Silica gel (Silica gel; Silica) alias: Silicic acid gel is a kind of highly active adsorption material, which is an amorphous substance, its chemical formula is mSiO2·nH2O; it does not react with any substance except strong alkali and hydrofluoric acid. It is insoluble in water and any solvent, non-toxic and tasteless, and has stable chemical properties. Various types of silica gel have different microporous structures due to different manufacturing methods. The chemical composition and physical structure of silica gel determine that it has many characteristics that other similar materials are difficult to replace: high adsorption performance, good thermal stability, stable chemical properties, and high mechanical strength. Silica gel is divided into: large-pore silica gel, coarse-pore silica gel, B-type silica gel, fine-pore silica gel, etc. according to its pore size.