TELLURIUM

(Te), semimetallic chemical element in the oxygen family (Group VIa of the periodic table), closely allied with the element selenium in chemical and physical properties. It was discovered in 1782 by Franz Joseph Mller von Reichenstein, a mining inspector in Transylvania. Tellurium is not an abundant element, although it is widely distributed around the world. It is rarely found in the uncombined state and usually occurs as tellurides of copper, lead, silver, gold, iron, or bismuth. The chief sources from which the element is extracted are the slimes from copper and lead refineries in addition to flue dusts from the processing of telluride gold ores. Tellurium exists in two forms: a silvery white, brittle, crystalline solid that has a metallic lustre and an amorphous powder that is dark gray to brown. The element is not very metallic in character; it 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. 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 electron config. 2-8-18-18-6 or 1s22s22p63s23p6 3d104s24p64d105s25p4