Silicon , also known as polysiloxanes , is a polymer containing an inert, synthetic compound consisting of a recurrent siloxane unit, which is a chain of alternating silicon atoms and oxygen atoms, combined with carbon, hydrogen, and sometimes other elements. They are usually heat resistant and either liquid or rubber-like, and are used in sealants, adhesives, lubricants, pharmaceuticals, cooking utensils, and thermal and electrical insulation. Some common forms include silicone oil, silicone oil, silicone rubber, silicone resin, and sleeping silicone.
Video Silicone
Chemistry
More properly called polymerized siloxanes or polysiloxanes, silicones consist of an inorganic silicon-oxygen backbone chain (? -Si-O-Si-O-Si-O-?) With an organic side group attached to a silicon atom. These silicon atoms are tetravalent. Thus, silicon is a polymer built from inorganic-organic monomers. Silicon generally has the chemical formula [R 2 SiO] n , where R is an organic group such as alkyl (methyl, ethyl) or phenyl group.
In some cases, organic side groups can be used to connect two or more of these S-O-backbones together. By varying the length of the -Si-O chain, side groups, and crosslinking, silicon can be synthesized with various properties and compositions. They can vary the consistency from liquid to gel to rubber to hard plastic. The most common siloxanes are linear polydimethylsiloxane (PDMS), silicone oils. The second largest group of silicon materials is based on silicon resins, which are formed by branched oligosiloxanes and are similar to cages.
Terminology and history
FS Kipping invented the word silicon in 1901 to describe polydiphenylsiloxane by its formula analogue, Ph 2 SiO (Ph stands for phenyl, C 6 H < sub> 5 ), with the ketone benzophenone formula, Ph 2 CO (originally silicoketone ). Kipping is well aware that polydiphenylsiloxane is polymeric while benzophenone is a monomer and notes that Ph 2 SiO and Ph 2 CO have very different chemistry. The discovery of the structural difference between the Kippings' molecule and the ketone means that silicon is no longer an appropriate term (although it remains in common usage) and that the term siloxanes is correct according to modern chemical nomenclature.
Silicon is sometimes mistakenly referred to as silicon. The chemical element of silicon is a crystalline metalloid that is widely used in computers and other electronic equipment. Although silicon contains silicon atoms, they also include carbon, hydrogen, oxygen, and possibly other types of atoms, and have very different physical and chemical properties than elemental silicon.
Molecules containing silicon-oxygen double bonds do exist and are called silanons but they are highly reactive. Nevertheless, silanon is important as an intermediary in the gas phase processes such as chemical vapor deposition in the production of microelectronics, and in the formation of ceramics by combustion.
Synthesis
The most common are materials based on polydimethylsiloxane, derived from the hydrolysis of dimethyichichlorosilane. This dichloride reacts with water as follows:
Polymerization usually produces linear chains that are limited by Si-Cl or Si-OH (silanol) groups. Under different conditions the polymer is cyclic, not a chain.
For consumer applications such as caulks silyl acetate are used instead of silyl chlorides. Acetate hydrolysis produces less harmful acetic acid (an acid found in vinegar) as the reaction product of a much slower preservation process. This chemical is used in many consumer applications, such as sleeping silicone and adhesives.
Branches or crosslinks in the polymer chain can be introduced using the precursors of organosilicone with fewer alkyl groups, such as methyltrichlorosilane and methyltrimethoxysilane. Ideally, each molecule of the compound becomes a branch point. This process can be used to produce hard silicon resins. Similarly, precursors with three methyl groups can be used to limit the molecular weight, since each of these molecules has only one reactive site and forms the end of the siloxane chain.
Burning
When silicon is burned in air or oxygen, it forms solid silica (silicon dioxide) (SiO 2 ) as white powder, charcoal, and various gases. Easy-spread powders are sometimes called silica fumes.
Maps Silicone
Properties
Silicon shows many useful characteristics, including:
- Low thermal conductivity
- Low chemical reactivity
- Low toxicity
- Thermal stability (firmness of properties over a wide temperature range -100 to 250 Ã, Â ° C ).
- The ability to resist water and form a watertight seal.
- Not sticking to many media, but very attached to others, e.g. glass.
- Does not support microbiological growth.
- Resistant to oxygen, ozone, and ultraviolet (UV) rays. This property has led to widespread use of silicon in the construction industry (eg coatings, fire protection, glass seals) and the automotive industry (external gaskets, external trim).
- Properties of electrical insulation. Because silicon can be formulated to be electrically insulative or conductive, it is suitable for many electrical applications.
- High gas permeability: at room temperature (25 Ã, Â ° C), the permeability of silicone rubber for gases such as oxygen is about 400 times that of butyl rubber, making silicon useful for medical applications where aeration enhancement is desired. In contrast, silicone rubbers can not be used where a gas-tight seal is required.
Silicon can be developed into rubber sheeting, where it has other properties, such as FDA compliance. This expands the use of silicone sheets for industries that demand cleanliness, for example, food and beverages and pharmaceuticals.
Usage
Silicon is used in many products. Ullmann's Encyclopedia of Industrial Chemistry lists the following major categories of applications: Electrical (eg, insulation), electronics (eg, coatings), households (eg, sealants for cooking utensils), automobiles (eg, gaskets), aircraft (eg, seals) , office machines (eg, keyboard pads), drugs and dentistry (eg dental molds), textiles and paper (eg, coatings). For this application, an estimated 400,000 tons of silicon was produced in 1991. Specific examples, both large and small are presented below.
Automotive
In the automotive field, silicone lubricants are commonly used as lubricants for brake components because they are stable at high temperatures, insoluble in water, and much smaller than other lubricants. It is also used as a DOT 5 brake fluid.
Automotive spark plug wires are insulated by several layers of silicone to prevent sparks from jumping to adjacent cables, causing shootouts. Silicone tubes are sometimes used in automotive intake systems (especially for machines with forced induction).
Silicon sheets are used to produce gaskets used in automotive engines, transmissions, and other applications.
Manufacturers of automotive bodies and paint shops avoid silicones, because they can cause "fish eyes", small craters and circular at the end.
In addition, silicone compounds such as silicone rubber are used as coatings and sealants for air bags; the high strength of silicone rubber makes it an optimal adhesive and sealant for high impact airbags. Recent technological advances allow the use of comfortable silicon in combination with thermoplastics to provide an early increase and marriage resistance and decrease the coefficient of friction.
Coating
Silicone films can be applied to silica-based substrates such as glass to form a covalently bonded hydrophobic coating.
Many fabrics can be coated or impregnated with silicone to form strong and waterproof composites such as silnylon.
Cookware
- As a non-toxic and non-toxic material, silicone can be used when contact with food is required. Silicon becomes an important product in the cookware industry, especially bakeware equipment and kitchenware.
- Silicon is used as an insulator in heat resistant potholders and similar items; however, the conductivity is hotter than the less dense fiber-based products. Silicone oven gloves are able to withstand temperatures up to 260 ° C (500 ° F), allowing to reach boiling water.
- Prints for chocolate, ice, cakes, muffins, and various other foods.
- Non-stick bakeware and reusable base on baking sheet.
- Other products such as steamers, boilers or hunters, cookware lids, pots, trivets, and kitchen mats.
Foam removal
Silicon is used as an active compound in the foam prevention because of its low water solubility and good dispersion properties.
Dry cleaning
Liquid silicon can be used as a dry cleaning solvent, providing an alternative to the traditional chlorine perchloroethylene (mop) solvent. The use of silicone in dry cleaning reduces the environmental impact of highly polluting industries.
Electronics
Electronic components are sometimes encased in silicon to improve stability against mechanical and electrical shocks, radiation and vibration, a process called "pot".
Silicon is used where high durability and performance are requested components in harsh conditions, such as in space (satellite technology). They are selected via polyurethane or epoxy encapsulation when a wide operating temperature range is required (-65 to 315 ° C). Silicon also has the advantage of exothermic heat rise during healing, low toxicity, good electrical properties and high purity.
However, the use of silicon in electronics is not without problems. Silicon is relatively expensive and can be attacked by solvent. Silicones easily migrate as liquids or vapors to other components.
Silicone contact contamination of the electrical switch may cause failure by causing increased contact resistance, often late in the life of the contact, either after the test is complete. The use of silicone-based spray products in electronic devices during maintenance or repair may lead to failure in the future.
Firestops
Silicone foams have been used in North American buildings in an attempt to open openings inside fire-proof wall and floor assemblies to prevent the spread of fire and smoke from one room to another. When installed properly, silicone-foam firestops can be made for building code compliance. The advantages include high flexibility and dielectric strength. Losses include combustible properties (difficult to extinguish) and significant smoke developments.
Silicon-foam firestops have been the subject of controversy and the press attention due to the development of smoke from pyrolysis of combustible components in foam, hydrogen gas release, shrinkage and cracking. These problems have caused events that can be reported among license holders (nuclear power plant operators) of the Nuclear Regulatory Commission (NRC).
Silicone firestop is also used in aircraft.
Lubricant
Silicone grease is used for many purposes, such as bicycle chains, airsoft gun parts, and various other mechanisms. Typically, a dry-regulated lubricant is dispatched with a solvent carrier to penetrate the mechanism. The solvent then evaporates, leaving a translucent film that lubricates but does not attract dirt and sand as much as traditional oil or "wet" oils.
Silicone personal lubricants are also available for use in medical procedures or sexual activity. See below.
Medicine
Silicon is used in microfluidics, seals, gaskets, shrouds, and other applications that require high biocompatibility. In addition, gel forms are used in bandages and dressings, breast implants, testicle implants, pectoral implants, contact lenses, and various other medical uses.
Thin treatment sheets are often made from medical grade silicone because of their durability and biocompatibility. Polydimethylsiloxane is often used for this purpose, since its specific cross yields soft and flexible silicone with high durability and tack.
Polydimethylsiloxane (PDMS) has been used as a hydrophobic block of amphiphilic synthetic block copolymers used to form a vesicle membrane of polymersomes.
Moldmaking
The two-piece silicon system is used as a rubber mold to remove resins, foams, rubber, and low temperature alloys. Silicone molds generally require little or no mold preparation or surface preparation, since most materials do not stick to silicon. For experimental use, regular one-piece silicone can be used to make molds or molds. If necessary, common cooking oil or jelly petroleum may be used on the mating surface as a mold release agent.
Cooking molds used as bakeware do not require coating with cooking oil, allowing baked goods to be more easily removed from the mold after cooking.
Ophthalmology
Silicone has many applications such as silicone oil which is used to replace vitreous after vitrectomy, silicone intraocular lens after cataract extraction, silicone tube to maintain nasolacrimal passage following dacrycystorhinostomy, canisicular stent for stenosis canaluliuli, punctal plugs for faint occlusion on dry eye, silicone rubber and ribbon as an external tamponade in the retinal detachment trional, and an anterior break located in the retinal rhegmatogenous retest.
Personal care
Silicon is a material widely used in skin care, cosmetic colors and hair care applications. Some silicon, especially functional amine amodimethicones, are excellent conditioners, providing better compatibility, taste, and softness, and reduces wrinkles. Phenyltrimethicones, in other silicone families, are used in hair enhancing products of reflection and color-correction, in which they enhance luster and sparkle (and possibly subtle color change effects). Phenyltrimethicones, unlike amodimethicones, have an index of refraction (usually 1.46) close to human hair (1.54). However, if included in the same formulation, amodimethicone and phenyltrimethicone interact and dilute each other, making it difficult to achieve high luster and excellent conditioning in the same product.
Silicone rubber is commonly used on baby bottle nipples (dots) for cleanliness, aesthetic appearance, and low extraction content.
Silicon is used in personal shavers and lubricants.
Pipes and building construction
The strength and reliability of silicone rubber are widely recognized in the construction industry. Sealant and one-piece silicone caulks are commonly used to seal gaps, joints and cracks in buildings. One part of silicon heals by absorbing atmospheric moisture, which simplifies installation. In pipes, silicone oil is usually applied to O-rings in taps and brass valves, preventing lime from sticking to metals.
Toys and hobbies
Ridiculous Dempul and similar materials consist of silicone dimethyl siloxane, polydimethylsiloxane, and decamethyl cyclopentasiloxane, with other ingredients. This substance is noted for its unusual characteristics, for example, it bounces, but breaks when given a sharp blow; it can also flow like a liquid and will form a pool of water given enough time.
Silicone "rubber bands" are a durable popular replacement replacement for real rubber bands in 2013 "rubber band loom" toys for two to fourfold (in 2014). Silicone ribbon is also present in the size of the bracelet that can be made with name or message. Large silicone ribbons are also sold as utility binders.
Formerol is silicone rubber (marketed as Sugru) which is used as art and craft material, because its plasticity allows to be printed by hand like modeling clay. It hardens at room temperature and it is the adhesive for various substances including glass and aluminum.
In aquarium manufacturing, manufacturers now generally use 100% silicone sealants to join the glass plate. Glass joints made with silicone sealants can withstand enormous pressure, making the original construction methods of angle and putty iron become obsolete. This same silicon is used to make the hinges on the aquarium cover or for minor repairs. However, not all commercial silicon is safe for the manufacture of aquariums, as well as silicon used for the manufacture of acrylic aquariums because silicon does not have long-term adhesion on plastics.
Sex Toys and Lubricants
Silicon is the material of choice for soft sex toys, due to softness, durability, hygiene, non-degradation by petroleum-based lubricants, and lack of phthalates, chemicals suspected of having carcinogenic and mutagenic effects on skin and mucous membranes.
Production and marketing
Global demand for silicon reached US $ 12.5 billion in 2008, about 4% from a year earlier. This continued a similar growth in subsequent years to reach $ 13.5 billion in 2010. The annual growth is expected to be driven by wider applications, new product introductions and increased awareness of using more environmentally friendly materials.
The leading global producer of silicone base materials belongs to three regional organizations: the European Silicon Center (CES) in Brussels, Belgium; Board of Health and Environmental Safety (SEHSC) in Herndon, Virginia, USA; and the Japan Silicon Industry Association (SIAJ) in Tokyo, Japan. Dow Corning Silicones, Evonik Industries, Moment Performance Materials, Milliken and Company (SiVance Specialty Silicones), Shin-Etsu Silicones, Wacker Chemie, Bluestar Silicones, JNC Corporation, Asahikasei Silicone Wacker, and Dow Corning Toray represent the collective membership of these organizations. The fourth organization, the Global Silicone Council (GSC) acts as an umbrella structure of regional organizations. All four are nonprofits, have no commercial role; their primary mission is to promote the safety of silicon from a health, safety and environmental perspective. As the European chemical industry is preparing to implement the REACH Registration, Evaluation and Authorization Act (CES), CES leads the formation of a consortium of silica, silane, and siloxanes producers and importers to facilitate data and cost sharing.
Security and environmental considerations
No "marked harmful effects on organisms in the environment" have been noted for silicon. Because they are widely used, they are pervasive. They are easy to break down, a process that is accelerated by various catalysts, including clay. Cyclic silicon has been shown to involve the occurrence of silanol during biodegradation in mammals. The silanadiol and silanetriol produced are capable of inhibiting hydrolytic enzymes such as thermolysin, acetycholinesterase, but the doses required for inhibition are by orders of magnitude higher than those resulting from the accumulated exposure of consumer products containing cyclomethicone.
Approximately 200 ° C in an oxygen-containing atmosphere, PDMS releases formaldehyde trace but less than other common ingredients such as polyethylene, and with 200 ° C (392 ° F) Silicon (& lt; 3Ã,Âμg CH 2 O/(gÃ, Â · hr) for high consistency silicone rubber up to 48Ã,Âμg CH 2 O/(gÃ, Â · hr)) was found to be superior to mineral oil and plastics (~ 400Ã, Ã,Âμg CH 2 O/(gÃ, Â · hr)) at about 200 Ã, Â ° C (392Ã, Â ° F), with 250 Ã, Â ° C (482Ã, Â ° F) Excessive amounts of formaldehyde have been found to be produced for all silicon (1200Ã,Âμg CH 2 O/(gÃ, Â · hr) up to 4600Ã,Âμg CH 2 O/(gÃ, Â · hr)).
See also
- Injection molding of liquid silicone rubber
References
External links
- Silicon Polymer Science (Silicon On-line Science, EuropÃÆ'Â © Ã © en des Silicones - CES)
Source of the article : Wikipedia
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