[Physics Class Notes] on Cryogenics Pdf for Exam

Cryogenics is the prediction of the behaviour of materials at low temperatures. Ultra-cold or cold temperatures will change the chemical properties of materials, which provides an interesting area of study for all the researchers who wish to examine the materials. It is because they transit from gas to liquid to a solid-state. These studies have led to advancements not only in our understanding of different materials but also in the creation of totally new technologies and industries.

The temperature of any material is the measure of the energy that the material is containing. Rapidly moving molecules have a relatively higher temperature than molecules moving slowly. For instance, while water transforms from the liquid state to the solid at 32° F (0° C), then cryogenic temperatures range much lower that is from -150°C to -273° C. Temperature -273° C is the absolute lowest temperature that can be achieved. 

The actions of all molecules stop at this temperature by causing the molecules to be at the lowest possible state of energy. The liquid gases at -150 degrees Celsius or below -150° C can be used to freeze other materials. The environment is considered to be cryogenic once gas starts to liquefy. The most commonly used gases for turning to liquid for cryogenics are oxygen, nitrogen, hydrogen, as well as helium.

History of Cryogenics

The word cryogenics originates from the Greek word “Kyros”. The word Kyros means cold. Combined with the abbreviated English word “to generate” comes the word we know as cryogenics.

Temperatures that are extremely cold are not measured in degrees, in Fahrenheit, or in Celsius but they are measured in Kelvin. Kelvins use the unit symbol K and it is named after Baron Kelvin. He believed that at extremely low temperatures a new scale was needed that would not be measured by the material state change of water like the Fahrenheit or the Celsius. Zero degrees Kelvin (0 K) is theoretically considered to be the coldest possible temperature.

In 1877 Rasul Pictet, and Louis Cailletet liquefied oxygen for the first time. They both used different methods for the process. But in the end, a third method of liquefying oxygen was discovered. At this point in history, for the first time ever oxygen was able to be liquefied at 90 K, and soon after, liquid nitrogen was achieved at a temperature of 77 K. After this discovery, scientists all over the world began to compete to lower the temperature of matter to absolute zero.

In the year 1898, the next breakthrough came when James DeWar was able to liquefy the hydrogen at 20 K. This presented a further issue on handling and storing of the gases at such temperatures. Therefore, the creation of DeWar flasks, are used to store gases today. The last major advancement in the history of the cryogenics industry came in the year 1908. The physicist Heike Kamerling Onnes liquefied Helium at 4.2 K and then liquefied it at 3.2 K.  

The advancements in cryogenics following this development have been very few. It is smaller because the thermodynamic law states that you can approach absolute zero, but never actually reach it. Technology has advanced much more rapidly since this last major discovery. Now, we can freeze materials at very small distances from absolute zero. Though the scientists still have not been able to break the thermodynamic law which states that every particle has zero energy.

Applications and Uses of Cryogenics

• Cryosurgery- Cryosurgery is a type of surgery that uses cryogenic temperatures in order to eliminate unwanted tissue or tumours from the body. In history, cryosurgery has been used to treat a variety of diseases. It is most commonly used in benign and malignant skin conditions. This type of surgery is effective as it works using the freezing temperatures on the cells that are needed to be removed from the body. Ice crystals begin to form on the cells and eventually tear them apart.

• Cryoelectronics- Cryoelectronics is the ultra-frozen temperatures that cryogenic fluids can provide and also offer the ability for electrons in materials to move freely with very little resistance. This is very beneficial for the superconductors and in spacecraft design. For instance, oxygen and also hydrogen when stored as cryogenic fluids are highly advantageous sources to power space rockets.

1. The study of cold-adaptation of microorganisms, plants, animals, as well as of vertebrates.

2. Cryopreservation of cell tissues as well as the embryos used in in-vitro fertilization.

3. Preservation of the organs.

4. Lyophilization, and the freeze-drying of pharmaceuticals.

5. Cryosurgery falls under this category.

6. Supercooling as applied to biological systems.