Helium – Lighter than Air

A photograph showing a bunch of Helium red party balloons on strings over a sunny blue sky background.More Than Just Party Balloons…

Helium is the second most abundant element in the Universe, after hydrogen.  On Earth, helium is relatively rare, because it is one of the few elements that can escape gravity and leak away into space.  Therefore, helium exists as a finite resource.  But as our reserves of the precious element steadily decreases, helium is in increasing demand.  In medicine, helium supports the fight against cancer… 

Helium is a lot lighter than air.  The difference is not as great as it is between water and air – one litre of water weighs about 1,000 grams (1 kg), while a litre of air weighs about 1 gram.  Nevertheless, it is significant.

Helium weighs 0.1785 grams per litre.  Nitrogen weighs 1.2506 grams per litre.  Since nitrogen makes up about 80 % of the air we breathe, 1.25 grams is a good approximation for the weight of a litre of air.

If you were to fill a 1-litre soda bottle full of helium, the bottle would weigh about 1 gram less than the same bottle filled with air.  It doesn’t sound like much and the bottle itself weighs more than a gram, so it won’t float.  However, in larger volumes, the 1-gram-per-litre difference between air and helium can really add up.  This explains why blimps and balloons are generally quite large: they must displace a lot of air to float.

 

 

The following infogram shows the different lifting capacities corresponding to different volumes of helium:

A diagram explaining the buoyancy potential (lifting capacity) of differently sized Helium balloons. The captions read: "1 foot diameter balloon Volume = 0.5 cubic feet Lifting capacity = 14 grams." "3 foot diameter balloon Volume = 14.1 cubic feet Lifting capacity = 0.9 pounds." "6 foot diameter balloon Volume = 11.3 cubic feet Lifting capacity = 7.1 pounds." "12 foot diameter balloon Volume = 904 cubic feet Lifting capacity = 57 pounds."

A 100-foot-diameter balloon can lift 33,000 pounds!

Discover how to calculate the lifting capacity of a spherical helium balloon.

 

Inertia is Good

Most people know that helium is used as a lifting gas for party balloons and blimps, but most cannot name any other use for it. These include using helium for cooling super-conducting magnets in MRI scanners, and other medical applications, to making computer chips, and frictionless hard drives.

Odourless, tasteless, colourless, non-toxic, inert, the monatomic gas helium 42He has atomic number 2 and atomic weight 4.002.  The helium atom has two protons, two neutrons and two electrons.  From the Quantum Mechanics perspective, helium is the second simplest atom to model, following the hydrogen atom.

Helium is an inert gas, one of the noble gases that do not react with many other substances.  Inert gases are used generally to avoid unwanted chemical reactions degrading a sample.  These undesirable chemical reactions are often oxidation and hydrolysis reactions with the oxygen and moisture in the air.

A photograph showing a heavy welder at worker. Helium Argon Shielding Gas Primer for GTAW Gas Tungsten Arc Welding.
Photo: Praxair Inc.

Helium is a protective gas for welding, an inert gas for controlled atmosphere manufacturing, a fugitive gas used for leak detection, and a low viscosity gas for pressurised breathing mixtures in deep-sea diving.

For heat-conductive metals such as aluminium and copper alloys, an argon/helium shielding gas mixture will improve the weld deposit penetration profile and may enhance welding productivity when compared with using argon alone.

Helium is also used by NASA and the Department of Defence to purge liquid oxygen and liquid hydrogen from fuel tanks and fuel delivery systems of rocket engines.  With a freezing temperature that is so low, helium remains a gas through the purging process.  Flooding helium into these systems has even been used during emergencies to extinguish fires.

 

Cryogenics – Helium in Medicine

A pie chart representing the Uses of Helium in the United States. Cryogenics: 32%. Pressure/Purge Systems: 18%. Controlled Atmospheres: 18%. Welding: 13%. Leak Detection: 4%.Cryogenics refers to the specialised branches of physics and engineering that involve the study of very low temperatures, how to produce them, and how materials behave at such temperatures. 

Helium has a key importance for superconducting magnets used in magnetic resonance imaging (MRI) scanners, which must be super-cooled to generate the hugely powerful magnetic fields required.

Actually, the number one use for helium is as a cooling gas for MRI machines used for patient diagnostics in hospitals and medical facilities.  MRI has a wide range of applications in medical diagnosis and there are estimated to be over 25,000 scanners in use worldwide.

A diagram showing the cross-section of a MRI scanner.

Most medical applications rely on detecting a radio frequency signal emitted by excited hydrogen atoms in the body (present in any tissue containing water molecules) using energy from an oscillating magnetic field applied at the appropriate resonant frequency.  The orientation of the image is controlled by varying the main magnetic field using gradient coils.  These coils are rapidly switched on-and-off during the scanning procedure, which create the characteristic repetitive noises of an MRI scan.

Magnetic Resonance Imaging requires a strong and uniform magnetic field.  While the majority of systems operate at a field strength of 1.5 T (tesla), commercial systems are available between 0.2 T – 7 T. 

Most clinical magnets are superconducting, which requires liquid helium.

 

Cold Plasma Therapy

Any medical treatment should ideally mimic the body’s natural healing and renewal processes.  After all, the human body is designed to solve its problems in its own manner, only occasionally requiring external support.  Plasma therapy can provide that gentle support, while inflicting far less tissue damage than conventional treatments.

A photograph showing a (helium) plasma needle being used in dentistry.Researchers at the Eindhoven University of Technology (Netherlands) introduced the novel concept of using cold plasmas for medical treatment, and invented and tested a simple device called a plasma needle.

This plasma needle generates a low-power atmospheric discharge by the radio-frequency excitation of a mixture of helium and air.  The gas remains at room temperature and treatment with this device is non-contact and entirely painless.

The action of the plasma needle is not based on mechanical injury or thermal ablation, but on conveying chemical stimuli to the body’s cells.  These stimuli are provided by short-living species called radicals. 

Plasma’s most important therapeutic functions appear to be in vivo disinfection and non-inflammatory tissue removal.  The applicability of plasma disinfection to dermatology and wound care is obvious: it allows the non-contact treatment of painfully inflamed sites and skin infections without affecting the surrounding tissue and stimulates tissue regeneration.

Plasma may even become a true life-saving therapy when treating immuno-compromised patients.  When successful in healing chronic wounds (e.g. diabetic foot ulcers) and large-area burns, plasma treatment could prevent life-threatening septicaemia and amputations of extremities.  It can be used virtually anywhere, even in the most delicate of sites, for the treatment of bacterial conjunctivitis and keratitis in the eye.  A definite future possibility is the plasma treatment of internal infections in the respiratory, urinary and reproductive systems.

A medical image taken using Helium instead of air inside lungs.
Lung Imaging is another application of helium in medical diagnostics: Helium is insoluble, so once inhaled it stays in the lungs and gives us very high signal-to-noise images of ventilation and lung function.

Another vast area that came to benefit from the use of non-thermal plasma disinfection in recent years, is dentistry.

In this case, the specific advantage of plasma is its ability to treat irregular surfaces, and work round corners to reach fissures and cracks.  This could provide a tissue-saving and pain-free way to cure dental caries and perform root-canal treatment.  Gingival diseases, such as periodontal pockets and mucosal ulcerations, may also be healed.

The most obvious applications lie in dermatology for various cosmetic procedures, from the removal of benign skin imperfections to the treatment of skin cancer.  Other possibilities include: removal of arterial stenoses and malignant growths, as well as extraction of embryonic cells, with potential applications in brain, cardiovascular and microsurgery.

Most of helium present in the Universe is helium-4, and it is believed to have been formed during the Big Bang.  Since that time, large amounts of new helium are being created by nuclear fusion of hydrogen in stars.

Helium is collected as a by-product of the gas industry.  The gas forms through the radioactive decay of rocks in the Earth’s crust, and accumulates in natural gas deposits.

 

Natural Radioactivity at Work

On Earth, most helium forms as a result of the natural decay of radioactive elements, such as uranium (U) and thorium (Th).

Uranium-238 is the most common isotope of uranium that is found in Nature, around 99.284%.  Uranium-238 decays by way of thorium-234 (and protactinium-234) into uranium-234.

 

Alpha Decay of a Uranium-238 Nucleus

 

A diagram showing the Alpha Decay event of a Uranium atom (parent nucleus) into a Thorium atom (daughter nucleus) and Helium atom (or alpha particle).

 

The alpha decay, or α-decay, is a type of radioactive decay in which an atomic nucleus emits an alpha particle, and thereby transforms (or ‘decays’) into an atom with a mass number 4 less and atomic number 2 less.

The uranium nucleus spontaneously decays into the lighter element Thorium, while releasing alpha-radiation.

{}^{238}_{92} U \rightarrow {}^{234}_{90} Th + \alpha

 

The emitted α particle has two protons and two neutrons, enough to make it a new helium nucleus, which will go on to attract two electrons to form a helium atom.

{}^{238}_{92} U \rightarrow {}^{234}_{90} Th + {}^{4}_{2} He

 

Down to Earth

The concentration of helium in the Earth’s atmosphere, is fairly low (only 5.2 parts per million), despite the continuous production of new helium because most of it escapes into space by several processes.  In the heterosphere, helium and other lighter gases are the most abundant elements.

However, the biggest concentrations of helium are found in natural gas fields.

Most of the helium, removed from natural gas, is thought to form from radioactive decay of uranium and thorium in granitoid rocks of Earth’s continental crust.  As a very light gas, helium is buoyant and seeks to move upward as soon as it forms.

The richest helium accumulations are found where three conditions co-exist:

  1. Granitoid basement rocks are rich in uranium and thorium.
  2. The basement rocks are fractured and faulted to provide escape paths for the helium.
  3. Porous sedimentary rocks above the basement faults are capped by an impermeable seal of halite or anhydrite.

 

A photograph showing six geological samples of halites and anhydrites.
Halite and anhydrite samples

When all three of these conditions are met, helium might accumulate in the porous sedimentary rock layer.

Helium has the smallest atomic radius of any element, about 0.2 nanometres.  As soon as it forms, helium begins drifting upwards and it squeezes through the smallest of pores and spaces within the rock strata above it.

Halite and anhydrite are the only sedimentary rocks that can block the upward migration of helium atoms.  Shales that have their pore spaces plugged with abundant organic materials (kerogen) sometimes serve as a less effective barrier.

 

The Lowest Boiling Point of All Elements

Helium has a boiling point of -269°C, the lowest boiling point of any other element, just a few degrees above absolute zero (-273°C).

Natural gas can contain up to 7% of helium.  Extraction and purification processes are required to obtain helium from crude natural gas.

For large-scale use, helium is extracted by fractional distillation.  Since helium has a lower boiling point than other elements, low temperature and high pressure are used to liquefy nearly all the other extracted 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.  The final production step for helium production is liquefaction via a cryogenic process.

 

Where do you find Natural Gas Rich in Helium?

A natural gas source must contain at least 0.3% helium to be considered as a potential helium source.  Most unprocessed natural gas only contains trace amounts of helium. 

Very few natural gas fields contain enough to justify a helium recovery process.

 

Worldwide Helium Resources

CountryBillion Cubic Metres*
United States20.6
Qatar10.1
Algeria8.2
Russia6.8
Canada2.0
China1.1

*Estimated values from the USGS Mineral Commodity Summaries.

 

In 2010, all of the natural gas processed for helium in the United States came from fields in Colorado, Kansas, Oklahoma, Texas, Utah and Wyoming.  The Hugoton Field (Oklahoma, Kansas and Texas), the Panoma Field (Kansas), the Keyes Field (Oklahoma), the Panhandle West and Cliffside Fields (Texas) and the Riley Ridge Field (Wyoming) account for most of the helium production in the United States.

During 2010, the United States produced 128 million cubic metres of helium.  Of that amount, 53 million cubic metres were extracted from natural gas and 75 million cubic metres were withdrawn from the National Helium Reserve.  Other countries with known production amounts were: Algeria (18 million cubic metres), Qatar (13 mcm), Russia (6 mcm), and Poland (3 mcm).  Canada and China produced small but unreported amounts of helium.

 

A photograph showing the plant installations at Cliffside Helium Gas Field, near Amarillo, Texas in the United States.The US Helium National Reserve at Amarillo, Texas

The United States is currently the World’s biggest supplier, with the bulk of it stored near Amarillo, Texas, in the national helium reserve – which alone accounts for 35% of the World’s current supply.

The Cliffside Helium Gas Field supplies 42% of all he helium production in the United States.  Established in 1925, the US helium reserve was originally set up as a strategic store designed to supply lifting gas for airships, while after World War Two it provided coolant for missiles and rockets to the military and NASA.

But since the mid-1990s, with growing civilian demand for helium in the manufacture of semi-conductors and for MRI scanners, among other things, the US has been clawing back the cost of storing the gas by gradually selling it off on the open market.

The US sold off its helium reserve but even so, shortages have been occurring.  Scientists who believe a finite resource of helium could one day run out, have been should not be wasted on something as trivial as party balloons.

Despite all this, the price of helium has doubled over the past 10 years.

 

As Supply Falls, Demand for Helium Rises

Scare stories about mineral or chemical resources running out are fairly commonplace.  However, last autumn, the World got a taste of what a helium shortage could mean when the US helium reserve was legally obliged to turn off the tap in October.

“We’re going to be looking back and thinking, I can’t believe people just used to fill up their balloons with it, when it’s so precious and unique,” says Cambridge University chemist Peter Wothers, who has called for the end to helium-filled party balloons.  “It is something we need to think about.”

This would mean an end to the old party favourite of breathing in helium from a balloon, and talking in high-pitched voices – a result of helium’s fast-moving molecules.  Maybe this would be no bad thing though, as doing so can cause dizziness, headaches, even death.

US semiconductor manufacturers were under no illusions that under the terms of a 1996 law, shortfalls in helium supply were likely to become routine…

“For most of the past year, we have only been receiving about 80% of the helium for which we have contracted,” says Rodney Morgan of US chipmaker Micron Technology. 

Such was the sense of urgency from the IT industry and others, that the legislation to avert this crisis was among a handful of bills passed in haste by the US Congress on the eve of the recent US government shutdown.

“All of the other elements we’ve scattered around the globe, maybe we can go digging in garbage dumps to get them back,” says chemist Andrea Sella, of University College London (UCL).  “But helium is unique.  When it’s gone, it is lost to us forever.

As for those pesky balloons?  Well… Although the amount of helium used in party balloons remains comparatively small to its other main uses, it seems a rather trivial use of a very limited resource.

While a “helium cliff” may have been averted, it will take time for other countries to be able to step into the market to supply the gas.  Perhaps this is a good thing.  After all, if a resource is finite then we should value it a little bit more.

 

The era of cheap helium is over for now.