1.What is a silicon product?
The silicon content is between 14% and 99%, and the rest is impurities or another (individually two) main elements. Alloys obtained through smelting are commonly known as silicon products. It usually includes industrial silicon, ferrosilicon, silicon barium, silicon carbide, silicon calcium, etc., and the most commonly used ones are industrial silicon and ferrosilicon.
Smelting any silicon product must involve ore (including SiO2) as a raw material. Mining will destroy forests and vegetation, and at the same time, the smelting process will also generate a lot of pollution (such as CO, excessive dust, etc.), which is resource consumption, high pollution, Metallurgical industry with low technical content. Therefore, developed countries generally do not produce and mainly rely on imports. Due to the wide use of silicon products (automobile industry, information industry) and its largest consumer is developed countries, most of the silicon products produced in developing countries are used for export in exchange for foreign exchange except for their own consumption.
Silicon smelting products must meet the following two basic conditions: ① places with strong environmental purification capabilities (places that also allow mild pollution sources); ② abundant and low-cost power sources, because silicon smelting is a high-energy-consuming industry. Taking silicon as an example, the average power consumption per ton of finished products is 12,000 kWh, and usually only cheap hydropower (ranging from 0.2-0.5 yuan per kWh) can be used as production energy. Due to heavy pollution and high energy consumption, silicon smelting enterprises can only be distributed in remote areas with abundant hydropower (individual thermal power is abundant), and due to power shortage, production is often reduced or stopped due to power cuts in dry seasons.
2. Situation of silicon smelting industry in China.
The Sanming area of Fujian is the earliest place in China to produce industrial silicon and other silicon products. Due to the lack of hydropower and over-exploitation of resources in recent years. At present, the scale of silicon smelting in Fujian is mostly small. In the past 5 or 6 years, Guizhou and Yunnan have become the largest silicon production bases in China by taking advantage of their rich hydropower resources. In particular, Guizhou’s output accounts for more than 50% of the country’s production of silicon products. There are also Sichuan, Hunan, Jiangxi (some), Xining, Inner Mongolia, Northeast and other places. Except for a few small factories, the current ferrosilicon furnaces are generally above 6300KVA. With the country’s rectification of the ferroalloy industry and environmental protection requirements, small-capacity electric furnaces and furnaces that fail to meet environmental protection requirements will inevitably be eliminated.
3. Application of silicon-based products.
Industrial silicon, commonly known as metallic silicon or crystalline silicon, strictly speaking, industrial silicon does not belong to the ferroalloy industry. Traditionally, industrial silicon is classified into the ferroalloy industry because the smelting of industrial silicon is carried out by submerged arc furnaces. Industrial silicon refers to pure silicon products with a silicon content greater than or equal to 98.5%, which is divided into various sub-categories based on the content of three impurities: iron, aluminum, and calcium (arranged in order), such as 553, 441, 331, 2202, etc. Among them, 553 means that the variety of industrial silicon contains less than or equal to 0.5% iron, less than or equal to 0.5% aluminum, and less than or equal to 0.3% calcium; 331 industrial silicon means less than or equal to 0.3% iron, less than or equal to 0.3% aluminum, and less than or equal to calcium 0.1%, and so on. Due to customary reasons, 2202 is also abbreviated as 220, which means calcium is less than or equal to 0.02%. Industrial silicon starting with 2 is also called chemical silicon.
The main application of industrial silicon: Industrial silicon is used as an additive to non-ferrous alloys. Industrial silicon is also used as an alloying agent for silicon steel with strict requirements, a deoxidizer for smelting special steel and non-ferrous alloys. After a series of processes, industrial silicon can be drawn into single crystal silicon, which is used in the electronics industry and used in the chemical industry to produce organic silicon, etc. Therefore, it is called magic metal and has a wide range of uses.
Adding industrial silicon to aluminum, iron and other metals can improve or enhance the excellent properties of metals. Aluminum used in automobiles (including motorcycles) has a considerable demand for industrial silicon, so the development of the automobile industry in a region or country has a direct impact on the rise and fall of the industrial silicon market.
Industrial silicon is further purified to more than 99.999% (more than 4 nines, the more nines, the more valuable), made into polysilicon (cylindrical), and then mechanically cut into silicon single wafers, which are widely used in the electronic information industry. Such as various types of IC cards, VCD films, DVD films and so on. At present, my country’s purification technology is not very mature, and basically relies on imports from Japan, that is, Japan imports industrial silicon raw materials from my country at a price of about 7,300 to 7,600 yuan per ton, and further refines them and then exports them to my country at a price of about 300,000 yuan per ton. Related industries (such as monocrystalline silicon factories, etc.). In terms of cutting monocrystalline silicon wafers, there is still a certain technical gap between my country and developed countries, especially in the post-finishing of silicon wafers and surface “coating”.
Ferrosilicon is made from coke, steel shavings, quartz (or silica) and smelted in a submerged arc furnace. Silicon and oxygen are easily combined to form silicon dioxide. Therefore, ferrosilicon is often used as a deoxidizer in steelmaking. At the same time, due to the large amount of heat released when SiO2 is formed, it is also beneficial to increase the temperature of molten steel during deoxidation. Ferrosilicon is added as an alloying element. Widely used in low-alloy structural steel, bonded steel, spring steel, bearing steel, heat-resistant steel and electrical silicon steel. Ferrosilicon is often used as a reducing agent in ferroalloy production and chemical industry. The silicon content reaches 95%-99%. Pure silicon is often used to manufacture single crystal silicon or to prepare non-ferrous metal alloys.
Application: Ferrosilicon is widely used in steel industry, foundry industry and other industrial production.
Ferrosilicon is an essential deoxidizer in the steelmaking industry. In steelmaking, ferrosilicon is used for precipitation deoxidation and diffusion deoxidation. Brick iron is also used as an alloying agent in steelmaking. Adding a certain amount of silicon to steel can significantly increase the strength, hardness and elasticity of steel, increase the magnetic permeability of steel, and reduce the hysteresis loss of transformer steel. General steel contains 0.15%-0.35% silicon, structural steel contains 0.40%-1.75% silicon, tool steel contains silicon 0.30%-1.80%, spring steel contains silicon 0.40%-2.80%, and stainless acid-resistant steel contains Silicon is 3.40% to 4.00%, heat-resistant steel contains 1.00% to 3.00% silicon, and silicon steel contains 2% to 3% silicon or higher. In the steelmaking industry, about 3-5kg of 75% ferrosilicon is consumed for each ton of steel produced.
High-silicon ferrosilicon or silicon alloys are used as reducing agents in the production of low-carbon ferroalloys in the ferroalloy industry. Adding ferrosilicon to cast iron can be used as an inoculant for ductile iron, and can prevent the formation of carbides, promote the precipitation and spheroidization of graphite, and improve the performance of cast iron.
In addition, ferrosilicon powder can be used as a suspension phase in the beneficiation industry, and as a coating for welding rods in the electrode manufacturing industry; high-silicon ferrosilicon can be used to prepare semiconductor pure silicon in the electrical industry, and can be used to manufacture silicone in the chemical industry.