Cesium element characteristic. Cesium
The characteristics of cesium, its structural features and qualities inherent in this element, must be taken in the course of chemistry. Not only schoolchildren, but also students of chemical specialties should know the specific features of this compound. The use of cesium is currently quite wide - but in a specific area. This is largely due to the fact that at room temperature the element acquires a liquid state, and is practically never found in its pure form. Currently, only five metals have similar qualities. The properties of cesium determine the interest of scientists in it and the possibilities for using the compound.
What is this about?
The soft metal cesium is designated in the periodic table by the symbols Cs. Its serial number is 55. The soft metal has a silvery, golden hue. Melting point - 28 degrees Celsius.
Cesium is an alkali metal whose qualities and features are similar to potassium, rubidium. The structure of cesium causes increased reactivity. With water, the metal can react at a temperature on the Celsius scale of 116 degrees below zero. The chemical element cesium is highly pyrophoric. It is obtained from pollucite. Many radioactive isotopes of cesium (including cesium 137, which has found active use) are produced during the processing of waste generated during the operation of a nuclear reactor. Cesium 137 is the result of a fission reaction.
Historical background
The merit of discovering the electronic formula of cesium belongs to chemists from Germany, outstanding minds in their field, Kirchhoff, Bunsen. This event happened back in 1860. At that time, they began to actively change the newly invented method of flame spectroscopy, and in the course of their experiments, German scientists discovered a chemical element previously unknown to the public - cesium. At that moment, cesium was presented as a recipient, which is relevant for photocells and electronic lamps.
Noticeable changes in the history of the definition and isolation of the element occurred in 1967. Taking into account Einstein's statement that the speed of light can be considered the most constant measurement factor inherent in our universe, it was decided to isolate cesium 133. This was an important moment in expanding the range of applications of the chemical element cesium - in particular, atomic clocks are made on it.
Cesium in the nineties
It was in the last decade of the last century that the chemical element cesium began to be used by mankind especially actively. It has been found to be applicable in fluid drilling jobs. We also managed to find a fairly extensive area of application in the chemical industries. It turned out that cesium chloride and its other derivatives can be used in the design of complex electronics.
At the same time, in the nineties, special attention of the scientific community was riveted to everything that could become a new word in atomic, nuclear energy. It was then that radioactive cesium was most carefully studied. It was found that the half-life of this component requires about three decades. At present, radioactive isotopes of cesium are widely used in hydrology. Medicine and industry cannot do without them. The most widely used radioactive isotope is cesium 137. Cesium is characterized by a low level of toxic abilities, while radioactive derivatives in high concentrations can harm nature and humans.
Physical parameters
The specificity of cesium (as well as cesium chloride and other derivatives of this metal) determines the possibility of a wide application of the product. Among other elements, it is cesium that has the smallest hardness index - only 0.2 units in addition to softness, malleability is characteristic of the metal. In the normal state, the correct electronic formula of cesium allows the formation of a material that is pale in color, capable of changing color to a darker one at the slightest contact with oxygen compounds.
The melting point of the metal is only 28 degrees Celsius, which means that the compound is one of the five metals that are in the liquid phase at or near room temperature. An even lower melting point than that of cesium has been registered only for mercury. The boiling point of cesium is also low - only mercury has less. Features of the electrochemical potential regulate the combustion of the metal - it creates purple hues or blue.
Compatibility and features
Cesium has the ability to react with The element also forms cesium oxides. In addition, reactions with mercury mixtures and gold are observed. Features of interaction with other compounds, as well as temperature conditions under which reactions are possible, declare possible intermetallic compositions. In particular, cesium is the initial component for the formation of photosensitive compounds. For this, a metal reaction is carried out with the participation of thorium, antimony, gallium, and indium.
In addition to cesium oxide, chemists are also interested in the results of interaction with a number of alkaline elements. At the same time, it must be taken into account that the metal cannot react with lithium. Each of the cesium alloys has its own shade. Some mixtures are black-violet compounds, others are golden-colored, and still others are almost colorless, but with a pronounced metallic sheen.
Chemical features
The most pronounced feature of cesium is its pyrophoricity. In addition, the attention of scientists is attracted by the electrochemical potential of the metal. Cesium can spontaneously combust right in the air. When interacting with water, an explosion occurs, even if the reaction conditions assumed low temperatures. In this regard, cesium noticeably differs from the first group of the Mendeleev chemical table. When cesium and water interact in solid form, a reaction also occurs.
It was found that the half-life of cesium lasts about three decades. The material was recognized as dangerous due to its characteristics. To work with cesium, it is necessary to create an atmosphere of an inert gas. At the same time, the explosion upon contact with water with an equal amount of sodium and cesium in the second case will be noticeably weaker. Chemists explain this by the following feature: when cesium comes into contact with water, an instantaneous explosive reaction occurs, that is, there is not a sufficiently long time period for the accumulation of hydrogen. The best method for storing cesium is sealed containers made of a borosilicate compound.
Cesium: in compounds
Cesium in compounds acts as a cation. There are many different anions with which a compound formation reaction is possible. Most cesium salts are colorless unless the color is due to an anion. Simple salts are hygroscopic, although to a lesser extent than other light alkali metals. Many are soluble in water.
They have a relatively low degree of solubility. It has found quite a wide application in industry. For example, aluminum-cesium sulfate is actively used in ore treatment plants due to its low water solubility.
Cesium: unique and useful
Visually, this metal is similar to gold, but slightly lighter than the most popular precious metal. If you take a piece of cesium in your hand, it will quickly melt, and the resulting substance will be mobile, change color somewhat - closer to silver. In the molten state, cesium perfectly reflects light rays. Of the alkali metals, cesium is considered the heaviest, at the same time, it has the lowest density.
The history of the discovery of cesium contains references to the Durchheim source. It was from here that a water sample was sent for laboratory research. In the course of the analysis of the constituent components, special attention was paid to the solution of the question: which element provides the medicinal qualities of the liquid? The German scientist Bunsen decided to apply the method of spectral analysis. It was then that two unexpected lines of a blue tint appeared, which were not characteristic of compounds known at that time. It was the color of these bands that helped scientists choose a name for the new component - sky blue in Latin sounds like "cesium".
Where can I find you?
As it was revealed in the course of long-term tests, cesium is a trace element that is extremely rare in natural conditions. So, conducting a comparative analysis of the content of rubidium and cesium in the planet's crust, scientists found that the second is less than hundreds of times. A rough estimate of the concentration gave an indicator of 7 * 10 (-4)%. No other less sensitive method than spectroscopy would simply reveal such a rare compound. This explains the fact that earlier scientists did not even suspect the existence of cesium.
At present, it has been found out that cesium is more common in rocks extracted from mountains. Its concentration in this material does not exceed thousandths of a percent. Categorically small amounts were recorded in the waters of the seas. The level of concentration in lithium, potassium mineral compounds reaches tenths of a percent. Most often it can be detected in lepidolite.
When comparing the distinctive features of cesium and rubidium, as well as other elements that are extremely rare, it was possible to reveal that cesium is characterized by the formation of unique minerals, which other compounds are not capable of. This is how pollucite, rhodicite, avogadrite are obtained.
Rodicite, as scientists have found, is extremely rare. Similarly, avogadrite is very difficult to find. Pollucite is somewhat more common, in some cases small deposits were found. They have a very low power, but contain cesium in an amount of 20-35 percent of the total mass. The most important, from the point of view of the public, pollucites were found in the American bowels and on the territory of Russia. There are also Swedish developments, Kazakhstani ones. It is known that pollucite was found in the southwest of the African continent.
Work continues
It's no secret that discovering an element and obtaining it in its pure form are two completely different tasks, albeit related. When it became clear that cesium is very rare, scientists began to develop methods for synthesizing the metal in the laboratory. At first, it seemed that this was a completely impossible task, if we use the means and technology available at that time. For many years, Bunsen failed to isolate metallic cesium in its pure form. Only two decades later, advanced chemists were finally able to solve this problem.
The breakthrough came in 1882 when Setterberg of Sweden electrolyzed a mixture into four parts of cesium cyanide mixed with one part of barium. The last component was used to make the melting point lower. Cyanides, as scientists already knew at this point, were very dangerous components. At the same time, contamination formed due to barium, which did not allow obtaining a more or less satisfactory amount of cesium. It was clear that the methodology required significant improvements. A good proposal in this area was submitted for discussion by the scientific community Beketov. It was then that cesium hydroxide attracted attention. If this compound is reduced by using metallic magnesium, increasing the heat and using a hydrogen current, a slightly better result can be achieved than that proven by the Swedish chemist. However, real experiments have shown that the yield is half that calculated in theory.
What's next?
Cesium continued to be the focus of attention of the international chemical scientific community. In particular, the French scientist Axpil devoted much effort and time to him in his research. In 1911, he proposed a radically new approach to the extraction of pure cesium. It was necessary to carry out the reaction in a vacuum, metal chloride was taken as the starting material, and metallic calcium was used to reduce it.
Such a reaction, as experiments have shown, occurs almost to the end. To achieve a sufficient effect, it is necessary to use a special device. In laboratories, they usually resort to refractory glass or use quartz containers. The device must have a process. Inside, a pressure of about 0.001 mm Hg is maintained. Art. For a successful reaction, it is necessary to ensure that the container is heated to 675 degrees Celsius. In this case, cesium is released, which evaporates almost immediately. Pairs pass into the process intended for this. But potassium chloride mainly settles directly in the reactor. Under given conditions, the volatility of this salt is so small that it can be ignored altogether, since for this compound the characteristic melting point is 773 degrees (according to the same Celsius scale). This means that the precipitate can melt if the container is overheated by a hundred degrees relative to what was intended. To achieve the most effective result, it is necessary to repeat the distillation process. To do this, create a vacuum. The output will be ideal metallic cesium. Currently, the described method is used most widely and is considered optimal for obtaining the connection.
Activity and reactions
In the course of numerous studies, scientists were able to determine that cesium has an amazing activity that is not normally characteristic of metals. On contact with air, ignition occurs, which leads to the release of superoxide. Oxide can be achieved by limiting the access of oxygen to the reagents. There is a possibility of formation of suboxides.
If cesium comes into contact with phosphorus, sulfur, halogen, this provokes an explosion accompanied by an explosion. Also, the explosion accompanies the reaction with water. Using a crystallizer, a glass, you may encounter the fact that the container literally shatters into pieces. A reaction with ice is also possible if the temperature on the Celsius scale is not lower than 116 degrees. As a result of this reaction, hydrogen and hydroxide are produced.
Hydroxide: features
In the course of studying the reaction products produced by cesium, chemists have found that the resulting hydroxide is a very strong base. When interacting with it, it must be remembered that at a high concentration, this compound can easily destroy glass even without additional heating. But when the temperature rises, the hydroxide easily melts nickel, iron, cobalt. The effect on corundum, platinum will be similar. If oxygen takes part in the reaction, cesium hydroxide destroys silver and gold extremely quickly. If you limit the supply of oxygen, the process proceeds relatively slowly, but still does not stop. Rhodium and several alloys of this compound are resistant to cesium hydroxide.
Apply wisely
Not only cesium, but also compounds known on the basis of this metal are currently used very widely. Without them, it is impossible to imagine the design of radio engineering, they are also indispensable in electronics. The compound and variations of cesium are actively used in chemistry, industry, ophthalmology, and medicine. Cesium has not been ignored in the development of technologies applicable in space, as well as nuclear energy.
It is now common to use cesium in the design of solar cells. Bromide, iodide of this metal are necessary for the creation of infrared vision systems. Single crystals obtained industrially can be used as elements of detectors that allow detecting ionizing radiation. Some cesium-based compounds are actively used as catalysts in industrial processes. This is necessary for the creation of ammonia, the formation and production of butadiene.
Radiation and cesium
The isotope cesium 137 attracts the greatest attention of scientists. It belongs to the category of beta emitters. Currently, this element is indispensable in the process of sterilization of food products, medicinal compounds. It is customary to resort to it in the treatment of malignant neoplasms. Modern approaches have made it possible to use the element in gamma flaw detection. Based on it, level sensors, as well as current sources, are designed. The 137th isotope entered the environment in a very large amount after the accident at the Chernobyl nuclear power plant. It is he who is one of the most important factors of pollution after this catastrophe.
However, the 137th is not the only radioactive isotope of cesium that has found application in modern industry. So, atomic clocks are created on the isotope of cesium 133. At present, this is the most accurate device that allows you to control the passage of time. One second, as modern scientists have found out in the course of high-precision research, is 9192631770 periods of radiation. This makes it possible to use the atom of the cesium 133 isotope as a standard for determining frequency and time.
If the writer-fiction writer had to deal with the “biography” of cesium, then he might start like this: “Cesium was discovered relatively recently, in 1860, in the mineral waters of the famous healing springs of the Black Forest (Baden-Baden, etc.). In a short historical period, a brilliant path has passed - from a rare, unknown chemical element to a strategic metal. He belongs to the labor family of alkali metals, but the blue blood of the last of his kind flows in his veins ... However, this does not in the least prevent him from communicating with other elements, and even if they are not so famous, he willingly enters into contacts with them and establishes strong bonds. connections. Currently, he works simultaneously in several industries: in electronics and automation, in radar and cinema, in nuclear reactors and on space ships ... ".
Without taking seriously the playful top and some obviously literary exaggerations, this biography can be safely mistaken for a "novel without lies." The talk about the “blue blood” of cesium is not pointless - it was first detected by two bright lines in the blue region of the spectrum and the Latin word “caesius”, from which its name comes, means sky blue. The assertion that cesium is practically the last in the series of alkali metals is indisputable. True, even Mendeleev prudently left an empty cell in his table for "ecacesium", which was supposed to follow cesium in group I. And this element (francium) was discovered in 1939. However, francium exists only as rapidly decaying radioactive isotopes with half-lives of minutes, seconds, or even thousandths of a second. Finally, it is also true that cesium is used in some of the most important areas of modern technology and science.
The prevalence of cesium in nature and its production
There is no exact data in the literature on how much cesium is available on the globe. It is only known that it is one of the rare chemical elements. It is believed that its content in the earth's crust is at least several hundred times less than rubidium, and does not exceed 7·10–4%.
Cesium is found in an extremely dispersed state (on the order of thousandths of a percent) in many rocks; trace amounts of this metal have also been found in seawater. It is found in higher concentrations (up to several tenths of a percent) in some potassium and lithium minerals, mainly in lepidolite. But it is especially significant that, unlike rubidium and most other rare elements, cesium forms its own minerals - pollucite, avogadrite and rhodicite. Rhodicite is extremely rare, moreover, some authors classify it as a lithium mineral, since its composition (R 2 O 2Al 2 O 3 3B 2 O 3, where R 2 O is the sum of alkali metal oxides) usually contains more lithium than cesium . Avogadrite (K, Cs) is also rare, and pollucites are rare; their deposits are thin, but they contain at least 20, and sometimes up to 35% cesium. Pollucites of the USA (South Dakota and Maine), Southwest Africa, Sweden and the Soviet Union (Kazakhstan, etc.) are of the greatest practical importance.
Pollucites are aluminosilicates, complex and very strong compounds. Their composition is determined by the formula (Cs, Na) n H 2 O, and although there is a lot of cesium in them, it is not so easy to extract it. In order to "open" the mineral and convert valuable components into a soluble form, it is treated with concentrated mineral acids - hydrofluoric or hydrochloric and sulfuric when heated. Then the solution is freed from all heavy and light metals and, which is especially difficult, from the constant companions of cesium - alkali metals: potassium, sodium and rubidium.
Modern methods for extracting cesium from pollucites are based on the preliminary fusion of concentrates with an excess of lime and a small amount of fluorspar. If the process is carried out at 1200°C, then almost all cesium sublimates in the form of Cs 2 O oxide. This sublimation, of course, is contaminated with an admixture of other alkali metals, but it is soluble in mineral acids, which simplifies further operations.
From lepidolites, cesium is extracted along with rubidium along the way, as a by-product of lithium production. Lepidolites are preliminarily alloyed (or sintered) at about 1000°C with gypsum or potassium sulfate and barium carbonate. Under these conditions, all alkali metals are converted into easily soluble compounds - they can be leached with hot water. After the isolation of lithium, it remains to process the resulting filtrates, and here the most difficult operation is the separation of cesium from rubidium and a huge excess of potassium. As a result, some cesium salt is obtained - chloride, sulfate or carbonate. But this is only part of the story, since the cesium salt must be converted into cesium metal. To understand the complexity of the last stage, it is enough to point out that the discoverer of cesium - the largest German chemist Bunsen - did not manage to obtain element No. 55 in a free state. All methods suitable for the reduction of other metals did not give the desired results. Metallic cesium was first obtained only 20 years later, in 1882, by the Swedish chemist Setterberg in the process of electrolysis of a molten mixture of cesium and barium cyanides, taken in a ratio of 4:1. Barium cyanide was added to lower the melting point. However, barium contaminated the final product, and cyanides were difficult to work with due to their extreme toxicity, and the yield of cesium was very small. The ox its rational method was found in 1890 by the famous Russian chemist N.N. Beketov, who proposed the reduction of cesium hydroxide with metallic magnesium in a stream of hydrogen at an elevated temperature. Hydrogen fills the device and prevents the oxidation of cesium, which is distilled off into a special receiver. However, even in this case the yield of cesium does not exceed 50% of the theoretical one.
The best solution to the difficult problem of obtaining metallic cesium was found in 1911 by the French chemist Axpil. With the Axpil method, which is still the most common, cesium chloride is reduced with metallic calcium in a vacuum, and the reaction
2CsCl + Ca → CaCl 2 + 2Cs
goes almost to the end. The process is carried out in a special device (in laboratory conditions - from quartz or refractory glass), equipped with a process. If the pressure in the device is not more than 0.001 mm Hg. Art., the process temperature may not exceed 675°C. The released cesium evaporates and is distilled off into the offshoot, and calcium chloride remains completely in the reactor, since under these conditions the volatility of the salt is negligible (the melting point of CaCl 2 is 773°C, i.e., 100°C higher than the process temperature). As a result of repeated distillation in vacuum, absolutely pure metallic cesium is obtained.
Many other methods for obtaining metallic cesium from its compounds are described in the literature, but, as a rule, they do not promise any particular advantages. Thus, when metallic calcium is replaced by its carbide, the reaction temperature has to be raised to 800°C, and the final product becomes contaminated with additional impurities. It is possible to decompose cesium azide or reduce its bichromate with zirconium, but these reactions are explosive. However, when dichromate is replaced by cesium chromate, the reduction process proceeds smoothly, and, although the yield does not exceed 50%, very pure metallic cesium is distilled off. This method is applicable to obtain small amounts of metal in a special vacuum device.
World production of cesium is relatively small, but in recent years it has been constantly growing. One can only guess about the scale of this growth - the figures are not published.
Cesium properties
The shiny surface of metallic cesium has a pale golden color. It is one of the most fusible metals: it melts at 28.5°C, boils at 705°C under normal conditions and at 330°C in a vacuum. The fusibility of cesium is combined with great lightness. Despite the fairly large atomic mass (132.905) of the element, its density at 20°C is only 1.87. Cesium is many times lighter than its neighbors on the periodic table. Lanthanum, for example, which has almost the same atomic mass, is more than three times as dense as cesium. Cesium is only twice as heavy as sodium, and their atomic mass ratio is 6:1. Apparently, the reason for this lies in the peculiar electronic structure of cesium atoms. Each of its atoms contains 55 protons, 78 neutrons and 55 electrons, but all these numerous electrons are located relatively loosely - the ionic radius of cesium is very large - 1.65 Å*. The ionic radius of lanthanum, for example, is only 1.22 Å, although its atom contains 57 protons, 82 neutrons and 57 electrons.
* The atomic radius of cesium is 2.62 Å.
The most remarkable property of cesium is its exceptionally high activity. It is superior to all other metals in its sensitivity to light. The cesium cathode emits a stream of electrons even when exposed to infrared rays with a wavelength of 0.80 microns. In addition, the maximum electron emission, which exceeds the normal photoelectric effect by hundreds of times, occurs in cesium when illuminated with green light, while in other light-sensitive metals this maximum appears only when exposed to violet or ultraviolet rays.
For a long time, scientists hoped to find radioactive isotopes of cesium in nature, since rubidium and potassium have them. However, no other isotopes have been found in natural cesium, except for the quite stable 133 Cs. True, 22 radioactive isotopes of cesium with atomic masses from 123 to 144 were artificially obtained. In most cases, they are short-lived: half-lives are measured in seconds and minutes, less often - several hours or days. However, three of them do not decay so quickly - these are 134 Cs, 137 Cs and 135 Cs, living 2.07; 26.6 and 3 10 6 years. All three isotopes are formed in nuclear reactors during the decay of uranium, thorium and plutonium; their removal from reactors is quite difficult.
The chemical activity of cesium is extraordinary. It reacts very quickly with oxygen and not only instantly ignites in air, but is able to absorb the slightest traces of oxygen in a deep vacuum. It rapidly decomposes water already at ordinary temperature; in this case, a lot of heat is released, and the hydrogen displaced from the water immediately ignites. Cesium interacts even with ice at –116°C. Its storage requires great care.
Cesium also interacts with carbon. Only the most perfect modification of carbon - diamond - is able to withstand its "onslaught". Liquid molten cesium and its vapors loosen soot, charcoal and even graphite, penetrating between carbon atoms and forming peculiar, fairly strong golden-yellow compounds, which, in the limit, apparently correspond to the composition of C 8 Cs 5 . They ignite in air, displace hydrogen from water, and when heated, decompose and release all absorbed cesium.
Even at ordinary temperatures, the reactions of cesium with fluorine, chlorine, and other halogens are accompanied by ignition, and with sulfur and phosphorus, by an explosion. When heated, cesium combines with hydrogen, nitrogen and other elements, and at 300 ° C destroys glass and porcelain. Cesium hydrides and deuterides are highly flammable in air and in fluorine and chlorine atmospheres. Unstable, and sometimes flammable and explosive compounds of cesium with nitrogen, boron, silicon and germanium, as well as with carbon monoxide. Cesium halides and cesium salts of most acids, on the other hand, are very strong and stable. The activity of the original cesium is manifested in them only in the good solubility of the vast majority of salts. In addition, they are easily converted into more complex complex compounds.
Alloys and intermetallic compounds of cesium are always relatively fusible.
Cesium has another very important property closely related to its electronic structure. The point is that it loses its single valence electron more easily than any other metal; this requires very little energy - only 3.89 eV. Therefore, obtaining plasma from cesium requires much less energy than when using any other chemical element.
Where is cesium used?
It is not surprising that the remarkable properties of cesium have long opened access to various spheres of human activity.
First of all, he found application in radio engineering. Vacuum photocells with a complex silver-cesium photocathode are especially valuable for radar: they are sensitive not only to visible light, but also to invisible infrared rays and, unlike, for example, selenium cells, operate without inertia. Vacuum antimony-cesium photocells are widely used in television and sound films; their sensitivity even after 250 hours of operation drops by only 5...6%, they work reliably in the temperature range from -30° to +90°C. Of these are the so-called multi-stage photocells; in this case, under the action of electrons caused by light rays in one of the cathodes, secondary emission occurs - electrons are emitted by additional photocathodes of the device. As a result, the total electric current that occurs in the photocell is multiplied many times over. Current amplification and sensitivity increase are also achieved in cesium photocells filled with an inert gas (argon or neon).
Bromides, iodides and some other cesium salts are widely used in optics and electrical engineering. If, in the manufacture of fluorescent screens for televisions and scientific equipment, approximately 20% of cesium iodide is introduced between zinc sulfide crystals, the screens will better absorb X-rays and glow brighter when irradiated with an electron beam.
At the International Exhibition "Chemistry-65" held in Moscow in 1965 in the pavilion of the USSR, scintillation devices with single crystals of cesium iodide activated by thallium were demonstrated. These devices, designed to detect heavy charged particles, have the highest sensitivity of all devices of this type.
Cesium bromide and iodide crystals are transparent to infrared rays with a wavelength of 15 to 30 µm (CsBr) and 24 to 54 µm (CsI). Conventional sodium chloride prisms transmit only rays with a wavelength of 14 microns, and from potassium chloride - 25 microns. Therefore, the use of cesium bromide and cesium iodide made it possible to record the spectra of complex molecules in the far infrared region.
Compounds of cesium with stannic acid (ortostannates) and with zirconium oxide (metazirconates) are very sensitive to light. Luminescent tubes made on their basis, when irradiated with ultraviolet rays or electrons, give green luminescence.
The activity of many cesium compounds is manifested in their catalytic ability. It has been established that when synthol (synthetic oil) is obtained from water gas and styrene from ethylbenzene, as well as in some other syntheses, the addition of a small amount of cesium oxide to the catalyst (instead of potassium oxide) increases the yield of the final product and improves the process conditions. Cesium hydroxide is an excellent catalyst for the synthesis of formic acid. With this catalyst, the reaction proceeds at 300°C without high pressure. The yield of the final product is very high - 91.5%. Metallic cesium is better than other alkali metals in accelerating the hydrogenation reaction of aromatic hydrocarbons.
On the whole, the catalytic properties of cesium have been little studied, and its positive effect has been assessed rather qualitatively than quantitatively. This can probably be explained by the lack of relevance of the issue, since there is an urgent demand for cesium in a number of other very important areas. The latter include, in particular, medicine. The isotope 137 Cs, which is formed in all nuclear reactors (on average, out of 100 uranium nuclei 6 137 Cs nuclei), specialists in the field of X-ray therapy became interested. This isotope decomposes relatively slowly, losing only 2.4% of its original activity per year. It turned out to be suitable for the treatment of malignant tumors and has certain advantages over radioactive cobalt-60: a longer half-life (26.6 years versus 5.27) and four times less hard gamma radiation. In this regard, devices based on 137 Cs are more durable, and radiation protection is less cumbersome. However, these advantages become real only if 137 Cs is absolutely radiochemically pure and contains no 134 Cs impurity, which has a shorter half-life and harder gamma radiation.
Not only radioactive, but also stable metallic cesium is becoming increasingly important. It serves for the manufacture of special rectifiers, in many respects superior to mercury ones. In the military and navy, cesium vapor vacuum tubes are used for infrared signaling and control. In the United States, this kind of device, capable of detecting all kinds of objects in the dark, is called a "sniperscope".
But especially great attention has recently been paid to cesium plasma, to a comprehensive study of its properties and formation conditions. Perhaps it will become the "fuel" of the plasma engines of the future. In addition, work on the study of cesium plasma is closely related to the problem of controlled thermonuclear fusion. Many scientists believe that it is expedient to create cesium plasma using the high-temperature thermal energy of nuclear reactors, that is, to directly convert this thermal energy into electrical energy.
This is by no means a complete list of the possibilities of cesium.
Shortly after opening
Cesium is known to have been the first element to be discovered by spectral analysis. Scientists, however, had the opportunity to get acquainted with this element even before Bunsen and Kirchhoff created a new research method. In 1846, the German chemist Plattner, analyzing the mineral pollucite, found that the sum of its known components was only 93%, but he could not determine exactly what other element (or elements) is included in this mineral. Only in 1864, after the discovery of Bunsen, the Italian Pisani found cesium in pollucite and established that it was the compounds of this element that Plattner could not identify.
Cesium and pressure
All alkali metals change strongly under high pressure. But it is cesium that reacts to it most peculiarly and sharply. At a pressure of 100 thousand atm. its volume decreases almost three times - more than that of other alkali metals. In addition, it was under high pressure conditions that two new modifications of elemental cesium were discovered. The electrical resistance of all alkali metals increases with increasing pressure; in cesium, this property is especially pronounced.
atomic clock
The nucleus of the cesium atom and its valence electron have their own magnetic moments. These moments can be oriented in two ways - parallel or anti-parallel. The difference between the energies of both states is constant, and, naturally, the transition from one state to another is accompanied by oscillations with strictly constant characteristics (wavelength 3.26 cm). Using this property, scientists have created a cesium "atomic clock" - perhaps the most accurate in the world.
Cesium is included in the group of chemical elements with limited reserves, together with hafnium, tantalum, beryllium, rhenium, platinum group metals, cadmium, tellurium. The total identified world resources of ores are about 180 thousand tons (in terms of cesium oxide), but they are extremely dispersed. Super high prices are an integral feature that accompanies cesium and rubidium in the past and present. The world production of cesium is about 9 tons per year, and the need is over 85 tons per year and it is constantly growing. Cesium also has disadvantages that determine the constant search for its minerals: the extraction of this metal from ores is incomplete, during the operation of the material it dissipates and is therefore irretrievably lost, the reserves of cesium ores are very limited and cannot meet the ever-growing demand for metallic cesium (requirements for metal more than 8.5 times its production, and the situation in the metallurgy of cesium is even more alarming than, for example, in the metallurgy of tantalum or rhenium). Industry needs precisely very pure material (at the level of 99.9-99.999%), and this is one of the most difficult tasks in the metallurgy of rare elements. To obtain cesium of a sufficient degree of purity, multiple rectification in a vacuum, purification from mechanical impurities on cermet filters, heating with getters to remove traces of hydrogen, nitrogen, oxygen, and multiple stepwise crystallization are required. Cesium is very active and aggressive towards container materials and requires storage, for example, in vessels made of special glass in an atmosphere of argon or hydrogen (cesium destroys conventional grades of laboratory glass).
Place of Birth
Canada is the leader in the extraction of cesium ore (pollucite). The Bernick Lake deposit (southeastern Manitoba) contains about 70% of the world's cesium reserves. Pollucite is also mined in Namibia and Zimbabwe. In Russia, its powerful deposits are located on the Kola Peninsula, in the Eastern Sayan and Transbaikalia. There are also pollucite deposits in Kazakhstan, Mongolia and Italy (Elba Island), but they have small reserves and are not of great economic importance.
The annual production of cesium in the world is about 20 tons.
Geochemistry and mineralogy
The average content of cesium in the earth's crust is 3.7 g/t. There is some increase in the content of cesium from ultrabasic rocks (0.1 g/t) to acidic (5 g/t). Most of its mass in nature is in a scattered form and only a small part is contained in its own minerals. Constantly elevated amounts of cesium are observed in sparrowite (1-4%), rhodicite (about 5%), avogadrite and lepidolite (0.85%). In terms of crystal chemical properties, cesium is closest to rubidium, potassium, and thallium. In increased quantities, cesium is found in potassium minerals. Cesium, like rubidium, tends to accumulate in the late stages of magmatic processes, and its concentrations reach the highest values in pegmatites. The average content of cesium in granitic pegmatites is about 0.01%, and in individual pegmatite veins containing pollucite it even reaches 0.4%, which is about 400 times higher than in granites. The highest concentrations of cesium are observed in rare-metal-substituted microcline-albite pegmatites with spodumene. During the pneumatolithic-hydrothermal process, increased amounts of cesium are associated with massifs of greisenized alaskites and granites with quartz-beryl-wolframite veins, where it is present mainly in muscovites and feldspars. In the zone of hypergenesis (under surface conditions), cesium accumulates in small amounts in clays, clayey rocks and soils containing clay minerals, sometimes in manganese hydroxides. The maximum content of cesium is only 15 g/t. The role of clay minerals is reduced to sorption, cesium is involved in the interpacket space as an absorbed base. The active migration of this element in the waters is very limited. The main amount of cesium migrates "passively", in the clay particles of river waters. In sea water, the concentration of cesium is approx. 0.5 µg/l. Of the cesium minerals proper, the most common are pollucite (Cs, Na) nH2O (22–36% Cs2O), cesium beryl (vorobievite) Be2CsAl2(Si6O18) and avogadrite (KCs)BF4. The last two minerals contain up to 7.5% cesium oxide.
Obtaining cesium
The main cesium minerals are pollucite and the very rare avogadrite (K,Cs). In addition, in the form of impurities, cesium is included in a number of aluminosilicates: lepidolite, phlogopite, biotite, amazonite, petalite, beryl, zinnwaldite, leucite, carnallite. Pollucite and lepidolite are used as industrial raw materials.
In industrial production, cesium in the form of compounds is extracted from the mineral pollucite. This is done by chloride or sulfate opening. The first involves treating the original mineral with heated hydrochloric acid, adding antimony chloride SbCl3 to precipitate the Cs3 compound, and washing with hot water or an ammonia solution to form cesium chloride CsCl. In the second case, the mineral is treated with heated sulfuric acid to form cesium alum CsAl(SO4)2 12H2O.
In Russia, after the collapse of the USSR, industrial production of pollucite was not carried out, although colossal reserves of the mineral were discovered in the Voronya tundra near Murmansk back in Soviet times. By the time the Russian industry was able to get on its feet, it turned out that a Canadian company had bought the license to develop this field. Currently, the processing and extraction of cesium salts from pollucite is carried out in Novosibirsk at ZAO Rare Metals Plant.
There are several laboratory methods for obtaining cesium. It can be obtained:
heating in vacuum a mixture of cesium chromate or dichromate with zirconium;
decomposition of cesium azide in vacuum;
heating a mixture of cesium chloride and specially prepared calcium.
All methods are labor intensive. The second method makes it possible to obtain high-purity metal, however, it is explosive and requires several days to be realized.
Chemical properties
Cesium is the most reactive metal obtained in macroscopic quantities (since the activity of alkali metals increases with serial number, francium is probably even more active, but not obtained in macroscopic quantities, since all of its isotopes have a short half-life). It is the strongest restorer. In air, cesium instantly oxidizes with ignition, forming superoxide CsO2. With limited oxygen access, it is oxidized to Cs2O oxide. Interaction with water occurs with an explosion, the interaction product is hydroxide CsOH and hydrogen H2. Cesium reacts with ice (even at −120 °C), simple alcohols, organohalides, heavy metal halides, acids, dry ice (the interaction proceeds with a strong explosion). Reacts with benzene. The activity of cesium is due not only to a high negative electrochemical potential, but also to a low melting and boiling point (a very large contact surface quickly develops, which increases the reaction rate). Many salts formed by cesium - nitrates, chlorides, bromides, fluorides, iodides, chromates, manganates, azides, cyanides, carbonates, etc. - are extremely easily soluble in water and a number of organic solvents; perchlorates are the least soluble (which is important for the technology of obtaining and purifying cesium). Despite the fact that cesium is a very active metal, unlike lithium, it does not react with nitrogen under normal conditions and, unlike barium, calcium, magnesium and a number of other metals, is not able to form compounds with nitrogen even at strong heating.
Cesium hydroxide is the strongest base with the highest electrical conductivity in aqueous solution; so, for example, when working with it, it must be taken into account that a concentrated CsOH solution destroys glass even at ordinary temperatures, and the melt destroys iron, cobalt, nickel, as well as platinum, corundum and zirconium dioxide, and even gradually destroys silver and gold (in the presence of oxygen very quickly). The only metal stable in a cesium hydroxide melt is rhodium and some of its alloys.
Cesium
CESIUM-I; m.[from lat. caesius - blue] Chemical element (Cs), a soft silvery alkali metal (used in gas lasers).
◁ Cesium, -th, -th. C. cathode. C-th coating.
cesium(lat. Caesium), a chemical element of group I of the periodic system, belongs to the alkali metals. Name from lat. caesius - blue (discovered by bright blue spectral lines). Silver-white metal, fusible, soft as wax; density 1.904 g / cm 3, t pl 28.4°C. It ignites in air, reacts explosively with water. The main mineral is pollucite. Used in the manufacture of photocathodes and as a getter; cesium vapor - the working fluid in MHD generators, gas lasers.
CESIUMCesium (lat. Cesium), Cs (read "cesium"), a chemical element with atomic number 55, atomic mass 132.9054. It has one stable nuclide 133 Cs. It is located in group IA in the 6th period. Electronic configuration of outer layer 6 s 1, in compounds exhibits an oxidation state of +1 (valency I). The radius of the neutral cesium atom is 0.266 nm, the radius of the Cs + ion is 0.181 nm (coordination number 6), 0.202 (coordination number 12). The energies of successive ionization of an atom are 3.89397, 25.1 and 34.6 eV. Electron affinity 0.47 eV. The electron work function is 1.81 eV. Electronegativity according to Pauling (cm. PAULING Linus) 0,7.
Cesium was discovered in 1860 by German scientists R. W. Bunsen (cm. Bunsen, Robert Wilhelm) and G. Kirchhoff (cm. Kirchhoff Gustav Robert) in the waters of the Durchheim mineral spring in Germany by spectral analysis. Named cesium for two bright lines in the blue part of the spectrum (from Latin caesius - sky blue). Cesium metal was first isolated in 1882 by the Swedish chemist K. Setterberg during the electrolysis of a melted mixture of CsCN and Ba.
The content in the earth's crust is 3.7·10 -4% by weight. A typical rare, trace element. Geochemically it is closely associated with granitic magma, forming concentrations in pegmatites together with Li, Be, Ta, Nb. Two extremely rare cesium minerals are known: pollucite, (Cs,Na) n H 2 O and avogadrite, (K, Cs) 4 . As an impurity, 0.0003-5%, cesium is contained in lepidolite (cm. LEPIDOLITH),
phlogopite (cm. PHLOGOPITE),
carnallite (cm. CARNALLITE).
Receipt
Cesium is obtained from pollucite by vacuum thermal reduction. The ore is enriched, then the isolated concentrate is decomposed with hydrochloric or sulfuric acids or sintered with oxide-salt mixtures, CaO and CaCl 2 . Cesium is precipitated from pollucite decomposition products in the form of CsAl(SO 4) 2 or Cs 3 . The precipitates are then converted into soluble salts. Particularly pure cesium compounds are obtained by further fractional crystallization, sorption, extraction and ion exchange. Cesium metal is obtained by metallothermic reduction of cesium chloride CsCl with calcium (cm. CALCIUM) or magnesium (cm. MAGNESIUM) or electrolysis of a molten halide (cm. halides) cesium. Cesium is stored in Pyrex glass ampoules in an argon atmosphere or in sealed steel vessels under a layer of dehydrated vaseline or paraffin oil.
Physical and chemical properties
Cesium is a soft, silvery-white metal. At ordinary temperature, it is in a pasty state, melting point 28.44°C. Boiling point 669.2°C. Body-centered cubic crystal lattice, cell parameter a= 0.6141 nm. Density 1.904 kg / dm 3. Cesium has a high sensitivity to light, the cesium cathode emits electrons even under the influence of infrared (cm. INFRARED RADIATION) radiation with a wavelength of up to 0.80 microns.
Cesium is extremely reactive. Standard electrode potential -2.923 V. In air and in an oxygen atmosphere (cm. OXYGEN) cesium ignites instantly, forming a mixture of Cs 2 O 2 peroxide and CsO 2 cesium superoxide. With a low oxygen content in the gas with which cesium reacts, the formation of oxide Cs 2 O is possible. Cesium reacts explosively with water:
2Cs + 2H 2 O \u003d 2CsOH + H 2
When heated under high pressure in the presence of a catalyst, cesium reacts with hydrogen to form CsH hydride. Interacting with halogens, it gives CsCl halides, with sulfur - Cs 2 S sulfide. Under normal conditions, cesium does not react with nitrogen, and Cs 3 N cesium nitride is formed by passing an electric discharge between cesium electrodes placed in liquid nitrogen. When heated, cesium reacts with red phosphorus to form the phosphide Cs 2 P 5 .
When heated, it interacts with graphite, giving the following carbides C 8 Cs, C 24 Cs, C 36 Cs, Cs 2 C 2 (cesium acetylenide). Cesium reduces silicon from glass and from SiO 2 . Cesium forms intermetallic compounds with many metals. (cm. METALLIDES)(CsAu, CsSn 4). Cesium hydroxide CsOH is a strong, water-soluble base. Cesium salts (CsCl chloride, Cs 2 SO 4 sulfate, CsNO 3 nitrate, Cs 2 CO 3 carbonate and others) are highly soluble in water. Cesium perchlorate CsClO 4 , cesium chloroplatinate Cs 2 PtCl 6 and Cs 2 are poorly soluble in water.
Cesium is a component of various photocathodes, photocells, photomultipliers, cathode ray tubes. Cesium is used as a getter. (cm. GETTER) Extremely accurate "atomic cesium clock", the resonant frequency of the energy transition between the sublevels of the ground state of 133 Cs is the basis of the modern definition of the second (cm. SECOND). Radionuclide 137 Cs is a source of gamma radiation in radiology.
Cesium is a permanent chemical microcomponent of the organism of plants and animals. Seaweeds contain 0.01-0.1 µg/g of cesium, land plants - 0.05-0.2 µg/g. Mammals contain 0.05 µg/g of cesium, where it is concentrated in the muscles, heart, and liver. In the blood, up to 2.8 µg/l, cesium is relatively low toxic. Isotope 137 Cs b-, g-emitting radioisotope, one of the components of radioactive pollution of the atmosphere.
encyclopedic Dictionary. 2009 .
Synonyms:See what "cesium" is in other dictionaries:
Very soft silvery metal; does not occur in the free state, but only in compounds. A complete dictionary of foreign words that have come into use in the Russian language. Popov M., 1907. Cesium is an alkali metal recently discovered through ... ... Dictionary of foreign words of the Russian language
CESIUM- chem. element, symbol Cs (lat. Caesium), at. n. 55, at. m. 132.9, belongs to the group of alkali metals, always exhibits an oxidation state of + 1. Cesium is soft, like wax, pale golden in color, light (density 1900 kg / m3) metal, temperature ... ... Great Polytechnic Encyclopedia
- (symbol Cs), a rare silvery white metal of the first group of the periodic table. The most alkaline element, with a positive electrical charge. Cesium was discovered in 1860. It is ductile and is used in photovoltaic cells. Isotope ... ... Scientific and technical encyclopedic dictionary
Cs (from lat. caesius blue; lat. Caesium * a. caesium; n. Zasium; f. cesium; and. cesio), chem. element of group I periodic. system of Mendeleev, refers to alkali metals, at. n. 55, at. m. 132.9054. It occurs in nature in the form of ... ... Geological Encyclopedia
Pollucite Dictionary of Russian synonyms. cesium n., number of synonyms: 3 metal (86) pollucite ... Synonym dictionary
Cesium- (Cesium), Cs, chemical element of group I of the periodic system, atomic number 55, atomic mass 132.9054; soft alkali metal. Discovered by German scientists R. Bunsen and G. Kirchhoff in 1860; cesium metal was isolated by the Swedish chemist K. ... ... Illustrated Encyclopedic Dictionary
- (lat. Caesium) Cs, a chemical element of group I of the periodic system of Mendeleev, atomic number 55, atomic mass 132.9054. Named from the Latin caesius blue (discovered by bright blue spectral lines). Silvery white metal from the group ... ... Big Encyclopedic Dictionary
cesium, cesium, pl. no, husband. (from lat. caesius blue) (chem.). Chemical element, soft silver metal. Explanatory Dictionary of Ushakov. D.N. Ushakov. 1935 1940 ... Explanatory Dictionary of Ushakov
- (lat. Caesium), Cs, chem. element of group I, periodic. systems of elements, at. number 55, at. weight 132.9054, alkali metal. In nature, it is represented by stable Cs. External configuration electron shell 6s1. Energy will follow. ionization 3.894;… … Physical Encyclopedia
- (chem. Caesium; Cs=133 at O=16, average of the definitions of Bunsen, Johnson with Allen and Godefroy, 1861 1876) the first discovered metal with the assistance of spectral analysis. He got this name from caesius sky blue, azure for the color of two sharp ... ... Encyclopedia of Brockhaus and Efron
CESIUM- Cesium, Cs, chem. element with at. in. 132.7. It belongs to the II group of alkali metals. In its properties, zinc is very similar to the elements potassium and rubidium. C. discovered in 1860 by Bunsen and Kirchhoff .. It occurs in nature in very small quantities ... ... Big Medical Encyclopedia
No isotopes other than the stable 133 Cs have been found in natural cesium. There are 33 known radioactive isotopes of cesium with mass numbers from 114 to 148. In most cases, they are short-lived: half-lives are measured in seconds and minutes, less often - several hours or days. However, three of them do not decay so quickly - these are 134 Cs, 137 Cs and 135 Cs with half-lives of 2 years, 30 years and 3·10 6 years. All three isotopes are produced by the decay of uranium, thorium and plutonium in nuclear reactors or during nuclear weapons testing.
+1 oxidation state.
In 1846, cesium silicate, pollucite, was discovered in the pegmatites of Elba Island in the Tyrrhenian Sea. When studying this mineral, cesium, unknown at that time, was mistaken for potassium. The potassium content was calculated from the mass of the platinum compound, with the help of which the element was transferred to an insoluble state. Since potassium is lighter than cesium, the calculation of the results of chemical analysis showed a shortage of about 7%. This mystery was solved only after the discovery of the spectral method of analysis by the German scientists Robert Bunsen and Gustav Kirchhoff in 1859. Bunsen and Kirchhoff discovered cesium in 1861. Initially, it was found in the mineral waters of the healing springs of the Black Forest. Cesium was the first of the elements discovered by spectroscopy. Its name reflects the color of the brightest lines in the spectrum (from the Latin caesius - sky blue).
The discoverers of cesium failed to isolate this element in a free state. Metallic cesium was first obtained only 20 years later, in 1882, by the Swedish chemist K. Setterberg (Setterberg C.) by electrolysis of a molten mixture of cesium and barium cyanides, taken in a ratio of 4:1. Barium cyanide was added to lower the melting point, but it was difficult to work with cyanides due to their high toxicity, and barium contaminated the final product, and the yield of cesium was very small. A more rational method was found in 1890 by the famous Russian chemist N.N. Beketov, who proposed to reduce cesium hydroxide with metallic magnesium in a stream of hydrogen at elevated temperature. Hydrogen filled the device and prevented the oxidation of cesium, which was distilled off into a special receiver; however, in this case, the yield of cesium did not exceed 50% of the theoretical one.
Cesium in nature and its industrial extraction.
Cesium is a rare element. It occurs in a diffuse state (on the order of thousandths of a percent) in many rocks; trace amounts of this metal have also been found in seawater. It is found in higher concentrations (up to several tenths of a percent) in some potassium and lithium minerals, mainly in lepidolite. Unlike rubidium and most other rare elements, cesium forms its own minerals - pollucite, avogadrite and rhodicite.
Rodicite is extremely rare. It is often referred to as lithium minerals, since its composition (M 2 O 2Al 2 O 3 3B 2 O 3, where M 2 O is the sum of alkali metal oxides) usually contains more lithium than cesium. Avogadrite (K,Cs) is also rare. Most cesium is found in pollucite (Cs,Na) n H 2 O (Cs 2 O content is 29.8–36.7% by weight).
Data on world cesium resources are very limited. Their estimates are based on pollucite mined as a by-product along with other pegmatite minerals.
Canada is the leader in pollucite mining. The Bernick Lake deposit (southeastern Manitoba) contains 70% of the world's cesium reserves (about 73 thousand tons). Pollucite is also mined in Namibia and Zimbabwe, whose resources are estimated at 9 thousand tons and 23 thousand tons of cesium, respectively. In Russia, pollucite deposits are located on the Kola Peninsula, in the Eastern Sayan Mountains and Transbaikalia. They are also available in Kazakhstan, Mongolia and Italy (Elba Island).
To open this mineral and transfer valuable components, it is processed into a soluble form by heating with concentrated mineral acids. If the pollucite is decomposed with hydrochloric acid, then Cs 3 is precipitated from the resulting solution by the action of SbCl 3 , which is then treated with hot water or an ammonia solution. When pollucite is decomposed with sulfuric acid, cesium alum CsAl (SO 4) 2 12H 2 O is obtained.
Another method is also used: pollucite is sintered with a mixture of calcium oxide and calcium chloride, the cake is leached in an autoclave with hot water, the solution is evaporated to dryness with sulfuric acid, and the residue is treated with hot water. After separation of calcium sulfate, cesium compounds are isolated from the solution.
Modern methods for extracting cesium from pollucite are based on the preliminary fusion of concentrates with an excess of lime and a small amount of fluorspar. If the process is carried out at 1200 ° C, then almost all cesium sublimates in the form of Cs 2 O oxide. This sublimation is contaminated with an admixture of other alkali metals, but it is soluble in mineral acids, which simplifies further operations. Metallic cesium is extracted by heating a mixture (1:3) of crushed pollucite with calcium or aluminum to 900 ° C.
But, basically, cesium is obtained as a by-product in the production of lithium from lepidolite. Lepidolite is pre-fused (or sintered) at a temperature of about 1000 ° C with gypsum or potassium sulfate and barium carbonate. Under these conditions, all alkali metals are converted into easily soluble compounds - they can be leached with hot water. After the isolation of lithium, it remains to process the resulting filtrates, and here the most difficult operation is the separation of cesium from rubidium and a huge excess of potassium.
To separate cesium, rubidium and potassium and obtain pure cesium compounds, methods of multiple crystallization of alum and nitrates, precipitation and recrystallization of Cs 3 or Cs 2 are used. Chromatography and extraction are also used. Polyhalides are used to obtain high purity cesium compounds.
Most of the cesium produced comes from lithium production, so when lithium began to be used in fusion devices and widely used in automotive lubricants in the 1950s, the production of lithium, like cesium, increased and cesium compounds became more available than before.
Data on world production and consumption of cesium and its compounds have not been published since the late 1980s. The market for cesium is small and its annual consumption is estimated at only a few thousand kilograms. As a result, there is no trade and no official market prices.
Characterization of a simple substance, industrial production and use of metallic cesium.
Cesium is a golden yellow metal, one of three intensely colored metals (along with copper and gold). After mercury, it is the most fusible metal. Cesium melts at 28.44 ° C, boils at 669.2 ° C. Its vapors are colored greenish-blue.
The fusibility of cesium is combined with great lightness. Despite the rather large atomic mass of the element, its density at 20 ° C is only 1.904 g / cm 3. Cesium is much lighter than its neighbors on the Periodic Table. Lanthanum, for example, which has almost the same atomic mass, is more than three times as dense as cesium. Cesium is only twice as heavy as sodium, while their atomic mass ratio is 6:1. Apparently, the reason for this lies in the electronic structure of cesium atoms (one electron on the last s-sublevel), leading to the fact that the metallic radius of cesium is very large (0.266 nm).
Cesium has another very important property related to its electronic structure - it loses its single valence electron more easily than any other metal; this requires very little energy - only 3.89 eV, therefore, for example, obtaining plasma from cesium requires much less energy than when using any other chemical element.
In sensitivity to light, cesium is superior to all other metals. The cesium cathode emits a stream of electrons even when exposed to infrared rays with a wavelength of 0.80 microns. The maximum electron emission occurs in cesium when illuminated with green light, while in other light-sensitive metals this maximum appears only when exposed to violet or ultraviolet rays.
Chemically, cesium is very active. In air, it instantly oxidizes with ignition, forming CsO 2 superoxide with an admixture of Cs 2 O 2 peroxide. Cesium is capable of absorbing the smallest traces of oxygen in a deep vacuum. With water, it reacts explosively to form CsOH hydroxide and release hydrogen. Cesium reacts even with ice at -116°C. Its storage requires great care.
Cesium also interacts with carbon. Only the most perfect modification of carbon - diamond - is able to withstand cesium. Liquid molten cesium and its vapors loosen soot, charcoal and even graphite, penetrating between carbon atoms and giving fairly strong golden-yellow compounds. At 200–500°C, a compound of composition C 8 Cs 5 is formed, and at higher temperatures, C 24 Cs, C 36 Cs. They ignite in air, displace hydrogen from water, and when heated strongly decompose and release all absorbed cesium.
Even at ordinary temperatures, the reactions of cesium with fluorine, chlorine, and other halogens are accompanied by ignition, and with sulfur and phosphorus, by an explosion. When heated, cesium combines with hydrogen. Under normal conditions, cesium does not interact with nitrogen. Cs 3 N nitride is formed in reaction with liquid nitrogen during an electric discharge between electrodes made of cesium.
Cesium dissolves in liquid ammonia, alkylamines, and polyesters, forming blue solutions that are electronically conductive. In an ammonia solution, cesium slowly reacts with ammonia to release hydrogen and form the amide CsNH 2 .
Alloys and intermetallic compounds of cesium are relatively fusible. Cesium auride CsAu, in which a partially ionic bond is realized between gold and cesium atoms, is a semiconductor n-type.
The best solution to the problem of obtaining metallic cesium was found in 1911 by the French chemist A. Axpil. According to his method, which is still the most common, cesium chloride is reduced with metallic calcium in a vacuum:
2CsCl + Ca → CaCl 2 + 2Cs
while the reaction goes almost to the end. The process is carried out at a pressure of 0.1–10 Pa and a temperature of 700–800 ° C. The released cesium evaporates and is distilled off, and calcium chloride remains completely in the reactor, since under these conditions the volatility of the salt is negligible (the melting point of CaCl 2 is 773 ° C) . As a result of repeated distillation in vacuum, absolutely pure metallic cesium is obtained.
Many other methods for obtaining metallic cesium from its compounds have also been described. Metal calcium can be replaced by its carbide, however, the reaction temperature has to be increased to 800 ° C, so the final product is contaminated with additional impurities. The electrolysis of a cesium halide melt is also carried out using a liquid lead cathode. As a result, an alloy of cesium with lead is obtained, from which cesium metal is isolated by distillation in vacuum.
It is possible to decompose cesium azide or reduce its dichromate with zirconium, but these reactions are sometimes accompanied by an explosion. When cesium dichromate is replaced by chromate, the reduction process proceeds smoothly, and although the yield does not exceed 50%, very pure metallic cesium is distilled off. This method is applicable to obtain small amounts of metal in a special vacuum device.
World production of cesium is relatively small.
Metallic cesium is a component of the cathode material for photocells, photomultipliers, television transmitting cathode-ray tubes. Photocells with a complex silver-cesium photocathode are especially valuable for radar: they are sensitive not only to visible light, but also to invisible infrared rays and, unlike, for example, selenium ones, they work without inertia. Antimony-cesium photocells are widely used in television and cinema; their sensitivity even after 250 hours of operation falls by only 5-6%, they work reliably in the temperature range from -30 ° C to + 90 ° C. They are the so-called multi-stage photocells; in this case, under the action of electrons caused by light rays in one of the cathodes, secondary emission occurs - electrons are emitted by additional photocathodes of the device. As a result, the total electric current that occurs in the photocell is multiplied many times over. Current amplification and sensitivity increase are also achieved by filling cesium photocells with an inert gas (argon or neon).
Metallic cesium is used for the manufacture of special rectifiers, in many respects superior to mercury ones. It is used as a coolant in nuclear reactors, a component of lubricants for space technology, a getter in vacuum electronic devices. Metallic cesium also exhibits catalytic activity in the reactions of organic compounds.
Cesium is used in atomic time standards. Cesium clocks are remarkably accurate. Their action is based on transitions between two states of the cesium atom with parallel and antiparallel orientation of the intrinsic magnetic moments of the atomic nucleus and the valence electron. This transition is accompanied by oscillations with strictly constant characteristics (wavelength 3.26 cm). In 1967, the International General Conference on Weights and Measures established: "A second is a time equal to 9,192,631,770 periods of radiation corresponding to the transition between two hyperfine levels of the ground state of the cesium-133 atom."
Recently, much attention has been paid to cesium plasma, a comprehensive study of its properties and conditions of formation; perhaps it will be used in plasma engines of the future. In addition, work on the study of cesium plasma is closely related to the problem of controlled thermonuclear fusion. Many believe that it is expedient to create cesium plasma using the thermal energy of nuclear reactors.
Cesium is stored in glass ampoules in an argon atmosphere or in steel sealed vessels under a layer of dehydrated vaseline oil. Dispose of metal residues by treatment with pentanol.
Cesium compounds.
Cesium forms binary compounds with most non-metals. Cesium hydrides and deuterides are highly flammable in air and in fluorine and chlorine atmospheres. Unstable, and sometimes flammable and explosive compounds of cesium with nitrogen, boron, silicon and germanium. The halides and salts of most acids are more stable.
Compounds with oxygen. Cesium forms nine compounds with oxygen, ranging in composition from Cs 7 O to CsO 3 .
Cesium oxide Cs 2 O forms brown-red crystals, deliquescent in air. It is obtained by slow oxidation with insufficient (2/3 of the stoichiometric) amount of oxygen. The rest of the unreacted cesium is distilled off in a vacuum at 180–200°C. Cesium oxide sublimates in a vacuum at 350–450°C, and decomposes at 500°C:
2Cs 2 O = Cs 2 O 2 + 2Cs
Reacts vigorously with water to give cesium hydroxide.
Cesium oxide is a component of complex photocathodes, special glasses and catalysts. It has been established that when synthol (synthetic oil) is obtained from water gas and styrene from ethylbenzene, as well as in some other syntheses, the addition of a small amount of cesium oxide to the catalyst (instead of potassium oxide) increases the yield of the final product and improves the process conditions.
Hygroscopic pale yellow crystals of cesium peroxide Cs 2 O 2 can be obtained by oxidizing cesium (or its solution in liquid ammonia) with a dosed amount of oxygen. Above 650 ° C, cesium peroxide decomposes with the release of atomic oxygen and vigorously oxidizes nickel, silver, platinum and gold. Cesium peroxide dissolves in ice water without decomposition, and above 25 ° C reacts with it:
2Cs 2 O 2 + 2H 2 O \u003d 4CsOH + O 2
It dissolves in acids to form hydrogen peroxide.
When cesium is burned in air or in oxygen, a golden brown cesium superoxide CsO 2 is formed. Above 350 ° C, it dissociates with the release of oxygen. Cesium superoxide is a very strong oxidizing agent.
Cesium peroxide and superoxide serve as sources of oxygen and are used for its regeneration in space and submarine vehicles.
Cs 2 O 3 sesquioxide is formed as a dark paramagnetic powder upon careful thermal decomposition of cesium superoxide. It can also be obtained by the oxidation of a metal dissolved in liquid ammonia, or by the controlled oxidation of a peroxide. It is assumed that it is dinaperoxide-peroxide [(Cs +)4(O 2 2–)(O 2 –) 2].
Orange-red ozonide CsO 3 can be obtained by the action of ozone on anhydrous powder of cesium hydroxide or peroxide at low temperature. When standing, the ozonide slowly decomposes into oxygen and superoxide, and when hydrolyzed, it immediately turns into hydroxide.
Cesium also forms suboxides, in which the formal oxidation state of the element is much lower than +1. The oxide composition Cs 7 O has a bronze color, its melting point is 4.3 ° C, it actively reacts with oxygen and water. In the latter case, cesium hydroxide is formed. When heated slowly, Cs 7 O decomposes into Cs 3 O and cesium. Violet crystals of Cs 11 O 3 melt with decomposition at 52.5 ° C. Red-violet Cs 4 O decomposes above 10.5 ° C. Non-stoichiometric phase Cs 2+ x O changes composition up to Cs 3 O, which decomposes at 166 ° C.
Cesium hydroxide CsOH forms colorless crystals that melt at ° C. The melting points of hydrates are even lower, for example, CsOH H 2 O monohydrate melts with decomposition at 2.5 ° C, and CsOH 3H 2 O trihydrate even -5.5 ° C.
Cesium hydroxide serves as a catalyst for the synthesis of formic acid. With this catalyst, the reaction proceeds at 300°C without high pressure. The yield of the final product is very high - 91.5%.
Cesium halides CsF, CsCl, CsBr, CsI (colorless crystals) melt without decomposition, volatile above the melting point. Thermal stability decreases when moving from fluoride to iodide; bromide and iodide in vapors are partially decomposed into simple substances. Cesium halides are highly soluble in water. In 100 g of water at 25 ° C, 530 g of cesium fluoride, 191.8 g of cesium chloride, 123.5 g of cesium bromide, 85.6 g of cesium iodide are dissolved. Anhydrous chloride, bromide and iodide crystallize from aqueous solutions. Cesium fluoride is released in the form of CsF crystalline hydrates n H 2 O, where n = 1, 1,5, 3.
When interacting with halides of many elements, cesium halides easily form complex compounds. Some of them, such as Cs 3 , are used for the isolation and analytical determination of cesium.
Cesium fluoride is used to obtain organofluorine compounds, piezoelectric ceramics, and special glasses. Cesium chloride is an electrolyte in fuel cells, a flux for welding molybdenum.
Cesium bromide and iodide are widely used in optics and electrical engineering. The crystals of these compounds are transparent to infrared rays with a wavelength of 15 to 30 µm (CsBr) and 24 to 54 µm (CsI). Conventional sodium chloride prisms transmit rays with a wavelength of 14 microns, and potassium chloride - 25 microns, so the use of bromide and cesium iodide instead of sodium and potassium chlorides made it possible to record the spectra of complex molecules in the far infrared region.
If, in the manufacture of fluorescent screens for televisions and scientific equipment, approximately 20% of cesium iodide is introduced between the zinc sulfide crystals, the screens will absorb x-rays better and glow brighter when irradiated with an electron beam.
Scintillation devices for detecting heavy charged particles containing single crystals of cesium iodide activated by thallium have the highest sensitivity of all devices of this type.
Cesium-137.
The 137 Cs isotope is produced in all nuclear reactors (on average, 6 137 Cs nuclei out of 100 uranium nuclei).
Under normal operating conditions of nuclear power plants, releases of radionuclides, including radioactive cesium, are insignificant. The vast majority of nuclear fission products remain in the fuel. According to the data of dosimetric monitoring, the concentration of cesium in the areas where the nuclear power plant is located almost does not exceed the concentration of this nuclide in the control areas.
Difficult situations arise after accidents, when a huge amount of radionuclides enters the external environment and large areas are contaminated. The entry of cesium-137 into the atmosphere was noted during an accident in the South Urals in 1957, where a thermal explosion of a storage of radioactive waste occurred, during a fire at a radiochemical plant in Windenale in the UK in 1957, during the wind removal of radionuclides from the floodplain of Lake. Karachay in the Southern Urals in 1967. The accident at the Chernobyl nuclear power plant in 1986 became a disaster, about 15% of the total radiation contamination fell on the share of cesium-137. The main source of radioactive cesium in the human body is food of animal origin contaminated with the nuclide.
The radionuclide 137 Cs can also be used for human benefit. It is used in flaw detection, as well as in medicine for diagnosis and treatment. Caesium-137 interested specialists in the field of X-ray therapy. This isotope decomposes relatively slowly, losing only 2.4% of its original activity per year. It proved to be suitable for the treatment of malignant tumors. Cesium-137 has certain advantages over radioactive cobalt-60: a longer half-life and less hard g-radiation. In this regard, devices based on 137 Cs are more durable, and radiation protection is less cumbersome. However, these advantages become real only in the absence of 134 Cs impurities with a shorter half-life and harder g-radiation.
From solutions obtained during the processing of radioactive waste from nuclear reactors, 137 Cs is extracted by co-precipitation with iron, nickel, zinc hexacyanoferrates or ammonium fluorotungstate. Ion exchange and extraction are also used.
Elena Savinkina
