Conductive, catalytic, antimicrobial, optical important raw materials “ultrafine silver powder” preparation method

Ultrafine silver powder has excellent electrical and thermal conductivity, strong antioxidant properties, good solderability and low use price, is widely used in conductive paste, catalytic materials, environmental protection materials, antimicrobial materials, optical materials and other fields. Among them, conductive paste is the field with the largest amount of ultrafine silver powder, which is used to make conductive circuits, electrodes and other electrical connections, and is mainly used in thick-film integrated circuits, resistors, resistor networks, capacitors, MLCC, conductive inks, solar cell electrodes, LEDs, printed and high-resolution conductors, flexible circuits, conductive adhesives, sensitive components and other electronic components. With the arrival of the 5G era, the Internet of Everything opens up a new era of flexible screens, 5G ceramic filters and other popular emerging product development is not without the support of ultra-fine silver powder as a raw material. In this article, we will take a look at how the ultra-fine silver powder is made.

Powder processing technology

There are many ways to prepare ultrafine silver powder, including DC arc plasma method spray thermal decomposition, thermal decomposition, electrolysis, ultrasonic chemical method, precipitation conversion hair, microemulsion method, mechanical ball milling method and liquid phase chemical reduction method.

Powder processing technology

1, mechanical ball milling method
Mechanical ball milling method for the preparation of silver powder is usually selected spherical or spherical silver powder as a silver precursor, the use of ball mill mechanical vibration and rotation, through the ball milling ball on the silver precursor to the silver precursor for the strong impact and grinding so that the organization of the silver precursor to change the silver precursor structure, usually used in the preparation of flake silver powder, has a low cost of production, process is simple, and suitable for large-scale production, but the preparation of the silver powder particle size distribution is wider, it is difficult to ensure the uniformity of silver powder properties. However, the particle size distribution of the prepared silver powder is wide, which is difficult to ensure the homogeneity of the silver powder performance, and it may be contaminated by the grinding medium and the ball mill lining.

Gan Weiping of Central South University used spherical silver powder as precursor, ethanol as ball milling medium, with different sizes of zirconium oxide ball for the ball mill ball prepared a vibration density of up to 3.5g/cm3 of silver flake, and can be used for crystalline silicon solar cells on the back side of the preparation of silver paste.

2、Evaporation condensation method
Evaporation condensation method is in N2, He and other inert gases under the protection of plasma, laser radiation, electron beam irradiation and other ways to evaporate the silver raw materials, the formation of plasma and convection with inert gases, the sudden cold condensation for ultra-fine silver powder. Evaporation condensation method is mainly used for the preparation of nanoscale ultra-fine silver powder, the advantages of high purity, uniform particle size, good crystallinity, while the disadvantage is that the equipment requirements are high, difficult to industrialize production.

3, laser ablation
Laser ablation is the use of pulsed laser ablation of silver target to form ultra-high pressure, high temperature plasma, rapid cooling in the liquid phase medium to get nanoscale ultra-fine silver powder. Laser ablation method has the advantages of a simple process, high purity silver powder, good stability, the disadvantage is the higher cost.

4, spray thermal decomposition method
Spray pyrolysis (SP) is also known as solvent evaporation pyrolysis method, this method is the precursor solution of silver through the atomizer atomization, through the gas carrier will be brought into the high-temperature reaction equipment, rapid completion of the solvent evaporation, solute decomposition, melting, cooling and other steps, and ultimately get silver powder. This method has the advantages of simple process, high production efficiency and environmental friendly.

Yi Yu et al. studied the process of preparing ultrafine silver powder with AgNO3 as the silver raw material and citric acid as the additive in air atmosphere, and found that when the reaction temperature was 700°C, the concentration of AgNO3 solution was 2.0 mol-L-1, the addition amount of citric acid was 2.5% (molar ratio), the flow rate of compressed air was 1.0 m3-h-1, and the pH of the system was 6.0, the ultrafine silver powder was obtained by the method of thermal decomposition through spraying. Spherical ultrafine silver powder with single phase, smooth surface, good dispersion and average particle size of 3.16 μm was prepared by spray thermal decomposition method.

5、Thermal decomposition method
Thermal decomposition method is one of the common methods of metal smelting, thermal decomposition method for the preparation of ultrafine silver powder is the precursor of silver in water or organic system heating to make its own redox reaction to get the silver powder method.

Zhengzhou Institute of Light Industry, Wei Jianying, Han Zhouxiang, etc. Ag2C2O4 as a precursor, triethanolamine as a coordinating agent, Tween-80 as a dispersant at 85 ℃ under the conditions of thermal decomposition method to prepare a particle size distribution in the range of 4 ~ 25 nm, the average size of 10 nm face-centered cubic nano-silver powder.

Powder processing technology

6、Electrolysis
Electrolysis method for the preparation of ultra-fine silver powder is in the electrolytic solution containing Ag + electrolytic reaction, so that Ag + get electrons, in the cathode is reduced to get a method of silver powder. Electrolytic preparation of ultrafine silver powder equipment is simple, high product purity, the raw material requirements are not high, can be used in crude silver.

EZhTuleshova and ABBaeshov of Yasaveh Khatu International University prepared silver powder in Ag2SO46g/L, H2SO41g/L with Ti4+ and Ti3+