The Phenomenon: Occurrence and Characteristics

Abstract

The phenomenon of superconductivity has been observed only at low temperatures. Therefore, we shall first consider the efforts made and the achievements on the way to absolute zero temperature.

A very common way of liquefying gases is to compress them. This causes the gas molecules to come closer, and the role of cohesive forces increases. This makes gas–liquid transition to become possible: However, at temperatures higher than the critical point, it is not possible to turn the gas into a liquid, however, large the pressure applied. So, it is necessary to cool the gas first before compressing it. In 1877, French scientist Caillettet succeeded in liquefying oxygen at a temperature 90.2K. Six years later, N2 was liquefied at 77.4K. The hydrogen was found to be liquefied at a temperature of 20.4K. This was made possible by sir James Dewar in 1898, who invented a vacuum vessel, which is used even nowadays to store liquid hydrogen. Helium was discovered in 1869 in the spectrum of solar corona. For a long time, it could not be detected on earth. It was only in 1895 that Sir William Ramsay found it among gases released when certain minerals were heated. At the end of nine teenth century, it became known that the boiling point of helium was even lower than that of hydrogen. In the late 1890s, Dutch scientist K. Onnes began his experiments aimed at liquefying helium. It was ultimately found that the transition temperature is 4.2K and liquefaction was achieved in 1908.