; atomic number 92, atomic mass 238.029; metal. Natural Uranium consists of a mixture of three isotopes: 238 U - 99.2739% with a half-life T ½ = 4.51 10 9 years, 235 U - 0.7024% (T ½ = 7.13 10 8 years) and 234 U - 0.0057% (T ½ = 2.48·10 5 years).
Of the 11 artificial radioactive isotopes with mass numbers from 227 to 240, the long-lived one is 233 U (T ½ = 1.62·10 5 years); it is obtained by neutron irradiation of thorium. 238 U and 235 U are the ancestors of two radioactive series.
Historical reference. Uranium was discovered in 1789 by the German chemist M. G. Klaproth and named by him in honor of the planet Uranus, discovered by W. Herschel in 1781. In the metallic state, Uranium was obtained in 1841 by the French chemist E. Peligo during the reduction of UCl 4 with potassium metal. Initially, Uranus was assigned an atomic mass of 120, and only in 1871 D.I. Mendeleev came to the conclusion that this value should be doubled.
For a long time, uranium was of interest only to a narrow circle of chemists and found limited use in the production of paints and glass. With the discovery of the phenomenon of radioactivity in uranium in 1896 and radium in 1898, industrial processing of uranium ores began in order to extract and use radium in scientific research and medicine. Since 1942, after the discovery of nuclear fission in 1939, uranium has become the main nuclear fuel.
Distribution of Uranus in nature. Uranium is a characteristic element for the granite layer and sedimentary shell of the earth's crust. The average content of Uranium in the earth's crust (clarke) is 2.5 10 -4% by mass, in acidic igneous rocks 3.5 10 -4%, in clays and shales 3.2 10 -4%, in basic rocks 5 ·10 -5%, in ultrabasic rocks of the mantle 3·10 -7%. Uranium migrates vigorously in cold and hot, neutral and alkaline waters in the form of simple and complex ions, especially in the form of carbonate complexes. Redox reactions play an important role in the geochemistry of Uranium, since Uranium compounds, as a rule, are highly soluble in waters with an oxidizing environment and poorly soluble in waters with a reducing environment (for example, hydrogen sulfide).
About 100 Uranium minerals are known; 12 of them are of industrial importance. Over the course of geological history, the content of Uranium in the earth's crust has decreased due to radioactive decay; This process is associated with the accumulation of Pb and He atoms in the earth's crust. The radioactive decay of Uranium plays an important role in the energy of the earth's crust, being a significant source of deep heat.
Physical properties of Uranium. Uranium is similar in color to steel and is easy to process. It has three allotropic modifications - α, β and γ with phase transformation temperatures: α → β 668.8 °C, β → γ 772.2 °C; The α-form has a rhombic lattice (a = 2.8538Å, b = 5.8662Å, c = 4.9557Å), the β-form has a tetragonal lattice (at 720 °C a = 10.759Å, b = 5.656Å), the γ-form - body-centered cubic lattice (at 850 °C a = 3.538 Å). The density of Uranium in α-form (25 °C) is 19.05 g/cm 3 ; t pl 1132 °C; boiling point 3818 °C; thermal conductivity (100-200 °C), 28.05 W/(m K), (200-400 °C) 29.72 W/(m K); specific heat capacity (25 °C) 27.67 kJ/(kg K); specific electrical resistivity at room temperature is about 3·10 -7 ohm·cm, at 600 °C 5.5·10 -7 ohm·cm; has superconductivity at 0.68 K; weak paramagnetic, specific magnetic susceptibility at room temperature 1.72·10 -6.
The mechanical properties of Uranium depend on its purity and on the modes of mechanical and thermal treatment. The average value of the elastic modulus for cast Uranium is 20.5·10 -2 Mn/m 2 ; tensile strength at room temperature 372-470 Mn/m2; strength increases after hardening from β- and γ-phases; average Brinell hardness 19.6-21.6·10 2 MN/m 2 .
Irradiation by a neutron flow (which takes place in a nuclear reactor) changes the physical and mechanical properties of Uranium: creep develops and fragility increases, deformation of products is observed, which forces the use of Uranium in nuclear reactors in the form of various uranium alloys.
Uranium is a radioactive element. Nuclei 235 U and 233 U fission spontaneously, as well as upon capture of both slow (thermal) and fast neutrons with an effective fission cross section of 508 10 -24 cm 2 (508 barn) and 533 10 -24 cm 2 (533 barn) respectively. 238 U nuclei fission upon capturing only fast neutrons with an energy of at least 1 MeV; when capturing slow neutrons, 238 U turns into 239 Pu, the nuclear properties of which are close to 235 U. The critical mass of Uranium (93.5% 235 U) in aqueous solutions is less than 1 kg, for an open ball - about 50 kg, for a ball with a reflector - 15-23 kg; critical mass 233 U is approximately 1/3 of the critical mass 235 U.
Chemical properties of Uranium. The configuration of the outer electron shell of the Uranium atom is 7s 2 6d l 5f 3. Uranium is a reactive metal; in compounds it exhibits oxidation states of +3, +4, + 5, +6, sometimes +2; the most stable compounds are U (IV) and U (VI). In air it slowly oxidizes with the formation of an oxide (IV) film on the surface, which does not protect the metal from further oxidation. In its powdered state, Uranium is pyrophoric and burns with a bright flame. With oxygen it forms oxide (IV) UO 2, oxide (VI) UO 3 and a large number of intermediate oxides, the most important of which is U 3 O 8. These intermediate oxides have properties similar to UO 2 and UO 3 . At high temperatures, UO 2 has a wide range of homogeneity from UO 1.60 to UO 2.27. With fluorine at 500-600 ° C it forms UF 4 tetrafluoride (green needle-shaped crystals, slightly soluble in water and acids) and UF 6 hexafluoride (a white crystalline substance that sublimes without melting at 56.4 ° C); with sulfur - a number of compounds, of which US (nuclear fuel) is the most important. When Uranium interacts with hydrogen at 220 °C, the hydride UH 3 is obtained; with nitrogen at temperatures from 450 to 700 ° C and atmospheric pressure - U 4 N 7 nitride; at a higher nitrogen pressure and the same temperature, UN, U 2 N 3 and UN 2 can be obtained; with carbon at 750-800 °C - monocarbide UC, dicarbide UC 2, as well as U 2 C 3; with metals it forms alloys of various types. Uranium reacts slowly with boiling water to form UO 2 nH 2, with water vapor - in the temperature range 150-250 ° C; soluble in hydrochloric and nitric acids, slightly soluble in concentrated hydrofluoric acid. U(VI) is characterized by the formation of the uranyl ion UO 2 2+; uranyl salts are yellow in color and are highly soluble in water and mineral acids; U(IV) salts are green and less soluble; uranyl ion is extremely capable of complex formation in aqueous solutions with both inorganic and organic substances; The most important for technology are carbonate, sulfate, fluoride, phosphate and other complexes. A large number of uranates (salts of uranic acid not isolated in pure form) are known, the composition of which varies depending on the conditions of production; All uranates have low solubility in water.
Uranium and its compounds are radiation and chemically toxic. The maximum permissible dose (MAD) for occupational exposure is 5 rem per year.
Receiving Uranus. Uranium is obtained from uranium ores containing 0.05-0.5% U. The ores are practically not enriched, with the exception of a limited radiometric sorting method based on the γ-radiation of radium, which always accompanies uranium. Basically, ores are leached with solutions of sulfuric, sometimes nitric acids or soda solutions with the transfer of Uranium into an acidic solution in the form of UO 2 SO 4 or complex anions 4-, and into a soda solution - in the form of 4-. To extract and concentrate Uranium from solutions and pulps, as well as to purify it from impurities, sorption on ion exchange resins and extraction with organic solvents (tributyl phosphate, alkylphosphoric acids, amines) are used. Next, ammonium or sodium uranates or U(OH) 4 hydroxide are precipitated from the solutions by adding alkali. To obtain compounds of high purity, technical products are dissolved in nitric acid and subjected to refining purification operations, the final products of which are UO 3 or U 3 O 8; these oxides are reduced at 650-800 °C by hydrogen or dissociated ammonia to UO 2, followed by its conversion to UF 4 by treatment with hydrogen fluoride gas at 500-600 °C. UF 4 can also be obtained by precipitation of crystalline hydrate UF 4 nH 2 O with hydrofluoric acid from solutions, followed by dehydration of the product at 450 °C in a stream of hydrogen. In industry, the main method of obtaining Uranium from UF 4 is its calcium-thermal or magnesium-thermal reduction with the release of Uranium in the form of ingots weighing up to 1.5 tons. The ingots are refined in vacuum furnaces.
A very important process in Uranium technology is the enrichment of its 235 U isotope above the natural content in ores or the isolation of this isotope in its pure form, since 235 U is the main nuclear fuel; This is done by gas thermal diffusion, centrifugal and other methods based on the difference in the masses of 238 U and 235 U; in separation processes, uranium is used in the form of volatile hexafluoride UF 6. When obtaining highly enriched Uranium or isotopes, their critical masses are taken into account; the most convenient method in this case is the reduction of uranium oxides with calcium; the resulting CaO slag is easily separated from Uranium by dissolution in acids. To obtain powdered uranium, oxide (IV), carbides, nitrides and other refractory compounds, powder metallurgy methods are used.
Application of Uranus. Uranium metal or its compounds are used primarily as nuclear fuel in nuclear reactors. A natural or low-enriched mixture of Uranium isotopes is used in stationary reactors of nuclear power plants, a highly enriched product is used in nuclear power plants or in reactors operating on fast neutrons. 235 U is the source of nuclear energy in nuclear weapons. 238 U serves as a source of secondary nuclear fuel - plutonium.
Uranium in the body. It is found in microquantities (10 -5 -10 -8%) in the tissues of plants, animals and humans. In plant ash (with a Uranium content of about 10 -4% in the soil), its concentration is 1.5·10 -5%. To the greatest extent, Uranium is accumulated by some fungi and algae (the latter actively participate in the biogenic migration of Uranium along the chain water - aquatic plants - fish - humans). Uranium enters the body of animals and humans with food and water in the gastrointestinal tract, with air in the respiratory tract, as well as through the skin and mucous membranes. Uranium compounds are absorbed in the gastrointestinal tract - about 1% of the incoming amount of soluble compounds and no more than 0.1% of sparingly soluble ones; 50% and 20% are absorbed in the lungs, respectively. Uranium is distributed unevenly in the body. The main depot (places of deposition and accumulation) is the spleen, kidneys, skeleton, liver and, when inhaling poorly soluble compounds, the lungs and bronchopulmonary lymph nodes. Uranium (in the form of carbonates and complexes with proteins) does not circulate in the blood for a long time. The content of uranium in the organs and tissues of animals and humans does not exceed 10 -7 g/g. Thus, cattle blood contains 1·10 -8 g/ml, liver 8·10 -8 g/g, muscles 4·10 -11 g/g, spleen 9·10 8-8 g/g. The content of Uranium in human organs is: in the liver 6·10 -9 g/g, in the lungs 6·10 -9 -9·10 -9 g/g, in the spleen 4.7·10 -7 g/g, in the blood 4-10 -10 g/ml, in the kidneys 5.3·10 -9 (cortical layer) and 1.3·10 -8 g/g (medullary layer), in the bones 1·10 -9 g/g, in bone marrow 1-10 -8 g/g, in hair 1.3·10 -7 g/g. Uranium contained in bone tissue causes its constant irradiation (the half-life of Uranium from the skeleton is about 300 days). The lowest concentrations of Uranium are in the brain and heart (10 -10 g/g). The daily intake of Uranium with food and liquids is 1.9·10 -6 g, with air - 7·10 -9 g. The daily excretion of Uranium from the human body is: with urine 0.5·10 -7 - 5·10 -7 g, with feces - 1.4·10 -6 -1.8·10 -6 g, with hair - 2·10 -8 g.
According to the International Commission on Radiation Protection, the average content of Uranium in the human body is 9·10 -5 g. This value may vary for different regions. It is believed that Uranium is necessary for the normal functioning of animals and plants.
The toxic effect of uranium is determined by its chemical properties and depends on solubility: uranyl and other soluble compounds of uranium are more toxic. Poisoning by uranium and its compounds is possible at enterprises for the extraction and processing of uranium raw materials and other industrial facilities where it is used in the technological process. When it enters the body, Uranium affects all organs and tissues, being a general cellular poison. Signs of poisoning are caused by primary damage to the kidneys (the appearance of protein and sugar in the urine, subsequent oliguria); the liver and gastrointestinal tract are also affected. There are acute and chronic poisonings; the latter are characterized by gradual development and less severe symptoms. With chronic intoxication, disorders of hematopoiesis, the nervous system, etc. are possible. It is believed that the molecular mechanism of action of Uranium is associated with its ability to suppress the activity of enzymes.
URANIUM (from the name of the planet Uranus), U - radioactive chemical. element of group III of the periodic system of elements; at. n. 92, at. m. 238.029; belongs to actinides. Silvery white shiny metal. In compounds it exhibits oxidation states from +2 to +6, the most characteristic being +4 and +6.
Natural Uranium consists of the isotopes 238U (99.282%), 235U (0.712%) and 234U (0.006%). Among artificial isotopes, the 233U isotope is of practical importance. U. in the form of oxide U02 was discovered (1789) by German. chemist M.-G. Klaproth. Uranium metal was received (1841) by the French. chemist E.-M. Peligo. Since the 40s 20th century U. has acquired importance as a source of nuclear energy released during the fission of its atoms during the capture of neutrons; 235U and 233U have this property. The isotope 238U, when capturing neutrons, turns into (239Pu), which is also a nuclear fuel. The uranium content in the earth's crust is 0.3-0.0004%. Its main mineral is a variety of uranite - pitchblende (uranium pitch) (40-76% U). Uranium is found in small quantities in granites (0.0004%), soils (0.0001 -0.00004%) and waters (~10 -8%).
Three of its allotropic modifications are known: alpha-uranium with an orthorhombic crystal lattice and with periods a = 2.8541 A, b = 5.8692 A and c = 4.9563 A (temperature 25 ° C), which transforms at t-re 667.7 ° C in beta-uranium with a tetragonal crystal lattice and with periods a = 10.759 A and c = 5.656 A (t-ra 720 ° C); above the temperature of 774.8° C gamma-uranium is stable with a body-centered cubic lattice and with a period a = 3.524 A (temperature 805° C).
The density of alpha-uranium at room temperature is 19.05 g/cm3; melting point 1132° C; boiling point 3820° C (pressure 1 at). Heat of transformations alpha⇄ beta, beta ⇄ gamma, melting and evaporation of uranium, respectively ~ 0.70; 1.15; 4.75 and 107-117 kcal/mol. Heat capacity c = 6.4 cal/mol (temperature 25°C). Average coefficient thermal expansion of alpha uranium along the a, b and c axes in the temperature range 20-500 ° C, respectively 32.9; -6.3 and 27.6 10-6 deg-1. The thermal conductivity coefficient of uranium at room temperature is ~ 0.06 cal/cm sec deg and increases with increasing temperature. The electrical resistivity of alpha uranium depends on the crystallographic direction; its averaged value for uranium of a polycrystalline sample of high purity is ~ 30 μΩ x cm at room temperature and increases to ~ 54 μΩ x cm at 600 ° C. Anisotropy of the Young's modulus is also observed in alpha uranium. Polycrystalline alpha uranium has a Young's modulus of 2.09 x 10 4 kgf/mm2; shear modulus 0.85 x 10 4 kgf/mm2; coefficient Poisson 0.23. The hardness of alpha-uranium at room temperature is HV = 200, but decreases to 12 at a temperature of 600° C.
During the transition from alpha to beta uranium, the hardness increases from ~ 10 to ~ 30. The tensile strength of annealed alpha uranium (0.02% C) at a temperature of 20 ° C is ~ 42 kgf/mm2, increases to 49 kgf/mm2 at a temperature of 100 9 C and then almost linearly decreases to ~ 11 kgf/mm2 with an increase in temperature to 600° C. At a temperature of 20° C, the yield strength, relative elongation and relative contraction, respectively, are 26 kgf/ mm2, 8 and 11%, and at a temperature of 600° C - 9 kgf/mm2, 26 and 65%. Increasing the carbon content from 0.01 to 0.20% increases the strength and yield limitsσ 0.2, respectively, from 37 and 24 to 52 and 32 kgf/mm2. All mechanical characteristics of uranium significantly depend on the presence of impurities and pre-treatment.
The creep of uranium is especially dependent on cyclic changes in temperature, which is associated with additional thermal stresses arising due to the large difference in the coefficient. thermal expansion along various crystallographic directions of alpha-uranium. The impact strength of alpha uranium (0.03% C), low at temperatures of 20 and 100 ° C (1.4 and 2.3 kgf-m/cm2, respectively), increases almost linearly to 11.7 kgf-m/ cm2 at a temperature of 500° C. A characteristic feature is the elongation of polycrystalline alpha-uranium rods with a texture along the axis under the influence of repeated heating and cooling.
When uranium atoms fission, and insoluble in uranium are formed, which leads to swelling of the metal (very undesirable for nuclear fuel). Even at room temperature, uranium oxidizes in dry air with the formation of a thin oxide film; when heated to a temperature of 200° C, scale dioxide U02 is formed, at a temperature of 200-400° C - U308, at a higher temperature - U308. U03 (more precisely, solid solutions based on these oxides). The oxidation rate is low at a temperature of 50°C and very high at a temperature of 300°C. Uranium reacts slowly with nitrogen below a temperature of 400°C, but quite quickly at a temperature of 750-800°C. Interaction with hydrogen occurs already at room temperature with the formation of hydride UH3.
In water at temperatures up to 70° C, a film of dioxide is formed on uranium, which has a protective effect; at a temperature of 100° C, the interaction accelerates significantly. To obtain U., its ores are enriched with wet chemicals. method, leaching with sulfuric acid in the presence of an oxidizing agent - manganese dioxide. Uranium is extracted from a sulfate solution with organic solvents or isolated with phenolic resins. The resulting concentrate is dissolved in nitrogen solution. The resulting uranyl nitrate U02 (N03)2 is extracted, for example, with butyl phosphate and, after liberation from the latter, the U compounds are decomposed at a temperature of 500-700 ° C. The resulting high-purity U308 and U03 are reduced with hydrogen at a temperature of 600-800 ° C to dioxide U02.
Uranium metal is obtained by metallothermic reduction (with calcium or magnesium) of uranium dioxide UO2 or uranium tetrafluoride UF4, previously obtained from the dioxide by the action of anhydrous hydrogen fluoride at a temperature of 500 ° C. The latter method is more common and allows one to obtain high-purity ingots (0.0045% Fe, 0.001% Si, 0.003% C) and weighing more than a ton. Uranium metal is also obtained by electrolysis in salt baths containing UF4 at a temperature of 800-1200° C. Crude uranium is usually subjected to refining smelting (temperature 1450-1600° C) in graphite crucibles, in high-frequency vacuum furnaces with casting into graphite molds.
Small prototypes are deformed by forging in the alpha state, which is also used, along with pressing in the alpha or gamma state, to deform large ingots. Cold rolling increases the strength characteristics of uranium, hardness during compression by 40%, increases HV from 235 to 325. Removal of hardening occurs mainly at a temperature of 350-450 ° C in metal of technical purity and is accompanied by recrystallization under these conditions; secondary, collective recrystallization develops at a temperature of 600-650° C. Cooling uranium in water or oil from the beta or gamma state does not suppress the formation of the alpha phase, but refines the grain of alpha uranium, especially in the presence of impurities. Metal U.,
In a message from the Iraqi Ambassador to the UN Mohammed Ali al-Hakim dated July 9, it is said that ISIS extremists (Islamic State of Iraq and the Levant) are at their disposal. The IAEA (International Atomic Energy Agency) hastened to declare that the nuclear substances previously used by Iraq have low toxic properties, and therefore the materials seized by the Islamists.
A US government source familiar with the situation told Reuters that the uranium stolen by the militants was most likely not enriched and therefore unlikely to be used to make nuclear weapons. The Iraqi authorities officially notified the United Nations about this incident and called on them to “prevent the threat of its use,” RIA Novosti reports.
Uranium compounds are extremely dangerous. AiF.ru talks about what exactly, as well as who and how can produce nuclear fuel.
What is uranium?
Uranium is a chemical element with atomic number 92, a silvery-white shiny metal, designated in the periodic table by the symbol U. In its pure form, it is slightly softer than steel, malleable, flexible, found in the earth's crust (lithosphere) and in sea water, and in its pure form is practically does not occur. Nuclear fuel is made from uranium isotopes.
Uranium is a heavy, silvery-white, shiny metal. Photo: Commons.wikimedia.org / Original uploader was Zxctypo at en.wikipedia.
Radioactivity of uranium
In 1938 the German physicists Otto Hahn and Fritz Strassmann irradiated the uranium nucleus with neutrons and made a discovery: capturing a free neutron, the uranium isotope nucleus divides and releases enormous energy due to the kinetic energy of fragments and radiation. In 1939-1940 Yuliy Khariton And Yakov Zeldovich for the first time theoretically explained that with a small enrichment of natural uranium with uranium-235, it is possible to create conditions for the continuous fission of atomic nuclei, that is, give the process a chain character.
What is enriched uranium?
Enriched uranium is uranium that is produced using technological process of increasing the share of the 235U isotope in uranium. As a result, natural uranium is divided into enriched uranium and depleted uranium. After 235U and 234U are extracted from natural uranium, the remaining material (uranium-238) is called "depleted uranium" because it is depleted in the 235 isotope. According to some estimates, the United States stores about 560,000 tons of depleted uranium hexafluoride (UF6). Depleted uranium is half as radioactive as natural uranium, mainly due to the removal of 234U from it. Because the primary use of uranium is energy production, depleted uranium is a low-use product with low economic value.
In nuclear energy, only enriched uranium is used. The most widely used isotope of uranium is 235U, in which a self-sustaining nuclear chain reaction is possible. Therefore, this isotope is used as fuel in nuclear reactors and nuclear weapons. Isolation of the U235 isotope from natural uranium is a complex technology that not many countries can implement. Uranium enrichment allows the production of atomic nuclear weapons - single-phase or single-stage explosive devices in which the main energy output comes from the nuclear reaction of heavy nuclei fission to form lighter elements.
Uranium-233, artificially produced in reactors from thorium (thorium-232 captures a neutron and turns into thorium-233, which decays into protactinium-233 and then into uranium-233), may in the future become a common nuclear fuel for nuclear power plants (already now there are reactors that use this nuclide as fuel, for example KAMINI in India) and the production of atomic bombs (critical mass of about 16 kg).
The core of a 30 mm caliber projectile (GAU-8 cannon of an A-10 aircraft) with a diameter of about 20 mm is made of depleted uranium. Photo: Commons.wikimedia.org / Original uploader was Nrcprm2026 at en.wikipedia
Which countries produce enriched uranium?
- France
- Germany
- Holland
- England
- Japan
- Russia
- China
- Pakistan
- Brazil
10 countries producing 94% of world uranium production. Photo: Commons.wikimedia.org / KarteUrangewinnung
Why are uranium compounds dangerous?
Uranium and its compounds are toxic. Aerosols of uranium and its compounds are especially dangerous. For aerosols of water-soluble uranium compounds, the maximum permissible concentration (MPC) in the air is 0.015 mg/m³, for insoluble forms of uranium the MAC is 0.075 mg/m³. When uranium enters the body, it affects all organs, being a general cellular poison. Uranium, like many other heavy metals, almost irreversibly binds to proteins, primarily to sulfide groups of amino acids, disrupting their function. The molecular mechanism of action of uranium is associated with its ability to suppress enzyme activity. The kidneys are primarily affected (protein and sugar appear in the urine, oliguria). With chronic intoxication, disorders of hematopoiesis and the nervous system are possible.
Use of uranium for peaceful purposes
- A small addition of uranium gives the glass a beautiful yellow-green color.
- Sodium uranium is used as a yellow pigment in painting.
- Uranium compounds were used as paints for painting on porcelain and for ceramic glazes and enamels (painted in colors: yellow, brown, green and black, depending on the degree of oxidation).
- At the beginning of the 20th century, uranyl nitrate was widely used to enhance negatives and color (tint) positives (photographic prints) brown.
- Alloys of iron and depleted uranium (uranium-238) are used as powerful magnetostrictive materials.
An isotope is a variety of atoms of a chemical element that have the same atomic (ordinal) number, but different mass numbers.
An element of group III of the periodic table, belonging to the actinides; heavy, slightly radioactive metal. Thorium has a number of applications in which it sometimes plays an irreplaceable role. The position of this metal in the periodic table of elements and the structure of the nucleus predetermined its use in the field of peaceful uses of atomic energy.
*** Oliguria (from the Greek oligos - small and ouron - urine) - a decrease in the amount of urine excreted by the kidneys.
Uranus is the seventh planet in the solar system and the third gas giant. The planet is the third largest and fourth largest in mass, and received its name in honor of the father of the Roman god Saturn.
Exactly Uranus has the honor of being the first planet discovered in modern history. However, in reality, his initial discovery of it as a planet did not actually happen. In 1781, the astronomer William Herschel while observing stars in the constellation Gemini, he noticed a certain disk-shaped object, which he initially recorded as a comet, which he reported to the Royal Scientific Society of England. However, later Herschel himself was puzzled by the fact that the object’s orbit turned out to be practically circular, and not elliptical, as is the case with comets. It was only when this observation was confirmed by other astronomers that Herschel came to the conclusion that he had actually discovered a planet, not a comet, and the discovery was finally widely accepted.
After confirming the data that the discovered object was a planet, Herschel received the extraordinary privilege of giving it his name. Without hesitation, the astronomer chose the name of King George III of England and named the planet Georgium Sidus, which translated means “George’s Star.” However, the name never received scientific recognition and scientists, for the most part, came to the conclusion that it is better to adhere to a certain tradition in naming the planets of the solar system, namely to name them in honor of the ancient Roman gods. This is how Uranus got its modern name.
Currently, the only planetary mission that has managed to collect information about Uranus is Voyager 2.
This meeting, which took place in 1986, allowed scientists to obtain a fairly large amount of data about the planet and make many discoveries. The spacecraft transmitted thousands of photographs of Uranus, its moons and rings. Although many photographs of the planet showed little more than the blue-green color that could be seen from ground-based telescopes, other images showed the presence of ten previously unknown moons and two new rings. No new missions to Uranus are planned for the near future.
Due to the dark blue color of Uranus, it turned out to be much more difficult to create an atmospheric model of the planet than models of the same or even . Fortunately, images from the Hubble Space Telescope have provided a broader picture. More modern telescope imaging technologies have made it possible to obtain much more detailed images than those of Voyager 2. Thus, thanks to Hubble photographs, it was possible to find out that there are latitudinal bands on Uranus, like on other gas giants. In addition, wind speeds on the planet can reach more than 576 km/hour.
It is believed that the reason for the appearance of a monotonous atmosphere is the composition of its uppermost layer. The visible layers of clouds are composed primarily of methane, which absorbs these observed wavelengths corresponding to the color red. Thus, the reflected waves are represented as blue and green colors.
Beneath this outer layer of methane, the atmosphere consists of approximately 83% hydrogen (H2) and 15% helium, with some methane and acetylene present. This composition is similar to other gas giants in the Solar System. However, Uranus's atmosphere is strikingly different in another way. While Jupiter and Saturn have mostly gaseous atmospheres, Uranus' atmosphere contains much more ice. Evidence of this is the extremely low temperatures on the surface. Considering the fact that the temperature of the atmosphere of Uranus reaches -224 ° C, it can be called the coldest atmosphere in the solar system. In addition, available data indicate that such extremely low temperatures are present around almost the entire surface of Uranus, even on the side that is not illuminated by the Sun.
Uranus, according to planetary scientists, consists of two layers: the core and the mantle. Current models suggest that the core is mainly composed of rock and ice and is about 55 times the mass. The planet's mantle weighs 8.01 x 10 to the power of 24 kg, or about 13.4 Earth masses. In addition, the mantle consists of water, ammonia and other volatile elements. The main difference between the mantle of Uranus and Jupiter and Saturn is that it is icy, albeit not in the traditional sense of the word. The fact is that the ice is very hot and thick, and the thickness of the mantle is 5.111 km.
What is most surprising about the composition of Uranus, and what distinguishes it from the other gas giants of our star system, is that it does not radiate more energy than it receives from the Sun. Given the fact that even , which is very close in size to Uranus, produces about 2.6 times more heat than it receives from the Sun, scientists today are very intrigued by such a weak power generated by Uranus. At the moment, there are two explanations for this phenomenon. The first indicates that Uranus was exposed to a massive space object in the past, causing the planet to lose much of its internal heat (gained during formation) into space. The second theory states that there is some kind of barrier inside the planet that does not allow the internal heat of the planet to escape to the surface.
Orbit and rotation of Uranus
The very discovery of Uranus allowed scientists to almost double the radius of the known Solar System. This means that on average the orbit of Uranus is about 2.87 x 10 to the power of 9 km. The reason for such a huge distance is the duration of passage of solar radiation from the Sun to the planet. It takes about two hours and forty minutes for sunlight to reach Uranus, which is almost twenty times longer than it takes for sunlight to reach Earth. The enormous distance also affects the length of the year on Uranus; it lasts almost 84 Earth years.
The orbital eccentricity of Uranus is 0.0473, which is only slightly less than that of Jupiter - 0.0484. This factor makes Uranus the fourth of all the planets in the Solar System in terms of circular orbit. The reason for such a small eccentricity of Uranus's orbit is that the difference between its perihelion of 2.74 x 10 to the power of 9 km and its aphelion of 3.01 x 109 km is only 2.71 x 10 to the power of 8 km.
The most interesting point about the rotation of Uranus is the position of the axis. The fact is that the axis of rotation for every planet except Uranus is approximately perpendicular to their orbital plane, but Uranus' axis is tilted almost 98°, which effectively means that Uranus rotates on its side. The result of this position of the planet's axis is that the north pole of Uranus is on the Sun for half of the planetary year, and the other half is on the south pole of the planet. In other words, daytime on one hemisphere of Uranus lasts 42 Earth years, and nighttime on the other hemisphere lasts the same amount. Scientists again cite a collision with a huge cosmic body as the reason why Uranus “turned on its side.”
Considering the fact that the most popular of the rings in our solar system for a long time remained the rings of Saturn, the rings of Uranus could not be discovered until 1977. However, this is not the only reason; there are two more reasons for such a late detection: the distance of the planet from the Earth and the low reflectivity of the rings themselves. In 1986, the Voyager 2 spacecraft was able to determine the presence of two more rings on the planet, in addition to those known at that time. In 2005, the Hubble Space Telescope spotted two more. Today, planetary scientists know of 13 rings of Uranus, the brightest of which is the Epsilon ring.
The rings of Uranus differ from Saturn's in almost every way - from particle size to composition. First, the particles that make up the rings of Saturn are small, little more than a few meters in diameter, while the rings of Uranus contain many bodies up to twenty meters in diameter. Second, the particles in Saturn's rings are mostly made of ice. The rings of Uranus, however, are composed of both ice and significant dust and debris.
William Herschel only discovered Uranus in 1781 because the planet was too dim to be seen by ancient civilizations. Herschel himself initially believed that Uranus was a comet, but later revised his opinion and science confirmed the planetary status of the object. Thus, Uranus became the first planet discovered in modern history. The original name proposed by Herschel was "George's Star" - in honor of King George III, but the scientific community did not accept it. The name "Uranus" was proposed by astronomer Johann Bode, in honor of the ancient Roman god Uranus.
Uranus rotates on its axis once every 17 hours and 14 minutes. Like , the planet rotates in a retrograde direction, opposite to the direction of the Earth and the other six planets.
It is believed that the unusual tilt of Uranus's axis could cause a huge collision with another cosmic body. The theory is that a planet supposedly the size of Earth collided sharply with Uranus, which shifted its axis by almost 90 degrees.
Wind speeds on Uranus can reach up to 900 km per hour.
Uranus has a mass of about 14.5 times the mass of Earth, making it the lightest of the four gas giants of our solar system.
Uranus is often referred to as the "ice giant". In addition to hydrogen and helium in its upper layer (like other gas giants), Uranus also has an icy mantle that surrounds its iron core. The upper atmosphere consists of ammonia and icy methane crystals, which gives Uranus its characteristic pale blue color.
Uranus is the second least dense planet in the solar system, after Saturn.
Uranium (U) is an element with atomic number 92 and atomic weight 238.029. It is a radioactive chemical element of group III of the periodic table of Dmitry Ivanovich Mendeleev, belongs to the actinide family. Uranium is a very heavy (2.5 times heavier than iron, more than 1.5 times heavier than lead), silvery-white, shiny metal. In its pure form, it is slightly softer than steel, malleable, flexible, and has slight paramagnetic properties.
Natural uranium consists of a mixture of three isotopes: 238U (99.274%) with a half-life of 4.51∙109 years; 235U (0.702%) with a half-life of 7.13∙108 years; 234U (0.006%) with a half-life of 2.48∙105 years. The latter isotope is not primary, but radiogenic; it is part of the radioactive 238U series. The uranium isotopes 238U and 235U are the ancestors of two radioactive series. The final elements of these series are the lead isotopes 206Pb and 207Pb.
Currently, 23 artificial radioactive isotopes of uranium are known with mass numbers from 217 to 242. The “long-lived” among them is 233U with a half-life of 1.62∙105 years. It is obtained as a result of neutron irradiation of thorium and is capable of fission under the influence of thermal neutrons.
Uranium was discovered in 1789 by the German chemist Martin Heinrich Klaproth as a result of his experiments with the mineral pitchblende - “uranium pitch”. The new element was named in honor of the planet Uranus, recently discovered (1781) by William Herschel. For the next half century, the substance obtained by Klaproth was considered a metal, but in 1841 this was refuted by the French chemist Eugene Melchior Peligo, who proved the oxide nature of uranium (UO2), obtained by the German chemist. Peligo himself managed to obtain uranium metal by reducing UCl4 with potassium metal, and also determined the atomic weight of the new element. The next in the development of knowledge about uranium and its properties was D.I. Mendeleev - in 1874, based on the theory he developed about the periodization of chemical elements, he placed uranium in the farthest cell of his table. The Russian chemist doubled the atomic weight of uranium (120), previously determined by Peligo; the correctness of such assumptions was confirmed twelve years later by the experiments of the German chemist Zimmermann.
For many decades, uranium was of interest only to a narrow circle of chemists and natural scientists; its use was also limited - the production of glass and paints. Only with the discovery of the radioactivity of this metal (in 1896 by Henri Becquerel) did the industrial processing of uranium ores begin in 1898. Much later (1939) the phenomenon of nuclear fission was discovered, and since 1942 uranium has become the main nuclear fuel.
The most important property of uranium is that the nuclei of some of its isotopes are capable of fission when capturing neutrons; as a result of this process, a huge amount of energy is released. This property of element No. 92 is used in nuclear reactors, which serve as energy sources, and also underlies the operation of the atomic bomb. Uranium is used in geology to determine the age of minerals and rocks in order to determine the sequence of geological processes (geochronology). Due to the fact that rocks contain different concentrations of uranium, they have different radioactivity. This property is used when identifying rocks using geophysical methods. This method is most widely used in petroleum geology during geophysical surveys of wells. Uranium compounds were used as paints for painting on porcelain and for ceramic glazes and enamels (painted in colors: yellow, brown, green and black, depending on the degree of oxidation), for example, sodium uranate Na2U2O7 was used as a yellow pigment in painting.
Biological properties
Uranium is a fairly common element in the biological environment; concentrators of this metal are considered to be some types of fungi and algae, which are included in the chain of biological cycle of uranium in nature according to the scheme: water - aquatic plants - fish - humans. Thus, with food and water, uranium enters the body of humans and animals, or rather the gastrointestinal tract, where about a percent of the incoming readily soluble compounds and no more than 0.1% of the sparingly soluble ones are absorbed. This element enters the respiratory tract and lungs, as well as the mucous membranes and skin with air. In the respiratory tract, and especially the lungs, absorption occurs much more intensely: easily soluble compounds are absorbed by 50%, and sparingly soluble ones by 20%. Thus, uranium is found in small quantities (10-5 - 10-8%) in animal and human tissues. In plants (in dry residue), the concentration of uranium depends on its content in the soil, so with a soil concentration of 10-4%, the plant contains 1.5∙10-5% or less. The distribution of uranium among tissues and organs is uneven; the main places of accumulation are bone tissue (skeleton), liver, spleen, kidneys, as well as lungs and bronchopulmonary lymph nodes (if poorly soluble compounds enter the lungs). Uranium (carbonates and complexes with proteins) is removed from the blood quite quickly. On average, the content of the 92nd element in the organs and tissues of animals and humans is 10-7%. For example, the blood of cattle contains 1∙10-8 g/ml of uranium, and human blood contains 4∙10-10 g/g. Cattle liver contains 8∙10-8 g/g, in humans in the same organ 6∙10-9 g/g; the spleen of cattle contains 9∙10-8 g/g, in humans - 4.7∙10-7 g/g. In the muscle tissues of cattle, it accumulates up to 4∙10-11 g/g. In addition, in the human body, uranium is contained in the lungs in the range of 6∙10-9 - 9∙10-9 g/g; in the kidneys 5.3∙10-9 g/g (cortical layer) and 1.3∙10-8 g/g (medullary layer); in bone tissue 1∙10-9 g/g; in bone marrow 1∙10-8 g/g; in hair 1.3∙10-7 g/g. The uranium found in the bones causes constant irradiation of the bone tissue (the period of complete removal of uranium from the skeleton is 600 days). The least amount of this metal is in the brain and heart (about 10-10 g/g). As mentioned earlier, the main ways uranium enters the body are water, food and air. The daily dose of metal entering the body with food and liquids is 1.9∙10-6 g, with air - 7∙10-9 g. However, every day uranium is excreted from the body: with urine from 0.5∙10-7 g up to 5∙10-7 g; with feces from 1.4∙10-6 g to 1.8∙10-6 g. Losses from hair, nails and dead skin flakes - 2∙10-8 g.
Scientists suggest that uranium in minute quantities is necessary for the normal functioning of the human body, animals and plants. However, its role in physiology has not yet been clarified. It has been established that the average content of element 92 in the human body is about 9∙10-5 g (International Commission on Radiation Protection). True, this figure fluctuates somewhat for different regions and territories.
Despite its still unknown but definite biological role in living organisms, uranium remains one of the most dangerous elements. First of all, this is manifested in the toxic effect of this metal, which is due to its chemical properties, in particular the solubility of compounds. For example, soluble compounds (uranyl and others) are more toxic. Most often, poisoning with uranium and its compounds occurs at enrichment factories, enterprises for the extraction and processing of uranium raw materials and other production facilities where uranium is involved in technological processes.
Penetrating into the body, uranium affects absolutely all organs and their tissues, because the action occurs at the cellular level: it suppresses the activity of enzymes. The kidneys are primarily affected, which manifests itself in a sharp increase in sugar and protein in the urine, subsequently developing oliguria. The gastrointestinal tract and liver are affected. Uranium poisoning is divided into acute and chronic, the latter developing gradually and can be asymptomatic or with mild symptoms. However, subsequently chronic poisoning leads to disorders of hematopoiesis, the nervous system and other serious health problems.
A ton of granite rock contains approximately 25 grams of uranium. The energy that can be released during the combustion of these 25 grams in a reactor is comparable to the energy that is released during the combustion of 125 tons of coal in the furnaces of powerful thermal boilers! Based on these data, it can be assumed that in the near future granite will be considered one of the types of mineral fuel. In total, the relatively thin twenty-kilometer surface layer of the earth’s crust contains approximately 1014 tons of uranium; when converted into energy equivalent, the result is simply a colossal figure - 2.36.1024 kilowatt-hours. Even all the developed, explored and proposed fossil fuel deposits taken together are not capable of providing even a millionth of this energy!
It is known that uranium alloys subjected to heat treatment are distinguished by greater yield limits, creep and increased corrosion resistance, and a lesser tendency to change the shape of products under temperature fluctuations and under the influence of irradiation. Based on these principles, at the beginning of the 20th century and until the thirties, uranium in the form of carbide was used in the production of tool steels. In addition, it was used to replace tungsten in some alloys, which was cheaper and more accessible. In the production of ferrouranium, the share of U was up to 30%. True, in the second third of the 20th century such use of uranium came to naught.
As is known, in the depths of our Earth there is a constant process of decay of urn isotopes. So, scientists have calculated that the instant release of energy from the entire mass of this metal enclosed in the earth’s shell would heat our planet to a temperature of several thousand degrees! However, such a phenomenon, fortunately, is impossible - after all, the release of heat occurs gradually as the nuclei of uranium and its derivatives undergo a series of long-term radioactive transformations. The duration of such transformations can be judged by the half-lives of natural isotopes of uranium, for example, for 235U it is 7,108 years, and for 238U - 4.51,109 years. However, uranium heat significantly warms the Earth. If the entire mass of the Earth contained the same amount of uranium as in the upper twenty-kilometer layer, then the temperature on the planet would be much higher than it is now. However, as you move towards the center of the Earth, the concentration of uranium decreases.
In nuclear reactors, only a small part of the loaded uranium is processed, this is due to the slagging of the fuel with fission products: 235U burns out, the chain reaction gradually dies out. However, the fuel rods are still filled with nuclear fuel, which must be consumed again. To do this, old fuel elements are dismantled and sent for recycling - they are dissolved in acids, and uranium is extracted from the resulting solution by extraction; the fission fragments that need to be disposed of remain in the solution. Thus, it turns out that the uranium industry is practically a waste-free chemical production!
Plants for the separation of uranium isotopes occupy an area of several tens of hectares, and the area of the porous partitions in the separation cascades of the plant is approximately the same. This is due to the complexity of the diffusion method for separating uranium isotopes - after all, in order to increase the concentration of 235U from 0.72 to 99%, several thousand diffusion steps are required!
Using the uranium-lead method, geologists were able to find out the age of the most ancient minerals; when studying meteorite rocks, they were able to determine the approximate date of the birth of our planet. Thanks to the “uranium clock,” the age of the lunar soil was determined. Interestingly, it turned out that for 3 billion years there has been no volcanic activity on the Moon and the Earth’s natural satellite remains a passive body. After all, even the youngest pieces of lunar matter lived longer than the age of the oldest terrestrial minerals.
Story
The use of uranium dates back a very long time - as early as the 1st century BC, natural uranium oxide was used to make a yellow glaze used to color ceramics.
In modern times, the study of uranium occurred gradually - in several stages, with continuous growth. The beginning was the discovery of this element in 1789 by the German natural philosopher and chemist Martin Heinrich Klaproth, who reduced the golden-yellow “earth” mined from Saxon pitch ore (“uranium pitch”) to a black metal-like substance (uranium oxide - UO2). The name was given in honor of the most distant planet known at that time - Uranus, which in turn was discovered in 1781 by William Herschel. At this point, the first stage in the study of the new element (Klaproth was confident that he had discovered a new metal) ends, and there comes a break of more than fifty years.
The year 1840 can be considered the beginning of a new milestone in the history of uranium research. It was from this year that a young chemist from France, Eugene Melchior Peligo (1811-1890), took up the problem of obtaining metallic uranium; soon (1841) he succeeded - metallic uranium was obtained by reducing UCl4 with metallic potassium. In addition, he proved that the uranium discovered by Klaproth is in fact just its oxide. The Frenchman also determined the estimated atomic weight of the new element - 120. Then again there was a long break in the study of the properties of uranium.
Only in 1874 did new assumptions about the nature of uranium appear: Dmitry Ivanovich Mendeleev, following the theory he developed about the periodization of chemical elements, finds a place for a new metal in his table, placing uranium in the last cell. In addition, Mendeleev doubled the previously assumed atomic weight of uranium, without making a mistake in this either, which was confirmed by the experiments of the German chemist Zimmermann 12 years later.
Since 1896, discoveries in the field of studying the properties of uranium have “fallen down” one after another: in the above-mentioned year, quite by accident (while studying the phosphorescence of potassium uranyl sulfate crystals), 43-year-old physics professor Antoine Henri Becquerel opens “Becquerel’s Rays”, later renamed radioactivity by Marie Curie . In the same year, Henri Moissan (again a chemist from France) develops a method for producing pure uranium metal.
In 1899, Ernest Rutherford discovered the heterogeneity of radiation from uranium preparations. It turned out that there are two types of radiation - alpha and beta rays, different in their properties: they carry different electrical charges, have different path lengths in matter and their ionizing ability is also different. A year later, gamma rays were also discovered by Paul Villar.
Ernest Rutherford and Frederick Soddy jointly developed the theory of radioactivity of uranium. Based on this theory, in 1907, Rutherford undertook the first experiments to determine the age of minerals when studying radioactive uranium and thorium. In 1913, F. Soddy introduced the concept of isotopes (from the ancient Greek iso - “equal”, “identical”, and topos - “place”). In 1920, the same scientist suggested that isotopes could be used to determine the geological age of rocks. His assumptions turned out to be correct: in 1939, Alfred Otto Karl Nier created the first equations for calculating ages and used a mass spectrometer to separate isotopes.
In 1934, Enrico Fermi conducted a series of experiments on bombarding chemical elements with neutrons - particles discovered by J. Chadwick in 1932. As a result of this operation, previously unknown radioactive substances appeared in uranium. Fermi and other scientists who participated in his experiments suggested that they had discovered transuranium elements. For four years, attempts were made to detect transuranium elements among the products of neutron bombardment. It all ended in 1938, when German chemists Otto Hahn and Fritz Strassmann established that, by capturing a free neutron, the nucleus of the uranium isotope 235U splits, releasing (per one uranium nucleus) quite a large amount of energy, mainly due to kinetic energy fragments and radiation. The German chemists failed to advance further. Lise Meitner and Otto Frisch were able to substantiate their theory. This discovery was the origin of the use of intra-atomic energy for both peaceful and military purposes.
Being in nature
The average content of uranium in the earth's crust (clarke) is 3∙10-4% by mass, which means that there is more of it in the bowels of the earth than silver, mercury, and bismuth. Uranium is a characteristic element for the granite layer and sedimentary shell of the earth's crust. So, in a ton of granite there is about 25 grams of element No. 92. In total, more than 1000 tons of uranium are contained in the relatively thin, twenty-kilometer upper layer of the Earth. In acidic igneous rocks 3.5∙10-4%, in clays and shales 3.2∙10-4%, especially enriched in organic matter, in basic rocks 5∙10-5%, in ultramafic rocks of the mantle 3∙10-7% .
Uranium migrates vigorously in cold and hot, neutral and alkaline waters in the form of simple and complex ions, especially in the form of carbonate complexes. Redox reactions play an important role in the geochemistry of uranium, all because uranium compounds, as a rule, are highly soluble in waters with an oxidizing environment and poorly soluble in waters with a reducing environment (hydrogen sulfide).
More than a hundred mineral ores of uranium are known; they differ in chemical composition, origin, and uranium concentration; of the entire variety, only a dozen are of practical interest. The main representatives of uranium, which have the greatest industrial importance, in nature can be considered oxides - uraninite and its varieties (pitched pitch and uranium black), as well as silicates - coffinit, titanates - davidite and brannerite; hydrous phosphates and uranyl arsenates - uranium micas.
Uraninite - UO2 is present predominantly in ancient - Precambrian rocks in the form of clear crystalline forms. Uraninite forms isomorphic series with thorianite ThO2 and yttrocerianite (Y,Ce)O2. In addition, all uraninites contain radiogenic decay products of uranium and thorium: K, Po, He, Ac, Pb, as well as Ca and Zn. Uraninite itself is a high-temperature mineral, characteristic of granite and syenite pegmatites in association with complex niobate-tantalum-titanates of uranium (columbite, pyrochlore, samarskite and others), zircon, monazite. In addition, uraninite occurs in hydrothermal, skarn, and sedimentary rocks. Large deposits of uraninite are known in Canada, Africa, the United States of America, France and Australia.
Pitchblende (U3O8), also known as uranium tar or resin blende, which forms cryptocrystalline collomorphic aggregates - a volcanic and hydrothermal mineral, is represented in Paleozoic and younger high- and medium-temperature formations. Constant satellites of pitchblende are sulfides, arsenides, native bismuth, arsenic and silver, carbonates and some other elements. These ores are very rich in uranium, but are extremely rare, often accompanied by radium, this is easily explained: radium is a direct product of the isotopic decay of uranium.
Uranium blacks (loose earthy aggregates) are presented mainly in young - Cenozoic and younger formations, characteristic of hydrothermal sulfide-uranium and sedimentary deposits.
Uranium is also extracted as a by-product from ores containing less than 0.1%, for example, from gold-bearing conglomerates.
The main deposits of uranium ores are located in the USA (Colorado, North and South Dakota), Canada (provinces of Ontario and Saskatchewan), South Africa (Witwatersrand), France (Massif Central), Australia (Northern Territory) and many other countries. In Russia, the main uranium ore region is Transbaikalia. About 93% of Russian uranium is mined at the deposit in the Chita region (near the city of Krasnokamensk).
Application
Modern nuclear energy is simply unthinkable without element No. 92 and its properties. Although not so long ago - before the launch of the first nuclear reactor, uranium ores were mined mainly to extract radium from them. Small amounts of uranium compounds have been used in some dyes and catalysts. In fact, uranium was considered an element that had almost no industrial significance, and how radically the situation changed after the discovery of the ability of uranium isotopes to fission! This metal instantly received the status of strategic raw material No. 1.
Nowadays, the main area of application of uranium metal, as well as its compounds, is fuel for nuclear reactors. Thus, in stationary nuclear power plant reactors, a low-enriched (natural) mixture of uranium isotopes is used, and in nuclear power plants and fast neutron reactors, highly enriched uranium is used.
The uranium isotope 235U is most widely used, because a self-sustaining nuclear chain reaction is possible in it, which is not typical for other uranium isotopes. Thanks to this property, 235U is used as fuel in nuclear reactors, as well as in nuclear weapons. However, the separation of the 235U isotope from natural uranium is a complex and expensive technological problem.
The most common isotope of uranium in nature, 238U, can fission when bombarded with high-energy neutrons. This property of this isotope is used to increase the power of thermonuclear weapons - neutrons generated by a thermonuclear reaction are used. In addition, the plutonium isotope 239Pu is obtained from the 238U isotope, which in turn can also be used in nuclear reactors and in an atomic bomb.
Recently, the uranium isotope 233U, artificially produced in reactors from thorium, has found great use; it is obtained by irradiating thorium in the neutron flux of a nuclear reactor:
23290Th + 10n → 23390Th -(β–)→ 23391Pa –(β–)→ 23392U
233U fissile thermal neutrons; in addition, in reactors with 233U, expanded reproduction of nuclear fuel can occur. So, when a kilogram of 233U burns out in a thorium reactor, 1.1 kg of new 233U should accumulate in it (as a result of the capture of neutrons by thorium nuclei). In the near future, the uranium-thorium cycle in thermal neutron reactors will be the main competitor to the uranium-plutonium cycle for the reproduction of nuclear fuel in fast neutron reactors. Reactors using this nuclide as fuel already exist and are operating (KAMINI in India). 233U is also the most promising fuel for gas-phase nuclear rocket engines.
Other artificial isotopes of uranium do not play a significant role.
After the “necessary” isotopes 234U and 235U are extracted from natural uranium, the remaining raw material (238U) is called “depleted uranium”, it is half as radioactive as natural uranium, mainly due to the removal of 234U from it. Since the main use of uranium is energy production, for this reason depleted uranium is a low-use product with low economic value. However, due to its low price, as well as its high density and extremely high capture cross-section, it is used for radiation protection, and as ballast in aerospace applications such as aircraft control surfaces. In addition, depleted uranium is used as ballast in space landers and racing yachts; in high-speed gyroscope rotors, large flywheels, and when drilling oil wells.
However, the most famous use of depleted uranium is in military applications - as cores for armor-piercing shells and modern tank armor, such as the M-1 Abrams tank.
Lesser-known uses of uranium mainly involve its compounds. So a small addition of uranium gives a beautiful yellow-green fluorescence to glass, some uranium compounds are photosensitive, for this reason uranyl nitrate was widely used to enhance negatives and color (tint) positives (photographic prints) brown.
235U carbide alloyed with niobium carbide and zirconium carbide is used as fuel for nuclear jet engines. Alloys of iron and depleted uranium (238U) are used as powerful magnetostrictive materials. Sodium uranate Na2U2O7 was used as a yellow pigment in painting; previously, uranium compounds were used as paints for painting on porcelain and for ceramic glazes and enamels (painted in colors: yellow, brown, green and black, depending on the degree of oxidation).
Production
Uranium is obtained from uranium ores, which differ significantly in a number of characteristics (formation conditions, “contrast”, content of useful impurities, etc.), the main of which is the percentage of uranium. According to this criterion, five types of ores are distinguished: very rich (contain over 1% uranium); rich (1-0.5%); average (0.5-0.25%); ordinary (0.25-0.1%) and poor (less than 0.1%). However, even from ores containing 0.01-0.015% uranium, this metal is extracted as a by-product.
Over the years of development of uranium raw materials, many methods for separating uranium from ores have been developed. This is due to both the strategic importance of uranium in some areas and the diversity of its natural manifestations. However, despite all the variety of methods and raw materials, any uranium production consists of three stages: preliminary concentration of uranium ore; leaching of uranium and obtaining sufficiently pure uranium compounds by precipitation, extraction or ion exchange. Next, depending on the purpose of the resulting uranium, the product is enriched with the 235U isotope or immediately reduced to elemental uranium.
So, the ore is initially concentrated - the rock is crushed and filled with water. In this case, the heavier elements of the mixture settle faster. In rocks containing primary uranium minerals, their rapid precipitation occurs, since they are very heavy. When ores containing secondary uranium minerals are concentrated, waste rock is deposited, which is much heavier than the secondary minerals, but can contain very useful elements.
Uranium ores are almost never enriched, with the exception of the organic method of radiometric sorting, based on the γ-radiation of radium, which always accompanies uranium.
The next stage in uranium production is leaching, thus bringing the uranium into solution. Basically, ores are leached with solutions of sulfuric, sometimes nitric acids or soda solutions with the transfer of uranium into an acidic solution in the form of UO2SO4 or complex anions, and into a soda solution in the form of a 4-complex anion. The method that uses sulfuric acid is cheaper, however, it is not always applicable if the raw material contains tetravalent uranium (uranium resin), which is not soluble in sulfuric acid. In such cases, alkaline leaching is used or tetravalent uranium is oxidized to a hexavalent state. The use of caustic soda (caustic soda) is advisable when leaching ores containing magnesite or dolomite, which require too much acid to dissolve.
After the leaching stage, the solution contains not only uranium, but also other elements, which, like uranium, are extracted with the same organic solvents, deposited on the same ion exchange resins, and precipitate under the same conditions. In such a situation, to selectively isolate uranium, it is necessary to use many redox reactions in order to eliminate the unwanted element at different stages. One of the advantages of ion exchange and extraction methods is that uranium is quite completely extracted from poor solutions.
After all the above operations, uranium is converted into a solid state - into one of the oxides or into UF4 tetrafluoride. Such uranium contains impurities with a large thermal neutron capture cross section - lithium, boron, cadmium, and rare earth metals. In the final product their content should not exceed hundred thousandths and millionths of a percent! To do this, uranium is dissolved again, this time in nitric acid. Uranyl nitrate UO2(NO3)2 during extraction with tributyl phosphate and some other substances is additionally purified to the required standards. This substance is then crystallized (or precipitated) and carefully calcined. As a result of this operation, uranium trioxide UO3 is formed, which is reduced with hydrogen to UO2. At temperatures from 430 to 600° C, uranium oxide reacts with dry hydrogen fluoride and turns into UF4 tetrafluoride. Already from this compound, uranium metal is usually obtained with the help of calcium or magnesium by ordinary reduction.
Physical properties
Uranium metal is very heavy, it is two and a half times heavier than iron, and one and a half times heavier than lead! This is one of the heaviest elements stored in the bowels of the Earth. With its silvery-white color and shine, uranium resembles steel. Pure metal It is plastic, soft, has a high density, but at the same time is easy to process. Uranium is electropositive and has minor paramagnetic properties - specific magnetic susceptibility at room temperature is 1.72·10 -6, has low electrical conductivity but high reactivity. This element has three allotropic modifications: α, β and γ. The α-form has an orthorhombic crystal lattice with the following parameters: a = 2.8538 Å, b = 5.8662 Å, c = 469557 Å. This form is stable in the temperature range from room temperatures to 667.7° C. The density of uranium in the α-form at a temperature of 25° C is 19.05 ± 0.2 g/cm 3 . The β-form has a tetragonal crystal lattice, stable in the temperature range from 667.7° C to 774.8° C. Parameters of the tetragonal lattice: a = 10.759 Å, b = 5.656 Å. γ-form with a body-centered cubic structure, stable from 774.8°C to melting point (1132°C).
All three phases can be seen during the recovery process of uranium. For this, a special apparatus is used, which is a seamless steel pipe, which is lined with calcium oxide; this is necessary so that the steel of the pipe does not interact with uranium. A mixture of uranium tetrafluoride and magnesium (or calcium) is loaded into the apparatus, after which it is heated to 600 ° C. When this temperature is reached, the electric igniter is turned on, and the an exothermic reduction reaction, in which the loaded mixture completely melts. Liquid uranium (temperature 1132 ° C) due to its weight completely sinks to the bottom. After complete deposition of uranium to the bottom of the apparatus, cooling begins, the uranium crystallizes, its atoms are arranged in strict order, forming a cubic lattice - this is the γ-phase. The next transition occurs at 774° C - the crystal lattice of the cooling metal becomes tetragonal, which corresponds to the β-phase. When the temperature of the ingot drops to 668° C, the atoms again rearrange their rows, arranged in waves in parallel layers - the α phase. Further no changes occur.
The main parameters of uranium always refer to the α phase. Melting point (tmelting) 1132° C, boiling point of uranium (tboiling) 3818° C. Specific heat capacity at room temperature 27.67 kJ/(kg·K) or 6.612 cal/(g·°С). The electrical resistivity at a temperature of 25°C is approximately 3·10 -7 ohm·cm, and already at 600°С it is 5.5·10 -7 ohm·cm. The thermal conductivity of uranium also changes depending on temperature: in the range of 100-200 ° C it is equal to 28.05 W/(m K) or 0.067 cal/(cm sec ° C), and when increased to 400 ° C it increases up to 29.72 W/(m K) 0.071 cal/(cm sec ° C). Uranium has superconductivity at 0.68 K. The average Brinell hardness is 19.6 - 21.6·10 2 Mn/m 2 or 200-220 kgf/mm 2.
Many mechanical properties of the 92nd element depend on its purity and on the modes of thermal and mechanical treatment. So for cast uranium tensile strength at room temperature is 372-470 MN/m2 or 38-48 kgf/mm2, the average elastic modulus is 20.5·10 -2 MN/m2 or 20.9·10 -3 kgf/mm2. The strength of uranium increases after quenching from the β- and γ-phases.
Irradiation of uranium by a neutron flux, interaction with water cooling fuel elements made of metallic uranium, and other factors of operation in powerful thermal neutron reactors - all this leads to changes in the physical and mechanical properties of uranium: the metal becomes brittle, creep develops, and products made of metallic uranium are deformed . For this reason, uranium alloys, for example with molybdenum, are used in nuclear reactors; such an alloy is resistant to water, strengthens the metal, maintaining a high-temperature cubic lattice.
Chemical properties
Chemically, uranium is a very active metal. In air, it oxidizes with the formation of an iridescent film of UO2 dioxide on the surface, which does not protect the metal from further oxidation, as happens with titanium, zirconium and a number of other metals. With oxygen, uranium forms UO2 dioxide, UO3 trioxide and a large number of intermediate oxides, the most important of which is U3O8; the properties of these oxides are similar to UO2 and UO3. In a powdered state, uranium is pyrophoric and can ignite with slight heating (150 °C and above), combustion is accompanied by a bright flame, ultimately forming U3O8. At a temperature of 500-600 °C, uranium interacts with fluorine to form green needle-shaped crystals, slightly soluble in water and acids - uranium tetrafluoride UF4, as well as UF6 - hexafluoride (white crystals that sublime without melting at a temperature of 56.4 °C). UF4, UF6 are examples of the interaction of uranium with halogens to form uranium halides. Uranium easily combines with sulfur, forming a number of compounds, of which the most important is US - nuclear fuel. Uranium reacts with hydrogen at 220 °C to form the hydride UH3, which is chemically very active. With further heating, UH3 decomposes into hydrogen and powdered uranium. Interaction with nitrogen occurs at higher temperatures - from 450 to 700 °C and atmospheric pressure - nitride U4N7 is obtained; with increasing nitrogen pressure at the same temperatures, UN, U2N3 and UN2 can be obtained. At higher temperatures (750-800 °C), uranium reacts with carbon to form UC monocarbide, UC2 dicarbide, and also U2C3. Uranium reacts with water to form UO2 and H2, more slowly with cold water and more actively with hot water. In addition, the reaction also occurs with water vapor at temperatures from 150 to 250 °C. This metal dissolves in hydrochloric HCl and nitric acids HNO3, less actively in highly concentrated hydrofluoric acid, and reacts slowly with sulfuric H2SO4 and orthophosphoric acids H3PO4. The products of reactions with acids are tetravalent uranium salts. From inorganic acids and salts of some metals (gold, platinum, copper, silver, tin and mercury), uranium is capable of displacing hydrogen. Uranium does not interact with alkalis.
In compounds, uranium is capable of exhibiting the following oxidation states: +3, +4, +5, +6, sometimes +2. U3+ does not exist in nature and can only be obtained in the laboratory. Compounds of pentavalent uranium are for the most part unstable and quite easily decompose into compounds of tetravalent and hexavalent uranium, which are the most stable. Hexavalent uranium is characterized by the formation of the uranyl ion UO22+, the salts of which are yellow in color and are highly soluble in water and mineral acids. An example of hexavalent uranium compounds is uranium trioxide or uranium anhydride UO3 (orange powder), which is an amphoteric oxide. When dissolved in acids, salts are formed, for example, uranium uranium chloride UO2Cl2. When alkalis act on solutions of uranyl salts, salts of uranic acid H2UO4 - uranates and diuranic acid H2U2O7 - diuranates are obtained, for example, sodium uranate Na2UO4 and sodium diuranate Na2U2O7. Salts of tetravalent uranium (uranium tetrachloride UCl4) are green and less soluble. When exposed to air for a long time, compounds containing tetravalent uranium are usually unstable and turn into hexavalent ones. Uranyl salts such as uranyl chloride decompose in the presence of bright light or organic matter.
