Silicone, << SIHL uh kohn, >> is any of a group of synthetic materials. It is unlike anything found in nature. Silicones are a cross between organic materials such as oil, rubber, and plastics; and inorganic materials such as sand, glass, and quartz. Their key material is the element silicon. Except for oxygen, silicon is the most abundant material in the earth’s crust.
Uses.
Silicones, which come in solid, liquid, and gaseous forms, have thousands of uses. Scientists are continually discovering new applications for silicones. As release agents, silicones keep bread from sticking to pans in commercial bakeries. Clean and smokeless, they work better than grease. Silicones also keep tires and other rubber and plastic parts from sticking in the molds. Silicone fluids are used in waxes and polishing agents for automobiles, furniture, and eyeglasses. Fabric and leather that is treated with silicone will not absorb water or water-based products such as ink and tomato juice. Repeated washing or dry cleaning will not remove the silicone. Yet silicone will not stiffen the fabric.
Many silicones are not harmful to the human body. They also are not affected by chemicals in the body. For these reasons, they are used in making artificial human parts, including heart valves, that can be permanently implanted in the body.
Silicone oils and greases serve as permanent lubricants for clocks and ball bearings. Silicone water repellents keep brick and concrete walls dry in the rain. Silicones are also widely used as waterproof sealants around windows and for bathroom and kitchen tiles. Paints made with silicone resins do not blister and peel off at temperatures of 500 °F to 1000 °F (260 °C to 540 °C). In addition, outdoor weathering does not make them lose their gloss and color. Silicone paints are often used on ships.
Silicones are also used as electrical insulating materials. As insulating materials, silicones make hard-working motors, generators, and transformers last longer and work harder than they ever did before.
Silicone rubber does not melt at oven temperatures or become hard and brittle at temperatures as low as -110 °F (-79 °C). It is used to seal oven doors and rocker boxes on aircraft and tank engines. Silicone rubber insulates communications cables on ships and motor coils in diesel-electric locomotives.
Composition.
The amount of heat, weathering, and aging a material can withstand is partly due to the strength of the bonds that hold together the atoms which make up the material. Like sand and glass, silicones have a molecular skeleton of alternating atoms of silicon and oxygen. The bonds between silicon and oxygen atoms are about 11/2 times as strong as those between carbon atoms in organic materials. As a result, silicones are several times more resistant to heat and weathering than are organic materials.
In addition, silicones, unlike sand and glass, have various organic groups attached to the silicon-oxygen skeleton. Together, these structures provide the heat stability, water repellency, lubricating properties, and flexibility required in a number of household and industrial applications.
