Metal silicon is classified according to the content of three main impurities: iron, aluminum and calcium. 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 brands.
Metal silicon is mainly composed of silicon, so it has similar properties to silicon. Silicon can be divided into amorphous silicon and crystalline silicon. Crystalline silicon has the crystal structure and semiconductor properties of diamond, with melting point of 1410 ℃, boiling point of 2355 ℃, Mohs hardness of 7 and brittleness. Amorphous silicon is chemically active and can burn violently in oxygen. It reacts with halogen, nitrogen, carbon and other non metals at high temperature, and can also interact with magnesium, calcium, iron and other metals to form silicide. Amorphous silicon is almost insoluble in all inorganic and organic acids including hydrofluoric acid, but can be dissolved in the mixed acid 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. It is also insoluble in any kind of inorganic and organic acids, but soluble in the mixed acid of nitric acid and hydrofluoric acid and concentrated sodium hydroxide solution.
