Rare Gases

The properties of each rare gas dictate its specific commercial applications. Because they are the most abundant, and therefore the least expensive to produce, helium and argon find the most commercial applications. Helium's low density and inertness make it ideal for use in lighter-than-air craft, such as balloons and blimps. Although helium has nearly twice the density of hydrogen, it has about 98% of hydrogen's lifting power. A little over 324.7 gal (1,230 l) of helium lifts 2.2 lb (1 kg). Helium is also nonflammable and therefore considerably safer than hydrogen, which was once widely used in gas-filled aircraft. Liquid helium has the lowest boiling point of any known substance (about -452°F; -269°C) and therefore has many low-temperature applications in research and industry. Divers breathe an artificial oxygen-helium mixture to prevent gas bubbles forming in the blood as they swim to the surface from great depths. Other uses for helium have been in supersonic wind tunnels, as a protective gas in growing silicon and germanium crystals and, together with neon, to make gas lasers.

Neon is well known for its use in neon signs. Glass tubes of any shape can be filled with neon and when an electrical charge is passed through the tube, an orange-red glow is emitted. By contrast, ordinary incandescent light bulbs are filled with argon. Because argon is so inert, it does not react with the hot metal filament and prolongs the bulb's life. Argon is also used to provide an inert atmosphere in welding and high-temperature metallurgical processes. By surrounding hot metals with inert argon, the metals are protected from potential oxidation by oxygen in the air. Krypton and xenon also find commercial lighting applications. Krypton can be used in incandescentlight bulbs and in fluorescent lamps. Both are also employed in flashing stroboscopic lights that outline commercial airport runways. Because they emit a brilliant white light when electrified, they are also used in photographic flash equipment. Due to the radioactive nature of radon, it has found medical applications in radiotherapy.