CN116944511A

CN116944511A - Method for continuously producing composite silver powder and composite silver powder

Info

Publication number: CN116944511A
Application number: CN202310783750.XA
Authority: CN
Inventors: 赵维巍; 陆国锋
Original assignee: Shenzhen Hushen Intelligent Material Technology Co ltd
Current assignee: Shenzhen Hushen Intelligent Material Technology Co ltd
Priority date: 2023-06-29
Filing date: 2023-06-29
Publication date: 2023-10-27

Abstract

The invention discloses a method for continuously producing composite silver powder and the composite silver powder, and relates to the technical field of silver powder preparation. The method for continuously producing the composite silver powder comprises the steps of adopting a plurality of microfluidic reactors to prepare silver powder with different morphologies, wherein each microfluidic reactor is provided with a reaction cavity, a silver salt solution input pipe, a reduction solution input pipe and a product output pipe, the silver salt solution input pipe and the reduction solution input pipe are communicated with the reaction cavity, the bottom of the reaction cavity is communicated with the product output pipe, silver salt solution and reduction solution are respectively introduced into the silver salt solution input pipe and the reduction solution input pipe of the different microfluidic reactors and react in the reaction cavity, and the silver powder with different morphologies is regulated and controlled by controlling the flow rate, the residence time, the reaction time and the pipe diameters of the silver salt solution input pipe and the reduction solution input pipe of raw materials. The prepared nano silver has controllable morphology and particle size, stable product and high powder tap density, and can be finished in one step by utilizing multiple chambers or multiple channels to realize high flux.

Description

Method for continuously producing composite silver powder and composite silver powder

Technical Field

The invention relates to the technical field of silver powder preparation, in particular to a method for continuously producing composite silver powder and the composite silver powder.

Background

Silver has been widely used in conductive coatings, soldering and conductive contacts, and has many applications in the optical, electronic, energy and medical fields. In recent years, with the requirements of electronic circuits in the directions of small size, high precision, high reliability and the like, the focus of research is on the preparation of nano-micron silver powder. The general preparation method can only meet the preparation of a single morphology. So that the filling degree of the powder is insufficient. The tap density of these powders tends not to be high. Polyol reduction methods in synthetic chemistry are currently widely studied. Chemical reduction (including autoclave) directly in aqueous and nonaqueous solutions or thermal decomposition using silver compounds, as well as other auxiliary reduction means such as laser, microwave, electrochemical, sonochemical, and the like are commonly employed. During the process, the addition of different reducing agents can carefully control the growth of silver cores and silver powder. However, the traditional reaction kettle cannot accurately control thermodynamics and dynamics. But the product in the reaction kettle is mixed with the stock solution, so that the reduction environment cannot be fixed, and the morphology of the prepared silver particles is changed greatly. Therefore, the superfine silver powder prepared by the current chemical method has low popularization rate and single product morphology. Therefore, how to produce the composite silver powder on a large scale and simply and effectively control the particle size and the morphology of the nano silver particles is a main difficult problem of the wet chemical method.

The micro-fluidic droplet technology is a micro-processing technology based on accurate fluid control of a micro-fluidic chip, and can realize continuous sample injection, fast production of monodispersity and accurate size control. And droplets having a uniform size are prepared by a microfluidic device having a T-shaped flow channel or a fluidic structure. And the reaction can be regulated and controlled by different mixing modes by taking the reaction mixture as a template. At present, the scheme of preparing silver powder by a microfluidic droplet technology is less, and CN 107866577B designs a method for preparing monodisperse silver powder by a transient microfluidic tube reactor, but the transient microfluidic tube has only the function of cutting off flow, and the reaction also needs continuous multistage reaction by adding alkaline solution, gas, oil, a heating field and the like, and the flow rate is low by 20ml/min, so that the process requirement cannot be met.

In view of this, the present invention has been made.

Disclosure of Invention

The invention aims to provide a method for continuously producing composite silver powder and the composite silver powder.

The invention is realized in the following way:

in a first aspect, the invention provides a method for continuously producing composite silver powder, which comprises the steps of adopting a plurality of microfluidic reactors to prepare silver powder with different morphologies, wherein each microfluidic reactor is provided with a reaction cavity, a silver salt solution input pipe, a reduction solution input pipe and a product output pipe, the silver salt solution input pipe and the reduction solution input pipe are both communicated with the reaction cavity, and the bottom of the reaction cavity is communicated with the product output pipe;

And respectively introducing silver salt solution and reducing solution into the silver salt solution input pipe and the reducing solution input pipe of different microfluidic reactors, reacting in the reaction cavity, and regulating and controlling the flow rate and the residence time of the silver salt solution and the reducing solution in different silver salt solution input pipes and reducing solution input pipes, the pipe diameters of the silver salt solution input pipe and the reducing solution input pipe and the mixing reaction time of the silver salt solution and the reducing solution in different reaction cavities to generate silver powder with different morphologies.

In an alternative embodiment, the output flow rate of the product output pipe is greater than the sum of the input flow rate of the silver salt solution input pipe and the input flow rate of the reducing solution input pipe; the input flow rate of the reducing solution input pipe is larger than that of the silver salt solution input pipe;

preferably, the flow rates of the silver salt solution and the reducing solution are 0.05-3L/min;

preferably, residence time of the silver salt solution and the reducing solution in the different silver salt solution input pipe and the reducing solution input pipe is 0.05-90s;

preferably, the mixing reaction time of the silver salt solution and the reducing solution in different reaction chambers is 0.05-90s;

Preferably, the pipe diameters of the silver salt solution input pipe and the reducing solution input pipe are 5-75 μm.

In an alternative embodiment, the temperature in each reaction chamber is 5-68 ℃ and the pH value is 1.0-4.5;

preferably, a temperature sensor and a pH detector are arranged in each reaction cavity; when the pH is below 1.0, the pH is raised by adding ammonia to the reducing solution.

In an alternative embodiment, the microfluidic reactor is made of PDMS or glass;

preferably, the silver salt solution and the reducing solution are fed into different microfluidic reactors by a flow regulating pump;

preferably, the flow regulating pump is a peristaltic pump, a metering pump or a flow pump.

In an alternative embodiment, the bottoms of the microfluidic reactors are also provided with a collecting tray for collecting the products discharged from the product output pipe, and the collecting tray is filled with a plurality of polymer coating agents;

preferably, the polymer coating agent comprises 2.5-15% of polyvinylpyrrolidone, 0.05-1.5% of dispersing agent and 0.05-12% of powder surface treating agent by mass percent;

preferably, the dispersing agent comprises at least one of gelatin, tween 40 and tween 80;

Preferably, the powder surface treatment agent includes at least one of oleic acid, fatty acid, and lauric acid.

In an alternative embodiment, a stirring device for stirring the liquid in the collecting tray is arranged in the collecting tray;

preferably, the rotating speed of the stirring device is 250-3000r/min;

preferably, the stirring time of the stirring device is 1-90min;

preferably, the stirring device is a stirring blade or a stirring magnet;

preferably, a temperature regulator for regulating the temperature of the liquid in the collecting tray is arranged in the collecting tray;

preferably, the temperature regulator has a regulating temperature of 5-120 ℃.

In an alternative embodiment, the method for continuously producing the composite silver powder further comprises the steps of carrying out solid-liquid separation on the product in the collecting tray, and sequentially cleaning, drying and baking the separated product.

In an alternative embodiment, the silver salt solution is a 7.5-75% silver nitrate solution by mass fraction; the reducing solution is an aqueous solution of a reducing agent with the mass fraction of 5-45%, and the reducing agent comprises at least one of vitamin C, glucose, hydrazine hydrate and hydrogen peroxide;

preferably, the reducing solution also contains silver nano particles as seed crystal auxiliary agent, and the addition amount of the silver nano particles is 0.015 per mill-0.45 per mill of the mass of silver nitrate.

In an alternative embodiment, the silver salt solution and the reducing solution are both added with a macromolecule protecting agent solution, the adding amount of the macromolecule protecting agent solution in the silver salt solution is 1% -15%, and the adding amount of the macromolecule protecting agent solution in the reducing solution is 1% -15%;

preferably, the polymer protectant is polyvinylpyrrolidone.

In a second aspect, the present application provides a composite silver powder prepared by the method for continuously producing a composite silver powder according to any one of the preceding embodiments.

The application has the following beneficial effects:

compared with the method for preparing silver powder with different particle diameters by adopting microfluidic reactors to adjust the size of fluid, and finally converging outside the reactor at a certain included angle and realizing rapid mixing of silver nitrate solution and reducing solution outside the reactor, the method for continuously producing composite silver powder provided by the application has the advantages that the reaction is realized in the reaction cavity by utilizing the reaction cavity of the microfluidic reactors, the direct atmospheric reduction reaction is effectively avoided, the interference of oxygen on the reduction reaction is almost avoided, the prepared powder is mainly influenced by the reducing agent, so that the powder is stable and better in dispersibility, the silver powder with smaller particle diameter is favorable to be obtained, and even the silver powder with larger particle diameter is smaller than 2 microns, the problem of sediment blockage in a microchannel is effectively avoided, and the continuous reduction silver powder preparation is ensured. In addition, in the application, one microfluidic reactor prepares silver powder with a particle size, and the preparation of the silver powder with different particle sizes is realized through a plurality of different microfluidic reactors, so that the control of each microfluidic reactor is simpler, and each microfluidic reactor is also integrated with temperature and pH detection functions, so that the reaction process is easier to regulate and control. The nano silver prepared by the method has controllable morphology and particle size, stable product and high powder tap density, and can be finished in one step by utilizing multiple chambers or multiple channels to realize high flux. Has great advantages in the aspect of industrial continuous production.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are needed in the embodiments will be briefly described below, it being understood that the following drawings only illustrate some embodiments of the present application and therefore should not be considered as limiting the scope, and other related drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

FIG. 1 is a schematic diagram of a single microfluidic reactor according to the present application;

fig. 2 is a schematic structural diagram of 2 microfluidic reactors and a collection tray provided by the application;

FIG. 3 is an SEM characterization chart of silver powder obtained by the continuous production method of composite silver powder according to example 1 of the present application;

FIG. 4 is a SEM characterization chart of the silver powder prepared by the method for continuously producing composite silver powder according to comparative example 1 of the present application;

FIG. 5 is a SEM characterization chart of the silver powder prepared by the method for continuously producing composite silver powder according to comparative example 2 of the present application;

FIG. 6 is a SEM characterization chart of the silver powder prepared by the method for continuously producing composite silver powder according to comparative example 3 of the present application;

FIG. 7 is a SEM characterization view of the silver powder prepared by the method for continuously producing composite silver powder according to comparative example 4 of the present application;

Fig. 8 is a schematic view of a microfluidic reactor used in the method for preparing silver powder provided in comparative example 8 of the present application.

Icon: 110-microfluidic reactor; 1101-microfluidic reactor a; 1102-microfluidic reactor B; 111-reaction chamber; 1111-reaction chamber A; 1112-reaction chamber B; 112-silver salt solution input pipe; 1121-silver salt solution input pipe A; 1122-silver salt solution input pipe B; 113-a reducing solution input pipe; 1131-reducing solution input line A; 1132-reducing solution input line B; 114-output of product; 1141-product takeoff pipe A; 1142-product takeoff pipe B; 120-collection tray.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions of the embodiments of the present application will be clearly and completely described below. The specific conditions are not noted in the examples and are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or apparatus used were conventional products commercially available without the manufacturer's attention.

The application provides a method for continuously producing composite silver powder, which comprises the following steps:

s1, preparing silver salt solution.

A certain amount of silver nitrate is weighed and dissolved in water to prepare a silver nitrate solution with the mass fraction of 7.5-75% as silver salt solution in the application. And then adding a certain amount of polymer protective agent solution into the silver salt solution, wherein the addition amount of the polymer protective agent solution in the silver salt solution is 2-10%, and the polymer protective agent is polyvinylpyrrolidone.

S2, preparing a reducing solution.

Weighing a certain amount of reducing agent to be dissolved in water to prepare an aqueous solution of the reducing agent with the mass fraction of 5-45% as the reducing solution, wherein the reducing agent comprises at least one of vitamin C, glucose, hydrazine hydrate and hydrogen peroxide.

Then adding a macromolecule protecting agent solution into the reducing solution, wherein the adding amount of the macromolecule protecting agent solution in the reducing solution is 1% -15%; the polymer protective agent is polyvinylpyrrolidone.

In the application, the reducing solution also contains silver nano particles as seed crystal auxiliary agent, and the addition amount of the silver nano particles is 0.015 per mill-0.45 per mill of the mass of silver nitrate.

S3, preparing a collecting tray 120 and base fluid.

Adding a plurality of polymer coating agents to the collection tray 120; preferably, the polymer coating agent comprises 2.5-15% of polyvinylpyrrolidone, 0.05-1.5% of dispersing agent and 0.05-12% of powder surface treating agent by mass percent; wherein the dispersing agent includes, but is not limited to, at least one of gelatin, tween 40 and tween 80; the powder surface treatment agent includes, but is not limited to, at least one of oleic acid, fatty acid, and lauric acid.

A stirring device for stirring the liquid in the collecting tray 120 is arranged in the collecting tray 120; the stirring device can fully stir the base solution in the collecting tray 120, and simultaneously after the silver powder is collected in the collecting tray 120, the silver powder with different particle sizes and morphologies can be fully mixed with the base solution through the stirring device, so that the aggregation phenomenon of the silver powder in the base solution is reduced. Preferably, the rotation speed of the stirring device is 250-3000r/min (preferably 500-2000 r/min); the stirring time of the stirring device is 1-90min (preferably 1-60 min); stirring devices include, but are not limited to, stirring paddles or stirring magnets.

Further, a temperature regulator for regulating the temperature of the liquid in the collection tray 120 is provided in the collection tray 120; there are various choices of the temperature regulator, for example, the temperature regulator is carried out by injecting water through a jacket or heating by a resistance wire, and a structure capable of regulating the temperature of the liquid in the collecting tray 120 can be used as the temperature regulator of the present application, and the regulating temperature of the temperature regulator is preferably 5-120 ℃.

S4, carrying out microflow control reaction.

The microfluidic reaction is carried out in a plurality of microfluidic reactors 110, each microfluidic reactor 110 prepares silver powder with one particle size and morphology, and the silver powder with multiple particle sizes and multiple morphologies are prepared simultaneously through a plurality of different microfluidic reactors 110, so that composite silver powder is formed.

In order to more clearly illustrate the microfluidic control reaction of the present application, the structure of the microfluidic reactor 110 is illustrated in the present application.

Referring to fig. 1 and 2, in the present application, a plurality of microfluidic reactors 110 are provided, each of the microfluidic reactors 110 has a substantially identical structure, and only has a slight difference in internal dimension, each of the microfluidic reactors 110 is provided with a reaction chamber 111, a silver salt solution input pipe 112, a reducing solution input pipe 113 and a product output pipe 114, the silver salt solution input pipe 112 and the reducing solution input pipe 113 are both communicated with the reaction chamber 111, and the bottom of the reaction chamber 111 is communicated with the product output pipe 114. In the application, for the composite silver powder with two particle sizes, two different microfluidic reactors 110 are provided, namely a microfluidic reactor A1101 and a microfluidic reactor B1102, wherein the microfluidic reactor A1101 is provided with a reaction cavity A1111, a silver salt solution input pipe A1121, a reduction solution input pipe A1131 and a product output pipe A1141, and the microfluidic reactor B1102 is provided with a reaction cavity B1112, a silver salt solution input pipe B1122, a reduction solution input pipe B1132 and a product output pipe B1142.

In the present application, a temperature sensor (not shown) and a pH meter (not shown) are provided in each reaction chamber 111; the temperature sensor and the pH meter can detect and feed back the temperature and the pH in the reaction cavity 111, so that an operator can know the reaction condition in the reaction cavity 111 in time, and then adjust the temperature and the pH in the reaction cavity 111 in time within a proper range, preferably, the proper temperature range in each reaction cavity 111 is between 5 and 68 ℃, the proper pH range is between 1.0 and 4.5, if the temperature is higher than 68 ℃, the temperature is controlled by introducing a reducing solution and a silver salt solution with lower temperature into the system, and when the pH value is lower than 1.0, ammonia water is added into the reducing solution to improve the pH value.

In the present application, the silver salt solution input pipe 112, the reducing solution input pipe 113 and the product output pipe 114 may be connected to the reaction chamber 111 in a multi-angle, for example, the silver salt solution input pipe 112, the reducing solution input pipe 113 and the product output pipe 114 may be connected to the reaction chamber 111 in a Y-shape; the silver salt solution input pipe 112, the reducing solution input pipe 113 and the product output pipe 114 may also be connected to the reaction chamber 111 in the same direction (i.e., in the same flow direction); any two of the silver salt solution input pipe 112, the reducing solution input pipe 113 and the product output pipe 114 may also be connected to the reaction chamber 111 in opposite directions (i.e., in the same flow direction); the silver salt solution input pipe 112, the reducing solution input pipe 113, and the product output pipe 114 may also be connected to the reaction chamber 111 in a vertical state; the silver salt solution and the reducing solution are discharged into the reaction cavity 111 for reaction in a specific mode, a pneumatic micro valve is further arranged in the reactor, and the mixing reaction time of the silver salt solution and the reducing solution in different reaction cavities 111 can be flexibly controlled by adjusting the opening and closing time of the pneumatic micro valve, so that the formation and the size of micro liquid drops are controlled.

In this embodiment, the silver salt solution and the reducing solution may be introduced into different microfluidic reactors 110 by a flow rate regulating pump; the flow regulating pump is a peristaltic pump, a metering pump or a flow pump. Wherein the tube diameters of the silver salt solution input tube 112 and the reducing solution input tube 113 are selected in the range of 5-75 μm. The application can select microfluidic reactors 110 with different pipe diameters for reaction according to the requirements of different grain diameters and morphologies. Further, in the present application, the microfluidic reactors 110 are made of PDMS or glass, and the collection tray 120 is disposed at the bottom of the microfluidic reactors 110, for collecting the product discharged from the product outlet pipe 114.

Next, the present application will focus on how to realize the preparation of composite silver powder with different morphologies using the above-mentioned plurality of different microfluidic reactors 110.

Specifically, the silver salt solution and the reducing solution are respectively introduced into the silver salt solution input pipe 112 and the reducing solution input pipe 113 of different microfluidic reactors 110 and react in the reaction cavity 111, and the flow rate, the residence time and the pipe diameters of the silver salt solution input pipe 112 and the reducing solution input pipe 113 and the mixing reaction time of the silver salt solution and the reducing solution in different reaction cavities 111 are controlled to generate silver powder with different morphologies by controlling the flow rates and the residence time of the silver salt solution and the reducing solution in different silver salt solution input pipes 112 and reducing solution input pipes 113.

Control of flow rate: the output flow rate of the product output pipe 114 is greater than the sum of the input flow rate of the silver salt solution input pipe 112 and the input flow rate of the reducing solution input pipe 113; the input flow rate of the reducing solution input pipe 113 is greater than the input flow rate of the silver salt solution input pipe 112; preferably, the flow rates of the silver salt solution and the reducing solution are 0.05 to 3L/min (preferably 0.1 to 2L/min);

in the present embodiment, by controlling the flow rates of the silver salt solution and the reducing solution, the pipe diameters of the silver salt solution input pipe 112 and the reducing solution input pipe 113, it is possible to limit the residence time of the silver salt solution and the reducing solution in the silver salt solution input pipe 112 and the reducing solution input pipe 113, in the present application, the residence time of the silver salt solution and the reducing solution in the different silver salt solution input pipe 112 and the reducing solution input pipe 113 is 0.05-90s (preferably 0.1-60 s); further, the mixing reaction time of the silver salt solution and the reducing solution in the different reaction chambers 111 can be controlled to be 0.05-90s (preferably 0.1-60 s) by the pneumatic micro valve and the PLC device.

S5, post-treatment of the composite silver powder.

The products in the collecting tray 120 are subjected to solid-liquid separation, and the separated products are sequentially washed, dried and baked. The solid-liquid separation method is various, including but not limited to, centrifugal machine, filtration, press filtration, etc., in the present application, the separation is preferably performed by using a centrifugal machine, and when the separation is performed by using filtration, the mesh size of the filter screen or the filter cloth is preferably 500-2000 mesh. The method comprises the steps of firstly adopting deionized water to remove surface water-soluble polymer residual liquid, then adopting ethanol to carry out rinsing, accelerating subsequent drying, drying under the low-temperature condition (35-50 ℃) after the cleaning is finished until no obvious residual liquid exists on the surface, and then placing the dried product in a vacuum oven (35-50 ℃) for baking for 3 hours.

Compared with other conventional microfluidic reactors 110 which are used for adjusting the size of fluid and reacting outside the cavity, the reaction cavity 111 of the composite silver powder prepared by the method can realize the functions of temperature and pH detection and the like, so that the reaction is easier to regulate and control, silver powder with single particle size is realized in each microfluidic reactor 110, the silver powder with single particle size is easier to control, simultaneously, the silver powder with various particle sizes and shapes is simultaneously prepared by a plurality of different microfluidic reactors 110, the operation is simple, continuous production can be realized, the prepared silver powder falls into a collecting disc 120 provided with a high-molecular dispersing agent, and the high-molecular dispersing agent is more beneficial to protecting nano or micron silver powder particles flowing in the microfluidic reaction, so that the adhesion among the silver powder is prevented, and the dispersibility of the powder is improved.

The features and capabilities of the present application are described in further detail below in connection with the examples.

Example 1

The embodiment provides a method for continuously producing composite silver powder, which comprises the following steps:

(1) 2kg of silver nitrate was weighed into 8L of water and dissolved after stirring. Then storing at 15 ℃ for standby;

(2) 1kg of glucose is weighed and placed in 9L of water, and after stirring, the glucose is dissolved, and then 0.1kg of hydrogen peroxide, 0.1kg of hydrazine hydrate and other auxiliary reducing agents can be added. Simultaneously adding a certain amount of seed crystal solution (0.06 g), wherein the grain diameter of the seed crystal is 20-50 nanometers, and then storing at a low temperature of 15 ℃ for later use;

(3) Weighing 0.5kg of polyvinylpyrrolidone (PVP) and placing in 9.5L of water, stirring, dissolving, adding dispersant (gelatin 0.5kg, tween 40.3 kg, tween 80 0.1 kg) and powder surface treating agent (oleic acid 1g, fatty acid 1g, lauric acid 1 g), mixing uniformly to obtain polymer coating agent, and placing the polymer coating agent into a 5L collecting tray 120 in batches;

(4) The silver salt solution and the reducing solution are respectively injected into a silver salt solution input pipe A1121 and a reducing solution input pipe A1131 of a microfluidic reactor A1101 in a constant flow maintaining mode through an injector, and a silver salt solution input pipe B1122 and a reducing solution input pipe B1132 of a microfluidic reactor B1102. Wherein, the internal flow rate of the silver salt solution input pipe 112 and the reducing solution input pipe 113 in the microfluidic reactor A1101 is 0.5L/min, and the pipe diameter is 25 μm; the residence time of the silver salt solution and the reducing solution in the silver salt solution input pipe A1121 and the reducing solution input pipe A1131 in the microfluidic reactor A1101 is 30s; the mixing reaction time of the silver salt solution and the reducing solution in the reaction chamber a1111 of the microfluidic reactor a1101 was 10s. The internal flow rate of the silver salt solution input pipe B1122 and the reducing solution input pipe B1132 in the microfluidic reactor B1102 was 1L/min, and the pipe diameter was 50. Mu.m. At this time, the residence time of the silver salt solution and the reducing solution in the silver salt solution input tube B1122 and the reducing solution input tube B1132 in the microfluidic reactor B1102 is 40s; the mixing reaction time of the silver salt solution and the reducing solution in the reaction chamber B1112 of the microfluidic reactor B1102 was 20s. The product produced by the micro-channels was collected by the collection tray 120 and chassis replacement was completed using a shut-off gap, maintaining the rotational speed of the base solution at 500r/min and the temperature at 20 ℃.

(5) After continuous material conveying, the pH value in the micro channel is reduced and the temperature is increased, and at the moment, the reaction can be regulated and controlled by adding ammonia water into the reducing solution with lower temperature until the reaction is finished.

(6) And taking out the composite silver powder solution, and carrying out solid-liquid separation through a separation membrane to obtain the composite wet silver powder. After ethanol washing and deionized water system for several times, putting into a vacuum oven to obtain composite silver powder, refer to FIG. 3, wherein the particle size of the silver powder obtained by the microfluidic reactor A1101 is 0.5 μm, the particle size of the silver powder obtained by the microfluidic reactor B1102 is 1.5 μm, and the tap density of the composite silver powder is 5.7g/cm ³ 。

As can be seen from fig. 3, silver powder particles with various morphologies can be obtained in one step by using the method provided by the embodiment, and good dispersibility is maintained. The grain diameter of the silver powder prepared by the method is between 0.2 and 2 mu m, and meets the requirement of superfine silver powder. The silver powder prepared by the method has higher tap density due to the fact that the silver powder contains various particle sizes, and the range of values is 5.5-6.5g/cm ³ Between them. Can meet the requirement of subsequent high-precision slurry.

Examples 2 to 3

Examples 2-3 are substantially identical to example 1, except that: the reaction parameters of the microfluidic reactor 110 are different.

In step (4) of example 2, the silver salt solution and the reducing solution were injected into the silver salt solution input pipe a1121 and the reducing solution input pipe a1131 of the microfluidic reactor a1101 and the silver salt solution input pipe B1122 and the reducing solution input pipe B1132 of the microfluidic reactor B1102, respectively, by means of a syringe, while maintaining constant flow. Wherein, the micro The internal flow rate of the silver salt solution input pipe A1121 and the reducing solution input pipe A1131 in the flow control reactor A1101 is 0.5L/mins, and the pipe diameter is 25 mu m; the residence time of the silver salt solution and the reducing solution in the silver salt solution input pipe A1121 and the reducing solution input pipe A1131 in the microfluidic reactor A1101 is 10s; the mixing reaction time of the silver salt solution and the reducing solution in the reaction chamber a1111 of the microfluidic reactor a1101 was 10s. The internal flow rate of the silver salt solution input pipe B1122 and the reducing solution input pipe B1132 in the microfluidic reactor B1102 was 2L/min, and the pipe diameter was 50. Mu.m. At this time, the residence time of the silver salt solution and the reducing solution in the silver salt solution input tube B1122 and the reducing solution input tube B1132 in the microfluidic reactor B1102 is 40s; the mixing reaction time of the silver salt solution and the reducing solution in the reaction chamber B1112 of the microfluidic reactor B1102 was 60s. The product produced by the micro-channels was collected by the collection tray 120 and chassis replacement was completed using a shut-off gap, maintaining the rotational speed of the base solution at 500r/min and the temperature at 20 ℃. The grain diameter of silver powder obtained by the microfluidic reactor A1101 is 0.9 mu m, the grain diameter of silver powder obtained by the microfluidic reactor B1102 is 2.5 mu m, and the tap density of composite silver powder is 5.9g/cm ³ 。

In step (4) of example 3, the silver salt solution and the reducing solution were injected into the silver salt solution input pipe a1121 and the reducing solution input pipe a1131 of the microfluidic reactor a1101 and the silver salt solution input pipe B1122 and the reducing solution input pipe B1132 of the microfluidic reactor B1102, respectively, by means of a syringe, while maintaining constant flow. Wherein, the internal flow rate of the silver salt solution input pipe A1121 and the reducing solution input pipe A1131 in the microfluidic reactor A1101 is 0.5L/mins, and the pipe diameter is 25 μm; the residence time of the silver salt solution and the reducing solution in the silver salt solution input pipe A1121 and the reducing solution input pipe A1131 in the microfluidic reactor A1101 is 60s; the mixing reaction time of the silver salt solution and the reducing solution in the reaction chamber a1111 of the microfluidic reactor a1101 was 50s. The internal flow rate of the silver salt solution input pipe B1122 and the reducing solution input pipe B1132 in the microfluidic reactor B1102 was 2L/min, and the pipe diameter was 20. Mu.m. At this time, residence time of silver salt solution and reducing solution in the silver salt solution input tube B1122 and reducing solution input tube B1132 in the microfluidic reactor B110240s; the mixing reaction time of the silver salt solution and the reducing solution in the reaction chamber B1112 of the microfluidic reactor B1102 was 40s. The product produced by the micro-channels was collected by the collection tray 120 and chassis replacement was completed using a shut-off gap, maintaining the rotational speed of the base solution at 500r/min and the temperature at 25 ℃. The grain diameter of silver powder obtained by the microfluidic reactor A1101 is 1.2 mu m, the grain diameter of silver powder obtained by the microfluidic reactor B1102 is 2.8 mu m, and the tap density of composite silver powder is 6.2g/cm ³ 。

Example 4

(1) 1.5kg of silver nitrate was weighed into 8.5L of water and dissolved after stirring. Then storing at 18 ℃ for standby;

(2) Weighing 0.5kg of glucose, putting into 9.5L of water, stirring, dissolving, and adding 0.5kg of hydrogen peroxide, 0.5kg of hydrazine hydrate and other auxiliary reducing agents. Simultaneously adding a certain amount of seed crystal solution (0.03 kg), wherein the grain diameter of the seed crystal is 20-50 nanometers, and then storing at a low temperature of 18 ℃ for later use;

(3) Weighing 0.5kg of polyvinylpyrrolidone (PVP) and putting into 9.5L of water, dissolving after stirring, adding dispersing agent (gelatin 0.1kg, tween 40 0.5kg, tween 80 0.6 kg) and powder surface treating agent (oleic acid 0.5g, fatty acid 1.5g and lauric acid 1 g), uniformly mixing to obtain polymer coating agent, and putting the polymer coating agent into a 5L collecting tray 120 in batches;

(4) The silver salt solution and the reducing solution are respectively injected into a silver salt solution input pipe A1121 and a reducing solution input pipe A1131 of a microfluidic reactor A1101 in a constant current maintaining mode through an injector, and a silver salt solution input pipe B1122 and a reducing solution input pipe B1132 of a microfluidic reactor B1102. Wherein, the internal flow rate of the silver salt solution input pipe A1121 and the reducing solution input pipe A1131 in the microfluidic reactor A1101 is 0.5L/mins, and the pipe diameter is 25 μm; the residence time of the silver salt solution and the reducing solution in the silver salt solution input pipe A1121 and the reducing solution input pipe A1131 in the microfluidic reactor A1101 is 30s; the mixing reaction time of the silver salt solution and the reducing solution in the reaction chamber a1111 of the microfluidic reactor a1101 was 60s. The internal flow rate of the silver salt solution input pipe B1122 and the reducing solution input pipe B1132 in the microfluidic reactor B1102 was 1L/min, and the pipe diameter was 50. Mu.m. At this time, the residence time of the silver salt solution and the reducing solution in the silver salt solution input tube B1122 and the reducing solution input tube B1132 in the microfluidic reactor B1102 is 40s; the mixing reaction time of the silver salt solution and the reducing solution in the reaction chamber B1112 of the microfluidic reactor B1102 was 60s. The product produced by the micro-channels was collected by the collection tray 120 and chassis replacement was completed using a shut-off gap, maintaining the rotational speed of the base solution at 500r/min and the temperature at 18 ℃.

(6) And taking out the composite silver powder solution, and carrying out solid-liquid separation through a separation membrane to obtain the composite wet silver powder. Then the silver powder is put into a vacuum oven after ethanol washing and deionized water system are carried out for several times, wherein the average grain diameter of the silver powder obtained by the microfluidic reactor A1101 is 1.5 mu m, the average grain diameter of the silver powder obtained by the microfluidic reactor B1102 is 2.5 mu m, and the tap density of the composite silver powder is 6.4g/cm ³ 。

Example 5

(1) 4kg of silver nitrate was weighed into 6L of water and dissolved after stirring. Then storing at a low temperature of 16 ℃ for standby;

(2) Weighing 0.8kg of glucose, putting into 9.2L of water, stirring, dissolving, and adding 0.4kg of hydrogen peroxide, 0.2kg of hydrazine hydrate and other auxiliary reducing agents. Simultaneously adding a certain amount of seed crystal solution (0.05 g), wherein the grain diameter of the seed crystal is 20-50 nanometers, and then storing at a low temperature of 16 ℃ for later use;

(3) Weighing 0.8kg of polyvinylpyrrolidone (PVP) and putting into 9.2L of water, dissolving after stirring, adding dispersing agent (gelatin 0.5kg, tween 40 0.2kg, tween 80 0.05 kg) and powder surface treating agent (oleic acid 3g, fatty acid 0.5g and lauric acid 0.5 g), uniformly mixing to obtain polymer coating agent, and putting the polymer coating agent into a 5L collecting tray 120 in batches;

(4) The silver salt solution and the reducing solution are respectively injected into a silver salt solution input pipe A1121 and a reducing solution input pipe A1131 of a microfluidic reactor A1101 in a constant current maintaining mode through an injector, and a silver salt solution input pipe B1122 and a reducing solution input pipe B1132 of a microfluidic reactor B1102. Wherein, the internal flow rate of the silver salt solution input pipe A1121 and the reducing solution input pipe A1131 in the microfluidic reactor A1101 is 0.5L/mins, and the pipe diameter is 25 μm; the residence time of the silver salt solution and the reducing solution in the silver salt solution input pipe A1121 and the reducing solution input pipe A1131 in the microfluidic reactor A1101 is 10s; the mixing reaction time of the silver salt solution and the reducing solution in the reaction chamber a1111 of the microfluidic reactor a1101 was 5s. The internal flow rate of the silver salt solution input pipe B1122 and the reducing solution input pipe B1132 in the microfluidic reactor B1102 was 1L/min, and the pipe diameter was 50. Mu.m. At this time, the residence time of the silver salt solution and the reducing solution in the silver salt solution input tube B1122 and the reducing solution input tube B1132 in the microfluidic reactor B1102 is 20s; the mixing reaction time of the silver salt solution and the reducing solution in the reaction chamber B1112 of the microfluidic reactor B1102 was 10s. The product produced by the micro-channels was collected by the collection tray 120 and chassis replacement was completed using a shut-off gap, maintaining the rotational speed of the base solution at 500r/min and the temperature at 16 ℃.

(6) And taking out the composite silver powder solution, and carrying out solid-liquid separation through a separation membrane to obtain the composite wet silver powder. Then the silver powder is put into a vacuum oven after ethanol washing and deionized water system are carried out for several times, wherein the grain diameter of the silver powder obtained by the microfluidic reactor A1101 is 0.8 mu m, the grain diameter of the silver powder obtained by the microfluidic reactor B1102 is 2.2 mu m, and the tap density of the composite silver powder is 5.5g/cm ³ 。

Comparative example 1

This comparative example is substantially the same as example 1, except that the reaction parameters of the microfluidic reactor 110 are different.

In the comparative example, the internal flow rate of the silver salt solution input pipe A1121 and the reducing solution input pipe A1131 in the microfluidic reactor A1101 is 0.5L/min, and the pipe diameter is 25 μm; the residence time of the silver salt solution and the reducing solution in the silver salt solution input pipe A1121 and the reducing solution input pipe A1131 in the microfluidic reactor A1101 is 160s; the mixing reaction time of the silver salt solution and the reducing solution in the reaction chamber a1111 of the microfluidic reactor a1101 was 160s.

The internal flow rate of the silver salt solution input pipe B1122 and the reducing solution input pipe B1132 in the microfluidic reactor B1102 was 3L/min, and the pipe diameter was 10. Mu.m. At this time, the residence time of the silver salt solution and the reducing solution in the silver salt solution input tube B1122 and the reducing solution input tube B1132 in the microfluidic reactor B1102 is 200s; the mixing reaction time of the silver salt solution and the reducing solution in the reaction chamber B1112 of the microfluidic reactor B1102 was 100s.

Referring to FIG. 4, it can be seen from FIG. 4 that the particle size of the silver powder is significantly larger than 2-4um, and the morphology is more uniform, so that larger gaps exist between the silver powder, resulting in smaller tap density of 4.5-5.5g/cm ³ Between them.

Comparative example 2

In the comparative example, the internal flow rate of the silver salt solution input pipe A1121 and the reducing solution input pipe A1131 in the microfluidic reactor A1101 is 5L/min, and the pipe diameter is 5 μm; the residence time of the silver salt solution and the reducing solution in the silver salt solution input pipe A1121 and the reducing solution input pipe A1131 in the microfluidic reactor A1101 is 60s; the mixing reaction time of the silver salt solution and the reducing solution in the reaction chamber a1111 of the microfluidic reactor a1101 was 30s.

The internal flow rate of the silver salt solution input pipe B1122 and the reducing solution input pipe B1132 in the microfluidic reactor B1102 was 3L/min, and the pipe diameter was 20. Mu.m. At this time, the residence time of the silver salt solution and the reducing solution in the silver salt solution input tube B1122 and the reducing solution input tube B1132 in the microfluidic reactor B1102 is 60s; the mixing reaction time of the silver salt solution and the reducing solution in the reaction chamber B1112 of the microfluidic reactor B1102 was 90s.

As can be seen from FIG. 5, the silver powder prepared by the method has a particle size of 1-2um which is obviously smaller and a single morphology, so that soft agglomeration exists between the silver powder, and the tap density is smaller and is 4.5-5.5g/cm ³ Left and right.

Comparative example 3

This comparative example is substantially the same as comparative example 1 except that no seed crystal was added in step (2) of this comparative example, and specifically comprises the steps of:

(1) 2kg of silver nitrate was weighed into 8L of water and dissolved after stirring. Then storing at a higher temperature of 30 ℃ for later use;

(2) 1kg of glucose is weighed and placed in 9L of water, and after stirring, the glucose is dissolved, and then 0.2kg of hydrogen peroxide, 0.1kg of hydrazine hydrate and other auxiliary reducing agents can be added. No seed crystal is added, and then the mixture is stored at a higher temperature of 30 ℃ for standby;

(3) Weighing 0.5kg of polyvinylpyrrolidone (PVP) and putting into 9.5L of water, dissolving after stirring, adding dispersing agent (gelatin 0.5kg, tween 40 0.5kg, tween 80 0.2 kg) and powder surface treating agent (oleic acid 0.1g, fatty acid 0.2g and lauric acid 0.2 g), uniformly mixing to obtain polymer coating agent, and putting the polymer coating agent into a 5L collecting tray 120 in batches;

(4) The silver salt solution and the reducing solution are respectively injected into a silver salt solution input pipe A1121 and a reducing solution input pipe A1131 of a microfluidic reactor A1101 in a constant current maintaining mode through an injector, and a silver salt solution input pipe B1122 and a reducing solution input pipe B1132 of a microfluidic reactor B1102. Wherein, the internal flow rate of the silver salt solution input pipe A1121 and the reducing solution input pipe A1131 in the microfluidic reactor A1101 is 0.5L/mins, and the pipe diameter is 25 μm; the residence time of the silver salt solution and the reducing solution in the silver salt solution input pipe A1121 and the reducing solution input pipe A1131 in the microfluidic reactor A1101 is 50s; the mixing reaction time of the silver salt solution and the reducing solution in the reaction chamber a1111 of the microfluidic reactor a1101 was 60s. The internal flow rate of the silver salt solution input pipe B1122 and the reducing solution input pipe B1132 in the microfluidic reactor B1102 was 3L/min, and the pipe diameter was 10. Mu.m. At this time, the residence time of the silver salt solution and the reducing solution in the silver salt solution input tube B1122 and the reducing solution input tube B1132 in the microfluidic reactor B1102 is 50s; the mixing reaction time of the silver salt solution and the reducing solution in the reaction chamber B1112 of the microfluidic reactor B1102 was 60s. The product produced by the micro-channels was collected by the collection tray 120 and chassis replacement was completed using a shut-off gap, maintaining the rotational speed of the base solution at 500r/min and the temperature at 30 ℃.

(6) And taking out the composite silver powder solution, and carrying out solid-liquid separation through a separation membrane to obtain the composite wet silver powder. And then, after ethanol washing and deionized water system are carried out for several times, putting the silver powder into a vacuum oven to obtain the composite silver powder.

As can be seen from FIG. 6, the silver powder prepared by the method has a particle size of 0.5-2um, and single powder grows unordered, so that hard agglomeration exists between the silver powder, and the tap density is 5.5g/cm ³ Left and right.

Comparative example 4

This comparative example is basically the same as example 1 except that the base liquid in the collecting tray 120 in this comparative example is pure water.

Referring to fig. 7, it can be seen from fig. 7 that using pure water as a base liquid, the silver powder particles produced become large and the silver powder particles easily adhere to each other.

Comparative example 5

This comparative example was substantially the same as example 1 except that the polymer coating agent in this comparative example was composed of polyvinylpyrrolidone alone, and 0.5kg of polyvinylpyrrolidone (PVP) was dissolved in 9.5L of water with stirring. The silver powder obtained by the preparation is irregular.

Comparative example 6

This comparative example was substantially the same as example 1 except that the polymer coating agent of this comparative example was composed of only a dispersant and a powder surface treating agent, and the dispersant (gelatin 0.5kg, tween 40.5 kg, tween 80 1 kg) and the powder surface treating agent (oleic acid 2g, fatty acid 1g, lauric acid 1 kg) were dissolved in 9.5L of water with stirring. The silver powder obtained by the preparation is also irregular.

Comparative example 7

This comparative example is substantially the same as example 1 except that the operation of adjusting the temperature and pH of the reaction chamber 111 in example 1 is omitted. The silver powder obtained by the preparation has serious agglomeration.

Comparative example 8

The present comparative example provides a method for preparing silver powder, which comprises the steps of:

FIG. 8 is a schematic diagram of the operation of a microfluidic reactor according to the present invention, wherein the 1-solution A inlet, the 2-solution B inlet, the 3-microchannel I, the 4-microchannel II, the 5-solution A outlet, the 6-solution B outlet, and the 7-micromixing point;

17g AgNO was isolated from light ₃ Dissolving in 1000ml deionized water to prepare a solution with the molar concentration of 0.1mol/L, adding 1g of sulfuric acid, adjusting the PH of the solution to 2, magnetically stirring for 10 minutes to obtain a fully and uniformly dissolved solution A, and keeping the solution A in a water bath kettle with the temperature of 25 ℃ for later use; dissolving 8.8g of ascorbic acid in 1000mL of deionized water to prepare a solution with the mass concentration of 0.05mol/L, adding 0.017g of lauric acid as a surface dispersing agent, magnetically stirring for 10 minutes to obtain a fully and uniformly dissolved solution B, and keeping the solution B in a water bath kettle with the temperature of 25 ℃ for later use; 200ml of deionized water is added into a clean beaker with the capacity of 3000ml to be used as base solution, and the solution is kept in a water bath kettle with the temperature of 25 ℃ for standby; the solution A and the solution B are respectively injected into a solution A inlet 1 and a solution B inlet 2 of a micro-jet reactor shown in figure 8 through a advection pump A and a advection pump B at the flow rate of 50mL/min, then enter a micro-channel I3 and a micro-channel II 4, the inner diameter of the micro-channel is 0.5mm, and after being sprayed out from a micro-channel outlet (a solution A outlet 5 and a solution B outlet 6) of the micro-jet reactor, the solution A and the solution B are converged at a micro-mixing point 7 at an included angle of 90 degrees, so that the rapid mixing of the solution A and the solution B is realized at the micro-mixing point 7. The mixed solution forms a stream of confluent liquid, the confluent liquid falls into a beaker filled with deionized water at a height of 200mm from the liquid level, the solution in the beaker is continuously stirred at 200r/min by a magnetic stirring device in the process, and the advection pump stops pumping A, B solution and then continuously stirs for 2min to complete the reaction; the silver particle-containing solution in the beaker is adopted And (3) carrying out vacuum suction filtration on 600-mesh nylon filter cloth, washing with deionized water for 4 times, washing with ethanol for 1 time, and drying for 8 hours at 60 ℃ by adopting a hot air circulation drying oven to obtain the gray flaky silver powder, wherein the average particle size of the prepared flaky silver powder is 3.5 microns, the morphology and the particle size are uniform, and the particle-to-particle dispersibility is good.

In summary, according to the method for continuously producing the composite silver powder, the preparation of the silver powder with different particle sizes is realized by using the different microfluidic reactors 110, compared with the scheme that the size of fluid is regulated by adopting the microfluidic reactors 110, and finally, the silver powder with smaller particle sizes is converged outside the reactors at a certain included angle and the rapid mixing of the silver nitrate solution and the reducing solution is realized outside the reactors, the reaction is performed by using the reaction cavity 111 of the microfluidic reactors 110, the whole reaction process is realized in the reaction cavity 111, the direct implementation of the reduction reaction in the atmosphere is effectively avoided, the interference of oxygen on the reduction reaction is almost avoided, the prepared powder is mainly influenced by the reducing agent, the powder is stable and better in dispersibility, the silver powder with smaller particle sizes is favorable to be obtained, and even the silver powder with larger particle sizes is smaller than 2 microns, the problem of blocking of sediments in a microchannel is effectively avoided, and the continuous reduction preparation of the silver powder is ensured. In addition, in the application, one microfluidic reactor 110 prepares silver powder with a particle size, and the preparation of the silver powder with different particle sizes is realized through a plurality of different microfluidic reactors 110, so that the control of each microfluidic reactor 110 is simpler, and each microfluidic reactor 110 is also integrated with temperature and pH detection functions, so that the reaction process is easier to regulate and control. The nano silver prepared by the method has controllable morphology and particle size, stable product and high powder tap density, and can be finished in one step by utilizing multiple chambers or multiple channels to realize high flux. Has great advantages in the aspect of industrial continuous production.

The above description is only of the preferred embodiments of the present invention and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for continuously producing composite silver powder is characterized by comprising the steps of adopting a plurality of microfluidic reactors to prepare silver powder with different morphologies, wherein each microfluidic reactor is provided with a reaction cavity, a silver salt solution input pipe, a reducing solution input pipe and a product output pipe, the silver salt solution input pipe and the reducing solution input pipe are both communicated with the reaction cavity, the bottom of the reaction cavity is communicated with the product output pipe,

2. The method for continuously producing composite silver powder according to claim 1, wherein the output flow rate of the product output pipe is greater than the sum of the input flow rate of the silver salt solution input pipe and the input flow rate of the reducing solution input pipe; the input flow rate of the reducing solution input pipe is larger than that of the silver salt solution input pipe;

3. The method for continuously producing composite silver powder according to claim 1, wherein the temperature in each of said reaction chambers is 5 to 68 ℃ and the pH is 1.0 to 4.5;

4. The method for continuously producing composite silver powder according to claim 1, wherein the microfluidic reactor is made of PDMS or glass,

5. The method for continuously producing composite silver powder according to claim 1, wherein the bottoms of the microfluidic reactors are further provided with a collecting tray for collecting the product discharged from the product output pipe, and the collecting tray contains a plurality of polymer coating agents;

6. The method for continuously producing composite silver powder according to claim 5, wherein a stirring device for stirring the liquid in the collecting tray is provided in the collecting tray;

Preferably, the rotating speed of the stirring device is 250-3000r/min;

preferably, the stirring time of the stirring device is 1-90min;

preferably, the stirring device is a stirring blade or a stirring magnet;

7. The method for continuously producing composite silver powder according to claim 5, further comprising subjecting the product in the collecting tray to solid-liquid separation, and subjecting the separated product to washing, drying and baking in this order.

8. The method for continuously producing a composite silver powder according to any one of claims 1 to 7, wherein the silver salt solution is a silver nitrate solution having a mass fraction of 7.5 to 75%; the reducing solution is an aqueous solution of a reducing agent with the mass fraction of 5-45%, and the reducing agent comprises at least one of vitamin C, glucose, hydrazine hydrate and hydrogen peroxide;

9. The method for continuously producing composite silver powder according to any one of claims 1 to 7, wherein a polymer protectant solution is added to both the silver salt solution and the reducing solution, the addition amount of the polymer protectant solution in the silver salt solution is 1% to 15%, and the addition amount of the polymer protectant solution in the reducing solution is 1% to 15%;

preferably, the polymer protectant is polyvinylpyrrolidone.

10. A composite silver powder, characterized in that it is produced by the method for continuously producing a composite silver powder according to any one of claims 1 to 9.