Classification of metallic silicon

Usually classified according to the content of the three main impurities, iron, aluminum, and calcium, contained in the metal silicon component. According to the content of iron, aluminum, and calcium in metal silicon, it can be divided into different grades such as 553, 441, 411, 421, 3303, 3305, 2202, 2502, 1501, 1101, etc.
In industry, silicon metal is usually produced by reducing silicon dioxide by carbon in an electric furnace. The chemical reaction equation is SiO2+2C → Si+2CO. The purity of silicon obtained by this method is 97~98%, which is called metallic silicon. After melting and recrystallizing, impurities are removed with acid to obtain metallic silicon with a purity of 99.7-99.8%.
The main component of metallic silicon is silicon, therefore it has similar properties to silicon. Silicon has two Allotropy, amorphous silicon and crystalline silicon. Amorphous silicon is a gray black powder, which is actually a microcrystalline material. Crystalline silicon has the crystal structure and semiconductor properties of diamond, melting point 1410 ℃, boiling point 2355 ℃, Mohs scale hardness 7, and is brittle. Amorphous silicon has active chemical properties 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 Mineral acid 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. It does not combine with oxygen even at high temperature. It is also insoluble in any Mineral acid and organic acid, but soluble in mixed acid of nitric acid and hydrofluoric acid and concentrated sodium hydroxide solution.