Zirconium

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Zirconium (IPA: /zəˈkəʊniəm, ˌzɛːˈkəʊniəm, zɜːɹ'kəʊniəm) 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.

[edit] 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 in chemical compounds.

[edit] Applications

The major end-uses of the mineral zircon (ZrSiO₄) are refractories, foundry sands (including investment casting) and ceramic opacification. Zircon is also marketed as a natural gemstone used in jewelry. Zirconium oxide is processed to produce cubic zirconia. This forms a brilliant clear crystal used as a low-cost substitute for diamond.

[edit] Other uses

• Zirconium has a low capture cross section for thermal neutrons,^[1] which makes it ideal for nuclear energy uses, such as the cladding for nuclear fuel rod. More than 90% of zirconium metal production is used in commercial & naval nuclear power reactors. Modern commercial-scale reactors can use as much as a 150,000 meters of zirconium alloy (Zircaloy) tubing. Reactor-grade zirconium has to be purified of hafnium, which has 600 times higher neutron-capture cross-section. Hafnium-free zirconium can be 10 times more expensive than zirconium with the naturally-occurring 1-5% of hafnium.
• Human tissues can easily tolerate this metal which makes it suitable for biocompatible implants. In one such application (Oxinium), zirconium metal (alloyed with niobium) is intentionally oxidized to produce an abrasion-resistant, high-integrity zirconium oxide ceramic surface on hip replacement or knee replacement replacements. The ceramic surface decreases wear of the polyethylene counterface, while the substrate retains the strength and ductility of a metal.
• Zirconium is extensively used by the chemical industry for piping in corrosive environments, especially high-temperature ones.
• Zirconium is pyrophoric (flammable) and has been used in military incendiaries such as the Dragon's Breath. It is also planned for use in the baseline variant of the AGM-154 Joint Standoff Weapon for incendiary effects.
• Zirconium carbonate was used in poison-ivy lotions until it was evident that many people were allergic to it (allergies greatly vary between people).
• Impure zirconium oxide, zirconia, is used to make laboratory crucibles that can withstand heat shock, for linings of metallurgical furnaces, and by the ceramic and glass industries as a refractory material.
• Zirconium is used in heat exchangers, as a "getter" in vacuum tubes, in lamp filaments, and in various specialty alloys.
• When alloyed with niobium, zirconium becomes superconductive at low temperatures, and it is used to make superconductive magnets with hypothetical large-scale electrical power uses.
• Zirconium diamide-diamine complexes can be used to catalyse the polymerisation of alkenes, especially ethene, when activated with Trityl-BArF.
• Zirconium nitride has been used more recently as an alternative to titanium nitride for coating drill bits. Both coatings keep the bits sharper and cooler during cutting.
• Zirconium compounds can be used as abrasives in sandpaper and other applications.
• Bis(cyclopentadienyl)zirconium(IV) chloride hydride (Schwartz's Reagent) is a commercially available metallocene used in the hydrozirconation of alkenes and alkynes.
• Bicycle manufacturers incorporate zirconium-aluminium alloys in their high-end bicycle frames. This combination provides the frame with tougher durability; likewise, the frame is lighter and stronger. Zirconium is also used in the manufacture of high strength lacrosse sticks.
• Zirconium is also applied in the molecule aluminium zirconium octachlorohydrex GLY, which is an anti-perspirant.
• Zirconium is also used to line shaped charges in military applications.

In 2007, zirconium costs about $150/kg.

[edit] Hafnium-free zirconium

Nuclear reactor-grade zirconium alloys must be made of purified zirconium - free of hafnium contamination, since hafnium has very high neutron absorption cross-section, 600 times higher than zirconium's. Commercial zirconium naturally contains 1-5% of hafnium which must be removed. This removal process is difficult. (Zirconium and hafnium are two of the most difficult elements to separate.) Two main process are in use: liquid-liquid extraction, exploiting the difference of solubility of metal thiocyanates in methyl isobutyl ketone, used mainly in United States; and extractive distillation, used primarily in Europe. The resulting reactor-grade zirconium is about 10 times as expensive as the hafnium-contaminated commercial grade. The separated hafnium is used for nuclear-reactor control rods. The zirconium is mostly used in an almost pure state, in the form of "low" alloys, most often from the zircaloy group.

[edit] History

Zirconium (Arabic zarkûn from Persian zargûn زرگون meaning "gold like") was discovered in 1789 by Martin Heinrich Klaproth, and it was isolated in 1824 by Jöns Jakob Berzelius.

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 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.

[edit] 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.

[edit] Isotopes

Main article: isotopes of zirconium

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.

[edit] Compounds

Some common zirconium compunds are: ZrC, ZrO₂, ZrN, ZrCl₄, ZrS₂, ZrSi₂, ZrSiO₄, ZrF₄, ZrBr₄, ZrI₄, Zr(OH)₄, C₁₀H₁₁ClZr, Zr(CH₃CH₂COO)₄, Zr(WO₄)₂, ZrH₂, Pb(Zr_xTi_1-x)O₃

[edit] 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.