Spherical silicon powder is a critical material in various industries, prized for its unique properties and applications. Its production involves multiple techniques categorized into physical methods and chemical methods. It depends on whether a chemical transformation occurs during the process.
What Are the Methods for Producing Spherical Silicon Powder?
1. Physical Methods:
These methods do not involve chemical reactions. They include techniques such as: mechanical ball milling, spraying, flame spheroidization, plasma treatment, high-temperature calcination spheroidization.
2. Chemical Methods:
These involve chemical transformations and include: gas phase method, precipitation method, hydrothermal synthesis, sol-gel process, microemulsion method.
This guide explores 14 preparation methods that ensure precision in achieving the desired spherical shape.
Spherical silicon micropowder production process
01 Mechanical grinding method
Mechanical grinding uses professional crushing equipment and auxiliary screening equipment to produce ultrafine powders. According to the state of the material, there’re dry grinding and wet grinding. Wet grinding uses water as the carrier medium, and the particles are ground by stirring and grinding. This can produce ultrafine products with good dispersion and uniform particle size.
02 Spray method
Spray drying is a method of obtaining samples by quickly drying liquid raw materials through a spray dryer. The liquid raw materials pass through an atomizer to form extremely fine droplets. The droplets come into contact with hot air and the internal moisture migrates outward. The raw material particles agglomerate. After drying, people can obatin the desired product.
03 Flame spheroidization method
Under 1600-2000℃, the edges on the surface of the powder will gradually melt. A sphere is formed under the action of surface tension. Ordinary quartz powder is used as raw material, spherical silicon micropowder is prepared by oxygen-acetylene flame method. This can ensure its surface is smooth and the spheroidization rate reaches 95%.
04 Flame melting method
Using angular silicon micropowder as raw material, we crush, screen, purify, and perform other pre-treatments. An air flow crusher crushes the angular silicon micropowder. After multi-stage pretreatment, we screen it to a suitable particle size. We use acetylene, natural gas, and other gases as the heat source for melting the powder, and the flame remains clean and pollution-free. A high-temperature flame melts the angular silicon micropowder of suitable particle size instantly, and we quickly cool it to spheroidize. We obtain high-purity and uniform particle size spherical silicon micropowder.
05 Plasma method
The plasma method uses the high temperature generated by the arc plasma. It melts the silicon dioxide powder or quartz powder into droplets. They are spheroidized under the action of surface tension and cooled to form spherical silicon dioxide particles.
06 High temperature calcination spheroidization method
The high temperature calcination spheroidization method refers to aging the rough selected natural quartz ore powder under alkaline conditions and then filtering. Dehydrating and drying the filter material, adding a binder to obtain a block sample, and calcining it in a high temperature furnace, cooling and then dispersing it, through grinding spheroidization, magnetic separation and air separation classification. Finally high-purity ultrafine spherical silicon powders are made. The product obtained by this method has a high spheroidization rate, good whiteness, high purity, good fluidity and dispersibility. However, it’s still in the laboratory stage.
07 Direct Combustion Method
Since flame molten spherical silicon is a natural mineral powder melt spheroidization, there are certain limitations in terms of purity and particle size distribution. A few leading foreign companies use the direct combustion method (VMC) preparation method. It’s to prepare silicon dioxide microspheres with high purity, small particle size and relatively controllable particle size distribution through the direct reaction of metal silicon powder with oxygen.
08 High-temperature melt spraying method
The high-temperature melt spraying method is to melt high-purity quartz into liquid at 2100-2500 ℃, and obtain spherical silicon micropowder after spraying and cooling. The product surface is smooth, and the spheroidization rate and amorphous rate can reach 100%. Some manufactures in the United States and Japan use this method to produce spherical silicon micropowder. But it is strictly confidential to the outside. The high-temperature melt spraying method is easy to ensure the spheroidization rate and amorphous rate, but the difficulty of tgdrgddddddddhis technology is the atomization system of high-temperature materials, viscous quartz molten liquid, atomization particle size adjustment, and solving problems such as pollution prevention and further purification.
09 Self-propagating low-temperature combustion method
The process flow of the self-propagating low-temperature combustion method includes the preparation of sodium silicate, the preparation of silicate sol, the preparation of mixed combustion liquid, combustion reaction, annealing and decarbonization, washing treatment and other steps. The advantage of this method is that it uses natural crystalline silicon micropowder or molten silicon micropowder as raw materials. This is easy to obtain. The process is simple, no special equipment, the operation is easy to control, and the production cost is low. The materials used in the production process only contain sodium ions and nitrate ions that are very soluble in water, and no other impurity ions are introduced, which is conducive to the preparation of high-purity silicon micropowder. At present, this method is only in the laboratory stage and cannot be well mass-produced.
10 Gas phase method
The production process uses materials that only contain sodium ions and nitrate ions, which are highly soluble in water, and we do not introduce any other impurity ions. This approach is conducive to preparing high-purity silicon micropowder. Currently, this method is only at the laboratory stage and we cannot yet mass-produce it effectively.
11 Precipitation method
We use water glass, acidifier, and other raw materials, adding an appropriate amount of surfactant. We pay close attention to temperature control throughout the entire preparation process. If the pH value exceeds 8, we add a stabilizer. After washing, drying, and calcining, we form spherical silicon micropowder. The spherical silicon micropowder prepared by this method has a very uniform particle size, low cost, simple process flow, and is easy to control. We can use it in industrial production, but the defect is that it may agglomerate.
12 Hydrothermal synthesis method
We widely use the hydrothermal synthesis method to prepare nanoparticles in the liquid phase. Generally, we combine inorganic and organic compounds with water under high temperature and high pressure conditions of 150℃ to 350℃. We allow ions, molecules, ion clusters, etc., to enter the growth zone with seed crystals through strong convection, and finally, we obtain a supersaturated solution and crystals.Filtering, washing and drying inorganic substances can form ultrafine and high-purity microparticles. The use of hydrothermal synthesis method to prepare spherical silicon micropowder eliminates the process of conversion to oxides required by general liquid phase synthesis methods, which reduces the probability of hard agglomeration.
13 Sol-gel method
The sol-gel method is to uniformly mix the raw materials with the liquid phase, hydrolyze them under certain conditions, form a sol through chemical condensation, and form a silica gel with a three-dimensional network structure after a period of time. After filtering, washing, drying and sintering, we can obtainnano-silicon dioxide or nano-quartz particles.
14 Microemulsion method
Microemulsion is a method in which two incompatible phases form a uniform emulsion under the action of a surfactant. This method uses the tiny space between the two phases to form nuclei under the guidance of a silicon source, and obtains spherical silica or quartz particles after heat treatment. Due to the limited space for nucleation and growth, the silica particles generated by this method are small in size and not easy to agglomerate.