Fumed silica

Fumed silica (CAS number 7631-86-9, also 112945-52-5), 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 3000 °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.

References

^ Flörke, Otto W.; Graetsch, Heribert A.; Brunk, Fred; Benda, Leopold; Paschen, Siegfried; Bergna, Horacio E.; Roberts, William O.; Welsh, William A.; Libanati, Cristian; Ettlinger, Manfred; Kerner, Dieter; Maier, Monika; Meon, Walter; Schmoll, Ralf; Gies, Hermann; Schiffmann, Dietmar (15 April 2008). "Silica". Ullmann's Encyclopedia of Industrial Chemistry: a23_583.pub3. doi:10.1002/14356007.a23_583.pub3. ISBN 978-3527306732.
^ "Fumed Silica". American Elements. Retrieved 19 June 2023.
^ Garrett, P.R. (1992). Defoaming. Theory and Industrial applications. USA: CRC Press. pp. 239–240. ISBN 0-8247-8770-6.
^ Fumed Silica Manufacturer Overview
^ "Reade Fumed Silica Powder (SiO2)". Fumed Silica Powder (SiO2). reade.com. Retrieved 27 January 2021.
^ Zhou, Shengxiong; Li, Siqi; Yan, Chuanqi (2023-09-15). "Influence of fumed silica nanoparticles on the rheological and anti-aging properties of bitumen". Construction and Building Materials. 397: 132388. doi:10.1016/j.conbuildmat.2023.132388. ISSN 0950-0618.

[Ull-1] Flörke, Otto W.; Graetsch, Heribert A.; Brunk, Fred; Benda, Leopold; Paschen, Siegfried; Bergna, Horacio E.; Roberts, William O.; Welsh, William A.; Libanati, Cristian; Ettlinger, Manfred; Kerner, Dieter; Maier, Monika; Meon, Walter; Schmoll, Ralf; Gies, Hermann; Schiffmann, Dietmar (15 April 2008). "Silica". Ullmann's Encyclopedia of Industrial Chemistry: a23_583.pub3. doi:10.1002/14356007.a23_583.pub3. ISBN 978-3527306732.

[2] "Fumed Silica". American Elements. Retrieved 19 June 2023.

[3] Garrett, P.R. (1992). Defoaming. Theory and Industrial applications. USA: CRC Press. pp. 239–240. ISBN 0-8247-8770-6.

[4] Fumed Silica Manufacturer Overview

[5] "Reade Fumed Silica Powder (SiO2)". Fumed Silica Powder (SiO2). reade.com. Retrieved 27 January 2021.

[6] Zhou, Shengxiong; Li, Siqi; Yan, Chuanqi (2023-09-15). "Influence of fumed silica nanoparticles on the rheological and anti-aging properties of bitumen". Construction and Building Materials. 397: 132388. doi:10.1016/j.conbuildmat.2023.132388. ISSN 0950-0618.

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