What’s the Freezing Point of Helium?
- October 29, 2020
- Cryogenic Processing
The chemical elements in group 18 of the periodic table are called noble gases. They’re called noble gases because they’re the most stable as they have the maximum number of valence electrons their outer shell is capable of holding. This means that they rarely react with other elements because they’re already stable.
All of the noble gases conduct electricity and they’re odorless and colorless. Previously, they used to be called inert gases but that term is not technically accurate. That’s because several noble gases do take part in chemical reactions.
One of the six noble gases, Helium, is widely used in the cryogenics processing industry. It has specific properties that make it suitable for cryogenics.
What is Helium and where is it found?
Bearing the symbol He and atomic number 2, Helium is a colorless, non-toxic, monatomic gas that’s the first and lightest member of the noble gas group in the periodic table.
It happens to be the second lightest and second most abundant element in the universe, second only to Hydrogen.
A unique characteristic of Helium is that unlike any other element, it can remain liquid down to absolute zero at normal pressures. That’s due to quantum mechanics. Specifically, the zero point energy of the system is high enough to allow freezing.
While Helium is the second most abundant element in the universe, it’s actually quite rare on Earth. As such, there’s no chemical method of manufacturing Helium.
The supplies that are being used today are obtained due to the alpha-particle delay of radioactive elements in the Earth. It was and still is being formed because of this decay.
It’s not economically viable to extract Helium from the air even though the atmosphere contains around 5 parts per million by volume.
According to some estimates, extracting Helium from the air may cost around 10,000 times more than to extract it from rocks and natural gas reserves. The major source is natural gas which can contain up to 7% Helium.
What’s the freezing point of Helium?
While the gas does have a variety of industrial uses, cryogenics is the largest single use of liquid Helium. It absorbs around the quarter of the total production of the gas. It’s particularly used in the cooling of superconducting magnets with MRI scanners being its main commercial application.
That’s due to the fact that Helium has the lowest boiling and freezing points of any other known substance. Helium happens to be the only element that can’t be solidified or frozen at normal atmospheric pressure.
Only once you apply a pressure of 25 atmospheres at Helium’s freezing point of −458 °F can you solidify it.
Does Helium freeze at absolute zero?
Helium behaves unlike any other element because it remains liquid down to absolute zero temperatures at normal pressures. This is entirely due to quantum mechanical effects.
Even at absolute zero 0K temperatures, the particles have energy which is known as zero point motion. This zero point motion is significant enough that it prevents the atoms from sticking together as a solid. This is why Helium doesn’t freeze at absolute zero.
Is Liquid Nitrogen colder?
Liquid nitrogen is not colder than liquid helium. The simple fact is that that liquid helium is the coldest known material as it has a boiling point of -452°F. It also happens to be the only material that doesn’t exist as a solid, it either exists as a gas or as a cryogenic liquid.
On the other hand, liquid nitrogen has a boiling point of -320°F but there’s another reason why it’s also widely used for cryogenic treatment. Liquid helium is significantly cheaper than Helium even though the latter is the second most common element in the universe.
As discussed previously, extracting Helium from the air is not viable and there’s only a fixed amount available on Earth. Liquid nitrogen is inexpensive and easily available because it can be extracted from the air without incurring a great cost.
Using Helium in cryogenic treatment
Helium is used for a variety of applications in the field of cryogenics. It’s able to yield interesting properties due to its extremely low molecular weight and weak interatomic reactions when cooled below its critical temperature of 5.2K to form a liquid.
One of the primary uses of liquid helium in cryogenics is as a coolant for superconducting applications.
For example, it’s used in particle accelerators which use magnets to steer charged particles. Superconducting magnets are used in applications where large magnetic fields are required.
Superconductors can only be efficient when they are kept below their respective critical temperature.
Liquid helium then transfers heat away from superconductors. The most notable example is that of CERN’s Large Hadron Collider, which uses 96 metric tons of liquid helium to maintain the temperature at 1.9K.
Beyond that, there’s significant benefit to be derived from using liquid helium for cryogenic treatment of metals. Using it as a cryogen enables the process to reach much lower temperatures that would otherwise not be possible with other cryogenic liquids.
Cryogenic helium processing is useful for relieving residual material stresses, thermal cycling of experimental materials or sensitive aerospace components, preconditioning of material, and more.
Handling liquid helium does require great care. When being transported, the vessels and piping should be designed to the American Society of Mechanical Engineers (ASME) specifications or the Department of Transportation (DOT) codes to anticipate the pressures and temperatures.
Containers filled with liquid helium should be kept in a well ventilated storage area when they’re not in use or connected to a closed system.
The containers should be kept vertical at all times. They should be moved by pushing, not pulling, and never tipped, slided or rolled on their side.
Our Liquid Helium cryogenic process
Controlled Thermal Processing Cryogenics is a leader in deep cryogenic treatment and the thermal processing of metals and specialized plastics.
Using our proprietary systems, we can treat a variety of metals and plastics, including but not limited to brake rotors, machine components, aerospace components, and more.
We are highly skilled in providing liquid helium based cryogenic processing of materials in addition to our other services which include sales of cryogenic equipment, micropolishing of components, and metallurgical consulting.
The process that we use is called DCT or Deep Cryogenic Treatment. It’s carried out to refine the structure of the metal or plastic into a more uniform and durable formation.
The materials are first submerged in our cryocoolers for up to 24 hours and then slowly brought back up to room temperature to achieve a more perfect crystalline alignment.
The DCT process considerably improves the life of metal components. Studies have shown that brake rotors that have been cryogenically treated can last three times as long, the same holds true for industrial dies and tools.
CTP Cryogenics has three decades of experience in the field of cryogenics processing. We offer our services and state-of-the-art equipment through three locations across the United States.
Over the years we have worked with many clients and partners that have included NASA’s Space Shuttle program, the US Postal Service, Remington Firearms, Dupont, and others.
Reach out today for a free quote for the thermal processing of metal parts with liquid helium.