Silicone grease
Silicone grease is a waterproof grease made by combining a silicone oil with a thickener. Most commonly, the silicone oil is polydimethylsiloxane (PDMS) and the thickener is amorphous fumed silica. Using this formulation, silicone grease is a translucent white viscous paste, with exact properties dependent on the type and proportion of the components. More specialized silicone greases are made from fluorinated silicones or, for low temperature applications, PDMS containing some phenyl substituents in place of methyl groups. For food applications, the thickener is calcium stearate. For applications involving highly reactive substances, powdered Teflon is the thickener.
Silicone grease is commonly used for lubricating and preserving rubber parts, such as O-rings. Additionally, silicone grease does not swell or soften the rubber, which can be a problem with hydrocarbon based greases. It functions well as a corrosion-inhibitor and lubricant for purposes that require a thicker lubricant.
Thermal grease often consists of a silicone grease base, along with added thermally conductive fillers. It is used for heat transfer abilities, rather than friction reduction.
Special versions of silicone grease are also used widely by the plumbing industry in faucets and seals, as well as dental equipment. These special versions are formulated using components not known to be an ingestion hazard. Electrical utilities use silicone grease to lubricate separable elbows on lines which must endure high temperatures. Silicone greases generally have an operating temperature range of approximately −40 to 200 °C (−40 to 392 °F) with some high-temperature versions extending that range slightly.
Silicone grease is widely used as a temporary sealant and a lubricant for interconnecting ground glass joints, as is typically used in laboratory glassware. Although silicones are normally assumed to be chemically inert, several historically significant compounds have resulted from unintended reactions with silicones. The first salts of crown ethers (OSi(CH3)2)n (n = 6, 7) were produced by reactions of organolithium and organopotassium compounds with silicone greases or the serendipitous reaction of stannanetriol with silicone grease to afford a cage-like compound having three Sn-O-Si-O-Sn linkages in the molecule.
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