Tantalum - chemistry.

Tantalum - chemistry. I INTRODUCTION Tantalum, symbol Ta, white, ductile, malleable metallic element. Tantalum is one of the transition elements of the periodic table (see Periodic Law). The atomic number of tantalum is 73. Tantalum was first obtained in pure form in 1820 by the Swedish chemist Baron Jöns Jakob Berzelius, who heated potassium tantalifluoride, K2TaF7, with excess potassium. The element was named for Tantalus, king of Lydia and son of Zeus in Greek mythology. II PROPERTIES AND OCCURRENCE Tantalum is soluble in fused alkalies, insoluble in sulfuric, hydrochloric, and nitric acids, and soluble in hydrofluoric acid. It ignites in air to form tantalum pentoxide (sometimes referred to as tantalum(V) oxide or tantalic acid anhydride), Ta2O 5, a white infusible substance that combines with metallic oxides or hydroxides to form compounds called tantalites. Tantalic acid (also know as tantalum(V) oxide hydrate), Ta2O 5 xH2O, is a gelatinous precipitate that has a varying number of water molecules associated with each tantalum pentoxide molecule. Tantalum melts at about 3017°C (about 5463°F), boils at about 5458°C (about 9856°F), and has a specific gravity of 16.65. The atomic weight of tantalum is 180.948. Tantalum belongs to the group of metals that includes vanadium and niobium. It occurs mainly in the mineral tantalite (see Columbite), FeTa2O 6. Tantalum ranks about 53rd among the elements in natural abundance in Earth's crust. Principal deposits of the metal occur in Australia and Scandinavia. In the United States, small deposits are found associated with the pegmatite veins of the Black Hills of South Dakota. Most tantalum minerals contain some niobium metal, which is separated by solvent extraction or selective-crystallization procedures. Commercially, tantalum is prepared by the electrolysis of fused potassium tantalifluoride or of tantalum compounds dissolved in dilute sulfuric acid. III USES Because it is more resistant than platinum to many corrosive agents, tantalum has largely replaced platinum in standard weights and in laboratory ware. The largest use of tantalum is for capacitors in electronic circuits and rectifiers in low-voltage circuits, such as railway-signaling systems. Because of its resistance to attack by acids of the human body and its compatability with body tissue, it is used to pin together broken bones. Tantalum is also used in surgical and dental instruments and in chemical heat exchangers. The oxide is an ingredient in special optical glass for aerial camera lenses. Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.