Fumed silica

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Schematic of the production of fumed silica
Image Credit: Wikipedia


[Degussa] A lightweight, fluffy white powder that is a colloidal form of Silica. Fumed silica, also called aerosol silica, is made by the combustion of silicon tetrachloride in a hydrogen-oxygen furnace. The tiny, amorphous, spherical particles fuse into three-dimensional secondary particles of varying sizes. The resulting powder has an extremely low bulk density and high surface area. Untreated fumed silica is hydrophilic, but many commercial products have been treated to make them hydrophobic. Generally, silanes or siloxanes are used to replace hydroxyl groups on the surface and thus prevent the absorption of moisture. Fumed silica is approved by the U.S. FDA for use in food products.

Synonyms and Related Terms

aerosol silica; colloidal silica; pyrogenic silica; thermal silica;

Commercial products: Aerosil® [Evonik]; Cab-O-Sil [Cabot]; HDK [Wacker Chemie]; Zandosil [Dow Corning]; Reolosil [Tokuyama Corp.]; Konasil [OCI]; Orisil [Orisil]; XYSIL [Xunyuchem]


  • Matting agent
  • Thickener
  • Filler
  • Desiccant to kill insects


  • Inhalation may cause silicosis; used dust mask.
  • Integra Chem: SDS

Physical and Chemical Properties

  • CAS = 112945-52-5
  • Composition = SiO2
  • Density = 2.0 - 2.2 g/cm3
  • Melting point = 1700 C
  • Decomposition = >2000C
  • Moisture content = 0.5-2.5 % (Hydrophilic); 0.5% (hydrophobic)
  • Adsorbed moisture = 6%
  • Refractive index = 1.46
  • Particle size = 5-40 nm

Resources and Citations

  • Wikipedia: Fumed silica Accessed July 2023
  • George Wypych, 'FILLERS – ORIGIN, CHEMICAL COMPOSITION, PROPERTIES, AND MORPHOLOGY, in Handbook of Fillers (Fourth Edition), 2016Chapter Fumed Silica

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