Zirconium

Zirconium is a chemical element that has the symbol Zr and has the atomic number 40. A lustrous, very corrosion resistant, gray-white, strong transition metal that resembles titanium, zirconium is obtained mainly from the mineral zircon. Zirconium is primarily used in nuclear reactors, especially in the cladding of the fuel rods, due to its low neutron-capture cross-section and its resistance to corrosion.

Characteristics
Zirconium is a grayish-white metal, lustrous, and quite corrosion-resistant. Zirconium is lighter than steel and its hardness is similar to copper. When it is finely divided into a powder, zirconium can spontaneously ignite in air, especially at high temperatures. (It is much more difficult to ignite the solid metal.) The Zirconium-zinc alloy becomes magnetic at temperatures below 35 K. The oxidation state of zirconium is usually +4, although +3 and +2 can also be obtained inside of chemical compounds.

History
Zirconium (from Syriac zargono, Arabic zarkûn from Persian zargûn زرگون meaning "gold like") was discovered in 1789 by Martin Heinrich Klaproth, isolated in 1824 by Jöns Jakob Berzelius, and finally put in a pure form in 1914.

The zirconium-containing mineral zircon, or its variations (jargon, hyacinth, jacinth, or ligure), were mentioned in biblical writings. The mineral was not known to contain a new element until Klaproth analyzed a jargon (what's a 'jargon' -- no answer in WK) from the island of Ceylon in the Indian Ocean. He named the new element Zirkonertz (zirconia). The impure metal was isolated first by Berzelius by heating a mixture of potassium and potassium-zirconium fluoride in a small decomposition process conducted in an iron tube. Pure zirconium wasn't prepared until 1914.

The crystal bar process (or Iodide process), discovered by Anton Eduard van Arkel and Jan Hendrik de Boer in 1925, was the first industrial process for the commercial production of pure metallic zirconium. It was later superseded by the Kroll process.

Occurrence
Zirconium is never found in nature as a native metal. The principal economic source of zirconium is the zirconium silicate mineral, zircon (ZrSiO4), which is found in deposits located in Australia, South Africa and the United States, as reported by the British Geological Survey. It is extracted either as a dark sooty powder, or as a gray metallic crystalline substance. Zirconium and hafnium are contained in zircon at a ratio of about 50 to 1, and they are quite difficult to separate chemically. Zircon is a co-product or by-product of the mining and processing of heavy-mineral sands for the titanium minerals, ilmenite and rutile, or from tin minerals. Zirconium also occurs in about 30 other recognized mineral species including baddeleyite. This metal is commercially produced mostly by the reduction of the zirconium(IV) chloride with magnesium metal in the Kroll process. Commercial-quality zirconium for most uses still has a content of 1% to 3% hafnium.

This element is relatively-abundant in S-type stars, and it has been detected in the sun and in meteorites. Lunar rock samples brought back from several Apollo program missions to the moon have a quite high zirconium oxide content relative to terrestrial rocks.

See also zirconium minerals.

Isotopes
Naturally-occurring zirconium is composed of four stable isotopes, and one extremely long-lived radioisotope (96Zr). The second most stable radioisotope is 93Zr which has a half-life of 1.53 million years. Eighteen other radioisotopes have been observed. Most of these have half-lives that are less than a day except for 95Zr (64.02 days), 88Zr (63.4 days), and 89Zr (78.41 hours). The primary decay mode is electron capture for isotopes lighter than 92Zr, and the primary mode for heavier isotopes is beta decay. Other isotopes of zirconium include 90Zr, 91Zr, and 94Zr

Compounds
Some common zirconium compounds are: ZrC, ZrO2, ZrN, ZrCl4, ZrS2, ZrSi2, ZrSiO4, ZrF4, ZrBr4, ZrI4, Zr(OH)4, C10H11ClZr, Zr(CH3CH2COO)4, Zr(WO4)2, ZrH2, Pb(ZrxTi1-x)O3

Precautions
Compounds containing zirconium are not noted for toxicity. The metal dust can ignite in air and should be regarded as a major fire and explosion hazard. Zirconium has no known biological role.