Tellurium

From Free net encyclopedia

Tellurium is a chemical element in the periodic table that has the symbol Te and atomic number 52. A brittle silver-white metalloid which looks like tin, tellurium is chemically related to selenium and sulfur. This element is primarily used in alloys and as a semiconductor.

1 Notable characteristics
2 Applications
3 History
4 Occurrence
5 Compounds
6 Isotopes
7 Precautions
8 References
9 External links

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Notable characteristics

Image:Tellurium crystal.jpg Tellurium is a relatively rare element, in the same chemical family as oxygen, sulfur, selenium, and polonium (the chalcogens).

When crystalline, tellurium is silvery-white and when it is in its pure state it has a metallic luster. This is a brittle and easily pulverized metalloid. Amorphous tellurium is found by precipitating it from a solution of tellurous or telluric acid (Te(OH)₆). However, there is some debate whether this form is really amorphous or made of minute crystals. Tellurium is a p-type semiconductor that shows a greater conductivity in certain directions which depends on atomic alignment.

Chemically related to selenium and sulfur, the conductivity of this element increases slightly when exposed to light. It can be doped with copper, gold, silver, tin, or other metals. Tellurium has a greenish-blue flame when burned in normal air and forms tellurium dioxide as a result. When in its molten state, tellurium is corrosive to copper, iron, and stainless steel.

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Applications

It is mostly used in alloys with other metals. It is added to lead to improve its strength, durability and to decrease the corrosive action of sulfuric acid. When added to stainless steel and copper it makes these metals more workable. Other uses:

It is alloyed into cast iron for chill control.
Used in ceramics.
It is used in chalcogenide glasses.
Bismuth telluride (Bi₂Te₃) has found use in thermoelectric devices.

Tellurium is also used in blasting caps, and has potential applications in cadmium telluride (CdTe) solar panels. Some of the highest efficiencies for solar cell electric power generation have been obtained by using this material, but this application has not yet caused demand to increase significantly. If some of the cadmium in CdTe is replaced by zinc then CdZnTe is formed which is used in solid-state x-ray detectors.

Alloyed with both cadmium and mercury, to form mercury cadmium telluride, an infrared sensitive semiconductor material is formed.

Organic tellurides have been employed as initiators for living radical polymerisation and electron-rich mono- and di-tellurides possess antioxidant activity.

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History

Tellurium (Latin tellus meaning "earth") was discovered in 1782 by the Hungarian Franz-Joseph Müller von Reichenstein (Müller Ferenc) in Transylvania. In 1789 another Hungarian scientist, Pál Kitaibel, also discovered the element independently, but later he gave the credit to Müller. In 1798 it was named by Martin Heinrich Klaproth who earlier isolated it.

The 1960s brought growth in thermoelectric applications for tellurium, as well as its use in free-machining steel, which became the dominant use.

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Occurrence

Tellurium is sometimes found in its native form, but is more often found as the telluride of gold (calaverite), and combined with other metals. The principal source of tellurium is from anode sludges produced during the electrolytic refining of blister copper. It is a component of dusts from blast furnace refining of lead. Tellurium is produced mainly in the US, Canada, Peru, and Japan.

Commercial-grade tellurium, which is not toxic, is usually marketed as minus 200-mesh powder but is also available as slabs, ingots, sticks, or lumps. The yearend price for tellurium in 2000 was US$ 14 per pound.

See also: Telluride, Colorado, category:Telluride minerals

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Compounds

Tellurium is in the same series as sulfur and selenium and forms similar compounds. A compound with metal or hydrogen and similar ions is called a telluride. Gold and silver tellurides are considered good ores. See also Cadmium zinc telluride (CdZnTe), Telluric acid (H₆TeO₆). Compounds with tellurate ions complexes TeO₄^2- or TeO₆^6- are known as tellurates.

See also: Category:Tellurium compounds

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Isotopes

There are 30 known isotopes of tellurium with atomic masses that range from 108 to 137. Naturally found tellurium consists of eight isotopes (listed in the table to the right); two of them are observed to be radioactive. ¹²⁸Te has the longest known half-life time (2.2×10²⁴ years) among all radioactive isotopes.

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Precautions

Humans exposed to as little as 0.01 mg/m³ or less in air develop "tellurium breath", which has a garlic-like odor. The garlic odour that is associated with human intake of tellurium compounds is caused from the tellurium being metabolized by the body. When the body metabolizes tellurium in any oxidation state, the tellurium gets converted into dimethyl telluride. Dimethyl telluride is volatile and produces the garlic-like smell.

Tellurium and tellurium compounds should be considered to be toxic and need to be handled with care.

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