Tellurium

Tellurium, symbol Te, silver-white, brittle, semimetallic element. The atomic number of tellurium is 52. Tellurium was first discovered in 1782 by the German scientist Franz Joseph Müller von Reichenstein. The German chemist Martin Heinrich Klaproth recognized it as an element in 1798 and gave it the name tellurium from the Latin word tellus (“earth”).

Tellurium is a comparatively stable element, insoluble in water and hydrochloric acid but soluble in nitric acid and aqua regia. Tellurium reacts with an excess of chlorine to form tellurium dichloride, TeCl₂, and tellurium tetrachloride, TeCl₄. It is oxidized by nitric acid to produce tellurium dioxide, TeO₂, and by chromic acid to produce telluric acid, H₂TeO₄. In combination with hydrogen or certain metals, it forms tellurides such as hydrogen telluride, H₂Te, and sodium telluride, Na₂Te. Tellurium melts at about 450°C (about 842°F), boils at about 988°C (about 1810°F), and has a specific gravity of 6.25. The atomic weight of tellurium is 127.60.

Tellurium is quite rare; it ranks about 78th in natural abundance among the elements in Earth’s crust. It occurs in the pure state or is found in combination with gold, silver, copper, lead, and nickel in such minerals as sylvanite, petzite, and tetradymite. Occasionally it is found in rocks as tellurite (or tellurium dioxide), TeO₂. The slime from lead and copper refineries and the flue dust from metal smelting have been major commercial sources. It has also been prepared by reduction of telluric oxide, forming a grayish-white, metallic powder. Tellurium deposits have been found in Mexico, South America, western Australia, and Canada.

Tellurium is used as an additive in steel alloys and in the manufacture of rectifiers and thermoelectric devices, as well as in semiconductor research. It is also used in cadmium-tellurium solar cells. With various organic substances, it has been employed as a vulcanizing agent in the processing of natural and synthetic rubber; and in antiknock compounds for gasoline. It has also been used to impart a blue color to glass. Colloidal tellurium is an insecticide, germicide, and fungicide.