Helium: properties, characteristics, application

Helium is an inert gas of the 18th group of the periodic table. This is the second lightest element after hydrogen. Helium is a gas without color, odor and taste, which becomes liquid at a temperature of -268.9 ° C. The boiling point and freezing point is lower than that of any other known substance. This is the only element that does not solidify upon cooling at normal atmospheric pressure. For helium to pass into a solid state, 25 atmospheres are necessary at a temperature of 1 K.

History of the discovery

Helium was found in the gas atmosphere surrounding the Sun, the French astronomer Pierre Zhansen, who in 1868 during the eclipse discovered a bright yellow line in the spectrum of the solar chromosphere. Originally, it was assumed that this line represented the element sodium. In the same year, the English astronomer Joseph Norman Lockyer observed a yellow line in the solar spectrum that did not correspond to the known sodium lines D ₁ and D ₂ , and so he called it the D ₃ line. Lockyer came to the conclusion that it was caused by a substance on the Sun, unknown on Earth. He and the chemist Edward Frankland in the name of the element used the Greek name of the Sun "helios".

In 1895, the British chemist Sir William Ramsay proved the existence of helium on Earth. He obtained a sample of the uraniferous mineral of the claveite, and after studying the gases formed during its heating, he found that the bright yellow line in the spectrum coincides with the D ₃ line observed in the solar spectrum. Thus, the new element was finally established. In 1903, Ramzi and Frederic Sodd determined that helium is the product of the spontaneous decay of radioactive substances.

Distribution in nature

The mass of helium is about 23% of the total mass of the universe, and the element is the second most abundant in space. It is concentrated in stars, where it is formed from hydrogen as a result of thermonuclear fusion. Although in the terrestrial atmosphere, helium is in the concentration of 1 part per 200 thousand (5 ppm) and in small amounts is contained in radioactive minerals, meteorite iron, and also in mineral sources, large amounts of element are found in the United States (especially in Texas, Mexico, Kansas, Oklahoma, Arizona and Utah) as a component (up to 7.6%) of natural gas. Its small reserves were found in Australia, Algeria, Poland, Qatar and Russia. In the earth's crust, the concentration of helium is only about 8 parts per billion.

Isotopes

The nucleus of each helium atom contains two protons, but, like other elements, it has isotopes. They contain from one to six neutrons, so their mass numbers are in the range of three to eight. Stable of them are elements in which the mass of helium is determined by the atomic numbers 3 ( ³ He) and 4 ( ⁴ He). All the rest are radioactive and very quickly break down into other substances. Earth helium is not the original constituent of the planet, it was formed as a result of radioactive decay. Alpha particles emitted by the nuclei of heavy radioactive substances are the nuclei of the isotope ⁴ He. Helium does not accumulate in large quantities in the atmosphere, because the Earth's gravity is not enough to prevent its gradual leakage into space. Traces of ³ He on the Earth are explained by the negative beta decay of a rare element of hydrogen-3 (tritium). ⁴ He is the most common stable isotope: the ratio of the number of atoms of ⁴ He to ³ He is about 700 thousand to 1 in the atmosphere and about 7 million to 1 in some helium-containing minerals.

Physical properties of helium

The boiling point and melting point of this element are the lowest. For this reason, helium exists as a gas, with the exception of extreme conditions. Gaseous He in water dissolves less than any other gas, and the rate of diffusion through solid bodies is three times greater than that of air. Its refractive index is closest to 1.

The thermal conductivity of helium is second only to the thermal conductivity of hydrogen, and its specific heat is unusually high. At ordinary temperatures, during expansion, it heats up, and below 40 K it cools. Therefore, at T <40 K, helium can be converted into a liquid by expansion.

An element is a dielectric if it is not in an ionized state. Like other noble gases, helium has metastable energy levels that allow it to remain ionized in an electrical discharge when the voltage remains below the ionization potential.

Helium-4 is unique in that it has two liquid forms. The usual one is called helium I and exists at temperatures from the boiling point of 4.21 K (-268.9 ° C) to about 2.18 K (-271 ° C). Below 2.18 K, the thermal conductivity of ⁴ He becomes 1000 times greater than that of copper. This form is called helium II, in order to distinguish it from ordinary. It has superfluidity: the viscosity is so low that it can not be measured. Helium II spreads into a thin film on the surface of any substance touched, and this film flows without friction, even against gravity.

Less abundant helium-3 forms three different liquid phases, two of which are superfluids. Superfluidity in ⁴ He was discovered by the Soviet physicist Petr Leonidovich Kapitsa in the mid-1930s, and the same phenomenon in ³ He was first noticed by Douglas D. Osherov, David M. Lee, and Robert S. Richardson from the United States in 1972.

A liquid mixture of two isotopes of helium-3 and -4 at temperatures below 0.8 K (-272.4 ° C) is divided into two layers - practically pure ³ He and a mixture of ⁴ He and 6% helium-3. The dissolution of ³ He to ⁴ He is accompanied by a cooling effect, which is used in the design of cryostats in which the helium temperature falls below 0.01 K (-273.14 ° C) and is maintained for several days.

Connections

Under normal conditions, helium is chemically inert. In extreme cases, it is possible to create element connections that are not stable under normal temperature and pressure conditions. For example, helium can form compounds with iodine, tungsten, fluorine, phosphorus and sulfur when it is exposed to an electric glow discharge when bombarded with electrons or in a state of plasma. Thus, HeNe, HgHe ₁₀ , WHe ₂ and molecular ions He ₂ ⁺ , He ₂ ⁺⁺ , HeH ⁺ and HeD ^{+ were created} . This technique also made it possible to obtain neutral He ₂ and HgHe molecules.

Plasma

In the Universe, ionized helium is predominantly distributed, the properties of which differ substantially from the molecular one. Electrons and protons are not connected, and it has a very high electrical conductivity, even in a partially ionized state. Charged particles are strongly affected by magnetic and electric fields. For example, in a solar wind, helium ions, together with ionized hydrogen, interact with the magnetosphere of the Earth, causing northern lights.

Discovery of deposits in the USA

After drilling the well in 1903 in Dexter, Kansas, incombustible gas was obtained. Initially, it was not known that it contained helium. What kind of gas was found was determined by the geologist of the state Erasmus Haworth, who collected his samples and found that at the University of Kansas with the help of chemists Cady Hamilton and David McFarland found that it contains 72% of nitrogen, 15% methane, 1% hydrogen and 12% was not identified. After further analysis, the researchers found that 1.84% of the sample is helium. So learned that this chemical element is present in huge quantities in the bowels of the Great Plains, from where it can be extracted from natural gas.

Industrial production

This made the United States the world leader in helium production. At the suggestion of Sir Richard Trelfall, the US Navy financed three small experimental plants to obtain this substance during the First World War in order to provide a barrage balloon with light non-flammable lift gas. For this program, a total of 5,700 m ^{3 of} 92% He was produced, although only less than 100 liters of gas had been produced before. Part of this volume was used in the world's first helium airship of the US Navy, the C-7, which made its first flight from Hampton Roads , Va. , To Bolling Field, Washington, DC, on December 7, 1921.

Although the process of low-temperature gas liquefaction at that time was not sufficiently developed to prove significant during the First World War, production continued. Helium was mainly used as an elevating gas in aircraft. The demand for it grew during the Second World War, when it began to be used for shielded arc welding. Element was also important in the project to create the atomic bomb "Manhattan".

National Reserve of the USA

In 1925, the United States government created the National Helium Reserve in Amarillo, Texas, to provide military airships during the war and commercial aircraft in peacetime. The use of gas after World War II declined, but the stock was increased in the 1950s to ensure, among other things, its supply as a coolant used in the production of oxygen-hydrogen rocket fuel during the space race and the Cold War. The use of helium in the USA in 1965 was eight times higher than the peak consumption of wartime.

After the adoption of the law on helium in 1960, the Mountain Bureau contracted 5 private enterprises to extract an element from natural gas. For this program, a 425-km gas pipeline was built, connecting these plants to a government partially depleted gas field near Amarillo, Texas. The helium-nitrogen mixture was pumped into the underground storage and remained there until it became necessary.

By 1995, a stock of one billion cubic meters was collected, and the National Reserve was $ 1.4 billion, prompting the US Congress to phase out in 1996. After the adoption in 1996 of the law on the privatization of helium, the Ministry of Natural Resources began to liquidate the depository in 2005.

Purity and production volumes

Helium, produced before 1945, had a purity of about 98%, the remaining 2% accounted for nitrogen, which was sufficient for airships. In 1945, a small amount of 99.9-percent gas was produced for use in arc welding. By 1949, the purity of the resulting element reached 99.995%.

Over the years, the United States produced more than 90% of the world's commercial helium. Since 2004, it has produced 140 million m ³ per year, 85% of which is in the United States, 10% in Algeria, and the rest in Russia and Poland. The main sources of helium in the world are gas fields of Texas, Oklahoma and Kansas.

The process of obtaining

Helium (purity 98.2%) is isolated from natural gas by liquefaction of other components at low temperatures and at high pressures. Adsorption of other gases by the cooled activated carbon allows to achieve purity of 99.995%. A small volume of helium is produced when liquefying air on a large scale. From 900 tons of air you can get about 3.17 cu. M of gas.

Applications

Noble gas has found application in various fields.

• Helium, whose properties make it possible to obtain ultra-low temperatures, is used as a cooling agent in the Large Hadron Collider, superconducting magnets of MRI devices and nuclear magnetic resonance spectrometers, satellite equipment, as well as for liquefying oxygen and hydrogen in Apollo missiles.
• As an inert gas for welding aluminum and other metals, in the production of optical fibers and semiconductors.
• To create pressure in the fuel tanks of rocket engines, especially those that work on liquid hydrogen, since only helium gas retains its aggregate state when hydrogen remains liquid);
• He-Ne gas lasers are used to scan barcodes at the box office in supermarkets.
• Helium-ion microscope allows you to get better images than electronic.
• Due to its high permeability, noble gas is used to check for leaks, for example, in car air-conditioning systems, as well as for quick filling of airbags in a collision.
• Low density allows filling decorative spheres with helium. The inert gas replaced explosive hydrogen in airships and balloons. For example, in meteorology, spheres with helium are used for lifting measuring instruments.
• In cryogenic technology it serves as a coolant, since the temperature of this chemical element in the liquid state is the lowest possible.
• Helium, the properties of which provide it with low reactivity and solubility in water (and blood), in a mixture with oxygen, has found application in respiratory compositions for scuba diving and performing coffer work.
• Meteorites and rocks are analyzed for the content of this element to determine their age.

Helium: element properties

The main physical properties of He are as follows:

• Atomic number: 2.
• Relative mass of the helium atom: 4,0026.
• Melting point: no.
• Boiling point: -268.9 ° C.
• Density (1 atm, 0 ° C): 0.1785 g / p.
• Oxidation states: 0.