Fumed silica

Fumed silica (CAS 7631-86-9, EC 231-545-4, SiO2) is a synthetic amorphous silicon dioxide produced by flame hydrolysis of silicon tetrachloride. It is sold under trade names including Aerosil, Cab-O-Sil, and HDK, and carries no assigned E-code, distinguishing it from precipitated silica grades used in food applications.

In rubber and tire compounding, fumed silica reinforces polymer networks by forming covalent bonds with silane coupling agents, improving tensile strength and wet grip. In coatings and adhesives, it modifies flow behavior by forming hydrogen-bonded particle networks that resist sagging under gravity while breaking down under shear. Personal care formulators use it as a carrier and flow agent in powder systems.

Fumed silica is supplied in hydrophilic and hydrophobic surface-treated grades, with BET surface areas typically ranging from 90 to 380 m2/g. It is REACH-registered and available in multi-wall paper bags or bulk containers. Grades conforming to Ph.Eur. and FCC monographs are available for regulated applications.