Silicon metal, also known as crystalline silicon or industrial silicon, is mainly used as an additive for non-iron-based alloys. Silicon is a non-metallic element, gray in color, metallic in color, hard and brittle. The content of silicon accounts for about 26% of the mass of the crust; the relative atomic mass is 28.8, the density is 2.33g/cm3, the melting point is 1410°C, the boiling point is 2355°C, and the resistivity is 2140Ω·m.
According to the content of iron, aluminum, and calcium in silicon metal, silicon metal can be divided into different grades such as 553, 441, 411, 421,3303, 3305,2202, 2502, 1501, and 1101.
Additional products of silicon metal include silicon powder, edge silicon, black silicon, silicon metal slag, etc. Among them, silica powder, also known as silica fume, micro silica fume, or silica fume, is widely used in the refractory and concrete industries.
Silicon metal is usually produced by reducing silica with carbon in an electric furnace. Chemical reaction equation: SiO2 + 2C → Si + 2CO The purity of the silicon produced in this way is 97~98%, which is called silicon metal. It is then melted and recrystallized, and impurities are removed with acid to obtain silicon metal with a purity of 99.7~99.8%. The main component of silicon metal is silicon, so it has similar properties to silicon. Silicon has two allotropes: amorphous silicon and crystalline silicon. Amorphous silicon is a gray-black powder, which is a microcrystal. Crystalline silicon has the crystal structure and semiconductor properties of diamond, with a melting point of 1410°C, a boiling point of 2355°C, Mohs hardness of 7, and brittleness. Amorphous silicon is chemically active and can burn violently in oxygen. It reacts with non-metals such as halogen, nitrogen, and carbon at high temperatures, and can also react with metals such as magnesium, calcium, and iron to form silicides. Amorphous silicon is almost insoluble in all inorganic and organic acids, including hydrofluoric acid, but is soluble in a mixed acid of nitric acid and hydrofluoric acid. Concentrated sodium hydroxide solution can dissolve amorphous silicon and release hydrogen gas. Crystalline silicon is relatively inactive and does not combine with oxygen even at high temperatures. It is not soluble in any inorganic acid or organic acid but is soluble in mixed acids of nitric acid hydrofluoric acid and concentrated sodium hydroxide solution.
Silicon metal is industrially purified elemental silicon, which is mainly used to produce organic silicon, prepare high-purity semiconductor materials, and prepare alloys for special purposes. In the refractory industry, it is mainly used as an antioxidant. The main industrial applications of silicon metal are as follows:
(1)Production of silicones such as silicone rubber, silicone resin, and silicone oil
Silicone rubber has good elasticity and high-temperature resistance and is used to make medical supplies, high-temperature-resistant gaskets, etc.
Silicone resin is used to produce insulating paint, high-temperature coatings, etc.
Silicone oil is an oily substance whose viscosity is very little affected by temperature. It is used to produce high-grade lubricants, polishes, fluid springs, dielectric liquids, etc. It can also be processed into a colorless and transparent liquid and sprayed as a high-grade waterproofing agent. on building surfaces.
(2) Manufacturing high-purity semiconductors
Modern large-scale integrated circuits are almost all made of high-purity silicon metal, and high-purity silicon metal is also the main raw material for the production of optical fibers. It can be said that silicon metal has become a basic pillar of industry in the information age.
Silicon-aluminum alloy is the most commonly used silicon alloy. Silicon-aluminum alloy is a strong composite deoxidizer. Replacing pure aluminum in the steelmaking process can improve the utilization rate of the deoxidizer, purify molten steel, and improve steel quality. Silicon-aluminum alloy density Small, low thermal expansion coefficient, good casting performance, and anti-wear properties. Alloy castings cast with it have high impact resistance and good high-pressure densification, which can greatly increase the service life. It is commonly used in the production of aerospace vehicles and automobile parts.
Silicon-copper alloy has good welding performance and is not prone to sparks when impacted. It has an explosion-proof function and can be used to make storage tanks.
Adding silicon to steel to make silicon steel sheets can greatly improve the magnetic permeability of steel, reduce hysteresis and eddy current losses, and can be used to make iron cores for transformers and motors to improve the performance of transformers and motors.
The main producing areas of silicon metal are: Yunnan, Sichuan, Guizhou, and Guangxi in the southwest; Hunan and Hubei in central China; Fujian in east China; and the northeastern region is mainly Heihe and Linjiang areas in Heilongjiang, Jilin and Liaoning, and Inner Mongolia.