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Study on preparation method of high purity nanometer silicon powder

Silicon is an important semiconductor material and an important industrial raw material for the development of information technology.Silicon is an almost inexhaustible source of renewable energy.The transformation of silicon material to nanometer size gives its unique size effect and physical and chemical properties.As a new functional powder material, nanometer silicon powder has been used in lithium battery, photocell, composite material, ceramic material, biological material, refractory material and other fields.For example, adding nanometer silicon powder to the anode material of lithium ion battery can greatly improve the electrochemical performance of lithium ion battery and alleviate the volumetric expansion effect of ordinary silicon powder due to its high theoretical specific capacity of 4200 mAh /g.At the same time, nano-silica powder has a very high specific surface area, the surface activity of particles increases dramatically, and the gravity between particles also increases, which leads to the easy agglomeration between powders, making it difficult to meet the large-scale enterprise production of nano-silica powder with high purity and high dispersion.
At present, there are three main preparation methods of nanometer silicon powder: mechanical ball grinding, chemical vapor deposition and plasma evaporation and condensation.

1. Mechanical ball grinding
Mechanical ball grinding is the grinding of large-sized silicon materials into nano-sized powder by mechanical grinding pressure and shear force generated by mechanical rotation and interaction between particles.
The grinding process of this method requires adding grinding aid, which is easy to introduce impurities. The product purity is low, and the particles are of irregular shape, the particle size distribution cannot be effectively controlled, the post-treatment is cumbersome, the production efficiency is low, and it is not suitable for large-scale industrial production.

2. Chemical vapor deposition
Chemical vapor deposition (CVD) is a technique of producing nanometer silicon powder with silane (SiH4) as reaction material.According to the different energy sources that induce SiH4 pyrolysis, they can be divided into plasma enhanced chemical vapor deposition (PECVD), laser-induced chemical vapor deposition (LICVD) and fluidized bed (FBR), among which PECVD and LICVD are the most important industrial production technologies for nanometer silicon powder production at present.

3. Plasma evaporation and condensation method
This method is a safe and efficient method for producing high purity, ultra-fine, spherical and high value added powders in recent 10 years.The reaction materials are gasified into gaseous atoms, molecules or partially ionized into ions by plasma heat source, and condensed into solid powder by rapid condensation technology.The local electron temperature (Te), ion temperature (Ti) and gas temperature (Tg) of the plasma are almost the same and can reach more than 10000 K, which is very suitable for the preparation and synthesis of various kinds of metal nano powders, as well as nano powders of carbide and nitride.The ultrafine powders prepared by this method are characterized by high purity and narrow particle size distribution. The particle size and yield of ultrafine powders can be controlled by changing parameters such as current, inflation pressure, hydrogen/argon ratio, etc., and have been successfully applied to the large-scale production of ultrafine powders such as Fe, Cu, Co, Ag, Zn, Sn and so on.