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Applications in the electrical engineering
The use of sulphur hexafluoride in place of solid and liquid insulators offers a number of important advantages:
High dielectric strength at lower cost
When pressurized, sulphur hexafluoride can exhibit the same dielectric strength as liquid insulators. However, the per-unit-volume cost of SF6 is only a fraction of that of liquid dielectrics.
Regeneration capacity
Following a breakdown, sulphur hexafluoride regenerates itself. Its original strength is spontaneously restored and, in most cases, is even slightly enhanced.
Low pressure-increase in the case of breakdown
Due to the very low adiabatic coefficient of sulphur hexafluoride, the pressure rise as a result of thermal expansion following dielectric breakdowns is less than that with other gases and very considerably less than is the case with liquid dielectrics.
High-voltage switchgear and switching stations
The excellent quenching and insulating properties of sulphur hexafluoride have permitted the construction of completely new types of high-voltage circuit breakers and switching stations with outstanding features: compact and space-saving design, low noise-levels, protection against accidental contact of live parts, against intrusion of foreign matter through the metal cladding and elimination of the fire hazard. 
Substations using sulphur hexafluoride for insulation purposes are particularly in demand where, on account of limited space, a compact design is required. These substations occupy only 10-15% of the space required by conventional units. New SF6-filled equipment can thus be installed at distribution points in densely-populated areas where site costs would prohibit the use of traditional methods.
Thanks to their insensitivity to polluted air, enclosed outdoor versions of SF6 -insulated substations are installed in the chemical industry, in desert regions and in coastal areas.
SF6 is used as a quenching agent both in power circuit breakers for enclosed substations and in circuit breakers for open outdoor substations.
SF6 for the Itaipú hydroelectric station 
Solvay Fluor GmbH supplied the SF6 for the world's largest hydroelectric power station at Itaipú in Brazil. The output at Itaipú is particularly impressive: 18 turbines supply 12.6 billion watts, equivalent to the output of 10 nuclear power stations. The largest SF6 -insulated high-voltage switching station in the world was installed at Itaipú, and contains more than 100 tons of sulphur hexafluoride.
Gas insulated transmission line (GIL)
Gas insulated transmission lines are particularly well suited for high power transmission. Conventional designs are filled with pure SF6, and have been operating safely and reliably in all parts of the world for more than 20 years.  Fig. 11 SF6 / N2 -membran-separation plant
with condenser unit
The advantage of this technology is the higher capacity compared with cables. GIL's are either buried or laid in tunnels. They are a viable alternative for energy supply where overhead power lines are either not possible or where the capacity of cables is insufficient. For long distances the replacement of pure SF6 with more economical SF6 / N2 mixtures has been researched because the arc extinguishing properties of SF6 are not relevant in insulating applications. Today the overall optimisation of gas mixtures, gas pressure and dimensions of GIL mean this technology is a highly competitive transmission medium in a broad range of applications. Solvay Fluor GmbH Technical Service supports this application with a spectrum of services ranging from the initial production of SF6 / N2 mixtures through to the separation of SF6 / N2 mixtures at end of service life or whenever required (Fig. 11). This technical service allows Solvay to provide a closed product loop for SF6 / N2 mixtures. 
Fig. 10 SF6 / N2 mixture in transmission lines,
in tunnel (Siemens, Germany)
Medium-voltage switchgear
 Fig.12
Medium-voltage, heavy-duty power circuit breakers of the Minex type. SF6-insulated for installation in local-network and consumer stations (Driescher, Germany) The advantages of SF6 technology, in particular its excellent arc-quenching capacity, are also put to good use in circuit breakers for the 10-40 kV range. They replace conventional, low-oil-volume circuit breakers and also satisfy heavy-duty requirements such as those occurring under short-circuit conditions and repeated switch-off under load. As with high-voltage circuit breakers, medium-voltage switchgear requires little maintenance and are particularly suitable for locations where oil-filled equipment is undesirable.
High-voltage cables and tubular transmission lines
 Fig.14
SF6-insulated high-voltage cable in the JET nuclear-fusion plant (kabelmetal electro, Germany) In recent times, increasing interest has been shown in the application of sulphur hexafluoride in the manufacture of gas-insulated high-voltage cables and tubular transmission lines used for high-power distribution in heavily concentrated industrial areas. Tubular transmission lines are also used to connect power stations with transformers or switching stations, as for example in the case of underground power stations. Appropriately-dimensioned tubular transmission lines filled with pressurized SF6 permit unusually high current levels. Compared to those values achieved with conventional types of cables, figures for charging-current and electric loss are insignificant. In high-frequency carrier sytems, output has been increased almost tenfold through the use of SF6-filled tubular transmission lines. An advantage from the constructional point of view is the ability to build high-performance UHF transmission stations with greatly reduced dimensions.
Transformers
Fig.15
SF6-insulated transformer, 23-107 kV (Fuji, Japan) Its excellent heat-transfer capacity, non-flammability and non-toxicity have also promoted the use of sulphur hexafluoride in the construction of transformers.
On account of their high operational safety, SF6-gas transformers are installed in mines and department stores. Their relatively light weight, compact design and low noise levels are decisive advantages.
Other high-voltage applications 
Fig 16
525 kV SF6 instrument transformer (AREVA, Belgium) The use of sulphur hexafluoride has also established itself in the insulation of super-voltage generators in particle-accelerating machines, such as in Van de Graaf accelerators, betatrons, neutron generators and other such equipment used for radiation applications in scientific institutions, medicine and industry. By virtue of the high dielectric strength of the gas, pressure vessels can be constructed in considerably lighter fashion. The use of SF6 in older units, previously insulated with mixtures of air and carbon dioxide, has resulted in a marked increase in efficiency. SF6 fulfills a similar function in voltage stabilizers for electron microscopes and in X-ray equipment used in production control and the non-destructive testing of materials. Parallel to the development of SF6 plant technology in the high-voltage sector, SF6-insulated, high-voltage measuring instruments and calibrated power sources have also been produced. SF6-fillings are also used in instrument transformers, pressurized gas capacitors and surge arresters for super voltages.
SF6 for the Vivitron accelerator
 The largest electrostatic accelerator in the world is already in operation in Strasbourg.
Using new technology, the Tandem Van de Graaf Vivitron accelerator is designed to achieve an accelerating potential of 35 million volts. It is 51 m long, has a maximum diameter of 8.5 m and a volume of 1200 m3. The SF6-gas supply is contained in two storage tanks whose total SF6-capacity is 60 tonnes. Solvay Fluor GmbH was responsible for both the supply of SF6 and the associated logistics for this project.
SF6 as a process gas in the semiconductor industry
SF6 is used in the manufacture of magnesium as a protective agent to prevent the vaporisation and ignition of melts and also to prevent the formation of oxides and nitrites. SF6 is used to clean the melt in aluminium manufacturing processes.
Magnesium
Fig. 19
Diagram of a protective gas system for a magnesium smelting furnace
Have a full screen of the graph. Magnesium is a reactive metal and therefore has to be protected against ignition, oxidation and nitride formation during foundry processing (Fig. 18) at temperatures up to 800 °C. As a protective agent SF6 can replace protective salts, SO2 or sulphur powder and pure inert gases (argon). This eliminates many side effects such as unpleasant odours, corrosion, salt inclusions in castings and magnesium vaporisation. Sulphur hexafluoride is mixed with a carrier gas as shown in figure 19, because the larger total quantity of gas ensures faster and better distribution of the SF6 over the melt. Generally, the mixture, which is distributed evenly over the surface of the melt [1], comprises around 0.04 - 0.3 % SF6 by volume and more than 99 % Air / CO2 by volume. The optimum quantity and concentration of the protective gas depends on various factors such as the furnace design, pig flow and molten metal discharge, and must be determined in trials. Because only very small amounts of SF6 are used, there are no problems with cleavage products (MAC of HF << 3 ppmv or 2 mg / m³). Consequently, SF6 is an ideal protective gas for magnesium melts, also for occupational safety aspects.
Aluminium 
Fig. 20
Cross-section of aluminium castings with and without SF6 treatment (from top to bottom) In the manufacture of aluminium castings, porosity in the casting is a fundamental problem because of the hydrogen content in the aluminium melt. This can reduce the strength of the finished part. The aluminium melt must be pretreated to improve the quality. SF6 can replace existing cleaning methods using chlorine or chlorine/inert gas mixtures, pure inert gases (argon), powder or pellet-shaped hexachloroethane and CFC. The formation of aggressive chlorine gases and the use of ozone endangering substances can be avoided by using SF6. Unlike chlorine, no additional precautions are required when handling SF6. Feeding SF6/inert gas mixtures into the liquid aluminium dramatically reduces the hydrogen content and also removes oxides and inclusions, as illustrated in figure 20. Handling the SF6 gas mixtures is easy because SF6 is completely safe physiologically. Thus, the use of SF6 improves working conditions and product quality.
SF6 as a process gas in the semiconductor industry To manufacture wafers, the semiconductor industry requires gaseous fluorinated compounds, silanes (e.g. SiH4) and doping gases (e.g. AsH3, PH3). Wafers consist of high-purity silicon and are the basic building blocks for all semiconductor components. Essentially, the high-purity gases (e.g. SF6) are used as etching gases for plasma etching or as cleaning gases to clean the chambers after the etching process. Gases for plasma etching
Etching produces structures on the surface of the silicon. In the wafer manufacturing process, fluorine ions and radicals are needed to etch the silicon. Structures with a width of 0.15 µm or smaller can be created with this method. Chamber cleaning after the etching process
When the silicon layers are being applied, a fraction of the silicon does not end up on the wafer, but is deposited in the CVD (Chemical Vapour Deposition) chamber. To prevent the wafers becoming contaminated by these deposits in downstream processes, the chambers are cleaned at defined intervals. The SF6 decomposed by the plasma, allows the chambers to be cleaned. Consistent use of retention and cleaning systems, as well as the SF6 ReUse Concept, allows SF6 to be used in an environmentally friendly manner and to be kept in a closed cycle. Grade 5.0 SF6 , i.e. with 99.999 % purity, is supplied throughout the world by Solvay Fluor GmbH. 
Fig. 21
Silicon wafer
Other areas of application 
Fig. 22
Ophthalmology Even at the lowest concentration levels, sulphur hexafluoride is detected by modern halogen leak detectors. For this reason it is used increasingly as a test gas for detecting leaks in boilers, fuel tanks, pneumatic devices, pipeline systems, plastic tubing, containers for carrying radioactive materials and many other vessels. By carrying out a calibrated leak, quantitative measurements are also possible. With the increasing demands imposed by ever stricter standards of environmental protection, work safety and energy saving, this technique is gaining steadily in significance. Residence-time distributions in high-velocity-flow assemblies can be determined using SF6. This method is primarily applied in those cases where a radiometric method cannot be employed [2]. On account of its very low detection limit, SF6 is used as a tracer gas for meteorological measurements. When added in measured quantities at an emission source, the distribution of the emitted substances can be determined even at relatively long distances. Its high stability and the low solubility of SF6 in water are of particular advantage in this respect. SF6 is also widely used in medical technology. For example as a contrast agent in ultrasonic examinations as well as in ophthalmology, pneumonectomy and diseases of the middle ear, e.g. treating loss of hearing in middle ear infections [3].
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Cleaning
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