Silicone 65827 223610174 2008-07-04T21:38:15Z John Nixon 213224 spelling {{Distinguish2|the element [[silicon]]}} {{Unreferenced|date=June 2007}} {{Mergefrom|silicone rubber|date=June 2007}} '''Silicones''' are largely inert compounds with a wide variety of forms and uses. Typically heat-resistant, nonstick, and [[rubber]]like, they are frequently used in [[cookware]], [[medicine|medical applications]], [[sealant]]s, [[lubricant]]s, and [[insulation]]. Silicones are [[polymers]] that include [[silicon]] together with [[carbon]], [[hydrogen]], [[oxygen]], and sometimes other [[chemical element]]s. [[Image:Nelson clk 6 foot head of water.jpg|thumb|right|1/2" thickness of silicone [[firestop]] sealant being successfully tested to hold a 6-foot head of water to prove water-resistance in new construction applications.]] ==Properties== Some of the most useful properties of silicone include: # Thermal stability (constancy of properties over a wide operating range of −100 to 250 °C). # Though not [[lipophilic]], the ability to repel water and form watertight seals. # Excellent resistance to oxygen, ozone and sunlight. # Flexibility. # Good electrical insulation. # Nonstick. # Low chemical reactivity. # Low toxicity. # High gas permeability: at room temperature (25 °C) the permeability of silicone rubber for gases like oxygen is approximately 400 times that of butyl rubber, making silicone useful for medical applications (though precluding it from applications where gas-tight seals are necessary). ==Technical details== {{technical}} More precisely called [[polymer]]ized [[siloxane]]s or polysiloxanes, silicones are mixed [[Inorganic compound|inorganic]]-[[Organic compound|organic]] [[polymer]]s with the chemical formula [R<sub>2</sub>SiO]<sub>n</sub>, where [[functional group|R]] = organic groups such as [[methyl]], [[ethyl]], and [[phenyl]]. These materials consist of an inorganic [[silicon]]-[[oxygen]] 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 [[Cross-link|crosslinking]], 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]] (PDMS), a [[silicone oil]]. The second largest group of silicone materials is based on [[silicone resin]]s, which are formed by branched and cage-like oligosiloxanes. ===Synthesis=== Silicones are synthesized from [[chlorosilane]]s, [[tetraethoxysilane]], and related compounds. In the case of PDMS, the starting material is dimethyl[[chlorosilane]], which reacts with [[water]] as follows: :n [Si(CH<sub>3</sub>)<sub>2</sub>Cl<sub>2</sub>] + n [H<sub>2</sub>O] → [Si(CH<sub>3</sub>)<sub>2</sub>O]<sub>n</sub> + 2n HCl During [[polymerization]], this reaction evolves potentially hazardous [[hydrogen chloride]] gas. For medical uses, a process was developed where the chlorine atoms in the silane precursor were replaced with acetate groups, so that the reaction product of the final curing process is nontoxic [[acetic acid]] (vinegar). As a side effect, the curing process is also much slower in this case. This is the chemistry used in many consumer applications, such as silicone [[caulk]] and [[adhesive]]s. Silane precursors with more acid-forming groups and fewer methyl groups, such as methyltrichlorosilane, can be used to introduce [[Branching (chemistry)|branches]] or [[cross-link]]s in the polymer chain. Ideally, each molecule of such a compound becomes a branch point. This can be used to produce hard [[silicone resin]]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 made with [[tetraethoxysilane]], which reacts in a more mild and controllable manner than chlorosilanes. ===Chemical terminology=== Silicone is often mistakenly referred to as "silicon." Although silicones contain [[silicon]] atoms, they are not made up exclusively of silicon, and have completely different physical characteristics from elemental silicon. The word "silicone" is derived from ''[[ketone]]''. Dimethylsilicone and dimethyl ketone (a.k.a. [[acetone]]) have analogous formulas, thus it was surmised (incorrectly) that they have analogous structures. The same terminology is used for compounds such as [[silane]] (an analogue of [[methane]]). A true ''silicone group'' with a double bond between oxygen and silicon (see figure) does not exist in nature; chemists find that the silicon atom forms a single bond with each of two oxygen atoms, rather than a double bond to a single atom. Polysiloxanes are called "silicone" due to early mistaken assumptions about their structure. == Uses == ===Aquarium joints=== Aquarium manufacturers have used silicone sealant exclusively from its inception in order to join glass plates, making aquariums of every size and shape. Glass joints made with silicone sealant can withstand hundreds of metric tons of pressure, making obsolete the original aquarium construction method using angle-iron and putty. ===Automotive=== In the automotive field, silicone grease is typically used as a lubricant for [[brake]] 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 often insulated by multiple layers of silicone to prevent sparks from jumping to adjacent wires, causing misfires. The insulation also minimizes [[RFI]], which can interfere with an engine management computer. Silicone tubing is sometimes used in automotive intake systems (especially for engines with [[forced-induction]]) . Sheet silicone is used to manufacture [[gasket#Sheet gaskets|gasket]]s used in [[automotive engine]]s, [[transmission (mechanics)#Automotive basics|transmission]]s and other applications. Automotive body manufacturing plants and paint shops must avoid the presence of all silicones, as they may cause "fish eyes," small, circular craters that appear in the finish. ===Coatings=== Silicone films can be applied to silica-based substrates like [[glass]] to form a [[covalently]] bonded [[hydrophobic]] coating. ===Cookware=== Silicone is becoming an important product in the cookware industry, particularly [[bakeware]] and kitchen utensils. It is also used as an insulator in heat resistant potholders and similar, however it is more conductive of heat than the less dense fiber-based ones. Silicone oven mitts are able to withstand temperatures up to 675°F (357°C), and allow reaching into boiling water.[http://www.wisegeek.com/what-are-silicone-oven-mitts.htm] ===Dry cleaning=== Liquid silicone can be used as a [[dry cleaning]] [[solvent]]. Touted as an "environmentally friendly" alternative to the traditional [[perchloroethylene]] (or perc) solvent, the [[siloxane|decamethylpentacyclosiloxane]] (D5) process has been patented by the company [[GreenEarth Cleaning]]. The solvent degrades into [[silica]] and trace amounts of water and [[CO2]], and waste produced from the D5 drycleaning process is nontoxic and nonhazardous. This significantly reduces the environmental impact of a typically high-polluting industry. Additionally, liquid silicone is chemically inert, meaning it does not react with fabrics or dyes during the cleaning process. This reduces the amount of fading and shrinking that most dry-cleaned garments experience. ===Electronic=== Electronic components are sometimes protected by [[resin casting|enclosing]] them in silicone to increase stability against mechanical and electrical shock, radiation and vibration. This is often called "potting". Silicones are used when durability and high performance are demanded of components under hard conditions, as in space (satellite technology). They are selected over [[polyurethane]] or [[epoxy]] encapsulation when a wide operating temperature 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.<ref>See [[Resin casting]] for how silicones can be dispensed in circuit board production.</ref> 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.<ref>See chapter 16.4.1 of Electrical Contacts: Principles and Applications By Paul G. Slade (image available online via GoogleBooks). Also, "A Comparison for the Effects of Various Forms of Silicon Contamination on Contact Performance" by Witter, G. (Published in "Components, Hybrids, and Manufacturing Technology, IEEE Transactions on" Mar 1979).</ref> Use of silicone-based spray products in electronic devices during maintenance or repairs can cause later failures. ===Firestops=== Silicone foams have been used in North American buildings in an attempt to [[firestop]] openings within fire-resistance-rated wall and floor assemblies to prevent the spread of flames and smoke from one room to another. 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]] gas escape, shrinkage and cracking. These problems have been exposed by [[whistleblower]] [[Gerald W. Brown]] and have led to a large number or reportable events among licensees (operators of [[nuclear power plant]]s) of the [[Nuclear Regulatory Commission]] (NRC). When properly installed, silicone-foam firestops can be fabricated for building code compliance. Advantages include flexibility and high [[dielectric]] strength. Disadvantages include combustibility (hard to extinguish) and significant smoke development. === Lubricants === Silicone [[grease (lubricant)|grease]]s are used for many purposes, such as bicycle chains. A dry-set lubricant is delivered with a solvent carrier to penetrate the chain. The solvent evaporates, leaving a clear film that lubricates but does not attract dirt and grit as much as a traditional "wet" lubricant. Silicone spray is one lubricant well suited for a [[Rubik's Cube]]. ===Medicine=== Silicone, particularly the gel form, is used in [[bandage]]s and dressings, in [[Breast implant#Silicone gel implants|breast implants]] and a variety of other medical uses. ===Moldmaking=== Two-part silicone systems are used to create rubber molds which can be used for production casting of resins, foams, rubber and low-temp alloys. A mold made of silicone generally requires little or no mold release or surface preparation as most materials do not adhere to moldmaking silicone. For experimental uses, ordinary one-part silicone can also be used, either to make molds, or to mold into shapes. Common vegetable cooking oils and petroleum jelly can be used on mating surfaces as a mold release agent. [http://www.myheap.com/book/chapter-07/siliconecaulkmolds.php Silicone Caulk Molds] [http://www.fiberlay.com/howto/silicone.pdf RTV SILICONE RUBBER MOLD] ===Personal care=== Silicones are ingredients in some leave-in [[hair conditioner]] products. These lessen [[frizz]] by using silicone's water resistance to prevent humidity from entering a dry hair shaft. Silicones are also used in some [[shaving]] products <ref>[http://www.shave.com/site/docs/products_kos.stm?sid=SEMOzcZBZnAAAHFzRPs]</ref> and [[personal lubricants]]. [[Menstrual cup]]s are often made of silicone for its durability and reusability. Silicone is also material of choice for soft [[sex toys]], due to its durability, cleanability and lack of [[phthalates]], chemicals suspected of having carcinogenic and mutagenic effects on the skin and mucus membranes.<ref>[http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1474699] W.M. Kluwe, "Carcinogenic potential of phthalic acid esters and related compounds: structure-activity relationships", ''Environmental Health Perspectives'', Vol. 65: pp. 271–278 (March 1986).</ref><ref>[http://www3.interscience.wiley.com/cgi-bin/abstract/69504565/ABSTRACT?CRETRY=1&SRETRY=0] Norbert H. Kleinsasser, Ernst R. Kastenbauer, Herbert Weissacher, Ruth K. Muenzenrieder, Ulrich A. Harréus, "Phthalates demonstrate genotoxicity on human mucosa of the upper aerodigestive tract", ''Environmental and Molecular Mutagenesis'' Vol. 35, No. 1, pp. 9-12 (2000)</ref><ref>[http://links.jstor.org/sici?sici=0091-6765%28198211%2945%3C103%3AAOTMOP%3E2.0.CO%3B2-U&size=LARGE&origin=JSTOR-enlargePage] Walter J. Kozumbo, Rosanna Kroll, Robert J. Rubin, "Assessment of the Mutagenicity of Phthalate Esters", ''Environmental Health Perspectives'', Vol. 45, pp. 103-109 (Nov. 1982)</ref> One review of the health risks of phthalates advocated moving away from medical devices containing phthalates because of their toxicity.<ref>[http://www3.interscience.wiley.com/cgi-bin/abstract/76505754/ABSTRACT] Joel A. Tickner, Ted Schettler, Tee Guidotti, Michael McCally, Mark Rossi "Health risks posed by use of Di-2-ethylhexyl phthalate (DEHP) in PVC medical devices: A critical review", ''American Journal of Industrial Medicine'' Vol. 39, No. 1, pp. 100-111 (2001)</ref> ===Plumbing and building construction=== The strength and reliability of [[silicone rubber]] is widely acknowledged in the construction industry. One-part silicone [[sealant]]s and [[caulk]]s 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 faucets and valves. Whist the film is extant it prevents lime from sticking to the brasswork. ===Toys=== Silicone balls have become a [[juggling|juggler]]'s favorite due to the high bounce back, and are used as a response system in many low response yo-yos.{{Fact|date=April 2008}} ===Versatile applications=== <gallery> Image:Caulking.jpg|Silicone caulk can be used as a basic sealant against water and air penetration. Image:PDMS.png|Chemical structure of polydimethylsiloxane (PDMS). Image:Silicone.png|A hypothetical silicone group. Such species do not exist, see text. Image:Sl_silicone_pipes.jpg|Self-leveling silicone [[firestop]] [[system]] used around [[copper]] [[pipe (material)|pipe]] through-penetrations in a two-hour [[Fire-resistance rating|fire-resistance rated]] [[concrete]] floor assembly. Image:Self_level_silicone.jpg|Self-levelling silicone [[firestop]] installation in mechanical service penetration in [[Fire-resistance rating|2 hour rated]] [[concrete]] floor. Image:Silicone_foam_sakno1.jpg|Faulty Sakno Silicone Foam [[Firestop]] Installation in [[Calgary]] Sewage Treatment Plant in the 1980s, to seal opening above a [[fire door]] in a cast [[concrete]] [[fire]] separation. Image:Foamfixer.jpg|Silicone "foamfixer" pump used to apply silicone [[foam]] [[firestop]] materials. Image:Kieselsaeure380m2prog.jpg|[[Silicon dioxide]] (silica) used in the manufacture of all silicones. This is what remains when one burns silicone; burning silicone caulking or foam produces silica (as well as char) as a white powder &ndash; silica fume. </gallery> ==Silicone Industry Trade Organizations== The leading global manufacturers of silicone base materials belong to three regional organizations: the [http://www.silicones.eu European Silicone Center(CES)] in Brussels, Belgium; the [http://www.sehsc.com Silicone Environment Health and Safety Council(SEHSC)] in Washington, USA; and the [http://www.siaj.jp Silicone Industry Association of Japan (SIAJ)] in Tokyo, Japan. A fourth organization, the [http://www.globalsilicones.org Global Silicone Council (GSC)] acts as an umbrella structure over the regional organizations. All four are nonprofit making and have no commercial role. Their primary mission is to promote the safety of silicones from a health, safety and environmental perspective. As the European chemical industry is getting prepared to implement the [[Registration, Evaluation and Authorisation of Chemicals| REACH legislation]], CES is leading the formation of a consortium<ref>[http://reach.silicones.eu REACH consortium]</ref> of silicones, silanes and siloxanes producers and importers to facilitate data and cost sharing. ==See also== <div style="-moz-column-count:3; column-count:3;"> * [[Gerald W. Brown]] * [[Breast implant]] * [[Breast prosthesis]] * [[Firestop]] * [[Sealant]] * [[Injection molding of liquid silicone rubber]] * [[Negev Nuclear Research Center]] * [[Neuticles]] (Animal testicular implants) * [[Nuclear Reactor]] * [[Nuclear Regulatory Commission]] * [[Parchment]] * [[Dry cleaning]] * [[Dental dam]] </div> ==References== <references/> == External links == {{commons|Category:Silicones|Silicones}} {{commons|Category:Caulking|Caulking}} {{Wiktionary}} * [http://www.ontla.on.ca/web/committee-proceedings/committee_transcripts_details.do?locale=en&Date=1997-10-27&ParlCommID=828&BillID=&Business=Hydro+Stakeholders Proceedings Of The Select Committee On Ontario Hydro Nuclear Affairs] * [http://www.nirs.org/reactorwatch/mox/nirsmcguirecatawbacontentions.htm NIRS Reactorwatch] * [http://www.ccnr.org/nucaware_foam_pr.html ccnr.org] Representative [[Ed Markey]]'s Statements concerning flammable firestops * [http://www.nrc.gov/reading-rm/doc-collections/gen-comm/info-notices/1988/in88056.html USNRC Information Notice 88-56] * [http://www.elmhurst.edu/~chm/vchembook/404silicone.html Silicone Polymers] (Virtual Chembook, Elmhurst College) * [http://www.silicones-science.eu/ Science of Silicone Polymers] (Silicone Science On-line, Centre Européen des Silicones - CES) * [http://www.dowcorning.com/content/sitech/sitechbasics/default.asp Silicon Chemistry] (Silicon Chemistry Basics, Dow Corning) * [http://wiki.diyfaq.org.uk/index.php?title=Silicone_Sealant Types of silicone] [[Category:Adhesives]] [[Category:Cosmetic chemicals]] [[Category:Lubricants]] [[Category:Organosilicon compounds]] [[Category:Silicones|*]] [[ar:سيليكون]] [[bg:Силикон]] [[ca:Silicona]] [[cs:Silikon]] [[da:Silikone]] [[de:Silikone]] [[es:Silicona]] [[fr:Silicone]] [[ko:실리콘 (중합체)]] [[id:Silikone]] [[it:Siliconi]] [[he:סיליקון (תרכובת)]] [[nl:Silicone]] [[ja:シリコーン]] [[no:Silikon]] [[pl:Silikony]] [[pt:Silicone]] [[ru:Силиконы]] [[sr:Силикон]] [[fi:Silikoni]] [[sv:Silikon]] [[tr:Silikon]] [[zh:矽氧樹脂]]