An open-chain or cyclic polymer containing the repeating unit SiR2O, where R is an alkyl group. Odourless, colourless, insoluble in and unreactive with water, and having high flashpoints, silicones are used in high-temperature lubricants, hydraulic fluids, and varnishes.
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. By varying the -Si-O- chain lengths, side groups, and crosslinking, silicones can be synthesized with a wide variety of properties and compositions. The second largest group of silicone materials is based on silicone resins, which are formed by branched and cage-like oligosiloxanes.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. A true silicone group with a double bond between oxygen and silicon do not exist (see figure), Polysiloxanes are called "silicone" due to early mistaken assumptions about structure.
Safety
Controversy developed during the 1990s around allegations that the silicone gel in breast implants was responsible for several health problems, including autoimmune diseases. A clear consensus has emerged from these independent scientific reviews that, to date, there is no evidence of a causal link between the implantation of silicones and connective tissue disease.
Firestops
Silicone foams have been used in North American as well as the Israeli Dimona nuclear reactor 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. (The Israelis wisely switched to the somewhat more expensive yet much safer "elastomer" version of this product, which avoids most safety concerns associated with the foamed version.) Silicone foam firestops have been the subject of serious controversy and press attention due to lack of proper bounding and smoke development due to the pyrolysis of combustible components within the foam, hydrogen gas escape, shrinkage and cracking. When properly installed, silicone foam firestops can be fabricated for building code compliance.
Sealants in building construction and maintenance
One-part silicone sealants are in common use to seal gaps, joints and crevices in buildings. To make a very smooth silicone seal, apart from masking the edges with tape, if practical, professional caulkers often wet wooden spoons and assorted, hand-crafted wooden tools, which they soak in water with diluted dishsoap.
Similar methods work for urethane caulking, against which silicones compete quite heavily.
The strength and reliability of silicone rubber is widely acknowledged in the construction industry. Automotive body manufacturing plants and paint shops must avoid the presence of all silicones, as a mere hint of its presence in any form can cause severe failures in automotive paints.
In the plumbing and automotive fields, silicone grease is often used as a lubricant. 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 to foul brake pads.
Cooking Applications
Silicone is also impregnated into parchment paper and used as a non-stick material for applications such as baking and steaming.
Silicone rubber is also used to make utensils (notably spatulas) and bakeware.
Electronic Components
Electronic components sometimes are protected from environmental influence by enclosing them in silicone.
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