Trimethylsilanol (TMS) is an organosilicon compound with the formula (CH₃)₃SiOH. The Si centre bears three methyl groups and one hydroxyl group. It is a colourless volatile liquid.

TMS is a contaminant in the atmospheres of spacecraft, where it arises from the degradation of silicone-based materials. Specifically, it is the volatile product from the hydrolysis of polydimethylsiloxane, which are generally terminated with trimethylsilyl groups:

TMS and related volatile siloxanes are formed by hydrolysis of silicones-based containing materials, which are found in detergents and cosmetic products.

Traces of TMS, together with other volatile siloxanes, are present in biogas and landfill gas, again resulting from the degradation of silicones. As their combustion forms particles of silicates and microcrystalline quartz, which cause abrasion of combustion engine parts, they pose problems for the use of such gases in combustion engines.

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