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Physical & Chemical properties

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Trimethylsilane is a gas at standard temperature and pressure, with melting point of -135.9°C and boiling point of 6.7°C. The requirement to conduct a relative density study was waived because the substance is a gas; a density value of 3.1 kg/m3 at 20°C was calculated for the substance on the basis of molecular weight of 74.2 g/mol and Ideal Gas Laws. The vapour pressure of the substance is expected to be greater than the limit of measurement, i.e. >1E+05 Pa at 20°C, due to the boiling point of the substance <30°C.

The substance is classified as an extremely flammable gas according to Regulation (EC) No. 1272/2008. This is on the basis of a measured Lower Flammability Limit and Upper Flammability Limit of 1.38 (vol%) in a 5 litre chamber and 51.3 (vol%) in a 1 litre chamber respectively, at 25°C and 1013 hPa. It has a measured auto-ignition temperature of 245°C.

On the basis of structural examination, the substance is not considered to be surface active, it is not oxidising and does not have any of the chemical structures that are associated with explosive properties.

In contact with water trimethylsilane reacts slowly (half-life of about 3 days at 24.7°C) to produce trimethylsilanol and hydrogen according to the following equation:

(CH3)3SiH + H2O → (CH3)3SiOH + H2


Trimethylsilane has a predicted log Kow of 2.2 at 20°C. Measurement of the solubility in water of the substance is considered technically not feasible because trimethylsilane is a gas under standard conditions of temperature and pressure, with an expected vapour pressure of >1E+05 Pa.

The silanol hydrolysis product, trimethylsilanol, has the potential to form dimers in solution. The concentration of trimethylsilanol in water may be determined by this condensation reaction rather than by the solubility of trimethylsilanol itself. It has a measured solubility of 995 mg/l at 20°C and a measured log Kow of 1.19 at 20°C and is not surface active. Trimethylsilanol has a measured vapour pressure of 1290 Pa at 20°C and 1900 Pa at 25°C.