Cryogenics is the production of and behavior of materials at very low temperatures.
Ultra-cold temperatures change the chemical properties of materials. This has become an area of study for researchers who examine different materials as they transition from gas to liquid to a solid state. These studies have lead to advances in not only our understanding of different materials, but the creation of entirely new technologies and industries.
The temperature of any material is the measure of the energy that it contains. Rapidly moving molecules have a higher temperature than slower moving molecules.
For example, while water transforms from a liquid to a solid at 32° F (0° C), cryogenic temperatures range much lower; from -150°C to -273° C. The temperature -273° C is the absolute lowest that can be achieved. At this temperature the actions of all molecules stop, causing the molecules to be at the lowest possible state of energy.
Liquid gases at or below -150° C are also used to freeze other materials. Once a gas begins to liquefy, the environment is considered a cryogenic one. The most common gases that are turned to liquid for cryogenics are oxygen, nitrogen, hydrogen and helium.
History of Cryogenics
The word cryogenics comes from the Greek word “kyros,” which means cold. This combined with the abbreviated English word “to generate” make the word we know as cryogenics.
Temperatures that are very cold are not measured in degrees Fahrenheit or Celsius, but in Kelvins. Kelvins use the unit symbol K. It is named after Baron Kelvin who believed that at very low temperatures a new scale was needed that was not measured by the material state change of water like Fahrenheit or Celsius. Zero degrees Kelvin (0 K) is the theoretically coldest possible temperature.
In 1877 Rasul Pictet and Louis Cailletet liquefied oxygen for the first time, both using different methods for the process. Eventually a third method of liquefying oxygen was discovered, and at this point in history oxygen was able to be liquefied at 90 K. Soon after, liquid nitrogen was achieved at 77 K. Scientists all over the world began competing to lower the temperature of matter to absolute zero.
The next breakthrough came in 1898 when James DeWar liquefied hydrogen at 20 K. This presented a new problem to researchers, as 20 K is also at a boiling temperature. However, this presented a further issue on how to handle and store gases at such temperatures. Hence the creation of DeWar flasks, which are used to store gases today.
The last major advance in the cryogenics industry came in 1908 when the physicist Heike Kamerling Onnes liquefied Helium at 4.2 K and then 3.2 K. The advances in cryogenics following this development have been much smaller because it is thermodynamic law that you can approach absolute zero, but never actually reach it. Technology has advanced much more since this last major discovery, and we can now freeze materials within very small distances from absolute zero, yet scientists still have not been able to break thermodynamic law where every particle has zero energy.
What Is Cryogenics Used For?
Cryogenics is used in a variety of applications. It can be used to produce cryogenic fields for rockets, in MRI machines that use liquid helium and require cryogenic cooling, storing large quantities of food, special effects fog, recycling, freezing blood and tissue samples, and even cooling superconductors.
Applications and uses:
Cryosurgery is a type of surgery that uses cryogenic temperatures to eliminate unwanted tissue or tumors. Historically, cryosurgery has been used to treat a variety of diseases, most commonly, benign and malignant skin conditions. This type of surgery is effective because it works by using the freezing temperatures on cells that need to be removed from the body. Ice crystals begin to form on the cells and ultimately tear them apart.
The ultra-frozen temperatures that cryogenic fluids can provide offer the ability for electrons in materials to move freely with little resistance. This is of great benefit for superconductors and in spacecraft design. For example, oxygen and hydrogen when stored as cryogenic fluids are highly advantageous sources that can be used to power space rockets.
Cryobiology is the study of the effects of low temperatures on organisms. There are six major areas of cryobiology:
- The study of cold-adaptation of microorganisms, plants, animals and vertebrates
- Cryopreservation of cell tissues and embryos used in invitro fertilization
- Preservation of organs
- Lyophilization, the freeze-drying of pharmaceuticals
- Cryosurgery falls under this category
- Supercooling as applied to biological systems
To preserve packaged foods such as produce, the food items can be sprayed with liquid nitrogen to absorb the heat within the produce. Eventually, the nitrogen evaporates before the food is consumed. With this application of cryogenics, foods can be kept preserved longer without any chemical threat to human consumption.
Transportation of Gases
Cryogenics is also used to transport gases that are not typically cryogenic. For example, using cryotechnology, gases can be transformed into liquids to make them easier to transport from one place to another. Take natural gas (LNG) which is a combination of ethane, methane and other gases. When these gases become liquefied, they take up far less space than if they remained gaseous. Therefore, transportation expenses become lower and the process becomes much easier.
Cryotherapy is the term used to describe when the human body is exposed to extremely cold temperatures. The most common use of this application is the new trend of cryospas. In these areas, people can stand in a cryosauna filled with cryogenic fluids for several minutes. Studies have shown that this treatment touts many benefits to the body, such as reducing inflammation, increasing energy, managing pain, and even can boost metabolism, amongst other claims. Research on cryotherapy is still very new, and benefits have not been fully researched or understood.
The cryo-preservation of animals and humans is called cryonics. Researchers in this field give their subjects hope that by freezing their body they may be able to resuscitate them in the future. Hundreds of people (and their pets!) are currently frozen via cryo-preservation worldwide. The science of cryonics is not proven and most scientists are dubious of the claims.
What's Next for Cryogenics?
As technology rapidly evolves areas of cryogenics will continue to develop and eventually expand to more applications. While we can’t predict what developments will come next, what we do know is that safety around cryogenic fluids is a must, no matter which direction the research will progress.
It is important that all applications handling, studying and using cryogenic liquids use the proper safety precautions and oxygen depletion monitors to ensure both safe and accurate monitoring of gas concentrations.