Fumed silica

Not to be confused with silica fume.

130m²/g surface area fumed silica

Fumed silica, 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.

Properties

Fumed silica has a very strong thickening effect. Primary particle size is 5–50 nm. The particles are non-porous and have a surface area of 50–600 m²/g. Density 160-190kg/m³.

Production

Fumed silica is made from flame pyrolysis of silicon tetrachloride or from quartz sand vaporized in a 3000°C electric arc. Major global producers are Evonik (who sells it under the name Aerosil), Cabot Corporation (Cab-O-Sil) and Wacker Chemie-Dow Corning.

Applications

Fumed silica serves as a universal thickening agent, in milkshakes for example, 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. It is also used in the production of cat box filler.

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 risk, capable of causing irritation.

See also

• Fused quartz
• Hydrophobic silica
• Precipitated silica