Helium

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… an inert gas shield for arc welding in countries where helium is cheaper than argon  protective gas in growing silicon and germanium crystals, and in titanium and zirconium production  cooling medium for nuclear reactors  a mixture of 80% helium and 20% oxygen is used as an artificial atmosphere for divers and others working under pressure  cryogenic applications as a gas for supersonic wind tunnels  a protective gas for semiconductor materials pressurizing liquid fuel rockets Bibliography none