Fumed silica
Encyclopedia
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 2.2 g/cm3.

Production

Fumed silica is made from flame pyrolysis
Pyrolysis
Pyrolysis is a thermochemical decomposition of organic material at elevated temperatures without the participation of oxygen. It involves the simultaneous change of chemical composition and physical phase, and is irreversible...

 of silicon tetrachloride
Silicon tetrachloride
Silicon tetrachloride is the inorganic compound with the formula SiCl4. It is a colourless volatile liquid that fumes in air. It is used to produce high purity silicon and silica for commercial applications.-Preparation:...

 or from quartz sand vaporized in a 3000°C electric arc. Major global producers are Evonik (Aerosil
Aerosil
Aerosil is a registered trademark for fumed silica product developed in 1942 by Degussa AG in Germany.- Properties :...

), Cabot
Cabot
-People:* Bruce Cabot , American actor* John Cabot , Italian navigator and explorer* Godfrey Lowell Cabot , founder of the Cabot Corporation, philanthropist, and aviation pioneer...

 (Cab-O-Sil) and Wacker Chemie
Wacker Chemie
Wacker Chemie AG is a worldwide operating company in the chemical business, founded 1914. The company is controlled by the Wacker-family holding more than 50 percent of the shares. The corporation is operating more than 25 production sites in Europe, Asia, and the Americas...

-Dow Corning
Dow Corning
Dow Corning is a multinational corporation headquartered in Midland, Michigan, USA. Dow Corning specializes in silicon and silicone-based technology, offering more than 7,000 products and services...

.

Applications

Fumed silica serves as a universal thickening agent
Thickening agent
Thickening agents, or thickeners, is the term applied to substances which increase the viscosity of a solution or liquid/solid mixture without substantially modifying its other properties; although most frequently applied to foods where the target property is taste, the term also is applicable to...

, in milkshake
Milkshake
A milkshake is a sweet, cold beverage which is made from milk, ice cream or iced milk, and flavorings or sweeteners such as fruit syrup or chocolate sauce....

s for example, and an anticaking agent
Anticaking agent
An anticaking agent is an additive placed in powdered or granulated materials, such as table salt, to prevent the formation of lumps, easing packaging, transport, and consumption....

 (free-flow agent) in powders. Like silica gel
Silica gel
Silica gel is a granular, vitreous, porous form of silica made synthetically from sodium silicate. Despite its name, silica gel is a solid. It is a naturally occurring mineral that is purified and processed into either granular or beaded form...

, it serves as a desiccant
Desiccant
A desiccant is a hygroscopic substance that induces or sustains a state of dryness in its local vicinity in a moderately well-sealed container....

. It is used in cosmetics
Cosmetics
Cosmetics are substances used to enhance the appearance or odor of the human body. Cosmetics include skin-care creams, lotions, powders, perfumes, lipsticks, fingernail and toe nail polish, eye and facial makeup, towelettes, permanent waves, colored contact lenses, hair colors, hair sprays and...

 for its light-diffusing properties. It is used as a light abrasive
Abrasive
An abrasive is a material, often a mineral, that is used to shape or finish a workpiece through rubbing which leads to part of the workpiece being worn away...

, in products like toothpaste
Toothpaste
Toothpaste is a paste or gel dentifrice used with a toothbrush as an accessory to clean and maintain the aesthetics and health of teeth. Toothpaste is used to promote oral hygiene: it serves as an abrasive that aids in removing the dental plaque and food from the teeth, assists in suppressing...

. Other uses include filler in silicone elastomer and viscosity adjustment in paint
Paint
Paint is any liquid, liquefiable, or mastic composition which after application to a substrate in a thin layer is converted to an opaque solid film. One may also consider the digital mimicry thereof...

s, coating
Coating
Coating is a covering that is applied to the surface of an object, usually referred to as the substrate. In many cases coatings are applied to improve surface properties of the substrate, such as appearance, adhesion, wetability, corrosion resistance, wear resistance, and scratch resistance...

s, printing inks, adhesive
Adhesive
An adhesive, or glue, is a mixture in a liquid or semi-liquid state that adheres or bonds items together. Adhesives may come from either natural or synthetic sources. The types of materials that can be bonded are vast but they are especially useful for bonding thin materials...

s and unsaturated polyester resins.
It is also used in the production of cat box filler
Litter box
A litter box, sometimes called a sandbox, sand box, litter tray, litter pan, dirt box, catbox, or cat box, is an indoor feces and urine disposal box for cats that are permitted free roam of a home but who cannot or do not always go outside...

.

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.
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