Uranium metals. Why are uranium and its compounds dangerous? Applications and types of uranium isotopes

Where did uranium come from? Most likely, it appears during supernova explosions. The fact is that for the nucleosynthesis of elements heavier than iron, there must be a powerful flow of neutrons, which occurs precisely during a supernova explosion. It would seem that then, during condensation from the cloud of new star systems formed by it, uranium, having collected in a protoplanetary cloud and being very heavy, should sink into the depths of the planets. But that's not true. Uranium is a radioactive element and when it decays it releases heat. Calculations show that if uranium were evenly distributed throughout the entire thickness of the planet, at least with the same concentration as on the surface, it would emit too much heat. Moreover, its flow should weaken as uranium is consumed. Since nothing like this has been observed, geologists believe that at least a third of uranium, and perhaps all of it, is concentrated in the earth’s crust, where its content is 2.5∙10 –4%. Why this happened is not discussed.

Where is uranium mined? There is not so little uranium on Earth - it is in 38th place in terms of abundance. And most of this element is found in sedimentary rocks - carbonaceous shales and phosphorites: up to 8∙10 –3 and 2.5∙10 –2%, respectively. In total, the earth's crust contains 10 14 tons of uranium, but the main problem is that it is very dispersed and does not form powerful deposits. Approximately 15 uranium minerals are of industrial importance. This is uranium tar - its basis is tetravalent uranium oxide, uranium mica - various silicates, phosphates and more complex compounds with vanadium or titanium based on hexavalent uranium.

What are Becquerel's rays? After the discovery of X-rays by Wolfgang Roentgen, French physicist Antoine-Henri Becquerel became interested in the glow of uranium salts, which occurs under the influence of sunlight. He wanted to understand if there were X-rays here too. Indeed, they were present - the salt illuminated the photographic plate through the black paper. In one of the experiments, however, the salt was not illuminated, but the photographic plate still darkened. When a metal object was placed between the salt and the photographic plate, the darkening underneath was less. Therefore, new rays did not arise due to the excitation of uranium by light and did not partially pass through the metal. They were initially called “Becquerel’s rays.” It was subsequently discovered that these are mainly alpha rays with a small addition of beta rays: the fact is that the main isotopes of uranium emit an alpha particle during decay, and the daughter products also experience beta decay.

How radioactive is uranium? Uranium has no stable isotopes; they are all radioactive. The longest-lived is uranium-238 with a half-life of 4.4 billion years. Next comes uranium-235 - 0.7 billion years. They both undergo alpha decay and become the corresponding isotopes of thorium. Uranium-238 makes up more than 99% of all natural uranium. Due to its huge half-life, the radioactivity of this element is low, and in addition, alpha particles are not able to penetrate the stratum corneum on the surface of the human body. They say that after working with uranium, I.V. Kurchatov simply wiped his hands with a handkerchief and did not suffer from any diseases associated with radioactivity.

Researchers have repeatedly turned to the statistics of diseases of workers in uranium mines and processing plants. Here, for example, is a recent article by Canadian and American specialists who analyzed health data of more than 17 thousand workers at the Eldorado mine in the Canadian province of Saskatchewan for the years 1950–1999 ( Environmental Research, 2014, 130, 43–50, DOI:10.1016/j.envres.2014.01.002). They proceeded from the fact that radiation has the strongest effect on rapidly multiplying blood cells, leading to the corresponding types of cancer. Statistics have shown that mine workers have a lower incidence of various types of blood cancer than the average Canadian population. In this case, the main source of radiation is not considered to be uranium itself, but the gaseous radon it generates and its decay products, which can enter the body through the lungs.

Why is uranium harmful?? It, like other heavy metals, is highly toxic and can cause kidney and liver failure. On the other hand, uranium, being a dispersed element, is inevitably present in water, soil and, concentrating in the food chain, enters the human body. It is reasonable to assume that in the process of evolution, living beings have learned to neutralize uranium in natural concentrations. Uranium is the most dangerous in water, so the WHO set a limit: initially it was 15 µg/l, but in 2011 the standard was increased to 30 µg/g. As a rule, there is much less uranium in water: in the USA on average 6.7 µg/l, in China and France - 2.2 µg/l. But there are also strong deviations. So in some areas of California it is a hundred times more than the standard - 2.5 mg/l, and in Southern Finland it reaches 7.8 mg/l. Researchers are trying to understand whether the WHO standard is too strict by studying the effect of uranium on animals. Here is a typical job ( BioMed Research International, 2014, ID 181989; DOI:10.1155/2014/181989). French scientists fed rats water for nine months with additives of depleted uranium, and in relatively high concentrations - from 0.2 to 120 mg/l. The lower value is water near the mine, while the upper value is not found anywhere - the maximum concentration of uranium, measured in Finland, is 20 mg/l. To the surprise of the authors - the article is called: “The unexpected absence of a noticeable effect of uranium on physiological systems ...” - uranium had practically no effect on the health of rats. The animals ate well, gained weight properly, did not complain of illness and did not die from cancer. Uranium, as it should be, was deposited primarily in the kidneys and bones and in a hundred times smaller quantities in the liver, and its accumulation expectedly depended on the content in the water. However, this did not lead to renal failure or even the noticeable appearance of any molecular markers of inflammation. The authors suggested that a review of the WHO's strict guidelines should begin. However, there is one caveat: the effect on the brain. There was less uranium in the rats' brains than in the liver, but its content did not depend on the amount in the water. But uranium affected the functioning of the brain’s antioxidant system: the activity of catalase increased by 20%, glutathione peroxidase by 68–90%, and the activity of superoxide dismutase decreased by 50%, regardless of the dose. This means that the uranium clearly caused oxidative stress in the brain and the body responded to it. This effect - the strong effect of uranium on the brain in the absence of its accumulation in it, by the way, as well as in the genitals - was noticed before. Moreover, water with uranium in a concentration of 75–150 mg/l, which researchers from the University of Nebraska fed rats for six months ( Neurotoxicology and Teratology, 2005, 27, 1, 135–144; DOI:10.1016/j.ntt.2004.09.001), affected the behavior of animals, mainly males, released into the field: they crossed lines, stood up on their hind legs and preened their fur differently than the control ones. There is evidence that uranium also leads to memory impairment in animals. Behavioral changes were correlated with levels of lipid oxidation in the brain. It turns out that the uranium water made the rats healthy, but rather stupid. These data will be useful to us in the analysis of the so-called Gulf War Syndrome.

Does uranium contaminate shale gas development sites? It depends on how much uranium is in the gas-containing rocks and how it is associated with them. For example, Associate Professor Tracy Bank of the University at Buffalo studied the Marcellus Shale, which stretches from western New York through Pennsylvania and Ohio to West Virginia. It turned out that uranium is chemically related precisely to the source of hydrocarbons (remember that related carbonaceous shales have the highest uranium content). Experiments have shown that the solution used during fracturing perfectly dissolves uranium. “When the uranium in these waters reaches the surface, it can cause contamination of the surrounding area. This does not pose a radiation risk, but uranium is a poisonous element,” notes Tracy Bank in a university press release dated October 25, 2010. No detailed articles have yet been prepared on the risk of environmental contamination with uranium or thorium during shale gas production.

Why is uranium needed? Previously, it was used as a pigment for making ceramics and colored glass. Now uranium is the basis of nuclear energy and atomic weapons. In this case, its unique property is used - the ability of the nucleus to divide.

What is nuclear fission? The decay of a nucleus into two unequal large pieces. It is because of this property that during nucleosynthesis due to neutron irradiation, nuclei heavier than uranium are formed with great difficulty. The essence of the phenomenon is as follows. If the ratio of the number of neutrons and protons in the nucleus is not optimal, it becomes unstable. Typically, such a nucleus emits either an alpha particle - two protons and two neutrons, or a beta particle - a positron, which is accompanied by the transformation of one of the neutrons into a proton. In the first case, an element of the periodic table is obtained, spaced two cells back, in the second - one cell forward. However, in addition to emitting alpha and beta particles, the uranium nucleus is capable of fission - decaying into the nuclei of two elements in the middle of the periodic table, for example barium and krypton, which it does, having received a new neutron. This phenomenon was discovered shortly after the discovery of radioactivity, when physicists exposed the newly discovered radiation to everything they could. Here is how Otto Frisch, a participant in the events, writes about this (“Advances in Physical Sciences,” 1968, 96, 4). After the discovery of beryllium rays - neutrons - Enrico Fermi irradiated uranium with them, in particular, to cause beta decay - he hoped to use it to obtain the next, 93rd element, now called neptunium. It was he who discovered a new type of radioactivity in irradiated uranium, which he associated with the appearance of transuranium elements. At the same time, slowing down the neutrons, for which the beryllium source was covered with a layer of paraffin, increased this induced radioactivity. American radiochemist Aristide von Grosse suggested that one of these elements was protactinium, but he was wrong. But Otto Hahn, who was then working at the University of Vienna and considered protactinium discovered in 1917 to be his brainchild, decided that he was obliged to find out what elements were obtained. Together with Lise Meitner, at the beginning of 1938, Hahn suggested, based on experimental results, that entire chains of radioactive elements are formed due to multiple beta decays of neutron-absorbing nuclei of uranium-238 and its daughter elements. Soon Lise Meitner was forced to flee to Sweden, fearing possible reprisals from the Nazis after the Anschluss of Austria. Hahn, having continued his experiments with Fritz Strassmann, discovered that among the products there was also barium, element number 56, which in no way could be obtained from uranium: all chains of alpha decays of uranium end with much heavier lead. The researchers were so surprised by the result that they did not publish it; they only wrote letters to friends, in particular to Lise Meitner in Gothenburg. There, at Christmas 1938, her nephew, Otto Frisch, visited her, and, walking in the vicinity of the winter city - he on skis, the aunt on foot - they discussed the possibility of the appearance of barium during the irradiation of uranium as a result of nuclear fission (for more information about Lise Meitner, see “Chemistry and Life ", 2013, No. 4). Returning to Copenhagen, Frisch literally caught Niels Bohr on the gangway of a ship departing for the United States and told him about the idea of ​​fission. Bohr, slapping himself on the forehead, said: “Oh, what fools we were! We should have noticed this earlier." In January 1939, Frisch and Meitner published an article on the fission of uranium nuclei under the influence of neutrons. By that time, Otto Frisch had already carried out a control experiment, as well as many American groups who received the message from Bohr. They say that physicists began to disperse to their laboratories right during his report on January 26, 1939 in Washington at the annual conference on theoretical physics, when they grasped the essence of the idea. After the discovery of fission, Hahn and Strassmann revised their experiments and found, just like their colleagues, that the radioactivity of irradiated uranium is associated not with transuraniums, but with the decay of radioactive elements formed during fission from the middle of the periodic table.

How does a chain reaction occur in uranium? Soon after the possibility of fission of uranium and thorium nuclei was experimentally proven (and there are no other fissile elements on Earth in any significant quantity), Niels Bohr and John Wheeler, who worked at Princeton, as well as, independently of them, the Soviet theoretical physicist Ya. I. Frenkel and the Germans Siegfried Flügge and Gottfried von Droste created the theory of nuclear fission. Two mechanisms followed from it. One is associated with the threshold absorption of fast neutrons. According to it, to initiate fission, a neutron must have a fairly high energy, more than 1 MeV for the nuclei of the main isotopes - uranium-238 and thorium-232. At lower energies, neutron absorption by uranium-238 has a resonant character. Thus, a neutron with an energy of 25 eV has a capture cross-sectional area that is thousands of times larger than with other energies. In this case, there will be no fission: uranium-238 will become uranium-239, which with a half-life of 23.54 minutes will turn into neptunium-239, which with a half-life of 2.33 days will turn into long-lived plutonium-239. Thorium-232 will become uranium-233.

The second mechanism is the non-threshold absorption of a neutron, it is followed by the third more or less common fissile isotope - uranium-235 (as well as plutonium-239 and uranium-233, which are not found in nature): by absorbing any neutron, even slow, so-called thermal, with energy as for molecules participating in thermal motion - 0.025 eV, such a nucleus will split. And this is very good: thermal neutrons have a capture cross-sectional area four times higher than fast, megaelectronvolt neutrons. This is the significance of uranium-235 for the entire subsequent history of nuclear energy: it is it that ensures the multiplication of neutrons in natural uranium. After being hit by a neutron, the uranium-235 nucleus becomes unstable and quickly splits into two unequal parts. Along the way, several (on average 2.75) new neutrons are emitted. If they hit the nuclei of the same uranium, they will cause neutrons to multiply exponentially - a chain reaction will occur, which will lead to an explosion due to the rapid release of a huge amount of heat. Neither uranium-238 nor thorium-232 can work like that: after all, during fission, neutrons are emitted with an average energy of 1–3 MeV, that is, if there is an energy threshold of 1 MeV, a significant part of the neutrons will certainly not be able to cause a reaction, and there will be no reproduction. This means that these isotopes should be forgotten and the neutrons will have to be slowed down to thermal energy so that they interact as efficiently as possible with the nuclei of uranium-235. At the same time, their resonant absorption by uranium-238 cannot be allowed: after all, in natural uranium this isotope is slightly less than 99.3% and neutrons more often collide with it, and not with the target uranium-235. And by acting as a moderator, it is possible to maintain the multiplication of neutrons at a constant level and prevent an explosion - control the chain reaction.

A calculation carried out by Ya. B. Zeldovich and Yu. B. Khariton in the same fateful year of 1939 showed that for this it is necessary to use a neutron moderator in the form of heavy water or graphite and enrich natural uranium with uranium-235 at least 1.83 times. Then this idea seemed to them pure fantasy: “It should be noted that approximately double the enrichment of those rather significant quantities of uranium that are necessary to carry out a chain explosion,<...>is an extremely cumbersome task, close to practical impossibility.” Now this problem has been solved, and the nuclear industry is mass-producing uranium enriched with uranium-235 to 3.5% for power plants.

What is spontaneous nuclear fission? In 1940, G. N. Flerov and K. A. Petrzhak discovered that fission of uranium can occur spontaneously, without any external influence, although the half-life is much longer than with ordinary alpha decay. Since such fission also produces neutrons, if they are not allowed to escape from the reaction zone, they will serve as the initiators of the chain reaction. It is this phenomenon that is used in the creation of nuclear reactors.

Why is nuclear energy needed? Zeldovich and Khariton were among the first to calculate the economic effect of nuclear energy (Uspekhi Fizicheskikh Nauk, 1940, 23, 4). “...At the moment, it is still impossible to make final conclusions about the possibility or impossibility of carrying out a nuclear fission reaction with infinitely branching chains in uranium. If such a reaction is feasible, then the reaction rate is automatically adjusted to ensure its smooth progress, despite the enormous amount of energy at the experimenter’s disposal. This circumstance is extremely favorable for the energy use of the reaction. Let us therefore present - although this is a division of the skin of an unkilled bear - some numbers characterizing the possibilities of the energy use of uranium. If the fission process proceeds with fast neutrons, therefore, the reaction captures the main isotope of uranium (U238), then<исходя из соотношения теплотворных способностей и цен на уголь и уран>the cost of a calorie from the main isotope of uranium turns out to be approximately 4000 times cheaper than from coal (unless, of course, the processes of “combustion” and heat removal turn out to be much more expensive in the case of uranium than in the case of coal). In the case of slow neutrons, the cost of a “uranium” calorie (based on the above figures) will be, taking into account that the abundance of the U235 isotope is 0.007, already only 30 times cheaper than a “coal” calorie, all other things being equal.”

The first controlled chain reaction was carried out in 1942 by Enrico Fermi at the University of Chicago, and the reactor was controlled manually - pushing graphite rods in and out as the neutron flux changed. The first power plant was built in Obninsk in 1954. In addition to generating energy, the first reactors also worked to produce weapons-grade plutonium.

How does a nuclear power plant operate? Nowadays, most reactors operate on slow neutrons. Enriched uranium in the form of a metal, an alloy such as aluminum, or an oxide is placed in long cylinders called fuel elements. They are installed in a certain way in the reactor, and moderator rods are inserted between them, which control the chain reaction. Over time, reactor poisons accumulate in the fuel element - uranium fission products, which are also capable of absorbing neutrons. When the concentration of uranium-235 falls below a critical level, the element is taken out of service. However, it contains many fission fragments with strong radioactivity, which decreases over the years, causing the elements to emit a significant amount of heat for a long time. They are kept in cooling pools, and then either buried or tried to be processed - to extract unburned uranium-235, produced plutonium (it was used to make atomic bombs) and other isotopes that can be used. The unused part is sent to burial grounds.

In so-called fast reactors, or breeder reactors, reflectors made of uranium-238 or thorium-232 are installed around the elements. They slow down and send back into the reaction zone neutrons that are too fast. Neutrons slowed down to resonant speeds absorb these isotopes, turning into plutonium-239 or uranium-233, respectively, which can serve as fuel for a nuclear power plant. Since fast neutrons react poorly with uranium-235, its concentration must be significantly increased, but this pays off with a stronger neutron flux. Despite the fact that breeder reactors are considered the future of nuclear energy, since they produce more nuclear fuel than they consume, experiments have shown that they are difficult to manage. Now there is only one such reactor left in the world - at the fourth power unit of the Beloyarsk NPP.

How is nuclear energy criticized? If we do not talk about accidents, then the main point in the arguments of opponents of nuclear energy today is the proposal to add to the calculation of its efficiency the costs of protecting the environment after decommissioning the station and when working with fuel. In both cases, the challenges of reliable disposal of radioactive waste arise, and these are costs borne by the state. There is an opinion that if you transfer them to the cost of energy, then its economic attractiveness will disappear.

There is also opposition among supporters of nuclear energy. Its representatives point to the uniqueness of uranium-235, which has no replacement, because alternative isotopes fissile by thermal neutrons - plutonium-239 and uranium-233 - due to their half-lives of thousands of years, are not found in nature. And they are obtained precisely as a result of the fission of uranium-235. If it runs out, a wonderful natural source of neutrons for a nuclear chain reaction will disappear. As a result of such wastefulness, humanity will lose the opportunity in the future to involve thorium-232, the reserves of which are several times greater than uranium, into the energy cycle.

Theoretically, particle accelerators can be used to produce a flux of fast neutrons with megaelectronvolt energies. However, if we are talking, for example, about interplanetary flights on a nuclear engine, then implementing a scheme with a bulky accelerator will be very difficult. The depletion of uranium-235 puts an end to such projects.

What is weapons-grade uranium? This is highly enriched uranium-235. Its critical mass - it corresponds to the size of a piece of substance in which a chain reaction occurs spontaneously - is small enough to produce ammunition. Such uranium can be used to make an atomic bomb, and also as a fuse for a thermonuclear bomb.

What disasters are associated with the use of uranium? The energy stored in the nuclei of fissile elements is enormous. If it gets out of control due to oversight or intentionally, this energy can cause a lot of trouble. The two worst nuclear disasters occurred on August 6 and 8, 1945, when the US Air Force dropped atomic bombs on Hiroshima and Nagasaki, killing and injuring hundreds of thousands of civilians. Smaller scale disasters are associated with accidents at nuclear power plants and nuclear cycle enterprises. The first major accident occurred in 1949 in the USSR at the Mayak plant near Chelyabinsk, where plutonium was produced; Liquid radioactive waste ended up in the Techa River. In September 1957, an explosion occurred on it, releasing a large amount of radioactive material. Eleven days later, the British plutonium production reactor at Windscale burned down, and the cloud with the explosion products dispersed over Western Europe. In 1979, a reactor at the Three Mail Island Nuclear Power Plant in Pennsylvania burned down. The most widespread consequences were caused by the accidents at the Chernobyl nuclear power plant (1986) and the Fukushima nuclear power plant (2011), when millions of people were exposed to radiation. The first littered vast areas, releasing 8 tons of uranium fuel and decay products as a result of the explosion, which spread across Europe. The second polluted and, three years after the accident, continues to pollute the Pacific Ocean in fishing areas. Eliminating the consequences of these accidents was very expensive, and if these costs were broken down into the cost of electricity, it would increase significantly.

A separate issue is the consequences for human health. According to official statistics, many people who survived the bombing or living in contaminated areas benefited from radiation - the former have a higher life expectancy, the latter have less cancer, and experts attribute some increase in mortality to social stress. The number of people who died precisely from the consequences of accidents or as a result of their liquidation amounts to hundreds of people. Opponents of nuclear power plants point out that the accidents have led to several million premature deaths on the European continent, but they are simply invisible in the statistical context.

Removing lands from human use in accident zones leads to an interesting result: they become a kind of nature reserves where biodiversity grows. True, some animals suffer from radiation-related diseases. The question of how quickly they will adapt to the increased background remains open. There is also an opinion that the consequence of chronic irradiation is “selection for fools” (see “Chemistry and Life”, 2010, No. 5): even at the embryonic stage, more primitive organisms survive. In particular, in relation to people, this should lead to a decrease in mental abilities in the generation born in contaminated areas shortly after the accident.

What is depleted uranium? This is uranium-238, remaining after the separation of uranium-235 from it. The volumes of waste from the production of weapons-grade uranium and fuel elements are large - in the United States alone, 600 thousand tons of such uranium hexafluoride have accumulated (for problems with it, see Chemistry and Life, 2008, No. 5). The content of uranium-235 in it is 0.2%. This waste must either be stored until better times, when fast neutron reactors will be created and it will be possible to process uranium-238 into plutonium, or used somehow.

They found a use for it. Uranium, like other transition elements, is used as a catalyst. For example, the authors of the article in ACS Nano dated June 30, 2014, they write that a catalyst made of uranium or thorium with graphene for the reduction of oxygen and hydrogen peroxide “has enormous potential for use in the energy sector.” Because uranium has a high density, it serves as ballast for ships and counterweights for aircraft. This metal is also suitable for radiation protection in medical devices with radiation sources.

What weapons can be made from depleted uranium? Bullets and cores for armor-piercing projectiles. The calculation here is as follows. The heavier the projectile, the higher its kinetic energy. But the larger the projectile, the less concentrated its impact. This means that heavy metals with high density are needed. Bullets are made of lead (Ural hunters at one time also used native platinum, until they realized that it was a precious metal), while the shell cores are made of tungsten alloy. Environmentalists point out that lead contaminates the soil in places of military operations or hunting and it would be better to replace it with something less harmful, for example, tungsten. But tungsten is not cheap, and uranium, similar in density, is a harmful waste. At the same time, the permissible contamination of soil and water with uranium is approximately twice as high as for lead. This happens because the weak radioactivity of depleted uranium (and it is also 40% less than that of natural uranium) is neglected and a truly dangerous chemical factor is taken into account: uranium, as we remember, is poisonous. At the same time, its density is 1.7 times greater than that of lead, which means that the size of uranium bullets can be reduced by half; uranium is much more refractory and hard than lead - it evaporates less when fired, and when it hits a target it produces fewer microparticles. In general, a uranium bullet is less polluting than a lead bullet, although such use of uranium is not known for certain.

But it is known that plates made of depleted uranium are used to strengthen the armor of American tanks (this is facilitated by its high density and melting point), and also instead of tungsten alloy in cores for armor-piercing projectiles. The uranium core is also good because uranium is pyrophoric: its hot small particles formed upon impact with the armor flare up and set fire to everything around. Both applications are considered radiation safe. Thus, the calculation showed that even after sitting for a year in a tank with uranium armor loaded with uranium ammunition, the crew would receive only a quarter of the permissible dose. And to get the annual permissible dose, you need to screw such ammunition to the surface of the skin for 250 hours.

Shells with uranium cores - for 30-mm aircraft cannons or artillery sub-calibers - have been used by the Americans in recent wars, starting with the Iraq campaign of 1991. That year they rained down on Iraqi armored units in Kuwait and during their retreat, 300 tons of depleted uranium, of which 250 tons, or 780 thousand rounds, were fired at aircraft guns. In Bosnia and Herzegovina, during the bombing of the army of the unrecognized Republika Srpska, 2.75 tons of uranium were spent, and during the shelling of the Yugoslav army in the region of Kosovo and Metohija - 8.5 tons, or 31 thousand rounds. Since WHO was by that time concerned about the consequences of the use of uranium, monitoring was carried out. He showed that one salvo consisted of approximately 300 rounds, of which 80% contained depleted uranium. 10% hit targets, and 82% fell within 100 meters of them. The rest dispersed within 1.85 km. A shell that hit a tank burned up and turned into an aerosol; the uranium shell pierced through light targets like armored personnel carriers. Thus, at most one and a half tons of shells could turn into uranium dust in Iraq. According to experts from the American strategic research center RAND Corporation, more, from 10 to 35% of the used uranium, turned into aerosol. Croatian anti-uranium munitions activist Asaf Durakovic, who has worked in a variety of organizations from Riyadh's King Faisal Hospital to the Washington Uranium Medical Research Center, estimates that in southern Iraq alone in 1991, 3-6 tons of submicron uranium particles were formed, which were scattered over a wide area , that is, uranium contamination there is comparable to Chernobyl.

Uranium is not a very typical actinide; its five valence states are known - from 2+ to 6+. Some uranium compounds have a characteristic color. Thus, solutions of trivalent uranium are red, tetravalent uranium is green, and hexavalent uranium - it exists in the form of uranyl ion (UO 2) 2+ - colors the solutions yellow... The fact that hexavalent uranium forms compounds with many organic complexing agents, turned out to be very important for the extraction technology of element No. 92.

It is characteristic that the outer electron shell of uranium ions is always completely filled; The valence electrons are in the previous electron layer, in the 5f subshell. If we compare uranium with other elements, it is obvious that plutonium is most similar to it. The main difference between them is the large ionic radius of uranium. In addition, plutonium is most stable in the tetravalent state, and uranium is most stable in the hexavalent state. This helps to separate them, which is very important: the nuclear fuel plutonium-239 is obtained exclusively from uranium, ballast from the energy point of view of uranium-238. Plutonium is formed in a mass of uranium, and they must be separated!

However, first you need to get this very mass of uranium, going through a long technological chain, starting with ore. Typically a multi-component, uranium-poor ore.

Light isotope of a heavy element

When we talked about obtaining element No. 92, we deliberately omitted one important stage. As you know, not all uranium is capable of supporting a nuclear chain reaction. Uranium-238, which accounts for 99.28% of the natural mixture of isotopes, is not capable of this. Because of this, uranium-238 is converted into plutonium, and the natural mixture of uranium isotopes is sought to either be separated or enriched with the isotope uranium-235, which is capable of fissioning thermal neutrons.

Many methods have been developed for separating uranium-235 and uranium-238. The gas diffusion method is most often used. Its essence is that if a mixture of two gases is passed through a porous partition, then the light will pass faster. Back in 1913, F. Aston partially separated neon isotopes in this way.

Most uranium compounds under normal conditions are solids and can be converted into a gaseous state only at very high temperatures, when there can be no talk of any subtle processes of isotope separation. However, the colorless compound of uranium with fluorine, UF 6 hexafluoride, sublimes already at 56.5 ° C (at atmospheric pressure). UF 6 is the most volatile uranium compound and is best suited for separating its isotopes by gaseous diffusion.

Uranium hexafluoride is characterized by high chemical activity. Corrosion of pipes, pumps, containers, interaction with the lubrication of mechanisms - a small but impressive list of troubles that the creators of diffusion plants had to overcome. We encountered even more serious difficulties.

Uranium hexafluoride, obtained by fluoridation of a natural mixture of uranium isotopes, from a “diffusion” point of view, can be considered as a mixture of two gases with very similar molecular masses - 349 (235+19*6) and 352 (238+19*6). The maximum theoretical separation coefficient in one diffusion stage for gases that differ so slightly in molecular weight is only 1.0043. In real conditions this value is even less. It turns out that it is possible to increase the concentration of uranium-235 from 0.72 to 99% only with the help of several thousand diffusion steps. Therefore, uranium isotope separation plants occupy an area of ​​several tens of hectares. The area of ​​porous partitions in the separation cascades of factories is approximately the same order of magnitude.

Briefly about other isotopes of uranium

Natural uranium, in addition to uranium-235 and uranium-238, includes uranium-234. The abundance of this rare isotope is expressed as a number with four zeros after the decimal point. A much more accessible artificial isotope is uranium-233. It is obtained by irradiating thorium in the neutron flux of a nuclear reactor:

232 90 Th + 10n → 233 90 Th -β-→ 233 91 Pa -β-→ 233 92 U
According to all the rules of nuclear physics, uranium-233, as an odd isotope, is divided by thermal neutrons. And most importantly, in reactors with uranium-233, expanded reproduction of nuclear fuel can (and does) occur. In a conventional thermal neutron reactor! Calculations show that when a kilogram of uranium-233 burns up in a thorium reactor, 1.1 kg of new uranium-233 should accumulate in it. A miracle, and that’s all! We burned a kilogram of fuel, but the amount of fuel did not decrease.

However, such miracles are only possible with nuclear fuel.

The uranium-thorium cycle in thermal neutron reactors is the main competitor of the uranium-plutonium cycle for the reproduction of nuclear fuel in fast neutron reactors... Actually, only because of this, element No. 90 - thorium - was classified as a strategic material.

Other artificial isotopes of uranium do not play a significant role. It is only worth mentioning uranium-239 - the first isotope in the chain of transformations of uranium-238 plutonium-239. Its half-life is only 23 minutes.

Isotopes of uranium with a mass number greater than 240 do not have time to form in modern reactors. The lifetime of uranium-240 is too short, and it decays before it has time to capture a neutron.

In the super-powerful neutron fluxes of a thermonuclear explosion, a uranium nucleus manages to capture up to 19 neutrons in a millionth of a second. In this case, uranium isotopes with mass numbers from 239 to 257 are born. Their existence was learned from the appearance of distant transuranium elements - descendants of heavy isotopes of uranium - in the products of a thermonuclear explosion. The “founders of the genus” themselves are too unstable to beta decay and pass into higher elements long before the products of nuclear reactions are extracted from the rock mixed by the explosion.

Modern thermal reactors burn uranium-235. In already existing fast neutron reactors, the energy of the nuclei of a common isotope, uranium-238, is released, and if energy is true wealth, then uranium nuclei will benefit humanity in the near future: the energy of element N° 92 will become the basis of our existence.

It is vitally important to ensure that uranium and its derivatives burn only in nuclear reactors of peaceful power plants, burn slowly, without smoke and flame.

ANOTHER SOURCE OF URANIUM. Nowadays, it has become sea water. Pilot-industrial installations are already in operation for extracting uranium from water using special sorbents: titanium oxide or acrylic fiber treated with certain reagents.

WHO HOW MUCH. In the early 80s, uranium production in capitalist countries was about 50,000 g per year (in terms of U3Os). About a third of this amount was provided by US industry. Canada is in second place, followed by South Africa. Nigor, Gabon, Namibia. Of the European countries, France produces the most uranium and its compounds, but its share was almost seven times less than the United States.

NON-TRADITIONAL CONNECTIONS. Although it is not without foundation that the chemistry of uranium and plutonium is better studied than the chemistry of traditional elements such as iron, chemists are still discovering new uranium compounds. So, in 1977, the journal “Radiochemistry”, vol. XIX, no. 6 reported two new uranyl compounds. Their composition is MU02(S04)2-SH20, where M is a divalent manganese or cobalt ion. X-ray diffraction patterns indicated that the new compounds were double salts, and not a mixture of two similar salts.

Nuclear technologies are largely based on the use of radiochemistry methods, which in turn are based on the nuclear physical, physical, chemical and toxic properties of radioactive elements.

In this chapter we will limit ourselves to a brief description of the properties of the main fissile isotopes - uranium and plutonium.

Uranus

Uranus ( uranium) U - element of the actinide group, 7-0th period of the periodic system, Z=92, atomic mass 238.029; the heaviest found in nature.

There are 25 known isotopes of uranium, all of them radioactive. The easiest 217U (Tj/ 2 =26 ms), the heaviest 2 4 2 U (7 T J / 2 =i6.8 min). There are 6 nuclear isomers. Natural uranium contains three radioactive isotopes: 2 8 and (99, 2 739%, Ti/ 2 = 4.47109 l), 2 35 U (0.7205%, G, / 2 = 7.04-109 years) and 2 34 U ( 0.0056%, Ti/ 2=2.48-yuz l). The specific radioactivity of natural uranium is 2.48104 Bq, divided almost in half between 2 34 U and 288 U; 2 35U makes a small contribution (the specific activity of the 2 zi isotope in natural uranium is 21 times less than the activity of 2 3 8 U). Thermal neutron capture cross-sections are 46, 98 and 2.7 barn for 2 zzi, 2 35U and 2 3 8 U, respectively; division section 527 and 584 barn for 2 zzi and 2 z 8 and, respectively; natural mixture of isotopes (0.7% 235U) 4.2 barn.

Table 1. Nuclear physical properties 2 h9 Ri and 2 35Ts.

Table 2. Neutron capture 2 35Ts and 2 z 8 C.

Six isotopes of uranium are capable of spontaneous fission: 282 U, 2 zzi, 234 U, 235 U, 2 z 6 i and 2 z 8 i. The natural isotopes 2 33 and 2 35 U fission under the influence of both thermal and fast neutrons, and 2 3 8 nuclei are capable of fission only when they capture neutrons with an energy of more than 1.1 MeV. When capturing neutrons with lower energy, the 288 U nuclei first transform into 2 -i9U nuclei, which then undergo p-decay and transform first into 2 -"*9Np, and then into 2 39Pu. The effective cross sections for the capture of thermal neutrons of 2 34U, 2 nuclei 35U and 2 3 8 and are equal to 98, 683 and 2.7 barn, respectively. Complete fission of 2 35 U leads to a “thermal energy equivalent” of 2-107 kWh / kg. The isotopes 2 35 U and 2 zzi are used as nuclear fuel, capable of supporting fission chain reaction.

Nuclear reactors produce n artificial isotopes of uranium with mass numbers 227-^240, of which the longest-lived is 233U (7 V 2 =i.62 *io 5 years); it is obtained by neutron irradiation of thorium. In the super-powerful neutron fluxes of a thermonuclear explosion, uranium isotopes with mass numbers of 239^257 are born.

Uran-232- technogenic nuclide, a-emitter, T x / 2=68.9 years, parent isotopes 2 h 6 Pu(a), 23 2 Np(p*) and 23 2 Ra(p), daughter nuclide 228 Th. The intensity of spontaneous fission is 0.47 divisions/s kg.

Uranium-232 is formed as a result of the following decays:

P + -decay of nuclide *3 a Np (Ti/ 2 =14.7 min):

In the nuclear industry, 2 3 2 U is produced as a by-product during the synthesis of the fissile (weapon-grade) nuclide 2 zzi in the thorium fuel cycle. When 2 3 2 Th is irradiated with neutrons, the main reaction occurs:

and a two-step side reaction:

The production of 232 U from thorium occurs only with fast neutrons (E„>6 MeV). If the starting substance contains 2 3°TH, then the formation of 2 3 2 U is complemented by the reaction: 2 3°TH + u-> 2 3'TH. This reaction occurs using thermal neutrons. Generation of 2 3 2 U is undesirable for a number of reasons. It is suppressed by using thorium with a minimum concentration of 2 3°TH.

The decay of 2 × 2 occurs in the following directions:

A decay in 228 Th (probability 10%, decay energy 5.414 MeV):

the energy of emitted alpha particles is 5.263 MeV (in 31.6% of cases) and 5.320 MeV (in 68.2% of cases).

• - spontaneous fission (probability less than ~ 12%);
• - cluster decay with the formation of nuclide 28 Mg (probability of decay less than 5*10" 12%):

Cluster decay with the formation of nuclide 2

Uranium-232 is the founder of a long decay chain, which includes nuclides - emitters of hard y-quanta:

^U-(3.64 days, a,y)-> 220 Rn-> (55.6 s, a)-> 21b Po->(0.155 s, a)-> 212 Pb->(10.64 hours , p, y) -> 212 Bi -> (60.6 m, p, y) -> 212 Po a, y) -> 208x1, 212 Po -> (3 "Yu' 7 s, a) -> 2o8 Pb (stab), 2o8 T1->(3.06 m, p, y-> 2o8 Pb.

The accumulation of 2 3 2 U is inevitable during the production of 2 zi in the thorium energy cycle. Intense y-radiation arising from the decay of 2 3 2 U hinders the development of thorium energy. What is unusual is that the even isotope 2 3 2 11 has a high fission cross section under the influence of neutrons (75 barns for thermal neutrons), as well as a high neutron capture cross section - 73 barns. 2 3 2 U is used in the radioactive tracer method in chemical research.

2 h 2 and is the founder of a long decay chain (according to the 2 h 2 T scheme), which includes nuclides emitters of hard y-quanta. The accumulation of 2 3 2 U is inevitable during the production of 2 zi in the thorium energy cycle. Intense y-radiation arising from the decay of 232 U hinders the development of thorium energy. What is unusual is that the even isotope 2 3 2 U has a high fission cross section under the influence of neutrons (75 barns for thermal neutrons), as well as a high neutron capture cross section - 73 barns. 2 3 2 U is often used in the radioactive tracer method in chemical and physical research.

Uran-233- man-made radionuclide, a-emitter (energy 4.824 (82.7%) and 4.783 MeV (14.9%)), Tvi= 1.585105 years, parent nuclides 2 37Pu(a)-? 2 33Np(p +)-> 2 ззРа(р), daughter nuclide 22 9Th. 2 zzi is obtained in nuclear reactors from thorium: 2 z 2 Th captures a neutron and turns into 2 zzT, which decays into 2 zzRa, and then into 2 zzi. The nuclei of 2 zi (odd isotope) are capable of both spontaneous fission and fission under the influence of neutrons of any energy, which makes it suitable for the production of both atomic weapons and reactor fuel. Effective fission cross section is 533 barn, capture cross section is 52 barn, neutron yield: per fission event - 2.54, per absorbed neutron - 2.31. The critical mass of 2 zzi is three times less than the critical mass of 2 35U (-16 kg). The intensity of spontaneous fission is 720 divisions/s kg.

Uranium-233 is formed as a result of the following decays:

- (3 + -decay of nuclide 2 33Np (7^=36.2 min):

On an industrial scale, 2 zi is obtained from 2 32Th by irradiation with neutrons:

When a neutron is absorbed, the 2 zzi nucleus usually splits, but occasionally captures a neutron, turning into 2 34U. Although 2 zzi usually divides after absorbing a neutron, it sometimes retains a neutron, turning into 2 34U. The production of 2 zirs is carried out in both fast and thermal reactors.

From a weapons point of view, 2 ZZI is comparable to 2 39Pu: its radioactivity is 1/7 of the activity of 2 39Pu (Ti/ 2 = 159200 liters versus 24100 liters for Pu), the critical mass of 2 zi is 60% higher than that of ^Pu (16 kg versus 10 kg), and the rate of spontaneous fission is 20 times higher (bth - ' versus 310 10). The neutron flux from 2 zzi is three times higher than that of 2 39Pi. Creating a nuclear charge based on 2 zi requires more effort than on ^Pi. The main obstacle is the presence of 232 U impurity in 2ZZI, the y-radiation of decay projects of which makes it difficult to work with 2ZZI and makes it easy to detect finished weapons. In addition, the short half-life of 2 3 2 U makes it an active source of alpha particles. 2 zi with 1% 232 and has three times stronger a-activity than weapons-grade plutonium and, accordingly, greater radiotoxicity. This a-activity causes the creation of neutrons in the light elements of the weapon charge. To minimize this problem, the presence of elements such as Be, B, F, Li should be minimal. The presence of a neutron background does not affect the operation of implosion systems, but cannon circuits require a high level of purity for light elements. The content of 23 2 U in weapons-grade 2 zis should not exceed 5 parts per million (0.0005%). In the fuel of thermal power reactors, the presence of 2 3G is not harmful, and even desirable, because it reduces the possibility of using uranium for weapons purposes.After spent fuel reprocessing and fuel reuse, the 232U content reaches about 1+0.2%.

The decay of 2 zi occurs in the following directions:

A decay in 22 9Th (probability 10%, decay energy 4.909 MeV):

the energy of emitted yahr particles is 4.729 MeV (in 1.61% of cases), 4.784 MeV (in 13.2% of cases) and 4.824 MeV (in 84.4% of cases).

• - spontaneous division (probability
• - cluster decay with the formation of nuclide 28 Mg (decay probability less than 1.3*10_13%):

Cluster decay with the formation of the nuclide 24 Ne (decay probability 7.3-10-“%):

The decay chain of 2 zzi belongs to the neptunium series.

The specific radioactivity of 2 zi is 3.57-8 Bq/g, which corresponds to a-activity (and radiotoxicity) of -15% of plutonium. Just 1% 2 3 2 U increases radioactivity to 212 mCi/g.

Uran-234(Uranus II, UII) part of natural uranium (0.0055%), 2.445105 years, a-emitter (energy of a-particles 4.777 (72%) and

4.723 (28%) MeV), parent radionuclides: 2 h 8 Pu(a), 234 Pa(P), 234 Np(p +),

daughter isotope in 2 z”th.

Typically, 234 U is in equilibrium with 2 h 8 u, decaying and forming at the same rate. Approximately half of the radioactivity of natural uranium is contributed by 234U. Typically, 234U is obtained by ion-exchange chromatography of old preparations of pure 2 × 8 Pu. During a-decay, *zRi yields 2 34U, so old preparations of 2 h 8 Ru are good sources of 2 34U. yuo g 238Pi contain after a year 776 mg 2 34U, after 3 years

2.2 g 2 34U. The concentration of 2 34U in highly enriched uranium is quite high due to preferential enrichment with light isotopes. Since 2 34u is a strong y-emitter, there are restrictions on its concentration in uranium intended for processing into fuel. Increased levels of 234i are acceptable for reactors, but reprocessed spent fuel already contains unacceptable levels of this isotope.

The decay of 234i occurs in the following directions:

A-decay at 2 3°Т (probability 100%, decay energy 4.857 MeV):

the energy of emitted alpha particles is 4.722 MeV (in 28.4% of cases) and 4.775 MeV (in 71.4% of cases).

• - spontaneous division (probability 1.73-10-9%).
• - cluster decay with the formation of nuclide 28 Mg (probability of decay 1.4-10%, according to other data 3.9-10%):

• - cluster decay with the formation of nuclides 2 4Ne and 26 Ne (decay probability 9-10", 2%, according to other data 2,3-10_11%):

The only known isomer is 2 34ti (Tx/ 2 = 33.5 μs).

The absorption cross section of 2 34U thermal neutrons is 100 barn, and for the resonance integral averaged over various intermediate neutrons it is 700 barn. Therefore, in thermal neutron reactors it is converted to fissile 235U at a faster rate than the much larger amount of 238U (with a cross-section of 2.7 barn) is converted to 2 39Ru. As a result, spent fuel contains less 2 34U than fresh fuel.

Uran-235 belongs to the 4P+3 family, capable of producing a fission chain reaction. This is the first isotope in which the reaction of forced nuclear fission under the influence of neutrons was discovered. By absorbing a neutron, 235U becomes 2 zbi, which is divided into two parts, releasing energy and emitting several neutrons. Fissile by neutrons of any energy and capable of spontaneous fission, the isotope 2 35U is part of natural ufan (0.72%), an a-emitter (energies 4.397 (57%) and 4.367 (18%) MeV), Ti/j=7.038-8 years, mother nuclides 2 35Pa, 2 35Np and 2 39Pu, daughter - 23Th. Spontaneous fission rate 2 3su 0.16 fission/s kg. When one 2 35U nucleus fissions, 200 MeV of energy = 3.210 p J is released, i.e. 18 TJ/mol=77 TJ/kg. The cross section of fission by thermal neutrons is 545 barns, and by fast neutrons - 1.22 barns, neutron yield: per fission act - 2.5, per absorbed neutron - 2.08.

Comment. The cross section for slow neutron capture to produce the isotope 2 sii (oo barn), so that the total slow neutron absorption cross section is 645 barn.

• - spontaneous fission (probability 7*10~9%);
• - cluster decay with the formation of nuclides 2 °Ne, 2 5Ne and 28 Mg (the probabilities, respectively, are 8-io_10%, 8-kg 10%, 8*10",0%):

Rice. 1.

The only known isomer is 2 35n»u (7/ 2 = 2b min).

Specific activity 2 35C 7.77-4 Bq/g. The critical mass of weapons-grade uranium (93.5% 2 35U) for a ball with a reflector is 15-7-23 kg.

Fission 2 » 5U is used in atomic weapons, for energy production and for the synthesis of important actinides. The chain reaction is maintained by the excess of neutrons produced during the fission of 2 35C.

Uran-236 found naturally on Earth in trace quantities (there is more of it on the Moon), a-emitter (?

Rice. 2. Radioactive family 4/7+2 (including -з 8 и).

In an atomic reactor, 2 sz absorbs a thermal neutron, after which it fissions with a probability of 82%, and with a probability of 18% it emits a y-quantum and turns into 2 sb and (for 100 fissioned nuclei 2 35U there are 22 formed nuclei 2 3 6 U) . In small quantities it is part of fresh fuel; accumulates when uranium is irradiated with neutrons in a reactor, and is therefore used as a “signaling device” for spent nuclear fuel. 2 hb and is formed as a by-product during the separation of isotopes by gas diffusion during the regeneration of used nuclear fuel. 236 U is a neutron poison formed in a power reactor; its presence in nuclear fuel is compensated for by a high level of enrichment 2 35 U.

2 z b and is used as a tracer of mixing ocean waters.

Uranium-237,T&= 6.75 days, beta and gamma emitter, can be obtained from nuclear reactions:

Detection 287 and carried out along lines with Ey= o,ob MeV (36%), 0.114 MeV (0.06%), 0.165 MeV (2.0%), 0.208 MeV (23%)

237U is used in the radiotracer method in chemical research. Measuring the concentration (2-4°Am) in fallout from atomic weapons tests provides valuable information about the type of charge and the equipment used.

Uran-238- belongs to the 4P+2 family, is fissile by high-energy neutrons (more than 1.1 MeV), capable of spontaneous fission, forms the basis of natural uranium (99.27%), a-emitter, 7’; /2=4>468-109 years, directly decays into 2 34Th, forms a number of genetically related radionuclides, and after 18 products turns into 206 Рb. Pure 2 3 8 U has a specific radioactivity of 1.22-104 Bq. The half-life is very long - about 10 16 years, so the probability of fission in relation to the main process - the emission of an alpha particle - is only 10" 7. One kilogram of uranium gives only 10 spontaneous fissions per second, and during the same time alpha particles emit 20 million nuclei. Mother nuclides: 2 4 2 Pu(a), *38ra(p-) 234Th, daughter T,/ 2 = 2 :i 4 Th.

Uranium-238 is formed as a result of the following decays:

2 (V0 4) 2 ] 8H 2 0. Among the secondary minerals, hydrated calcium uranyl phosphate Ca(U0 2) 2 (P0 4) 2 -8H 2 0 is common. Often uranium in minerals is accompanied by other useful elements - titanium, tantalum, rare earths. Therefore, it is natural to strive for complex processing of uranium-containing ores.

Basic physical properties of uranium: atomic mass 238.0289 amu. (g/mol); atomic radius 138 pm (1 pm = 12 m); ionization energy (first electron 7.11 eV; electronic configuration -5f36d‘7s 2; oxidation states 6, 5, 4, 3; GP l = 113 2, 2 °; T t,1=3818°; density 19.05; specific heat capacity 0.115 JDKmol); tensile strength 450 MPa, heat of fusion 12.6 kJ/mol, heat of evaporation 417 kJ/mol, specific heat 0.115 J/(mol-K); molar volume 12.5 cm3/mol; characteristic Debye temperature © D =200K, temperature of transition to the superconducting state about.68K.

Uranium is a heavy, silvery-white, shiny metal. It is slightly softer than steel, malleable, flexible, has slight paramagnetic properties, and is pyrophoric in powder form. Uranium has three allotropic forms: alpha (orthorhombic, a-U, lattice parameters 0=285, b= 587, c=49b pm, stable up to 667.7°), beta (tetragonal, p-U, stable from 667.7 to 774.8°), gamma (with a cubic body-centered lattice, y-U, existing from 774.8° to melting points, frm=ii34 0), at which uranium is most malleable and convenient for processing.

At room temperature, the orthorhombic a-phase is stable; the prismatic structure consists of wavy atomic layers parallel to the plane ABC, in an extremely asymmetrical prismatic lattice. Within layers, atoms are tightly connected, while the strength of bonds between atoms in adjacent layers is much weaker (Figure 4). This anisotropic structure makes it difficult to alloy uranium with other metals. Only molybdenum and niobium create solid-phase alloys with uranium. However, uranium metal can interact with many alloys, forming intermetallic compounds.

In the range 668^775° there is (3-uranium. The tetragonal type lattice has a layered structure with layers parallel to the plane ab in positions 1/4С, 1/2 With and 3/4C of the unit cell. At temperatures above 775°, y-uranium with a body-centered cubic lattice is formed. The addition of molybdenum allows the y-phase to be present at room temperature. Molybdenum forms a wide range of solid solutions with y-uranium and stabilizes the y-phase at room temperature. y-Uranium is much softer and more malleable than the brittle a- and (3-phases.

Neutron irradiation has a significant impact on the physical and mechanical properties of uranium, causing an increase in the size of the sample, a change in shape, as well as a sharp deterioration in the mechanical properties (creep, embrittlement) of uranium blocks during the operation of a nuclear reactor. The increase in volume is due to the accumulation in uranium during fission of impurities of elements with a lower density (translation 1% uranium into fragmentation elements increases the volume by 3.4%).

Rice. 4. Some crystal structures of uranium: a - a-uranium, b - p-uranium.

The most common methods for obtaining uranium in the metallic state are the reduction of their fluorides with alkali or alkaline earth metals or the electrolysis of molten salts. Uranium can also be obtained by metallothermic reduction from carbides with tungsten or tantalum.

The ability to easily give up electrons determines the reducing properties of uranium and its greater chemical activity. Uranium can interact with almost all elements except noble gases, acquiring oxidation states +2, +3, +4, +5, +6. In solution the main valence is 6+.

Rapidly oxidizing in air, metallic uranium is covered with an iridescent film of oxide. Fine uranium powder spontaneously ignites in air (at temperatures of 1504-175°), forming and;) Ov. At 1000°, uranium combines with nitrogen, forming yellow uranium nitride. Water can react with metal, slowly at low temperatures and quickly at high temperatures. Uranium reacts violently with boiling water and steam to release hydrogen, which forms a hydride with uranium

This reaction is more energetic than the combustion of uranium in oxygen. This chemical activity of uranium makes it necessary to protect uranium in nuclear reactors from contact with water.

Uranium dissolves in hydrochloric, nitric and other acids, forming U(IV) salts, but does not interact with alkalis. Uranium displaces hydrogen from inorganic acids and salt solutions of metals such as mercury, silver, copper, tin, platinum and gold. When shaken vigorously, the metal particles of uranium begin to glow.

The structural features of the electron shells of the uranium atom (the presence of ^/-electrons) and some of its physicochemical properties serve as the basis for classifying uranium as a member of the actinide series. However, there is a chemical analogy between uranium and Cr, Mo and W. Uranium is highly reactive and reacts with all elements except noble gases. In the solid phase, examples of U(VI) are uranyl trioxide U0 3 and uranyl chloride U0 2 C1 2. Uranium tetrachloride UC1 4 and uranium dioxide U0 2

Examples of U(IV). Substances containing U(IV) are usually unstable and become hexavalent when exposed to air for a long time.

Six oxides are installed in the uranium-oxygen system: UO, U0 2, U 4 0 9, and 3 Ov, U0 3. They are characterized by a wide range of homogeneity. U0 2 is a basic oxide, while U0 3 is amphoteric. U0 3 - interacts with water to form a number of hydrates, the most important of which are diuranic acid H 2 U 2 0 7 and uranic acid H 2 1U 4. With alkalis, U0 3 forms salts of these acids - uranates. When U0 3 is dissolved in acids, salts of the doubly charged uranyl cation U0 2 a+ are formed.

Uranium dioxide, U0 2, of stoichiometric composition is brown. As the oxygen content in the oxide increases, the color changes from dark brown to black. Crystal structure of the CaF 2 type, A = 0.547 nm; density 10.96 g/cm"* (the highest density among uranium oxides). T , pl =2875 0 , Tk „ = 3450°, D#°298 = -1084.5 kJ/mol. Uranium dioxide is a semiconductor with hole conductivity and a strong paramagnetic. MPC = o.015 mg/m3. Insoluble in water. At a temperature of -200° it adds oxygen, reaching the composition U0 2>25.

Uranium (IV) oxide can be prepared by the following reactions:

Uranium dioxide exhibits only basic properties; it corresponds to the basic hydroxide U(OH) 4, which is then converted into hydrated hydroxide U0 2 H 2 0. Uranium dioxide slowly dissolves in strong non-oxidizing acids in the absence of atmospheric oxygen with the formation of III + ions:

U0 2 + 2H 2 S0 4 ->U(S0 4) 2 + 2H 2 0. (38)

It is soluble in concentrated acids, and the rate of dissolution can be significantly increased by adding fluorine ion.

When dissolved in nitric acid, the formation of uranyl ion 1O 2 2+ occurs:

Triuran octaoxide U 3 0s (uranium oxide) is a powder whose color varies from black to dark green; when strongly crushed, it turns olive-green in color. Large black crystals leave green streaks on the porcelain. Three crystal modifications of U 3 0 are known h: a-U 3 C>8 - rhombic crystal structure (space group C222; 0 = 0.671 nm; 6 = 1.197 nm; c = o.83 nm; d =0.839 nm); p-U 3 0e - rhombic crystal structure (space group Stst; 0=0.705 nm; 6=1.172 nm; 0=0.829 nm. The beginning of decomposition is oooo° (transitions to 100 2), MPC = 0.075 mg/m3.

U 3 C>8 can be obtained by the reaction:

By calcination U0 2, U0 2 (N0 3) 2, U0 2 C 2 0 4 3H 2 0, U0 4 -2H 2 0 or (NH 4) 2 U 2 0 7 at 750 0 in air or in an oxygen atmosphere (p = 150+750 mmHg) obtain stoichiometrically pure U 3 08.

When U 3 0s is calcined at T>oooo°, it is reduced to 10 2 , but upon cooling in air it returns to U 3 0s. U 3 0e dissolves only in concentrated strong acids. In hydrochloric and sulfuric acids a mixture of U(IV) and U(VI) is formed, and in nitric acid - uranyl nitrate. Dilute sulfuric and hydrochloric acids react very weakly with U 3 Os even when heated; the addition of oxidizing agents (nitric acid, pyrolusite) sharply increases the dissolution rate. Concentrated H 2 S0 4 dissolves U 3 Os to form U(S0 4) 2 and U0 2 S0 4 . Nitric acid dissolves U 3 Oe to form uranyl nitrate.

Uranium trioxide, U0 3 - a crystalline or amorphous substance of bright yellow color. Reacts with water. MPC = 0.075 mg/m3.

It is obtained by calcining ammonium polyuranates, uranium peroxide, uranyl oxalate at 300-500° and uranyl nitrate hexahydrate. This produces an orange powder of an amorphous structure with a density

6.8 g/cmz. The crystalline form of IU 3 can be obtained by oxidation of U 3 0 8 at temperatures of 450°h-750° in a flow of oxygen. There are six crystalline modifications of U0 3 (a, (3, y> §> ?, n) - U0 3 is hygroscopic and in moist air turns into uranyl hydroxide. Its heating at 520°-^6oo° gives a compound of composition 1U 2>9, further heating to 6oo° allows one to obtain U 3 Os.

Hydrogen, ammonia, carbon, alkali and alkaline earth metals reduce U0 3 to U0 2. When passing a mixture of gases HF and NH 3, UF 4 is formed. At higher valence, uranium exhibits amphoteric properties. When exposed to acids U0 3 or its hydrates, uranyl salts (U0 2 2+) are formed, colored yellow-green:

Most uranyl salts are highly soluble in water.

When fused with alkalis, U0 3 forms uranic acid salts - MDKH uranates:

With alkaline solutions, uranium trioxide forms salts of polyuranic acids - polyuranates DHM 2 0y1U 3 pH^O.

Uranic acid salts are practically insoluble in water.

The acidic properties of U(VI) are less pronounced than the basic ones.

Uranium reacts with fluorine at room temperature. The stability of higher halides decreases from fluorides to iodides. Fluorides UF 3, U4F17, U2F9 and UF 4 are non-volatile, and UFe is volatile. The most important fluorides are UF 4 and UFe.

Ftppippiyanir okgilya t"yanya ppptrkart according to the practice:

The reaction in a fluidized bed is carried out according to the equation:

It is possible to use fluorinating agents: BrF 3, CC1 3 F (Freon-11) or CC1 2 F 2 (Freon-12):

Uranium fluoride (1U) UF 4 (“green salt”) is a bluish-greenish to emerald-colored powder. G 11L = yuz6°; Гк,«,.=-1730°. DN° 29 8= 1856 kJ/mol. The crystal structure is monoclinic (sp. gp. C2/s; 0=1.273 nm; 5=1.075 nm; 0=0.843 nm; d= 6.7 nm; p=12b°20"; density 6.72 g/cm3. UF 4 is a stable, inactive, non-volatile compound, poorly soluble in water. The best solvent for UF 4 is fuming perchloric acid HC10 4. Dissolves in oxidizing acids to form a uranyl salt ; quickly dissolves in a hot solution of Al(N0 3) 3 or AlCl 3, as well as in a solution of boric acid acidified with H 2 S0 4, HC10 4 or HC1. Complexing agents that bind fluoride ions, for example, Fe3 +, Al3 + or boric acid, also contribute to the dissolution of UF 4. With fluorides of other metals it forms a number of poorly soluble double salts (MeUFe, Me 2 UF6, Me 3 UF 7, etc.).NH 4 UF 5 is of industrial importance.

U(IV) fluoride is an intermediate product in the preparation

both UF6 and uranium metal.

UF 4 can be obtained by reactions:

or by electrolytic reduction of uranyl fluoride.

Uranium hexafluoride UFe - at room temperature, ivory-colored crystals with a high refractive index. Density

5.09 g/cmz, density of liquid UFe - 3.63 g/cmz. Volatile compound. Tvoag = 5^>5°> Gil=b4.5° (under pressure). The saturated vapor pressure reaches the atmosphere at 560°. Enthalpy of formation AH° 29 8 = -211b kJ/mol. The crystal structure is orthorhombic (space group. Rpt; 0=0.999 nm; fe= 0.8962 nm; c=o.5207 nm; d 5.060 nm (25 0). MPC - 0.015 mg/m3. From the solid state, UF6 can sublimate (sublimate) into a gas, bypassing the liquid phase over a wide range of pressures. Heat of sublimation at 50 0 50 kJ/mg. The molecule has no dipole moment, so UF6 does not associate. UFr vapor is an ideal gas.

It is obtained by the action of fluorine on its U compound:

In addition to gas-phase reactions, there are also liquid-phase reactions

producing UF6 using halofluorides, for example

There is a way to obtain UF6 without the use of fluorine - by oxidation of UF 4:

UFe does not react with dry air, oxygen, nitrogen and C0 2, but upon contact with water, even traces of it, it undergoes hydrolysis:

It interacts with most metals, forming their fluorides, which complicates the methods of its storage. Suitable vessel materials for working with UF6 are: when heated, Ni, Monel and Pt, in the cold - also Teflon, absolutely dry quartz and glass, copper and aluminum. At temperatures of 25-0°C it forms complex compounds with fluorides of alkali metals and silver of the type 3NaFUFr>, 3KF2UF6.

It dissolves well in various organic liquids, inorganic acids and all halofluorides. Inert to dry 0 2, N 2, C0 2, C1 2, Br 2. UFr is characterized by reduction reactions with most pure metals. UF6 reacts vigorously with hydrocarbons and other organic substances, so closed containers with UFe can explode. UF6 in the range of 25 -r100° forms complex salts with fluorides of alkali and other metals. This property is used in technology for selective extraction of UF

Uranium hydrides UH 2 and UH 3 occupy an intermediate position between salt-like hydrides and hydrides of the type of solid solutions of hydrogen in the metal.

When uranium reacts with nitrogen, nitrides are formed. There are four known phases in the U-N system: UN (uranium nitride), a-U 2 N 3 (sesquinitride), p- U 2 N 3 and UN If90. It is not possible to achieve the composition UN 2 (dinitride). Syntheses of uranium mononitride UN are reliable and well controlled, which are best carried out directly from the elements. Uranium nitrides are powdery substances, the color of which varies from dark gray to gray; look like metal. UN has a cubic face-centered crystal structure, like NaCl (0 = 4.8892 A); (/=14.324, 7^=2855°, stable in vacuum up to 1700 0. It is prepared by reacting U or U hydride with N 2 or NH 3 , decomposition of higher U nitrides at 1300° or their reduction with uranium metal. U 2 N 3 is known in two polymorphic modifications: cubic a and hexagonal p (0 = 0.3688 nm, 6 = 0.5839 nm), releases N 2 in a vacuum above 8oo°. It is obtained by reducing UN 2 with hydrogen. UN2 dinitride is synthesized by reacting U with N2 under high N2 pressure. Uranium nitrides are easily soluble in acids and alkali solutions, but are decomposed by molten alkalis.

Uranium nitride is obtained by two-stage carbothermic reduction of uranium oxide:

Heating in argon at 7M450 0 for 10*20 hours

Uranium nitride of a composition close to dinitride, UN 2, can be obtained by exposing UF 4 to ammonia at high temperature and pressure.

Uranium dinitride decomposes when heated:

Uranium nitride, enriched at 2 35 U, has a higher fission density, thermal conductivity and melting point than uranium oxides - the traditional fuel of modern power reactors. It also has good mechanical properties and stability superior to traditional fuels. Therefore, this compound is considered as a promising basis for nuclear fuel in fast neutron reactors (generation IV nuclear reactors).

Comment. It is very useful to enrich UN by ‘5N, because .4 N tends to capture neutrons, generating the radioactive isotope 14 C through the (n,p) reaction.

Uranium carbide UC 2 (?-phase) is a light gray crystalline substance with a metallic luster. In the U-C system (uranium carbides), there are UC 2 (?-phase), UC 2 (b 2-phase), U 2 C 3 (e-phase), UC (b 2-phase) - uranium carbides. Uranium dicarbide UC 2 can be obtained by the reactions:

U + 2C^UC 2 (54v)

Uranium carbides are used as fuel for nuclear reactors; they are promising as fuel for space rocket engines.

Uranyl nitrate, uranyl nitrate, U0 2 (N0 3) 2 -6H 2 0. The role of the metal in this salt is played by the uranyl 2+ cation. Yellow crystals with a greenish tint, easily soluble in water. An aqueous solution is acidic. Soluble in ethanol, acetone and ether, insoluble in benzene, toluene and chloroform. When heated, the crystals melt and release HN0 3 and H 2 0. Crystalline hydrate is easily evaporated in air. A characteristic reaction is that under the action of NH 3 a yellow precipitate of ammonium uranium is formed.

Uranium is capable of forming metal-organic compounds. Examples are cyclopentadienyl derivatives of the composition U(C 5 H 5) 4 and their halogen-substituted u(C 5 H 5) 3 G or u(C 5 H 5) 2 G 2.

In aqueous solutions, uranium is most stable in the oxidation state of U(VI) in the form of the uranyl ion U0 2 2+. To a lesser extent, it is characterized by the U(IV) state, but it can even occur in the U(III) form. The oxidation state of U(V) can exist as the IO2+ ion, but this state is rarely observed due to its tendency to disproportionation and hydrolysis.

In neutral and acidic solutions, U(VI) exists in the form of U0 2 2+ - a yellow uranyl ion. Well-soluble uranyl salts include nitrate U0 2 (N0 3) 2, sulfate U0 2 S0 4, chloride U0 2 C1 2, fluoride U0 2 F 2, acetate U0 2 (CH 3 C00) 2. These salts are released from solutions in the form of crystalline hydrates with different numbers of water molecules. Slightly soluble uranyl salts are: oxalate U0 2 C 2 0 4, phosphates U0 2 HP0., and UO2P2O4, ammonium uranyl phosphate UO2NH4PO4, sodium uranyl vanadate NaU0 2 V0 4, ferrocyanide (U0 2) 2. The uranyl ion is characterized by a tendency to form complex compounds. Thus, complexes with fluorine ions of the -, 4- type are known; nitrate complexes ‘ and 2 *; sulfuric acid complexes 2 " and 4-; carbonate complexes 4 " and 2 ", etc. When alkalis act on solutions of uranyl salts, sparingly soluble precipitates of diuranates of the type Me 2 U 2 0 7 are released (monouranates Me 2 U0 4 are not isolated from solutions, they are obtained by fusion uranium oxides with alkalis).Me 2 U n 0 3 n+i polyuranates are known (for example, Na 2 U60i 9).

U(VI) is reduced in acidic solutions to U(IV) by iron, zinc, aluminum, sodium hydrosulfite, and sodium amalgam. The solutions are colored green. Alkalis precipitate from them hydroxide U0 2 (0H) 2, hydrofluoric acid - fluoride UF 4 -2.5H 2 0, oxalic acid - oxalate U(C 2 0 4) 2 -6H 2 0. The U 4+ ion has a tendency to form complexes less than that of uranyl ions.

Uranium (IV) in solution is in the form of U 4+ ions, which are highly hydrolyzed and hydrated:

In acidic solutions, hydrolysis is suppressed.

Uranium (VI) in solution forms the uranyl oxocation - U0 2 2+ Numerous uranyl compounds are known, examples of which are: U0 3, U0 2 (C 2 H 3 0 2) 2, U0 2 C0 3 -2(NH 4) 2 C0 3 U0 2 C0 3, U0 2 C1 2, U0 2 (0H) 2, U0 2 (N0 3) 2, UO0SO4, ZnU0 2 (CH 3 C00) 4, etc.

Upon hydrolysis of uranyl ion, a number of multinuclear complexes are formed:

With further hydrolysis, U 3 0s(0H) 2 and then U 3 0 8 (0H) 4 2 - appear.

For the qualitative detection of uranium, methods of chemical, luminescent, radiometric and spectral analyzes are used. Chemical methods are predominantly based on the formation of colored compounds (for example, red-brown color of a compound with ferrocyanide, yellow with hydrogen peroxide, blue with arsenazo reagent). The luminescent method is based on the ability of many uranium compounds to produce a yellowish-greenish glow when exposed to UV rays.

Quantitative determination of uranium is carried out by various methods. The most important of them are: volumetric methods, consisting of the reduction of U(VI) to U(IV) followed by titration with solutions of oxidizing agents; gravimetric methods - precipitation of uranates, peroxide, U(IV) cupferranates, hydroxyquinolate, oxalate, etc. followed by calcination at 00° and weighing U 3 0s; polarographic methods in nitrate solution make it possible to determine 10*7-g10-9 g of uranium; numerous colorimetric methods (for example, with H 2 0 2 in an alkaline medium, with the arsenazo reagent in the presence of EDTA, with dibenzoylmethane, in the form of a thiocyanate complex, etc.); luminescent method, which makes it possible to determine when fused with NaF to Yu 11 g uranium.

235U belongs to radiation hazard group A, the minimum significant activity is MZA = 3.7-10 4 Bq, 2 3 8 and - to group D, MZA = 3.7-6 Bq (300 g).

The content of the article

URANUS, U (uranium), a metal chemical element of the actinide family, which includes Ac, Th, Pa, U and transuranium elements (Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, No, Lr). Uranium has gained prominence due to its use in nuclear weapons and nuclear power. Uranium oxides are also used to color glass and ceramics.

Being in nature.

The uranium content in the earth's crust is 0.003%, and it is found in the surface layer of the earth in the form of four types of deposits. First, these are veins of uraninite, or uranium pitch (uranium dioxide UO 2), very rich in uranium, but rare. They are accompanied by radium deposits, since radium is a direct product of the isotopic decay of uranium. Such veins are found in Zaire, Canada (Great Bear Lake), Czech Republic and France. The second source of uranium is conglomerates of thorium and uranium ores together with ores of other important minerals. Conglomerates usually contain sufficient amounts of gold and silver to be recovered, with uranium and thorium being associated elements. Large deposits of these ores are located in Canada, South Africa, Russia and Australia. The third source of uranium is sedimentary rocks and sandstones rich in the mineral carnotite (potassium uranyl vanadate), which contains, in addition to uranium, a significant amount of vanadium and other elements. Such ores are found in the western states of the United States. Iron-uranium shales and phosphate ores constitute a fourth source of sediment. Rich deposits are found in the shales of Sweden. Some phosphate ores in Morocco and the United States contain significant amounts of uranium, and phosphate deposits in Angola and the Central African Republic are even richer in uranium. Most lignites and some coals usually contain uranium impurities. Uranium-rich lignite deposits have been found in North and South Dakota (USA) and bituminous coals in Spain and the Czech Republic.

Opening.

Uranus was discovered in 1789 by the German chemist M. Klaproth, who named the element in honor of the discovery of the planet Uranus 8 years earlier. (Klaproth was the leading chemist of his time; he also discovered other elements, including Ce, Ti and Zr.) In fact, the substance Klaproth obtained was not elemental uranium, but an oxidized form of it, and elemental uranium was first obtained by the French chemist E. .Peligo in 1841. From the moment of discovery until the 20th century. uranium did not have the significance it has today, although many of its physical properties, as well as its atomic mass and density, were determined. In 1896, A. Becquerel established that uranium salts have radiation that illuminates a photographic plate in the dark. This discovery activated chemists to research in the field of radioactivity and in 1898, the French physicists spouses P. Curie and M. Sklodowska-Curie isolated salts of the radioactive elements polonium and radium, and E. Rutherford, F. Soddy, K. Fayans and other scientists developed the theory of radioactive decay, which laid the foundations of modern nuclear chemistry and nuclear energy.

First uses of uranium.

Although the radioactivity of uranium salts was known, its ores in the first third of this century were used only to obtain accompanying radium, and uranium was considered an undesirable by-product. Its use was concentrated mainly in ceramic technology and metallurgy; Uranium oxides were widely used to color glass in colors ranging from pale yellow to dark green, which contributed to the development of inexpensive glass production. Today, products from these industries are identified as fluorescent under ultraviolet rays. During World War I and shortly thereafter, uranium in the form of carbide was used in the production of tool steels, similar to Mo and W; 4–8% uranium replaced tungsten, the production of which was limited at the time. To obtain tool steels in 1914–1926, several tons of ferrouranium containing up to 30% (mass) U were produced annually. However, this use of uranium did not last long.

Modern uses of uranium.

The uranium industry began to take shape in 1939, when the fission of the uranium isotope 235 U was carried out, which led to the technical implementation of controlled chain reactions of uranium fission in December 1942. This was the birth of the age of the atom, when uranium grew from an insignificant element to one of the most important elements in life society. The military importance of uranium for the production of the atomic bomb and its use as fuel in nuclear reactors caused the demand for uranium to increase astronomically. The chronology of the growth in uranium demand based on the history of sediments in Great Bear Lake (Canada) is interesting. In 1930, resin blende, a mixture of uranium oxides, was discovered in this lake, and in 1932, radium purification technology was established in this area. From each ton of ore (resin blende) 1 g of radium and about half a ton of by-product, uranium concentrate, were obtained. However, there was little radium and its mining was stopped. From 1940 to 1942, development was resumed and uranium ore began to be shipped to the United States. In 1949, similar uranium purification, with some improvements, was used to produce pure UO 2 . This production has grown and is now one of the largest uranium production facilities.

Properties.

Uranium is one of the heaviest elements found in nature. Pure metal is very dense, ductile, electropositive with low electrical conductivity, and highly reactive.

Uranium has three allotropic modifications: a-uranium (orthorhombic crystal lattice), exists in the range from room temperature to 668 ° C; b-uranium (complex crystal lattice of tetragonal type), stable in the range of 668–774° C; g-uranium (body-centered cubic crystal lattice), stable from 774°C up to the melting point (1132°C). Since all isotopes of uranium are unstable, all its compounds exhibit radioactivity.

Isotopes of uranium

238 U, 235 U, 234 U occur in nature in a ratio of 99.3:0.7:0.0058, and 236 U occurs in trace amounts. All other isotopes of uranium from 226 U to 242 U are obtained artificially. The isotope 235 U is particularly important. Under the influence of slow (thermal) neutrons, it divides, releasing enormous energy. Complete fission of 235 U results in the release of a “thermal energy equivalent” of 2H 10 7 kWh h/kg. The fission of 235 U can be used not only to produce large amounts of energy, but also to synthesize other important actinide elements. Natural isotope uranium can be used in nuclear reactors to produce neutrons produced by the fission of 235 U, while excess neutrons not required by the chain reaction can be captured by another natural isotope, resulting in the production of plutonium:

When 238 U is bombarded with fast neutrons, the following reactions occur:

According to this scheme, the most common isotope 238 U can be converted into plutonium-239, which, like 235 U, is also capable of fission under the influence of slow neutrons.

Currently, a large number of artificial isotopes of uranium have been obtained. Among them, 233 U is particularly notable because it also fissions when interacting with slow neutrons.

Some other artificial isotopes of uranium are often used as radioactive tracers in chemical and physical research; this is first of all b- emitter 237 U and a- emitter 232 U.

Connections.

Uranium, a highly reactive metal, has oxidation states from +3 to +6, is close to beryllium in the activity series, interacts with all non-metals and forms intermetallic compounds with Al, Be, Bi, Co, Cu, Fe, Hg, Mg, Ni, Pb, Sn and Zn. Finely crushed uranium is especially reactive and at temperatures above 500 ° C it often enters into reactions characteristic of uranium hydride. Lump uranium or shavings burn brightly at 700–1000° C, and uranium vapor burns already at 150–250° C; uranium reacts with HF at 200–400° C, forming UF 4 and H 2 . Uranium dissolves slowly in concentrated HF or H 2 SO 4 and 85% H 3 PO 4 even at 90 ° C, but easily reacts with conc. HCl and less active with HBr or HI. The most active and rapid reactions of uranium with dilute and concentrated HNO 3 occur with the formation of uranyl nitrate ( see below). In the presence of HCl, uranium quickly dissolves in organic acids, forming organic U4+ salts. Depending on the degree of oxidation, uranium forms several types of salts (the most important among them are with U 4+, one of them UCl 4 is an easily oxidized green salt); uranyl salts (radical UO 2 2+) of the type UO 2 (NO 3) 2 are yellow in color and fluoresce green. Uranyl salts are formed by dissolving the amphoteric oxide UO 3 (yellow color) in an acidic medium. In an alkaline environment, UO 3 forms uranates such as Na 2 UO 4 or Na 2 U 2 O 7. The latter compound (“yellow uranyl”) is used for the manufacture of porcelain glazes and in the production of fluorescent glasses.

Uranium halides were widely studied in 1940–1950, as they were used to develop methods for separating uranium isotopes for the atomic bomb or nuclear reactor. Uranium trifluoride UF 3 was obtained by the reduction of UF 4 with hydrogen, and uranium tetrafluoride UF 4 is obtained in various ways by reactions of HF with oxides such as UO 3 or U 3 O 8 or by electrolytic reduction of uranyl compounds. Uranium hexafluoride UF 6 is obtained by fluorination of U or UF 4 with elemental fluorine or by the action of oxygen on UF 4 . Hexafluoride forms transparent crystals with a high refractive index at 64 ° C (1137 mm Hg); the compound is volatile (under normal pressure it sublimes at 56.54 ° C). Uranium oxohalides, for example, oxofluorides, have the composition UO 2 F 2 (uranyl fluoride), UOF 2 (uranium oxide difluoride).

And Saturn), is notable, first of all, for its unusual movement around the Sun, namely, unlike all other planets, Uranus rotates “retrograde”. What does it mean? And the fact is that if other planets, including our Earth, are like moving spinning tops (due to torsion, the change of day and night occurs), then Uranus is like a rolling ball, and as a result, the change of day/night, as well as the seasons on this the planets are significantly different.

Who discovered Uranus

But let's start our story about this unusual planet with the history of its discovery. The planet Uranus was discovered by the English astronomer William Herschel in 1781. Interestingly, observing its unusual movement, the astronomer first mistook it for, and only after a couple of years of observations did it receive planetary status. Herschel wanted to call it “Georg’s Star,” but the scientific community preferred the name proposed by Johann Bode - Uranus, in honor of the ancient god Uranus, who is the personification of the sky.

The god Uranus in ancient mythology is the oldest of the gods, the creator of everything and everyone (including other gods), and also the grandfather of the supreme god Zeus (Jupiter).

Features of the planet Uranus

Uranium is 14.5 times heavier than our Earth. Nevertheless, it is the lightest planet among the giant planets, since its neighboring planet, although smaller in size, has a greater mass than Uranus. The relative lightness of this planet is due to its composition, a significant part of which is ice, and the ice on Uranus is the most diverse: there is ammonia, water, and methane ice. The density of Uranus is 1.27 g/cm3.

Temperature of Uranus

What is the temperature on Uranus? Due to its distance from the Sun, it is, of course, very cold, and the point here is not only its remoteness, but also the fact that the internal heat of Uranus is several times less than that of other planets. The planet's heat flow is extremely small, less than that of the Earth. As a result, one of the lowest temperatures in the solar system was recorded on Uranus - 224 C, which is even lower than that of Neptune, located even further from the Sun.

Is there life on Uranus

At the temperature described in the paragraph above, it is obvious that the origin of life on Uranus is not possible.

Atmosphere of Uranus

What is the atmosphere like on Uranus? The atmosphere of this planet is divided into layers, which are determined by temperature and surface. The outer layer of the atmosphere begins at a distance of 300 km from the conventional surface of the planet and is called the atmospheric corona; this is the coldest part of the atmosphere. Further closer to the surface there is the stratosphere and troposphere. The latter is the lowest and densest part of the planet’s atmosphere. The troposphere of Uranus has a complex structure: it consists of water clouds, ammonia clouds, and methane clouds mixed together in a chaotic manner.

The composition of the atmosphere of Uranus differs from the atmospheres of other planets due to the high content of helium and molecular helium. Also, a large proportion of the atmosphere of Uranus belongs to methane, a chemical compound that makes up 2.3% of all molecules in the atmosphere there.

Photo of the planet Uranus

Surface of Uranus

The surface of Uranus consists of three layers: a rocky core, an icy mantle and an outer shell of hydrogen and helium, which are in a gaseous state. It is also worth noting another important element that is part of the surface of Uranus - methane ice, which creates what is called the signature blue color of the planet.

Scientists also used spectroscopy to detect carbon monoxide and carbon dioxide in the upper layers of the atmosphere.

Yes, Uranus also has rings (as do other giant planets), albeit not as large and beautiful as those of its colleague. On the contrary, the rings of Uranus are dim and almost invisible, as they consist of many very dark and small particles, ranging in diameter from a micrometer to a few meters. Interestingly, the rings of Uranus were discovered earlier than the rings of other planets with the exception of Saturn; even the discoverer of the planet W. Herschel claimed that he saw rings on Uranus, but then they did not believe him, since the telescopes of that time did not have enough power for other astronomers to confirm what Herschel saw. Only two centuries later, in 1977, American astronomers Jameson Eliot, Douglas Mincom and Edward Dunham, using the Kuiper Observatory, were able to observe the rings of Uranus with their own eyes. Moreover, this happened by accident, since scientists were simply going to observe the atmosphere of the planet and, without expecting it, discovered the presence of rings.

There are currently 13 known rings of Uranus, the brightest of which is the epsilon ring. The rings of this planet are relatively young; they were formed after its birth. There is a hypothesis that the rings of Uranus are formed from the remains of some destroyed satellite of the planet.

Moons of Uranus

Speaking of moons, how many moons do you think Uranus has? And he has as many as 27 of them (at least those known at the moment). The largest are: Miranda, Ariel, Umbriel, Oberon and Titania. All of Uranus' moons are a mixture of rock and ice, with the exception of Miranda, which is made entirely of ice.

This is what the satellites of Uranus look like compared to the planet itself.

Many satellites do not have an atmosphere, and some of them move inside the rings of the planet, through which they are also called inner satellites, and all of them have a strong connection with the ring system of Uranus. Scientists believe that many moons were captured by Uranus.

Rotation of Uranus

The rotation of Uranus around the Sun is perhaps the most interesting feature of this planet. Since we wrote above, Uranus rotates differently than all other planets, namely “retrograde”, just like a ball rolling on the earth. As a result of this, the change of day and night (in our usual understanding) on ​​Uranus occurs only near the equator of the planet, despite the fact that it is located very low above the horizon, approximately like in the polar latitudes on Earth. As for the poles of the planet, “polar day” and “polar night” replace each other once every 42 Earth years.

As for the year on Uranus, one year there is equal to our 84 earthly years; it is during this time that the planet circles in its orbit around the Sun.

How long does it take to fly to Uranus?

How long is the flight to Uranus from Earth? If, with modern technologies, a flight to our closest neighbors, Venus, and Mars, takes several years, then a flight to such distant planets as Uranus can take decades. To date, only one spacecraft has made such a journey: Voyager 2, launched by NASA in 1977, reached Uranus in 1986, as you can see, the one-way flight took almost a decade.

It was also planned to send the Cassini apparatus, which was engaged in studying Saturn, to Uranus, but then it was decided to leave Cassini near Saturn, where it died quite recently - in September last 2017.

• Three years after its discovery, the planet Uranus became the setting for a satirical pamphlet. Science fiction writers often mention this planet in their science fiction works.
• Uranus can be seen in the night sky with the naked eye, you just need to know where to look, and the sky must be perfectly dark (which, unfortunately, is not possible in modern cities).
• There is water on the planet Uranus. But the water on Uranus is frozen, like ice.
• The planet Uranus can confidently be awarded the laurels of “the coldest planet” in the solar system.

Planet Uranus, video

And in conclusion, an interesting video about the planet Uranus.

This article is available in English - .