Transition metal
Zirconium is a chemical element; it has symbol Zr and atomic number 40. First identified in 1789, isolated in impure form in 1824, and manufactured at scale by 1925, pure zirconium is a lustrous transition metal with a greyish-white color that closely resembles hafnium and, to a lesser extent, titanium. It is solid at room temperature, ductile, malleable and corrosion-resistant. The name zirconium is derived from the name of the mineral zircon, the most important source of zirconium. The word is related to Persian zargun (zircon; zar-gun, "gold-like" or "as gold"). Besides zircon, zirconium occurs in over 140 other minerals, including baddeleyite and eudialyte; most zirconium is produced as a byproduct of minerals mined for titanium and tin.
Zirconium forms a variety of inorganic compounds, such as zirconium dioxide, and organometallic compounds, such as zirconocene dichloride. Five isotopes occur naturally, four of which are stable. The metal and its alloys are mainly used as a refractory and opacifier; zirconium alloys are used to clad nuclear fuel rods due to their low neutron absorption and strong resistance to corrosion, and in space vehicles and turbine blades where high heat resistance is necessary. Zirconium also finds uses in flashbulbs, biomedical applications such as dental implants and prosthetics, deodorant, and water purification systems. …
The zirconium-containing mineral zircon and related minerals (jargoon, jacinth, or hyacinth, ligure) were mentioned in biblical writings. The mineral was not known to contain a new element until 1789, when Klaproth analyzed a jargoon from the island of Ceylon (now Sri Lanka). He named the new element Zirkonerde (zirconia), related to the Persian zargun (zircon; zar-gun, "gold-like" or "as gold"). Humphry Davy attempted to isolate this new element in 1808 through electrolysis, but failed. Zirconium metal was first obtained in an impure form in 1824 by Berzelius by heating a mixture of potassium and potassium zirconium fluoride in an iron tube.
The crystal bar process (also known as the 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 metallic zirconium. It involves the formation and subsequent thermal decomposition of zirconium tetraiodide (ZrI4), and was superseded in 1945 by the much cheaper Kroll process developed by William Justin Kroll, in which zirconium tetrachloride (ZrCl4) is reduced by magnesium:
ZrCl4 + 2 Mg → Zr + 2 MgCl2
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. In powder form, zirconium is highly flammable, but the solid form is much less prone to ignition. Zirconium is highly resistant to corrosion by alkalis, acids, salt water, and other agents. However, it will dissolve in hydrochloric and sulfuric acid, especially when fluorine is present. Alloys with zinc are magnetic at less than 35 K.
The melting point of zirconium is 1855 °C (3371 °F), and the boiling point is 4409 °C (7968 °F). 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.
Naturally occurring zirconium is composed of five isotopes. 90Zr, 91Zr, 92Zr, 94Zr, and 96Zr. The first four are stable, while 96Zr 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%. …
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. It is not found in nature as a native metal, reflecting its intrinsic instability with respect to water. The principal commercial source of zirconium is zircon (ZrSiO4), a silicate mineral, which is found primarily in Australia, Brazil, India, Russia, South Africa and the United States, as well as in smaller deposits around the world. As of 2023, Australia and South Africa are the leading producers, together accounting for approximately half of global zircon production. 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. …
Approximately 900,000 tonnes of zirconium ores were mined in 1995, mostly as zircon.
Most zircon is used directly in high-temperature applications. Because it is refractory, hard, and resistant to chemical attack, zircon finds many applications. Its main use is as an opacifier, conferring a white, opaque appearance to ceramic materials. Because of its chemical resistance, zircon is also used in aggressive environments, such as moulds for molten metals.
Zirconium dioxide (ZrO2) is used in laboratory crucibles, in metallurgical furnaces, and as a refractory material Because it is mechanically strong and flexible, it can be sintered into ceramic knives and other blades. 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. Zircon is also used in dating of rocks from about the time of the Earth's formation through the measurement of its inherent radioisotopes, most often uranium and lead.
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. …
Naturally occurring zirconium is composed of five isotopes. 90Zr, 91Zr, 92Zr, 94Zr, and 96Zr. The first four are stable, while 96Zr 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.
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. …