Introduction of siliconeSilicones, also known as polysiloxanes, are polymers that include any inert, synthetic compound made up of repeating units of siloxane, which is a chain of alternating silicon atoms and oxygen atoms, frequently combined with carbon and/or hydrogen. They are typically heat-resistant and rubber-like, and are used in sealants, adhesives, lubricants, medicine, cooking utensils, and thermal and electrical insulation. Some common forms include silicone oil, silicone grease, silicone rubber, silicone resin, and silicone caulk.
Silicones exhibit many useful characteristics, including:
Low thermal conductivity
Low chemical reactivity
Thermal stability (constancy of properties over a wide temperature range of −100 to 250 °C).
The ability to repel water and form watertight seals.
Does not stick to many substrates, but adheres very well to others, e.g. glass.
Does not support microbiological growth.
Resistance to oxygen, ozone, and ultraviolet (UV) light. 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).
Electrical insulation properties. Because silicone can be formulated to be electrically insulative or conductive, it is suitable for a wide range of electrical applications.
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, making silicone useful for medical applications in which increased aeration is desired. Conversely, silicone rubbers cannot be used where gas-tight seals are necessary.
Silicones are used in many products. Ullmann‘s Encyclopedia of Industrial Chemistry lists the following major categories of application: Electrical (e.g., insulation), electronics (e.g., coatings), household (e.g., sealants for cooking apparatus), automobile (e.g., gaskets), aeroplane (e.g., seals), office machines (e.g., keyboard pads), medicine/dentistry (e.g., teeth impression molds), textiles/paper (e.g., coatings). For these applications, an estimated 400,000 tons of silicones were produced in 1991. Specific examples, both large and small are presented below.
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. It is also used as DOT 5 brake fluid.
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 airbags; the high strength of silicone rubber makes it an optimal adhesive/sealant for high impact airbags. Recent technological advancements allow convenient use of silicone in combination with thermoplastics to provide improvements in scratch and mar resistance and lowered coefficient of friction.
Silicone films can be applied to such silica-based substrates as glass 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.
Soup ladle and pasta ladle made of silicone.
A silicone food steamer to be placed inside a pot of boiling water.
Ice cube trays made of silicone.