Tellurium
Tellurium, a lustrous, silvery-white chemical element that has both metallic and nonmetallic properties. Tellurium is widely used in alloys. Tin and lead, when alloyed with a small amount of tellurium, become harder; aluminum, more ductile (capable of being drawn into wire); and copper and stainless steels, easier to machine. Because tellurium-lead alloys are resistant to corrosion and abrasion, they are used as linings of chemical tanks, as heating coils, and as cable sheathing.
Tellurium and its compounds are used in the manufacture of dyes to color glass and ceramics and as vulcanizing agents in the manufacture of rubber.
Tellurium was discovered in 1782 by the Austrian mineralogist Franz Joseph Mller (Baron von Reichenstein). It sometimes occurs free (chemically uncombined) in nature, but is usually found combined with a metal (most commonly copper, gold, silver, lead, or bismuth) in ores called tellurides. Most commercial tellurium is recovered as a by-product in the refining of copper and lead tellurides. The leading tellurium producers are the United States, Japan, Canada, Hong Kong, and Peru.
Symbol: Te. Atomic number: 52. Atomic weight: 127.60. Specific gravity: 6.24. Melting point: 841 F. (449.5 C.). Boiling point: 1,813.6 F. (989.8 C.). Tellurium has eight stable isotopes: Te-120, Te-122 through 126, Te-128, and Te-130. It belongs to Group VIA of the Periodic Table and can have a valence of -2, +4, or +6.