Silicone
Overview
Silicones are inert, synthetic compounds with a variety of forms and uses. Typically heat-resistant and rubber
Elastomer
An elastomer is a polymer with the property of viscoelasticity , generally having notably low Young's modulus and high yield strain compared with other materials. The term, which is derived from elastic polymer, is often used interchangeably with the term rubber, although the latter is preferred...

-like, they are used in sealant
Sealant
A sealant may be viscous material that has little or no flow characteristics and stay where they are applied or thin and runny so as to allow it to penetrate the substrate by means of capillary reaction...

s, 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, lubricant
Lubricant
A lubricant is a substance introduced to reduce friction between moving surfaces. It may also have the function of transporting foreign particles and of distributing heat...

s, medical applications
Medicine
Medicine is the science and art of healing. It encompasses a variety of health care practices evolved to maintain and restore health by the prevention and treatment of illness....

 (e.g., breast implants), cookware, and insulation
Thermal insulation
Thermal insulation is the reduction of the effects of the various processes of heat transfer between objects in thermal contact or in range of radiative influence. Heat transfer is the transfer of thermal energy between objects of differing temperature...

.

Silicones are polymers that include silicon
Silicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...

 together with carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

, hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

, oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

, and sometimes other chemical element
Chemical element
A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. Familiar examples of elements include carbon, oxygen, aluminum, iron, copper, gold, mercury, and lead.As of November 2011, 118 elements...

s. Some common forms include silicone oil
Silicone oil
A silicone oil is any polymerized siloxanes with organic side chains. They are formed of alternating silicon-oxygen atoms or siloxane, rather than carbon atoms . Other species attach to the tetravalent silicon atoms, not to the divalent oxygen atoms which are fully committed to forming the...

, silicone grease
Silicone grease
Silicone grease is a waterproof grease made by combining a silicone oil with a thickener. Most commonly, the silicone oil is polydimethylsiloxane and the thickener is amorphous fumed silica...

, silicone rubber
Silicone rubber
Silicone rubber is an elastomer composed of silicone—itself a polymer—containing silicon together with carbon, hydrogen, and oxygen. Silicone rubbers are widely used in industry, and there are multiple formulations...

, and silicone resin
Silicone resin
Silicone resins are a type of silicone material which is formed by branched, cage-like oligosiloxanes with the general formula of RnSiXmOy, where R is a non reactive substituent, usually Me or Ph, and X is a functional group H, OH, Cl or OR...

.
Some of the most useful properties of silicones include:
  • Low thermal conductivity
    Thermal conductivity
    In physics, thermal conductivity, k, is the property of a material's ability to conduct heat. It appears primarily in Fourier's Law for heat conduction....

  • Low chemical reactivity.
  • Low toxicity
    Toxicity
    Toxicity is the degree to which a substance can damage a living or non-living organisms. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a substructure of the organism, such as a cell or an organ , such as the liver...

    .
  • Thermal stability (constancy of properties over a wide temperature range of −100 to 250 °C).
  • The ability to repel water and form watertight seals, although silicones are not hydrophobe
    Hydrophobe
    In chemistry, hydrophobicity is the physical property of a molecule that is repelled from a mass of water....

    s.
  • Excellent resistance to oxygen, ozone, and ultraviolet (UV) light
    Ultraviolet
    Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...

     such as that in sunlight.
Encyclopedia
Silicones are inert, synthetic compounds with a variety of forms and uses. Typically heat-resistant and rubber
Elastomer
An elastomer is a polymer with the property of viscoelasticity , generally having notably low Young's modulus and high yield strain compared with other materials. The term, which is derived from elastic polymer, is often used interchangeably with the term rubber, although the latter is preferred...

-like, they are used in sealant
Sealant
A sealant may be viscous material that has little or no flow characteristics and stay where they are applied or thin and runny so as to allow it to penetrate the substrate by means of capillary reaction...

s, 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, lubricant
Lubricant
A lubricant is a substance introduced to reduce friction between moving surfaces. It may also have the function of transporting foreign particles and of distributing heat...

s, medical applications
Medicine
Medicine is the science and art of healing. It encompasses a variety of health care practices evolved to maintain and restore health by the prevention and treatment of illness....

 (e.g., breast implants), cookware, and insulation
Thermal insulation
Thermal insulation is the reduction of the effects of the various processes of heat transfer between objects in thermal contact or in range of radiative influence. Heat transfer is the transfer of thermal energy between objects of differing temperature...

.

Silicones are polymers that include silicon
Silicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...

 together with carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

, hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

, oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

, and sometimes other chemical element
Chemical element
A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. Familiar examples of elements include carbon, oxygen, aluminum, iron, copper, gold, mercury, and lead.As of November 2011, 118 elements...

s. Some common forms include silicone oil
Silicone oil
A silicone oil is any polymerized siloxanes with organic side chains. They are formed of alternating silicon-oxygen atoms or siloxane, rather than carbon atoms . Other species attach to the tetravalent silicon atoms, not to the divalent oxygen atoms which are fully committed to forming the...

, silicone grease
Silicone grease
Silicone grease is a waterproof grease made by combining a silicone oil with a thickener. Most commonly, the silicone oil is polydimethylsiloxane and the thickener is amorphous fumed silica...

, silicone rubber
Silicone rubber
Silicone rubber is an elastomer composed of silicone—itself a polymer—containing silicon together with carbon, hydrogen, and oxygen. Silicone rubbers are widely used in industry, and there are multiple formulations...

, and silicone resin
Silicone resin
Silicone resins are a type of silicone material which is formed by branched, cage-like oligosiloxanes with the general formula of RnSiXmOy, where R is a non reactive substituent, usually Me or Ph, and X is a functional group H, OH, Cl or OR...

.

Properties

Some of the most useful properties of silicones include:
  • Low thermal conductivity
    Thermal conductivity
    In physics, thermal conductivity, k, is the property of a material's ability to conduct heat. It appears primarily in Fourier's Law for heat conduction....

  • Low chemical reactivity.
  • Low toxicity
    Toxicity
    Toxicity is the degree to which a substance can damage a living or non-living organisms. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a substructure of the organism, such as a cell or an organ , such as the liver...

    .
  • Thermal stability (constancy of properties over a wide temperature range of −100 to 250 °C).
  • The ability to repel water and form watertight seals, although silicones are not hydrophobe
    Hydrophobe
    In chemistry, hydrophobicity is the physical property of a molecule that is repelled from a mass of water....

    s.
  • Excellent resistance to oxygen, ozone, and ultraviolet (UV) light
    Ultraviolet
    Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...

     such as that in sunlight. This property has led to widespread use of silicones in the construction industry (e.g. coatings, fire protection, glazing seals) and the automotive industry (external gaskets, external trim).
  • Good electrical insulation
    Electrical insulation
    thumb|250px|[[Coaxial Cable]] with dielectric insulator supporting a central coreThis article refers to electrical insulation. For insulation of heat, see Thermal insulation...

    . Because silicone can be formulated to be electrically insulative or conductive, it is suitable for a wide range of electrical applications.
  • Does not stick.
  • Does not support microbiological growth.
  • High gas permeability: At room temperature (25 °C), the permeability of silicone rubber for such gases as oxygen is approximately 400 times that of butyl rubber
    Butyl rubber
    Butyl rubber is a synthetic rubber, a copolymer of isobutylene with isoprene. The abbreviation IIR stands for Isobutylene Isoprene Rubber. Polyisobutylene, also known as "PIB" or polyisobutene, n, is the homopolymer of isobutylene, or 2-methyl-1-propene, on which butyl rubber is based...

    , making silicone useful for medical applications in which increased aeration is desired. However, silicone rubbers cannot be used where gas-tight seals are necessary.

History

The chemist
Chemist
A chemist is a scientist trained in the study of chemistry. Chemists study the composition of matter and its properties such as density and acidity. Chemists carefully describe the properties they study in terms of quantities, with detail on the level of molecules and their component atoms...

 Frederick Kipping
Frederick Kipping
Professor Frederick Stanley Kipping FRS was an English chemist.He was born in Manchester, England, the son of James Kipping, a Bank of England official, and educated at Manchester Grammar School before enrolling in 1879 at Owens College for an external degree from the University of London...

 pioneered the study of the organic compounds of silicon (organosilicon
Organosilicon
Organosilicon compounds are organic compounds containing carbon silicon bonds. Organosilicon chemistry is the corresponding science exploring their properties and reactivity.Like carbon, the organically bound silicon is tetravalent and tetrahedral...

s) and coined the term silicone.

Chemistry

More precisely called polymer
Polymer
A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...

ized siloxane
Siloxane
A siloxane is any chemical compound composed of units of the form R2SiO, where R is a hydrogen atom or a hydrocarbon group. They belong to the wider class of organosilicon compounds....

s or polysiloxanes, silicones are mixed inorganic
Inorganic compound
Inorganic compounds have traditionally been considered to be of inanimate, non-biological origin. In contrast, organic compounds have an explicit biological origin. However, over the past century, the classification of inorganic vs organic compounds has become less important to scientists,...

-organic
Organic compound
An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...

 polymer
Polymer
A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...

s with the chemical formula [R2SiO]n, where R is an organic group such as methyl, ethyl
Ethyl group
In chemistry, an ethyl group is an alkyl substituent derived from ethane . It has the formula -C2H5 and is very often abbreviated -Et.Ethylation is the formation of a compound by introduction of the ethyl functional group, C2H5....

, or phenyl. These materials consist of an inorganic silicon-oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 backbone (⋯-Si-O-Si-O-Si-O-⋯) with organic side groups attached to the silicon atoms, which are four-coordinate.

In some cases, organic side groups can be used to link two or more of these -Si-O- backbones together. By varying the -Si-O- chain lengths, side groups, and crosslinking
Cross-link
Cross-links are bonds that link one polymer chain to another. They can be covalent bonds or ionic bonds. "Polymer chains" can refer to synthetic polymers or natural polymers . When the term "cross-linking" is used in the synthetic polymer science field, it usually refers to the use of...

, silicones can be synthesized with a wide variety of properties and compositions. They can vary in consistency from liquid to gel to rubber to hard plastic. The most common siloxane is linear polydimethylsiloxane
Polydimethylsiloxane
Polydimethylsiloxane belongs to a group of polymeric organosilicon compounds that are commonly referred to as silicones. PDMS is the most widely used silicon-based organic polymer, and is particularly known for its unusual rheological properties. PDMS is optically clear, and, in general, is...

 (PDMS), a silicone oil
Silicone oil
A silicone oil is any polymerized siloxanes with organic side chains. They are formed of alternating silicon-oxygen atoms or siloxane, rather than carbon atoms . Other species attach to the tetravalent silicon atoms, not to the divalent oxygen atoms which are fully committed to forming the...

. The second largest group of silicone materials is based on silicone resin
Silicone resin
Silicone resins are a type of silicone material which is formed by branched, cage-like oligosiloxanes with the general formula of RnSiXmOy, where R is a non reactive substituent, usually Me or Ph, and X is a functional group H, OH, Cl or OR...

s, which are formed by branched and cage-like oligosiloxanes.

Terminology

Silicone is not to be confused with the chemical element silicon
Silicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...

, a crystalline metalloid
Metalloid
Metalloid is a term used in chemistry when classifying the chemical elements. On the basis of their general physical and chemical properties, each element can usually be classified as a metal or a nonmetal. However, some elements with intermediate or mixed properties can be harder to characterize...

 widely used in computer
Computer
A computer is a programmable machine designed to sequentially and automatically carry out a sequence of arithmetic or logical operations. The particular sequence of operations can be changed readily, allowing the computer to solve more than one kind of problem...

s and other electronic equipment
Electronics
Electronics is the branch of science, engineering and technology that deals with electrical circuits involving active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies...

. Although silicones contain silicon atoms, they also include carbon, hydrogen, oxygen, and perhaps other kinds of atoms as well, and have different physical and chemical properties than elemental silicon.

F. S. Kipping
Frederick Kipping
Professor Frederick Stanley Kipping FRS was an English chemist.He was born in Manchester, England, the son of James Kipping, a Bank of England official, and educated at Manchester Grammar School before enrolling in 1879 at Owens College for an external degree from the University of London...

 coined the word "silicone" in 1901 to describe polydiphenylsiloxane by analogy of its formula, Ph2SiO, with the formula of the ketone benzophenone
Benzophenone
Benzophenone is the organic compound with the formula 2CO, generally abbreviated Ph2CO. Benzophenone is a widely used building block in organic chemistry, being the parent diarylketone.-Uses:...

, Ph2CO (Ph stands for phenyl, C6H5). Kipping was well aware that polydiphenylsiloxane is polymeric whereas benzophenone is monomeric and noted that Ph2SiO and Ph2CO had very different chemistry.

A true silicone group with a double bond between oxygen and silicon does not commonly exist in nature; chemists find that the silicon atom usually forms single bonds with each of two oxygen atoms, rather than a double bond to a single atom. Polysiloxanes are among the many substances commonly known as "silicones".

Molecules containing silicon-oxygen double bonds do exist and are called silanones. Several silanones have been studied in argon
Argon
Argon is a chemical element represented by the symbol Ar. Argon has atomic number 18 and is the third element in group 18 of the periodic table . Argon is the third most common gas in the Earth's atmosphere, at 0.93%, making it more common than carbon dioxide...

 matrices
Matrix Isolation
Matrix isolation is an experimental technique used in chemistry and physics which generally involves a material being trapped within an unreactive matrix. A host matrix is a continuous solid phase in which guest particles are embedded. The guest is said to be isolated within the host matrix...

 and in the gas phase, but they are highly reactive. Despite their reactivity, silanones are important as intermediates
Reaction intermediate
A reaction intermediate or an intermediate is a molecular entity that is formed from the reactants and reacts further to give the directly observed products of a chemical reaction. Most chemical reactions are stepwise, that is they take more than one elementary step to complete...

 in gas-phase processes such as chemical vapor deposition
Chemical vapor deposition
Chemical vapor deposition is a chemical process used to produce high-purity, high-performance solid materials. The process is often used in the semiconductor industry to produce thin films. In a typical CVD process, the wafer is exposed to one or more volatile precursors, which react and/or...

 in microelectronics
Microelectronics
Microelectronics is a subfield of electronics. As the name suggests, microelectronics relates to the study and manufacture of very small electronic components. Usually, but not always, this means micrometre-scale or smaller,. These devices are made from semiconductors...

 production, in the formation of ceramics
Ceramic forming techniques
Ceramic forming techniques are ways of forming ceramic shapes. This can be used to make everyday tableware from teapots, to engineering ceramics such as computer parts. Methods for forming powders of ceramic raw materials into complex shapes are desirable in many areas of technology...

 by combustion, and in astrochemistry.

Synthesis

Silica (silicon dioxide)
Silicon dioxide
The chemical compound silicon dioxide, also known as silica , is an oxide of silicon with the chemical formula '. It has been known for its hardness since antiquity...

, common in sandstone
Sandstone
Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...

, beach sand
Sand
Sand is a naturally occurring granular material composed of finely divided rock and mineral particles.The composition of sand is highly variable, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal...

, and similar natural materials, is the initial material from which silicones are produced; silica is also widely used in producing glass
Glass
Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...

. Silicones are synthesized from chlorosilane
Chlorosilane
Chlorosilanes are a group of reactive, chlorine-containing chemical compounds, related to silane and used in many chemical processes. Each such chemical has at least one silicon-chlorine bond.-Synthesis:...

s, tetraethoxysilane, and related compounds.

In producing the silicone PDMS
Polydimethylsiloxane
Polydimethylsiloxane belongs to a group of polymeric organosilicon compounds that are commonly referred to as silicones. PDMS is the most widely used silicon-based organic polymer, and is particularly known for its unusual rheological properties. PDMS is optically clear, and, in general, is...

, the starting material is dimethyldichlorosilane
Dimethyldichlorosilane
Dimethyldichlorosilane is a tetrahedral, organosilicon compound with the formula Si2Cl2. At room temperature it is a colorless liquid that readily reacts with water to form both linear and cyclic Si-O chains...

, which reacts with water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

 as follows:
n Si(CH3)2Cl2 + n H2O → [Si(CH3)2O]n + 2n HCl


During polymerization
Polymerization
In polymer chemistry, polymerization is a process of reacting monomer molecules together in a chemical reaction to form three-dimensional networks or polymer chains...

, this reaction evolves hazardous hydrogen chloride
Hydrogen chloride
The compound hydrogen chloride has the formula HCl. At room temperature, it is a colorless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric humidity. Hydrogen chloride gas and hydrochloric acid are important in technology and industry...

 gas.

For consumer and medical uses, a process was developed in which the chlorine atoms in the silane precursor were replaced with acetate
Acetate
An acetate is a derivative of acetic acid. This term includes salts and esters, as well as the anion found in solution. Most of the approximately 5 billion kilograms of acetic acid produced annually in industry are used in the production of acetates, which usually take the form of polymers. In...

 groups,which produce the less dangerous acetic acid
Acetic acid
Acetic acid is an organic compound with the chemical formula CH3CO2H . It is a colourless liquid that when undiluted is also called glacial acetic acid. Acetic acid is the main component of vinegar , and has a distinctive sour taste and pungent smell...

 (the acid found in vinegar) as the reaction product of a much slower curing process. This chemistry is used in many consumer applications, such as silicone caulk and 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.

Branches
Branching (chemistry)
In polymer chemistry, branching occurs by the replacement of a substituent, e.g., a hydrogen atom, on a monomer subunit, by another covalently bonded chain of that polymer; or, in the case of a graft copolymer, by a chain of another type...

 or cross-link
Cross-link
Cross-links are bonds that link one polymer chain to another. They can be covalent bonds or ionic bonds. "Polymer chains" can refer to synthetic polymers or natural polymers . When the term "cross-linking" is used in the synthetic polymer science field, it usually refers to the use of...

s in the polymer chain can be introduced by using silane precursors with more acid-forming groups and fewer methyl groups, such as methyltrichlorosilane, . Ideally, each molecule of such a compound becomes a branch point. This process can be used to produce hard silicone resin
Silicone resin
Silicone resins are a type of silicone material which is formed by branched, cage-like oligosiloxanes with the general formula of RnSiXmOy, where R is a non reactive substituent, usually Me or Ph, and X is a functional group H, OH, Cl or OR...

s. Similarly, precursors with three methyl groups can be used to limit molecular weight, since each such molecule has only one reactive site and so forms the end of a siloxane chain.
Modern silicone resins are generally made using tetraethoxysilane, which reacts in a more mild and controllable manner than chlorosilanes.

Combustion

When silicone is burned in air or oxygen, it forms solid silica (silicon dioxide) as a white powder, char, and various gases. The readily dispersed powder is sometimes called silica fume.

Aquarium joints

In making aquarium
Aquarium
An aquarium is a vivarium consisting of at least one transparent side in which water-dwelling plants or animals are kept. Fishkeepers use aquaria to keep fish, invertebrates, amphibians, marine mammals, turtles, and aquatic plants...

s, manufacturers now commonly use 100% silicone sealant to join glass plates. Glass joints made with silicone sealant can withstand great pressure, making obsolete the original aquarium construction method of angle-iron and putty.
This same silicone is used to make hinges in aquarium lids or for minor repairs. However, not all commercial silicones are safe for aquarium manufacture, nor is silicone used for the manufacture of acrylic aquariums as silicones do not have long-term adhesion to plastics.

Automotive

In the automotive
Automobile
An automobile, autocar, motor car or car is a wheeled motor vehicle used for transporting passengers, which also carries its own engine or motor...

 field, silicone grease
Silicone grease
Silicone grease is a waterproof grease made by combining a silicone oil with a thickener. Most commonly, the silicone oil is polydimethylsiloxane and the thickener is amorphous fumed silica...

 is typically used as a lubricant for brake
Brake
A brake is a mechanical device which inhibits motion. Its opposite component is a clutch. The rest of this article is dedicated to various types of vehicular brakes....

 components since it is stable at high temperatures, is not water-soluble, and is far less likely than other lubricants to foul. Automotive spark plug wires are insulated by multiple layers of silicone to prevent sparks from jumping to adjacent wires, causing misfires. Silicone tubing is sometimes used in automotive intake systems (especially for engines with forced induction). Sheet silicone is used to manufacture gaskets used in automotive engines, transmissions, and other applications. Automotive body manufacturing plants and paint shops avoid silicones, as they may cause "fish eyes", small, circular craters in the finish. Additionally, silicone compounds such as silicone rubber are used as coatings and sealants for airbag
Airbag
An Airbag is a vehicle safety device. It is an occupant restraint consisting of a flexible envelope designed to inflate rapidly during an automobile collision, to prevent occupants from striking interior objects such as the steering wheel or a window...

s; the high strength of silicone rubber makes it an optimal adhesive/sealant for high impact airbags.

Coatings

Silicone films can be applied to such silica-based substrates as glass
Glass
Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...

 to form a covalently bonded hydrophobic coating.

Many fabrics can be coated or impregnated with silicone to form a strong, waterproof composite such as silnylon
Silnylon
Silnylon, a portmanteau of "silicone" and "nylon", is a synthetic fabric used mainly in lightweight outdoor gear. It is made by impregnating a thin woven nylon fabric with liquid silicone from both sides. This makes it strong for its weight, as the silicone substantially improves the tear strength....

.

Cookware

  • As a low-taint, non-toxic material, silicone can be used where contact with food is required. Silicone is becoming an important product in the cookware industry, particularly bakeware and kitchen utensils.
  • Silicone is used as an insulator in heat-resistant potholders and similar items, however it is more conductive of heat than similar less dense fiber-based products. Silicone oven mitts are able to withstand temperatures up to 260 °C (500 °F), allowing reaching into boiling water.
  • Mold
    Mold
    Molds are fungi that grow in the form of multicellular filaments called hyphae. Molds are not considered to be microbes but microscopic fungi that grow as single cells called yeasts...

    s for chocolate, ice, cookies, muffins and various other foods.
  • Other products such as steamer
    Steamer
    -In locomotion:* Steamboat, a boat propelled by a paddlewheel or propeller under steam power* Steam locomotive, a locomotive propelled by steam-operated pistons* Stanley Steamer, a steam-powered automobile* Fastball, nickname for the baseball pitch...

    s, egg boilers or poacher
    Poacher
    Poacher may refer to:*One who engages in poaching, the theft or illegal killing of animals or plants*A device used for poaching *Poacher , a family of fish...

    s, cookware lids, pot holders, trivet
    Trivet
    A trivet is an object placed between a serving dish or bowl, and a dining table, usually to protect the table from heat damage.Trivet also refers to a tripod used to elevate pots from the coals of an open fire...

    s, and kitchen mats.

Defoaming

Silicones are used as active compound in defoamer
Defoamer
A defoamer or an anti-foaming agent is a chemical additive that reduces and hinders the formation of foam in industrial process liquids. The terms anti-foam agent and defoamer are often used interchangeably....

s due to their low water solubility and good spreading properties.

Dry cleaning

Liquid silicone can be used as a dry cleaning
Dry cleaning
Dry cleaning is any cleaning process for clothing and textiles using a chemical solvent other than water. The solvent used is typically tetrachloroethylene , abbreviated "perc" in the industry and "dry-cleaning fluid" by the public...

 solvent
Solvent
A solvent is a liquid, solid, or gas that dissolves another solid, liquid, or gaseous solute, resulting in a solution that is soluble in a certain volume of solvent at a specified temperature...

, providing an "environmentally friendly" alternative to the traditional chlorine
Chlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...

-containing perchloroethylene (perc) solvent. Also, liquid silicone is chemically inert, not reacting with fabrics or dyes during the cleaning process, thus reducing the amount of fading and shrinking experienced by many garments dry-cleaned with the more reactive perc. Use of silicones in dry cleaning reduces the environmental impact of a typically high-polluting industry. A siloxane-based decamethylpentacyclosiloxane (DS)
Siloxane
A siloxane is any chemical compound composed of units of the form R2SiO, where R is a hydrogen atom or a hydrocarbon group. They belong to the wider class of organosilicon compounds....

 process has been patented by the company GreenEarth Cleaning
GreenEarth Cleaning
GreenEarth Cleaning is a patented process for drycleaning using liquid silicone , a clear, odorless, non-toxic solvent solution in a closed loop system. D5 degrades into silica and trace amounts of water and carbon dioxide within days if spilled or disposed of...

.

Electronics

Electronic components are sometimes encased
Resin dispensing
A resin dispensing system is a technical installation to process casting resin for the purpose of filling, sealing, covering or soaking technical parts, especially in the field of electricity and electronics like transformers, LCDs and other devices of various size.Due to progressing...

 in silicone to increase stability against mechanical and electrical shock, radiation and vibration, a process called "potting".

Silicones are used where durability and high performance are demanded of components under hard conditions, such as in space (satellite technology). They are selected over polyurethane
Polyurethane
A polyurethane is any polymer composed of a chain of organic units joined by carbamate links. Polyurethane polymers are formed through step-growth polymerization, by reacting a monomer with another monomer in the presence of a catalyst.Polyurethanes are...

 or epoxy
Epoxy
Epoxy, also known as polyepoxide, is a thermosetting polymer formed from reaction of an epoxide "resin" with polyamine "hardener". Epoxy has a wide range of applications, including fiber-reinforced plastic materials and general purpose adhesives....

 encapsulation when a wide operating temperature
Operating temperature
An operating temperature is the temperature at which an electrical or mechanical device operates. The device will operate effectively within a specified temperature range which varies based on the device function and application context, and ranges from the minimum operating temperature to the...

 range is required (−65 to 315 °C). Silicones also have the advantage of little exothermic heat rise during cure, low toxicity, good electrical properties and high purity.

The use of silicones in electronics is not without problems, however. Silicones are relatively expensive and can be attacked by solvents. Silicone easily migrates as either a liquid or vapor onto other components.

Silicone contamination of electrical switch contacts can lead to failures by causing an increase in contact resistance, often late in the life of the contact, well after any testing is completed. Use of silicone-based spray products in electronic devices during maintenance or repairs can cause later failures.

Firestops

Silicone foam
Silicone foam
Silicone foam is a synthetic rubber product used in gasketing, sheets and firestops. It is available in solid, cured form as well as in individual liquid components for field installations.-Uses:*Gaskets*Sheets*High temperature tubes for autoclaves...

 has been used in North American buildings in an attempt to firestop
Firestop
A firestop is a passive fire protection system of various components used to seal openings and joints in fire-resistance rated wall and/or floor assemblies, based on fire testing and certification listings....

 openings within fire-resistance-rated wall and floor assemblies to prevent the spread of flames and smoke from one room to another. When properly installed, silicone-foam firestops can be fabricated for building code compliance. Advantages include flexibility and high dielectric
Dielectric
A dielectric is an electrical insulator that can be polarized by an applied electric field. When a dielectric is placed in an electric field, electric charges do not flow through the material, as in a conductor, but only slightly shift from their average equilibrium positions causing dielectric...

 strength. Disadvantages include combustibility (hard to extinguish) and significant smoke development.

However, silicone-foam firestops have been the subject of controversy and press attention due to smoke development from pyrolysis of combustible components within the foam, hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

 gas escape, shrinkage, and cracking. These problems have been exposed by whistleblower
Whistleblower
A whistleblower is a person who tells the public or someone in authority about alleged dishonest or illegal activities occurring in a government department, a public or private organization, or a company...

 Gerald W. Brown
Gerald W. Brown
Gerald W. "Jerry" Brown is an American whistleblower who concerned himself with deficiencies in passive fire protection systems in US and Canadian nuclear power plants.-Thermo-Lag scandal:...

, and have led to reportable events among licensees (operators of nuclear power plant
Nuclear power plant
A nuclear power plant is a thermal power station in which the heat source is one or more nuclear reactors. As in a conventional thermal power station the heat is used to generate steam which drives a steam turbine connected to a generator which produces electricity.Nuclear power plants are usually...

s) of the Nuclear Regulatory Commission (NRC)
Nuclear Regulatory Commission
The Nuclear Regulatory Commission is an independent agency of the United States government that was established by the Energy Reorganization Act of 1974 from the United States Atomic Energy Commission, and was first opened January 19, 1975...

.

Silicone firestops are also used in aircraft.

Lubricants

Silicone grease
Grease (lubricant)
The term grease is used to describe semisolid lubricants. Although the word grease is also used to describe rendered fat of animals, in the context of lubrication, grease typically applies to a material consisting of a soap emulsified with mineral or vegetable oil...

s are used for many purposes, such as bicycle chain
Bicycle chain
A bicycle chain is a roller chain that transfers power from the pedals to the drive-wheel of a bicycle, thus propelling it. Most bicycle chains are made from plain carbon or alloy steel, but some are nickel-plated to prevent rust, or simply for aesthetics. Nickel also confers a measure of...

s, airsoft gun parts, and a wide range of other mechanism
Mechanism
Mechanism may refer to:*Mechanism , rigid bodies connected by joints in order to accomplish a desired force and/or motion transmission*Mechanism , explaining how a feature is created...

s. Typically, a dry-set lubricant is delivered with a solvent carrier to penetrate the mechanism. The solvent then evaporates, leaving a clear film that lubricates but does not attract dirt and grit as much as an oil
Oil
An oil is any substance that is liquid at ambient temperatures and does not mix with water but may mix with other oils and organic solvents. This general definition includes vegetable oils, volatile essential oils, petrochemical oils, and synthetic oils....

-based or other traditional "wet" lubricant.

Silicone personal lubricants are also available for use in medical procedures or sexual activity. See below.

Medicine

Silicone, particularly the gel form, is used in bandage
Bandage
A bandage is a piece of material used either to support a medical device such as a dressing or splint, or on its own to provide support to the body; they can also be used to restrict a part of the body. During heavy bleeding or following a poisonous bite it is important to slow the flow of blood,...

s and dressings, energy bracelets, breast implants, contact lenses, and a variety of other medical uses.

Scar treatment sheets are often made of medical grade silicone
Medical grade silicone
Medical grade silicones are silicones tested for biocompatibility and are appropriate to be used for medical applications. In the United States, the Food and Drug Administration regulates materials implanted into the body. Medical grade silicones are generally grouped into three categories: non...

 due to its durability and biocompatibility
Biocompatibility
Biocompatibility is related to the behavior of biomaterials in various contexts. The term may refer to specific properties of a material without specifying where or how the material is used , or to more empirical clinical success of a whole device in...

. Polydimethylsiloxane is often used for this purpose, since its specific crosslinking results in a flexible and soft silcone with high durability and tack.

Polydimethylsiloxane (PDMS)
Polydimethylsiloxane
Polydimethylsiloxane belongs to a group of polymeric organosilicon compounds that are commonly referred to as silicones. PDMS is the most widely used silicon-based organic polymer, and is particularly known for its unusual rheological properties. PDMS is optically clear, and, in general, is...

 has been used as the hydrophobic block of amphiphilic synthetic block copolymers used to form the vesicle membrane of polymersome
Polymersome
In biotechnology, polymersomes are a class of artificial vesicles, tiny hollow spheres that enclose a solution. Polymersomes are made using amphiphilic synthetic block copolymers to form the vesicle membrane, and have radii ranging from 50 nm to 5 µm or more...

s.

Moldmaking

Two-part silicone systems are used to create rubber molds used to cast resins
Resin casting
Resin casting is a method of plastic casting where a mold is filled with a liquid synthetic resin, which then hardens. It is primarily used for small scale production like industrial prototypes and dentistry...

, foams, rubber, and low-temperature alloys. A silicone mold generally requires little or no mold-release or surface preparation, as most materials do not adhere to silicone. For experimental uses, ordinary one-part silicone can be used to make molds or to mold into shapes. If needed, common vegetable cooking oils
Cooking oil
Cooking oil is purified fat of plant origin, which is usually liquid at room temperature ....

 or petroleum jelly
Petroleum jelly
Petroleum jelly, petrolatum, white petrolatum or soft paraffin, CAS number 8009-03-8, is a semi-solid mixture of hydrocarbons , originally promoted as a topical ointment for its healing properties...

 can be used on mating surfaces as a mold-release agent.

Cooking molds used as bakeware do not require coating with cooking oil, allowing the baked food to be more easily removed from the mold after cooking.

Personal care

Silicones are ingredients in many hair conditioner
Hair conditioner
Hair conditioner is a hair care product that alters the texture and appearance of hair.-History:For centuries, natural oils have been used to condition human hair. These natural products are still used today, including essential oils such as tea tree oil and carrier oils such as jojoba oil...

s, shampoo
Shampoo
Shampoo is a hair care product used for the removal of oils, dirt, skin particles, dandruff, environmental pollutants and other contaminant particles that gradually build up in hair...

s, and hair gel
Hair gel
Hair gel is a hairstyling product that is used to stiffen hair into a particular hairstyle. The results it produces are usually similar to, but stronger than, those of hair spray and hair wax, and weaker than those of hair glue.-Types:...

 products. Some silicones, notably the amine
Amine
Amines are organic compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are derivatives of ammonia, wherein one or more hydrogen atoms have been replaced by a substituent such as an alkyl or aryl group. Important amines include amino acids, biogenic amines,...

 functionalized amodimethicones, are excellent conditioners, providing improved combability, feel, and softness, and lessening frizz. The phenyltrimethicones, in another silicone family, are used in reflection-enhancing and color-correcting hair products, where they increase shine and glossiness (and possibly effect subtle color changes). Phenyltrimethicones, unlike the conditioning amodimethicones, have refractive indices (typically 1.46) close to that of human hair (1.54). However, if included in the same formulation, amodimethicone and phenyltrimethicone interact and dilute each other, making it difficult to achieve both high shine and excellent conditioning in the same product.

Silicone rubber is commonly used in baby bottle
Baby bottle
A baby bottle is a bottle with a teat to drink directly from. It is typically used by infants and young children when a mother does not breastfeed, or if someone cannot drink from a cup, for feeding oneself or being fed.In particular it is used to feed infant formula, expressed breast milk or...

 nipples (teats) for its cleanliness, aesthetic appearance, and low extractable content.

Silicones are used in shaving products
Shaving
Shaving is the removal of hair, by using a razor or any other kind of bladed implement, to slice it down to the level of the skin. Shaving is most commonly practiced by men to remove their facial hair and by women to remove their leg and underarm hair...

 and personal lubricants.

Menstrual cup
Menstrual cup
A menstrual cup is a type of cup or barrier worn inside the vagina during menstruation to collect menstrual fluid. Unlike tampons and pads, the cup collects menstrual fluid rather than absorbing it...

s are often made of medical grade silicone
Medical grade silicone
Medical grade silicones are silicones tested for biocompatibility and are appropriate to be used for medical applications. In the United States, the Food and Drug Administration regulates materials implanted into the body. Medical grade silicones are generally grouped into three categories: non...

 due to its durability, reusability, and biocompatibility
Biocompatibility
Biocompatibility is related to the behavior of biomaterials in various contexts. The term may refer to specific properties of a material without specifying where or how the material is used , or to more empirical clinical success of a whole device in...

.

Silicone is a material of choice for soft sex toys, due to its durability, cleanability, and lack of phthalates
Phthalates
Phthalates , or phthalate esters, are esters of phthalic acid and are mainly used as plasticizers . They are used primarily to soften polyvinyl chloride...

, chemicals suspected of having carcinogenic and mutagenic effects on the skin and mucous membranes.

Plumbing and building construction

The strength and reliability of silicone rubber
Silicone rubber
Silicone rubber is an elastomer composed of silicone—itself a polymer—containing silicon together with carbon, hydrogen, and oxygen. Silicone rubbers are widely used in industry, and there are multiple formulations...

 is widely acknowledged in the construction industry.

One-part silicone sealant
Sealant
A sealant may be viscous material that has little or no flow characteristics and stay where they are applied or thin and runny so as to allow it to penetrate the substrate by means of capillary reaction...

s and caulks are in common use to seal gaps, joints and crevices in buildings. One-part silicones cure by absorbing atmospheric moisture, which helps in the professional installation.

In plumbing, silicone grease is typically applied to O-rings in brass
Brass
Brass is an alloy of copper and zinc; the proportions of zinc and copper can be varied to create a range of brasses with varying properties.In comparison, bronze is principally an alloy of copper and tin...

 taps and valves
Valve
A valve is a device that regulates, directs or controls the flow of a fluid by opening, closing, or partially obstructing various passageways. Valves are technically pipe fittings, but are usually discussed as a separate category...

, preventing lime
Calcium carbonate
Calcium carbonate is a chemical compound with the formula CaCO3. It is a common substance found in rocks in all parts of the world, and is the main component of shells of marine organisms, snails, coal balls, pearls, and eggshells. Calcium carbonate is the active ingredient in agricultural lime,...

 from sticking to the metal.

Toys

Silicone balls have become a juggler
Juggling
Juggling is a skill involving moving objects for entertainment or sport. The most recognizable form of juggling is toss juggling, in which the juggler throws objects up to catch and toss up again. This may be one object or many objects, at the same time with one or many hands. Jugglers often refer...

's favorite due to the high bounce back, and are used as a response system in low-response yo-yo
Yo-yo
The yo-yo in its simplest form is an object consisting of an axle connected to two disks, and a length of twine looped around the axle, similar to a slender spool...

s.

Silly Putty
Silly Putty
Silly Putty , is the Crayola-owned trademark name for a class of silicone polymers. It is marketed today as a toy for children, but was originally created by accident during research into potential rubber substitutes for use by the United States in World War II...

 (a Crayola
Crayola
Crayola is a brand of artists' supplies manufactured by Crayola LLC, which was founded in 1885 as Binney & Smith. It is best known for its crayons...

 product) and similar materials include the silicones dimethyl siloxane
Siloxane
A siloxane is any chemical compound composed of units of the form R2SiO, where R is a hydrogen atom or a hydrocarbon group. They belong to the wider class of organosilicon compounds....

, polydimethylsiloxane
Polydimethylsiloxane
Polydimethylsiloxane belongs to a group of polymeric organosilicon compounds that are commonly referred to as silicones. PDMS is the most widely used silicon-based organic polymer, and is particularly known for its unusual rheological properties. PDMS is optically clear, and, in general, is...

, and decamethyl cyclopentasiloxane
Cyclopentasiloxane
Decamethylcyclopentasiloxane is a silicone fluid commonly used in cosmetics such as deodorants, sunblocks, hair sprays and skin care products. It is becoming more common in hair conditioners, as it makes the hair easier to brush without breakage. It is also used as part of silicone based personal...

, with other ingredients. This substance is noted for its unusual characteristics: It bounces, but breaks when given a sharp blow; it can also flow like a liquid, and will form a puddle given enough time.

Silicone has the potential of replacing plastic in creating many forms of toys.

Production and marketing

The global demand on silicones approached US$ 12.5 billion in 2008, approximately 4% up from the previous year. It continues similar growth in the following years to reach US$13.5 billion by 2010. The annual growth is expected to rebound to 7% when the economy revives, boosted by broader applications, introduction of novel products and increasing awareness of using more environmentally friendly materials.

The leading global manufacturers of silicone base materials belong to three regional organizations: the European Silicone Center(CES) in Brussels, Belgium; the Silicone Environment Health and Safety Council (SEHSC) in Herndon, Virginia
Herndon, Virginia
Herndon is a town in Fairfax County, Virginia, in the Washington, D.C. metropolitan area of the United States. The population was 21,655 at the 2000 census, which makes it the largest of three towns in the county.-History:...

, USA; and the Silicone Industry Association of Japan (SIAJ) in Tokyo, Japan. A fourth organization, the Global Silicone Council (GSC) acts as an umbrella structure over the regional organizations. All four are non-profit, having no commercial role; their primary missions are to promote the safety of silicones from a health, safety, and environmental perspective. As the European chemical industry is preparing to implement the Registration, Evaluation and Authorisation of Chemicals (REACH) legislation
Registration, Evaluation and Authorisation of Chemicals
Registration, Evaluation, Authorisation and Restriction of Chemicals is a European Union Regulation of 18 December 2006. REACH addresses the production and use of chemical substances, and their potential impacts on both human health and the environment...

, CES is leading the formation of a consortium of silicones, silanes, and siloxanes producers and importers to facilitate data and cost sharing.

See also

  • Injection molding of liquid silicone rubber
    Injection molding of liquid silicone rubber
    Injection molding of liquid silicone rubber is a process to produce pliable, durable parts in high volume.Liquid silicone rubber is a high purity platinum cured silicone with low compression set, great stability and ability to resist extreme temperatures of heat and cold ideally suitable for...

  • Organosilicon
    Organosilicon
    Organosilicon compounds are organic compounds containing carbon silicon bonds. Organosilicon chemistry is the corresponding science exploring their properties and reactivity.Like carbon, the organically bound silicon is tetravalent and tetrahedral...

  • Silicone grease
    Silicone grease
    Silicone grease is a waterproof grease made by combining a silicone oil with a thickener. Most commonly, the silicone oil is polydimethylsiloxane and the thickener is amorphous fumed silica...

  • Silicone oil
    Silicone oil
    A silicone oil is any polymerized siloxanes with organic side chains. They are formed of alternating silicon-oxygen atoms or siloxane, rather than carbon atoms . Other species attach to the tetravalent silicon atoms, not to the divalent oxygen atoms which are fully committed to forming the...

  • Silicone resin
    Silicone resin
    Silicone resins are a type of silicone material which is formed by branched, cage-like oligosiloxanes with the general formula of RnSiXmOy, where R is a non reactive substituent, usually Me or Ph, and X is a functional group H, OH, Cl or OR...

  • Silicone rubber
    Silicone rubber
    Silicone rubber is an elastomer composed of silicone—itself a polymer—containing silicon together with carbon, hydrogen, and oxygen. Silicone rubbers are widely used in industry, and there are multiple formulations...

  • Siloxane
    Siloxane
    A siloxane is any chemical compound composed of units of the form R2SiO, where R is a hydrogen atom or a hydrocarbon group. They belong to the wider class of organosilicon compounds....

  • Medical grade silicone
    Medical grade silicone
    Medical grade silicones are silicones tested for biocompatibility and are appropriate to be used for medical applications. In the United States, the Food and Drug Administration regulates materials implanted into the body. Medical grade silicones are generally grouped into three categories: non...



External links

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