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Jai Ganesh

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Tellurium

Tellurium

Gist

Tellurium is a semi-metallic chemical element with the symbol Te and atomic number 52. It's a brittle, silver-white metalloid, chemically similar to selenium and sulfur. Tellurium is a rare element found naturally, sometimes as a mineral, and is also obtained as a byproduct of copper refining. It has various applications, including use in alloys, ceramics, and electronics.

Tellurium has been used to vulcanise rubber, to tint glass and ceramics, in solar cells, in rewritable CDs and DVDs and as a catalyst in oil refining. It can be doped with silver, gold, copper or tin in semiconductor applications.

Summary

Tellurium is a chemical element; it has symbol Te and atomic number 52. It is a brittle, mildly toxic, rare, silver-white metalloid. Tellurium is chemically related to selenium and sulfur, all three of which are chalcogens. It is occasionally found in its native form as elemental crystals. Tellurium is far more common in the Universe as a whole than on Earth. Its extreme rarity in the Earth's crust, comparable to that of platinum, is due partly to its formation of a volatile hydride that caused tellurium to be lost to space as a gas during the hot nebular formation of Earth.

Tellurium-bearing compounds were first discovered in 1782 in a gold mine in Kleinschlatten, Transylvania (now Zlatna, Romania) by Austrian mineralogist Franz-Joseph Müller von Reichenstein, although it was Martin Heinrich Klaproth who named the new element in 1798 after the Latin tellus 'earth'. Gold telluride minerals are the most notable natural gold compounds. However, they are not a commercially significant source of tellurium itself, which is normally extracted as a by-product of copper and lead production.

Commercially, the primary use of tellurium is CdTe solar panels and thermoelectric devices. A more traditional application in copper (tellurium copper) and steel alloys, where tellurium improves machinability, also consumes a considerable portion of tellurium production.

Tellurium has no biological function, although fungi can use it in place of sulfur and selenium in amino acids such as tellurocysteine and telluromethionine. In humans, tellurium is partly metabolized into dimethyl telluride, (CH3)2Te, a gas with a garlic-like odor exhaled in the breath of victims of tellurium exposure or poisoning.

Details

Tellurium (Te) semimetallic chemical element in the oxygen group (Group 16 [VIa] of the periodic table), closely allied with the element selenium in chemical and physical properties. Tellurium is a silvery white element with properties intermediate between those of metals and nonmetals; it makes up approximately one part per billion of Earth’s crust. Like selenium, it is less often found uncombined than as compounds of metals such as copper, lead, silver, or gold and is obtained chiefly as a by-product of the refining of copper or lead. No large use for tellurium has been found.

Element Properties

atomic number  :  52
atomic weight  :  127.60
masses of stable isotopes  :  120, 122, 123, 124, 125, 126, 128, 130
melting point  :  449.8 °C (841.6 °F)
boiling point  :  989.9 °C (1,813.8 °F)
oxidation states  :  −2, +2, +4, +6

History

The element tellurium was isolated before it was actually known to be an elemental species. About 1782 Franz Joseph Müller von Reichenstein, an Austrian mineralogist, worked with an ore referred to as German gold. From this ore he obtained a material that defied his attempts at analysis and was called by him metallum problematicum. In 1798 Martin Heinrich Klaproth confirmed Müller’s observations and established the elemental nature of the substance. He named the element after man’s “heavenly body” Tellus, or Earth.

Occurrence and preparation

The demand for tellurium does not match that for selenium. The two elements are found together in many ores; they may be isolated by employing the processes described in connection with selenium, obtaining solutions containing salts of both selenious and tellurous acids, H2SeO3 and H2TeO3. Upon treatment of these solutions with sulfuric acid, tellurium dioxide, TeO2, separates because of its low solubility, while the selenious acid remains dissolved. The tellurium dioxide can be converted into elemental tellurium by treatment with sulfur dioxide; an electrolytic process is used to purify the product.

Physical and chemical properties

In tellurium, the covalent bonding necessary to provide large ring- and chain-molecules by catenation is almost nonexistent. The element crystallizes in the rhombohedral form. It is silvery white and isomorphous with gray selenium—that is, the structure and dimensions of the crystals are very similar. It is brittle but not very hard. The tellurium atoms form spiral chains in the crystal with Te–Te distances of 3.74 Å.

The element is a poor conductor of heat and only a fair conductor of electricity. Tellurium burns in air or in oxygen with a blue-green flame, forming the dioxide (TeO2). It is unaffected by hydrochloric acid, but either nitric acid or aqua regia (a mixture of nitric acid and hydrochloric acid) oxidizes it to tellurous acid (H2TeO3). It reacts with the halogens (fluorine, chlorine, bromine, and iodine) to form halides, and it combines with most metals at elevated temperatures to form tellurides.

Although there are adequate supplies of the element, no single use has been developed that creates a large demand for it. Small amounts of tellurium increase the ductility of aluminum alloys, the hardness and tensile strength of tin alloys, and the machinability of stainless steel and copper; in lead and in manganese-magnesium alloys, it increases resistance to corrosion. Bismuth telluride and lead telluride are semiconducting materials that have been used in thermoelectric devices either as sources of electricity or for cooling purposes.

Additional Information:

Appearance

A semi-metal usually obtained as a grey powder.

Uses

Tellurium is used in alloys, mostly with copper and stainless steel, to improve their machinability. When added to lead it makes it more resistant to acids and improves its strength and hardness.

Tellurium has been used to vulcanise rubber, to tint glass and ceramics, in solar cells, in rewritable CDs and DVDs and as a catalyst in oil refining. It can be doped with silver, gold, copper or tin in semiconductor applications.

Biological role

Tellurium has no known biological role. It is very toxic and teratogenic (disturbs the development of an embryo or foetus). Workers exposed to very small quantities of tellurium in the air develop ‘tellurium breath’, which has a garlic-like odour.

Natural abundance

Tellurium is present in the Earth’s crust only in about 0.001 parts per million. Tellurium minerals include calaverite, sylvanite and tellurite. It is also found uncombined in nature, but only very rarely. It is obtained commercially from the anode muds produced during the electrolytic refining of copper. These contain up to about 8% tellurium.

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