Helium

Applications

Pressurized helium is commercially available. Helium is used for many purposes that require one or more of its unique properties; low boiling point, low density, low solubility, high thermal conductivity, or its inertness.

Related Topics:
Boiling point - Density - Solubility - Thermal conductivity - Inert

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Airships and balloons (toy, weather, and research) are inflated with helium because it is lighter than air (1 m³ of helium will lift 1 kg). Helium is currently preferred to hydrogen in airships because, while it is more expensive, it is not flammable and has 92.64% of the lifting power of hydrogen.

Related Topics:
Airship - Balloon - Toy - Weather - Research - Lighter than air - Hydrogen

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Trimix, a mixture of helium, oxygen, and nitrogen, is used in deep-sea breathing gas systems to reduce the risk of nitrogen narcosis (high pressure nitrogen having a narcotic effect on the brain) and oxygen toxicity at high pressures. Higher pressures require a greater proportion of helium and reduced amounts of nitrogen and oxygen (every ten-meter increase in depth yields a one atmosphere increase of pressure). Heliox, a mixture of helium and oxygen, and heliair, a mixture of air and helium, is also used in this way. Below 600 meters (2000 ft) a mixture of hydrogen, helium, and oxygen called hydreliox is used to help prevent high pressure nervous syndrome

Related Topics:
Trimix - Oxygen - Nitrogen - Breathing gas - Nitrogen narcosis - Narcotic - Brain - Oxygen toxicity - Heliox - Heliair - Air - Hydreliox - High pressure nervous syndrome

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The extremely low boiling point makes helium useful as a coolant in magnetic resonance imaging, superconducting magnets, cryogenics, and to remove thermal noise from detectors used in astronomy. The extreme coldness of liquid helium is also used to produce superconductivity in some ordinary metals such as lead (lead becomes superconductive at 7.3 K), allowing for a completely free flow of electrons in the metal.

Related Topics:
Boiling point - Magnetic resonance imaging - Superconducting magnet - Cryogenics - Astronomy - Superconductivity - Metal - Lead

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Other uses:

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• Because of its high thermal conductivity and inertness, helium is used as a coolant in some nuclear reactors (for example, pebble-bed reactors) and in arc welding air-sensitive metals that require heavy welds.
• Its inertness makes it useful as a protective gas in growing silicon and germanium crystals, in titanium and zirconium production, protecting important historical documents, and in gas chromatography. This property also makes it useful in pressurizing liquid fuel rockets (see below) and in supersonic wind tunnels.
• The gain medium of the helium-neon laser (the first gas laser) most commonly used to scan bar codes is a mixture of helium and neon.
• This gas' rate of diffusion through solids is three times that of normal air, making it an excellent component in leak detection in high-vacuum equipment and high pressure containers.
• In rocketry helium is used as an ullage medium to displace fuel and oxidizers in storage tanks and to condense hydrogen and oxygen to make rocket fuel. It is also used to purge fuel and oxidizer from ground support equipment prior to launch and to precool liquid hydrogen in space vehicles. For example, the Saturn 5 booster used in the Apollo program needed about 13 million ft³ (370,000 m³) of helium to launch.
• Physics researchers use alpha particles (helium nuclei) in particle accelerators and nuclear reaction experiments.
• Helium gas is used to fill the space between lenses in some solar telescopes because its extremely low index of refraction reduces the distorting effect of temperature variations in the gas filling the telescope (some telescopes are filled with vacuum instead).
• Radioactive decay of uranium and thorium produces alpha particles that quickly become helium. This happens at a known constant rate so if the containing rock or mineral can retain its helium then the ratio of helium to its radioactive parent atoms indicates its age. Alternatively, if the helium is not well-retained, the ratio of helium-3 to helium-4 contains some of the same information, since only helium-4 is produced by radioactive decay. Use of helium in this way is called helium dating.