Six industrial gases are chosen as the components of the majority of shielding gases, because the chemical and physical properties are useful in optimising the performance of the various processes in use.
Among the major gases used are the inert gases. Argon is usually extracted from air as a by-product of making oxygen via a cryogenic ASU and as one of the ‘noble’ gases, it is chemically inert so reverts back the atmosphere after use. It is available in different grades to suit varying purity requirements.
Helium is another ‘noble’ gas utilised and is usually extracted from natural gas, as part of the cleaning-up process, before use. It is considerably more difficult to extract, liquefy, process and transport and that is why it normally costs more. Its physical properties are quite different from argon and it is invaluable for applications that require high heat input.
Finally, carbon dioxide is a much talked about greenhouse gas, often extracted from the waste gas out of processes like fermentation or ammonia production, and is one of the six gases most used.
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