Gaseous and Liquid Helium

Helium is the second lightest element on the periodic table. At standard temperature and pressure, it exists as a colorless, odorless, and tasteless gas known as gaseous helium. Below 4 Kelvin (-452° F), it becomes a clear liquid called liquid helium. Both gaseous and liquid helium have unique properties and important applications in science, medicine, and technology.

Properties of Gaseous Helium

Gaseous helium has several characteristic properties that differentiate it from other gases. It has an atomic number of 2 and molecular weight of 4. Due to its light atomic mass, it is the least dense gas and has the lowest boiling point of any element. Gaseous helium is an inert gas, meaning it is chemically unreactive. It is used as a shielding gas for arc welding to prevent oxidation. Another interesting property is that helium's low density allows it to produce higher-pitched sounds compared to other gases when used in pressurized equipment.

Uses of Gaseous Helium

As a lifting gas, Gaseous Helium finds widespread application in balloons and airships since it is about 7 times lighter than air. It is commonly used as a pressurizing and purge gas in the aerospace industry for its inert qualities. Liquid fueled rockets use gaseous helium to pressurize propellant tanks. The gas is also employed as a tracer and carrier in leak testing and helps detect gas leaks in industrial plants. Due to its high thermal conductivity, gaseous helium is utilized in cryogenic applications as well as to cool superconducting magnets to low temperatures near absolute zero. It has become an essential component of MRI machines that employ superconducting magnets.

Discovery of Liquid Helium

In 1908, Dutch physicist Heike Kamerlingh Onnes was the first to liquefy helium by cooling it to below 4.2 K (-452° F) using a new cryogenic technique he pioneered. This milestone marked the first time an element was liquefied at ambient pressures. Others had liquefied hydrogen earlier by pressurizing it, but Kamerlingh Onnes achieved liquefaction of helium by heating gaseous hydrogen and then recondensing its vapors. In doing so, he initiated the new field of cryogenics and opened up possibilities to study matter at ultra-low temperatures.

Properties of Liquid Helium

Liquid helium possesses some fascinating properties below its boiling point of 4.2 K. It is the only substance known to exhibit superfluidity - the ability to flow without any viscosity. Under very low temperatures and pressures, it enters the superfluid phase where frictionless flow allows it to climb walls of its container. Liquid helium also has one of the highest thermal conductivity values of any known material. This unique ability to absorb heat arises from its quantum mechanical properties near absolute zero. Besides remaining in liquid form through evaporation, it can change phases from liquid to superfluid without crossing the boiling point.

Applications of Liquid Helium

Key applications stem from liquid helium's capacity to maintain extremely low temperatures. It serves as a coolant for superconducting magnets in advanced research facilities andMRI machines. Liquid helium vaporizes when cooling magnets and transfers the absorbed heat out of the system. It has enabled new frontiers in physics by facilitating studies on superconductivity, semiconductor, and properties of exotic quantum states of matter. Cryogenic laboratories rely on liquid helium refrigerators to reach sub-Kelvin temperatures for experimental research. The electronics industry uses it to test semiconductors and microchips at close to absolute zero conditions. Other important uses include rocket engine testing, infrared sensors, laser guides, and space telescopes requiring ultra-low temperature operation.

Helium Reserves and Supply Concerns

Most of the world's helium originates as a byproduct of natural gas extraction from underground reserves. The US Federal Helium Reserve is the largest supplier globally but is expected to be depleted in the coming decades. Only about 1% of the helium consumed is recovered and recycled. While deposits in Qatar and Algeria can fulfill demand temporarily, long term availability is uncertain especially for specialty applications. The shortage of helium has driven prices to spike in the last few years. Conservation efforts through recycling recovered helium and adoption of alternatives are needed to avert a looming helium crisis. New extraction techniques may help tap remote reservoirs, but addressing supply variability remains a pressing challenge.

Both gaseous and liquid helium have revolutionized areas as diverse as ballooning, space technology, medicine, and fundamental scientific research. Their extraordinary properties near absolute zero have enabled novel applications and discovery of new states of matter. However, rising demand and limited reserves threaten their sustained availability. Improved recycling and policies to encourage new extraction projects can help avoid future supply disruptions. While alternatives may work for some uses, helium is irreplaceable for key technologies. Careful management of stockpiles and incentivizing private sector investment remain critical to ensure secure access to this wonder gas.