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 the rare scattered elements. In nature, it occurs 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 1/2 = 105 days) and 129 te (T 1/2 = 33,5 days) . T. was discovered by F. Müller in 1782. The German scientist MG Klaproth confirmed this discovery and gave the element the name tellurium (from the Latin tellus, genitive telluris - Earth). The first systematic studies of the chemistry of T. were carried out in the 1930's. 19th century AND I. Berzelius.

Distribution in nature ... T. is one of the rarest elements; average content in the earth's crust (clarke) ~ 1? 10 -7% by weight. T. is dispersed in magma and biosphere; from some hot underground springs it is deposited together with s, ag, au, pb and other elements. Known hydrothermal deposits of au and non-ferrous metals, enriched in T .; about 40 minerals of this element are associated with them (the most important are altaite, telluric bismuthite, etc. natural tellurides) . An admixture of T. in pyrite and other sulfides is characteristic. T. is extracted from polymetallic ores.

Physical and chemical properties. T. is silvery-white in color with a metallic luster, is fragile, and becomes plastic when heated. Crystallizes in a hexagonal system: a= 4.4570 A; with= 5.9290 A; density 6.25 G/ cm 3 at 20 ° C; t pl 450 ° C; t kip 990 ± 1.0 ° С; specific heat at 20 ° С 0.204 kJ /(kg? TO); thermal conductivity at 20 ° С 5.999 Tue /(m? TO) ; temperature coefficient of linear expansion 1.68? 10 -5 (20 ° C). T. is diamagnetic; the specific magnetic susceptibility at 18 ° C is 0.31 10 -6. Brinell hardness 184.3 Mn / m 2 (18,43 kgf / mm 2) . Atomic radius 1.7 A, ionic radii: Te 2 - 2.22 A, te 4+ 0.89 A, te 6+ 0.56 A.

T. is a semiconductor. Bandgap 0.34 ev. Under normal conditions and up to the melting point, pure T. has a conductivity R-type. With a decrease in temperature in the range (-100 ° C) - (-80 ° C), a transition occurs: the conductivity of T. becomes n-type. the temperature of this transition depends on the purity of the sample, and it is the lower, the cleaner the sample.

The configuration of the outer electron shell of an atom te 5 s 2 5 p 4. In compounds, it exhibits oxidation states of –2; +4; +6, rarely +2. T. - chemical analogue sulfur and Selena with more pronounced metallic properties. With oxygen, T. forms teo oxide, teo 2 dioxide, and teo 3 trioxide. teo exists above 1000 ° C in the gas phase. teo 2 is obtained by combustion of te in air, has amphoteric properties, is hardly soluble in water, but readily in acidic and alkaline solutions. teo 3 is unstable and can only be obtained from the decomposition of telluric acid. When heated, T. 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 halogenides of the tex 2 and tex 4 types (where X is cl and Br); received also tef 4, tef 6; all of them are highly volatile, hydrolyzed by water. T. interacts directly with non-metals (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: telluric acid (solution of h 2 te in water), telluric acid h 2 teo 3 and telluric acid h 6 teo 6; their salts (respectively tellurides, tellurites and tellurites) are slightly or completely insoluble in water (with the exception of alkali metal and ammonium salts). Some organic derivatives of T. are known, for example rteh, dialkyl tellurides r 2 te - low-boiling liquids with an unpleasant odor.

Receiving. T. is extracted along the way during the processing of sulfide ores from intermediate products of copper, lead-zinc production, and also from some gold ores. The main source of raw materials for the production of copper is copper electrolysis slimes 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 remelted in order to obtain an alloy of gold and silver. Thus, in the form of na 2 teo 3, it transforms into soda-telluric slags, where its content reaches 20-35%. Slag is crushed, ground and leached with water. From the solution, T. is deposited by electrolysis at the cathode. The obtained tellurium concentrate is treated with alkali in the presence of aluminum powder, converting the T. into a solution in the form of tellurides. The solution is separated from the insoluble residue, which concentrates the impurities of heavy metals, and is blown through with air. In this case, T. (99% purity) is precipitated in an elemental state. Soap of higher purity is obtained by repeating telluride processing. The purest fuel is obtained by a combination of methods of chemical purification, distillation, and zone melting.

Application. T. is used in semiconductor technology. ; as an alloying additive - in lead alloys, cast iron and steel to improve their machinability and increase mechanical characteristics; bi 2 te 3 and sb 2 te 3 are used in thermogenerators, and cdte - in solar powered and as semiconductor laser materials. T. is also used for bleaching cast iron, vulcanizing latex mixtures, and producing brown and red glasses and enamels.

T.N. Graver.

Tellurium in the body ... T. is constantly present in the tissues of plants and animals. In plants growing on soils rich in T., its concentration reaches 2? 10 -4 -2.5? 10 -3%, in land animals - about 2? 10 -6%. In humans, the daily intake of T. with food and water is about 0.6 mg. excreted from the body mainly in the urine (over 80%), as well as in the feces. Moderately toxic to plants and highly toxic to mammals (causes growth retardation, hair loss, paralysis, etc.).

Occupational poisoning of T. is possible during its smelting and other production operations. Chills, headache, weakness, rapid pulse, lack of appetite, metallic taste in the mouth, garlic smell of exhaled air, nausea, dark color of the tongue, irritation of the respiratory tract, sweating, hair loss are observed. Prevention: compliance with occupational health requirements, personal skin protection measures, medical examinations of workers.

Lit .: Kudryavtsev A, A. Chemistry and technology of selenium and tellurium, 2nd ed., M .. 1968; Fundamentals of Metallurgy, vol. 4, ch. viii, M. 1967; Filyand M. A. Semenova E. I. Properties of rare elements, 2nd ed., M .. 1964; Buketov EA, Malyshev VP. Extraction of selenium and tellurium from copper electrolyte sludge, A.-A .. 1969; bowen h. i. M .. trace elements in biochemistry, l.-n. y .. 1966.

Tellurium Tellurium (lat. Tellurium) is a chemical element with atomic number 52 in the periodic table and atomic weight 127.60; denoted by the symbol Te, belongs to the family of metalloids. In nature, it occurs in the form of eight stable isotopes with mass numbers 120, 128, 130, of which the most common are 128Te and 130Te. Of the artificially obtained radioactive isotopes, 127Te and 129Te are widely used as labeled atoms.

From history It was first found in 1782 in the gold-bearing ores of Transylvania by the mining inspector Franz Josef Müller (later Baron von Reichenstein), on the territory of Austria-Hungary. In 1798 Martin Heinrich Klaproth isolated tellurium and determined its most important properties. The first systematic studies of the chemistry of tellurium were carried out in the 30s. 19th century I. Ya. Berzelius.

"Aurum paradoxum" is a paradoxical gold, so tellurium was called, after it was discovered by Reichenstein at the end of the 18th century in combination with silver and yellow metal in the mineral sylvanite. An unexpected phenomenon seemed the fact that gold, usually always found in a native state, was found in conjunction with tellurium. That is why, having ascribed properties similar to the yellow metal, it was called the paradoxical yellow metal.

The origin of the name Later (1798), when M. Klaproth investigated the new substance in more detail, he named it tellurium in honor of the Earth, the bearer of chemical "miracles" (from the Latin word "tellus" - earth). This name is used by chemists of all countries.

Being in nature The content in the earth's crust is 1 · 10-6% by weight. Metallic tellurium can be found only in the laboratory, but its compounds can be found around us much more often than you might think. About 100 tellurium minerals are known. The most important of them: altaite PbTe, sylvanite AgAuTe 4, calaverite AuTe 2, tetradymite Bi 2 Te 2 S, krennsrite AuTe 2, petcite AgAuTe 2. There are oxygen compounds of tellurium, for example TeO2 telluric ocher. Native tellurium is also found together with selenium and sulfur (Japanese tellurium sulfur contains 0.17% Te and 0.06% Se).

Peltier Module Many people are familiar with Peltier thermoelectric modules, which are used in portable refrigerators, thermoelectric generators and sometimes for extreme cooling of computers. The main semiconductor material in such modules is bismuth telluride. It is currently the most widely used semiconductor material. If you look at the thermoelectric module from the side, you can see rows of small "cubes".

Physical properties Tellurium is silvery-white in color with a metallic luster, brittle, and becomes ductile when heated. Crystallizes in a hexagonal system. Tellurium is a semiconductor. Under normal conditions and up to the melting point, pure Tellurium has p-type conductivity. With a decrease in temperature 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 it is the lower, the cleaner the sample. Density = 6.24 g / cm³ Melting point = 450 ° C Boiling point = 990 ° C Heat of fusion = 17.91 kJ / mol Heat of vaporization = 49.8 kJ / mol Molar heat capacity = 25.8 J / (K mol) Molar volume = 20.5 cm³ / mol

Tellurium is a non-metal. In compounds tellurium exhibits oxidation states: -2, +4, +6 (valence II, IV, VI). Tellurium is chemically less active than sulfur and oxygen. Tellurium is stable in air, but at high temperatures it burns with the formation of TeO 2 dioxide. Te interacts with halogens in the cold. When heated, it reacts with many metals to give tellurides. Let's dissolve in alkalis. Under the action of nitric acid, Te is converted into telluric acid, and under the action of aqua regia or 30% hydrogen peroxide, into telluric acid. Chemical properties 128 Te))))) e = 52, p = 52, n = e 8e 8e 8e 6e

Physiological action When heated, Tellurium interacts with hydrogen to form hydrogen telluride - H 2 Te, a colorless poisonous gas with a pungent, unpleasant odor. Tellurium and its volatile compounds are toxic. Ingestion causes nausea, bronchitis, pneumonia. The maximum permissible concentration in air varies for various compounds 0.0070.01 mg / m³, in water 0.0010.01 mg / l.

Obtaining Main source of copper and lead electrolytic refining sludge. The sludge is calcined, the tellurium remains in the cinder, which is washed with hydrochloric acid. Tellurium is isolated from the obtained hydrochloric acid solution by passing sulfur dioxide SO 2 through it. Sulfuric acid is added to separate selenium and tellurium. This precipitates tellurium dioxide TeO 2, and H 2 SeO 3 remains in solution. Tellurium is reduced from TeO 2 oxide with coal. To purify tellurium from sulfur and selenium, use is made of its ability, under the action of a reducing agent (Al) in an alkaline medium, to transform into soluble disodium ditelluride Na 2 Te 2: 6Te + 2Al + 8NaOH = 3Na 2 Te 2 + 2Na. To precipitate tellurium, air or oxygen is passed through the solution: 2Na 2 Te 2 + 2H 2 O + O 2 = 4Te + 4NaOH. To obtain tellurium of special purity, it is chlorinated with Te + 2Cl 2 = TeCl 4. The resulting tetrachloride is purified by distillation or rectification. Then the tetrachloride is hydrolyzed with water: TeCl 4 + 2H 2 O = TeO 2 + 4HCl, and the formed TeO 2 is reduced with hydrogen: TeO 2 + 4H 2 = Te + 2H 2 O.

Discovered by F. Müller in 1782. The name of the element comes from the Latin tellus, genitive telluris, Earth (the name was suggested by M. G. Klaproth, who singled out the element in the form of a simple substance and determined its most important properties).

Receiving:

In nature, it exists as a mixture of 8 stable isotopes (120, 122-126, 128, 130). Content in the earth's crust is 10 -7%. The main minerals - altaite (PbTe), tellurium bismuthite (Bi 2 Te 3), tetradymite (Bi 2 Te 2 S), are found in many sulfide ores.
It is obtained from copper production slimes by leaching with a NaOH solution in the form of Na 2 TeO 3, from where tellurium is electrolytically released. Further purification - 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 ° С, boiling point - 990 ° С). It precipitates from solutions 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. Reacts with halogens, reacts with many metals when heated.
When heated, tellurium is oxidized by steam to form tellurium (II) oxide, interacts with concentrated sulfuric and nitric acids. When boiled in aqueous solutions of alkalis, it disproportionates similarly to sulfur:
8 Te + 6NаОН = 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, poorly soluble in water, acidic oxide, reacts with alkalis, forming tellurous acid salts. It is 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. Prepared by decomposition of telluric acid.
Tellurous acid, H 2 TeO 3, slightly soluble, prone to polymerization, therefore, it usually represents a precipitate with a 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, readily soluble in hot water. A very weak acid, in solution 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 gradually turns into telluric acid in solution. Salts - tellurates... It is also obtained by fusing tellurium (IV) oxide with alkalis in the presence of oxidizing agents, fusing telluric acid with a carbonate or metal oxide. Alkali metal tellurites are soluble. They are used as ferroelectrics, ion exchangers, 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 rapidly oxidized by oxygen to tellurium. In an aqueous solution, an acid is stronger than hydrogen sulfide and hydrogen selenide. Salts - tellurides, are usually obtained by the interaction of simple substances, tellurides of alkali metals are soluble. Many tellurides of p- and d-elements are semiconductors.
Halides... Tellurium (II) halides are known, for example TeCl 2, which are salt-like; when heated and in solution, they disproportionate to Te and Te (IV) compounds. Tellurium tetrahalides are solids; in solution they hydrolyze to form tellurous acid, easily form complex halides (for example, K 2). Hexafluoride TeF 6, a colorless gas, unlike sulfur hexafluoride, readily hydrolyzes to form telluric acid.

Application:

Semiconductor material component; alloying additive for cast iron, steels, lead alloys.
World production (excluding the USSR) - about 216 tons / year (1976).
Tellurium and its compounds are toxic. MPC is about 0.01 mg / m 3.

See also: Tellurium // Wikipedia. (date of access: 23.12.2019).
"Discovery of elements and the origin of their names".

Hardly anyone will believe the story of the sea captain, who is, moreover, a professional circus wrestler, a famous metallurgist and a consultant doctor of a surgical clinic. In the world of chemical elements, such a variety of professions is a very common phenomenon, and the expression of Kozma Prutkov is inapplicable to them: "A specialist is like a gumboil: his completeness is one-sided." Let's remember (even before talking about the main object of our story) iron in cars and iron in blood, iron is a concentrator of the magnetic field and iron is an integral part of ocher ... True, it sometimes took much more time to "professionalize" the elements than to prepare yoga of average skill. So the element number 52, which we are about to tell, was used for many years only in order 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 Josef Müller (later Baron von Reichenstein) investigated the gold-bearing ore found in Semigorye, on the territory of what was then Austria-Hungary. It turned out to be so difficult to decipher the composition of the ore that it was named Aurum problematicum - "doubtful gold". It was from this "gold" that Muller singled out a new metal, but there was no complete confidence that it was really new. (Subsequently, it turned out that Mueller was wrong about something else: the element he discovered was new, but it can only be attributed to the number of metals with a great stretch.)

To dispel doubts, Müller turned to a prominent specialist, the Swedish mineralogist and analytical chemist Bergman.

Unfortunately, the scientist died before he could finish 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 tried to study the element discovered by Müller, but only 16 years after its discovery, Martin Heinrich Klaproth, one of the greatest chemists of that time, irrefutably proved that this element was actually new, and suggested the name "tellurium" for it.

As always, following the discovery of the element, the search for its applications began. Apparently, proceeding from the old, even from the times of iatrochemistry, the principle - 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 tellurium was able to provide doctors with some "minor services". More precisely, not tellurium itself, but the salts of telluric acid K 2 TeO 3 and Na 2 TeO 3, which began to be used in microbiology as dyes that impart a certain color to the bacteria under study. So, with the help of tellurium compounds, the diphtheria bacillus is reliably isolated from the mass of bacteria. If not in treatment, then at least in diagnostics, element No. 52 was useful to doctors.

But sometimes this element, and to an even greater extent some of its compounds, add hassle to doctors. Tellurium is quite toxic. In our country, the maximum permissible concentration of tellurium in the air is 0.01 mg / m 3. The most dangerous of tellurium compounds 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 Н 2 Te should be similar to hydrogen sulfide. It irritates the bronchi, has a harmful effect on the nervous system.

These unpleasant properties did not prevent tellurium from entering technology, acquiring many "professions".

Metallurgists are interested in tellurium because even its 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 devices for sulfuric acid production, coated from the inside with a lead-tellurium alloy (up to 0.5% Te), is twice as long as that of the same devices, simply lined 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, as an analogue of sulfur, it is sometimes used for vulcanizing rubbers.

Tellurium - semiconductor

However, these industries were not responsible for the jump in prices and demand for item # 52. This leap took place in the early 60s of our century. Tellurium is a typical semiconductor, and the semiconductor is technologically advanced. Unlike germanium and silicon, it melts relatively easily (melting point 449.8 ° C) and evaporates (boils at just below 1000 ° C). Hence, it is easy to obtain thin semiconductor films from it, which are of particular interest in 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, an impurity of tellurium is deliberately introduced into gallium arsenide (the third most important semiconductor after silicon and germanium) in order to create an electronic type of conductivity *.

* The two types of conductivity inherent in semiconductors are described in detail in the article "Germanium".

The area of ​​application of some tellurides - tellurium compounds with metals is much broader. Bismuth tellurides Bi 2 Te 3 and antimony Sb 2 Te 3 have become the most important materials for thermoelectric generators. To explain why this happened, we will make a small digression into the field of physics and history.

A century and a half ago (in 1821), the German physicist Seebeck discovered that an electromotive force (called thermo-EMF) is created in a closed electrical circuit consisting of different materials, contacts between which are at different temperatures. After 12 years, the Swiss Peltier discovered an effect opposite to the Seebeck effect: when an electric current flows through a circuit made up of different materials, in the places of contacts, in addition to the usual Joule heat, a certain amount of heat is released or absorbed (depending on the direction of the current).

For about 100 years, these discoveries remained a "thing in itself", curious facts, nothing more. And it will not be an exaggeration to say that a new life for both of these effects began after the Hero of Socialist Labor, academician A.F. Ioffe and his co-workers developed a theory of the use of 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, in which bismuth, lead and antimony tellurides are used, provide energy to artificial earth satellites, navigational 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 chemical compound of tellurium with semiconducting properties, cadmium telluride CdTe, has been of great interest. This material is used for the manufacture of solar cells, lasers, photoresistors, and counters of radioactive radiation. Cadmium telluride is also famous for the fact that it is one of the few semiconductors in which the Hahn 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 applications in radar technology.

In conclusion, we can say that quantitatively the main "profession" of tellurium is alloying of 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, the place of tellurium is 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%, only selenium is 10–5%, and tellurium is still 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 at the same time either with selenium, or with gold, or with other metals.

Copper-nickel tellurium-bearing ores of Pechenga and Monchegorsk, tellurium-bearing lead-zinc ores of Altai and a number of other deposits are known in the USSR.

Tellurium is isolated from copper ore at the stage of purification of blister copper by electrolysis. A sludge precipitates at the bottom of the electrolyzer. This is a very expensive intermediate product. Here, for illustration, 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 most valuable components of the sludge must be separated, and there are several ways for this. Here is one of them.

The sludge is melted in a furnace and air is passed through the melt. Metals, except for gold and silver, are oxidized and pass 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 SeO 3 and telluride H 2 TeO 3. If sulfur dioxide SO 2 is passed through this solution, reactions will occur:

H 2 SeO 3 + 2SO 2 + H 2 O → Se ↓ + 2H 2 SO 4,

H 2 TeO 3 + 2SO 2 + H 2 O → Te ↓ + 2H 2 SO 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, predominantly selenium is reduced first. This is facilitated by the selection of the optimal concentration of hydrochloric acid added to the solution.

Then tellurium is besieged. The fallen 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 has to be purified from all these elements first by chemical methods, then by distillation or zone melting. Naturally, tellurium is extracted in different ways from different ores.

Tellurium is harmful

Tellurium is used more and more widely and, therefore, the number of those working with it is increasing. In the first part of the story about element No. 52, we have 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, which were injected with tellurium aerosol, "showed anxiety, sneezed, rubbed their faces, became lethargic and drowsy." Tellurium has a similar effect on humans.

And tellurium itself and its compounds can bring troubles of different "calibers". They, for example, cause baldness, affect the composition of the blood, and can block various enzyme systems. Symptoms of chronic poisoning with elemental tellurium - nausea, drowsiness, emaciation; exhaled air takes on a nasty garlic smell of alkyl tellurides.

In acute poisoning with tellurium, serum with glucose is administered intravenously, and sometimes even morphine. As a prophylactic agent, ascorbic acid is used. But the main prevention is the accidental sealing of devices, the automation of processes in which tellurium and its compounds are involved.

Element number 52 brings a lot of benefits and therefore deserves attention. But working with him requires caution, clarity and, again, focused attention.

Tellurium appearance

Crystalline tellurium is most similar to antimony. Its color is silvery white. Crystals are hexagonal, the atoms in them form spiral chains and are linked by covalent bonds with the nearest neighbors. Therefore, elemental tellurium can be considered an inorganic polymer. Crystalline tellurium is characterized by a metallic luster, although by its complex of chemical properties it can rather be attributed to non-metals. Tellurium is fragile and can be easily turned into powder. The question of the existence of an amorphous modification of tellurium has not been unambiguously resolved. When tellurium is reduced from telluric or telluric acids, a precipitate is formed, but it is still not clear whether these particles are truly amorphous or just very small crystals.

Bicolor anhydride

As befits an analogue of sulfur, tellurium exhibits valencies 2–, 4+, and 6+, and much less often 2+. Tellurium monoxide TeO can exist only in gaseous form and is easily oxidized to TeO 2. It is a white, non-hygroscopic, completely stable crystalline substance that melts without decomposition at 733 ° C; it has a polymer structure, the molecules of which are structured as follows:

Tellurium dioxide hardly dissolves in water - only one part of TeO 2 per 1.5 million parts of water goes into solution and a solution of weak tellurous acid H 2 TeO 3 of negligible concentration is formed. The acidic properties of telluric acid H 6 TeO 6 are also weakly expressed. This formula (and not H 2 TeO 4) was assigned to it after salts of the composition Ag 6 TeO 6 and Hg 3 TeO 6, which are readily soluble in water, were obtained. The anhydride TeO 3, which forms telluric acid, is practically insoluble in water. This substance exists in two modifications - yellow and gray: α-TeO 3 and β-TeO 3. Gray telluric 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 potassium hydroxide.

Second exception

When creating the periodic table, Mendeleev put tellurium and the neighboring iodine (as well as argon and potassium) in groups VI and VII not in accordance with, but in spite of their atomic weights. Indeed, the atomic mass of tellurium is 127.61, and that of iodine is 126.91. This means that iodine should have stood not behind tellurium, but in front of it. Mendeleev, however, did not doubt 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 legitimacy of the exceptions confirming the rule was established only when the basis of the periodic table was formed not by atomic weights, but by the charges of nuclei, when the isotopic composition of both elements became known. Tellurium, unlike iodine, is dominated by heavy isotopes.

By the way, about isotopes. Now there are 22 known isotopes of element 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 on Earth is significantly less than selenium, there are more minerals known for element 52 than minerals of its analogue. By their composition, tellurium minerals are twofold: either tellurides, or the oxidation products of tellurides in the earth's crust. Among the first are calaverite AuTe 2 and krennerite (Au, Ag) Te 2, 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 value - all industrial tellurium is a by-product of processing other metal ores.

Those are chem. element of group VI of the periodic table of elements; at. n. 52, at. m. 127.60. A lustrous silvery-gray fragile substance with a metallic sheen. In compounds, it exhibits oxidation states -2, +4 and +6. Natural B consists of eight stable isotopes with mass numbers 120,122-126, 128 and 130. There are 16 known radioactive isotopes with a half-decay period from 2 to 154 days. The most widespread are heavy isotopes with mass numbers 128 and 130. T. discovered (1782) Hung. researcher F. Müller von Reichenstein. Tellurium belongs to scattered rare elements, its content in the earth's crust is 10-7%. Contained in many minerals with gold, silver, platinum, copper, iron, lead, bismuth, sulfide minerals. The crystal lattice of T. is hexagonal with periods a - 4.4570 A and c = 5.9290 A. Density (m-pa 20p C) 6.22 g / cm3; / pl 449.5 ° C; tboil 990 ± 2 ° С.

Known "amorphous" modification of Tellurium (dark brown powder), which irreversibly transforms into crystalline when heated. Temperature coefficient linear expansion of polycrystalline T. (16-17) 10-6 deg-1, at coeff. thermal conductivity (t-ra 20 ° C) 0.014 cal / cm X X sec x deg; specific heat (t-ra 25 ° C) 0.048 cal / g x deg. T. is a semiconductor with a band gap of 0.34 eV. The electrical conductivity of T. depends on the purity and degree of perfection of the crystal. In the purest samples, it is ~ 0.02 ohm-1 x cm-1. The electron mobility is 1700, the hole mobility is 1200 cm2 / in x sec. When melted, Tellurium transforms into a metallic state. Tellurium is diamagnetic, the specific magnetic susceptibility is 0.3 10-6 cm3 / g (at room temperature). Mohs scale hardness 2.0-2.5; Wed microhardness 58 kgf / mm2, modulus of norms, elasticity 4200 kgf / mm2, coefficient. compressibility (t-ra 30 ° C) 1.5-10 6 cm2 / kgf. Tellurium single crystals with orientation along (0001) brittle fracture at a stress of 14 kgf / mm2.

By chem. St. you T. reminds me of sulfur. but less active. At room temperature, it does not oxidize in air, when heated, it burns out with the formation of TeO2 dioxide - white crystalline, slightly soluble in water. TeO and TeO3 are also known, which are less stable than TeO2. Under normal conditions, Tellurium very slowly interacts with water with the evolution of hydrogen and the formation of sulfuric acid to form a red solution of TeS03; when diluted with water, the reverse reaction occurs with the release of tellurium. T. dissolves in nitrogen to - those with the formation of tellurous to - you H2Te03, in dilute hydrochloric to - those dissolves slightly.

Tellurium dissolves slowly in alkalis. With hydrogen, it forms telluride H2Te - a colorless gas with an unpleasant odor, condensing at temperature -2 ° C and solidifying at temperature -51.2 ° C, an unstable compound that easily decomposes under the action of even weak oxidants. Tellurium does not form sulphides that are stable under normal conditions; the TeS2 compound is stable at temperatures up to -20 ° C. With selenium, T. forms continuous solid solutions. Known composition TeXv (only fluoride), TeX4 and TeX2, to-rye 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 material for the production of Tellurium is the slimes of copper-nickel and sulfuric acid production, as well as products obtained during the refining of lead. The anode sludge is processed by an acidic or alkaline method, converting T. into a tetravalent state and then reducing it with sulfur dioxide from solutions at the end of titer. hydrochloric to-those or electrolytically. In addition, materials containing T. can be processed by the chlorine method. Tellurium of high purity is obtained by sublimation and zone recrystallization (the most effective method of deep purification, which makes it possible to obtain a substance with a purity of 99.9999%).

Tellurium compounds are toxic, their effect on the human body is similar to that 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 for vulcanization of rubber, in the production of lead cables (an additive up to 0.1% of Te improves the mechanical properties of lead). T. compounds are used in the glass industry (for painting glass and porcelain) and in photography. Tellurium is widely used in the synthesis of semiconductor compounds. Compounds T. - the main material for the production of thermoelements.

Tellurium belongs to the scattered elements (their content in the earth's crust is 1 ⋅ 10⁻ ⁷ %. Tellurium rarely forms independent. It usually occurs naturally in the form of impurities to sulfides, as well as in native sulfur. The main sources of tellurium and selenium are sulfuric acid production wastes that accumulate in dust chambers, as well as sediments (sludge) formed during the electrolytic purification of copper. The sludge, among other impurities, also contains silver selenide Ag 2 Se and some. When sludge is fired, tellurium oxide TeO is formed 2 and also oxides of heavy metals. Tellurium is reduced from TeO oxides 2 when exposed to sulfur dioxide in an aqueous medium:

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 it, forms allotropic modifications - crystalline and amorphous. Crystalline tellurium is silvery-gray in color, brittle, easily ground into powder. Its electrical conductivity is negligible, but it increases with illumination. Amorphous tellurium is brown, less stable than amorphous and at 25 degrees. becomes crystalline.

Tellurium is chemically very similar to sulfur. It burns in air (greenish blue), forming the corresponding TeO oxides 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, interacts with many metals, forming the corresponding salts (), for example, K 2 Te. Tellurium, even under normal conditions, reacts with water:

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 oxidants:

Te + 3H 2 O 2 (30%) = H 6 TeO 6

Tellurium, like sulfur, slowly dissolves in boiling aqueous solutions of alkalis:

3Te + 6KOH = 6K 2 Te + K 2 TeO 3 + 3H 2 O

Tellurium is mainly used as a semiconductor material.

Tellurium properties

Hydrogen telluride can be obtained by acting on 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 less toxic). Tellurium hydrides exhibit reducing properties to a greater extent than, and H 2 Te in water is about the same as in hydrogen sulfide. Aqueous solutions of hydrides show a pronounced acidic reaction due to their dissociation in aqueous solutions according to the scheme:

H 2 Te ↔ H + HTe ⁺

↓

H + Te ² ⁺

In the O - S - Se - Te series, the radii of their ions are E² ⁺ hold the hydrogen ion. This is confirmed by experimental data, which confirmed that hydrofluoric acid is stronger than hydrogen sulfic acid.

In the O - S - Se - Te series, the capacity for thermal dissociation of hydrides increases: it is most difficult to decompose water upon heating, while tellurium hydrides are unstable and decompose even upon weak heating.

Hydrogen telluric acid salt (tellurides) are similar in properties to sulfides. They are obtained, like sulfides, by the action of hydrogen telluride on soluble metal salts.

Tellurides are similar to sulfides in terms of solubility in water and acids. For example, when passing hydrogen telluride through an aqueous solution of Cu 2 SO 4 copper telluride is obtained:

H 2 Te + CuSO 4 = H 2 SO 4 + CuTe

With oxygen, Te forms TeO compounds 2 and TeO 3 they are formed during the combustion of tellurium in air, during the burning 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

TeO 2 - 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 weaker than sulfurous acid. Tellurous 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 mainly act as reducing agents, with an increase in the oxidation state of sulfur to 6 +, TeO 2 and the corresponding acids show mainly oxidizing properties, respectively, reducing to Te. In this way, in practice, tellurium is obtained in free form:

H 2 TeO 3 + 2SO 2 + H 2 O = 2H 2 SO 4 + Te

Tellurous acid exhibits reducing properties only when interacting with strong oxidants:

3H 2 TeO 3 + HClO 3 = 3H 2 TeO 4 + HCl

Free telluric acid H 2 TeO 4 - usually released in the form of 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 salts Na6TeO6.