Metallic silicon is usually classified according to the content of iron, aluminum and calcium in the metal silicon. According to the content of iron, aluminum and calcium in metallic silicon, metallic silicon can be divided into 553, 441, 411, 421, 3303, 3305, 2202, 2502, 1501, 1101 and other different brands.
In industry, metal silicon is usually made from carbon dioxide and reduced silica in an electric furnace. Chemical reaction equation: SiO2 + 2C Si + 2CO so that the purity of silicon produced 97 ~ 98%, called metallic silicon. Then melt it, recrystallize it, remove impurities with acid, and get 99.7~99.8% silicon metal.
Silicon is mainly composed of silicon, so it has similar properties with silicon. Silicon has two allotypes of amorphous silicon and crystalline silicon. Amorphous silicon is a gray black powder and is actually a microcrystalline body. Crystalline silicon has diamond crystal structure and semiconductor properties, melting point 1410 C, boiling point 2355 C, Mohr hardness 7, brittleness. Amorphous silicon is active in chemistry and can burn violently in oxygen. It reacts with halogen, nitrogen, carbon and other non-metals at high temperature, and also reacts with magnesium, calcium, iron and other metals to form silicides. Amorphous silicon is insoluble in almost all inorganic and organic acids, including hydrofluoric acid, but is 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 inert and does not combine with oxygen even at high temperatures. It is insoluble in any inorganic and organic acids, but is soluble in mixed acids of nitric acid and hydrofluoric acid, and in concentrated sodium hydroxide solutions.