Tellurium exists in two modifications - crystalline and amorphous.
Crystalline tellurium is obtained by cooling tellurium vapor, and amorphous tellurium is obtained by reducing telluric acid with sulfur dioxide or another similar reagent:
Amorphous tellurium is a fine black powder that turns into tellurium metal when heated. The density of amorphous tellurium is 5.85-5.1 g/cm3.
For crystalline tellurium, two polymorphic varieties are known: α-Te and β-Te. The α→β transition occurs at 354° C. 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 and easily breaks 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 by the following figures:
Tellurium has a semiconductor conductivity. The electrical resistance of polycrystalline tellurium at 0° C is 0.102 ohm*cm. With increasing temperature, specific electrical resistance tellurium decreases:
In contrast to selenium, the electrical resistance of tellurium is little sensitive to light. However, when low temperatures the influence of lighting still has an effect; Thus, at -180° C, the electrical resistance of tellurium under the influence of lighting 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, but 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 oxidizes at ordinary temperatures. Tellurium at room temperature reacts with halogens and forms chemically stronger halides (TeCl4; TeBr4) than selenium.
Tellurium does not combine directly with hydrogen under normal conditions, but when heated 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 deposited (amorphous tellurium) - at room temperature:
Te + 2H2O → TeO2 + 2H2.
Tellurium does not dissolve in CS2; dissolves very slowly in dilute HCl. In concentrated and dilute HNO3, tellurium is oxidized to form H2TeO3:
3Te + 4HNO3 + H2O = 3H2TeO3 + 4NO.
Telluric acid is easily decomposed by sulfur dioxide, releasing tellurium:
H2TeO3 + 2SO2 + H2O → Te + 2H2SO4.
This reaction is used to obtain pure tellurium.
Tellurium is almost constant companion heavy non-ferrous metals in sulfides (iron and copper pyrites, lead luster), but also found in the form of minerals sylvanite, calaverite (Au, Ag)Te2, etc.
The main source of industrial tellurium is waste from the processing of sulfide ores of copper and lead - dust in which tellurium is present in the form of TeO2, obtained by roasting sulfide ores; as well as anode sludge obtained from the electrolytic refining of copper and lead.
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Tellurium
TELLURIUM[te], -a; m.[from lat. tellus (telluris) - earth] Chemical element (Te), fragile crystalline metal silver-gray color (used in the manufacture of brown dyes and semiconductor materials).
◁ Tellurium, oh, oh.
tellurium(lat. Tellurium), chemical element of group VI periodic table. Named from lat. tellus, gen. n. telluris - Earth. Silver-gray, very brittle crystals with a metallic luster, density 6.25 g/cm 3 , t pl 450°C; semiconductor. It is stable in air and burns at high temperatures to form TeO 2 dioxide. It occurs in nature in the form of tellurides and as native tellurium; often accompanies sulfur and selenium; extracted from copper electrolysis waste. Component of alloys (copper, lead, cast iron); dye for glass and ceramics ( Brown color). Many tellurium compounds are semiconductor materials that are receivers of IR radiation.
TELLURIUMTELLURUM (Latin Tellurium from the Latin tellus - Earth), Te (read “tellurium”), a chemical element with atomic number 52, atomic mass 127.60. Natural tellurium consists of eight stable isotopes: 120 Te (content 0.089% by weight), 122 Te (2.46%), 123 Te (2.46%), 124 Te (4.74%), 125 Te (7. 03%), 126 Te (18.72%), 128 Te (31.75%) and 130 Te (34.27%). Atomic radius 0.17 nm. Ion radii: Te 2– - 0.207 nm (coordination number 6), Te 4+ - 0.066 nm (3), 0.08 nm (4), 0.111 nm (6), Te 6+ - 0.057 (4) and 0.070 nm (6). Sequential ionization energies: 9.009, 18.6, 28.0, 37.42 and 58.8 eV. (Located in the VIA group, in period 5 of the periodic table of elements. Chalcogen cm.,
CHALCOGENS) non-metal. Outer electron layer configuration 5 2
s 4
p (Located in the VIA group, in period 5 of the periodic table of elements. Chalcogen. Oxidation states: –2, +2, +4, +6 (valency II, IV and VI). Electronegativity according to Pauling 2,10.
PAULING Linus)
Tellurium is a brittle, silvery-white substance with a metallic luster.
History of discovery (Located in the VIA group, in period 5 of the periodic table of elements. Chalcogen It was first discovered in 1782 in the gold ores of Transylvania by mining inspector F. I. Muller, who mistook it for a new metal. In 1798 M. G. Klaproth KLAPROT Martin Heinrich)
isolated tellurium and determined its most important properties.
Being in nature Contents in earth's crust 1·10–6% by mass. About 100 tellurium minerals are known. The most important of them are: PbTe altaite, AgAuTe 4 sylvanite, AuTe 2 calaverite, Bi 2 Te 2 S tetradymite. oxygen compounds (Located in the VIA group, in period 5 of the periodic table of elements. Chalcogen tellurium, for example TeO 2 - tellurium ocher. Native tellurium also occurs together with selenium SELENIUM) (Located in the VIA group, in period 5 of the periodic table of elements. Chalcogen and gray SULFUR)
An important source of tellurium is copper and lead ores.
Receipt
The main source is sludge from electrolytic copper refining (Located in the VIA group, in period 5 of the periodic table of elements. Chalcogen COPPER) and lead. (Located in the VIA group, in period 5 of the periodic table of elements. Chalcogen LEAD) The sludge is fired, the tellurium remains in the cinder, which is washed hydrochloric acid. Tellurium is isolated from the resulting hydrochloric acid solution by passing sulfur dioxide SO 2 through it.
To separate selenium and tellurium, add sulfuric acid. In this case, tellurium dioxide TeO 2 falls out, and selenous acid remains in solution.
To separate Te from sludges, they are sintered with soda followed by leaching. Te goes into an alkaline solution, from which, upon neutralization, it precipitates in the form of TeO 2:
Na 2 TeO 3 +2HC=TeO 2 Ї+2NaCl.
Tellurium is reduced from TeO2 oxide with coal.
To purify tellurium from S and Se, its ability, under the action of a reducing agent (Al) in an alkaline medium, to transform into soluble disodium ditelluride Na 2 Te 2 is used:
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. The tetrachloride is then hydrolyzed with water:
TeCl 4 +2H 2 O=TeO 2 Ї+4HCl,
and the resulting TeO 2 is reduced with hydrogen:
TeO 2 +4H 2 =Te+2H 2 O.
Physical and chemical properties
Tallurium is a brittle silvery-white substance with a metallic luster. Hexagonal crystal lattice, a=0.44566 nm, c=0.59268 nm. The structure consists of parallel helical chains. Density 6.247 g/cm3. Melting point 449.8°C, boiling point 990°C. In thin layers, when exposed to light, it is red-brown, in vapors it is golden-yellow.
p-type semiconductor. The band gap is 0.32 eV. Electrical conductivity increases when illuminated.
During deposition, amorphous tellurium is released from solutions, density 5.9 g/cm 3 . At 4.2 GPa and 25°C, a modification with a b-Sn (Te-II) type structure is formed. At 6.3 GPa, the Te-III modification with a rhombohedral structure was obtained. Te-II and Te-III exhibit the properties of metals.
Stable in air at room temperature even in a finely dispersed state. When heated in air, it burns with a bluish-green flame to form TeO 2 dioxide. Standard potential half-reactions:
TeO 3 2– +3H 2 O+4e=Te+6OH –: 0.56V.
At 100–160°C it is oxidized by water:
Te+2H 2 O= TeO 2 +2H 2
When boiled in alkaline solutions, tellurium disproportionates to form telluride and tellurite:
8Te+6KOH=2K 2 Te+ K 2 TeO 3 +3H 2 O.
Te does not interact with hydrochloric and dilute sulfuric acids. Concentrated H 2 SO 4 dissolves Te, the resulting Te 4 2+ cations color the solution red. Dilute HNO 3 oxidizes Te to telluric acid H 2 TeO 3:
3Te+4HNO 3 +H 2 O=3H 2 TeO 3 +4NO.
Strong oxidizing agents (HClO 3, KMnO 4) oxidize Te to weak telluric acid H 6 TeO 6:
Te+HClO 3 +3H 2 O=HCl+H 6 TeO 6.
With halogens (Located in the VIA group, in period 5 of the periodic table of elements. Chalcogen HALOGEN)(except fluorine) forms tetrahalides. Fluorine oxidizes Te to TeF6 hexafluoride.
Hydrogen telluride H 2 Te - a colorless poisonous gas with an unpleasant odor is formed during the hydrolysis of tellurides.
Tellurium compounds (+2) are unstable and prone to disproportionation:
2TeCl 2 =TeCl 4 +Te.
Application
The main application of Te and its compounds is semiconductor technology. Additives of Te to cast iron (Located in the VIA group, in period 5 of the periodic table of elements. Chalcogen CAST IRON) and steel (Located in the VIA group, in period 5 of the periodic table of elements. Chalcogen STEEL), lead (Located in the VIA group, in period 5 of the periodic table of elements. Chalcogen LEAD) or copper increase their mechanical and chemical resistance. Those and its compounds are used in the production of catalysts, special glasses, insecticides, and herbicides.
Physiological action
Tellurium and its volatile compounds are toxic. If it enters the body it causes nausea, bronchitis, and pneumonia. MPC in air is 0.01 mg/m 3, in water 0.01 mg/l. In case of poisoning, tellurium is excreted from the body in the form of foul-smelling organotellurium compounds.
Microquantities of Te are always contained in living organisms, it biological role not clear.
encyclopedic Dictionary. 2009 .
Synonyms:See what “tellurium” is in other dictionaries:
- (new lat., from lat. Tellus, Telluris earth, goddess of the earth). A simple body, similar in properties to sulfur, was discovered in gold ore in 1872 and belongs to the group of metals and metalloids. Dictionary foreign words, included in the Russian language.... ... Dictionary of foreign words of the Russian language
M l, Te. Trig. Gab. prisms, to needle-like. Sp. owls by prism. Ag.: fine-grained and columnar. Tin white. Bl. metal TV 2 2.5. Ud. V. 6.3. In hydrothermal veins with native Au, Au and Ag tellurides, and sulfides. Geological... ... Geological encyclopedia
- (lat. Tellurium) Te, chemical element of group VI of the periodic system, atomic number 52, atomic mass 127.60. Name from lat. tellus gen. n. telluris Earth. Silver-gray, very brittle crystals with a metallic luster, density 6.24... ... Big Encyclopedic Dictionary
Tellurium, chalcogen, sylvan Dictionary of Russian synonyms. tellurium noun, number of synonyms: 8 mineral (5627) ... Synonym dictionary
TELLURIUM- TELLURIUM, Tellurium, chemical. The Te symbol occupies 52nd place in the periodic table. Homologue of sulfur and selenium (VI group). At. weight 127.5. T. amorphous black powder or brittle pieces of silver-white color, with a metallic sheen; beat weight 6.24, t°… … Great Medical Encyclopedia
- (Tellurium), Te, chemical element of group VI of the periodic system, atomic number 52, atomic mass 127.60; refers to chalcogens; non-metal. Identified by the Hungarian scientist F. Müller von Reichenstein in 1782... Modern encyclopedia
- (symbol Te), a silvery-white chemical element discovered in 1782. Occurs naturally in combination with gold in sylvanite. Its main source is a by-product of electrolytic refining of copper. The shiny, fragile element is used in... Scientific and technical encyclopedic dictionary
TELLURURE, tellurium, pl. no, husband (from Latin tellus earth) (chem.). Chemical element, crystalline substance silvery white color. Dictionary Ushakova. D.N. Ushakov. 1935 1940 … Ushakov's Explanatory Dictionary
Tellurium is a non-metal that has a metallic luster. Its color is silvery-white. This element is very rare and dispersed. It was discovered by mining inspector Franz Josef Müller in 1782. Tellurium is extracted from polymetallic ore. This substance is contained in the form of compounds in hydrothermal deposits of gold and others.
Thallium is a brittle material that, when heated, acquires plastic properties. The density of this non-metal is 6.25 g/cm3. Tellium begins to melt when the temperature reaches 450 °C, and boils at 990 °C. The material has diamagnetic properties and at 18 °C the specific magnetic susceptibility value is -0.31.10-6.
Tellurium is a p-type semiconductor when conditions environment normal or when the material is heated to a boil. When a nonmetal is cooled, at a transition of about -100 °C, it changes its properties and acquires n-type conductivity. The band gap width is 0.34 eV. The transition temperature decreases depending on the purity of the substance.
Thallium is used as an alloying additive in the production of lead. It helps improve strength and chemical resistance. Lead-tellurium alloy is used in cable and chemical production. Copper and steel are also alloyed with tellurium. This allows for improved machining.
Tellurium is also used in glass production. Glass, thanks to this impurity, acquires a brown color, and its refractive index increases. In the rubber industry, tellurium is used to carry out the rubber vulcanization process.
Significant demand for tellurium is driven by its semiconductor properties. It is considered both a typical and technologically advanced semiconductor. This substance is used in microelectronics. A thin film is obtained from it, which is capable of melting at lower temperatures compared to many metals.
In its pure form, tellurium, in the form of a semiconductor, is rarely used due to its limited supply in the bowels of the Earth. In most cases, it is used in the manufacture of transistors and devices that are designed to measure the intensity of gamma radiation.
Most often in industry, it is not pure non-metal that is used, but its compounds with metals, which are called tellurides. They are used to produce important parts of thermoelectric generators.
Sale of non-ferrous metals in Moscow -.
It is unlikely that anyone will believe the story about the captain long voyage, who, in addition, is a professional circus wrestler, a famous metallurgist and a consultant physician at a surgical clinic. In the world 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: its 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 concentrator magnetic field and iron - component ocher... True, the “professional training” of the elements sometimes took much more time than the training of an average qualified yogi. 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 in fact 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 it is extremely permissible concentration Tellurium in the air is considered to be 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 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, a electromotive force(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 new life 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 using tellurides of bismuth, lead and antimony provide energy artificial satellites Earth, navigation and meteorological installations, cathodic protection devices for main pipelines. The same materials help maintain the desired temperature in many electronic and microelectronic devices.
IN last years One more thing is of great interest chemical compound tellurium, which has semiconductor properties, is cadmium telluride CdTe. 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 chemical thermodynamics At first, it was mainly selenium that was restored. 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. chemical methods, then by distillation or zone smelting. 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 everyone has to work with tellurium more of people. 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 spiral chains and are connected covalent bonds with the closest neighbors. Therefore, elemental tellurium can be considered an inorganic polymer. Crystalline tellurium has a metallic luster, although the complex 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. Also weakly expressed acid properties and telluric acid
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 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 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 now 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. Practical significance minerals do not have tellurium - all industrial tellurium is a by-product of processing ores of other metals.
Discovered by F. Muller 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 in the form of 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, interacts with concentrated sulfur 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. Tellurates alkali metals soluble. They are used as ferroelectrics, ion exchangers, and components of luminescent compositions.
Telluride hydrogen, 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 aqueous solution acid, stronger than sulfur and hydrogen selenide. Salts - tellurides, are usually obtained by interaction 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 - solids, hydrolyze in solution to form telluric acid, easily forming complex halides (for example K 2 ). TeF 6 hexafluoride, a colorless gas, unlike sulfur hexafluoride, is easily hydrolyzed, forming telluric acid.
Application:
Component of semiconductor materials; alloying additive to 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. (access date: 12/23/2019).
"Discovery of the elements and the origin of their names."
