SF6 Monitoring

Carbon dioxide (CO2) and methane (CH4) immediately come to mind when we think of greenhouse gases- after all, they are the talk of the town. Sulfur hexafluoride (SF6) and its harmful effect on the climate, on the other hand, is rather unknown to many.

Sulfur hexafluoride is a colorless and odorless gas that is not toxic to humans. Since it does not react with other gases, it is very popular as a tracer gas, e.g. in medicine. If it enters the atmosphere, however, it is very persistent and contributes significantly to the greenhouse effect. Although it occurs in the atmosphere in much lower concentrations than CO2, its greenhouse potential is 24,000 times higher than that of CO2. This is why it was included in the Kyoto Protocol as one of the six gases that are harmful to the climate in order to reduce these gas emissions.

Early Detection of Leaks is Important

Due to its chemical properties, sulfur hexafluoride is very popular as an electrical insulator and dielectric medium for high-voltage and switchgear as well as for power transmission in modern high-speed trains. More than 10,000 tons of it are produced annually for this purpose.

Naturally, leaks can occur in these plants and systems and release SF6 into the atmosphere. As a preventative measure plants should be continuously monitored. At the Institute for Environmental Physics at the University of Heidelberg, the content of various greenhouse gases in the atmosphere is measured regularly. It was noticed that especially the content of SF6 in the atmosphere is inexplicably high. According to the Kyoto Protocol, all member countries must report their emissions. Interestingly, the reported data do not match the measured data; leakages could be a reason for the indiscrepancy. With the help of optical spectroscopy, especially non-dispersive infrared spectroscopy (NDIR), such measurement tasks could be solved easily and reliably. The infrared sources from Axetris guarantee a continuously high emissivity in the entire mid-infrared spectrum, which is necessary to detect the smallest leaks of harmful SF6 through NDIR technique.

Measurement of Gas Purity for Highest Demands

Another important use for sulfur hexafluoride is in semiconductor production. Today's high-precision manufactured components from semiconductor and microtechnology go through many individual steps in their production process.

One important step is etching, which is used to produce microstructures. These microstructures are realized during etching by means of material removal. The various etching techniques distinguish between dry etching and wet chemical etching. SF6 is used as an etching gas in dry etching processes. Since even the smallest amounts of particles or foreign gases can damage the sensitive semiconductors, the purity of the gases used is extremely important. Non-dispersive infrared spectroscopy can be used for continuous monitoring of gas purity.