Helium
Helium is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table. Helium has the lowest boiling and melting points among all elements and exists only as a gas except under extreme conditions.
Helium is the second lightest element and the second most abundant element in the observable universe, constituting 24% of the total elemental mass; its mass is more than 12 times the mass of all heavier elements combined. This abundance is similar to that found in the Sun and Jupiter. This is due to the very high binding energy (per nucleon) of helium-4 with respect to the next three elements after helium. This high binding energy of helium-4 means it is a common product of both nuclear fusion and radioactive decay. Most helium in the universe is helium-4, and it is believed to have been formed during the Big Bang. Most new helium is created by nuclear fusion of hydrogen in stars.
Helium is used in cryogenics (its largest single use, consuming about a quarter of production), particularly for cooling superconducting magnets, with Magnetic Resonance Imaging (MRI) being the main application. Reportedly constituting half of the industrially produced gas, helium is also used for the following purposes: as a pressurizing and purge gas, as a protective atmosphere for arc welding, and in processes such as growing crystals to make silicon wafers. A well-known but minor application of helium is as a lifting gas in balloons and airships. Like other gases with a density different from air, inhaling helium temporarily changes the timbre and quality of a person's voice. In scientific research, the behavior of the two liquid phases of helium-4 (helium I and helium II) is important to researchers studying quantum mechanics (particularly the property of superfluidity) and to those looking at phenomena, such as superconductivity, that occur near absolute zero.
Although filling balloons with helium is its best-known application, this accounts for a minor part of its total use. Helium is used for many purposes that require some of its unique properties, such as its low boiling point, low density, low solubility, high thermal conductivity, or inertness. In 2008, approximately 22% of the roughly 32 million kg (193 million cubic meters) of helium produced worldwide annually was used in cryogenic applications, primarily for cooling superconducting magnets in Medical Magnetic Resonance Imaging (MRI) scanners. Other major applications (totaling about 60% in 1996) were pressurizing and purging systems, controlled atmospheres, welding, and leak detection. Other applications by category are comparatively minor.
Because it is inert, helium is used as a protective atmosphere in growing silicon and germanium crystals, in titanium and zirconium production, and in gas chromatography. Due to its inertness, high thermal conductivity, high speed of sound, and high value of the heat capacity ratio (Cp/Cv), helium is also suitable for use in supersonic wind tunnels and impulse facilities.
Helium acts as a shielding gas in electric arc welding processes on materials that would be contaminated or embrittled by air or nitrogen. A number of inert shielding gases are used in Gas Tungsten Arc Welding (GTAW/TIG); helium is often used, sometimes preferred over argon (which is generally cheaper), especially for welding materials with higher thermal conductivity such as aluminum or copper.
Acetylene (systematic name: ethyne) is a chemical compound with the formula C₂H₂.
Argon is a chemical element with the symbol Ar and atomic number 18.
Argon-Carbon Dioxide C-50 (50% argon / 50% CO₂)
Carbon dioxide (chemical formula CO₂)
Nitrogen is a chemical element with the symbol N and atomic number seven.
Oxygen is a chemical element with the symbol O and atomic number 8.
Propane (molecular formula C₃H₈) is an alkane with three carbon atoms.