Basic Characteristics of Ordinary Silicone Oil
Nov 7, 2024
Density and volume of silicone oil
The relative density of silicone oil increases with its molar mass or viscosity, and eventually approaches a constant. After the viscosity of dimethyl silicone oil (25 ° C) exceeds 350 mm2 • s-1, its relative density tends to a constant of 0 After partial substitution of 9730 methyl with phenyl to form methyl phenyl silicone oil, its relative density is higher than that of dimethyl silicone oil. The relative density of silicone oil decreases regularly with increasing temperature.
The thermal expansion coefficient of dimethyl silicone oil is larger than that of water and mercury, on the same order of magnitude as mineral oil, and decreases with increasing polymerization degree and viscosity. When the viscosity exceeds 100 mm2 • s1, it tends to a constant value. The thermal expansion coefficient of methylphenyl silicone oil is slightly lower than that of dimethyl silicone oil.
Thermal conductivity and specific heat capacity of silicone oil
The thermal conductivity of silicone oil depends on its molar mass and viscosity. In the dimethyl silicone oil series, thermal conductivity initially increases rapidly with viscosity.
The volatility and vapor pressure of silicone oil
The boiling point of dimethyl silicone oil depends on its viscosity or molar mass. Silicone oil with a viscosity (25 ° C) less than 2 mm2 • s ^ 1 can be distilled at atmospheric pressure and its boiling point can be determined. Silicone oil with a viscosity below 25 mm2- s ^ 1 can be evaporated under reduced pressure, and even higher viscosity silicone oil can be heated to 250 ° C at 67 Pa without boiling.
Low molar mass methylphenyl silicone oils, such as tetramethyltetraphenyltrisiloxane and trimethylpentaphenyltrisiloxane, have very steep vapor pressure curves and low vapor pressure values at room temperature, with the former being 10-6Pa and the latter being 10-8Pa; When used as diffusion pump oil, it can achieve a vacuum degree on the order of 10-8Pa.
Compared to regular engine oil, silicone oil has lower volatility. Except for low viscosity varieties, silicone oils that remove low molar mass siloxanes have almost no volatility. Above a certain temperature, the volatilization is not only due to vapor pressure or evaporation, but also involves thermal oxidation stability.
Flash point and ignition point of silicone oil
Except for varieties with viscosity (25 ° C) below 30 mm2 • s ^ 1, the flash point of dimethyl silicone oil is above 300 ° C, but it no longer continues to burn after being removed from the heat source.
Sound Transmission Characteristics of Silicone Oil
The propagation speed (referred to as sound velocity) and temperature coefficient of sound in dimethyl silicone oil are the same as those in general organic liquids, but the viscosity temperature change of silicone oil is small, so it has certain sound propagation characteristics over a wide temperature range. The speed of sound increases with the viscosity of silicone oil.
Surface tension of silicone oil
The surface tension of silicone oil is very low, such as viscosity (25 ° C) 0 The surface tension of 65 mm2 • s ^ 1 dimethyl silicone oil is 15.9 mN • nT1. As the viscosity of silicone oil increases, the surface tension also increases;
The surface tension of methyl phenyl silicone oil is slightly higher than that of dimethyl silicone oil, and the surface tension increases with the increase of phenyl content. Due to the low surface tension of silicone oil, it is prone to spreading on metal surfaces, resulting in "crawling".
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