Sulfur hexafluoride molecular formula SF6, relative molecular weight is 146.06, room temperature and pressure for colorless, tasteless, non-toxic, non-corrosive, non-flammable, non-explosive gas, density is about 5 times that of air, standard state density is 6.0886kg/ m3. It is liquid at low temperatures and under pressure and turns white solid when frozen. The sublimation temperature was -63.9℃, the melting point was -50.8℃, the critical temperature was 45.55℃, and the critical pressure was 3.759MPa.

Temperature of liquefied sulfur hexafluoride: The liquefaction temperature of sulfur hexafluoride is -62℃ at one atmosphere pressure (i.e. 0.1mpa); Under 1.2MPa pressure, the liquefaction temperature was 0℃. Generally, the sulfur hexafluoride gas pressure into the circuit breaker is 0.35 ~ 0.65mpa (determined by the specific ambient temperature when aerating), and its liquefaction temperature is -40℃.

The electric strength of sulfur hexafluoride is about 2.5 times of air, and the arc extinguishing ability is more than 100 times of air. Therefore, in the category of ultra-high voltage and ultra-high voltage, it has completely replaced insulating oil and compressed air and become the only arc extinguishing medium of circuit breaker.

The critical temperature is the maximum temperature at which the gas can be converted from sulfur hexafluoride to liquefied sulfur hexafluoride, and the critical pressure is the pressure at which the liquefaction occurs. Sulfur hexafluoride remains a gaseous state only when the temperature is above 45 degrees, and it has the potential to liquefy sulfur hexafluoride under normal conditions of use, so sulfur hexafluoride cannot be used at low temperatures and too low pressures.