Zirconium

Zirconium is a lustrous, greyish-white, soft, ductile, malleable metal that is solid at room temperature, though it is hard and brittle at lesser purities. Alloys with zinc are magnetic at less than 35 K. Zirconium has an electronegativity of 1.33 on the Pauling scale. Of the elements within the d-block with known electronegativities, zirconium has the fourth lowest electronegativity after hafnium, yttrium, and lutetium. At room temperature zirconium exhibits a hexagonally close-packed crystal structure, α-Zr, which changes to β-Zr, a body-centered cubic crystal structure, at 863 °C. Zirconium exists in the β-phase until the melting point. Isotopes Naturally occurring zirconium is composed of five isotopes. 90Zr, 91Zr, 92Zr, 94Zr, and 96Zr. The first four are stable, while 96 is observed to decay with a half-life of 2.34×1019 years by double beta emission; this is theoretically possible also for 94Zr. Of these natural isotopes, 90Zr is the most common, making up 51.45% of all zirconium, and 96Zr is the least common, comprising only 2.80%. The artificial radioisotopes of zirconium known range from 77Zr to 114Zr, and 13 nuclear isomers are also listed. The most stable among them is 93Zr, a long-lived fission product, with a half-life of 1.61 million years. Radioactive isotopes at or above mass number 93 decay by electron emission resulting in niobium isotopes, whereas those at or below 89 decay by positron emission or electron capture, resulting in yttrium isotopes. Occurrence Zirconium has a concentration of about 130 mg/kg within the Earth's crust and about 0.026 μg/L in sea water. It is the 18th most abundant element in the crust. Zircon resources exceed 60 million tonnes worldwide and annual worldwide zirconium production is approximately 900,000 tonnes. Zirconium also occurs in more than 140 other minerals, including the commercially useful ores baddeleyite and eudialyte. Zirconium is relatively abundant in S-type stars, and has been detected in the sun and in meteorites. Lunar rock samples brought back from several Apollo missions to the moon have a high zirconium oxide content relative to terrestrial rocks. EPR spectroscopy has been used in investigations of the unusual 3+ valence state of zirconium. The EPR spectrum of Zr3+, which has been initially observed as a parasitic signal in Fe‐doped single crystals of ScPO4, was definitively identified by preparing single crystals of ScPO4 doped with isotopically enriched (94.6%)91Zr. Single crystals of LuPO4 and YPO4 doped with both naturally abundant and isotopically enriched Zr have also been grown and investigated. ==Production==

Occurrence Zirconium is a by-product formed after mining and processing of the titanium minerals ilmenite and rutile, as well as tin mining. From 2003 to 2007, while prices for the mineral zircon steadily increased from $360 to $840 per tonne, the price for unwrought zirconium metal decreased from $39,900 to $22,700 per ton. Zirconium metal is much more expensive than zircon because the reduction processes are costly. Most zircon is used directly in commercial applications, but a small percentage is converted to the metal. Most Zr metal is produced by the reduction of the zirconium(IV) chloride with magnesium metal in the Kroll process. The liquid–liquid extraction of the thiocyanate-oxide derivatives exploits the fact that the hafnium derivative is slightly more soluble in methyl isobutyl ketone than in water. This method accounts for roughly two-thirds of pure zirconium production, though other methods are being researched; for instance, in India, a TBP-nitrate solvent extraction process is used for the separation of zirconium from other metals. Zr and Hf can also be separated by fractional crystallization of potassium hexafluorozirconate (K2ZrF6), which is less soluble in water than the analogous hafnium derivative. Fractional distillation of the tetrachlorides, also called extractive distillation, is also used. Vacuum arc melting, combined with the use of hot extruding techniques and supercooled copper hearths, is capable of producing zirconium that has been purified of oxygen, nitrogen, and carbon. Hafnium must be removed from zirconium for nuclear applications because hafnium has a neutron absorption cross-section 600 times greater than zirconium. The separated hafnium can be used for reactor control rods. ==Compounds==

Like other transition metals, zirconium forms a wide range of inorganic compounds and coordination complexes. In general, these compounds are colourless diamagnetic solids wherein zirconium has the oxidation state +4. Some organometallic compounds are considered to have Zr(II) oxidation state. These properties make zirconia useful as a thermal barrier coating, although it is also a common diamond substitute. Zirconium tungstate has the unusual property of shrinking in all dimensions when heated, whereas most other substances expand when heated. Zirconium hydride phases are known to form when zirconium alloys are exposed to large quantities of hydrogen over time; due to the brittleness of zirconium hydrides relative to zirconium alloys, the mitigation of zirconium hydride formation was highly studied during the development of the first commercial nuclear reactors, in which zirconium carbide was a frequently used material. Lead zirconate titanate (PZT) is the most commonly used piezoelectric material, being used as transducers and actuators in medical and microelectromechanical systems applications. Halides and pseudohalides All four common halides are known, ZrF4, ZrCl4, ZrBr4, and ZrI4. All have polymeric structures and are far less volatile than the corresponding titanium tetrahalides; they find applications in the formation of organic complexes such as zirconocene dichloride. All tend to hydrolyse to give the so-called oxyhalides and dioxides. The corresponding tetraalkoxides are also known. Unlike the halides, the alkoxides dissolve in nonpolar solvents. Dihydrogen hexafluorozirconate is used in the metal finishing industry as an etching agent to promote paint adhesion. Organic derivatives , a representative organozirconium compound Organozirconium chemistry is key to Ziegler–Natta catalysts, used to produce polypropylene. This application exploits the ability of zirconium to reversibly form bonds to carbon. Zirconocene dibromide ((C5H5)2ZrBr2), reported in 1952 by Birmingham and Wilkinson, was the first organozirconium compound. Schwartz's reagent, prepared in 1970 by P. C. Wailes and H. Weigold, is a metallocene used in organic synthesis for transformations of alkenes and alkynes. Many complexes of Zr(II) are derivatives of zirconocene, one example being (C5Me5)2Zr(CO)2. ==History==

The zirconium-containing mineral zircon and related minerals (jargoon, jacinth, or hyacinth, ligure) were mentioned in biblical writings. when Klaproth analyzed a jargoon from the island of Ceylon (now Sri Lanka). He named the new element Zirkonerde (zirconia), : ==Applications==

Approximately 900,000 tonnes of zirconium ores were mined in 1995, mostly as zircon. Zircon (ZrSiO4) and cubic zirconia (ZrO2) are cut into gemstones for use in jewelry. Zirconium dioxide is a component in some abrasives, such as grinding wheels and sandpaper. A small fraction of the zircon is converted to the metal, which finds various niche applications. Because of zirconium's excellent resistance to corrosion, it is often used as an alloying agent in materials that are exposed to aggressive environments, such as surgical appliances, light filaments, and watch cases. The high reactivity of zirconium with oxygen at high temperatures is exploited in some specialised applications such as explosive primers and as getters in vacuum tubes. Zirconium powder is used as a degassing agent in electron tubes, while zirconium wire and sheets are utilized for grid and anode supports. Burning zirconium was used as a light source in some photographic flashbulbs. Zirconium powder with a mesh size from 10 to 80 is occasionally used in pyrotechnic compositions to generate sparks. The high reactivity of zirconium leads to bright white sparks. Nuclear applications Cladding for nuclear reactor fuels consumes about 1% of the zirconium supply, : Hydrolysis is very slow below 100 °C, but rapid at temperature above 900 °C. Most metals undergo similar reactions. The redox reaction is relevant to the instability of fuel assemblies at high temperatures. This reaction occurred in the reactors 1, 2 and 3 of the Fukushima I Nuclear Power Plant (Japan) after the reactor cooling was interrupted by the earthquake and tsunami disaster of March 11, 2011, leading to the Fukushima I nuclear accidents. After venting the hydrogen in the maintenance hall of those three reactors, the mixture of hydrogen with atmospheric oxygen exploded, severely damaging the installations and at least one of the containment buildings. Zirconium is a constituent of uranium zirconium hydrides, nuclear fuels used in research reactors. Space and aeronautic industries Materials fabricated from zirconium metal and ZrO2 are used in space vehicles where resistance to heat is needed. High temperature parts such as combustors, blades, and vanes in jet engines and stationary gas turbines are increasingly being protected by thin ceramic layers and/or paintable coatings, usually composed of a mixture of zirconia and yttria. Zirconium is also used as a material of first choice for hydrogen peroxide () tanks, propellant lines, valves, and thrusters, in propulsion space systems such as these equipping the Sierra Space's Dream Chaser spaceplane Medical uses Zirconium-bearing compounds are used in many biomedical applications, including dental implants and crowns, knee and hip replacements, middle-ear ossicular chain reconstruction, and other restorative and prosthetic devices. Although the REDY system was superseded in the 1990s by less expensive alternatives, new sorbent-based dialysis systems are being evaluated and approved by the U.S. Food and Drug Administration (FDA). Renal Solutions developed the DIALISORB technology, a portable, low water dialysis system. Also, developmental versions of a Wearable Artificial Kidney have incorporated sorbent-based technologies. Sodium zirconium cyclosilicate is used by mouth in the treatment of hyperkalemia. It is a selective sorbent designed to trap potassium ions in preference to other ions throughout the gastrointestinal tract. Mixtures of monomeric and polymeric Zr4+ and Al3+ complexes with hydroxide, chloride and glycine, called aluminium zirconium glycine salts, are used in a preparation as an antiperspirant in many deodorant products. It has been used since the early 1960s, as it was determined more efficacious as an antiperspirant than contemporary active ingredients such as aluminium chlorohydrate. Defunct applications Zirconium carbonate (3ZrO2·CO2·H2O) was used in lotions to treat poison ivy but was discontinued because it occasionally caused skin reactions. ==Safety==

}} Although zirconium has no known biological role, the human body contains, on average, 250 milligrams of zirconium, and daily intake is approximately 4.15 milligrams (3.5 milligrams from food and 0.65 milligrams from water), depending on dietary habits. Zirconium is widely distributed in nature and is found in all biological systems, for example: 2.86 μg/g in whole wheat, 3.09 μg/g in brown rice, 0.55 μg/g in spinach, 1.23 μg/g in eggs, and 0.86 μg/g in ground beef. Further, zirconium is commonly used in commercial products (e.g. deodorant sticks, aerosol antiperspirants) and also in water purification (e.g. control of phosphorus pollution, bacteria- and pyrogen-contaminated water). Short-term exposure to zirconium powder can cause irritation, but only contact with the eyes requires medical attention. Persistent exposure to zirconium tetrachloride results in increased mortality in rats and guinea pigs and a decrease of blood hemoglobin and red blood cells in dogs. However, in a study of 20 rats given a standard diet containing ~4% zirconium oxide, there were no adverse effects on growth rate, blood and urine parameters, or mortality. The U.S. Occupational Safety and Health Administration (OSHA) legal limit (permissible exposure limit) for zirconium exposure is 5 mg/m3 over an 8-hour workday. The National Institute for Occupational Safety and Health (NIOSH) recommended exposure limit (REL) is 5 mg/m3 over an 8-hour workday and a short term limit of 10 mg/m3. At levels of 25 mg/m3, zirconium is immediately dangerous to life and health. However, zirconium is not considered an industrial health hazard. or genotoxic. Among the numerous radioactive isotopes of zirconium, 93Zr is among the most common. It is released as a product of nuclear fission of 235U and 239Pu, mainly in nuclear power plants and during nuclear weapons tests in the 1950s and 1960s. It has a very long half-life (1.53 million years), its decay emits only low energy radiations, and it is not considered particularly hazardous. ==See also==