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Essay on “Cryogenics” Complete Essay for Class 9, Class 10, Class 12 and Graduation and other classes.

Cryogenics 

Cryogenics is the study and use of materials at very low temperatures. The upper limit of cryogenic temperatures has not been agreed on, but the United States National Institute of Standards and Technology has suggested that the term cryogenics be applied to all temperatures below -150° C (-238° F or 123 K). Some scientists take the normal boiling point of oxygen (-183° C or -297° F), as the upper limit. Cryogenic temperatures are achieved either by the rapid evaporation of volatile liquids or by the expansion of gases confined initially at pressures of 150 to 200 atmospheres. The expansion may be simple, that is, through a valve to a region of lower pressure, or it may occur in the cylinder of a reciprocating engine, with the gas driving the piston of the engine. The second method is more efficient but is also more difficult to apply.

Pioneering work in low-temperature physics by the British. chemists Humphry Davy and Michael Faraday, between 1823 and 1845, prepared the way for the development of cryogenics. Day); and Faraday generated gases by heating an appropriate mixture at one end of a sealed tube shaped like an inverted V. The other end, was chilled in a salt-ice mixture. The combination of reduced  temperature and increased pressure caused the evolved gas to liquefy. When the tube was opened, the liquid evaporated rapidly and cooled to its normal boiling point. By evaporating solid carbon dioxide mixed with ether, at low pressure, Faraday finally succeeded in reaching a temperature of about 163 K (-110° CI-166° F).

The Dutch physicist Heike Kamerlingh Onnes set up the first liquid-air plant in 1894, using the cascade principle. Investigators in Great Britain, France, Germany, and Russia developed various improvements in the process during the following 40 years. The British chemist Sir James Dewar first liquefied hydrogen in 1898 and Kamerlingh Onnes liquefied helium, the most difficult of the gases to liquefy, in 1908. Since then increased attention has been given to studying phenomena at low temperatures. The increased efficiency of having a refrigerant gas operate in a reciprocating engine or in a turbine has continued to be a challenge. The work of the Soviet physicist Peter Leonidovich Kapitza and the American mechanical engineer Samuel Collins has been noteworthy. A helium-liquefier based on Collins’s design has provided the opportunity for many non-specialist laboratories to conduct experiments at the normal boiling point of helium, 4.2 K (-268.9° C/-452.0° F).

Dewar flasks have proved useful for storing liquids at cryogenic temperatures. Such vessels consist of two flasks, one within the other, separated by an evacuated space. The outside of the inner flask and the inside of the outer flask are silvered to prevent radiant heat from passing across the vacuum. Substances colder than liquid air cannot be handled in open Dewar flasks because air would condense in the sample or would form a solid plug preventing the escape of released vapours; the accumulated vapours would eventually rupture the container.

At cryogenic temperatures many materials behave in ways unfamiliar under ordinary conditions. Mercury solidifies and rubber becomes as brittle as glass. The specific heats of gases and solids decrease in a way that confirms the predictions of quantum theory. The electrical resistance of many, but not all, metals and metalloids decrease abruptly to zero at temperatures of a few Kelvin.

Among the many important industrial applications of cryogenics is the large-scale production of oxygen and nitrogen from air. The oxygen can be used in a variety of ways: for example, in rocket engines, for cutting and welding torches, for supporting life j spacecraft and deep-sea vehicles, and for blast furnace operation: The nitrogen goes into the making of ammonia for fertilizers, and it is used to prepare frozen foods by cooling them rapidly enough to prevent destruction of cell tissues. It can also serve as a refrigerant and for transporting frozen foods.

Cryogenics has also made possible the commercial transport of liquefied natural gas. Without cryogenics, nuclear research would lack liquid hydrogen and helium for use in particle detectors and for the powerful electromagnets needed in large particle accelerators. Such magnets are also being used in nuclear fusion research. Infrared devices, masers, and lasers can employ cryogenic temperatures as well. Cryogenic surgery, or cryosurgery, is being used for the treatment of Parkinson’s disease, the technique being based on the selective destruction of tissue by freezing it with a small cryogenic probe. A similar technique has also been employed to destroy brain tumours and to arrest cervical cancer.

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