Tellurium

Notable Characteristics

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. 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.

Applications

It is mostly used in alloys with other metals. It is added to lead to improve its strength, durability and to decreases 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.
• Bismuth telluride has found use in thermoelectric devices.

Tellurium is also used in blasting caps[?], and has potential applications in cadmium telluride 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.

History

Tellurium (Latin tellus meaning "earth") was discovered in 1782 by Franz Joseph Muller von Reichstein[?] in Romania. 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.

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 muds produced during the electrolytic refining of blister copper.

Commercial-grade tellurium, which isn't 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.

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 ore.

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) .

Precautions

Humans exposed to as little as 0.01 mg/m³ or less in air develop "tellurium breath", which has a garlic-like odor. Tellurium and tellurium compounds should be considered to be toxic and need to be handled with care.

External Links

• WebElements.com - Tellurium (http://www.webelements.com/webelements/elements/text/Te/index.html)
• EnvironmentalChemistry.com - Tellurium (http://environmentalchemistry.com/yogi/periodic/Te.html)

Common misspelling and questions (FAQ)

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