Silica, also known as hydrated silicon dioxide or light silicon dioxide, has its chemical composition and structural characteristics described in detail as follows:

1. Chemical composition

Silica is a porous substance, and its composition can be expressed as SiO2·nH2O, where SiO2 is silicon dioxide and nH2O exists in the form of surface hydroxyl groups. Silica is a general term for white powdered X-ray amorphous silicic acid and silicate products, mainly referring to precipitated silica, fumed silica and ultrafine silica gel, and also including powdered synthetic aluminum silicate and calcium silicate.

2. Structural characteristics

Crystal structure: Crystalline silica is a crystal in which silicon atoms and oxygen atoms form a three-dimensional network with covalent bonds. There is no single silica molecule in the crystal. The silicon atom of silica is at the center of a regular tetrahedron, and is bonded to four oxygen atoms at the apex of the regular tetrahedron with covalent single bonds to form a regular tetrahedron. The Si-O bond is repeated in space to form a "macromolecule". In the crystal, there are 6 silicon atoms and 6 oxygen atoms on the small ring, a total of 12 atoms, and the ratio of silicon and oxygen atoms is 1:2, so the composition formula is SiO2, and there is no single molecule in the crystal.

Physical form: Silica appears as white powder or granules or irregular blocks. The appearance of precipitation silica includes microbeads, powder, blocks and ultrafine, and the appearance of gas phase silica is ultrafine powder.

Chemical properties: Silica is soluble in caustic alkali and hydrofluoric acid, insoluble in water, solvents and general acids (except hydrofluoric acid). Silica can react with alkaline oxides, alkalis, soda ash, etc. at high temperature to form silicates. Silica does not react with general acids and has good acid resistance, but can be corroded by hydrofluoric acid.

Specific surface area: Silica has a large specific surface area, with different ranges for different uses, generally 145~165m^2/g (HT2), 165~185m^2/g (HT1), 200~300m^2/g (HT3).

In addition, silica also has good high temperature resistance, non-flammability, tasteless and odorless, and excellent electrical insulation.