Industrial silicon four kinds of smelting methods

Silicon accounts for about 28% of the earth's crust, and is present in large quantities after oxygen. Natural minerals are mainly present in the form of oxides ( silica , quartz ) or silicates. Generally, industrial silicon is obtained by reducing oxides with carbon. Further refining, melting, a semi-conductive silicon can be obtained.

1. Industrial silicon production method

The most common method is to combine silica (more than 98% SiO2) with a high-purity coke stick and heat it in a lidless Epp furnace with three carbon electrodes. The above reaction occurs above 1720K: SiO2+2C=Si+2CO (6-28) The purity of silicon is 97-99%. The main impurities are iron , calcium, aluminum , magnesium, etc., almost all in the form of silicic acid pots or silicides. When preparing aluminum, keyhole, nickel alloy, silicon can be directly used for this purity.

2. Refinement of silicon

(1) Acid treatment. This is the easiest way. The crushed industrial silicon is selected by the most suitable pot acid, nitric acid, sulfuric acid, aqua regia, hydrogen acid and the like. The purified purity can reach 99.7-99.9%.

(2) Nitrogen reduction method of SiCl4. Silicon reacts at 623-773K to form SiC14 with a boiling point of 330K, which can be condensed. When adding calcium powder to boil, arsenic , vanadium, etc. can be removed. After rectification and pyrolysis, high purity SiCl4, SiCl4+2H2=Si+4HCl4 (6-29) is obtained. The hydrogen reduction reaction rate is still slow at 1270-42 OK. . The molar ratio of H2 to SiCl4 is stoichiometric, for example, the recovery of silicon is very low. Therefore, to add an excess of hydrogen, the molar ratio should be 60-100. The most common purification method is to use trichlorosilane (SiHCl3) as the initial. raw material.

(3) Hydrogen reduction of SiHCl3. When silicon is reacted with 570-67OK and dry HCI gas, SIHCI3 is obtained. The boiling point of SIHCI3 is 304.9K, which is more volatile than SiCI4. The reaction is as follows: Si + 3HCL = H2 + SiFICI3 (6-30) is said to add about 5% copper-containing silicon alloy, the 513K and the following reaction gases IICI better. After rectification of SiHCI2, it is reduced with hydrogen at 1270-1370K, and the mixed Lier ratio of appropriate H2/SiHCI3 is 60-100. The higher the value, the higher the recovery rate of silicon. The resulting silicon precipitates on the crucible or heated silicon rod in the quartz reactor. Pyrolysis of SiH4 LiAIH4 and SiCI4. In ether, the reaction is carried out at a low temperature of 195K or less, and the generated SiH4 (silane) is discharged through a vacuum system, passed through a stage trap, and finally trapped in a 77K trap. LiAIH4 + SiC14 = SiH4 + AMC13 + LiCI (6-31) In addition, there is also a method of reacting between Ca(ALH4)2 and SiCI4, SiHCI3 and 2C2H5OH, Ag2Si and HCl. SiH4 has a boiling point of 162K, is toxic, and is easily ignited in the air, making it difficult to handle. Therefore, it is not as popular as the hydrogen reduction method of SiHCI3. SiH4 is pyrolyzed above 770K, and dense silicon is obtained when silicon is deposited on a heated silicon rod.

3. Method for preparing silica melting and semiconductor silicon

The refined powdered silicon is melted in a transparent quartz crucible at 10 -3 Pa or in argon or nitrogen. For semiconductor use, it requires a higher purity single product silicon. For rod-shaped multi-product silicon germanium, the suspended area is used for refining, and the molten silicon adheres to the seed crystal of silicon. The rotary drawing method of drawing a single crystal while rotating - the Czochralski method is also commonly used.

4. Ferrosilicon

97% or more of silica containing silica is mixed with secondary scales and various carbonaceous reducing agent ingredients, and is reduced and smelted in electric protection to obtain various kinds of ferrosilicon containing 76%, 50% or 45% of silicon. As described in the magnesium smelting section, as a reducing agent for dolomite, it is necessary to use silicon iron containing 75% or more of silicon. In addition, ferrosilicon is also widely used in the de-weighting of steel and the inoculation of cast iron.

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