Silicone Basics

What is silicone?

Silicones, 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 or hydrogen or both. 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 are of three types: 1. straight chain silicones; 2. cyclic silicones; 3. crosslinked silicones.

Silicone is sometimes mistakenly referred to as silicon. The chemical element silicon is a crystalline metalloid widely used in computers and other electronic equipment. Although silicones contain silicon atoms, they also include carbon, hydrogen, oxygen, and perhaps other kinds of atoms as well, and have physical and chemical properties that are very different from elemental silicon.

Properties:

Silicones exhibit many useful characteristics, including:

Low thermal conductivity

Low chemical reactivity

Low toxicity

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.

Silicone can be developed into rubber sheeting, where it has other properties, such as being FDA compliant. This extends the uses of silicone sheeting to industries that demand hygiene, for example, food and beverage and pharmaceutical.

Uses:

Silicones are used in many products. Electrical (e.g., insulation), electronics (e.g., coatings), household (e.g., sealants for cooking apparatus), automobile (e.g., gaskets), aerospace (e.g., seals), office machines (e.g., keyboard pads), medicine and dentistry (e.g., tooth impression molds), textiles and 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.

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. 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.

Sheet silicone is used to manufacture gaskets used in automotive engines, transmissions, and other applications.

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 and 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 Coatings:

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.

Cookware:

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.

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.

Molds for chocolate, ice, cookies, muffins and various other foods.

Non-stick bakeware and reusable mats used on baking sheets.

Defoaming:

Silicones are used as active compound in defoamers due to their low water solubility and good spreading properties.

Electronics:

Electronic components are sometimes encased 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 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.

Lubricants:

Silicone greases are used for many purposes, such as bicycle chains, airsoft gun parts, and a wide range of other mechanisms. 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-based or other traditional “wet” lubricant.

Medicine:

Silicone is used in microfluidics, seals, gaskets, shrouds, and other applications requiring high biocompatibility. Additionally, the gel form is used in bandages and dressings, breast implants, testicle implants, pectoral implants, contact lenses, and a variety of other medical uses. Scar treatment sheets are often made of medical grade silicone due to its durability and biocompatibility.

Moldmaking:

Two-part silicone systems are used as rubber molds to cast resins, foams, rubber, and low-temperature metals. A silicone mold generally requires little or no mold-release or surface preparation, as most materials do not adhere to silicone.

Personal Care:

Silicones are ingredients widely used in skin care, color cosmetic and hair care applications. Some silicones are excellent conditioners, providing improved compatibility, feel, and softness, and lessening frizz. Silicones are used in reflection-enhancing and color-correcting hair products where they increase shine and glossiness. Silicones are used in shaving products and personal lubricants.

 

 

GT-6250​ Silicone Putty

– GT​ Products©​ 6250​ is an addition cure (platinum catalyzed) system. As such, it can​ be heat​ accelerated​ and is subject to inhibition/poisoning​ by the usual factors which include (but​ are not limited to) sulfur, sulfur compounds and amines.
While​ GT-6250 can​ be mixed with clean​ dry​ hands (use your palms not your fingers) we recommend coating your​ hands with​ a slight amount​ of mineral​ oil​ or petroleum​ jelly.
Typical​ properties: cured 1:1​ at​ room temperature (overnight – 15-24 hrs) and​ 625 psi

  • tensile​ > 190 psi
  • elongation​ > 180%
  • tear​ > 35 pli
  • durometer​ (A) 35