Sulfur hexafluoride SF6 physical properties
Sulfur hexafluoride SF6 is a colorless, odorless, non-toxic, non-flammable inert gas with a molecular weight of 146.07 and a density of 6.1kg/m3 at 20°C and 0.1 MPa, which is about 5 times the density of air. Sulfur hexafluoride SF6 is gaseous at room temperature and pressure, with a critical temperature of 45.6°C and a triple point temperature of -50.8°C. The sublimation point temperature of sulfur hexafluoride at normal pressure is -63.8°C. The molecular structure of sulfur hexafluoride is octahedral, with a small bonding distance and high bonding energy, so it is very stable. When the temperature does not exceed 180°C, its compatibility with electrical structural materials is similar to that of nitrogen.
Sulfur hexafluoride SF6 chemical properties
It is an inert gas at room temperature. It generally does not react with other materials.
Sulfur hexafluoride SF6 electrical properties
It has excellent insulation performance and unique thermal and electrical properties. SF6 gas is an electronegative gas. Its molecules and atoms have a strong ability to absorb free electrons. It can absorb a large number of free electrons in the arc gap to generate negative ions. The movement of negative ions is much slower than that of free electrons. It is easy to recombine with positive ions to form neutral molecules and atoms, which greatly accelerates the recovery of the arc gap dielectric strength when the current passes through zero.
Sulfur hexafluoride SF6 decomposition characteristics
Pure SF6 gas is generally recognized as non-toxic. There will be a small amount of accompanying products in the production process of SF6, among which S2F10 is recognized as a highly toxic gas, but it can be completely removed after purification. Although pure SF6 gas is non-toxic, it is necessary to prevent the concentration of SF6 gas from rising to the level of hypoxia in the workplace. The density of SF6 gas is about five times that of air. If SF6 gas leaks, it will be deposited in low-lying areas, such as cable trenches. Excessive concentration will cause suffocation, and this situation should be taken into consideration when designing indoor ventilation devices. SF6 gas can mix with air through convection, but the speed is very slow. Once the gases are mixed, they form a mixed gas of SF6 and air and will not separate again. The serious problem is that the decomposition products of SF6 under the action of arc, such as SF4, S2F2, SF2, SOF2, SO2F2, SOF4 and HF, are all highly corrosive and toxic.
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