Tellurium color. World tellurium market. Being in nature

Physical properties
Tellurium exists in two modifications - crystalline and amorphous.
Crystalline tellurium is obtained by cooling tellurium vapor, and amorphous tellurium - by reducing telluric acid with sulfur dioxide or another similar reagent:

Amorphous tellurium is a fine black powder that transforms into metallic tellurium when heated. The density of amorphous tellurium is 5.85-5.1 g / cm3.
For crystalline tellurium, two polymorphic species are known: α-Te and β-Te. The α → β transition occurs at 354 ° С. Crystalline tellurium has a white-silver color. Its density is 6.25 g / cm2. The hardness of crystalline tellurium is 2.3; at ordinary temperatures it is brittle, easily crushed into powder, and at higher temperatures it becomes so plastic that it can be pressed.
The melting point of tellurium is 438-452 ° C, and the boiling point is 1390 ° C. Tellurium is characterized by high vapor pressure, which, depending on the temperature, is expressed in the following numbers:

Tellurium has a semiconducting character of conductivity. The electrical resistance of polycrystalline tellurium at 0 ° C is 0.102 ohm * cm. With increasing temperature, the electrical resistivity of tellurium decreases:

In contrast to selenium, the electrical resistance of tellurium is not very sensitive to light. However, at low temperatures, the effect of lighting is still felt; so, at -180 ° C, the electrical resistance of tellurium under the influence of illumination decreases by 70%.
Chemical properties
In terms of its chemical properties, tellurium is similar to selenium, but has a more pronounced metallic character. At room temperature, compact tellurium is resistant to air and oxygen; when heated, it oxidizes and burns with a blue flame with a green border, forming TeO2.
In a dispersed state and in the presence of moisture, tellurium is oxidized at ordinary temperatures. Tellurium at room temperature reacts with halogens and forms chemically stronger halides (TeCl4; TeBr4) than selenium.
Tellurium does not directly combine with hydrogen under normal conditions, but upon heating it forms H2Te. When heated with many metals, tellurium forms tellurides: K2Te, Ag2Te, MgTe, Al2Te, etc.
Metallic tellurium reacts with water at 100-160 ° C, and freshly precipitated (amorphous tellurium) - at room temperature:

Te + 2Н2О → TeO2 + 2Н2.

Tellurium does not dissolve in CS2; dissolves very slowly in dilute HCl. In concentrated and diluted HNO3, tellurium is oxidized to form H2TeO3:

3Те + 4HNО3 + H2O = 3Н2ТеО3 + 4NO.

Tellurous acid is readily decomposed by sulfur dioxide with the release of tellurium:

H2TeO3 + 2SO2 + H2O → Te + 2H2SO4.

This reaction is used to obtain pure tellurium.
Tellurium is an almost constant companion of heavy non-ferrous metals in sulfides (iron and copper pyrite, lead luster), but it also occurs in the form of minerals sylvanite, calaverite (Au, Ag) Te2, etc.
The main source of production of industrial tellurium is the waste of processing sulfide ores of copper and lead - dust, in which tellurium is present in the form of TeO2, obtained during the roasting of sulfide ores; as well as anode sludge obtained during the electrolytic refining of copper and lead.

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This element was discovered almost two centuries ago. In 1782, the 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 apparatus 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 apparatus, 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 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 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.

V last years another one is of great interest chemical compound tellurium with semiconducting properties - cadmium telluride CdTe. This material is used for the manufacture of solar cells, lasers, photoresistors, counters. 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 cleaned of all these elements first. chemical methods, then 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 they use ascorbic acid... 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. Just as weakly expressed acidic properties and telluric acid H 6 TeO 6. This formula (and not H 2 TeO 4) was assigned to it after the 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 compounds gold. 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.

Tellurium Tellurium (Latin 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. To separate selenium and tellurium, add sulfuric acid... 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.

Tellurium
Atomic number	52
Appearance simple substance
Atom properties
Atomic mass (molar mass)	127.6 a. e.m. (g / mol)
Atom radius	160 pm
Ionization energy (first electron)	869.0 (9.01) kJ / mol (eV)
Electronic configuration	4d 10 5s 2 5p 4
Chemical properties
Covalent radius	136 pm
Ion radius	(+ 6e) 56 211 (-2e) pm
Electronegativity (according to Pauling)	2,1
Electrode potential	0
Oxidation states	+6, +4, +2
Thermodynamic properties of a simple substance
Density	6.24 / cm ³
Molar heat capacity	25.8 J / (mol)
Thermal conductivity	14.3 W / ()
Melting temperature	722,7
Heat of fusion	17.91 kJ / mol
Boiling temperature	1 263
Heat of vaporization	49.8 kJ / mol
Molar volume	20.5 cm ³ / mol
Crystal lattice of a simple substance
Lattice structure	hexagonal
Lattice parameters	4,450
C / a ratio	1,330
Debye temperature	n / a

Tellurium- chemical element with atomic number 52 in the periodic table and atomic mass 127.60; denoted by the symbol Te (Tellurium), belongs to the family of metalloids.

Story

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.

origin of name

From latin tellus, Genitive telluris, Land.

Being in nature

Native tellurium is also found together with selenium and sulfur (Japanese tellurium sulfur contains 0.17% Te and 0.06% Se).

An important source of tellurium is copper and lead ores.

Receiving

The main source is sludge from electrolytic refining of copper and lead. 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

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.

Prices

Tellurium is a rare element, and significant demand with a small production volume determines its high price (about $ 200-300 per kg, depending on purity), but, despite this, the range of its applications is constantly expanding.

Physicochemical characteristics

Tellurium is a fragile silvery-white substance with a metallic luster. In thin layers, red-brown in the light, in pairs - golden-yellow.

Tellurium is chemically less active than sulfur. It dissolves in alkalis, lends itself to the action of nitric and sulfuric acids, but in dilute hydrochloric acid dissolves slightly. Metallic tellurium begins to react with water at 100 ° C, and in the form of a powder it oxidizes in air even at room temperature, forming oxide TeO2.

When heated in air, tellurium burns out, forming Te0 2. This strong compound is less volatile than tellurium itself. Therefore, to purify tellurium from oxides, they are reduced with flowing hydrogen at 500-600 ° C.

In the molten state, tellurium is rather inert; therefore, graphite and quartz are used as container materials for its melting.

Application

Alloys

Tellurium is used in the production of lead alloys with increased ductility and strength (used, for example, in the production of cables). With the introduction of 0.05% tellurium, lead losses due to dissolution under the influence of sulfuric acid are reduced by 10 times, and this is used in the production of lead-acid batteries. It is also important that lead doped with tellurium does not soften during processing by plastic deformation, and this makes it possible to carry out the technology of manufacturing down conductors of battery plates by the method of cold cutting and significantly increase the service life and specific characteristics of the battery.

Thermoelectric materials

Bismuth telluride single crystal

Its role is also great in the production of semiconductor materials and, in particular, tellurides of lead, bismuth, antimony, cesium. In the coming years, the production of lanthanide tellurides, their alloys and alloys with metal selenides for the production of thermoelectric generators with a very high (up to 72–78%) efficiency, which will make it possible to use them in the energy sector and in the automotive industry, will become very important.

So, for example, a very high thermo-EMF was recently discovered in manganese telluride (500 μV / K) and in its combination with selenides of bismuth, antimony and lanthanides, which allows not only to achieve a very high efficiency in thermogenerators, but also to carry out semiconductor refrigerator cooling down to the cryogenic (temperature level of liquid nitrogen) temperatures and even lower. The best tellurium-based material for the production of semiconductor refrigerators in recent years has been tellurium alloy,

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 Fairly 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 like 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 apparatus 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 apparatus, 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 element No. 52. This jump 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 a temperature 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 in it.
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 would not be an exaggeration to say that a new life for both of these effects began after Academician A.F. Ioffe and his co-workers 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, in which bismuth, lead and antimony tellurides are used, 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 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, photoreflection sensors, and radioactive radiation counters. 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%, selenium is only 10-5%, 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 Russia.

Tellurium is isolated from copper ore at the stage of purification of blister copper by electrolysis. A sediment - sludge - flows to 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 apparatuses (scrubbers), then dissolved and converted into acids - selenium H 2 SeO3 and telluride 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, 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

And myself tellurium and its compounds can bring misfortunes 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 reliable sealing of the apparatus, the automation of processes in which tellurium and its compounds are involved.

Element number 52 is very useful and therefore deserves attention. But working with him requires caution, clarity and, again, focused attention.
APPEARANCE OF TELLURIUM. 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.
TWO-COLOR ANHYDRID. 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 polymeric structure.
Tellurium dioxide almost does not dissolve in water - only one part of TeO 2 per 1.5 million parts of water passes into the solution and a solution of weak tellurous acid H 2 TeO 3 of negligible concentration is formed. The acidic properties of telluric acid are also weakly expressed.

H 6 TeO 6. This formula (and not Н 2 TeO 4 was assigned to it after salts of the composition Ag 6 Te0 6 and Hg 3 Te0 6, which are readily soluble in water, were obtained. modifications - yellow and gray: α-TheOs and β-TeOs. Gray telluric anhydride is very stable: even when heated, acids and concentrated alkalis do not act on it. 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 right
the validity 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 isotones. Now there are 22 known isotopes of element number 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.

MINERALS TELLURIUM. Although tellurium is much less abundant on earth than selenium, there are more minerals known for element 52 than its counterpart. 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) 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 value - all industrial tellurium is a by-product of processing other metal ores.