Helium belongs to the group of noble gases. Liquid helium is the coldest liquid in the world. In this aggregate state, it has a number of unique features, such as superfluidity and superconductivity. We will learn more about its properties later.
Helium gas
Helium is a simple substance widely distributed in the Universe in a gaseous state. In the periodic table of Mendeleev, he is the second and is immediately after hydrogen. It refers to inert or noble gases.
The element is designated as "He". From ancient Greek, its name means "Sun". At first it was assumed that it was metal. However, it turned out that this is a monatomic gas. Helium is the second lightest chemical and is tasteless, colorless and odorless. Has the lowest boiling point.
Under normal conditions, it is an ideal gas. In addition to gaseous, it is capable of being in a solid and liquid state. Its inertness is manifested in inactive interaction with other substances. It is practically insoluble in water. For industrial purposes, it is extracted from natural gas, separating it from impurities withusing strong cooling.
Gas can be dangerous to humans. An increase in its concentration in the air leads to a lack of oxygen in the blood, which in medicine is called oxygen starvation. When ingested in large quantities, it causes vomiting, loss of consciousness, and sometimes death.
Liquefaction of helium
Any gas can go into a liquid state of aggregation under certain conditions. Liquefaction is commonly used in industry as well as in scientific research. For some substances, it is enough to simply increase the pressure. Others, such as helium, only become liquid when cooled.
If the gas temperature is above the critical point, it will not condense, no matter what the pressure. For helium, the critical point is 5.19 Kelvin, for its 3He isotope it is 3.35 K.
Liquid helium is an almost perfect liquid. It is characterized by the absence of surface tension, viscosity. After changing pressure and temperature, its volume remains the same. Liquid helium has extremely low tension. The substance is colorless and highly fluid.
Properties of liquid helium
In a liquid state, helium is poorly distinguishable, because it weakly refracts light rays. Under certain conditions, it has the properties of a quantum liquid. Due to this, at normal pressure, it does not crystallize even at a temperature of −273.15 Celsius (absolute zero). All other known substances solidify under these conditions.
The temperature at which liquid helium begins to boil is -268.9 degrees Celsius. The physical properties of its isotopes vary considerably. For example, helium-4 boils at 4.215 K.
It is a Bose liquid, which is characterized by phase transitions at temperatures of 2, 172 Kelvin and below. The He II phase is characterized by superfluidity and superthermal conductivity. At temperatures below the phase, He I and He II occur simultaneously, due to which two speeds of sound appear in the liquid.
Helium-3 is a Fermi liquid. It boils at 3.19 Kelvin. An isotope can only achieve superfluidity at very low temperatures (a few millikelvins) when there is sufficient attraction between its particles.
Helium superfluidity
Science owes the study of the concept of superfluidity to Academicians S. P. Kapitsa and L. D. Landau.
The academician concluded that after the temperature of helium falls below 2, 172 K, the substance passes from the phase of the normal state to a completely new one, called helium-II. In this phase, the substance passes through the capillaries and narrow holes without the slightest friction. This state is called "superfluidity".
In 1941, L. D. Landau continued to study the properties of liquid helium and developed the theory of superfluidity. Explainhe took it by quantum methods, applying the concept of the energy spectrum of excitations.
Helium applications
The element helium was discovered in the spectrum of the Sun in 1868. On Earth, it was discovered by William Ramsay in 1895, after which it was studied for a long time and was not used in the economic sphere. In industrial activity, it began to be used as fuel for airships during the First World War.
Gas is actively used for packaging in the food industry, in the smelting of metals. Geologists use it to detect faults in the earth's crust. Liquid helium is mainly used as a refrigerant capable of maintaining ultra-low temperatures. This property is necessary for scientific research.
The coolant liquid is used in cryogenic electric machines, in scanning tunneling microscopes, in devices of medical NMR tomographs, in charged particle accelerators.
Conclusion
Helium is an inert or noble gas that exhibits low activity in interaction with other substances. In the periodic table of chemical elements, it is in second place, behind hydrogen. In nature, matter is in the gaseous state. Under certain conditions, it can go into other states of aggregation.
The main feature of liquid helium is its superfluidity and inability to crystallize at normal pressure, even if the temperature reaches absolute zero. The properties of the isotopes of a substance are not the same. Their critic altemperatures, their boiling conditions, and the spins of their particles.
