What is the smelting process of metallic silicon?

Smelting process of silicon for chemical industry

1. The technological process of chemical silicon includes charge preparation, electric furnace smelting, silicon refining and casting, slag removal and crushing. Before batching, all raw materials should be treated as necessary. Crushing the silicon dioxide in a jaw crusher to a size not exceeding 100mm, sieving out fragments smaller than 5mm and washing with water. Because the fragments in the furnace melt in the upper part of the furnace, the permeability of the charge decreases and the production process is difficult. Petroleum coke has a high conductivity, so it should be crushed to a particle size not greater than 10mm, and the powder amount of petroleum coke should be controlled. Because it burns directly on the furnace mouth, it will cause insufficient reducing agent.

2. In the production of silicon for chemical industry, bituminous coal can completely replace charcoal, such as fine washed bituminous coal in Zhuzhou, Hunan Province, with fixed charcoal reaching 77. 19%, volatile 19.4%, ash 3.4 1%, Fe2O3 content 0.22%, Al2O3 content 0.99% and CaO content 0. Through production practice, it is feasible to smelt industrial silicon with this bituminous coal.

3. Wood blocks and chips used to produce chemical silicon are processed with woodworking tools and chips. The carbonaceous reductants in the furnace charge are mainly petroleum coke and bituminous coal, and the amount of wood blocks and sawdust depends on the furnace condition. Wood is not used in production, but the product quality is more stable. The charging ratio depends on the required product level. The ratio of petroleum coke to bituminous coal is determined according to the carbon required for each batch of ore silicon. The ratio of petroleum coke to bituminous coal has a great influence on the working resistance of charge.

4. After weighing the components of the furnace charge, mix the furnace charge evenly, and after tamping the furnace, concentrate the mixed furnace charge into the furnace. Maintain a certain level height and feed evenly.

5. Chemical silicon production is continuous. Conditions in the furnace are not eternal. Chemical silicon production is a process of converting electric energy into heat energy in an electric furnace, and then directly heating materials with heat energy to make them react chemically. Therefore, the electrical characteristics in the furnace are very important. In order to maintain the high-temperature furnace and improve the thermal efficiency and utilization rate of the electric furnace, metal silicon furnaces with capacities of 3200KVA and 6300KVA were adopted in this study. Melting is carried out by stewing for a certain period of time and feeding at regular intervals. Under normal circumstances, it is difficult for the baggage to sink automatically, and it is generally necessary to force it to sink. The furnace condition is easy to fluctuate and difficult to control. Therefore, we must make correct judgments and deal with them in time in production. Take out the furnace every 4 hours, refine and cast, crush and pick up slag and put it in storage.

I. Overview/Metal Silicon?

Metallic silicon, also known as crystalline silicon or industrial silicon, is mainly used as an additive for non-iron-based alloys, which is a trade name that appeared in the mid-1960s. Its appearance is related to the rise of semiconductor industry. At present, the international practice is to divide commercial silicon into metal silicon and semiconductor silicon. Metal silicon is a product made by melting timely and coke in an electric furnace. The content of silicon is about 98%, and the rest impurities are iron, aluminum and calcium. Silicon metal is very expensive. [2]? In industry, metallic silicon is usually made by reducing silicon dioxide with carbon in an electric furnace. ? Chemical reaction equation:? Silicon dioxide? +? 2C？ →? Is it? +? 2CO？ The purity of metallic silicon thus prepared is 97-98%. Then melting and recrystallizing, and removing impurities with acid to obtain metallic silicon with the purity of 99.7-99.8%. [3]

Second, properties/metallic silicon?

Silicon is one of the semi-metals, formerly known as "silicon". The melting point is 1420℃ and the density is 2.34g/cm3. Hard and brittle. Insoluble in acid at room temperature, soluble in alkali. The composition of metallic silicon is mainly silicon, so it has similar properties with silicon. The properties of metallic silicon are similar to those of germanium, lead and tin, and it has semiconductor properties. [3]? Silicon is very abundant in the earth's crust, second only to oxygen, accounting for more than a quarter of the total weight of the earth's crust, and exists in the form of silicon dioxide or silicate. The purest silicon mineral is timely or silica. There are two kinds of allotropes of silicon: one is dark brown amorphous powder, which is active and can burn in air; The other is a crystal with stable properties (crystalline silicon). Generally, silicon dioxide is used in glass and other building materials, and high-quality silicon dioxide is used in making alloys, metals and single crystals.

Third, classification/metallic silicon?

1, the classification of metallic silicon is usually based on the contents of iron, aluminum and calcium in the composition of metallic silicon. According to the contents of iron, aluminum and calcium in silicon metal, silicon metal can be divided into 553, 44 1, 41,42 1, 3303, 3305, 2202, 2502 and150.

2. In industry, metallic silicon is usually made by reducing silicon dioxide with carbon in an electric furnace. ? Chemical reaction equation:? Silicon dioxide? +? 2C？ →? Is it? +? 2CO？ The purity of silicon prepared in this way is 97~98%, which is called metallic silicon. Then melting and recrystallizing, and removing impurities with acid to obtain metallic silicon with the purity of 99.7-99.8%.

3. The composition of metallic silicon is mainly silicon, so it has similar properties with silicon. There are two allotropes of silicon: amorphous silicon and crystalline silicon. Amorphous silicon is a gray-black powder, which is actually a kind of microcrystal. Does crystalline silicon have the crystal structure and semiconductor characteristics of diamond? ,? Melting point? 14 10℃? ,? Boiling point? 2355℃? , density 2.32 ~ 2.34 g/cm3, Mohs hardness? 7. Brittle? . Amorphous silicon is chemically active and will burn violently in oxygen. It can react with nonmetals such as halogen, nitrogen and carbon at high temperature, and can also react with metals such as magnesium, calcium and iron to form silicide. Amorphous silicon is almost insoluble in all inorganic acids and organic acids including hydrofluoric acid, but soluble in mixed acids of nitric acid and hydrofluoric acid. Concentrated sodium hydroxide solution can dissolve amorphous silicon and release hydrogen. Crystalline silicon is relatively inactive and does not combine with oxygen even at high temperature. Insoluble in any inorganic acid and organic acid, soluble in mixed acid of nitric acid and hydrofluoric acid and concentrated sodium hydroxide solution.

Four. Additional products/metallic silicon

Include silicon micropowder, edge skin silicon, black skin silicon, metal silicon slag, etc. Among them, silica fume, also known as silica fume, silica fume or silica fume, is widely used in refractory and concrete industries.

Verb (abbreviation for verb) uses/metal silicon?

Metal silicon is used to produce silicon, prepare high-purity semiconductor materials and prepare alloys for special purposes.

(1) produces silicone rubber, silicone oil and other silicones.

Silicone rubber has good elasticity and high temperature resistance, and is used to make medical supplies and high temperature resistant gaskets.

Silicone resin is used to produce insulating paint, high temperature coating and so on.

Silicone oil is an oil whose viscosity is little affected by temperature. It can be used to produce advanced lubricants, polishing agents, fluid springs, dielectric liquids, etc. It can also be processed into colorless and transparent liquid and sprayed on the surface of buildings as a high-grade waterproof agent.

(2) manufacturing high-purity semiconductors.

Modern large-scale integrated circuits are almost all made of high-purity metallic silicon, which is also the main raw material for producing optical fibers. It can be said that metallic silicon has become the basic pillar industry in the information age.

(3) alloying.

Silicon-aluminum alloy is the most used silicon alloy. Si-Al alloy is a strong composite deoxidizer. Replacing pure aluminum in steelmaking process can improve the utilization rate of deoxidizer, purify molten steel and improve the quality of steel. Silicon-aluminum alloy has low density, low thermal expansion coefficient and good castability and wear resistance. The alloy castings cast with it have high impact resistance and good high-pressure compactness, which can greatly improve the service life. It is often used to produce space vehicles and automobile parts.

Silicon-copper alloy has good weldability and is not easy to generate sparks when it is impacted. It has explosion-proof function and can be used to make storage tanks.

Adding silicon into steel to make silicon steel sheet can greatly improve the permeability of steel, reduce hysteresis and eddy current loss, and can be used to make iron cores of transformers and motors, thus improving the performance of transformers and motors.

With the development of science and technology, the application field of metallic silicon will be further expanded.

reference data

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