Sulphur Hexafluoride SF

Sulphur hexafluoride is a gas at room temperature. It has excellent dielectric properties and is used in gas-insulated electrical devices at high and very high voltage such as switches. 

In the absence of humidity, sulphur hexafluoride SFe has no action on aluminium. Humidity decomposes it into hydrofluoric acid that attacks aluminium. 

Envelopes of gas-insulated electrical switches are in alloys 5754 and 5083, because of the good resistance of aluminium to SFe and its amagnetic properties. 

In alkaline media, aluminium dissolves as aluminate AIO2 under hydrogen release, according to the reactions  

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Sulphur hexafluoride, SF, m.p. — 5LC. Formed S plus Fj. Very inert material used as an inert dielectric. S2F10 (toxic) is also formed from S plus F2 and there is an extensive chemistry of SFj derivatives (e.g. SF5CI, CIF plus SFJ. 

Whereas some atoms have only one valency, others have several, e.g. sulphur has valencies of two, four and six and can form compounds as diverse as hydrogen sulphide, H2S (valency two), sulphur dioxide, SO2 (valency four) and sulphur hexafluoride, SFs (valency six). Clearly some compounds comprise more than two different elements. Thus hydrogen, sulphur and oxygen can combine to produce sulphuric acid, H2SO4. From the structure it can be seen that hydrogen maintains its valency of one, oxygen two and sulphur is in a six valency state. 

With the availability of 3.3 and 6.6 kV vacuum contactors the control of HT motors up to 6.6 kV systems has now become easier and economical, compact and even more reliable. For 11 kV. systems, vacuum as well as SF (Sulphur hexafluoride) breakers can be used. The HT motor s switching and protection through a vacuum contactor provides a replica of an LT system. The earlier practice of using an HT OCB, MOCB, or an air blast circuit breaker for the interruption of an HT circuit is now a concept of the past. 

Laser excitation of a SF6-O2-CH4 mixture gives as products CO, CO2, H2O, SO2, SOF2, HF, CF4, and F2O. However, no photoreaction is observed if SF6-CH4 and SF6-O2 are irradiated separately. Sulphur hexafluoride-sensitized dissociation of UF in the presence of H2 and CO as scavengers has also been investigated. A search for a light-induced drift of SF in a mixture with He, MeF, or SF buffer particles has appeared. No positive result was obtained and this is thought to arise as a consequence of various factors, including the complex structure of the SF absorption spectrum. The pressure... 

Sulphur Hexafluoride. As a result of a chemical laser study it has been proposed that collision-induced dissociation (78) rather than abstraction (79) is the principal path in the reaction of atoms of energy up to 430 kJ mol with SF . 

Sulphur exhibits its highest oxidation state +6 in sulphur hexafluoride. Though a number of halides of sulphur are known (SF, SCl, SClj etc.) only hexafluoride is the stable compound among hexahalides. Hexachloride, hexabromide and hexaiodide are not known. This may be attributed to the small size of the fluorine atom. 

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