The classification of metal silicon is usually classified according to the content of three kinds of main impurities, iron, aluminum and calcium contained in the metal silicon component.
Metal silicon can be divided into 553, 441, 411, 421, 3303, 3305, 2202, 2502, 1501, 1101, etc. according to the content of iron, aluminum and calcium in metal silicon. In industry, metal silicon is usually made from carbon-reduced silica in electric furnaces. Chemical reaction equation: SiO2 + 2c→si + 2CO The purity of the silicon is 97~98%, called metal silicon.
Then it melts and then recrystallization, removing impurities with acid, and getting the metal silicon with 99.7~99.8% purity. Metal silicon is mainly silicon, so it has similar properties to silicon. Silicon has amorphous silicon and crystalline silicon two kinds of allotrope. Amorphous silicon is a grayish-black powder and is actually a micro-crystal. Crystalline silicon has the crystal structure and semiconductor properties of diamond, melting point 1410 ℃, boiling point 2,355 ℃, MO hardness 7, brittle. Amorphous silicon is lively in nature and can burn violently in oxygen. It reacts with the nonmetal such as halogen, nitrogen and carbon at high temperature, also can work with the metal such as magnesium, calcium, iron, and produce silicide. Amorphous silicon is almost insoluble in all inorganic acids and organic acids, including hydrofluoric acid, but can dissolve in mixed acids of nitric acid and hydrofluoric acid. The concentrated sodium hydroxide solution dissolves amorphous silicon and emits hydrogen. Crystalline silicon is more inactive, even at high temperatures and does not combine with oxygen, it is not soluble in any kind of inorganic acids and organic acids, but soluble in nitric acid and hydrofluoric acids and concentrated sodium hydroxide solution.