Zirconium - chemistry.

Zirconium - chemistry. I INTRODUCTION Zirconium, symbol Zr, metallic element with an atomic number of 40. Zirconium is one of the transition elements of the periodic table (see Periodic Law). The element was discovered in a gemstone in 1789 by the German chemist Martin Heinrich Klaproth and isolated 1824 by the Swedish chemist Baron Jöns Jacob Berzelius. The gemstone's color may have inspired the element's name, which is similar to the Arabic word zargun, "gold color." II PROPERTIES AND OCCURRENCE In its pure state zirconium exists in two forms: the crystalline form, a soft, white, ductile metal; and the amorphous form, a bluish-black powder. Both forms are insoluble in water, slightly soluble in alcohol, and completely soluble in hydrofluoric acid. The metal burns in air at 500°C (932°F). Zirconium ranks about 18th in abundance among the elements in Earth's crust. Zirconium melts at about 1855°C (about 3371°F), boils at about 4409°C (about 7968°F), and has a specific gravity of 6.5. The atomic weight of the element is 91.22. Zirconium is never found free in nature; it occurs chiefly as a silicate in the mineral zircon and as an oxide in the mineral baddeleyite, which is found in commercial quantities in Brazil. Zirconium ores also contain the element hafnium, a metal with properties similar to those of zirconium. III USES Zirconium is used in the manufacture of steel, porcelain, certain nonferrous alloys, and refractories. It is also used in vacuum tubes to remove traces of gases because it combines readily with oxygen, hydrogen, and nitrogen at high temperatures. Zirconium is used in heat exchangers, pump housings, valves, and other equipment subject to corrosion by acids. Special alloys of the metal called zircaloy-2 and zircaloy-4, which contain 1.5 percent tin, are used in nuclear reactors as a cladding material for uranium-fuel elements and as a structural material. Zirconium is especially suitable in water-moderated reactors because of its low neutron-absorption cross section, excellent corrosion resistance at moderately elevated temperatures, strength, ductility, and ease of fabrication. Australia is the largest producer of zirconium in the world, accounting for more than 70 percent of world production. The other major producer of the metal is the former Union of Soviet Socialist Republics (USSR). Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.