The invention carries out reduction reaction under the action of ultrasound, and can effectively improve the crystallinity of the silver powder. Compared with the prior art, the silver intermediate is not introduced in the implementation process of the invention, the silver nitrate and the reducing agent are both liquid phases, and the ion collision is intensified under the action of ultrasonic oscillation, so that the nucleation and growth of silver crystals are promoted in a short time, and the generated silver powder particles have a more regular crystal structure.
3. The invention uses high-speed airflow as a carrier to carry out dispersion treatment and surface smoothing treatment on the silver powder, and can improve the tap density and the particle fluidity of the silver powder. Compared with a mechanical treatment mode, the method utilizes the energy of high-speed airflow to enable particles to generate mutual impact, collision and friction shearing to realize silver powder dispersion and smooth surface, avoids silver powder particle agglomeration and surface damage caused by the mechanical treatment mode, and enables the treated silver powder to have smoother surface and better dispersibility.
4. According to the invention, the high-energy pulse current is used for recrystallizing the silver powder crystal structure, so that the thermal shrinkage rate of the silver powder can be effectively reduced and the crystallinity of the silver powder can be improved. According to the method, high heat energy and strain energy are simultaneously input to the silver powder by using high-energy pulse current, so that the atom migration rate is improved, and the microscopic defects in the silver powder particles are improved. Compared with the traditional recrystallization technology, the high-energy pulse current can provide higher energy in a very short time, so that the silver powder crystals are promoted to be recrystallized at lower temperature in a faster way, and the dispersity of the silver powder is ensured while the crystallinity of the silver powder is improved. Compared with the traditional recrystallization technology, the method has lower energy consumption and higher production efficiency in terms of production benefit.
5. The silver powder prepared by the method has the thermal shrinkage rate of not more than 5% at 700 ℃, good sphericity and dispersibility, particle size D100 of not more than 5 mu m, and tap density of not less than 4g/cm3And the method has wide application prospect in the field of miniaturized high-reliability circuits.
Drawings
FIG. 1 is an XRD diffraction pattern of the silver powders obtained in example 1 and comparative example 1.
FIG. 2 is a scanning electron micrograph of the silver powder obtained in example 1.
FIG. 3 is a scanning electron micrograph of the silver powder obtained in comparative example 4.
Fig. 4 is a graph comparing the dynamic thermomechanical data of the silver powders obtained in example 1 and comparative example 1.
FIG. 5 is a graph comparing the dynamic thermo-mechanical data of the silver powder prepared in example 1 and the commercially available silver powder in comparative example 2.
Detailed Description
The invention will be described in more detail below with reference to the drawings and examples, but the scope of the invention is not limited to these examples.
The silver powders prepared in the following examples and comparative examples were tested and evaluated for their properties by the following methods:
1. tap density
The tap density of the silver powder thus prepared was measured by the method of GB/T5162 (measurement of tap density of metal powder) using a JZ-7 type powder tap density instrument manufactured by Tokyo Fine powder test Equipment Co., Ltd.
2. Particle diameter D100
Particle diameter D100 of silver powder D100 based on the volume-based particle size distribution was measured at a dispersion pressure of 4.5bar using a HELOS particle size distribution measuring apparatus manufactured by SYMPATEC.
3. Silver powder electron microscope picture
The silver powder was subjected to morphological analysis at a magnification of 10000 times using a scanning electron microscope model VEGA3 manufactured by TESCAN.
4. Thermal shrinkage of silver powder
10g of the prepared silver powder was weighed and applied with a load of 800kg to prepare a cylindrical silver powder compact having a diameter of 5 mm. The linear shrinkage of the silver powder compact was measured at a temperature rise rate of 5 ℃/min and a load of 200mN in an air atmosphere using a thermomechanical analyzer model TMA 402F 3 Hyperion manufactured by NETZSCH, and the thermal shrinkage at 700 ℃ was obtained.
5. XRD diffraction pattern of silver powder
The diffraction pattern of the silver powder was measured under a wide angle diffraction condition using an ARLEQUINOX 3500X-ray diffractometer (XRD) manufactured by siemer fly, usa, to qualitatively compare the crystallinity of the silver powder.
6. Silver powder burning loss analysis and test method
Two clean porcelain cups are taken, residual powder or other impurities cannot be remained on the porcelain cups, and the weight W1 of the porcelain cups is weighed and recorded. 3-5 g of silver powder is accurately weighed in a porcelain cup and then recorded as W2. And putting the silver powder into a high-temperature box-type resistance furnace, keeping the temperature at 538 ℃ for 30min, putting the silver powder into a drying bottle, cooling the silver powder to room temperature, weighing and recording W3. According to the following formula: burning loss = (W2-W3)/(W2-W1). times.100%, and silver powder burning loss was calculated.
Example 1
Step 1: dissolving 40kg of high-purity silver nitrate crystal by 80L of deionized water in a temperature-controllable dissolving tank to prepare 500g/L of silver nitrate aqueous solution, and turning on a heating device to stabilize the temperature of the silver nitrate aqueous solution at 50 ℃; dissolving 24kg of ascorbic acid crystals in 160L of deionized water in a temperature-controllable dissolving tank, adjusting the pH value of the solution with sodium hydroxide to prepare a reducing agent solution with pH =3, and opening a heating device to stabilize the temperature of the reducing agent solution at 50 ℃; adding 440L of deionized water into a reaction kettle, turning on a stirring motor and setting the rotating speed at 100r/min, turning on a heating device to stabilize the temperature of the deionized water at 50 ℃, then adding 1.25kg of gum arabic into the reaction kettle, and fully dissolving the gum arabic under the stirring action to prepare a dispersant aqueous solution; setting the speed of a silver nitrate aqueous solution feeding peristaltic pump to be 3.8L/min, setting the speed of a reducing agent solution feeding peristaltic pump to be 7.8L/min, turning on an ultrasonic generator to set the frequency to be 35kHz, confirming that the tail end of an ultrasonic rod is below the liquid level of a dispersing agent aqueous solution, simultaneously adding the silver nitrate aqueous solution and the reducing agent aqueous solution into the dispersing agent aqueous solution in a reaction kettle under the action of stirring and ultrasonic, and keeping stirring and ultrasonic for 20min after the feeding is finished; and then, putting the materials in the reaction kettle into a filter washing pot, filtering and washing the materials for 5 times by using deionized water, measuring the conductivity of the filtrate to be 17us/cm, stopping filtering and washing, and pumping to dry to obtain the silver powder.
Step 2: weighing 50g of analytically pure oleic acid, and dissolving in 4L of absolute ethyl alcohol to obtain a surfactant solution; transferring the silver powder dried in the step 1 into a stainless steel pot, setting the rotating speed of a high-speed stirrer to be 3400r/min, adding the surfactant solution into the stainless steel pot under the action of high-speed stirring, and keeping the high-speed stirring for 20 min; then transferring the silver powder coated with the surfactant to a vacuum oven by using a stainless steel tray, and carrying out vacuum drying for 48h at 100 ℃; subsequently, the dried silver powder was sieved using an 80 mesh standard sieve.
And step 3: and (3) introducing the silver powder sieved in the step (2) into a stainless steel spiral tubular channel with zirconia as an inner wall by using compressed air of 350m/s in an adding amount of 5kg/h for surface smoothing and dispersion treatment.
And 4, step 4: 25kg of the silver powder treated in step 3 was charged into a glass tube and pressedIn practice, high-energy pulse current, output current 30A of the high-energy pulse current, output voltage 220V, alternating of positive and negative output polarities once, output current waveform 8/20us, discharge frequency setting 300 times, and interval time setting 30s were applied to both ends of the glass tube. The tap density of the finally obtained silver powder was 4.71g/cm3The particle diameter D100 was 4.20 μm, the burning loss was 0.38%, the XRD diffraction pattern is shown in FIG. 1, and the result of electron microscopic analysis was spherical or spheroidal particles having good dispersibility (see FIG. 2), and the heat shrinkage at 700 ℃ was 4.60%.
Example 2
Step 1: dissolving 25kg of high-purity silver nitrate crystal by 80L of deionized water in a temperature-controllable dissolving tank to prepare 312.5g/L of silver nitrate aqueous solution, and turning on a heating device to stabilize the temperature of the silver nitrate aqueous solution at 25 ℃; dissolving 20kg of hydroquinone crystals in a temperature-controllable dissolving tank by using 160L of deionized water to prepare a reducing agent solution with the pH =6, and opening a heating device to stabilize the temperature of the reducing agent solution at 25 ℃; adding 440L of deionized water into a reaction kettle, turning on a stirring motor and setting the rotating speed to be 300r/min, turning on a heating device to enable the temperature of the deionized water to be stabilized at 25 ℃, then adding 0.8kg of polyethylene glycol with the molecular weight of 1000 into the reaction kettle, and fully dissolving the polyethylene glycol under the stirring action to prepare a dispersant aqueous solution; setting the speed of a silver nitrate aqueous solution feeding peristaltic pump to be 21L/min, setting the speed of a reducing agent solution feeding peristaltic pump to be 43L/min, turning on an ultrasonic generator to set the frequency to be 38kHz, confirming that the tail end of an ultrasonic rod is below the liquid level of a dispersing agent aqueous solution, simultaneously adding the silver nitrate aqueous solution and the reducing agent aqueous solution into the dispersing agent aqueous solution in a reaction kettle under the action of stirring and ultrasonic, and keeping stirring and ultrasonic for 20min after the feeding is finished; and then, putting the materials in the reaction kettle into a filter washing pot, filtering and washing the materials for 5 times by using deionized water, measuring the conductivity of the filtrate to be 11us/cm, stopping filtering and washing, and pumping to dry to obtain the silver powder.
Step 2: weighing 50g of analytically pure oleylamine, and dissolving in 4L of isopropanol to obtain a surfactant solution; transferring the silver powder drained in the step 1 into a stainless steel pot, setting the rotating speed of a high-speed stirrer to be 4500r/min, adding the surfactant solution into the stainless steel pot under the action of high-speed stirring, and keeping the high-speed stirring for 20 min; then transferring the silver powder coated with the surfactant to a vacuum oven by using a stainless steel tray, and carrying out vacuum drying for 48h at the temperature of 80 ℃; subsequently, the dried silver powder was sieved using an 80 mesh standard sieve.
And step 3: and (3) introducing the silver powder sieved in the step (2) into a stainless steel spiral tubular channel with zirconia as an inner wall by using compressed air of 450m/s in an adding amount of 8kg/h for surface smoothing and dispersion treatment.
And 4, step 4: 15.9kg of the silver powder treated in the step 3 was charged into a glass tube and compacted, and high-energy pulse current, output current of 50A and output voltage of 220V, alternation of positive and negative output polarities at each time, output current wave of 8/20us, discharge frequency of 150 times, and interval time of 30s were applied to both ends of the glass tube. The tap density of the finally obtained silver powder was 4.14g/cm3The particle diameter D100 was 3.60 μm, the burning loss was 0.43%, and as a result of electron microscope analysis, the spherical or spheroidal particles had good dispersibility and the heat shrinkage at 700 ℃ was 4.90%.
Example 3
Step 1: dissolving 30kg of high-purity silver nitrate crystal by 50L of deionized water in a temperature-controllable dissolving tank to prepare 600g/L of silver nitrate aqueous solution, and turning on a heating device to stabilize the temperature of the silver nitrate aqueous solution at 60 ℃; dissolving 8kg of sodium hypophosphite crystals in 55L of deionized water in a temperature-controllable dissolving tank, adjusting the pH value of the solution by using sodium hydroxide to prepare a reducing agent solution with the pH =8, and opening a heating device to stabilize the temperature of the reducing agent solution at 60 ℃; adding 580L of deionized water into a reaction kettle, turning on a stirring motor and setting the rotating speed to be 150r/min, turning on a heating device to stabilize the temperature of the deionized water to be 60 ℃, then adding 1.5kg of polyacrylic acid with the number average molecular weight of 2000 into the reaction kettle, and fully dissolving the polyacrylic acid under the stirring action to prepare a dispersant aqueous solution; setting the speed of a silver nitrate aqueous solution feeding peristaltic pump to be 1L/min, setting the speed of a reducing agent solution feeding peristaltic pump to be 1L/min, turning on an ultrasonic generator to set the frequency to be 33kHz, confirming that the tail end of an ultrasonic rod is below the liquid level of a dispersing agent aqueous solution, simultaneously adding the silver nitrate aqueous solution and the reducing agent aqueous solution into the dispersing agent aqueous solution in a reaction kettle under the action of stirring and ultrasonic, and keeping stirring and ultrasonic for 20min after the feeding is finished; and then, putting the materials in the reaction kettle into a filter washing pot, filtering and washing the materials for 6 times by using deionized water, measuring that the conductivity of the filtrate is 23us/cm, stopping filtering and washing, and pumping to dry to obtain the silver powder.
Step 2: weighing 50g of analytically pure palmitic acid, and dissolving in 4L of ethylene glycol to obtain a surfactant solution; transferring the silver powder drained in the step 1 into a stainless steel pot, setting the rotating speed of a high-speed stirrer to be 4000r/min, adding a surfactant solution into the stainless steel pot under the action of high-speed stirring, and keeping the high-speed stirring for 20 min; then transferring the silver powder coated with the surfactant to a vacuum oven by using a stainless steel tray, and carrying out vacuum drying for 48h at 100 ℃; subsequently, the dried silver powder was sieved using an 80 mesh standard sieve.
And step 3: and 2kg/h of silver powder sieved in the step 2 is taken into a stainless steel spiral tubular channel with zirconia as an inner wall by 400m/s of compressed air for surface smoothing and dispersion treatment.
And 4, step 4: and (3) putting 19kg of the silver powder treated in the step (3) into a glass tube, compacting the silver powder, applying high-energy pulse current to two ends of the glass tube, wherein the output current of the high-energy pulse current is 80A, the output voltage is 220V, the positive and negative polarities are alternately output once, the output current wave is 8/20us, the discharge frequency is set to be 100 times, and the interval time is set to be 30 s. The tap density of the finally obtained silver powder was 4.45g/cm3The particle diameter D100 was 4.00. mu.m, the burning loss was 0.39%, and as a result of electron microscope analysis, spherical or spheroidal particles having good dispersibility and a heat shrinkage at 700 ℃ of 4.30% were obtained.
Comparative example 1
In example 1, the operation of step 4 was not performed, and the other steps were the same as in example 1. The tap density of the finally obtained silver powder was 3.85g/cm3The particle size D100 is 4.60 μm, the XRD diffraction pattern is shown in figure 1, and the result of electron microscope analysis shows that the silver powder has spherical or spheroidal particles with better dispersibility, and the thermal shrinkage rate at 700 ℃ is 9.10 percent and is obviously higher than that of the silver powder in example 1 (shown in figure 4).
Comparative example 2
For the low shrinkage spherical silver powder of Tonghe mining company, LtdThe tap density, the particle diameter D100 and the shrinkage at 700 ℃ of the silver powder were measured by the same method as described above, and the test results were as follows: tap density 5.32g/cm3The particle diameter D100 was 10.60 μm, and as a result of electron microscope analysis, the spherical or spheroidal particles had good dispersibility and the heat shrinkage at 700 ℃ was 9.70% (see FIG. 5).
Comparative example 3
In step 1 of example 1, after the reducing agent solution was completely added to the dispersant aqueous solution, a silver nitrate aqueous solution was added (conventional process for preparing silver powder by liquid phase reduction), and the other steps were the same as in example 1. The burning loss of the finally obtained silver powder is 0.87 percent and is obviously higher than that of the silver powder in the example 1.
Comparative example 4
In example 1, the operation of step 3 was not performed, and the other steps were the same as in example 1. The finally obtained silver powder was spherical or spheroidal particles having poor dispersibility and non-smooth surface (see FIG. 3), which is clearly different from the silver powder of example 1.
Claims (10)
1. A preparation method of silver powder with low thermal shrinkage rate is characterized by comprising the following steps:
step 1: under the action of stirring and ultrasound, simultaneously adding a silver nitrate aqueous solution and a reducing agent solution with the pH of 2-8 into a dispersing agent aqueous solution, continuing stirring and continuing ultrasound for 15-30 min after the silver nitrate aqueous solution and the reducing agent solution are added, and filtering and washing the obtained silver powder particles by using deionized water until the conductivity of filtrate is less than 30 us/cm;
step 2: adding the filtered and washed silver powder into a surfactant solution under the stirring action, and keeping stirring for 10-30 min; then, fully drying the silver powder coated with the surfactant, and screening the dried silver powder; wherein the surfactant solution is prepared by dissolving a surfactant in an organic solvent;
and step 3: taking high-speed airflow as a carrier, and bringing the silver powder screened in the step 2 into a stainless steel spiral tubular channel with zirconia as an inner wall to perform surface smoothing and dispersion treatment;
and 4, step 4: filling the silver powder treated in the step 3 into glassCompacting in a glass tube, applying high-energy pulse current at two ends of the glass tube, and adjusting the crystal structure of the silver powder to obtain a glass tube with a thermal shrinkage rate of not more than 5%, a particle diameter D100 of not more than 5 μm, and a tap density of not less than 4g/cm at 700 DEG C3The silver powder of (1); the high-energy pulse current has an output current of 20-120A, an output voltage of 220V, an alternating of positive and negative output polarities, an output current wave of 8/20us, a discharge frequency of 100-500 times, and an interval time of 30 s.
2. The method for preparing the silver powder with low thermal shrinkage according to claim 1, wherein: in the step 1, the concentration of silver nitrate in the silver nitrate aqueous solution is 300-800 g/L, and the temperature of the silver nitrate aqueous solution is 25-60 ℃.
3. The method for preparing the silver powder with low thermal shrinkage according to claim 1, wherein: in the step 1, the reducing agent solution with the pH of 2-8 is prepared by adding a reducing agent into deionized water and adjusting the pH to 2-8 by using sodium hydroxide or nitric acid, wherein the reducing agent is any one or more of sodium hypophosphite, sodium formate, ethylene glycol, ascorbic acid, triethanolamine, hydroquinone and sodium citrate, and the temperature of the reducing agent solution is 25-60 ℃.
4. The method for preparing the silver powder with low thermal shrinkage according to claim 1, wherein: in the step 1, the dispersing agent is any one or more of gum arabic, polyvinyl alcohol, polyethylene glycol, polyacrylic acid and polyvinylpyrrolidone, and the temperature of the aqueous solution of the dispersing agent is 25-60 ℃.
5. The method for preparing the silver powder with low thermal shrinkage according to any one of claims 1 to 4, wherein: in the step 1, the molar ratio of the silver nitrate to the reducing agent is 1: 0.5-3, and the mass ratio of the silver nitrate to the dispersing agent is 1: 0.005-0.05.
6. The method for preparing the silver powder with low thermal shrinkage according to claim 1, wherein: in the step 1, the rotating speed of stirring is 50-300 r/min, and the ultrasonic frequency is 33-38 kHz.
7. The method for preparing the silver powder with low thermal shrinkage according to claim 1, wherein: in the step 2, the surfactant is any one or more of oleic acid, oleylamine and palmitic acid; the organic solvent is one or more of absolute ethyl alcohol, ethylene glycol and isopropanol; the mass ratio of the surfactant to the silver nitrate is 0.001-0.01: 1.
8. The method for preparing the silver powder with low thermal shrinkage according to claim 1, wherein: in the step 2, the rotating speed of stirring is 3000-5000 r/min; the drying is vacuum drying, the drying temperature is 85-145 ℃, and the drying time is 24-48 h; the screen used for screening is an 80-mesh standard screen.
9. The method for preparing the silver powder with low thermal shrinkage according to claim 1, wherein: in the step 3, the high-speed airflow is 300-500 m/s of compressed air, and the amount of silver powder entering the stainless steel spiral tubular channel with the zirconia as the inner wall is 1-10 kg/h.
10. The method for preparing the silver powder with low thermal shrinkage according to claim 1, wherein: in step 4, the parameters of the high-energy pulse current are output current of 30-80A, output voltage of 220V, alternation of positive and negative output polarities once respectively, output current wave of 8/20us, discharge times of 100-300 times and interval time of 30 s.
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