Fumed silica

Silicon dioxide with branched chains on micro scale

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Not to be confused with silica fume

"Aerosil" redirects here. Not to be confused with aerosol

Fumed silica (CAS number -86-9, also -52-5), also known as pyrogenic silica because it is produced in a flame, consists of microscopic droplets of amorphous silica fused into branched, chainlike, three-dimensional secondary particles which then agglomerate into tertiary particles. The resulting powder has an extremely low bulk density and high surface area. Its three-dimensional structure results in viscosity-increasing, thixotropic behavior when used as a thickener or reinforcing filler.[1]

Properties

Fumed silica has a very strong thickening effect. Primary particle size is 5&#;50 nm.[2] The particles are non-porous and have a surface area of 50&#;600 m2/g. The density is 160&#;190 kg/m3.

Production

Fumed silica is made from flame pyrolysis of silicon tetrachloride or from quartz sand vaporized in a  °C electric arc.[3] Major global producers are Evonik (who sells it under the name Aerosil), Cabot Corporation (Cab-O-Sil), Wacker Chemie (HDK), Dow Corning, Heraeus (Zandosil), Tokuyama Corporation (Reolosil), OCI (Konasil), Orisil (Orisil) and Xunyuchem(XYSIL).[4]

Applications

Fumed silica serves as a universal thickening agent and an anticaking agent (free-flow agent) in powders. Like silica gel, it serves as a desiccant. It is used in cosmetics for its light-diffusing properties. It is used as a light abrasive, in products like toothpaste. Other uses include filler in silicone elastomer and viscosity adjustment in paints, coatings, printing inks, adhesives and unsaturated polyester resins.[5] Fumed silica readily forms a network structure within bitumen and enhances its elasticity.[6]

Health issues

Fumed silica is not listed as a carcinogen by OSHA, IARC, or NTP. Due to its fineness and thinness, fumed silica can easily become airborne, making it an inhalation hazard capable of causing irritation.

See also

References