Helium

Infobox on Helium
Example of Helium
Facts
Origin	-
Stowage factor (in m3/t)	-
Humidity / moisture	-
Ventilation	-
Risk factors	See text

Helium

Description

For large-scale use, helium is extracted by fractional distillation from natural gas, which can contain up to 7% helium. Since helium has a lower boiling point than any other element, low temperature and high pressure are used to liquefy nearly all the other gases (mostly nitrogen and methane). The resulting crude helium gas is purified by successive exposures to lowering temperatures, in which almost all of the remaining nitrogen and other gases are precipitated out of the gaseous mixture. Activated charcoal is used as a final purification step, usually resulting in 99.995% pure Grade-A helium.] The principal impurity in Grade-A helium is neon. In a final production step, most of the helium that is produced is liquefied via a cryogenic process. This is necessary for applications requiring liquid helium and also allows helium suppliers to reduce the cost of long distance transportation, as the largest liquid helium containers have more than five times the capacity of the largest gaseous helium tube trailers.

Helium is a chemical element with symbol He and atomic number 2. It is a colourless, odourless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table. Its boiling and melting points are the lowest among the elements and it exists only as a gas except in extreme conditions.

Helium is the second lightest element and is the second most abundant element in the observable universe, being present at about 24% of the total elemental mass, which is more than 12 times the mass of all the heavier elements combined. Its abundance is similar to this figure in the Sun and in Jupiter. This is due to the very high nuclear binding energy (per nucleon) of helium-4 with respect to the next three elements after helium. This helium-4 binding energy also accounts for its commonality as a product in both nuclear fusion and radioactive decay. Most helium in the universe is helium-4, and is believed to have been formed during the Big Bang. Some new helium is being created currently as a result of the nuclear fusion of hydrogen in stars.

Helium is used in cryogenics (its largest single use, absorbing about a quarter of production), particularly in the cooling of superconducting magnets, with the main commercial application being in MRI scanners. Helium's other industrial uses—as a pressurizing and purge gas, as a protective atmosphere for arc welding and in processes such as growing crystals to make silicon wafers—account for half of the gas produced. A well-known but minor use is as a lifting gas in balloons and airships. As with any gas with differing density from air, inhaling a small volume of helium temporarily changes the timbre and quality of the human voice. In scientific research, the behaviour of the two fluid phases of helium-4 (helium I and helium II), is important to researchers studying quantum mechanics (in particular the property of superfluidity) and to those looking at the phenomena, such as superconductivity, that temperatures near absolute zero produce in matter.

On Earth it is thus relatively rare—0.00052% by volume in the atmosphere. Most terrestrial helium present today is created by the natural radioactive decay of heavy radioactive elements (thorium and uranium), as the alpha particles emitted by such decays consist of helium-4 nuclei. This radiogenic helium is trapped with natural gas in concentrations up to 7% by volume, from which it is extracted commercially by a low-temperature separation process called fractional distillation.

Helium is a chemical element and is a noble or inert gas and is found in the IMDG Code as follows:

• UNNO 1046: Helium, compressed - An inert gas. Lighter than air
• UNNO 1963: Helium, refrigerated liquid - Liquefied inert gas and lighter than air.
  
  

Derivation:
From natural gas, by liquefaction of all other components, followed by purification over activated charcoal.

Properties
Helium is a colourless, odourless, tasteless, non-toxic, inert, monatomic, chemical element that heads the noble gas series in the periodic table and whose atomic number is 2. However it is a simple asphyxiant which means that it supplants oxygen in the air.

Solid and liquid phases
Liquefied helium. This helium is not only liquid, but has been cooled to the point of superfluidity. The drop of liquid at the bottom of the glass represents helium spontaneously escaping from the container over the side, to empty out of the container. The energy to drive this process is supplied by the potential energy of the falling helium. Unlike any other element, helium will remain liquid down to absolute zero at normal pressures. This is a direct effect of quantum mechanics: specifically, the zero point energy of the system is too high to allow freezing. Solid helium requires a temperature of 1–1.5 K (about −272°C or −457°F) and about 25 bar (2.5 MPa) of pressure. It is often hard to distinguish solid from liquid helium since the refractive index of the two phases are nearly the same. The solid has a sharp melting point and has a crystalline structure, but it is highly compressible; applying pressure in a laboratory can decrease its volume by more than 30%. With a bulk modulus of about 27 MPa it is ~100 times more compressible than water. Solid helium has a density of 0.214 ± 0.006 g/cm³ at 1.15 K and 66 atm; the projected density at 0 K and 25 bar (2.5 MPa) is 0.187 ± 0.009 g/cm³.

Helium I state
Below its boiling point of 4.22 kelvins and above the lambda point of 2.1768 kelvins, the isotope helium-4 exists in a normal colourless liquid state, called helium I. Like other cryogenic liquids, helium I boils when it is heated and contracts when its temperature is lowered. Below the lambda point, however, helium does not boil, and it expands as the temperature is lowered further.

Helium I has a gas-like index of refraction of 1.026 which makes its surface so hard to see that floats of styrofoam are often used to show where the surface is. This colourless liquid has a very low viscosity and a density of 0.145–0.125 g/mL (between about 0 and 4 K),[47] which is only one-fourth the value expected from classical physics. Quantum mechanics is needed to explain this property and thus both types of liquid helium are called quantum fluids, meaning they display atomic properties on a macroscopic scale. This may be an effect of its boiling point being so close to absolute zero, preventing random molecular motion (thermal energy) from masking the atomic properties.

Helium II state
Liquid helium below its lambda point begins to exhibit very unusual characteristics, in a state called helium II. Boiling of helium II is not possible due to its high thermal conductivity; heat input instead causes evaporation of the liquid directly to gas. Helium-3 also has a superfluid phase, but only at much lower temperatures; as a result, less is known about such properties in the isotope.[5] A cross-sectional drawing showing one vessel inside another. There is a liquid in the outer vessel, and it tends to flow into the inner vessel over its walls. Unlike ordinary liquids, helium II will creep along surfaces in order to reach an equal level; after a short while, the levels in the two containers will equalize. The Rollin film also covers the interior of the larger container; if it were not sealed, the helium II would creep out and escape.

Helium II is a superfluid, a quantum mechanical state (see: macroscopic quantum phenomena) of matter with strange properties . For example, when it flows through capillaries as thin as 10−7 to 10−8 m it has no measurable viscosity. However, when measurements were done between two moving discs, a viscosity comparable to that of gaseous helium was observed. Current theory explains this using the two-fluid model for helium II. In this model, liquid helium below the lambda point is viewed as containing a proportion of helium atoms in a ground state, which are superfluid and flow with exactly zero viscosity, and a proportion of helium atoms in an excited state, which behave more like an ordinary fluid.

Application

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. The largest use is in cryogenic applications, most of which involves cooling the superconducting magnets in medical MRI scanners. Other major uses were pressurizing and purging systems, maintenance of controlled atmospheres, and welding. Other uses by category were relatively minor fractions.

Use: to pressurize rock fuels, welding, inert atmosphere (growing germanium and silicon crystals) inflation of weather and research balloons, heat-transfer medium, leak detection, chromatography, cryogenic research, magnetohydrodynamics, luminous signs, geological dating, aero-dynamic research, lasers, diving and space vehicle breathing equipment. Possible future uses include coolant for nuclear fusion power plants and in superconducting electric systems.

Shipment / Storage / Risk factors

Transport methods according to IMDG Code regulations:

• UNNO 1046: cylinders as per packing instruction code P200. Tanks are not allowed.
• UNNO 1963: closed cryogenic receptacles as per packing instruction code P203. The following tank is allowed: UN tank code T75.
• UNNO 1046: Helium, compressed - An inert gas. Lighter than air
• UNNO 1963: Helium, refrigerated liquid - Liquefied inert gas and lighter than air.
  

Portable tank special provision TP5 and TP34 are applicable. The provision of TP5 is related to the filling degree as described in chapter 4.2.3.6 of the IMDG code and the provision of TP34 is related to there being no need to impact test if tank is marked “NOT FOR RAIL TRANSPORT”. Vessels are frequently required to carry liquid argon UNNO 1951 in shipper owned tank containers, stowed ON DECK only. These tanks are normally constructed as a double tank with an outer tank surrounding an inner tank under the provisions of T75 of the IMDG Code. The inner tank contains the cargo of argon and the outer tank contains the cooling agent, e.g. nitrogen. Due to the cooling of the argon a lower pressure can be obtained. During the voyage the cooling agent is released to the air in order to cool the cargo in the inner tank.

Normally the amount of cooling agent is sufficient to cool the argon for approximately 30 days. If a tank is malfunctioning the cooling agent may be released faster than calculated and will consequently not last for 30 days. In the event of a release of cooling agent and the resulting loss of cooling protection, there will be an increase in internal pressure as the argon reverts back to a gas. This pressure will cause a safety valve to release a controlled flow of argon to the air. In the unlikely event of a major build up of pressure, rupture discs will release a large quantity of helium/argon, bringing the tank back to safe condition.

All tank containers carrying liquid argon are equipped with various gauges to monitor the condition of the tank. Care must be taken that the Shipper’s Own tank gauges can be sighted from the front or back of the container as containers will be stowed either side of these units on board. If vacant space is required to maintain/monitor these units, additional costs will be encountered for use of the additional slots utilised. For this reason normally monitoring equipment can be viewed from one end of the container; however this needs to be confirmed at time of booking. A tank container with liquid argon shall not be loaded unless a proper manual covering the operation of the tank is delivered to the vessel prior to loading of the tank. A tank container with liquid argon should always be stowed in a position, where crew easily can obtain access to all gauges, handles, etc. and always as per stowage stated in accompanying manual. Usually the shippers of liquid argon may require the carrying vessel to monitor such tanks daily and email/telex the findings to their office. In this respect it is imperative that the vessels are in possession of a manual covering the functions of the individual tank and with contact addresses included.