Tellurium

Tellurium (Te) is a chemical element with atomic number 52. It belongs to the chalcogens group in the periodic table, the same group that includes oxygen, sulfur, and selenium. In its standard form it is a brittle solid with a silvery-white appearance and metallic luster, but its electrical and chemical properties make it intermediate between metals and non-metals; it is therefore classified as a metalloid.

Tellurium is among the rarest elements in the Earth's crust. It is seldom found on its own, but occurs in copper ore as part of sulfides; it is therefore obtained mainly from copper refining residues and anode slimes produced during copper purification. Its principal uses lie in semiconductors, metal alloys, and certain solar power technologies.

Physical and chemical properties

Tellurium exists in two forms: a crystalline variety with metallic luster, and an amorphous variety with a dark, dull appearance. It is brittle and fractures readily under impact, which makes it difficult to work into shaped objects. When exposed to air it burns to form tellurium dioxide. It combines with many metals to form tellurides, such as cadmium telluride and bismuth telluride. Common oxidation states are −2, +4, and +6.

Applications

The primary use is in semiconductors. Bismuth telluride is the fundamental material in thermoelectric devices—those that convert electric current into temperature differences or produce cooling. Cadmium telluride is used in thin-film photovoltaics. In addition, small amounts of tellurium added to steel and copper facilitate machining, while small quantities are used in the vulcanization of rubber.

Health and safety

Tellurium and its compounds are considered toxic when ingested or inhaled. A notable characteristic is that workers exposed to it produce dimethyl telluride in the body, giving breath and sweat a persistent garlic-like odor. Industrial operations require adequate ventilation and protective equipment.