The classification of silicon metal is usually based on the content of iron, aluminum and calcium, the three main impurities contained in the composition of silicon metal.According to the content of iron, aluminum and calcium in metal silicon, metal silicon can be divided into 553, 441, 411, 421, 3303, 3305, 2202, 2502, 1501, 1101 and other different grades.
Industrially, silicon metal is usually made by reducing silicon dioxide from carbon in an electric furnace.Chemical reaction equation: SiO2 + 2C Si + 2CO so made of silicon purity for 97~98%, called silicon metal.After melting it again recrystallize, remove impurity with acid, get purity of 99.7~99.8% silicon metal.
The silicon metal is mainly composed of silicon, so it has similar properties to silicon.Silicon has two allotropes: amorphous silicon and crystalline silicon.Amorphous silicon is a gray-black powder that is actually a microcrystal.Crystal silicon has the crystal structure and semiconductor properties of diamond, melting point 1410℃, boiling point 2355℃, Mohs hardness 7, brittle.Amorphous silicides are active and can burn violently in oxygen.It reacts with non-metals such as halogens, nitrogen and carbon at high temperatures, and can also react with metals such as magnesium, calcium and iron to produce silicides.Amorphous silicon is almost insoluble in all inorganic and organic acids, including hydrofluoric acid, but soluble in the mixture of nitric acid and hydrofluoric acid.The concentrated sodium hydroxide solution dissolves amorphous silicon and gives off hydrogen gas.Crystal silicon is less reactive and does not combine with oxygen even at high temperatures. It is also insoluble in either inorganic or organic acids, but soluble in a mixture of nitric and hydrofluoric acids as well as in concentrated sodium hydroxide solutions.
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