The discovery of tellurium (English Tellurium, German Tellur, French Tellure) dates back to the beginning of the heyday of chemical analytical research in the second half of the 18th century. By that time, new gold-bearing ore had been discovered in Austria in the Semigorye region (Transylvania). It was then called paradoxical gold (Aurum paradoxicum), white gold (Aurum album), problematic gold (Aurum problematicum), since mineralogists knew nothing about the nature of this ore, but miners believed that it contained bismuth or antimony. In 1782, Müller (later Baron Reichenstein), a mining inspector in Semigorye, examined the ore and isolated from it, as he believed, a new metal. To verify his discovery, Müller sent a sample of the “metal” to the Swedish analytical chemist Bergman. Bergman, then already seriously ill, began research, but managed to establish only that the new metal differed in chemical properties from antimony. Bergman's death, which soon followed, interrupted the research and more than 16 years passed before it resumed. Meanwhile, in 1786, Kitaibel, a professor of botany and chemistry at the University of Pest, isolated from the mineral wehrlite (containing tellurides of silver, iron and bismuth) some metal that he considered hitherto unknown. Kitaibel compiled a description of the new metal, but did not publish it, but only sent it to some scientists. So it came to the Viennese mineralogist Estner, who introduced Klaproth to it. The latter gave a favorable review of Kitaibel's work, but the existence of the new metal had not yet been conclusively confirmed. Klaproth continued his research on Kitaibel and as a result completely eliminated all doubts. In January 1798, he made a presentation to the Berlin Academy of Sciences about his discovery of a special metal (!) in Transylvanian “white gold”, which was obtained “from mother earth” and was therefore named tellurium (Tellur) from the word tellus earth (planet). Indeed, the first decades of the 19th century. tellurium was classified as a metal. In 1832 Berzelius drew attention to the similarity of tellurium with selenium and sulfur (which had been pointed out before), after which tellurium was classified as a metalloid (according to Berzelius’ nomenclature). In Russian chemical literature of the early 19th century. the new element was called tellurium, tellurium, tellurium, tellurium; After the appearance of Hess's chemistry textbook, the name tellurium took root.
It is unlikely that anyone will believe the story about the sea captain, who, in addition, is a professional circus wrestler, a famous metallurgist and a consultant physician at a surgical clinic. In the world of chemical elements, such a variety of professions is a very common phenomenon, and Kozma Prutkov’s expression does not apply to them: “A specialist is like gumboil: his completeness is one-sided.” Let us remember (even before talking about the main object of our story) iron in cars and iron in blood, iron is a magnetic field concentrator and iron is an integral part of ocher... True, the “professional training” of elements sometimes took much more time than preparation intermediate yoga. So element No. 52, which we are about to talk about, was used for many years only to demonstrate what it really is, this element named after our planet: “tellurium” - from tellus, which in Latin means “Earth” "
This element was discovered almost two centuries ago. In 1782, mining inspector Franz Joseph Müller (later Baron von Reichenstein) examined gold ore found in Semigorye, in what was then Austria-Hungary. It turned out to be so difficult to decipher the composition of the ore that it was called Aurum problematicum - “doubtful gold.” It was from this “gold” that Muller isolated a new metal, but there was no complete confidence that it was truly new. (It later turned out that Müller was wrong about something else: the element he discovered was new, but it can only be classified as a metal with great reserve.)
To dispel doubts, Müller turned for help to a prominent specialist, the Swedish mineralogist and analytical chemist Bergman.
Unfortunately, the scientist died before finishing the analysis of the sent substance - in those years, analytical methods were already quite accurate, but the analysis took a lot of time.
Other scientists also tried to study the element discovered by Müller, but only 16 years after its discovery, Martin Heinrich Klaproth, one of the leading chemists of that time, irrefutably proved that this element was actually new and proposed the name “tellurium” for it.
As always, after the discovery of the element, the search for its applications began. Apparently, based on the old principle dating back to the times of atrochemistry - the world is a pharmacy, the Frenchman Fournier tried to treat some serious diseases with tellurium, in particular leprosy. But without success - only many years later was tellurium able to provide doctors with some “minor services”. More precisely, not tellurium itself, but salts of telluric acid K 2 Te0 3 and Na 2 Te0 3, which began to be used in microbiology as dyes that give a certain color to the bacteria being studied. Thus, with the help of tellurium compounds, the diphtheria bacillus is reliably isolated from a mass of bacteria. If not in treatment, then at least in diagnosis, element No. 52 turned out to be useful to doctors.
But sometimes this element, and even more so some of its compounds, add trouble to doctors. Tellurium is quite toxic. In our country, the maximum permissible concentration of tellurium in the air is 0.01 mg/m3. Of the tellurium compounds, the most dangerous is hydrogen telluride H 2 Te, a colorless poisonous gas with an unpleasant odor. The latter is quite natural: tellurium is an analogue of sulfur, which means that H 2 Te should be similar to hydrogen sulfide. It irritates the bronchi and has a harmful effect on the nervous system.
These unpleasant properties did not prevent tellurium from entering technology and acquiring many “professions.”
Metallurgists are interested in tellurium because even small additions to lead greatly increase the strength and chemical resistance of this important metal. Lead doped with tellurium is used in the cable and chemical industries. Thus, the service life of sulfuric acid production devices coated on the inside with a lead-tellurium alloy (up to 0.5% Te) is twice as long as that of the same devices lined simply with lead. The addition of tellurium to copper and steel facilitates their machining.
In glass production, tellurium is used to give glass a brown color and a higher refractive index. In the rubber industry, it is sometimes used as an analogue of sulfur for the vulcanization of rubbers.
Tellurium - semiconductor
However, these industries were not responsible for the jump in prices and demand for element No. 52. This jump occurred in the early 60s of our century. Tellurium is a typical semiconductor, and a technological semiconductor. Unlike germanium and silicon, it melts relatively easily (melting point 449.8 ° C) and evaporates (boils at a temperature just below 1000 ° C). Consequently, it is easy to obtain thin semiconductor films from it, which are of particular interest to modern microelectronics.
However, pure tellurium as a semiconductor is used to a limited extent - for the manufacture of field-effect transistors of some types and in devices that measure the intensity of gamma radiation. Moreover, a tellurium impurity is deliberately introduced into gallium arsenide (the third most important semiconductor after silicon and germanium) in order to create electronic-type conductivity in it.
The scope of application of some tellurides - compounds of tellurium with metals - is much broader. Tellurides of bismuth Bi 2 Te 3 and antimony Sb 2 Te 3 have become the most important materials for thermoelectric generators. To explain why this happened, let's take a short digression into the field of physics and history.
A century and a half ago (in 1821), the German physicist Seebeck discovered that in a closed electrical circuit consisting of different materials, the contacts between which are at different temperatures, an electromotive force is created (it is called thermo-emf). After 12 years, the Swiss Peltier discovered an effect opposite to the Seebeck effect: when an electric current flows through a circuit composed of different materials, at the contact points, in addition to the usual Joule heat, a certain amount of heat is released or absorbed (depending on the direction of the current).
For approximately 100 years, these discoveries remained “things in themselves”, curious facts, nothing more. And it would not be an exaggeration to say that a new life for both of these effects began after Academician A.F. Ioffe and his colleagues developed the theory of using semiconductor materials for the manufacture of thermoelements. And soon this theory was embodied in real thermoelectric generators and thermoelectric refrigerators for various purposes.
In particular, thermoelectric generators, which use tellurides of bismuth, lead and antimony, provide energy to artificial Earth satellites, navigation and meteorological installations, and cathodic protection devices for main pipelines. The same materials help maintain the desired temperature in many electronic and microelectronic devices.
In recent years, another tellurium chemical compound with semiconductor properties, cadmium telluride CdTe, has attracted great interest. This material is used for the manufacture of solar cells, lasers, photoresistors, and radioactive radiation counters. Cadmium telluride is also famous for the fact that it is one of the few semiconductors in which the Han effect is noticeably manifested.
The essence of the latter is that the very introduction of a small plate of the corresponding semiconductor into a sufficiently strong electric field leads to the generation of high-frequency radio emission. The Hahn effect has already found application in radar technology.
In conclusion, we can say that quantitatively the main “profession” of tellurium is alloying lead and other metals. Qualitatively, the main thing, of course, is the work of tellurium and tellurides as semiconductors.
Useful admixture
In the periodic table, tellurium is located in the main subgroup of group VI next to sulfur and selenium. These three elements are similar in chemical properties and often accompany each other in nature. But the share of sulfur in the earth's crust is 0.03%, selenium is only 10-5%, tellurium is even an order of magnitude less - 10-6%. Naturally, tellurium, like selenium, is most often found in natural sulfur compounds - as an impurity. It happens, however (remember the mineral in which tellurium was discovered) that it comes into contact with gold, silver, copper and other elements. More than 110 deposits of forty tellurium minerals have been discovered on our planet. But it is always mined together with either selenium, or gold, or other metals.
In Russia, copper-nickel tellurium-containing ores of Pechenga and Monchegorsk, tellurium-containing lead-zinc ores of Altai and a number of other deposits are known.
Tellurium is isolated from copper ore at the stage of purifying blister copper by electrolysis. A sediment - sludge - falls to the bottom of the electrolyser. This is a very expensive intermediate product. To illustrate the composition of the sludge from one of the Canadian plants: 49.8% copper, 1.976% gold, 10.52% silver, 28.42% selenium and 3.83% tellurium. All these valuable components of the sludge must be separated, and there are several ways to do this. Here's one of them.
The sludge is melted in a furnace and air is passed through the melt. Metals, except gold and silver, oxidize and turn into slag. Selenium and tellurium are also oxidized, but into volatile oxides, which are captured in special devices (scrubbers), then dissolved and converted into acids - selenium H 2 SeO3 and telluric H 2 TeO3. If sulfur dioxide S0 2 is passed through this solution, reactions will occur
H 2 Se0 3 + 2S0 2 + H 2 0 → Se ↓ + 2H 2 S0 4 .
H2Te03 + 2S02 + H20 → Te ↓ + 2H 2 S0 4.
Tellurium and selenium fall out at the same time, which is highly undesirable - we need them separately. Therefore, the process conditions are selected in such a way that, in accordance with the laws of chemical thermodynamics, selenium is primarily reduced first. This is helped by selecting the optimal concentration of hydrochloric acid added to the solution.
Tellurium is then deposited. The resulting gray powder, of course, contains a certain amount of selenium and, in addition, sulfur, lead, copper, sodium, silicon, aluminum, iron, tin, antimony, bismuth, silver, magnesium, gold, arsenic, chlorine. Tellurium must first be purified from all these elements by chemical methods, then by distillation or zone melting. Naturally, tellurium is extracted from different ores in different ways.
Tellurium is harmful
Tellurium is being used more and more widely and, therefore, the number of people working with it is increasing. In the first part of the story about element No. 52, we already mentioned the toxicity of tellurium and its compounds. Let's talk about this in more detail - precisely because more and more people have to work with tellurium. Here is a quote from a dissertation on tellurium as an industrial poison: white rats injected with tellurium aerosol “showed restlessness, sneezed, rubbed their faces, and became lethargic and drowsy.” Tellurium has a similar effect on people.
And myself tellurium and its connections can bring troubles of different “calibers”. They, for example, cause baldness, affect blood composition, and can block various enzyme systems. Symptoms of chronic poisoning with elemental tellurium are nausea, drowsiness, emaciation; the exhaled air acquires a foul, garlicky odor of alkyl tellurides.
In case of acute tellurium poisoning, serum with glucose is administered intravenously, and sometimes even morphine. Ascorbic acid is used as a prophylactic. But the main prevention is the reliable sealing of devices, automation of processes in which tellurium and its compounds are involved.
Element No. 52 brings a lot of benefits and therefore deserves attention. But working with it requires caution, clarity and, again, concentrated attention.
APPEARANCE OF TELLURIUM. Crystalline tellurium is most similar to antimony. Its color is silver-white. Crystals are hexagonal, the atoms in them form helical chains and are connected by covalent bonds to their nearest neighbors. Therefore, elemental tellurium can be considered an inorganic polymer. Crystalline tellurium is characterized by a metallic luster, although due to its complex of chemical properties it can rather be classified as a non-metal. Tellurium is brittle and quite easy to turn into powder. The question of the existence of an amorphous modification of tellurium has not been clearly resolved. When tellurium is reduced from telluric or telluric acid, a precipitate forms, but it is still not clear whether these particles are truly amorphous or just very small crystals.
BI-COLORED ANHYDRIDE. As befits an analogue of sulfur, tellurium exhibits valences of 2-, 4+ and 6+ and much less often 2+. Tellurium monoxide TeO can only exist in gaseous form and is easily oxidized to Te0 2. This is a white, non-hygroscopic, completely stable crystalline substance that melts without decomposition at 733 ° C; it has a polymer structure.
Tellurium dioxide is almost insoluble in water - only one part of Te0 2 per 1.5 million parts of water passes into the solution and a solution of weak telluric acid H 2 Te0 3 of negligible concentration is formed. The acidic properties of telluric acid are also weakly expressed.
H 6 TeO 6 . This formula (and not H 2 TeO 4 was assigned to it after salts of the composition Ag 6 Te0 6 and Hg 3 Te0 6 were obtained, which are highly soluble in water. TeO3 anhydride, which forms telluric acid, is practically insoluble in water. This substance exists in two modifications - yellow and gray: α-TeO3 and β-TeO3. Gray tellurium anhydride is very stable: even when heated, it is not affected by acids and concentrated alkalis. It is purified from the yellow variety by boiling the mixture in concentrated caustic potassium.
SECOND EXCEPTION. When creating the periodic table, Mendeleev placed tellurium and its neighboring iodine (as well as argon and potassium) in groups VI and VII not in accordance with, but contrary to their atomic weights. Indeed, the atomic mass of tellurium is 127.61, and that of iodine is 126.91. This means that iodine should not be behind tellurium, but in front of it. Mendeleev, however, did not doubt the right
the correctness of his reasoning, since he believed that the atomic weights of these elements were not determined accurately enough. Mendeleev's close friend, the Czech chemist Boguslav Brauner, carefully checked the atomic weights of tellurium and iodine, but his data coincided with the previous ones. The validity of exceptions confirming the rule was established only when the periodic system was based not on atomic weights, but on nuclear charges, when the isotopic composition of both elements became known. Tellurium, unlike iodine, is dominated by heavy isotopes.
By the way, about isotones. There are currently 22 known isotopes of element No. 52. Eight of them - with mass numbers 120, 122, 123, 124, 125, 126, 128 and 130 - are stable. The last two isotopes are the most common: 31.79 and 34.48%, respectively.
TELLURIUM MINERALS. Although tellurium is significantly less abundant on Earth than selenium, more minerals of element No. 52 are known than those of its counterpart. Tellurium minerals are of two types in composition: either tellurides or products of the oxidation of tellurides in the earth's crust. Among the first are calaverite AuTe 2 and krennerite (Au, Ag) Te2, which are among the few natural gold compounds. Natural tellurides of bismuth, lead, and mercury are also known. Native tellurium is very rarely found in nature. Even before the discovery of this element, it was sometimes found in sulfide ores, but could not be correctly identified. Tellurium minerals have no practical significance - all industrial tellurium is a by-product of processing ores of other metals.
Those - chem. element VI of group of the periodic system of elements; at. n. 52, at. m. 127.60. A shiny silver-gray brittle substance with a metallic sheen. In compounds it exhibits oxidation states of -2, +4 and +6. Natural B consists of eight stable isotopes with mass numbers 120, 122-126, 128 and 130. 16 radioactive isotopes are known with half-lives from 2 to 154 days. The most common are heavy ones with mass numbers 128 and 130. T. was discovered (1782) by the Hungarian. researcher F. Muller von Reichenstein. Tellurium is a trace element; its content in the earth's crust is 10-7%. Contained in many minerals with gold, silver, platinum, copper, iron, lead, bismuth, and sulfide minerals. The crystal lattice of T. is hexagonal with periods a - 4.4570 A and c = 5.9290 A. Density (t-pa 20p C) 6.22 g/cm3; /pl 449.5° C; boiling point 990±2° C.
An “amorphous” modification of Tellurium (dark brown powder) is known, which irreversibly turns crystalline when heated. Temperature coefficient linear expansion of polycrystalline T. (16-17) 10-6 deg-1, y coefficient. thermal conductivity (temperature 20° C) 0.014 cal/cm X X sec x deg; specific heat capacity (temperature 25° C) 0.048 cal/g x deg. T. is a semiconductor with a band gap of 0.34 eV. The electrical conductivity of crystal depends on the purity and degree of perfection of the crystal. In the purest samples it is equal to ~0.02 ohm-1 x cm-1. Electron mobility 1700, hole mobility 1200 cm2/v x sec. When melted, Tellurium transforms into a metallic state. Tellurium is diamagnetic, specific magnetic susceptibility is 0.3 10-6 cm3/g (at room temperature). Hardness on the Mohs scale 2.0-2.5; Wed microhardness 58 kgf/mm2, modulus of elasticity 4200 kgf/mm2, coefficient. compressibility (temperature 30° C) 1.5-10 6 cm2/kgf. Tellurium single crystals with (0001) orientation break brittlely at a stress of 14 kgf/mm2.
According to chemistry Holy T. reminds you of sulfur. , but less active. At room temperature it does not oxidize in air; when heated, it burns to form Te02 dioxide - white crystalline, slightly soluble in water. TeO and Te03, which are less stable than Te02, are also known. Under normal conditions, Tellurium very slowly reacts with water with the release of hydrogen and the formation of sulfuric acid with the formation of a red TeS03 solution; when diluted with water, a reverse reaction occurs with the release of tellurium. T. dissolves in nitric acid to form telluric acid H2TeO3; in dilute hydrochloric acid it dissolves slightly.
Tellurium dissolves slowly in alkalis. With hydrogen it forms telluride H2Te - a colorless gas with an unpleasant odor, condensing at a temperature of -2°C and solidifying at a temperature of -51.2°C, an unstable compound that easily decomposes under the influence of even weak oxidizing agents. Tellurium does not form sulfides that are stable under normal conditions; the TeS2 compound is stable at temperatures down to -20° C. T forms continuous solid solutions with selenium. The known compositions are TeXb (fluoride only), TeX4 and TeX2, which are obtained by direct interaction of elements. At room temperature, everything is solid, partially decomposing with water; only TeFe is a colorless gas with an unpleasant odor. When heated, T. reacts with many metals, forming.
The raw materials for the production of Tellurium are sludge from copper-nickel and sulfuric acid production, as well as products obtained from lead refining. Anode sludge is processed using an acidic or alkaline method, converting sulfur into the tetravalent state and then reducing it with sulfur dioxide from solutions at the end of the solution. hydrochloric or electrolytic. In addition, materials containing T. can be processed using the chlorine method. High-purity tellurium is obtained by sublimation and zone recrystallization (the most effective method of deep purification, allowing to obtain a substance with a purity of 99.9999%).
Tellurium compounds are toxic, their effect on the human body is similar to the effect of selenium and arsenic compounds. The most powerful poison is telluride. The maximum permissible concentration of T in the air is 0.01 mg/mV. T is used in the vulcanization of rubber and in the production of lead cables (the addition of up to 0.1% Te improves the mechanical properties of lead). T. compounds are used in the glass industry (for coloring glass and porcelain) and in photography. Tellurium is widely used in the synthesis of semiconductor compounds. T. connections are the main material for the production of thermoelements.
Tellurium is a trace element (their content in the earth's crust is 1 ⋅ 10⁻ ⁷ %. Tellurium rarely forms independent . It is usually found in nature as impurities in sulfides, as well as in native sulfur. The main sources of tellurium and selenium are waste from sulfuric acid production, which accumulates in dust chambers, as well as sediments (sludge) formed during electrolytic purification of copper. The sludge, among other impurities, also contains silver selenide Ag 2 Se and some. When burning sludge, tellurium oxide TeO is formed 2 , as well as oxides of heavy metals. Tellurium is reduced from TeO oxides 2 when exposed to sulfur dioxide in an aquatic environment:
TeO 2 + H 2 O = H 2 TeO 3
H 2 SeO 3 + 2SO 2 + H 2 O = Se + 2H 2 SO 4
Tellurium, like , forms allotropic modifications - crystalline and amorphous. Crystalline tellurium is silver-gray in color, fragile, and easily ground into powder. Its electrical conductivity is insignificant, but increases when illuminated. Amorphous tellurium is brown in color and less stable than amorphous tellurium at 25 degrees. becomes crystalline.
In terms of chemical properties, tellurium has significant similarities with sulfur. It burns in air (greenish-blue), forming the corresponding oxides TeO 2. Unlike SO 2 Tellurium oxide is a crystalline substance and is poorly soluble in water.
Tellurium does not combine directly with hydrogen. When heated, it reacts with many metals, forming the corresponding salts (), for example K 2 Te. Tellurium reacts with water even under normal conditions:
Te + 2H 2 O = TeO 2 + 2H 2
Like selenium, tellurium is oxidized to the corresponding acids H 2 TeO 4 , but under more severe conditions and the action of other oxidizing agents:
Te + 3H 2 O 2 (30%) = H 6 TeO 6
In boiling aqueous solutions of alkalis, tellurium, like sulfur, slowly dissolves:
3Te + 6KOH = 6K 2 Te + K 2 TeO 3 + 3H 2 O
Tellurium is used primarily as a semiconductor material.
Properties of tellurium
Hydrogen telluride can be prepared by treating tellurides with dilute acids:
Na 2 Te + H 2 SO 4 = Na 2 SO 4 + H 2 Te
Hydrogen telluride under normal conditions is a colorless gas with characteristic unpleasant odors (more unpleasant than the smell of H 2 S, but more toxic, and hydrogen telluride is less toxic). Tellurium hydrides exhibit reducing properties to a greater extent than, and H 2 Te in water is approximately the same as that of hydrogen sulfide. Aqueous solutions of hydrides exhibit a pronounced acidic reaction due to their dissociation in aqueous solutions according to the following scheme:
H 2 Te ↔ H + HTe ⁺
↓
H+Te²⁺
In the series O - S - Se - Te, the radii of their ions are E² ⁺ hold a hydrogen ion. This is confirmed by experimental data, which confirmed that hydrotelluric acid is stronger than hydrosulfide acid.
In the series O - S - Se - Te, the ability for thermal dissociation of hydrides increases: it is most difficult to decompose water when heated, and tellurium hydrides are unstable and decompose even with low heating.
Salts of hydrotelluric acid (tellurides) are similar in properties to sulfides. They are obtained, like sulfides, by the action of tellurium hydrogen on soluble metal salts.
Tellurides are similar to sulfides in terms of solubility in water and acids. For example, when hydrogen tellurium is passed through an aqueous solution of Cu 2 SO 4 copper telluride is obtained:
H 2 Te + CuSO 4 = H 2 SO 4 + CuTe
Te forms TeO compounds with oxygen 2 and TeO 3 they are formed during the combustion of tellurium in air, during the firing of tellurides, and also during the combustion of tellurium hydrides:
Te + O 2 = TeO 2
2ZnTe + 3O 2 = 2ZnO + 2TeO 2
2H 2 Te + 3O 2 = 2H 2 O + 2TeO 2
TeO2 - acid oxides (anhydrides). When dissolved in water, they form, respectively, telluric acid:
TeO 2 + H 2 O = H 2 TeO 3
This acid dissociates in an aqueous solution somewhat less strongly than sulfurous acid. Telluric acid has not been obtained in free form and exists only in aqueous solutions.
While sulfur compounds with an oxidation state of 4+ in chemical reactions predominantly act as reducing agents, with an increase in the oxidation state of sulfur to 6+, TeO 2 and the corresponding acids exhibit mainly oxidizing properties, respectively being reduced to Te. In practice, tellurium is obtained in free form using these methods:
H 2 TeO 3 + 2SO 2 + H 2 O = 2H 2 SO 4 + Te
Telluric acid exhibits reducing properties only when interacting with strong oxidizing agents:
3H 2 TeO 3 + HClO 3 = 3H 2 TeO 4 + HCl
Free telluric acid H 2 TeO 4 - usually isolated as crystalline hydrate H 2 TeO 4 2H 2 O which is written as H 6 TeO 6 . In orthotelluric acid H 6 TeO 6 hydrogen atoms can be partially or completely replaced by metal atoms, forming Na6TeO6 salts.
Discovered by F. Müller in 1782. The name of the element comes from the Latin tellus, genitive telluris, Earth (the name was proposed by M. G. Klaproth, who isolated the element as a simple substance and determined its most important properties).
Receipt:
In nature, it exists as a mixture of 8 stable isotopes (120, 122-126, 128, 130). The content in the earth's crust is 10 -7%. The main minerals are altaite (PbTe), tellurobismuthite (Bi 2 Te 3), tetradymite (Bi 2 Te 2 S), found in many sulfide ores.
It is obtained from copper production sludge by leaching with a NaOH solution in the form of Na 2 TeO 3 , from which tellurium is separated electrolytically. Further purification is by sublimation and zone melting.
Physical properties:
Compact tellurium is a silvery-gray substance with a metallic luster, having a hexagonal crystal lattice (density 6.24 g/cm 3, melting point - 450°C, boiling point - 990°C). From solutions it precipitates in the form of a brown powder; in vapor it consists of Te 2 molecules.
Chemical properties:
Tellurium is stable in air at room temperature; when heated, it reacts with oxygen. Interacts with halogens and reacts with many metals when heated.
When heated, tellurium is oxidized by water vapor to form tellurium(II) oxide and reacts with concentrated sulfuric and nitric acids. When boiled in aqueous solutions of alkalis, it disproportions similarly to sulfur:
8 Te + 6NaOH = Na 2 TeO 3 + 2Na 2 Te + 3H 2 O
In compounds it exhibits oxidation states -2, +4, +6, less often +2.
The most important connections:
Tellurium(IV) oxide Tellurium dioxide, TeO 2, is poorly soluble in water, an acidic oxide, reacts with alkalis to form telluric acid salts. Used in laser technology, a component of optical glasses.
Tellurium(VI) oxide, tellurium trioxide, TeO 3, yellow or gray substance, practically insoluble in water, decomposes when heated to form dioxide, reacts with alkalis. Obtained by the decomposition of telluric acid.
Telluric acid, H 2 TeO 3 , slightly soluble, prone to polymerization, therefore it usually represents a precipitate with variable water content TeO 2 *nH 2 O. Salts - tellurites(M 2 TeO 3) and polytellurites (M 2 Te 2 O 5, etc.), usually obtained by sintering carbonates with TeO 2, are used as components of optical glasses.
Telluric acid, H 6 TeO 6 , white crystals, highly soluble in hot water. A very weak acid, in solution it forms salts of the composition MH 5 TeO 6 and M 2 H 4 TeO 6. When heated in a sealed ampoule, metatelluric acid H 2 TeO 4 was also obtained, which in solution gradually turns into telluric acid. Salts - tellurates. It is also obtained by fusing tellurium(IV) oxide with alkalis in the presence of oxidizing agents, or by fusing telluric acid with carbonate or metal oxide. Alkali metal tellurates are soluble. They are used as ferroelectrics, ion exchangers, and components of luminescent compositions.
Hydrogen telluride, H 2 Te is a poisonous gas with an unpleasant odor, obtained by hydrolysis of aluminum telluride. A strong reducing agent, in solution it is quickly oxidized by oxygen to tellurium. In an aqueous solution, the acid is stronger than sulfur and hydrogen selenide. Salts - tellurides, usually obtained by the interaction of simple substances, alkali metal tellurides are soluble. Many p- and d-element tellurides are semiconductors.
Halides. Tellurium(II) halides, for example TeCl 2 , are known to be salt-like and, when heated and in solution, disproportionate into Te and Te(IV) compounds. Tellurium tetrahalides are solid substances that hydrolyze in solution to form telluric acid and easily form complex halides (for example, K2). TeF 6 hexafluoride, a colorless gas, unlike sulfur hexafluoride, is easily hydrolyzed, forming telluric acid.
Application:
Component of semiconductor materials; alloying additive for cast iron, steel, lead alloys.
World production (without the USSR) is about 216 tons/year (1976).
Tellurium and its compounds are toxic. MPC is about 0.01 mg/m3.
See also:
Tellurium // Wikipedia. . Update date: 12/20/2017. URL: http://ru.wikipedia.org/?oldid=89757888 (access date: 12/25/2017).
Discovery of elements and origin of their names. Tellurium //
URL: http://www.chem.msu.su/rus/history/element/Te.html
Tellurium(lat. Tellurium), Te, chemical element of group VI of the main subgroup of Mendeleev’s periodic system; atomic number 52, atomic mass 127.60, belongs to rare trace elements. It occurs in nature in the form of eight stable isotopes with mass numbers 120, 122-126, 128, 130, of which the most common are 128 Te (31.79%) and 130 Te (34.48%). Of the artificially obtained radioactive isotopes, 127 Te (T ½ = 105 days) and 129 Te (T ½ = 33.5 days) are widely used as labeled atoms. Tellurium was discovered by F. Muller in 1782. The German scientist M. G. Klaproth confirmed this discovery and gave the element the name “tellurium” (from Latin tellus, genus telluris - Earth). The first systematic studies of the chemistry of Tellurium were carried out in the 30s of the 19th century by I. Ya. Berzelius.
Distribution of Tellurium in nature. Tellurium is one of the rarest elements; the average content in the earth's crust (clarke) is ~1·10 -7% by mass. Tellurium is scattered in magma and the biosphere; from some hot underground springs it is deposited along with S, Ag, Au, Pb and other elements. Hydrothermal deposits of Au and non-ferrous metals enriched in Tellurium are known; About 40 minerals of this element are associated with them (the most important are altaite, tellurobismuthite and other natural tellurides). A characteristic admixture of Tellurium in pyrite and other sulfides. Tellurium is extracted from polymetallic ores.
Physical properties of Tellurium. Tellurium is silvery-white in color with a metallic sheen, brittle, and becomes ductile when heated. Crystallizes in the hexagonal system: a = 4.4570Å; c = 5.9290Å; density 6.25 g/cm 3 at 20 "C; melting point 450°C; boiling point 990°C; specific heat at 20°C 0.204 kJ/(kg K); thermal conductivity at 20°C 5.999 W/(m K); temperature coefficient of linear expansion 1.68 10 -5 (20 ° C). Tellurium is diamagnetic, specific magnetic susceptibility at 18 ° C -0.31 10 -6. Brinell hardness 184.3 Mn/m 2 (18.43 kgf/mm 2) Atomic radius 1.7 Å, ionic radii: Te 2- 2.22 Å, Te 4+ 0.89 Å, Te 6+ 0.56 Å.
Tellurium is a semiconductor. The band gap is 0.34 eV. Under ordinary conditions and up to the melting point, pure Tellurium has p-type conductivity. As the temperature decreases in the range (-100 °C) - (-80 °C), a transition occurs: the conductivity of Tellurium becomes n-type. The temperature of this transition depends on the purity of the sample, and the purer the sample, the lower it is.
Chemical properties of Tellurium. The configuration of the outer electron shell of the Te atom is 5s 2 5p 4. In compounds it exhibits oxidation states of -2; +4; + 6, less often +2. Tellurium is a chemical analogue of sulfur and selenium with more pronounced metallic properties. With oxygen, Tellurium forms oxide (II) TeO, oxide (IV) TeO 2 and oxide (VI) TeO 3. TeO exists above 1000 °C in the gas phase. TeO 2 is obtained by combustion of Te in air, has amphoteric properties, is difficult to dissolve in water, but easily soluble in acidic and alkaline solutions. TeO 3 is unstable and can only be obtained from the decomposition of telluric acid. When heated, Tellurium reacts with hydrogen to form hydrogen telluride H 2 Te - a colorless poisonous gas with a pungent, unpleasant odor. Reacts easily with halogens; it is characterized by halides of the type TeX 2 and TeX 4 (where X is Cl and Br); TeF 4 and TeF 6 were also obtained; All of them are highly volatile and hydrolyze with water. Tellurium directly interacts with nonmetals (S, P), as well as with metals; it reacts at room temperature with concentrated nitric and sulfuric acids, in the latter case TeSO 3 is formed, which oxidizes when heated to TeOSO 4. Relatively weak Te acids are known: hydrotelluric acid (solution of H 2 Te in water), telluric acid H 2 TeO 3 and telluric acid H 6 TeO 6 ; their salts (tellurides, tellurites and tellurates, respectively) are slightly or completely insoluble in water (with the exception of alkali metal and ammonium salts). Some organic derivatives of Tellurium are known, for example RTeH, dialkyl tellurides R 2 Te - low-boiling liquids with an unpleasant odor.
Obtaining Tellurium. Tellurium is extracted as a by-product during the processing of sulfide ores from intermediate products of copper and lead-zinc production, as well as from some gold ores. The main source of raw materials for the production of Tellurium is copper electrolysis sludge containing from 0.5 to 2% Te, as well as Ag, Au, Se, Cu and other elements. The sludge is first freed from Cu, Se, the residue containing noble metals, Te, Pb, Sb and other components is melted down to obtain an alloy of gold and silver. In this case, tellurium in the form of Na 2 TeO 3 passes into soda-tellurium slag, where its content reaches 20-35%. The slag is crushed, ground and leached with water. Tellurium is deposited from solution by electrolysis at the cathode. The resulting tellurium concentrate is treated with alkali in the presence of aluminum powder, transferring tellurium into solution in the form of tellurides. The solution is separated from the insoluble residue, which concentrates heavy metal impurities, and is blown with air. In this case, Tellurium (99% pure) is deposited in the elemental state. Tellurium of increased purity is obtained by repeating telluride processing. The purest Tellurium is obtained by a combination of chemical purification, distillation, and zone smelting methods.
Applications of Tellurium. Tellurium is used in semiconductor technology; as an alloying additive - in lead alloys, cast iron and steel to improve their workability and increase mechanical characteristics; Bi 2 Te 3 and Sb 2 Te 3 are used in thermogenerators, and CdTe is used in solar cells and as semiconductor laser materials. Tellurium is also used for bleaching cast iron, vulcanizing latex mixtures, and producing brown and red glasses and enamels.
Tellurium in the body. Tellurium is constantly present in the tissues of plants and animals. In plants growing on soils rich in Tellurium, its concentration reaches 2·10 -4 - 2.5·10 -3%, in terrestrial animals - about 2·10 -6%. In humans, the daily intake of tellurium from food and water is about 0.6 mg; is excreted from the body mainly in urine (over 80%), as well as in feces. Moderately toxic to plants and highly toxic to mammals (causes growth retardation, hair loss, paralysis, etc.).
Occupational poisoning of tellurium is possible during its smelting and other production operations. Chills, headache, weakness, rapid pulse, lack of appetite, metallic taste in the mouth, garlicky smell of exhaled air, nausea, dark coloration of the tongue, irritation of the respiratory tract, sweating, hair loss are observed.
