In this ScienceStruck article, we will shed light on the freezing point of salt water and also explain why it differs from the same for freshwater.
Key Things You Need to Know About the Idea of Cryogenic Freezing
In the mysterious world of cryogenics, metals have no resistance, gases are liquids, and life can be preserved forever. In this ScienceStruck article, we shall explore this strange world, and find out how these low temperatures affect the living and non-living things that exist around us. We will also talk about what the implications of cryogenic freezing for humans are.
Did You Know?
The lowest temperature on Earth was a bone chilling -126.4ºF (-88ºC), recorded at the Vostok Station in Antarctica. However, interestingly, it is still 111.6ºF or 62ºC higher than the lowest temperature in the cryogenic range, which extends from -238ºF (-150ºC) to -460ºF (-273ºC).
Since the dawn of man, cold has been our cruelest enemy. Even today, blizzards claim a yearly toll of the unprepared. Below the freezing point of water, human flesh can freeze solid, our hands and feet become vulnerable to frostbite, and in severe cases, tissues and cells can be damaged irreversibly. In the winters, death by freezing remains a constant threat. Yet, strangely, this murderous cold has also been accoladed with the title of the greatest preserver.
We all know that food keeps better in the low temperatures of a refrigerator. It lasts even longer within the freezer. These are tell-tale evidences of the ability of cold temperatures to preserve organic matter. But for how long can it do so, before the elements of nature come recycling? What all is cold capable of preserving? How does it affect inorganic materials?
To answer these questions, we will have to go much further below the average freezer temperature, diving deep into the subzero world. We will have to enter the realm of cryogenics – the world of the very, very cold.
What is Cryogenics?
When temperatures are steadily lowered, below the freezing point of water, i.e. 32ºF (0ºC), at -320.8ºF (-160ºC), nitrogen, the main component of air, turns into liquid. Further downwards, at -452ºF (-269ºC), helium, the gas that is most resistant to cold, also liquefies
As the temperatures descend to the lowermost limits, at -459.67ºF (-273.15ºC), we reach the point of absolute zero. At absolute zero, no heat can possibly exist within a body. This results in some very remarkable changes in the behavior of, both, organic and inorganic matter. The science of cryogenics studies these effects produced by extremely low temperatures approaching absolute zero.
Cryogenic temperature range has been defined as being between -238ºF (-150ºC) and absolute zero, which is -459.67ºF (-273.15ºC). Cryogenicists are responsible for studying the behavior of various materials and matter within this temperature range.
Typically, cryogenic temperatures are measured in the Kelvin scale, where absolute zero is represented by 0K. Notice that it doesn’t have a degree (º) notation.
How Cryogenic Freezing Works
The extremely low temperatures required for cryogenic freezing are rarely encountered in nature, and therefore, have to be created artificially. One method of producing these ultra-low temperatures is through magnetism.
Some materials heat up when they are magnetized, and cool down when they are demagnetized. A precisely controlled magnetic freezer can be used to freeze substances to extremely low temperatures. Gases can be cooled to super-low temperatures, by first compressing them, removing their heat through normal refrigeration, and then letting them expand.
The known natural properties of various materials at normal temperatures on the Earth tend to be altered significantly when they reach cryogenic temperatures. The motion of molecules within the materials is responsible for the production of heat. When a body is steadily cooled, the molecular motion within it begins slowing down steadily, until finally, at absolute zero, it ceases completely. This is the reason why no heat is produced at absolute zero.
The molecules cooled to cryogenic temperatures are nearly static, achieving an almost perfectly ordered state. This causes the internal properties of inorganic materials, such as thermal conductivity, electrical conductance, ductility, malleability, strength, etc., which are all dependent on molecular activity, to be altered in ways which are proving to be of scientific as well as commercial importance.
Cooling down to cryogenic temperatures also causes all biological activities to cease. Both growth as well as decomposition of living matter tends to significantly slow down and even completely stop. As such, it becomes possible to preserve various organic substances for very long durations using cryogenic freezing.
Brief History of Cryogenics
In the year 1877, cryogenics was first brought into practice when oxygen was cooled to -297.4ºF (-183ºC, 90K) at which point, it liquefied. This was a great achievement at that time. However, after this initial success, further practical development in cryogenics came to a grinding halt, owing to the lack of technology required to attain even lower temperatures that were required to freeze other elements. Therefore, the study of cryogenics continued more in theory and less in practice back then.
In the year 1895, significant technological advancements in the cooling capacity of refrigeration systems were made. It became possible to reach temperatures as low as 40K. At this point, air was liquefied to separate it into its major components. Later, in 1908, even lower temperatures could be attained, allowing for the liquefaction of helium at 4.2K.
Three years later, testing was carried out on metals at cryogenic temperatures. It was found that supercooled metals were able to lose all of their electric resistance. This property later came to be known as superconductivity.
Even further advancements in refrigeration technology, in the following years, made it possible to attain even lower temperatures, and by the year 1930, reaching temperatures in the vicinity of absolute zero finally started seeming like a reality. Though the laws of thermodynamics dictate that reaching the exact point of absolute zero isn’t possible, in 1960, laboratories demonstrated temperatures as low as 0.000001K, which is but a millionth of a degree above absolute zero.
In 1980, cryogenics led to the development of cold electronics, allowing scientists to attain previously unreachable levels of precision. Cryogenics has since been employed in many different fields of science, and today, it finds applications in varied fields, including, biology, medicine, food preservation, transportation, communications, and even in the fuels and devices used in outer space.
Applications of Cryogenics
The uses of cryogenic freezing today are multiple and diverse. To list out all of them is beyond the scope of this article. In the following lines, therefore, we shall go through only a few of the major ones.
1) LNG Transportation
The transportation of LNG, or liquefied natural gas, is one of the most important commercial applications of cryogenics. LNG is made up of methane, ethane, and other combustible gases. When it is liquefied at 110K, it compresses to 1/600 of its normal volume at room temperature. This allows large volumes of LNG to be filled into specially designed insulated tankers and transported very cost effectively.
2) Cryogenic Freezing of Food using LN2
Most food items are perishable, and thus require preservation if they are to be stored for long durations. Low temperatures reduce biological activity, including those of bacteria and other microorganisms responsible for food decomposing. At cryogenic temperatures, biological activity almost completely ceases, allowing for long-term preservation, making cryogenic freezing a perfect solution for long-term storage of perishable food items.
For cryogenic freezing of food, a special cryogen – liquid nitrogen (LN2) is used. Nitrogen is liquefied at -265ºF (-165ºC, 108.15K). The food to be preserved is placed in a chamber for cryogenic freezing, which is sprayed with liquid nitrogen. The LN2 absorbs the heat of the food transferred through the walls of the container, which immediately evaporates. This causes ultra-rapid cooling to very low temperatures, which allows effective food preservation for long durations.
3) Medical Science
Cryogenics also finds applications in the field of medical science. A special type of surgery, known as cryosurgery, involves using a super-cooled scalpel or a cryoprobe for performing operations. When live cells come in contact with this scalpel, they immediately freeze and die. This property is used to remove tonsils, warts, hemorrhoids, and even tumors in cryosurgical operations.
The process of cryogenic freezing has also been used to freeze small areas in the brains of people suffering from Parkinson’s disease, with good results. It has even found applications in the preservation of biological products, such as semen, blood, and bone marrow.
4) Particle Accelerators
The search for the Higgs Boson, also known as God’s particle, is believed to be the final frontier in the world of physics. For that, scientists are trying to recreate the conditions similar to those that were present shortly after the Big Bang, with the help of gigantic particle accelerators.
These accelerators require powerful super-electromagnets to accelerate the particles inside them. The current requirement of these super-electromagnets is so immense, that even the best conductors would melt due to enormous heat that is generated.
Superconductors, however, have almost zero resistance. This allows them to carry a huge amount of current without much heat generation. In the particle accelerators, liquid helium is used to cool the conductors connected to the super-electromagnets to almost 4K. This imparts superconductivity in them, making it possible to transmit large currents.
Superfluidity is an interesting phenomenon displayed by liquids and gases which have been cooled to cryogenic temperatures. This property was first observed in the gas helium.
When helium is cooled to 4.2K, it turns into a liquid known as helium I. If it is cooled further, then at 2.19K, it gets converted to helium II, which is a liquid having such a low viscosity, that it is literally able to crawl up the side of a glass panel, and flow through microscopic holes which wouldn’t allow the passage of normal liquids. This ultra low viscosity is attributed to the property of superfluidity, seen at cryogenic temperatures.
Though it is a very interesting phenomenon, superfluidity has but a limited number of applications as compared to superconductivity. It does find some practical use in the workings of large refrigerators, and in spectroscopy. Mostly, however, it has only a theoretical significance, especially in physics, when trying to combine the theory of gravity with quantum mechanics.
6) Cryogenic Engines
A cryogenic rocket engine is one which uses cryogenic fuel. It means that the fuel is cooled down to cryogenic temperatures, before being used to power these engines.
Cryogenic engines were first conceived during World War 2, when Germany, America, and Russia, each individually found out that to power big rocket engines, a high mass-flow rate of fuels was required. The fuel pair of oxygen and low molecular weight hydrocarbons used back then would remain in the gaseous sate at normal temperatures. So, to achieve the required high mass-flows rate, it had to be compressed. However, the increased mass of the fuel tanks required to hold this pressurized mixture made it most impractical when fitted inside a rocket.
To solve this problem, scientists froze the gaseous rocket fuel mixture to cryogenic temperatures, which liquefied it. This allowed it to be stored in much smaller fuel tanks, and also made it possible to achieve the required high mass-flow-rate.
It is interesting to note that, the cryogenic rocket engine used in Saturn V was what helped NASA to successfully launch it to the moon. Even till date, cryogenic engines are used across the world for putting satellites into outer space.
Special Application – Cryonics
Cryonics is a technique derived from cryogenics, which involves the low-temperature preservation of animals and human beings. It is based on the several evidences in nature which indicate towards the possibility of cold preservation of living creatures.
Many Alaskan animals, trees, and plants, have developed adaptations that allow them to survive and resist the damage brought on by very low temperatures. One particular creature of interest is the Alaskan insect tardigrade, which is known to survive at temperatures even below -58ºF (-50ºC). But can humans and other animals also survive such low temperatures?
Studies using cyromicroscopes show that low temperatures cause ice crystals to form in the fluids within the cells and blood vessels, which causes them to sustain damage and die, as a consequence.
So how is it that the cells in the body of the tardigrade do not suffer similar damage? The answer lies in ‘glycerol’, which is the chemical produced by tardigrades to protect themselves against freezing damage. This chemical is now being produced in labs, and by using it, several separate elements of life have been frozen successfully. These include blood, sperm, embryos, etc. Scientists have even been able to freeze entire pancreas taken from mice, and have managed to replant them successfully.
One more interesting application has been in the process of freezing human embryos. Protected by a chemical known as DMSO, embryos have been preserved successfully by freezing them to -148ºF (-100ºC), at which point the embryos stop growing and enter a state of suspended animation. Scientists have been able to maintain this state for up to ten years, and have also been able to successfully revive them by thawing, which allowed them to resume their growth process.
The Future of Cryonics
Going to sleep today in a special sleeping pod, and waking up hundreds of years in the future… seems like a scene from a Sci-Fi movie, doesn’t it? Well, guess what! Through the science of cryogenics, this might become a real possibility one day.
All the achievements in the field of cryonics up to now beg the question – is it possible to freeze an entire human being and successfully revive him/her by thawing the body? Well, right now, due to the limitations in technology, the answer is no. We can freeze a person, but cannot bring him/her back from that state of suspended animation.
However, this hasn’t stopped people from believing that, one day, such a technology shall exist. Already, there are special cryonic facilities around the world, where humans are having themselves frozen with the hopes that they will someday be revived. Currently, however, cryogenic freezing is only legal after death. As such, to be allowed to be frozen, a person first needs to be pronounced legally dead by a qualified medical practitioner.
A legally dead person is one whose heart has stopped. Such a person can still be medically alive if his/her brain is functioning. Many people who have legally died of terminal illnesses have been frozen in special cryonic pods in the hopes that they will be unfrozen in the future, brought back to life, and also have their illnesses treated and cured with the help of advanced future medicines.
Cryonic companies engaged in human freezing and preservation use special equipment and chemicals to prevent freezing damage to the bodies of qualified individuals, and store them within special cryonic chambers. Note however, that the cost of cryogenic freezing, which includes the cost of these equipment, is huge. For preserving your entire body, you would be required to shell out nearly $200,000. For the highly optimistic ones, there is also the option of having only your brain preserved for $60,000. However, whether the people frozen today will be revived in the future or not, only time can tell.
Thus, the science of cryogenics has been beneficially employed for the preservation of several organic materials, as well as for improving the properties of inorganic ones. It has also led to the development of cryonics, which may one day help in the preservation of entire human beings, thus bringing us one step closer to immortality.